Climate Change Impacts to Hydro Power Reservoir Systems in British Columbia, Canada: Modelling, Validation and Projection of Historic and Future Streamflow and Snowpack

NASA Astrophysics Data System (ADS)

Bennett, K. E.; Schnorbus, M.; Werner, A. T.; Berland, A. J.

2010-12-01

The British Columbia Hydro Electric Corporation (BC Hydro) has a mandate to provide clean, renewable and reliable sources of hydro-electric power into the future, hence managing those resources in the context of climate change will be an important component of reservoir operational planning in British Columbia. The Pacific Climate Impacts Consortium (www.PacificClimate.org) has implemented the Variable Infiltration Capacity hydrologic model parameterized at 1/16th degree (~32 km2) to provide BC Hydro with future projections of changes to streamflow and snowpack to the 2050s. The headwaters of the Peace, Columbia, and Campbell River basins were selected for study; the Upper Peace River basin (101,000 km2) is a snowmelt-dominated watershed, and the Upper Columbia River Basin (104,000 km2) has a mixed snowmelt-glacier melt runoff regime, with glacier runoff contributing up to 15 to 20% of late summer discharge. The Upper Campbell River watershed (1,200 km2) has a mixed rainfall and snowmelt (hybrid) hydrologic regime. The model has been calibrated using historical streamflow observations and validated against these observations, as well as automated snow pillow measurements. Future streamflow changes are estimated based on eight Global Climate Models (GCMs) from the CMIP3 suite, downscaled using the Bias Correction Spatial Downscaling (BCSD) technique, run under three emissions scenarios (A2, A1B and B1; A1B is specifically reported on herein). Climate impacts by the 2050s in the three watersheds illustrate an increase in annual average temperature and precipitation ranging between +2.2°C to +2.8°C and +2% to +10% depending on basin, and an annual change in streamflow of -1% to +12% for the three watersheds. Changes are more profound on the seasonal time-scale and differ across basins. Summer streamflow in the Upper Campbell River watershed is projected to decline by -60%, where as the Upper Peace and Columbia systems are projected to decline by -25% and -22%, respectively. Streamflow is projected to increase during winter months for all basins, ranging from increases of +54% (Upper Campbell), +77% (Upper Peace) to +94% (Upper Columbia). These changes in streamflow illustrate a shift towards more rainfall dominated systems with lower snowpacks during the winter months, particularly in the Campbell system (shifting from 23% to 13% snow dominated by the 2050s), which is located at a relatively low elevation and proximal to the Pacific Ocean. Shifts in the distribution of water resources, and in particular snowpack reserves, may require BC Hydro to reconsider their operational planning framework for impacted systems.

Mantle beneath the Gibraltar Arc from receiver functions

NASA Astrophysics Data System (ADS)

Morais, Iolanda; Vinnik, Lev; Silveira, Graça; Kiselev, Sergey; Matias, Luís

2015-02-01

P and S receiver functions (PRF and SRF) from 19 seismograph stations in the Gibraltar Arc and the Iberian Massif reveal new details of the regional deep structure. Within the high-velocity mantle body below southern Spain the 660-km discontinuity is depressed by at least 20 km. The Ps phase from the 410-km discontinuity is missing at most stations in the Gibraltar Arc. A thin (˜50 km) low-S-velocity layer atop the 410-km discontinuity is found under the Atlantic margin. At most stations the S410p phase in the SRFs arrives 1.0-2.5 s earlier than predicted by IASP91 model, but, for the propagation paths through the upper mantle below southern Spain, the arrivals of S410p are delayed by up to +1.5 s. The early arrivals can be explained by elevated Vp/Vs ratio in the upper mantle or by a depressed 410-km discontinuity. The positive residuals are indicative of a low (˜1.7 versus ˜ 1.8 in IASP91) Vp/Vs ratio. Previously, the low ratio was found in depleted lithosphere of Precambrian cratons. From simultaneous inversion of the PRFs and SRFs we recognize two types of the mantle: `continental' and `oceanic'. In the `continental' upper mantle the S-wave velocity in the high-velocity lid is 4.4-4.5 km s-1, the S-velocity contrast between the lid and the underlying mantle is often near the limit of resolution (0.1 km s-1), and the bottom of the lid is at a depth reaching 90-100 km. In the `oceanic' domain, the S-wave velocities in the lid and the underlying mantle are typically 4.2-4.3 and ˜ 4.0 km s-1, respectively. The bottom of the lid is at a shallow depth (around 50 km), and at some locations the lid is replaced by a low S-wave velocity layer. The narrow S-N-oriented band of earthquakes at depths from 70 to 120 km in the Alboran Sea is in the `continental' domain, near the boundary between the `continental' and `oceanic' domains, and the intermediate seismicity may be an effect of ongoing destruction of the continental lithosphere.

VP and VS structure of the Yellowstone hot spot from teleseismic tomography: Evidence for an upper mantle plume

USGS Publications Warehouse

Waite, Gregory P.; Smith, Robert B.; Allen, Richard M.

2006-01-01

The movement of the lithosphere over a stationary mantle magmatic source, often thought to be a mantle plume, explains key features of the 16 Ma Yellowstone–Snake River Plain volcanic system. However, the seismic signature of a Yellowstone plume has remained elusive because of the lack of adequate data. We employ new teleseismic P and S wave traveltime data to develop tomographic images of the Yellowstone hot spot upper mantle. The teleseismic data were recorded with two temporary seismograph arrays deployed in a 500 km by 600 km area centered on Yellowstone. Additional data from nearby regional seismic networks were incorporated into the data set. The VP and VS models reveal a strong low-velocity anomaly from ∼50 to 200 km directly beneath the Yellowstone caldera and eastern Snake River Plain, as has been imaged in previous studies. Peak anomalies are −2.3% for VP and −5.5% for VS. A weaker, anomaly with a velocity perturbation of up to −1.0% VP and −2.5% VS continues to at least 400 km depth. This anomaly dips 30° from vertical, west-northwest to a location beneath the northern Rocky Mountains. We interpret the low-velocity body as a plume of upwelling hot, and possibly wet rock, from the mantle transition zone that promotes small-scale convection in the upper ∼200 km of the mantle and long-lived volcanism. A high-velocity anomaly, 1.2%VP and 1.9% VS, is located at ∼100 to 250 km depth southeast of Yellowstone and may represent a downwelling of colder, denser mantle material.

Structure and composition of Pluto's atmosphere from the New Horizons solar ultraviolet occultation

NASA Astrophysics Data System (ADS)

Young, Leslie A.; Kammer, Joshua A.; Steffl, Andrew J.; Gladstone, G. Randall; Summers, Michael E.; Strobel, Darrell F.; Hinson, David P.; Stern, S. Alan; Weaver, Harold A.; Olkin, Catherine B.; Ennico, Kimberly; McComas, David J.; Cheng, Andrew F.; Gao, Peter; Lavvas, Panayotis; Linscott, Ivan R.; Wong, Michael L.; Yung, Yuk L.; Cunningham, Nathanial; Davis, Michael; Parker, Joel Wm.; Schindhelm, Eric; Siegmund, Oswald H. W.; Stone, John; Retherford, Kurt; Versteeg, Maarten

2018-01-01

The Alice instrument on NASA's New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14. The transmission vs. altitude was sensitive to the presence of N2, CH4, C2H2, C2H4, C2H6, and haze. We derived line-of-sight abundances and local number densities for the 5 molecular species, and line-of-sight optical depth and extinction coefficients for the haze. We found the following major conclusions: (1) We confirmed temperatures in Pluto's upper atmosphere that were colder than expected before the New Horizons flyby, with upper atmospheric temperatures near 65-68 K. The inferred enhanced Jeans escape rates were (3-7) × 1022 N2 s-1 and (4-8) × 1025 CH4 s-1 at the exobase (at a radius of ∼ 2900 km, or an altitude of ∼1710 km). (2) We measured CH4 abundances from 80 to 1200 km above the surface. A joint analysis of the Alice CH4 and Alice and REX N2 measurements implied a very stable lower atmosphere with a small eddy diffusion coefficient, most likely between 550 and 4000 cm2 s-1. Such a small eddy diffusion coefficient placed the homopause within 12 km of the surface, giving Pluto a small planetary boundary layer. The inferred CH4 surface mixing ratio was ∼ 0.28-0.35%. (3) The abundance profiles of the ;C2Hx hydrocarbons; (C2H2, C2H4, C2H6) were not simply exponential with altitude. We detected local maxima in line-of-sight abundance near 410 km altitude for C2H4, near 320 km for C2H2, and an inflection point or the suggestion of a local maximum at 260 km for C2H6. We also detected local minima near 200 km altitude for C2H4, near 170 km for C2H2, and an inflection point or minimum near 170-200 km for C2H6. These compared favorably with models for hydrocarbon production near 300-400 km and haze condensation near 200 km, especially for C2H2 and C2H4 (Wong et al., 2017). (4) We found haze that had an extinction coefficient approximately proportional to N2 density.

The Structure of Chariklo’s Rings from Stellar Occultations

NASA Astrophysics Data System (ADS)

Bérard, D.; Sicardy, B.; Camargo, J. I. B.; Desmars, J.; Braga-Ribas, F.; Ortiz, J.-L.; Duffard, R.; Morales, N.; Meza, E.; Leiva, R.; Benedetti-Rossi, G.; Vieira-Martins, R.; Gomes Júnior, A.-R.; Assafin, M.; Colas, F.; Dauvergne, J.-L.; Kervella, P.; Lecacheux, J.; Maquet, L.; Vachier, F.; Renner, S.; Monard, B.; Sickafoose, A. A.; Breytenbach, H.; Genade, A.; Beisker, W.; Bath, K.-L.; Bode, H.-J.; Backes, M.; Ivanov, V. D.; Jehin, E.; Gillon, M.; Manfroid, J.; Pollock, J.; Tancredi, G.; Roland, S.; Salvo, R.; Vanzi, L.; Herald, D.; Gault, D.; Kerr, S.; Pavlov, H.; Hill, K. M.; Bradshaw, J.; Barry, M. A.; Cool, A.; Lade, B.; Cole, A.; Broughton, J.; Newman, J.; Horvat, R.; Maybour, D.; Giles, D.; Davis, L.; Paton, R. A.; Loader, B.; Pennell, A.; Jaquiery, P.-D.; Brillant, S.; Selman, F.; Dumas, C.; Herrera, C.; Carraro, G.; Monaco, L.; Maury, A.; Peyrot, A.; Teng-Chuen-Yu, J.-P.; Richichi, A.; Irawati, P.; De Witt, C.; Schoenau, P.; Prager, R.; Colazo, C.; Melia, R.; Spagnotto, J.; Blain, A.; Alonso, S.; Román, A.; Santos-Sanz, P.; Rizos, J.-L.; Maestre, J.-L.; Dunham, D.

2017-10-01

Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklo’s system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the ±3.3 km formal uncertainty for the ring radii derived by Braga-Ribas et al. The six resolved C1R profiles reveal significant width variations from ˜5 to 7.5 km. The width of the fainter ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and outer edges of C1R are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. No constraint on the sharpness of C2R’s edges is available. A 1σ upper limit of ˜20 m is derived for the equivalent width of narrow (physical width < 4 km) rings up to distances of 12,000 km, counted in the ring plane.

Recent Seismic Experiments of OBS in the South China Sea

NASA Astrophysics Data System (ADS)

Ruan, A.; Li, J.; Wu, Z.

2012-12-01

Since 2006 some research institutions of China have carried out some important seismic experiments by using ocean bottom seismometer(OBS) in the South China Sea (SCS) and obtained many concrete progresses in modeling the crustal structure of SCS and also in understanding of its formation and evolution as well. In 2006 three wide-angle profiles were completed in the northern margin, named OBS2006-1 across the northwestern sub-basin, OBS2006-2 parallel to the sea basin boundary and OBS2006-3 across the Dongsha Rise and Chaoshan Depression respectively. In 2010 two wide- angle profiles were completed, named OBS2010-1 and OBS 2010-2 both perpendicular to the northern off-shore faulting system. During 2009-2011 four wide-angle profiles were completed in the southern margin, named OBS973-1 from southern margin to the southwestern sub-basin, OBS973-2 from Liyue Bank to the southwestern sub-basin and OBS973-3 from Xisha to the southwestern sub-basin, OBS2011-2 from Xisha to Hainan Island respectively. In 2011 two 3D seismic array of OBS were completed in the Zhongnan-Changlong sea mount chain and Huangyan-Zhenbei sea mount chain respectively. Here we present some primary but important results as follows. (1) The velocity model of OBS2006-1 indicates that the crust under the continental slope decreases from 21km to 11km, and to 7.7km in the northwestern sub-basin with Moho depth ascends from 21km to 11km. The tectonic geometry and velocity structure of the northwestern sub-basin and its margins on both sides shows symmetrical and conjugate and indicates pure shear mode of continental margin rifting mechanism. (2) The velocity model of OBS2006-3 reveals remarkable thickness with maximum 8 km of the Mesozoic sediment in Chaoshan Depression in which velocity increases downward from 4.4 km/s at top to 5.3 km/s at the bottom. The buried depth of Moho decreases from 24-25 km under Dongsha Rise to 17 km in the lower slope and an obviously velocity abnormal is detected in the upper crust of the Dongsha Rise and its velocity raises to 6.9 km/s due to the mantle underplating and magma activities. A high velocity layer (HVL) of 3-12 km thick is found in the lower crust, and its velocity is 7.1-7.4 km/s. (3) The wide angle seismic profile-OBS973-2 that extends in NW-SE direction 369km long from the northeastern Liyue Bank to the central sub-basin. It indicates that there are some small volcanoes on the top of crust in Liyue Bank and P wave velocities downward increase from 5.5~6.4km/s in the upper crust (9~10km thick) to 6.6~7.1km/s in the lower crust (11km thick). In the transition zone and sea basin P wave velocities downward increase from 5.9~6.1km/s in the upper curst (4~5km thick) to 6.6~6.9km/s in the lower crust (2~4km thick). The buried depth of Moho is 23km in Liyue Bank and 8~12km in the sea basin. The comparison of profile OBS973-2 with profile OBS2006-1 in the northern margin shows remarkable similarity between them and suggests a possibility of conjugation relationship between Liyue Bank and Zhongsha Massif. Acknowledgements This work was supported by the National Natural Science Foundation of China (91028006,40876035,41106053 and 41176046) and the National Basic Research Program of China (2007CB411701) .

The effects of deep convection on the concentration and size distribution of aerosol particles within the upper troposphere: A case study

NASA Astrophysics Data System (ADS)

Yin, Yan; Chen, Qian; Jin, Lianji; Chen, Baojun; Zhu, Shichao; Zhang, Xiaopei

2012-11-01

A cloud resolving model coupled with a spectral bin microphysical scheme was used to investigate the effects of deep convection on the concentration and size distribution of aerosol particles within the upper troposphere. A deep convective storm that occurred on 1 December, 2005 in Darwin, Australia was simulated, and was compared with available radar observations. The results showed that the radar echo of the storm in the developing stage was well reproduced by the model. Sensitivity tests for aerosol layers at different altitudes were conducted in order to understand how the concentration and size distribution of aerosol particles within the upper troposphere can be influenced by the vertical transport of aerosols as a result of deep convection. The results indicated that aerosols originating from the boundary layer can be more efficiently transported upward, as compared to those from the mid-troposphere, due to significantly increased vertical velocity through the reinforced homogeneous freezing of droplets. Precipitation increased when aerosol layers were lofted at different altitudes, except for the case where an aerosol layer appeared at 5.4-8.0 km, in which relatively more efficient heterogeneous ice nucleation and subsequent Wegener-Bergeron-Findeisen process resulted in more pronounced production of ice crystals, and prohibited the formation of graupel particles via accretion. Sensitivity tests revealed, at least for the cases considered, that the concentration of aerosol particles within the upper troposphere increased by a factor of 7.71, 5.36, and 5.16, respectively, when enhanced aerosol layers existed at 0-2.2 km, 2.2-5.4 km, and 5.4-8.0 km, with Aitken mode and a portion of accumulation mode (0.1-0.2μm) particles being the most susceptible to upward transport.

Balloon-borne and aircraft infrared measurements of ethane (C2H6) in the upper troposphere and lower stratosphere

NASA Technical Reports Server (NTRS)

Goldman, A.; Murcray, F. J.; Murcray, D. G.; Rinsland, C. P.; Coffey, M. T.; Mankin, W. G.

1984-01-01

Quantitative infrared measurements of ethane (C2H6) in the upper troposphere and lower stratosphere are reported. The results have been obtained from the analysis of absorption features of the nu9 band at 12.2 microns, which have been identified in high-resolution balloon-borne and aircraft solar absorption spectra. The balloon-borne spectral data were recorded at sunset with the 0.02/cm resolution University of Denver interferometer system, from a float altitude of 33.5 km near Alamogordo, New Mexico, on March 23, 1981. The aircraft spectra were recorded at sunset in July 1978 with a 0.06/cm resolution interferometer aboard a jet aircraft at 12 km altitude, near 35 deg N, 96 deg W. The balloon analysis indicates the C2H6 mixing ratio decreased from 3.5 ppbv near 8.8 km to 0.91 ppbv near 12.1 km. The results are consistent with the column value obtained from the aircraft data.

Aerodynamic characteristics of the upper stages of a launch vehicle in low-density regime

NASA Astrophysics Data System (ADS)

Oh, Bum Seok; Lee, Joon Ho

2016-11-01

Aerodynamic characteristics of the orbital block (remaining configuration after separation of nose fairing and 1st and 2nd stages of the launch vehicle) and the upper 2-3stage (configuration after separation of 1st stage) of the 3 stages launch vehicle (KSLV-II, Korea Space Launch Vehicle) at high altitude of low-density regime are analyzed by SMILE code which is based on DSMC (Direct Simulation Monte-Carlo) method. To validating of the SMILE code, coefficients of axial force and normal forces of Apollo capsule are also calculated and the results agree very well with the data predicted by others. For the additional validations and applications of the DSMC code, aerodynamic calculation results of simple shapes of plate and wedge in low-density regime are also introduced. Generally, aerodynamic characteristics in low-density regime differ from those of continuum regime. To understand those kinds of differences, aerodynamic coefficients of the upper stages (including upper 2-3 stage and the orbital block) of the launch vehicle in low-density regime are analyzed as a function of Mach numbers and altitudes. The predicted axial force coefficients of the upper stages of the launch vehicle are very high compared to those in continuum regime. In case of the orbital block which flies at very high altitude (higher than 250km), all aerodynamic coefficients are more dependent on velocity variations than altitude variations. In case of the upper 2-3 stage which flies at high altitude (80km-150km), while the axial force coefficients and the locations of center of pressure are less changed with the variations of Knudsen numbers (altitudes), the normal force coefficients and pitching moment coefficients are more affected by variations of Knudsen numbers (altitude).

Night side distribution of SO2 content in Venus' upper mesosphere

NASA Astrophysics Data System (ADS)

Belyaev, D. A.; Evdokimova, D. G.; Montmessin, F.; Bertaux, J.-L.; Korablev, O. I.; Fedorova, A. A.; Marcq, E.; Soret, L.; Luginin, M. S.

2017-09-01

In this paper we present the first night side distribution of SO2 content in Venus' upper mesosphere (altitudes from 85 to 105 km). The dataset is based on the SPICAV UV stellar occultation experiment which took place onboard ESA's Venus Express (VEX) orbiter in 2006-2014. The UV channel of SPICAV spectrometer detected absorption bands of SO2 and CO2 in the spectral range 180-300 nm with a resolution of 1-2 nm while stellar light was occulted by the mesosphere. Altitude profiles of sulfur dioxide's volume mixing ratio (VMR) could be retrieved in the upper part of the mesosphere covering the whole night side on Venus. In parallel, we have reprocessed the terminator UV solar occultations dataset (Belyaev et al., 2012. Icarus 217, 740-751) in the same altitude range and extended its statistics until 2014. On average the SO2 VMR increases with altitude from 10-30 ppb at 85 km to 100-300 ppb at 100 km in both regimes of occultation. The midnight SO2 abundance appears to be 3-4 times higher than in the terminator region: 150-200 ppbv versus 50 pppv at altitude around 95 km. These new results were compared with the distribution of oxygen atoms, which are tracers of the global subsolar-antisolar (SS-AS) circulation at ∼100 km (the data provided by Soret et al., 2012 Icarus, 217, 849-855). The night time behavior looks similar for SO2 molecules and O atoms with a correlation coefficient Rcorr = 0.73. Moreover, the retrieved SO2 enrichment above 85 km appears to correlate with the density of H2SO4 droplets (Luginin et al., 2016; Icarus 277, 154-170).

Study on glacier changes from multi-source remote sensing data in the mountainous areas of the upper reaches of Shule River Basin

NASA Astrophysics Data System (ADS)

Zhang, S.; Li, H.

2017-12-01

The changes of glacier area, ice surface elevation and ice storage in the upper reaches of the Shule River Basin were investigated by the Landsat TM series SRTM and stereo image pairs of Third Resources Satellite (ZY-3)from 2000 to 2015. There are 510 glaciers with areas large than 0.01 km2 in 2015, and the glacier area is 435 km2 in the upper reach of Shule River basin. 96 glaciers were disappeared from 2000 to 2015, and the total glacier area decreased by 57.6±2.68km2 (11.7 %). After correcting the elevation difference between ZY-3 DEM and SRTM and aspect, we found that the average ice surface elevation of glaciers reduced by 2.58±0.6m from 2000 to 2015 , with average reduction 0.172 ±0.04m a-1, and the ice storage reduced by 1.277±0.311km3. Elevation variation of ice surface in different sub-regions reflects the complexity of glacier change. The ice storage change calculated from the sum of single glacier area-volume relationship is glacier 1.46 times higher than that estimated from ice surface elevation change, indicating that the global ice storage change estimated from glacier area-volume change probably overestimated. The shrinkage of glacier increased glacier runoff, and led the significant increase of river runoff. The accuracy of projecting the potential glacier change, glacier runoff and river runoff is the key issues of delicacy water resource management in Shule River Basin.

Recent observations of HF and HCl in the upper stratosphere

NASA Technical Reports Server (NTRS)

Zander, R.

1981-01-01

Concentrations of gas phase hydrofluoric acid and hydrochloric acid have been determined in the upper stratosphere from near-infrared solar spectra recorded in the course of balloon flights from Palestine, Texas, in October 1978 and in September 1979. The average mixing ratios for HF deduced respectively from these flights are (4.8 plus or minus .3) x 10 to the -10th ppv above 30.3km and (6.2 plus or minus .5) x 10 to the -10th ppv above 36.8km. This observed difference is ascribed to an increase in the HF concentration out to at least 37km. The HCl mixing ratios deduced from the 1978 flight yield (4.5 plus or minus .6) x 10 to the -10th ppv at 21.7km, (7.5 plus or minus .7) x 10 to the -10th ppv at 27.5 km and (2.1 plus or minus .4) x 10 to the -9th ppv above 30.5km. Observations in 1979 imply an average HCl mixing ratio above 36.8km of (2.4 plus or minus .4) x 10 to the -9th ppv. Our data do not indicate a measurable temporal trend of the HCl concentration above 30km.

ATMOS/ATLAS 1 measurements of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere

NASA Technical Reports Server (NTRS)

Rinsland, C. P.; Gunson, M. R.; Abrams, M. C.; Lowes, L. L.; Zander, R.; Mahieu, E.

1993-01-01

Vertical profiles of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere have been retrieved from 0.01/cm resolution infrared solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the ATLAS (Atmospheric Laboratory for Applications and Science) 1 shuttle mission of March 24 to April 2, 1992. Based on measurements of the unresolved absorption by the SF6 mu(sub 3) band Q branch at 947.9/cm, average SF6 volume mixing ratios and 1-sigma uncertainties of 3.20 +/- 0.54 parts per trillion by volume (pptv; 10(exp -12) ppv) at 200 mbar (approximately 11.8 km) declining to 2.86 +/- 0.29 pptv at 100 mbar (approximately 16.2 km) and 1.95 +/- 0.50 pptv at 30 mbar (approximately 23.9 km) have been retrieved. The profiles show no obvious dependence with latitude over the range of the measurements (eight occultations spanning 28 deg S to 54 deg S). Assuming an exponential growth model and applying a correction for the interhemispheric concentration difference, an average SF6 rate of increase of 8.7 +/- 2.2% per year, 2 sigma, between 12 and 18 km has been derived by fitting the present measurements, ATMOS measurements from the April-May 1985 Spacelab 3 mission, and balloon-borne IR measurements obtained in March 1981 and June 1988.

Upper crustal structure of Madeira Island revealed from ambient noise tomography

NASA Astrophysics Data System (ADS)

Matos, Catarina; Silveira, Graça; Matias, Luís; Caldeira, Rita; Ribeiro, M. Luísa; Dias, Nuno A.; Krüger, Frank; Bento dos Santos, Telmo

2015-06-01

We present the first image of the Madeira upper crustal structure, using ambient seismic noise tomography. 16 months of ambient noise, recorded in a dense network of 26 seismometers deployed across Madeira, allowed reconstructing Rayleigh wave Green's functions between receivers. Dispersion analysis was performed in the short period band from 1.0 to 4.0 s. Group velocity measurements were regionalized to obtain 2D tomographic images, with a lateral resolution of 2.0 km in central Madeira. Afterwards, the dispersion curves, extracted from each cell of the 2D group velocity maps, were inverted as a function of depth to obtain a 3D shear wave velocity model of the upper crust, from the surface to a depth of 2.0 km. The obtained 3D velocity model reveals features throughout the island that correlates well with surface geology and island evolution.

Pluto's Solar Occultation from New Horizons

NASA Astrophysics Data System (ADS)

Young, Leslie; Kammer, Joshua; Steffl, Andrew J.; Gladstone, Randy; Summers, Michael; Strobel, Darrell F.; Hinson, David P.; Stern, S. Alan; Weaver, Harold A.; Olkin, Catherine; Ennico, Kimberly; McComas, Dave; New Horizons Atmospheres Science Theme Team

2017-10-01

The Alice instrument on NASA’s New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14. We derived line-of-sight abundances and local number densities for the major species (N2 and CH4) and minor hydrocarbons (C2H2, C2H4, C2H6), and line-of-sight optical depth and extinction coefficients for the haze. Our major conclusions are that (1) we confirmed temperatures in Pluto’s upper atmosphere that were colder than expected before the New Horizons flyby, with upper atmospheric temperatures near 65-68 K, and subsequently lower escape rates, (2) the lower atmosphere was very stable, placing the homopause within 12 km of the surface, (3) the abundance profiles of the “C2Hx hydrocarbons” had non-exponential density profiles that compare favorably with models for hydrocarbon production near 300-400 km and haze condensation near 200 km, and (4) haze had an extinction coefficient approximately proportional to N2 density.This work was supported by NASA’s New Horizons project.

Lithospheric velocity structure of the Anatolian plateau-Caucasus-Caspian region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gök, R.; Mellors, R. J.; Sandvol, E.

The Anatolian plateau-Caucasus-Caspian region is an area of complex lithospheric structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region, little is known about the detailed lithospheric structure. Using data from 31 new, permanent broadband seismic stations along with results from a previous 29 temporary seismic stations and 3 existing global seismic stations in the region, a 3-D velocity model is developed using joint inversion of teleseismic receiver functions and surface waves. Both group and phase dispersion curves (Love and Rayleigh) were derived from regional and teleseismic events. Additional Rayleigh wave group dispersion curves weremore » determined using ambient noise correlation. Receiver functions were calculated using P arrivals from 789 teleseismic (30°–90°) earthquakes. The stacked receiver functions and surface wave dispersion curves were jointly inverted to yield the absolute shear wave velocity to a depth of 100 km at each station. The depths of major discontinuities (sediment-basement, crust-mantle, and lithosphere-asthenosphere) were inferred from the velocity-depth profiles at the location of each station. Distinct spatial variations in crustal and upper mantle shear velocities were observed. The Kura basin showed slow (~2.7–2.9 km/s) upper crustal (0–11 km) velocities but elevated (~3.8–3.9 km/s) velocities in the lower crust. The Anatolian plateau varied from ~3.1–3.2 in the upper crust to ~3.5–3.7 in the lower crust, while velocities in the Arabian plate (south of the Bitlis suture) were slightly faster (upper crust between 3.3 and 3.4 km/s and lower crust between 3.8 and 3.9 km/s). The depth of the Moho, which was estimated from the shear velocity profiles, was 35 km in the Arabian plate and increased northward to 54 km at the southern edge of the Greater Caucasus. Moho depths in the Kura and at the edge of the Caspian showed more spatial variability but ranged between 35 and 45 km. Upper mantle velocities were slow under the Anatolian plateau but increased to the south under the Arabian plate and to the east (4.3–4.4 km/s) under the Kura basin and Greater Caucasus. The areas of slow mantle coincided with the locations of Holocene volcanoes. Differences between Rayleigh and Love dispersions at long wavelengths reveal a pronounced variation in anisotropy between the Anatolian plateau and the Kura basin.« less

Lithospheric velocity structure of the Anatolian plateau-Caucasus-Caspian region

DOE PAGES

Gök, R.; Mellors, R. J.; Sandvol, E.; ...

2011-05-07

The Anatolian plateau-Caucasus-Caspian region is an area of complex lithospheric structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region, little is known about the detailed lithospheric structure. Using data from 31 new, permanent broadband seismic stations along with results from a previous 29 temporary seismic stations and 3 existing global seismic stations in the region, a 3-D velocity model is developed using joint inversion of teleseismic receiver functions and surface waves. Both group and phase dispersion curves (Love and Rayleigh) were derived from regional and teleseismic events. Additional Rayleigh wave group dispersion curves weremore » determined using ambient noise correlation. Receiver functions were calculated using P arrivals from 789 teleseismic (30°–90°) earthquakes. The stacked receiver functions and surface wave dispersion curves were jointly inverted to yield the absolute shear wave velocity to a depth of 100 km at each station. The depths of major discontinuities (sediment-basement, crust-mantle, and lithosphere-asthenosphere) were inferred from the velocity-depth profiles at the location of each station. Distinct spatial variations in crustal and upper mantle shear velocities were observed. The Kura basin showed slow (~2.7–2.9 km/s) upper crustal (0–11 km) velocities but elevated (~3.8–3.9 km/s) velocities in the lower crust. The Anatolian plateau varied from ~3.1–3.2 in the upper crust to ~3.5–3.7 in the lower crust, while velocities in the Arabian plate (south of the Bitlis suture) were slightly faster (upper crust between 3.3 and 3.4 km/s and lower crust between 3.8 and 3.9 km/s). The depth of the Moho, which was estimated from the shear velocity profiles, was 35 km in the Arabian plate and increased northward to 54 km at the southern edge of the Greater Caucasus. Moho depths in the Kura and at the edge of the Caspian showed more spatial variability but ranged between 35 and 45 km. Upper mantle velocities were slow under the Anatolian plateau but increased to the south under the Arabian plate and to the east (4.3–4.4 km/s) under the Kura basin and Greater Caucasus. The areas of slow mantle coincided with the locations of Holocene volcanoes. Differences between Rayleigh and Love dispersions at long wavelengths reveal a pronounced variation in anisotropy between the Anatolian plateau and the Kura basin.« less

Remote-sensing-based analysis of the 1996 surge of Northern Inylchek Glacier, central Tien Shan, Kyrgyzstan

NASA Astrophysics Data System (ADS)

Häusler, Hermann; Ng, Felix; Kopecny, Alexander; Leber, Diethard

2016-11-01

The evolution of Northern Inylchek Glacier and its proglacial lake - Upper Lake Merzbacher - during its 1996 surge and the surrounding decades is analyzed with remote sensing imagery. Overall retreat of the glacier from 1943 to 1996 enlarged the lake to 4 km long and ≈ 100 m deep. The surge in 1996 initiated between 12 September and 7 October and advanced the glacier by 3.7 km to override most of Upper Lake Merzbacher. The surge phase probably ended in December 1996 and involved mean flow velocities across the lower trunk of the glacier that reached 50 m d- 1 over a 32-day period. Water displaced by the surge from Upper Lake Merzbacher, totalling 1.5 × 108 m3 in volume, accelerated filling of Lower Lake Merzbacher downvalley and helped trigger this marginal ice-dammed lake to outburst in a jökulhlaup around late November/early December. The characteristics and duration of the surge render it as similar to temperate glacier surges elsewhere. It may have been facilitated by low basal friction caused by water-saturated sediments in the upper lake bed. Furthermore, bathymetric measurements show that the surge evacuated much sediment into the upper lake, causing its depth to reduce from 20 to 30 m in 1996 to 8 m by 2005 and 2 m by 2011; the corresponding deposition rates imply glacier-catchment specific mean sediment yields of 1.4 to 3.4 × 103 Mg km- 2 a- 1 in the years after the surge. Our study documents novel interactions within a cascade system of glaciers and lakes that exhibits surging and outburst-flood behavior.

Crustal structure beneath the Kenya Rift from axial profile data

USGS Publications Warehouse

Mechie, J.; Keller, Gordon R.; Prodehl, C.; Gaciri, S.; Braile, L.W.; Mooney, W.D.; Gajewski, D.; Sandmeier, K.-J.

1994-01-01

Modelling of the KRISP 90 axial line data shows that major crustal thinning occurs along the axis of the Kenya Rift from Moho depths of 35 km in the south beneath the Kenya Dome in the vicinity of Lake Naivasha to 20 km in the north beneath Lake Turkana. Low Pn velocities of 7.5-7.7 km/s are found beneath the whole of the axial line. The results indicate that crustal extension increases to the north and that the low Pn velocities are probably caused by magma (partial melt) rising from below and being trapped in the uppermost kilometres of the mantle. Along the axial line, the rift infill consisting of volcanics and a minor amount of sediments varies in thickness from zero where Precambrian crystalline basement highs occur to 5-6 km beneath the lakes Turkana and Naivasha. Analysis of the Pg phase shows that the upper crystalline crust has velocities of 6.1-6.3 km/s. Bearing in mind the Cainozoic volcanism associated with the rift, these velocities most probably represent Precambrian basement intruded by small amounts of igneous material. The boundary between the upper and lower crusts occurs at about 10 km depth beneath the northern part of the rift and 15 km depth beneath the southern part of the rift. The upper part of the lower crust has velocities of 6.4-6.5 km/s. The basal crustal layer which varies in thickness from a maximum of 2 km in the north to around 9 km in the south has a velocity of about 6.8 km/s. ?? 1994.

A Northern Sky Survey for Point-like Sources of EeV Neutral Particles with the Telescope Array Experiment

NASA Astrophysics Data System (ADS)

Abbasi, R. U.; Abe, M.; Abu-Zayyad, T.; Allen, M.; Anderson, R.; Azuma, R.; Barcikowski, E.; Belz, J. W.; Bergman, D. R.; Blake, S. A.; Cady, R.; Chae, M. J.; Cheon, B. G.; Chiba, J.; Chikawa, M.; Cho, W. R.; Fujii, T.; Fukushima, M.; Goto, T.; Hanlon, W.; Hayashi, Y.; Hayashida, N.; Hibino, K.; Honda, K.; Ikeda, D.; Inoue, N.; Ishii, T.; Ishimori, R.; Ito, H.; Ivanov, D.; Jui, C. C. H.; Kadota, K.; Kakimoto, F.; Kalashev, O.; Kasahara, K.; Kawai, H.; Kawakami, S.; Kawana, S.; Kawata, K.; Kido, E.; Kim, H. B.; Kim, J. H.; Kim, J. H.; Kitamura, S.; Kitamura, Y.; Kuzmin, V.; Kwon, Y. J.; Lan, J.; Lim, S. I.; Lundquist, J. P.; Machida, K.; Martens, K.; Matsuda, T.; Matsuyama, T.; Matthews, J. N.; Minamino, M.; Mukai, K.; Myers, I.; Nagasawa, K.; Nagataki, S.; Nakamura, T.; Nonaka, T.; Nozato, A.; Ogio, S.; Ogura, J.; Ohnishi, M.; Ohoka, H.; Oki, K.; Okuda, T.; Ono, M.; Oshima, A.; Ozawa, S.; Park, I. H.; Pshirkov, M. S.; Rodriguez, D. C.; Rubtsov, G.; Ryu, D.; Sagawa, H.; Sakurai, N.; Sampson, A. L.; Scott, L. M.; Shah, P. D.; Shibata, F.; Shibata, T.; Shimodaira, H.; Shin, B. K.; Smith, J. D.; Sokolsky, P.; Springer, R. W.; Stokes, B. T.; Stratton, S. R.; Stroman, T. A.; Suzawa, T.; Takamura, M.; Takeda, M.; Takeishi, R.; Taketa, A.; Takita, M.; Tameda, Y.; Tanaka, H.; Tanaka, K.; Tanaka, M.; Thomas, S. B.; Thomson, G. B.; Tinyakov, P.; Tkachev, I.; Tokuno, H.; Tomida, T.; Troitsky, S.; Tsunesada, Y.; Tsutsumi, K.; Uchihori, Y.; Udo, S.; Urban, F.; Vasiloff, G.; Wong, T.; Yamane, R.; Yamaoka, H.; Yamazaki, K.; Yang, J.; Yashiro, K.; Yoneda, Y.; Yoshida, S.; Yoshii, H.; Zollinger, R.; Zundel, Z.

2015-05-01

We report on the search for steady point-like sources of neutral particles around 1018 eV between 2008 and 2013 May with the scintillator SD of the Telescope Array experiment. We found overall no significant point-like excess above 0.5 EeV in the northern sky. Subsequently, we also searched for coincidence with the Fermi bright Galactic sources. No significant coincidence was found within the statistical uncertainty. Hence, we set an upper limit on the neutron flux that corresponds to an averaged flux of 0.07 km-2 yr-1 for E\\gt 1 EeV in the northern sky at the 95% confidence level. This is the most stringent flux upper limit in a northern sky survey assuming point-like sources. The upper limit at the 95% confidence level on the neutron flux from Cygnus X-3 is also set to 0.2 km-2 yr-1 for E\\gt 0.5 EeV. This is an order of magnitude lower than previous flux measurements.

Vertical Distribution of NO, NO(2), and HNO(3) as Derived from Stratospheric Absorption Infrared Spectra.

PubMed

Fontanella, J C; Girard, A; Gramont, L; Louisnard, N

1975-04-01

This paper is devoted to the results concerning NO, NO(2), and HNO(3) obtained during airborne experiments performed in June-July 1973 on Concorde 001. The altitude of flight was about 16 km. Results concerning NO are, within the accuracy of measurement, in agreement with results of a previousspectrometric balloonborne experiment conducted jointly by IASB and ONERA (14 May 1973). Nitric oxide is concentrated in stratospheric layers clearly above the flight altitude. Integrated amount of NO along the optical path is (4 +/- 1.5) x 10(16) mol cm(-2) for a solar elevation varying from +2 degrees above the horizontal plane to -1 degrees . A value of 6 x 10(8) mol cm(-3) may be given as an upper limit for the local concentration at the flight altitude. Thereis no significant difference in the integrated amount observed at sunset and sunrise. Measured value of NO(2) local concentration at 15.5 km is (1.1 +/- 0.2) x 10(9) mol cm(-3), in sunset conditions. This value is not greatly modified between 15 km and 30 km. Measured value of HNO(3). This value increases with altitude between 15 km and 20 km. The local concentration is maximum at 20 km. The measured value is (2 +/- 1) x 10(10) mol cm(-3) at 20 km. It seems that local concentration decreases rapidly above 20 km.

Stable Isotopes of Tilted Ignimbrite Calderas in Nevada

NASA Astrophysics Data System (ADS)

John, D. A.; Watts, K. E.; Hofstra, A. H.; Colgan, J. P.; Henry, C.; Bindeman, I. N.

2013-12-01

Mid-Tertiary calderas are exceptionally well exposed in tilted fault blocks of the northern Great Basin, facilitating detailed evolutionary models of their magmatic-hydrothermal systems. The 29.4 Ma Job Canyon caldera, the oldest of 3 overlapping calderas in the Stillwater Range, west-central Nevada, is tilted ~90° exposing a 10-km-thick section of the crust. Large parts of the >7 km-diameter caldera system, including >2 km thickness of intracaldera rhyolitic tuff, lower parts of an ~2 km thick sequence of post-caldera intermediate lavas, and the upper 500 m of the resurgent granodioritic IXL pluton, were pervasively altered to propylitic, argillic, and sericitic assemblages. Sparse quartz×calcite veins cut the tuff. δ18O values of altered whole rock samples range from +4.8 to -9.1‰ but are mostly -6 to -9‰ at paleodepths >2 km. Calculated magmatic δ18O and δD values range from +6.4 to 8.2‰ and ~-70‰, respectively. Calculated fluid compositions using temperatures from fluid inclusions and mineral assemblages are δ18OH2O=-9.5 to -15‰ and δDH2O=-125 to -135‰ (chlorite) and -70 to -80‰ (epidote). Chlorite-whole rock data suggest fluids that were derived from moderately 18O-exchanged meteoric water. Fault blocks in north-central Nevada expose a >5 km upper crustal cross section through the 12-17 x 20 km, 34 Ma Caetano caldera, including >3 km thickness intracaldera rhyolitic Caetano Tuff. Asymmetric caldera subsidence left a depression >1 km deep partly filled with a lake. Magma resurgence and emplacement of shallow granite porphyry plutons drove a hydrothermal system that altered >120 km2 of the caldera to depths >1.5 km. Alteration was focused in an early granite porphyry intrusion and surrounding upper Caetano Tuff and lacustrine sediments. Early pervasive quartz-kaolinite-pyrite alteration grades outward and downward into more restricted quartz-illite/smectite-pyrite alteration. Hematite, quartz, and barite veins and hydrothermal breccias cut early alteration. Whole rock δ18O values of kaolinite-altered tuff and intrusions are +1.7 to +4.7‰. Magmatic δ18O values of Caetano rocks calculated from zircon and major phenocrysts range narrowly from +10.0 to +10.5‰. Calculated fluid compositions from kaolinite are δ18OH2O=-3 to -7‰ and δDH2O=-148 to -160‰, and from quartz and barite veins are δ18OH2O=-4 to -11‰, indicating that hydrothermal fluids also were dominantly 18O-exchanged meteoric water. Compared to the Job Canyon caldera, δDH2O values for Caetano hydrothermal fluids are ~25‰ lower, suggesting that Caetano formed at an elevation about 1 km higher than Job Canyon along the crest of the Nevadaplano. Both calderas hosted vigorous hydrothermal systems driven by heat from magma resurgence that pervasively altered and exchanged 18O and D with 10s to 100s km3 of rock. However, significant assimilation of low-18O hydrothermally altered rocks is not apparent by the exclusively normal-δ18O values of Job Canyon, Caetano, and adjacent younger magmas. Neither caldera is strongly mineralized, probably in part due to low sulfur contents of the hydrothermal fluids. More acidic fluids at Caetano suggest a larger magmatic gas (HCl) input likely resulting from degassing of shallow resurgent magma into the caldera lake.

Contrasting Patterns of Fine Fluvial Sediment Delivery in Two Adjacent Upland Catchments

NASA Astrophysics Data System (ADS)

Perks, M.; Bracken, L.; Warburton, J.

2010-12-01

Quantifying patterns of fine suspended sediment transfer in UK upland rivers is of vital importance in combating the damaging effects of elevated fluxes of suspended sediment, and sediment associated transport of contaminants, on in-stream biota. In many catchments of the UK there is still a lack of catchment-wide understanding of both the spatial patterns and temporal variation in fine sediment delivery. This poster describes the spatial and temporal distribution of in-stream fine sediment delivery from a network of 44 time-integrated mass flux samplers (TIMs) in two adjacent upland catchments. The two catchments are the Esk (210 km2) and Upper Derwent (236 km2) which drain the North York Moors National Park. Annual suspended sediment loads in the Upper Derwent are 1273 t, whereas in the Esk catchment they are greater at 1778 t. Maximum yields of 22 t km-2 yr -1 were measured in the headwater tributaries of the Rye River (Derwent), whereas peak yields in the Esk are four times greater (98 t km-2 yr-1) on the Butter Beck subcatchment. Analysis of the within-storm sediment dynamics, indicates that the sediment sources within the Upper Derwent catchment are from distal locations possibly mobilised by hillslope runoff processes, whereas in the Esk, sediment sources are more proximal to the channel e.g. within channel stores or bank failures. These estimates of suspended sediment flux are compared with the diffuse pollution potential generated by a risk-based model of sediment transfer (SCIMAP) in order to assess the similarity between the model predictions and observed fluxes.

Seismic Velocity Variation and Evolution of the Upper Oceanic Crust across the Mid-Atlantic Ridge at 1.3°S

NASA Astrophysics Data System (ADS)

Jian, H.; Singh, S. C.

2017-12-01

The oceanic crust that covers >70% of the solid earth is formed at mid-ocean ridges, but get modified as it ages. Understanding the evolution of oceanic crust requires investigations of crustal structures that extend from zero-age on the ridge axis to old crust. In this study, we analyze a part of a 2000-km-long seismic transect that crosses the Mid-Atlantic Ridge segment at 1.3°S, south of the Chain transform fault. The seismic data were acquired using a 12-km-long multi-sensor streamer and dense air-gun shots. Using a combination of downward continuation and seismic tomography methods, we have derived a high-resolution upper crustal velocity structure down to 2-2.5 km depth below the seafloor, from the ridge axis to 3.5 Ma on both sides of the ridge axis. The results demonstrate that velocities increase at all depths in the upper crust as the crust ages, suggesting that hydrothermal precipitations seal the upper crustal pore spaces. This effect is most significant in layer 2A, causing a velocity increase of 0.5-1 km/s after 1-1.5 Ma, beyond which the velocity increase is very small. Furthermore, the results exhibit a significant decrease in both the frequency and amplitude of the low-velocity anomalies associated with faults beyond 1-1.5 Ma, when faults become inactive, suggesting a linkage between the sealing of fault space and the extinction of hydrothermal activity. Besides, the off-axis velocities are systematically higher on the eastern side of the ridge axis compared to on the western side, suggesting that a higher hydrothermal activity should exist on the outside-corner ridge flank than on the inside-corner flank. While the tomography results shown here cover 0-3.5 Ma crust, the ongoing research will further extend the study area to older crust and also incorporating pre-stack migration and full waveform inversion methods to improve the seismic structure.

Aleutian basin oceanic crust

USGS Publications Warehouse

Christeson, Gail L.; Barth, Ginger A.

2015-01-01

We present two-dimensional P-wave velocity structure along two wide-angle ocean bottom seismometer profiles from the Aleutian basin in the Bering Sea. The basement here is commonly considered to be trapped oceanic crust, yet there is a change in orientation of magnetic lineations and gravity features within the basin that might reflect later processes. Line 1 extends ∼225 km from southwest to northeast, while Line 2 extends ∼225 km from northwest to southeast and crosses the observed change in magnetic lineation orientation. Velocities of the sediment layer increase from 2.0 km/s at the seafloor to 3.0–3.4 km/s just above basement, crustal velocities increase from 5.1–5.6 km/s at the top of basement to 7.0–7.1 km/s at the base of the crust, and upper mantle velocities are 8.1–8.2 km/s. Average sediment thickness is 3.8–3.9 km for both profiles. Crustal thickness varies from 6.2 to 9.6 km, with average thickness of 7.2 km on Line 1 and 8.8 km on Line 2. There is no clear change in crustal structure associated with a change in orientation of magnetic lineations and gravity features. The velocity structure is consistent with that of normal or thickened oceanic crust. The observed increase in crustal thickness from west to east is interpreted as reflecting an increase in melt supply during crustal formation.

Mars: A water-rich planet?

USGS Publications Warehouse

Carr, M.H.

1986-01-01

Mars had outgassed at least 0.5 to 1 km of water, 10 to 20 bar of CO2, and 0.1 to 0.3 bar of N2. The volatiles that have been retained are mostly in the cratered uplands. Terrain softening, fretted channels, debris flows, and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes (>30??) contain ice in amounts that exceed the porosity, estimated to be 10-20%. Theoretical studies, and lack of these features in the cratered uplands at low latitudes, suggest that the upper 1 km of the uplands at low latitudes is ice poor. However, valley networks indicate that water was present near the surface early in the planet's history, although in amounts smaller than at high latitudes. The entire upper 1 km, planetwide is estimated to have contained 75-125 m of water at the end of heavy bombardment. The largest sink for water is the megaregolith below 1 km. Episodic eruption of water from the deep megaregolith cut many of the large outflow channels. From the volume of water needed to cut the circum-Chryse channels, and assuming uniform planetwide distribution of water, the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment, thereby giving a total minimum inventory of 424-475 m planetwide. Most of the water lost from the low-latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains. Most of the water involved in cutting the outflow channels is in the low-lying northern plains where a variety of features that have been attributed to ground ice is present. A large fraction of the planet's surface has been overplated with water-poor volcanics, of which we have samples in the SNC meteorites. The younger volcanics have reacted extensively with the old volatile-rich basement. Some of the CO2 and N2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes. The remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment. ?? 1986.

Radiative Heating of the ISCCP Upper Level Cloud Regimes and its Impact on the Large-scale Tropical Circulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Wei; Schumacher, Courtney; McFarlane, Sally A.

2013-01-31

Radiative heating profiles of the International Satellite Cloud Climatology Project (ISCCP) cloud regimes (or weather states) were estimated by matching ISCCP observations with radiative properties derived from cloud radar and lidar measurements from the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) sites at Manus, Papua New Guinea, and Darwin, Australia. Focus was placed on the ISCCP cloud regimes containing the majority of upper level clouds in the tropics, i.e., mesoscale convective systems (MCSs), deep cumulonimbus with cirrus, mixed shallow and deep convection, and thin cirrus. At upper levels, these regimes have average maximum cloud occurrences ranging from 30% tomore » 55% near 12 km with variations depending on the location and cloud regime. The resulting radiative heating profiles have maxima of approximately 1 K/day near 12 km, with equal heating contributions from the longwave and shortwave components. Upper level minima occur near 15 km, with the MCS regime showing the strongest cooling of 0.2 K/day and the thin cirrus showing no cooling. The gradient of upper level heating ranges from 0.2 to 0.4 K/(day∙km), with the most convectively active regimes (i.e., MCSs and deep cumulonimbus with cirrus) having the largest gradient. When the above heating profiles were applied to the 25-year ISCCP data set, the tropics-wide average profile has a radiative heating maximum of 0.45Kday-1 near 250 hPa. Column-integrated radiative heating of upper level cloud accounts for about 20% of the latent heating estimated by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). The ISCCP radiative heating of tropical upper level cloud only slightly modifies the response of an idealized primitive equation model forced with the tropics-wide TRMM PR latent heating, which suggests that the impact of upper level cloud is more important to large-scale tropical circulation variations because of convective feedbacks rather than direct forcing by the cloud radiative heating profiles. However, the height of the radiative heating maxima and gradient of the heating profiles are important to determine the sign and patterns of the horizontal circulation anomaly driven by radiative heating at upper levels.« less

Measurement of middle and upper atmospheric horizontal winds with a submillimeter/THz limb sounder: results from JEM/SMILES and simulation study for SMILES-2

NASA Astrophysics Data System (ADS)

Baron, Philippe; Manago, Naohiro; Ozeki, Hiroyuki; Yoshihisa, Irimajiri; Donal, Murtagh; Yoshinori, Uzawa; Satoshi, Ochiai; Masato, Shiotani; Makoto, Suzuki

2016-04-01

In a near future, ESA will launch the Atmospheric Dynamics Mission (ADM) equipped with a lidar for measuring tropospheric and lower stratospheric winds. NASA will continue a long-term series of upper atmospheric wind measurements (altitudes >80 km) with the new Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) on the Ionospheric Connection Explorer (ICON) satellite. No mission is planned to observe winds in the middle atmosphere (30-80 km), though they are recognized as essential parameters for understanding atmospheric dynamics and the vertical coupling between atmospheric regions. They are also promising data for improving long-term weather forecast and climate modelling. It has been demonstrated with the Superconducting Submillimeter Wave Limb Emission Sounder (SMILES, Oct 2009 - Apr 2010) that a 4-K cooled microwave radiometer can provide data to fill the altitude gap in the wind measurements. Its possible successor named SMILES-2, is being designed in Japan for the study of the middle and upper atmospheric chemistry and dynamics (O3, H2O, T, atomic O, OH, HO2, ClO, BrO, ...). If realized, the instrument will measure sub-millimeter and THz molecular spectral lines (616-150 μm) with high sensitivity and frequency resolution. The SMILES-2 characteristics are very well suited for horizontal wind observations between 20 km to more than 160 km. The best performances are found between 35-90 km where the retrieval precision is better than 3 m/s for a vertical resolution of 2-3 km [1]. In this presentation, we summarize the results obtained from SMILES and assess the measurement performances of SMILES-2 to measure horizontal winds. [1] P. Baron, N. Manago, H. Ozeki, Y. Irimajiri, D. Murtagh, Y. Uzawa, S. Ochiai, M. Shiotani, M. Suzuki: "Measurement of stratospheric and mesospheric winds with a SubMillimeter wave limb sounder: Results from JEM/SMILES and simulation study for SMILES-2"; Proc. of SPIE Remote sensing, 96390N-96390N-20, 2015

Long-term temperature observations from the troposphere to upper mesosphere over Mauna Loa, HI (19.5N, 155.6W) and Table Mountain, CA (34.4N, 117.7W) by JPL Lidars and nearby Radiosondes

NASA Astrophysics Data System (ADS)

Li, T.; Leblanc, T.; McDermid, S.; Wu, D. L.

2007-12-01

The JPL Rayleigh lidars at Mauna Loa Observatory (MLO), HI (19.5N, 155.6W) and Table Mountain Observatory (TMO), CA (34.4N, 117.7W) have been operated for the regular nighttime data acquisition of temperature since 1994 and 1989 respectively. Using the monthly mean temperature vertical profiles observed by the JPL lidars (35- 85km) and nearby radiosondes (5-30km), and with the linear regression analysis, we are able to extract the temperature trend, solar cycle, El Nino South Oscillation (ENSO), and Quasi-Biennial Oscillation (QBO) signals from the troposphere to upper mesosphere over MLO and TMO. The temperature trends show different behaviors at two sites, minor trend at MLO, but more negative trend at TMO. The solar cycle responses in temperature are generally positive above the middle stratosphere at both sites, but negative response at MLO and positive at TMO below. During the El Nino events, the warmer temperatures in the troposphere and upper mesosphere, and the colder temperatures in the stratosphere and lower mesosphere were observed at MLO and almost visa verse at TMO. The significant QBO oscillations were observed in the stratosphere with amplitudes of ~2-3K and with clearer downward phase progression at MLO than that at TMO. The mesospheric QBO near 75-85km is clearly present at both sites with amplitude of ~2K and with longer vertical wavelength than that in stratosphere. In addition, we calculated the GW variances using lidar temperature profiles with 30min and 1km resolutions in the upper stratosphere (38-50km) and lower mesosphere (50-62km), and nearby radiosondes in the lower stratosphere (18-30km). The monthly mean GW variances clearly show an annual oscillation with a maximum in the winter and minimum in the summer. The QBO signature could be clearly seen in the lower stratosphere. In the upper stratosphere, a longer period oscillation (~5-6 years) with maxima in 2000-2001 and 2006 was revealed to synchronize with the solar maximum and minimum. No clear signature of GW activity in the lower mesosphere could be associated to that in the upper stratosphere, suggesting that part of gravity waves may either dissipated or reflected when crossing the stratopause region.

Structure of the middle atmosphere of Venus

NASA Astrophysics Data System (ADS)

Zasova, Ludmila

Middle atmosphere of Venus (55-100 km), its mesosphere, is the important layer of atmosphere, where 70 % of the solar energy is absorbed. Most of this absorption takes place in the upper clouds in the altitude range 58-68 km in the spectral range 0.32-0.5 µm. It leads to generation of the thermal tides, playing important role in support of the superrotation. In the frame of COSPAR model VIRA (ASR, 11,1985) the model of the thermal structure of the middle atmosphere was constructed for 5 latitude ranges, based mainly on the Pioneer Venus ORO and OIR data. Using Venera-15 Fourier Spectrometry data, which allow to retrieve the temperature and aerosol profiles in a self consistent way from each spectrum, we enable to update the model of the middle atmosphere, including the local time variation of the temperature for VIRA latitude ranges (Cosmic Research, 44, 4, 2006). From Venera-15 data it was shown that variation of temperature in the middle atmosphere is well described by thermal tides with harmonics 1, 1/2, 1/3, 1/4 Venusian day, the amplitudes and phases of which depend on latitude and altitude. The model of the upper clouds (VIRA) may also be updated using Venera-15 data. It was shown that the main latitude trend is the decreasing of the upper cloud boundary from 68 km at low latitudes to 60-62 km at high latitudes. Local time variation has a solar related dependence: 1 and 1/2 day components were revealed. Venus Express continues to obtain a lot of data, which may be used for the improvement of the model of the middle atmosphere and the clouds.

Global water vapor distributions in the stratosphere and upper troposphere derived from 5.5 years of SAGE II observations (1986-1991)

NASA Astrophysics Data System (ADS)

Chiou, E. W.; McCormick, M. P.; Chu, W. P.

1997-08-01

Global distributions of water vapor in the stratosphere and upper troposphere are presented on the basis of ˜5.5 years (January 1986 to May 1991) of observations from the Stratospheric Aerosol and Gas Experiment II (SAGE II) aboard the Earth Radiation Budget Satellite (ERBS). Tabulations are included for seasonal zonal mean water vapor mixing ratios (in parts per million by volume) with 1-km vertical resolution and an altitude range from 6 to 40 km. Several climatological features identified in a previous study [McCormick et al., 1993], based on 3 years of observations, have been confirmed by this study: (1) the existence of a region of minimum water vapor (the hygropause) at all latitude bands; (2) the increase in the distance between the tropopause and the hygropause from 1 km at low latitudes to 4 km at high latitudes; and (3) the appearance of a positive poleward gradient throughout all seasons for fixed altitudes between 20 km and 40 km. The latitudinal variation of water vapor mixing ratio at 20 km is characterized by a symmetric pattern with a minimum occurring at the equator. However, the corresponding variations at 25 and 30 km indicate a shift of the minimum toward the summer hemisphere. For the latitude zones 0°-20° and 20°-40° in both hemispheres, the seasonal variations of the hygropause reveal that the altitude as well as the value of the minimum water vapor mixing ratio remain essentially unchanged from December, January, and February to March, April, and May. During September, October, and November the weakening of the hygropause and the spreading of the region of minimum water vapor to a wider altitude range are identified throughout these low-latitude and midlatitude zones. For the upper troposphere the clear-sky relative humidities at 300 mbar show a typical range of 5-60%, which is consistent with previous findings based on Meteosat 6.3 μm measurements. In addition, the unique capability of SAGE II observations has provided us with unprecedented vertically resolved moisture information for the upper troposphere. For example, the integrated column water vapor content for the 300- to 100-mbar layer ranges from 0.002 to 0.01 g/cm2 with larger longitudinal variability in the tropics. The integrated column water vapor content from 500 to 100 mbar is found to be significantly larger in the eastern hemisphere than in the western hemisphere. The corresponding integrated water vapor content at high latitudes increases by a factor of 6 from winter to summer (0.02 g/cm2 compared with 0.13 g/cm2).

Sound velocities of olivine at high pressures and temperatures and the composition of Earth's upper mantle

NASA Astrophysics Data System (ADS)

Zhang, Jin S.; Bass, Jay D.

2016-09-01

We present the elastic properties of San Carlos olivine up to P = 12.8(8) GPa and T = 1300(200) K using Brillouin spectroscopy with CO2 laser heating. A comparison of our results with the global seismic model AK135 yields average olivine content near 410 km depth of about 37% and 43% in a dry and wet (1.9 wt % H2O) upper mantle, respectively. These olivine contents are far less than in the pyrolite model. However, comparisons of our results with regional seismic models lead to very different conclusions. High olivine contents of up to 87% are implied by seismic models of the western U.S. and eastern Pacific regions. In contrast, we infer less than 35% olivine under the central Pacific. Strong variations of olivine content and upper mantle lithologies near the 410 km discontinuity are suggested by regional seismic models.

Evaluation of Satellite-Based Upper Troposphere Cloud Top Height Retrievals in Multilayer Cloud Conditions During TC4

NASA Technical Reports Server (NTRS)

Chang, Fu-Lung; Minnis, Patrick; Ayers, J. Kirk; McGill, Matthew J.; Palikonda, Rabindra; Spangenberg, Douglas A.; Smith, William L., Jr.; Yost, Christopher R.

2010-01-01

Upper troposphere cloud top heights (CTHs), restricted to cloud top pressures (CTPs) less than 500 hPa, inferred using four satellite retrieval methods applied to Twelfth Geostationary Operational Environmental Satellite (GOES-12) data are evaluated using measurements during the July August 2007 Tropical Composition, Cloud and Climate Coupling Experiment (TC4). The four methods are the single-layer CO2-absorption technique (SCO2AT), a modified CO2-absorption technique (MCO2AT) developed for improving both single-layered and multilayered cloud retrievals, a standard version of the Visible Infrared Solar-infrared Split-window Technique (old VISST), and a new version of VISST (new VISST) recently developed to improve cloud property retrievals. They are evaluated by comparing with ER-2 aircraft-based Cloud Physics Lidar (CPL) data taken during 9 days having extensive upper troposphere cirrus, anvil, and convective clouds. Compared to the 89% coverage by upper tropospheric clouds detected by the CPL, the SCO2AT, MCO2AT, old VISST, and new VISST retrieved CTPs less than 500 hPa in 76, 76, 69, and 74% of the matched pixels, respectively. Most of the differences are due to subvisible and optically thin cirrus clouds occurring near the tropopause that were detected only by the CPL. The mean upper tropospheric CTHs for the 9 days are 14.2 (+/- 2.1) km from the CPL and 10.7 (+/- 2.1), 12.1 (+/- 1.6), 9.7 (+/- 2.9), and 11.4 (+/- 2.8) km from the SCO2AT, MCO2AT, old VISST, and new VISST, respectively. Compared to the CPL, the MCO2AT CTHs had the smallest mean biases for semitransparent high clouds in both single-layered and multilayered situations whereas the new VISST CTHs had the smallest mean biases when upper clouds were opaque and optically thick. The biases for all techniques increased with increasing numbers of cloud layers. The transparency of the upper layer clouds tends to increase with the numbers of cloud layers.

Glacial stages and post-glacial environmental evolution in the Upper Garonne valley, Central Pyrenees.

PubMed

Fernandes, M; Oliva, M; Palma, P; Ruiz-Fernández, J; Lopes, L

2017-04-15

The maximum glacial extent in the Central Pyrenees during the Last Glaciation is known to have occurred before the global Last Glacial Maximum, but the succession of cold events afterwards and their impact on the landscape are still relatively unknown. This study focuses on the environmental evolution in the upper valley of the Garonne River since the Last Glaciation. Geomorphological mapping allows analysis of the spatial distribution of inherited and current processes and landforms in the study area. The distribution of glacial records (moraines, till, erratic boulders, glacial thresholds) suggests the existence of four glacial stages, from the maximum expansion to the end of the glaciation. GIS modeling allows quantification of the Equilibrium Line Altitude, extent, thickness and volume of ice in each glacial stage. During the first stage, the Garonne glacier reached 460m in the Loures-Barousse-Barbazan basin, where it formed a piedmont glacier 88km from the head and extended over 960km 2 . At a second stage of glacier stabilization during the deglaciation process, the valley glaciers were 12-23km from the head until elevations of 1000-1850m, covering an area of 157km 2 . Glaciers during stage three remained isolated in the upper parts of the valley, at heights of 2050-2200m and 2.6-4.5km from the head, with a glacial surface of 16km 2 . In stage four, cirque glaciers were formed between 2260m and 2590m, with a length of 0.4-2km and a glacial area of 5.7km 2 . Also, the wide range of periglacial, slope, nival and alluvial landforms existing in the formerly glaciated environments allows reconstruction of the post-glacial environmental dynamics in the upper Garonne basin. Today, the highest lands are organized following three elevation belts: subnival (1500-1900m), nival (1900-2300m) and periglacial/cryonival (2300-2800m). Copyright © 2017 Elsevier B.V. All rights reserved.

Effects of upper mantle heterogeneities on the lithospheric stress field and dynamic topography

NASA Astrophysics Data System (ADS)

Osei Tutu, Anthony; Steinberger, Bernhard; Sobolev, Stephan V.; Rogozhina, Irina; Popov, Anton A.

2018-05-01

The orientation and tectonic regime of the observed crustal/lithospheric stress field contribute to our knowledge of different deformation processes occurring within the Earth's crust and lithosphere. In this study, we analyze the influence of the thermal and density structure of the upper mantle on the lithospheric stress field and topography. We use a 3-D lithosphere-asthenosphere numerical model with power-law rheology, coupled to a spectral mantle flow code at 300 km depth. Our results are validated against the World Stress Map 2016 (WSM2016) and the observation-based residual topography. We derive the upper mantle thermal structure from either a heat flow model combined with a seafloor age model (TM1) or a global S-wave velocity model (TM2). We show that lateral density heterogeneities in the upper 300 km have a limited influence on the modeled horizontal stress field as opposed to the resulting dynamic topography that appears more sensitive to such heterogeneities. The modeled stress field directions, using only the mantle heterogeneities below 300 km, are not perturbed much when the effects of lithosphere and crust above 300 km are added. In contrast, modeled stress magnitudes and dynamic topography are to a greater extent controlled by the upper mantle density structure. After correction for the chemical depletion of continents, the TM2 model leads to a much better fit with the observed residual topography giving a good correlation of 0.51 in continents, but this correction leads to no significant improvement of the fit between the WSM2016 and the resulting lithosphere stresses. In continental regions with abundant heat flow data, TM1 results in relatively small angular misfits. For example, in western Europe the misfit between the modeled and observation-based stress is 18.3°. Our findings emphasize that the relative contributions coming from shallow and deep mantle dynamic forces are quite different for the lithospheric stress field and dynamic topography.

The crust and uppermost mantle structure in Southern Peru from ambient noise and earthquake surface wave analysis

NASA Astrophysics Data System (ADS)

Ma, Y.; Clayton, R. W.

2012-12-01

We determine the Vs structure to a depth of 140 km of Southern Peru, where the subducted Nazca slab changes from normal to flat subduction. The data are from a box-like array that is approximately 300 km on a side, and with 150 stations in total. The structure is inverted from surface wave dispersion curves measured between 5 s to 23 s period from ambient noise cross-correlations, and between 25 s to 69 s from earthquake two-plane-wave analysis. From the map views of different depths, we observe that: (1) The forearc region is characterized by shallow crustal thickness and higher crustal velocity compared with the backarc. (2) The upper-crust velocity in the backarc above normal subduction (3.0-3.2 km/s) is lower compared with that above flat subduction region (3.2-3.4 km/s). The low velocity coincides with the deep sediments above the Altiplano plateau. (3) The transition from the normal to flat subduction is characterized by a comparatively lower upper-mid crust velocity (3.2-3.4 km/s). The lower velocity zone also coincides with the highest topography (>4700 m) in the study area. (4) The mantle wedge velocity above the flat subduction (4.6-4.9 km/s) is higher than the surrounding mantle and the mantle above the normal subduction region (4.3-4.5 km/s). We deduce that the upper-mid crust above the transition of the slab geometry is probably more felsic, which can be due to the old volcanic activity during the normal-flat transition, and thus can more easily accommodate the crustal shortening. The lack of present volcanism above the flat subduction, however, could be explained by the high velocity anomaly related to the flat slab. It may indicate a cold environment, and thus the lack of mantle melting.

Precise hypocenter distribution and earthquake generating and stress in and around the upper-plane seismic belt in the subducting Pacific slab beneath NE Japan

NASA Astrophysics Data System (ADS)

Kita, S.; Okada, T.; Nakajima, J.; Matsuzawa, T.; Uchida, N.; Hasegawa, A.

2007-12-01

1. Introduction We found an intraslab seismic belt (upper-plane seismic belt) in the upper plane of the double seismic zone within the Pacific slab, running interface at depths of 70-100km beneath the forearc area. The location of the deeper limits of this belt appears to correspond to one of the facies boundaries (from jadeite lawsonite blueschist to lawsonite amphibole eclogite) in the oceanic crust [Kita et al., 2006, GRL]. In this study, we precisely relocated intraslab earthquakes by using travel time differences calculated by the waveform cross-spectrum analysis to obtain more detailed distribution of the upper plane-seismic belt within the Pacific slab beneath NE Japan. We also discuss the stress field in the slab by examining focal mechanisms of the earthquakes. 2. Data and Method We relocated events at depths of 50-00 km for the period from March 2003 to November 2006 from the JMA earthquake catalog. We applied the double-difference hypocenter location method (DDLM) by Waldhauser and Ellsworth (2000) to the arrival time data of the events. We use relative earthquake arrival times determined both by the waveform cross-spectrum analysis and by the catalog-picking data. We also determine focal mechanisms using the P wave polarity. 3. Spatial distribution of relocated hypocenters In the upper portion of the slab crust, seismicity is very active and distributed relatively homogeneously at depths of about 70-100km parallel to the volcanic front, where the upper-plane seismic belt has been found. In the lower portion of slab crust and/or the uppermost portion of the slab mantle, seismicity is spatially very limited to some small areas (each size is about 20 x 20km) at depths around 65km. Two of them correspond to the aftershock area of the 2003 Miyagi (M7.1) intraslab earthquake and that of the 1987 Iwaizumi (M6.6) intraslab earthquake, respectively. Based on the dehydration embrittelment hypothesis, the difference of the spatial distribution of the seismicity in the slab should correspond to the difference of the spatial distribution of the hydrated minerals and their dehydration reactions. In the upper slab crust, the upper-plane seismic belt is found because the hydrated minerals could be distributed homogeneously and the dehydration reaction (from jadeite lawsonite blueschist to lawsonite amphibole eclogite [Hacker et al., 2003b]) occurs perhaps largely at depth of 70-100km. Our result also suggests that in the lower portion of the slab crust and/or the uppermost portion of the slab mantle, the hydrated minerals could be inhomogeneously distributed and the seismicity occurs at depths around 65km, where another dehydration reaction may exist. 4. Characteristics of the focal mechanisms We examined the stress distribution within the slab by using focal mechanisms of the upper plane, interplane and lower plane events. From the plate interface to about 20 km below it, downdip-compressional (DC) type events are dominant. Below 20km from the plate interface, downdip-tensional (DT) type events are dominant. Many of interplane events have DC type focal mechanisms because of their locations in the uppermost portions of the slab mantle. These results indicate that the stress neutral plane from the DC type to DT type could be located at depth of about 20km from the plate interface.

Differences in the Upper Mantle Structure between 'Hot' and 'Cold' Areas in North America based on USArray Seismic Data along California - Virginia Profile

NASA Astrophysics Data System (ADS)

Dec, M.; Sroda, P.; Tesauro, M.; Kaban, M. K.; Perchuc, E.

2013-12-01

Nowadays, United States is an area extensively studied by seismic research due to the fact that the EarthScope USArray project provides an unique opportunity to verify previous seismological models and improve our understanding of the upper mantle structure. The data from this experiment are fundamental to study the upper mantle structure because they allow us to present much more detailed analysis. In this study we use the data recorded by the Transportable Array of the USArray and data from the ISC bulletin. We refer also to data from longitudinal Early Rise project while analysing New Madrid Seismic Zone. We use the travel time data from the earthquakes recorded at a distance up to 3500 km in order to image the upper mantle down to about 600 km depth. We present P- and S-wave velocity models for the tectonically stable central part of US and for the active western part. The 1D models are constructed based on the forward modelling of traveltimes from the events located along the California - Virginia profile, for e.g. in California, Colorado or Virginia. This provides a possibility to update the previous MP-1 model (Malinowski et al., 2010). The models were corrected for the crustal effect using the crustal model of Tesauro et al. (2013). All the models have been verified by synthetic seismograms calculated using the reflectivity method. The models show significant differences in the first-arrivals observed at the 800-1800 km epicentral distance range. In the Western, tectonically active region, the 300-km discontinuity is observed. It is interpreted based on the refracted phases with the apparent velocity of 8.9-9.0 km/s and clearly observed reflections. In this area, a low-velocity zone at the bottom of the upper mantle significantly deepens the 410-km discontinuity. The stable North American Craton is characterized by blurred arrivals from the 300-km discontinuity. These 1D models of the upper mantle structure in North America served as a starting point for calculation of a 2D model along the profile using forward and inversion approach. We distinguish three parts in our profile: western - tectonically active, central cratonic - stable one and eastern - tectonically active. The New Madrid Seismic Zone is characterized by an anomalous structure in the lower lithosphere at the offset ~2500km. Very interesting part of the studied area is the marginal part of North American Craton, which separates two tectonically different areas. The seismic P- and S-wave velocity models were inverted for temperature using different mantle composition and anelasticity models. The modelling results are in agreement with those obtained for the strength and the elastic thickness of the lithosphere.

Snaring to control feral pigs sus scrofa in a remote Hawaiian rain forest

USGS Publications Warehouse

Anderson, Stephen J.; Stone, Charles P.

1993-01-01

Feral pig Sus scrofa control in Kipahulu Valley, a remote rain forest in Haleakala National Park, Maui, Hawaiian Islands, has been achieved with snares over a 45-month period. Initial pig densities in fenced management units of 6·2 km2 and 7·8 km2were estimated at 6 animals/km2 and 14·3 animals/km2 for the two units, based on population reconstruction from animals killed and aged. During the 45 months of the study, 1978 snares were set, and 1·6 million snare nights were logged. Snare density reached 96/km2 and 200/km2 for the two management units by the end of the study. A mean effort of 43 worker hours/pig was used to remove 53 pigs from the upper management unit, and a mean of 7 worker hours/pig to remove 175 animals from the more densely populated lower unit. Pig activity monitoring along transects provided a good measure of control effectiveness until densities of about 1 pig/km2 were achieved, after which transects became less useful than scouting for determining pig activity.

Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust

USGS Publications Warehouse

von Huene, Roland E.; Scholl, D. W.

1991-01-01

At ocean margins where two plates converge, the oceanic plate sinks or is subducted beneath an upper one topped by a layer of terrestrial crust. This crust is constructed of continental or island arc material. The subduction process either builds juvenile masses of terrestrial crust through arc volcanism or new areas of crust through the piling up of accretionary masses (prisms) of sedimentary deposits and fragments of thicker crustal bodies scraped off the subducting lower plate. At convergent margins, terrestrial material can also bypass the accretionary prism as a result of sediment subduction, and terrestrial matter can be removed from the upper plate by processes of subduction erosion. Sediment subduction occurs where sediment remains attached to the subducting oceanic plate and underthrusts the seaward position of the upper plate's resistive buttress (backstop) of consolidated sediment and rock. Sediment subduction occurs at two types of convergent margins: type 1 margins where accretionary prisms form and type 2 margins where little net accretion takes place. At type 2 margins (???19,000 km in global length), effectively all incoming sediment is subducted beneath the massif of basement or framework rocks forming the landward trench slope. At accreting or type 1 margins, sediment subduction begins at the seaward position of an active buttress of consolidated accretionary material that accumulated in front of a starting or core buttress of framework rocks. Where small-to-mediumsized prisms have formed (???16,300 km), approximately 20% of the incoming sediment is skimmed off a detachment surface or decollement and frontally accreted to the active buttress. The remaining 80% subducts beneath the buttress and may either underplate older parts of the frontal body or bypass the prism entirely and underthrust the leading edge of the margin's rock framework. At margins bordered by large prisms (???8,200 km), roughly 70% of the incoming trench floor section is subducted beneath the frontal accretionary body and its active buttress. In rounded figures the contemporary rate of solid-volume sediment subduction at convergent ocean margins (???43,500 km) is calculated to be 1.5 km3/yr. Correcting type 1 margins for high rates of terrigenous seafloor sedimentation during the past 30 m.y. or so sets the long-term rate of sediment subduction at 1.0 km3/yr. The bulk of the subducted material is derived directly or indirectly from continental denudation. Interstitial water currently expulsed from accreted and deeply subducted sediment and recycled to the ocean basins is estimated at 0.9 km3/yr. The thinning and truncation caused by subduction erosion of the margin's framework rock and overlying sedimentary deposits have been demonstrated at many convergent margins but only off northern Japan, central Peru, and northern Chile has sufficient information been collected to determine average or long-term rates, which range from 25 to 50 km3/m.y. per kilometer of margin. A conservative long-term rate applicable to many sectors of convergent margins is 30 km3/km/m.y. If applied to the length of type 2 margins, subduction erosion removes and transports approximately 0.6 km3/yr of upper plate material to greater depths. At various places, subduction erosion also affects sectors of type 1 margins bordered by small- to medium-sized accretionary prisms (for example, Japan and Peru), thus increasing the global rate by possibly 0.5 km3/yr to a total of 1.1 km3/yr. Little information is available to assess subduction erosion at margins bordered by large accretionary prisms. Mass balance calculations allow assessments to be made of the amount of subducted sediment that bypasses the prism and underthrusts the margin's rock framework. This subcrustally subducted sediment is estimated at 0.7 km3/yr. Combined with the range of terrestrial matter removed from the margin's rock framework by subduction erosion, the global volume of subcrustally subducted materia

Crustal and upper mantle S-wave velocity structures across the Taiwan Strait from ambient seismic noise and teleseismic Rayleigh wave analyses

NASA Astrophysics Data System (ADS)

Huang, Y.; Yao, H.; Wu, F. T.; Liang, W.; Huang, B.; Lin, C.; Wen, K.

2013-12-01

Although orogeny seems to have stopped in western Taiwan large and small earthquakes do occur in the Taiwan Strait. Limited studies have focused on this region before and were barely within reach for comprehensive projects like TAICRUST and TAIGER for logistical reasons; thus, the overall crustal structures of the Taiwan Strait remain unknown. Time domain empirical Green's function (TDEGF) from ambient seismic noise to determine crustal velocity structure allows us to study an area using station pairs on its periphery. This research aims to resolve 1-D average crustal and upper mantle S-wave velocity (Vs) structures alone paths of several broadband station-pairs across the Taiwan Strait; 5-120 s Rayleigh wave phase velocity dispersion data derived by combining TDEGF and traditional surface wave two-station method (TS). The average Vs structures show significant differences in the upper 15 km as expected. In general, the highest Vs are observed in the coastal area of Mainland China and the lowest Vs appear along the southwest offshore of the Taiwan Island; they differ by about 0.6-1.1 km/s. For different parts of the Strait, the Vs are lower in the middle by about 0.1-0.2 km/s relative to those in the northern and southern parts. The overall crustal thickness is approximately 30 km, much thinner and less variable than under the Taiwan Island.

Observations of planetary mixed Rossby-gravity waves in the upper stratosphere

NASA Technical Reports Server (NTRS)

Randel, William J.; Boville, Byron A.; Gille, John C.

1990-01-01

Observational evidence is presented for planetary scale (zonal wave number 1-2) mixed Rossby-gravity (MRG) waves in the equatorial upper stratosphere (35-50 km). These waves are detected in LIMS measurements as coherently propagating temperature maxima of amplitude 0.1-0.3 K, which are antisymmetric (out of phase) about the equator, centered near 10-15 deg north and south latitude. These features have vertical wavelengths of order 10-15 km, periods near 2-3 days, and zonal phase velocities close to 200 m/s. Both eastward and westward propagating waves are found, and the observed vertical wavelengths and meridional structures are in good agreement with the MRG dispersion relation. Theoretical estimates of the zonal accelerations attributable to these waves suggest they do not contribute substantially to the zonal momentum balance in the middle atmosphere.

Seismic velocity and attenuation structures in the Earth's inner core

NASA Astrophysics Data System (ADS)

Yu, Wen-Che

2007-12-01

I study seismic velocity and attenuation structures in the top 400 km of the Earth's inner core along equatorial paths, velocity-attenuation relationship, and seismic anisotropy in the top of the inner core beneath Africa. Seismic observations exhibit "east-west" hemispheric differences in seismic velocity, attenuation, and anisotropy. Joint modeling of the PKiKP-PKIKP and PKPbc-PKIKP phases is used to constrain seismic velocity and attenuation structures in the top 400 km of the inner core for the eastern and western hemispheres. The velocity and attenuation models for the western hemisphere are simple, having a constant velocity gradient and a Q value of 600 in the top 400 km of the inner core. The velocity and attenuation models for the eastern hemisphere appear complex. The velocity model for the eastern hemisphere has a small velocity gradient in the top 235 km, a steeper velocity gradient at the depth range of 235 - 375 km, and a gradient similar to PREM in the deeper portion of the inner core. The attenuation model for the eastern hemisphere has a Q value of 300 in the top 300 km and a Q value of 600 in the deeper portion of the inner core. The study of velocity-attenuation relationship reveals that inner core is anisotropic in both velocity and attenuation, and the direction of high attenuation corresponding to that of high velocity. I hypothesize that the hexagonal close packed (hcp) iron crystal is anisotropic in attenuation, with the axis of high attenuation corresponding to that of high velocity. Anisotropy in the top of the inner core beneath Africa is complex. Beneath eastern Africa, the thickness of the isotropic upper inner core is about 0 km. Beneath central and western Africa, the thickness of the isotropic upper inner core increases from 20 to 50 km. The velocity increase across the isotropic upper inner core and anisotropic lower inner core boundary is sharp, laterally varying from 1.6% - 2.2%. The attenuation model has a Q value of 600 for the isotropic upper inner core and 150 to 400 for the anisotropic lower inner core.

Upper Limit for $$\

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abadias, Juan Bofill

1984-01-01

Limits on the mass squared difference of neutrino mass eigenstatesmore » $$\\delta2 = m^2_1 - m^2_2$$, have been determined in a fine grained calorimeter exposed to the dichromatic beam at Fermilab. The fine grained calorimeter is located at a distance of 1.3 Km from the neutrino source making it suitable for oscillations studies. The interaction of a $$\

Version 1.3 AIM SOFIE measured methane (CH4): Validation and seasonal climatology

NASA Astrophysics Data System (ADS)

Rong, P. P.; Russell, J. M.; Marshall, B. T.; Siskind, D. E.; Hervig, M. E.; Gordley, L. L.; Bernath, P. F.; Walker, K. A.

2016-11-01

The V1.3 methane (CH4) measured by the Aeronomy of Ice in the Mesosphere (AIM) Solar Occultation for Ice Experiment (SOFIE) instrument is validated in the vertical range of 25-70 km. The random error for SOFIE CH4 is 0.1-1% up to 50 km and degrades to 9% at ˜ 70 km. The systematic error remains at 4% throughout the stratosphere and lower mesosphere. Comparisons with CH4 data taken by the SCISAT Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) and the Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) show an agreement within 15% in the altitude range 30-60 km. Below 25 km SOFIE CH4 is systematically higher (≥20%), while above 65 km it is lower by a similar percentage. The sign change from the positive to negative bias occurs between 55 km and 60 km (or 40 km and 45 km) in the Northern (or Southern) Hemisphere. Methane, H2O, and 2CH4 + H2O yearly differences from their values in 2009 are examined using SOFIE and MIPAS CH4 and the Aura Microwave Limb Sounder (MLS) measured H2O. It is concluded that 2CH4 + H2O is conserved with altitude up to an upper limit between 35 km and 50 km depending on the season. In summer this altitude is higher. In the Northern Hemisphere the difference relative to 2009 is the largest in late spring and the established difference prevails throughout summer and fall, suggesting that summer and fall are dynamically quiet. In both hemispheres during winter there are disturbances (with a period of 1 month) that travel downward throughout the stratosphere with a speed similar to the winter descent.

Latest Cretaceous and Paleocene extension in SE California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tosdal, R.M.; Conrad, J.E.; Murphy, G.P.

1993-04-01

Two ductile deformations formed the 3.5-km-thick, south dipping American Girl shear zone in the Cargo Muchancho Mountains, SE California. The older event (D1) imprints crystalloblastic fabrics that record contractional strains at midcrustal depths in the Middle( ) and Late Jurassic. The second event (D2) is marked by superposed mylonitic fabrics that are coplanar and colinear with fabrics of D1. Small mylonitic shear zones of D2 cut undeformed rocks in the hanging wall of the American Girl shear zone. Folded sheets of Jurassic granite geneiss and kinematic indicators in mylonites indicative southward directed transport down the present dip of the foliationmore » during D2. [sup 40]Ar/[sup 39]Ar release spectrum on hornblende from undeformed upper-plate monzo-diorite (173 Ma, U-Pb zircon), about 2 km above the top of shear zone has a plateau age of 96.7[+-]0.9 Ma. In contrast, hornblende release spectra from granite gneiss about 200 m below the top of the shear zone and from hornblende gneiss about 3 km below the top of the shear zone are flat and have identical ages. Hornblende from monzodiorite at the base of the upper plate has a more complicated spectrum that is interpreted to indicate a cooling age of 60.4[+-]1.3 Ma.« less

Development and implications of a sediment budget for the upper Elk River watershed, Humboldt County

Treesearch

Lee H. MacDonald; Michael W. Miles; Shane Beach; Nicolas M. Harrison; Matthew R. House; Patrick Belmont; Ken L. Ferrier

2017-01-01

A number of watersheds on the North Coast of California have been designated as sediment impaired under the Clean Water Act, including the 112 km2 upper Elk River watershed that flows into Humboldt Bay just south of Eureka. The objectives of this paper are to: 1) briefly explain the geomorphic context and anthropogenic uses of the Elk River...

PATHOGEN TRANSPORT AND FATE MODELING IN THE UPPER SALEM RIVER WATERSHED USING SWAT MODEL - PEER-REVIEWED JOURNAL ARTICLE

EPA Science Inventory

Simulation of the fate and transport of pathogen contamination was conducted with SWAT for the Upper Salem River Watershed, located in Salem County, New Jersey. This watershed is 37 km² and land uses are predominantly agricultural. The watershed drains to a 32 km str...

Small-scale variability in tropical tropopause layer humidity

NASA Astrophysics Data System (ADS)

Jensen, E. J.; Ueyama, R.; Pfister, L.; Karcher, B.; Podglajen, A.; Diskin, G. S.; DiGangi, J. P.; Thornberry, T. D.; Rollins, A. W.; Bui, T. V.; Woods, S.; Lawson, P.

2016-12-01

Recent advances in statistical parameterizations of cirrus cloud processes for use in global models are highlighting the need for information about small-scale fluctuations in upper tropospheric humidity and the physical processes that control the humidity variability. To address these issues, we have analyzed high-resolution airborne water vapor measurements obtained in the Airborne Tropical TRopopause EXperiment over the tropical Pacific between 14 and 20 km. Using accurate and precise 1-Hz water vapor measurements along approximately-level aircraft flight legs, we calculate structure functions spanning horizontal scales ranging from about 0.2 to 50 km, and we compare the water vapor variability in the lower (about 14 km) and upper (16-19 km) Tropical Tropopause Layer (TTL). We also compare the magnitudes and scales of variability inside TTL cirrus versus in clear-sky regions. The measurements show that in the upper TTL, water vapor concentration variance is stronger inside cirrus than in clear-sky regions. Using simulations of TTL cirrus formation, we show that small variability in clear-sky humidity is amplified by the strong sensitivity of ice nucleation rate to supersaturation, which results in highly-structured clouds that subsequently drive variability in the water vapor field. In the lower TTL, humidity variability is correlated with recent detrainment from deep convection. The structure functions indicate approximately power-law scaling with spectral slopes ranging from about -5/3 to -2.

P wave velocity of Proterozoic upper mantle beneath central and southern Asia

NASA Astrophysics Data System (ADS)

Nyblade, Andrew A.; Vogfjord, Kristin S.; Langston, Charles A.

1996-05-01

P wave velocity structure of Proterozoic upper mantle beneath central and southern Africa was investigated by forward modeling of Pnl waveforms from four moderate size earthquakes. The source-receiver path of one event crosses central Africa and lies outside the African superswell while the source-receiver paths for the other events cross Proterozoic lithosphere within southern Africa, inside the African superswell. Three observables (Pn waveshape, PL-Pn time, and Pn/PL amplitude ratio) from the Pnl waveform were used to constrain upper mantle velocity models in a grid search procedure. For central Africa, synthetic seismograms were computed for 5880 upper mantle models using the generalized ray method and wavenumber integration; synthetic seismograms for 216 models were computed for southern Africa. Successful models were taken as those whose synthetic seismograms had similar waveshapes to the observed waveforms, as well as PL-Pn times within 3 s of the observed times and Pn/PL amplitude ratios within 30% of the observed ratio. Successful models for central Africa yield a range of uppermost mantle velocity between 7.9 and 8.3 km s-1, velocities between 8.3 and 8.5 km s-1 at a depth of 200 km, and velocity gradients that are constant or slightly positive. For southern Africa, successful models yield uppermost mantle velocities between 8.1 and 8.3 km s-1, velocities between 7.9 and 8.4 km s-1 at a depth of 130 km, and velocity gradients between -0.001 and 0.001 s-1. Because velocity gradients are controlled strongly by structure at the bottoming depths for Pn waves, it is not easy to compare the velocity gradients obtained for central and southern Africa. For central Africa, Pn waves turn at depths of about 150-200 km, whereas for southern Africa they bottom at ˜100-150 km depth. With regard to the origin of the African superswell, our results do not have sufficient resolution to test hypotheses that invoke simple lithospheric reheating. However, our models are not consistent with explanations for the African superswell invoking extensive amounts of lithospheric thinning. If extensive lithospheric thinning had occurred beneath southern Africa, as suggested previously, then upper mantle P wave velocities beneath southern Africa would likely be lower than those in our models.

Group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the eastern Indian craton

NASA Astrophysics Data System (ADS)

Mandal, Prantik

2017-02-01

In the past three years, a semi-permanent network of fifteen 3-component broadband seismographs has become operational in the eastern Indian shield region occupying the Archean (∼2.5-3.6 Ga) Singhbhum-Odisha craton (SOC) and the Proterozoic (∼1.0-2.5 Ga) Chotanagpur Granitic Gneissic terrane (CGGT). The reliable and accurate broadband data for the recent 2015 Nepal earthquake sequence from 10 broadband stations of this network enabled us to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the region. First, we measure fundamental mode Rayleigh- and Love-wave group velocity dispersion curves in the period range of 7-70 s and then invert these curves to estimate the crustal and upper mantle structure below the eastern Indian craton (EIC). We observe that group velocities of Rayleigh and Love waves in SOC are relatively high in comparison to those of CGGT. This could be attributed to a relatively mafic-rich crust-mantle structure in SOC resulting from two episodes of magmatism associated with the 1.6 Ga Dalma and ∼117 Ma Rajmahal volcanisms. The best model for the EIC from the present study is found to be a two-layered crust, with a 14-km thick upper-crust (UC) of average shear velocity (Vs) of 3.0 km/s and a 26-km thick lower-crust (LC) of average Vs of 3.6 km/s. The present study detects a sharp drop in Vs (∼-2 to 3%) at 120-260 km depths, underlying the EIC, representing the probable seismic lithosphere-asthenosphere boundary (LAB) at 120 km depth. Such sharp fall in Vs below the LAB indicates a partially molten layer. Further, a geothermal gradient extrapolated from the surface heat flow shows that such a gradient would intercept the wet basalt solidus at 88-103 km depths, suggesting a 88-103 km thick thermal lithosphere below the EIC. This could also signal the presence of small amounts of partial melts. Thus, this 2-3% drop in Vs could be attributed to the presence of partial melts in the upper mantle related to the earlier volcanic episodes viz. back-arc volcanism associated with the Archean/Proterozoic subduction, 1.6 Ga Dalma volcanism, and ∼117 Ma Rajmahal volcanism. The main result of our modeling provides evidences for the absence of Keel or thick lithosphere below the EIC.

Crustal volumes of the continents and of oceanic and continental submarine plateaus

NASA Technical Reports Server (NTRS)

Schubert, G.; Sandwell, D.

1989-01-01

Using global topographic data and the assumption of Airy isostasy, it is estimated that the crustal volume of the continents is 7182 X 10 to the 6th cu km. The crustal volumes of the oceanic and continental submarine plateaus are calculated at 369 X 10 to the 6th cu km and 242 X 10 to the 6th cu km, respectively. The total continental crustal volume is found to be 7581 X 10 to the 6th cu km, 3.2 percent of which is comprised of continental submarine plateaus on the seafloor. An upper bound on the contintental crust addition rate by the accretion of oceanic plateaus is set at 3.7 cu km/yr. Subduction of continental submarine plateaus with the oceanic lithosphere on a 100 Myr time scale yields an upper bound to the continental crustal subtraction rate of 2.4 cu km/yr.

Seismic anisotropy of the crust and upper mantle in central Tibetan Plateau revealed by shear-wave splitting

NASA Astrophysics Data System (ADS)

Wu, C.; Tian, X.; Xu, T.; Liang, X.; Chen, Y.; Teng, J.

2017-12-01

Seismic anisotropy that results from deformation of the materials in the Earth is essentially important for understanding the deformation styles at different depths. In the central Tibetan Plateau the shear wave splitting measurements of local S-wave, Pms and SKS phases were calculated applying the broadband seismic data of SANDWICH array, and the anisotropy features of the crust and upper mantle were displayed. SKS splitting results show that the study area is strongly anisotropic as a whole. The average splitting parameters are 65.2°/1.28 s, and there are 17 stations existing individual splitting results larger than 2.0 s. The southeastern part is weakly anisotropic with average splitting parameters 61.0°/0.64 s. Applying spatial coherence technique the optimal depth of the source of anisotropy is 130 160 km, located in the asthenosphere. The subducting Indian plate advancing in NE direction and rigid blocks such as Qaidam basin obstructing in the north cause NEE direction asthenospheric flow which produces the anisotropy. The weak anisotropy of southeastern part is corresponding to the low velocity anomalies in the upper mantle, which may be attributed to local upwelling of asthenosphere from the slab tearing region. The crust media also make contribution to the strong anisotropy. S-wave splitting results which reflect upper crust anisotropy show that the average parameters of three stations in western part are 60.4°/1.53 ms/km, and those of two stations in eastern part are 10.9°/4.64 ms/km. The principle compressive stress controlled by structures varies from NE in the west to nearly NS in the east. Under the assumption that the thickness of upper crust is 20 km, the delay time of upper crust is smaller than 0.1 s. Whole crust anisotropy is obtained by calculating receiver functions and fitting the variation of arrival times of Pms phases with the backazimuths. The fast directions are NE-EW direction with average value 76.4°, nearly consistent with SKS fast directions, and the average delay time is about 0.5 s. The source of crust anisotropy mainly comes from middle-lower crust, which is possibly related to middle-lower crust flow.

Geophysical evidence for the extent of crustal types and the type of margin along a profile in the northeastern Baffin Bay

NASA Astrophysics Data System (ADS)

Altenbernd, Tabea; Jokat, Wilfried; Heyde, Ingo; Damm, Volkmar

2015-11-01

Investigating the crust of northern Baffin Bay provides valuable indications for the still debated evolution of this area. The crust of the southern Melville Bay is examined based on wide-angle seismic and gravity data. The resulting P wave velocity, density, and geological models give insights into the crustal structure. A stretched and rifted continental crust underneath southern Melville Bay is up to 30 km thick, with crustal velocities ranging between 5.5 and 6.9 km/s. The deep Melville Bay Graben contains a 9 km thick infill with velocities of 4 to 5.2 km/s in its lowermost part. West of the Melville Bay Ridge, a ~80 km wide and partly only 5 km thick Continent-Ocean Transition (COT) is present. West of the COT, up to 5 km thick sedimentary layers cover a 4.3 to 7 km thick, two-layered oceanic crust. The upper oceanic layer 2 has velocities of 5.2 to 6.0 km/s; the oceanic layer 3 has been modeled with rather low velocities of 6.3 to 6.9 km/s. Low velocities of 7.8 km/s characterize the probably serpentinized upper mantle underneath the thin crust. The serpentinized upper mantle and low thickness of the oceanic crust are another indication for slow or ultraslow spreading during the formation of the oceanic part of the Baffin Bay. By comparing our results on the crustal structure with other wide-angle seismic profiles recently published, differences in the geometry and structure of the crust and the overlying sedimentary cover are revealed. Moreover, the type of margin and the extent of crustal types in the Melville Bay area are discussed.

The Gale Crater Mound in a Regional Geologic Setting: Mapping and Probing Surrounding Outcrops for Areas Akin to the Central Mound at Gale

NASA Technical Reports Server (NTRS)

Korn, Lisa; Allen, Carlton

2013-01-01

There are several hypotheses on the origin of Gale Crater s central mound. These include ground water upwelling [1], aeolian, ice, volcanic [1-3], lacustrine [1-3], hydrothermal [1-3], and polar deposits [2]. The Mars Science Laboratory rover, Curiosity, landed in Gale Crater on August 6, 2012. It is currently analyzing samples along its traverse towards a channel and layered deposits that will provide insight into the sedimentary history of the crater [4]. Located at 5S, 138E, Gale is a 155km diameter, Late Noachian/Early Hesperian crater. It is situated along the southern highlands/northern lowlands dichotomy boundary and contains a central mound that rises approximately 5km from the crater floor [1]. The highest parts of Mt. Sharp are higher than the northern rim, but are roughly the same height as the southern rim. Mt. Sharp is divided into an upper mound and a lower mound, which are separated by an erosional unconformity [2]. The lower mound s sequences span the Late Noachian/Early Hesperian Epoch [1], while the upper mound s age is poorly constrained. The lower mound s sequences feature parallel beds of varying thickness, albedo, texture, and dip angle that are eroded into channels and yardangs [2]. The upper mound has finer layers at higher angles [1] with yardangs, serrated erosional patterns, and lobate features [3]. The lower mound also exhibits an upward progression of phyllosilicate to sulfate rich sediments, contrasting the upper mound s lack of hydrated minerals [4].

Inner core boundary topography explored with reflected and diffracted P waves

NASA Astrophysics Data System (ADS)

deSilva, Susini; Cormier, Vernon F.; Zheng, Yingcai

2018-03-01

The existence of topography of the inner core boundary (ICB) can affect the amplitude, phase, and coda of body waves incident on the inner core. By applying pseudospectral and boundary element methods to synthesize compressional waves interacting with the ICB, these effects are predicted and compared with waveform observations in pre-critical, critical, post-critical, and diffraction ranges of the PKiKP wave reflected from the ICB. These data sample overlapping regions of the inner core beneath the circum-Pacific belt and the Eurasian, North American, and Australian continents, but exclude large areas beneath the Pacific and Indian Oceans and the poles. In the pre-critical range, PKiKP waveforms require an upper bound of 2 km at 1-20 km wavelength for any ICB topography. Higher topography sharply reduces PKiKP amplitude and produces time-extended coda not observed in PKiKP waveforms. The existence of topography of this scale smooths over minima and zeros in the pre-critical ICB reflection coefficient predicted from standard earth models. In the range surrounding critical incidence (108-130 °), this upper bound of topography does not strongly affect the amplitude and waveform behavior of PKIKP + PKiKP at 1.5 Hz, which is relatively insensitive to 10-20 km wavelength topography height approaching 5 km. These data, however, have a strong overlap in the regions of the ICB sampled by pre-critical PKiKP that require a 2 km upper bound to topography height. In the diffracted range (>152°), topography as high as 5 km attenuates the peak amplitudes of PKIKP and PKPCdiff by similar amounts, leaving the PKPCdiff/PKIKP amplitude ratio unchanged from that predicted by a smooth ICB. The observed decay of PKPCdiff into the inner core shadow and the PKIKP-PKPCdiff differential travel time are consistent with a flattening of the outer core P velocity gradient near the ICB and iron enrichment at the bottom of the outer core.

The New Horizons Ultraviolet Solar Occultation by Pluto's Atmosphere

NASA Astrophysics Data System (ADS)

Young, L. A.; Kammer, J.; Steffl, A.; Gladstone, R.; Summers, M. E.; Strobel, D. F.; Hinson, D. P.; Stern, A.; Weaver, H. A., Jr.; Olkin, C.; Ennico Smith, K.; McComas, D. J.

2017-12-01

The Alice instrument on NASA's New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14, as the spacecraft flew nearly diametrically though the solar shadow. The resulting dataset was a time-series of spectra from 52 to 187 nm with a spectral resolution of 0.3 nm. From these, we derived line-of-sight abundances and local number densities for the major species (N2 and CH4) and minor hydrocarbons (C2H2, C2H4, C2H6), and line-of-sight optical depth and extinction coefficients for the haze. Analysis of these data imply that (1) temperatures in Pluto's upper atmosphere were colder than expected before the New Horizons flyby, with upper atmospheric temperatures near 65-68 K, and subsequently lower escape rates, dominated by CH4 escape over N2; (2) the lower atmosphere was very stable, placing the homopause within 12 km of the surface, (3) the abundance profiles of the "C2Hx hydrocarbons" had non-exponential density profiles that compared favorably with models for hydrocarbon production near 300-400 km and haze condensation near 200 km, and (4) haze had an extinction coefficient approximately proportional to N2 density.

A search for X-ray emission from a nearby pulsar - PSR 1929 + 10

NASA Technical Reports Server (NTRS)

Alpar, A.; Brinkmann, W.; Oegelman, H.; Kiziloglu, U.; Pines, D.

1987-01-01

Observations of the radio pulsar PSR 1929 + 10 with the Exosat observatory are reported. A 2 sigma upper limit of 0.0005 cts/s was obtained in the 0.04-2.4 keV range, which translates into a luminosity upper limit of 2 x 10 to the 29th erg/s for a power-law source with photon number index 1-3, and a luminosity upper limit of 10 to the 30th erg/s corresponding to a temperature of 190,000 K for a blackbody with radius 10 km. The implications of these upper limits for various models and their compatibility with the positive detection of this source by the Einstein Observatory are discussed.

Changes in river discharge and hydrograph separation in the upper basins of Yangtze and Yellow Rivers on the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Ding, Y.

2017-12-01

Systematic changes of river discharge and the concentration-discharge relation were explored to elucidate the response of river discharge to climate change as well as the connectivity of hydrologic and hydrochemical processes using hydrological data during 1956-2015 and chemical data during 2013-2015 at Yanshiping (YSP, 4,538 km2), Tuotuohe (TTH, 15,924 km2) and Zhimenda (ZMD, 137,704 km2) gauging sections in the upper basin of Yangtze River (UBYA), and at Huangheyan (HHY, 20,930 km2), Jimai (JM, 45,019 km2), Jungong (JG, 98,414 km2) and Tangnaihai (TNH, 121,972 km2) gauging sections in the upper basin of Yellow River (UBYE) on the Tibetan Plateau (TP). Results showed that annual discharge in UBYA presents a decreasing trend from 1950s to late 1970s and exhibits an increasing trend since 1970s due to increased temperature and precipitation. However, discharge in UBYE increases from 1950s to 1980s and decrease since late 1980s due to increased temperature and decreased precipitation. Snow/ice meltwater may play an important role on changes in river discharge from the most upper catchments, particularly for periods with increasing temperature, where snow cover, glaciers and frozen soils are widely distributed. Concentration/flux-discharge in discharge was dominated by a well-defined power law relation, with R2 values lower on rising than falling limbs. This finding has important implications for efforts to estimate annual concentrations and export of major solutes from similar catchments in cold regions where only river discharge is available. Concentrations of conservative solutes in discharge resulted from mixing of two end-members at the most upper gauging sections (YSP, TTH and HHY), and three end-members at the lower gauging sections (ZMD, JM, JG and TNH), with relatively constant solute concentrations in end-members. Relationship between the fractional contributions of meltwater and/or precipitation and groundwater and river discharge followed the same relation as the concentration-discharge as a result of end-member mixing. This study suggests that combining concentration-discharge and end-member mixing analyses can be used as a tool to understand runoff generation and hydrochemical process, and the export of water and solutes from the TP may affect water balance and ecosystems downstream.

Lateral carbon export in the Mississippi River Basin, integrating fluxes from the headwaters to the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Stackpoole, S. M.; Crawford, J.; Santi, L. M.; Stets, E.; Sebestyen, S. D.; Wilson, S.; Striegl, R. G.

2017-12-01

Large-scale river studies have documented that lateral fluxes are an important component of the global carbon cycle. This study focuses on river lateral C fluxes for the Mississippi River Basin (MRB), the largest river in North America. Our lateral river C fluxes are based on data from 23 nested watersheds within the Upper MRB, for water years 2015 and 2016. The study area covers 170,000 km2 and is comprised of both catchment <10 km2 and intermediate-scale watersheds (20,000 to 40,000 km2) in Wisconsin and Minnesota, USA. Total alkalinity yields (flux derived by drainage area) ranged from 0 to 16 g C m2 yr-1 and dissolved organic C (DOC) yields ranged from 1 to 13 g C m2 yr-1. In comparison, published estimates for Mississippi River export to the Gulf of Mexico, estimated at St. Francisville, LA, were 16 g C m-2 yr-1 for alkalinity and 0.6 g m2 yr-1 for DOC. In the Upper MRB, alkalinity yields had a significant negative relationship with DOC yields (R2 = 0.53, p-value<0.0001), and alkalinity yields were significantly higher in basins where the lithology was dominated by carbonates and the land-use was >50% agriculture. There was significant inter-annual variability in the total C fluxes, and the increase in discharge in 2016 relative to 2015 increased the proportion of DOC:alkalinity for watersheds with higher forest and wetland coverage. The integration of these recent C flux estimates for the Upper MRB integrated with the fluxes estimated from the USGS long-term monitoring program dataset provide a comprehensive analysis of alkalinity and DOC fluxes for the entire basin. These results, which represent C fluxes across a gradient of lithology, soil type, and land use, will be used to address questions related to our understanding of carbon sources, transport, and loss that can be applied to other river systems.

In situ stratospheric measurements of HNO3 and HCl near 30 km using the balloon-borne laser in situ sensor tunable diode laser spectrometer

NASA Technical Reports Server (NTRS)

May, R. D.; Webster, C. R.

1989-01-01

In situ stratospheric measurements of the concentrations of the reservoir species HNO3 and HCl made during two flights of the high-resolution (0.0005/cm) balloon-borne laser in situ sensor instrument from Palestine, Texas, are reported. A measured HNO3 volume mixing ratio of 4.3 parts per billion by volume (ppbv) at 31 km altitude is about 1 ppbv larger than previously reported measurements at 32 deg N. An HCl mixing ratio of 1.6 ppbv at 29 km is in agreement with values obtained from earlier remote sensing techniques within the experimental uncertainties. Upper limits at 31 km of 0.4 ppbv for H2O2 and 0.2 ppbv for HOCl are also derived from analyses of spectra recorded near 1252/cm.

High-resolution spectroscopy of Venus: Detection of OCS, upper limit to H 2S, and latitudinal variations of CO and HF in the upper cloud layer

NASA Astrophysics Data System (ADS)

Krasnopolsky, Vladimir A.

2008-10-01

Venus was observed at 2.4 and 3.7 μm with a resolving power of 4×10 using the long-slit high-resolution spectrograph CSHELL at NASA IRTF. The observations were made along a chord that covered a latitude range of ± 60° at a local time near 8:00. The continuous reflectivity and limb brightening at 2.4 μm are fitted by the clouds with a single scattering albedo 1-a=0.01 and a pure absorbing layer with τ=0.09 above the clouds. The value of 1-a agrees with the refractive index of H 2SO 4 (85%) and the particle radius of 1 μm. The absorbing layer is similar to that observed by the UV spectrometer at the Pioneer Venus orbiter. However, its nature is puzzling. CO 2 was measured using its R32 and R34 lines. The retrieved product of the CO 2 abundance and airmass is constant at 1.9 km-atm along the instrument slit in the latitude range of ± 60°. The CO mixing ratio (measured using the P21 line) is rather constant at 70 ppm, and its variations of ˜10% may be caused by atmospheric dynamics. The observed value is higher than the 50 ppm retrieved previously from a spectrum of the full disk, possibly, because of some downward extension of the mesospheric morningside bulge of CO. The observations of the HF R3 line reveal a constant HF mixing ratio of 3.5±0.5 ppb within ± 60° of latitude, which is within the scatter in the previous measurements of HF. OCS has been detected for the first time at the cloud tops by summing 17 lines of the P-branch. The previous detections of OCS refer to the lower atmosphere at 30-35 km. The retrieved OCS mixing ratio varies with a scale height of 1 to 3 km. The mean OCS mixing ratio is ˜2 ppb at 70 km and ˜14 ppb at 64 km. Vertical motions in the atmosphere may change the OCS abundance. The detected OCS should significantly affect Venus' photochemistry. A sensitive search for H 2S using its line at 2688.93 cm -1 results in a 3 sigma upper limit of 23 ppb, which is more restrictive than the previous limit of 100 ppb.

Lunar crater volumes - Interpretation by models of impact cratering and upper crustal structure

NASA Technical Reports Server (NTRS)

Croft, S. K.

1978-01-01

Lunar crater volumes can be divided by size into two general classes with distinctly different functional dependence on diameter. Craters smaller than approximately 12 km in diameter are morphologically simple and increase in volume as the cube of the diameter, while craters larger than about 20 km are complex and increase in volume at a significantly lower rate implying shallowing. Ejecta and interior volumes are not identical and their ratio, Schroeters Ratio (SR), increases from about 0.5 for simple craters to about 1.5 for complex craters. The excess of ejecta volume causing the increase, can be accounted for by a discontinuity in lunar crust porosity at 1.5-2 km depth. The diameter range of significant increase in SR corresponds with the diameter range of transition from simple to complex crater morphology. This observation, combined with theoretical rebound calculation, indicates control of the transition diameter by the porosity structure of the upper crust.

Lightning and related phenomena in thunderstorms and squall lines

NASA Technical Reports Server (NTRS)

Rust, W. D.; Taylor, W. L.; Macgorman, D. R.; Brandes, E.; Mazur, V.; Arnold, R.; Marshall, T.; Christian, H.; Goodman, S. J.

1984-01-01

During the past few years, cooperative research on storm electricity has yielded the following results of both basic and applied interest: (1) the intracloud to cloud-to-ground flashing ratio can be as great as 40:1; (2) as storm cells in a squall line dissipate, longer flashes become predominant; (3) there are two centers of lightning activity maxima that are vertically separated, the lower maximum at about 5 km and the upper at about 12 km. In addition, (4) storms produce lightning in their upper regions at a high rate; (5) lightning appears to be related in time to convective motions; (6) positive cloud-to-ground flashes occur in the severe stage of storms and in the later, well-developed stage of squall line storms; (7) mesoscale convective complexes have been observed to have cloud-to-ground flashing rates of more than 48/min; and (8) the electric field in anvils well away from the main storm core (more than 60 km) can be very high, more than 94 kV/m.

Rocket Observations of Kelvin Waves in the Upper Stratosphere over India.

NASA Astrophysics Data System (ADS)

Devarajan, M.; Reddy, C. A.; Ragrava Reddi, C.

1985-09-01

The upper atmospheric winds (20-40 km) at two Indian stations, Sriharikota Range (SHAR 13.7°N, 80.2°E) and Balasore (2 1.5°N, 86.93°E) during the years 1979-80 were analyzed for short scale vertical variations (6-16 km) of the zonal wind. The analysis involves high-pass filtering of the wind profiles to extract the short-scale wavelike perturbations and Fourier analysis of the wave disturbances.The results of the analysis are presented. The dominant vertical wavelengths are in the 6-12 km range in 67% of the observed cases, and the amplitudes are significantly larger during the easterly background wind. The amplitudes are systematically larger by about a factor of 2 at Sriharikota (13.7°N) than at 1Wasore (21.5°N). Corresponding wave perturbations are absent in the meridional wind in as much as 70% of the observations. These characteristics lead to the conclusion that the observed wavelike disturbances are the manifestation of Kelvin waves in the upper stratosphere. In some cases, the periods of the waves are inferred to be in the range of 4-8 days. The short vertical wavelengths, together with the shorter periods, indicate the possible dominance of zonal wavenumber 2 during many disturbance events.The observations of the wave activity in relation to the semiannual oscillation (SAO) and the annual oscillation (AO) show that 1) the more active periods correspond to the easterly phase of the SAO in the middle stratosphere and that 2) the wave activity persists for a longer duration when both the AO and SAO are in easterly phase.

First incoherent scatter radar observations of radio wave pumping in the ionosphere around the second electron gyroharmonic

NASA Astrophysics Data System (ADS)

Kosch, Michael; Bristow, Bill; Gustavsson, Bjorn; Heinselman, Craig; Hughes, John; Isham, Brett; Mutiso, Charles; Nielsen, Kim; Pedersen, Todd; Wang, Weiyuan; Wong, Alfred

We report results from a unique experiment performed at the HIPAS ionospheric modification facility in Alaska. High power radio waves at 2.85 MHz, which corresponds to the second electron gyroharmonic at 240 km altitude, were transmitted into the nighttime ionosphere. Diagnostics included optical equipment at HIPAS and HAARP, 288 km to the south-east, the PFISR radar at Poker Flat, 32 km to the north-west, and the Kodiak SuperDARN radar, 856 km to the south-west. Camera observations of the stimulated optical emissions at 557.7 nm (O1S, threshold 4.2 eV) and 630 nm (O1D, threshold 2 eV) were made, allowing tomographic reconstruction of the volume emission. The first observations of pump-induced 732 nm (O+, threshold 18.6 eV) emissions are reported. Kodiak radar backscatter, which is a proxy for upper-hybrid resonance, shows strong production of striations without a minimum on the second gyroharmonic, confirming previous results. PFISR analysis shows clear evidence of electron temperature enhancements, consistent with previous EISCAT results, maximizing when the pump frequency matches the second gyroharmonic and when double resonance occurs, i.e. the upper-hybrid resonance frequency matches the second gyroharmonic. This is consistent with the optical observations. From the above data, we are able to infer the efficiency of different groups of electron-accelerating mechanisms.

Orbiting lidar simulations. I - Aerosol and cloud measurements by an independent-wavelength technique

NASA Technical Reports Server (NTRS)

Russell, P. B.; Morley, B. M.; Livingston, J. M.; Grams, G. W.; Patterson, E. M.

1982-01-01

Aerosol and cloud measurements have been simulated for a Space Shuttle lidar. Expected errors - in signal, transmission, density, and calibration - are calculated algebraically and checked by simulating measurements and retrievals using random-number generators. By day, vertical structure is retrieved for tenuous clouds, Saharan aerosols, and boundary layer aerosols (at 0.53 and 1.06 micron) as well as strong volcanic stratospheric aerosols (at 0.53 micron). By night, all these constituents are retrieved plus upper tropospheric and stratospheric aerosols (at 1.06 micron), mesospheric aerosols (at 0.53 micron), and noctilucent clouds (at 1.06 and 0.53 micron). The vertical resolution was 0.1-0.5 km in the troposphere, 0.5-2.0 km above, except 0.25-1.0 km in the mesospheric cloud and aerosol layers; horizontal resolution was 100-2000 km.

Structure and Evolution of the Forearc-Arc Crust Along the Tonga-Kermadec Subduction System from Integrated Geophysical Data

NASA Astrophysics Data System (ADS)

Funnell, M.; Peirce, C.; Robinson, A. H.; Watts, A. B.; Grevemeyer, I.

2016-12-01

Variations in tectonic forces and inputs to subduction systems generate, alter, and deform overriding crustal material. Although these processes are recorded in the crustal structure of volcanic arcs and their backarcs, the continuous nature of plate convergence superimposes subsequent episodes of crustal evolution on older features. Seismic imaging at modern subduction zones enhances our understanding of forearc development and variations in present-day deformation caused by inherited structures. In 2011 a set of multichannel and wide-angle seismic profiles imaged the forearc-arc crust and upper mantle structure along the 2700 km-long NNE-SSW trending Tonga-Kermadec subduction zone. The Tonga forearc region exhibits an 100 km-wide, 2 km high bathymetric elevation, with a 3 km-thick upper and mid-crust (Vp <6 km s-1), and a lower-crustal ridge 30 km wide comprising velocities up to 7.4 km s-1 that characterize an extinct Eocene ( 50 Ma) arc. By contrast, the active arc is <10 km wide and exhibits lower-crustal velocities below 7.0 km s-1, most likely representing intermediate compositions. This structural change suggests significant evolution, alteration, and modification of the overriding crust since the onset of subduction at this margin. Gravity anomaly modelling suggests that the extinct arc within the Tonga forearc region comprises relatively dense mafic-ultrabasic material that extends south beneath the Kermadec forearc and terminates at 32°S. The apparent southern termination of the extinct arc coincides with the partitioning of morphological features at 32°S, including a 10-km westward-step of the active arc and a 1.5 km deeper backarc to the south. We propose that tectonic partitioning about the 32°S boundary is the result of variations in the inherited crustal structure, which is divided by the presence and absence, to the north and south respectively, of the extinct volcanic arc.

Glacier elevation and mass change over the upper Maipo Basin, Central Andes, Chile.

NASA Astrophysics Data System (ADS)

Farías, David; Seehaus, Thorsten; Vivero, Sebastian; Braun, Matthias H.; Casassa, Gino

2017-04-01

The upper Maipo basin (33° S, 70° W, 5400 km2) is located 15 km from the eastern outskirts of the mega-city of Santiago. The basin is characterized by Mediterranean climate with marked winter and summer seasons and occasionally disturbed by large annual and multi-annual variations in temperature and precipitation (ENSO). The upper Maipo basin is the main glacierized region of Chile, where the last Chilean glacier inventory revealed a glacier extent of about 397.6 km2 distributed over 1009 glaciers larger than 0.01 km2. The glaciers located in this basin represent 2% of the total glacierized area in Chile. The 1009 glaciers in this area, compose of 708 rock glaciers (159.91 km2), 126 glaciarets (5.85 km2) and 175 valley and mountain glaciers (231.84 km2). Our focus in this study is to evaluate the suitability of TanDEM-X to derive geodetic glacier mass balance on small mountain glaciers. Our database comprises different digital elevation models (DEM) from historical cartography based on aerial photographs (1955), SRTM (2000), Lidar data and TanDEM-X (2015). The historical cartography was scanned and georeferenced with the aid of several GCPs derived from the Lidar dataset. The TanDEM-X data was processed using differential interferometry using SRTM C-band DEM as reference. Differences resulting from X- and C-band penetration are considered comparing X- and C-band SRTM data. All DEMs were horizontal and vertically co-registered to each other. Error assessment was done over stable ground (off-glacier). On our poster we present preliminary results about detailed quantification of glacier elevation and mass change in this area.

Near surface structure of the North Anatolian Fault Zone near 30°E from Rayleigh and Love wave tomography using ambient seismic noise.

NASA Astrophysics Data System (ADS)

Taylor, G.; Rost, S.; Houseman, G. A.; Hillers, G.

2017-12-01

By utilising short period surface waves present in the noise field, we can construct images of shallow structure in the Earth's upper crust: a depth-range that is usually poorly resolved in earthquake tomography. Here, we use data from a dense seismic array (Dense Array for Northern Anatolia - DANA) deployed across the North Anatolian Fault Zone (NAFZ) in the source region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip system that extends 1200 km across northern Turkey and continues to pose a high level of seismic hazard, in particular to the mega-city of Istanbul. We obtain maps of group velocity variation using surface wave tomography applied to short period (1- 6 s) Rayleigh and Love waves to construct high-resolution images of SV and SH-wave velocity in the upper 5 km of a 70 km x 35 km region centred on the eastern end of the fault segment that ruptured in the 1999 Izmit earthquake. The average Rayleigh wave group velocities in the region vary between 1.8 km/s at 1.5 s period, to 2.2 km/s at 6 s period. The NAFZ bifurcates into northern and southern strands in this region; both are active but only the northern strand ruptured in the 1999 event. The signatures of both the northern and southern branches of the NAFZ are clearly associated with strong gradients in seismic velocity that also denote the boundaries of major tectonic units. This observation implies that the fault zone exploits the pre-existing structure of the Intra-Pontide suture zone. To the north of the NAFZ, we observe low S-wave velocities ( 2.0 km/s) associated with the unconsolidated sediments of the Adapazari basin, and blocks of weathered terrigenous clastic sediments. To the south of the northern branch of the NAFZ in the Armutlu block, we detect higher velocities ( 2.9 km/s) associated with a shallow crystalline basement, in particular a block of metamorphosed schists and marbles that bound the northern branch of the NAFZ.

Crustal and upper mantle velocity model along the DOBRE-4 profile from North Dobruja to the central region of the Ukrainian Shield: 1. seismic data

NASA Astrophysics Data System (ADS)

Starostenko, V. I.; Janik, T.; Gintov, O. B.; Lysynchuk, D. V.; Środa, P.; Czuba, W.; Kolomiyets, E. V.; Aleksandrowski, P.; Omelchenko, V. D.; Komminaho, K.; Guterch, A.; Tiira, T.; Gryn, D. N.; Legostaeva, O. V.; Thybo, G.; Tolkunov, A. V.

2017-03-01

For studying the structure of the lithosphere in southern Ukraine, wide-angle seismic studies that recorded the reflected and refracted waves were carried out under the DOBRE-4 project. The field works were conducted in October 2009. Thirteen chemical shot points spaced 35-50 km apart from each other were implemented with a charge weight varying from 600 to 1000 kg. Overall 230 recording stations with an interval of 2.5 km between them were used. The high quality of the obtained data allowed us to model the velocity section along the profile for P- and S-waves. Seismic modeling was carried out by two methods. Initially, trial-and-error ray tracing using the arrival times of the main reflected and refracted P- and S-phases was conducted. Next, the amplitudes of the recorded phases were analyzed by the finite-difference full waveform method. The resulting velocity model demonstrates a fairly homogeneous structure from the middle to lower crust both in the vertical and horizontal directions. A drastically different situation is observed in the upper crust, where the V p velocities decrease upwards along the section from 6.35 km/s at a depth of 15-20 km to 5.9-5.8 km/s on the surface of the crystalline basement; in the Neoproterozoic and Paleozoic deposits, it diminishes from 5.15 to 3.80 km/s, and in the Mesozoic layers, it decreases from 2.70 to 2.30 km/s. The subcrustal V p gradually increases downwards from 6.50 to 6.7-6.8 km/s at the crustal base, which complicates the problem of separating the middle and lower crust. The V p velocities above 6.80 km/s have not been revealed even in the lowermost part of the crust, in contrast to the similar profiles in the East European Platform. The Moho is clearly delineated by the velocity contrast of 1.3-1.7 km/s. The alternating pattern of the changes in the Moho depths corresponding to Moho undulations with a wavelength of about 150 km and the amplitude reaching 8 to 17 km is a peculiarity of the velocity model.

Determining the Upper Mantle Seismic Structure beneath the Northern Transantarctic Mountains from Regional P- and S-wave Tomography

NASA Astrophysics Data System (ADS)

Brenn, G.; Hansen, S. E.; Park, Y.

2016-12-01

Stretching 3500 km across Antarctica, the Transantarctic Mountains (TAMs) are the largest non-compressional mountain range on Earth. It has been suggested that the TAMs may have served as a nucleation point for the large-scale glaciation of Antarctica, and understanding their tectonic history has important implications for ice sheet modeling. However, the origin and uplift mechanism associated with the TAMs is controversial, and multiple models have been proposed. Seismic investigations of the TAM's subsurface structure can provide key constraints to help evaluate these models, but previous studies have been primarily focused on the central TAMs near Ross Island. Using data from the new 15-station Transantarctic Mountain Northern Network as well as data from several smaller networks, this study investigates the upper mantle velocity structure beneath a previously unexplored portion of the northern TAMs through regional body wave tomography. Relative travel-times were calculated for 11,182 P-wave and 8,285 S-wave arrivals from 790 and 581 Mw ≥ 5.5 events, respectively, using multi-channel cross correlation, and these data were then inverted for models of the upper mantle seismic structure. Resulting P- and S-wave tomography images reveal two focused low velocity anomalies beneath Ross Island (RI; δVP= -2.0%; δVS=-1.5% to -4.0%) and Terra Nova Bay (TNB; δVP=-1.5% to -2.0%; δVS= -1.0% to -4.0%) that extend to depths of 200 and 150 km, respectively. The RI and TNB slow anomalies also extend 50-100 km laterally beneath the TAMs front and sharply abut fast velocities beneath the EA craton (δVP=0.5% to 2%; δVS=1.5% to 4.0%). A low velocity region (δVP= -1.5%), centered at 150 km depth beneath the Terror Rift (TR) and primarily constrained within the Victoria Land Basin, connects the RI and TNB anomalies. The focused low velocities are interpreted as regions of partial melt and buoyancy-driven upwelling, connected by a broad region of slow (presumably warm) upper mantle associated with Cenozoic extension along the TR. Dynamic topography estimates based on the imaged S-wave velocity perturbations are consistent with observed surface topography in the central and northern TAMs, thereby providing support for uplift models that advocate for thermal loading and a flexural origin for the mountain range.

Local Upper Mantle Upwelling beneath New England: Evidence from Seismic Anisotropy.

NASA Astrophysics Data System (ADS)

Levin, V. L.; Long, M. D.; Lopez, I.; Li, Y.; Skryzalin, P. A.

2017-12-01

The upper mantle beneath eastern North America contains regions where seismic wave speed is significantly reduced. As they cut across the trend of the Appalachian terranes, these anomalies likely post-date the Paleozoic assembly of Pangea. Most prominent of them, the North Appalachian Anomaly (NAA), has been alternatively explained by the localized disruption of lithospheric fabric, the passage of the Great Meteor Hot Spot, and the current local upwelling of the asthenosphere. Comprehensive mapping of shear wave splitting identified a local perturbation of an otherwise uniform regional pattern, with no apparent splitting occurring at a site within the NAA. To evaluate the reality of this apparent localized disruption in the anisotropic fabric of the upper mantle beneath northeastern North America we used observations of shear wave splitting from a set of long-running observatories not included in previous studies. Three methods of evaluating shear wave splitting (rotation-correlation, minimization of the transverse component, and the splitting intensity) yield complementary results. We show that splitting of core-refracted shear waves within the outline of the NAA is significantly weaker than towards its edges and beyond them (Figure 1). Average fast orientations are close to the absolute plate motion in the hot-spot reference frame, thus we can attribute a large fraction of this signal to the coherently sheared sub-lithospheric upper mantle. A decrease in average delay we observe, from 1 s outside the NAA to under 0.2 s within it, translates into a reduction of the vertical extent of the sheared layer from 130 km to 16 km (assuming 4% anisotropy), or alternatively into a weakening of the azimuthal anisotropy from 5% to 0.6% (assuming a 100 km thick layer). The splitting reduction within the NAA is consistent with a localized change in anisotropic fabric that would be expected in case of geologically recent sub-vertical flow overprinting the broadly uniform upper mantle fabric detected throughout the region. Figure 1. Splitting intensity (red circles) plotted over best-fitting sinusoidal functions (blue, parameters in upper right) and predictions based on average delays and fast polarizations (green, parameters in upper left). Outlines of the NAA at 200 km depth from tomographic studies using Earthscope data.

Structure of the crust and upper mantle beneath the Balearic Islands (Western Mediterranean)

NASA Astrophysics Data System (ADS)

Banda, E.; Ansorge, J.; Boloix, M.; Córdoba, D.

1980-09-01

Data are presented from deep seismic sounding along the strike of the Balearic Islands carried out in 1976. The interpretation of the data gives the following results: A sedimentary cover of 4 km around Ibiza to 7 km under Mallorca overlies the crystalline basement. This basement with a P-wave velocity of 6.0 km/s at the top reaches a depth of at least 15 km under Ibiza and 17 km under Mallorca with an increase to 6.1 km/s at these depths. The crust-mantle boundary lies at a depth of 20 km and 25 km, respectively. A well documented upper-mantle velocity of 7.7 km/s is found along the entire profile. The Moho rises to a depth of 20 km about 30 km north of Mallorca and probably continues rising towards the center of the North Balearic Sea. The newly deduced crustal structure together with previously determined velocity-depth sections in the North Balearic Sea as well as heat flow and aeromagnetic data can be interpreted as an extended rift structure caused by large-scale tensional processes in the upper mantle. The available data suggest that the entire zone from the eastern Alboran Sea to the area north of the Balearic Islands represents the southeastern flank of this rift system. In this model the provinces of Spain along the east coast would represent the northwestern rift flank.

The velocity structure of the lunar crust.

NASA Technical Reports Server (NTRS)

Kovach, R. L.; Watkins, J. S.

1973-01-01

Seismic refraction data, obtained at the Apollo 14 and 16 sites, when combined with other lunar seismic data, allow a compressional wave velocity profile of the lunar near-surface and crust to be derived. The regolith, although variable in thickness over the lunar surface, possesses surprisingly similar seismic properties. Underlying the regolith at both the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is low-velocity brecciated material or impact derived debris. Key features of the lunar seismic velocity profile are: (1) velocity increases from 100 to 300 m/sec in the upper 100 m to about 4 km/sec at 5 km depth, (2) a more gradual increase from about 4 km/sec to about 6 km/sec at 25 km depth,(3) a discontinuity at a depth of 25 km, and (4) a constant value of about 7 km/sec at depths from 25 km to about 60 km.

Monitoring regional effects of high pressure injection of wastewater in a limestone aquifer

USGS Publications Warehouse

Faulkner, Glen L.; Pascale, Charles A.

1975-01-01

More than 10 billion gallons (38 × 106 m3) of acid industrial liquid waste has been injected in about 11 years under high pressure into a saline-water-filled part of a limestone aquifer of low transmissivity between 1,400 and 1,700 feet (430 and 520 m) below land surface near Pensacola, Florida. A similar waste disposal system is planned for the same zone at a site about 8.5 miles (13.7 km) to the east. The injection zone is the lower limestone of the Floridan aquifer. The lower limestone is overlain by a confining layer of plastic clay about 220 feet (67 m) thick at the active injection site and underlain by another confining layer of shale and clay. The upper confining layer is overlain by the upper limestone of the Floridan aquifer.The active injection system consists of two injection wells about a quarter of a mile (0.4 km) apart and three monitor wells. Two of the monitor wells (deep monitors) are used to observe hydraulic and geochemical effects of waste injection in the injection zone at locations about 1.5 miles (2.4 km) south and 1.9 miles (3.1 km) north of the center of the injection site. The third well (shallow monitor), used to observe any effects in the upper limestone, is about 100 feet (30 m) from one of the injection wells. Since 1972 the injection zone has also been monitored at a test well at the planned new injection site. Three more monitor wells in the injection zone were activated in early 1974 at sites 17 miles (27 km) northeast, 22 miles (35 km) east and 33 miles (53 km) northeast of the injection site. The six deep monitors provide a system for evaluating the regional effects of injecting wastes. No change in pressure or water quality due to injection was, by mid-1974, evident in the upper limestone at the injection site, but static pressures in the lower limestone at the site had increased 8 fold since injection began in 1963. Chemical analyses indicated probable arrival of the diluted waste at the south monitor well in 1973. By mid-1974 waste evidently had not reached the north monitor well.Calculations indicate that by mid-1974 pressure effects from waste injection extended radially more than 40 miles (64 km) from the injection site. By mid-1974 pressure effects of injection were evident from water-level measurements made at the five deep monitor wells nearest the active injection site. No effects were recognized at the well 33 miles (53 km) away. Less than 20 miles (32 km) northeast of the active injection site, the lower limestone contains fresh water. Changes in the pressure regime due to injection indicate a tendency for northeastward movement of the fresh-water/salt-water interface in the lower limestone.

3D Crustal Velocity Structure Model of the Middle-eastern North China Craton

NASA Astrophysics Data System (ADS)

Duan, Y.; Wang, F.; Lin, J.; Wei, Y.

2017-12-01

Lithosphere thinning and destruction in the middle-eastern North China Craton (NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. Up to 42 wide-angle reflection/refraction deep seismic sounding (DSS) profiles have been completed in the middle-eastern NCC, we collect all the 2D profiling results and perform gridding of the velocity and interface depth data, and build a 3D crustal velocity structure model for the middle-eastern NCC, named HBCrust1.0, using the Kriging interpolation method. In this model, four layers are divided by three interfaces: G is the interface between the sedimentary cover and crystalline crust, with velocities of 5.0-5.5 km/s above and 5.8-6.0 km/s below. C is the interface of the upper and lower crust, with velocity jump from 6.2-6.4 km/s to 6.5-6.6 km/s. M is the interface between the crust and upper mantle, with velocity 6.7-7.0 km/s at the crust bottom and 7.9-8.0 km/s on mantle top. Our results show that the first arrival time calculated from HBCust1.0 fit well with the observation. It also demonstrates that the upper crust is the main seismogenic layer, and the brittle-ductile transition occurs at depths near interface C. The depth of interface Moho varies beneath the source area of the Tangshan earth-quake, and a low-velocity structure is found to extend from the source area to the lower crust. Based on these observations, it can be inferred that stress accumulation responsible for the Tangshan earthquake may have been closely related to the migration and deformation of the mantle materials. Comparisons of the average velocities of the whole crust, the upper and the lower crust show that the average velocity of the lower crust under the central part of the North China Basin (NCB) in the east of the craton is obviously higher than the regional average, this high-velocity probably results from longterm underplating of the mantle magma. This research is founded by the Natural Science Foundation of China (91414301 and 41174052).

Geodetic exploration of strain along the El Pilar Fault in northeastern Venezuela

NASA Astrophysics Data System (ADS)

Reinoza, C.; Jouanne, F.; Audemard, F. A.; Schmitz, M.; Beck, C.

2015-03-01

We use Global Navigation Satellite Systems observations in northeastern Venezuela to constrain the El Pilar Fault (EPF) kinematics and to explore the effects of the variable elastic properties of the surrounding medium and of the fault geometry on inferred slip rates and locking depth. The velocity field exhibits an asymmetric velocity gradient on either side of the EPF. We use five different approaches to explore possible models to explain this asymmetry. First, we infer a 1.6 km locking depth using a classic elastic half-space dislocation model. Second, we infer a 1.5 km locking depth and a 0.33 asymmetry coefficient using a heterogeneous asymmetric model, including contrasting material properties on either side of a vertical fault, suggesting that the igneous-metamorphic terranes on the northern side are ~2 times more rigid than the sedimentary southern side. Third, we use a three-dimensional elastostatic model to evaluate the presence of a compliant zone, suggesting a 30% reduction of rigidity in the upper 3 km at the depth of a 1 to 5 km wide fault zone. Fourth, we evaluate the distribution of fault slip, revealing a widespread partial creep pattern in the eastern upper segment, while the upper western segment exhibits a partially locked area, which coincides with the rupture surface of the 1797 and 1929 earthquakes. To supplement these models, we upgrade the previously published displacement simulation method using nonvertical dislocations with data acquired between 2003 and 2013. The localized aseismic displacement pattern associated with creeping or partially creeping fault segments could explain the low level of historic seismicity.

UNAM Scientific Drilling Program of Chicxulub Impact Structure-Evidence for a 300 kilometer crater diameter

NASA Astrophysics Data System (ADS)

Urrutia-Fucugauchi, J.; Marin, L.; Trejo-Garcia, A.

As part of the UNAM drilling program at the Chicxulub structure, two 700 m deep continuously cored boreholes were completed between April and July, 1995. The Peto UNAM-6 and Tekax UNAM-7 drilling sites are ˜150 km and 125 km, respectively, SSE of Chicxulub Puerto, near the crater's center. Core samples from both sites show a sequence of post-crater carbonates on top of a thick impact breccia pile covering the disturbed Mesozoic platform rocks. At UNAM-7, two impact breccia units were encountered: (1) an upper breccia, mean magnetic susceptibility is high (˜55 × 10-6 SI units), indicating a large component of silicate basement has been incorporated into this breccia, and (2) an evaporite-rich, low susceptibility impact breccia similar in character to the evaporite-rich breccias observed at the PEMEX drill sites further out. The upper breccia was encountered at ˜226 m below the surface and is ˜125 m thick; the lower breccia is immediately subjacent and is >240 m thick. This two-breccia sequence is typical of the suevite-Bunte breccia sequence found within other well preserved impact craters. The suevitic upper unit is not present at UNAM-6. Instead, a >240 m thick evaporite-rich breccia unit, similar to the lower breccia at UNAM-7, was encountered at a depth of ˜280 m. The absence of an upper breccia equivalent at UNAM-6 suggests some portion of the breccia sequence has been removed by erosion. This is consistent with interpretations that place the high-standing crater rim at 130-150 km from the center. Consequently, the stratigraphic observations and magnetic susceptibiity records on the upper and lower breccias (depth and thickness) support a ˜300 km diameter crater model.

Crustal modeling of the central part of the Northern Western Desert, Egypt using gravity data

NASA Astrophysics Data System (ADS)

Alrefaee, H. A.

2017-05-01

The Bouguer anomaly map of the central part of the Northern Western Desert, Egypt was used to construct six 2D gravity models to investigate the nature, physical properties and structures of the crust and upper mantle. The crustal models were constrained and constructed by integrating results from different geophysical techniques and available geological information. The depth to the basement surface, from eight wells existed across the study area, and the depth to the Conrad and Moho interfaces as well as physical properties of sediments, basement, crust and upper mantle from previous petrophysical and crustal studies were used to establish the gravity models. Euler deconvolution technique was carried on the Bouguer anomaly map to detect the subsurface fault trends. Edge detection techniques were calculated to outlines the boundaries of subsurface structural features. Basement structural map was interpreted to reveal the subsurface structural setting of the area. The crustal models reveals increasing of gravity field from the south to the north due to northward thinning of the crust. The models reveals also deformed and rugged basement surface with northward depth increasing from 1.6 km to 6 km. In contrast to the basement, the Conrad and Moho interfaces are nearly flat and get shallower northward where the depth to the Conrad or the thickness of the upper crust ranges from 18 km to 21 km while the depth to the Moho (crustal thickness) ranges from 31.5 km to 34 km. The crust beneath the study area is normal continental crust with obvious thinning toward the continental margin at the Mediterranean coast.

More South Polar "Swiss Cheese"

NASA Image and Video Library

2000-04-24

This image is illuminated by sunlight from the upper left. Some of the surface of the residual south polar cap has a pattern that resembles that of sliced, swiss cheese. Shown here at the very start of southern spring is a frost-covered surface in which there are two layers evident--a brighter upper layer into which are set swiss cheese-like holes, and a darker, lower layer that lies beneath the "swiss cheese" pattern. Nothing like this exists anywhere on Mars except within the south polar cap. This is a Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image acquired on August 2, 1999. It is located near 84.8°S, 71.8°W, and covers an area 3 km across and about 6.1 km long (1.9 by 3.8 miles). http://photojournal.jpl.nasa.gov/catalog/PIA02368

Stratospheric aerosols from the Sarychev volcano eruption in the 2009 Arctic summer

NASA Astrophysics Data System (ADS)

Jégou, F.; Berthet, G.; Brogniez, C.; Renard, J.-B.; François, P.; Haywood, J. M.; Jones, A.; Bourgeois, Q.; Lurton, T.; Auriol, F.; Godin-Beekmann, S.; Guimbaud, C.; Krysztofiak, G.; Gaubicher, B.; Chartier, M.; Clarisse, L.; Clerbaux, C.; Balois, J. Y.; Verwaerde, C.

2013-02-01

Aerosols from the Sarychev volcano eruption (Kuril Islands, northeast of Japan) were observed in the Arctic lower stratosphere a few days after the strongest SO2 injection which occurred on 15 and 16 June 2009. From the observations provided by the Infrared Atmospheric Sounding Interferometer (IASI) an estimated 0.9 Tg of sulphur dioxide was injected into the Upper Troposphere and Lower Stratosphere (UTLS). The resultant stratospheric sulphate aerosols were detected by the Optical Spectrograph and Infrared Imaging System (OSIRIS) limb sounder and by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instruments. By the first week of July the aerosol plume had spread out over the entire Arctic region. The Sarychev-induced stratospheric aerosol over the Kiruna region (north of Sweden) was measured by the Stratospheric and Tropospheric Aerosol Counter (STAC) during eight balloon flights planned in August and September 2009. During this balloon campaign the Micro RADIomètre BALlon (MicroRADIBAL) and the Spectroscopie d'Absorption Lunaire pour l'Observation des Minoritaires Ozone et NOx (SALOMON) remote-sensing instruments also observed these aerosols. Aerosol concentrations returned to near-background levels by spring 2010. The effective radius, the Surface Area Density (SAD), the aerosol extinction, and the total sulphur mass from STAC in situ measurements are enhanced with mean values in the range 0.15-0.21 μm, 5.5-14.7 μm2 cm-3, 5.5-29.5×10-4 km-1, and 4.9-12.6×10-10 kg [S] kg-1 [air], respectively, between 14 km and 18 km. The observed and modelled e-folding time of sulphate aerosols from the Sarychev eruption is around 70-80 days, a value much shorter than the 12-14 months calculated for aerosols from the 1991 eruption of Mt. Pinatubo. The OSIRIS stratospheric Aerosol Optical Depth (AOD) at 750 nm is enhanced by a factor of 6 with a value of 0.02 in late July compared to 0.0035 before the eruption. The HadGEM2 and MIMOSA model outputs indicate that aerosol layers in polar region up to 14-15 km are largely modulated by stratosphere-troposphere exchange processes. The spatial extension of the Sarychev plume is well represented in the HadGEM2 model with lower altitudes of the plume being controlled by upper tropospheric troughs which displace the plume downward and upper altitudes around 18-20 km in agreement with lidar observations. A good consistency is found between the HadGEM2 sulphur mass density and the value inferred from the STAC observations with a maximum located about 1 km above the tropopause ranging from 1 to 2×10-9 kg [S] kg-1 [air], which is one order of magnitude higher than the background level.

ARC-1979-A79-7099

NASA Image and Video Library

1979-07-10

Range : 1.2 million kilometers (750,000 miles) This picture of Io is one of the last sequence of 'volcano watch' pictures planned as a time lapse study of the nearest of Jupiter's Galilean satellites. The sunlit crescent of Io is seen at the left, and the night side illuminated by light reflected from Jupiter can also be seen. Three volcanic eruption plumes are visible on the limb. All three were previously seen by Voyager 1. On the bright limb Plume 5 (upper) and Plume 6 (lower) are about 100 km high, while Plume 2 on the dark limb is about 185 km high and 325 km wide. The dimensions of Plume 2 are about 1 1/2 times greater than during the Boyager 1 encounter, indicating that the intensity of the eruptions has increased during the four-month time interval between the Boyager encounters. The three volcanic eruptions and at least three others have apparently been active at roughly the same intesity or greater for a period of at least four months.

Coachella Valley, CA

NASA Image and Video Library

2001-10-22

These band composites, acquired on June 4, 2000, cover a 11 by 13.5 km sub-scene in the Coachella Valley, CA. The area is shown by the yellow box on the full scene in the LOWER RIGHT corner, northwest of the Salton Sea. This is a major agricultural region of California, growing fruit and produce throughout the year. Different combinations of ASTER bands help identify the different crop types. UPPER LEFT: bands 3, 2, 1 as red, green, and blue (RGB); UPPER RIGHT: bands 4, 2, 1 as RGB; LOWER LEFT: bands 4, 3, 2 as RGB. The image is centered at 33.6 degrees north latitude, 116.1 degrees west longitude. http://photojournal.jpl.nasa.gov/catalog/PIA11161

Trends in ozone profile measurements

NASA Technical Reports Server (NTRS)

Johnston, H.; Aikin, A.; Barnes, R.; Chandra, S.; Cunnold, D.; Deluisi, J.; Gille, J. C.; Hudson, R.; Mccormick, M. P.; Mcmaster, L.

1989-01-01

From an examination of the agreements and differences between different satellite instruments, it is difficult to believe that existing satellite instruments determine upper stratospheric ozone much better than 4 pct.; by extension, it probably would require at least a 4 pct. change to be reliably detected as a change. The best estimates of the vertical profiles of ozone change in the upper stratosphere between 1979 and 1986 are judged to be those given by the two SAGE satellite instruments. SAGE-2 minus SAGE-1 gives a much lower ozone reduction than that given by the archived Solar Backscatter UV data. The average SAGE profiles of ozone changes between 20 and 50 degs north and between 20 and 50 degs south are given. The SAGE-1 and SAGE-2 comparison gives an ozone reduction of about 4 pct. at 25 km over temperate latitudes. Five ground based Umkehr stations between 36 and 52 degs north, corrected for the effects of volcanic aerosols, report an ozone reduction between 1979 and 1987 at Umkehr layer 8 of 9 + or - 5 pct. The central estimate of upper stratospheric ozone reduction given by SAGE at 40 km is less than the central value estimated by the Umkehr method at layer 8.

Crustal structure of the southern Dead Sea basin derived from project DESIRE wide-angle seismic data

NASA Astrophysics Data System (ADS)

Mechie, J.; Abu-Ayyash, K.; Ben-Avraham, Z.; El-Kelani, R.; Qabbani, I.; Weber, M.

2009-07-01

As part of the DEad Sea Integrated REsearch project (DESIRE) a 235 km long seismic wide-angle reflection/refraction (WRR) profile was completed in spring 2006 across the Dead Sea Transform (DST) in the region of the southern Dead Sea basin (DSB). The DST with a total of about 107 km multi-stage left-lateral shear since about 18 Ma ago, accommodates the movement between the Arabian and African plates. It connects the spreading centre in the Red Sea with the Taurus collision zone in Turkey over a length of about 1100 km. With a sedimentary infill of about 10 km in places, the southern DSB is the largest pull-apart basin along the DST and one of the largest pull-apart basins on Earth. The WRR measurements comprised 11 shots recorded by 200 three-component and 400 one-component instruments spaced 300 m to 1.2 km apart along the whole length of the E-W trending profile. Models of the P-wave velocity structure derived from the WRR data show that the sedimentary infill associated with the formation of the southern DSB is about 8.5 km thick beneath the profile. With around an additional 2 km of older sediments, the depth to the seismic basement beneath the southern DSB is about 11 km below sea level beneath the profile. Seismic refraction data from an earlier experiment suggest that the seismic basement continues to deepen to a maximum depth of about 14 km, about 10 km south of the DESIRE profile. In contrast, the interfaces below about 20 km depth, including the top of the lower crust and the Moho, probably show less than 3 km variation in depth beneath the profile as it crosses the southern DSB. Thus the Dead Sea pull-apart basin may be essentially an upper crustal feature with upper crustal extension associated with the left-lateral motion along the DST. The boundary between the upper and lower crust at about 20 km depth might act as a decoupling zone. Below this boundary the two plates move past each other in what is essentially a shearing motion. Thermo-mechanical modelling of the DSB supports such a scenario. As the DESIRE seismic profile crosses the DST about 100 km north of where the DESERT seismic profile crosses the DST, it has been possible to construct a crustal cross-section of the region before the 107 km left-lateral shear on the DST occurred.

Evaluating the Sensitivity of Glacial Isostatic Adjustment to a Hydrous Melt at 410 km Depth

NASA Astrophysics Data System (ADS)

Hill, A. M.; Milne, G. A.; Ranalli, G.

2017-12-01

We present a sensitivity analysis aimed at testing whether observables related to GIA can support or refute the existence of a low viscosity partial melt layer located above the mantle transition zone, as required by the so-called "Transition Zone Water Filter" model (Bercovici and Karato 2003). In total, 400 model runs were performed sampling a range of melt layer thicknesses (1, 10 & 20 km) and viscosities (1015 - 1019 Pas) as well as plausible viscosity values in the upper and lower mantle. Comparing model output of postglacial decay times and j2, 18 of the considered viscosity models were found to be compatible with all of the observational constraints. Amongst these, only three `background' upper and lower mantle viscosities are permitted regardless of the properties of the melt layer: an upper mantle value of 3×1020 Pas and lower mantle values of 1022, 3×1022 and 5×1022 Pas. Concerning the properties of the melt layer itself, a thin (1 km) layer may have any of the investigated viscosities (1015 to 1019 Pas). For thicker melt layers, the viscosity must be ≥1018 Pas (20 km) or ≥1017 Pas (10 km). Our results indicate clear parameter trade-offs between the properties of the melt layer and the background viscosity structure. Given that the observations permit several values of lower mantle viscosity, we conclude that tightening constraints on this parameter would be valuable for future investigation of the type presented here. Furthermore, while decay times from both locations considered in this investigation (Ångerman River, Sweden; Richmond Gulf, Canada) offer meaningful constraints on viscosity structure, the value for Richmond Gulf is significantly more uncertain and so increasing its precision would likely result in improved viscosity constraints.

Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study

USGS Publications Warehouse

Soares, J.E.; Berrocal, J.; Fuck, R.A.; Mooney, W.D.; Ventura, D.B.R.

2006-01-01

A two-dimensional model of the Brazilian central crust and upper mantle was obtained from the traveltime interpretation of deep seismic refraction data from the Porangatu and Cavalcante lines, each approximately 300 km long. When the lines were deployed, they overlapped by 50 km, forming an E-W transect approximately 530 km long across the Tocantins Province and western Sa??o Francisco Craton. The Tocantins Province formed during the Neoproterozoic when the Sa??o Francisco, the Paranapanema, and the Amazon cratons collided, following the subduction of the former Goia??s ocean basin. Average crustal VP and VP/VS ratios, Moho topography, and lateral discontinuities within crustal layers suggest that the crust beneath central Brazil can be associated with major geological domains recognized at the surface. The Moho is an irregular interface, between 36 and 44 km deep, that shows evidences of first-order tectonic structures. The 8.05 and 8.23 km s-1 P wave velocities identify the upper mantle beneath the Porangatu and Cavalcante lines, respectively. The observed seismic features allow for the identification of (1) the crust has largely felsic composition in the studied region, (2) the absence of the mafic-ultramafic root beneath the Goia??s magmatic arc, and (3) block tectonics in the foreland fold-and-thrust belt of the northern Brasi??lia Belt during the Neoproterozoic. Seismic data also suggested that the Bouguer gravimetric discontinuities are mainly compensated by differences in mass distribution within the lithospheric mantle. Finally, the Goia??s-Tocantins seismic belt can be interpreted as a natural seismic alignment related to the Neoproterozoic mantle domain. Copyright 2006 by the American Geophysical Union.

Crustal structure across the NE Tibetan Plateau and Ordos Block from the joint inversion of receiver functions and Rayleigh-wave dispersions

NASA Astrophysics Data System (ADS)

Li, Yonghua; Wang, Xingchen; Zhang, Ruiqing; Wu, Qingju; Ding, Zhifeng

2017-05-01

We investigated the crustal structure at 34 stations using the H-κ stacking method and jointly inverting receiver functions with Rayleigh-wave phase and group velocities. These seismic stations are distributed along a profile extending across the Songpan-Ganzi Terrane, Qinling-Qilian terranes and southwestern Ordos Basin. Our results reveal the variation in crustal thickness across this profile. We found thick crust beneath the Songpan-Ganzi Terrane (47-59 km) that decreases to 45-47 km in the west Qinling and Qilian terranes, and reaches its local minimum beneath the southwestern Ordos Block (43-51 km) at an average crustal thickness of 46.7 ± 2.5 km. A low-velocity zone in the upper crust was found beneath most of the stations in NE Tibet, which may be indicative of partial melt or a weak detachment layer. Our observations of low to moderate Vp/Vs (1.67-1.79) represent a felsic to intermediate crustal composition. The shear velocity models estimated from joint inversions also reveal substantial lateral variations in velocity beneath the profile, which is mainly reflected in the lower crustal velocities. For the Ordos Block, the average shear wave velocities below 20 km are 3.8 km/s, indicating an intermediate-to-felsic lower crust. The thick NE Tibet crust is characterized by slow shear wave velocities (3.3-3.6 km/s) below 20 km and lacks high-velocity material (Vs ≥ 4.0 km/s) in the lower crust, which may be attributed to mafic lower crustal delamination or/and the thickening of the upper and middle crust.

Tectonics and kinematics of a foreland folded belt influenced by salt, arctic Canada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harrison, J.C.

1996-12-31

The Ordovician (upper Arenig-Llanvirn) Bay Fiord Formation is one of three widespread evaporite units known to have profoundly influenced the style of contractional tectonics within the Innuitian orogen of Arctic Canada. In the western Arctic Islands, the salt-bearing Bay Fiord Formation has accommodated buckling and mostly subsurface thrusting in the west-trending Parry Islands foldbelt. A characteristic feature of this belt is a stratigraphic succession more than 10 km thick featuring three rigid and widespread sedimentary layers and two intervening ductile layers (lower salt and upper shale). The ductile strata have migrated to anticlinal welts during buckling. Other features of themore » foldbelt include (1) an extreme length of individual upright folds (up to 330 km), (2) extreme foldbelt width (up to 11%), (5) a shallow dipping salt decollement system (0.1{degrees}-0.6{degrees}) that has also been folded in the hinterland and later extended, and (6) a complete absence of halokinetic piercing diapirs. The progression from simple thrust-fold structure on the foldbelt periphery to complex in the interior provides a viable kinematic model for this and other contractional salt provinces. One feature of this model is a single massive triangle zone structure (passive roof duplex) that may envelop the entire 200-km width of the foldbelt and underlie an area exceeding 52,000 km{sup 2}.« less

Variations in the crustal structure beneath western Turkey

NASA Astrophysics Data System (ADS)

Saunders, Paul; Priestley, Keith; Taymaz, Tuncay

1998-08-01

We use teleseismic receiver functions to investigate the crustal structure at two locations in western Turkey using seismic data recorded on small arrays of temporary broad-band seismographs. The results from these analyses are compared with receiver function results from the GDSN station ANTO on the Anatolian Plateau in central Turkey. The crust is ~ 30 km thick in the region of western Turkey where active normal faulting reveals present-day extension in the upper crust and alkali-basaltic volcanism reveals recent extension within the subcrustal lithosphere The crust is ~ 34 km thick further east where crustal extension is still evident but less pronounced. In the Anatolian Plateau, which is not currently extending, the crust is ~ 38 km thick. The level of extension estimated from these measurements of crustal thickness implies a β -factor of ~ 1.2. This value agrees with the amount of extension estimated in the upper crust from the integrated seismic strain rate (β -factor of ~ 1.3), from surface faulting(β -factor of ~ 1.25) and from the amount of extension in the subcrustal lithosphere estimated from the volcanism (β -factor < 2), all indicating that the extension is approximately uniformly distributed vertically throughout the lithosphere. The Moho transition in this region appears to thin slightly as the degree of extension increases westwards.

In situ observations of midlatitude stratospheric ClO and BrO

NASA Technical Reports Server (NTRS)

Brune, William H.; Anderson, James C.

1986-01-01

A balloon-borne experiment to measure midlatitude stratospheric BrO and ClO concentrations by NO chemical conversion/atomic resonance fluorescence was flown from Palestine, Texas, on May 20 1986. In this first study of BrO, no signal attributable to BrO was detected, and upper limits (2 sigma uncertainty) between 35 and 24 km altitude give BrO mixing ratios less than 15 pptv. Current models predict mixing ratios that are 1.7 times larger. Measurements of ClO were obtained at less than 0.2-km altitude resolution from 41 to 22 km. The smoothly varying altitude profile lies within the range of two-dimensional model calculations.

Retrieval of ozone profiles from OMPS limb scattering observations

NASA Astrophysics Data System (ADS)

Arosio, Carlo; Rozanov, Alexei; Malinina, Elizaveta; Eichmann, Kai-Uwe; von Clarmann, Thomas; Burrows, John P.

2018-04-01

This study describes a retrieval algorithm developed at the University of Bremen to obtain vertical profiles of ozone from limb observations performed by the Ozone Mapper and Profiler Suite (OMPS). This algorithm is based on the technique originally developed for use with data from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument. As both instruments make limb measurements of the scattered solar radiation in the ultraviolet (UV) and visible (Vis) spectral ranges, an underlying objective of the study is to obtain consolidated and consistent ozone profiles from the two satellites and to produce a combined data set. The retrieval algorithm uses radiances in the UV and Vis wavelength ranges normalized to the radiance at an upper tangent height to obtain ozone concentrations in the altitude range of 12-60 km. Measurements at altitudes contaminated by clouds in the instrument field of view are identified and filtered out. An independent aerosol retrieval is performed beforehand and its results are used to account for the stratospheric aerosol load in the ozone inversion. The typical vertical resolution of the retrieved profiles varies from ˜ 2.5 km at lower altitudes ( < 30 km) to ˜ 1.5 km (about 45 km) and becomes coarser at upper altitudes. The retrieval errors resulting from the measurement noise are estimated to be 1-4 % above 25 km, increasing to 10-30 % in the upper troposphere. OMPS data are processed for the whole of 2016. The results are compared with the NASA product and validated against profiles derived from passive satellite observations or measured in situ by balloon-borne sondes. Between 20 and 60 km, OMPS ozone profiles typically agree with data from the Microwave Limb Sounder (MLS) v4.2 within 5-10 %, whereas in the lower altitude range the bias becomes larger, especially in the tropics. The comparison of OMPS profiles with ozonesonde measurements shows differences within ±5 % between 13 and 30 km at northern middle and high latitudes. At southern middle and high latitudes, an agreement within 5-7 % is also achieved in the same altitude range. An unexpected bias of approximately 10-20 % is detected in the lower tropical stratosphere. The processing of the 2013 data set using the same retrieval settings and its validation against ozonesondes reveals a much smaller bias; a possible reason for this behaviour is discussed.

Evolution of Slow to Intermediate-Spreading Oceanic Crust in the South Atlantic: The Effects of Age, Sediment Thickness, and Spreading Rate on the Heterogeneity of Upper Crustal Velocities

NASA Astrophysics Data System (ADS)

Kardell, D. A.; Christeson, G. L.; Reece, R.; Carlson, R. L.

2017-12-01

The upper section of oceanic crust (layer 2A) commonly exhibits relatively low seismic velocities due to abundant pore and crack space created by the extrusive emplacement of magma and extensional faulting at the spreading ridge. While this is generally true for all spreading rates, previous studies have shown that slow seafloor spreading can yield much higher levels of upper crustal heterogeneity than observed for faster spreading rates. We use a recent multichannel seismic dataset collected with a 12.5 km streamer during the CREST cruise (Crustal Reflectivity Experiment Southern Transect) to build eleven 60-80 km-long tomographic velocity models. These two-dimensional models include both ridge-normal and ridge-parallel orientations and cover oceanic crust produced at slow to intermediate spreading rates. Crustal ages range between 0 and 70 m.y., spreading rates range between slow-spreading and intermediate-spreading, and sedimentary cover thickness ranges from 0 m close to the spreading center to 500 m proximal to the Rio Grande Rise. Our results show a trend of increasing layer 2A velocities with age out to the midpoint of the seismic transect. There is a rapid increase in velocities from 2.8 km/s near the ridge to 4.3 km/s around 10 Ma, and a slower increase to velocities around 5 km/s in 37 m.y. old crust. While this indicates an ongoing evolution in oceanic crust older than expected, the velocities do level off in the older half of the transect, averaging 5 km/s. Crust covered by a thicker sedimentary section can exhibit velocities up to 1 km/s faster than adjacent non-sedimented crust, accounting for much of the local variations. This is possibly due to the effects of a sealed hydrothermal system. We also observe a more heterogeneous velocity structure parallel to the ridge than in the ridge-normal orientation, and more velocity heterogeneity for slow-spreading crust compared to intermediate-spreading crust.

Permeability of the continental crust: Implications of geothermal data and metamorphic systems

USGS Publications Warehouse

Manning, C.E.; Ingebritsen, S.E.

1999-01-01

In the upper crust, where hydraulic gradients are typically 10 MPa km-1, the mean permeabilities required to accommodate the estimated metamorphic fluid fluxes decrease from ~10-16 m2 to ~10-18 m2 between 5- and 12-km depth. Below ~12 km, which broadly corresponds to the brittle-plastic transition, mean k is effectively independent of depth at ~10(-18.5??1) m2. Consideration of the permeability values inferred from thermal modeling and metamorphic fluxes suggests a quasi-exponential decay of permeability with depth of log k ~ -3.2 log z - 14, where k is in meters squared and z is in kilometers. At mid to lower crustal depths this curve lies just below the threshold value for significant advection of heat. Such conditions may represent an optimum for metamorphism, allowing the maximum transport of fluid and solute mass that is possible without advective cooling.

Anatomy of a metamorphic core complex: seismic refraction/wide-angle reflection profiling in southeastern California and western Arizona

USGS Publications Warehouse

McCarthy, J.; Larkin, S.P.; Fuis, G.S.; Simpson, R.W.; Howard, K.A.

1991-01-01

The metamorphic core complex belt in southeastern California and western Arizona is a NW-SE trending zone of unusually large Tertiary extension and uplift. Midcrustal rocks exposed in this belt raise questions about the crustal thickness, crustal structure, and the tectonic evolution of the region. Three seismic refraction/wide-angle reflection profiles were collected to address these issues. The results presented here, which focus on the Whipple and Buckskin-Rawhide mountains, yield a consistent three-dimensiional image of this part of the metamorphic core complex belt. The final model consists of a thin veneer (<2 km) of upper plate and fractured lower plate rocks (1.5-5.5 km s-1) overlying a fairly homogeneous basement (~6.0 km s-1) and a localized high-velocity (6.4 km s -1) body situated beneath the western Whipple Mountains. A prominent midcrustal reflection is identified beneath the Whipple and Buckskin Rawhide mountains between 10 and 20km depth. -from Authors

Crustal structure beneath northeast India inferred from receiver function modeling

NASA Astrophysics Data System (ADS)

Borah, Kajaljyoti; Bora, Dipok K.; Goyal, Ayush; Kumar, Raju

2016-09-01

We estimated crustal shear velocity structure beneath ten broadband seismic stations of northeast India, by using H-Vp/Vs stacking method and a non-linear direct search approach, Neighbourhood Algorithm (NA) technique followed by joint inversion of Rayleigh wave group velocity and receiver function, calculated from teleseismic earthquakes data. Results show significant variations of thickness, shear velocities (Vs) and Vp/Vs ratio in the crust of the study region. The inverted shear wave velocity models show crustal thickness variations of 32-36 km in Shillong Plateau (North), 36-40 in Assam Valley and ∼44 km in Lesser Himalaya (South). Average Vp/Vs ratio in Shillong Plateau is less (1.73-1.77) compared to Assam Valley and Lesser Himalaya (∼1.80). Average crustal shear velocity beneath the study region varies from 3.4 to 3.5 km/s. Sediment structure beneath Shillong Plateau and Assam Valley shows 1-2 km thick sediment layer with low Vs (2.5-2.9 km/s) and high Vp/Vs ratio (1.8-2.1), while it is observed to be of greater thickness (4 km) with similar Vs and high Vp/Vs (∼2.5) in RUP (Lesser Himalaya). Both Shillong Plateau and Assam Valley show thick upper and middle crust (10-20 km), and thin (4-9 km) lower crust. Average Vp/Vs ratio in Assam Valley and Shillong Plateau suggest that the crust is felsic-to-intermediate and intermediate-to-mafic beneath Shillong Plateau and Assam Valley, respectively. Results show that lower crust rocks beneath the Shillong Plateau and Assam Valley lies between mafic granulite and mafic garnet granulite.

Energy Deposition Processes in Titan's Upper Atmosphere

NASA Technical Reports Server (NTRS)

Sittler, Edward C., Jr.; Bertucci, Cesar; Coates, Andrew; Cravens, Tom; Dandouras, Iannis; Shemansky, Don

2008-01-01

Most of Titan's atmospheric organic and nitrogen chemistry, aerosol formation, and atmospheric loss are driven from external energy sources such as Solar UV, Saturn's magnetosphere, solar wind and galactic cosmic rays. The Solar UV tends to dominate the energy input at lower altitudes of approximately 1100 km but which can extend down to approximately 400 km, while the plasma interaction from Saturn's magnetosphere, Saturn's magnetosheath or solar wind are more important at higher altitudes of approximately 1400 km, but the heavy ion plasma [O(+)] of approximately 2 keV and energetic ions [H(+)] of approximately 30 keV or higher from Saturn's magnetosphere can penetrate below 950km. Cosmic rays with energies of greater than 1 GeV can penetrate much deeper into Titan's atmosphere with most of its energy deposited at approximately 100 km altitude. The haze layer tends to dominate between 100 km and 300 km. The induced magnetic field from Titan's interaction with the external plasma can be very complex and will tend to channel the flow of energy into Titan's upper atmosphere. Cassini observations combined with advanced hybrid simulations of the plasma interaction with Titan's upper atmosphere show significant changes in the character of the interaction with Saturn local time at Titan's orbit where the magnetosphere displays large and systematic changes with local time. The external solar wind can also drive sub-storms within the magnetosphere which can then modify the magnetospheric interaction with Titan. Another important parameter is solar zenith angle (SZA) with respect to the co-rotation direction of the magnetospheric flow. Titan's interaction can contribute to atmospheric loss via pickup ion loss, scavenging of Titan's ionospheric plasma, loss of ionospheric plasma down its induced magnetotail via an ionospheric wind, and non-thermal loss of the atmosphere via heating and sputtering induced by the bombardment of magnetospheric keV ions and electrons. This energy input evidently drives the large positive and negative ions observed below approximately 1100 km altitude with ion masses exceeding 10,000 daltons. We refer to these ions as seed particles for the aerosols observed below 300 km altitude. These seed particles can be formed, for example, from the polymerization of acetylene (C2H2) and benzene (C6H6) molecules in Titan's upper atmosphere to form polycyclic aromatic hydrocarbons (PAH) and/or fullerenes (C60). In the case of fullerenes, which are hollow spherical carbon shells, magnetospheric keV [O(+)] ions can become trapped inside the fullerenes and eventually find themselves inside the aerosols as free oxygen. The aerosols are then expected to fall to Titan's surface as polymerized hydrocarbons with trapped free oxygen where unknown surface chemistry can take place.

ARC-1989-A89-7005

NASA Image and Video Library

1989-08-17

August 17 to 19, 1989 Range : 11.5 million km (7.1 million mi.) to 7.9 million km (4.9 million mi.) Four black and white images of Neptune's largest satellite, Triton, show it's rotation between the first (upper left) image and the last (lower right). Resolution improves from about 200 km (124 miles) to 150 km (93 miles) per line pair. Triton's south pole lies in the dark area near the bottom of the disk. Dark spots, roughly 1,000 km (620 miles) across, occur near the equator, and show Triton rotation between images. The rotation appears to be synchronous with Triton's 5.88-day orbital period (i.e., Triton rotates on its axis in the same time it revolves around Neptune.) The spots' constant rotation rate and their visibility near the edge of the disk suggest the spots are surface features. Whatever atmosphere is present on Triton appears transparent enough that Voyager 2's cameras can see through it.

A First Layered Crustal Velocity Model for the Western Solomon Islands: Inversion of Measured Group Velocity of Surface Waves using Ambient Noise Cross-Correlation

NASA Astrophysics Data System (ADS)

Ku, C. S.; Kuo, Y. T.; Chao, W. A.; You, S. H.; Huang, B. S.; Chen, Y. G.; Taylor, F. W.; Yih-Min, W.

2017-12-01

Two earthquakes, MW 8.1 in 2007 and MW 7.1 in 2010, hit the Western Province of Solomon Islands and caused extensive damage, but motivated us to set up the first seismic network in this area. During the first phase, eight broadband seismic stations (BBS) were installed around the rupture zone of 2007 earthquake. With one-year seismic records, we cross-correlated the vertical component of ambient noise recorded in our BBS and calculated Rayleigh-wave group velocity dispersion curves on inter-station paths. The genetic algorithm to invert one-dimensional crustal velocity model is applied by fitting the averaged dispersion curves. The one-dimensional crustal velocity model is constituted by two layers and one half-space, representing the upper crust, lower crust, and uppermost mantle respectively. The resulted thickness values of the upper and lower crust are 6.4 and 14.2 km, respectively. Shear-wave velocities (VS) of the upper crust, lower crust, and uppermost mantle are 2.53, 3.57 and 4.23 km/s with the VP/VS ratios of 1.737, 1.742 and 1.759, respectively. This first layered crustal velocity model can be used as a preliminary reference to further study seismic sources such as earthquake activity and tectonic tremor.

Lithospheric Structure Beneath the Hangay Dome, Central Mongolia

NASA Astrophysics Data System (ADS)

Stachnik, J. C.; Meltzer, A.; Souza, S.; Munkhuu, U.; Tsaagan, B.; Russo, R. M.

2014-12-01

The Mongolian Plateau is a broad regional uplift positioned between the Siberian Craton to the north and the far northern edge of the India-Asia collision to the south. Within this intracontinental setting of high topography, the Hangay Dome in central Mongolia reaches elevations of 4 km and contains intermittent basaltic magmatism over the last 30 Ma. The relationship between high topography, magmatism, and geodynamic processes remains largely unsolved although processes ranging from lithospheric delamination to mantle plume effects have been proposed. A temporary array of seismic stations was deployed around the Hangay Dome to determine lithospheric structure. Preliminary results are shown from receiver function analysis, ambient noise tomography, and teleseismic P-wave tomography. Crustal thickness measurements from H-k stacking of receiver functions range from 42 km to 57 km across the array, with thicker crust beneath the highest topography. The bulk crustal Vp/Vs ratio ranges from 1.71 to 1.9 with a median value for the array of 1.77, perhaps indicating a variable crustal composition with some regions having a more mafic crust. The stacked receiver functions are also combined with ambient noise phase velocity dispersion measurements in a joint inversion for shear velocity profiles at each station which reveals crustal thickness estimates consistent with the H-k stacks while also determining the shear velocity step at the Moho. Teleseismic P-wave travel time residuals ranging between +/-1 second are inverted for a 3D P-wave velocity model using finite-frequency kernels. Notable features include 1) a low velocity anomaly (-3%) in the upper 200 km beneath the eastern part of the Hangay Dome near the Orkhon River Valley, , 2) a steeply dipping low velocity anomaly to the north of the Hangay Dome, perhaps related to the nearby Baikal Rift, and 3) generally higher velocities in the upper 200 km surrounding the high topography. To first order, the high topography of the Hangay Dome appears to be largely supported by thickened crust. However, lower P-wave velocities in the upper mantle beneath the dome are observed. The relative contributions of crustal thickness and upper mantle structure for support of topography and their relationship to magmatism will be determined with further refinement of the models.

Diagenetic Layers in the Upper Walls of Valles Marineris, Mars: Evidence for Drastic Climate Change Since the Mid-Hesperian

NASA Technical Reports Server (NTRS)

Treiman, Allan H.; Fuks, Kelly H.; Murchie, Scott

1995-01-01

A packet of relatively resistant layers, totaling approx. 400 m thickness, is present at the tops of the chasma walls throughout Valles Marineris. The packet consists of an upper dark layer (approx. 50 m thick), a central bright layer (approx. 250 m thick), and a lower dark layer (approx. 100 m thick). The packet appears continuous and of nearly constant thickness and depth below ground surface over the whole Valles system (4000 km E-W, 800 km N-S), independent of elevation (3-10 km) and age of plateau surface (Noachian through upper Hesperian). The packet continues undisturbed beneath the boundary between surface units of Noachian and Hesperian ages, and continues undisturbed beneath impact craters transected by chasma walls. These attributes are not consistent with layer formation by volcanic or sedimentary deposition, and are consistent with layer formation in situ, i.e., by diagenesis, during or after upper Hesperian time. Diagenesis seems to require the action of aqueous solutions in the near subsurface, which are not now stable in the Valles Marineris area. To permit the stability of aqueous solutions, Mars must have had a fairly dense atmosphere, greater than or equal to 1 bar CO2, when the layers formed. Obliquity variations appear to be incapable of producing such a massive atmosphere so late in Mars' history.

Seismic imaging of the upper mantle beneath the northern Central Andean Plateau: Implications for surface topography

NASA Astrophysics Data System (ADS)

Ward, K. M.; Zandt, G.; Beck, S. L.; Wagner, L. S.

2015-12-01

Extending over 1,800 km along the active South American Cordilleran margin, the Central Andean Plateau (CAP) as defined by the 3 km elevation contour is second only to the Tibetan Plateau in geographic extent. The uplift history of the 4 km high Plateau remains uncertain with paleoelevation studies along the CAP suggesting a complex, non-uniform uplift history. As part of the Central Andean Uplift and the Geodynamics of High Topography (CAUGHT) project, we use surface waves measured from ambient noise and two-plane wave tomography to image the S-wave velocity structure of the crust and upper mantle to investigate the upper mantle component of plateau uplift. We observe three main features in our S-wave velocity model including (1), a high velocity slab (2), a low velocity anomaly above the slab where the slab changes dip from near horizontal to a normal dip, and (3), a high-velocity feature in the mantle above the slab that extends along the length of the Altiplano from the base of the Moho to a depth of ~120 km with the highest velocities observed under Lake Titicaca. A strong spatial correlation exists between the lateral extent of this high-velocity feature beneath the Altiplano and the lower elevations of the Altiplano basin suggesting a potential relationship. Non-uniqueness in our seismic models preclude uniquely constraining this feature as an uppermost mantle feature bellow the Moho or as a connected eastward dipping feature extending up to 300 km in the mantle as seen in deeper mantle tomography studies. Determining if the high velocity feature represents a small lithospheric root or a delaminating lithospheric root extending ~300 km into the mantle requires more integration of observations, but either interpretation shows a strong geodynamic connection with the uppermost mantle and the current topography of the northern CAP.

Spatial Heterodyne Observations of Water (SHOW) vapour in the upper troposphere and lower stratosphere from a high altitude aircraft: Modelling and sensitivity analysis

NASA Astrophysics Data System (ADS)

Langille, J. A.; Letros, D.; Zawada, D.; Bourassa, A.; Degenstein, D.; Solheim, B.

2018-04-01

A spatial heterodyne spectrometer (SHS) has been developed to measure the vertical distribution of water vapour in the upper troposphere and the lower stratosphere with a high vertical resolution (∼500 m). The Spatial Heterodyne Observations of Water (SHOW) instrument combines an imaging system with a monolithic field-widened SHS to observe limb scattered sunlight in a vibrational band of water (1363 nm-1366 nm). The instrument has been optimized for observations from NASA's ER-2 aircraft as a proof-of-concept for a future low earth orbit satellite deployment. A robust model has been developed to simulate SHOW ER-2 limb measurements and retrievals. This paper presents the simulation of the SHOW ER-2 limb measurements along a hypothetical flight track and examines the sensitivity of the measurement and retrieval approach. Water vapour fields from an Environment and Climate Change Canada forecast model are used to represent realistic spatial variability along the flight path. High spectral resolution limb scattered radiances are simulated using the SASKTRAN radiative transfer model. It is shown that the SHOW instrument onboard the ER-2 is capable of resolving the water vapour variability in the UTLS from approximately 12 km - 18 km with ±1 ppm accuracy. Vertical resolutions between 500 m and 1 km are feasible. The along track sampling capability of the instrument is also discussed.

Electric structure of the Copahue Volcano (Neuquén Province, Argentina), from magnetotelluric soundings: 1D and 2D modellings

NASA Astrophysics Data System (ADS)

Mamaní, M. J.; Borzotta, E.; Venencia, J. E.; Maidana, A.; Moyano, C. E.; Castiglione, B.

2000-05-01

Four magnetotelluric soundings were carried out in 1993 in the region of the Copahue active volcano located at the border between Chile and Argentina (37°45'S, 71°18'W). Three soundings were located inside the caldera of the ancient stratovolcano (east of Copahue) and the fourth outside it. The soundings inside the caldera were situated at about 6, 11, and 14 km from the volcano. Digital data were obtained covering the range of periods from 1 sec to 10,000 sec using induction coils and a flux-gate magnetometer to obtain the magnetic data and Cu-SO 4Cu electrodes for electric field measurements. The apparent resistivity curves corresponding to principal directions were analyzed in conjunction with the geological background in order to eliminate distortion — which is very important in this hot volcanic region. Then, 1D modellings were performed using the "normal" curves — i.e., curves without distortions. Using the apparent resistivity curves with distortions, 2D modelling was also performed along a profile perpendicular to the regional tectonic trend suggested by MT soundings into the caldera. Results show low resistivity values of about 3-15 Ωm between 9 km to 20 km depth in the crust, suggesting high temperatures, with minimum values of about 700°C with partially melted zones in the upper crust between 9 km to 20 km depth under the caldera. The presence of a possible sulphide-carbonaceous layer (SC layer) in the upper basement could play an important role in lowering the electrical resistivities because of its high electronic conductivity.

New observations of molecular nitrogen in the Martian upper atmosphere by IUVS on MAVEN

NASA Astrophysics Data System (ADS)

Stevens, M. H.; Evans, J. S.; Schneider, N. M.; Stewart, A. I. F.; Deighan, J.; Jain, S. K.; Crismani, M.; Stiepen, A.; Chaffin, M. S.; McClintock, W. E.; Holsclaw, G. M.; Lefèvre, F.; Lo, D. Y.; Clarke, J. T.; Montmessin, F.; Bougher, S. W.; Jakosky, B. M.

2015-11-01

We identify molecular nitrogen (N2) emissions in the Martian upper atmosphere using the Imaging Ultraviolet Spectrograph (IUVS) on NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We report the first observations of the N2 Lyman-Birge-Hopfield (LBH) bands at Mars and confirm the tentative identification of the N2 Vegard-Kaplan (VK) bands. We retrieve N2 density profiles from the VK limb emissions and compare calculated limb radiances between 90 and 210 km against both observations and predictions from a Mars general circulation model (GCM). Contrary to earlier analyses using other satellite data, we find that N2 abundances exceed GCM results by about a factor of 2 at 130 km but are in agreement at 150 km. The analysis and interpretation are enabled by a linear regression method used to extract components of UV spectra from IUVS limb observations.

Continuous Spectrum of Crustal Structures and Spreading Processes from Volcanic Rifted Margins to Mid-Ocean Ridges

NASA Astrophysics Data System (ADS)

Karson, J. A.

2016-12-01

Structures generated by seafloor spreading in oceanic crust (and ophiolites) and thick oceanic crust of Iceland show a continuous spectrum of features that formed by similar mechanisms but at different scales. A high magma budget near the Iceland hotspot generates thick (40-25 km) mafic crust in a plate boundary zone about 50 km wide. The upper crust ( 10 km thick) is constructed by the subaxial subsidence and thickening of lavas fed by dense dike swarms over a hot, weak lower crust to produce structures analogous to seaward-dipping reflectors of volcanic rifted margins. Segmented rift zones propagate away from the hotspot creating migrating transform fault zones, microplate-like crustal blocks and rift-parallel strike-slip faults. These structures are decoupled from the underlying lower crustal gabbroic rocks that thin by along-axis flow that reduces the overall crustal thickness and smooths-out local crustal thickness variations. Spreading on mid-ocean ridges with high magma budgets have much thinner crust (10-5 km) generated at a much narrower (few km) plate boundary zone. Subaxial subsidence accommodates the thickening of the upper crust of inward-dipping lavas and outward-dipping dikes about 1-2 km thick over a hot weak lower crust. Along-axis (high-temperature ductile and magmatic) flow of lower crustal material may help account for the relatively uniform seismic thickness of oceanic crust worldwide. Spreading along even slow-spreading mid-ocean ridges near hotspots (e.g., the Reykjanes Ridge) probably have similar features that are transitional between these extremes. In all of these settings, upper crustal and lower crustal structures are decoupled near the plate boundary but eventually welded together as the crust ages and cools. Similar processes are likely to occur along volcanic rifted margins as spreading begins.

Evidence of slope failure in the Sines Contourite Drift area (SW Portuguese Continental Margin) - preliminary results

NASA Astrophysics Data System (ADS)

Teixeira, Manuel; Roque, Cristina; Terrinha, Pedro; Rodrigues, Sara; Ercilla, Gemma; Casas, David

2017-04-01

Slope instability, expressed by landslide activity, is an important natural hazard both onshore as well as offshore. Offshore processes create great concern on coastal areas constituting one of the major and most prominent hazards, directly by the damages they generate and indirectly by the possibility of generating tsunamis, which may affect the coast line. The Southwest Portuguese Continental Margin has been identified as an area where several mass movements occurred from Late Pleistocene to Present. Recently, an area of 52 km long by 34 km wide, affected by slope failure has been recognized in the Sines contourite drift located off the Alentejo. SWIM and CONDRIBER multibeam swath bathymetry has been used for the geomorphologic analysis and for recognition of mass movement scars on the seabed. Scars' areas and volumes were calculated by reconstructing paleo-bathymetry. The net gain and net loss were calculated using both paleo and present day bathymetry. Geomorphologically, the study area presents 4 morphologic domains with landslide scars: I) Shelf and upper slope display an irregular boundary with domain II with a sharp step ( 150m - 600m); II) Smooth area with gentle slope angles making the transition from smoother area to the continental slope (scarp), with large scars, suggesting slow rate and distributed mass wasting processes over this area ( 600 - 1200m); III) Scarp with high rates of retrograding instability, where faster processes are verified and a great number of gullies is feeding downslope area (1200m - 3200m); IV) Lebre Basin where mass movements deposits accumulate (> 3200m). A total of 51 landslide scars were identified with a total affected area of 137.67 km2, with 80.9 km2 being located in the continental slope with about 59% of the disrupted area, between 1200 and 3200m, and 41% (56.6 km2) lies in the continental shelf and upper slope, on a range of depths between 150 and 800m. The mean scar area is 2.7 km2 and the maximum area recorded on a scar is 7.63 km2, while the minimum is 0.14 km2. About 43% of the scars present areas below 2 km2 and 63% below 3 km2. Only 3.9% of the scars present areas higher than 7 km2. There is a total volume of displaced material of 4.46 km3 with a mean volume of 0.1 km3. The maximum volume recorded on a scar is 0.45 km3, while the minimum is 0.01 km3. The volume of material removed is quite variable, although the major part of the scars corresponds to a very small volume of removed material, with 69% of the scars presenting less than 0.1 km3. About 55% of the scars are located in slopes <=7° and 20% in slopes between 0 and 2°, while 24% of the scars belong to the class of slope gradient between 1.5 and 3°. We may conclude that there is, apparently, a reverse relationship between slope angle and scar area, meaning that slope is not the main condition for big landslide scars and that the areas with steep slopes, such as fault escarpments, favour continuous fast retrograde erosion. Publication supported by FCT- project UID/GEO/50019/2013 - Instituto Dom Luiz

Upper mantle velocity structure beneath southern Africa from modeling regional seismic data

NASA Astrophysics Data System (ADS)

Zhao, Ming; Langston, Charles A.; Nyblade, Andrew A.; Owens, Thomas J.

1999-03-01

The upper mantle seismic velocity structure beneath southern Africa is investigated using travel time and waveform data which come from a large mine tremor in South Africa (mb 5.6) recorded by the Tanzania broadband seismic experiment and by several stations in southern Africa. The waveform data show upper mantle triplications for both the 410- and 670-km discontinuities between distances of 2100 and 3000 km. Auxiliary travel time data along similar profiles obtained from other moderate events are also used. P wave travel times are inverted for velocity structure down to ˜800-km depth using the Wiechert-Herglotz technique, and the resulting model is evaluated by perturbing it at three depth intervals and then testing the perturbed model against the travel time and waveform data. The results indicate a typical upper mantle P wave velocity structure for a shield. P wave velocities from the top of the mantle down to 300-km depth are as much as 3% higher than the global average and are slightly slower than the global average between 300- and 420-km depth. Little evidence is found for a pronounced low-velocity zone in the upper mantle. A high-velocity gradient zone is required above the 410-km discontinuity, but both sharp and smooth 410-km discontinuities are permitted by the data. The 670-km discontinuity is characterized by high-velocity gradients over a depth range of ˜80 km around 660-km depth. Limited S wave travel time data suggest fast S wave velocities above ˜150-km depth. These results suggest that the bouyant support for the African superswell does not reside at shallow depths in the upper mantle.

Spectral-element global waveform tomography: A second-generation upper-mantle model

NASA Astrophysics Data System (ADS)

French, S. W.; Lekic, V.; Romanowicz, B. A.

2012-12-01

The SEMum model of Lekic and Romanowicz (2011a) was the first global upper-mantle VS model obtained using whole-waveform inversion with spectral element (SEM: Komatitsch and Vilotte, 1998) forward modeling of time domain three component waveforms. SEMum exhibits stronger amplitudes of heterogeneity in the upper 200km of the mantle compared to previous global models - particularly with respect to low-velocity anomalies. To make SEM-based waveform inversion tractable at global scales, SEMum was developed using: (1) a version of SEM coupled to 1D mode computation in the earth's core (C-SEM, Capdeville et al., 2003); (2) asymptotic normal-mode sensitivity kernels, incorporating multiple forward scattering and finite-frequency effects in the great-circle plane (NACT: Li and Romanowicz, 1995); and (3) a smooth anisotropic crustal layer of uniform 60km thickness, designed to match global surface-wave dispersion while reducing the cost of time integration in the SEM. The use of asymptotic kernels reduced the number of SEM computations considerably (≥ 3x) relative to purely numerical approaches (e.g. Tarantola, 1984), while remaining sufficiently accurate at the periods of interest (down to 60s). However, while the choice of a 60km crustal-layer thickness is justifiable in the continents, it can complicate interpretation of shallow oceanic upper-mantle structure. We here present an update to the SEMum model, designed primarily to address these concerns. The resulting model, SEMum2, was derived using a crustal layer that again fits global surface-wave dispersion, but with a more geologically consistent laterally varying thickness: approximately honoring Crust2.0 (Bassin, et al., 2000) Moho depth in the continents, while saturating at 30km in the oceans. We demonstrate that this approach does not bias our upper mantle model, which is constrained not only by fundamental mode surface waves, but also by overtone waveforms. We have also improved our data-selection and assimilation scheme, more readily allowing for additional and higher-quality data to be incorporated into our inversion as the model improves. Further, we have been able to refine the parameterization of the isotropic component of our model, previously limited by our ability to solve the large dense linear system that governs model updates (Tarantola and Valette, 1982). The construction of SEMum2 involved 3 additional inversion iterations away from SEMum. Overall, the combined effect of these improvements confirms and validates the general structure of the original SEMum. Model amplitudes remain an impressive feature in SEMum2, wherein peak-to-peak variation in VS can exceed 15% in close lateral juxtaposition. Further, many intriguing structures present in SEMum are now imaged with improved resolution in the updated model. In particular, the geographic extents of the anomalous oceanic cluster identified by Lekic and Romanowicz (2011b) are consistent with our findings and now allow us to further identify alternating bands of lower and higher velocities in the 200-300km depth range beneath the Pacific basin, with a characteristic spacing of ˜2000km normal to absolute plate motion. Possible dynamic interpretation of these and other features in the ocean basins is explored in a companion presentation (Romanowicz et al., this meeting).

Photographer : JPL Range : 76 million km. ( 47 million miles) P-22892C This, Voyager 1 image shows

NASA Technical Reports Server (NTRS)

1980-01-01

Photographer : JPL Range : 76 million km. ( 47 million miles) P-22892C This, Voyager 1 image shows Saturn and five of its satellites. Saturn's largest moon, Titan, is clearly seen in the upper right corner. The smaller satellites, Dione & Tethys, are shown in the upper left corner, top and bottom respectively. Two of the innermost satellites, Mimas & Enceladus, appear to the lower right of the planet, with Mimas closest to Satun. The bright object to the left of the rings is not a moon, but an artifact of processing. Voyager 1 will make its closest approach November 12th, 1980, ata distance of 124,200 km. (77,176 mi.). this photo is just one of 17,000 images taken of Saturn, its rings, and its satellites by Voyager 1.

Saudi Arabian seismic-refraction profile: A traveltime interpretation of crustal and upper mantle structure

USGS Publications Warehouse

Mooney, W.D.; Gettings, M.E.; Blank, H.R.; Healy, J.H.

1985-01-01

The crustal and upper mantle compressional-wave velocity structure across the southwestern Arabian Shield has been investigated by a 1000-km-long seismic refraction profile. The profile begins in Mesozoic cover rocks near Riyadh on the Arabian Platform, trends southwesterly across three major Precambrian tectonic provinces, traverses Cenozoic rocks of the coastal plain near Jizan, and terminates at the outer edge of the Farasan Bank in the southern Red Sea. More than 500 surveyed recording sites were occupied, and six shot points were used, including one in the Red Sea. Two-dimensional ray-tracing techniques, used to analyze amplitude-normalized record sections indicate that the Arabian Shield is composed, to first order, of two layers, each about 20 km thick, with average velocities of about 6.3 km/s and 7.0 km/s, respectively. West of the Shield-Red Sea margin, the crust thins to a total thickness of less than 20 km, beyond which the Red Sea shelf and coastal plain are interpreted to be underlain by oceanic crust. A major crustal inhomogeneity at the northeast end of the profile probably represents the suture zone between two crustal blocks of different composition. Elsewhere along the profile, several high-velocity anomalies in the upper crust correlate with mapped gneiss domes, the most prominent of which is the Khamis Mushayt gneiss. Based on their velocities, these domes may constitute areas where lower crustal rocks have been raised some 20 km. Two intracrustal reflectors in the center of the Shield at 13 km depth probably represent the tops of mafic intrusives. The Mohorovic??ic?? discontinuity beneath the Shield varies from a depth of 43 km and mantle velocity of 8.2 km/s in the northeast to a depth of 38 km and mantle velocity of 8.0 km/s depth in the southwest near the Shield-Red Sea transition. Two velocity discontinuities occur in the upper mantle, at 59 and 70 km depth. The crustal and upper mantle velocity structure of the Arabian Shield is interpreted as revealing a complex crust derived from the suturing of island arcs in the Precarnbrian. The Shield is currently flanked by the active spreading boundary in the Red Sea. ?? 1985.

Measurements of the rotation rate of the jovian mid-to-low latitude ionosphere

NASA Astrophysics Data System (ADS)

Johnson, Rosie E.; Stallard, Tom S.; Melin, Henrik; Miller, Steve; Nichols, Jonathan D.

2016-12-01

Previous studies of Jupiter's upper atmosphere often assume that the mid-to-low latitude ionosphere is corotating, but a model describing an observed asymmetry in hydrogen Lyman-α emission (∼1000 km above the 1 bar level) disagrees with this assumption. From measurements of the Doppler shifted H3+ν2 Q (1 ,0-) line at 3.953 μm using the IRTF, the line-of-sight velocities of the H3+ ions were derived in the planetary reference frame and found to be 0.091 ± 0.25 km s-1, 0.0082 ± 0.30 km s-1 and 0.31 ± 0.51 km s-1 in 1998, 2007 and 2013 respectively. These zero velocities represent corotation at the mid-to-low latitude region of Jupiter's ionosphere. There is no evidence of flows associated with the hydrogen Lyman-α emission asymmetries detected in the peak H3+ emission layer (∼550 km above the 1 bar level), and we assert that the H3+ ions in Jupiter's mid-to-low latitude are rigidly corotating.

Determining the upper mantle seismic structure beneath the northern Transantarctic Mountains, Antarctica, from regional P- and S-wave tomography

NASA Astrophysics Data System (ADS)

Brenn, Gregory Randall

Stretching 3,500 km across Antarctica, with peak elevations up to 4,500 m, the Transantarctic Mountains (TAMs) are the largest non-compressional continental mountain range on Earth and represent a tectonic boundary between the East Antarctica (EA) craton and the West Antarctic Rift System. The origin and uplift mechanism associated with the TAMs is controversial, and multiple models have been proposed. Seismic investigations of the TAM's subsurface structure can provide key constraints to help evaluate these models, but previous studies have been primarily focused only on the central TAMs near Ross Island. Using data from the new 15-station Transantarctic Mountain Northern Network as well as data from several smaller networks, this study investigates the upper mantle velocity structure beneath a previously unexplored portion of the northern TAMs through regional body wave tomography. Relative travel-times were calculated for 11,182 P-wave and 8,285 S-wave arrivals from 790 and 581 Mw ≥ 5.5 events, respectively, using multi-channel cross correlation, and these data were then inverted for models of the upper mantle seismic structure. Resulting P- and S-wave tomography images reveal two focused low velocity anomalies beneath Ross Island (RI; deltaVP ≈ -2.0%; deltaV S ≈ -1.5% to -4.0%) and Terra Nova Bay (TNB; deltaVP ≈ -1.5% to -2.0%; deltaVS ≈ -1.0% to -4.0%) that extend to depths of 200 and 150 km, respectively. The RI and TNB slow anomalies also extend 50-100 km laterally beneath the TAMs front and sharply abut fast velocities beneath the EA craton (deltaVP ≈ 0.5% to 2%; deltaV S ≈ 1.5% to 4.0%). A low velocity region (deltaVP ≈ -1.5%), centered at 150 km depth beneath the Terror Rift (TR) and primarily constrained within the Victoria Land Basin, connects the RI and TNB anomalies. The focused low velocities are interpreted as regions of partial melt and buoyancy-driven upwelling, connected by a broad region of slow (presumably warm) upper mantle associated with Cenozoic extension along the TR. Dynamic topography estimates based on the imaged S-wave velocity perturbations are consistent with observed surface topography in the central and northern TAMs, thereby providing support for uplift models that advocate for thermal loading and a flexural origin for the mountain range.

South Polar Cap

NASA Technical Reports Server (NTRS)

2005-01-01

17 March 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows mesas and pits formed by sublimation of carbon dioxide of the south polar cap.

Location near: 85.8oS, 351.5oW Image width: 2 km (1.2 mi) Illumination from: upper left Season: Southern Summer

Antarctic Polar Descent and Planetary Wave Activity Observed in ISAMS CO from April to July 1992

NASA Technical Reports Server (NTRS)

Allen, D. R.; Stanford, J. L.; Nakamura, N.; Lopez-Valverde, M. A.; Lopez-Puertas, M.; Taylor, F. W.; Remedios, J. J.

2000-01-01

Antarctic polar descent and planetary wave activity in the upper stratosphere and lower mesosphere are observed in ISAMS CO data from April to July 1992. CO-derived mean April-to-May upper stratosphere descent rates of 15 K/day (0.25 km/day) at 60 S and 20 K/day (0.33 km/day) at 80 S are compared with descent rates from diabatic trajectory analyses. At 60 S there is excellent agreement, while at 80 S the trajectory-derived descent is significantly larger in early April. Zonal wavenumber 1 enhancement of CO is observed on 9 and 28 May, coincident with enhanced wave 1 in UKMO geopotential height. The 9 May event extends from 40 to 70 km and shows westward phase tilt with height, while the 28 May event extends from 40 to 50 km and shows virtually no phase tilt with height.

Infrared Measurements of Atmospheric Ethane (C2H6) From Aircraft and Ground-Based Solar Absorption Spectra in the 3000/ cm Region

NASA Technical Reports Server (NTRS)

Coffey, M. T.; Mankin, W. G.; Goldman, A.; Rinsland, C. P.; Harvey, G. A.; Devi, V. Malathy; Stokes, G. M.

1985-01-01

A number or prominent Q-branches or the upsilon(sub 7) band or C2H6 have been identified near 3000/ cm in aircraft and ground-based infrared solar absorption spectra. The aircraft spectra provide the column amount above 12 km at various altitudes. The column amount is strongly correlated with tropopause height and can be described by a constant mixing ratio of 0.46 ppbv in the upper troposphere and a mixing ratio scale height of 3.9 km above the tropopause. The, ground-based spectra yield a column of 9.0 x 10(exp 15) molecules/sq cm above 2.1 km; combining these results implies a tropospheric mixing ratio of approximately 0.63 ppbv.

Infrared measurements of atmospheric ethane (C2H6) from aircraft and ground-based solar absorption spectra in the 3000/cm region

NASA Technical Reports Server (NTRS)

Coffey, M. T.; Mankin, W. G.; Goldman, A.; Rinsland, C. P.; Harvey, G. A.; Devi, V. M.; Stokes, G. M.

1985-01-01

A number of prominent Q-branches of the nu-7 band of C2H6 have been identified near 3000/cm in aircraft and ground-based infrared solar absorption spectra. The aircraft spectra provide the column amount above 12 km at various altitudes. The column amount is strongly correlated with tropopause height and can be described by a constant mixing ratio of 0.46 ppbv in the upper troposphere and a mixing ratio scale height of 3.9 km above the tropopause. The ground-based spectra yield a column of 9.0 x 10 to the 15th molecules/sq cm above 2.1 km; combining these results implies a tropospheric mixing ratio of approximately 0.63 ppbv.

Formation of continental crust in a temporally linked arc magma system from 5 to 30 km depth: ~ 90 Ma plutonism in the Cascades Crystalline Core composite arc section

NASA Astrophysics Data System (ADS)

Ratschbacher, B. C.; Miller, J. S.; Kent, A. J.; Miller, R. B.; Anderson, J. L.; Paterson, S. R.

2015-12-01

Continental crust has an andesitic bulk composition with a mafic lower crust and a granodioritic upper crust. The formation of stratified continental crust in general and the vertical extent of processes active in arc crustal columns leading to the differentiation of primitive, mantle-derived melts entering the lower crust are highly debated. To investigate where in the crustal column magma mixing, fractionation, assimilation and crystal growth occur and to what extent, we study the ~ 90 Ma magmatic flare-up event of the Cascades arc, a magma plumbing system from ~ 5 to 30 km depth. We focus on three intrusive complexes, emplaced at different depths during major regional shortening in an exceptionally thick crust (≥ 55 km1) but which are temporally related: the upper crustal Black Peak intrusion (1-3 kbar at 3.7 to 11 km; ~ 86.8 to 91.7 Ma2), the mid-crustal Mt. Stuart intrusion (3.5-4.0 kbar at 13 to 15 km; 90.8 and 96.3 Ma3) and the deep crustal Tenpeak intrusion (7 to 10 kbar at 25 to 37 km; 89.7 to 92.3 Ma4). These intrusive complexes are well characterized by geochronology showing that they have been constructed incrementally by multiple magma batches over their lifespans and thus allow the monitoring and comparison of geochemical parameters over time at different depths. We use a combination of whole rock major and trace element data and isotopes combined with detailed investigation of amphibole, which has been recognized to be important in the generation of calc-alkaline rocks in arcs to test the following hypotheses: (a) compositional bimodality is produced in the lower crust, whereas upper crustal levels are dominated by mixing to form intermediate compositions, or (b) differentiation occurs throughout the crustal column with different crystallizing phases and their compositions controlling the bulk chemistry. 1. Miller et al. 2009: GSA Special Paper 456, p. 125-149 2. Shea 2014: PhD thesis, Massachusetts Institute of Technology 3. Anderson et al. 2012: International Geology Review, v. 54, no. 5, p. 491-508 4. Matzel et al. 2006: GSA Bulletin, v. 118, no. 11-12, p. 1412-1430

A Search for Molecular Gas in the Host Galaxy of FRB 121102

NASA Astrophysics Data System (ADS)

Bower, Geoffrey C.; Rao, Ramprasad; Krips, Melanie; Maddox, Natasha; Bassa, Cees; Adams, Elizabeth A. K.; Law, C. J.; Tendulkar, Shriharsh P.; van Langevelde, Huib Jan; Paragi, Zsolt; Butler, Bryan J.; Chatterjee, Shami

2018-06-01

We present Submillimeter Array and Northern Extended Millimeter Array observations of the host galaxy of FRB 121102 in the CO 3–2 and 1–0 transitions, respectively. We do not detect emission from either transition. We set 3σ upper limits to the CO luminosity L CO < 2.5 × 107 K km s‑1 pc‑2 for CO 3–2 and L CO < 2.3 × 109 K km s‑1 pc‑2 for CO 1–0. For Milky Way–like star formation properties, we set a 3σ upper limit on the H2 mass of 2.5 × 108 M ⊙, slightly less than the predictions for the H2 mass based on the star formation rate. The true constraint on the H2 mass may be significantly higher, however, because of the reduction in CO luminosity that is common for low-metallicity dwarf galaxies like the FRB host galaxy. These results demonstrate the challenge of identifying the nature of FRB progenitors through study of the host galaxy molecular gas. We also place a limit of 42 μJy (3σ) on the continuum flux density of the persistent radio source at 97 GHz, consistent with a power-law extrapolation of the low-frequency spectrum, which may arise from an active galactic nucleus or other nonthermal source.

Modeling the three-dimensional structure of macroscopic magma transport systems: Application to Kilauea volcano, Hawaii

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryan, M.P.; Koyanagi, R.Y.; Fiske, R.S.

1981-08-10

We report the results of modeling the three-dimensional internal structure of Kilauea's magmatic passageways. The approach uses a clear plexiglass model containing equally-spaced levels upon which well-located seismic hypocenters are plotted. Application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures. Four magma transport and storage structures produce have been identified within and beneath Kilauea: (1) Primary conduit. The conduit transporting magma into Kilauea's summit storage reservoir rises from the model base (14.6 km) to 6.5 km depth level. It ismore » a zone of intense fracturing and inferred intrusion, whose horizontal sections are elliptical in planform. Over its height, the average major axis of component horizontal section is 3.3 km, with an average minor axis of 1.7 km. This yields an aspect ratio of xi = 0.52. At the 14.6 km level, the strike of the major axis is N67 /sup 0/E. During passage from the upper mantle through the oceanic crust, this axis rotates in a right-handed sense, until the strike is N41 /sup 0/W at the 6.5 km level. (2) Magma chamber complex floor. The interval from 6.5 to 5.7 km, immediately over the primary conduit, is aseismic. This suggests differentially high fluid-to-rock ratios, and relatively weak pathways for further vertical transport into higher levels of the storage complex, as well as lateral leakage eastward into the Mauna Ulu staging area: for later vertical ascent beneath the upper east rift zone. Seismicity within the immediately subjacent rocks that form the top of the primary conduit (at 6.5 km) suggests that this inferred magma-rich horizon forms the effective floor of the summit storage complex. (3) Magma chamber crown. Intense seismicity over the 1.1--1.9 km depth interval defines an elliptical region in plan view.« less

Stratospheric aerosols from the Sarychev volcano eruption in the 2009 Arctic summer

NASA Astrophysics Data System (ADS)

Jégou, F.; Berthet, G.; Brogniez, C.; Renard, J.-B.; François, P.; Haywood, J. M.; Jones, A.; Bourgeois, Q.; Lurton, T.; Auriol, F.; Godin-Beekmann, S.; Guimbaud, C.; Krysztofiak, G.; Gaubicher, B.; Chartier, M.; Clarisse, L.; Clerbaux, C.; Balois, J. Y.; Verwaerde, C.; Daugeron, D.

2013-07-01

Aerosols from the Sarychev volcano eruption (Kuril Islands, northeast of Japan) were observed in the Arctic lower stratosphere a few days after the strongest SO2 injection which occurred on 15 and 16 June 2009. From the observations provided by the Infrared Atmospheric Sounding Interferometer (IASI) an estimated 0.9 Tg of sulphur dioxide was injected into the upper troposphere and lower stratosphere (UTLS). The resultant stratospheric sulphate aerosols were detected from satellites by the Optical Spectrograph and Infrared Imaging System (OSIRIS) limb sounder and by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and from the surface by the Network for the Detection of Atmospheric Composition Changes (NDACC) lidar deployed at OHP (Observatoire de Haute-Provence, France). By the first week of July the aerosol plume had spread out over the entire Arctic region. The Sarychev-induced stratospheric aerosol over the Kiruna region (north of Sweden) was measured by the Stratospheric and Tropospheric Aerosol Counter (STAC) during eight balloon flights planned in August and September 2009. During this balloon campaign the Micro Radiomètre Ballon (MicroRADIBAL) and the Spectroscopie d'Absorption Lunaire pour l'Observation des Minoritaires Ozone et NOx (SALOMON) remote-sensing instruments also observed these aerosols. Aerosol concentrations returned to near-background levels by spring 2010. The effective radius, the surface area density (SAD), the aerosol extinction, and the total sulphur mass from STAC in situ measurements are enhanced with mean values in the range 0.15-0.21 μm, 5.5-14.7 μm2 cm-3, 5.5-29.5 × 10-4 km-1, and 4.9-12.6 × 10-10 kg[S] kg-1[air], respectively, between 14 km and 18 km. The observed and modelled e-folding time of sulphate aerosols from the Sarychev eruption is around 70-80 days, a value much shorter than the 12-14 months calculated for aerosols from the 1991 eruption of Mt Pinatubo. The OSIRIS stratospheric aerosol optical depth (AOD) at 750 nm is enhanced by a factor of 6, with a value of 0.02 in late July compared to 0.0035 before the eruption. The HadGEM2 and MIMOSA model outputs indicate that aerosol layers in polar region up to 14-15 km are largely modulated by stratosphere-troposphere exchange processes. The spatial extent of the Sarychev plume is well represented in the HadGEM2 model with lower altitudes of the plume being controlled by upper tropospheric troughs which displace the plume downward and upper altitudes around 18-20 km, in agreement with lidar observations. Good consistency is found between the HadGEM2 sulphur mass density and the value inferred from the STAC observations, with a maximum located about 1 km above the tropopause ranging from 1 to 2 × 10-9 kg[S] kg-1[air], which is one order of magnitude higher than the background level.

Glacier changes in the Ravi basin, North-Western Himalaya (India) during the last four decades (1971-2010/13)

NASA Astrophysics Data System (ADS)

Chand, Pritam; Sharma, Milap Chand

2015-12-01

A glacier inventory of the Ravi basin, north-western Himalaya has been generated for the year 2002 using Landsat ETM + and ASTER Global DEM (GDEM V2) as the baseline data for the change analysis. The Ravi basin consists of 285 glaciers (> 0.02 km2) covering an area of 164.5 ± 7.5 km2, including 71 debris-covered glaciers with an area of 36.1 ± 2.1 km2 (22% of total glacierized area) in 2002. Change analysis based on Corona KH-4B (1971), Worldview (2010) and Landsat 8 OLI/TRIS (2013) images was restricted to a subset of 157 glaciers (covering an area of 121.4 ± 5.4 km2 in 2002) due to cloud cover. Glacier area decreased from 125.8 ± 1.9 km2 (1971) to 119.9 ± 4.8 km2 (2010/13), a loss of 4.7 ± 4.1% or 0.1 ± 0.1% a- 1. The glacier recession rate has decreased, to a minimum for the recent decades (2002-2010/13). The debris-covered glacier area increased by 19.2 ± 2.2% (0.5 ± 0.05% a- 1) in the Ravi basin. However, there were significant variation in its sub-basins i.e. in Budhil and Upper Ravi sub-basin, where the debris-covered area increased by 28.6 ± 3.1% (0.7 ± 0.1% a- 1) and 14 ± 1.6% (0.3 ± 0.04% a- 1), respectively, between 1971 and 2010/13. Field investigation of selected glaciers (2010-2014) supports glacier recession trend from remote sensing data. Glacier retreat rates in the Ravi basin were lower than previously reported for selected glaciers in the similar basin and other basins (e.g. Chenab, Beas, Parbati, Baspa and Tirungkhad) of the Himachal Himalaya.

New constraints on the upper mantle structure of the Slave craton from Rayleigh wave inversion

NASA Astrophysics Data System (ADS)

Chen, Chin-Wu; Rondenay, Stéphane; Weeraratne, Dayanthie S.; Snyder, David B.

2007-05-01

Rayleigh wave phase and amplitude data are analyzed to provide new insight into the velocity structure of the upper mantle beneath the Slave craton, in the northwestern Canadian Shield. We invert for phase velocities at periods between 20 s-142 s (with greatest sensitivity at depths of 28-200 km) using crossing ray paths from events recorded by the POLARIS broadband seismic network and the Yellowknife array. Phase velocities obtained for the Slave province are comparable to those from other cratons at shorter periods, but exceed the global average by ~2% at periods above 60 s, suggesting that the Slave craton may be an end member in terms of its high degree of mantle depletion. The one-dimensional inversion of phase velocities yields high upper-mantle S-wave velocities of 4.7 +/- 0.2 km/s that persist to 220 +/- 65 km depth and thus define the cratonic lithosphere. Azimuthal anisotropy is well resolved at all periods with a dominant fast direction of N59°E +/- 20°, suggesting that upper mantle anisotropy beneath the Slave craton is influenced by both lithospheric fabric and sub-lithospheric flow.

Fate of Ice Grains in Saturn's Ionosphere

NASA Astrophysics Data System (ADS)

Hamil, O.; Cravens, T. E.; Reedy, N. L.; Sakai, S.

2018-02-01

It has been proposed that the rings of Saturn can contribute both material (i.e., water) and energy to its upper atmosphere and ionosphere. Ionospheric models require the presence of molecular species such as water that can chemically remove ionospheric protons, which otherwise are associated with electron densities that greatly exceed those from observation. These models adopt topside fluxes of water molecules. Other models have shown that ice grains from Saturn's rings can impact the atmosphere, but the effects of these grains have not been previously studied. In the current paper, we model how ice grains deposit both material and energy in Saturn's upper atmosphere as a function of grain size, initial velocity (at the "top" of the atmosphere, defined at an altitude above the cloud tops of 3,000 km), and incident angle. Typical grain speeds are expected to be roughly 15-25 km/s. Grains with radii on the order of 1-10 nm deposit most of their energy in the altitude range of 1,700-1,900 km, and can vaporize, depending on initial velocity and impact angle, contributing water mass to the upper atmosphere. We show that grains in this radius range do not significantly vaporize in our model at initial velocities lower than about 20 km/s.

A geophysical perspective on mantle water content and melting: Inverting electromagnetic sounding data using laboratory-based electrical conductivity profiles

NASA Astrophysics Data System (ADS)

Khan, A.; Shankland, T. J.

2012-02-01

This paper applies electromagnetic sounding methods for Earth's mantle to constrain its thermal state, chemical composition, and "water" content. We consider long-period inductive response functions in the form of C-responses from four stations distributed across the Earth (Europe, North America, Asia and Australia) covering a period range from 3.9 to 95.2 days and sensitivity to ~ 1200 km depth. We invert C-responses directly for thermo-chemical state using a self-consistent thermodynamic method that computes phase equilibria as functions of pressure, temperature, and composition (in the Na2O-CaO-FeO-MgO-Al2O3-SiO2 model system). Computed mineral modes are combined with recent laboratory-based electrical conductivity models from independent experimental research groups (Yoshino (2010) and Karato (2011)) to compute bulk conductivity structure beneath each of the four stations from which C-responses are estimated. To reliably allocate water between the various mineral phases we include laboratory-measured water partition coefficients for major upper mantle and transition zone minerals. This scheme is interfaced with a sampling-based algorithm to solve the resulting non-linear inverse problem. This approach has two advantages: (1) It anchors temperatures, composition, electrical conductivities, and discontinuities that are in laboratory-based forward models, and (2) At the same time it permits the use of geophysical inverse methods to optimize conductivity profiles to match geophysical data. The results show lateral variations in upper mantle temperatures beneath the four stations that appear to persist throughout the upper mantle and parts of the transition zone. Calculated mantle temperatures at 410 and 660 km depth lie in the range 1250-1650 °C and 1500-1750 °C, respectively, and generally agree with the experimentally-determined temperatures at which the measured phase reactions olivine → β-spinel and γ-spinel → ferropericlase + perovskite occur. The retrieved conductivity structures beneath the various stations tend to follow trends observed for temperature with the strongest lateral variations in the uppermost mantle; for depths > 300 km conductivities appear to depend less on the particular conductivity database. Conductivities at 410 km and at 660 km depth are found to agree overall with purely geophysically-derived global and semi-global one-dimensional conductivity models. Both electrical conductivity databases point to < 0.01 wt.% H2O in the upper mantle. For transition zone minerals results from the laboratory database of Yoshino (2010) suggest that a much higher water content (up to 2 wt.% H2O) is required than in the other database (Karato, 2011), which favors a relatively "dry" transition zone (< 0.01 wt.% H2O). Incorporating laboratory measurements of hydrous silicate melting relations and available conductivity data allows us to consider the possibility of hydration melting and a high-conductivity melt layer above the 410-km discontinuity. The latter appears to be 1) regionally localized and 2) principally a feature from the Yoshino (2010) database. Further, there is evidence of lateral heterogeneity: The mantle beneath southwestern North America and central China appears "wetter" than that beneath central Europe or Australia.

Dynamics of upper mantle rocks decompression melting above hot spots under continental plates

NASA Astrophysics Data System (ADS)

Perepechko, Yury; Sorokin, Konstantin; Sharapov, Victor

2014-05-01

Numeric 2D simulation of the decompression melting above the hot spots (HS) was accomplished under the following conditions: initial temperature within crust mantle section was postulated; thickness of the metasomatized lithospheric mantle is determined by the mantle rheology and position of upper asthenosphere boundary; upper and lower boundaries were postulated to be not permeable and the condition for adhesion and the distribution of temperature (1400-2050°C); lateral boundaries imitated infinity of layer. Sizes and distribution of lateral points, their symmetry, and maximum temperature varied between the thermodynamic condition for existences of perovskite - majorite transition and its excess above transition temperature. Problem was solved numerically a cell-vertex finite volume method for thermo hydrodynamic problems. For increasing convergence of iterative process the method of lower relaxation with different value of relaxation parameter for each equation was used. The method of through calculation was used for the increase in the computing rate for the two-layered upper mantle - lithosphere system. Calculated region was selected as 700 x (2100-4900) km. The time step for the study of the asthenosphere dynamics composed 0.15-0.65 Ma. The following factors controlling the sizes and melting degree of the convective upper mantle, are shown: a) the initial temperature distribution along the section of upper mantleb) sizes and the symmetry of HS, c) temperature excess within the HS above the temperature on the upper and lower mantle border TB=1500-2000oC with 5-15% deviation but not exceed 2350oC. It is found, that appearance of decompression melting with HS presence initiate primitive mantle melting at TB > of 1600oC. Initial upper mantle heating influence on asthenolens dimensions with a constant HS size is controlled mainly by decompression melting degree. Thus, with lateral sizes of HS = 400 km the decompression melting appears at TB > 1600oC and HS temperature (THS) > 1900oC asthenolens size ~700 km. When THS = of 2000oC the maximum melting degree of the primitive mantle is near 40%. An increase in the TB > 1900oC the maximum degree of melting could rich 100% with the same size of decompression melting zone (700 km). We examined decompression melting above the HS having LHS = 100 km - 780 km at a TB 1850- 2100oC with the thickness of lithosphere = 100 km.It is shown that asthenolens size (Lln) does not change substantially: Lln=700 km at LHS = of 100 km; Lln= 800 km at LHS = of 780 km. In presence of asymmetry of large HS the region of advection is developed above the HS maximum with the formation of asymmetrical cell. Influence of lithospheric plate thicknesses on appearance and evolution of asthenolens above the HS were investigated for the model stepped profile for the TB ≤ of 1750oS with Lhs = 100km and maximum of THS =2350oC. With an increase of TB the Lln difference beneath lithospheric steps is leveled with retention of a certain difference to melting degrees and time of the melting appearance a top of the HS. RFBR grant 12-05-00625.

Seismic Evidence of Imprints of Malani and Deccan Volcanism in Northwestern India

NASA Astrophysics Data System (ADS)

Mohan, G.; Mangalampally, R. K.; Ahmad, F.

2017-12-01

The evolution of the Neoproterozoic (750 Ma) Malani igneous province(MIP), the site of the largest felsic magmatism in India is debatable with theories supporting extensional tectonics, mantle plume or subduction processes. The MIP that lies to the west of the Proterozoic Aravalli mountain range and east of the Late Mesozoic-Teritary Barmer-Sanchor rift systems, hosts acidic volcanics in an area of 0.5 million sq.km in northwestern India. In this study, the crustal and upper mantle structure beneath the MIP is investigated through a deployment of 12 broadband seismographs in phases, at 18 locations during a period of five years from 2011-2016. The P wave receiver function(RF) analysis was carried out to image the crust and the 410 km and 660 km mantle transition zone discontinuities. About 1500 teleseismic waveforms with signal to noise ratios > 2.5 are utilized. The RFs at most stations are marked by strong conversions from the base of the sediments and the Moho. The crustal thickness estimated through the Neighbourhood algorithm approach, ranges from 35 to 42km. The crustal Poisson's ratio ranges from 0.26 - 0.29. The crustal thickness and Poisson's ratio are observed to increase from west to east viz., from the rift zone to the mountain belt. A significant finding is the presence of a 5-10km thick mid-crustal low velocity zone with a reduced shear velocity of 3.0-3.2km/s. The Ps conversions from the 410km and 660km mantle discontinuities are delayed by about 1sec with respect to the timings predicted by the IASP91 standard earth model. The observed delays are attributed to the reduction in velocity due to compositional/thermal perturbations in the uppermost upper mantle above the 410km discontinuity. The presence of alkaline complexes in MIP which are of pre-Deccan age (68 Ma) led us to surmise that the low velocity anomalies observed in the upper mantle might be linked to the mantle source associated with the 65 Ma Deccan volcanism which erupted further south of MIP. It is likely that the mantle source may have overprinted or obliterated the mantle signatures of the Neoproterozoic tectonic event. However, the intracrustal low velocities overlying an underplated crust in MIP are interpreted to be the compositional imprints of the felsic magma associated with the bimodel Malani volcanism.

Spatial properties of snow cover in the Upper Merced River Basin: implications for a distributed snow measurement network

NASA Astrophysics Data System (ADS)

Bouffon, T.; Rice, R.; Bales, R.

2006-12-01

The spatial distributions of snow water equivalent (SWE) and snow depth within a 1, 4, and 16 km2 grid element around two automated snow pillows in a forested and open- forested region of the Upper Merced River Basin (2,800 km2) of Yosemite National Park were characterized using field observations and analyzed using binary regression trees. Snow surveys occurred at the forested site during the accumulation and ablation seasons, while at the open-forest site a survey was performed only during the accumulation season. An average of 130 snow depth and 7 snow density measurements were made on each survey, within the 4 km2 grid. Snow depth was distributed using binary regression trees and geostatistical methods using the physiographic parameters (e.g. elevation, slope, vegetation, aspect). Results in the forest region indicate that the snow pillow overestimated average SWE within the 1, 4, and 16 km2 areas by 34 percent during ablation, but during accumulation the snow pillow provides a good estimate of the modeled mean SWE grid value, however it is suspected that the snow pillow was underestimating SWE. However, at the open forest site, during accumulation, the snow pillow was 28 percent greater than the mean modeled grid element. In addition, the binary regression trees indicate that the independent variables of vegetation, slope, and aspect are the most influential parameters of snow depth distribution. The binary regression tree and multivariate linear regression models explain about 60 percent of the initial variance for snow depth and 80 percent for density, respectively. This short-term study provides motivation and direction for the installation of a distributed snow measurement network to fill the information gap in basin-wide SWE and snow depth measurements. Guided by these results, a distributed snow measurement network was installed in the Fall 2006 at Gin Flat in the Upper Merced River Basin with the specific objective of measuring accumulation and ablation across topographic variables with the aim of providing guidance for future larger scale observation network designs.

Geometries of geoelectrical structures in central Tibetan Plateau from INDEPTH magnetotelluric data

NASA Astrophysics Data System (ADS)

Vozar, Jan; Jones, Alan G.; Le Pape, Florian

2013-04-01

Magnetotelluric (MT) data collected on N-S profiles crossing the Banggong-Nujiang Suture, which separates the Qiangtang and Lhasa Terranes in central Tibet, as a part of InterNational DEep Profiling of Tibet and the Himalaya project (INDEPTH) are modeled by 2D and 3D inversion codes. The 2D deep MT model of line 500 confirms previous observations concluding that the region is characterized to first-order by a resistive upper crust and a conductive, partially melted, middle to lower crust that extends from the Lhasa Terrane to the Qiangtang Terrane with varying depth. The same conductive structure setting, but in shallower depths is also present on the eastern 400 line. From deep electromagnetic sounding, supported by independent 1D integrated petro-physical investigation, we can estimate the next upper-mantle conductive layer at depths from 200 km to 250 km below the Lhasa Terrane and less resistive Tibetan lithosphere below the Qiangtang Terrane with conductive upper-mantle in depths about 120 km. The anisotropic 2D modeling reveals lower crustal anisotropy in Lhasa Terrane, which can interpreted as crustal channel flow. The 3D inversion models of all MT data from central Tibet show dominant 2D regional strike of mid and lower crustal structures equal N110E. This orientation is parallel to Shuanghu suture, BengCo Jiali strike-slip fault system and perpendicular to convergence direction. The lower crust conductor in central Lhasa Terrane can be interpreted more likely as 3D lower Indian crust structure, located to the east from line 500, than geoelectrical anisotropic crustal flow.

3D upper crustal seismic structure across Santorini volcanic field: Constraints on magmatic and tectonic interactions

NASA Astrophysics Data System (ADS)

Heath, B.; Hooft, E. E. E.; Toomey, D. R.; Papazachos, C. V.; Walls, K.; Paulatto, M.; Morgan, J. V.; Nomikou, P.; Warner, M.

2017-12-01

To investigate magmatic-tectonic interactions at an arc volcano, we collected a dense, active-source, seismic dataset across the Santorini Volcano, Greece, with 90 ocean bottom seismometers, 65 land seismometers, and 14,300 marine sound sources. We use over 140,000 travel-time picks to obtain a P-wave tomography model of the upper crustal structure of the Santorini volcano and surrounding tectonically extended region. Regionally, the shallow (<2 km) velocity structure is dominated by low- and high-velocity anomalies of several sediment-filled grabens and horsts of Attico-Cycladic metamorphic basement, which correlate well with Bouguer gravity anomalies and preliminary shallow attenuation results (using waveform amplitudes and t* values). We find regional Pliocene and younger faults bounding basement grabens and horsts to be predominately oriented in a NE-SW direction with Santorini itself located in a graben bounded by faults striking in this direction. In contrast, volcanic vents and dikes expressed at the surface seem to strike about 20° clockwise relative to these regional faults. In the northern caldera of Santorini, a 4-km wide region of anomalously low velocities and high attenuation directly overlies an inferred source of 2011-2012 inflation (4-4.5 km depth), however it is located at shallower depths ( 1-2km). The imaged low-velocity anomaly may correspond to hydrothermal activity (due to increased porosity and alteration) and/or brecciation from a prior episode of caldera collapse. It is bounded by anomalously fast velocities (at 1-2 km depth) that parallel the regional fault orientation and are correspondingly rotated 20° to surface dikes. At 4-5 km depth beneath the northern caldera basin, low-velocity anomalies and attenuated seismic arrivals provide preliminary evidence for a magma body; the low-velocity anomaly is elongated in the same direction as regional volcanic vents. The difference in strike of volcanic and tectonic features indicates oblique extension and potential time-variation in the minimum stress direction.

Structure of the crust and upper mantle in the western United States

USGS Publications Warehouse

Pakiser, L.C.

1963-01-01

Seismic waves generated by underground nuclear and chemical explosions have been recorded in a network of nearly 2,000 stations in the western conterminous United States as a part of the VELA UNIFORM program. The network extends from eastern Colorado to the California coastline and from central Idaho to the border of the United States and Mexico. The speed of compressional waves in the upper-mantle rocks ranges from 7.7 km/sec in the southern part of the Basin and Range province to 8.2 km/sec in the Great Plains province. In general, the speed of compressional waves in the upper-mantle rocks tends to be nearly the same over large areas within individual geologic provinces. Measured crustal thickness ranges from less than 20 km in the Central Valley of California to 50 km in the Great Plains province. Changes in crustal thickness across provincial boundaries are not controlled by regional altitude above sea level unless the properties of the upper mantle are the same across those boundaries. The crust tends to be thick in regions where the speed of compressional waves in the upper-mantle rocks (and presumably the density) is high, and tends to be relatively thin where the speed of compressional waves in the upper-mantle rocks (and density) is lower. With in the Basin and Range province, crustal thickness seems to vary directly with regional altitude above sea level. Evidence that a layer of intermediate compressional-wave speed exists in the lower part of the crust has been accumulated from seismic waves that have traveled least-time paths, as well as secondary arrivals (particularly reflections). On a scale that includes many geologic provinces, isostatic compensation is related largely to variations in the density of the upper- mantle rocks. Within geologic provinces or adjacent provinces, isostatic compensation may be related to variations in the thickness of crustal layers. Regions of thick crust and dense upper mantle have been relatively stable in Cenozoic time. Regions of thinner crust and low-density upper mantle have had a Cenozoic history of intense diastrophism and silicic volcanism.

Upper transition height at European mid-latitudes for the years of 2010 and 2016: surprising changes

NASA Astrophysics Data System (ADS)

Kotov, Dmytro; Truhlík, Vladimír; Richards, Philip; Podolská, Kateřina; Bogomaz, Oleksandr; Chernogor, Leonid; Siusiuk, Maryna; Shulha, Maryna; Domnin, Igor

2017-04-01

Our previous studies with the Kharkiv incoherent scatter radar (49.6 N, 36.3 E) data in 2006-2010 revealed that the upper (O+ to H++He+) transition height at mid-latitudes is much more sensitive to the changes in solar and geomagnetic activity than was previously thought [1]. In 2016, solar activity was decreasing and both daily and average F10.7 indices were approaching those in 2010. Solar activity was 12% higher in June and 6% higher in September 2016. Geomagnetic activity was low for the measurements in both 2010 and 2016. Given the difference in solar activity, the 2016 nighttime upper transition heights would be expected to be 55 km higher in June and 30 km higher in September. On the contrary, the observed nighttime minimum of the upper transition heights were 18 km higher in June 2016 and 28 km lower in September 2016. This is a surprising result given that the measured ion temperatures indicate that the exospheric temperature in 2010 and 2016 were similar. The unexpectedly low values of the upper transition height in 2016 may be caused by reduced thermospheric hydrogen escape during the 2012-2014 solar maximum, which was notably weaker than previous maxima. We also show results of the upper transition height obtained from processing of the COSMIC electron density vertical profiles. A comparison with the latest version of the IRI ion composition model (TBT) is also presented. [1] Kotov, D. V., V. Truhlík, P. G. Richards, S. Stankov, O. V. Bogomaz, L. F. Chernogor, and I. F. Domnin (2015), Night-time light ion transition height behaviour over the Kharkiv (50°N, 36°E) IS radar during the equinoxes of 2006-2010, J. Atmos. Sol. Terr. Phys., 132, 1-12, doi:10.1016/j.jastp.2015.06.004.

Evidence for mafic lower crust in Tanzania, East Africa, from joint inversion of receiver functions and Rayleigh wave dispersion velocities

NASA Astrophysics Data System (ADS)

Julià, Jordi; Ammon, Charles J.; Nyblade, Andrew A.

2005-08-01

The S-wave velocity structure of Precambrian terranes in Tanzania, East Africa is modelled by jointly inverting receiver functions and surface wave dispersion velocities from the 1994-1995 Tanzania broad-band seismic experiment. The study region, which consists of an Archean craton surrounded by Proterozoic mobile belts, forms a unique setting for evaluating Precambrian crustal evolution. Our results show a uniform crustal structure across the region, with a 10-15 km thick upper crust with VS= 3.4-3.5 km s-1, overlying a gradational lower crust with S-wave velocities up to 4.1 km s-1 at 38-42 km depth. The upper-mantle lid displays uniform S-wave velocities of 4.5-4.7 km s-1 to depths of 100-150 km and overlays a prominent low-velocity zone. This low-velocity zone is required by the dispersion and receiver function data, but its depth interval is uncertain. The high crustal velocities within the lowermost crust characterize the entire region and suggest that mafic lithologies are present in both Archean and Proterozoic terranes. The ubiquitous mafic lower crust can be attributed to underplating associated with mafic dyke emplacement. This finding suggests that in East Africa there has been little secular variation in Precambrian crustal development.

South Mid-latitude Gullies

NASA Technical Reports Server (NTRS)

2005-01-01

19 November 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows deep gullies cut into the wall of a south mid-latitude crater. Erosion has exposed layers in the upper wall of the crater; it is possible that groundwater seeping through a layer or layers in the wall led to the genesis of the gullies. The banked nature of the gully channels suggests that a liquid was involved.

Location near: 35.5oS, 194.8oW Image width: width: 2 km (1.2 mi) Illumination from: upper left Season: Southern Spring

Assessment of Land Degradation and Greening in Ken River Basin of Central India

NASA Astrophysics Data System (ADS)

Pandey, Ashish; Palmate, Santosh S.

2017-04-01

Natural systems have significant impact of land degradation on biodiversity loss, food and water insecurity. To achieve the sustainable development goals, advances in remote sensing and geographical information systems (GIS) are progressively utilized to combat climate change, land degradation and poverty issues of developing country. The Ken River Basin (KRB) has dominating land cover pattern of agriculture and forest area. Nowadays, this pattern is affected due to climate change and anthropogenic activity like deforestation. In this study, land degradation and greening status of KRB of Central India during the years 2001 to 2013 have been assessed using MODIS land cover (MCD12Q1) data sets. International Geosphere Biosphere Programme (IGBP) land cover data has been extracted from the MCD12Q1 data product. Multiple rasters of MODIS landcover were analyzed and compared for assigning unique combination of land cover dynamics employing ArcGIS software. Result reveals that 14.38% natural vegetation was degraded, and crop land and woody savannas were greened by 9.68% to 6.94% respectively. Natural vegetation degradation have been observed in the upper KRB area, and resulted to increase in crop land (3418.87 km2) and woody savannas (1242.23 km2) area. Due to transition of 1043.6 km2 area of deciduous broadleaf forest to woody savannas greening was also observed. Moreover, both crop land and woody savannas showed inter-transitions of 669.31 km2 into crop land to woody savannas, and 874.09 km2 into woody savannas to crop land. The present analysis reveals that natural vegetation has more land conversions into woody savannas and crop land in the KRB area. Further, Spatial change analysis shows that land degradation and greening has occurred mostly in the upper part of the KRB. The study reveals that the land transition information can be useful for proper planning and management of natural resources.

Azimuthal anisotropy layering and plate motion in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Yuan, H.; Romanowicz, B. A.

2012-12-01

We recently developed a three dimensional radially and azimuthally anisotropic model of the upper mantle in north America, using a combination of long-period 3-component surface and overtone waveforms, and SKS splitting measurements (Yuan and Romanowicz, 2010, Yuan et al., 2011). We showed that azimuthal anisotropy is a powerful tool to detect layering in the upper mantle, revealing two domains in the cratonic lithosphere, separated by a sharp laterally varying boundary in the depth range 100-150 km, which seems to coincide with the mid-lithospheric boundary (MLD) found in receiver function studies. Contrary to receiver functions, azimuthal anisotropy also detects the lithosphere-asthenosphere boundary (LAB) as manifested by a change in the fast axis direction, which becomes quasi-parallel to the absolute plate motion below ~250 km depth. A zone of stronger azimuthal anisotropy is found below the LAB both in the western US (peaking at depths of 100-150km) and in the craton (peaking at a depth of about 300 km). Here we show preliminary attempts at expanding our approach to the global scale, with a specific goal of determining whether such an anisotropic LAB can also be observed in the Pacific ocean. We started with our most recent global upper mantle radially anisotropic shear velocity model, determined using the Spectral Element Method (SEMum2; French et al., this meeting). We augment the corresponding global surface wave and overtone dataset (period range 60 to 400 s) with deep events and shorter period body waves, in order to ensure optimal deeper depth (>250km) anisotropy recovery due to the paucity of shear wave splitting measurements in the oceans. Our preliminary results, which do not yet incorporate SKS splitting measurements, look promising as they confirm the layering found previously in North America, using a different, global dataset and starting model. In the Pacific, our study confirms earlier azimuthal anisotropy results in the region (e.g. Smith et al. 2004; Maggi et al. 2006) that the shallow upper mantle beneath the ocean basin is strongly stratified. Our results further illustrate that 1) a shallow anisotropy domain (~100 km) is present, which is high in velocity and has in general a northward anisotropy direction where the plate is old (>80 Ma); and 2) there is a deeper domain (100-200 km) with stronger anisotropy, which correlates spatially with the low velocity zone and has a fast axis direction in good agreement with the absolute plate motion direction (HS3 NUVEL-1A). The boundary between the anisotropy domains clearly follows the age progressive deepening of the fast velocity in the shallow domain, suggesting an oceanic LAB that separates the Pacific lithosphere and the underlying asthenosphere.

A regional view of urban sedimentary basins in Northern California based on oil industry compressional-wave velocity and density logs

USGS Publications Warehouse

Brocher, T.M.

2005-01-01

Compressional-wave (sonic) and density logs from 119 oil test wells provide knowledge of the physical properties and impedance contrasts within urban sedimentary basins in northern California, which is needed to better understand basin amplification. These wire-line logs provide estimates of sonic velocities and densities for primarily Upper Cretaceous to Pliocene clastic rocks between 0.1 - and 5.6-km depth to an average depth of 1.8 km. Regional differences in the sonic velocities and densities in these basins largely 1reflect variations in the lithology, depth of burial, porosity, and grain size of the strata, but not necessarily formation age. For example, Miocene basin filling strata west of the Calaveras Fault exhibit higher sonic velocities and densities than older but finer-grained and/or higher-porosity rocks of the Upper Cretaceous Great Valley Sequence. As another example, hard Eocene sandstones west of the San Andreas Fault have much higher impedances than Eocene strata, mainly higher-porosity sandstones and shales, located to the east of this fault, and approach those expected for Franciscan Complex basement rocks. Basement penetrations define large impedence contrasts at the sediment/basement contact along the margins of several basins, where Quaternary, Pliocene, and even Miocene deposits directly overlie Franciscan or Salinian basement rocks at depths as much as 1.7 km. In contrast, in the deepest, geographic centers of the basins, such logs exhibit only a modest impedance contrast at the sediment/basement contact at depths exceeding 2 km. Prominent (up to 1 km/sec) and thick (up to several hundred meters) velocity and density reversals in the logs refute the common assumption that velocities and densities increase monotonically with depth.

Seismic properties of Leg 195 serpentinites and their geophysical implications

USGS Publications Warehouse

Courtier, Anna M.; Hart, David J.; Christensen, Nikolas I.; Shinohara, Masanao; Salisbury, Matthew H.; Richter, Carl

2006-01-01

Knowledge of seismic velocities is necessary to constrain the lithologies encountered in seismic studies. We measured the seismic velocities, both compressional and shear wave, of clasts recovered during Ocean Drilling Program Leg 195 from a serpentine mud volcano, the South Chamorro Seamount. The compressional wave velocities of these clasts vary from a lower value of 5.5 km/s to an upper value of 6.1 km/s at a confining stress of 200 MPa. The shear wave velocities vary from a lower value of 2.8 km/s to an upper value of 3.3 km/s at a confining stress of 200 MPa. The densities of the samples vary from 2548 to 2701 kg/m3. These velocities and densities are representative of the highly serpentinized harzburgite and dunite mineralogy of the clasts. Velocities from a seismic study of the Izu-Bonin forearc wedge were used to calculate the degree of serpentinization in the forearc wedge. The seismic velocities of the forearc wedge are higher than the velocities of the clasts recovered from the South Chamorro Seamount, suggesting that the clasts are more serpentinized than the forearc wedge.

Lithospheric structure of the Arabian Shield from the joint inversion of receiver functions and surface-wave group velocities

NASA Astrophysics Data System (ADS)

Julià, Jordi; Ammon, Charles J.; Herrmann, Robert B.

2003-08-01

We estimate lithospheric velocity structure for the Arabian Shield by jointly modeling receiver functions and fundamental-mode group velocities from events recorded by the 1995-1997 Saudi Arabian Portable Broadband Deployment. Receiver functions are primarily sensitive to shear-wave velocity contrasts and vertical travel times, and surface-wave dispersion measurements are sensitive to vertical shear-wave velocity averages, so that their combination bridge resolution gaps associated with each individual data set. Our resulting models correlate well with the observed surface geology; the Asir terrane to the West consists of a 10-km-thick upper crust of 3.3 km/s overlying a lower crust of 3.7-3.8 km/s; in the Afif terrane to the East, the upper crust is 20 km thick and has an average velocity of 3.6 km/s, and the lower crust is about 3.8 km/s; separating the terranes, the Nabitah mobile belt is made of a gradational upper crust up to 3.6 km/s at 15 km overlying an also gradational lower crust up to 4.0 km/s. The crust-mantle transition is found to be sharp in terranes of continental affinity (east) and gradual in terranes of oceanic affinity (west). The upper mantle shear velocities range from 4.3 to 4.6 km/s. Temperatures around 1000 °C are obtained from our velocity models for a thin upper mantle lid observed beneath station TAIF, and suggest that the lithosphere could be as thin as 50-60 km under this station.

Source Parameters of the 8 October, 2005 Mw7.6 Kashmir Earthquake

NASA Astrophysics Data System (ADS)

Mandal, Prantik; Chadha, R. K.; Kumar, N.; Raju, I. P.; Satyamurty, C.

2007-12-01

During the last six years, the National Geophysical Research Institute, Hyderabad has established a semi-permanent seismological network of 5 broadband seismographs and 10 accelerographs in the Kachchh seismic zone, Gujarat, with the prime objective to monitor the continued aftershock activity of the 2001 Mw7.7 Bhuj mainshock. The reliable and accurate broadband data for the Mw 7.6 (8 Oct., 2005) Kashmir earthquake and its aftershocks from this network, as well as from the Hyderabad Geoscope station, enabled us to estimate the group velocity dispersion characteristics and the one-dimensional regional shear-velocity structure of peninsular India. Firstly, we measure Rayleigh- and Love-wave group velocity dispersion curves in the range of 8 to 35 sec and invert these curves to estimate the crustal and upper mantle structure below the western part of peninsular India. Our best model suggests a two-layered crust: The upper crust is 13.8-km thick with a shear velocity (Vs) of 3.2 km/s; the corresponding values for the lower crust are 24.9 km and 3.7 km/sec. The shear velocity for the upper mantle is found to be 4.65 km/sec. Based on this structure, we perform a moment tensor (MT) inversion of the bandpass (0.05 0.02 Hz) filtered seismograms of the Kashmir earthquake. The best fit is obtained for a source located at a depth of 30 km, with a seismic moment, Mo, of 1.6 × 1027 dyne-cm, and a focal mechanism with strike 19.5°, dip 42°, and rake 167°. The long-period magnitude (MA ~ Mw) of this earthquake is estimated to be 7.31. An analysis of well-developed sPn and sSn regional crustal phases from the bandpassed (0.02 0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggests a focal depth of 30.8 km.

S-wave velocity down to the uppermost mantle below the East European Craton in northern Poland from the inversion of ambient noise recorded at "13 BB star" seismic array

NASA Astrophysics Data System (ADS)

Lepore, S.; Polkowski, M.; Grad, M.

2016-12-01

The East European Craton (EEC) occupies the northeastern half of Europe. In the most external sedimentary crust (SC), the P-wave velocity (Vp) raises from 2.5 to 4.3 km/s. In the underlying upper crust (UC) the Vp ranges within 6.1-6.4 km/s, 6.5-6.8 km/s in the middle crust (MC), and 6.9-7.2 km/s in the lower crust (LC). The Moho, whose depth is 40-45 km, shows a relatively flat topography, which is advantageous when studying the deep velocity structure. The Vp in the uppermost mantle (UM) down to 100 km is 8.3 km/s. Seismic experiments conducted in Poland along refraction profiles provided significant information about the structure in any layer, but not sufficient for the study of the S-wave velocity (Vs). Thus, Vs and Vp/Vs profiles down to 100 m were evaluated by the Monte Carlo inversion of surface wave velocity dispersion (SWVD) curves retrieved from the crosscorrelation (CC) of ambient noise recorded in northern Poland. The records were carried out during 2014 at the "13 BB star" array equipped with thirteen broadband stations installed during 2013 and scheduled to operate until the end of 2016. Those stations, covering an area of 120 km in diameter, are arranged in a circular, regular geometry, allowing a thorough study of the deep structures. The extraction of the SWVD was performed in the 0.1-1 Hz and 0.02-0.1 Hz frequency bands, to have a good resolution within 0-20 km and 20-100 km. The dispersion curves show different modes because remarkable changes of surface wave attenuation are present in the different layers. All the modes of the SWVD curves were together inverted assuming the characteristics and the Vp values in every layer as known. The Vs [km/s] ranges within 1.0-2.4 in SC, 3.1-3.6 in UC, 3.2-4.3 in MC, 3.2-4.3 in LC, and 4.5-5.1 in UM; Vp/Vs within 1.8-2.0 in SC, 1.7-2.0 in UC, 1.5-2.1 in MC, 1.8-2.1 in LC, and 1.6-1.8 in UM. National Science Centre Poland provided financial support for this work by NCN grant DEC-2011/02/A/ST10/00284.

Long wavelength magnetic anomalies over continental rifts in cratonic region

NASA Astrophysics Data System (ADS)

Friedman, S. A.; Persaud, P.; Ferre, E. C.; Martín-Hernández, F.; Feinberg, J. M.

2017-12-01

New collections of unaltered mantle xenoliths shed light on potential upper mantle contributions to long wavelength magnetic anomalies (LWMA) in continental rifts in cratonic / shield areas. The new material originates from the East African Rift (Tanzania), the Rio Grande Rift (U.S.A.), the Rhine Rift (Germany), and the West Antarctic Rift (Antarctica). The xenoliths sample the uppermost (<80 km depth) lithospheric mantle in these regions in the spinel-peridotite and plagioclase-peridotite stability fields. The most common lithology by far (95% of samples) is a spinel-lherzolite indicating relatively low oxygen fugacities (FMQ -1). Chrome spinel in these peridotites is non-magnetic (Al + Mg > 0.2 or Fe < 0.3) and primary magnetite (Fe3O4) occurs only in trace amounts, typically yielding low natural remanent magnetizations (NRM < 10-2 A/m). The low Koenigsberger ratios (Qn < 1) of these materials, combined with high geotherms (>60ºC/km) that are characteristic of rifted regions preclude any contribution to LWMA at depths >10 km. Hence, only upper basalts and hypovolcanic mafic sills would constitute potential magnetic sources. In contrast, the margins of these rifted regions consist of refractory cratonic domains, often characterized by oxidized sublithospheric mantle that host significant concentrations of primary magnetite. The higher NRMs of these peridotites (up to 15 A/m, Qn > 2.5) combined with much lower geotherms (as low as 15ºC/km) allows for a 5 to 10 km layer of uppermost mantle to potentially contribute to LWMA. Assuming that Qn values in rift margins are also <1, the new data presented here suggests that relatively young rifts would display a central negative magnetic anomaly surrounded by two broad positive anomalies. The latitude of the rift is predicted to exert a primary control on the magnitude of such anomalies, while the steepness of the magnetic gradient across the rift would primarily reflect thermal equilibration over time.

Estimation of weathering rates and CO2 drawdown based on solute load: Significance of granulites and gneisses dominated weathering in the Kaveri River basin, Southern India

NASA Astrophysics Data System (ADS)

Pattanaik, J. K.; Balakrishnan, S.; Bhutani, R.; Singh, P.

2013-11-01

The solute load of the Kaveri River (South India) and its tributaries draining diverse Precambrian terrains during pre-monsoon and monsoon periods was determined. Using average annual flow, total drainage area and atmospheric input corrected major ion concentrations of these rivers chemical weathering rates, annual fluxes of different ionic species to the ocean and CO2 consumption rates were estimated. Bicarbonate is the most dominant ion (27-79% of anion budget) in all the river samples collected during monsoon period followed by Ca2+, whereas, in case of pre-monsoon water samples Na+ is the most dominant ion (in meq/l). Two approaches were adopted to estimate silicate and carbonate weathering rates in the drainage basin. At Musuri silicate weathering rate (SWR) is 9.44 ± 0.29 tons/km2/a and carbonate weathering rate (CWR) is 1.46 ± 0.16 tons/km2/a. More than 90% of the total ionic budget is derived from weathering of silicates in the Kaveri basin. CO2 consumption rate in the basin for silicate weathering FCO2sil is 3.83 ± 0.12 × 105 mol/km2/a (upper limit), which is comparable with the Himalayan rivers at upper reaches. For carbonate weathering (FCO2carb) CO2 consumption rate is 0.15 ± 0.03 × 105 mol/km2/a in the Kaveri basin. The lower limit of CO2 consumption rate corrected for H2SO4 during silicate and carbonate weathering is FCO2sil is 3.24 × 1005 mol/km2/a and FCO2carb 0.13 × 105 mol/km2/a respectively. CO2 sequestered due to silicate weathering in the Kaveri basin is 25.41 (±0.82) × 109 mol/a which represents 0.21 (±0.01)% of global CO2 drawdown. This may be due to tropical climatic condition, high rainfall during both SW and NE monsoon and predominance of silicate rocks in the Kaveri basin.

Aviation Fuel Tracer Simulation: Model Intercomparison and Implications

NASA Technical Reports Server (NTRS)

Danilin, M. Y.; Fahey, D. W.; Schumann, U.; Prather, M. J.; Penner, J. E.; Ko, M. K. W.; Weisenstein, D. K.; Jackman, C. H.; Pitari, G.; Koehler, I.;

Aviation Fuel Tracer Simulation: Model Intercomparison and Implications

NASA Technical Reports Server (NTRS)

Danilin, M. Y.; Fahey, D. W.; Schumann, U.; Prather, M. J.; Penner, J. E.; Ko, M. K. W.; Weisenstein, D. K.; Jackman, C. H.; Pitari, G.; Koehler, I.;

Nearest neighbor: The low-mass Milky Way satellite Tucana III

DOE PAGES

Simon, J. D.; Li, T. S.; Drlica-Wagner, A.; ...

2017-03-17

Here, we present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite Tucana III (Tuc III). We identify 26 member stars in Tuc III from which we measure a mean radial velocity of v hel = -102.3 ± 0.4 (stat.) ± 2.0 (sys.)more » $$\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$, a velocity dispersion of $${0.1}_{-0.1}^{+0.7}$$ $$\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$, and a mean metallicity of $${\\rm{[Fe/H]}}=-{2.42}_{-0.08}^{+0.07}$$. The upper limit on the velocity dispersion is σ < 1.5 $$\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$ at 95.5% confidence, and the corresponding upper limit on the mass within the half-light radius of Tuc III is 9.0 × 10 4 M ⊙. We cannot rule out mass-to-light ratios as large as 240 M ⊙/L ⊙ for Tuc III, but much lower mass-to-light ratios that would leave the system baryon-dominated are also allowed. We measure an upper limit on the metallicity spread of the stars in Tuc III of 0.19 dex at 95.5% confidence. Tuc III has a smaller metallicity dispersion and likely a smaller velocity dispersion than any known dwarf galaxy, but a larger size and lower surface brightness than any known globular cluster. Its metallicity is also much lower than those of the clusters with similar luminosity. We therefore tentatively suggest that Tuc III is the tidally stripped remnant of a dark matter-dominated dwarf galaxy, but additional precise velocity and metallicity measurements will be necessary for a definitive classification. If Tuc III is indeed a dwarf galaxy, it is one of the closest external galaxies to the Sun. Because of its proximity, the most luminous stars in Tuc III are quite bright, including one star at V = 15.7 that is the brightest known member star of an ultra-faint satellite.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simon, J. D.; Li, T. S.; Drlica-Wagner, A.

Here, we present Magellan/IMACS spectroscopy of the recently discovered Milky Way satellite Tucana III (Tuc III). We identify 26 member stars in Tuc III from which we measure a mean radial velocity of v hel = -102.3 ± 0.4 (stat.) ± 2.0 (sys.)more » $$\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$, a velocity dispersion of $${0.1}_{-0.1}^{+0.7}$$ $$\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$, and a mean metallicity of $${\\rm{[Fe/H]}}=-{2.42}_{-0.08}^{+0.07}$$. The upper limit on the velocity dispersion is σ < 1.5 $$\\mathrm{km}\\,{{\\rm{s}}}^{-1}$$ at 95.5% confidence, and the corresponding upper limit on the mass within the half-light radius of Tuc III is 9.0 × 10 4 M ⊙. We cannot rule out mass-to-light ratios as large as 240 M ⊙/L ⊙ for Tuc III, but much lower mass-to-light ratios that would leave the system baryon-dominated are also allowed. We measure an upper limit on the metallicity spread of the stars in Tuc III of 0.19 dex at 95.5% confidence. Tuc III has a smaller metallicity dispersion and likely a smaller velocity dispersion than any known dwarf galaxy, but a larger size and lower surface brightness than any known globular cluster. Its metallicity is also much lower than those of the clusters with similar luminosity. We therefore tentatively suggest that Tuc III is the tidally stripped remnant of a dark matter-dominated dwarf galaxy, but additional precise velocity and metallicity measurements will be necessary for a definitive classification. If Tuc III is indeed a dwarf galaxy, it is one of the closest external galaxies to the Sun. Because of its proximity, the most luminous stars in Tuc III are quite bright, including one star at V = 15.7 that is the brightest known member star of an ultra-faint satellite.« less

SAGE III solar ozone measurements: Initial results

NASA Technical Reports Server (NTRS)

Wang, Hsiang-Jui; Cunnold, Derek M.; Trepte, Chip; Thomason, Larry W.; Zawodny, Joseph M.

2006-01-01

Results from two retrieval algorithms, o3-aer and o3-mlr , used for SAGE III solar occultation ozone measurements in the stratosphere and upper troposphere are compared. The main differences between these two retrieved (version 3.0) ozone are found at altitudes above 40 km and below 15 km. Compared to correlative measurements, the SAGE II type ozone retrievals (o3-aer) provide better precisions above 40 km and do not induce artificial hemispheric differences in upper stratospheric ozone. The multiple linear regression technique (o3_mlr), however, can yield slightly more accurate ozone (by a few percent) in the lower stratosphere and upper troposphere. By using SAGE III (version 3.0) ozone from both algorithms and in their preferred regions, the agreement between SAGE III and correlative measurements is shown to be approx.5% down to 17 km. Below 17 km SAGE III ozone values are systematically higher, by 10% at 13 km, and a small hemispheric difference (a few percent) appears. Compared to SAGE III and HALOE, SAGE II ozone has the best accuracy in the lowest few kilometers of the stratosphere. Estimated precision in SAGE III ozone is about 5% or better between 20 and 40 km and approx.10% at 50 km. The precision below 20 km is difficult to evaluate because of limited coincidences between SAGE III and sondes. SAGE III ozone values are systematically slightly larger (2-3%) than those from SAGE II but the profile shapes are remarkably similar for altitudes above 15 km. There is no evidence of any relative drift or time dependent differences between these two instruments for altitudes above 15-20 km.

Evidence for an upper mantle low velocity zone beneath the southern Basin and Range-Colorado Plateau transition zone

USGS Publications Warehouse

Benz, H.M.; McCarthy, J.

1994-01-01

A 370-km-long seismic refraction/wide-angle reflection profile recorded during the Pacific to Arizona Crustal Experiment (PACE) detected an upper mantle P-wave low-velocity zone (LVZ) in the depth range 40 to 55 km beneath the Basin and Range in southern Arizona. Interpretation of seismic data places constraints on the sub-crustal lithosphere of the southern Basin and Range Province, which is important in light of the active tectonics of the region and the unknown role of the sub-crustal lithosphere in the development of the western United States. Forward travel time and synthetic seismogram techniques are used to model this shallow upper mantle LVZ. Modeling results show that the LVZ is defined by a 5% velocity decrease relative to a Pn velocity of 7.95 km s−1, suggesting either a ∼3–5% mafic partial melt or high-temperature, sub-solidus peridotite.

Traces of influence of the surface topography in the Venus atmosphere

NASA Astrophysics Data System (ADS)

Zasova, Ludmila; Khatuntsev, Igor; Patsaeva, Marina; Ignatiev, Nikolay; Gorinov, Dmitry

2017-04-01

We study the traces of influence of the Venus' topography like Ishtar , Beta Regio, Atalanta Planitia in the Venus atmosphere. From the Fourier Spectrometry on Venera-15 (FS-V15) the 3-D temperature and clouds fields in mesosphere were retrieved [Zasova et al, PSS,2007]. It was found that distribution of temperature is described by the Fourier decomposition with 1, 1/2, 1/3, and 1/4days and upper boundary of clouds (1, 1/2 days) harmonics in Solar-fixed coordinates. The amplitudes of the thermal tide harmonics with wavenumbers 1 and 2 reach 10 K. We found that in the Sun- fixed frame of reference, both maxima and minima are shifted from noon and from midnight to westwards, in direction of the superrotation. Comparison the fields of temperature at isobaric levels (from 60 to 95 km), altitude of upper boundary of the upper and middle clouds, the thermal zonal wind with the Magellan topography maps shows that for all cases the high correlation with the images of the structures in Ishtar, Beta Regio, Atalanta Planitia are observed. For example, it was found that temperature field near upper boundary of clouds (at 65 km) in latitude-longitude coordinates shows a good correspondence between topography (Ishtar, Beta Regio and Atalanta Planitia) and temperature perturbations with coefficient of correlation CC>0.9. The temperature and clouds maps in comparison to the map of Magellan topography show that the perturbations are shifted by 30° also in the direction of superrotation. Venera-15 had geometry observations very convenient for thermal tides observation (polar orbit with pericenter near N-pole), the important results was obtained even with spatial coverage not enough. Interpretation of observed phenomena still not clear. Detailed study continues, also in comparison with VMS and VIRTIS observations for the Southern hemisphere.

Confirmation of a change in the global shear velocity pattern at around 1,000 km depth

NASA Astrophysics Data System (ADS)

Debayle, E.; Durand, S.; Ricard, Y. R.; Zaroli, C.; Lambotte, S.

2017-12-01

In this study, we confirm the existence of a change in the shear velocity spectrum around 1,000 km depth based on a new shear velocity tomographic model of the Earth's mantle, SEISGLOB2. This model is based on Rayleigh surface wave phase velocities, self- and cross- coupling structure coefficients of spheroidal normal modes and body wave travel times which are, for the first time, combined in a tomographic inversion. SEISGLOB2 is developed up to spherical harmonic degree 40 and in 21 radial spline functions. The spectrum of SEISGLOB2 is the flattest (i.e., richest in "short" wavelengths corresponding to spherical harmonic degrees greater than 10) around 1,000 km depth and this flattening occurs between 670 and 1,500 km depth. We also confirm various changes in the continuity of slabs and mantle plumes all around 1,000 km depth where we also observed the upper boundary of LLSVPs. The existence of a flatter spectrum, richer in short wavelength heterogeneities, in a region of the mid-mantle can have great impacts on our understanding of the mantle dynamics and should thus be better understood in the future. Although a viscosity increase, a phase change or a compositional change can all concur to induce this change of pattern, its precise origin is still very uncertain.

Crustal and upper mantle velocity structure of the Salton Trough, southeast California

USGS Publications Warehouse

Parsons, T.; McCarthy, J.

1996-01-01

This paper presents data and modelling results from a crustal and upper mantle wide-angle seismic transect across the Salton Trough region in southeast California. The Salton Trough is a unique part of the Basin and Range province where mid-ocean ridge/transform spreading in the Gulf of California has evolved northward into the continent. In 1992, the U.S. Geological Survey (USGS) conducted the final leg of the Pacific to Arizona Crustal Experiment (PACE). Two perpendicular models of the crust and upper mantle were fit to wide-angle reflection and refraction travel times, seismic amplitudes, and Bouguer gravity anomalies. The first profile crossed the Salton Trough from the southwest to the northeast, and the second was a strike line that paralleled the Salton Sea along its western edge. We found thin crust (???21-22 km thick) beneath the axis of the Salton Trough (Imperial Valley) and locally thicker crust (???27 km) beneath the Chocolate Mountains to the northeast. We modelled a slight thinning of the crust further to the northeast beneath the Colorado River (???24 km) and subsequent thickening beneath the metamorphic core complex belt northeast of the Colorado River. There is a deep, apparently young basin (???5-6 km unmetamorphosed sediments) beneath the Imperial Valley and a shallower (???2-3 km) basin beneath the Colorado River. A regional 6.9-km/s layer (between ???15-km depth and the Moho) underlies the Salton Trough as well as the Chocolate Mountains where it pinches out at the Moho. This lower crustal layer is spatially associated with a low-velocity (7.6-7.7 km/s) upper mantle. We found that our crustal model is locally compatible with the previously suggested notion that the crust of the Salton Trough has formed almost entirely from magmatism in the lower crust and sedimentation in the upper crust. However, we observe an apparently magmatically emplaced lower crust to the northeast, outside of the Salton Trough, and propose that this layer in part predates Salton Trough rifting. It may also in part result from migration of magmatic spreading centers associated with the southern San Andreas fault system. These spreading centers may have existed east of their current locations in the past and may have influenced the lower crust and upper mantle to the east of the current Salton Trough.

Light-toned Rock Outcrop in Aureum Chaos

NASA Technical Reports Server (NTRS)

2006-01-01

30 October 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an outcrop of light-toned, layered, sedimentary rock in Aureum Chaos. The darker material, which includes ripples, is composed of windblown sand and granules. This scene is located near 3.8oS, 26.2oW, and covers an area roughly 7.7 km by 3 km (4.8 by 1.9 mi) wide. Sunlight illuminates the terrain from the top/upper right. This southern autumn image was acquired on 14 July 2006.

Artificial auroras in the upper atmosphere. I - Electron beam injections

NASA Technical Reports Server (NTRS)

Burch, J. L.; Mende, S. B.; Kawashima, N.; Roberts, W. T.; Taylor, W. W. L.; Neubert, T.; Gibson, W. C.; Marshall, J. A.; Swenson, G. R.

1993-01-01

The Atlas-1 Spacelab payload's Space Experiments with Particle Accelerators generated artificial electron beams for the stimulation of auroral emissions at southern auroral latitudes. Optical measurements were made by the Shuttle Orbiter's onboard TV cameras, as well as by the Atmospheric Emissions Photometric Imager (in both white light and the 427.8 nm N2(+) emission line). Shuttle-based auroral imaging furnished a novel perspective on the artificial auroras; the emissions were traced from 295 km to the 110 km level along the curved magnetic-field lines.

Structural variability of the Tonga-Kermadec forearc characterized using robustly constrained geophysical data

NASA Astrophysics Data System (ADS)

Funnell, M. J.; Peirce, C.; Robinson, A. H.

2017-09-01

Subducting bathymetric anomalies enhance erosion of the overriding forearc crust. The deformation associated with this process is superimposed on pre-existing variable crustal and sedimentary structures developed as a subduction system evolves. Recent attempts to determine the effect and timescale of Louisville Ridge seamount subduction on the Tonga-Kermadec forearc have been limited by simplistic models of inherited overriding crustal structure that neglect along-strike variability. Synthesis of new robustly tested seismic velocity and density models with existing data sets from the region, highlight along-strike variations in the structure of the Tonga-Kermadec subducting and overriding plates. As the subducting plate undergoes bend-faulting and hydration throughout the trench-outer rise region, observed oceanic upper- and mid-crustal velocities are reduced by ∼1.0 km s-1 and upper mantle velocities by ∼0.5 km s-1. In the vicinity of the Louisville Ridge Seamount Chain (LRSC), the trench shallows by 4 km and normal fault throw is reduced by >1 km, suggesting that the subduction of seamounts reduces plate deformation. We find that the extinct Eocene frontal arc, defined by a high velocity (7.0-7.4 km s-1) and density (3.2 g cm-3) lower-crustal anomaly, increases in thickness by ∼6 km, from 12 to >18 km, over 300 km laterally along the Tonga-Kermadec forearc. Coincident variations in bathymetry and free-air gravity anomaly indicate a regional trend of northward-increasing crustal thickness that predates LRSC subduction, and highlight the present-day extent of the Eocene arc between 32°S and ∼18°S. Within this framework of existing forearc crustal structure, the subduction of seamounts of the LRSC promotes erosion of the overriding crust, forming steep, gravitationally unstable, lower-trench slopes. Trench-slope stability is most likely re-established by the collapse of the mid-trench slope and the trenchward side of the extinct Eocene arc, which, within the framework of forearc characterization, implies seamount subduction commenced at ∼22°S.

Electrical conductivity anomaly beneath Mare Serenitatis detected by Lunokhod 2 and Apollo 16 magnetometers

NASA Technical Reports Server (NTRS)

Vanian, L. L.; Vnuchkova, T. A.; Egorov, I. V.; Basilevskii, A. T.; Eroshenko, E. G.; Fainberg, E. B.; Dyal, P.; Daily, W. D.

1979-01-01

Magnetic fluctuations measured by the Lunokhod 2 magnetometer in the Bay Le Monnier are distinctly anisotropic when compared to simultaneous Apollo 16 magnetometer data measured 1100 km away in the Descartes highlands. This anisotropy can be explained by an anomalous electrical conductivity of the upper mantle beneath Mare Serenitatis. A model is presented of anomalously lower electrical conductivity beneath Serenitatis and the simultaneous magnetic data from the Lunokhod 2 site at the mare edge and the Apollo 16 site are compared to the numerically calculated model solutions. This comparison indicates that the anisotropic fluctuations can be modeled by a nonconducting layer in the lunar lithosphere which is 150 km thick beneath the highlands and 300 km thick beneath Mare Serenitatis. A decreased electrical conductivity in the upper mantle beneath the mare may be due to a lower temperature resulting from heat carried out the magma source regions to the surface during mare flooding.

Variability of the geothermal gradient across two differently aged magma-rich continental rifted margins of the Atlantic Ocean: the Southwest African and the Norwegian margins

NASA Astrophysics Data System (ADS)

Gholamrezaie, Ershad; Scheck-Wenderoth, Magdalena; Sippel, Judith; Strecker, Manfred R.

2018-02-01

The aim of this study is to investigate the shallow thermal field differences for two differently aged passive continental margins by analyzing regional variations in geothermal gradient and exploring the controlling factors for these variations. Hence, we analyzed two previously published 3-D conductive and lithospheric-scale thermal models of the Southwest African and the Norwegian passive margins. These 3-D models differentiate various sedimentary, crustal, and mantle units and integrate different geophysical data such as seismic observations and the gravity field. We extracted the temperature-depth distributions in 1 km intervals down to 6 km below the upper thermal boundary condition. The geothermal gradient was then calculated for these intervals between the upper thermal boundary condition and the respective depth levels (1, 2, 3, 4, 5, and 6 km below the upper thermal boundary condition). According to our results, the geothermal gradient decreases with increasing depth and shows varying lateral trends and values for these two different margins. We compare the 3-D geological structural models and the geothermal gradient variations for both thermal models and show how radiogenic heat production, sediment insulating effect, and thermal lithosphere-asthenosphere boundary (LAB) depth influence the shallow thermal field pattern. The results indicate an ongoing process of oceanic mantle cooling at the young Norwegian margin compared with the old SW African passive margin that seems to be thermally equilibrated in the present day.

Imaging of Upper-Mantle Upwelling Beneath the Salton Trough, Southern California, by Joint Inversion of Ambient Noise Dispersion Curves and Receiver Functions

NASA Astrophysics Data System (ADS)

Klemperer, S. L.; Barak, S.

2016-12-01

We present a new 2D shear-wave velocity model of the crust and upper-mantle across the Salton Trough, southern California, obtained by jointly inverting our new dataset of receiver functions and our previously published Rayleigh-wave group-velocity model (Barak et al., G-cubed, 2015), obtained from ambient-noise tomography. Our results show an upper-mantle low-velocity zone (LVZ) with Vs ≤4.2 km/s extending from the Elsinore Fault to the Sand Hills Fault, that together bracket the full width of major San Andreas dextral motion since its inception 6 Ma b.p., and underlying the full width of low topography of the Imperial Valley and Salton Trough. The lateral extent of the LVZ is coincident with the lateral extent of an upper-mantle anisotropic region interpreted as a zone of SAF-parallel melt pockets (Barak & Klemperer, Geology, 2016). The shallowest part of the LVZ is 40 km depth, coincident with S-receiver function images. The western part of the LVZ, between the Elsinore and San Jacinto faults (the region of greatest modern dextral slip), appears to continue to significantly greater depth; but a puzzling feature of our preliminary models is that the eastern part of the LVZ, from the San Jacinto Fault to the Sand Hills Fault, appears to be underlain by more-normalvelocity upper mantle (Vs ≥ 4.5 km/s) below 75 km depth. We compare our model to the current SCEC community models CVM-H and CVM-S, and to P-wave velocity models obtained by the active-source Salton Sea Imaging Project (SSIP). The hypothesized lower-crustal low-velocity zone beneath the Salton Trough in our previous model (Barak et al., G-cubed, 2015), there interpreted as a region of partial melt, is not supported by our new modeling. Melt may be largely absent from the lower crust of the Salton trough; but appears required in the upper mantle at depths as shallow as 40 km.

Potential geologic hazards on the eastern Gulf of Cadiz slope (SW Spain)

USGS Publications Warehouse

Baraza, J.; Ercilla, G.; Nelson, C.H.

1999-01-01

Geologic hazards resulting from sedimentary, oceanographic and tectonic processes affect more than one third of the offshore Gulf of Cadiz, and are identified by interpreting high-resolution seismic profiles and sonographs. Hazards of sedimentary origin include the occurrence of slope instability processes in the form of single or multiple slumps occupying up to 147 km2 mainly concentrated in the steeper, upper slope area. Besides the presence of steep slopes, the triggering of submarine landslides is probably due to seismic activity and favoured by the presence of biogenic gas within the sediment. Gassy sediments and associated seafloor pockmarks cover more than 240 km2 in the upper slope. Hazards from oceanographic processes result from the complex system of bottom currents created by the interaction of the strong Mediterranean Undercurrent and the rough seafloor physiography. The local intensification of bottom currents is responsible for erosive processes along more than 1900 km2 in the upper slope and in the canyons eroded in the central area of the slope, undermining slopes and causing instability. The strong bottom currents also create a mobile seafloor containing bedforms in an area of the Gulf that extends more than 2500 km2, mostly in the continental slope terraces. Hazards of tectonic origin are important because the Gulf of Cadiz straddles two major tectonic regions, the Azores-Gibraltar fracture zone and the Betic range, which results in diapir uplift over an area of more than 1000 km2, and in active seismicity with earthquakes of moderate magnitude. Also, tsunamis produced by strong earthquakes occur in the Gulf of Cadiz, and are related to the tectonic activity along the Azores-Gibraltar fracture zone.

The effect of breast support on upper body muscle activity during 5 km treadmill running.

PubMed

Milligan, Alexandra; Mills, Chris; Scurr, Joanna

2014-12-01

Breast support has previously been shown to influence surface EMG of the pectoralis major during running. Reductions in muscle activity have previously been associated with a reduction in energy cost, which may be advantageous for female runners. Ten female participants performed two self-paced (average pace 9 km h(-1)) 5 km treadmill runs under two breast support conditions (low and high); an additional bare-breasted 2 min run was also conducted. Surface EMG electrodes were positioned on the pectoralis major, anterior deltoid, medial deltoid, and upper trapezius, with data collected during the first 2 min of running and each kilometer interval thereafter. Reductions in peak EMG of the pectoralis major, anterior and medial deltoid were reported when participants ran in the high breast support during the initial intervals of the run (up to the second kilometer). The increased activation in the pectoralis major, anterior and medial deltoid in the low breast support may be due to increased tension within these muscles, induced by the greater breast pain experienced in the low breast support. This may be a strategy to reduce the independent breast movement causing the pain through increased muscular activation. This study further promotes the use of a high breast support during running with potential benefits for treadmill running associated with reductions in muscular demand during a 5 km run. Copyright © 2014 Elsevier B.V. All rights reserved.

New insight into the Upper Mantle Structure Beneath the Pacific Ocean Using PP and SS Precursors

NASA Astrophysics Data System (ADS)

Gurrola, H.; Rogers, K. D.

2013-12-01

The passing of the EarthScope Transportable array has provided a dense data set that enabled beam forming of SS and PP data that resultes in improved frequency content to as much a 1 Hz in the imaging of upper mantle structure. This combined with the application of simultaneous iterative deconvolution has resulted in images to as much as 4 Hz. The processing however results in structure being averaged over regions of 60 to 100 km in radius. This is becomes a powerful new tool to image the upper mantle beneath Oceanic regions where locating stations is expensive and difficult. This presentation will summarize work from a number of regions as to new observations of the upper mantle beneath the Pacific and Arctic Oceans. Images from a region of the Pacific Ocean furthest from hot spots or subduction zones (we will refer to this as the 'reference region'). show considerable layering in the upper mantle. The 410 km discontinuity is always imaged using these tools and appears to be a very sharp boundary. It does usually appear as an isolated positive phase. There appears to be a LAB at ~100 km as expected but there is a strong negative phase at ~ 200 km with a positive phase 15 km deeper. This is best explained as a lens of partial melt as expected for this depth based on the geothermal gradient. If so this should be a low friction point and so we would expect it to accommodate plate motion. Imaging of the Aleutian subduction zone does show the 100 km deep LAB as it descends but this 200 km deep horizon appears as a week descending positive anomaly without the shallower negative pulse. In addition to the 410, 100 and 200 km discontinuities there are a number of paired anomalies, between the 200 and 400 km depths, with a negative pulse 15 to 20 km shallower then the positive pulse. We do not believe these are side lobes or we would see side lobes on the 100 km and 410 km discontinuities. We believe these to be the result of friction induced partial melt along zones of critical failure to accommodate differential mantle flow with depth. The paired layers disappear beneath the Hawaiian Island chain. We believe heat from the hot spot warms the mantle beneath the Hawaiian island chain so flow is more easily accommodated. As a result the lenses of melt disappear in the region near hot spots.

Hypervelocity impact survivability experiments for carbonaceous impactors, part 2

NASA Technical Reports Server (NTRS)

Bunch, T. E.; Paque, Julie M.; Becker, Luann; Vedder, James F.; Erlichman, Jozef

1995-01-01

Hypervelocity impact experiments were performed to further test the survivability of carbonaceous impactors and to determine potential products that may have been synthesized during impact. Diamonds were launched by the Ames two-stage light gas gun into Al plate at velocities of 2.75 and 3.1 km sec(exp -1). FESEM imagery confirms that diamond fragments survived in both experiments. Earlier experiments found that diamonds were destroyed on impact above 4.3 km sec(exp -1). Thus, the upper stability limit for diamond on impact into Al, as determined from our experimental conditions, is between 3.1 and 4.3 km sec(exp -1). Particles of the carbonaceous chondrite Nogoya were also launched into Al at a velocity of 6.2 km sec (exp -1). Laser desorption (L (exp 2) MS) analyses of the impactor residues indicate that the lowest and highest mass polycyclic aromatic hydrocarbons (PAH's) were largely destroyed on impact; those of intermediate mass (202-220 amu) remained at the same level or increased in abundance. In addition, alkyl-substituted homologs of the most abundant pre-impacted PAH's were synthesized during impact. These results suggest that an unknown fraction of some organic compounds can survive low to moderate impact velocities and that synthesized products can be expected to form up to velocities of, at least, 6.5 km sec(exp -1). We also present examples of craters formed by a unique microparticle accelerator that could launch micron-sized particles of almost any coherent material at velocities up to approximately 15 km sec(exp -1). Many of the experiments have a direct bearing on the interpretation of LDEF craters.

Gravity Spectra from the Density Distribution of Earth's Uppermost 435 km

NASA Astrophysics Data System (ADS)

Sebera, Josef; Haagmans, Roger; Floberghagen, Rune; Ebbing, Jörg

2018-03-01

The Earth masses reside in a near-hydrostatic equilibrium, while the deviations are, for example, manifested in the geoid, which is nowadays well determined by satellite gravimetry. Recent progress in estimating the density distribution of the Earth allows us to examine individual Earth layers and to directly see how the sum approaches the observed anomalous gravitational field. This study evaluates contributions from the crust and the upper mantle taken from the LITHO1.0 model and quantifies the gravitational spectra of the density structure to the depth of 435 km. This is done without isostatic adjustments to see what can be revealed with models like LITHO1.0 alone. At the resolution of 290 km (spherical harmonic degree 70), the crustal contribution starts to dominate over the upper mantle and at about 150 km (degree 130) the upper mantle contribution is nearly negligible. At the spatial resolution <150 km, the spectra behavior is driven by the crust, the mantle lid and the asthenosphere. The LITHO1.0 model was furthermore referenced by adding deeper Earth layers from ak135, and the gravity signal of the merged model was then compared with the observed satellite-only model GOCO05s. The largest differences are found over the tectonothermal cold and old (such as cratonic), and over warm and young areas (such as oceanic ridges). The misfit encountered comes from the mantle lid where a velocity-density relation helped to reduce the RMS error by 40%. Global residuals are also provided in terms of the gravitational gradients as they provide better spatial localization than gravity, and there is strong observational support from ESA's satellite gradiometry mission GOCE down to the spatial resolution of 80-90 km.

Lower crustal earthquakes in the North China Basin and implications for crustal rheology

NASA Astrophysics Data System (ADS)

Yuen, D. A.; Dong, Y.; Ni, S.; LI, Z.

2017-12-01

The North China Basin is a Mesozoic-Cenozoic continental rift basin on the eastern North China Craton. It is the central region of craton destruction, also a very seismically active area suffering severely from devastating earthquakes, such as the 1966 Xingtai M7.2 earthquake, the 1967 Hejian M6.3 earthquake, and the 1976 Tangshan M7.8 earthquake. We found remarkable discrepancies of depth distribution among the three earthquakes, for instance, the Xingtai and Tangshan earthquakes are both upper-crustal earthquakes occurring between 9 and 15 km on depth, but the depth of the Hejian earthquake was reported of about 30 72 km, ranging from lowermost crust to upper mantle. In order to investigate the focal depth of earthquakes near Hejian area, we developed a method to resolve focal depth for local earthquakes occurring beneath sedimentary regions by P and S converted waves. With this method, we obtained well-resolved depths of 44 local events with magnitudes between M1.0 and M3.0 during 2008 to 2016 at the Hejian seismic zone, with a mean depth uncertainty of about 2 km. The depth distribution shows abundant earthquakes at depth of 20 km, with some events in the lower crust, but absence of seismicity deeper than 25 km. In particular, we aimed at deducing some constraints on the local crustal rheology from depth-frequency distribution. Therefore, we performed a comparison between the depth-frequency distribution and the crustal strength envelop, and found a good fit between the depth profile in the Hejian seismic zone and the yield strength envelop in the Baikal Rift Systems. As a conclusion, we infer that the seismogenic thickness is 25 km and the main deformation mechanism is brittle fracture in the North China Basin . And we made two hypotheses: (1) the rheological layering of dominant rheology in the North China Basin is similar to that of the Baikal Rift Systems, which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km depth; (2) the temperature is moderate in the seismogenic zone of crust and relative high below 25 km. We also suggest that, many accurately resolved earthquake locations can shed light on the nature of the crustal rheology locally, and that our method can be employed in other sedimentary regions which are seismically active.

The inventory and distribution of water on Mars

USGS Publications Warehouse

Carr, M.H.

1987-01-01

Terrain softening, fretted channels, debris flows, and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes (>30??) contain ice in amounts that exceed the porosity, estimated to be 10-20 percent. Theoretical studies, and lack of these features in the cratered uplands at low latitudes, suggest that the upper 1 km of the uplands at low latitudes is ice poor. However, valley networks indicate that water was present near the surface early in the planet's history, although in amounts smaller than at high latitudes. On the basis of these observations, the entire upper 1 km, planet-wide is estimated to have contained 75-125 meters of water at the end of heavy bombardment. From the volume of water needed to cut the circum-Chryse channels, and assuming uniform planet-wide distribution of water, the deep megaregolith is estimated to have contained at least 350 meters of water at the end of heavy bombardment, thereby giving a total minimum inventory of 425-475 meters planet-wide. Most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains. Most of the water involved in cutting the outflow channels is in the low-lying northern plains where a variety of features that have been attributed to ground ice is present. Since the end of heavy bombardment, a large fraction of the planet's surface has been overplated with water-poor volcanics, of which we have samples in the SNC meteorites. The younger volcanics have reacted extensively with the old volatile-rich basement. Part of the 10-20 bars of CO2 and 0.1 to 0.3 bars of N2 outgassed with the water was lost during heavy bombardment by impact erosion of the atmosphere and other processes. The remaining was fixed carbonates and nitrates and folded deep into the megaregolith during heavy bombardment. ?? 1987.

The formation of giant clastic extrusions at the end of the Messinian Salinity Crisis

NASA Astrophysics Data System (ADS)

Kirkham, Christopher; Cartwright, Joe; Hermanrud, Christian; Jebsen, Christopher

2018-01-01

This paper documents the discovery of five multi-km scale lensoid bodies that directly overlie the upper surface of the thick (>1 km) Messinian Evaporite sequence. They were identified through the analysis of 3D seismic data from the western Nile Cone. The convergence of the upper and lower bounding reflections of these lensoid bodies, their external and internal reflection configuration, the positive 'depositional' relief at their upper surface, and the stratal relationship with underlying and overlying deposits supports the interpretation that these are giant clastic extrusions. The interpretations combined with the stratal position of these clastic extrusions demonstrate a prior unsuspected link between periods of major environment change and basin hydrodynamics on a plate scale. All five lensoid bodies were extruded onto a single, seismically resolvable marker horizon correlatable with the end of the Messinian Salinity Crisis (Horizon M). It is argued that the source of these clastic extrusions is pre-Messinian in origin, which implies massive sediment remobilisation at depth in the pre-evaporitic succession and intrusion through the thick evaporite layer. We propose that the scale and timing of this dramatic event was primed and triggered by near-lithostatic overpressure in the pre-evaporitic sediments generated through (1) their rapid burial and loading during the Messinian Salinity Crisis and (2) catastrophic re-flooding during its immediate aftermath. The largest of these clastic extrusions has a volume of over c. 116 km3, making it amongst the largest extruded sedimentary bodies described on Earth. The findings extend the understanding of the upper scale of other analogous clastic extrusions such as mud volcanoes and sediment-hosted hydrothermal systems. Following the 2006 eruption of the Lusi sediment-hosted hydrothermal system in Indonesia, an understanding of the upper scale limit of clastic extrusions has even greater societal relevance, in order to increase awareness of the risk posed by the potential size and longevity of future giant clastic extrusions.

ATMOS/ATLAS-3 Observations of Long-Lived Tracers and Descent in the Antarctic Vortex in November 1994

NASA Technical Reports Server (NTRS)

Abrams, M. C.; Manney, G. L.; Gunson, M. R.; Abbas, M. M.; Chang, A. Y.; Goldman, A.; Irion, F. W.; Michelsen, H. A.; Newchurch, M. J.; Rinsland, C. P.;

Magnetic and gravity constraints on forearc upper crustal structure and composition, offshore northeast Japan

USGS Publications Warehouse

Finn, C.

1994-01-01

Marine magnetic and gravity data from the northeast Japan forearc offer insight to the subsurface structure, density and magnetization from which geologic interpretations and tectonic reconstructions can be made. Positive marine magnetic anomalies, on-land geology, drill hole data, and 2-1/2-dimensional models reveal that Kitakami plutons and possibly their associated volcanic rocks constitute part of the modern forearc basement and lie 100-150 km further east than previously thought. A method to create magnetization and density contrast maps was employed to produce a three-dimensional picture of the forearc basement rock properties averaged over a 14-km thickness. -Author

GLIMPCE Seismic reflection evidence of deep-crustal and upper-mantle intrusions and magmatic underplating associated with the Midcontinent Rift system of North America

USGS Publications Warehouse

Behrendt, John C.; Hutchinson, D.R.; Lee, M.; Thornber, C.R.; Tréhu, A.; Cannon, W.; Green, A.

1990-01-01

Deep-crustal and Moho reflections, recorded on vertical incidence and wide angle ocean bottom Seismometer (OBS) data in the 1986 GLIMPCE (Great Lakes International Multidisciplinary Program on Crustal Evolution) experiment, provide evidence for magmatic underplating and intrusions within the lower crust and upper mantle contemporaneous with crustal extension in the Midcontinent Rift system at 1100 Ma. The rift fill consists of 20-30 km (7-10 s) of basalt flows, secondary syn-rift volcaniclastic and post-basalt sedimentary rock. Moho reflections recorded in Lake Superior over the Midcontinent Rift system have times from 14-18 s (about 46 km to as great as 58 km) in contrast to times of about 11-13 s (about 36-42 km crustal thickness) beneath the surrounding Great Lakes. The Seismically complex deep-crust to mantle transition zone (30-60 km) in north-central Lake Superior, which is 100 km wider than the rift half-graben, reflects the complicated products of tectonic and magmatic interaction of lower-crustal and mantle components during evolution or shutdown of the aborted Midcontinent Rift. In effect, mantle was changed into crust by lowering Seismic velocity (through intrusion of lower density magmatic rocks) and increasing Moho (about 8.1 km s-1 depth. 

Whole-body kinematic and dynamic response of restrained PMHS in frontal sled tests.

PubMed

Forman, Jason; Lessley, David; Kent, Richard; Bostrom, Ola; Pipkorn, Bengt

2006-11-01

The literature contains a wide range of response data describing the biomechanics of isolated body regions. Current data for the validation of frontal anthropomorphic test devices and human body computational models lack, however, a detailed description of the whole-body response to loading with contemporary restraints in automobile crashes. This study presents data from 14 frontal sled tests describing the physical response of postmortem human surrogates (PMHS) in the following frontal crash environments: A) (5 tests) driver position, force-limited 3-point belt plus airbag restraint (FLB+AB), 48 km/h deltaV. B) (3 tests) passenger position, FLB+AB restraint, 48 km/h deltaV. C) (3 tests) passenger position, standard (not force-limited) 3-point belt plus air bag restraint (SB+AB), 48 km/h deltaV. D) (3 tests) passenger position, standard 3-point belt restraint (SB), 29 km/h deltaV. Reported data include x-axis and z-axis (SAE occupant reference frame) accelerations of the head, spine (upper, middle, and lower), and pelvis; rate of angular rotation of the head about y-axis; displacements of the head, upper spine, pelvis and knee relative to the vehicle buck; and deformation contours of the upper and lower chest. A variety of kinematic trends are identified across the different test conditions, including a decrease in head and thorax excursion and a change in the nature of the excursion in the driver position compared to the passenger position. Despite this increase in forward excursion when compared to the driver's side FLB+AB tests, the passenger's side FLB+AB tests resulted in greater peak thoracic (T8) x-axis accelerations (passenger's side -29 g; driver's side -22 g;) and comparable maximum chest deflection (passenger's side - 23+/-3.1% of the undeformed chest depth; driver's side - 23+/-5.6%; ). In the 48 km/h passenger's side tests, the head excursion associated with the force-limiting belt system was approximately 15% greater than that for a standard belt system in tests that were otherwise identical. This was accompanied by a decrease in chest deflection of approximately 20% with the force-limiting system. Despite the decrease in test speed, the 29 km/h passenger's side tests with standard (not force-limiting) 3-point belt restraints resulted in maximum chest deflection (16+/-5.6% average) comparable to that observed in the 48 km/h, FLB+AB, driver's side tests (21+/-3.1% average). Finally, forward head excursion was slightly higher in the 29 km/h passenger's side tests (33+/-1.1 cm average) than in the 48 km/h driver's side tests (27+/-3.7 cm average), and was lower than that in the 48 km/h FLB+AB (58+/-4.4 cm average) and SB+AB (46+/-2.1 cm average) passenger's side tests.

The Origin of Titan’s External Oxygen: Further Constraints from ALMA Upper Limits on CS and CH2NH

NASA Astrophysics Data System (ADS)

Teanby, N. A.; Cordiner, M. A.; Nixon, C. A.; Irwin, P. G. J.; Hörst, S. M.; Sylvestre, M.; Serigano, J.; Thelen, A. E.; Richards, A. M. S.; Charnley, S. B.

2018-06-01

Titan’s atmospheric inventory of oxygen compounds (H2O, CO2, CO) are thought to result from photochemistry acting on externally supplied oxygen species (O+, OH, H2O). These species potentially originate from two main sources: (1) cryogenic plumes from the active moon Enceladus and (2) micrometeoroid ablation. Enceladus is already suspected to be the major O+ source, which is required for CO creation. However, photochemical models also require H2O and OH influx to reproduce observed quantities of CO2 and H2O. Here, we exploit sulphur as a tracer to investigate the oxygen source because it has very different relative abundances in micrometeorites (S/O ∼ 10‑2) and Enceladus’ plumes (S/O ∼ 10‑5). Photochemical models predict most sulphur is converted to CS in the upper atmosphere, so we use Atacama Large Millimeter/submillimeter Array (ALMA) observations at ∼340 GHz to search for CS emission. We determined stringent CS 3σ stratospheric upper limits of 0.0074 ppb (uniform above 100 km) and 0.0256 ppb (uniform above 200 km). These upper limits are not quite stringent enough to distinguish between Enceladus and micrometeorite sources at the 3σ level and a contribution from micrometeorites cannot be ruled out, especially if external flux is toward the lower end of current estimates. Only the high-flux micrometeorite source model of Hickson et al. can be rejected at 3σ. We determined a 3σ stratospheric upper limit for CH2NH of 0.35 ppb, which suggests cosmic rays may have a smaller influence in the lower stratosphere than predicted by some photochemical models. Disk-averaged C3H4 and C2H5CN profiles were determined and are consistent with previous ALMA and Cassini/CIRS measurements.

Resistivity structures across the Humboldt River basin, north-central Nevada

USGS Publications Warehouse

Rodriguez, Brian D.; Williams, Jackie M.

2002-01-01

Magnetotelluric data collected along five profiles show deep resistivity structures beneath the Battle Mountain-Eureka and Carlin gold trends in north-central Nevada, which appear consistent with tectonic breaks in the crust that possibly served as channels for hydrothermal fluids. It seems likely that gold deposits along these linear trends were, therefore, controlled by deep regional crustal fault systems. Two-dimensional resistivity modeling of the magnetotelluric data generally show resistive (30 to 1,000 ohm-m) crustal blocks broken by sub-vertical, two-dimensional, conductive (1 to 10 ohmm) zones that are indicative of large-scale crustal fault zones. These inferred fault zones are regional in scale, trend northeast-southwest, north-south, and northwest-southeast, and extend to mid-crustal (20 km) depths. The conductors are about 2- to 15-km wide, extend from about 1 to 4 km below the surface to about 20 km depth, and show two-dimensional electrical structure. By connecting the locations of similar trending conductors together, individual regional crustal fault zones within the upper crust can be inferred that range from about 4- to 10-km wide and about 30- to 150-km long. One of these crustal fault zones coincides with the Battle Mountain-Eureka mineral trend. The interpreted electrical property sections also show regional changes in the resistive crust from south to north. Most of the subsurface in the upper 20 km beneath Reese River Valley and southern Boulder Valley are underlain by rock that is generally more conductive than the subsurface beneath Kelly Creek Basin and northern Boulder Valley. This suggests that either elevated-temperature or high-salinity fluids, alteration, or carbonaceous rocks are more pervasive in the more conductive area (Battle Mountain Heat-Flow High), which implies that the crust beneath these valleys is either more fractured or has more carbonaceous rocks than in the area surveyed along the 41st parallel.

Crustal Deformation In the Northwestern Margin of the South China Sea: Results From Wide-angle Seismic Modeling

NASA Astrophysics Data System (ADS)

Huang, H.; Klingelhoefer, F.

2017-12-01

The South China Sea (SCS) has undergone episodic spreading during the Cenozoic Era. The long-term extension has shaped the continental margins of the SCS, leading to a progressive breakup of the lithosphere. Separated blocks and rift troughs, as controlled by tectonic stretching, contains key information about the deforming mechanism of the crust. In this work, we present a P-wave velocity model of a wide-angle seismic profile OBS2013-1 which passes through the NW margin of the SCS. Modeling of 25 ocean bottom seismometers (OBS) data revealed a detailed crustal structure and shallow complexities along the profile (Figure 1). The crust thins symmetrically across the Xisha Trough, from more than 20 km on flanks to 10 km in the central valley where the sediments thickens over 5 km; A volcano is situated on top of the centre basement high where the Moho drops slightly. At the distal margin around the Zhongsha Trough, the upper crust was detached and accordingly made the middle crust exhumed in a narrow area ( 20 km wide). Meanwhile, materials from the lower crust rises asymmetrically, increasing the crustal velocity by 0.3 km/s and may also giving rise to volcanisms along the hanging side. A 40 km wide hyper-stretched crust (with thickness of 5 km) was identified next to the Zhongsha Trough and covered by overflowing magma and post-rift sediments on the top. These observations argue for a depth-related and asymmetrically extension of the crust, including (1) detachment fault controls the deformation of the upper crust, leading to exhumation of the middle crust and asymmetrically rising of the lower crust, (2) The region adjacent to the exhumation region and with highly thinned crust can be considered as extinct OCT due to magma-starved supplying.

Experiments and theory on parametric instabilities excited in HF heating experiments at HAARP

NASA Astrophysics Data System (ADS)

Kuo, Spencer; Snyder, Arnold; Lee, M. C.

2014-06-01

Parametric instabilities excited by O-mode HF heater and the induced ionospheric modification were explored via HAARP digisonde operated in a fast mode. The impact of excited Langmuir waves and upper hybrid waves on the ionosphere are manifested by bumps in the virtual spread, which expand the ionogram echoes upward as much as 140 km and the downward range spread of the sounding echoes, which exceeds 50 km over a significant frequency range. The theory of parametric instabilities is presented. The theory identifies the ionogram bump located between the 3.2 MHz heater frequency and the upper hybrid resonance frequency and the bump below the upper hybrid resonance frequency to be associated with the Langmuir and upper hybrid instabilities, respectively. The Langmuir bump is located close to the upper hybrid resonance frequency, rather than to the heater frequency, consistent with the theory. Each bump in the virtual height spread of the ionogram is similar to the cusp occurring in daytime ionograms at the E-F2 layer transition, indicating that there is a small ledge in the density profile similar to E-F2 layer transitions. The experimental results also show that the strong impact of the upper hybrid instability on the ionosphere can suppress the Langmuir instability.

Experiments and theory on parametric instabilities excited in HF heating experiments at HAARP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuo, Spencer; Snyder, Arnold; Lee, M. C.

2014-06-15

Parametric instabilities excited by O-mode HF heater and the induced ionospheric modification were explored via HAARP digisonde operated in a fast mode. The impact of excited Langmuir waves and upper hybrid waves on the ionosphere are manifested by bumps in the virtual spread, which expand the ionogram echoes upward as much as 140 km and the downward range spread of the sounding echoes, which exceeds 50 km over a significant frequency range. The theory of parametric instabilities is presented. The theory identifies the ionogram bump located between the 3.2 MHz heater frequency and the upper hybrid resonance frequency and the bump below themore » upper hybrid resonance frequency to be associated with the Langmuir and upper hybrid instabilities, respectively. The Langmuir bump is located close to the upper hybrid resonance frequency, rather than to the heater frequency, consistent with the theory. Each bump in the virtual height spread of the ionogram is similar to the cusp occurring in daytime ionograms at the E-F2 layer transition, indicating that there is a small ledge in the density profile similar to E-F2 layer transitions. The experimental results also show that the strong impact of the upper hybrid instability on the ionosphere can suppress the Langmuir instability.« less

Ocean plateau-seamount origin of basaltic rocks, Angayucham terrane, central Alaska

USGS Publications Warehouse

Barker, F.; Jones, D.L.; Budahn, J.R.; Coney, P.J.

1988-01-01

The Angayucham terrane of north-central Alaska (immediately S of the Brooks Range) is a large (ca. 500 km E-W), allochthonous complex of Devonian to Lower Jurassic pillow basalt, diabase sills, gabbro plutons, and chert. The mafic rocks are transitional normal-to-enriched, mid-ocean-ridge (MORB) type tholeiites (TiO2 1.2-3.4%, Nb 7-23 ppm, Ta 0.24-1.08 ppm, Zr 69-214 ppm, and light REE's slightly depleted to moderately enriched). Geologic and geochemical constraints indicate that Angayucham terrane is the upper "skin' (ca. 3-4 km thick) of a long-lived (ca. 170-200 ma) oceanic plateau whose basaltic-gabbroic rocks are like those of seamounts of the East Pacific Rise. -Authors

Structure and Deformation of the Hikurangi-Kermadec Subduction Zone - Transitions Revealed by Seismic Wide-angle Data

NASA Astrophysics Data System (ADS)

Scherwath, M.; Kopp, H.; Flueh, E. R.; Henrys, S. A.; Sutherland, R.

2008-12-01

The Hikurangi-Kermadec subduction zone northeast of New Zealand represents an ideal target to study lateral variations of subduction zone processes. The incoming Pacific plate changes from being a large igneous province, called the Hikurangi Plateau, in the south to normal oceanic plate north of the Rapuhia Scarp. The overriding Australian plate of continental character in the south, forming the North Island of New Zealand, and changes to an island arc in the north. Further lateral variability exists in changes in volcanic and hydro-thermal activity, transitions from accretion to subduction erosion, backarc spreading and rifting, and is accompanied by northward increasing seismicity. As part of the MANGO project (Marine Geoscientific Investigations on the Input and Output of the Kermadec Subduction Zone), four marine geophysical transects of largely seismic reflection and refraction data provide constraints on the upper lithospheric structures across the Hikurangi-Kermadec Trench between 29-38 deg S. On MANGO profile 1 in the south, the initially shallow subduction of the incoming plateau coincides with crustal underplating beneath the East Cape ridge. To the west lies the 100 km wide and over 10 km deep Raukumara Basin. Seismic velocities of the upper mantle of both plates are around 8 km/s and are considered normal. In contrast, on MANGO profile 4, about 1000 km to the north around the volcanically active Raoul Island, the incoming oceanic crust appears to bend considerably steeper and thus causes a 50 km narrower forearc with a smaller forearc basin. Furthermore, the upper mantle velocities in both plates are relatively low (7.4-7.7 km/s), likely indicating strong bending related deformation of the incoming plate and thermal activity within the arc possibly due to spreading. The central two transects MANGO 2 and 3, though without data coverage of the structure of the incoming plate, are more similar to MANGO 4. The arc regions appear to be strongly affected by the activity of the arc. The arc crust of the northern MANGO 3 becomes significantly thinner in the backarc region due to extension, whereas the data from MANGO 2 likely show thermal activity from the adjacent arc volcanism.

Effect of convection on the thermal structure of the troposphere and lower stratosphere including the tropical tropopause layer in the South Asian monsoon region

NASA Astrophysics Data System (ADS)

Muhsin, M.; Sunilkumar, S. V.; Venkat Ratnam, M.; Parameswaran, K.; Krishna Murthy, B. V.; Emmanuel, Maria

2018-04-01

Influence of convection on the thermal structure of Troposphere and Lower Stratosphere (TLS) is investigated using radiosonde data, obtained from Trivandrum (8.5°N, 76.9°E), Gadanki (13.5°N, 79.2°E), Bhubaneswar (20.25°N, 85.83°E), Kolkata (22.65°N, 88.45°E) and Singapore (1.37°N, 103.98°E), collected during different convective categories classified based on the altitude of deep convective cloud tops (CT) in the period 2008-2014. During deep convective events, the temperature showed lower tropospheric cooling, an upper tropospheric warming and an anomalous cooling (warming) below (above) the cold point tropopause (CPT) with respect to the clear-sky value. While warming in the upper troposphere is strongest (∼2-4 K) around 10-12 km, anomalous cooling (warming) below (above) the CPT is maximum around 15.5 km (17.5 km) with values in the range of-2 to -4 K (3-6 K). These temperature perturbations are observed 5-6 days prior to the convective events. In response to deep convection, surface cooling up to ∼ -4 K is also observed. This study showed that the magnitude of cold and warm anomalies increases with strength of convection. During deep convection, the potential temperature (θ) shows a decrease (<5 K) in the tropical tropopause layer (TTL) from the TTL-base up to CPT compared to that on clear-sky days, confirming the vertical mixing of convective air from the lower atmosphere to the TTL-levels. Correlation analysis between different TTL parameters suggests that, as the cloud top altitude increases, along with the adiabatic process, diabatic process also plays a major role in the TTL. An interesting feature observed during deep convection is the ascent of TTL-base by ∼1.5 km and descent of CPT and TTL-top by 0.5 km, which effectively thins the TTL by ∼2 km.

The crustal structure of the Cocos ridge off Costa Rica

NASA Astrophysics Data System (ADS)

Walther, Christian H. E.

2003-03-01

The submarine Cocos ridge in the northwestern Panamá basin, a bathymetric feature more than 1000-km long and 250-500 km broad, is about 2 km shallower than the adjacent basin. It is generally interpreted as the trace of the Galápagos hot spot. Two 127- and 260-km long seismic wide-angle sections were recorded along and across this ridge, offshore the Osa peninsula, Costa Rica. Crustal thickening is seen everywhere along the sections. On the northwestern outer ridge flank, increased thickness is exclusively attributed to the upper crust and expressed by 2-km thick flow basalts. The Quepos plateau caps the upper crust in this area. Toward the center of the Cocos ridge, the Moho deepens from 11-12 to 21 km depth and crustal thickening is almost entirely attributed to the lower crust which makes up 80% of the crust and is three times the thickness of normal oceanic lower crust. It is homogeneously structured and the velocities which range from 6.5 km/s at the top to 7.35 km/s at the base are comparable to normal lower crust under these depth conditions and suggest no differences to a gabbroic rock composition. Similarities to the crustal velocity structure of Iceland, central Kerguelen plateau, and Broken ridge are consistent with a formation of this 13-15 Ma old Cocos ridge segment by excessive magmatism in a near-plate boundary setting.

High resolution P-wave velocity structure beneath Northeastern Tibet from multiscale seismic tomography

NASA Astrophysics Data System (ADS)

Guo, B.; Gao, X.; Chen, J.; Liu, Q.; Li, S.

2016-12-01

The continuing collision of the northward advancing Indian continent with the Eurasia results in the high elevations and thickened Tibetan Plateau. Numerous geologic and geophysical studies engaged in the mechanics of the Tibetan Plateau deformation and uplift. Many seismic experiments were deployed in south and central Tibet, such as INDEPTH and Hi-climb, but very few in northeastern Tibet. Between 2013 and 2015, The China Seismic Array-experiment operated 670 broadband seismic stations with an average station spacing of 35km. This seismic array located in northeastern Tibet and covered the Qilian Mountains, Qaidam Basin, and part of Songpan-Ganzi, Gobi-Alashan, Yangzi, and Ordos. A new multiscale seismic traveltime tomography technique with sparsity constrains were used to map the upper mantle P-wave velocity structure beneath northeastern Tibet. The seismic tomography algorithm employs sparsity constrains on the wavelet representation velocity model via the L1-norm regularization. This algorithm can efficiently deal with the uneven-sampled volume, and give multiscale images of the model. Our preliminary results can be summarized as follows: 1) in the upper mantle down to 200km, significate low-velocity anomalies exist beneath the northeastern Tibet, and slight high-velocity anomalies beneath the Qaidam basin; 2) under Gobi-Alashan, Yangzi, and Ordos, high-velocity anomalies appear to extend to a depth of 250km, this high-velocity may correspond to the lithosphere; 3) there exist relative high-velocity anomalies at depth of 250km-350km underneath north Tibet, which suggests lithospheric delamination; 4) the strong velocity contrast between north Tibet and Yangzi, Gabi-Alashan is visible down to 200km, which implies the north Tibet boundary.

Proximity to natural gas wells and reported health status: results of a household survey in Washington County, Pennsylvania.

PubMed

Rabinowitz, Peter M; Slizovskiy, Ilya B; Lamers, Vanessa; Trufan, Sally J; Holford, Theodore R; Dziura, James D; Peduzzi, Peter N; Kane, Michael J; Reif, John S; Weiss, Theresa R; Stowe, Meredith H

2015-01-01

Little is known about the environmental and public health impact of unconventional natural gas extraction activities, including hydraulic fracturing, that occur near residential areas. Our aim was to assess the relationship between household proximity to natural gas wells and reported health symptoms. We conducted a hypothesis-generating health symptom survey of 492 persons in 180 randomly selected households with ground-fed wells in an area of active natural gas drilling. Gas well proximity for each household was compared with the prevalence and frequency of reported dermal, respiratory, gastrointestinal, cardiovascular, and neurological symptoms. The number of reported health symptoms per person was higher among residents living < 1 km (mean ± SD, 3.27 ± 3.72) compared with > 2 km from the nearest gas well (mean ± SD, 1.60 ± 2.14; p = 0.0002). In a model that adjusted for age, sex, household education, smoking, awareness of environmental risk, work type, and animals in house, reported skin conditions were more common in households < 1 km compared with > 2 km from the nearest gas well (odds ratio = 4.1; 95% CI: 1.4, 12.3; p = 0.01). Upper respiratory symptoms were also more frequently reported in persons living in households < 1 km from gas wells (39%) compared with households 1-2 km or > 2 km from the nearest well (31 and 18%, respectively) (p = 0.004). No equivalent correlation was found between well proximity and other reported groups of respiratory, neurological, cardiovascular, or gastrointestinal conditions. Although these results should be viewed as hypothesis generating, and the population studied was limited to households with a ground-fed water supply, proximity of natural gas wells may be associated with the prevalence of health symptoms including dermal and respiratory conditions in residents living near natural gas extraction activities. Further study of these associations, including the role of specific air and water exposures, is warranted.

Retrieval of O2(1Σ) and O2(1Δ) volume emission rates in the mesosphere and lower thermosphere using SCIAMACHY MLT limb scans

NASA Astrophysics Data System (ADS)

Zarboo, Amirmahdi; Bender, Stefan; Burrows, John P.; Orphal, Johannes; Sinnhuber, Miriam

2018-01-01

We present the retrieved volume emission rates (VERs) from the airglow of both the daytime and twilight O2(1Σ) band and O2(1Δ) band emissions in the mesosphere and lower thermosphere (MLT). The SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) onboard the European Space Agency Envisat satellite observes upwelling radiances in limb-viewing geometry during its special MLT mode over the range 50-150 km. In this study we use the limb observations in the visible (595-811 nm) and near-infrared (1200-1360 nm) bands. We have investigated the daily mean latitudinal distributions and the time series of the retrieved VER in the altitude range from 53 to 149 km. The maximal observed VERs of O2(1Δ) during daytime are typically 1 to 2 orders of magnitude larger than those of O2(1Σ). The latter peaks at around 90 km, whereas the O2(1Δ) emissivity decreases with altitude, with the largest values at the lower edge of the observations (about 53 km). The VER values in the upper mesosphere (above 80 km) are found to depend on the position of the sun, with pronounced high values occurring during summer for O2(1Δ). O2(1Σ) emissions show additional high values at polar latitudes during winter and spring. These additional high values are presumably related to the downwelling of atomic oxygen after large sudden stratospheric warmings (SSWs). Accurate measurements of the O2(1Σ) and O2(1Δ) airglow, provided that the mechanism of their production is understood, yield valuable information about both the chemistry and dynamics in the MLT. For example, they can be used to infer the amounts and distribution of ozone, solar heating rates, and temperature in the MLT.

Chemical Composition of African Biomass Burning Aerosols Over the Southeast Atlantic: Aerosol Mass Spectrometer Results from the 2016 and 2017 ORACLES Field Campaigns.

NASA Astrophysics Data System (ADS)

Dobracki, A. N.; Howell, S. G.; Freitag, S.; Smirnow, N.; Podolske, J. R.

2017-12-01

Biomass burning (BB) is one of the largest contributors of anthropogenic aerosols in the atmosphere. During BB events, organic and inorganic gases and particles are emitted into the atmosphere. Because of their abundance, particle size, and radiative properties, BB aerosols play an important role in global climate. Southern Africa produces 30% of the Earth's BB aerosol particles. Organics, Nitrates, sulfates, and refractory black carbon, along with other chemical species are lofted into the free troposphere and transported over the Southeast Atlantic Ocean. However, considerate uncertainty remains in the chemical composition of these plumes with its large variety of organic and inorganic species. As part of the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) 2016 and 2017 airborne field campaigns, an Aerosol Mass Spectrometer (AMS) was used to sample the chemical composition and chemical structure of the aerosol in this region. Results show constant vertical stratification within the plume over the course of the campaign (August 2017 / September 2016). Using nitrate (NO3) and organic carbon (OC) as two tracers, the structure of the September 2016 plume had a ratio of 1:8 (NO3:OC) in the upper plume (3km-5km), while the lower plume (1km-2.5km) had a ratio of 1:12 (NO3:OC). AMS measurements were supported by carbon monoxide (CO) and carbon dioxide (CO2) measurements. This data revealed a modified combustion efficiency (MCE= ΔCO2/ΔCO2 + ΔCO) of <0.97 in the upper plume, and a higher MCE > 0.97 in the lower plume. An MCE above 0.9 represents efficient burning processes. Additionally, concentrations of C2(H2O)2 (m/z60), a common chemical fragment from breaking up carbohydrates (primarily levoglucosan) emitted by burning biomass only represented <1% of total organics throughout the campaign. These low concentrations are due to efficient combustion rather than oxidation during transport. These results are consistent with earlier studies of efficient fires.

Postglacial volcanic deposits at Glacier Peak, Washington, and potential hazards from future eruptions; a preliminary report

USGS Publications Warehouse

Beget, J.E.

1982-01-01

Eruptions and other geologic events at Glacier Peak volcano in northern Washington have repeatedly affected areas near the volcano as well as areas far downwind and downstream. This report describes the evidence of this activity preserved in deposits on the west and east flanks of the volcano. On the west side of Glacier Peak the oldest postglacial deposit is a large, clayey mudflow which traveled at least 35 km down the White Chuck River valley sometime after 14,000 years ago. Subsequent large explosive eruptions produced lahars and at least 10 pyroclastic-flow deposits, including a semiwelded vitric tuff in the White Chuck River valley. These deposits, known collectively as the White Chuck assemblage, form a valley fill which is locally preserved as far as 100 km downstream from the volcano in the Stillaguamish River valley. At least some of the assemblage is about 11,670-11,500 radiocarbon years old. A small clayey lahar, containing reworked blocks of the vitric tuff, subsequently traveled at least 15 km down the White Chuck River. This lahar is overlain by lake sediments containing charred wood which is about 5,500 years old. A 150-m-thick assemblage of pyroclastic-flow deposits and lahars, called the Kennedy Creek assemblage, is in part about 5,500-5,100 radiocarbon years old. Lithic lahars from this assemblage extend at least 100 km downstream in the Skagit River drainage. The younger lahar assemblages, each containing at least three lahars and reaching at least 18 km downstream from Glacier Peak in the White Chuck River valley, are about 2,800 and 1,800 years old, respectively. These are postdated by a lahar containing abundant oxyhornblende dacite, which extends at least 30 km to the Sauk River. A still younger lahar assemblage that contains at least five lahars, and that also extends at least 30 km to the Sauk River, is older than a mature forest growing on its surface. At least one lahar and a flood deposit form a low terrace at the confluence of the White Chuck and Sauk Rivers, and were deposited before 300 years ago, but more recently than about 1,800 years ago. Several small outburst floods, including one in 1975, have affected Kennedy and Baekos Creek and the upper White Chuck River in the last hundred years. East of Glacier Peak the oldest postglacial deposits consist of ash-cloud deposits that underlie tephra erupted by Glacier Peak between 12,750 and 11,250 radiocarbon years ago. Although pyroclastic-flow deposits correlative with the ash-cloud deposits have not been recognized, late Pleistocene pumiceous lahars extend at least 50 km downstream in the Suiattle River valley. A younger clayey mudflow extends at least 6 km down Dusty Creek. This lahar is overlain by deposits of lithic pyroclastic flows and lahars that form the Dusty assemblage. This assemblage is at least 300 m thick in the upper valleys of Dusty and Chocolate Creeks, and contains more than 10 km3 of lithic debris. Lahars derived from the Dusty assemblage extend at least 100 km down the Skagit River valley from Glacier Peak. This assemblage is younger than tephra layer 0 from Mount Mazama, and older than tephra layer Yn from Mount St. Helens, and thus was formed between about 7,000 and 3,400 years ago. The Dusty assemblage may have been formed at the same time as the Kennedy Creek assemblage. A 100-m-thick assemblage of pyroclastic flows and lahars preserved in the Chocolate Creek valley is about 1,800 radiocarbon years old. A clayey lahar in the upper Chocolate Creek valley extended at least 2 km downvalley after 1,800 years ago, but before pyroclastic flows and lahars were deposited in upper Chocolate Creek 1,100 radiocarbon years ago. Several clayey lahars in the Dusty Creek valley east of Glacier Peak are also about 1,100 years old. A lahar in the valley of Dusty Creek, which contains rare prismatically jointed blocks of vesiculated dacite, and a white ash that is locally as much as 50 cm thick may be the products of small

Old groundwater in parts of the upper Patapsco aquifer, Atlantic Coastal Plain, Maryland, USA: Evidence from radiocarbon, chlorine-36 and helium-4

USGS Publications Warehouse

Plummer, Niel; Eggleston, John R.; Raffensperger, Jeff P.; Hunt, Andrew G.; Casile, Gerolamo C.; Andreasen, D.C.

2012-01-01

Apparent groundwater ages along two flow paths in the upper Patapsco aquifer of the Maryland Atlantic Coastal Plain, USA, were estimated using 14C, 36Cl and 4He data. Most of the ages range from modern to about 500 ka, with one sample at 117 km downgradient from the recharge area dated by radiogenic 4He accumulation at more than one Ma. Last glacial maximum (LGM) water was located about 20 km downgradient on the northern flow path, where the radiocarbon age was 21.5 ka, paleorecharge temperatures were 0.5–1.5  °C (a maximum cooling of about 12 °C relative to the modern mean annual temperature of 13 °C), and Cl–, Cl/Br, and stable isotopes of water were minimum. Low recharge temperatures (typically 5–7 °C) indicate that recharge occurred predominantly during glacial periods when coastal heads were lowest due to low sea-level stand. Flow velocities averaged about 1.0 m a–1 in upgradient parts of the upper Patapsco aquifer and decreased from 0.13 to 0.04 m a–1 at 40 and 80 km further downgradient, respectively. This study demonstrates that most water in the upper Patapsco aquifer is non-renewable on human timescales under natural gradients, thus highlighting the importance of effective water-supply management to prolong the resource.

Earth's crust model of the South-Okhotsk Basin by wide-angle OBS data

NASA Astrophysics Data System (ADS)

Kashubin, Sergey N.; Petrov, Oleg V.; Rybalka, Alexander V.; Milshtein, Evgenia D.; Shokalsky, Sergey P.; Verba, Mark L.; Petrov, Evgeniy O.

2017-07-01

Deep seismic studies of the Sea of Okhotsk region started in late 1950s. Since that time, wide-angle reflection and refraction data on more than two dozen profiles were acquired. Only five of those profiles either crossed or entered the deep-water area of the South-Okhotsk Basin (also known as the Kuril Basin or the South-Okhotsk Deep-Water Trough). Only P-waves were used to develop velocity-interface models in all the early research. Thus, all seismic and geodynamic models of the Okhotsk region were based only on the information on compressional waves. Nevertheless, the use of Vp/Vs ratio in addition to P-wave velocity allows discriminating felsic and mafic crustal layers with similar Vp values. In 2007 the Russian seismic service company Sevmorgeo acquired multi-component data with ocean bottom seismometers (OBS) along the 1700-km-long north-south 2-DV-M Profile. Only P-wave information was used previously to develop models for the entire profile. In this study, a multi-wave processing, analysis, and interpretation of the OBS data are presented for the 550-km-long southern segment of this Profile that crosses the deep-water South-Okhotsk Basin. Within this segment 50 seismometers were deployed with nominal OBS station spacing of 10-12 km. Shot point spacing was 250 m. Not only primary P-waves and S-waves but also multiples and P-S, S-P converted waves were analyzed in this study to constrain velocity-interface models by means of travel time forward modeling. In offshore deep seismic studies, thick water layer hinders an estimation of velocities in the sedimentary cover and in the upper consolidated crust. Primarily, this is due to the fact that refracted waves propagating in low-velocity solid upper layers interfere with high-amplitude direct water wave. However, in multi-component measurements with ocean bottom seismometers, it is possible to use converted and multiple waves for velocity estimations in these layers. Consequently, one can obtain P- and S-waves velocity models of the sedimentary strata and the upper consolidated crust. Velocity values in the upper consolidated crust beneath the South-Okhotsk Basin (Vp = 5.50-5.80 km/s, Vp/Vs = 1.74-1.76) allow interpretation of this 2.5-3.5-km-thick layer to be consistent with a felsic (granodioritic) crust. These results suggest that the Earth's crust in this region can be considered continental in nature, rather than previously accepted oceanic crust. Even though, the crust is thinned and stretched at this location.

Crust and uppermost-mantle structure of Greenland and the Northwest Atlantic from Rayleigh wave group velocity tomography

NASA Astrophysics Data System (ADS)

Darbyshire, Fiona A.; Dahl-Jensen, Trine; Larsen, Tine B.; Voss, Peter H.; Joyal, Guillaume

2018-03-01

The Greenland landmass preserves ˜4 billion years of tectonic history, but much of the continent is inaccessible to geological study due to the extensive inland ice cap. We map out, for the first time, the 3-D crustal structure of Greenland and the NW Atlantic ocean, using Rayleigh wave anisotropic group velocity tomography, in the period range 10-80 s, from regional earthquakes and the ongoing GLATIS/GLISN seismograph networks. 1-D inversion gives a pseudo-3-D model of shear wave velocity structure to depths of ˜100 km with a horizontal resolution of ˜200 km. Crustal thickness across mainland Greenland ranges from ˜25 km to over 50 km, and the velocity structure shows considerable heterogeneity. The large sedimentary basins on the continental shelf are clearly visible as low velocities in the upper ˜5-15 km. Within the upper continental basement, velocities are systematically lower in northern Greenland than in the south, and exhibit a broadly NW-SE trend. The thinning of the crust at the continental margins is also clearly imaged. Upper-mantle velocities show a clear distinction between typical fast cratonic lithosphere (Vs ≥4.6 km s-1) beneath Greenland and its NE margin and anomalously slow oceanic mantle (Vs ˜4.3-4.4 km s-1) beneath the NW Atlantic. We do not observe any sign of pervasive lithospheric modification across Greenland in the regions associated with the presumed Iceland hotspot track, though the average crustal velocity in this region is higher than that of areas to the north and south. Crustal anisotropy beneath Greenland is strong and complex, likely reflecting numerous episodes of tectonic deformation. Beneath the North Atlantic and Baffin Bay, the dominant anisotropy directions are perpendicular to the active and extinct spreading centres. Anisotropy in the subcontinental lithosphere is weaker than that of the crust, but still significant, consistent with cratonic lithosphere worldwide.

Upper Lithospheric Sources of Magnetic and Gravity Anomalies of The Fennoscandian Shield

NASA Astrophysics Data System (ADS)

Korhonen, J. V.; Koistinen, T.; Working GroupFennoscandian Geophysical Maps

Magnetic total intensity anomalies (DGRF-65), Bouguer anomalies (d=2670 kg/m3) and geological units from 3400 Ma to present of the Fennoscandian Shield have been digitally compiled and printed as maps 1:2 000 000. Insert maps 1:15,000,000 com- pare anomaly components in different source scales: pseudogravimetric anomaly ver- sus Bouguer anomaly, DGRF-65 anomaly versus pseudomagnetic anomaly, magnetic vertical derivative versus second derivative of Bouguer anomaly. Data on bulk density, total magnetisation and lithology of samples have been presented as scatter diagrams and distribution maps of the average petrophysical properties in space and time. In sample level, the bulk density correlates with the lithology and, together with mag- netisation, establishes four principal populations of petrophysical properties. The av- erage properties, calculated for 5 km x 5 km cells, correlate only weakly with av- erage Bouguer-anomaly and magnetic anomaly, revealing major deep seated sources of anomalies. Pseudogravimetric and Bouguer anomalies correlate only locally with each other. The correlation is negative in the area of felsic Palaeoproterozoic rocks in W- and NW-parts of the Shield. In 2D models the sources of gravity anomalies are explained by lateral variation of density in upper and lower crust. Smoothly varying regional components are explained by boundaries of the lower crust, the upper mantle and the astenosphere. Magnetic anomalies are explained by lateral variation of magnetisation in the upper crust. Re- gional components are due to the lateral variation of magnetisation in the lower crust and the boundaries of lower crust and mantle and the Curie isotherm of magnetite.

Topography of the shield volcano, Olympus Mons on Mars

USGS Publications Warehouse

Wu, S.S.C.; Garcia, P.A.; Jordan, R.; Schafer, F.J.; Skiff, B.A.

1984-01-01

Olympus Mons, one of the largest known shield volcanoes in the Solar System, covers an area of >3.2 ?? 105 km2and has a diameter of >600 km, excluding its vast aureole deposits. The structure is five times larger than the largest shield volcano on the Earth. It is situated on the north-west flank of the Tharsis volcanic region, a broad topographic rise on the martian surface. The volcano has three physical subdivisions: the summit caldera, the terraced upper flanks, and the lower flanks, which terminate in a scarp 2-10 km high that nearly surrounds the structure. A large block of images of the Tharsis region, including Olympus Mons, was obtained by the Viking mission1. Here we present a topographic map of Olympus Mons, compiled using various combinations of stereo pairs of these images, together with stereoscopic perspective views generated by image processing techniques. ?? 1984 Nature Publishing Group.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lepage, A.

Despite scheduling complications caused by annual monsoons, the Yadana project to bring offshore Myanmar gas ashore and into neighboring Thailand has met it first-gas target of July 1, 1998. The Yadana field is a dry-gas reservoir in the reef upper Birman limestone formation t 1,260 m and a pressure of 174 bara (approximately 2,500 psi). It extends nearly 7 km (west to east) and 10 km (south to north). The water-saturated reservoir gas contains mostly methane mixed with CO{sub 2} and N{sub 2}. No production of condensate is anticipated. The Yadana field contains certified gas reserves of 5.7 tcf, calculatedmore » on the basis of 2D and 3D seismic data-acquisition campaigns and of seven appraisal wells. The paper discusses early interest, development sequences, offshore platforms, the gas-export pipeline, safety, environmental steps, and schedule constraints.« less

Premiers résultats du réseau sismique (CRLN) de la partie ouest du rift de Corinthe : évidence de la réactivation d'une ancienne faille

NASA Astrophysics Data System (ADS)

Lyon-Caen, Hélène; Papadimitriou, Panayotis; Deschamps, Anne; Bernard, Pascal; Makropoulos, Kostas; Pacchiani, Francesco; Patau, Geneviève

2004-03-01

The 12 stations Corinth Rift Laboratory Seismological Network (CRLNET) aims at monitoring the seismicity ( Ml>1) in the CRL area and at constraining the geometry of active structures at depth. Two years of microseismicity (2000-2001) recorded by the CRLNET in the Aigion area shows: (1) background seismicity inside the Corinth rift at depth of 4.5-11 km, deepening towards the north and no activity in the upper 4 km of the crust - this seismicity is not clearly related to major faults observed at the surface -; (2) a swarm, 6 km south of the city of Aigion, associated with the Mw=4.2, 8 April 2001 earthquake. This earthquake occurred at 6 km depth, on a SW-NE oriented fault dipping 40° to the northwest and corresponds to normal faulting with a right lateral component of slip. It likely occurred on an old structure reactivated in the present stress field. To cite this article: H. Lyon-Caen et al., C. R. Geoscience 336 (2004).

Cloud Condensation in Titan's Lower Stratosphere

NASA Technical Reports Server (NTRS)

Romani, Paul N.; Anderson, Carrie M.

2011-01-01

A 1-D condensation model is developed for the purpose of reproducing ice clouds in Titan's lower stratosphere observed by the Composite Infrared Spectrometer (CIRS) onboard Cassini. Hydrogen cyanide (HCN), cyanoacetylene (HC3N), and ethane (C2H6) vapors are treated as chemically inert gas species that flow from an upper boundary at 500 km to a condensation sink near Titan's tropopause (-45 km). Gas vertical profiles are determined from eddy mixing and a downward flux at the upper boundary. The condensation sink is based upon diffusive growth of the cloud particles and is proportional to the degree of supersaturation in the cloud formation regIOn. Observations of the vapor phase abundances above the condensation levels and the locations and properties of the ice clouds provide constraints on the free parameters in the model. Vapor phase abundances are determined from CIRS mid-IR observations, whereas cloud particle sizes, altitudes, and latitudinal distributions are derived from analyses of CIRS far-IR observations of Titan. Specific cloud constraints include: I) mean particle radii of2-3 J.lm inferred from the V6 506 cm- band of HC3N, 2) latitudinal abundance distributions of condensed nitriles, inferred from a composite emission feature that peaks at 160/cm , and 3) a possible hydrocarbon cloud layer at high latitudes, located near an altitude of 60 km, which peaks between 60 and 80 cm l . Nitrile abundances appear to diminish substantially at high northern latitudes over the time period 2005 to 2010 (northern mid winter to early spring). Use of multiple gas species provides a consistency check on the eddy mixing coefficient profile. The flux at the upper boundary is the net column chemical production from the upper atmosphere and provides a constraint on chemical pathways leading to the production of these compounds. Comparison of the differing lifetimes, vapor phase transport, vapor phase loss rate, and particle sedimentation, sheds light on temporal stability of the clouds.

Integrated seismic model of the crust and upper mantle of the Trans-European Suture zone between the Precambrian craton and Phanerozoic terranes in Central Europe

NASA Astrophysics Data System (ADS)

Wilde-Piórko, Monika; Świeczak, Marzena; Grad, Marek; Majdański, Mariusz

2010-01-01

The structure and evolution of the Trans-European Suture zone (TESZ), contact between Precambrian Europe to the northeast and Phanerozoic terranes to the southwest is one of the main tectonic questions in Europe. The knowledge of the crustal structure, lithosphere-asthenosphere boundary and mantle transition zone between two seismic discontinuities at depths "410" and "660" km, is one of the most important issues to understand the Earth's dynamics. To create a mantle model of the TESZ and surroundings we used different seismic data collected along the 950 km long POLONAISE'97 profile P4. Previous results of 2-D ray-tracing and P-wave travel time modelling and new results of P-wave travel time residuals methods and receiver function sections provide facts about the seismic structure from the surface down to 900 km depth. In the TESZ a large basin, about 125 km wide, is filled with sedimentary strata (Vp < 6.0 km s - 1 ) to about 20 km depth. This basin is asymmetric with its northeast margin being most abrupt. The crystalline crust under this basin is only about 20 km thick today indicating that the lithosphere of Baltica was either thinned drastically or terminated along the northeast margin of the basin. The East European craton (EEC) has a ~ 45 km thick three-layered crust. The crust of the accreted terranes to the southwest is relatively thin (~ 30 km) and similar to that found in other non-cratonal areas of Western Europe. The lower crust is relatively fast (Vp > 7.0 km s - 1 ) along most of the P4 profile. However, lower values to the southwest may indicate the termination of Baltica. High velocity (~ 8.35 km s - 1 ) uppermost mantle lies beneath the Avalonia/Variscan terranes, and may be due to rifting and/or subduction. The seismic lithosphere thickness for the EEC is about 200 km, while it is only 90 km in the Palaeozoic platform (PP). The mantle transition zone is shallower and about 30 km thicker under the EEC, which could be due to thermal conditions (lower temperature) and/or the presence of water and FeO. The result of this paper is a new compiled and integrated seismic velocity model, available in digital form down to 900 km depth ( http://www.igf.fuw.edu.pl/p4-mantle), which can be used as a preliminary model of the crust and upper mantle in the TESZ area in Central Europe.

Three-dimensional structure across the Tintina strike-slip fault, northern Canadian Cordillera, from seismic refraction and reflection tomography

NASA Astrophysics Data System (ADS)

Zelt, Colin A.; Ellis, Robert M.; Zelt, Barry C.

2006-12-01

The development of the northern Canadian Cordillera involved major strike-slip displacement of accreted terranes relative to North America along faults such as the Tintina, which has experienced ~425 km of dextral motion since the Palaeocene. The SNORE seismic refraction/wide-angle reflection experiment was carried out in 1997 as one component of Lithoprobe's Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) transect. In addition to four 2-D profiles, two sets of broadside recordings were acquired to image the 3-D structure across the Tintina fault (TF) in areas centred at about 59.5°N and 62°N. Simultaneous and independent refraction and reflection traveltime tomography were applied to the combined inline and broadside data set for each region to establish the range of lower crustal velocity, Moho depth and upper mantle velocity structure consistent with the data. Our preferred models are the average of the simultaneous and independent models since they represent the robust features required by the data. The preferred 3-D models are generally consistent with the 2-D models obtained from the inline data in previous independent studies. There are along-strike variations across the TF, perhaps due to the change in strike direction or the amount of motion along the fault in the north compared to the south. In the lower crust, the only correlation with the TF that is required by the data is a 0.1 km s-1 drop in velocity to the southwest of the fault in the northern study area. The absence of a strong correlation with the TF in the lower crust is consistent with the interpreted continuity of lower crustal units across the fault in the SNORCLE reflection data. The Moho is relatively flat throughout the study area, 34-35 km depth, but there is broad crustal thickening of a few kilometres centred ~50 km southwest of the TF in the northern and southern study areas. This thickening may be the result of a period when there was a component of compression along the TF. There is strong evidence for a 0.3-0.4 km s-1 drop in upper mantle velocity to the west of the TF in the south, and weak evidence for ~0.1 km s-1 drop to the southwest in the north. The upper mantle variations in the south indicate that the TF is the boundary between cooler and/or more refractory ancestral North American mantle to the east and warmer and/or more fertile mantle beneath accreted North America to the west. In the north, the mantle appears to be more intermediate in its properties on both sides of the TF.

Near-infrared oxygen airglow from the Venus nightside

NASA Technical Reports Server (NTRS)

Crisp, D.; Meadows, V. S.; Allen, D. A.; Bezard, B.; Debergh, C.; Maillard, J.-P.

1992-01-01

Groundbased imaging and spectroscopic observations of Venus reveal intense near-infrared oxygen airglow emission from the upper atmosphere and provide new constraints on the oxygen photochemistry and dynamics near the mesopause (approximately 100 km). Atomic oxygen is produced by the Photolysis of CO2 on the dayside of Venus. These atoms are transported by the general circulation, and eventually recombine to form molecular oxygen. Because this recombination reaction is exothermic, many of these molecules are created in an excited state known as O2(delta-1). The airglow is produced as these molecules emit a photon and return to their ground state. New imaging and spectroscopic observations acquired during the summer and fall of 1991 show unexpected spatial and temporal variations in the O2(delta-1) airglow. The implications of these observations for the composition and general circulation of the upper venusian atmosphere are not yet understood but they provide important new constraints on comprehensive dynamical and chemical models of the upper mesosphere and lower thermosphere of Venus.

The response of middle atmospheric ozone to solar UV irradiance variations with a period of 27 days

NASA Technical Reports Server (NTRS)

Chen, LI; Brasseur, Guy; London, Julius

1994-01-01

A one-dimensional photochemical-dynamical-radiative time-dependent model was used to study the response of middle atmospheric temperature and ozone to solar UV irradiance variations with the period of 27 days. The model solar UV O(x), HO(x), NO(x), and CIO(x)families and modeled solar UV variations. The amplitude of the primary temperature response to the solar UV variation is plus 0.4 K at 85-90 km with a phase lag of about 6 days. A secondary maximum response of plus 0.3 K at 45-50 km appears with a phase lag of 1 day. There is a maximum positive ozone response to the 27-day solar UV oscillation of 2.5 percent at 80-90 km with a phase lag of about 10 days after the solar irradiance maximum. At 70 km the ozone response is about 1.2 percent and is out of phase with the solar variation. In the upper stratosphere (40-50 km) the relative ozone variation is small, about 0.2 percent to 0.3 percent, and there is a negative phase of about 4 days between the ozone and solar oscillations. These oscillations are in phase in the middle stratosphere (35-40 km) where there is again a maximum relative response of about 0.6 percent. The reasons for these ozone amplitude and phase variations are discussed.

Comparison of the USGS 2001 NLCD to the 2002 USDA Census of Agriculture for the Upper Midwest United States

USGS Publications Warehouse

Maxwell, S.K.; Wood, E.C.; Janus, A.

2008-01-01

The U.S. Geological Survey (USGS) 2001 National Land Cover Database (NLCD) was compared to the U.S. Department of Agriculture (USDA) 2002 Census of Agriculture. We compared areal estimates for cropland at the state and county level for 14 States in the Upper Midwest region of the United States. Absolute differences between the NLCD and Census cropland areal estimates at the state level ranged from 1.3% (Minnesota) to 37.0% (Wisconsin). The majority of counties (74.5%) had differences of less than 100 km2. 7.2% of the counties had differences of more than 200 km2. Regions where the largest areal differences occurred were in southern Illinois, North Dakota, South Dakota, and Wisconsin, and generally occurred in areas with the lowest proportions of cropland (i.e., dominated by forest or grassland). Before using the 2001 NLCD for agricultural applications, such as mapping of specific crop types, users should be aware of the potential for misclassification errors, especially where the proportion of cropland to other land cover types is fairly low.

No influence of ischemic preconditioning on running economy.

PubMed

Kaur, Gungeet; Binger, Megan; Evans, Claire; Trachte, Tiffany; Van Guilder, Gary P

2017-02-01

Many of the potential performance-enhancing properties of ischemic preconditioning suggest that the oxygen cost for a given endurance exercise workload will be reduced, thereby improving the economy of locomotion. The aim of this study was to identify whether ischemic preconditioning improves exercise economy in recreational runners. A randomized sham-controlled crossover study was employed in which 18 adults (age 27 ± 7 years; BMI 24.6 ± 3 kg/m 2 ) completed two, incremental submaximal (65-85% VO 2max ) treadmill running protocols (3 × 5 min stages from 7.2-14.5 km/h) coupled with indirect calorimetry to assess running economy following ischemic preconditioning (3 × 5 min bilateral upper thigh ischemia) and sham control. Running economy was expressed as mlO 2 /kg/km and as the energy in kilocalories required to cover 1 km of horizontal distance (kcal/kg/km). Ischemic preconditioning did not influence steady-state heart rate, oxygen consumption, minute ventilation, respiratory exchange ratio, energy expenditure, and blood lactate. Likewise, running economy was similar (P = 0.647) between the sham (from 201.6 ± 17.7 to 204.0 ± 16.1 mlO 2 /kg/km) and ischemic preconditioning trials (from 202.8 ± 16.2 to 203.1 ± 15.6 mlO 2 /kg/km). There was no influence (P = 0.21) of ischemic preconditioning on running economy expressed as the caloric unit cost (from 0.96 ± 0.12 to 1.01 ± 0.11 kcal/kg/km) compared with sham (from 1.00 ± 0.10 to 1.00 ± 0.08 kcal/kg/km). The properties of ischemic preconditioning thought to affect exercise performance at vigorous to severe exercise intensities, which generate more extensive physiological challenge, are ineffective at submaximal workloads and, therefore, do not change running economy.

Planar covariance of upper and lower limb elevation angles during hand-foot crawling in healthy young adults.

PubMed

MacLellan, M J; Catavitello, G; Ivanenko, Y P; Lacquaniti, F

2017-11-01

Habitual quadrupeds have been shown to display a planar covariance of segment elevation angle waveforms in the fore and hind limbs during many forms of locomotion. The purpose of the current study was to determine if humans generate similar patterns in the upper and lower limbs during hand-foot crawling. Nine healthy young adults performed hand-foot crawling on a treadmill at speeds of 1, 2, and 3 km/h. A principal component analysis (PCA) was applied to the segment elevation angle waveforms for the upper (upper arm, lower arm, and hand) and lower (thigh, shank, and foot) limbs separately. The planarity of the elevation angle waveforms was determined using the sum of the variance explained by the first two PCs and the orientation of the covariance plane was quantified using the direction cosines of the eigenvector orthogonal to the plane, projected upon each of the segmental semi-axes. Results showed that planarity of segment elevation angles was maintained in the upper and lower limbs (explained variance >97%), although a slight decrease was present in the upper limb when crawling at 3 km/h. The orientation of the covariance plane was highly limb-specific, consistent with animal studies and possibly related to the functional neural control differences between the upper and lower limbs. These results may suggest that the motor patterns stored in the central nervous system for quadrupedal locomotion may be retained through evolution and may still be exploited when humans perform such tasks.

Limits on modes of lithospheric heat transport on Venus from impact crater density

NASA Technical Reports Server (NTRS)

Grimm, Robert E.; Solomon, Sean C.

1987-01-01

Based on the observed density of impact craters on the Venus surface obtained from Venera 15-16 radar images, a formalism to estimate the upper bounds on the contributions made to lithospheric heat transport by volcanism and lithospheric recycling is presented. The Venera 15-16 data, if representative of the entire planet, limit the average rate of volcanic resurfacing on Venus to less than 2 cu km/yr (corresponding to less than 1 percent of the global heat loss), and limit the rate of lithospheric recycling to less than 1.5 sq km/yr (and probably to less than 0.5 sq km/yr), corresponding to 25 percent (and to 9 percent) of the global heat loss. The present results indicate that heat loss at lithospheric levels in Venus is dominated by conduction.

Upper mantle beneath foothills of the western Himalaya: subducted lithospheric slab or a keel of the Indian shield?

NASA Astrophysics Data System (ADS)

Vinnik, L.; Singh, A.; Kiselev, S.; Kumar, M. Ravi

2007-12-01

The fate of the mantle lithosphere of the Indian Plate in the India-Eurasia collision zone is not well understood. Tomographic studies reveal high P velocity in the uppermost mantle to the south of the western Himalaya, and these high velocities are sometimes interpreted as an image of subducting Indian lithosphere. We suggest that these high velocities are unrelated to the ongoing subduction but correspond to a near-horizontal mantle keel of the Indian shield. In the south of the Indian shield upper-mantle velocities are anomalously low, and relatively high velocities may signify a recovery of the normal shield structure in the north. Our analysis is based on the recordings of seismograph station NIL in the foothills of the western Himalaya. The T component of the P receiver functions is weak relative to the Q component, which is indicative of a subhorizontally layered structure. Joint inversion of the P and S receiver functions favours high uppermost mantle velocities, typical of the lithosphere of Archean cratons. The arrival of the Ps converted phase from 410 km discontinuity at NIL is 2.2 s earlier than in IASP91 global model. This can be an effect of remnants of Tethys subduction in the mantle transition zone and of high velocities in the keel of the Indian shield. Joint inversion of SKS particle motions and P receiver functions reveals a change in the fast direction of seismic azimuthal anisotropy from 60° at 80-160 km depths to 150° at 160-220 km. The fast direction in the lower layer is parallel to the trend of the Himalaya. The change of deformation regimes at a depth of 160 km suggests that this is the base of the lithosphere of the Indian shield. A similar boundary was found with similar techniques in central Europe and the Tien Shan region, but the base of the lithosphere in these regions is relatively shallow, in agreement with the higher upper-mantle temperatures. The ongoing continental collision is expressed in crustal structure: the crust beneath NIL is very thick (58 +/- 2 km), and the S velocity in the intermediate and lower crust is around 4.0 km s-1. This anomalously large velocity and thickness can be explained by scraping off the lower crust, when the Indian lithosphere underthrusts the Himalaya.

Composition and thermal profiles of the Jovian upper atmosphere determined by the Voyager ultraviolet stellar occultation experiment

NASA Technical Reports Server (NTRS)

Festou, M. C.; Atreya, S. K.; Donahue, T. M.; Sandel, B. R.; Shemansky, D. E.; Broadfoot, A. L.

1981-01-01

During the occultation of the star Regulus (B7 type) by Jupiter as seen from the Voyager 2 spacecraft on July 9, 1979, two absorbing regions were detected. Between 911 and 1200 A, H2 was absorbing over a 600 km altitude range. Above 1300 A, the rapid increase of the absorption by the hydrocarbons was observed over an altitude interval of approximately 100 km with a height resolution of 3 km. The analysis of these absorption features has provided the height profiles of molecular hydrogen, methane, ethane, and acetylene, as well as the thermal profile in the upper atmosphere of Jupiter. Combining the Voyager ultraviolet spectrometer results with other data, such as those obtained by the Voyager infrared and radioscience instruments, has yielded a comprehensive model of the composition and structure of the atmosphere of Jupiter.

Geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings: The Tyrrhenian Sea and surroundings

NASA Astrophysics Data System (ADS)

Panza, G. F.; Peccerillo, A.; Aoudia, A.; Farina, B.

2007-01-01

Information on the physical and chemical properties of the lithosphere-asthenosphere system (LAS) can be obtained by geophysical investigation and by studies of petrology-geochemistry of magmatic rocks and entrained xenoliths. Integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism, such as in the Tyrrhenian Sea and surroundings. A thin crust, less than 10 km, overlying a soft mantle (where partial melting can reach about 10%) is observed for Magnaghi, Vavilov and Marsili, which belong to the Central Tyrrhenian Sea backarc volcanism where subalkaline rocks dominate. Similar characteristics are seen for the uppermost crust of Ischia. A crust about 20 km thick is observed for the majority of the continental volcanoes, including Amiata-Vulsini, Roccamonfina, Phlegraean Fields-Vesuvius, Vulture, Stromboli, Vulcano-Lipari, Etna and Ustica. A thicker crust is present at Albani - about 25 km - and at Cimino-Vico-Sabatini — about 30 km. The structure of the upper mantle, in contrast, shows striking differences among various volcanic provinces. Volcanoes of the Roman region (Vulsini-Sabatini-Alban Hills) sit over an upper mantle characterised by Vs mostly ranging from about 4.2 to 4.4 km/s. At the Alban Hills, however, slightly lower Vs values of about 4.1 km/s are detected between 60 and 120 km of depth. This parallels the similar and rather homogeneous compositional features of the Roman volcanoes, whereas the lower Vs values detected at the Alban Hills may reflect the occurrence of small amounts of melts within the mantle, in agreement with the younger age of this volcano. The axial zone of the Apennines, where ultrapotassic kamafugitic volcanoes are present, has a mantle structure with high-velocity lid ( Vs ˜ 4.5 km/s) occurring at the base of a 40-km-thick crust. Beneath the Campanian volcanoes of Vesuvius and Phlegraean Fields, the mantle structure shows a rigid body dipping westward, a feature that continues southward, up to the eastern Aeolian arc. In contrast, at Ischia the upper mantle contains a shallow low-velocity layer ( Vs = 3.5-4.0 km/s) just beneath a thin but complex crust. The western Aeolian arc and Ustica sit over an upper mantle with Vs ˜ 4.2-4.4 km/s, although a rigid layer ( Vs = 4.55 km/s) from about 80 to 150 km occurs beneath the western Aeolian arc. In Sardinia, no significant differences in the LAS structure are detected from north to south. The petrological-geochemical signatures of Italian volcanoes show strong variations that allow us to distinguish several magmatic provinces. These often coincide with mantle sectors identified by Vs tomography. For instance, the Roman volcanoes show remarkable similar petrological and geochemical characteristics, mirroring similar structure of the LAS. The structure and geochemical-isotopic composition of the upper mantle change significantly when we move to the Stromboli-Campanian volcanoes. The geochemical signatures of Ischia and Procida volcanoes are similar to other Campanian centres, but Sr-Pb isotopic ratios are lower marking a transition to the backarc mantle of the Central Tyrrhenian Sea. The structural variations from Stromboli to the central (Vulcano and Lipari) and western Aeolian arc are accompanied by strong variations of geochemical signatures, such as a decrease of Sr-isotope ratios and an increase of Nd-, Pb-isotope and LILE/HFSE ratios. The dominance of mafic subalkaline magmatism in the Tyrrhenian Sea basin denotes large degrees of partial melting, well in agreement with the soft characteristics of the uppermost mantle in this area. In contrast, striking isotopic differences of Plio-Quaternary volcanic rocks from southern to northern Sardinia does not find a match in the LAS geophysical characteristics. The combination of petrological and geophysical constraints allows us to propose a 3D schematic geodynamic model of the Tyrrhenian basin and bordering volcanic areas, including the subduction of the Ionian-Adria lithosphere in the southern Tyrrhenian Sea, and to place constraints on the geodynamic evolution of the whole region.

Inertio Gravity Waves in the Upper Mesosphere

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Mengel, J. G.; Talaat, E. L.; Porter, H. S.; Chan, K. L.

2003-01-01

In the polar region of the upper mesosphere, horizontal wind oscillations have been observed with periods around 10 hours (Hernandez et al., 1992). Such waves are generated in our Numerical Spectral Model (NSM) and appear to be inertio gravity waves (IGW). Like the planetary waves (PW) in the model, the IGWs are generated by instabilities that arise in the mean zonal circulation. In addition to stationary waves for m = 0, eastward and westward propagating waves for m = 1 to 4 appear above 70 km that grow in magnitude up to about 110 km, having periods between 9 and 11 hours. The m = 1 westward propagating IGWs have the largest amplitudes, which can reach at the poles 30 m/s. Like PWs, the IGWs are intermittent but reveal systematic seasonal variations, with the largest amplitudes occurring generally in winter and spring. The IGWs propagate upward with a vertical wavelength of about 20 km.

Validity of Lactate Thresholds in Inline Speed Skating.

PubMed

Hecksteden, Anne; Heinze, Tobias; Faude, Oliver; Kindermann, Wilfried; Meyer, Tim

2015-09-01

Lactate thresholds are commonly used as estimates of the highest workload where lactate production and elimination are in equilibrium (maximum lactate steady state [MLSS]). However, because of the high static load on propulsive muscles, lactate kinetics in inline speed skating may differ significantly from other endurance exercise modes. Therefore, the discipline-specific validity of lactate thresholds has to be verified. Sixteen competitive inline-speed skaters (age: 30 ± 10 years; training per week: 10 ± 4 hours) completed an exhaustive stepwise incremental exercise test (start 24 km·h, step duration 3 minutes, increment 2 km·h) to determine individual anaerobic threshold (IAT) and the workload corresponding to a blood lactate concentration of 4 mmol·L (LT4) and 2-5 continuous load tests of (up to) 30 minutes to determine MLSS. The IAT and LT4 correlated significantly with MLSS, and the mean differences were almost negligible (MLSS 29.5 ± 2.5 km·h; IAT 29.2 ± 2.0 km·h; LT4 29.6 ± 2.3 km·h; p > 0.1 for all differences). However, the variability of differences was considerable resulting in 95% limits of agreement in the upper range of values known from other endurance disciplines (2.6 km·h [8.8%] for IAT and 3.1 km·h [10.3%] for LT4). Consequently, IAT and LT4 may be considered as valid estimates of the MLSS in inline speed skating, but verification by means of a constant load test should be considered in cases of doubt or when optimal accuracy is needed (e.g., in elite athletes or scientific studies).

Validation of UARS Microwave Limb Sounder 183 GHz H2O Measurements

NASA Technical Reports Server (NTRS)

Lahoz, W. A.; Suttie, M. R.; Froidevaux, L.; Harwood, R. S.; Lau, C. L.; Lungu, T. A.; Peckham, G. E.; Pumphrey, H. C.; Read, W. G.; Shippony, Z.;

Structure of the California Coast Ranges and San Andreas Fault at SAFOD from seismic waveform inversion and reflection imaging

USGS Publications Warehouse

Bleibinhaus, F.; Hole, J.A.; Ryberg, T.; Fuis, G.S.

2007-01-01

A seismic reflection and refraction survey across the San Andreas Fault (SAF) near Parkfield provides a detailed characterization of crustal structure across the location of the San Andreas Fault Observatory at Depth (SAFOD). Steep-dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the SAF. The resulting velocity model constrains the top of the Salinian granite with great detail. Steep-dip reflection seismic images show several strong-amplitude vertical reflectors in the uppermost crust near SAFOD that define an ???2-km-wide zone comprising the main SAF and two or more local faults. Another prominent subvertical reflector at 2-4 km depth ???9 km to the northeast of the SAF marks the boundary between the Franciscan terrane and the Great Valley Sequence. A deep seismic section of low resolution shows several reflectors in the Salinian crust west of the SAF. Two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along-strike of the SAF. They represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust. The deepest reflections from ???25 km depth are interpreted as crust-mantle boundary. Copyright 2007 by the American Geophysical Union.

Winds and Waves (4 Min - 11 Yrs) in the Upper Middle Atmosphere (60-110 Km) at Saskatoon, Canada (52 Deg N, 107 Deg W): MF Radar (2.2 Mhz) Soundings 1973 - 1983

NASA Technical Reports Server (NTRS)

Manson, A. H.; Meek, C. E.; Gregory, J. B.

1984-01-01

Examples of gravity waves (GW), tides, planetary waves (PW), and circulation effects in the upper middle atmosphere are presented. Energy densities of GW, tides, and PW are compared. Fourier and spectral analyses are applied to the data.

Spatiotemporal evolution of magmatic pulses and regional metamorphism during a Cretaceous flare-up event: Constraints from the Ryoke belt (Mikawa area, central Japan)

NASA Astrophysics Data System (ADS)

Takatsuka, Kota; Kawakami, Tetsuo; Skrzypek, Etienne; Sakata, Shuhei; Obayashi, Hideyuki; Hirata, Takafumi

2018-05-01

The spatiotemporal relationship between granitoid intrusions and low-pressure/temperature type regional metamorphism in the Ryoke belt (Mikawa area) is investigated to understand the tectono-thermal evolution of the upper- to middle-crust during a Cretaceous flare-up event at the Eurasian active continental margin. Three plutono-metamorphic stages are recognized; (1) 99-84 Ma: intrusion of granitoids (99-95 Ma pulse) into the upper crust and high-T regional metamorphism reaching sillimanite-grade (97.0 ± 4.4 Ma to 88.5 ± 2.5 Ma) in the middle crust, (2) 81-75 Ma: intrusion of gneissose granitoids (81-75 Ma Ma pulse) into the middle crust at 19-24 km depth, and (3) 75-69 Ma: voluminous intrusions of massive to weakly-foliated granitoids (75-69 Ma pulse) at 9-13 km depth and formation of contact metamorphic aureoles. Cooling of the highest-grade metamorphic zone below the wet solidus of granitic rocks is estimated at 88.5 ± 2.5 Ma. At ca. 75 Ma, the upper-middle crustal section underwent northward tilting, resulting in the exhumation of regional metamorphic zones to 9-13 km depth. Although the highest-grade metamorphic rocks and the 99-95 Ma pulse granitoids preserve similar U-Pb zircon ages, the absence of spatial association suggests that the regional metamorphic zones were mainly produced by a transient thermal anomaly in the mantle and thermal conduction through the crust, supplemented by localized advection due to granitoid intrusions. The successive emplacement of granitoids into shallow, deep and shallow levels of the crust was probably controlled by the combination of change in thermal structure of the crust and tectonics during granitoid intrusions.

Xenolith constraints on seismic velocities in the upper mantle beneath southern Africa

NASA Astrophysics Data System (ADS)

James, D. E.; Boyd, F. R.; Schutt, D.; Bell, D. R.; Carlson, R. W.

2004-01-01

We impose geologic constraints on seismic three-dimensional (3-D) images of the upper mantle beneath southern Africa by calculating seismic velocities and rock densities from approximately 120 geothermobarometrically calibrated mantle xenoliths from the Archean Kaapvaal craton and adjacent Proterozoic mobile belts. Velocity and density estimates are based on the elastic and thermal moduli of constituent minerals under equilibrium P-T conditions at the mantle source. The largest sources of error in the velocity estimates derive from inaccurate thermo-barometry and, to a lesser extent, from uncertainties in the elastic constants of the constituent minerals. Results are consistent with tomographic evidence that cratonic mantle is higher in velocity by 0.5-1.5% and lower in density by about 1% relative to off-craton Proterozoic samples at comparable depths. Seismic velocity variations between cratonic and noncratonic xenoliths are controlled dominantly by differences in calculated temperatures, with compositional effects secondary. Different temperature profiles between cratonic and noncratonic regions have a relatively minor influence on density, where composition remains the dominant control. Low-T cratonic xenoliths exhibit a positive velocity-depth curve, rising from about 8.13 km/s at uppermost mantle depths to about 8.25 km/s at 180-km depth. S velocities decrease slightly over the same depth interval, from about 4.7 km/s in the uppermost mantle to 4.65 km/s at 180-km depth. P and S velocities for high-T lherzolites are highly scattered, ranging from highs close to those of the low-T xenoliths to lows of 8.05 km/s and 4.5 km/s at depths in excess of 200 km. These low velocities, while not asthenospheric, are inconsistent with seismic tomographic images that indicate high velocity root material extending to depths of at least 250 km. One plausible explanation is that high temperatures determined for the high-T xenoliths are a nonequilibrium consequence of relatively recent thermal perturbation and compositional modification associated with emplacement of kimberlitic fluids into the deep tectospheric root. Seismic velocities and densities for cratonic xenoliths differ significantly from those predicted for both primitive mantle peridotite and mantle eclogite. A model primitive mantle under cratonic P-T conditions exhibits velocities about 1% lower for P and about 1.5% lower for S, a consequence of a more fertile composition and different modal composition. Primitive mantle is also about 2% more dense at 150-km depth than low-T garnet lherzolite at cratonic P-T conditions. Similar calculations based on an oceanic geotherm are consistent with the isopycnic hypothesis of comparable density columns beneath oceanic and cratonic regions. Calculations for a hypothetical "cratonic" eclogite (50:50 garnet/omphacite) with an assumed cratonic geotherm produce extremely high VP and VS (8.68 km/s and 4.84 km/s, respectively, at 150 km depth) as well as high density (˜3.54 gm/cc). The very high velocity of eclogite should render it seismically conspicuous in the cratonic mantle if present as large volume blocks or slabs. We discuss how the seismic velocity data we have compiled in this paper from both xenoliths and generic petrologic models of the upper mantle differ from commonly used standard earth models IASPEI and PREM.

ARC-1980-AC80-7001

NASA Image and Video Library

1980-09-17

Range : 76 million km. ( 47 million miles) P-22892C This, Voyager 1 image shows Saturn and five of its satellites. Saturn's largest moon, Titan, is clearly seen in the upper right corner. The smaller satellites, Dione & Tethys, are shown in the upper left corner, top and bottom respectively. Two of the innermost satellites, Mimas & Enceladus, appear to the lower right of the planet, with Mimas closest to Satun. The bright object to the left of the rings is not a moon, but an artifact of processing. Voyager 1 will make its closest approach November 12th, 1980, ata distance of 124,200 km. (77,176 mi.). this photo is just one of 17,000 images taken of Saturn, its rings, and its satellites by Voyager 1.

Causes of complexity in a fallout dominated plinian eruption sequence: 312 ka Fasnia Member, Diego Hernández Formation, Tenerife, Spain

NASA Astrophysics Data System (ADS)

Edgar, C. J.; Cas, R. A. F.; Olin, P. H.; Wolff, J. A.; Martí, J.; Simmons, J. M.

2017-10-01

The 312 ka Fasnia eruption from the Las Cañadas Caldera on Tenerife, Canary Islands, Spain, produced a complex sequence of twenty-two intercalated units, including 7 pumice fall, 7 ignimbrite and 8 ash surge and fall deposits that define two distinct eruption sequences (Lower and Upper Fasnia sequences). The fallout units themselves are internally complex, reflecting waxing and waning of the eruption column, while many of the ignimbrites reflect multiple intra-plinian partial column collapse events associated with the injection of lithic clasts into the eruption column. The Lower and Upper Fasnia eruption phases were each terminated by caldera collapse and complete column collapse events. Probable blockage of the conduit and vent system during Lower Fasnia caldera collapse event briefly terminated the eruption, resulting in a short-lived period of erosion and sedimentation prior to the onset of the Upper Fasnia phase. The transition to the Upper Fasnia eruption phase coincided with the eruption of more geochemically homogeneous pyroclasts. In total, 62 km3 of tephra were erupted, including 49 km3 of juvenile clasts and > 12 km3 of lithic clasts. The DRE volume of magma erupted was 13 km3 (Lower Fasnia > 5 km3, Upper Fasnia > 8 km3), two thirds of which ( 9-10 km3) was deposited purely by fallout. The Fasnia Member is one of the most complex plinian sequences known.

Precambrian crust beneath the Mesozoic northern Canadian Cordillera discovered by Lithoprobe seismic reflection profiling

NASA Astrophysics Data System (ADS)

Cook, Frederick A.; Clowes, Ronald M.; Snyder, David B.; van der Velden, Arie J.; Hall, Kevin W.; Erdmer, Philippe; Evenchick, Carol A.

2004-04-01

The Cordillera in northern Canada is underlain by westward tapering layers that can be followed from outcrops of Proterozoic strata in the Foreland belt to the lowermost crust of the orogenic interior, a distance of as much as 500 km across strike. They are interpreted as stratified Proterozoic rocks, including ˜1.8-0.7 Ga supracrustal rocks and their basement. The layering was discovered on two new deep seismic reflection profiles in the Yukon (Line 3; ˜650 km) and northern British Columbia (Line 2; ˜1245 km in two segments) that were acquired as part of the Lithoprobe Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) transect. In the Mackenzie Mountains of the eastern Yukon, the layering in Line 3 is visible between 5.0 and 12.0 s (˜15 to 36 km depth). It is followed southwestward for nearly 650 km (˜500 km across strike) and thins to less than 1.0 s (˜3.0-3.5 km thickness) near the Moho at the Yukon-Alaska international boundary. In the northern Rocky Mountains of British Columbia, the upper part of the layering on Line 2 correlates with outcrops of Proterozoic (1.76-1.0 Ga) strata in the Muskwa anticlinorium. At this location, the layering is at least 15 km thick and is followed westward then southward into the middle and lower crust for ˜700 km (˜300 km across strike). It disappears as a thin taper at the base of the crust ˜150 km east of the coast of the Alaskan panhandle. The only significant disruption in the layering occurs at the Tintina fault zone, a late to postorogenic strike-slip fault with up to 800 km of displacement, which appears as a vertical zone of little reflectivity that disrupts the continuity of the deep layering on both profiles (˜300 km apart). The base of the layered reflection zone coincides with the Moho, which exhibits variable character and undulates in a series of broad arches with widths of ˜150 km. In general, the mantle appears to have few reflections. However, at the southwest end of Line 3 near the Alaska-British Columbia border, a reflection dips eastward from ˜14.0 s to ˜21.0 s (˜45 to 73 km depth) beneath exposed Eocene magmatic rocks. It is interpreted as a relict subduction surface of the Kula plate. Our interpretation of Proterozoic layered rocks beneath most of the northern Cordillera suggests a much different crustal structure than previously considered: (1) Ancient North American crust comprising up to 25 km of metamorphosed Proterozoic to Paleozoic sediments plus 5-10 km of pre-1.8 Ga crystalline basement projects westward beneath most of the northern Canadian Cordillera. (2) The lateral (500 km by at least 1000 km) and vertical (up to 25 km) extent of the Proterozoic layers and their internal deformation are consistent with a long-lived margin for northwestern North America with alternating episodes of extension and contraction. (3) The detachments that carry deformed rocks of the Mackenzie Mountains and northern Rocky Mountains are largely confined to the upper crustal region above the layering. (4) Accreted terranes include thin klippen that were thrust over North American pericratonic strata (e.g., Yukon-Tanana), and terranes such as Nisling and Stikinia that thicken westward as the underlying Proterozoic layers taper and disappear. (5) The ages of exposed rocks are not necessarily indicative of the ages of underlying crust, a frequent observation in Lithoprobe interpretations, so that estimates of crustal growth based on surface geology may not be representative.

Influence of peroxyacetyl nitrate (PAN) on odd nitrogen in the troposphere and lower stratosphere

NASA Technical Reports Server (NTRS)

Aikin, A. C.; Herman, J. R.; Maier, E. J. R.; Mcquillan, C. J.

1983-01-01

Nonmethane hydrocarbon breakdown in the atmosphere produces aldehydes of which a fraction are transferred into peroxyacetyl nitrates (PAN) in the presence of NO and NO2. Since ethane is destroyed photochemically primarily above 1 km, PAN can be introduced into the upper troposphere and lower stratosphere without the need to be transported from the boundary layer where most hydrocarbons are destroyed and where PAN may be lost due to thermal decomposition and heterogeneous loss. Mixing ratios of ethane in the lower troposphere increase by a factor of 4-8 from equatorial to northern mid-latitudes. This difference is directly translatable into a PAN latitude gradient. At mid-latitudes the concentration of PAN below 20 km is 0.1 ppb comparable to and in some instances larger than predicted HO2NO2 mixing ratios. Like HO2NO2 and HNO3, PAN serves as a reservoir for odd nitrogen.

Ripples and Dunes

NASA Technical Reports Server (NTRS)

2006-01-01

21 July 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small portion of the floor of Kaiser Crater in the Noachis Terra region, Mars. The terrain in the upper (northern) half of the image is covered by large windblown ripples and a few smoother-surfaced sand dunes. The dominant winds responsible for these features blew from the west/southwest (left/lower left).

Location near: 47.2oS, 341.3oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Winter

Titan's Upper Atmosphere from Cassini/UVIS Solar Occultations

NASA Astrophysics Data System (ADS)

Capalbo, Fernando J.; Bénilan, Yves; Yelle, Roger V.; Koskinen, Tommi T.

2015-12-01

Titan’s atmosphere is composed mainly of molecular nitrogen, methane being the principal trace gas. From the analysis of 8 solar occultations measured by the Extreme Ultraviolet channel of the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini, we derived vertical profiles of N2 in the range 1100-1600 km and vertical profiles of CH4 in the range 850-1300 km. The correction of instrument effects and observational effects applied to the data are described. We present CH4 mole fractions, and average temperatures for the upper atmosphere obtained from the N2 profiles. The occultations correspond to different times and locations, and an analysis of variability of density and temperature is presented. The temperatures were analyzed as a function of geographical and temporal variables, without finding a clear correlation with any of them, although a trend of decreasing temperature toward the north pole was observed. The globally averaged temperature obtained is (150 ± 1) K. We compared our results from solar occultations with those derived from other UVIS observations, as well as studies performed with other instruments. The observational data we present confirm the atmospheric variability previously observed, add new information to the global picture of Titan’s upper atmosphere composition, variability, and dynamics, and provide new constraints to photochemical models.

Stability of carbonated basaltic melt at the base of the Earth's upper mantle

NASA Astrophysics Data System (ADS)

Ghosh, S.; Litasov, K.; Ohtani, E.; Suzuki, A.

2006-12-01

Seismological observations of low velocity zones (LVZ) at the top of the 410-km discontinuity reveal possible existence of dense melt at this boundary (e.g. Reveanugh and Sipkin, 1994). Density measurements of anhydrous basaltic melts indicate that it is denser than surrounding mantle near 410-km depth (Ohtani and Maeda, 2001). However, melting temperature of peridotite is much higher than about 1400°C, estimated at 410-km depth. It has been shown recently that hydrous basaltic melt containing up to 2 wt.% H2O is denser than peridotite atop 410-km and therefore can be accumulated at the base of the upper mantle (Sakamaki et al., 2006). CO2 is another major volatile component in the mantle and it could be also important for explanation of LVZ near 410 km. In the present study, we have measured the density of carbonated basaltic melt at high pressures and high temperatures and discussed its possible stability at the base of the upper mantle. The density of the melt was determined using sink/float technique. The starting material was synthetic MORB glass. 5 and 10 wt.% CO2 was added to the glass as CaCO3 and Na2CO3, adjusting to proportions of related oxides. Experiments were carried out at 16-22 GPa and 2200-2300°C using a multianvil apparatus at Tohoku University, Japan. We observed neutral buoyancy of diamond density marker in MORB + 5 wt.% CO2 at 18 GPa and 2300°C, whereas, diamond was completely dissolved in the carbonated MORB melt containing 10 wt.% CO2 in 0.5-1 minute experiments. Based on the buoyancy test, the density of the carbonated basaltic melt, containing 5 wt.% CO2, is 3.56 g/cm3 at 18 GPa and 2300°C using an equation of state of diamond. To calculate the bulk modulus we assume that the pressure derivative of the isothermal bulk modulus is the same as that of the dry MORB melt, dKT/dP=5.0 and zero-pressure partial molar volume of CO2 is 32 cm3/mol (based on low-pressure experiments on carbonated basaltic melts and carbonatites, e.g. Dobson et al., 1996; Liu and Lange, 2003). Accordingly, the isothermal bulk modulus (KT) of the carbonated MORB melt containing 5 wt.% CO2 calculated using the Birch-Murnaghan equation of state is 16.3 ± 1 GPa. This value is close to that of dry MORB (KT=18 GPa) and indicates that addition of 5 wt.% CO2 to basaltic melt has minor influence on its compressibility. Density of MORB + 5 wt.% CO2 is almost same with the density of MORB + 2 wt.% H2O at 15-20 GPa. Comparison of the density of carbonated basaltic melt with PREM density profile at 1600°C indicates that it is buoyant above the 410 km discontinuity in the mantle only if it contains more than about 5 wt.% CO2.

Investigation of Earthquake and Geyser Events in the Upper Geyser Basin of Yellowstone National Park from a Nodal Array

NASA Astrophysics Data System (ADS)

Garcia, S.; Karplus, M. S.; Farrell, J.; Lin, F. C.; Smith, R. B.

2017-12-01

A large seismic nodal array incorporating 133 three-component, 5-Hz geophones deployed for two weeks in early November 2015 in the Upper Geyser Basin recorded earthquake and hydrothermal activity. The University of Utah, the University of Texas at El Paso, and Yellowstone National Park collaborated to deploy Fairfield Nodal ZLand 3-C geophones concentrically centered around the Old Faithful Geyser with an average station spacing of 50 m and an aperture of 1 km. The array provided a unique dataset to investigate wave propagation through various fractures and active geysers in a hydrothermal field located over the Yellowstone hotspot. The complicated sub-surface features associated with the hydrothermal field appear to impact earthquake wave propagation in the Upper Geyser Basin and to generate seismic signals. Previous work using ambient noise cross-correlation has found an intricately fractured sub-surface that provides pathways for water beneath parts of the Upper Geyser Basin that likely feed Old Faithful and other nearby geysers and hot springs. For this study, we used the data to create visualizations of local earthquake, teleseismic earthquake, and hydrothermal events as they propagate through the array. These ground motion visualizations allow observation of wave propagation through the geyser field, which may indicate the presence of anomalous structure impacting seismic velocities and attenuation. Three teleseismic events were observed in the data, two 6.9MW earthquakes that occurred off the coast of Coquimbo, Colombia 9,000km from the array and one 6.5MW near the Aleutian Islands 4,500km from the array. All three teleseismic events observed in the data exhibited strong direct P-wave arrivals and several additional phases. One local earthquake event (2.5ML) 100km from the Upper Geyser Basin was also well-recorded by the array. Time-domain spectrograms show the dominant frequencies present in the recordings of these events. The two 6.9MW earthquakes in Chile were one hour apart and offered interesting signals that also included a geyser tremor between the two events.

Long-term responses of rainforest erosional systems at different spatial scales to selective logging and climatic change.

PubMed

Walsh, R P D; Bidin, K; Blake, W H; Chappell, N A; Clarke, M A; Douglas, I; Ghazali, R; Sayer, A M; Suhaimi, J; Tych, W; Annammala, K V

2011-11-27

Long-term (21-30 years) erosional responses of rainforest terrain in the Upper Segama catchment, Sabah, to selective logging are assessed at slope, small and large catchment scales. In the 0.44 km(2) Baru catchment, slope erosion measurements over 1990-2010 and sediment fingerprinting indicate that sediment sources 21 years after logging in 1989 are mainly road-linked, including fresh landslips and gullying of scars and toe deposits of 1994-1996 landslides. Analysis and modelling of 5-15 min stream-suspended sediment and discharge data demonstrate a reduction in storm-sediment response between 1996 and 2009, but not yet to pre-logging levels. An unmixing model using bed-sediment geochemical data indicates that 49 per cent of the 216 t km(-2) a(-1) 2009 sediment yield comes from 10 per cent of its area affected by road-linked landslides. Fallout (210)Pb and (137)Cs values from a lateral bench core indicate that sedimentation rates in the 721 km(2) Upper Segama catchment less than doubled with initially highly selective, low-slope logging in the 1980s, but rose 7-13 times when steep terrain was logged in 1992-1993 and 1999-2000. The need to keep steeplands under forest is emphasized if landsliding associated with current and predicted rises in extreme rainstorm magnitude-frequency is to be reduced in scale.

Modern Sedimentation off the Kaoping River, SW Taiwan: A Comparison with Eel River's S2S System

NASA Astrophysics Data System (ADS)

Huh, C.; Lin, H.; Lin, S.

2006-12-01

The Kaoping (KP) River in SW Taiwan has a watershed area of 3257 km2 and an annual sediment discharge of 49 MT. Although the sediment yield of the KP River basin (1.5×104 ton km-2 yr^{- 1}) is the 4th highest among Taiwan's catchment basins, it is nearly one order of magnitude higher than that of the Eel River's basin (~1.8×103 ton km-2 yr-1; the highest in the U.S.). The KP canyon extends almost immediately seaward from the river's mouth and terminates in the northwestern corner of the South China Sea. The head of the canyon is characterized by high and steep walls exceeding 600 m. The KP river's source-to-sink system offers a dramatic case of mountainous rivers at active margins for S2S study. Here we report some results about modern sedimentation in KP river's dispersal system. Seventy-six sediment cores collected from an area of ~3000 km2 were analyzed for fallout nuclides 7Be, 137Cs and 210Pb by gamma spectrometry. From profiles of excess 210Pb and 137Cs sediment accumulation rates in the coring sites were estimated, which vary from 0.06 to 1.6 cm/yr, with the highest rates (>1 cm/yr) distributed in the upper slope (<600 m) on both sides of the KP canyon. The area with high sedimentation rates on Pb-210 time scale coincides with the area covered by a flood layer resulting from Typhoon Haitang during July 18-20, 2005. This suggests that the open margin on the upper slope is a depocenter for sediment dispersed via a surface component of the river's plume on various timescales (from events to centennial). With a total of 76 sampling points laid out, a framework consisting of 105 triangular grids is configured to calculate the budget of sediment in the study area. The calculated budget, at 7.2 MT/yr, accounts for only ~15% of KP river's sediment discharge. We speculate that most of the remainder is exported out of the study area via the KP canyon to the deep sea by gravity-driven turbidity or hyperpycnal flows.

Seismic tomography shows that upwelling beneath Iceland is confined to the upper mantle

USGS Publications Warehouse

Foulger, G.R.; Pritchard, M.J.; Julian, B.R.; Evans, J.R.; Allen, R.M.; Nolet, G.; Morgan, W.J.; Bergsson, B.H.; Erlendsson, P.; Jakobsdottir, S.; Ragnarsson, S.; Stefansson, R.; Vogfjord, K.

2001-01-01

We report the results of the highest-resolution teleseismic tomography study yet performed of the upper mantle beneath Iceland. The experiment used data gathered by the Iceland Hotspot Project, which operated a 35-station network of continuously recording, digital, broad-band seismometers over all of Iceland 1996-1998. The structure of the upper mantle was determined using the ACH damped least-squares method and involved 42 stations, 3159 P-wave, and 1338 S-wave arrival times, including the phases P, pP, sP, PP, SP, PcP, PKIKP, pPKIKP, S, sS, SS, SKS and Sdiff. Artefacts, both perceptual and parametric, were minimized by well-tested smoothing techniques involving layer thinning and offset-and-averaging. Resolution is good beneath most of Iceland from ??? 60 km depth to a maximum of ??? 450 km depth and beneath the Tjornes Fracture Zone and near-shore parts of the Reykjanes ridge. The results reveal a coherent, negative wave-speed anomaly with a diameter of 200-250 km and anomalies in P-wave speed, Vp, as strong as -2.7 per cent and in S-wave speed, Vs, as strong as -4.9 per cent. The anomaly extends from the surface to the limit of good resolution at ??? 450 km depth. In the upper ??? 250 km it is centred beneath the eastern part of the Middle Volcanic Zone, coincident with the centre of the ??? 100 mGal Bouguer gravity low over Iceland, and a lower crustal low-velocity zone identified by receiver functions. This is probably the true centre of the Iceland hotspot. In the upper ??? 200 km, the low-wave-speed body extends along the Reykjanes ridge but is sharply truncated beneath the Tjornes Fracture Zone. This suggests that material may flow unimpeded along the Reykjanes ridge from beneath Iceland but is blocked beneath the Tjornes Fracture Zone. The magnitudes of the Vp, Vs and Vp/Vs anomalies cannot be explained by elevated temperature alone, but favour a model of maximum temperature anomalies <200 K, along with up to ??? 2 per cent of partial melt in the depth range ??? 100-300 km beneath east-central Iceland. The anomalous body is approximately cylindrical in the top 250 km but tabular in shape at greater depth, elongated north-south and generally underlying the spreading plate boundary. Such a morphological change and its relationship to surface rift zones are predicted to occur in convective upwellings driven by basal heating, passive upwelling in response to plate separation and lateral temperature gradients. Although we cannot resolve structure deeper than ??? 450 km, and do not detect a bottom to the anomaly, these models suggest that it extends no deeper than the mantle transition zone. Such models thus suggest a shallow origin for the Iceland hotspot rather than a deep mantle plume, and imply that the hotspot has been located on the spreading ridge in the centre of the north Atlantic for its entire history, and is not fixed relative to other Atlantic hotspots. The results are consistent with recent, regional full-thickness mantle tomography and whole-mantle tomography images that show a strong, low-wave-speed anomaly beneath the Iceland region that is confined to the upper mantle and thus do not require a plume in the lower mantle. Seismic and geochemical observations that are interpreted as indicating a lower mantle, or core-mantle boundary origin for the North Atlantic Igneous Province and the Iceland hotspot should be re-examined to consider whether they are consistent with upper mantle processes.

Modeled Full-Flight Aircraft Emissions Impacts on Air Quality and Their Sensitivity to Grid Resolution

NASA Astrophysics Data System (ADS)

Vennam, L. P.; Vizuete, W.; Talgo, K.; Omary, M.; Binkowski, F. S.; Xing, J.; Mathur, R.; Arunachalam, S.

2017-12-01

Aviation is a unique anthropogenic source with four-dimensional varying emissions, peaking at cruise altitudes (9-12 km). Aircraft emission budgets in the upper troposphere lower stratosphere region and their potential impacts on upper troposphere and surface air quality are not well understood. Our key objective is to use chemical transport models (with prescribed meteorology) to predict aircraft emissions impacts on the troposphere and surface air quality. We quantified the importance of including full-flight intercontinental emissions and increased horizontal grid resolution. The full-flight aviation emissions in the Northern Hemisphere contributed 1.3% (mean, min-max: 0.46, 0.3-0.5 ppbv) and 0.2% (0.013, 0.004-0.02 μg/m3) of total O3 and PM2.5 concentrations at the surface, with Europe showing slightly higher impacts (1.9% (O3 0.69, 0.5-0.85 ppbv) and 0.5% (PM2.5 0.03, 0.01-0.05 μg/m3)) than North America (NA) and East Asia. We computed seasonal aviation-attributable mass flux vertical profiles and aviation perturbations along isentropic surfaces to quantify the transport of cruise altitude emissions at the hemispheric scale. The comparison of coarse (108 × 108 km2) and fine (36 × 36 km2) grid resolutions in NA showed 70 times and 13 times higher aviation impacts for O3 and PM2.5 in coarser domain. These differences are mainly due to the inability of the coarse resolution simulation to capture nonlinearities in chemical processes near airport locations and other urban areas. Future global studies quantifying aircraft contributions should consider model resolution and perhaps use finer scales near major aviation source regions.

Modeled Full-Flight Aircraft Emissions Impacts on Air Quality and Their Sensitivity to Grid Resolution

PubMed Central

Vennam, L. P.; Vizuete, W.; Talgo, K.; Omary, M.; Binkowski, F. S.; Xing, J.; Mathur, R.; Arunachalam, S.

2018-01-01

Aviation is a unique anthropogenic source with four-dimensional varying emissions, peaking at cruise altitudes (9–12 km). Aircraft emission budgets in the upper troposphere lower stratosphere region and their potential impacts on upper troposphere and surface air quality are not well understood. Our key objective is to use chemical transport models (with prescribed meteorology) to predict aircraft emissions impacts on the troposphere and surface air quality. We quantified the importance of including full-flight intercontinental emissions and increased horizontal grid resolution. The full-flight aviation emissions in the Northern Hemisphere contributed ~1.3% (mean, min–max: 0.46, 0.3–0.5 ppbv) and 0.2% (0.013, 0.004–0.02 μg/m3) of total O3 and PM2.5 concentrations at the surface, with Europe showing slightly higher impacts (1.9% (O3 0.69, 0.5–0.85 ppbv) and 0.5% (PM2.5 0.03, 0.01–0.05 μg/m3)) than North America (NA) and East Asia. We computed seasonal aviation-attributable mass flux vertical profiles and aviation perturbations along isentropic surfaces to quantify the transport of cruise altitude emissions at the hemispheric scale. The comparison of coarse (108 × 108 km2) and fine (36 × 36 km2) grid resolutions in NA showed ~70 times and ~13 times higher aviation impacts for O3 and PM2.5 in coarser domain. These differences are mainly due to the inability of the coarse resolution simulation to capture nonlinearities in chemical processes near airport locations and other urban areas. Future global studies quantifying aircraft contributions should consider model resolution and perhaps use finer scales near major aviation source regions. PMID:29707471

Modeled Full-Flight Aircraft Emissions Impacts on Air Quality and Their Sensitivity to Grid Resolution.

PubMed

Vennam, L P; Vizuete, W; Talgo, K; Omary, M; Binkowski, F S; Xing, J; Mathur, R; Arunachalam, S

2017-01-01

Aviation is a unique anthropogenic source with four-dimensional varying emissions, peaking at cruise altitudes (9-12 km). Aircraft emission budgets in the upper troposphere lower stratosphere region and their potential impacts on upper troposphere and surface air quality are not well understood. Our key objective is to use chemical transport models (with prescribed meteorology) to predict aircraft emissions impacts on the troposphere and surface air quality. We quantified the importance of including full-flight intercontinental emissions and increased horizontal grid resolution. The full-flight aviation emissions in the Northern Hemisphere contributed ~1.3% (mean, min-max: 0.46, 0.3-0.5 ppbv) and 0.2% (0.013, 0.004-0.02 μg/m 3 ) of total O 3 and PM 2.5 concentrations at the surface, with Europe showing slightly higher impacts (1.9% (O 3 0.69, 0.5-0.85 ppbv) and 0.5% (PM 2.5 0.03, 0.01-0.05 μg/m 3 )) than North America (NA) and East Asia. We computed seasonal aviation-attributable mass flux vertical profiles and aviation perturbations along isentropic surfaces to quantify the transport of cruise altitude emissions at the hemispheric scale. The comparison of coarse (108 × 108 km 2 ) and fine (36 × 36 km 2 ) grid resolutions in NA showed ~70 times and ~13 times higher aviation impacts for O 3 and PM 2.5 in coarser domain. These differences are mainly due to the inability of the coarse resolution simulation to capture nonlinearities in chemical processes near airport locations and other urban areas. Future global studies quantifying aircraft contributions should consider model resolution and perhaps use finer scales near major aviation source regions.

Topographic Control of Aboveground Carbon Pools Across an Environmental Gradient, Eastern Slope of the Rocky Mountains, Colorado.

NASA Astrophysics Data System (ADS)

Swetnam, T. L.; Brooks, P. D.; Gallo, E. L.; Barnard, H. R.; Harpold, A. A.

2015-12-01

Evaluating at high spatial-resolution the topographical and ecological structures of the critical zone (CZ) are now routine with aerial LiDAR. Here we evaluated the eco-hydrological differences of topographic metrics (the independent variables) versus individual tree and gridded aboveground carbon (AGC) pools (as dependent variables) at multiple length-scales across an elevation modified gradient of precipitation and temperature in the Boulder Creek CZ Observatory Watershed, Colorado USA. We describe the responses in AGC within the context of a three-zone eco-hydrological model, e.g. toe slope and valley bottoms (Zone 1), transitional hillslopes (Zone 2), and upper slopes to ridges (Zone 3). In a GIS we compared three separate zero-order basins: (1) the Betasso Preserve: 1,810-2,024 meters above mean sea level (m aμsl), area = 0.45 km2, n = 17,286 trees; (2) Upper and Lower Gordon Gulch: 2,446-2,737 m aμsl, area = 3.57 km2, n = 178,469 trees; and (3) Como Creek: 2,900m-3,560 m aμsl, area = 6.64 km2, n = 317,274 trees. In each of the three catchments Zone 1 held the greatest mean AGC (μ = 52.88-60.97 Mg C ha-1) and maximum AGC (99% confidence interval (CI, p = 0.01) = 152.95-184.95 Mg C ha-1) relative to Zone 2 (μ = 27.84-44.52 Mg C ha-1, 99% CI = 99.67-122.4 Mg C ha-1) and Zone 3 (μ = 12.63-30.33 Mg C ha-1, 99% CI = 62.16-92.65 Mg C ha-1). Topography with negative general curvatures (i.e. convergent shapes) had greater AGC (μ = 73.7-96.3 Mg C ha-1, 99% CI = 189.0-355.8 Mg C ha-1) than positive general curvatures (i.e. divergent shapes) (μ = 17.4-30.8 Mg C ha-1, 99% CI = 88.2-120.4 Mg C ha-1), but only when evaluated at longer length scales (<10 m). Larger AGC pools are postulated to be related to (1) increased soil depth which provides larger rooting zones and (2) access to groundwater along Zone 1, vs Zones 2 and 3 which have (a) shallower soils and (b) less or zero accessibility to groundwater.

Upper Mantle Anisotropy Under Fast Spreading Mid-ocean Ridges: 2-D Whole Mantle Convection Model With Subduction

NASA Astrophysics Data System (ADS)

Lee, C.; Zhou, Y.; King, S. D.

2008-12-01

Analyses of seismic anisotropy caused by spatial alignments of anisotropic minerals (e.g., olivine) have been widely used to infer mantle flow directions in the upper mantle. Deep seismic anisotropy beneath fast spreading mid-ocean ridges (e.g., East Pacific Rise) has been recently observed at depths of 200-300 km and even down to the transition zone, with polarization changes in radial anisotropy from VSH < VSV (shallow) to VSH < VSV (deep). We investigate the origin of the observed deep seismic anisotropy and polarization changes beneath the EPR in 2-D Cartesian numerical models using both kinematically (prescribed velocity) and dynamically (negative buoyancy) driven ridge spreading. Because subduction is thought to be an important controlling factor in the style of ridge spreading and mantle convection, we consider a subduction zone developing at the prescribed weak zone. A whole mantle domain expressed by a one by four box (2890 by 11560 km) is used to minimize the boundary effects on the subducting slab. For the upper mantle rheology, we consider composite viscosity of diffusion and dislocation creep for dry olivine to evaluate the effects of lateral variation of mantle viscosity and the rheological changes from dislocation to diffusion creep under the mid-ocean ridge. For the lower mantle rheology, we use diffusion creep for dry olivine by increasing grain size to match relevant lower mantle viscosity. We also consider the 660 km phase transition with density and viscosity jump as well as Clapeyron slope. Anisotropy is evaluated using finite-strain ellipses based on the assumption that a-axes of olivine crystals are parallel to the major axes of the finite-strain ellipses. Our preliminary results show 1) in general, the development of VSH < VSV anisotropy is confined only in a narrow region under the ridge axis at depths of 200- 300 km; 2) strong VSH > VSV anisotropy can be found in the 'asthenosphere' beneath the entire spreading oceanic lithosphere; and 3) the dominate creep mechanism changes from dislocation creep to diffusion creep at depths of 300-400 km; indicating a more isotropic lower upper mantle. We conclude that our geodynamical modeling in a passive ridge spreading system does not produce the deep seismic anisotropy recently observed beneath the EPR. However, we do not consider partial melting, dynamic recrystallization and anisotropic viscosity which would change seismic interpretation and mantle flow, and thus further study is required.

Extending water vapor trend observations over Boulder into the tropopause region: Trend uncertainties and resulting radiative forcing.

PubMed

Kunz, A; Müller, R; Homonnai, V; Jánosi, I M; Hurst, D; Rap, A; Forster, P M; Rohrer, F; Spelten, N; Riese, M

2013-10-16

Thirty years of balloon-borne measurements over Boulder (40°N, 105°W) are used to investigate the water vapor trend in the tropopause region. This analysis extends previously published trends, usually focusing on altitudes greater than 16 km, to lower altitudes. Two new concepts are applied: (1) Trends are presented in a thermal tropopause (TP) relative coordinate system from -2 km below to 10 km above the TP, and (2) sonde profiles are selected according to TP height. Tropical (TP z > 14 km), extratropical (TP z < 12 km), and transitional air mass types (12 km < TP z < 14 km) reveal three different water vapor reservoirs. The analysis based on these concepts reduces the dynamically induced water vapor variability at the TP and principally favors refined water vapor trend studies in the upper troposphere and lower stratosphere. Nonetheless, this study shows how uncertain trends are at altitudes -2 to +4 km around the TP. This uncertainty in turn has an influence on the uncertainty and interpretation of water vapor radiative effects at the TP, which are locally estimated for the 30 year period to be of uncertain sign. The much discussed decrease in water vapor at the beginning of 2001 is not detectable between -2 and 2 km around the TP. On lower stratospheric isentropes, the water vapor change at the beginning of 2001 is more intense for extratropical than for tropical air mass types. This suggests a possible link with changing dynamics above the jet stream such as changes in the shallow branch of the Brewer-Dobson circulation.

Kinematics of a large-scale intraplate extending lithosphere: The Basin-Range

NASA Technical Reports Server (NTRS)

Smith, R. B.; Eddington, P. K.

1985-01-01

Upper lithospheric structure of the Cordilleran Basin Range (B-R) is characterised by an E-W symmetry of velocity layering. The crust is 25 km thick on its eastern active margin, thickening to 30 km within the central portion and thinning to approx. 25 km on the west. Pn velocities of 7.8 to 7.9 km/s characterize the upper mantle low velocity cushion, 7.4 km/s to 7.5 km/s, occurs at a depth of approx. 25 km in the eastern B-R and underlies the area of active extension. An upper-crustal low-velocity zone in the eastern B-R shows a marked P-wave velocity inversion of 7% at depths of 7 to 10 km also in the area of greatest extension. The seismic velocity models for this region of intraplate extension suggest major differences from that of a normal, thermally underformed continental lithosphere. Interpretations of seismic reflection data demonstrate the presence of extensive low-angle reflections in the upper-crust of the eastern B-R at depths from near-surface to 7 to 10 km. These reflections have been interpreted to represent low-angle normal fault detachments or reactivated thrusts. Seismic profiles across steeply-dipping normal faults in unconsolidated sediments show reflections from both planar to downward flatening (listric) faults that in most cases do not penetrate the low-angle detachments. These faults are interpreted as late Cenozoic and cataclastic mylonitic zones of shear displacement.

Upper Ocean Meso-Submesoscale Eddy Variability in the Northwestern Pacific from Repeat ADCP Measurements and 1/48-deg MITgcm Simulation

NASA Astrophysics Data System (ADS)

Qiu, B.; Nakano, T.; Chen, S.; Wang, J.; Fu, L. L.; Klein, P.

2016-12-01

With the use of Ka-band radar interferometry, the Surface Water and Ocean Topography (SWOT) satellite will improve the measured sea surface height (SSH) resolution down to the spectral wavelength of 15km, allowing us to investigate for the first time the upper oceancirculation variability at the submesoscale range on the global scale. By analyzing repeat shipboardAcoustic Doppler Current Profiler (ADCP) measurements along 137°E, as well as the 1/48-deg MITgcm simulation output, in the northwest Pacific, we demonstrate that the observed/modeled upper ocean velocities are comprised of balanced geostrophic motions and unbalanced ageostrophic wave motions. The length scale, Lc, that separates the dominance between these two types of motions is found to depend sensitively on the energy level of local mesoscale eddy variability. In the eddy-abundant western boundary current region of Kuroshio, Lc can be shorter than 15km, whereas Lc exceeds 200km along the path of relatively stable North Equatorial Current. Judicious separation between the balanced and unbalanced surface ocean signals will both be a challenge and opportunity for the SWOT mission.

Blue sheep in the Annapurna Conservation Area, Nepal: habitat use, population biomass and their contribution to the carrying capacity of snow leopards.

PubMed

Aryal, Achyut; Brunton, Dianne; Ji, Weihong; Raubenheimer, David

2014-01-01

The Himalaya region of Nepal provides a habitat for the endangered snow leopard (Panthera uncia) and its principal prey species, the blue sheep (Pseudois nayaur). The aim of this study was to describe the habitat, the distribution and the population structure of blue sheep, and to estimate their contribution to the carrying capacity of snow leopard in the upper Mustang region of Nepal. Blue sheep were recorded at altitudes from 3209-5498 m on slopes with gradients of 16-60° and aspects of 40°NE to 140°SE. A total of 939 blue sheep were counted in the upper Mustang region, and 98 were counted in the Yak Kharka region of Manang district; however, upper Mustang had the lowest population density of blue sheep recorded within their distribution range in Nepal (0.86 blue sheep/km(2)). The results of the study show that a higher density of blue sheep is associated with greater plant species diversity. The most important species present in the blue sheep habitat were Kobresia pygmaea, Artemesia spp., Lonicera spp., Lancea tibetica, Poa spp., Astragalus spp. and Ephedra gerardiana. It is estimated that the existing blue sheep population biomass of approximately 38 925 kg in the upper Mustang region could support approximately 19 snow leopards (1.6 snow leopards/100 km(2)). © 2012 Wiley Publishing Asia Pty Ltd, ISZS and IOZ/CAS.

Identification of the dominant runoff pathways from data-based mechanistic modelling of nested catchments in temperate UK

NASA Astrophysics Data System (ADS)

Ockenden, M. C.; Chappell, N. A.

2011-05-01

SummaryUnderstanding hydrological flow pathways is important for modelling stream response, in order to address a range of environmental problems such as flood prediction, prediction of chemical loads and identification of contaminant pathways for subsequent remediation. This paper describes the use of parametrically efficient, low order models to identify the dominant modes of stream response for catchments within the Upper Eden, UK. A first order linear model adequately identified the dominant mode in all but one of the sub-catchments. A consistent pattern of time constants and pure time delays between catchments was observed over different periods of data. In the nested catchments, time constants increased as the catchment size increased from 1.1 km 2 at Gais Gill (2-7 h) to 69.4 km 2 at Kirkby Stephen (5-10 h) to 223.4 km 2 at Great Musgrave (7-16 h) to 616.4 km 2 at Temple Sowerby (11-22 h), but Blind Beck (a small catchment 8.8 km 2, time constants 11-21 h) had time constants most similar to Temple Sowerby. This was attributed to a combination of the storage role of permeable rock strata, where present, and the effect of scale on sub-surface and channel routing. A first order model could not be identified for the 1.0 km 2 Low Hall catchment, which comprises permeable sandstone overlain by Quaternary sediments. A second-order model of Low Hall stream showed a higher proportion of water taking a slower pathway (76% via a slow pathway; time constant 252 h) than a model with the same structure for the 8.8 km 2 Blind Beck (46% via slow pathway; time constant 60 h), where only 38% of the basin was underlain by the same permeable sandstone. This highlights the need to quantify the role of deep pathways through permeable rock, where present, in addition to the effect of catchment size on response times.

Cross-terminator ion flow in the ionospheres of Mars and Venus

NASA Astrophysics Data System (ADS)

Fraenz, Markus; Dubinin, Eduard; Angsmann, Anne; Nielsen, Erling; Woch, Joachim; Barabash, Stas; Lundin, Rickard; Fedorov, A.

The upper ionospheres of Mars and Venus are permeated by the magnetic fields induced by the solar wind. It is a long-standing question wether these fields can put the dense ionospheric plasma into motion. If so, the cross-terminator flow of the upper ionosphere could explain a significant part of the ion escape from the planets atmospheres. But it has been technically very challenging to measure the ion flow at energies below 20eV. The only such measurements have been made by the ORPA instrument of the Pioneer Venus Orbiter reporting speeds of 1-5km/s for O+ ions at Venus above 300km altitude at the terminator (Knudsen et al, GRL 1982). At Venus the flow has been explained by the pressure gradient force between dayside and nightside. It can explain the ion supply to the nightside ionosphere. At Mars comparable measurements have never been made. We here report on new measurements of the cross-terminator ion flow at Mars by the ASPERA 3 experiment onboard Mars Express with support from the MARSIS radar experiment which confirm O+ flow speeds of around 6km/s with fluxes of 1.2 ∗ 109 /cm2 s. We also discuss the complicated influence of the spacecraft potential on low energy measurements. At Mars the nightside ionosphere is much weaker than on Venus and the escape velocity only 5km/s. This means that the observed flow leads to escape from the planet. We discuss the implication of these new observation on the total ion escape and possible extensions of the analysis to dayside observations which might allow us to infer the flow structure imposed by the induced magnetic field. We then discuss the observational situation at Venus where the ASPERA-4 instrument allows similar measurements.

Hybrid Stars in the Light of GW170817

NASA Astrophysics Data System (ADS)

Nandi, Rana; Char, Prasanta

2018-04-01

We have studied the effect of the tidal deformability constraint given by the binary neutron star merger event GW170817 on the equations of state (EOS) of hybrid stars. The EOS are constructed by matching the hadronic EOS described by the relativistic mean-field model and parameter sets NL3, TM1, and NL3ωρ with the quark matter EOS described by the modified MIT bag model, via a Gibbs construction. It is found that the tidal deformability constraints along with the lower bound on the maximum mass (M max = 2.01 ± 0.04 M ⊙) significantly limits the bag model parameter space ({B}eff}1/4, a 4). We also obtain upper limits on the radius of 1.4 M ⊙ and 1.6 M ⊙ stars as R 1.4 ≤ 13.2–13.5 km and R 1.6 ≤ 13.2–13.4 km, respectively, for the different hadronic EOS considered here.

Seismic belt in the upper plane of the double seismic zone extending in the along-arc direction at depths of 70-100km beneath NE Japan, and its relation with the dehydration embrittlement hypothesis

NASA Astrophysics Data System (ADS)

Kita, S.; Okada, T.; Nakajima, J.; Matsuzawa, T.; Hasegawa, A.

2006-12-01

1. Introduction Dehydration embrittlement or CO2¨Cbearing devolatization embrittlement hypothesis has been proposed as a possible cause of intraslab earthquakes in several studies [e.g., Peacock, 2001; Kirby et al., 1996; Meade and Jeanloz, 1991]. Precise location of intraslab seismicity is needed to discuss its cause in these studies. Recently, a very dense nationwide seismic network (Hi-net) has been constructed by NIED in Japan. In this study, we relocate microearthquakes more precisely by using data obtained by this dense seismic network to detect the characteristic distribution of the seismicity within the Pacific slab beneath Hokkaido and Tohoku, NE Japan. 2. Data and method In the present study, we relocated events at depths of 20¨C300 km for the period from January 2002 to August 2005 from the JMA earthquake catalog. Hypocenter locations and arrival time data in the JMA catalog were used as the initial hypocenters and data for relocations. We applied the double-difference hypocenter location method (DDLM) by Waldhauser and Ellsworth (2000) to the arrival time data of the events. We also checked spatial distribution of the focal mechanisms of the events in the seismic belts and the surrounding upper seismic plane. We used focal mechanism solutions determined by Igarashi et al. (2001). 3. Results and discussion 1) There exist earthquakes occurring in the area between the upper and lower seismic planes (interplane earthquakes), and their focal mechanisms tend to be the down-dip compressional (DC-) type like those of upper plane events. 2) We found a seismic "belt" which is parallel to the iso-depth contour of the plate interface beneath the forearc area at depths of 80¨C100 km. The location of the seismic belt seems to correspond to one phase boundary (from jadeite lawsonite blueschist (H2O content: 5.4 wt% ) to lawsonite amphibole eclogite (3.0wt %) (Hacker et al., 2003)) with dehydration reaction. 3) The location of the deeper limit of seismicity of the upper seismic plane in the slab crust also seems to correspond to another phase boundary (the jadeite lawsonite blueschist to lawsonite amphibole eclogite (Hacker et al., 2003)) with dehydration reaction. 4) Events of the upper seismic plane mainly have down-dip compression type focal mechanisms, but several events have the normal fault type (NF-type) ones, whose spatial distribution seems to correspond to these phase boundaries. These NF events might induced by the tensional stress field, which is caused by the volume reduction due to the dehydration reactions [Kirby et al., 1996; Igarashi et al., 2001].

Esr Observations of Tid In The Polar Cusp/cap Ionosphere

NASA Astrophysics Data System (ADS)

Yin, F.; Ma, S. Y.; Schlegel, K.

EISCAT-Svalbard radar provides new opportunity to study TIDs in the polar cusp/cap ionosphere. Propagation characteristics of AGW-caused TIDs in quiet days are stud- ied by means of maximum entropy cross-spectral analysis of ESR CP1 and CP2 data. Apparent vertical wave-number of the TIDs as a function of height and the horizontal wave-number vector are obtained for main period of disturbances. It is observed as the first time that some of TIDs in the polar cap/cusp ionosphere can propagate vertically from the height lower than 200 km up to as high as about 700 km with little attenu- ation. In the auroral ionosphere, however, they usually fade away below 500 km. In the region from about 100 to 180 km height, downward propagating mode is seen ob- viously. The possible relations of the TIDs with cusp particle precipitation and upper E-region heating are discussed.

Three-dimensional crustal structure of Long Valley caldera, California, and evidence for the migration of CO2 under Mammoth Mountain

USGS Publications Warehouse

Foulger, G.R.; Julian, B.R.; Pitt, A.M.; Hill, D.P.; Malin, P.E.; Shalev, E.

2003-01-01

A temporary network of 69 three-component seismic stations captured a major seismic sequence in Long Valley caldera in 1997. We performed a tomographic inversion for crustal structure beneath a 28 km ?? 16 km area encompassing part of the resurgent dome, the south moat, and Mammoth Mountain. Resolution of crustal structure beneath the center of the study volume was good down to ???3 km below sea level (???5 km below the surface). Relatively high wave speeds are associated with the Bishop Tuff and lower wave speeds characterize debris in the surrounding moat. A low-Vp/Vs anomaly extending from near the surface to ???1 km below sea level beneath Mammoth Mountain may represent a CO2 reservoir that is supplying CO2-rich springs, venting at the surface, and killing trees. We investigated temporal variations in structure beneath Mammoth Mountain by differencing our results with tomographic images obtained using data from 1989/1990. Significant changes in both Vp and Vs were consistent with the migration of CO2 into the upper 2 km or so beneath Mammoth Mountain and its depletion in peripheral volumes that correlate with surface venting areas. Repeat tomography is capable of detecting the migration of gas beneath active silicic volcanoes and may thus provide a useful volcano monitoring tool.

Hot Dog and Butterfly, Nereidum Montes

NASA Technical Reports Server (NTRS)

1999-01-01

Some of the pictures returned from Mars by the Mars Orbiter Camera (MOC) onboard the Mars Global Surveyor (MGS) spacecraft show features that--at a glance--resemble familiar, non-geological objects on Earth. For example, the picture above at the left shows several low, relatively flat-topped hills (mesas) on the floor of a broad valley among the mountains of the Nereidum Montes region, northeast of Argyre Planitia. One of the mesas seen here looks like half of a butterfly (upper subframe on right). Another hill looks something like a snail or a hot dog wrapped and baked in a croissant roll (lower subframe on right). These mesas were formed by natural processes and are most likely the eroded remnants of a formerly more extensive layer of bedrock. In the frame on the left, illumination is from the upper left and the scene covers an area 2.7 km (1.7 miles) wide by 6.8 km (4.2 miles) high. The 'butterfly' is about 800 meters (875 yards) in length and the 'hot dog' is about 1 km (0.62 miles) long.

Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

Space imaging of a 300 years old cooling magma chamber: Timanfaya volcano (Lanzarote, Canary Islands)

NASA Astrophysics Data System (ADS)

Gonzalez, P. J.; Tiampo, K. F.

2010-12-01

Multitemporal space radar interferometry analysis between 1992 and 2000 revealed significantly deforming areas with a magnitude of 4-6 mm/yr of lengthening in the radar line of sight at Timanfaya volcano (Lanzarote, Canary Island). Timanfaya volcano erupted almost 300 years ago (1730-1736), along a 15 km-long fissure-feeding magmatic system, resulting in the longest and largest historical eruption of the Canarian archipelago to date, with >1 km3 of erupted basaltic lavas covering 200 km2. High surficial temperature (600 degrees-C at 13 m) and high heat flux measurements (150 mW/m2) suggest that the remnants of the magmatic chamber that fed the 1730-1736 are still partly molten. Here, we present preliminary models of the subsidence taking into account all available data, including geophysical data (heat flux, seismic, magnetotelluric and gravity), the geochemistry of freshly erupted lavas, upper mantle and crustal xenoliths, and structural geology.

Velocity structure around the 410 km discontinuity beneath the East China Sea based on the waveform modeling method

NASA Astrophysics Data System (ADS)

Li, W.; Cui, Q.; Gao, Y.; Wei, R.; Zhou, Y.; Yu, J.

2017-12-01

The 410 km discontinuity is the upper boundary of the mantle transition zone. Seismic detections on the structure and morphology of the 410 km discontinuity are helpful to understand the compositions of the Earth's interior and the relevant geodynamics. In this paper, we select the broadband P waveforms of an intermediate earthquake that occurred in the Ryukyu subduction zone and retrieved from the China Digital Seismograph Network, and study the fine velocity structure around the 410 km discontinuity by matching the observed triplicated waveforms with the theoretical ones. Our results reveal that (1) the 410 km discontinuity beneath the East China Sea is mostly a sharp boundary with a small-scale uplift of 8-15 km and a gradient boundary up to 20 km in the most southern part, and (2) there exist a low velocity layer atop the 410 km discontinuity with the thickness of 50-62 km and P-wave velocity decrease of 0.5%-1.5%, and (3) a high velocity anomaly with P-wave decrease of 1.0%-3.0% below 440 km. Combining with the previous topographic results in this area, we speculate that the high velocity anomaly is relevant to the stagnancy of the western Pacific slab in the mantle transition zone, the decomposition of phase E in the slab results in the increase of water content, which would cause the uplift of the 410 km discontinuity, and the low velocity layer atop the discontinuity should be related to the partial melting of the mantle peridotite induced by the dehydration of the hydrous minerals.

Northern and Southern Hemisphere Ground-Based Infrared Spectroscopic Measurements of Tropospheric Carbon Monoxide and Ethane

NASA Technical Reports Server (NTRS)

Rinsland, Curtis P.; Jones, Nicholas B.; Connor, Brian J.; Logan, Jennifer A.; Pougatchev, Nikita S.; Goldman, Aaron; Murcray, Frank J.; Stephen, Thomas M.; Pine, Alan S.; Zander, Rodolphe

1998-01-01

Time series of CO and C2H, measurements have been derived from high-resolution infrared solar spectra recorded in Lauder, New Zealand (45.0 degrees S, 169.7 degrees E, altitude 0.37 km), and at the U.S. National Solar Observatory (31.9 degrees N, 11, 1.6 degrees W, altitude 2.09 km) on Kitt Peak. Lauder observations were obtained between July 1993 and November 1997, while the Kitt Peak measurements were recorded between May 1977 and December 1997. Both databases were analyzed with spectroscopic parameters that included significant improvements for C2H6 relative to previous studies. Target CO and C2H6 lines were selected to achieve similar vertical samplings based on averaging kernels. These calculations show that partial columns from layers extending from the surface to the mean tropopause and from the mean tropopause to 100 km are nearly independent. Retrievals based on a semiempirical application of the Rodgers optimal estimation technique are reported for the lower layer, which has a broad maximum in sensitivity in the upper troposphere. The Lauder CO and C2H, partial columns exhibit highly asymmetrical seasonal cycles with minima in austral autumn and sharp peaks in austral spring. The spring maxima are the result of tropical biomass burning emissions followed by deep convective vertical transport to the upper troposphere and long-range horizontal transport. Significant year-to-year variations are observed for both CO and C2H6, but the measured trends, (+0.37 +/- 0.57)% yr(exp -1) and (-0.64 +/- 0.79)% yr(exp -1), I sigma, respectively, indicate no significant long-term changes. The Kitt Peak data also exhibit CO and C2H6, seasonal variations in the lower layer with trends equal to (-0.27 +/- 0.17)% yr(exp -1) and (-1.20 +/- 0.35)% yr(exp -1), 1 sigma, respectively. Hence a decrease in the Kitt Peak tropospheric C2H6 column has been detected, though the CO trend is not significant. Both measurement sets are compared with previous observations, reported trends, and three-dimensional model calculations.

Seismic Structure of India from Regional Waveform Matching

NASA Astrophysics Data System (ADS)

Gaur, V.; Maggi, A.; Priestley, K.; Rai, S.

2003-12-01

We use a neighborhood adaptive grid search procedure and reflectivity synthetics to model regional distance range (500-2000~km) seismograms recorded in India and to determine the variation in the crust and uppermost mantle structure across the subcontinent. The portions of the regional waveform which are most influenced by the crust and uppermost mantle structure are the 10-100~s period Pnl and fundamental mode surface waves. We use the adaptive grid search algorithm to match both portions of the seismogram simultaneously. This procedure results in a family of 1-D path average crust and upper mantle velocity and attenuation models whose propagation characteristics closely match those of the real Earth. Our data set currently consist of ˜20 seismograms whose propagation paths are primarily confined to the Ganges Basin in north India and the East Dharwar Craton of south India. The East Dharwar Craton has a simple and uniform structure consisting of a 36+/-2 km thick two layer crust, and an uppermost mantle with a sub-Moho velocity of 4.5~km/s. The structure of northern India is more complicated, with pronounced low velocities in the upper crustal layer due to the large sediment thicknesses in the Ganges basin.

Extremely High Magma Emplacement Rates Recorded in the Golden Horn Batholith, WA

NASA Astrophysics Data System (ADS)

Eddy, M. P.; Bowring, S. A.; Tepper, J. H.; Miller, R. B.

2015-12-01

High SiO2 rhyolites emplaced during 'super-eruptions' demonstrate that large volumes of eruptible magma can exist in the upper crust. However, the timescale over which the magma reservoirs that source these eruptions are built remains controversial. Thermal models suggest that magma emplacement rates need to be > 0.005-0.01 km3/yr in order to accumulate enough eruptible magma to source a 'super-eruption'. Yet, these rates are higher than the time-averaged rates (< 0.001 km3/yr) for nearly all well-studied granitoid plutonic complexes. This disparity contradicts geologic evidence suggesting that the high SiO2 rhyolites emplaced during 'super-eruptions' are extracted from crystal rich magma chambers that should be preserved in the geologic record as granodioritic and granitic plutons. We quantify time-averaged magma emplacement rates for the upper crustal Golden Horn batholith, WA based on new geologic mapping and U-Pb zircon CA-IDTIMS geochronology. The batholith is exposed over 310 km3 and can be separated in the field into five intrusive units. High topography allows the 3D geometry of each phase to be constrained and their volumes range from < 100 km3 to > 400 km3. U-Pb zircon geochronology reveals that four of the five phases were assembled incrementally and distinct zircon populations from samples within these phases suggest that individual magmatic pulses had fully crystallized before the next arrived. However, six nearly identical U-Pb zircon dates from a > 400 km3 rapakivi granite show that this phase was built in ca. 50 kyr and that large portions may have been emplaced nearly simultaneously. The implied emplacement rate for this phase (≥ 0.008 km3/yr) is in agreement with those predicted for assembly of the upper crustal magma chambers that source 'super-eruptions', and it may provide a rare and unprecedented opportunity to study the processes that occur in such chambers.

Crustal structure beneath western and eastern Iceland from surface waves and receiver functions

USGS Publications Warehouse

Du, Z.; Foulger, G.R.; Julian, B.R.; Allen, R.M.; Nolet, G.; Morgan, W.J.; Bergsson, B.H.; Erlendsson, P.; Jakobsdottir, S.; Ragnarsson, S.; Stefansson, R.; Vogfjord, K.

2002-01-01

We determine the crustal structures beneath 14 broad-band seismic stations, deployed in western, eastern, central and southern Iceland, using surface wave dispersion curves and receiver functions. We implement a method to invert receiver functions using constraints obtained from genetic algorithm inversion of surface waves. Our final models satisfy both data sets. The thickness of the upper crust, as defined by the velocity horizon Vs = 3.7 km s-1, is fairly uniform at ???6.5-9 km beneath the Tertiary intraplate areas of western and eastern Iceland, and unusually thick at 11 km beneath station HOT22 in the far south of Iceland. The depth to the base of the lower crust, as defined by the velocity horizon Vs = 4.1 km s-1 is ???20-26 km in western Iceland and ???27-33 km in eastern Iceland. These results agree with those of explosion profiles that detect a thinner crust beneath western Iceland than beneath eastern Iceland. An earlier report of a substantial low-velocity zone beneath the Middle Volcanic Zone in the lower crust is confirmed by a similar observation beneath an additional station there. As was found in previous receiver function studies, the most reliable feature of the results is the clear division into an upper sequence that is a few kilometres thick where velocity gradients are high, and a lower, thicker sequence where velocity gradients are low. The transition to typical mantle velocities is variable, and may range from being very gradational to being relatively sharp and clear. A clear Moho, by any definition, is rarely seen, and there is thus uncertainty in estimates of the thickness of the crust in many areas. Although a great deal of seismic data are now available constraining the structures of the crust and upper mantle beneath Iceland, their geological nature is not well understood.

Paroxysmal dome explosion during the Merapi 2010 eruption: Processes and facies relationships of associated high-energy pyroclastic density currents

NASA Astrophysics Data System (ADS)

Komorowski, Jean-Christophe; Jenkins, Susanna; Baxter, Peter J.; Picquout, Adrien; Lavigne, Franck; Charbonnier, Sylvain; Gertisser, Ralf; Preece, Katie; Cholik, Noer; Budi-Santoso, Agus; Surono

2013-07-01

An 11-minute sequence of laterally-directed explosions and retrogressive collapses on 5 November 2010 at Merapi (Indonesia) destroyed a rapidly-growing dome and generated high-energy pyroclastic density currents (PDCs) spreading over 22 km2 with a runout of 8.4 km while contemporaneous co-genetic valley-confined PDCs reached 15.5 km. This event formed Stage 4 of the multi-stage 2010 eruption, the most intense eruptive episode at Merapi since 1872. The deposits and the widespread devastating impact of associated high-energy PDCs on trees and buildings show striking similarities with those from historical volcanic blasts (Montagne Pelée, Martinique, Bezymianny, Russia, Mount St. Helens, USA, Soufrière Hills, Montserrat). We provide data from stratigraphic and sedimentologic analyses of 62 sections of the first unequivocal blast-like deposits in Merapi's recent history. We used high resolution satellite imagery to map eruptive units and flow direction from the pattern of extensive tree blowdown. The stratigraphy of Stage 4 consists of three depositional units (U0, U1, U2) that we correlate to the second, third and fourth explosions of the seismic record. Both U1 and U2 show a bi-partite layer stratigraphy consisting each of a lower L1 layer and an upper L2 layer. The lower L1 layer is typically very coarse-grained, fines-poor, poorly-sorted and massive, and was deposited by the erosive waxing flow head. The overlying L2 layer is much finer grained, fines-rich, moderately to well-sorted, with laminar to wavy stratification. L2 was deposited from the waning upper part and wake of the PDC. Field observations indicate that PDC height reached ~ 330 m with an internal velocity of ~ 100 m s- 1 within 3 km from the source. The summit's geometry and the terrain morphology formed by a major transversal ridge and a funneling deep canyon strongly focused PDC mass towards a major constriction, thereby limiting the loss of kinetic energy. This favored elevated PDC velocities and high particle concentration, promoted overspilling of PDCs across high ridges into other river valleys, and generated significant dynamic pressures to distances of 6 km that caused total destruction of buildings and the forest. The Merapi 2010 eruption highlights that explosive and gravitational disintegration of a rapidly growing dome can generate devastating high-energy, high-velocity PDCs. This constitutes a credible high impact scenario for future multi-stage eruptions at Merapi and at other volcanoes that pose particular monitoring, crisis response, and risk reduction challenges.

Constraints on the shear speed, crust thickness and residual topography of western Tibet from surface wave tomography and virtual deep seismic sounding

NASA Astrophysics Data System (ADS)

Matchette-Downes, H.; van der Hilst, R. D.; Priestley, K. F.

2017-12-01

We have estimated the thickness of the crust in western Tibet by measuring the time delays between the direct S and the SsPmp seismic phases. We find that the thickness of the crust increases from around 50 km beneath the Tethyan Himalayas to around 80 km beneath the Lhasa block, and then decreases to around 70 km beneath the Qiangtang terrane.This method, virtual deep seismic sounding (VDSS), also yields robust estimates of the contribution of crust buoyancy to elevation. By subtracting the predicted elevation from the real topography, we find there is no observable deviation from hydrostatic topography beneath the Tethyan Himalaya, but there is negative residual topography of 1.5 to 2.0 km beneath the Lhasa and Qiangtang terranes. It is also known that the interior of the Plateau is isostatically compensated, as it has small free air gravity anomalies.Additionally, we have estimated the 3D shear speed structure of the crust and upper mantle. This model is derived from maps of the fundamental mode Rayleigh wave phase speed dispersion in the period range from 20 to 140 s, obtained from a standard two-plane-wave inversion constrained with receiver functions and group speeds from ambient noise. The observations agree with previous observations of a low-wavespeed zone in the mid-crust and a gradual Moho. Furthermore, the long-period Rayleigh waves detect a high-wavespeed upper mantle.Together, the observations of high upper mantle wavespeeds, negative residual topography, and small free air gravity anomalies support the hypothesis that cold, dense Indian lithosphere has underthrust the Plateau in this region. However, in the presentation we also consider contributions to residual topography from plate flexure, lower crustal flow, or deeper mantle flow (dynamic topography).

Thickening the outer margins of the Tibetan Plateau: The role of crustal shortening

NASA Astrophysics Data System (ADS)

Lease, R. O.; Burbank, D. W.

2012-12-01

One of the most direct consequences of the collision of two buoyant continents is large-scale crustal thickening that results in the upward and outward growth of high terrain. As the stronger Indian continent has collided with weaker Asia over at least the past 50 Myr, widespread crustal thickening has occurred over an area that is approximately 2.5 million km^2 at present. The resultant Tibetan crust is the thickest observed on Earth today with an average thickness of 65 km and a maximum that may reach 90 km in places. The mechanisms by which Tibetan crust has thickened, however, as well as the timing and distribution of these mechanisms across the plateau, remain debatable. Two of the most popular mechanisms for thickening the crust beneath the margins of the Tibetan Plateau are: 1) pure shear with faulting and folding in the upper crust and horizontal shortening below; and 2) flow and inflation of lower or middle crust without significant shortening of the upper crust. To help discriminate between the relative contributions of these two mechanisms, well-constrained estimates of upper crustal shortening are needed. Here we document the Cenozoic shortening budget across the northeastern Tibetan Plateau margin near 36°N 102.5°E with several 100- to 145-km-long balanced cross sections. Thermochronological and magnetostratigraphic data indicate that modest NNE-SSW shortening began in middle Eocene time, shortly after initial India-Asia collision. Accelerated east-west shortening, however, did not commence until ~35 Myr later. A five-fold acceleration in shortening rates in middle Miocene-to-Recent time accounts for more than half of the total Cenozoic crustal shortening and thickening in this region. Overall, the balanced cross sections indicate 11 ± 2 % east-west shortening since middle Miocene time, and ~9 ± 2 % NNE-SSW shortening between middle Eocene and middle Miocene times. Given the present-day crustal thickness of 56 ± 4 km in northeastern Tibet, crustal restorations that remove Cenozoic shortening suggest that the northeastern Tibetan crust was 45 ± 5 km thick prior to India-Asia continental collision. This pre-collision thickness estimate is equivalent to average continental crustal thicknesses both adjacent to the Tibetan plateau (44 ± 4 km) and globally (41 ± 6 km) and suggests that pure shear alone may account for Cenozoic crustal thickening in northeastern Tibet, obviating the need for lower crustal flow. Furthermore, a growing number of balanced cross sections across the margins of the Tibetan Plateau document Cenozoic shortening sufficient to generate modern crustal thicknesses: in northern Tibet [Yin et al., 2007; 2008a; 2008b], eastern Tibet [Hubbard et al., 2009; 2010], and northeastern Tibet [this work]. Collectively, these similar findings suggest that lower crustal flow is either unnecessary to account for Cenozoic crustal thickening beneath the outer margins of the Tibetan Plateau or, alternatively, has a more restricted role than originally proposed.

MIPAS observations of ozone in the middle atmosphere

NASA Astrophysics Data System (ADS)

López-Puertas, Manuel; García-Comas, Maya; Funke, Bernd; Gardini, Angela; Stiller, Gabriele P.; von Clarmann, Thomas; Glatthor, Norbert; Laeng, Alexandra; Kaufmann, Martin; Sofieva, Viktoria F.; Froidevaux, Lucien; Walker, Kaley A.; Shiotani, Masato

2018-04-01

In this paper we describe the stratospheric and mesospheric ozone (version V5r_O3_m22) distributions retrieved from MIPAS observations in the three middle atmosphere modes (MA, NLC, and UA) taken with an unapodized spectral resolution of 0.0625 cm-1 from 2005 until April 2012. O3 is retrieved from microwindows in the 14.8 and 10 µm spectral regions and requires non-local thermodynamic equilibrium (non-LTE) modelling of the O3 v1 and v3 vibrational levels. Ozone is reliably retrieved from 20 km in the MA mode (40 km for UA and NLC) up to ˜ 105 km during dark conditions and up to ˜ 95 km during illuminated conditions. Daytime MIPAS O3 has an average vertical resolution of 3-4 km below 70 km, 6-8 km at 70-80 km, 8-10 km at 80-90, and 5-7 km at the secondary maximum (90-100 km). For nighttime conditions, the vertical resolution is similar below 70 km and better in the upper mesosphere and lower thermosphere: 4-6 km at 70-100 km, 4-5 km at the secondary maximum, and 6-8 km at 100-105 km. The noise error for daytime conditions is typically smaller than 2 % below 50 km, 2-10 % between 50 and 70 km, 10-20 % at 70-90 km, and ˜ 30 % above 95 km. For nighttime, the noise errors are very similar below around 70 km but significantly smaller above, being 10-20 % at 75-95 km, 20-30 % at 95-100 km, and larger than 30 % above 100 km. The additional major O3 errors are the spectroscopic data uncertainties below 50 km (10-12 %) and the non-LTE and temperature errors above 70 km. The validation performed suggests that the spectroscopic errors below 50 km, mainly caused by the O3 air-broadened half-widths of the v2 band, are overestimated. The non-LTE error (including the uncertainty of atomic oxygen in nighttime) is relevant only above ˜ 85 km with values of 15-20 %. The temperature error varies from ˜ 3 % up to 80 km to 15-20 % near 100 km. Between 50 and 70 km, the pointing and spectroscopic errors are the dominant uncertainties. The validation performed in comparisons with SABER, GOMOS, MLS, SMILES, and ACE-FTS shows that MIPAS O3 has an accuracy better than 5 % at and below 50 km, with a positive bias of a few percent. In the 50-75 km region, MIPAS O3 has a positive bias of ≈ 10 %, which is possibly caused in part by O3 spectroscopic errors in the 10 µm region. Between 75 and 90 km, MIPAS nighttime O3 is in agreement with other instruments by 10 %, but for daytime the agreement is slightly larger, ˜ 10-20 %. Above 90 km, MIPAS daytime O3 is in agreement with other instruments by 10 %. At night, however, it shows a positive bias increasing from 10 % at 90 km to 20 % at 95-100 km, the latter of which is attributed to the large atomic oxygen abundance used. We also present MIPAS O3 distributions as function of altitude, latitude, and time, showing the major O3 features in the middle and upper mesosphere. In addition to the rapid diurnal variation due to photochemistry, the data also show apparent signatures of the diurnal migrating tide during both day- and nighttime, as well as the effects of the semi-annual oscillation above ˜ 70 km in the tropics and mid-latitudes. The tropical daytime O3 at 90 km shows a solar signature in phase with the solar cycle.

Diurnal variation of nitric oxide in the upper stratosphere

NASA Technical Reports Server (NTRS)

Kondo, Y.; Aimedieu, P.; Pirre, M.; Ramaroson, R.; Matthews, W. A.

1990-01-01

Two recent measurements of the temporal variation of nitric oxide at constant altitude near 40 km are reported. The observations were made at float altitude with a balloon-borne chemiluminescence detector together with in situ ozone measurements. The first measurement was made at 44 N on September 17, 1987, at an altitude of 40 km from before sunrise until 1000 LT. The second observation was made at the same latitude on June 18, 1988, at 39 km from 0800 to 1230 LT. At an altitude of 40 km, nitric oxide was observed to start increasing very rapidly at sunrise when the solar zenith angle reached about 95 deg. After the rapid initial buildup, the rate of NO increase stabilized for 3 hours at about 1.2 ppbv/hour. Near 1100 LT at 39 km in summer, the NO mixing ratio was observed to become nearly constant. These features of the diurnal variation of NO are in accord with the temporal variation expected from a time-dependent zero-dimensional photochemical model.

ARC-1981-A86-7005

NASA Image and Video Library

1981-01-18

Range : 7.7 million km. ( 4.8 million miles ) P-29465 In this image captured by Voyager 2, three newly discovered satellites of Uranus can be seen orbiting outside of the nine known rings of Uranus. The outermost of the rings, the Epsilon Ring can be seen here at upper right. The largest of the three moons viewed here, 1986U1, was discovered January 3rd. it is an estimated 90 km. ( 55 mi. ) across and its orbits Uranus every 12 hours, 19 minutes ata distance of 66,090 km. ( 41,040 mi.) from the planets center. the other two moons are slightly smaller, 1986U3 orbits every 11 hours, 6 minutes at 61,750 km. ( 38,350 mi.),1986U4 every 13 hours, 24 minutes at 69,920 km. ( 43,420 mi.). They were dicovered on January 9th and 13th, respectively. Long exposures were required to bring out these small objects. As a result of the relative motions of the spacecraft and the moons, they appear slightly elongated.

Double-difference Relocation of the Aftershocks of the Tecomán, Colima, Mexico Earthquake of 22 January 2003

NASA Astrophysics Data System (ADS)

Andrews, Vanessa; Stock, Joann; Ramírez Vázquez, Carlos Ariel; Reyes-Dávila, Gabriel

2011-08-01

On 22 January 2003, the M w = 7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0 km in depth and 1.4 km in the north-south and east-west directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8 km in depth, 0.3 km in the east-west direction, and 0.7 km in the north-south direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3 months after the mainshock.

Geological Structures in the WaIls of Vestan Craters

NASA Technical Reports Server (NTRS)

Mittlefehldt, David; Nathues, A.; Beck, A. W.; Hoffmann, M.; Schaefer, M.; Williams, D. A.

2014-01-01

A compelling case can be made that Vesta is the parent asteroid for the howardite, eucrite and diogenite (HED) meteorites [1], although this interpretation has been questioned [2]. Generalized models for the structure of the crust of Vesta have been developed based on petrologic studies of basaltic eucrites, cumulate eucrites and diogenites. These models use inferred cooling rates for different types of HEDs and compositional variations within the clan to posit that the lower crust is dominantly diogenitic in character, cumulate eucrites occur deep in the upper crust, and basaltic eucrites dominate the higher levels of the upper crust [3-5]. These models lack fine-scale resolution and thus do not allow for detailed predictions of crustal structure. Geophysical models predict dike and sill intrusions ought to be present, but their widths may be quite small [6]. The northern hemisphere of Vesta is heavily cratered, and the southern hemisphere is dominated by two 400-500 km diameter basins that excavated deep into the crust [7-8]. Physical modeling of regolith formation on 300 km diameter asteroids predicts that debris layers would reach a few km in thickness, while on asteroids of Vesta's diameter regolith thicknesses would be less [9]. This agrees well with the estimated =1 km thickness of local debris excavated by a 45 km diameter vestan crater [10]. Large craters and basins may have punched through the regolith/megaregolith and exposed primary vestan crustal structures. We will use Dawn Framing Camera (FC) [11] images and color ratio maps from the High Altitude and Low Altitude Mapping Orbits (HAMO, 65 m/pixel; LAMO, 20 m/pixel) to evaluate structures exposed on the walls of craters: two examples are discussed here.

The Mafic Lower Crust of Neoproterozoic age beneath Western Arabia: Implications for Understanding African Lower Crust

NASA Astrophysics Data System (ADS)

Stern, R. J.; Mooney, W. D.

2011-12-01

We review evidence that the lower crust of Arabia - and by implication, that beneath much of Africa was formed at the same time as the upper crust, rather than being a product of Cenozoic magmatic underplating. Arabia is a recent orphan of Africa, separated by opening of the Red Sea ~20 Ma, so our understanding of its lower crust provides insights into that of Africa. Arabian Shield (exposed in W. Arabia) is mostly Neoproterozoic (880-540 Ma) reflecting a 300-million year process of continental crustal growth due to amalgamated juvenile magmatic arcs welded together by granitoid intrusions that make up as much as 50% of the Shield's surface. Seismic refraction studies of SW Arabia (Mooney et al., 1985) reveal two layers, each ~20 km thick, separated by a well-defined Conrad discontinuity. The upper crust has average Vp ~6.3 km/sec whereas the lower crust has average Vp ~7.0 km/sec, corresponding to a granitic upper crust and gabbroic lower crust. Neogene (<30 ma) lava fields in Arabia (harrats) extend over 2500 km, from Yemen to Syria. Many of these lavas contain xenoliths, providing a remarkable glimpse of the lower-crustal and upper-mantle lithosphere beneath W. Arabia. Lower crustal xenoliths brought up in 8 harrats in Saudi Arabia, Jordan, and Syria are mostly 2-pyroxene granulites of igneous (gabbroic, anorthositic, and dioritic) origin. They contain plagioclase, orthopyroxene, and clinopyroxene, and a few contain garnet and rare amphibole and yield mineral-equilibrium temperatures of 700-900°C. Pyroxene-rich and plagioclase-rich suites have mean Al2O3 contents of 13% and 19%, respectively: otherwise the two groups have similar elemental compositions, with ~50% SiO2 and ~1% TiO2, with low K2O (<0.5%) and Na2O (1-3%). Both groups show tholeiitic affinities, unrelated to their alkali basalt hosts. Mean pyroxene-rich and plagioclase-rich suites show distinct mean MgO contents (11% vs. 7%), Mg# (67 vs. 55), and contents of compatible elements Ni (169 vs. 66 ppm) and Cr (435 vs. 117 ppm). Despite high Mg# in pyroxene-rich xenoliths, mineral compositions of labradoritic plagioclase (mean ~An64) and relatively Fe-rich pyroxenes (mean OPX ~En63; mean CPX~ WO48 En35 Fs17) indicate that these are somewhat fractionated. Trace element patterns are similar to those expected for convergent-margin magmatic suites. Nd-model ages define a mean of 0.76±0.08 Ga, similar to the age of exposed Arabian Shield upper crust. An isochron plot (147Sm/144Nd vs. 143Nd/144Nd) is consistent with formation in Neoproterozoic time. Lower crust of Arabia clearly formed during Neoproterozoic time, about the same time as its upper crust complement; a similar origin for the lower crust beneath the broad expanses of Neoproterozoic crust in N and E Africa is likely. There is no evidence that any of the mafic lower crust of Arabia formed due to underplating by Cenozoic magmas, which may also be true for NE Africa and perhaps mafic lower crust on the flanks of the East African Rift. Such an interpretation predicts a strong lower crust for those regions underlain by anhydrous mafic lower crust of Neoproterozoic age.

Impact of the 1993 flood on the distribution of organic contaminants in bed sediments of the Upper Mississippi River

USGS Publications Warehouse

Barber, L.B.; Writer, J.H.

1998-01-01

The 1500 km Upper Mississippi River (UMR) consists of 29 navigation pools and can be divided into the upper reach (pools 1-4), the middle reach (pools 5-13), and the lower reach (pools 14-26). Comparison of composite bed sediment samples collected from the downstream third of 24 pools before and after the 1993 UMR flood provides fieldscale data on the effect of the flood on sediment organic compound distributions. The sediments were analyzed for organic carbon, coprostanol, polynuclear aromatic hydrocarbons including pyrene, linear alkylbenzene-sulfonates, polychlorinated biphenyls (PCBs), and organochlorine pesticides. Most of the target compounds were detected in all of the sediment samples, although concentrations were generally <1 mg/kg. The highest concentrations typically occurred in the upper reach, an urbanized area on a relatively small river. Pool 4 (Lake Pepin) is an efficient sediment trap, and concentrations of the compounds below pool 4 were substantially lower than those in pools 2-4. Differences in concentrations before and after the 1993 flood also were greatest in the upper reach. In pools 1-4, concentrations of pyrene and PCBs decreased after the flood whereas coprostanol increased. These results suggest that bed sediments stored in the pools were diluted or buried by sediments with different organic compound compositions washed in from urban and agricultural portions of the watershed.The 1500 km Upper Mississippi River (UMR) consists of 29 navigation pools and can be divided into the upper reach (pools 1-4), the middle reach (pools 5-13), and the lower reach (pools 14-26). Comparison of composite bed sediment samples collected from the downstream third of 24 pools before and after the 1993 UMR flood provides field-scale data on the effect of the flood on sediment organic compound distributions. The sediments were analyzed for organic carbon, coprostanol, polynuclear aromatic hydrocarbons including pyrene, linear alkylbenzene-sulfonates, polychlorinated biphenyls (PCBs), and organochlorine pesticides. Most of the target compounds were detected in all of the sediment samples, although concentrations were generally <1 mg/kg. The highest concentrations typically occurred in the upper reach, an urbanized area on a relatively small river. Pool 4 (Lake Pepin) is an efficient sediment trap, and concentrations of the compounds below pool 4 were substantially lower than those in pools 2-4. Differences in concentrations before and after the 1993 flood also were greatest in the upper reach. In pools 1-4, concentrations of pyrene and PCBs decreased after the flood whereas coprostanol increased. These results suggest that bed sediments stored in the pools were diluted or buried by sediments with different organic compound compositions washed in from urban and agricultural portions of the watershed.

Three-Dimensional Slowness Images of the Upper Crust Beneath the Lucky Strike Hydrothermal Vent Sites

NASA Astrophysics Data System (ADS)

Seher, T.; Crawford, W.; Singh, S.; Canales, J. P.; Combier, V.; Cannat, M.; Carton, H.; Dusunur, D.; Escartin, J.; Miranda, M. J.; Pouillet-Erguy, A.

2005-12-01

In June-July 2005 we carried out the SISMOMAR cruise, as part of the MOMAR project (Monitoring the Mid-Atlantic Ridge). Within this cruise, we conducted a 3D seismic reflection survey over an 18 km km x 3.8 km area covering both the Lucky Strike volcano and hydrothermal vents field. In order to have a full coverage inside the 3D box, shots continued for 2.25 km on either side of the box and extended out to the median valley bounding faults. To complement the streamer measurements 25 Ocean Bottom Seismometers (OBS) were placed in an 18 km x 18 km area. 11 OBS positions lie inside the 3D box and can be used to determine a very detailed image of the 3D velocity structure beneath the Lucky Strike volcano and hydrothermal vents field. For the 3D box a tuned array of 14 air guns (2600 cubic inches) was fired at an interval of 37.5 m for a total of 39 lines. We will present the first results of the OBS measurements near the Lucky Strike volcano. As a first step towards a joint 3D travel time and slowness (the inverse of velocity at turning depth) tomography, we present the 3D slowness function (latitude, longitude, offset), which can be considered as a 3D brute stack velocity image of the sub-surface (c.f. Barton and Edwards, 1999). The presence of fluid in the upper crust due to hydrothermal circulation should appear as a low velocity anomaly beneath the hydrothermal vents. In the next step the OBS measurements will be used to corroborate the reflection images of layer 2A observed in the streamer data for the 3D box. The OBS inside the 3D box recorded turning ray arrivals from the upper crust at a very fine sampling interval (37.5 m x 100 m) over a large azimuth. This provides the unique opportunity for jointly inverting travel time and slowness. Hence the measurements contain information on local gradients and should provide a very detailed velocity model of the subsurface, including information on hydrothermal systems and a possilbe anisotropy (e.g. Cherret and Singh, 1999). References: P. Barton, R. Edwards: Velocity imaging by tau-p transformation, LITHOS Science Report, 1999, 1, 67-75. A. Cherrett, S. Singh: 3D anisotropic models from multi-component data, LITHOS Science Report, 1999, 1, 29-34.

Modeling water quality, temperature, and flow in Link River, south-central Oregon

USGS Publications Warehouse

Sullivan, Annett B.; Rounds, Stewart A.

2016-09-09

The 2.1-km (1.3-mi) Link River connects Upper Klamath Lake to the Klamath River in south-central Oregon. A CE-QUAL-W2 flow and water-quality model of Link River was developed to provide a connection between an existing model of the upper Klamath River and any existing or future models of Upper Klamath Lake. Water-quality sampling at six locations in Link River was done during 2013–15 to support model development and to provide a better understanding of instream biogeochemical processes. The short reach and high velocities in Link River resulted in fast travel times and limited water-quality transformations, except for dissolved oxygen. Reaeration through the reach, especially at the falls in Link River, was particularly important in moderating dissolved oxygen concentrations that at times entered the reach at Link River Dam with marked supersaturation or subsaturation. This reaeration resulted in concentrations closer to saturation downstream at the mouth of Link River.

Morphology, distribution, and development of submarine canyons on the United States Atlantic continental slope between Hudson arid Baltimore Canyons

NASA Astrophysics Data System (ADS)

Twichell, David C.; Roberts, David G.

1982-08-01

The distribution and morphology of submarine canyons off the eastern United States between Hudson and Baltimore Canyons have been mapped by long-range sidescan sonar. In this area canyons are numerous, and their spacing correlates with overall slope gradient; they are absent where the gradient is less than 3°, are 2 to 10 km apart where the gradient is 3° to 5°, and are 1.5 to 4 km apart where the gradient exceeds 6°. Canyons range from straight to sinuous; those having sinuous axes indent the edge of the continental shelf and appear to be older than those that head on the upper slope and have straighter axes. A difference in canyon age would suggest that canyons are initiated on the continental slope and only with greater age erode headward to indent the shelf. Shallow gullies on the middle and upper slope parts of the canyon walls suggest that submarine erosion has been a major process in a recent phase of canyon development. *Present address: British Petroleum, Moorgate, London EC2Y 9BU, England

Evidence for Recent Liquid Water on Mars: Gullies at 70oS in Polar Pit Walls

NASA Technical Reports Server (NTRS)

2000-01-01

[figure removed for brevity, see original site]

Gully landforms proposed to have been caused by geologically-recent seepage and runoff of liquid water on Mars are found in the most unlikely places. They typically occur in areas that are quite cold--well below freezing--all year round. Like the old adage about moss on trees, nearly all of them form on slopes that face away from sunlight. Most of the gullies occur at latitudes between 30o and 70o.

The highest latitude at which martian gullies have been found is around 70o-75oS on the walls of pits developed in the south polar pitted plains. If you were at this same latitude on Earth, you would be in Antarctica. This region spends much of the winter--which lasts approximately 6 months on Mars--in darkness and at temperatures cold enough to freeze carbon dioxide (around -130oC or -200oF). Nevertheless, gullies with very sharp, deep, v-shaped channels are seen on the pit walls (above, left).

Based upon the locations of the tops of the channels on the slope shown here, the inferred site of liquid seepage is located at a layer in the pit wall about 1/3 of the way down from the top of the MOC image. The channels start wide and taper downslope. The area above the channels is layered and has been eroded by mass movement--dry avalanching of debris--to form a pattern of chutes and ridges on the upper slope of the pit wall. The top layer appears to have many boulders in it (each about the size of a small house), these boulders are left behind on the upper slopes of the pit wall as debris is removed.

Centered near 70.7oS, 355.7oW, the MOC image was acquired July 14, 1999, and covers an area approximately 2.8 km (1.7 mi) wide by 2.1 km (1.3 mi) high. Sunlight illuminates the MOC image from the upper left and north is toward the upper left. The context view (right) is from the Viking 2 orbiter and was acquired in 1977. The Viking picture is illuminated from the top/upper left; north is toward the upper right. The small white box in the context frame (upper right corner) shows the location of the high resolution MOC view.

Lateral density anomalies and the earth's gravitational field

NASA Technical Reports Server (NTRS)

Lowrey, B. E.

1978-01-01

The interpretation of gravity is valuable for understanding lithospheric plate motion and mantle convection. Postulated models of anomalous mass distributions in the earth and the observed geopotential as expressed in the spherical harmonic expansion are compared. In particular, models of the anomalous density as a function of radius are found which can closely match the average magnitude of the spherical harmonic coefficients of a degree. These models include: (1) a two-component model consisting of an anomalous layer at 200 km depth (below the earth's surface) and at 1500 km depth (2) a two-component model where the upper component is distributed in the region between 1000 and 2800 km depth, and(3) a model with density anomalies which continuously increase with depth more than an order of magnitude.

Three-dimenstional crustal velocity structure beneath the strait of georgia, British Columbia

USGS Publications Warehouse

Zelt, B.C.; Ellis, R.M.; Zelt, C.A.; Hyndman, R.D.; Lowe, C.; Spence, G.D.; Fisher, M.A.

2001-01-01

The Strait of Georgia is a topographic depression straddling the boundary between the Insular and Coast belts in southwestern British Columbia. Two shallow earthquakes located within the strait (M = 4.6 in 1997 and M = 5.0 in 1975) and felt throughout the Vancouver area illustrate the seismic potential of this region. As part of the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS) experiment, seismic instruments were placed in and around the Strait of Georgia to record shots from a marine source within the strait. We apply a tomographic inversion procedure to first-arrival travel-time data to derive a minimum-structure 3-D P-wave velocity model for the upper crust to about 13 km depth. We also present a 2-D velocity model for a profile orientated across the Strait of Georgia derived using a minimum-parameter traveltime inversion approach. This paper represents the first detailed look at crustal velocity variations within the major Cretaceous to Cenozoic Georgia Basin, which underlies the Strait of Georgia. The 3-D velocity model clearly delineates the structure of the Georgia Basin. Taking the 6 km s-1 isovelocity contour to represent the top of the underlying basement, the basin thickens from between 2 and 4 km in the northwestern half of the strait to between 8 and 9 km at the southeastern end of the study region. Basin velocities in the northeastern half are 4.5-6 km s-1 and primarily represent the Upper Cretaceous Nanaimo Group. Velocities to the south are lower (3-6 km s-1) because of the additional presence of the overlying Tertiary Huntingdon Formation and more recent sediments, including glacial and modern Fraser River deposits. In contrast to the relatively smoothly varying velocity structure of the basin, velocities of the basement rocks, which comprise primarily Palaeozoic to Jurassic rocks of the Wrangellia Terrane and possibly Jurassic to mid-Cretaceous granitic rocks of the Coast Belt, show significantly more structure, probably an indication of the varying basement rock lithologies. The 2-D velocity model more clearly reveals the velocity layering associated with the recent sediments, Huntingdon Formation and Nanaimo Group of the southern Georgia Basin, as well as the underlying basement. We interpret lateral variation in sub-basin velocities of the 2-D model as a transition from Wrangellian to Coast Belt basement rocks. The effect of the narrow, onshore-offshore recording geometry of the seismic experiment on model resolution was tested to allow a critical assessment of the validity of the 3-D velocity model. Lateral resolution throughout the model to a depth of 3-5 km below the top of the basement is generally 10-20 km.

Regional difference in small-scale heterogeneities in the crust and upper mantle in Japan derived by the analysis of high-frequency P-wave

NASA Astrophysics Data System (ADS)

Takemura, S.; Furumura, T.

2010-12-01

In order to understand distribution properties of small-scale heterogeneities in the crust and upper mantle structure, we analyze three-component seismograms recorded by Hi-net in Japan. We examined relative strength of the P-wave in the transverse (T) component and its change as a function of frequency and propagation distances, which is strongly relating to the strength of seismic wave scattering in the lithosphere. We analyzed 53,220 Hi-net record from 310 shallow (h<30km) crustal earthquakes with MJMA =2.0-5.3. The three-component seismograms are firstly applied by band-pass filter with pass band frequency of f=1-2, 2-4, 4-8, 8-16, 16-32 Hz and then the Hilbert transform is used to synthesize envelope of each component. Then, the energy partition (EP) of P wave in the T component relative to total P-wave energy is evaluated around the P wave in 3-sec time window. The estimated EP value is almost constant 0.2 in high-frequencies (8-16 Hz) at shorter distance, while it is 0.07 in low-frequencies (1-2 Hz). We found clearly frequency-change property of EP value. But at larger distance over 150 km, EP values gradually increase with increasing distance. In high-frequencies (8-16, 16-32 Hz), especially EP values asymptotically reach from 0.2 to 0.33, equi-partitioning of P-wave energy into three components. This may because Pn-phase dominates in larger hypocentral distances. In order to examine difference in the EP in each area of Japan which would be relating to the strength of crustal heterogeneities in each area we divided the area of Japan into three regions, fore-arc side of Tohoku, back-arc side of Tohoku and Chugoku-Shikoku area. The difference in EP value in each area is clearly found in the high-frequency (4-8 Hz) band, where larger EP (0.2) was obtained at back-arc side of Tohoku relative to smaller EP (0.1) at fore-arc side of Tohoku and Chugoku-Shikoku. This is consistent with the results of Carcole and Sato (2009) who estimated the strength of crustal heterogeneities based on the multi lapse time-window analysis. In order to clarify the cause of such regional difference of EP, we conduct 3-D FDM simulations using stochastic random media. The model covers a zone 204.8 km by 204.8 km by 64.0 km descretized with 0.1 km in horizontal direction and 0.05 km in vertical direction. The small-scale heterogeneity in the lithosphere is constructed by velocity fluctuation from average velocity. The fluctuation is characterized by von Karman-type ACF with the correlation length a, the rms value e and decay order k. We assume average background velocities of P-wave and S-wave are VP = 5.8 km and VS = 3.36 km, respectively. We employ an explosive point source into the model. The FDM simulations were conducted on the Earth Simulator at JAMSTEC. We conducted a number of FDM simulation using different model parameters of stochastic random media for different e (= 0.03, 0.05, 0.07, 0.09) and fixed a and k (a = 5km, k = 0.5). The simulation results confirm EP value increases linearly with increasing e. We also found that larger EP obtained in the back-arc side of Tohoku can be explained by 4% larger e relative to those of other regions.

CCP Receiver-Function Imaging of the Moho beneath Volcanic Fields in Western Saudi Arabia

NASA Astrophysics Data System (ADS)

Blanchette, A. R.; Mooney, W. D.; Klemperer, S. L.; Zahran, H. M.; El-Hadidy, S. Y.

2015-12-01

We are searching for structural complexity in the crust and upper mantle beneath the Neogene volcanic fields ('harrats') of western Saudi Arabia. We determined P-wave seismic receiver functions for 50 broadband seismographic stations located within or adjacent to three volcanic fields: Harrats Lunayyir, Rahat, and Khaybar. There are 18 seismographic stations within Lunayyir, 11 in Khaybar, and 15 in Rahat with average interstation spacing of 10 km, 30km, and 50 km. For each station we calculated 300 to 600 receiver functions with an iterative time-domain deconvolution; noisy receiver functions (outliers) were rejected by cross correlating each receiver function with a station stack; we only accepted those with a cross correlation coefficient ≥ 0.6. We used these receiver functions to create a common-conversion point (CCP) image of the crust and upper mantle. The Moho and lithosphere-asthenosphere boundary (LAB) are clearly imaged, particularly beneath Lunayyir, and have average depths of about 38 km and 60 km. We do not find any evidence for structural disruption of the Moho within our ~70 km x 70 km image of the Moho beneath Lunayyir. We image a clear crust-mantle boundary beneath Rahat and Khaybar also at ~38 km, 2-3 km deeper than anticipated from prior receiver function results outside of the harrats. Mid-crustal low velocity zones seen locally beneath all three harrats, most commonly at 10-15 km or 15-20 km in depth, may more likely represent silicic Precambrian basement than accumulations of magma. Estimates of up to ~0.5 km3 of magma erupted during each eruptive episode are consistent with the lack of a disrupted Moho. However, the total erupted volume of magma, e.g. > 1000 km3 at Rahat, together with associated intrusions from the mantle, is consistent with crustal thickening of ~2 km beneath the harrats.

Probing Venus' polar upper atmosphere in situ: Preliminary results of the Venus Express Atmospheric Drag Experiment (VExADE).

NASA Astrophysics Data System (ADS)

Rosenblatt, Pascal; Bruinsma, Sean; Mueller-Wodarg, Ingo; Haeusler, Bernd

On its highly elliptical 24 hour orbit around Venus, the Venus Express (VEx) spacecraft briefly reaches a pericenter altitude of nominally 250 km. Recently, however, dedicated and intense radio tracking campaigns have taken place in August 2008 (campaign1), October 2009 (cam-paign2), February and April 2010 (campaign3), for which the pericenter altitude was lowered to about 175 km in order to be able to probe the upper atmosphere of Venus above the North Pole for the first time ever in-situ. As the spacecraft experiences atmospheric drag, its trajectory is measurably perturbed during the pericenter pass, allowing us to infer total atmospheric mass density at the pericenter altitude. The GINS software (Géodésie par Intégration Numérique e e Simultanées) is used to accurately reconstruct the orbital motion of VEx through an iterative least-squares fitting process to the Doppler tracking data. The drag acceleration is modelled using an initial atmospheric density model (VTS model, A. Hedin). A drag scale factor is estimated for each pericenter pass, which scales Hedin's density model in order to best fit the radio tracking data. About 20 density scale factors have been obtained mainly from the second and third VExADE campaigns, which indicate a lower density by a factor of about one-third than Hedin's model predicts. These first ever polar density measurements at solar minimum have allowed us to construct a diffusive equilibrium density model for Venus' thermosphere, constrained in the lower thermosphere primarily by SPICAV-SOIR measurements and above 175 km by the VExADE drag measurements. The preliminary results of the VExADE cam-paigns show that it is possible to obtain reliable estimates of Venus' upper atmosphere densities at an altitude of around 175 km. Future VExADE campaigns will benefit from the planned further lowering of VEx pericenter altitude to below 170 Km.

[Dynamics of soil erosion at upper reaches of Minjiang River based on GIS].

PubMed

He, Xingyuan; Hu, Zhibi; Li, Yuehui; Hu, Yuanman

2005-12-01

Based on TM and ETM imagines, and employing GIS technique and empirical Revised Universal Soil Loss Equation (RUSLE) model, this paper studied the dynamics of soil erosion at the upper reaches of Minjiang River during three typical periods, with the main affecting factors analyzed. The results showed that the soil erosion area was increased by 1.28%, 1.84 % and 1.70% in 1986, 1995 and 2000, respectively. The average erosion modulus was increased from 832.64 t x km(-2) x yr(-1) in 1986 to 1048.74 t x km(-2) yr(-2) in 1995 and reached 1362.11 t x km(-2) yr(-1) in 2000, and soil loss was mainly of slight and light erosion, companying with a small quantity of middling erosion. The area of soil erosion was small, and the degree was light. There was a significant correlation between slope and soil loss, which mainly happened in the regions with a slope larger than 25 degrees, and accounted for 93.65%, 93.81% and 92.71% of the total erosion in 1986, 1995 and 2000, respectively. As for the altitude, middling, semi-high and high mountains and dry valley were liable to soil erosion, which accounted for 98.21%, 97.63% and 99.27% of the total erosion in 1986, 1995 and 2000, respectively. Different vegetation had a significant effect on soil erosion, and shrub and newly restored forest were the main erosion area. Excessive depasture not only resulted in the degradation of pasture, but also led to slight soil erosion. Land use type and soil type also contributed to soil loss, among which, dry-cinnamon soil and calcic gray-cinnamon soil were the most dangerous ones needing more protection. Soil loss was also linearly increased with increasing population and households, which suggested that the increase of population and households was the driving factor for soil loss increase in this area.

Climatic variability of soil water in the American Midwest: Part 2. Spatio-temporal analysis

NASA Astrophysics Data System (ADS)

Georgakakos, Konstantine P.; Bae, Deg-Hyo

1994-11-01

A study of the model-estimated soil water, aggregated over three large drainage basins of the Midwestern USA, is reported. The basin areas are in the range from 2000 km 2 to 3500 km 2, and allow the study of mesoscale (1000-10000 km 2) soil water features. In each case, a conceptual hydrologic model was used to produce upper and lower soil water estimates that are consistent with the atmospheric forcing of daily precipitation, potential evapotranspiration and air temperature, and with the observed daily streamflow divergence over a 40 year period. It is shown that the water contents of the upper and lower soil reach peaks in different months, with the soil column being most saturated in June, when the area is prone to serious flooding. Temporal and spatial features of the variability of model-estimated soil water content are identified. The autocorrelation function of monthly averaged soil water shows that the upper soil water remains persistent for about a season, whereas the persistence of the lower soil water extends to several seasons. The soil water estimates of the three study basins exhibit strong similarities in annual cycles and interannual variability. It is shown that the frequency of significant positive (wet) soil water anomalies that extend over a 2° × 2° region is lower than that of significant negative (dry) ones of the same extent in this region of the USA.

The rheological structure of the lithosphere in the Eastern Marmara region, Turkey

NASA Astrophysics Data System (ADS)

Oruç, Bülent; Sönmez, Tuba

2017-05-01

The aim of this work is to propose the geometries of the crustal-lithospheric mantle boundary (Moho) and lithosphere-asthenosphere boundary (LAB) and the 1D thermal structure of the lithosphere, in order to establish a rheological model of the Eastern Marmara region. The average depths of Moho and LAB are respectively 35 km and 51 km from radially averaged amplitude spectra of EGM08 Bouguer anomalies. The geometries of Moho and LAB interfaces are estimated from the Parker-Oldenburg gravity inversion algorithm. Our results show the Moho depth varies from 31 km at the northern part of North Anatolian Fault Zone (NAFZ) to 39 km below the mountain belt in the southern part of the NAFZ. The depth to the LAB beneath the same parts of the region ranges from 45 km to 55 km. Having lithospheric strength and thermal boundary layer structure, we analyzed the conditions of development of lithosphere thinning. A two-dimensional strength profile has been estimated for rheology model of the study area. Thus we suggest that the rheological structure consists of a strong upper crust, a weak lower crust, and a partly molten upper lithospheric mantle.

An image of the Columbia Plateau from inversion of high-resolution seismic data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lutter, W.J.; Catchings, R.D.; Jarchow, C.M.

1994-08-01

The authors use a method of traveltime inversion of high-resolution seismic data to provide the first reliable images of internal details of the Columbia River Basalt Group (CRBG), the subsurface basalt/sediment interface, and the deeper sediment/basement interface. Velocity structure within the basalts, delineated on the order of 1 km horizontally and 0.2 km vertically, is constrained to within [plus minus]0.1 km/s for most of the seismic profile. Over 5,000 observed traveltimes fit their model with an rms error of 0.018 s. The maximum depth of penetration of the basalt diving waves (truncated by underlying low-velocity sediments) provides a reliable estimatemore » of the depth to the base of the basalt, which agrees with well-log measurements to within 0.05 km (165 ft). The authors use image blurring, calculated from the resolution matrix, to estimate the aspect ratio of images velocity anomaly widths to true widths for velocity features within the basalt. From their calculations of image blurring, they interpret low velocity zones (LVZ) within the basalts at Boylston Mountain and the Whiskey Dick anticline to have widths of 4.5 and 3 km, respectively, within the upper 1.5 km of the model. At greater depth, the widths of these imaged LVZs thin to approximately 2 km or less. They interpret these linear, subparallel, low-velocity zones imaged adjacent to anticlines of the Yakima Fold Belt to be brecciated fault zones. These fault zones dip to the south at angles between 15 to 45 degrees.« less

Evidence for the contemporary magmatic system beneath Long Valley Caldera from local earthquake tomography and receiver function analysis

USGS Publications Warehouse

Seccia, D.; Chiarabba, C.; De Gori, P.; Bianchi, I.; Hill, D.P.

2011-01-01

We present a new P wave and S wave velocity model for the upper crust beneath Long Valley Caldera obtained using local earthquake tomography and receiver function analysis. We computed the tomographic model using both a graded inversion scheme and a traditional approach. We complement the tomographic I/P model with a teleseismic receiver function model based on data from broadband seismic stations (MLAC and MKV) located on the SE and SW margins of the resurgent dome inside the caldera. The inversions resolve (1) a shallow, high-velocity P wave anomaly associated with the structural uplift of a resurgent dome; (2) an elongated, WNW striking low-velocity anomaly (8%–10 % reduction in I/P) at a depth of 6 km (4 km below mean sea level) beneath the southern section of the resurgent dome; and (3) a broad, low-velocity volume (–5% reduction in I/P and as much as 40% reduction in I/S) in the depth interval 8–14 km (6–12 km below mean sea level) beneath the central section of the caldera. The two low-velocity volumes partially overlap the geodetically inferred inflation sources that drove uplift of the resurgent dome associated with caldera unrest between 1980 and 2000, and they likely reflect the ascent path for magma or magmatic fluids into the upper crust beneath the caldera.

Thin-skinned tectonics of the Upper Ojai Valley and Sulphur Mountain area, Ventura basin, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huftile, G.J.

1991-08-01

By integrating surface mapping with subsurface well data and drawing cross sections and subsurface maps, the geometry of shallow structures and their geologic history of the Upper Ojai Valley of California can be reconstructed. The geometry of shallow structures, the geologic history, and the location of earthquake foci then offer constraints on the deep structure of this complex area. The Upper Ojai Valley is a tectonic depression between opposing reverse faults. Its northern border is formed by the active, north-dipping San Cayetano fault, which has 6.0 km of stratigraphic separation in the Silverthread area of the Ojai oil field andmore » 2.6 km of stratigraphic separation west of Sisar Creek. The fault dies out farther west in Ojai Valley, where the south-vergent shortening is transferred to a blind thrust. The southern border of the Upper Ojai Valley is formed by the Quaternary Lion fault set, which dips south and merges into the Sisar decollement within the south-dipping, ductile, lower Miocene Rincon formation. By the middle Pleistocene, the Sulphur Mountain anticlinorium and the Big Canyon syncline began forming as a fault-propagation fold; the fault-propagation fold is rooted in the Sisar decollement, a passive backthrust rising from a blind thrust at depth. The formation of the Sulphur Mountain anticlinorium was followed closely by the ramping of the south-dipping Lion fault set to the surface over the nonmarine upper Pleistocene Saugus Formation. To the east, the San Cayetano fault overrides and folds the Lion Fault set near the surface. Area-balancing of the deformation shows shortening of 15.5 km, and suggests a 17 km depth to the brittle-ductile transition.« less

Validation of GOSAT/TANSO-FTS TIR V01.00 CO2 and CH4 products

NASA Astrophysics Data System (ADS)

Saitoh, N.; Kimoto, S.; Sugimura, R.; Imasu, R.; Kawakami, S.; Shiomi, K.; Machida, T.; Sawa, Y.; Matsuda, H.

2014-12-01

Greenhouse Gases Observing Satellite (GOSAT) has been making observations continuously for more than five years since its launch on 23 January 2009. Thermal and Near-infrared Sensor for Carbon Observation Fourier Transform Spectrometer (TANSO-FTS) on board the GOSAT simultaneously observes column abundances and profiles of CO2 and CH4 in the same field of view, from the shortwave infrared (SWIR) and thermal infrared (TIR) bands, respectively. We have just released the latest TIR CO2 and CH4 products, V01.00, to registered researchers. To validate the data quality of the V01.00 TIR CO2 product, we compared the TIR data with CO2 data obtained by Continuous CO2 Measuring Equipment (CME) on board JAL aircraft in Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project. The aircraft CO2 data obtained during the level flights were compared with the V01.00 TIR upper tropospheric CO2 data. The CONTRAIL CO2 "profile" data obtained during the ascending and descending flights over several airports were compared with the TIR CO2 profiles. In the profile comparisons, we applied the TIR averaging kernel functions to the coincident CONTRAIL CO2 profiles. The V01.00 upper atmospheric CO2 data agreed to the CONTRAIL level flight CO2 data on average within 0.5-1%. Some TIR CO2 data showed relatively large differences from the nearest aircraft data, which suggests the existence of several problems such as L1B spectral calibration and nighttime cloud detection issues. The TIR V01.00 CO2 profile data from 9 to 13 km showed better agreement to CONTRAIL CO2 data than the a priori. However, the TIR CO2 data at around and below 5 km had low bias of 1-1.5%. The TIR V01.00 CH4 data generally showed reasonable latitudinal distributions as the previous version. In the Antarctic, unexpected high amounts of CH4 were seen in upper troposphere and lower stratosphere in autumn. This is probably because of the problem of simultaneously retrieved ozone concentration.

Crustal and upper-mantle structure beneath ice-covered regions in Antarctica from S-wave receiver functions and implications for heat flow

NASA Astrophysics Data System (ADS)

Ramirez, C.; Nyblade, A.; Hansen, S. E.; Wiens, D. A.; Anandakrishnan, S.; Aster, R. C.; Huerta, A. D.; Shore, P.; Wilson, T.

2016-03-01

S-wave receiver functions (SRFs) are used to investigate crustal and upper-mantle structure beneath several ice-covered areas of Antarctica. Moho S-to-P (Sp) arrivals are observed at ˜6-8 s in SRF stacks for stations in the Gamburtsev Mountains (GAM) and Vostok Highlands (VHIG), ˜5-6 s for stations in the Transantarctic Mountains (TAM) and the Wilkes Basin (WILK), and ˜3-4 s for stations in the West Antarctic Rift System (WARS) and the Marie Byrd Land Dome (MBLD). A grid search is used to model the Moho Sp conversion time with Rayleigh wave phase velocities from 18 to 30 s period to estimate crustal thickness and mean crustal shear wave velocity. The Moho depths obtained are between 43 and 58 km for GAM, 36 and 47 km for VHIG, 39 and 46 km for WILK, 39 and 45 km for TAM, 19 and 29 km for WARS and 20 and 35 km for MBLD. SRF stacks for GAM, VHIG, WILK and TAM show little evidence of Sp arrivals coming from upper-mantle depths. SRF stacks for WARS and MBLD show Sp energy arriving from upper-mantle depths but arrival amplitudes do not rise above bootstrapped uncertainty bounds. The age and thickness of the crust is used as a heat flow proxy through comparison with other similar terrains where heat flow has been measured. Crustal structure in GAM, VHIG and WILK is similar to Precambrian terrains in other continents where heat flow ranges from ˜41 to 58 mW m-2, suggesting that heat flow across those areas of East Antarctica is not elevated. For the WARS, we use the Cretaceous Newfoundland-Iberia rifted margins and the Mesozoic-Tertiary North Sea rift as tectonic analogues. The low-to-moderate heat flow reported for the Newfoundland-Iberia margins (40-65 mW m-2) and North Sea rift (60-85 mW m-2) suggest that heat flow across the WARS also may not be elevated. However, the possibility of high heat flow associated with localized Cenozoic extension or Cenozoic-recent magmatic activity in some parts of the WARS cannot be ruled out.

Meteoroid mayhem in Ole Virginny: Source of the North American tektite strewn field

USGS Publications Warehouse

Poag, C. Wylie; Powars, David S.; Poppe, Lawrence J.; Mixon, Robert B.

1994-01-01

New seismic reflection data from Chesapeake Bay reveal a buried, 85-km-wide, 1.5-2.0-km-deep, peak-ring impact crater, carved through upper Eocene to Lower Cretaceous sedimentary strata and into underlying pre-Mesozoic crystalline basement rocks. A polymictic, late Eocene impact breccia, composed mainly of locally derived sedimentary debris (determined from four continuous cores), surrounds and partly fills the crater. Structural and sedimentary characteristics of the Chesapeake Bay crater closely resemble those of the Miocene Ries peakring crater in southern Germany. We speculate that the Chesapeake Bay crater is the source of the North American tektite strewn field.

Meteoroid mayhem in Ole Virginny: source of the North American tektite strewn field

USGS Publications Warehouse

Poag, C.W.; Powars, D.S.; Poppe, L.J.; Mixon, R.B.

1994-01-01

New seismic reflection data from Chesapeake Bay reveal a buried, 85-km-wide, 1.5-2.0-km-deep, peak-ring impact crater, carved through upper Eocene to Lower Cretaceous sedimentary strata and into underlying pre-Mesozoic crystalline basement rocks. A polymictic, late Eocene impact breccia, composed mainly of locally derived sedimentary debris (determined from four continuous cores), surrounds and partly fills the crater. Structural and sedimentary characteristics of the Chesapeake Bay crater closely resemble those of the Miocene Ries peak-ring crater in southern Germany. It is speculated that the Chesapeake Bay crater is the source of the North American tektite strewn field. -Authors

Fore- and Back-Arc Structures Along the Hikurangi-Kermadec Subduction Zone

NASA Astrophysics Data System (ADS)

Scherwath, M.; Kopp, H.; Flueh, E. R.; Henrys, S. A.; Sutherland, R.

2009-04-01

The Hikurangi-Kermadec subduction zone northeast of New Zealand represents an ideal target to study lateral variations of subduction zone processes. The incoming Pacific plate changes from being a large igneous province, called the Hikurangi Plateau, in the south to normal oceanic plate north of the Rapuhia Scarp. The overriding Australian plate is continental in the south, forming the North Island of New Zealand, and changes to an island arc in the north. Further lateral variability exists in changes in volcanic and hydro-thermal activity, transitions from accretion to subduction erosion, backarc spreading and rifting, and is accompanied by northward increasing seismicity. As part of the MANGO project (Marine Geoscientific Investigations on the Input and Output of the Kermadec Subduction Zone), four marine geophysical transects of largely seismic reflection and refraction data provide constraints on the upper lithospheric structures across the Hikurangi-Kermadec Trench between 29-38 degrees South. On MANGO profile 1 in the south, the initially shallow subduction of the incoming plateau coincides with crustal underplating beneath the East Cape ridge. To the west lies the 100 km wide and over 10 km deep Raukumara Basin. Seismic velocities of the upper arc mantle are around 8 km/s and are considered normal. In contrast, on MANGO profile 4, about 1000 km to the north around the volcanically active Raoul Island, the incoming oceanic crust appears to bend considerably steeper and thus causes a 50 km narrower forearc with a smaller forearc basin. Furthermore, the upper mantle velocities in both plates are relatively low (7.4-7.7 km/s), likely indicating strong bending related deformation of the incoming plate and thermal activity within the arc possibly due to spreading. Here, arc volcanism is relatively active, with many large volcanoes directly on the ridge. The central two transects MANGO 2 and 3, though without data coverage of the structure of the incoming plate, are more similar to MANGO 4. The arc regions appear to be strongly affected by the activity of the arc. The arc crust of the northern MANGO 3 becomes significantly thinner in the backarc region due to extension, and much reduced volcanism behind the ridge. The structures on MANGO 2, on the other hand, cover strong and densely spaced thermal activity from the adjacent arc volcanism, possibly linked to a recent, fluid-rich passage of the Hikurangi Plateau.

Petrology and Geochemistry of an Upper Crustal Mafic Complex- Hidden Lakes, Sierra Nevada Batholith, California

NASA Astrophysics Data System (ADS)

Lewis, M.; Bucholz, C. E.; Jagoutz, O. E.; Eddy, M. P.

2017-12-01

Magmatic differentiation in arc settings is likely a polybaric process, with crystallization of primitive basalts occurring primarily in the lower crust and more evolved melts in the upper crust. The general lack of mafic-ultramafic cumulates in the silicic paleo-arc upper crust supports this model. However, the Sierra Nevada Batholith preserves numerous mafic intrusions up to 25 km2, suggesting that significant volumes of mafic magma may differentiate at shallow crustal levels. Previous studies on several such intrusions report ages contemporaneous with Cretaceous batholith emplacement (Coleman et al., 1995), but only a few have investigated their chemistry and relationship to arc magmatism (Frost, 1987; Frost & Mahood, 1987; Sisson et al., 1996). We present field observations, petrography, mineral chemistry, and bulk rock compositional data for the Hidden Lakes Mafic Complex (HLMC), located in the Central Sierra Nevada Batholith. Preliminary CA-ID-TIMS U-Pb zircon ages constrain crystallization between 90 and 95 Ma, slightly older than the surrounding Cretaceous felsic plutons (89-90 Ma) and younger than adjacent Jurassic granodiorites (172 Ma). This 2.2 km2 complex consists of biotite+amphibole gabbros through qtz-monzonites, in gradational contact, and contains local pods of biotite- and amphibole-bearing olivine-orthopyroxenites and gabbronorites. Mineral compositions and field relations suggest that these lithologies were derived from a common crystallization sequence. The most primitive olivine-pyroxenite contains olivine and orthopyroxene in equilibrium with a melt with Mg# 54. Subsequent crystallization over a temperature range of 1025 to 700°C produced more evolved lithologies up to qtz-monzonites. Al-in-hornblende calculations for HLMC qtz-monzonites indicate a crystallization depth of 9-10 km, well into the upper crust. The early crystallization of amphibole requires a parental basalt with >6 wt% H2O, which may have enabled it to ascend into the upper crust due to decreased density and viscosity. However, the estimated parental melt is not primitive (rather than Mg# 70), suggesting that differentiation of a more mafic precursor parental melt in the lower crust modified the chemistry and rheological properties of the melt prior to its ascent into the upper crust.

Dust Devil Art

NASA Technical Reports Server (NTRS)

2005-01-01

12 December 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark squiggles and streaks created by passing spring and summer dust devils near Pallacopas Vallis in the martian southern hemisphere.

Location near: 53.9oS, 17.2oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

CCD imaging and photometry of 46P/Wirtanen during October 1996

NASA Astrophysics Data System (ADS)

Fink, Uwe; Fevig, Ron A.; Tegler, Stephen C.; Romanishin, William

1997-11-01

During the period of 96 Oct. 7.16 to Oct. 12.14 comet P/Wirtanen was observed with our CCD system at the 154 cm Catalina Observatory telescope at a heliocentric distance near 2.1 AU. The comet exhibited a coma of about 7 in in diameter with a tail of about 14 in. The observed B, V and R magnitudes within a 9.3 in diameter aperture were 19.94, 19.11 and 18.73, respectively. The large majority of our observations were carried out with a filter combining the V and R passbands (V+R). The average V+R magnitudes for Oct. 7.16, 8.14, 9.12 and 10.15, respectively, were 18.91, 18.87, 18,87 and 18.86. The data did not allow the extraction of a lightcurve but hopefully can be used in conjunction with other observations to constrain the comet's rotation period. An attempt to separate the nucleus contribution from the coma resulted in an upper limit to the nuclear magnitude of ≈20.6 in V+R at a phase of 26° or ≈19.6 at 0° phase angle. This results in an upper limit of 1.2 km for the comet's radius assuming a geometric albedo of 0.04. Calculating the Afϱ yielded a value of 7 cm which is a factor of 170 smaller than P/Halley at a comparable heliocentric distance and phase angle. Making the simple assumption that the comet's activity is proportional to its surface area makes the surface area of Wirtanen about 2.4 km 2, equivalent to an effective radius of ≈0.44 km.

Simultaneous observations of a Mesospheric Inversion Layer and turbulence during the ECOMA-2010 rocket campaign

NASA Astrophysics Data System (ADS)

Szewczyk, A.; Strelnikov, B.; Rapp, M.; Strelnikova, I.; Baumgarten, G.; Kaifler, N.; Dunker, T.; Hoppe, U.-P.

2013-05-01

From 19 November to 19 December 2010 the fourth and final ECOMA rocket campaign was conducted at Andøya Rocket Range (69° N, 16° E) in northern Norway. We present and discuss measurement results obtained during the last rocket launch labelled ECOMA09 when simultaneous and true common volume in situ measurements of temperature and turbulence supported by ground-based lidar observations reveal two Mesospheric Inversion Layers (MIL) at heights between 71 and 73 km and between 86 and 89 km. Strong turbulence was measured in the region of the upper inversion layer, with the turbulent energy dissipation rates maximising at 2 W kg-1. This upper MIL was observed by the ALOMAR Weber Na lidar over the period of several hours. The spatial extension of this MIL as observed by the MLS instrument onboard AURA satellite was found to be more than two thousand kilometres. Our analysis suggests that both observed MILs could possibly have been produced by neutral air turbulence.

An upper bound on the radius of a highly electrically conducting lunar core

NASA Technical Reports Server (NTRS)

Hobbs, B. A.; Hood, L. L.; Herbert, F.; Sonett, C. P.

1983-01-01

Parker's (1980) nonlinear inverse theory for the electromagnetic sounding problem is converted to a form suitable for analysis of lunar day-side transfer function data by: (1) transforming the solution in plane geometry to that in spherical geometry; and (2) transforming the theoretical lunar transfer function in the dipole limit to an apparent resistivity function. The theory is applied to the revised lunar transfer function data set of Hood et al. (1982), which extends in frequency from 10 to the -5th to 10 to the -3rd Hz. On the assumption that an iron-rich lunar core, whether molten or solid, can be represented by a perfect conductor at the minimum sampled frequency, an upper bound of 435 km on the maximum radius of such a core is calculated. This bound is somewhat larger than values of 360-375 km previously estimated from the same data set via forward model calculations because the prior work did not consider all possible mantle conductivity functions.

On the CO and N2 abundance in Comet Halley

NASA Technical Reports Server (NTRS)

Eberhardt, P.; Krankowsky, D.; Schulte, W.; Dolder, U.; Laemmerzahl, P.; Berthelier, J. J.; Woweries, J.; Stubbemann, U.; Hodges, R. R.; Hoffmann, J. H.

1986-01-01

The mass 28 amu/e signal observed in the neutral mode of the Giotto neutral gas mass spectrometer (NMS) is evaluated. At 1000 km from the nucleus number density n(CO)/ n(H2O) is less than or = 0.07. The production rate of CO as a parent molecule directly from the nucleus is thus less than 7% of the H2O production rate. However, CO is also produced from an extended source in the inner coma (r is less than 20,000 km) and at 20,000 km from the nucleus, for the total equivalent CO production rate 0.05 is less than or = Q(CO)/Q(H2O) is less than or = 0.15. For N2 an upper limit Q(N2)/Q(H2O) is less than or = 0.1 is derived. No parent molecule for the CO is identified in agreement with the NMS measurements. It is proposed that CO or a very short-lived parent is released in the coma from cometary dust grains, such as the CHON particles.

Threatened fishes of the world: Moapa coriacea Hubbs and Miller, 1948 (cyprinidae)

USGS Publications Warehouse

Scoppettone, G.G.; Goodchild, S.

2009-01-01

Moapa dace. Conservation status: Endangered (U.S. Department of the Interior 1967), Critically Endangered, IUCN (Gimenez 1996). Identification: Small embedded scales, narrow caudal peduncle and a bright black spot at the base of deeply forked tail. Pharyngeal teeth (0,5–4,0) hooked but with a grinding surface. Adults 50 to 120 mm total length. Drawing adapted from La Rivers (1962). Distribution: Endemic to the upper Muddy River system, Clark County, Nevada where the river originates from over 20 thermal springs. Prior to 1995 Moapa dace occupied 9.5 stream km including the upper Muddy River and spring-fed tributaries (U.S. Fish and Wildlife Service 1995). Distribution has contracted to 2 km (unpublished data) since the 1995 invasion of blue tilapia, Oreochromis aurea. Abundance: In 1994 the population was about 3,800, but after tilapia invasion dropped below 1,600 (Scoppettone et al. 1998) where it has remained (unpublished data). Habitat and ecology: Omnivorous but tends toward carnivory. Feed primarily on drift in areas adjacent to fast water 26–32°C. Reproduction: Occurs year round in spring-fed tributaries to the Muddy River in water temperature of 30–32°C (Scoppettone et al. 1992). Threats: Nonnative species (Scoppettone 1993; Scoppettone et al. 1998) and ground-water pumping (Mayer and Congdon 2008). Conservation actions: Moapa Valley National Wildlife Refuge was established in the upper Muddy River for the protection and perpetuation of Moapa dace. Barrier installation and chemical removal of blue tilapia downstream of refuge habitat provides 2 km of stream without tilapia. Conservation recommendations: Eliminate tilapia from the Muddy River system and control or eliminate other nonnative species. Protect spring discharge from excessive water withdrawal. Remarks: Given a high priority for recovery by the U.S. Government.

Pavonis Mons Features

NASA Technical Reports Server (NTRS)

2005-01-01

27 February 2005 This Mars Global Surveyor (MGS) Orbiter Camera (MOC) image shows wind streaks and a thick mantling of dust in the summit region of the martian volcano, Pavonis Mons. The surface texture gives the impression that the MOC image is blurry, but several very small, sharp impact craters reveal that the picture is not blurry.

Location near: 1.1oN, 113.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Northern Summer

The Mega Mesospheric Parachute

NASA Technical Reports Server (NTRS)

Kloesel, Kurt J.; Oberto, Robert; Kinsey, Robert

2005-01-01

The current understanding and modeling of the upper reaches of the atmosphere is incomplete. Upper atmospheric interactions with the lower atmosphere, effects of ionizing radiation, high altitude cloud phenomena, and the dynamical interaction with the magnetosphere require greater definition. The scientific objective of obtaining a greater understanding of the upper atmosphere can be achieved by designing, implementing, testing, and utilizing a facility that provides long period in-situ measurements of the mesosphere. Current direct sub-sonic measurements of the upper atmosphere are hampered by the approximately one minute sub-sonic observation window of a ballistic sounding rocket regardless of the launch angle. In-situ measurements at greater than transonic speeds impart energy into the molecular atmospheric system and distort the true atmospheric chemistry. A long duration, sub-sonic capability will significantly enhance our ability to observe and measure: (1) mesospheric lightning phenomena (sprites and blue jets) (2) composition, structure and stratification of noctilucent clouds (3) physics of seasonal radar echoes, gravity wave phenomena (4) chemistry of mesospheric gaseous ratio mixing (5) mesospheric interaction of ionizing radiation (6) dynamic electric and magnetic fields This new facility will also provide local field measurements which complement those that can be obtained through external measurements from satellite and ground-based platforms. The 400 foot (approximately 130 meter) diameter lightweight mega-mesospheric parachute system, deployed with a sounding rocket, is proposed herein as a method to increase sub-sonic mesospheric measurement time periods by more than an order of magnitude. The report outlines a multi-year evolving science instrumentation suite in parallel with the development of the mega meso-chute facility. The developmental issues surrounding the meso-chute are chiefly materials selection (thermal and structural) and deployment mechanism physics. Three mission cases were conceived and developed to include cost and schedules estimates. Each scenario has increasing scientific utility with paralleling launch weight, parachute hang-time, deployment altitude, and parachute size: (1) Case #1: $8.4M@24 months, 6kg payload, 20 min., 50km alt., 80 m. dia. (2) Case #2: $10.4M@24 months, 6kg payload, 20 min., 60km alt, 130m. dia. (3) Case #3: $13.6M@36 months, 30kg payload, 30 min., 90km alt., 200m. dia. The initial breakout cost for the parachute system is approximately $2M@24 months. This report identifies that although the challenges of the mega-meso-chute may be difficult, they can be surmounted and valuable results can be achieved.

Sunda-Banda Arc Transition: Marine Wide-Angle Seismic Modeling

NASA Astrophysics Data System (ADS)

Shulgin, A.; Planert, L.; Kopp, H.; Mueller, C.; Lueschen, E.; Engels, M.; Flueh, E.; Djajadihardja, Y.; Sindbad Working Group, T

2008-12-01

The Sunda-Banda Arc transition is the region of active convergence and collision of the Indo-Australian and Eurasian Plates. The style of subduction changes from an oceanic-island arc subduction to a continental- island arc collision. The character of the incoming plate varies from the rough topography of the Roo Rise, to the smooth seafloor of the Abyssal Plain off Bali, Sumbawa. Forearc structures include well-developed forearc basins and an accretionary prism/outer forearc high of variable size and shape. To quantify the variability of structure of the lower plate and the effects on the upper plate a refraction seismic survey was carried during cruise SO190-2. A total of 245 ocean bottom seismometers were deployed along 1020 nm of wide-angle seismic profiles in four major north-south oriented corridors. To assess the velocity structure we used a tomographic method which jointly inverts for refracted and reflected phases. The sedimentary layers of the models, obtained by the analysis of high-resolution MCS data (see Lueschen et al), were incorporated into the starting model. The obtained models exhibit strong changes of the incoming oceanic crust for the different portions of the margin: The westernmost profile off eastern Java shows a crustal thickness of more than 15 km, most likely related to the presence of an oceanic plateau. Profiles off Lombok reveal an oceanic crust of 8-9 km average thickness in the Argo Abyssal Plain. Crustal and upper mantle velocities are slightly decreased within an area of about 50-60 km seaward of the trench, indicating fracturing and related serpentinization due to bending of the oceanic crust and associated normal faulting. The outer forearc high is characterized by velocities of 2.5-5.5 km/s. For the Lombok Basin, the profiles show a sedimentary infill of up to 3.5 km thick and typical sediment velocities of 1.75-3.0 km/s. A reflector at 16 km depth and velocity values of 7.4-7.8 km/s beneath it suggest the presence of a shallow forearc mantle and a hydrated mantle wedge in this part of the margin. See in this session Planert et al.

The Paleoflood Record of the Upper Colorado River near Moab, Utah

NASA Astrophysics Data System (ADS)

Greenbaum, N.; Harden, T.; Baker, V. R.; Weisheit, J. S.; Cline, M. L.; Halevi, R.; Dohrenwend, J. C.

2011-12-01

The paleoflood record of the Upper Colorado River was reconstructed 17 km upstream of the town of Moab, Utah (drainage area about 62,470 km2) using paleostage indicaters. The 4.5 km long study reach is a bedrock canyon incised some 300-350 m into the sandstone of the Colorado Plateau with a general gradient of 0.0004. The largest floods documented at the Cisco gauging station (1914-2011) - 30 km upstream, is the historical 1884 flood - 3540 m3s-1, the 1917 flood - 2175 m3s-1 and the 1984 flood - 1990 m3s-1. The paleostage indicators in the form of slackwater deposits and driftwood lines at this site are up to 15 m above the summer water discharge of July 2005 (425 m3 s-1). The detailed paleoflood stratigraphy was performed using a series of 14 pits across the SWD relict with a depth of up to 2 m. Dating of the paleoflood deposits include 14 OSL ages and 4 radiocarbon ages of wooden debris and charcoal. The canyon and channel geometry was reconstructed using a field survey of 24 cross sections during 2005. In 2010 a complementary survey of the underwater channel geometry using a sonar was conducted. Water surface profiles, peak discharges and hydraulic analyses where preformed using HECRAS hydraulic program. The water surface profiles were calibrated using the observed water levels of the floods of 25-26.5.2005 - 1140 m3s-1 and the 25-26 June 2011 - 260 m3s-1. The results indicate evidence of about 40 floods that occurred during the last 2140 +/- 220 years. The flow regime for the high-magnitude floods is subcritical and the canyon is relatively narrow, therefore the peak discharges are very sensitive to Manning`s n roughness coefficient. Due to the very low gradient the discharge results are also sensitive to the initial boundary conditions downstream. The peak discharges range from about 1600 m3s-1 and up to between 8,500 and 10,500 m3s-1 depending on the Manning n. At least 2 floods in this record exceeded the conservative value (8500 m3s-1) which is higher than the probable maximum flood (8300 m3s-1) and 24 floods exceeded 3400 m3s-1 (the 500-year flood) calculated for the Moab Vally.

Artificial plasma cusp generated by upper hybrid instabilities in HF heating experiments at HAARP

NASA Astrophysics Data System (ADS)

Kuo, Spencer; Snyder, Arnold

2013-05-01

High Frequency Active Auroral Research Program digisonde was operated in a fast mode to record ionospheric modifications by the HF heating wave. With the O mode heater of 3.2 MHz turned on for 2 min, significant virtual height spread was observed in the heater off ionograms, acquired beginning the moment the heater turned off. Moreover, there is a noticeable bump in the virtual height spread of the ionogram trace that appears next to the plasma frequency (~ 2.88 MHz) of the upper hybrid resonance layer of the HF heating wave. The enhanced spread and the bump disappear in the subsequent heater off ionograms recorded 1 min later. The height distribution of the ionosphere in the spread situation indicates that both electron density and temperature increases exceed 10% over a large altitude region (> 30 km) from below to above the upper hybrid resonance layer. This "mini cusp" (bump) is similar to the cusp occurring in daytime ionograms at the F1-F2 layer transition, indicating that there is a small ledge in the density profile reminiscent of F1-F2 layer transitions. Two parametric processes exciting upper hybrid waves as the sidebands by the HF heating waves are studied. Field-aligned purely growing mode and lower hybrid wave are the respective decay modes. The excited upper hybrid and lower hybrid waves introduce the anomalous electron heating which results in the ionization enhancement and localized density ledge. The large-scale density irregularities formed in the heat flow, together with the density irregularities formed through the parametric instability, give rise to the enhanced virtual height spread. The results of upper hybrid instability analysis are also applied to explain the descending feature in the development of the artificial ionization layers observed in electron cyclotron harmonic resonance heating experiments.

Upper mantle seismic velocity structure beneath the Kenya Rift and the Arabian Shield

NASA Astrophysics Data System (ADS)

Park, Yongcheol

Upper mantle structure beneath the Kenya Rift and Arabian Shield has been investigated to advance our understanding of the origin of the Cenozoic hotspot tectonism found there. A new seismic tomographic model of the upper mantle beneath the Kenya Rift has been obtained by inverting teleseismic P-wave travel time residuals. The model shows a 0.5--1.5% low velocity anomaly below the Kenya Rift extending to about 150 km depth. Below ˜150 km depth, the anomaly broadens to the west toward the Tanzania Craton, suggesting a westward dip to the structure. The P- and S-wave velocity structure beneath the Arabian Shield has been investigated using travel-time tomography. Models for the seismic velocity structure of the upper mantle between 150 and 400 depths reveal a low velocity region (˜1.5% in the P model and ˜3% in the S model) trending NW-SE along the western side of the Arabian Shield and broadening to the northeast beneath the MMN volcanic line. The models have limited resolution above 150 km depth everywhere under the Shield, and in the middle part of the Shield the resolution is limited at all depths. Rayleigh wave phase velocity measurements have been inverted to image regions of the upper mantle under the Arabian Shield not well resolved by the body wave tomography. The shear wave velocity model obtained shows upper mantle structure above 200 km depth. A broad low velocity region in the lithospheric mantle (depths of ≤ ˜100 km) across the Shield is observed, and below ˜150 km depth a region of low shear velocity is imaged along the Red Sea coast and MMN volcanic line. A westward dipping low velocity zone beneath the Kenya Rift is consistent with an interpretation by Nyblade et al. [2000] suggesting that a plume head is located under the eastern margin of the Tanzania Craton, or alternatively a superplume rising from the lower mantle from the west and reaching the surface under Kenya [e.g., Debayle et al., 2001; Grand et al., 1997; Ritsema et al., 1999]. For the Arabian Shield, the models are not consistent with a two plume model [Camp and Roobol, 1992] because there is a continuous low velocity zone at depths ≥ 150 km along the western side of the Shield and not separate anomalies. The NW-SE trending low velocity anomaly beneath the western side of the Shield supports the Ebinger and Sleep [1998] model invoking plume flow channeled by thinner lithosphere along the Red Sea coast. The NW-SE low velocity structure beneath the western side of the Shield could also be the northern-most extent of the African Superplume. A low velocity anomaly beneath Ethiopia [Benoit et al., 2006a,b] dips to the west and may extend through the mantle transition zone. The observed low velocities in the upper mantle beneath the Arabian Shield could be caused by hot mantle rock rising beneath Ethiopia and flowing to the north under the Arabian Shield.

Modeled Impact of Cirrus Cloud Increases Along Aircraft Flight Paths

NASA Technical Reports Server (NTRS)

Rind, David; Lonergan, P.; Shah, K.

1999-01-01

The potential impact of contrails and alterations in the lifetime of background cirrus due to subsonic airplane water and aerosol emissions has been investigated in a set of experiments using the GISS GCM connected to a q-flux ocean. Cirrus clouds at a height of 12-15km, with an optical thickness of 0.33, were input to the model "x" percentage of clear-sky occasions along subsonic aircraft flight paths, where x is varied from .05% to 6%. Two types of experiments were performed: one with the percentage cirrus cloud increase independent of flight density, as long as a certain minimum density was exceeded; the other with the percentage related to the density of fuel expenditure. The overall climate impact was similar with the two approaches, due to the feedbacks of the climate system. Fifty years were run for eight such experiments, with the following conclusions based on the stable results from years 30-50 for each. The experiments show that adding cirrus to the upper troposphere results in a stabilization of the atmosphere, which leads to some decrease in cloud cover at levels below the insertion altitude. Considering then the total effect on upper level cloud cover (above 5 km altitude), the equilibrium global mean temperature response shows that altering high level clouds by 1% changes the global mean temperature by 0.43C. The response is highly linear (linear correlation coefficient of 0.996) for high cloud cover changes between 0. 1% and 5%. The effect is amplified in the Northern Hemisphere, more so with greater cloud cover change. The temperature effect maximizes around 10 km (at greater than 40C warming with a 4.8% increase in upper level clouds), again more so with greater warming. The high cloud cover change shows the flight path influence most clearly with the smallest warming magnitudes; with greater warming, the model feedbacks introduce a strong tropical response. Similarly, the surface temperature response is dominated by the feedbacks, and shows little geographical relationship to the high cloud input. Considering whether these effects would be observable, changing upper level cloud cover by as little as 0.4% produces warming greater than 2 standard deviations in the Microwave Sounding Unit (MSU) channels 4, 2 and 2r, in flight path regions and in the subtropics. Despite the simplified nature of these experiments, the results emphasize the sensitivity of the modeled climate to high level cloud cover changes, and thus the potential ability of aircraft to influence climate by altering clouds in the upper troposphere.

Crater in Marte Vallis

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-566, 6 December 2003

This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a streamlined tail-pointing toward the upper right (northeast)--in the lee of a meteor impact crater in Marte Vallis, a large valley and channel complex southeast and east of the Elysium volcanic region. The fluid that went through Marte Vallis, whether water, mud, lava, or otherwise, created this form as it moved from the lower left (southwest) toward the upper right. The crater is located near 19.0oN, 174.9oW. The image covers an area 3 km (1.9 mi) wide and is illuminated from the left.

Seismic and GPS constraints on the dynamics and kinematics of the Yellowstone volcanic field

NASA Astrophysics Data System (ADS)

Smith, R. B.; Farrell, J.; Jordan, M.; Puskas, C.; Waite, G. P.

2007-12-01

The seismically and volcanically Yellowstone hotspot resulted from interaction of a mantle plume with the overriding North America plate. This feature and related processes have modified continental lithosphere producing the Yellowstone-Snake River Plain-Newberry silicic volcanic field (YSRPN) system, with its NE volcanically active Yellowstone volcanic field. The size and accessibility of the Yellowstone area has allowed a range of geophysical experiments including earthquake monitoring and seismic and GPS imaging of this system. Seismicity is dominated by small-magnitude normal- to oblique-slip faulting earthquake swarms with shallow focal depths, maximum of ~5 km, restricted by high temperatures and a weak elastic layer. There is developing evidence of non-double couple events. Outside the caldera, earthquakes are deeper, ~20 km, and capable of M 7+ earthquakes. We integrate the results from a multi-institution experiment that recorded data from 110 seismic stations and 180 GPS stations for 1999-2004. The tomographic images confirm the existence of a low Vp-body beneath the Yellowstone caldera at depths greater than 8 km, possibly representing hot, crystallizing magma. A key result of our study is a volume of anomalously low Vp and Vp/Vs in the northwestern part of the volcanic field at shallow depths of <2.0 km. Theoretical calculations of changes in P- to S-wave velocity ratios indicate that these anomalies can be interpreted as porous, gas-filled rock. GPS-measured episodes of caldera kinematics reveals uplift and subsidence of the caldera at decadal scales with average rates of ~20 mm/yr but much higher short-term rates of up to 70 mm/yr of accelerated uplift, 2004-2007. The stress field inverted from seismic and GPS data is dominated by regional SW extension with superimposed volumetric expansion and uplift from local volcanic sources. Mantle tomography derived from integrated inversion of teleseismic and local earthquake data constrained by geoid, crustal structure, discontinuity structure reveals an upper-mantle low P and S velocity body extends from 80 km to ~250 km directly beneath Yellowstone and then continues to 650 km with unexpected westward tilt to the west at ~60° with a 1% to 2% melt. This geometry is consistent with the ascent of the buoyant magma entrained in eastward return-flow of the upper mantle. Some remaining issues to be discussed are: 1) the interaction dynamics and magma path from the tilted plume to the lithosphere, 2) the transfer mechanism of mantle magma through the lithosphere into the upper crust, 3) how the high potential energy of the large 12 m+ geoid high drives the dominant extensional strain and concomitant crustal magma emplacement, 4) how the crustal magma interacts with the surface hydrothermal features, and 5) how stress interaction of faults and volcanic features behave at short- to decadal time scales.

Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater - Clan Alpine caldera complex, western Nevada, USA

NASA Astrophysics Data System (ADS)

Colgan, Joseph P.; John, David A.; Henry, Christopher D.; Watts, Kathryn E.

2018-01-01

Geologic mapping, new U-Pb zircon ages, and new and published 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4-28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3-24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1-2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of 1500 km2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500-5000 km3.

Chandra Discovery of a Tree in the X-Ray Forest toward PKS 2155-304: The Local Filament?

NASA Astrophysics Data System (ADS)

Nicastro, Fabrizio; Zezas, Andreas; Drake, Jeremy; Elvis, Martin; Fiore, Fabrizio; Fruscione, Antonella; Marengo, Massimo; Mathur, Smita; Bianchi, Stefano

2002-07-01

We present the first X-ray detection of resonant absorption from warm/hot local gas either in our Galaxy, or in the intergalactic space surrounding our Galaxy, along the line of sight toward the blazar PKS 2155-304. The Chandra HRCS/LETG spectrum of this z=0.116 source clearly shows, at >=5 σ level, unresolved (FWHM<=800 km s-1 at a 2 σ confidence level) O VII Kα and Ne IX Kα resonant absorption lines at 21.603+0.014-0.024 and 13.448+0.022-0.024 Å (i.e., cz=14+190-330 km s-1 in the rest frame, from the O VII Kα line). O VIII Kα and O VII Kβ from the same system are also detected at a lower significance level (i.e., ~3 σ), while upper limits are set on O VIII Kβ, Ne X Kα, and Ne IX Kβ. The Far Ultraviolet Spectroscopic Explorer spectrum of this source shows complex O VI 2s-->2p absorption at the same redshift as the X-ray system, made by at least two components: one relatively narrow (FWHM=106+/-9 km s-1) and slightly redshifted (cz=36+/-6 km s-1), and one broader (FWHM=158+/-26 km s-1) and blueshifted (cz=-135+/-14 km s-1). We demonstrate that the physical states of the UV and X-ray absorbers are hard to reconcile with a single, purely collisionally ionized, equilibrium plasma. We propose instead that the X-ray and at least the broader and blueshifted UV absorber are produced in a low-density intergalactic plasma, collapsing toward our Galaxy, consistent with the predictions of a warm-hot intergalactic medium from numerical simulations. We find that any reasonable solution requires overabundance of Ne compared to O by a factor of ~2, with respect to the solar value. We propose several scenarios to account for this observation.

Population assessment and potential functional roles of native mussels in the Upper Mississippi River

USGS Publications Warehouse

Newton, Teresa J.; Zigler, Steven J.; Rogala, James T.; Gray, Brian R.; Davis, Mike

2011-01-01

1. Despite a heightened global concern for native mussels, fundamental research on mussel ecology in large rivers is lacking. These gaps in knowledge about where mussels occur, and why, are limiting habitat restoration activities. 2. Large-scale systematic surveys for native mussels in three reaches of the Upper Mississippi River documented mussel communities composed of 16–23 species and ranging from 2.9–4.5 live mussels m-2 that were actively recruiting new cohorts into their populations (87–100% of the species were found as juveniles 5 years old). Estimates of mean tissue biomass and production in these reaches ranged from 2.1–3.1 g C m-2 and 0.4–0.6 g C m-2year-1, respectively. 3. Mussels filtered a significant amount of water (range, 0.05–0.07 m3m-2d-1) over a 480 km reach of the Upper Mississippi River — amounting to a filtration rate of 53.1 million m3day-1. The filtration rate of mussels as a percentage of river discharge ranged from 0.5–1.4% at high flows (5% exceedance), from 1.5–4.4% at moderate flows (50% exceedance) and from 4.4–12.2% during low flows (95% exceedance). 4. Collectively, these data suggest that native mussels play an integral role in this ecosystem by sequestering suspended materials that can be used by other benthic organisms.

The NASA/MSFC Global Reference Atmospheric Model: 1999 Version (GRAM-99)

NASA Technical Reports Server (NTRS)

Justus, C. G.; Johnson, D. L.

1999-01-01

The latest version of Global Reference Atmospheric Model (GRAM-99) is presented and discussed. GRAM-99 uses either (binary) Global Upper Air Climatic Atlas (GUACA) or (ASCII) Global Gridded Upper Air Statistics (GGUAS) CD-ROM data sets, for 0-27 km altitudes. As with earlier versions, GRAM-99 provides complete geographical and altitude coverage for each month of the year. GRAM-99 uses a specially-developed data set, based on Middle Atmosphere Program (MAP) data, for 20-120 km altitudes, and NASA's 1999 version Marshall Engineering Thermosphere (MET-99) model for heights above 90 km. Fairing techniques assure smooth transition in overlap height ranges (20-27 km and 90-120 km). GRAM-99 includes water vapor and 11 other atmospheric constituents (O3, N2O, CO, CH4, CO2, N2, O2, O, A, He and H). A variable-scale perturbation model provides both large-scale (wave) and small-scale (stochastic) deviations from mean values for thermodynamic variables and horizontal and vertical wind components. The small-scale perturbation model includes improvements in representing intermittency ("patchiness"). A major new feature is an option to substitute Range Reference Atmosphere (RRA) data for conventional GRAM climatology when a trajectory passes sufficiently near any RRA site. A complete user's guide for running the program, plus sample input and output, is provided. An example is provided for how to incorporate GRAM-99 as subroutines in other programs (e.g., trajectory codes).

AN INTRIGUING CHROMOSPHERIC JET OBSERVED BY HINODE: FINE STRUCTURE KINEMATICS AND EVIDENCE OF UNWINDING TWISTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Wei; Berger, Thomas E.; Title, Alan M.

2009-12-10

We report a chromospheric jet lasting for more than 1 hr observed by the Hinode Solar Optical Telescope in unprecedented detail. The ejection occurred in three episodes separated by 12-14 minutes, with the amount and velocity of material decreasing with time. The upward velocities range from 438 to 33 km s{sup -1}, while the downward velocities of the material falling back have smaller values (mean: -56km s{sup -1}) and a narrower distribution (standard deviation: 14km s{sup -1}). The average acceleration inferred from parabolic spacetime tracks is 141 m s{sup -2}, a fraction of the solar gravitational acceleration. The jet consistsmore » of fine threads (0.''5-2'' wide), which exhibit coherent, oscillatory transverse motions perpendicular to the jet axis and about a common equilibrium position. These motions propagate upward along the jet, with the maximum phase speed of 744+-11 km s{sup -1}at the leading front of the jet. The transverse oscillation velocities range from 151 to 26 km s{sup -1}, amplitudes from 6.0 to 1.9 Mm, and periods from 250 to 536 s. The oscillations slow down with time and cease when the material starts to fall back. The falling material travels along almost straight lines in the original direction of ascent, showing no transverse motions. These observations are consistent with the scenario that the jet involves untwisting helical threads, which rotate about the axis of a single large cylinder and shed magnetic helicity into the upper atmosphere.« less

Sediment Budgeting in Dam-Affected Rivers: Assessing the Influence of Damming, Tributaries, and Alluvial Valley Sediment Storage on Sediment Regimes

NASA Astrophysics Data System (ADS)

Wilcox, A. C.; Dekker, F. J.; Riebe, C. S.

2014-12-01

Although sediment supply is recognized as a fundamental driver of fluvial processes, measuring how dams affect sediment regimes and incorporating such knowledge into management strategies remains challenging. To determine the influences of damming, tributary supply, and valley morphology and sediment storage on downstream sediment supply in a dryland river, the Bill Williams River (BWR) in western Arizona, we measured basin erosion rates using cosmogenic nuclide analysis of beryllium-10 (10Be) at sites upstream and downstream of a dam along the BWR, as well as from tributaries downstream of the dam. Riverbed sediment mixing calculations were used to test if the dam, which blocks sediment supply from the upper 85% of the basin's drainage area, increases the proportion of tributary sediment to residual upstream sediment in mainstem samples downstream of the dam. Erosion rates in the BWR watershed are more than twice as large in the upper catchment (136 t km-2 yr-1) than in tributaries downstream of Alamo Dam (61 t km-2 yr-1). Tributaries downstream of the dam have little influence on mainstem sediment dynamics. The effect of the dam on reducing sediment supply is limited, however, because of the presence of large alluvial valleys along the mainstem BWR downstream of the dam that store substantial sediment and mitigate supply reductions from the upper watershed. These inferences, from our 10Be derived erosion rates and mixing calculations, are consistent with field observations of downstream changes in bed material size, which suggest that sediment-deficit conditions are restricted to a 10 km reach downstream of the dam, and limited reservoir bathymetry data. Many studies have suggested that tributary sediment inputs downstream of dams play a key role in mitigating dam-induced sediment deficits, but here we show that in a dryland river with ephemeral tributaries, sediment stored in alluvial valleys can also play a key role and in some cases trumps the role of tributaries.

Inference of mantle viscosity for depth resolutions of GIA observations

NASA Astrophysics Data System (ADS)

Nakada, Masao; Okuno, Jun'ichi

2016-11-01

Inference of the mantle viscosity from observations for glacial isostatic adjustment (GIA) process has usually been conducted through the analyses based on the simple three-layer viscosity model characterized by lithospheric thickness, upper- and lower-mantle viscosities. Here, we examine the viscosity structures for the simple three-layer viscosity model and also for the two-layer lower-mantle viscosity model defined by viscosities of η670,D (670-D km depth) and ηD,2891 (D-2891 km depth) with D-values of 1191, 1691 and 2191 km. The upper-mantle rheological parameters for the two-layer lower-mantle viscosity model are the same as those for the simple three-layer one. For the simple three-layer viscosity model, rate of change of degree-two zonal harmonics of geopotential due to GIA process (GIA-induced J˙2) of -(6.0-6.5) × 10-11 yr-1 provides two permissible viscosity solutions for the lower mantle, (7-20) × 1021 and (5-9) × 1022 Pa s, and the analyses with observational constraints of the J˙2 and Last Glacial Maximum (LGM) sea levels at Barbados and Bonaparte Gulf indicate (5-9) × 1022 Pa s for the lower mantle. However, the analyses for the J˙2 based on the two-layer lower-mantle viscosity model only require a viscosity layer higher than (5-10) × 1021 Pa s for a depth above the core-mantle boundary (CMB), in which the value of (5-10) × 1021 Pa s corresponds to the solution of (7-20) × 1021 Pa s for the simple three-layer one. Moreover, the analyses with the J˙2 and LGM sea level constraints for the two-layer lower-mantle viscosity model indicate two viscosity solutions: η670,1191 > 3 × 1021 and η1191,2891 ˜ (5-10) × 1022 Pa s, and η670,1691 > 1022 and η1691,2891 ˜ (5-10) × 1022 Pa s. The inferred upper-mantle viscosity for such solutions is (1-4) × 1020 Pa s similar to the estimate for the simple three-layer viscosity model. That is, these analyses require a high viscosity layer of (5-10) × 1022 Pa s at least in the deep mantle, and suggest that the GIA-based lower-mantle viscosity structure should be treated carefully in discussing the mantle dynamics related to the viscosity jump at ˜670 km depth. We also preliminarily put additional constraints on these viscosity solutions by examining typical relative sea level (RSL) changes used to infer the lower-mantle viscosity. The viscosity solution inferred from the far-field RSL changes in the Australian region is consistent with those for the J˙2 and LGM sea levels, and the analyses for RSL changes at Southport and Bermuda in the intermediate region for the North American ice sheets suggest the solution of η670,D > 1022, ηD,2891 ˜ (5-10) × 1022 Pa s (D = 1191 or 1691 km) and upper-mantle viscosity higher than 6 × 1020 Pa s.

Volcano Near Pavonis Mons

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-549, 19 November 2003

The volcanic plains to the east, southeast, and south of the giant Tharsis volcano, Pavonis Mons, are dotted by dozens of small volcanoes. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example located near 2.1oS, 109.1oW. The elongate depression in the lower left (southwest) quarter of the image is the collapsed vent area for this small, unnamed volcano. A slightly sinuous, leveed channel runs from the depression toward the upper right (north-northeast); this is the trace of a collapsed lava tube. The entire scene has been mantled by dust, such that none of the original volcanic rocks are exposed--except minor occurrences on the steepest slopes in the vent area. The scene is 3 km (1.9 mi) wide and illuminated by sunlight from the left/upper left.

Crustal thickness and Vp/Vs beneath the southeastern United States: Constraints from receiver function stacking

NASA Astrophysics Data System (ADS)

Yang, Q.; Gao, S. S.; Liu, K. H.

2017-12-01

To provide new constraints on crustal structure and evolution models beneath a collage of tectonic provinces in the southeastern United States, a total of 10,753 teleseismic receiver functions recorded by 125 USArray and other seismic stations are used to compute crustal thickness and Vp/Vs values. The resulting crustal thicknesses range from 25 km at the coast to 51 km beneath the peak of the southern Appalachians with an average of 36.2 km ± 5.5 km. The resulting crustal thicknesses correlate well with surface elevation and Bouguer gravity anomalies. Beneath the Atlantic Coastal Plain, the crustal thicknesses show a clear eastward thinning with a magnitude of 10 km, from about 40 km beneath the western margin to 30 km beneath the coast. The Vp/Vs values for the entire study area range from 1.71 to 1.90 with a mean value of 1.80 ± 0.04. The mean Vp/Vs value is 1.82±0.035 in the southern Appalachian Mountain. The slightly larger than normal crustal Vp/Vs for this area might be the result of significant erosion of the felsic upper crust over the past 300 million years. Alternatively, it could also suggest the existence of pervasive magmatic intrusion into the Appalachian crust. The Vp/Vs measurements in the Atlantic Coastal Plain increase toward the east, ranging from 1.75 to 1.82, probably indicating a gradual increase of mafic magmatic intrusion into thinner crust during the development of the passive continental margin.

THE LITHOSPHERIC MAGNETIC FIELD ALONG THE NISHAN-GUYANG PROFILE, CHINA 6 datesYuan Jiehao1; Gu Zuowen1; Chen Bin1; Xu Rugang2; Wang Lie2; Wang Can1 1. Institute of Geophysics, China Earthquake Administration(IGP CEA), yjh810405@163.com 2. Anhui Earthquake Administration

NASA Astrophysics Data System (ADS)

Yuan, J.

2014-12-01

In order to research the lithospheric magnetic field and the magnetization structure, the geomagnetic field was surveyed along the Nishan-Guyang profile with 900 km long in the Neimenggu and Shanxi provinces in China. The distance between the adjacent geomagnetic sites is about 7 km along the profile. The geomagnetic data were analyzed, and the lithospheric magnetic field was obtained. Using the upward continuation method, the geomagnetic anomalies in different depths were obtained: the basement anomaly, the upper crust anomaly and the superficial anomaly. Basing on these geomagnetic anomalies, the magnetization structure was obtained by using the software of the ModelVision 11.0. The preliminary results show: (1) The geomagnetic anomalies have good relationship with the local geological structure. (2) The magnetization structure is related to the depth variation of the Curie interface, the values of the magnetic susceptibility, the seismic activity and the tectonic block.

Traveltimes and amplitudes from nuclear explosions; Nevada Test Site to Ordway, Colorado

USGS Publications Warehouse

Ryall, Alan; Stuart, David J.

1963-01-01

This paper treats the results of a study of seismic waves generated by eight nuclear explosions and recorded at 31 locations between the Nevada Test Site (NTS) and Ordway, Colorado. The line of recording stations crosses the eastern part of the Basin and Range Province, the Colorado Plateau, the southern Rocky Mountains, and extends into the Great Plains. In the eastern Basin and Range Province and the western margin of the Colorado Plateau (0 ≤ Δ ≤ 385 km ), the time-distance curves for Pg and Pn can be expressed, respectively, as T1 = 0.8 + Δ/6.0. T3 = 5.8 + Δ/7.6. A third phase, tentatively identified as P*, is represented by the equation T2 = 3.8 + Δ/6.5. Using the crustal structure and Pn velocity (7.9 km/ sec) found for the NTS region by other authors, these relations indicate that the thickness of the crust increases from about 25 km at NTS to about 42 km in the western part of the Colorado Plateau Province. East of this boundary the velocity of P in the upper mantle increases to 8.0 km/sec; depth to the Mohorovicic discontinuity is approximately constant over the range 435 ≤ Δ ≤ 645 km. Beyond 850 km, first arrivals indicate an apparent velocity of about 8.4 km/sec. Amplitudes of Pn attenuate according to the equation A = Ao Δ-1/2(Δ -d)-3/2 e-0.0022Δ over the distance range 150 ≤ Δ ≤ 850 km. This relation yields a value of Q, for Pn of about 520. The amplitudes of Pg attenuates extremely rapidly, and beyond about 130 km this phase cannot be identified with certainty. An extension of the Pg traveltime branch at large distances could be associated with waves reflected beyond the critical angle, from the base of the crust. This phase, called ?P after Mohorovicic, appears to attenuate as A = Ao e-0.076Δ Δ-1/2. The value of Q indicated by this equation is about 200.

Estimation of Water Within the Lithospheric Mantle of Central Tibet from Petrological-Geophysical Investigations

NASA Astrophysics Data System (ADS)

Vozar, J.; Fullea, J.; Jones, A. G.

2013-12-01

Investigations of the lithosphere and sub-lithospheric upper mantle by integrated petrological-geophysical modeling of magnetotelluric (MT) and seismic surface-wave data, which are differently sensitive to temperature and composition, allows us to reduce the uncertainties associated with modeling these two data sets independently, as commonly undertaken. We use selected INDEPTH MT data, which have appropriate dimensionality and large penetration depths, across central Tibet for 1D modeling. Our deep resistivity models from the data can be classified into two different and distinct groups: (i) the Lhasa Terrane and (ii) the Qiangtang Terrane. For the Lhasa Terrane group, the models show the existence of upper mantle conductive layer localized at depths of 200 km, whereas for the Qiangtang Terrane, this conductive layer is shallower at depths of 120 km. We perform the integrated geophysical-petrological modeling of the MT and surface-wave data using the software package LitMod. The program facilitates definition of realistic temperature and pressure distributions within the upper mantle for given thermal structure and oxide chemistry in the CFMAS system. This allows us to define a bulk geoelectric and seismic model of the upper mantle based on laboratory and xenolith data for the most relevant mantle minerals, and to compute synthetic geophysical observables. Our results suggest an 80-120 km-thick, dry lithosphere in the central part of the Qiangtang Terrane. In contrast, in the central Lhasa Terrane the predicted MT responses are too resistive for a dry lithosphere regardless its thickness; according to seismic and topography data the expected lithospheric thickness is about 200 km. The presence of small amounts of water significantly decreases the electrical resistivity of mantle rocks and is required to fit the MT responses. We test the hypothesis of small amounts of water (ppm scale) in the nominally anhydrous minerals of the lithospheric mantle. Such a small amount of water dramatically affects the resistivity but has no influence on the seismic velocities (and therefore, the calculated surface wave's dispersion curves are unaffected too). Three different proton conduction models for olivine conductivity (1 - Wang et al., 2006; 2 - Yoshino et al., 2009; 3 -Jones et al., 2012) and two water partition coefficients are tested. The presence of water in lithospheric mantle is decreased from 170 km to the LAB depth at 200 km. If we move this water-presentbottom boundary to shallower depth, the lithospheric mantle becomes too resistive. Our results favour a moderately wet (<0.01 wt%) mantle above the underthrusted Indian lithosphere, probably as a result of the dehydration processes. The presence of percolating water-rich fluids has the additional effect of lowering the solidus, and therefore facilitating partial melting in the warm lower crust of Lhasa.

Diode laser heterodyne observations of silicon monoxide in sunspots - A test of three sunspot models

NASA Technical Reports Server (NTRS)

Glenar, D. A.; Deming, D.; Jennings, D. E.; Kostiuk, T.; Mumma, M. J.

1983-01-01

Absorption features from the 8 micron SiO fundamental (upsilon = 1-0) and hot bands (upsilon = 2-1) have been observed in sunspots at sub-Doppler resolution using a ground-based tunable diode laser heterodyne spectrometer. The observed line widths suggest an upper limit of 0.5 km/s for the microturbulent velocity in sunspot umbrae. Since the silicon monoxide abundance is very sensitive to sunspot temperature, the measured equivalent widths permit an unambiguous determination of the temperature-pressure relation in the upper layers of the umbral atmosphere. In the region of SiO line formation (log P sub g = 3.0-4.5), the results support the sunspot model suggested by Stellmacher and Wiehr (1970).

TITAN’S UPPER ATMOSPHERE FROM CASSINI/UVIS SOLAR OCCULTATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capalbo, Fernando J.; Bénilan, Yves; Yelle, Roger V.

2015-12-01

Titan’s atmosphere is composed mainly of molecular nitrogen, methane being the principal trace gas. From the analysis of 8 solar occultations measured by the Extreme Ultraviolet channel of the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini, we derived vertical profiles of N{sub 2} in the range 1100–1600 km and vertical profiles of CH{sub 4} in the range 850–1300 km. The correction of instrument effects and observational effects applied to the data are described. We present CH{sub 4} mole fractions, and average temperatures for the upper atmosphere obtained from the N{sub 2} profiles. The occultations correspond to different times and locations,more » and an analysis of variability of density and temperature is presented. The temperatures were analyzed as a function of geographical and temporal variables, without finding a clear correlation with any of them, although a trend of decreasing temperature toward the north pole was observed. The globally averaged temperature obtained is (150 ± 1) K. We compared our results from solar occultations with those derived from other UVIS observations, as well as studies performed with other instruments. The observational data we present confirm the atmospheric variability previously observed, add new information to the global picture of Titan’s upper atmosphere composition, variability, and dynamics, and provide new constraints to photochemical models.« less

Resurfacing history of the northern plains of Mars based on geologic mapping of Mars Global Surveyor data

USGS Publications Warehouse

Tanaka, K.L.; Skinner, J.A.; Hare, T.M.; Joyal, T.; Wenker, A.

2003-01-01

Geologic mapping of the northern plains of Mars, based on Mars Orbiter Laser Altimeter topography and Viking and Mars Orbiter Camera images, reveals new insights into geologic processes and events in this region during the Hesperian and Amazonian Periods. We propose four successive stages of lowland resurfacing likely related to the activity of near-surface volatiles commencing at the highland-lowland boundary (HLB) and progressing to lower topographic levels as follows (highest elevations indicated): Stage 1, upper boundary plains, Early Hesperian, <-2.0 to -2.9 km; Stage 2, lower boundary plains and outflow channel dissection, Late Hesperian, <-2.7 to -4.0 km; Stage 3, Vastitas Borealis Formation (VBF) surface, Late Hesperian to Early Amazonian, <-3.1 to -4.1 km; and Stage 4, local chaos zones, Early Amazonian, <-3.8 to -5.0 km. At Acidalia Mensa, Stage 2 and 3 levels may be lower (<-4.4 and -4.8 km, respectively). Contractional ridges form the dominant structure in the plains and developed from near the end of the Early Hesperian to the Early Amazonian. Geomorphic evidence for a northern-plains-filling ocean during Stage 2 is absent because one did not form or its evidence was destroyed by Stage 3 resurfacing. Remnants of possible Amazonian dust mantles occur on top of the VBF. The north polar layered deposits appear to be made up of an up to kilometer-thick lower sequence of sandy layers Early to Middle Amazonian in age overlain by Late Amazonian ice-rich dust layers; both units appear to have outliers, suggesting that they once were more extensive.

Variabilities of Low-Latitude Migrating and Nonmigrating Tides in GPS-TEC and TIMED-SABER Temperature During the Sudden Stratospheric Warming Event of 2013

NASA Astrophysics Data System (ADS)

Sridharan, S.

2017-10-01

The Global Positioning System deduced total electron content (TEC) data at 15°N (geomagnetic), which is the crest region of equatorial ionization anomaly, are used to study tidal variabilities during the 2013 sudden stratospheric warming (SSW) event. The results from space-time spectral analysis reveal that the amplitudes of migrating diurnal (DW1) and semidiurnal (SW2) tides are larger than those of nonmigrating tides. After the SSW onset, the amplitudes of DW1, SW2, SW1, and DS0 increase. Moreover, they show 16 day variations similar to the periodicity of the high-latitude stratospheric planetary wave (PW), suggesting that the nonmigrating tides (SW1 and DS0) are possibly generated due to nonlinear interaction of migrating tides with PW. Similar spectral analysis on temperature at 10°N obtained from the Sounding of Atmosphere by Broadband Emission Radiometry (SABER) shows that the SW2 enhances at stratospheric heights and the SW2 is more dominant at 80-90 km, but its amplitude decreases around 100 km. The amplitudes of nonmigrating tides become comparable to those of SW2 around 100 km, and their contribution becomes increasingly important at higher heights. This suggests that the nonlinear interaction between migrating tides and PW occurs at low-latitude upper mesospheric heights, as SW2 exhibits 16 day periodicity in SABER temperature at 100 km as observed in TEC. Besides, it is observed that the eastward propagating tides are less dominant than westward propagating tides in both TEC and SABER temperatures.

ARC-1990-AC90-3007

NASA Image and Video Library

1990-11-16

This Magellan image reveals Sacajawea Patera, a large, elongate caldera located in wester Ishtar Terra on the smooth plateau of Lakshmi Planum. The image is centered at 64.5 degrees north latitude adn 337 degrees east longitude. It is approx. 420 km (252 mi.) wide at the base Sacajawea is a depression approx. 1-2 km (0.6-1.2 mi.) deep and 120 by 215 km (74 by 133 mi.) in diameter; it is elongate in a sousthwest-northeast direction. The depression is interpreted to be graben adn fault scarps. These structures are space 0.5 to 4 km (0.3 to 2.5 mi.) apart, are 0.6 to 4 km (0.4 to 2.5 mi.) in width and up to 100 km (62 mi.) in length. Extending up to 140 km (87 mi.) in length from the southeast of the patera is a system of linear structures thought to represent a flanking rift zone along which the lateral injection and eruption of magma may have occurred. A shield edifice 12 km (7 mi.) in diameter with a prominent central pit lies along the trend of one of these features. The impact crater zlata, approx. 6 km (4 mi.) in diameter is located within the zone of graben to the northwest of the patera. Few flow features are observed in association with sacajawea, possibly due to age and state of degradation of the flows. Mottled bright deposits 4 to 20 km (2.5 to 12 mi.) in width are located near the periphery and in the center of the patera floor within local topographic lows. Diffuse patches of dark material approx. 40 km (25 mi.) in width are observed southwest of the patera, superimposed on portions of the surrounding graben. The formation of sacajawea is thought to be related to the drainage and collapse of a large magma chamber. Gravitational relaxation may have caused the resultant caldera to sag, producing the numerous complex, highly deformed tessera-like terrain are located north and east of the patera and are seen in the upper portion of the image. Color has been added to this image to simulate the appearance of the Venus surface.

a View of the Marble-Cake Mantle from the Southeast Indian Ridge

NASA Astrophysics Data System (ADS)

Hanan, B. B.; Graham, D. W.; Hemond, C.; Blichert-Toft, J.; Albarede, F.

2014-12-01

Along the Southeast Indian Ridge, variations in axial depth, crustal thickness, hydrothermal venting [1], basaltic major elements and U-series disequilibria [2] all indicate a west-to-east decrease in magma supply and mantle temperature from the Amsterdam-St. Paul hotspot to the Australian-Antarctic Discordance. Paired Hf-Pb isotopes in closely spaced glasses (5-10 km) from 81-100°E define two populations revealing compositional streaks in the upper mantle [3]. The number density of the streaks follows a Poisson distribution with a characteristic thickness of ~20 km. K/Ti and Na8 do not correlate with Pb or Hf isotopes, and both isotopic domains encompass N- and E-MORB types indicating the variations represent mantle source heterogeneities. 3He/4He varies from 7.5 - 10.2 RA, more than half the range in global MORB away from hotspot influence [4]. No systematic relationship exists between 3He/4He and Pb or Hf isotopes. A general negative correlation between K/Ti and Fe8 for the SEIR resembles that for MORBs globally, with higher K/Ti associated with lower 3He/4He. Collectively the observations suggest the presence of lithologically heterogeneous mantle. Lower 3He/4He derives from a source containing a few percent pyroxenite or ecologite, while 3He/4He > 9 RA arises from peridotite. Mantle convection has folded together distinct composite reservoirs of heterogeneous mantle, and stretched them into streaks that remain discernible units. The mantle 'unit' giving rise to each MORB sample represents a 'mixture of mixtures' with a multi-stage mixing history. Spectral analysis of the length scales of Hf, Pb and He isotopic variability allows a visual representation of this upper mantle 'texture'. The dominant length scales reflect large (1000, 500 km) and regional scale (100-150 km) structures in mantle flow, and sampling of heterogeneities during partial melting (20-30 km). 1-Baker et al., doi:10.1002/2014GC005344; 2-Russo et al., doi:10.1016/j.epsl.2008.11.016; 3-Hanan et al., doi:10.1016/j.epsl.2013.05.028; 4-Graham et al., doi:10.1002/2014GC005264

Mesoscale variability of the Upper Colorado River snowpack

USGS Publications Warehouse

Ling, C.-H.; Josberger, E.G.; Thorndike, A.S.

1996-01-01

In the mountainous regions of the Upper Colorado River Basin, snow course observations give local measurements of snow water equivalent, which can be used to estimate regional averages of snow conditions. We develop a statistical technique to estimate the mesoscale average snow accumulation, using 8 years of snow course observations. For each of three major snow accumulation regions in the Upper Colorado River Basin - the Colorado Rocky Mountains, Colorado, the Uinta Mountains, Utah, and the Wind River Range, Wyoming - the snow course observations yield a correlation length scale of 38 km, 46 km, and 116 km respectively. This is the scale for which the snow course data at different sites are correlated with 70 per cent correlation. This correlation of snow accumulation over large distances allows for the estimation of the snow water equivalent on a mesoscale basis. With the snow course data binned into 1/4?? latitude by 1/4?? longitude pixels, an error analysis shows the following: for no snow course data in a given pixel, the uncertainty in the water equivalent estimate reaches 50 cm; that is, the climatological variability. However, as the number of snow courses in a pixel increases the uncertainty decreases, and approaches 5-10 cm when there are five snow courses in a pixel.

Chemical Characteristics of Continental Outflow from Asia to the Troposphere over the Western Pacific Ocean during September - October 1991: Results from PEM-West A

NASA Technical Reports Server (NTRS)

Talbot, R. W.; Dibb, J. E.; Klemm, K. I.; Bradshaw, J. D.; Sandholm, S. T.; Blake, D. R.; Sachse, G. W.; Collins, J.; Heikes, B. G.; Gregory, G. L.;

Northeastern Pacific mantle conductivity profile from long-period magnetotelluric sounding using Hawaii-to-California submarine cable data

NASA Astrophysics Data System (ADS)

Lizarralde, Daniel; Chave, Alan; Hirth, Greg; Schultz, Adam

1995-09-01

We present results of a long-period magnetotelluric (MT) investigation of the electrical structure beneath the eastern North Pacific. The electric field data consist of ˜2 years of continuously recorded voltages across an unpowered, ˜4000-km-long submarine telephone cable (HAW-1) extending from Point Arena, California, to Oahu, Hawaii. The electric field measurements are coherent to some degree with magnetic field measurements from Honolulu Observatory at periods of 0.1 to 45 days. This coherence is enhanced at long periods over that observed with point electric field sensors due to horizontal averaging of the motional electric fields of spatial scale smaller than the cable length, significantly diminishing their effect. Robust, controlled leverage MT response estimates and their jacknife confidence limits are computed for the HAW-1 to Honolulu data. An equivalent scalar MT response obtained from Honolulu magnetic variations data is used to correct the HAW-1 MT response for static shift and to extend the MT response estimate to periods of 100 days. The composite response function satisfies necessary and sufficient conditions for consistency with a one-dimensional conductivity structure and is most sensitive to structure between 150 and 1000 km. Inversion of the MT response reveals a conductive zone (0.05-0.1 S/m) between 150 and 400 km depth and a positive gradient below 500 km; these observations are consistent with previous MT studies in the North Pacific. This upper mantle conductivity is too high to be explained by solid-state conduction in dry olivine using reasonable mantle geotherms. Calculations based on measurements of hydrogen solubility and diffusivity in olivine indicate that H+ dissolved in olivine, possibly combined with a lattice preferred orientation consistent with measured seismic anisotropy, provide sufficient conductivity enhancement to explain the inversion results. The high conductivity may also be explained by the presence of gravitationally stable partial melt. Comparison of the HAW-1 results with long-period MT studies conducted on land reveals differences in upper mantle conductivity between different tectonic regimes. In particular, the upper mantle beneath the Pacific Ocean is considerably more conductive than that beneath the Canadian shield and similar in conductivity to that beneath the Basin and Range.

Limnological data from selected lakes in the San Francisco Bay region, California

USGS Publications Warehouse

Britton, Linda J.; Ferreira, Rodger F.; Averett, Robert C.

1974-01-01

The largest reservoir, Lake Berryessa, has a volume of 1,600,000 acre-ft (1,975 hm3), with a drainage. area of 576 mi2 (1,490 km2 ). Pilarcitos Lake is one of the smallest reservoirs, with a volume of 3,100 acre-ft (3. 8 hm3) and a drainage area of 3. 80 mi 2 (9.84km2). Eleven of the 21 reservoirs are open to the public for recreation. The most intensive shoreline development and use is at Lake Berryessa and Lake Merced. All but three of the 21 reservoirs (not including Upper Crystal Springs Reservoir) were thermally stratified during the summer. Eight of the reservoirs showed evidence of dissolvedoxygen depletion during the summer. Lafayette Reservoir and Loch Lomond are mechanically aerated in order to increase the dissolved-oxygen concentration and lower the surface water temperature. The lake waters ranged from the hard (320 mg/1 CaC03) of Calero Reservoir, to the soft (27 mg/1 CaC03) of Upper Crystal Springs Reservoir. Drainage from abandoned mercury mines in Santa Clara County has resulted in mercury concentrations in Calero and Lexington Reservoir fish which exceed U.S. Food and Drug limitations (0.5 μ/g) for acceptability of mercury in fish used for human food. In Loch Lomond, four major production periods of the blue-green algae, Anabaena sp. , occurred from May to October, 1967-69. Blue-green algae were the most numerous algae in Lake Del Valle from March through July 1971, with 5,400 blue-green algal organisms per millilitre collected in April.

Morphology of upper laurentian fan using GLORIA long-range side-scan sonar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masson, D.G.; Field, M.E.; Gardner, J.V.

1985-06-01

A long-range side-scan sonar (GLORIA) survey of the upper Laurentian Fan shows, for the first time, the regional geomorphology of this large and complex sedimentary body. The channels of the upper continental slope coalesce on the upper fan to form four major fan valleys. The largest of these, Eastern Valley, is U-shaped in cross section and up to 25 km (15 mi) wide with a large levee on the western flank that reaches a maximum height of more than 1 km (3,300 ft) above the valley floor. The remaining valleys, Western, Central, and Grand Banks, are typically more V-shaped inmore » cross section and are up to 5 km (3 mi) wide. Extensive gullying is observed on the walls of all the channels. Sonographs of the floor of Eastern Valley show a strong, linear fabric elongated parallel with the valley walls that appears to be related to mesoscale relief on the valley floor. At water depths between 3,500 and 4,100 m (11,550 and 13,530 ft), two major fan valleys are created by the merging of the four major valleys of the upper fan. Both fan valleys are associated with large, asymmetric levee complexes that reach heights of more than 500 m (1,650 ft) above the valley floors. The GLORIA data show evidence for several amphitheaterlike slump scars in the region of the 1929 earthquake epicenter. However, the authors see no evidence for movement of large coherent sediment blocks as postulated by earlier workers. They suggest that the turbidity currents that occurred after the 1929 earthquake may have formed by the coalescence of many small slumps rather than from a single large slump.« less

Detailed Configuration of the Underthrusting Indian Lithosphere Beneath Western Tibet Revealed by Receiver Function Images

NASA Astrophysics Data System (ADS)

Xu, Qiang; Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Pei, Shunping

2017-10-01

We analyze the teleseismic waveform data recorded by 42 temporary stations from the Y2 and ANTILOPE-1 arrays using the P and S receiver function techniques to investigate the lithospheric structure beneath western Tibet. The Moho is reliably identified as a prominent feature at depths of 55-82 km in the stacked traces and in depth migrated images. It has a concave shape and reaches the deepest location at about 80 km north of the Indus-Yarlung suture (IYS). An intracrustal discontinuity is observed at 55 km depth below the southern Lhasa terrane, which could represent the upper border of the eclogitized underthrusting Indian lower crust. Underthrusting of the Indian crust has been widely observed beneath the Lhasa terrane and correlates well with the Bouguer gravity low, suggesting that the gravity anomalies in the Lhasa terrane are induced by topography of the Moho. At 20 km depth, a midcrustal low-velocity zone (LVZ) is observed beneath the Tethyan Himalaya and southern Lhasa terrane, suggesting a layer of partial melts that decouples the thrust/fold deformation of the upper crust from the shortening and underthrusting in the lower crust. The Sp conversions at the lithosphere-asthenosphere boundary (LAB) can be recognized at depths of 130-200 km, showing that the Indian lithospheric mantle is underthrusting with a ramp-flat shape beneath southern Tibet and probably is detached from the lower crust immediately under the IYS. Our observations reconstruct the configuration of the underthrusting Indian lithosphere and indicate significant along strike variations.

Ozone profile measurements of McMurdo Station, Antarctica, during the spring of 1987

NASA Technical Reports Server (NTRS)

Hofmann, D. J.; Harder, J. W.; Rosen, J. M.; Hereford, J. V.; Carpenter, J. R.

1989-01-01

Ozone and temperature profiles were measured in 50 balloon flights at McMurdo Station (78 deg S) during the spring of 1987. Compared to similar data obtained in 1986, stratospheric temperatures were lower and the spring time Antarctic ozone reduction was greater in magnitude, extended to higher altitude, and proceeded at a higher rate in 1987. Ozone partial pressures reached values as low as 3 nbar (as compared to about 10 nbar in 1986) in the 16- to 18-km region in early and late October, down from about 150 nbar in late August. These low values suggest essentially complete removal of ozone in this region. The upper boundary of the depletion region was observed to be 2-3 km higher than in 1986, extending to altitudes as high as 24 km in mid-September. When averaged over September, the ozone mixing ratio at 18 km decayed with a half-life of only 12.4 days, as compared to about 28 days in 1986. Adiabatic vertical motions over 1- to 2-km intervals between 12 and 20 km with consequent ozone reductions were observed in association with the formation of nacreous clouds, indicating these to be rare events on a local scale probably associated with mountain lee waves.

Mantle transition zone structure and upper mantle S velocity variations beneath Ethiopia: Evidence for a broad, deep-seated thermal anomaly

NASA Astrophysics Data System (ADS)

Benoit, Margaret H.; Nyblade, Andrew A.; Owens, Thomas J.; Stuart, Graham

2006-11-01

Ethiopia has been subjected to widespread Cenozoic volcanism, rifting, and uplift associated with the Afar hot spot. The hot spot tectonism has been attributed to one or more thermal upwellings in the mantle, for example, starting thermal plumes and superplumes. We investigate the origin of the hot spot by imaging the S wave velocity structure of the upper mantle beneath Ethiopia using travel time tomography and by examining relief on transition zone discontinuities using receiver function stacks. The tomographic images reveal an elongated low-velocity region that is wide (>500 km) and extends deep into the upper mantle (>400 km). The anomaly is aligned with the Afar Depression and Main Ethiopian Rift in the uppermost mantle, but its center shifts westward with depth. The 410 km discontinuity is not well imaged, but the 660 km discontinuity is shallower than normal by ˜20-30 km beneath most of Ethiopia, but it is at a normal depth beneath Djibouti and the northwestern edge of the Ethiopian Plateau. The tomographic results combined with a shallow 660 km discontinuity indicate that upper mantle temperatures are elevated by ˜300 K and that the thermal anomaly is broad (>500 km wide) and extends to depths ≥660 km. The dimensions of the thermal anomaly are not consistent with a starting thermal plume but are consistent with a flux of excess heat coming from the lower mantle. Such a broad thermal upwelling could be part of the African Superplume found in the lower mantle beneath southern Africa.

Nonlinear 1D and 2D waveform inversions of SS precursors and their applications in mantle seismic imaging

NASA Astrophysics Data System (ADS)

Dokht, R.; Gu, Y. J.; Sacchi, M. D.

2016-12-01

Seismic velocities and the topography of mantle discontinuities are crucial for the understanding of mantle structure, dynamics and mineralogy. While these two observables are closely linked, the vast majority of high-resolution seismic images are retrieved under the assumption of horizontally stratified mantle interfaces. This conventional correction-based process could lead to considerable errors due to the inherent trade-off between velocity and discontinuity depth. In this study, we introduce a nonlinear joint waveform inversion method that simultaneously recovers discontinuity depths and seismic velocities using the waveforms of SS precursors. Our target region is the upper mantle and transition zone beneath Northeast Asia. In this region, the inversion outcomes clearly delineate a westward dipping high-velocity structure in association with the subducting Pacific plate. Above the flat part of the slab west of the Japan sea, our results show a shear wave velocity reduction of 1.5% in the upper mantle and 10-15 km depression of the 410 km discontinuity beneath the Changbaishan volcanic field. We also identify the maximum correlation between shear velocity and transition zone thickness at an approximate slab dip of 30 degrees, which is consistent with previously reported values in this region.To validate the results of the 1D waveform inversion of SS precursors, we discretize the mantle beneath the study region and conduct a 2D waveform tomographic survey using the same nonlinear approach. The problem is simplified by adopting the discontinuity depths from the 1D inversion and solving only for perturbations in shear velocities. The resulting models obtained from the 1D and 2D approaches are self-consistent. Low-velocities beneath the Changbai intraplate volcano likely persist to a depth of 500 km. Collectively, our seismic observations suggest that the active volcanoes in eastern China may be fueled by a hot thermal anomaly originating from the mantle transition zone.

Observations of Seven Blue/Gigantic Jets above One Storm over the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Liu, N.; Spiva, N.; Dwyer, J. R.; Rassoul, H.; Free, D. L.; Cummer, S. A.

2013-12-01

Blue/gigantic jets are electrical discharges developing from thundercloud tops and propagating to the upper atmosphere [e.g., Pasko et al., Nature, 416, 152, 2002; Su et al., Nature, 423, 973, 2003]. Not just producing an impressive display, gigantic jets establish a direct path of electrical contact between the upper troposphere and the lower ionosphere, capable of transferring a large amount of charge between them [Cummer et al., Nat. Geosci., 2, 617, 2009]. It has been suggested that they may play an important role in the earth's electrical environment [e. g., Pasko, Nature, 423, 927, 2003]. Upward discharges from thunderstorms like blue/gigantic jets are believed to originate from lightning leaders escaping from thunderclouds when the cloud's charges of different polarities are not balanced [Krehbiel et al., Nat. Geosci., 1, 233, 2008; Riousset et al., JGR, 115, A00E10, 2010]. On the evening of August 2, 2013, 4 gigantic jets, 2 blue jets and 1 blue starter were recorded within 26 min above a storm over the Atlantic Ocean by a low light level camera from the campus of Florida Institute of Technology. The events were also captured by two all-sky cameras: one again from the Florida Tech campus and the other from a nearby location. According to the NLDN data, positive intra-cloud flashes preceded all events except one gigantic jet. The distance between the observation site to the locations of the NLDN lightning discharges varies from 77 to 82 km. Optical signatures of intra-cloud discharge activities accompanied the events are clearly visible in the videos. The duration of each jet varies from about 300 ms to 1.2 s, and the 1.2 s duration is probably the longest that has been reported to date for jets. Rebrightening of gigantic jet structures occurs for at least two of the events. The upper terminal altitude of the 4 gigantic jets is greater than 76-81 km, the 2 blue jets reach about 48 and 51 km altitude, respectively, and the blue starter reaches 24 km altitude. The altitude of cloud tops varies from 14 to 20 km. All events exhibit a tree-like structure and develop in an impulsive manner. Similar to other observations of gigantic jets, bright beads appear at the tops of the gigantic jets. The impulsive upward propagation of the jets together with the positive polarity of the preceding intra-cloud discharges suggests that the jets originate from upward propagating negative leaders initiated inside the thundercloud. All events propagate upward from the top of the cloud nearly vertically except for one event that develops in a slanted direction, about twenty three degrees from the vertical. With only a few branches, the three blue jet/starter events display a structure very similar to a cloud-to-ground lightning stroke. Our observations support the unified view of the upward discharges from thunderclouds advanced by Krehbiel et al. [2008] and Riousset et al. [2010]. In this talk, we discuss the video observations of the events and the associated radio signatures in detail.

The OMPS Limb Profiler instrument

NASA Astrophysics Data System (ADS)

Rault, D. F.; Xu, P.

2011-12-01

The Ozone Mapping and Profiler Suite (OMPS) will continue the monitoring of the global distribution of the Earth's middle atmosphere ozone and aerosol. OMPS is composed of three instruments, namely the Total Column Mapper (heritage: TOMS, OMI), the Nadir Profiler (heritage: SBUV) and the Limb Profiler (heritage: SOLSE/LORE, OSIRIS, SCIAMACHY, SAGE III). The ultimate goal of the mission is to better understand and quantify the rate of stratospheric ozone recovery. OMPS is scheduled to be launched on the NPOESS Preparatory Project (NPP) platform in October 2011. The focus of the paper will be on the Limb Profiler (LP) instrument. The LP instrument will measure the Earth's limb radiance, from which ozone profile will be retrieved from the upper tropopause uo to 60km. End-to-end studies of the sensor and retrieval algorithm indicate the following expected performance for ozone: accuracy of 5% or better from the tropopause up to 50 km, precision of about 3-5% from 18 to 50 km, and vertical resolution of 1.5-2 km with vertical sampling of 1 km and along-track horizontal sampling of 1 deg latitude. The paper will describe the mission, discuss the retrieval algorithm, and summarize the expected performance. If available, the paper will also present early on-orbit data.

Arsinoes Chaos Landforms

NASA Technical Reports Server (NTRS)

2004-01-01

23 October 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows light-toned rock outcrops, possibly sedimentary rocks, in the Arsinoes Chaos region east of the Valles Marineris trough system. These rocky materials were once below the martian surface. These features are located near 7.2oS, 27.9oW. The image covers an area about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the upper left.

Ganges Landslides

NASA Technical Reports Server (NTRS)

2005-01-01

This Mars Global Surveyor (MGS) Orbiter Camera (MOC) image shows a high resolution view of portions of the lobes of several landslide deposits in Ganges Chasma. Dark material near the bottom (south) end of the image is windblown sand.

Location near: 8.2oS, 44.3oW Image width: 3.0 km (1.9 mi) Illumination from: upper left Season: Southern Winter

Evolution of Meso-Cenozoic lithospheric thermal-rheological structure in the Jiyang sub-basin, Bohai Bay Basin, eastern North China Craton

NASA Astrophysics Data System (ADS)

Xu, Wei; Qiu, Nansheng; Wang, Ye; Chang, Jian

2018-01-01

The Meso-Cenozoic lithospheric thermal-rheological structure and lithospheric strength evolution of the Jiyang sub-basin were modeled using thermal history, crustal structure, and rheological parameter data. Results indicate that the thermal-rheological structure of the Jiyang sub-basin has exhibited obvious rheological stratification and changes over time. During the Early Mesozoic, the uppermost portion of the upper crust, middle crust, and the top part of the upper mantle had a thick brittle layer. During the early Early Cretaceous, the top of the middle crust's brittle layer thinned because of lithosphere thinning and temperature increase, and the uppermost portion of the upper mantle was almost occupied by a ductile layer. During the late Early Cretaceous, the brittle layer of the middle crust and the upper mantle changed to a ductile one. Then, the uppermost portion of the middle crust changed to a thin brittle layer in the late Cretaceous. During the early Paleogene, the thin brittle layer of the middle crust became even thinner and shallower under the condition of crustal extension. Currently, with the decrease in lithospheric temperature, the top of the upper crust, middle crust, and the uppermost portion of the upper mantle are of a brittle layer. The total lithospheric strength and the effective elastic thickness ( T e) in Meso-Cenozoic indicate that the Jiyang sub-basin experienced two weakened stages: during the late Early Cretaceous and the early Paleogene. The total lithospheric strength (approximately 4-5 × 1013 N m-1) and T e (approximately 50-60 km) during the Early Mesozoic was larger than that after the Late Jurassic (2-7 × 1012 N m-1 and 19-39 km, respectively). The results also reflect the subduction, and rollback of Pacific plate is the geodynamic mechanism of the destruction of the eastern North China Craton.

Characteristics and Trends of River Discharge into Hudson, James, and Ungava Bays, 1964-2000.

NASA Astrophysics Data System (ADS)

Déry, Stephen J.; Stieglitz, Marc; McKenna, Edward C.; Wood, Eric F.

2005-07-01

The characteristics and trends of observed river discharge into the Hudson, James, and Ungava Bays (HJUBs) for the period 1964-2000 are investigated. Forty-two rivers with outlets into these bays contribute on average 714 km3 yr-1 [= 0.023 Sv (1 Sv 106 m3s-1)] of freshwater to high-latitude oceans. For the system as a whole, discharge attains an annual peak of 4.2 km3 day-1 on average in mid-June, whereas the minimum of 0.68 km3 day-1 occurs on average during the last week of March. The Nelson River contributes as much as 34% of the daily discharge for the entire system during winter but diminishes in relative importance during spring and summer. Runoff rates per contributing area are highest (lowest) on the eastern (western) shores of the Hudson and James Bays. Linear trend analyses reveal decreasing discharge over the 37-yr period in 36 out of the 42 rivers. By 2000, the total annual freshwater discharge into HJUBs diminished by 96 km3 (-13%) from its value in 1964, equivalent to a reduction of 0.003 Sv. The annual peak discharge rate associated with snowmelt has advanced by 8 days between 1964 and 2000 and has diminished by 0.036 km3 day-1 in intensity. There is a direct correlation between the timing of peak spring discharge rates and the latitude of a river's mouth; the spring freshet varies by 5 days for each degree of latitude. Continental snowmelt induces a seasonal pulse of freshwater from HJUBs that is tracked along its path into the Labrador Current. It is suggested that the annual upper-ocean salinity minimum observed on the inner Newfoundland Shelf can be explained by freshwater pulses composed of meltwater from three successive winter seasons in the river basins draining into HJUBs. A gradual salinization of the upper ocean during summer over the period 1966-94 on the inner Newfoundland Shelf is in accord with a decadal trend of a diminishing intensity in the continental meltwater pulses.

Upper mantle seismic structure beneath southwest Africa from finite-frequency P- and S-wave tomography

NASA Astrophysics Data System (ADS)

Youssof, Mohammad; Yuan, Xiaohui; Tilmann, Frederik; Heit, Benjamin; Weber, Michael; Jokat, Wilfried; Geissler, Wolfram; Laske, Gabi; Eken, Tuna; Lushetile, Bufelo

2015-04-01

We present a 3D high-resolution seismic model of the southwestern Africa region from teleseismic tomographic inversion of the P- and S- wave data recorded by the amphibious WALPASS network. We used 40 temporary stations in southwestern Africa with records for a period of 2 years (the OBS operated for 1 year), between November 2010 and November 2012. The array covers a surface area of approximately 600 by 1200 km and is located at the intersection of the Walvis Ridge, the continental margin of northern Namibia, and extends into the Congo craton. Major questions that need to be understood are related to the impact of asthenosphere-lithosphere interaction, (plume-related features), on the continental areas and the evolution of the continent-ocean transition that followed the break-up of Gondwana. This process is supposed to leave its imprint as distinct seismic signature in the upper mantle. Utilizing 3D sensitivity kernels, we invert traveltime residuals to image velocity perturbations in the upper mantle down to 1000 km depth. To test the robustness of our tomographic image we employed various resolution tests which allow us to evaluate the extent of smearing effects and help defining the optimum inversion parameters (i.e., damping and smoothness) used during the regularization of inversion process. Resolution assessment procedure includes also a detailed investigation of the effect of the crustal corrections on the final images, which strongly influenced the resolution for the mantle structures. We present detailed tomographic images of the oceanic and continental lithosphere beneath the study area. The fast lithospheric keel of the Congo Craton reaches a depth of ~250 km. Relatively low velocity perturbations have been imaged within the orogenic Damara Belt down to a depth of ~150 km, probably related to surficial suture zones and the presence of fertile material. A shallower depth extent of the lithospheric plate of ~100 km was observed beneath the ocean, consistent with plate-cooling models. In addition to tomographic images, the seismic anisotropy measurements within the upper mantle inferred from teleseismic shear waves indicate a predominant NE-SW orientation for most of the land stations. Current results indicate no evidence for a consistent signature of fossil plume.

Seismic stratigraphy of sedimentary cover in Amerasian Basin based on the results of Russian High Arctic expeditions

NASA Astrophysics Data System (ADS)

Poselov, Viktor; Kireev, Artem; Smirnov, Oleg; Butsenko, Viktor; Zholondz, Sergey; Savin, Vasily

2016-04-01

Massive amount of multichannel seismic (MCS) data were obtained by Russian High Arct ic expeditions "Arctica-2011", "Acrtica-2012" and "Arctica-2014". More than 40 MCS lines are located in the Amerasian basin and help to substantiate the seismic stratigraphy model of its sedimentary cover. The proposed seismic stratigraphy model was successively determined for the Cenozoic and pre-Cenozoic parts of the sedimentary section and was based on correlation of the Russian MCS data and seismic data documented by boreholes. Cenozoic part of the sedimentary cover is based on correlation of the Russian MCS data and AWI91090 section calibrated by ACEX-2004 boreholes on the Lomonosov Ridge. Two major unconformities are traced. The upper regional unconformity (RU) is associated with a major pre-Miocene hiatus. Another major hiatus is recorded in the borehole section between the Campanian and the Upper Paleocene units. It is recognized as the post-Campanian unconformity (pCU) in the seismic sections. Formation of the regional unconformities is associated with a fundamental change in depositional environment. Formation of RU was initiated by opening of the Fram Strait gateway at the Paleogene/Neogene boundary. Post-Campanian unconformity is linked with the initial stage of the Eurasian Basin opening between the Cretaceous and the Paleogene. Cenozoic sedimentary units are continuously traced from the East-Siberian and Chukchi sea shelves across the transit zone to the Amerasian basin. Paleogene unit (between pCU and RU) is formed under the neritic depositional environment and it is characterized by an extremely small thickness on the Lomonosov Ridge (less than 200 m), on the Mendeleev Rise and in the Podvodnikov Basin (not more than 300-400 m). Neogene unit (above RU) consists of hemipelagic deposits and occupies the essential part of thickness of the Cenozoic section in Podvodnikov and Makarov Basins. Interval velocities in the Paleogene unit vary within 2.8-3.2 km/s, in the Neogene unit they vary within 1.8-2.7 km/s. Pre-Cenozoic part of the sedimentary cover is based on tracing major unconformities from boreholes on the Chukchi shelf (Crackerjack, Klondike, Popcorn) to the North-Chuckchi Trough and further to the Mendeleev Rise as well as to the Vilkitsky Trough and the adjacent Podvodnikov Basin. Three regional unconformities are correlated: Jurassic (JU - top of the Upper Ellesmerian unit), Lower Cretaceous (LCU) and Brookian (BU - base of the Lower Brookian unit). Above the acoustic basement the pre-Cenozoic section is mainly represented by terrigenous units. Two major unconformities: RU and pCU are allocated on all MCS lines intersecting the Mendeleev Rise along its entire extent. BU is traced nearly everywhere along the rise excepting certain acoustic basement highs. All unconformities are also traced from the Mendeleev Rise to the continental structure of the Chuckchi Borderland. Sedimentary sequence between pCU and JU which underlies deposits of the Upper Ellesmerian unit is recorded as a synrift unit of the entire area of the Podvodnikov Basin. MCS data show a natural prolongation of the sedimentary cover from the shelf to the Podvodnikov Basin without any breaks and tectonic movements. Interval velocities in the Upper Cretaceous unit (between pCU and BU) vary within 3.2-3.9 km/s, in the pre-Upper Cretaceous units (between BU and the acoustic basement) vary within 4.1-4.8 km/s.

Trench-parallel variations in Pacific and Indo-Australian crustal velocity structure due to Louisville Ridge seamount subduction

NASA Astrophysics Data System (ADS)

Stratford, W. R.; Knight, T. P.; Peirce, C.; Watts, A. B.; Grevemeyer, I.; Paulatto, M.; Bassett, D.; Hunter, J.; Kalnins, L. M.

2012-12-01

Variations in trench and forearc morphology, and lithospheric velocity structure are observed where the Louisville Ridge seamount chain subducts at the Tonga-Kermadec Trench. Subduction of these seamounts has affected arc and back-arc processes along the trench for the last 5 Myr. High subduction rates (80 mm/yr in the north, 55 mm/yr in the south), a fast southwards migrating collision zone (~180 km/myr), and the obliquity of the subducting plate and the seamount chain to the trench, make this an ideal location to study the effects of seamount subduction on lithospheric structure. The "before and after" subduction regions have been targeted by several large-scale geophysical projects in recent years; the most recent being the R/V Sonne cruise SO215 in 2011. The crust and upper mantle velocity structure observed in profiles along strike of the seamount chain and perpendicular to the trench from this study, are compared to a similar profile from SO195, recorded ~100 km to the north. The affects of the passage of the seamounts through the subduction system are indicated by velocity anomalies in the crust and mantle of the overriding plate. Preliminary results indicate that in the present collision zone, mantle velocities (Pn) are reduced by ~5%. Around 100 km to the north, where seamounts are inferred to have subducted ~1 Myr ago, a reduction of 7% in mantle P-wave velocity is observed. The width of the trench slope and elevation of the forearc also vary along strike. At the collision zone a >100 km wide collapse region of kilometre-scale block faults comprise the trench slope, while the forearc is elevated. The elevated forearc has a 5 km think upper crust with a Vp of 2.5-5.5 km/s and the collapse zone also has upper crustal velocities as low as 2.5 km/s. To the east in the Pacific Plate, lower P-wave velocities are also observed and attributed to serpentinization due to deep fracturing in the outer trench high. Large bending faults permeate the crust and the Osbourn Seamount, currently on the verge of subduction, is fractured stepwise down into the trench. Pn velocities in the hinge zone of the Pacific Plate are as low as 7.3 km/s indicating that fracturing and serpentinization may also extend to sub-crustal depths. Finally, trench-parallel variations in subduction zone velocity structure are used to infer the degree to which seamount subduction has altered the physical state of the Pacific and Indo-Australian plates both pre- and post subduction.

Robustness of Global Radial Anisotropy Models of the Upper Mantle

NASA Astrophysics Data System (ADS)

Xing, Z.; Beghein, C.; Yuan, K.

2014-12-01

Radial anisotropy provides important constraints on mantle deformation. While its presence is well accepted in the uppermost mantle, large discrepancies remain among existing models, even at depths well sampled by seismic data, and its presence at greater depths is highly uncertain. Surface wave phase velocity dispersion measurements are routinely used to constrain lateral variations in mantle S-wave velocity (dlnVS) and radial anisotropy (ξ=VSH2/VSV2). Here, we employed the fundamental and higher mode surface wave phase velocity maps of Visser et al. (2008) that have unprecedented sensitivity to structure down to 800-1000km depth, and we adopted a probabilistic forward modeling approach, the Neighbourhood Algorithm, to quantify posterior model uncertainties and parameter trade-offs. We investigated the effect of prior crustal corrections on 3-D ξ and dlnVS models. To avoid mapping crustal structure onto mantle heterogeneities, it is indeed important to accurately account for 3-D crustal anomalies and variations in Moho depth. One approach is to solve the non-linear problem and simultaneously constrain Moho depth and mantle anomalies (Visser et al., 2008). Another approach, taken here, is to calculate non-linear crustal corrections with an a priori crustal model, which are then applied to the phase velocity maps before inverting the remaining signal for mantle structure. In this work, we also determined laterally varying sensitivity kernels to account for lateral changes in the crust. We compare models obtained using CRUST2.0 (Bassin et al., 2000) and the new CRUST1.0 (Laske et al., 2012) models, which mostly differ under continents. Our preliminary results show strong differences (ΔdlnVS>2%) between the two models in continental dlnVS for the upper 150-200km, and strong changes in x amplitudes in the top 200km (Δξ>2%). Some of the differences in ξ persist down to the transition zone, in particular beneath central Asia and South America. Despite these discrepancies, inferences on the depth of continental roots (~200-250km) based on either the extent of the dlnVS>0 anomalies or the depth at which ξ changes sign remain independent of the crustal model employed. We also note that VSV>VSH dominates the deep upper mantle except in central Pacific, which is characterized by VSH>VSV down to the transition zone.

Vertical deformation associated with normal fault systems evolved over coseismic, postseismic, and multiseismic periods

USGS Publications Warehouse

Thompson, George A.; Parsons, Thomas E.

2016-01-01

Vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways. Sparse but robust geodetic, seismic, and geologic observations in the Basin and Range province of the western United States indicate that immediately after an earthquake, vertical change primarily occurs as subsidence of the normal fault hanging wall. A few decades later, a ±100 km wide zone is symmetrically uplifted. The preserved topography of long-term rifting shows bent and tilted footwall flanks rising high above deep basins. We develop finite element models subjected to extensional and gravitational forces to study time-varying deformation associated with normal faulting. We replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust. A 60° dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone. Stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation. Focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall; the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width ( < 10 km), which is predicted to take place within 1-2 decades after each large earthquake. Thus the best-preserved topographic signature of rifting is expected to occur early in the postseismic period. The relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades.

Quasi-3-D Seismic Reflection Imaging and Wide-Angle Velocity Structure of Nearly Amagmatic Oceanic Lithosphere at the Ultraslow-Spreading Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Momoh, Ekeabino; Cannat, Mathilde; Watremez, Louise; Leroy, Sylvie; Singh, Satish C.

2017-12-01

We present results from 3-D processing of 2-D seismic data shot along 100 m spaced profiles in a 1.8 km wide by 24 km long box during the SISMOSMOOTH 2014 cruise. The study is aimed at understanding the oceanic crust formed at an end-member mid-ocean ridge environment of nearly zero melt supply. Three distinct packages of reflectors are imaged: (1) south facing reflectors, which we propose correspond to the damage zone induced by the active axial detachment fault: reflectors in the damage zone have dips up to 60° and are visible down to 5 km below the seafloor; (2) series of north dipping reflectors in the hanging wall of the detachment fault: these reflectors may correspond to damage zone inherited from a previous, north dipping detachment fault, or small offset recent faults, conjugate from the active detachment fault, that served as conduits for isolated magmatic dykes; and (3) discontinuous but coherent flat-lying reflectors at shallow depths (<1.5 km below the seafloor), and at depths between 4 and 5 km below the seafloor. Comparing these deeper flat-lying reflectors with the wide-angle velocity model obtained from ocean-bottom seismometers data next to the 3-D box shows that they correspond to parts of the model with P wave velocity of 6.5-8 km/s, suggesting that they occur in the transition between lower crust and upper mantle. The 4-5 km layer with crustal P wave velocities is interpreted as primarily due to serpentinization and fracturation of the exhumed mantle-derived peridotites in the footwall of active and past detachment faults.

Complex Burial and Exhumation of South Polar Cap Pitted Terrain

NASA Technical Reports Server (NTRS)

2000-01-01

This image is illuminated by sunlight from the upper left. The two prominent bright stripes at the left/center of the image are covered with bright frost and thus create the illusion that they are sunlit from the lower left.

The large pits, troughs, and 'swiss cheese' of the south polar residual cap appear to have been formed in the upper 4 or 5 layers of the polar material. Each layer is approximately 2 meters (6.6 feet) thick. Some Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images of this terrain show examples in which older pitted and eroded layers have been previously buried and are now being exhumed. The example shown here includes two narrow, diagonal slopes that trend from upper left toward lower right at the left/center portion of the frame. Along the bottoms of these slopes are revealed a layer that underlies them in which there are many more pits and troughs than in the upper layer. It is likely in this case that the lower layer formed its pits and troughs before it was covered by the upper layer. This observation suggests that the troughs, pits, and 'swiss cheese' features of the south polar cap are very old and form over long time scales.

The picture is located near 84.6oS, 45.1oW, and covers an area 3 km by 5 km (1.9 x 3.1 mi) at a resolution of about 3.8 meters (12 ft) per pixel. The image was taken during southern spring on August 29, 1999.

Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

Titania's radius and an upper limit on its atmosphere from the September 8, 2001 stellar occultation

NASA Astrophysics Data System (ADS)

Widemann, T.; Sicardy, B.; Dusser, R.; Martinez, C.; Beisker, W.; Bredner, E.; Dunham, D.; Maley, P.; Lellouch, E.; Arlot, J.-E.; Berthier, J.; Colas, F.; Hubbard, W. B.; Hill, R.; Lecacheux, J.; Lecampion, J.-F.; Pau, S.; Rapaport, M.; Roques, F.; Thuillot, W.; Hills, C. R.; Elliott, A. J.; Miles, R.; Platt, T.; Cremaschini, C.; Dubreuil, P.; Cavadore, C.; Demeautis, C.; Henriquet, P.; Labrevoir, O.; Rau, G.; Coliac, J.-F.; Piraux, J.; Marlot, Ch.; Marlot, C.; Gorry, F.; Sire, C.; Bayle, B.; Simian, E.; Blommers, A. M.; Fulgence, J.; Leyrat, C.; Sauzeaud, C.; Stephanus, B.; Rafaelli, T.; Buil, C.; Delmas, R.; Desnoux, V.; Jasinski, C.; Klotz, A.; Marchais, D.; Rieugnié, M.; Bouderand, G.; Cazard, J.-P.; Lambin, C.; Pujat, P.-O.; Schwartz, F.; Burlot, P.; Langlais, P.; Rivaud, S.; Brochard, E.; Dupouy, Ph.; Lavayssière, M.; Chaptal, O.; Daiffallah, K.; Clarasso-Llauger, C.; Aloy Doménech, J.; Gabaldá-Sánchez, M.; Otazu-Porter, X.; Fernández, D.; Masana, E.; Ardanuy, A.; Casas, R.; Ros, J. A.; Casarramona, F.; Schnabel, C.; Roca, A.; Labordena, C.; Canales-Moreno, O.; Ferrer, V.; Rivas, L.; Ortiz, J. L.; Fernández-Arozena, J.; Martín-Rodríguez, L. L.; Cidadão, A.; Coelho, P.; Figuereido, P.; Gonçalves, R.; Marciano, C.; Nunes, R.; Ré, P.; Saraiva, C.; Tonel, F.; Clérigo, J.; Oliveira, C.; Reis, C.; Ewen-Smith, B. M.; Ward, S.; Ford, D.; Gonçalves, J.; Porto, J.; Laurindo Sobrinho, J.; Teodoro de Gois, F.; Joaquim, M.; Afonso da Silva Mendes, J.; van Ballegoij, E.; Jones, R.; Callender, H.; Sutherland, W.; Bumgarner, S.; Imbert, M.; Mitchell, B.; Lockhart, J.; Barrow, W.; Cornwall, D.; Arnal, A.; Eleizalde, G.; Valencia, A.; Ladino, V.; Lizardo, T.; Guillén, C.; Sánchez, G.; Peña, A.; Radaelli, S.; Santiago, J.; Vieira, K.; Mendt, H.; Rosenzweig, P.; Naranjo, O.; Contreras, O.; Díaz, F.; Guzmán, E.; Moreno, F.; Omar Porras, L.; Recalde, E.; Mascaró, M.; Birnbaum, C.; Cósias, R.; López, E.; Pallo, E.; Percz, R.; Pulupa, D.; Simbaña, X.; Yajamín, A.; Rodas, P.; Denzau, H.; Kretlow, M.; Valdés Sada, P.; Hernández, R.; Hernández, A.; Wilson, B.; Castro, E.; Winkel, J. M.

2009-02-01

On September 8, 2001 around 2 h UT, the largest uranian moon, Titania, occulted Hipparcos star 106829 (alias SAO 164538, a V=7.2, K0 III star). This was the first-ever observed occultation by this satellite, a rare event as Titania subtends only 0.11 arcsec on the sky. The star's unusual brightness allowed many observers, both amateurs or professionals, to monitor this unique event, providing fifty-seven occultations chords over three continents, all reported here. Selecting the best 27 occultation chords, and assuming a circular limb, we derive Titania's radius: R=788.4±0.6km ( 1-σ error bar). This implies a density of ρ=1.711±0.005gcm using the value GM=(2.343±0.006)×10ms derived by Taylor [Taylor, D.B., 1998. Astron. Astrophys. 330, 362-374]. We do not detect any significant difference between equatorial and polar radii, in the limit r-r=-1.3±2.1km, in agreement with Voyager limb image retrieval during the 1986 flyby. Titania's offset with respect to the DE405 + URA027 (based on GUST86 theory) ephemeris is derived: Δαcos(δ)=-108±13 mas and Δδ=-62±7 mas (ICRF J2000.0 system). Most of this offset is attributable to a Uranus' barycentric offset with respect to DE405, that we estimate to be: Δαcos(δ)=-100±25mas and Δδ=-85±25 mas at the moment of occultation. This offset is confirmed by another Titania stellar occultation observed on August 1st, 2003, which provides an offset of Δαcos(δ)=-127±20 mas and Δδ=-97±13 mas for the satellite. The combined ingress and egress data do not show any significant hint for atmospheric refraction, allowing us to set surface pressure limits at the level of 10-20 nbar. More specifically, we find an upper limit of 13 nbar ( 1-σ level) at 70 K and 17 nbar at 80 K, for a putative isothermal CO 2 atmosphere. We also provide an upper limit of 8 nbar for a possible CH 4 atmosphere, and 22 nbar for pure N 2, again at the 1-σ level. We finally constrain the stellar size using the time-resolved star disappearance and reappearance at ingress and egress. We find an angular diameter of 0.54±0.03 mas (corresponding to 7.5±0.4km projected at Titania). With a distance of 170±25 parsecs, this corresponds to a radius of 9.8±0.2 solar radii for HIP 106829, typical of a K0 III giant.

Sequence stratigraphy, geodynamics, and detrital geothermochronology of Cretaceous foreland basin deposits, western interior U.S.A

NASA Astrophysics Data System (ADS)

Painter, Clayton S.

Three studies on Cordilleran foreland basin deposits in the western U.S.A. constitute this dissertation. These studies differ in scale, time and discipline. The first two studies include basin analysis, flexural modeling and detailed stratigraphic analysis of Upper Cretaceous depocenters and strata in the western U.S.A. The third study consists of detrital zircon U-Pb analysis (DZ U-Pb) and thermochronology, both zircon (U-Th)/He and apatite fission track (AFT), of Upper Jurassic to Upper Cretaceous foreland-basin conglomerates and sandstones. Five electronic supplementary files are a part of this dissertation and are available online; these include 3 raw data files (Appendix_A_raw_isopach_data.txt, Appendix_C_DZ_Data.xls, Appendix_C_U-Pb_apatite.xls), 1 oversized stratigraphic cross section (Appendix_B_figure_5.pdf), and 1 figure containing apatite U-Pb concordia plots (Appendix_C_Concordia.pdf). Appendix A is a combination of detailed isopach maps of the Upper Cretaceous Western Interior, flexural modeling and a comparison to dynamic subsidence models as applied to the region. Using these new isopach maps and modeling, I place the previously recognized but poorly constrained shift from flexural to non-flexural subsidence at 81 Ma. Appendix B is a detailed stratigraphic study of the Upper Cretaceous, (Campanian, ~76 Ma) Sego Sandstone Member of the Mesaverde Group in northwestern Colorado, an area where little research has been done on this formation. Appendix C is a geo-thermochronologic study to measure the lag time of Upper Jurassic to Upper Cretaceous conglomerates and sandstones in the Cordilleran foreland basin. The maximum depositional ages using DZ U-Pb match existing biostratigraphic age controls. AFT is an effective thermochronometer for Lower to Upper Cretaceous foreland stratigraphy and indicates that source material was exhumed from >4--5 km depth in the Cordilleran orogenic belt between 118 and 66 Ma, and zircon (U-Th)/He suggests that it was exhumed from <8--9 km depth. Apatite U-Pb analyses indicate that volcanic contamination is a significant issue, without which, one cannot exclude the possibility that the youngest detrital AFT population is contaminated with significant amounts of volcanogenic apatite and does not represent source exhumation. AFT lag times are <5 Myr with relatively steady-state to slightly increasing exhumation rates. Lag time measurements indicate exhumation rates of ~0.9->>1 km/Myr.

Three-dimensional magnetotelluric imaging of the 1997 Kagoshima earthquake doublet, Southwest Japan

NASA Astrophysics Data System (ADS)

Asamori, K.; Makuuchi, A.; Umeda, K.

2013-12-01

The 1997 Kagoshima earthquake doublet struck on unrecognized active faults lacking clear surface expression where very few large earthquakes have occurred. Two shallow moderate earthquakes occurred in the northwestern part of Kagoshima province, on March 26 (Mw 6.1) and May 13 (Mw 6.0) in 1997, both followed by intensive aftershock sequences. Aftershock distribution of the 1997 earthquake doublet reflects complicated rupture process attributed to the geological (rheological) conditions and coupling of hydraulic pressure as well as tectonic shear stress. For advanced understanding of dynamic interactions between fluids and faulting, it is imperative to obtain three-dimensional (3-D) images of the electrical resistivity structure around the seismogenic faults. In this study, we conduct magnetotelluric (MT) soundings in and around the source region of the 1997 Kagoshima earthquake sequence and perform a 3-D inversion of wideband MT data above a depth of 30 km. MT stations were deployed around the aftershock area of the 1997 Kagoshima earthquake. All of 42 MT sites were set up in the land area. The data were collected using five component (three magnetic and two telluric components) wide-band MT instruments (Phoenix MTU-5 system) in February, 2013. The data were acquired in the frequency range from 0.000343 to 320 Hz. The recording duration ranged from 2 to 8 days. As the cultural noises severely affect the measurements, the time series analysis focused on the nocturnal data when there were fewer noise. A simultaneous remote reference measurement was carried out at the Sawauchi site (1300 km northeast of the study area). Using the remote reference technique (Gamble et al., 1979), we were able to reduce the unfavorable cultural noises. The observed apparent resistivity and phase data were inverted simultaneously using the 3-D inversion code of Sasaki (2004). In this inversion, the 3-D blocks were set up in the crust and upper mantle. These block size in the horizontal and vertical directions were 2-6 km and 0.9-20 km, respectively. The obtained 3-D resistivity model acquired through the inversion shows as follows. (1) Two anomalous conductive bodies (< 30 ohm-m) are clearly visible in the upper and lower crust beneath the seismic source region, and seem to be combined and extend down to the uppermost mantle. (2) These conductive bodies are located just beside the two mainshocks in the upper crust. (3) These results suggest that the generation of two large earthquakes is not a pure mechanical process, but is closely related to heterogeneities in the material property and stress field due to the relatively effective transfer of fluids from the upper mantle.

The Impact of Model Configuration and Large-Scale, Upper-Level Forcing on CRM- Simulated Convective Systems

NASA Technical Reports Server (NTRS)

Tao, W.-K.; Zeng, X.; Shie, C.-L.; Starr, D.; Simpson, J.

2004-01-01

Real clouds and cloud systems are inherently three-dimensional (3D). Because of the limitations in computer resources, however, most cloud-resolving models (CRMs) today are still two-dimensional (2D, see a brief review by Tao 2003). Only recently have 3D experiments been performed for multi-day periods for tropical cloud systems with large horizontal domains at the National Center for Atmospheric Research, at NOAA GFDL, at the U. K. Met. Office, at Colorado State University and at NASA Goddard Space Flight Center (Tao 2003). At Goddard, a 3D Goddard Cumulus Ensemble (GCE) model was used to simulate periods during TOGA COARE (December 19-27, 1992), GATE (September 1-7, 1974), SCSMEX (June 2-11, 1998), ARM (June 26-30, 1997) and KWAJEX (August 7-13, August 18-21, and August 29-September 12, 1999) using a 512 by 512 km domain (with 2-km resolution). The results indicate that surface precipitation and latent heating profiles are similar between the 2D and 3D GCE model simulations. However, there are difference in radiation, surface fluxes and precipitation characteristics. The 2D GCE model was used to perform a long-term integration on ARM/GCSS case 4 (22 days at the ARM Southern Great Plains site in March 2000). Preliminary results showed a large temperature bias in the upper troposphere that had not been seen in previous tropical cases. The major objectives of this paper are: (1) to determine the sensitivities to model configuration (i.e., 2D in west-east, south-north or 3D), (2) to identify the differences and similarities in the organization and entrainment rates of convection between 2D- and 3D-simulated ARM cloud systems, and (3) assess the impact of upper tropospheric forcing on tropical and ARM case 4 cases.

Forearc structure beneath southwestern British Columbia: A three-dimensional tomographic velocity model

USGS Publications Warehouse

Ramachandran, K.; Dosso, S.E.; Spence, G.D.; Hyndman, R.D.; Brocher, T.M.

2005-01-01

This paper presents a three-dimensional compressional wave velocity model of the forearc crust and upper mantle and the subducting Juan de Fuca plate beneath southwestern British Columbia and the adjoining straits of Georgia and Juan de Fuca. The velocity model was constructed through joint tomographic inversion of 50,000 first-arrival times from earthquakes and active seismic sources. Wrangellia rocks of the accreted Paleozoic and Mesozoic island arc assemblage underlying southern Vancouver Island in the Cascadia forearc are imaged at some locations with higher than average lower crustal velocities of 6.5-7.2 km/s, similar to observations at other island arc terranes. The mafic Eocene Crescent terrane, thrust landward beneath southern Vancouver Island, exhibits crustal velocities in the range of 6.0-6.7 km/s and is inferred to extend to a depth of more than 20 km. The Cenozoic Olympic Subduction Complex, an accretionary prism thrust beneath the Crescent terrane in the Olympic Peninsula, is imaged as a low-velocity wedge to depths of at least 20 km. Three zones with velocities of 7.0-7.5 km/s, inferred to be mafic and/or ultramafic units, lie above the subducting Juan de Fuca plate at depths of 25-35 km. The forearc upper mantle wedge beneath southeastern Vancouver Island and the Strait of Georgia exhibits low velocities of 7.2-7.5 km/s, inferred to correspond to ???20% serpentinization of mantle peridotites, and consistent with similar observations in other warm subduction zones. Estimated dip of the Juan de Fuca plate beneath southern Vancouver Island is ???11??, 16??, and 27?? at depths of 30, 40, and 50 km, respectively. Copyright 2005 by the American Geophysical Union.

Seismic and petrological properties of the upper mantle between 300 and 400 km depth

NASA Astrophysics Data System (ADS)

Perchuc, E.; Malinowski, M.; Nita, B.

2008-12-01

We compare the traveltime data from the long range seismic profiles and from the earthquakes recorded to the offset of 3000 km with theoretical traveltimes predicted by standard seismological models: PREM, IASP- 91, AK-135 and especially from seismo-petrological model PREF (Cammarano and Romanowicz - 2007). We try to compare our models to earlier studies by Thybo and Perchuc (1997a). Our data suggests that for several events in the distance range 2000-2800 km, the first-arrivals are characterized by a relatively high velocity of 8.7-8.9 km/s. It is about 2.5% higher than P-wave velocity of the Lehmann phases, observed in the nearest offset and about 3% smaller than velocity below 410 km discontinuity. We suggest that this is a new first-order seismological boundary which can be interpreted as a top of the mantle transition zone. Seismological arguments for the existence of such a boundary are as follows: refracted waves with velocity 8.7-8.9 km/s and reflected waves find by Warren at al. (1967) and by Thybo and Perchuc (1997b). Also the interpretation of the SS precursor phases (Deuss and Woodhouse 2002) suggested a reflection boundary around 300 km (our interpretation). Depth of this boundary strongly depends on the thermal state of the mantle in particular regions. In conclusion we can say that the mantle transition zone starts much earlier and the lower part of the upper mantle is much faster than predicted by purely pyrolitic mantle model. Several petrological studies suggest influences of fluids (especialy H2O) on the character of the 410 km discontinuity and of the transition zone. All the differences in experimental data can be explained by the effect of temperature on the phase transformations within the olivine-wadsleyite system.

Polygons in Martian Frost

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-428, 21 July 2003

This June 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a polygonal pattern developed in seasonal carbon dioxide frost in the martian southern hemisphere. The frost accumulated during the recent southern winter; it is now spring, and the carbon dioxide frost is subliming away. This image is located near 80.4oS, 200.2oW; it is illuminated by sunlight from the upper left, and covers an area 3 km (1.9 mi) across.

Security Blanket

NASA Technical Reports Server (NTRS)

2006-01-01

2 June 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows material on the floor of a crater in Noachis Terra, west of Hellas Planitia. Windblown features, both the large, dark-toned sand dunes and smaller, light-toned ripples, obscure and perhaps, protect portions of the crater floor from further modification by erosional processes.

Location near: 45.4oS, 331.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

Dune and Dust Devil Tracks

NASA Technical Reports Server (NTRS)

2004-01-01

31 January 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a dark sand dune patch that occurs on the floor of a southern hemisphere crater near 64.1oS, 197.2oW. Passing dust devils have disrupted the fine, bright dust that coats the surrounding terrain, leaving wildly-varied streak patterns. Dark dots to the left (west) of the dune are boulders. The picture covers an area 3 km (1.9 mi) wide; sunlight illuminates the scene from the upper left.

Large Windblown Ripples

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-519, 20 October 2003

This April 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) high resolution image shows a depression in the martian southern cratered highlands near 1.3oS, 244.3oW. The floor of the depression and some nearby craters are covered by large windblown ripples or small sand dunes. This image of ancient martian terrain covers an area 3 km (1.9 mi) across and is illuminated by sunlight from the upper left.

Limit on possible narrow rings around Jupiter

NASA Technical Reports Server (NTRS)

Dunham, E.; Elliot, J. L.; Mink, D.; Klemola, A. R.

1982-01-01

An upper limit to the optical depth of the Jovian ring at high spatial resolution, determined from stellar occultation data, is reported. The spatial resolution of the observation is limited to about 13 km in Jupiter's equatorial plane by the projection of the Fresnel zone on the equatorial plane in the radial direction. At this resolution, the normal optical depth limit is about 0.008. This limit applies to a strip in the Jovian equatorial plane that crosses the orbits of Amalthea, 1979J1, 1979J3, and the ring. An upper limit on the number density of kilometer-size boulders has been set at one per 11.000 sq km in the equatorial plane.

The influence of larval migration and dispersal depth on potential larval trajectories of a deep-sea bivalve

NASA Astrophysics Data System (ADS)

McVeigh, Doreen M.; Eggleston, David B.; Todd, Austin C.; Young, Craig M.; He, Ruoying

2017-09-01

Many fundamental questions in marine ecology require an understanding of larval dispersal and connectivity, yet direct observations of larval trajectories are difficult or impossible to obtain. Although biophysical models provide an alternative approach, in the deep sea, essential biological parameters for these models have seldom been measured empirically. In this study, we used a biophysical model to explore the role of behaviorally mediated migration from two methane seep sites in the Gulf of Mexico on potential larval dispersal patterns and population connectivity of the deep-sea mussel ;Bathymodiolus; childressi, a species for which some biological information is available. Three possible larval dispersal strategies were evaluated for larvae with a Planktonic Larval Duration (PLD) of 395 days: (1) demersal drift, (2) dispersal near the surface early in larval life followed by an extended demersal period before settlement, and (3) dispersal near the surface until just before settlement. Upward swimming speeds varied in the model based on the best data available. Average dispersal distances for simulated larvae varied between 16 km and 1488 km. Dispersal in the upper water column resulted in the greatest dispersal distance (1173 km ± 2.00), followed by mixed dispersal depth (921 km ± 2.00). Larvae originating in the Gulf of Mexico can potentially seed most known seep metapopulations on the Atlantic continental margin, whereas larvae drifting demersally cannot (237 km ± 1.43). Depth of dispersal is therefore shown to be a critical parameter for models of deep-sea connectivity.

Mineralogic, Petrographic, Mechanical And Physical Properties Of Incesu Ignimbrite (Central Anatolia - Turkey) Used Building Stone In Historical Buildings

NASA Astrophysics Data System (ADS)

Tasdelen, S.; Korolay, T.; Kadioglu, Y. K.; Kumral, M.

2009-05-01

The Central Anatolian Volcanic Province (CAVP) is located in the Central Turkey and one of the four major volcanic provinces in Turkey. It extends 300 km along a NE-SW direction, over a large area (32500 km2). The CAVP includes various volcanic, pyroclastic rocks, which are related to collision volcanism between the Arabian and Eurasian plates, occurred in Neogene, and Quaternary times There are numerous natural stone pits in the CAVP. They have been commonly used in historical building which had been built in the Anatolian Seljuk and Ottoman empires times. The subject of this study is to figure out petrographic, geochemical, some mechanical and physical properties which include Schmidt hardness, density, porosity, water absorption by weight, point load index and failure load.Incesu ignimbrite is subdivided into three levels as lower, middle and upper according to color, welding degree, crystal contents and lithic components. All of the natural stone pits is the upper part which is characterized by grey pinkish in color, poorly welded, high porosity ratios, high amount of lithic fragments and almost 2 m thickness. In terms of the mineralogical composition, it is composed of plagioclase (oligoclase, andesine) + pyroxene (augite, clinoenstatite) + opaque minerals and low amount of amphibole, biotite and quartz. Vitrofiric texture is dominant in upper level. Al2O3 content of the upper level from 12.75-13.96wt%, SiO2 66.70-68.10wt%, MgO 0.73-1.40wt%, Fe2O3 3.77-4.04wt%, TiO2 0.46-0.51wt%, CaO 1.97-2.91wt%, Na2O 3.41-4.29wt%, K2O 3.21-4.20wt%, P2O5 0.13-0.18wt% and LOI 3.65-4.52wt%. Geochemical analyze results reveal that Incesu ignimbrite has rhyolite, rhyodacite-dacite composition, medium to high-K calc-alkaline and peraluminous nature.Building stones can be classified according to their mineralogy, mechanical and physical properties and processing types. Mechanical and physical properties are more significant depending on the stones practice aim. The mean schmidt hardness value of the upper level of Incesu ignimbrite is 35, bulk density ranges between 2.42 - 2.66 g/cm3, mean water absorption by weight is 90%, mean point load strength is 38.2 MPa and failure load is 1890 kgf/cm based on the mechanical and physical test results.

Receiver function imaging of mantle transition zone discontinuities beneath the Tanzania Craton and the Eastern and Western Branches of the East African Rift System

NASA Astrophysics Data System (ADS)

Sun, M.; Liu, K. H.; Fu, X.; Gao, S. S.

2017-12-01

To investigate the mechanism of initiation and development of the Eastern African Rifting System (EARS) circumfluent the Tanzania Craton (TC), over 7,100 P-to-S radial receiver functions (RFs) recorded by 87 broadband seismic stations are stacked to map the topography of mantle transition zone (MTZ) discontinuities beneath the TC and the Eastern and Western Branches of the EARS. After time-depth conversion using the 1-D IASP91 Earth model, the resulting 410 km (d410) and 660 km (d660) discontinuity apparent depths are found to be greater than the global averages beneath the whole study area, implying slower than normal upper mantle velocities. The mean thickness of the MTZ beneath the Western Branch and TC is about 252 km, which is comparable to the global average and is inconsistent with the existence of present-day thermal upwelling originating from the lower mantle. In contrast, beneath the Eastern Branch, an 30 km thinning of the MTZ is observed from an up to 50 km and 20 km apparent depression of the d410 and d660, respectively. On the basis of previous seismic tomographic results and empirical relationships between velocity and thermal anomalies, we propose that the most plausible explanation for the observations beneath the volcanic Eastern Branch is the existence of a low-velocity layer extending from the surface to the upper MTZ, probably caused by decompression partial melting associated with continental rifting. The observations are in general agreement with an upper mantle origin for the initiation and development of both the Western and Eastern Branches of the EARS beneath the study area.

Thin Lithosphere Beneath the Ethiopian Plateau Revealed by a Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions

NASA Astrophysics Data System (ADS)

Dugda, Mulugeta T.; Nyblade, Andrew A.; Julia, Jordi

2007-08-01

The seismic velocity structure of the crust and upper mantle beneath Ethiopia and Djibouti has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities to obtain new constraints on the thermal structure of the lithosphere. Most of the data for this study come from the Ethiopia broadband seismic experiment, conducted between 2000 and 2002. Shear velocity models obtained from the joint inversion show crustal structure that is similar to previously published models, with crustal thicknesses of 35 to 44 km beneath the Ethiopian Plateau, and 25 to 35 km beneath the Main Ethiopian Rift (MER) and the Afar. The lithospheric mantle beneath the Ethiopian Plateau has a maximum shear wave velocity of about 4.3 km/s and extends to a depth of ˜70-80 km. Beneath the MER and Afar, the lithospheric mantle has a maximum shear wave velocity of 4.1-4.2 km/s and extends to a depth of at most 50 km. In comparison to the lithosphere away from the East African Rift System in Tanzania, where the lid extends to depths of ˜100-125 km and has a maximum shear velocity of 4.6 km/s, the mantle lithosphere under the Ethiopian Plateau appears to have been thinned by ˜30-50 km and the maximum shear wave velocity reduced by ˜0.3 km/s. Results from a 1D conductive thermal model suggest that the shear velocity structure of the Ethiopian Plateau lithosphere can be explained by a plume model, if a plume rapidly thinned the lithosphere by ˜30-50 km at the time of the flood basalt volcanism (c. 30 Ma), and if warm plume material has remained beneath the lithosphere since then. About 45-65% of the 1-1.5 km of plateau uplift in Ethiopia can be attributed to the thermally perturbed lithospheric structure.

Salton Seismic Imaging Project Line 5—the San Andreas Fault and Northern Coachella Valley Structure, Riverside County, California

NASA Astrophysics Data System (ADS)

Rymer, M. J.; Fuis, G.; Catchings, R. D.; Goldman, M.; Tarnowski, J. M.; Hole, J. A.; Stock, J. M.; Matti, J. C.

2012-12-01

The Salton Seismic Imaging Project (SSIP) is a large-scale, active- and passive-source seismic project designed to image the San Andreas Fault (SAF) and the adjacent basins (Imperial and Coachella Valleys) in southern California. Here, we focus on SSIP Line 5, one of four 2-D NE-SW-oriented seismic profiles that were acquired across the Coachella Valley. The 38-km-long SSIP-Line-5 seismic profile extends from the Santa Rosa Ranges to the Little San Bernardino Mountains and crosses both strands of the SAF, the Mission Creek (MCF) and Banning (BF) strands, near Palm Desert. Data for Line 5 were generated from nine buried explosive sources (most spaced about 2 to 8 km apart) and were recorded on approximately 281 Texan seismographs (average spacing 138 m). First-arrival refractions were used to develop a refraction tomographic velocity image of the upper crust along the seismic profile. The seismic data were also stacked and migrated to develop low-fold reflection images of the crust. From the surface to about 8 km depth, P-wave velocities range from about 2 km/s to more than 7.5 km/s, with the lowest velocities within a well-defined (~2-km-deep, 15-km-wide) basin (< 4 km/s), and the highest velocities below the transition from the Coachella Valley to the Santa Rosa Ranges on the southwest and within the Little San Bernardino Mountains on the northeast. The MCF and BF strands of the SAF bound an approximately 2.5-km-wide horst-type structure on the northeastern side of the Coachella Valley, beneath which the upper crust is characterized by a pronounced low-velocity zone that extends to the bottom of the velocity image. Rocks within the low-velocity zone have significantly lower velocities than those to the northeast and the southwest at the same depths. Conversely, the velocities of rocks on both sides of the Coachella Valley are greater than 7 km/s at depths exceeding about 4 km. The relatively narrow zone of shallow high-velocity rocks between the surface traces of the MCF and BF strands is associated with a zone of uplifted strata. Along SSIP Line 5, we infer that the MCF and BF strands are steeply dipping and merge at about 2 km depth. We base our interpretation on a prominent basement low-velocity zone (fault zone) that is centered southwest of the MCF and BF strands and extends to at least 8 km depth.

Observational/Numerical Study of the Upper Ocean Response to Hurricanes.

DTIC Science & Technology

1987-12-01

current variance within 30-60 km of the storm center. The effect of the stress divergence and Eknan terms on the ocean current response rapidly...observed current variance within 30-60 km of the storm center. The effect of the stress divergence and Ekman terms on the ocean current response rapidly...110 2. M ode Splitting ....................................... IIl 3. M ixing Effects ....................................... 112 4

Shear velocity and intrinsic Q structure of the shallow crust in southeastern New England from Rg wave dispersion

NASA Astrophysics Data System (ADS)

Saikia, Chandan K.; Kafka, Alan L.; Gnewuch, Scott C.; McTigue, John W.

1990-06-01

In this study, we analyzed 0.5-2.0 s period Rayleigh waves (Rg) generated by quarry and construction blasting in southern New England (CNE). We investigated group velocity dispersion and attenuation of the observed Rg waves. The paths crossing the Hartford Rift basin (HRB) show an obvious correlation between geology and Rg dispersion. The entire region in the southeastern New England comprising a wide range of geological structures and rock types from the Bronson Hill Anticlinorium to the Avalonian Terrane can be represented as one dispersion region. Therefore the relationship between lateral changes in geologic structures mapped on the surface and Rg dispersion is not as straightforward as might be expected for a best fitting flat-layered model of the shallow crust. The shear wave velocities appear to vary between 2.55 and 3.63 km/s within the upper 2.5 km except for the central HRB where the variation is between 2.12 and 2.7 km/s. Intrinsic Q structure is considered to be the primary means for the loss of energy in the shallow crust and was analyzed by modelling the waveforms of several of the observed seismograms. For this aspect of our study, we used a modal summation of Rayleigh waves assuming a far-field radiation approximation. The observed seismograms were dominated primarily by contributions from the fundamental mode, but higher modes were also included in the synthesis of the waveform. We were unable to model the absolute amplitudes of the waveforms because of the problems with the instrument calibration. It is clear, however, that to predict correct waveforms, the shear wave Q values in the upper few tenths of a kilometer of the crust must be about an order of magnitude smaller than Q values at the depth of 1-3 km which is of order of 100-250.

Dynamics of the Venus upper atmosphere: Outstanding problems and new constraints expected from Venus Express

NASA Astrophysics Data System (ADS)

Bougher, S. W.; Rafkin, S.; Drossart, P.

2006-11-01

A consistent picture of the dynamics of the Venus upper atmosphere from ˜90 to 200 km has begun to emerge [e.g., Bougher, S.W., Alexander, M.J., Mayr, H.G., 1997. Upper Atmosphere Dynamics: Global Circulation and Gravity Waves. Venus II, CH. 2.4. University of Arizona Press, Tucson, pp. 259-292; Lellouch, E., Clancy, T., Crisp, D., Kliore, A., Titov, D., Bougher, S.W., 1997. Monitoring of Mesospheric Structure and Dynamics. Venus II, CH. 3.1. University of Arizona Press, Tucson, pp. 295-324]. The large-scale circulation of the Venus upper atmosphere (upper mesosphere and thermosphere) can be decomposed into two distinct flow patterns: (1) a relatively stable subsolar-to-antisolar (SS-AS) circulation cell driven by solar heating, and (2) a highly variable retrograde superrotating zonal (RSZ) flow. Wave-like perturbations have also been observed. However, the processes responsible for maintaining (and driving variations in) these SS-AS and RSZ winds are not well understood. Variations in winds are thought to result from gravity wave breaking and subsequent momentum and energy deposition in the upper atmosphere [Alexander, M.J., 1992. A mechanism for the Venus thermospheric superrotation. Geophys. Res. Lett. 19, 2207-2210; Zhang, S., Bougher, S.W., Alexander, M.J., 1996. The impact of gravity waves on the Venus thermosphere and O2 IR nightglow. J. Geophys. Res. 101, 23195-23205]. However, existing data sets are limited in their spatial and temporal coverage, thereby restricting our understanding of these changing circulation patterns. One of the major goals of the Venus Express (VEX) mission is focused upon increasing our understanding of the circulation and dynamical processes of the Venus atmosphere up to the exobase [Titov, D.V., Lellouch, E., Taylor, F.W., 2001. Venus Express: Response to ESA's call for ideas for the re-use of the Mars Express platform. Proposal to European Space Agency, 1-74]. Several VEX instruments are slated to obtain remote measurements (2006-2008) that will complement those obtained earlier by the Pioneer Venus Orbiter (PVO) between 1978 and 1992. These VEX measurements will provide a more comprehensive investigation of the Venus upper atmosphere (90-200 km) structure and dynamics over another period in the solar cycle and for variable lower atmosphere conditions. An expanded climatology of Venus upper atmosphere structure and wind components will be developed. In addition, gravity wave parameters above the cloud tops will be measured (or inferred), and used to constrain gravity wave breaking models. In this manner, the gravity wave breaking mechanism (thought to regulate highly variable RSZ winds) can be tested using Venus general circulation models (GCMs).

Large Scale Variability of Mid-Tropospheric Carbon Dioxide as Observed by the Atmospheric Infrared Sounder (AIRS) on the NASA EOS Aqua Platform

NASA Technical Reports Server (NTRS)

Pagano, Thomas S.; Olsen, Edward T.

2012-01-01

The Atmospheric Infrared Sounder (AIRS) is a hyperspectral infrared instrument on the EOS Aqua Spacecraft, launched on May 4, 2002. AIRS has 2378 infrared channels ranging from 3.7 microns to 15.4 microns and a 13.5 km footprint. AIRS, in conjunction with the Advanced Microwave Sounding Unit (AMSU), produces temperature profiles with 1K/km accuracy, water vapor profiles (20%/2km), infrared cloud height and fraction, and trace gas amounts for CO2, CO, SO2, O3 and CH4 in the mid to upper troposphere. AIRS wide swath(cedilla) +/-49.5 deg , enables daily global daily coverage for over 95% of the Earth's surface. AIRS data are used for weather forecasting, validating climate model distribution and processes, and observing long-range transport of greenhouse gases. In this study, we examine the large scale and regional horizontal variability in the AIRS Mid-tropospheric Carbon Dioxide product as a function of season and associate the observed variability with known atmospheric transport processes, and sources and sinks of CO2.

The possible influence of upstream upper-level baroclinic processes on the development of the QE II storm

NASA Technical Reports Server (NTRS)

Uccellini, L. W.

1986-01-01

An analysis of the QE II storm of September 9-11, 1978 presents evidence for the existence of upper-level baroclinic processes upstream of the rapidly developing cyclone. The analysis shows that a deepening shortwave trough was located 400 to 500 km upstream of the site of the storm 12 h prior to rapid cyclogenesis. The trough was associated with: (1) a polar jet marked by 65 m/s winds in its core and significant vertical and horizontal wind shear, (2) positive vorticity advection and divergence at the 300 mb level, and (3) an intense frontal zone that extended from 300 mb down to the surface. It also appears that a tropopause fold likely extruded stratospheric air down to the 700-800 mb level, 400-500 km upstream of the surface low and 12 h prior to the explosive development phase of the cyclone. These findings raise questions about Gyakum's (1983) assertion that the QE II storm developed in an area in which the baroclinic support was confined to the lower troposphere and the related assertion by Anthes et al. (1983) that upper-level forcing upstream of the area of rapid cyclogenesis was weak and apparently not important in this case.

High Altitude Plasma Instrument (HAPI) data analysis

NASA Technical Reports Server (NTRS)

Burch, J. L.

1994-01-01

The objectives of the Dynamics Explorer mission are to investigate the coupling of energy, mass, and momentum among the earth's magnetosphere, ionosphere, and upper atmosphere. At launch, on August 3, 1981, DE-1 was placed into an elliptical polar orbit having an apogee of 23,130 km to allow global auroral imaging and crossings of auroral field lines at altitudes of several thousand kilometers. At the same time DE-2 was placed into a polar orbit, coplanar with that of DE-1 but with a perigee altitude low enough (309 km) for neutral measurements and an apogee altitude of 1012 km. The DE-1 High Altitude Plasma Instrument (HAPI) provided data on low and medium energy electrons and ions from August 13, 1981 until December 1, 1981, when a high-voltage failure occured. Analysis of HAPI data for the time period of this contract has produced new results on the source mechanisms for electron conical distributions, particle acceleration phenomena in auroral acceleration regions, Birkeland currents throughout the nightside auroral regions, the source region for auroral kilometric radiation (AKR), and plasma injection phenomena in the polar cusp.

Upper mantle shear wave velocity structure beneath northern Victoria Land, Antarctica: Volcanism and uplift in the northern Transantarctic Mountains

NASA Astrophysics Data System (ADS)

Graw, Jordan H.; Adams, Aubreya N.; Hansen, Samantha E.; Wiens, Douglas A.; Hackworth, Lauren; Park, Yongcheol

2016-09-01

The Transantarctic Mountains (TAMs) are the largest non-compressional mountain range on Earth, and while a variety of uplift mechanisms have been proposed, the origin of the TAMs is still a matter of great debate. Most previous seismic investigations of the TAMs have focused on a central portion of the mountain range, near Ross Island, providing little along-strike constraint on the upper mantle structure, which is needed to better assess competing uplift models. Using data recorded by the recently deployed Transantarctic Mountains Northern Network, as well as data from the Transantarctic Mountains Seismic Experiment and from five stations operated by the Korea Polar Research Institute, we investigate the upper mantle structure beneath a previously unexplored portion of the mountain range. Rayleigh wave phase velocities are calculated using a two-plane wave approximation and are inverted for shear wave velocity structure. Our model shows a low velocity zone (LVZ; ∼4.24 km s-1) at ∼160 km depth offshore and adjacent to Mt. Melbourne. This LVZ extends inland and vertically upwards, with more lateral coverage above ∼100 km depth beneath the northern TAMs and Victoria Land. A prominent LVZ (∼4.16-4.24 km s-1) also exists at ∼150 km depth beneath Ross Island, which agrees with previous results in the TAMs near the McMurdo Dry Valleys, and relatively slow velocities (∼4.24-4.32 km s-1) along the Terror Rift connect the low velocity anomalies. We propose that the LVZs reflect rift-related decompression melting and provide thermally buoyant support for the TAMs uplift, consistent with proposed flexural models. We also suggest that heating, and hence uplift, along the mountain front is not uniform and that the shallower LVZ beneath northern Victoria Land provides greater thermal support, leading to higher bedrock topography in the northern TAMs. Young (0-15 Ma) volcanic rocks associated with the Hallett and the Erebus Volcanic Provinces are situated directly above the imaged LVZs, suggesting that these anomalies are also the source of Cenozoic volcanic rocks throughout the study area.

Temporal Variability of Atomic Hydrogen From the Mesopause to the Upper Thermosphere

NASA Astrophysics Data System (ADS)

Qian, Liying; Burns, Alan G.; Solomon, Stan S.; Smith, Anne K.; McInerney, Joseph M.; Hunt, Linda A.; Marsh, Daniel R.; Liu, Hanli; Mlynczak, Martin G.; Vitt, Francis M.

2018-01-01

We investigate atomic hydrogen (H) variability from the mesopause to the upper thermosphere, on time scales of solar cycle, seasonal, and diurnal, using measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite, and simulations by the National Center for Atmospheric Research Whole Atmosphere Community Climate Model-eXtended (WACCM-X). In the mesopause region (85 to 95 km), the seasonal and solar cycle variations of H simulated by WACCM-X are consistent with those from SABER observations: H density is higher in summer than in winter, and slightly higher at solar minimum than at solar maximum. However, mesopause region H density from the Mass-Spectrometer-Incoherent-Scatter (National Research Laboratory Mass-Spectrometer-Incoherent-Scatter 00 (NRLMSISE-00)) empirical model has reversed seasonal variation compared to WACCM-X and SABER. From the mesopause to the upper thermosphere, H density simulated by WACCM-X switches its solar cycle variation twice, and seasonal dependence once, and these changes of solar cycle and seasonal variability occur in the lower thermosphere ( 95 to 130 km), whereas H from NRLMSISE-00 does not change solar cycle and seasonal dependence from the mesopause through the thermosphere. In the upper thermosphere (above 150 km), H density simulated by WACCM-X is higher at solar minimum than at solar maximum, higher in winter than in summer, and also higher during nighttime than daytime. The amplitudes of these variations are on the order of factors of 10, 2, and 2, respectively. This is consistent with NRLMSISE-00.

Spatial and temporal variations in infrared emissions of the upper atmosphere. 2. 15-μm carbon dioxide emission

NASA Astrophysics Data System (ADS)

Semenov, A. I.; Medvedeva, I. V.; Perminov, V. I.; Zheleznov, Yu. A.

2017-09-01

The results of rocket and satellite measurements of carbon dioxide emissions at a wavelength of 15 μm in the upper atmosphere have been systematized and analyzed. Analytical expressions describing the dependence of the altitude distribution of 15-μm CO2 emission intensity and its variation in the altitude range from 100 to 130 km on the season, latitude, and solar activity have been obtained.

Geometry and spatial variations of seismic reflection intensity of the upper surface of the Philippine Sea plate off the Boso Peninsula, Japan

NASA Astrophysics Data System (ADS)

Kono, Akihiro; Sato, Toshinori; Shinohara, Masanao; Mochizuki, Kimihiro; Yamada, Tomoaki; Uehira, Kenji; Shinbo, Takashi; Machida, Yuya; Hino, Ryota; Azuma, Ryousuke

2017-07-01

In the region off the Boso Peninsula, Japan, the Pacific plate is subducting westward beneath both the Honshu island arc and Philippine Sea plate, while the Philippine Sea plate is subducting northwestward beneath the Honshu island arc. These complex tectonic interactions have caused numerous seismic events occurred in the past. To better understand these seismic events, it is important to determine the geometry of the plate boundary, in particular the upper surface of the Philippine Sea plate. We conducted an active-source seismic refraction survey in July and August 2009 from which we obtained a 2-D P-wave velocity structure model along a 216-km profile. We used the velocity model and previously published data that indicate a P-wave velocity of 5.0 km/s for the upper surface of the subducting Philippine Sea plate to delineate its boundary with the overriding Honshu island arc. Our isodepth contours of the upper surface of the Philippine Sea plate show that its dip is shallow at depths of 10 to 15 km, far off the Boso Peninsula. This shallow dip may be a result of interference from the Pacific plate slab, which is subducting westward under the Philippine Sea plate. Within our survey data, we recognized numerous seismic reflections of variable intensity, some of which came from the upper surface of the Philippine Sea plate. An area of high seismic reflection intensity corresponds with the main slip area of the Boso slow slip events. Our modeling indicates that those reflections can be explained by an inhomogeneous layer close to the upper surface of the Philippine Sea plate.

Aspects of fish conservation in the upper Patos Lagoon basin.

PubMed

Fontoura, N F; Vieira, J P; Becker, F G; Rodrigues, L R; Malabarba, L R; Schulz, U H; Möller, O O; Garcia, A M; Vilella, F S

2016-07-01

The Patos Lagoon basin is a large (201 626 km(2) ) and complex drainage system in southern Brazil. The lagoon is 250 km long and 60 km wide, covering an area of 10 360 km(2) . The exchange of water with the Atlantic Ocean occurs through a 0·8 km wide and 15 m deep inlet, fixed by 4 km long jetties, at the southernmost part of the Patos Lagoon. The estuarine area is restricted to its southern portion (10%), although the upper limit of saline waters migrates seasonally and year to year, influenced by the wind regime and river discharge. The known number of recorded limnetic fish species is 200, but this number is expected to increase. A higher endemism is observed in fish species occurring in upper tributaries. The basin suffers from the direct impact of almost 7 million inhabitants, concentrated in small to large cities, most with untreated domestic effluents. There are at least 16 non-native species recorded in natural habitats of the Patos Lagoon basin, about half of these being from other South American river basins. Concerning the fishery, although sport and commercial fisheries are widespread throughout the Patos Lagoon basin, the lagoon itself and the estuarine area are the main fishing areas. Landing statistics are not available on a regular basis or for the whole basin. The fishery in the northern Patos Lagoon captures 31 different species, nine of which are responsible for most of the commercial catches, but only three species are actually sustaining the artisanal fishery: the viola Loricariichthys anus: 455 kg per 10 000 m(2) gillnet per day, the mullet Mugil liza: 123 kg per 10 000 m(2) gillnet per day and the marine catfish Genidens barbus: 50 kg per 10 000 m(2) gillnet per day. A decline of the fish stocks can be attributed to inadequate fishery surveillance, which leads to overfishing and mortality of juveniles, or to decreasing water quality because of urban and industrial activities and power production. Global climatic changes also represent a major threat to the Patos system by changing the frequency of El Niño-La Niña-Southern Oscillation (ENSO). © 2016 The Fisheries Society of the British Isles.

Seismic Refraction & Wide-angle Reflection Experiment on the Northern Margin of North China Craton -Data Acquisition and Preliminary Processing Result

NASA Astrophysics Data System (ADS)

Li, W.; Gao, R.; Keller, G. R.; Hou, H.; Li, Q.; Cox, C. M.; Chang, J. C.; Zhang, J.; Guan, Y.

2010-12-01

The evolution history of Central Asian Orogen Belt (CAOB) is still the main tectonic problems in northeastern Asia. The Siberia Craton (NC), North China Craton (NCC) and several blocks collided, and the resulting tectonic collage formed as the Paleo-Asian Ocean disappeared. Concerning the northern margin of North China Craton, many different geological questions remain unanswered, such as: the intracontinental orogenic process in the Yanshan orogen and the nature and location of the suture between the southern NC and the northern NCC. In Dec 2009, a 400 km long seismic refraction and wide-angle reflection profile was completed jointly by Institute of Geology, CAGS and University of Oklahoma. The survey line extended from the west end of the Yanshan orogen, across a granitoid belt to the Solonker suture zone. The recording of seismic waves from 8 explosions (500~1500 kg each) was conducted in four deployments of 300 Reftek125 (Texan) seismic recorders, with an average spacing of 1 km. For the calculations, we used the Rayinvr, Vmed and Zplot programs for ray tracing, model modification and phase picking. The initial result show that: 1)the depth of low velocity sediment cover ranges from 0.6 to 2.7 km (velocity: 2.8~5.6 km/s); 2)the depth of basement is 5.6~10 km (the depth of basement under the granitoid belt deepens to 10 km and velocity increases to 6.2 km/s); 3)the upper crust extends to a depth of 15.5~21 km and has the P-wave velocities between 5.6 and 6.4 km/s; 4)the thickness of the lower crust ranges from 22~28 km(velocity: 6.4~6.9 km/s); and 5)the depth of Moho varies from 39.5 km under the granitoid belt to 49 km under the Yanshan orogen. Based on these results, we can preliminarily deduce that: 1) the concave depression of the Moho observed represents the root of the Yanshan orogen, and it may prove that the orogen is dominated by thick-skinned tectonics; 2) the shape of velocity variations under the granitoid belt is suggestive of a magma conduit. It may be connected with subduction-collision magmatism between the southern NC and the northern NCC along the Solonker suture zone. Supported by Sinoprobe-02 and US NSF PIRE grant (0730154)

A global geochemical model for the evolution of the mantle

NASA Technical Reports Server (NTRS)

Anderson, D. L.

1979-01-01

It is proposed that the upper mantle transition region, 220 to 670 km, is composed of eclogite which has been derived from primitive mantle by about 20 percent partial melting and that this is the source and sink of oceanic crust. The remainder of the upper mantle is garnet peridotite which is the source of continental basalts and hotspot magmas. This region is enriched in incompatible elements by hydrous and CO2 rich metasomatic fluids which have depleted the underlying layers in the L.I.L. elements and L.R.E.E. The volatiles make this a low-velocity, high attenuation, low viscosity region. The eclogite layer is internally heated and its controls the convection pattern in the upper mantle. Plate tectonics is intermittent. The continental thermal anomaly at a depth of 150-220 km triggers kimberlite and carbonatite activity, alkali and flood basalt volcanism, vertical tectonics and continental breakup. Hot spots remain active after the continents leave and build the oceanic islands. Mantle plumes rise from a depth of about 220 km. Midocean ridge basalts rise from the depleted layer below this depth. Material from this layer can also be displaced upwards by subducted oceanic lithosphere to form back-arc basins.

Compressional velocities from multichannel refraction arrivals on Georges Bank: northwest Atlantic Ocean

USGS Publications Warehouse

McGinnis, L. D.; Otis, R. M.

1979-01-01

Velocities were obtained from unreversed, refracted arrivals on analog records from a 48‐channel, 3.6-km hydrophone cable (3.89 km from the airgun array to the last hydrophone array). Approximately 200 records were analyzed along 1500 km of ship track on Georges Bank, northwest Atlantic Ocean, to obtain regional sediment velocity distribution to a depth of 1.4 km below sea level. This technique provides nearly continuous coverage of refraction velocities and vertical velocity gradients. Because of the length of the hydrophone cable and the vertical velocity gradients, the technique is applicable only to the Continental Shelf and the shallower parts of the Continental Slope in water depths less than 300 m. Sediment diagenesis, the influence of overburden pressure on compaction, lithology, density, and porosity are inferred from these data. Velocities of the sediment near the water‐sediment interface range from less than 1500 m/sec on the north edge of Georges Bank to 1830 m/sec for glacial deposits in the northcentral part of the bank. Velocity gradients in the upper 400 m range from 1.0km/sec/km(sec−1) on the south edge of the bank to 1.7sec−1 on the north. Minimum gradients of 0.8sec−1 were observed south of Nantucket Island. Velocities and velocity gradients are explained in relation to physical properties of the Cretaceous, Tertiary, and Pleistocene sediments. Isovelocity contours at 100-m/sec intervals are nearly horizontal in the upper 400 m. Isovelocity contours at greater depths show a greater difference from a mean depth because of the greater structural and lithological variation. Bottom densities inferred from the velocities range from 1.7 to 1.9g/cm3 and porosities range from 48 to 62 percent. The most significant factor controlling velocity distribution on Georges Bank is overburden pressure and resulting compaction. From the velocity data we conclude that Georges Bank has been partially overridden by a continental ice sheet.

Did the onset of high amplitude glacio-eustatic cycles trigger mass-transport processes on the Northwest Shelf of Australia? Insights from IODP expedition 356

NASA Astrophysics Data System (ADS)

Gallagher, S. J.; McCaffrey, J.; Wallace, M. W.; Keep, M.; Fulthorpe, C.; Bogus, K.; McHugh, C.

2017-12-01

Mass-transport processes on continental margins may have catastrophic consequences, causing tsunamis, major rock falls and avalanches and can destroy offshore hydrocarbon installations. Mass-transport deposits (MTD's) with volumes 17 to >162 km3 are common along the northwest margin of Australia. One of the largest is the Gorgon slide which is offshore from Barrow Island with a minimum volume of 250 km3. Age estimates for slides on the Northwest Shelf are variable and range from Miocene to Recent (Gorgon MTD), late Pliocene to Recent (Thebe/Bonaventure MTD's) and Pleistocene to Recent. This age uncertainty is related to a lack of cored sections through these slides and relies on pre-existing ages and correlations from poorly dated sections (usually industry well sections with minimal samples in the upper 500 m) distal from the MTD's. Therefore, the age, origin and history of these MTD's is not well known. A recent International Ocean Discovery Program Expedition (IODP Expedition 356) to the region obtained a series of continuous cores from the upper 600m to 1.1 km of the Northern Carnarvon and Roebuck Basins. Four sites were cored adjacent to hydrocarbon wells; West Tryal Rocks-2 (Site U1461), Fisher-1 (Site U1462), Picard-1 (Site U1463) and Minilya-1 (Site U1464). Site U1461 yielded 100% core recovery through the Gorgon Slide. Preliminary data from this section suggests that it is relatively young (<1 Ma) with ongoing activity from 0.5 Ma continuing to today. We suggest neotectonism combined with the onset of high amplitude glacio-eustatic cycles may have been triggering factors for this slide.

Upper Mantle of the Central Part of the Russian Platform by Receiver Function Data.

NASA Astrophysics Data System (ADS)

Goev, Andrey; Kosarev, Grigoriy; Sanina, Irina; Riznichenko, Oksana

2017-04-01

The study of the upper mantle of the Russian Platform (RP) with seismic methods remains limited due to the lack of broadband seismic stations. Existing velocity models have been obtained by using the P-wave travel-times from seismic events interpreted as explosions recorded at the NORSAR array in 1974-75 years. Another source of information is deep seismic sounding data from long-range profiles (exceeding 3000 km) such as QUARTZ, RUBIN-1 and GLOBUS and peaceful nuclear explosions (PNE) as sources. However, the data with the maximum distances larger than 1500 km have been acquired on the RP and only in the northern part. Being useful, these velocity models have low spatial resolution. This study analyzes and integrates all the existing RP upper mantle velocity models with the main focus on the central region. We discuss the completeness of the RP area of the LITHO 1.0 model. Based on results of our analysis, we conclude that it is necessary to get up-to-date velocity models of the upper mantle using broadband stations located at the central part of the RP using Vp/Vs ratio data and anisotropy parameters for robust estimation of the mantle boundaries. By applying the joint inversion of receiver-function (RF) data, travel-time residuals and dispersion curves of surface waves we get new models reaching 300 km depth at the locations of broadband seismic stations at the central part of the RP. We used IRIS stations OBN, ARU along with MHV and mobile array NOV. For each station we attempt to determine thickness of the lithosphere and to locate LVL, LAB, Lehman and Hales boundaries as well as the discontinuities in the transition zones at the depth of 410 and 660 km. Also we investigate the necessity of using short-period and broadband RF separately for more robust estimation of the velocity model of the upper mantle. This publication is based on work supported by the Russian Foundation for Basic Research (RFBR), project 15-05-04938 and by the leading scientific school NS-3345.2014.5

A New Approach to Ballistic Missile Defense for Countering Antiaccess/Area-Denial Threats from Precision-Guided Weapons

DTIC Science & Technology

2013-04-01

performance esti- mates. Four notional developments of the PAA surrogate were mod- eled , with burnout velocities of 5 km/second and 6 km/second (40...his weapon on the intended target. Interceptor Models The notional baseline surface-launch interceptor was modeled with 3.5 km/second burnout ...agility. The AWL upper-tier interceptor was modeled, based on employment from an F-35A.11 In general the upper-tier interceptor has a burnout

The p-wave upper mantle structure beneath an active spreading centre - The Gulf of California

NASA Technical Reports Server (NTRS)

Walck, M. C.

1984-01-01

Over 1400 seismograms of earthquakes in Mexico are analyzed and data sets for the travel time, apparent phase velocity, and relative amplitude information are utilized to produce a tightly constrained, detailed model for depths to 900 km beneath an active oceanic ridge region, the Gulf of California. The data are combined by first inverting the travel times, perturbing that model to fit the p-delta data, and then performing trial and error synthetic seismogram modelling to fit the short-period waveforms. The final model satisfies all three data sets. The ridge model is similar to existing upper mantle models for shield, tectonic-continental, and arc-trench regimes below 400 km, but differs significantly in the upper 350 km. Ridge model velocities are very low in this depth range; the model 'catches up' with the others with a very large velocity gradient from 225 to 390 km.

Meso-beta scale perturbations of the wind field by thunderstorm cells

NASA Technical Reports Server (NTRS)

Ulanski, S. L.; Heymsfield, G. M.

1986-01-01

Data from the high density storm-scale rawinsonde network of the Severe Environmental Storms and Mesoscale Experiment revealed temporal and spatial changes in the divergence fields of the troposphere in response to severe storm evolution on May 2, 1979; these changes were detectable on the meso-beta scale. This unique set of data was subsequently used to study the evolution of the wind, divergence and vertical motion fields in the presence of intense convection. Mid- and upper-tropospheric divergence was superimposed over low-level convergence. The divergence, which has a maximum value of .0004/s, occurred 75 to 100 km upwind as well as over the tornadic cells. To the south of the storm cells, the kinematic pattern was in reverse, upper level convergence was superimposed over low-level divergence. A vertical motion doublet was found to ascend over the squall line and descend about 70 km south of the squall line. It is suggested that the following effects are accountable for the nature of the kinematic fields: (1) blocking of tropospheric environmental flow by the storm cells, (2) anvil outflows, particularly from the tornadic cells, and (3) divergence from the exit region of the jet stream.

Jupiter's Great Red Spot upper cloud morphology and dynamics from JunoCam images

NASA Astrophysics Data System (ADS)

Sanchez-Lavega, A.; Hueso, R.; Eichstädt, G.; Orton, G.; Rogers, J.; Hansen, C. J.; Momary, T.; Tabataba-Vakili, F.

2017-12-01

We present an analysis of RGB color-composite images of the Great Red Spot (GRS) obtained with JunoCam during Juno's seventh close flyby (PJ7) on July 11, 2017. The images have been projected as 4 cylindrical maps with a resolution of 180 pixels per degree (about 7 km/pixel) spanning a temporal interval of 9 min 41s. The GRS shows a rich variety of cloud morphologies that reveal different dynamical processes in its interior. We consider three major regions. (1) An outer peripheral ring of homogeneous reddish clouds (width about 1,300 km) traces a laminar flow. A family of at least three packets of gravity waves with a mean wavelength of 75 km is present at the internal edge of the ring (in its northern side). They occupy an area of 2,500 km in length (East-West, EW) and 670 km in the North-South (NS) direction. Single clouds in the groups forming the wave have extents of 35 km EW and 70-135 km NS. (2) A large internal region of red clouds (width about 3,200 km) contains three morphologies: (a) fields of bright cumulus-like clusters, (b) long, dark curved filaments (about 7,000 km length with 100 km width), two of them converging into an arrowhead shape, and (c) individual anticyclonic vortices with radius of 500 km that grow due to the radial shear of the wind velocity in the GRS interior as previously measured. A cumulus cluster is conspicuous inside one such anticyclone. Each single cloud element is 50 km in size and the cluster has a 25-30 percent area coverage in cumulus-convective activity, presumably due to ammonia moist convection. (3) A central core has quasi-rectangular shape, extending about 5000 km EW and 3000 km NS, that is confined by elongated clouds distributed along its periphery. Its interior is filled with the redder clouds in the GRS that have a scale 100 km and form a turbulent pattern whose cloud orientations suggest three adjacent areas with alternating cyclonic-cyclonic-anticyclonic vorticity, each with radius 650-850 km.

On transient events in the upper atmosphere generated away of thunderstorm regions

NASA Astrophysics Data System (ADS)

Morozenko, V.; Garipov, G.; Khrenov, B.; Klimov, P.; Panasyuk, M.; Sharakin, S.; Zotov, M.

2011-12-01

Experimental data on transient events in UV and Red-IR ranges obtained in the MSU missions "Unversitetsky-Tatiana" (wavelengths 300-400 nm) and "Unversitetsky-Tatiana-2" (wavelengths 300-400 nm and 600-800 nm), published by Garipov et al, in 2010 at COSPAR session http://www.cospar2010.org, at TEPA conference http://www.aragats.am/Conferences/tepa2010 and in 2011 by Sadovnichy et al, Solar System Research, 45, #1, 3-29 (2011); Vedenkin et al, JETP, v. 140, issue 3(9), 1-11 (2011) demonstrated existence of transients at large distances (up to thousands km) away of cloud thunderstorm regions. Those "remote" transients are short (1-5 msec) and are less luminous than the transients above thunderstorm regions. The ratio of Red-IR to UV photon numbers in those transients indicates high altitude of their origin (~70 km). Important observation facts are also: 1. a change of the exponent in transient distribution on luminosity Q ("-1" for photon numbers Q=1020 -1023 to "-2" for Q>1023), 2. a change of global distribution of transient with their luminosity (transients with Q>1023 are concentrated in equatorial range above continents, while transients with low luminosity are distributed more uniformly), 3. a phenomenon of transient sequences in one satellite orbit which is close to geomagnetic meridian. In the present paper phenomenological features of transients are explained in assumption that the observed transients have to be divided in two classes: 1. transients related to local, lower in the atmosphere, lightning at distance not more than hundreds km from satellite detector field of view in the atmosphere and 2. transients generated by far away lightning. Local transients are luminous and presumably are events called "transient luminous events" (TLE). In distribution on luminosity those events have some threshold Q~1023 and their differential luminosity distribution is approximated by power law exponent "-2". Remote transients have to be considered separately. Their origin may be related to electromagnetic pulses (EMP) or waves (whistler, EMW) generated by lightning. The EMP-EMW is transmitted in the ionosphere- ground channel to large distances R with low absorption. The part of EMP-EMW "visible" in the detector aperture diminishes with distance as R-1 due to observation geometry. The EMP-EMW triggers the electric discharge in the upper atmosphere (lower ionosphere, ~70 km). Estimates of resulting transients luminosity and their correlation with geomagnetic field are in progress.

Saharan dust, convective lofting, aerosol enhancement zones, and potential impacts on ice nucleation in the tropical upper troposphere

NASA Astrophysics Data System (ADS)

Twohy, C. H.; Anderson, B. E.; Ferrare, R. A.; Sauter, K. E.; L'Ecuyer, T. S.; van den Heever, S. C.; Heymsfield, A. J.; Ismail, S.; Diskin, G. S.

2017-08-01

Dry aerosol size distributions and scattering coefficients were measured on 10 flights in 32 clear-air regions adjacent to tropical storm anvils over the eastern Atlantic Ocean. Aerosol properties in these regions were compared with those from background air in the upper troposphere at least 40 km from clouds. Median values for aerosol scattering coefficient and particle number concentration >0.3 μm diameter were higher at the anvil edges than in background air, showing that convective clouds loft particles from the lower troposphere to the upper troposphere. These differences are statistically significant. The aerosol enhancement zones extended 10-15 km horizontally and 0.25 km vertically below anvil cloud edges but were not due to hygroscopic growth since particles were measured under dry conditions. Number concentrations of particles >0.3 μm diameter were enhanced more for the cases where Saharan dust layers were identified below the clouds with airborne lidar. Median number concentrations in this size range increased from 100 l-1 in background air to 400 l-1 adjacent to cloud edges with dust below, with larger enhancements for stronger storm systems. Integration with satellite cloud frequency data indicates that this transfer of large particles from low to high altitudes by convection has little impact on dust concentrations within the Saharan Air Layer itself. However, it can lead to substantial enhancement in large dust particles and, therefore, heterogeneous ice nuclei in the upper troposphere over the Atlantic. This may induce a cloud/aerosol feedback effect that could impact cloud properties in the region and downwind.

More South Polar 'Swiss Cheese'

NASA Technical Reports Server (NTRS)

2000-01-01

This image is illuminated by sunlight from the upper left.

Some of the surface of the residual south polar cap has a pattern that resembles that of sliced, swiss cheese. Shown here at the very start of southern spring is a frost-covered surface in which there are two layers evident--a brighter upper layer into which are set swiss cheese-like holes, and a darker, lower layer that lies beneath the 'swiss cheese' pattern. Nothing like this exists anywhere on Mars except within the south polar cap.

This is a Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image acquired on August 2,1999. It is located near 84.8oS, 71.8oW, and covers an area 3 km across and about 6.1 km long (1.9 by 3.8 miles).

Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

Intersection

NASA Technical Reports Server (NTRS)

2006-01-01

9 June 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small portion of a dust-covered plain directly north of Labyrinthus Noctis which is cut by three linear troughs. The two long troughs running diagonally from the lower left (southwest) to the upper right (northeast) are connected by a third, shorter trough. Boulders derived from erosion of layered rock in the trough walls are seen perched on the sloping sidewalls and resting on the trough floors among giant windblown ripples.

Location near: 0.2oN, 105.0oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Northern Spring

Treadmill walking with load carriage increases aortic pressure wave reflection.

PubMed

Ribeiro, Fernando; Oliveira, Nórton L; Pires, Joana; Alves, Alberto J; Oliveira, José

2014-01-01

The study examined the effects of treadmill walking with load carriage on derived measures of central pressure and augmentation index in young healthy subjects. Fourteen male subjects (age 31.0 ± 1.0 years) volunteered in this study. Subjects walked 10 minutes on a treadmill at a speed of 5 km/h carrying no load during one session and a load of 10% of their body weight on both upper limbs in two water carboys with handle during the other session. Pulse wave analysis was performed at rest and immediately after exercise in the radial artery of the right upper limb by applanation tonometry. The main result indicates that walking with load carriage sharply increased augmentation index at 75 bpm (-5.5 ± 2.2 to -1.4 ± 2.2% vs. -5.2 ± 2.8 to -5.5 ± 2.1%, p<0.05), and also induced twice as high increments in central pulse pressure (7.4 ± 1.5 vs. 3.1 ± 1.4 mmHg, p<0.05) and peripheral (20.5 ± 2.7 vs. 10.3 ± 2.5 mmHg, p<0.05) and central systolic pressure (14.7 ± 2.1 vs. 7.4 ± 2.0 mmHg, p<0.05). Walking with additional load of 10% of their body weight (aerobic exercise accompanied by upper limb isometric contraction) increases derived measures of central pressure and augmentation index, an index of wave reflection and arterial stiffness. Copyright © 2013 Sociedade Portuguesa de Cardiologia. Published by Elsevier España. All rights reserved.

BSRs Elevated by Fluid Upwelling on the Upper Amazon Fan : Bottom-up Controls on Gas Hydrate Stability

NASA Astrophysics Data System (ADS)

Praeg, D.; Silva, C. G.; dos Reis, A. T.; Ketzer, J. M.; Unnithan, V.; Perovano Da Silva, R. J.; Cruz, A. M.; Gorini, C.

2017-12-01

The stability of natural gas hydrate accumulations on continental margins has mainly been considered in terms of changes in seawater pressures and temperatures driven from above by climate. We present evidence from the Amazon deep-sea fan for stability zone changes driven from below by fluid upwelling. A grid of 2D and 3D multichannel seismic data show the upper Amazon fan in water depths of 1200-2000 m to contain a discontinuous bottom-simulating seismic reflection (BSR) that forms `patches' 10-50 km wide and up to 140 km long, over a total area of at least 5000 km2. The elongate BSR patches coincide with anticlinal thrust-folds that record on-going gravitational collapse of the fan above décollements at depths of up to 10 km. The BSR lies within 100-300 m of seafloor, in places rising beneath features that seafloor imagery show to be pockmarks and mud volcanoes, some venting gas to the water column. The BSR patches are up to 500 m shallower than predicted for methane hydrate based on geothermal gradients as low as 17˚C/km measured within the upper fan, and inversion of the BSR to obtain temperatures at the phase boundary indicates gradients 2-5 times background levels. We interpret the strongly elevated BSR patches to record upwelling of warm gas-rich fluids through thrust-fault zones 101 km wide. We infer this process to favour gas hydrate occurrences that are concentrated in proportion to flux and locally pierced by vents, and that will be sensitive to temporal variations in the upward flux of heat and gas. Thus episodes of increased flux, e.g. during thrusting, could dissociate gas hydrates to trigger slope failures and/or enhanced gas venting to the ocean. Structurally-driven fluid flow episodes could account for evidence of recurrent large-scale failures from the compressive belt on the upper fan during its Neogene collapse, and provide a long-term alternative to sea level triggering. The proposed mechanism of upward flux links the distribution and stability of gas hydrate occurrences (and gas vents) to the internal dynamics of deep-sea depocentres, in all water depths that structural pathways for fluid migration may form. Gravitational collapse is increasingly recognized to affect passive continental margins, and our findings challenge global models of hydrate inventory over time based solely on in situ methanogenesis.

Topography of the lithosphere-asthenosphere boundary below the Upper Rhine Graben Rift and the volcanic Eifel region, Central Europe

NASA Astrophysics Data System (ADS)

Seiberlich, C. K. A.; Ritter, J. R. R.; Wawerzinek, B.

2013-09-01

We study the crust-mantle and lithosphere-asthenosphere boundaries (Moho and LAB) in Central Europe, specifically below the Upper Rhine Graben (URG) rift, the Eifel volcanic region and their surrounding areas. Teleseismic recordings at permanent and mobile stations are analysed to search for shear (S) wave to compressional (P) wave converted phases. After a special processing these phases are identified in shear wave receiver functions (S-RFs). Conversions from the Moho at 2.9-3.3 s arrival time are the clearest signals in the S-RFs and indicate a relatively flat Moho at 27-30 km depth. A negative polarity conversion signal at 7-9 s arrival time can be explained with a low shear wave velocity zone (LVsZ) in the upper mantle. We use forward S-RF waveform modelling and Monte-Carlo techniques to determine shear wave velocity (vs)-depth (z) profiles which explain the observed S-RF and which outline variations of the lithospheric thickness in the study region. Across the URG rift and its surrounding mountain ranges (Black Forest, Odenwald etc.) the LAB is at a depth of about 60 ± 5 km. This depth is found for the rift itself as well as for the rift shoulders. Southeast and southwest of the URG, in the regions of the Swabian Alb and Vosges Mountains, the LAB dips to about 78 ± 5 km depth. In the volcanic Eifel region the LAB is at a much shallower depth of just 41 ± 5 km. There an upwelling mantle plume thermally eroded the lower lithosphere. The reduction of vs is about 2%-4% in the upper asthenosphere compared to the lower lithosphere. This vs contrast may be explained with a low portion of partial melt or hydrous minerals in the asthenosphere.

High Resolution Optical Spectroscopy of Hot Post-AGB Star Candidates LS IV-04 1 and LB3116

NASA Astrophysics Data System (ADS)

Şahin, T.

2018-04-01

We present LTE analysis of high resolution optical spectra for B-type hot PAGB stars LS IV-04 1 and LB3116 (LSE 237). The spectra of these high Galactic latitude stars were obtained with the 3.9-m Anglo-Australian Telescope (AAT) and the UCLES spectrograph. The standard 1D LTE analysis with line-blanketed LTE model atmospheres and spectral synthesis provided fundamental atmospheric parameters of T eff= 15 000±1000 K, log g= 2.5±0.2, ξ = 5.0±1.0 km s-1, [M/H] = -1.81 dex, and v sin i= 5 km s-1 for LSIV-04 1 and T eff= 16 000±1000 K, log g= 2.5±0.1, v sin i= 25 km s-1, and [Fe/H] = -0.93 dex for LB 3116. Chemical abundances of ten different elements were obtained. For LS IV-04 1, its derived model temperature contradicts with previous analysis results. The upper limits for its nitrogen and oxygen abundances were reported for the first time. The magnesium, silicon and calcium were overabundant (i.e. [Mg/Fe] = 0.8 dex, [Si/Fe] = 0.5 dex, [Ca/Fe] = 0.9 dex). With its metal-poor photosphere and VLSR ≈ 96 km s-1, LSIV-04 1 is likely a population II star and most probably a PAGB star. LTE abundances of LB 3116 were reported for the first time. The spectrum of this helium rich star shows 0.9 dex enhancement in the nitrogen. The photosphere of the star is slightly deficient in Mg, Si, and S. (i.e. [Mg/Fe] = -0.2 dex, [Si/Fe] = -0.4 dex, [S/Fe] = -0.2 dex). The Al is slightly enhanced. The phosphorus is overabundant, i.e. [P/Fe] ≈ 1.7 ± 0.47 dex, hence LB3116 may be the first example of a PAGB star which is rich in phosphorus. With its high radial velocity (i.e. V LSR = 73 km s-1), and the deficiencies observed in C, Mg, Si, and S indicate that LB 3116 is likely a hot PAGB star at high galactic latitude.

Validation of ozone profile retrievals derived from the OMPS LP version 2.5 algorithm against correlative satellite measurements

NASA Astrophysics Data System (ADS)

Kramarova, Natalya A.; Bhartia, Pawan K.; Jaross, Glen; Moy, Leslie; Xu, Philippe; Chen, Zhong; DeLand, Matthew; Froidevaux, Lucien; Livesey, Nathaniel; Degenstein, Douglas; Bourassa, Adam; Walker, Kaley A.; Sheese, Patrick

2018-05-01

The Limb Profiler (LP) is a part of the Ozone Mapping and Profiler Suite launched on board of the Suomi NPP satellite in October 2011. The LP measures solar radiation scattered from the atmospheric limb in ultraviolet and visible spectral ranges between the surface and 80 km. These measurements of scattered solar radiances allow for the retrieval of ozone profiles from cloud tops up to 55 km. The LP started operational observations in April 2012. In this study we evaluate more than 5.5 years of ozone profile measurements from the OMPS LP processed with the new NASA GSFC version 2.5 retrieval algorithm. We provide a brief description of the key changes that had been implemented in this new algorithm, including a pointing correction, new cloud height detection, explicit aerosol correction and a reduction of the number of wavelengths used in the retrievals. The OMPS LP ozone retrievals have been compared with independent satellite profile measurements obtained from the Aura Microwave Limb Sounder (MLS), Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) and Odin Optical Spectrograph and InfraRed Imaging System (OSIRIS). We document observed biases and seasonal differences and evaluate the stability of the version 2.5 ozone record over 5.5 years. Our analysis indicates that the mean differences between LP and correlative measurements are well within required ±10 % between 18 and 42 km. In the upper stratosphere and lower mesosphere (> 43 km) LP tends to have a negative bias. We find larger biases in the lower stratosphere and upper troposphere, but LP ozone retrievals have significantly improved in version 2.5 compared to version 2 due to the implemented aerosol correction. In the northern high latitudes we observe larger biases between 20 and 32 km due to the remaining thermal sensitivity issue. Our analysis shows that LP ozone retrievals agree well with the correlative satellite observations in characterizing vertical, spatial and temporal ozone distribution associated with natural processes, like the seasonal cycle and quasi-biennial oscillations. We found a small positive drift ˜ 0.5 % yr-1 in the LP ozone record against MLS and OSIRIS that is more pronounced at altitudes above 35 km. This pattern in the relative drift is consistent with a possible 100 m drift in the LP sensor pointing detected by one of our altitude-resolving methods.

New seismic Vp- and Vp/Vs- models of HUKKA 2007 wide-angle reflection and refraction profile in northern Fennoscandian Shield

NASA Astrophysics Data System (ADS)

Tiira, T.; Janik, T.; Kozlovskaya, E.; Grad, M.; Korja, A.; Komminaho, K.; Hegedüs, E.; Kovács, C. A.; Silvennoinen, H.; Brückl, E.

2012-04-01

We study the block structure within accreationary orogens. We present an example from northern part of the Fennoscandian Shield transected by deep seismic sounding profile HUKKA 2007. The 455 km long profile runs in NNW-SSE direction from Kittilä in northwestern Finnish Lapland to Kostamush in Russia near central part of the border between Finland and Russia. We present 2-D seismic velocity model (Vp and Vp/Vs ratio in the crust, depth to the Moho and depth to the intracrustal reflectors) along HUKKA 2007 wide-angle reflection and refraction profile in northern Finland. Commercial and military chemical explosions at 7 shot points were used as sources of the seismic energy. The shots were recorded by 115 recording stations deployed along the profile with an average station spacing of 3.45 km. The field recordings were cut and sorted into shot gathers. The 2-D velocity model of the HUKKA 2007 profile was developed by SEIS83 forward raytracing package using arrivals of major refracted and reflected P- and S-wave phases. In general the velocities vary in the upper crust between 5.8 and 6.1 km/s. Interesting features are three high P wave velocity (6.30-6.35 km/s) bodies in the upper crust. Two small bodies lie close to surface at first 100 km and the third one can be followed from 200 to 350 km along the profile reaching depth of 5-10 km. The central part of the profile (between 120 and 220 km) has a zone of low (lower than 6 km/s) P-wave velocity in the uppermost crust. This zone is about 4 km thick. In addition, the velocity model along the HUKKA 2007 profile shows significant difference in crustal velocity structure between the northern (up to 120 km) and southern parts of the profile. The differences in P-wave velocities and Vp/Vs ratio can be followed throughout the crust down to the Moho boundary. This suggests that the HUKKA 2007 profile transects a major terrane boundary. However, the position of this boundary with respect to major crustal units is controversial. It may be the boundary that separates the pristine parts of the Archean Karelian craton from those parts reworked in the Paleoproterozoic. Alternatively, it can be the boundary that separates the Karelian craton from the Belomorian mobile belt.

Vertical sizes of 1-D and 2-D electrostatic solitons with nonextensive and trapped electrons in the upper ionosphere

NASA Astrophysics Data System (ADS)

Ali Shan, Shaukat; Saleem, Hamid

2018-05-01

The vertical sizes of one-dimensional (1-D) and two dimensional (2-D) electrostatic solitons are estimated in the oxygen-hydrogen (O - H) and pure oxygen plasmas of the upper ionosphere taking into account the effects of non-extensive and trapped electrons. The field-aligned flow of oxygen ions is also considered. It is found that both electron trapping and non-extensivity play a constructive role in the formation of 1-D and 2-D solitary structures. The vertical size of the solitons is not known through observations, but here it is pointed out that the vertical size of these structures should be of the order of a few meters at the altitude of 800 km in the 1-D case. On the other hand, in the 2-D case, the vertical size is much larger than the horizontal size and it turns out to be of the order of a few kilometers, while the width is about a few hundred meters in agreement with the observations.

Stationary waves and slowly moving features in the night upper clouds of Venus

NASA Astrophysics Data System (ADS)

Peralta, J.; Hueso, R.; Sánchez-Lavega, A.; Lee, Y. J.; Muñoz, A. García; Kouyama, T.; Sagawa, H.; Sato, T. M.; Piccioni, G.; Tellmann, S.; Imamura, T.; Satoh, T.

2017-08-01

At the cloud top level of Venus (65-70 km altitude) the atmosphere rotates 60 times faster than the underlying surface—a phenomenon known as superrotation1,2. Whereas on Venus's dayside the cloud top motions are well determined3,4,5,6 and Venus general circulation models predict the mean zonal flow at the upper clouds to be similar on both the day and nightside2, the nightside circulation remains poorly studied except for the polar region7,8. Here, we report global measurements of the nightside circulation at the upper cloud level. We tracked individual features in thermal emission images at 3.8 and 5.0 μm obtained between 2006 and 2008 by the Visible and Infrared Thermal Imaging Spectrometer-Mapper onboard Venus Express and in 2015 by ground-based measurements with the Medium-Resolution 0.8-5.5 Micron Spectrograph and Imager at the National Aeronautics and Space Administration Infrared Telescope Facility. The zonal motions range from -110 to -60 m s-1, which is consistent with those found for the dayside but with larger dispersion6. Slow motions (-50 to -20 m s-1) were also found and remain unexplained. In addition, abundant stationary wave patterns with zonal speeds from -10 to +10 m s-1 dominate the night upper clouds and concentrate over the regions of higher surface elevation.

ARC-1985-A86-7001

NASA Image and Video Library

1985-11-28

Range: 72.3 million km. ( 44.9 million miles ) P-29314B/W This Voyager 2 photograph of Uranus shows the planets outermost, or epsilon, ring. This is a computerized summation of six images shot by the narrow angle camera. It is the first photo to show the epsilon ring unblurred by Earth's atmosphere. The Epsilon ring, some 51,200 km. ( 31,800 miles ) from the planets center, is the most prominent of Uranus' nine known rings. Ground based observations of stellar occulations by the rings have determined that the Epsilon ring is eccentric, or elliptical, with its widest portion about 100 km. ( 60 miles ) wide and its narrowest portion about 20 km. (12 miles ). Estimates of the rings brightness suggest that it is also very dark, with a reflectance of only 1 or 2 percent and a probable composition of carbonaceous material similiar to that on dark asteroids and the dark side of Saturn's moon Lapetus. Because the ring is so narrow and dark, at this range, the Voyager camera could not resolve even the widest part, resulting in long exposure times so obtain a good image. six exposures of 11 or 15 second duration were added together by computer to produce this image. In this image, the central portion is greatly overexposed. Various artifacts due to electronic effects and image proccessing can be seen in the central portion of the frame, including the dark image just above the planets image, the diffuse brightening below it and the small, bright projection from the edge of the planet in the upper left. The ring is distinctly less prominent in the lower left portion and more prominent in the upper right. This is in agreement with the predicted locations of the narrow and wide portions of the ring, respectively.

South Polar Cap

NASA Technical Reports Server (NTRS)

2005-01-01

8 December 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows landforms created by sublimation processes on the south polar residual cap of Mars. The bulk of the ice in the south polar residual cap is frozen carbon dioxide.

Location near: 86.6oS, 342.2oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

Tectonic Configuration of the Western Arabian Continental Margin, Southern Red Sea

NASA Astrophysics Data System (ADS)

Bohannon, Robert G.

1986-08-01

The young continental margin of the western Arabian Peninsula is uplifted 3.5 to 4 km and is well exposed. Rift-related extensional deformation is confined to a zone 150 km wide inland of the present coastline at 17 to 18° N and its intensity increases gradually from east to west. Extension is negligible near the crest of the Arabian escarpment, but it reaches a value of 8 to 10% in the western Asir, a highly dissected mountainous region west of the escarpment. There is an abrupt increase in extensional deformation in the foothills and pediment west of the Asir (about 40 km inland of the shoreline) where rocks in the upper plate of a system of low-angle normal faults with west dips are extended by 60 to 110%. The faults were active 23 to 29 Ma ago and the uplift occurred after 25 Ma ago. Tertiary mafic dike swarms and plutons of gabbro and granophyre 20 to 23 Ma old are concentrated in the foothills and pediment as well. The chemistry of the dikes suggests (1) fractionation at 10 to 20 kbar, (2) a rapid rise through the upper mantle and lower crust, and (3) differentiation and cooling at 1 Atm to 5 kbar. Structural relations between dikes, faults and dipping beds indicate that the mechanical extension and intrusional expansion were partly coeval, but that most of the extension preceded the expansion. A tectonic reconstruction of pre-Red Sea Afro/Arabia suggests that the early rift was narrow with intense extension confined to an axial belt 20 to 40 km wide. Steep Moho slopes probably developed during rift formation as indicated by published gravity data, two published seismic interpretations and the surface geology.

Patches of Remnant Frost/Snow on Crater Rim in Northern Summer

NASA Technical Reports Server (NTRS)

1999-01-01

March 1999--it is summer in the martian northern hemisphere, yet patches of frost or snow persist in some areas of the northern plains. Winter ended eight months earlier, in July 1998. Recently, the Mars Orbiter Camera (MOC) passed over a relatively small impact crater located at latitude 68oN (on the Vastitas Borealis plain, north of Utopia Planitia) and took the picture seen at the left, above. The curved crater rims are visible in the upper and lower quarters of the image, and the crater floor is visible at the center right.

The picture on the right is a magnified view of the crater rim area outlined by a white box in the image on the left. The bright patches are snow or frost left over from the martian winter. These snowfields are so small that a human could walk across one of them in a matter of minutes--or perhaps sled down the small, sloping patch that is seen in a shadowed area near the lower left.

In winter, the entire scene shown here would be covered by frost. The long strip at the left covers an area 3 km (1.9 mi) wide by 26 km (16 mi) long. The expanded view on the right covers an area 2.9 km (1.8 mi) by 5.3 km (3.3 mi). Illumination is from the upper right.

Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

ARC-1991-AC91-0610-1

NASA Image and Video Library

1991-10-02

This data was acquired by the NASA C-130B Earth Resources Survey aircraft flying at 6,000 ft. mean sea level at 10:26 a. m. on October 21, 1991. The sensor used was the NS001 Thermatic Mapper Simulator, with a ground resolution of 4.6 meters (15ft). The image area is 4.7 x 3.2 km (2.9 x 2 mi.). The area covered is the Oakland Berkeley Hills near the Caldecott Tunnel (Upper right). Targets over 600 degrees centrigrade are shown as yellow in this composite of three infrared bands (11.6, 2.3, & 1.6 microns). A large condominium complex at the upper right is completely consumed. Areas already burned off sow as pale red. The blue clouds at left are condensed water vapor within the smoke plume, which blocks the infrared wavelength; the smoke itself is transparent. Many hundreds of individual structures can be seen either actively burning or as heat of smouldering debris.

Record of Subducting Topography revealed in 3D Seismic Imaging of Pleistocene unconformities, offshore Southern Costa Rica

NASA Astrophysics Data System (ADS)

Edwards, J. H.; Kluesner, J. W.; Silver, E. A.

2015-12-01

3D seismic reflection data (CRISP) collected across the southern Costa Rica forearc reveals broad, survey-wide erosional events in the upper ~1 km of slope sediments in the mid-slope to outer shelf. The upper 0-280 m of continuous, weakly deformed sediments, designated by IODP Expedition 344 as structural domain I, is bounded by a major erosional event, (CRISP-U1, dated near 1 Ma), suggesting wave-plain erosion from the present shelf break out to 25 km seaward, to a present-day water depth of 900-1300 m. The eastern toe of its surface is characterized by a large drainage system, likely including submarine channels that eroded to depths >1500 m below present-day water depth. CRISP-U1 is variably uplifted by a series of fault propagation folds and cut by an intersecting array of normal faults. Another, major erosional event, (CRISP-M1, approximately 2 Ma) extended from the outer shelf to the mid slope and removed 500-1000 m of material. Overlying CRISP-M1 is up to 1 km of sediments that are more deformed by fault propagation folds, back thrusts, and intersecting arrays of normal faults. Unconformities with smaller areal extent are variably found in these overlying sediments across the mid-slope to outer shelf, at present-day water depths >220 m. Below CRISP-M1, sediments are more densely deformed and also contain major unconformities that extend survey-wide. Both unconformities, CRISP-U1 and CRISP-M1, are encountered in well U1413 and are demarcated by major benthic foraminifera assemblage changes at 149 mbsf and ~504 mbsf (Harris et al., 2013, Proceeding of the IODP, Volume 344).CRISP-M1 is likely correlative to the major sediment facies and benthic foraminifera assemblage change found in U1379 at ~880 mbsf (Vannuchi et al., 2013). The unconformities and intersecting array of normal faults may demarcate the passing of topography on the downgoing Cocos plate, episodically lifting and then subsiding the Costa Rica margin, with amplitudes up to about 1 km.

Numerical study of heating the upper atmosphere by acoustic-gravity waves from a local source on the Earth's surface and influence of this heating on the wave propagation conditions

NASA Astrophysics Data System (ADS)

Karpov, I. V.; Kshevetskii, S. P.

2017-11-01

The propagation of acoustic-gravity waves (AGW) from a source on the Earth's surface to the upper atmosphere is investigated with methods of mathematical modeling. The applied non-linear model of wave propagation in the atmosphere is based on numerical integration of a complete set of two-dimensional hydrodynamic equations. The source on the Earth's surface generates waves with frequencies near to the Brunt-Vaisala frequency. The results of simulation have revealed that some region of heating the atmosphere by propagated upward and dissipated AGWs arises above the source at altitudes nearby of 200 km. The horizontal scale of this heated region is about 1000 km in the case of the source that radiates AGWs during approximately 1 h. The appearing of the heated region has changed the conditions of AGW propagation in the atmosphere. When the heated region in the upper atmosphere has been formed, further a waveguide regime of propagation of waves with the periods shorter the Brunt-Vaisala period is realized. The upper boundary of the wave-guide coincides with the arisen heated region in the upper atmosphere. The considered mechanism of formation of large-scale disturbances in the upper atmosphere may be useful for explanation of connections of processes in the upper and lower atmospheric layers.

Deep and persistent melt layer in the Archaean mantle

NASA Astrophysics Data System (ADS)

Andrault, Denis; Pesce, Giacomo; Manthilake, Geeth; Monteux, Julien; Bolfan-Casanova, Nathalie; Chantel, Julien; Novella, Davide; Guignot, Nicolas; King, Andrew; Itié, Jean-Paul; Hennet, Louis

2018-02-01

The transition from the Archaean to the Proterozoic eon ended a period of great instability at the Earth's surface. The origin of this transition could be a change in the dynamic regime of the Earth's interior. Here we use laboratory experiments to investigate the solidus of samples representative of the Archaean upper mantle. Our two complementary in situ measurements of the melting curve reveal a solidus that is 200-250 K lower than previously reported at depths higher than about 100 km. Such a lower solidus temperature makes partial melting today easier than previously thought, particularly in the presence of volatiles (H2O and CO2). A lower solidus could also account for the early high production of melts such as komatiites. For an Archaean mantle that was 200-300 K hotter than today, significant melting is expected at depths from 100-150 km to more than 400 km. Thus, a persistent layer of melt may have existed in the Archaean upper mantle. This shell of molten material may have progressively disappeared because of secular cooling of the mantle. Crystallization would have increased the upper mantle viscosity and could have enhanced mechanical coupling between the lithosphere and the asthenosphere. Such a change might explain the transition from surface dynamics dominated by a stagnant lid on the early Earth to modern-like plate tectonics with deep slab subduction.

Geologic setting, sedimentary architecture, and paragenesis of the Mesoproterozoic sediment-hosted Sheep Creek Cu-Co-Ag deposit, Helena embayment, Montana

USGS Publications Warehouse

Graham, Garth; Hitzman, Murray W.; Zieg, Jerry

2012-01-01

The northern margin of the Helena Embayment contains extensive syngenetic to diagenetic massive pyrite horizons that extend over 25 km along the Volcano Valley-Buttress fault zone and extend up to 8 km basinward (south) within the Mesoproterozoic Newland Formation. The Sheep Creek Cu-Co deposit occurs within a structural block along a bend in the fault system, where replacement-style chalcopyrite mineralization is spatially associated mostly with the two stratigraphically lowest massive pyrite zones. These mineralized pyritic horizons are intercalated with debris flows derived from synsedimentary movement along the Volcano Valley-Buttress fault zone. Cominco American Inc. delineated a geologic resource of 4.5 Mt at 2.5% Cu and 0.1% Co in the upper sulfide zone and 4 Mt at 4% Cu within the lower sulfide zone. More recently, Tintina Resources Inc. has delineated an inferred resource of 8.48 Mt at 2.96% Cu, 0.12% Co, and 16.4 g/t Ag in the upper sulfide zone. The more intact upper sulfide zone displays significant thickness variations along strike thought to represent formation in at least three separate subbasins. The largest accumulation of mineralized sulfide in the upper zone occurs as an N-S–trending body that thickens southward from the generally E trending Volcano Valley Fault and probably occupies a paleograben controlled by normal faults in the hanging wall of the Volcano Valley Fault. Early microcrystalline to framboidal pyrite was accompanied by abundant and local barite deposition in the upper and lower sulfide zones, respectively. The sulfide bodies underwent intense (lower sulfide zone) to localized (upper sulfide zone) recrystallization and overprinting by coarser-grained pyrite and minor marcasite that is intergrown with and replaces dolomite. Silicification and paragenetically late chalcopyrite, along with minor tennantite in the upper sulfide zone, replaces fine-grained pyrite, barite, and carbonate. The restriction of chalcopyrite to inferred synsedimentary E- and northerly trending faults and absence of definitive zonation with respect to the Laramide Volcano Valley Fault in the lower sulfide zone suggest a diagenetic age related to basin development for the Sheep Creek Cu-Co-Ag deposit.

Electron content of the ionosphere and the plasma sphere on the basis of ATS-6-Data, NNSS-data, and ionograms. [Navy Navigation Satellite System

NASA Technical Reports Server (NTRS)

Leitinger, R.; Hartmann, G. K.; Davies, K.

1976-01-01

The reported investigation takes into account data obtained with the aid of the geostationary satellite ATS-6, the satellites of the U.S. navy navigation system (NNSS) at an altitude between 900 and 1200 km, and the satellites ISIS 1 and ISIS 2. The altitude range between ground and ATS-6 is divided into two regions, including the 'ionosphere', involving the region with an upper limit of 2000 km, and the 'plasma sphere', involving the region above an altitude of 2000 km. Data concerning the electron content obtained from different sources are compared, taking into account discrepancies between ionogram-derived values and values computed on the basis of satellite measurements. Attention is also given to the vertical electron content of the ionosphere on the basis of a combination of data obtained with the aid of the ATS-6 and the NNSS.

Solar Wind Interaction with the Martian Upper Atmosphere at Early Mars/Extreme Solar Conditions

NASA Astrophysics Data System (ADS)

Dong, C.; Bougher, S. W.; Ma, Y.; Toth, G.; Lee, Y.; Nagy, A. F.; Tenishev, V.; Pawlowski, D. J.; Combi, M. R.

2014-12-01

The investigation of ion escape fluxes from Mars, resulting from the solar wind interaction with its upper atmosphere/ionosphere, is important due to its potential impact on the long-term evolution of Mars atmosphere (e.g., loss of water) over its history. In the present work, we adopt the 3-D Mars cold neutral atmosphere profiles (0 ~ 300 km) from the newly developed and validated Mars Global Ionosphere Thermosphere Model (M-GITM) and the 3-D hot oxygen profiles (100 km ~ 5 RM) from the exosphere Monte Carlo model Adaptive Mesh Particle Simulator (AMPS). We apply these 3-D model output fields into the 3-D BATS-R-US Mars multi-fluid MHD (MF-MHD) model (100 km ~ 20 RM) that can simulate the interplay between Mars upper atmosphere and solar wind by considering the dynamics of individual ion species. The multi-fluid MHD model solves separate continuity, momentum and energy equations for each ion species (H+, O+, O2+, CO2+). The M-GITM model together with the AMPS exosphere model take into account the effects of solar cycle and seasonal variations on both cold and hot neutral atmospheres. This feature allows us to investigate the corresponding effects on the Mars upper atmosphere ion escape by using a one-way coupling approach, i.e., both the M-GITM and AMPS model output fields are used as the input for the multi-fluid MHD model and the M-GITM is used as input into the AMPS exosphere model. In this study, we present M-GITM, AMPS, and MF-MHD calculations (1-way coupled) for 2.5 GYA conditions and/or extreme solar conditions for present day Mars (high solar wind velocities, high solar wind dynamic pressure, and high solar irradiance conditions, etc.). Present day extreme conditions may result in MF-MHD outputs that are similar to 2.5 GYA cases. The crustal field orientations are also considered in this study. By comparing estimates of past ion escape rates with the current ion loss rates to be returned by the MAVEN spacecraft (2013-2016), we can better constrain the total ion loss to space over Mars history, and thus enhance the science returned from the MAVEN mission.

Seismic imaging of a transform segment of the Maranhão-Barreirinhas-Ceará margin, NW Brazil

NASA Astrophysics Data System (ADS)

Schnurle, Philippe; Moulin, Maryline; Gallais, Flora; Afilhado, Alexandra; Afonso Dias, Nuno; Soares, José; Loureiro, Afonso; Fuck, Reinhardt; Cupertino, José; Viana, Adriano; Matias, Luís; Evain, Mikael; Aslanian, Daniel

2017-04-01

The structure of the North-East equatorial Brazilian margin was investigated during the MAGIC (Margins of brAzil, Ghana and Ivory Coast) seismic experiment, a project conducted by IFREMER (Institut Francais de Recherche pour l'Exploration de la Mer), UnB (University of Brasilia), FCUL (Faculdade de Ciências da Universidade de Lisboa) and Petrobras. The survey consists of 5 deep seismic profiles totaling 1900 km of marine multi-channel seismic reflection and wide angle acquisition with 143 deployments of short-period OBS's from the IFREMER pool. Three of the profiles were extended into land using Land Seismic Stations (LSS) from the Brazilian pool at a total of 50 points. This study focuses on the MC1 and MC5 wide-angle profiles: MC5 spans NW-SE 720 km in length, from the São Paulo Double Fracture Zone to the Borborema-Cearà margin. MC-1 spans parallel east of MC5, 360 km in length, in the presumed oceanic domain. Our main objective is to understand the fundamental processes which lead to the thinning and finally to the breakup of the continental crust in a specific context of a pull-apart system with two strike-slip borders. The experiment was devised to obtain the 2D structure along the profiles from joint pre-stack depth migration of the reflection data, and tomography and forward modeling of the OBS records. Along the MC1/MC5 wide-angle transects, 5 major sectors are identified: - the São Paulo Double Fracture Zone and the volcanic line associated to the southern São Paulo strike-slip zone presenting a 4.5 km thick volcano-sedimentary basin on top of a 5.5 km thick basement; - the intermediate domain, formed by the 4.5 km thick Basin III, the 7.5 km thick Basin II (interleaved by a 0.5-1 km thick volcanic layer), and the 5.5 km thick Basin I composing the continental slope. While the crust remains about 6 km thick, its acoustic velocity evolves from two-layer typical (4.8-6 km/s and 6.1-6.8 km/s) beneath Basin III to two-layer high velocity (6.1-6.8 km/s and 7.2-7.4 km/s) beneath Basin II and I, interpreted as exhumed lower continental crust; - to the east, the oceanic crust, evolves to an 2 layers crust 5 km thick, characterized by typical oceanic crustal velocities and also overlain by 5.5 km of sedimentary deposits, spanning between the two main fracture zones that fringe the Maranhão-Barreirinhas-Ceará segment; - the 50 km wide necking zone, forming the Parnaiba Platform and associated Ceará Basins, where the upper and lower crust thin abruptly; - the Medio Coreaù and Ceará Central thrust belt, where the unthinned continental crust thickness reaches 32 km. Keywords: North-East equatorial Brazil, transform margin, deep seismic structure

Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges

NASA Astrophysics Data System (ADS)

Haldar, C.; Kumar, P.; Kumar, M. Ravi

2014-05-01

Deciphering the seismic character of the young lithosphere near mid-oceanic ridges (MORs) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs using the P-to-S conversions isolated from quality data recorded at five broadband seismological stations situated on ocean islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform inversion of the P-receiver function stacks at individual stations reveal that the Moho depth varies between ~ 10 ± 1 km and ~ 20 ± 1 km with the depths of the lithosphere-asthenosphere boundary (LAB) varying between ~ 40 ± 4 and ~ 65 ± 7 km. We found evidence for an additional low-velocity layer below the expected LAB depths at stations on Ascension, São Jorge and Easter islands. The layer probably relates to the presence of a hot spot corresponding to a magma chamber. Further, thinning of the upper mantle transition zone suggests a hotter mantle transition zone due to the possible presence of plumes in the mantle beneath the stations.

3D crustal structure beneath the Costa Rica Rift from seismic tomography: insight into magmatic activity

NASA Astrophysics Data System (ADS)

Zhang, L.; Tong, V.; Wilson, D. J.; Hobbs, R. W.; Haughton, G.; Murton, B. J.

2016-12-01

During the cruise JC114, which was carried out in the intermediate-spreading Costa Rica Rift(CRR) in 2015, we acquired seismic records from 25 ocean-bottom seismographs in a 5x5 grid with an approximate node spacing of 5 km over the rift's axis. We picked 69,000 Pg and Pn events and inverted 3D crustal Vp structure beneath the CRR by using the First-Arrival Refraction Tomography (FAST). Our results show that at the depth of 1.0 2.0km below sea floor beneath the axis, there exists a 5km-wide low-velocity zone(LVZ), which extends along the axis but breaks into two segments at 83°48'W. At a deeper depth (>2.5km below sea floor), an underlying wider LVZ extends horizontally and vertically, probably stretching through the Moho. The shallower LVZ indicates the accretion of magma in the upper crust or the presence of highly porous or cracked rocks, while the deeper LVZ is inferred to be a partially molten zone, i.e. the representative of the axial magma chamber. The deeper LVZ is connected with the shallower one by upwelling conduits, which bifurcate and provide melts for both the west and east segments of the overlying LVZ. The conduit to the east segment is more prominent, providing more robust magma supply and leading to more intense negative velocity perturbation. It may reflect that the magma supply is fluctuating and migrating in the lower crust and the upper mantle. From analysing traveltime residual to study azimuthal anisotropy, we conclude that the fast direction varies roughly around 90° in the upper crust, implying that the vertically aligned cracks are nearly parallel to the axis and favour along-axis hydrothermal circulation. By comparing the anisotropy features of the two flanks of the CRR, we propose that the magmatic activity is more vigorous in the shallow subsurface of the north flank, i.e. the Cocos Plate. This research is part of a major, interdisciplinary NERC-funded collaboration entitled: Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR).

Northern and Southern Hemisphere Ground-Based Infrared Spectroscopic Measurements of Tropospheric Carbon Monoxide and Ethane

NASA Technical Reports Server (NTRS)

Rinsland, Curtis P.; Jones, Nicholas B.; Connor, Brian J.; Logan, Jennifer A.; Pougatchev, Nikita; Goldman, Aaron; Murcray, Frank J.; Stephen, Thomas M.; Pine, Alan S.; Zander, Rodolphe;

2.8-Ma ash-flow caldera at Chegem River in the northern Caucasus Mountains (Russia), contemporaneous granites, and associated ore deposits

USGS Publications Warehouse

Lipman, P.W.; Bogatikov, O.A.; Tsvetkov, A.A.; Gazis, C.; Gurbanov, A.G.; Hon, K.; Koronovsky, N.V.; Kovalenko, V.I.; Marchev, P.

1993-01-01

Diverse latest Pliocene volcanic and plutonic rocks in the north-central Caucasus Mountains of southern Russia are newly interpreted as components of a large caldera system that erupted a compositionally zoned rhyolite-dacite ash-flow sheet at 2.83 ?? 0.02 Ma (sanidine and biotite 40Ar/39Ar). Despite its location within a cratonic collision zone, the Chegem system is structurally and petrologically similar to typical calderas of continental-margin volcanic arcs. Erosional remnants of the outflow Chegem Tuff sheet extend at least 50 km north from the source caldera in the upper Chegem River. These outflow remnants were previously interpreted by others as erupted from several local vents, but petrologic similarities indicate a common origin and correlation with thick intracaldera Chegem Tuff. The 11 ?? 15 km caldera and associated intrusions are superbly exposed over a vertical range of 2,300 m in deep canyons above treeline (elev. to 3,800 m). Densely welded intracaldera Chegem Tuff, previously described by others as a rhyolite lava plateau, forms a single cooling unit, is > 2 km thick, and contains large slide blocks from the caldera walls. Caldera subsidence was accommodated along several concentric ring fractures. No prevolcanic floor is exposed within the central core of the caldera. The caldera-filling tuff is overlain by andesitic lavas and cut by a 2.84 ?? 0.03-Ma porphyritic granodiorite intrusion that has a cooling age analytically indistinguishable from that of the tuffs. The Eldjurta Granite, a pluton exposed low in the next large canyon (Baksan River) 10 km to the northwest of the caldera, yields variable K-feldspar and biotite ages (2.8 to 1.0 Ma) through a 5-km vertical range in surface and drill-hole samples. These variable dates appear to record a prolonged complex cooling history within upper parts of another caldera-related pluton. Major W-Mo ore deposits at the Tirniauz mine are hosted in skarns and hornfels along the roof of the Eldjurta Granite, and associated aplitic phases have textural features of Climax-type molybdenite porphyries in the western USA. Similar 40Ar/39Ar ages, mineral chemistry, and bulk-rock compositions indicate that the Chegem Tuff, intracaldera intrusion, and Eldjurta Granite are all parts of a large magmatic system that broadly resembles the middle Tertiary Questa caldera system and associated Mo deposits in northern New Mexico, USA. Because of their young age and superb three-dimensional exposures, rocks of the Chegem-Tirniauz region offer exceptional opportunities for detailed study of caldera structures, compositional gradients in volcanic rocks relative to cogenetic granites, and the thermal and fluid-flow history of a large young upper-crustal magmatic system. ?? 1993.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Qian; Fan, Jiwen; Hagos, Samson M.

Understanding of critical processes that contribute to the organization of mesoscale convective systems is important for accurate weather forecast and climate prediction. In this study, we investigate the effects of wind shear at different vertical levels on the organization and properties of cloud systems using the Weather Research & Forecasting (WRF) model with a spectral-bin microphysical scheme. The sensitivity experiments are performed by increasing wind shear at the lower (0-5 km), middle (5-10 km), upper (> 10 km) and the entire troposphere, respectively, based on a control run for a mesoscale convective system (MCS) with weak wind shear. We findmore » that increasing wind shear at the both lower and middle vertical levels reduces the domain-accumulated precipitation and the occurrence of heavy rain, while increasing wind shear at the upper levels changes little on precipitation. Although increasing wind shear at the lower-levels is favorable for a more organized quasi-line system which leads to enlarged updraft core area, and enhanced updraft velocities and vertical mass fluxes, the precipitation is still reduced by 18.6% compared with the control run due to stronger rain evaporation induced by the low-level wind shear. Strong wind shear in the middle levels only produces a strong super-cell over a narrow area, leading to 67.3% reduction of precipitation over the domain. By increasing wind shear at the upper levels only, the organization of the convection is not changed much, but the increased cloudiness at the upper-levels leads to stronger surface cooling and then stabilizes the atmosphere and weakens the convection. When strong wind shear exists over the entire vertical profile, a deep dry layer (2-9 km) is produced and convection is severely suppressed. There are fewer very-high (cloud top height (CTH) > 15 km) and very-deep (cloud thickness > 15 km) clouds, and the precipitation is only about 11.8% of the control run. The changes in cloud microphysical properties further explain the reduction of surface rain by strong wind shear especially at the lower- and middle-levels. The insights obtained from this study help us better understand the cloud system organization and provide foundation for better parameterizing organized MCS.« less

Crustal structure and tectonic deformation of the southern Ecuadorian margin

NASA Astrophysics Data System (ADS)

Calahorrano, Alcinoe; Collot, Jean-Yves; Sage, Françoise; Ranero, César R.

2010-05-01

Multichannel seismic lines acquired during the SISTEUR cruise (2000) provide new constraints on the structure and deformation of the subduction zone at the southern Ecuadorian margin, from the deformation front to the continental shelf of the Gulf of Guayaquil. The pre-stack depth migrated images allows to characterise the main structures of the downgoing and overriding plates and to map the margin stratigraphy in order to propose a chronology of the deformation, by means of integrating commercial well data and industry seismic lines located in the gulf area. The 100-km-long seismic lines show the oceanic Nazca plate underthrusting the South American plate, as well as the subduction channel and inter-plate contact from the deformation front to about 90 km landward and ~20 km depth. Based on seismic structure we identify four upper-plate units, consisting of basement and overlaying sedimentary sequences A, B and C. The sedimentary cover varies along the margin, being few hundreds of meters thick in the lower and middle slope, and ~2-3 km thick in the upper slope. Exceptionally, a ~10-km -thick basin, here named Banco Peru basin, is located on the upper slope at the southernmost part of the gulf. This basin seems to be the first evidence of the Gulf of Guayaquil opening resulting from the NE escaping of the North Andean Block. Below the continental shelf, thick sedimentary basins of ~6 to 8 km occupy most of the gulf area. Tectonic deformation across most of the upper-plate is dominated by extensional regime, locally disturbed by diapirism. Compression evidences are restricted to the deformation front and surrounding areas. Well data calibrating the seismic profiles indicate that an important portion of the total thickness of the sedimentary coverage of the overriding plate are Miocene or older. The data indicate the extensional deformation resulting from the NE motion of the North Andean Block and the opening of the Gulf of Guayaquil, evolves progressively in age from the southern edge of the gulf near Banco Peru, where main subsidence seems to be Miocene or older, toward the northern limit, where high subsidence rates are early Pleistocene.

Magnetotelluric Imaging of Lower Crustal Melt and Lithospheric Hydration in the Rocky Mountain Front Transition Zone, Colorado, USA

NASA Astrophysics Data System (ADS)

Feucht, D. W.; Sheehan, A. F.; Bedrosian, P. A.

2017-12-01

We present an electrical resistivity model of the crust and upper mantle from two-dimensional (2-D) anisotropic inversion of magnetotelluric data collected along a 450 km transect of the Rio Grande rift, southern Rocky Mountains, and High Plains in Colorado, USA. Our model provides a window into the modern-day lithosphere beneath the Rocky Mountain Front to depths in excess of 150 km. Two key features of the 2-D resistivity model are (1) a broad zone ( 200 km wide) of enhanced electrical conductivity (<20 Ωm) in the midcrust to lower crust that is centered beneath the highest elevations of the southern Rocky Mountains and (2) hydrated lithospheric mantle beneath the Great Plains with water content in excess of 100 ppm. We interpret the high conductivity region of the lower crust as a zone of partially molten basalt and associated deep-crustal fluids that is the result of recent (less than 10 Ma) tectonic activity in the region. The recent supply of volatiles and/or heat to the base of the crust in the late Cenozoic implies that modern-day tectonic activity in the western United States extends to at least the western margin of the Great Plains. The transition from conductive to resistive upper mantle is caused by a gradient in lithospheric modification, likely including hydration of nominally anhydrous minerals, with maximum hydration occurring beneath the Rocky Mountain Front. This lithospheric "hydration front" has implications for the tectonic evolution of the continental interior and the mechanisms by which water infiltrates the lithosphere.

Ultraviolet stellar occultation measurement of the H2 and O2 densities near 100 km in the earth's atmosphere

NASA Technical Reports Server (NTRS)

Atreya, S. K.; Wasser, B.; Donahue, T. M.; Sharp, W. E.; Drake, J. F.; Riegler, G. R.

1976-01-01

Results are presented for an experimental study designed to measure the density of H2 near 100 km in the earth's atmosphere from occultation of a star, Gamma Vel, by the earth's atmosphere at several wavelengths near the H2 absorption line at 1108.128 A by a spectrometer on an orbiting astronomical observatory. Measurement of the O2 density between 95 and 123 km is also reported. Attention is focused on testing the predictions of a model of the distribution of hydrogen constituents, H, H2, H2O, CH4, OH, and H2O in the upper atmosphere related to a theory of hydrogen escape developed by Hunten and Strobel (1974) and by Liu and Donahue (1974). The measured H2 densities are found to be in good agreement with recent theoretical predictions, whereas the measured O2 density profile generally agrees with the models except for a wavelike structure in the range 104-114 km.

An intraslab earthquake (M7.1) along a buried hydrated fault in the Pacific plate, triggered by the 2011 M9 Tohoku earthquake

NASA Astrophysics Data System (ADS)

Nakajima, J.; Hasegawa, A.; Kita, S.

2011-12-01

A M9.0 megathrust earthquake, the 2011 off the Pacific Coast of Tohoku Earthquake, occurred on 11 March 2011 on the plate boundary east off northeastern (NE) Japan. After this great earthquake, seismicity has been activated in the Pacific plate as well as along its upper surface, and a large earthquake (M7.1) occurred on April 7 in the Pacific slab at a depth of 66 km, located near the down-dip limit of the large interplate slip of the M9 event. Here we perform travel-time tomography to reveal heterogeneous seismic velocity structures around the focal area of the 2011 M7.1 intraslab event, and discuss the occurrence of the 2011 M7.1 event in terms of dehydration embrittlement hypothesis. We applied the double-difference tomography method (Zhang and Thurber, 2003) to large number of arrival-time data obtained at a nation-wide seismograph network in Japan. Arrival-time data were produced from 8911 earthquakes and 188 stations, and comprised 247,504 P waves and 196,057 S waves, with differential data of 1,608,230 for P waves and 1,114,068 for S waves. Grid intervals were set at 10-20 km in the along-arc direction, 5-10 km perpendicular to the arc, and 5-10 km in the vertical direction The final results were obtained after eight iterations, which reduced the travel-time residual from 0.17 s to 0.11 s for P waves, and from 0.33 s to 0.19 s for S waves. The results show a low-velocity zone around the focal area of the M7.1 event, and that the aftershock activity is limited to the upper 15 km of the oceanic mantle. The lateral extent of the low-velocity zone is comparable to the distribution of aftershocks, suggesting a concentration of fluids in the aftershock area. The angle between the aftershock alignment and the dip of the slab surface is estimated to be ~60°, which is consistent with the dip of an oceanward-dipping normal fault observed at the outer-trench slope. These observations suggest that the M7.1 intraslab event occurred as a result of reactivation of a buried hydrated fault that formed prior to subduction. The upper ~15 km of the oceanic mantle may be locally hydrated by bending-related tensional faulting at the outer-trench slope.

Universal charge-radius relation for subatomic and astrophysical compact objects.

PubMed

Madsen, Jes

2008-04-18

Electron-positron pair creation in supercritical electric fields limits the net charge of any static, spherical object, such as superheavy nuclei, strangelets, and Q balls, or compact stars like neutron stars, quark stars, and black holes. For radii between 4 x 10(2) and 10(4) fm the upper bound on the net charge is given by the universal relation Z=0.71R(fm), and for larger radii (measured in femtometers or kilometers) Z=7 x 10(-5)R_(2)(fm)=7 x 10(31)R_(2)(km). For objects with nuclear density the relation corresponds to Z approximately 0.7A(1/3)( (10(8)10(12)), where A is the baryon number. For some systems this universal upper bound improves existing charge limits in the literature.

Analysis of Titan's neutral upper atmosphere from Cassini Ion Neutral Mass Spectrometer measurements in the Closed Source Neutral mode

NASA Astrophysics Data System (ADS)

Cui, Jun

In this thesis I present an in-depth study of the distribution of various neutral species in Titan's upper atmosphere, at altitudes between 950 and 1,500 km for abundant species (N 2 , CH 4 as well as their isotopes) and between 950 and 1,200 km for most minor species. However, the study of the H 2 distribution on Titan is extended to an altitude as high as 6,000 km in the exosphere. The analysis is based on a large sample of Cassini/INMS (Ion Neutral Mass Spectrometer) measurements in the CSN (Closed Source Neutral) mode, obtained during 15 close flybys of Titan. The densities of abundant species including N 2 , CH 4 and H 2 are determined directly from their main channels. However, to untangle the overlapping cracking patterns of minor species, the technique of Singular Value Decomposition (SVD) is used to determine simultaneously the densities of various hydrocarbons, nitriles and oxygen compounds. All minor species except for 40 Ar present density enhancements measured during the outbound legs. This can be interpreted as a result of wall effects, which could be either adsorption/desorption or heterogeneous surface chemistry on the chamber walls. In the thesis, I use a simple model to describe the observed time behavior of minor species. Results on their atmospheric abundances are provided both in terms of direct inbound measurements assuming ram pressure enhancement and values corrected for wall adsorption/desorption. Among all minor species of photochemical interest, the INMS data provide direct observational evidences for C 2 H 2 , C 2 H 4 , C 2 H 6 , CH 3 C 2 H, C 4 H 2 , C 6 H 6 , HC 3 N and C 2 N 2 in Titan's upper atmosphere. Upper limits are put for other minor species. The globally averaged distribution of N 2 , CH 4 and H 2 are each modeled with the diffusion approximation. The N 2 profile suggests an average thermospheric temperature of 154 K. The CH 4 and H 2 distribution constrains their fluxes to be 3.0 × 10 9 cm -2 s -1 and 1.3 × 10 10 cm -2 s -1 , referred to Titan's surface. The H 2 escape flux is about a factor of ~3 higher than the Jeans value, which is interpreted as enhanced thermal escape driven primarily by an upward conductive heat flux. Such a conclusion is based on kinetic model calculations in the 13-moment approximation that require energy continuity at the upper boundary. On the other hand, a proper interpretation of the observed CH 4 escape has to rely on the detailed nonthermal processes, which are still unknown at the present time. The INMS observations of the nitrogen isotope ratio implies 14 N/ 15 N=131.6 near Titan's surface. The profile of carbon isotope ratio combining INMS and GCMS results implies that both CH 4 and its isotope escape from Titan's exobase with roughly the same drift velocity, in contrast to the Jeans case which requires that CH 4 escapes with a much larger velocity due to its smaller mass. The INMS data also suggest horizontal/diurnal variations of temperature and neutral gas distribution in Titan's thermosphere. The equatorial regions, the ramside, as well as the nightside hemisphere of Titan appear to be warmer and present some evidences for the depletion of light species such as CH 4 . Meridional variations of most heavy species are also observed, with a trend of depletion toward the north pole. Though some of the above variations might be interpreted by either the solar-driven models or plasma-driven models, a physical scenario that reconciles all the observed horizontal/diurnal variations in a consistent way is still missing, With a careful evaluation of the effect of restricted sampling, some of the features shown in the INMS data are more likely to be observational biases.

Spatial Distributions of Young Stars

NASA Astrophysics Data System (ADS)

Kraus, Adam L.; Hillenbrand, Lynne A.

2008-10-01

We analyze the spatial distribution of young stars in Taurus-Auriga and Upper Sco, as determined from the two-point correlation function (i.e., the mean surface density of neighbors). The corresponding power-law fits allow us to determine the fractal dimensions of each association's spatial distribution, measure the stellar velocity dispersions, and distinguish between the bound binary population and chance alignments of members. We find that the fractal dimension of Taurus is D ~ 1.05, consistent with its filamentary structure. The fractal dimension of Upper Sco may be even shallower (D ~ 0.7), but this fit is uncertain due to the limited area and possible spatially variable incompleteness. We also find that random stellar motions have erased all primordial structure on scales of lsim0.07° in Taurus and lsim1.7° in Upper Sco; given ages of ~1 and ~5 Myr, the corresponding internal velocity dispersions are ~0.2 and ~1.0 km s-1, respectively. Finally, we find that binaries can be distinguished from chance alignments at separations of lsim120'' (17,000 AU) in Taurus and lsim75'' (11,000 AU) in Upper Sco. The binary populations in these associations that we previously studied, spanning separations of 3''-30'', is dominated by binary systems. However, the few lowest mass pairs (Mprim <~ 0.3 M⊙) might be chance alignments.

Holocene volcanism of the upper McKenzie River catchment, central Oregon Cascades, USA

USGS Publications Warehouse

Deligne, Natalia I.; Conrey, Richard M.; Cashman, Katharine V.; Champion, Duane E.; Amidon, William H.

2016-01-01

To assess the complexity of eruptive activity within mafic volcanic fields, we present a detailed geologic investigation of Holocene volcanism in the upper McKenzie River catchment in the central Oregon Cascades, United States. We focus on the Sand Mountain volcanic field, which covers 76 km2 and consists of 23 vents, associated tephra deposits, and lava fields. We find that the Sand Mountain volcanic field was active for a few decades around 3 ka and involved at least 13 eruptive units. Despite the small total volume erupted (∼1 km3 dense rock equivalent [DRE]), Sand Mountain volcanic field lava geochemistry indicates that erupted magmas were derived from at least two, and likely three, different magma sources. Single units erupted from one or more vents, and field data provide evidence of both vent migration and reoccupation. Overall, our study shows that mafic volcanism was clustered in space and time, involved both explosive and effusive behavior, and tapped several magma sources. These observations provide important insights on possible future hazards from mafic volcanism in the central Oregon Cascades.

Comparisons of seismic and electromagnetic structures of the MELT area

NASA Astrophysics Data System (ADS)

Evans, R. L.; Hirth, G.; Forsyth, D.; Baba, K.; Chave, A.

2003-04-01

Both seismic and electromagnetic (EM) models from the MELT experiment show similar broad scale features in the mantle beneath the Southern EPR. In all EM models, the conductivity in the upper 50-60˜km is considerably higher to the west of the ridge than to the east. Similarly, seismic models of short period Love waves are asymmetric in velocity structure, with slower velocities to the west of the ridge within the upper 60˜km. Body wave data suggest a similar asymmetry, although the depth extent is not as well defined. West of the ridge, both the higher conductivities and lower velocities have been attributed to the presence of a small melt fraction, although the anomalous regions estimated from different techniques do not entirely agree. To the east, there is a rapid increase in resistivity and S-wave velocity, indicating that within 25˜km of the axis the mantle above 70˜km is both dry and melt-free. Further away from the ridge, the boundary between a conductive asthenospheric mantle and a resistive overlying mantle flattens, at a depth around 60-80˜km. Rayleigh wave inversions also show fairly flat velocity contours with a broad minimum centered at 60-80˜km. Both of these features are consistent with a transition from dry to damp mantle. Also away from the ridge, EM data, shear-wave splitting, and Rayleigh waves all require an azimuthally anisotropic mantle consistent with the a-axis of olivine being preferentially oriented horizontally and perpendicular to the ridge. Anisotropy in EM data suggests damp mantle conditions in the 100-200˜km depth range, with enhanced conduction along the a-axis of olivine. Rayleigh waves are most sensitive to shallower structure and require anisotropy in the upper 70˜km. In the uppermost 40˜km, the most conductive and lowest velocity regions are close to the axis but offset 5-10˜km to the west. Some anisotropic inversions recover a vertically conductive feature that could be interpreted as a few percent melt distributed in vertically aligned channels or tubes. However, modeling of seismic data rule out the presence of a vertical melt bearing channel larger than 5˜km wide with a velocity reduction of 0.5˜kms-1 (3-4% melt fraction). This apparent discrepancy may provide clues as to how melt is distributed.

Growth of the lower continental crust via the relamination of arc magma

NASA Astrophysics Data System (ADS)

He, Yumei; Zheng, Tianyu; Ai, Yinshuang; Hou, Guangbing; Chen, Qi-Fu

2018-01-01

How does continental crust transition from basaltic mantle-derived magmas into an andesitic composition? The relamination hypothesis has been presented as an alternative dynamical mechanism to classical delamination theory to explain new crust generation and has been supported by petrological and geochemical studies as well as by thermomechanical numerical modeling. However, direct evidence of this process from detailed seismic velocity structures is lacking. Here, we imaged the three-dimensional (3D) velocity structures of the crust and uppermost mantle beneath the geologically stable Ordos terrane of the North China Craton (NCC). We identify a region of continental crust that exhibits extreme growth using teleseismic data and an imaging technique that models the Common Conversion Point (CCP) stacking profiles. Our results show an approximately 400 × 400 km2 wide growth zone that underlies the primitive crust at depths of 30-50 km and exhibits a gradual increase of velocity with depth. The upper layer of the growth zone has a shear wave velocity of 3.6-3.9 km/s (Vp = 6.2-6.8 km/s), indicating felsic material, and the lower layer has a shear wave velocity of 4.1-4.3 km/s (Vp = 7.2-7.5 km/s), which corresponds to mafic material. We suggest that this vertical evolution of the layered structure could be created by relamination and that the keel structure formed by relamination may be the root of the supernormal stability of the ancient Ordos terrane.

Uppermost oceanic crust structure and properties from multichannel seismic data at the Alaska subduction zone

NASA Astrophysics Data System (ADS)

Becel, A.; Carton, H. D.; Shillington, D. J.

2017-12-01

The most heterogeneous, porous and permeable layer within a subducting oceanic crust is the uppermost layer called Layer 2A. This layer, made of extrusive basalts, forms at the ridge axis and persists as a thin ( 600 m) low-velocity cap in old crust. Nearing the trench axis, when oceanic plate bends, normal faults can be formed or reactivated at the outer-rise allowing a more vigorous hydrothermal circulation to resume within this layer. Porosity and heterogeneity within this layer are important to assess because these parameters might have a profound impact on subduction zone processes. However, conventional refraction data quality is rarely good enough to look into detail into the properties of the uppermost oceanic layer. Here we use 2D marine long-offset multi-channel seismic (MCS) reflection data collected offshore of the Alaska Peninsula during the ALEUT Program. The dataset was acquired aboard the R/V Marcus Langseth with a 636-channels, 8-km long streamer. We present initial results from three 140 km long profiles across the 52-56Myr old incoming Pacific oceanic crust formed at fast spreading rate: two perpendicular margin and one parallel margin profiles. Those profiles are located outboard of the Shumagin gaps. Outboard of this subduction zone segment, abundant bending related normal faults are imaged and concentrated within 50-60 km of the trench. Long-offset MCS data exhibit a prominent triplication that includes postcritical reflections and turning waves within the upper crust at offsets larger than 3 km. The triplication suggests the presence of a velocity discontinuity within the upper oceanic crust. We follow a systematic and uniform approach to extract upper crustal post-critical reflections and add them to them to the vertical incidence MCS images. Images reveal small-scale variations in the thickness of the Layer 2A and the strength of its base along the profiles. The second step consists of the downward continuation followed by travel-time modeling of the long streamer data. The downward continuation of the shots and receivers appears to be essential to unravel the refracted energy in the upper crust and is used to determine the detailed velocity-depth structure.

Megathrust Earthquakes and Sediment Input to the Subduction Channel

NASA Astrophysics Data System (ADS)

Scholl, David W.; Keranen, Katie; von Huene, Roland; Wells, Ray; Ryan, Holly; Kirby, Stephen

2010-05-01

HABITATS OF GREAT MEGATHRUST EARTHQUAKES: Great megathrust earthquakes (Mw8.5 or higher) most commonly (~65%) nucleate along subduction zones (SZ) bordered by laterally continuous (more than 500 km), sediment-flooded trenches. Examples include: south-central Chile (1922, Mw8.5; 1960, Mw9.5), eastern Alaska (1964, Mw9.2), Sumatra (2004, Mw9.1), Cascadia (1700, Mw9.0), Colombia (1906, Mw8.8), Sumatra (1883, Mw8.8), west-central Aleutian (1965, Mw8.7), central Aleutian (1986, Mw8.7), Sumatra (2005, Mw8.6), and Nankai (1707, Mw8.5). All known megathrust events greater than Mw9 ruptured at sediment-charged SZs (Alaska, S.C. Chile, Sumatra). Sediment entering high-seismicity SZs is typically a 1-3-km-thick wedge of trench-axis turbidite beds overlying a 0.3-2-km-thick sequence of hemipelagic or abyssal turbiditic deposits that accrued seaward of the trench. Most commonly, laterally-continuous turbidite wedges are built by down-axis flowing turbidity currents sourced from mountainous and/or glaciated drainages (e.g., SE Alaska, Cascadia, Southern Andes, Himalaya). Great rupture events also occur at SZs receiving little sediment, for example Kamchatka (1952, Mw9.0), Kuril Islands (1963, Mw8.5) and north Chile SZs (1868, Mw9.0). These SZs exhibit evidence of upper plate thinning, subsidence, and truncation effected by frontal and basal subduction erosion. They also have a SC filled with ~1 km or more of debris in transport toward the mantle. WORKINGS OF THE SUBDUCTION CHANNEL (SC): Beneath the submerged forearc, the SC functions to transport subducted ocean floor sediment and tectonically eroded forearc debris toward and ultimately into the mantle. The SC is the lowest structural unit containing upper plate crustal material and the seismogenic zone runs along the SC's upper boundary. It has long been conjectured (e.g., Ruff, 1989; PAGEOPH, v. 129. Nos 1/2) that a laterally uninterrupted, sediment- or debris-charged SC serves to smooth the surface of interplate slip to set up conditions for lengthy, high moment-release ruptures. Maximum slip is commonly concentrated beneath a locally thinned, upper plate crust underlying prominent forearc basins. These structures, in positive feed back, are likely deepened co-seismically by enhance basal subduction erosion. The removed material presumably lowers the effective stress on the decollement and sets up conditions for follow-on events of high, co-seismic slip. The SC also works tectonically to underplate the base of the inner submerged forearc and induce co-seismic uplift at high-angle reverse faults. SEISMIC CONSEQUENCES OF SUBDUCTION ZONE FEEDING: Observations imply that subducted bathymetric ridges and seamounts act to both nucleate seismic rupture and also arrest lateral rupturing. Thick sections of sedimentary and erosional debris entering the subduction channel appear to act differently and favor (1) continuation of rupture, (2) large slip beneath forearc basins, and (3) propogation of slip upward at outer-forearc splay faults and nearshore reverse faults to generate both local and trans-oceanic tsunamis. The potential for nucleation of great megathrust earthquakes along thickly sediment SZs, no matter the rate or lower plate underthrusting, obliquity of convergence, or crustal age, must be set high. Similarly, seismogenic risk for highly erosional SZs little perturbed by subducting relief must also be set high.

DE 1 and Viking observations associated with electron conical distributions

NASA Technical Reports Server (NTRS)

Menietti, J. D.; Weimer, D. R.; Andre, M.; Eliasson, L.

1994-01-01

Data from the electron detectors on board the Swedish Viking satellite launched during a period of low solar activity and from the Dynamic Explorer (DE) 1 satellite launched during active solar coditions have been examined for the occurrence and location of electron conical distributions and several conclusions can be drawn. First, we note that most of the best examples of electron conics observed by the V-3 experiment onboard Viking occurred in the afternoon sector in the range of magneitc local time 14 hours less than Magnetic Local Time (MLT) less than 18 hours, at midaltitudes in the range 10,000 km less than h less than 13,500 km, with few occurring in the nightside auroral region, a region poorly sampled at altitudes greater than 5000 km. For the Viking data there is an association of electron conics with upper hybrid waves. DE 1 observations made by the high-altitude plasma instrument (HAPI) indicate that electron conics were observed in the midmorning sector and the late evening sector, and as has been reported earlier, the correlation with upper hybird waves was good. The HAPI did not sample the afternoon sector. The electon conics observed on both satellites occurred in the presence of at least a modest (several kilovolts) potential difference beneath the satellite with a maximum energy that was usually, but not always, equal to or greater than the maximum energy of the electron conics. Two independent sets of observations by DE 1 suggest two distinct production mechanisms for electron conics. Examiniation of DE 1 electric field measurements from the plasma wave instrument during the observation of electron conics show simultaneous parallel oscillations in the frequency range of 0.2 Hz less than f less than 0.5 Hz during one and perhaps two of four events examined, and upper hybrid waves were observed on all four events. In addition, recent observations of '90-deg' electron conics associated with auroral kilometric radiation source regions suggest a perpendicular heating mechanism produced by wave-particle interaction. Such distributions may be observed as electron conics at higher altitudes. These results suggest more than one possible source mechanism may be responsible for electron conics.

Determinants of a simulated cross-country skiing sprint competition using V2 skating technique on roller skis.

PubMed

Mikkola, Jussi; Laaksonen, Marko; Holmberg, Hans-Christer; Vesterinen, Ville; Nummela, Ari

2010-04-01

The present study investigated the performance-predicting factors of a simulated cross-country (XC) skiing sprint competition on roller skis, on a slow surface. Sixteen elite male XC skiers performed a simulated sprint competition (4 x 850 m heat with a 20-minute recovery) using V2 skating technique on an indoor tartan track. Heat velocities, oxygen consumption, and peak lactate were measured during or after the heats. Maximal skiing velocity was measured by performing a 30-m speed test. Explosive and maximal force production in the upper body was determined by bench press (BP). Subjects also performed maximal anaerobic skiing test (MAST) and the 2 x 2-km double poling (DP) test. The maximal velocity of MAST (VMAST) and velocities at 3 (V3), 5 (V5), 7 (V7) mmol.L lactate levels in MAST were determined. In the 2 x 2-km test, DP economy (VO2SUBDP) and maximal 2-km DP velocity (VDP2KM) were determined. The best single performance-predicting factors for the sprint performance were VDP2KM (r = 0.73, p < 0.01), V7 (r = 0.70, p < 0.01), and VO2SUBDP (r = -0.70, p < 0.01). Faster skiers in sprint simulation had a higher absolute VO2 (L.min) (p < 0.05-0.01) during sprint heats, and higher anaerobic skiing power (VMAST, p < 0.05) and better anaerobic skiing economy (V3, V5, V7, p < 0.05-0.001) than slower skiers. Faster skiers were also stronger in BP, with regard to both absolute (p < 0.01) and relative (p < 0.05) values. In addition, anaerobic characteristics seem to be of importance at the beginning of the XC skiing sprint competition, whereas the aerobic characteristics become more important as the XC skiing sprint competition progressed. This study indicates that sprint skiers should emphasize sport-specific upper body training, and training skiing economy at high speeds.

Radial anisotropy of the North American upper mantle based on adjoint tomography with USArray

NASA Astrophysics Data System (ADS)

Zhu, Hejun; Komatitsch, Dimitri; Tromp, Jeroen

2017-10-01

We use seismic data from USArray to image the upper mantle underneath the United States based on a so-called `adjoint tomography', an iterative full waveform inversion technique. The inversion uses data from 180 regional earthquakes recorded by 4516 seismographic stations, resulting in 586 185 frequency-dependent measurements. Three-component short-period body waves and long-period surface waves are combined to simultaneously constrain deep and shallow structures. The transversely isotropic model US22 is the result of 22 pre-conditioned conjugate-gradient iterations. Approximate Hessian maps and point-spread function tests demonstrate good illumination of the study region and limited trade-offs among different model parameters. We observe a distinct wave-speed contrast between the stable eastern US and the tectonically active western US. This boundary is well correlated with the Rocky Mountain Front. Stable cratonic regions are characterized by fast anomalies down to 250-300 km, reflecting the thickness of the North American lithosphere. Several fast anomalies are observed beneath the North American lithosphere, suggesting the possibility of lithospheric delamination. Slow wave-speed channels are imaged beneath the lithosphere, which might indicate weak asthenosphere. Beneath the mantle transition zone of the central US, an elongated north-south fast anomaly is observed, which might be the ancient subducted Farallon slab. The tectonically active western US is dominated by prominent slow anomalies with magnitudes greater than -6 per cent down to approximately 250 km. No continuous lower to upper mantle upwellings are observed beneath Yellowstone. In addition, our results confirm previously observed differences between oceans and continents in the anisotropic parameter ξ = (βh/βv)2. A slow wave-speed channel with ξ > 1 is imaged beneath the eastern Pacific at depths from 100 to 200 km, reflecting horizontal shear within the asthenosphere. Underneath continental areas, regions with ξ > 1 are imaged at shallower depths around 100 km. They are characterized by fast shear wave speeds, suggesting different origins of anisotropy underneath oceans and continents. The wave speed and anisotropic signatures of the western Atlantic are similar to continental areas in comparison with the eastern Pacific. Furthermore, we observe regions with ξ < 1 beneath the tectonically active western US at depths between 300 and 400 km, which might reflect vertical flows induced by subduction of the Farallon and Juan de Fuca Plates. Comparing US22 with several previous tomographic models, we observe relatively good correlations for long-wavelength features. However, there are still large discrepancies for small-scale features.

Atmospheric structure prior to tornadoes as derived from proximity and precedent upper-air soundings, covering the period April 1977-June 1979

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, G.E.; Darkow, G.L.

1982-05-01

The uniqueness of the thermodynamic and dynamic structure of the atmosphere in the area of imminent tornado bearing storm development is analyzed by comparing 115 tornado proximity soundings with upper air soundings made at the same location 6 and 12 hours earlier (precedent soundings) and with soundings made simultaneously at neighboring upper air stations. The comparisons suggest that both the proximity station and the neighboring station upstream with respect to the mean flow in the low level moist air display very similar degrees of hydrostatic and potential-convective instability by late afternoon. The principal difference is in the wind profiles atmore » the two locations. The tornado proximity station displays significantly stronger wind speeds above 1 km with the most striking difference being in the vertical shear of the wind in the layer from 1 to 3 km above ground level. In this layer the winds at the proximity station show an average increase of about 3 m sec/sup -1/ while the upstream, non-tornadic, station shows a slight decrease of wind speed with height.« less

Understanding variability of the Southern Ocean overturning circulation in CORE-II models

NASA Astrophysics Data System (ADS)

Downes, S. M.; Spence, P.; Hogg, A. M.

2018-03-01

The current generation of climate models exhibit a large spread in the steady-state and projected Southern Ocean upper and lower overturning circulation, with mechanisms for deep ocean variability remaining less well understood. Here, common Southern Ocean metrics in twelve models from the Coordinated Ocean-ice Reference Experiment Phase II (CORE-II) are assessed over a 60 year period. Specifically, stratification, surface buoyancy fluxes, and eddies are linked to the magnitude of the strengthening trend in the upper overturning circulation, and a decreasing trend in the lower overturning circulation across the CORE-II models. The models evolve similarly in the upper 1 km and the deep ocean, with an almost equivalent poleward intensification trend in the Southern Hemisphere westerly winds. However, the models differ substantially in their eddy parameterisation and surface buoyancy fluxes. In general, models with a larger heat-driven water mass transformation where deep waters upwell at the surface ( ∼ 55°S) transport warmer waters into intermediate depths, thus weakening the stratification in the upper 2 km. Models with a weak eddy induced overturning and a warm bias in the intermediate waters are more likely to exhibit larger increases in the upper overturning circulation, and more significant weakening of the lower overturning circulation. We find the opposite holds for a cool model bias in intermediate depths, combined with a more complex 3D eddy parameterisation that acts to reduce isopycnal slope. In summary, the Southern Ocean overturning circulation decadal trends in the coarse resolution CORE-II models are governed by biases in surface buoyancy fluxes and the ocean density field, and the configuration of the eddy parameterisation.

Magnetically Controlled Upper Ionosphere of Mars

NASA Astrophysics Data System (ADS)

Majeed, T.; Al Aryani, O.; Al Mutawa, S.; Bougher, S. W.; Haider, S. A.

2017-12-01

The electron density (Ne) profiles measured by the Mars Express spacecraft over regions of strong crustal magnetic fields have shown anomalous characteristics of the topside plasma distribution with variable scale heights. One of such Ne profiles is located at 82oS and 180oE whose topside ionosphere is extended up to an altitude of 700 km. The crustal magnetic field at this southern site is nearly vertical and open to the access of solar wind plasma through magnetic reconnection with the interplanetary magnetic field. This can lead to the acceleration of electrons and ions during the daytime ionosphere. The downward accelerated electrons with energies >200 eV can penetrate deep into the Martian upper ionosphere along vertical magnetic field lines and cause heating, excitation and ionization of the background atmosphere. The upward acceleration of ions resulting from energy input by precipitating electrons can lead to enhance ion escape rate and modify scale heights of the topside ionosphere. We have developed a 1-D chemical diffusive model from 100 km to 400 km to interpret the Martian ionospheric structure at 82oS latitude. The primary source of ionization in the model is due to solar EUV radiation. An extra ionization source due to precipitating electrons of 0.25 keV, peaking near an altitude of 145 km is added in the model to reasonably reproduce the measured ionospheric structure below an altitude of 180 km. The behavior of the topside ionosphere can be interpreted by the vertical plasma transport caused by precipitating electrons. The vertical transport of plasma in our model is simulated by vertical ion velocities, whose values can be interpreted as drift velocities along magnetic field lines. We find that the variation of the topside Ne scale heights is sensitive to the magnitudes of upward and downward drifts with an imposed outward flux boundary condition at the top of the model. The model requires an upward flux of more than 107 ions cm-2 s-1 for both O2+ and O+, and drift speeds of 200 m/s to interpret the measured topside ionospheric structure for altitudes >180 km. The magnitudes of outward ion fluxes and drift velocities are compared with those simulated by existing models. The model results will be presented in comparison with the measured electron density profile. This work is supported by MBRSC, Dubai, UAE.

An inflatable belt system in the rear seat occupant environment: investigating feasibility and benefit in frontal impact sled tests with a 50th percentile male ATD

PubMed Central

Forman, Jason L.; Lopez-Valdes, Francisco J.; Dennis, Nate; Kent, Richard W.; Tanji, Hiromasa; Higuchi, Kazuo

2010-01-01

Frontal-impact airbag systems have the potential to provide a benefit to rear seat occupants by distributing restraining forces over the body in a manner not possible using belts alone. This study sought to investigate the effects of incorporating a belt-integrated airbag (“airbelt”) into a rear seat occupant restraint system. Frontal impact sled tests were performed with a Hybrid III 50th percentile male anthropomorphic test device (ATD) seated in the right-rear passenger position of a 2004 mid-sized sedan buck. Tests were performed at 48 km/h (20 g, 100 ms acceleration pulse) and 29 km/h (11 g, 100 ms). The restraints consisted of a 3-point belt system with a cylindrical airbag integrated into the upper portion of the shoulder belt. The airbag was tapered in shape, with a maximum diameter of 16 cm (at the shoulder) that decreased to 4 cm at the mid-chest. A 2.5 kN force-limiter was integrated into the shoulder-belt retractor, and a 2.3 kN pretensioner was present in the out-board anchor of the lap belt. Six ATD tests (three 48 km/h and three 29 km/h) were performed with the airbelt system. These were compared to previous frontal-impact, rear seat ATD tests with a standard (not-force-limited, not-pretensioned) 3-point belt system and a progressive force-limiting (peak 4.4 kN), pretensioning (FL+PT) 3-point belt system. In the 48 km/h tests, the airbelt resulted in significantly less (p<0.05, two-tailed Student’s t-test) posterior displacement of the sternum towards the spine (chest deflection) than both the standard and FL+PT belt systems (airbelt: average 13±1.1 mm standard deviation; standard belt: 33±2.3 mm; FL+PT belt: 23±2.6 mm). This was consistent with a significant reduction in the peak upper shoulder belt force (airbelt: 2.7±0.1 kN; standard belt: 8.7±0.3 kN; FL+PT belt: 4.4±0.1 kN), and was accompanied by a small increase in forward motion of the head (airbelt: 54±0.4 cm; standard belt: 45±1.3 cm; FL+PT belt: 47±1.1 cm) The airbelt system also significantly reduced the flexion moment in the lower neck (airbelt: 169±3.3 Nm; standard belt: 655±26 Nm; FL+PT belt: 308±19 Nm). Similar results were observed in the 29 km/h tests. These results suggest that this airbelt system may provide some benefit for adult rear seat occupants in frontal collisions, even in relatively low-speed impacts. Further study is needed to evaluate this type of restraint system for different size occupants (e.g., children), for out-of-position occupants, and with other occupant models (e.g., cadavers). PMID:21050596

Extending the NASA Ames Mars General Circulation Model to Explore Mars’ Middle Atmosphere

NASA Astrophysics Data System (ADS)

Brecht, Amanda; Hollingsworth, J.; Kahre, M.; Schaeffer, J.

2013-10-01

The NASA Ames Mars General Circulation Model (MGCM) upper boundary has been extended to ~120 km altitude (p ~10-5 mbar). The extension of the MGCM upper boundary initiates the ability to understand the connection between the lower and upper atmosphere of Mars through the middle atmosphere 70 - 120 km). Moreover, it provides the opportunity to support future missions (i.e. the 2013 MAVEN mission). A major factor in this extension is the incorporation of the Non-Local Thermodynamic Equilibrium (NLTE) heating (visible) and cooling (infrared). This modification to the radiative transfer forcing (i.e., RT code) has been significantly tested in a 1D vertical column and now has been ported to the full 3D Mars GCM. Initial results clearly show the effects of NLTE in the upper middle atmosphere. Diagnostic of seasonal mean fields and large-scale wave activity will be shown with insight into circulation patterns in the middle atmosphere. Furthermore, sensitivity tests with the resolution of the pressure and temperature grids, in which the k-coefficients are calculated upon, have been performed in the 1D RT code. Our progress on this research will be presented. Brecht is supported by NASA’s Postdoctoral Program at the Ames Research Center, administered by Oak Ridge Associated Universities through a contract with NASA.

Methane gas hydrate effect on sediment acoustic and strength properties

USGS Publications Warehouse

Winters, W.J.; Waite, W.F.; Mason, D.H.; Gilbert, L.Y.; Pecher, I.A.

2007-01-01

To improve our understanding of the interaction of methane gas hydrate with host sediment, we studied: (1) the effects of gas hydrate and ice on acoustic velocity in different sediment types, (2) effect of different hydrate formation mechanisms on measured acoustic properties (3) dependence of shear strength on pore space contents, and (4) pore pressure effects during undrained shear.A wide range in acoustic p-wave velocities (Vp) were measured in coarse-grained sediment for different pore space occupants. Vp ranged from less than 1 km/s for gas-charged sediment to 1.77–1.94 km/s for water-saturated sediment, 2.91–4.00 km/s for sediment with varying degrees of hydrate saturation, and 3.88–4.33 km/s for frozen sediment. Vp measured in fine-grained sediment containing gas hydrate was substantially lower (1.97 km/s). Acoustic models based on measured Vp indicate that hydrate which formed in high gas flux environments can cement coarse-grained sediment, whereas hydrate formed from methane dissolved in the pore fluid may not.The presence of gas hydrate and other solid pore-filling material, such as ice, increased the sediment shear strength. The magnitude of that increase is related to the amount of hydrate in the pore space and cementation characteristics between the hydrate and sediment grains. We have found, that for consolidation stresses associated with the upper several hundred meters of sub-bottom depth, pore pressures decreased during shear in coarse-grained sediment containing gas hydrate, whereas pore pressure in fine-grained sediment typically increased during shear. The presence of free gas in pore spaces damped pore pressure response during shear and reduced the strengthening effect of gas hydrate in sands.

Upper limits to the detection of ammonia from protoplanetary disks around HL Tauri and L1551-IRS 5

NASA Technical Reports Server (NTRS)

Gomez, Jose F.; Torrelles, Jose M.; Ho, Paul T. P.; Rodriguez, Luis F.; Canto, Jorge

1993-01-01

We present NH3(1, 1) and (2, 2) observations of the young stellar sources HL Tau and L1551-IRS 5 using the VLA in its B-configuration, which provides an angular resolution of about 0.4 arcsec (about 50 AU at 140 pc) at 1.3 cm wavelength. Our goal was to detect and resolve circumstellar molecular disks with radius of the order of 100 AU around these two sources. No ammonia emission was detected toward either of them. The 3-sigma levels were 2.7 mJy/beam and 3.9 mJy/beam for HL Tau and L1551-IRS 5, respectively, with a velocity resolution of about 5 km/s. With this nondetection, we estimate upper limits to the mass of the proposed protoplanetary molecular disks (within a radius of 10 AU from the central stars) on the order of 0.02/(X(NH3)/10 exp -8) solar mass for HL Tau and 0.1/(X(NH3)/10 exp -8) solar mass for L1551-IRS 5.

Structure of the Middle America trench in Oaxaca, Mexico

NASA Astrophysics Data System (ADS)

Nava, F.; Núñez-Cornú, F.; Córdoba, D.; Mena, M.; Ansorge, J.; González, J.; Rodríguez, M.; Banda, E.; Mueller, S.; Udías, A.; García-García, M.; Calderón, G.; the Mexican Working GroupDeep Seismic Profiling

1988-11-01

Deep seismic profiling was carried out in south and central Oaxaca as a multinational (Mexico, Spain and Switzerland) project. Sixteen sea-bottom explosions, ranging from 20 to 1000 kg were recorded by thirty portable instruments along three profiles, two along the coast and one going inland in an approximate N-S direction. Gravity surveys were carried out over the seismic profile lines, and the resulting Bouguer anomalies are interpreted together with the seismic data. Preliminary results indicate changes in the crustal thickness along the coast, near the town of Pinotepa Nacional, from 23.5 km in the northwest to 19 km in the southeast, reaching a minimum of some 15 km near the middle of the profile, about 140 km northwest of Puerto Angel. The coastal structure section consists roughly of two layers, an upper one with P-wave velocities that range from 5.1-5.4 to 5.8-6.0 km/s and a lower one where the P velocity range is from 6.0-6.2 to 6.3-6.4 km/s, overlying material with P-wave velocities of 7.45 km/s. Along the coast from Puerto Angel to Salina Cruz, the dip of the Cocos plate appears to be much less than it is to the northwest. A low-velocity zone, which corresponds to the top of the subducted oceanic crust, with P-wave velocities of 6.5-6.9 km/s, is found beneath the 2-3 km thick 7.45 km/s layer. The possible presence of an intrusive body is suggested by anomalous seismic arrivals and by a large gravimetric anomaly near Puerto Angel, close to the southern tip of Mexico.

The 1.4-2.7 micron spectrum of the point source at the galactic center

NASA Technical Reports Server (NTRS)

Treffers, R. R.; Fink, U.; Larson, H. P.; Gautier, T. N., III

1976-01-01

The spectrum of the 2-micron point source at the galactic center is presented over the range from 1.4 to 2.7 microns. The two-level-transition CO band heads are seen near 2.3 microns, confirming that the radiation from this source is due to a cool supergiant star. The heliocentric radial velocity is found to be - 173 (+ or -90) km/s and is consistent with the star being in orbit about a dense galactic nucleus. No evidence is found for Brackett-gamma emission, and no interstellar absorption features are seen. Upper limits for the column densities of interstellar H2, CH4, CO, and NH3 are derived.

Precambrian crust and lithosphere beneath the Northern Canadian Cordillera discovered by LITHOPROBE seismic reflection profiling

NASA Astrophysics Data System (ADS)

Clowes, R. M.; Cook, F. A.; Snyder, D. B.; van der Velden, A. J.; Hall, K. W.; Erdmer, P.; Evenchick, C. A.

2003-04-01

The Cordillera in northern Canada is underlain by westward tapering layers that can be followed from outcrops of Proterozoic strata in the Foreland Belt to the lowermost crust of the orogenic interior, a distance of as much as 500 km across strike. The layering was discovered on two new deep seismic reflection profiles in the Yukon (Line 3; ~650 km) and northern British Columbia (Line 2; ~1245 km in two segments) that were acquired as part of the LITHOPROBE Slave - Northern Cordillera Lithospheric Evolution (SNORCLE) transect. Along Line 3, the layering is visible between 5.0 and 12.0 s (~15 to 36 km depth). It is followed southwestward for nearly 650 km (~500 km across strike) and thins to less than 1.0 s (~3.0-3.5 km thickness) near the Moho at the Yukon-Alaska international boundary. Farther south, along Line 2, the upper part of the layering correlates with outcrops of Proterozoic (1.76-1.0 Ga) strata on the east. Near the outcrop, the layering is >15 km thick. It projects westward into the middle and lower crust for ~700 km (~300 km across strike) where it disappears as a thin taper at the base of the crust. The layering is disrupted at the Tintina fault zone, a late to post-orogenic strike-slip fault with up to 800 km of displacement, which appears as a vertical zone of little reflectivity on both profiles (~300 km apart). The base of the layered reflection zone coincides with the Moho, which exhibits variable character and undulates in a series of broad (~150 km) arches. Although the mantle is generally non-reflective, an event dips eastward from ~14.0 s (~45 km) at the western end of Line 3 near the coast to ~21.0 s (73 km depth) beneath exposed Eocene magmatic rocks. It is interpreted as a relict subduction surface of the Kula plate. Some implications of the interpretation of Proterozoic layered rocks beneath most of the northern Cordillera are: (1) ancient North American crust and lithosphere project westward beneath most of the Northern Cordillera, (2) the detachments that carry deformed rocks the northern Canadian Cordillera are largely confined to the crust above the layering, and (3) rocks of most of the accreted terranes overlie the layering. Most of the accreted rocks thus appear to be thin (<10 km thick), far-traveled flakes. However, one major terrane, Stikinia, may thicken westward as the underlying layered zone thins such that the lower crustal layering disappears beneath the northeastern portion of Stikinia; the boundary between Stikinia and adjacent rocks to the east may be a crustal-scale tectonic wedge above the deep layering.

Seismic images of the Brooks Range fold and thrust belt, Arctic Alaska, from an integrated seismic reflection/refraction experiment

USGS Publications Warehouse

Levander, A.; Fuis, G.S.; Wissinger, E.S.; Lutter, W.J.; Oldow, J.S.; Moore, Thomas E.

1994-01-01

We describe results of an integrated seismic reflection/refraction experiment across the Brooks Range and flanking geologic provinces in Arctic Alaska. The seismic acquisition was unusual in that reflection and refraction data were collected simultaneously with a 700 channel seismograph system deployed numerous times along a 315 km profile. Shot records show continuous Moho reflections from 0-180 km offset, as well as numerous upper- and mid-crustal wide-angle events. Single and low-fold near-vertical incidence common midpoint (CMP) reflection images show complex upper- and middle-crustal structure across the range from the unmetamorphosed Endicott Mountains allochthon (EMA) in the north, to the metamorphic belts in the south. Lower-crustal and Moho reflections are visible across the entire reflection profile. Travel-time inversion of PmP arrivals shows that the Moho, at 33 km depth beneath the North Slope foothills, deepens abruptly beneath the EMA to a maximum of 46 km, and then shallows southward to 35 km at the southern edge of the range. Two zones of upper- and middle-crustal reflections underlie the northern Brooks Range above ~ 12-15 km depth. The upper zone, interpreted as the base of the EMA, lies at a maximum depth of 6 km and extends over 50 km from the range front to the north central Brooks Range where the base of the EMA outcrops above the metasedimentary rocks exposed in the Doonerak window. We interpret the base of the lower zone, at ~ 12 km depth, to be from carbonate rocks above the master detachment upon which the Brooks Range formed. The seismic data suggest that the master detachment is connected to the faults in the EMA by several ramps. In the highly metamorphosed terranes south of the Doonerak window, the CMP section shows numerous south-dipping events which we interpret as a crustal scale duplex involving the Doonerak window rocks. The basal detachment reflections can be traced approximately 100 km, and dip southward from about 10-12 km near the range front, to 14-18 km beneath the Doonerak window, to 26-28 km beneath the metamorphic belts in the central Brooks Range. The section documents middle- and lower-crustal involvement in the formation of the Brooks Range. ?? 1994.

A NuSTAR Observation of the Reflection Spectrum of the Low-Mass X-Ray Binary 4U 1728-34

NASA Technical Reports Server (NTRS)

Sleator, Clio C.; Tomsick, John A.; King, Ashley L.; Miller, Jon M.; Boggs, Steven E.; Bachetti, Matteo; Barret, Didier; Chenevez, Jerome; Christensen, Finn E.; Craig, William W.;

Mushy Magma beneath Yellowstone

NASA Astrophysics Data System (ADS)

Chu, R.; Helmberger, D. V.; Sun, D.; Jackson, J. M.; Zhu, L.

2009-12-01

A recent prospective on the Yellowstone Caldera discounts its explosive potential based on inferences from tomographic studies on regional earthquake data which suggests a high degree of crystallization of the underlying magma body. In this study, we analyzed P-wave receiver functions recorded by broadband stations above the caldera from 100 teleseismic earthquakes between January and November 2008. After applying a number of waveform modeling tools, we obtained much lower seismic velocities than previous estimates, 2.3 km/sec (Vp) and 1.1 km/sec (Vs), with a thickness of 3.6 km in the upper crust. This shallow low velocity zone is severe enough to cause difficulties with seismic tool applications. In particular, seismologists expect teleseismic P-waves to arrive with motions up and away or down and back. Many of the observations recorded by the Yellowstone Intermountain Seismic Array, however, violate this assumption. We show that many of the first P-wave arrivals observed at seismic stations on the edge of the caldera do not travel through the magma body but have taken longer but faster paths around the edge or wrap-around phases. Three stations near the trailing edge have reversal radial-component motions, while stations near the leading edge do not. Adding our constraints on geometry, we conclude that this relatively shallow magma body has a volume of over 4,300 km3. We estimate the magma body by assuming a fluid-saturated porous material consisting of granite and a mixture of rhyolite melt and supercritical water and CO2 at temperatures of 800 oC and pressure at 5 km (0.1 GPa).Theoretical calculations of seismic wave speed suggests that the magma body beneath the Yellowstone Caldera has a porosity of 32% filled with 92% rhyolite melt and 8% water-CO2 by volume.

Lithospheric structure beneath Eastern Africa from joint inversion of receiver functions and Rayleigh wave velocities

NASA Astrophysics Data System (ADS)

Dugda, Mulugeta Tuji

Crust and upper mantle structure beneath eastern Africa has been investigated using receiver functions and surface wave dispersion measurements to understand the impact of the hotspot tectonism found there on the lithospheric structure of the region. In the first part of this thesis, I applied H-kappa stacking of receiver functions, and a joint inversion of receiver functions and Rayleigh wave group velocities to determine the crustal parameters under Djibouti. The two methods give consistent results. The crust beneath the GEOSCOPE station ATD has a thickness of 23+/-1.5 km and a Poisson's ratio of 0.31+/-0.02. Previous studies give crustal thickness beneath Djibouti to be between 8 and 10 km. I found it necessary to reinterprete refraction profiles for Djibouti from a previous study. The crustal structure obtained for ATD is similar to adjacent crustal structure in many other parts of central and eastern Afar. The high Poisson's ratio and Vp throughout most of the crust indicate a mafic composition, suggesting that the crust in Afar consists predominantly of new igneous rock emplaced during the late synrift stage where extension is accommodated within magmatic segments by diking. In the second part of this thesis, the seismic velocity structure of the crust and upper mantle beneath Ethiopia and Djibouti has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities to obtain new constraints on the thermal structure of the lithosphere. Crustal structure from the joint inversion for Ethiopia and Djibouti is similar to previously published models. Beneath the Main Ethiopian Rift (MER) and Afar, the lithospheric mantle has a maximum shear wave velocity of 4.1-4.2 km/s and extends to a depth of at most 50 km. In comparison to the lithosphere away from the East African Rift System in Tanzania, where the lid extends to depths of ˜100-125 km and has a maximum shear velocity of 4.6 km/s, the mantle lithosphere under the Ethiopian Plateau appears to have been thinned by ˜30-50 km and the maximum shear wave velocity reduced by ˜0.3 km/s. Results from a 1D conductive thermal model suggest that the shear velocity structure of the lithosphere beneath the Ethiopian Plateau can be explained by a plume model, if a plume rapidly thinned the lithosphere by ˜30--50 km at the time of the flood basalt volcanism (c. 30 Ma), and if warm plume material has remained beneath the lithosphere since then. About 45-65% of the 1-1.5 km of plateau uplift in Ethiopia can be attributed to the thermally perturbed lithospheric structure. In the final part of this thesis, the shear-wave velocity structure of the crust and upper mantle beneath Kenya has been obtained from a joint inversion of receiver functions, and Rayleigh wave group and phase velocities. The crustal structure from the joint inversion is consistent with crustal structure published previously by different authors. The lithospheric mantle beneath the East African Plateau in Kenya is similar to the lithosphere under the East African Plateau in Tanzania. Beneath the Kenya Rift, the lithosphere extends to a depth of at most ˜75 km. The lithosphere under the Kenya Plateau is not perturbed when compared to the highly perturbed lithosphere beneath the Ethiopian Plateau. On the other hand, the lithosphere under the Kenya Rift is perturbed as compared to the Kenya Plateau or the rest of the East African Plateau, but is not as perturbed as the lithosphere beneath the Main Ethiopian Rift or the Afar. Although Kenya and Ethiopia have similar uplift and rifting histories, they have different volcanic histories. Much of Ethiopia has been affected by the Afar Flood Basalt volcanism, which may be the cause of this difference in lithospheric structure between these two regions.

Aircraft Observation of CO2, CO, O3 and H2 over the North Pacific during the PACE-7 Campaign

NASA Astrophysics Data System (ADS)

Sawa, Y.; Matsueda, H.; Makino, Y.; Inoue, H. Y.; Murayama, S.; Hirota, M.; Tsutsumi, Y.; Zaizen, Y.; Ikegami, M.; Okada, K.

2004-02-01

Aircraft observation under the Pacific Atmospheric Chemistry Experiment (PACE) program was performed from February 13 to 21, 2000 to examine in detail the distributions of CO2 in the free troposphere between 5 and 11 km. Continuous measurements of CO2 mixing ratios were made using an on-board measuring system over the northern North Pacific between Nagoya, Japan and Anchorage, Alaska, and the western North Pacific between Nagoya and Saipan. Other trace gases, such as CO and O3, were also observed using continuous measuring systems at the same time. CO2 over the northern Pacific (35°N and higher) showed highly variable mixing ratios, ranging from 374 ppm in the upper troposphere to 366 ppm in the lowermost stratosphere. This highly variable distribution of CO2 was quite similar to that of CO, but the relationship between CO2 and O3 showed a strong negative correlation. These results indicated that the exchange process between the stratosphere and the troposphere significantly influences the large CO2 variation. On the other hand, the CO2 over the western North Pacific to the south of Japan showed no significant variation in the upper troposphere at 11 km but a relatively larger variability at 5 km. The CO2 enhancement at lower altitudes coincided with the CO elevation due to the intrusion of a polluted air mass. Trajectory analysis indicated that the Asian continental outflow perturbed the CO2 distributions over the western Pacific. Very low mixing ratios of O3 of less than 20 ppb were distributed in the latitude band of 15 30°N at 11 km, reflecting the effects of transport from the equatorial region.

In situ measurements and radar observations of a severe storm - Electricity, kinematics, and precipitation

NASA Technical Reports Server (NTRS)

Byrne, G. J.; Few, A. A.; Stewart, M. F.; Conrad, A. C.; Torczon, R. L.

1987-01-01

Electric field measurements made inside a multicell severe storm in Oklahoma in 1983 with a balloon-borne instrument are presented. The properties of the electric charge regions, such as altitude, thickness, and charge concentrations, are studied. These measurements are analzyed with meteorological measurements of temperature and humidity, and balloon tracking and radar observations. The relation between the electric charge structure and the precipitation and kinematic features of the storm is examined. The data reveal that the cell exhibits a bipolar charge structure with negative charge below positive charge. The average charge concentrations of the two regions are estimated as -1.2 and 0.15 nC/cu m, respectively; the upper positive charge is about 6 km in vertical extent, and the lower negative charge is less than 1 km in vertical extent.

Inference of viscosity jump at 670 km depth and lower mantle viscosity structure from GIA observations

NASA Astrophysics Data System (ADS)

Nakada, Masao; Okuno, Jun'ichi; Irie, Yoshiya

2018-03-01

A viscosity model with an exponential profile described by temperature (T) and pressure (P) distributions and constant activation energy (E_{{{um}}}^{{*}} for the upper mantle and E_{{{lm}}}^* for the lower mantle) and volume (V_{{{um}}}^{{*}} and V_{{{lm}}}^*) is employed in inferring the viscosity structure of the Earth's mantle from observations of glacial isostatic adjustment (GIA). We first construct standard viscosity models with an average upper-mantle viscosity ({\\bar{η }_{{{um}}}}) of 2 × 1020 Pa s, a typical value for the oceanic upper-mantle viscosity, satisfying the observationally derived three GIA-related observables, GIA-induced rate of change of the degree-two zonal harmonic of the geopotential, {\\dot{J}_2}, and differential relative sea level (RSL) changes for the Last Glacial Maximum sea levels at Barbados and Bonaparte Gulf in Australia and for RSL changes at 6 kyr BP for Karumba and Halifax Bay in Australia. Standard viscosity models inferred from three GIA-related observables are characterized by a viscosity of ˜1023 Pa s in the deep mantle for an assumed viscosity at 670 km depth, ηlm(670), of (1 - 50) × 1021 Pa s. Postglacial RSL changes at Southport, Bermuda and Everglades in the intermediate region of the North American ice sheet, largely dependent on its gross melting history, have a crucial potential for inference of a viscosity jump at 670 km depth. The analyses of these RSL changes based on the viscosity models with {\\bar{η }_{{{um}}}} ≥ 2 × 1020 Pa s and lower-mantle viscosity structures for the standard models yield permissible {\\bar{η }_{{{um}}}} and ηlm (670) values, although there is a trade-off between the viscosity and ice history models. Our preferred {\\bar{η }_{{{um}}}} and ηlm (670) values are ˜(7 - 9) × 1020 and ˜1022 Pa s, respectively, and the {\\bar{η }_{{{um}}}} is higher than that for the typical value of oceanic upper mantle, which may reflect a moderate laterally heterogeneous upper-mantle viscosity. The mantle viscosity structure adopted in this study depends on temperature distribution and activation energy and volume, and it is difficult to discuss the impact of each quantity on the inferred lower-mantle viscosity model. We conclude that models of smooth depth variation in the lower-mantle viscosity following η ( z ) ∝ {{ exp}}[ {( {E_{{{lm}}}^* + P( z )V_{{{lm}}}^*} )/{{R}}T( z )} ] with constant E_{{{lm}}}^* and V_{{{lm}}}^* are consistent with the GIA observations.

Seismic crustal structure of the North China Craton and surrounding area: Synthesis and analysis

NASA Astrophysics Data System (ADS)

Xia, B.; Thybo, H.; Artemieva, I. M.

2017-07-01

We present a new digital model (NCcrust) of the seismic crustal structure of the Neoarchean North China Craton (NCC) and its surrounding Paleozoic-Mesozoic orogenic belts (30°-45°N, 100°-130°E). All available seismic profiles, complemented by receiver function interpretations of crustal thickness, are used to constrain a new comprehensive crustal model NCcrust. The model, presented on a 0.25° × 0.25°grid, includes the Moho depth and the internal structure (thickness and velocity) of the crust specified for four layers (the sedimentary cover, upper, middle, and lower crust) and the Pn velocity in the uppermost mantle. The crust is thin (30-32 km) in the east, while the Moho depth in the western part of the NCC is 38-44 km. The Moho depth of the Sulu-Dabie-Qinling-Qilian orogenic belt ranges from 31 km to 51 km, with a general westward increase in crustal thickness. The sedimentary cover is 2-5 km thick in most of the region, and typical thicknesses of the upper crust, middle crust, and lower crust are 16-24 km, 6-24 km, and 0-6 km, respectively. We document a general trend of westward increase in the thickness of all crustal layers of the crystalline basement and as a consequence, the depth of the Moho. There is no systematic regional pattern in the average crustal Vp velocity and the Pn velocity. We examine correlation between the Moho depth and topography for seven tectonic provinces in the North China Craton and speculate on mechanisms of isostatic compensation.

Time-Varying Upper-Plate Deformation during the Megathrust Subduction Earthquake Cycle

NASA Astrophysics Data System (ADS)

Furlong, Kevin P.; Govers, Rob; Herman, Matthew

2015-04-01

Over the past several decades of the WEGENER era, our abilities to observe and image the deformational behavior of the upper plate in megathrust subduction zones has dramatically improved. Several intriguing inferences can be made from these observations including apparent lateral variations in locking along subduction zones, which differs from interseismic to coseismic periods; the significant magnitude of post-earthquake deformation (e.g. following the 20U14 Mw Iquique, Chile earthquake, observed on-land GPS post-EQ displacements are comparable to the co-seismic displacements); and incompatibilities between rates of slip deficit accumulation and resulting earthquake co-seismic slip (e.g. pre-Tohoku, inferred rates of slip deficit accumulation on the megathrust significantly exceed slip amounts for the ~ 1000 year recurrence.) Modeling capabilities have grown from fitting simple elastic accumulation/rebound curves to sparse data to having spatially dense continuous time series that allow us to infer details of plate boundary coupling, rheology-driven transient deformation, and partitioning among inter-earthquake and co-seismic displacements. In this research we utilize a 2D numerical modeling to explore the time-varying deformational behavior of subduction zones during the earthquake cycle with an emphasis on upper-plate and plate interface behavior. We have used a simplified model configuration to isolate fundamental processes associated with the earthquake cycle, rather than attempting to fit details of specific megathrust zones. Using a simple subduction geometry, but realistic rheologic layering we are evaluating the time-varying displacement and stress response through a multi-earthquake cycle history. We use a simple model configuration - an elastic subducting slab, an elastic upper plate (shallower than 40 km), and a visco-elastic upper plate (deeper than 40 km). This configuration leads to an upper plate that acts as a deforming elastic beam at inter-earthquake loading times and rates with a viscously relaxed regime at depths greater than 40 km. Analyses of our preliminary model results lead to the following: 1. Co-seismic stress transfer from the unloading elastic layer (shallow) into an elastically loading visco-elastic layer (deeper) - extends ~ 100 km inboard of locked zone. This stress transfer affects both coseismic and post-seismic surface displacements. 2. Post-seismic response of upper plate involves seaward motion for initial 10-20 years (~ 2 Maxwell times) after EQ. This occurs in spite of there being no slip on locked plate boundary - i.e. this is not plate boundary after-slip but rather is a consequence of stress relaxation in co-seismically loaded visco-elastic layer. However standard inversions of the surface displacement field would indicate significant after-slip along the locked plate interface. 3. By approximately 80 years (8 Maxwell times) system has returned to simple linear displacement pattern - the expected behavior for a shortening elastic beam. Prior to that time, the surface (observable) displacement pattern changes substantially over time and would result in an apparent temporal variation in coupling - from near-zero coupling to fully locked over ~ 80 years post-earthquake. These preliminary results indicate that care is needed in interpreting observed surface displacement fields from GPS, InSAR, etc. during the interseismic period. temporal variations in crustal deformation observed in regions such as the recent Tohoku, Maule, and Iquique megathrust events which are ascribed to fault plane after-slip may in fact reflect processes associated with re-equilibration of the visco-elastic subduction system.

Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

NASA Astrophysics Data System (ADS)

van der Werf, Thomas; Chatzaras, Vasileios; Marcel Kriegsman, Leo; Kronenberg, Andreas; Tikoff, Basil; Drury, Martyn R.

2017-12-01

The rheology of lower crust and its transient behavior in active strike-slip plate boundaries remain poorly understood. To address this issue, we analyzed a suite of granulite and lherzolite xenoliths from the upper Pleistocene-Holocene San Quintín volcanic field of northern Baja California, Mexico. The San Quintín volcanic field is located 20 km east of the Baja California shear zone, which accommodates the relative movement between the Pacific plate and Baja California microplate. The development of a strong foliation in both the mafic granulites and lherzolites, suggests that a lithospheric-scale shear zone exists beneath the San Quintín volcanic field. Combining microstructural observations, geothermometry, and phase equilibria modeling, we estimated that crystal-plastic deformation took place at temperatures of 750-890 °C and pressures of 400-560 MPa, corresponding to 15-22 km depth. A hot crustal geotherm of 40 ° C km-1 is required to explain the estimated deformation conditions. Infrared spectroscopy shows that plagioclase in the mafic granulites is relatively dry. Microstructures are interpreted to show that deformation in both the uppermost lower crust and upper mantle was accommodated by a combination of dislocation creep and grain-size-sensitive creep. Recrystallized grain size paleopiezometry yields low differential stresses of 12-33 and 17 MPa for plagioclase and olivine, respectively. The lower range of stresses (12-17 MPa) in the mafic granulite and lherzolite xenoliths is interpreted to be associated with transient deformation under decreasing stress conditions, following an event of stress increase. Using flow laws for dry plagioclase, we estimated a low viscosity of 1.1-1.3×1020 Pa ṡ s for the high temperature conditions (890 °C) in the lower crust. Significantly lower viscosities in the range of 1016-1019 Pa ṡ s, were estimated using flow laws for wet plagioclase. The shallow upper mantle has a low viscosity of 5.7×1019 Pa ṡ s, which indicates the lack of an upper-mantle lid beneath northern Baja California. Our data show that during post-seismic transients, the upper mantle and the lower crust in the Pacific-Baja California plate boundary are characterized by similar and low differential stress. Transient viscosity of the lower crust is similar to the viscosity of the upper mantle.

Shear velocity structure of central Eurasia from inversion of surface wave velocities

NASA Astrophysics Data System (ADS)

Villaseñor, A.; Ritzwoller, M. H.; Levshin, A. L.; Barmin, M. P.; Engdahl, E. R.; Spakman, W.; Trampert, J.

2001-04-01

We present a shear velocity model of the crust and upper mantle beneath central Eurasia by simultaneous inversion of broadband group and phase velocity maps of fundamental-mode Love and Rayleigh waves. The model is parameterized in terms of velocity depth profiles on a discrete 2°×2° grid. The model is isotropic for the crust and for the upper mantle below 220 km but, to fit simultaneously long period Love and Rayleigh waves, the model is transversely isotropic in the uppermost mantle, from the Moho discontinuity to 220 km depth. We have used newly available a priori models for the crust and sedimentary cover as starting models for the inversion. Therefore, the crustal part of the estimated model shows good correlation with known surface features such as sedimentary basins and mountain ranges. The velocity anomalies in the upper mantle are related to differences between tectonic and stable regions. Old, stable regions such as the East European, Siberian, and Indian cratons are characterized by high upper-mantle shear velocities. Other large high velocity anomalies occur beneath the Persian Gulf and the Tarim block. Slow shear velocity anomalies are related to regions of current extension (Red Sea and Andaman ridges) and are also found beneath the Tibetan and Turkish-Iranian Plateaus, structures originated by continent-continent collision. A large low velocity anomaly beneath western Mongolia corresponds to the location of a hypothesized mantle plume. A clear low velocity zone in vSH between Moho and 220 km exists across most of Eurasia, but is absent for vSV. The character and magnitude of anisotropy in the model is on average similar to PREM, with the most prominent anisotropic region occurring beneath the Tibetan Plateau.

Crustal structure of the Colorado Plateau, Arizona: Application of new long-offset seismic data analysis techniques

USGS Publications Warehouse

Parsons, T.; McCarthy, J.; Kohler, W.M.; Ammon, C.J.; Benz, H.M.; Hole, J.A.; Criley, E.E.

1996-01-01

The Colorado Plateau is a large crustal block in the southwestern United States that has been raised intact nearly 2 km above sea level since Cretaceous marine sediments were deposited on its surface. Controversy exists concerning the thickness of the plateau crust and the source of its buoyancy. Interpretations of seismic data collected on the plateau vary as to whether the crust is closer to 40 or 50 km thick. A thick crust could support the observed topography of the Colorado Plateau isostatically, while a thinner crust would indicate the presence of an underlying low-density mantle. This paper reports results on long-offset seismic data collected during the 1989 segment of the U.S. Geological Survey Pacific to Arizona Crustal Experiment that extended from the Transition Zone into the Colorado Plateau in northwest Arizona. We apply two new methods to analyze long-offset data that employ finite difference travel time calculations: (1) a first-arrival time inverter to find upper crustal velocity structure and (2) a forward-modeling technique that allows the direct use of the inverted upper crustal solution in modeling secondary reflected arrivals. We find that the crustal thickness increases from 30 km beneath the metamorphic core complexes in the southern Basin and Range province to about 42 km beneath the northern Transition Zone and southern Colorado Plateau margin. We observe some crustal thinning (to ???37 km thick) and slightly higher lower crustal velocities farther inboard; beneath the Kaibab uplift on the north rim of the Grand Canyon the crust thickens to a maximum of 48 km. We observe a nonuniform crustal thickness beneath the Colorado Plateau that varies by ???15% and corresponds approximately to variations in topography with the thickest crust underlying the highest elevations. Crustal compositions (as inferred from seismic velocities) appear to be the same beneath the Colorado Plateau as those in the Basin and Range province to the southwest, implying that the plateau crust represents an unextended version of the Basin and Range. Some of the variability in crustal structure appears to correspond to preserved lithospheric discontinuities that date back to the Proterozoic Era.

Deep seismic structure and tectonics of northern Alaska: Crustal-scale duplexing with deformation extending into the upper mantle

USGS Publications Warehouse

Fuis, G.S.; Murphy, J.M.; Lutter, W.J.; Moore, Thomas E.; Bird, K.J.; Christensen, N.I.

1997-01-01

Seismic reflection and refraction and laboratory velocity data collected along a transect of northern Alaska (including the east edge of the Koyukuk basin, the Brooks Range, and the North Slope) yield a composite picture of the crustal and upper mantle structure of this Mesozoic and Cenozoic compressional orogen. The following observations are made: (1) Northern Alaska is underlain by nested tectonic wedges, most with northward vergence (i.e., with their tips pointed north). (2) High reflectivity throughout the crust above a basal decollement, which deepens southward from about 10 km depth beneath the northern front of the Brooks Range to about 30 km depth beneath the southern Brooks Range, is interpreted as structural complexity due to the presence of these tectonic wedges, or duplexes. (3) Low reflectivity throughout the crust below the decollement is interpreted as minimal deformation, which appears to involve chiefly bending of a relatively rigid plate consisting of the parautochthonous North Slope crust and a 10- to 15-km-thick section of mantle material. (4) This plate is interpreted as a southward verging tectonic wedge, with its tip in the lower crust or at the Moho beneath the southern Brooks Range. In this interpretation the middle and upper crust, or all of the crust, is detached in the southern Brooks Range by the tectonic wedge, or indentor: as a result, crust is uplifted and deformed above the wedge, and mantle is depressed and underthrust beneath this wedge. (5) Underthrusting has juxtaposed mantle of two different origins (and seismic velocities), giving rise to a prominent sub-Moho reflector. Copyright 1997 by the American Geophysical Union.

A preliminary summary of a seismic-refraction survey in the vicinity of the Tonto Forest Observatory, Arizona

USGS Publications Warehouse

Roller, J.C.; Jackson, W.H.; Warren, D.H.; Healy, J.H.

1964-01-01

The U.S. Geological Survey complete d a seismic-refraction survey in the vicinity of the Tonto Forest Seismological Observatory (T.F.S.O.) in April and May 1964. More than 1200 km of reversed profiles were surveyed to determine the crustal structure and crustal and upper mantle velocities in this area. The purpose of this work was to provide information on wave-propagation paths of seismic events recorded at T.F.S.O. and to improve the performance of the Observatory in locating and identifying these events. First arrivals indicate that the Mohorovicic discontinuity dips to the northeast by as much as 6 degrees under T.F.S.O., and may even be displaced vertically by as much as 5 km immediately north of the Observatory near the boundary of the Basin and Range a n d t he Colorado Plateau Provinces. A preliminary examination of the first arrivals indicates that the crust at T.F.S.O. is at least 30 km thick and is made up of at least two seismic layers. A thin veneer at the surface with a velocity of approximately 4 km/sec is underlain by a layer with a velocity of approximately 5.9 km/sec to 6.1 km/sec. An intermediate layer with velocity of 6.6 to 7.0 km/sec is probably present in the lower crust, but is not revealed by first arrivals. The velocity of seismic waves in the upper mantle is about 7.9 km/sec.

Structure of the San Andreas fault zone at SAFOD from a seismic refraction survey

USGS Publications Warehouse

Hole, J.A.; Ryberg, T.; Fuis, G.S.; Bleibinhaus, F.; Sharma, A.K.

2006-01-01

Refraction traveltimes from a 46-km long seismic survey across the San Andreas Fault were inverted to obtain two-dimensional velocity structure of the upper crust near the SAFOD drilling project. The model contains strong vertical and lateral velocity variations from <2 km/s to ???6 km/s. The Salinian terrane west of the San Andreas Fault has much higher velocity than the Franciscan terrane east of the fault. Salinian basement deepens from 0.8 km subsurface at SAFOD to ???2.5 km subsurface 20 km to the southwest. A strong reflection and subtle velocity contrast suggest a steeply dipping fault separating the Franciscan terrane from the Great Valley Sequence. A low-velocity wedge of Cenozoic sedimentary rocks lies immediately southwest of the San Andreas Fault. This body is bounded by a steep fault just northeast of SAFOD and approaches the depth of the shallowest earthquakes. Multiple active and inactive fault strands complicate structure near SAFOD. Copyright 2006 by the American Geophysical Union.

The photodissociation lifetimes of the OH and OD radicals in comets

NASA Technical Reports Server (NTRS)

Singh, P. D.; Van Dishoeck, E. F.; Dalgarno, A.

1983-01-01

The photodissociation rates of OH and OD molecules due to absorption of solar radiation in the X(2)Pi-A(2)Sigma(+) electronic transition are calculated to lie between 3.5 and 6.7 x 10 to the -6th/sec for OH for heliocentric velocities between -60 and +60 km/sec and at about 4.7 x 10 to the -7th/sec for OD at 1 AU from the sun. The corresponding lifetimes, which are upper bounds to the actual lifetimes, are generally consistent with the observational cometary data.

South Polar Polygons

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-473, 4 September 2003

Looking somewhat like the roadmap of a city on Earth, this August 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows patterned ground--a mosaic of polygonal forms--highlighted by seasonal frost in the south polar region near 86.3oS, 310.2oW. Dark surfaces in this springtime view are areas from which cold, carbon dioxide frost has been subliming away. The picture covers an area 3 km (1.9 mi) across and is illuminated by sunlight from the upper left.

Compositional mantle layering revealed by slab stagnation at ~1000-km depth

PubMed Central

Ballmer, Maxim D.; Schmerr, Nicholas C.; Nakagawa, Takashi; Ritsema, Jeroen

2015-01-01

Improved constraints on lower-mantle composition are fundamental to understand the accretion, differentiation, and thermochemical evolution of our planet. Cosmochemical arguments indicate that lower-mantle rocks may be enriched in Si relative to upper-mantle pyrolite, whereas seismic tomography images suggest whole-mantle convection and hence appear to imply efficient mantle mixing. This study reconciles cosmochemical and geophysical constraints using the stagnation of some slab segments at ~1000-km depth as the key observation. Through numerical modeling of subduction, we show that lower-mantle enrichment in intrinsically dense basaltic lithologies can render slabs neutrally buoyant in the uppermost lower mantle. Slab stagnation (at depths of ~660 and ~1000 km) and unimpeded slab sinking to great depths can coexist if the basalt fraction is ~8% higher in the lower mantle than in the upper mantle, equivalent to a lower-mantle Mg/Si of ~1.18. Global-scale geodynamic models demonstrate that such a moderate compositional gradient across the mantle can persist can in the presence of whole-mantle convection. PMID:26824060

Anatomy of the dead sea transform from lithospheric to microscopic scale

USGS Publications Warehouse

Weber, M.; Abu-Ayyash, K.; Abueladas, A.; Agnon, A.; Alasonati-Tasarova, Z.; Al-Zubi, H.; Babeyko, A.; Bartov, Y.; Bauer, K.; Becken, M.; Bedrosian, P.A.; Ben-Avraham, Z.; Bock, G.; Bohnhoff, M.; Bribach, J.; Dulski, P.; Ebbing, J.; El-Kelani, R.; Forster, A.; Forster, H.-J.; Frieslander, U.; Garfunkel, Z.; Goetze, H.J.; Haak, V.; Haberland, C.; Hassouneh, M.; Helwig, S.; Hofstetter, A.; Hoffmann-Rotrie, A.; Jackel, K.H.; Janssen, C.; Jaser, D.; Kesten, D.; Khatib, M.; Kind, R.; Koch, O.; Koulakov, I.; Laske, Gabi; Maercklin, N.; Masarweh, R.; Masri, A.; Matar, A.; Mechie, J.; Meqbel, N.; Plessen, B.; Moller, P.; Mohsen, A.; Oberhansli, R.; Oreshin, S.; Petrunin, A.; Qabbani, I.; Rabba, I.; Ritter, O.; Romer, R.L.; Rumpker, G.; Rybakov, M.; Ryberg, T.; Saul, J.; Scherbaum, F.; Schmidt, S.; Schulze, A.; Sobolev, S.V.; Stiller, M.; Stromeyer, D.; Tarawneh, K.; Trela, C.; Weckmann, U.; Wetzel, U.; Wylegalla, K.

2009-01-01

Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of the Dead Sea Transform (DST) in the Middle East are as follows: (1) What are the structure and kinematics of a large fault zone? (2) What controls its structure and kinematics? (3) How does the DST compare to other plate boundary fault zones? The DST has accommodated a total of 105 km of leftlateral transform motion between the African and Arabian plates since early Miocene (???20 Ma). The DST segment between the Dead Sea and the Red Sea, called the Arava/ Araba Fault (AF), is studied here using a multidisciplinary and multiscale approach from the ??m to the plate tectonic scale. We observe that under the DST a narrow, subvertical zone cuts through crust and lithosphere. First, from west to east the crustal thickness increases smoothly from 26 to 39 km, and a subhorizontal lower crustal reflector is detected east of the AF. Second, several faults exist in the upper crust in a 40 km wide zone centered on the AF, but none have kilometer-size zones of decreased seismic velocities or zones of high electrical conductivities in the upper crust expected for large damage zones. Third, the AF is the main branch of the DST system, even though it has accommodated only a part (up to 60 km) of the overall 105 km of sinistral plate motion. Fourth, the AF acts as a barrier to fluids to a depth of 4 km, and the lithology changes abruptly across it. Fifth, in the top few hundred meters of the AF a locally transpressional regime is observed in a 100-300 m wide zone of deformed and displaced material, bordered by subparallel faults forming a positive flower structure. Other segments of the AF have a transtensional character with small pull-aparts along them. The damage zones of the individual faults are only 5-20 m wide at this depth range. Sixth, two areas on the AF show mesoscale to microscale faulting and veining in limestone sequences with faulting depths between 2 and 5 km. Seventh, fluids in the AF are carried downward into the fault zone. Only a minor fraction of fluids is derived from ascending hydrothermal fluids. However, we found that on the kilometer scale the AF does not act as an important fluid conduit. Most of these findings are corroborated using thermomechanical modeling where shear deformation in the upper crust is localized in one or two major faults; at larger depth, shear deformation occurs in a 20-40 km wide zone with a mechanically weak decoupling zone extending subvertically through the entire lithosphere. Copyright 2009 by the American Geophysical Union.

Anisotropy in the Australasian upper mantle from Love and Rayleigh waveform inversion

NASA Astrophysics Data System (ADS)

Debayle, Eric; Kennett, B. L. N.

2000-12-01

Records of both Rayleigh and Love waves have been analyzed to determine the pattern of anisotropy in the Australasian region. The approach is based on a two-stage inversion. Starting from a smooth PREM model with transverse isotropy about a vertical symmetry axis, the first step is an inversion of the waveforms of surface waves to produce path specific one-dimensional (1-D) upper mantle models. Under the assumption that the 1-D models represent averages along the paths, the results from 1584 Love and Rayleigh wave seismograms are combined in a tomographic inversion to provide a representation of three-dimensional structure for wavespeed heterogeneities and anisotropy. Polarization anisotropy with SH faster than SV is retrieved in the upper 200-250 km of the mantle for most of Precambrian Australia. In this depth interval, significant lateral variations in the level of polarization anisotropy are present. Locally, the anisotropy can be large, reaching an extreme value of 9% that is difficult to reconcile with current mineralogical models. However, the discrepancy may be explained in part by the presence of strong lateral heterogeneities along the path, or by effects introduced by the simplifying assumption of transverse isotropy for each path. The consistency between the location of polarization and azimuthal anisotropy in depth suggests that both observations share a common origin. The observation of polarization anisotropy down to at least 200 km supports a two-layered anisotropic model as constrained by the azimuthal anisotropy of SV waves. In the upper layer, 150 km thick, anisotropy would be related to past deformation frozen in the lithosphere while in the lower layer, anisotropy would reflect present day deformation due to plate motion.

Lithospheric Structure of the Zagros and Alborz Mountain Belts (Iran) from Seismic Imaging

NASA Astrophysics Data System (ADS)

Paul, A.; Hatzfeld, D.; Kaviani, A.; Tatar, M.

2008-12-01

We present a synthesis of the results of two dense temporary passive seismic experiments installed for a few months across Central Zagros for the first one, and from North-western Zagros to Alborz for the second one. On both transects, the receiver function analysis shows that the crust has an average thickness of ~ 43 km beneath the Zagros fold-and-thrust belt and the Iranian plateau. The crust is thicker in the back side of the Main Zagros Reverse Fault (MZRF), with a larger maximum Moho depth in Central Zagros (69 ± 2 km) than in North-western Zagros (56 ± 2 km). To reconcile Bouguer anomaly data and Moho depth profile of Central Zagros, we proposed that the thickening is related to overthrusting of the Arabian margin by Central Iran on the MZRF considered as a major thrust fault rooted at Moho depth. The better-quality receiver functions of NW Zagros display clear conversions on a low-velocity channel which cross-cuts the whole crust from the surface trace of the MZRF to the Moho on 250-km length. Waveform modeling shows that the crustal LVZ is ~ 10-km thick with a S-wave velocity 8-30 % smaller than the average crustal velocity. We interpret the low-velocity channel as the trace of the thrust fault and the suture between the Arabian and the Iranian lithospheres. We favour the hypothesis of the LVZ being due to sediments of the Arabian margin dragged to depth during the subduction of the Neotethyan Ocean. At upper mantle depth, we find shield-like shear-wave velocities in the Arabian upper-mantle, and lower velocities in the Iranian shallow mantle (50-150 km) which are likely due to higher temperature. The lack of a high-velocity anomaly in the mantle northeast of the MZRF suture suggests that the Neotethian oceanic lithosphere is now detached from the Arabian margin. The crust of the Alborz mountain range is not thickened in relation with its high elevations, but its upper mantle has low P-wave velocities.

Buoy observation for typhoon in southeast of Taiwan during summers of 2015 and 2016

NASA Astrophysics Data System (ADS)

Hsieh, C. Y.; Yang, Y. J.; Chang, M. H.; Chang, H. I.; Jan, S.; Wei, C. L.

2016-12-01

The western North Pacific is the most active area for the typhoon in the world, and typhoon caused disasters in this area. The marine observations are very important for the typhoon prediction. National Taiwan University (NTU) was developed a real-time data buoy system for typhoon observation. This buoy not only collected meteorological data, but also measured the temperature and salinity profiles of ocean's upper 500 m. The buoys, NTU1 and NTU2, were moored about 375 km and 175 km, respectively, from the southernmost tip of Taiwan. In summer of 2015, NTU1 buoy equipped with temperature and humidity probes, wind sensor, pyranometer, barometer, conductivity-temperature-depth (CTD) recorders, and temperature-pressure recorders. In summer of 2016, NTU1 and NTU2 buoys installed more instruments, such as rain gauge, net radiometer, and current meter, etc. During the observation period, there were three typhoons (Chan-hom, Soudler, and Goni) in 2015 and one typhoon (Nepartak) in 2016 approached buoy. Goni passed south and west side of NTU1 and the air pressure dropped around 25 hPa. Nepartak passed north side of NTU1 and south side of NTU2. The minimum distance between center of typhoon and NTU1 and NTU2 were about 11.48 km and 4.85 km, respectively. The NTU2 buoy recorded a maximum wind gust of 44 m/s, thickness of mixed layer increased to 120 m, and sea-surface temperature dropped 3 °C. In addition, the typhoon induced the near inertial internal motion for a couple of days. Applied the in-situ data to derive the net heat flux and its variations were from 600 W/m2 to -1000W/m2 during typhoon period. It indicate that the ocean provide energy to typhoon around this area. Moreover, the sum of sensible and latent heat flux calculated from observation data was 4.5 times than satellite-based products.

A simple Bouguer gravity anomaly map of southwestern Saudi Arabia and an initial interpretation

USGS Publications Warehouse

Gettings, M.E.

1983-01-01

Approximately 2,200 gravity stations on a 10-km2 grid were used to construct a simple Bouguer gravity anomaly map at 1:2,000,000 scale along a 150-km-wide by 850-km-long strip of the Arabian Peninsula from Sanam, southwest of Ar Riyad, through the Farasan Islands and including offshore islands, the coastal plain, and the Hijaz-Asir escarpment from Jiddah to the Yemen border. On the Precambrian Arabian Shield, local positive gravity anomalies are associated with greenstone belts, gneiss domes, and the Najd fault zones. Local negative gravity anomalies correlate with granitic plutonic rocks. A steep gravity gradient of as much as 4 mgal-km-1 marks the continental margin on the coastal plain near the southwestern end of the strip. Bouguer gravity anomaly values range from -10 to +40 mgal southwest of this gradient and from -170 to -100 mgal in a 300-km-wide gravity minimum northeast of the gradient. Farther northeast, the minimum is terminated by a regional gradient of about 0.1 mgal-km-1 that increases toward the Arabian Gulf. The regional gravity anomaly pattern has been modeled by using seismic refraction and Raleigh wave studies, heat-flow measurements, and isostatic considerations as constraints. The model is consistent with the hypothesis of upwelling of hot mantle material beneath the Red Sea and lateral mantle flow beneath the Arabian plate. The model yields best-fitting average crustal densities of 2.80 g-cm-3 (0-20 km depth) and 3.00 g-cm-3 (20-40 km depth) southwest of the Nabitah suture zone and 2.74 g-cm-3 (0-20 km depth) and 2.94 g-cm-3 (20-40 km depth) northeast of the suture zone. The gravity model requires that the crust be about 20 km thick at the continental margin and that the lower crust between the margin and Bishah (lat 20? N., long 42.5? E.) be somewhat denser than the lower crust to the northeast. Detailed correlations between 1:250,000- and 1:500,000-scale geologic maps and the gravity anomaly map suggest that the greenstone belts associated with gravity highs contain a large proportion of gabbroic and dioritic intrusive rocks and that the bulk density of the upper crust associated with some of the batholithic complexes has been lowered by the large-scale intrusion of granitic material at depth, as well as by that exposed at the surface. A comparison of known base and precious metals occurrences with the Bouguer gravity anomaly field shows, in some cases, a correlation between such occurrences and the features of the gravity anomaly map. Several areas were identified between known mineral occurrences along gravity-defined structures that may contain mineral deposits if the lithologic environment is favorable.

Non-LTE models of Titan's upper atmosphere

NASA Technical Reports Server (NTRS)

Yelle, Roger V.

1991-01-01

Models for the thermal structure of Titan's upper atmosphere, between 0.1 mbar and 0.01 nbar are presented. The calculations include non-LTE heating/cooling in the rotation-vibration bands of CH4, C2H2, and C2H6, absorption of solar IR radiation in the near-IR bands of CH4 and subsequent cascading to the nu-4 band of CH4, absorption of solar EUV and UV radiation, thermal conduction and cooling by HCN rotational lines. Unlike earlier models, the calculated exospheric temperature agrees well with observations, because of the importance of HCN cooling. The calculations predict a well-developed mesopause with a temperature of 135-140 K at an altitude of approximately 600 km and pressure of about 0.1 microbar. The mesopause is at a higher pressure than predicted by earlier calculations because non-LTE radiative transfer in the rotation-vibration bands of CH4, C2H2, and C2H6 is treated in an accurate manner. The accuracy of the LTE approximation for source functions and heating rates is discussed.

Non-LTE calculation of HCL earthlimb emission and implication for detection of HCl in the atmosphere

NASA Technical Reports Server (NTRS)

Kumer, J. B.; James, T. C.

1982-01-01

Calculation results are presented for the contribution of the non-Local Thermodynamic Equilibrium process of resonant scattering of sunlight in the 1-0 band of HCl to the earthlimb radiance, for the case of tangent altitudes from 20 to 90 km. It is established that the mechanism in question is a significant contributor to radiance at altitudes as low as 20 km, and that it becomes greater than the Local Thermodynamic Equilibrium contribution above 40 km. Attention is given to the prospects for detection of HCl at altitudes approaching 80 km, by means of the Cryogenic Limb Array Etalon Spectrometer scheduled for deployment by the NASA Upper Atmospheric Research Satellite.

Geologic and geophysical investigations of the Zuni-Bandera volcanic field, New Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ander, M.E.; Heiken, G.; Eichelberger, J.

1981-05-01

A positive, northeast-trending gravity anomaly, 90 km long and 30 km wide, extends southwest from the Zuni uplift, New Mexico. The Zuni-Bandera volcanic field, an alignment of 74 basaltic vents, is parallel to the eastern edge of the anomaly. Lavas display a bimodal distribution of tholeiitic and alkalic compositions, and were erupted over a period from 4 Myr to present. A residual gravity profile taken perpendicular to the major axis of the anomaly was analyzed using linear programming and ideal body theory to obtain bounds on the density contrast, depth, and minimum thickness of the gravity body. Two-dimensionality was assumed.more » The limiting case where the anomalous body reaches the surface gives 0.1 g/cm/sup 3/ as the greatest lower bound on the maximum density contrast. If 0.4 g/cm/sup 3/ is taken as the geologically reasonable upper limit on the maximum density contrast, the least upper bound on the depth of burial is 3.5 km and minimum thickness is 2 km. A shallow mafic intrusion, emplaced sometime before Laramide deformation, is proposed to account for the positive gravity anomaly. Analysis of a magnetotelluric survey suggests that the intrusion is not due to recent basaltic magma associated with the Zuni-Bandera volcanic field. This large basement structure has controlled the development of the volcanic field; vent orientations have changed somewhat through time, but the trend of the volcanic chain followed the edge of the basement structure. It has also exhibited some control on deformation of the sedimentary section.« less

Crustal Fractures of Ophir Planum

NASA Image and Video Library

2002-05-23

This NASA Mars Odyssey image covers a tract of plateau territory called Ophir Planum. The most obvious features in this scene are the fractures ranging from 1 to 5 km wide running from the upper left to lower right.

Analysis of the iron Kα line from 4U 1728-34 with NuSTAR and Swift

NASA Astrophysics Data System (ADS)

Sleator, Clio; Tomsick, John; King, Ashley L.; Miller, Jon M.; Boggs, Steven E.

2016-01-01

We report on a simultaneous NuSTAR and Swift observation of the neutron star low-mass X-ray binary 4U 1728-34. We detected and removed four Type 1 X-ray bursts during the observation in order to study the persistent emission. The continuum spectrum is hard and well described by a black body and cutoff power law. Residuals between 6-8 keV indicate strong evidence of a broad Fe Kα line. By modeling the spectrum with a relativistically blurred reflection model, we find an upper limit for the inner disk radius Rin ≤ 1.77 ISCO. From this upper limit, we find that RNS ≤ 20 km, assuming M=1.4M⊙ and a=0.15 (where a=cJ/GM2 is calculated from the previously measured burst oscillation frequency). We discuss how this limit could be improved for neutron star LMXBs in the future.

Formation of Martian araneiforms by gas-driven erosion of granular material

DOE Office of Scientific and Technical Information (OSTI.GOV)

S. de Villiers; A. Nermoen; B. Jamtveit

Sublimation at the lower surface of a seasonal sheet of translucent CO2 ice at high southern latitudes during the Martian spring, and rapid outflow of the CO2 gas generated in this manner through holes in the ice, has been proposed as the origin of dendritic 100 m-1 km scale branched channels known as spiders or araneiforms and dark dust fans deposited on top of the ice. We show that patterns very similar to araneiforms are formed in a Hele-Shaw cell filled with an unconsolidated granular material by slowly deforming the upper wall upward and allowing it to return rapidly tomore » its original position to drive air and entrained particles through a small hole in the upper wall. Straight, braided and quasiperiodic oscillating channels, unlike meandering channels on Earth were also formed.« less

Crustal characteristic variation in the central Yamato Basin, Japan Sea back-arc basin, deduced from seismic survey results

NASA Astrophysics Data System (ADS)

Sato, Takeshi; No, Tetsuo; Miura, Seiichi; Kodaira, Shuichi

2018-02-01

The crustal structure of the Yamato Bank, the central Yamato Basin, and the continental shelf in the southern Japan Sea back-arc basin is obtained based on a seismic survey using ocean bottom seismographs and seismic shot to elucidate the back-arc basin formation processes. The central Yamato Basin can be divided into three domains based on the crustal structure: the deep basin, the seamount, and the transition domains. In the deep basin domain, the crust without the sedimentary layer is about 12-13 km thick. Very few units have P-wave velocity of 5.4-6.0 km/s, which corresponds to the continental upper crust. In the seamount and transition domains, the crust without the sedimentary layer is about 12-16 km thick. The P-wave velocities of the upper and lower crusts differs among the deep basin, the seamount, and the transition domains. These results indicate that the central Yamato Basin displays crustal variability in different domains. The crust of the deep basin domain is oceanic in nature and suggests advanced back-arc basin development. The seamount domain might have been affected by volcanic activity after basin opening. In the transition domain, the crust comprises mixed characters of continental and oceanic crust. This crustal variation might represent the influence of different processes in the central Yamato Basin, suggesting that crustal development was influenced not only by back-arc opening processes but also by later volcanic activity. In the Yamato Bank and continental shelf, the upper crust has thickness of about 17-18 km and P-wave velocities of 3.3-4.1 to 6.6 km/s. The Yamato Bank and the continental shelf suggest a continental crustal character.

Insights into the emplacement of upper-crustal plutons and their relationship to large silicic calderas, from field relationships, geochronology, and zircon trace element geochemistry in the Stillwater – Clan Alpine caldera complex, western Nevada, USA

USGS Publications Warehouse

Colgan, Joseph P.; John, David A.; Henry, Christopher D.; Watts, Kathryn E.

2018-01-01

Geologic mapping, new U-Pb zircon ages, and new and published 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed at least six nested silicic calderas and underlying granitic plutons to crustal depths locally ≥ 9 km. Both caldera-forming rhyolitic tuffs and underlying plutons were emplaced in two episodes, one from about 30.4–28.2 Ma that included the Deep Canyon, Job Canyon, and Campbell Creek calderas and underlying plutons, and one from about 25.3–24.8 Ma that included the Louderback Mountains, Poco Canyon, and Elevenmile Canyon calderas and underlying plutons. In these two 1–2 m.y. periods, almost the entire Mesozoic upper crust was replaced by Oligocene intrusive and extrusive rocks to depths ≥ 9 km over an estimated total area of ~ 1500 km2 (pre-extension). Zircon trace element geochemistry indicates that some plutonic rock can be solidified residual magma from the tuff eruptions. Most plutons are not solidified residual magma, although they directly underlie calderas and were emplaced along the same structures shortly after to as much as one million years after caldera formation. Magma chambers and plutons grew by floor subsidence accommodated by downward transfer of country rocks. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada is underlain by a complexly zoned mid-Cenozoic batholith assembled in discrete pulses that coincided with formation of large silicic calderas up to 2500–5000 km3.

Geochemical homogeneity of a long-lived, large silicic system; evidence from the Cerro Galán caldera, NW Argentina

NASA Astrophysics Data System (ADS)

Folkes, Chris B.; de Silva, Shanaka L.; Wright, Heather M.; Cas, Raymond A. F.

2011-12-01

By applying a number of analytical techniques across a spectrum of spatial scales (centimeter to micrometer) in juvenile components, we show that the Cerro Galán volcanic system has repeatedly erupted magmas with nearly identical geochemistries over >3.5 Myr. The Cerro Galán system produced nine ignimbrites (˜5.6 to 2 Ma) with a cumulative volume of >1,200 km3 (DRE; dense rock equivalent) of calc-alkaline, high-K rhyodacitic magmas (68-71 wt.% SiO2). The mineralogy is broadly constant throughout the eruptive sequence, comprising plagioclase, quartz, biotite, Fe-Ti oxides, apatite, and titanite. Early ignimbrite magmas also contained amphibole, while the final eruption, the most voluminous Cerro Galán ignimbrite (CGI; 2.08 ± 0.02 Ma) erupted a magma containing rare amphibole, but significant sanidine. Each ignimbrite contains two main juvenile clast types; dominant "white" pumice and ubiquitous but subordinate "grey" pumice. Fe-Ti oxide and amphibole-plagioclase thermometry coupled with amphibole barometry suggest that the grey pumice originated from potentially hotter and deeper magmas (800-840°C, 3-5 kbar) than the more voluminous white pumice (770-810°C, 1.5-2.5 kbar). The grey pumice is interpreted to represent the parental magmas to the Galán system emplaced into the upper crust from a deeper storage zone. Most inter-ignimbrite variations can be accounted for by differences in modal mineralogy and crystal contents that vary from 40 to 55 vol.% on a vesicle-free basis. Geochemical modeling shows that subtle bulk-rock variations in Ta, Y, Nb, Dy, and Yb between the Galán ignimbrites can be reconciled with differences in amounts of crystal fractionation from the "grey" parent magma. The amount of fractionation is inversely correlated with volume; the CGI (˜630 km3) and Real Grande Ignimbrite (˜390 km3) return higher F values (proportion of liquid remaining) than the older Toconquis Group ignimbrites (<50 km3), implying less crystal fractionation took place during the upper-crustal evolution of these larger volume magmas. We attribute this relationship to variations in magma chamber geometry; the younger, largest volume ignimbrites came from flat sill-like magma chambers, reducing the relative proportion of sidewall crystallization and fractionation compared to the older, smaller-volume ignimbrite eruptions. The grey pumice clasts also show evidence of silicic recharge throughout the history of the Cerro Galán system, and recharge days prior to eruption has previously been suggested based on reversely zoned (OH and Cl) apatite phenocrysts. A rare population of plagioclase phenocrysts with thin An-rich rims in juvenile clasts in many ignimbrites supports the importance of recharge in the evolution and potential triggering of eruptions. This study extends the notion that large volumes of nearly identical silicic magmas can be generated repeatedly, producing prolonged geochemical homogeneity from a long-lived magma source in a subduction zone volcanic setting. At Cerro Galán, we propose that there is a zone between mantle magma input and upper crustal chambers, where magmas are geochemically "buffered", producing the underlying geochemical and isotopic signatures. This produces the same parental magmas that are delivered repeatedly to the upper crust. A lower-crustal MASH (melting, assimilation, storage, and homogenization) zone is proposed to act as this buffer zone. Subsequent upper crustal magmatic processes serve only to slightly modify the geochemistry of the magmas.

Stratification of earth's outermost core inferred from SmKS array data

NASA Astrophysics Data System (ADS)

Kaneshima, Satoshi; Matsuzawa, Takanori

2015-12-01

S mKS arrivals recorded by large-scale broadband seismometer arrays are analyzed to investigate the depth profile of P wave speed ( V p ) in the outermost core. The V p structure of the upper 700 km of the outer core has been determined using S mKS waves of Fiji-Tonga events recorded at stations in Europe. According to a recent outer core model (KHOMC), the V p value is 0.45 % slower at the core mantle boundary (CMB) than produced by the Preliminary Reference Earth Model (PREM), and the slow anomaly gradually diminishes to insignificant values at ˜300 km below the CMB. In this study, after verifying these KHOMC features, we show that the differential travel times measured for S mKS waves that are recorded by other large-scale arrays sampling laterally different regions are well matched by KHOMC. We also show that KHOMC precisely fits the observed relative slowness values between S2KS, S3KS, and S4KS (S mKS waves with m= 2, 3, and 4). Based on these observations, we conclude that S mKS predominantly reflect the outer core structure. Then we evaluate biases of secondary importance which may be caused by mantle heterogeneity. The KHOMC V p profile can be characterized by a significant difference in the radial V p gradient between the shallower 300 km and the deeper part of the upper 700 km of the core. The shallower part has a V p gradient of -0.0018 s -1, which is steeper by 0.0001 s -1 when compared to the deeper core presented by PREM. The steeper V p gradient anomaly of the uppermost core corresponds to a radial variation in the pressure derivative of the bulk modulus, K '= d K/ d P. The K ' value is 3.7, which is larger by about 0.2 than that of the deeper core. The radial variation in K ' is too large to have a purely thermal origin, according to recent ab initio calculations on liquid iron alloys, and thus requires a thick and compositionally stratified layering at the outermost outer core.

Mid-range sidescan-sonar images covering parts of proposed tracts for OCS lease sale 56 and contiguous areas, Manteo, Cape Fear, and adjacent quadrangles off North Carolina

USGS Publications Warehouse

Popenoe, Peter; Cashman, K.V.; Chayes, Dale; Ryan, William B. F.

1981-01-01

The U.S. Geological Survey (USGS), in cooperation with the U.S. Bureau of Land Management (BLM) and the Lamont-Doherty Geological Observatory (LDGO), collected 335 km of mid-range sidescan-sonar data in some of the tracts proposed for inclusion in Federal OCS (Outer Continental Shelf) Oil and Gas Lease Sale 56 and in some contiguous areas (R.V. GYRE, September 18-25, 1980 [GYRE 80-9, leg 1]). The data were collected by use of the Sea Mark I mid-range sidescan-sonar system designed by International Submarine Technology, Ltd. (IST). This system surveys a swath having a width of approximately 2-1/2 km on each side of the deep-towed fish. Transducers were towed about 300 m above the bottom on a neutrally bouyant vehicle at a speed of 1-1/2 to 2 knots. Transducers were pulsed at 4-second intervals at a frequency of 27 kHz on one side and 30 kHz on the other. Data recorded on seven EPC recorders aboard ship included slant-range corrected port channel, starboard channel, and port and starboard channels; uncorrected port channel, starboard channel, and port and starboard channels, and a 3.5-kHz tuned-transducer record of the bottom. Fish height or the altitude above the bottom was recorded on a strip-chart recorder. Distance of the fish from the ship (slant range) was recorded by use of a sled-mounted 4.5-kHz transducer.Data recorded on sonograms lagged the 3.5-kHz tuned-transducer record and ship navigational fix by as much as 1 hour (2 km) owing to tow-cable length (up to 5 km). Navigation of the ship was by Loran-C at a 5-minute fix interval, supplemented by satellite fixes.Data are of excellent quality and bottom features several meters high and about 6-12 m wide can be identified. Figures 1 and 2 show the location of track lines in the Manteo (NI 18-2) quadrangle just east of Cape Hatteras where the upper slope within proposed lease tract areas was surveyed. Figures 3 and 4 show track lines in the Cape Fear (NI 18-7) and contiguous quandrangles where data were recorded over the outer Blake Plateau, the Continental Slope, and the upper Continental Rise.The original records may be examined at the U.S. Survey, Woods Hole, MA 02543. Microfilm copies of the data are available for purchase only from the National Geophysical and Solar-Terrestrial Data c,nt er, NOAA/EDIS/NGSDC, Code D621, 325 Broadway, Boulder, CO 80303 (303-497-6338).

Magmatic plumbing system from lower mantle of Hainan plume

NASA Astrophysics Data System (ADS)

Xia, Shaohong; Sun, Jinlong; Xu, Huilong; Huang, Haibo; Cao, Jinghe

2017-04-01

Intraplate volcanism during Late Cenozoic in the Leiqiong area of southernmost South China, with basaltic lava flows covering a total of more than 7000 km2, has been attributed to an underlying Hainan plume. However, detailed features of Hainan plume, such as morphology of magmatic conduits, depth of magmatic pool in the upper mantle and pattern of mantle upwelling, are still enigmatic. Here we present seismic tomographic images of the upper 1100 km of the mantle beneath the southern South China. Our results show a mushroom-like continuous low-velocity anomaly characterized by a columnar tail with diameter of about 200-300 km that tilts downward to lower mantle beneath north of Hainan hotspot and a head that spreads laterally near the mantle transition zone, indicating a magmatic pool in the upper mantle. Further upward, this head is decomposed into small patches, but when encountering the base of the lithosphere, a pancake-like anomaly is shaped again to feed the Hainan volcanism. Our results challenge the classical model of a fixed thermal plume that rises vertically to the surface, and propose the new layering-style pattern of magmatic upwelling of Hainan plume. This work indicates the spatial complexities and differences of global mantle plumes probably due to heterogeneous compositions and changefully thermochemical structures of deep mantle.

Multi-Satellite Measurements and Model Predictions of Mesospheric and Upper Stratospheric Influences from the Very Large July 14-16, 2000, Solar Proton Event

NASA Technical Reports Server (NTRS)

Jackman, Charles H.; McPeters, Richard D.; Russell, James M.; Bevilacqua, Richard; Labow, Gordon J.; Fleming, Eric L.; Einaudi, Franco (Technical Monitor)

2000-01-01

A large solar flare with an associated coronal mass ejection occurred in mid-July and caused a very large solar proton event at the earth in the time period July 14-16, 2000. So far this is the largest solar storm of solar cycle 23. The solar proton fluxes were measured by instruments aboard the GOES-10 satellite and used in our proton energy deposition model to help quantify the energy input to the middle atmosphere during this large solar event. Using this computed energy deposition in the GSFC 2D atmospheric model resulted in a prediction of $>$ 20\\% increases in HO$-(x)$ (H, OH, HO$-(2)$) and $>$ 100\\% increases in NO$-(x)$ (N, NO, NO$-(2)$) constituents in the mesosphere and upper stratosphere at polar latitudes ($>$ 60 degrees geomagnetic). Both the HO$-(x)$ and NO$_fx)$ increases impacted ozone. Large atmospheric impacts have been measured with the NOAA 14 SBUV/2 instrument (0$_(3)$), the UARS HALOE instrument (NO, NO$-(2)$, 0$-(3)$), and the POAM III instrument (0$_{3}$, NO$-(2)$). Preliminary analysis indicates that measured (SBUV/2) and modelled 0$_{3}$ decreases from this solar event are generally in agreement in the Northern Hemisphere. Short-term ozone changes (during the event) indicate $\\sim$ 15% reduction at 2 hPa ($\\sim$ 45 km) up to $\\sim$ 40% reduction at 0.5 hPa ($\\sim$ 55 km). A longer-term ozone depletion of $\\sim$ 5% is indicated between 4 and 2 hPa ($\\sim$ 40-45 km). The middle atmospheric changes caused by this solar event were very large and occurred fairly quickly ($\\sim$ 1-2 days). Such a significant natural perturbation provides a good test of our understanding of the middle atmosphere. The measured and modelled impacts of this solar event will be compared and discussed in this paper.

Effects of detrital influx in the Pennsylvanian Upper Freeport peat swamp

USGS Publications Warehouse

Ruppert, L.F.; Stanton, R.W.; Blaine, Cecil C.; Eble, C.F.; Dulong, F.T.

1991-01-01

Quartz cathodoluminescence properties and mineralogy of three sets of samples and vegetal and/ or miospore data from two sets of samples from the Upper Freeport coal bed, west-central Pennsylvania, show that detrital influence from a penecontemporaneous channel is limited to an area less than three km from the channel. The sets of samples examined include localities of the coal bed where (1) the coal is thin, split by partings, and near a penecontemporaneous fluvial channel, (2) the coal is relatively thick and located approximately three km from the channel, and (3) the coal is thick and located approximately 12 km from the channel. Samples from locality 1 (nearest the channel) have relatively high-ash yields (low-temperature ash average = 27.3% on a pyrite- and calcite-free basis) and high proportions of quartz and clay minerals. The quartz is primarily detrital, as determined by cathodoluminescent properties, and the ratio of kaolinite to illite is low. In addition, most of the plant remains and miospores indicate peat-forming plants that required low nutrient levels for growth. In contrast, samples from localities 2 and 3, from the more interior parts of the bed, contained predominantly authigenic quartz grains nd yielded low-temperature ash values of less than 14% on a pyrite- and calcite-free basis. The low-temperature ash contains low concentrations of quartz and clay minerals and the ratio of kaolinite to illite is relatively high. Although intact core was not available for paleobotanical analyses, another core collected within 1 km from locality 3 contained plant types interpreted to have required high nutrient levels for growth. These data indicate that mineral formation is dominated by authigenic processes in interior parts of the coal body. Some of the authigenic quartz may have been derived from herbaceous ferns as indicated by patterns in the palynological and paleobotanical data. In contrast, detrital processes appeared to be limited to in areas directly adjacent to the penecontemporaneous channel where the coal bed is high in ash, split by mineral-rich partings, and of little or no economic value. ?? 1991.

New Insights on Seismicity and the Velocity Structure beneath the Western Segment of the North Anatolian Fault Zone

NASA Astrophysics Data System (ADS)

Teoman, U.; Altuncu Poyraz, S.; Kahraman, M.; Mutlu, A. K.; Cambaz, D.; Turkelli, N.; Thompson, D. A.; Rost, S.; Houseman, G. A.; Utkucu, M.

2014-12-01

To extensively investigate the upper crustal structure beneath the western segment of the North Anatolian Fault Zone (NAFZ) in Sakarya and the surroundings, a temporary seismic network consisting of 70 stations (with nearly 7km station spacing) was deployed in early May 2012 and operated for 18 months during the Faultlab experiment encompassing both the northern and southern strands of the fault in between the area of 1999 İzmit and Düzce mainshock ruptures. With the help of this new and extensive data set, our main objective is to provide new insights on the most recent micro-seismic activity and the velocity structure beneath the region. Out of 2437 events contaminated by the explosions, we extracted 1344 well located earthquakes with a total of 31595 P and 18512 S phase readings which lead to an avarage Vp/Vs ratio of ~1.82 extracted from the wadati diagram. The enhanced station coverage decreased the magnitude threshold to 0.1 where the horizontal and vertical location errors did not exceed 0.5 km and 2.0 km, respectively. Average RMS values were calculated within the range of 0.05-0.4 seconds. We observed significant seismic activity along both branches of the fault where the depth of the seismogenic zone was confined to 15 km. Focal parameters of 41 earthquakes with magnitudes greater than 1.8 were also determined using both Regional Moment Tensor Inversion and P first arrival time methods. Focal mechanism solutions confirm that Sakarya and its vicinity could be defined by a compressional regime showing a primarily oblique-slip motion character. Furthermore, we selected the earthquakes recorded by at least 8 stations with azimuthal gaps less than 200° for the ongoing tomographic inversion that would enable us to accurately map the complex upper crustal velocity structure with high resolution beneath this segment of the NAFZ.

Long-term Behaviour Of Venus Winds At Cloud Level From Virtis/vex Observations

NASA Astrophysics Data System (ADS)

Hueso, Ricardo; Peralta, J.; Sánchez-Lavega, A.; Pérez-Hoyos, S.; Piccioni, G.; Drossart, P.

2009-09-01

The Venus Express (VEX) mission has been in orbit to Venus for more than three years now. The VIRTIS instrument onboard VEX observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet. Images in the ultraviolet range are used to study the upper cloud at 66 km while images in the infrared (1.74 μm) map the opacity of the lower cloud deck at 48 km. Here we present an analysis of the overall dynamics of Venus’ atmosphere at both levels using observations that cover a large fraction of the VIRTIS dataset. We will present our latest results concerning the zonal winds, the overall stability in the lower cloud deck motions and the variability in the upper cloud. Meridional winds are also observed in the upper and lower cloud in the UV and IR images obtained with VIRTIS. While the upper clouds present a net meridional motion consistent with the upper branch of a Hadley cell the lower cloud present more irregular, variable and less intense motions in the meridional direction. Acknowledgements This work has been funded by Spanish MEC AYA2006-07735 with FEDER support and Grupos Gobierno Vasco IT-464-07. RH acknowledges a "Ramón y Cajal” contract from MEC.

Mechanical stratification during extreme sediment accretion in the Indo-Burman Ranges: geological and theoretical constraints on the megathrust geometry

NASA Astrophysics Data System (ADS)

Betka, P. M.; Seeber, L.; Buck, W. R.; Steckler, M. S.; Sincavage, R.; Zoramthara, C.; Thomson, S.

2017-12-01

The Indo-Burma Ranges (IBR) are the result of ongoing oblique subduction along the northern Sunda subduction zone and accretion of the 19 km thick Ganges-Brahmaputra delta. The IBR forearc is subaerial and in one of the most densely populated (>200M people) regions of the planet, with the potential to generate a >Mw 8.2 megathrust earthquake. Despite the seismic hazard, the structure of the accretionary prism and up-dip part of the megathrust is poorly known. We present a geologically constrained structural model of the frontal part ( 150 km wide) of the IBR. A shallow, 3.1-3.2 ± 0.1 km deep, blind, subhorizontal décollement separates sandy shallow marine and fluvial deposits in the upper plate from under-thrust, fine-grained deep marine strata that are overpressured. Upper plate shortening of 42 ­± 6 km yields a minimum geologic shortening rate of 4.6 mm/yr based on maximum detrital ages ( 9 Ma) of the deformed strata, about 35% of the geodetic convergence rate ( 13-17 mm/yr). The existence of the shallow décollement implies that either the 16 km thick sediment pile below it is subducted, or an additional, deep, blind décollement must exist to accrete the incoming sediment. We combine the structural results with critical taper theory and mechanical modeling to predict a range of plausible megathrust geometries. The IBR has an extremely low slope (0.1-0.5˚), thus, highly elevated pore-fluid pressures (>0.95 of the lithostatic pressure) are required to produce the low taper (0.3-0.6˚). These theoretical constraints are consistent with pore-fluid pressure ratios of 0.92-0.97 that were measured at 3 km depth in a well that pierces an anticline near the front of the wedge. We carried out a numerical modeling experiment to predict the formation of the shallow décollement. If the effective friction coefficient for several layers of the core of the wedge is reduced by a factor of 15 to account for high pore-fluid pressures, two subhorizontal décollements localize at the top and bottom of the weak overpressured zone. A ramp that links the two décollements propagates forward to accrete the incoming sediment. We argue that a mechanically stratified incoming sedimentary pile may result in the formation of multiple décollement horizons, and thus, influence the development of the critical wedge and the magnitude of the seismic hazard.

Combined Constraints on the Equation of State of Dense Neutron-rich Matter from Terrestrial Nuclear Experiments and Observations of Neutron Stars

NASA Astrophysics Data System (ADS)

Zhang, Nai-Bo; Li, Bao-An; Xu, Jun

2018-06-01

Within the parameter space of the equation of state (EOS) of dense neutron-rich matter limited by existing constraints mainly from terrestrial nuclear experiments, we investigate how the neutron star maximum mass M max > 2.01 ± 0.04 M ⊙, radius 10.62 km < R 1.4 < 12.83 km and tidal deformability Λ1.4 ≤ 800 of canonical neutron stars together constrain the EOS of dense neutron-rich nucleonic matter. While the 3D parameter space of K sym (curvature of nuclear symmetry energy), J sym, and J 0 (skewness of the symmetry energy and EOS of symmetric nuclear matter, respectively) is narrowed down significantly by the observational constraints, more data are needed to pin down the individual values of K sym, J sym, and J 0. The J 0 largely controls the maximum mass of neutron stars. While the EOS with J 0 = 0 is sufficiently stiff to support neutron stars as massive as 2.37 M ⊙, supporting the hypothetical ones as massive as 2.74 M ⊙ (composite mass of GW170817) requires J 0 to be larger than its currently known maximum value of about 400 MeV and beyond the causality limit. The upper limit on the tidal deformability of Λ1.4 = 800 from the recent observation of GW170817 is found to provide upper limits on some EOS parameters consistent with but far less restrictive than the existing constraints of other observables studied.

A chemical perspective of day and night tropical (10°N-15°N) mesospheric inversion layers

NASA Astrophysics Data System (ADS)

Ramesh, K.; Sridharan, S.; Raghunath, K.; Rao, S. Vijaya Bhaskara

2017-03-01

The various occurrence characteristics of day and night tropical (10°N-15°N, 60°E-90°E) mesospheric inversion layers (MILs) are studied by using TIMED Sounding of the Atmosphere using Broadband Emission Radiometry satellite data products of kinetic temperature; volume mixing ratios of O, H, and O3; volume emission rates of O2 (1Δ) and OH (1.6 µm channel), and chemical heating rates due to seven dominant exothermic reactions among H, O, O2, O3, OH, HO2, and CO2 cooling rates for the year 2011. Although both dynamics and chemistry play important roles, the present study mainly focuses on the chemical processes involved in the formation of day and night MILs. It is found that the upper level height of daytime (nighttime) MIL descends (ascends) from 88 km ( 80 km) in winter to 72 km ( 90 km) in summer. The day and night inversion amplitudes are correlated with total chemical heating rates and CO2 cooling rates, and they show semi annual variation with larger (smaller) values during equinoxes (solstices). The daytime (nighttime) inversion layers are predominantly due to the exothermic reaction, R5: O + O + M → O2 + M and R6: O + O2 + M → O3 + M (R3: H + O3 → OH + O2). In addition, the CO2 causes large cooling at the top and small heating at the bottom levels of both day and night MILs. In the absence of dynamical effects, the chemical heating and CO2 cooling jointly contribute for the occurrence of day and night MILs.

Evidence of a significant rotational non-LTE effect in the CO2 4.3 µm PFS-MEX limb spectra

NASA Astrophysics Data System (ADS)

Kutepov, Alexander A.; Rezac, Ladislav; Feofilov, Artem G.

2017-01-01

Since January 2004, the planetary Fourier spectrometer (PFS) on board the Mars Express satellite has been recording near-infrared limb spectra of high quality up to the tangent altitudes ≈ 150 km, with potential information on density and thermal structure of the upper Martian atmosphere. We present first results of our modeling of the PFS short wavelength channel (SWC) daytime limb spectra for the altitude region above 90 km. We applied a ro-vibrational non-LTE model based on the stellar astrophysics technique of accelerated lambda iteration (ALI) to solve the multi-species and multi-level CO2 problem in the Martian atmosphere. We show that the long-standing discrepancy between observed and calculated spectra in the cores and wings of 4.3 µm region is explained by the non-thermal rotational distribution of molecules in the upper vibrational states 10011 and 10012 of the CO2 main isotope second hot (SH) bands above 90 km altitude. The redistribution of SH band intensities from band branch cores into their wings is caused (a) by intensive production of the CO2 molecules in rotational states with j > 30 due to the absorption of solar radiation in optically thin wings of 2.7 µm bands and (b) by a short radiative lifetime of excited molecules, which is insufficient at altitudes above 90 km for collisions to maintain rotation of excited molecules thermalized. Implications for developing operational algorithms for massive processing of PFS and other instrument limb observations are discussed.

Effect of eight weeks of upper-body plyometric training during the competitive season on professional female volleyball players.

PubMed

Valades, David; Palao, José M; Femia, Pedro; Ureña, Aurelio

2017-07-25

The purpose of this study was to assess the effect of incorporating specific upper-body plyometric training for the spike into the competitive season of a women's professional volleyball team. A professional team from the Spanish first division participated in the study. An A-B-A' quasi-experimental design with experimental and control groups was used. The independent variable was the upper-body plyometric training for eight weeks during the competitive season. The dependent variables were the spiked ball's speed (Km/h); the player's body weight (Kg), BMI (Kg/m2), and muscle percentage in arms (%); 1 repetition maximum (1RM) in the bench press (Kg); 1RM in the pullover (Kg); and overhead medicine ball throws of 1, 2, 3, 4, and 5 kg (m). Inter-player and inter-group statistical analyses of the results were carried out (Wilcoxon test and linear regression model). The experimental group significantly improved their spike speed 3.8% from phase A to phase B, and they maintained this improvement after the retention phase. No improvements were found in the control group. The experimental group presented a significant improvement from phase A to phase B in dominant arm muscle area (+10.8%), 1RM for the bench press (+8.41%), 1RM for the pullover (+14.75%), and overhead medicine ball throws with 1 kg (+7.19%), 2 kg (+7.69%), and 3 kg (+5.26%). The control group did not present differences in these variables. Data showed the plyometric exercises that were tested could be used by performance-level volleyball teams to improve spike speed. The experimental group increased their upper-body maximal strength, their power application, and spike speed.

The crustal structure of the north-eastern Gulf of Aden continental margin: insights from wide-angle seismic data

NASA Astrophysics Data System (ADS)

Watremez, L.; Leroy, S.; Rouzo, S.; D'Acremont, E.; Unternehr, P.; Ebinger, C.; Lucazeau, F.; Al-Lazki, A.

2011-02-01

The wide-angle seismic (WAS) and gravity data of the Encens survey allow us to determine the deep crustal structure of the north-eastern Gulf of Aden non-volcanic passive margin. The Gulf of Aden is a young oceanic basin that began to open at least 17.6 Ma ago. Its current geometry shows first- and second-order segmentation: our study focusses on the Ashawq-Salalah second-order segment, between Alula-Fartak and Socotra-Hadbeen fracture zones. Modelling of the WAS and gravity data (three profiles across and three along the margin) gives insights into the first- and second-order structures. (1) Continental thinning is abrupt (15-20 km thinning across 50-100 km distance). It is accommodated by several tilted blocks. (2) The ocean-continent transition (OCT) is narrow (15 km wide). The velocity modelling provides indications on its geometry: oceanic-type upper-crust (4.5 km s-1) and continental-type lower crust (>6.5 km s-1). (3) The thickness of the oceanic crust decreases from West (10 km) to the East (5.5 km). This pattern is probably linked to a variation of magma supply along the nascent slow-spreading ridge axis. (4) A 5 km thick intermediate velocity body (7.6 to 7.8 km s-1) exists at the crust-mantle interface below the thinned margin, the OCT and the oceanic crust. We interpret it as an underplated mafic body, or partly intruded mafic material emplaced during a `post-rift' event, according to the presence of a young volcano evidenced by heat-flow measurement (Encens-Flux survey) and multichannel seismic reflection (Encens survey). We propose that the non-volcanic passive margin is affected by post-rift volcanism suggesting that post-rift melting anomalies may influence the late evolution of non-volcanic passive margins.

Chemical Characteristics of Continental Outflow Over the Tropical South Atlantic Ocean from Brazil and Africa

NASA Technical Reports Server (NTRS)

Talbot, R. W.; Bradshaw, J. D.; Sandholm, S. T.; Smyth, S.; Blake, D. R.; Blake, N. R.; Sachse, G. W.; Collins, J. E.; Heikes, B. G.; Anderson, B. E.;

Cerberus Plains: A most excellent Pathfinder landing site

NASA Technical Reports Server (NTRS)

Plescia, Jeff B.

1994-01-01

The Cerberus Plains in southeastern Elysium and western Amazonis cover greater than 10(exp 5) sq km, extending an east-west distance of approximately 3000 km and a north-south distance of up to 700 km near 195 deg. Crater numbers are 89 plus or minus 15 craters greater than 1 km/10(exp 6) sq km, indicating a stratigraphic age of Upper Amazonian and an absolute age of 200-500 Ma. The material forming the surface is referred to as the Cerberus Formation. The two ideas postulated about the unit's origin are fluvial and volcanic. Regardless of which interpretation is correct, the Cerberus Plains is an important candidate for a pathfinder landing site because it represents the youngest major geologic event (be it fluvial or volcanic) on Mars.

Crustal-scale shear zones and heterogeneous structure beneath the North Anatolian Fault Zone, Turkey, revealed by a high-density seismometer array

NASA Astrophysics Data System (ADS)

Kahraman, Metin; Cornwell, David G.; Thompson, David A.; Rost, Sebastian; Houseman, Gregory A.; Türkelli, Niyazi; Teoman, Uğur; Altuncu Poyraz, Selda; Utkucu, Murat; Gülen, Levent

2015-11-01

Continental scale deformation is often localised along strike-slip faults constituting considerable seismic hazard in many locations. Nonetheless, the depth extent and precise geometry of such faults, key factors in how strain is accumulated in the earthquake cycle and the assessment of seismic hazard, are poorly constrained in the mid to lower crust. Using a dense broadband network of 71 seismic stations with a nominal station spacing of 7 km in the vicinity of the 1999 Izmit earthquake we map previously unknown small-scale structure in the crust and upper mantle along this part of the North Anatolian Fault Zone (NAFZ). We show that lithological and structural variations exist in the upper, mid and lower crust on length scales of less than 10 km and less than 20 km in the upper mantle. The surface expression of the NAFZ in this region comprises two major branches; both are shown to continue at depth with differences in dip, depth extent and (possibly) width. We interpret a <10 km wide northern branch that passes downward into a shear zone that traverses the entire crust and penetrates the upper mantle to a depth of at least 50 km. The dip of this structure appears to decrease west-east from ∼90° to ∼65° to the north over a distance of 30 to 40 km. Deformation along the southern branch may be accommodated over a wider (>10 km) zone in the crust with a similar variation of dip but there is no clear evidence that this shear zone penetrates the Moho. Layers of anomalously low velocity in the mid crust (20-25 km depth) and high velocity in the lower crust (extending from depths of 28-30 km to the Moho) are best developed in the Armutlu-Almacik block between the two shear zones. A mafic lower crust, possibly resulting from ophiolitic obduction or magmatic intrusion, can best explain the coherent lower crustal structure of this block. Our images show that strain has developed in the lower crust beneath both northern and southern strands of the North Anatolian Fault. Our new high resolution images provide new insights into the structure and evolution of the NAFZ and show that a small and dense passive seismic network is able to image previously undetectable crust and upper mantle heterogeneity on lateral length scales of less than 10 km.

Magsat equivalent source anomalies over the southeastern United States - Implications for crustal magnetization

NASA Technical Reports Server (NTRS)

Ruder, M. E.; Alexander, S. S.

1986-01-01

The Magsat crustal anomaly field depicts a previously-unidentified long-wavelength negative anomaly centered over southeastern Georgia. Examination of Magsat ascending and descending passes clearly identifies the anomalous region, despite the high-frequency noise present in the data. Using ancillary seismic, electrical conductivity, Bouguer gravity, and aeromagnetic data, a preliminary model of crustal magnetization for the southern Appalachian region is presented. A lower crust characterized by a pervasive negative magnetization contrast extends from the New York-Alabama lineament southeast to the Fall Line. In southern Georgia and eastern Alabama (coincident with the Brunswick Terrane), the model calls for lower crustal magnetization contrast of -2.4 A/m; northern Georgia and the Carolinas are modeled with contrasts of -1.5 A/m. Large-scale blocks in the upper crust which correspond to the Blue Ridge, Charlotte belt, and Carolina Slate belt, are modeled with magnetization contrasts of -1.2 A/m, 1.2 A/m, and 1.2 A/m respectively. The model accurately reproduces the amplitude of the observed low in the equivalent source Magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass-filtered aeromagnetic map of the region.

Airborne CH2O measurements over the North Atlantic during the 1997 NARE campaign: Instrument comparisons and distributions

NASA Astrophysics Data System (ADS)

Fried, Alan; Lee, Yin-Nan; Frost, Greg; Wert, Bryan; Henry, Bruce; Drummond, James R.; Hübler, Gerd; Jobson, Tom

2002-02-01

Airborne CH2O measurements were acquired by tunable diode laser absorption spectroscopy (TDLAS) and coil/2,4-dinitrophenylhydrazine (CDNPH) techniques over remote regions of the North Atlantic Ocean from the surface to 8 km during the North Atlantic Regional Experiment (NARE-97) in September of 1997. There were eight aircraft flights when both instruments were simultaneously operating, producing 665 overlapping time intervals for comparisons. A number of approaches were used in the comparisons, and indicated that on average both instruments measured identical ambient CH2O concentrations to within 0.1 ppbv, and more typically within 0.08 ppbv, over the 0 to 0.8 ppbv-concentration range. However, significant differences, larger than the combined 2σ total uncertainty estimates, were observed in 29% of the full time-coincident data set. The two instruments produced very similar altitude trends. Under clean background conditions in the 35° to 55°N latitude band, the median TDLAS and CDNPH CH2O concentrations were 0.399 and 0.410 ppbv for 0-2 km, 0.250 and 0.355 ppbv for 2-4 km, and 0.217 and 0.280 ppbv for 4-8 km, respectively. Elevated CH2O concentrations were observed in this study at both high altitudes (4-8 km) and in the marine boundary layer by both instruments. Thus vertical transport of CH2O and/or its precursors may provide a greater contribution to upper tropospheric HOx than previously thought. The results of this study, which are based upon instruments employing entirely different measurement principles, calibration, and sampling approaches, not only reinforce this conclusion but also provide a high-quality database necessary to further explore CH2O measurement-model relationships in the clean background atmosphere.

Kinetic analysis of the function of the upper body for elite race walkers during official men 20 km walking race.

PubMed

Hoga-Miura, Koji; Ae, Michiyoshi; Fujii, Norihisa; Yokozawa, Toshiharu

2016-10-01

This study investigated the function of the upper extremities of elite race walkers during official 20 km races, focusing on the angular momentum about the vertical axis and other parameters of the upper extremities. Sixteen walkers were analysed using the three-dimensional direct linear transformation method during three official men's 20 km walking races. The subjects, included participants at the Olympics and World Championships, who finished without disqualification and had not been disqualified during the two years prior to or following the races analysed in the present study. The angular momenta of the upper and lower body were counterbalanced as in running and normal walking. The momentum of the upper body was mainly generated by the upper extremities. The joint force moment of the right shoulder and the joint torque at the left shoulder just before right toe-off were significantly correlated with the walking speed. These were counterbalanced by other moments and torques to the torso torque, which worked to obtain a large mechanical energy flow from the recovery leg to the support leg in the final phase of the support phase. Therefore, a function of the shoulder torque was to counterbalance the torso torque to gain a fast walking speed with substantial mechanical energy flow.

Concentrations of CH4, CO, CO2, H2, H2O and N2O in the upper stratosphere

NASA Technical Reports Server (NTRS)

Ehhalt, D. H.; Heidt, L. E.; Lueb, R. H.; Martell, E. A.

1975-01-01

On 23 May 1973 a cryogenic air sampler was flown on an Aerobee rocket from White Sands Missile Range. A large air sample was collected between 40 and 50 km altitude and successfully recovered for water vapor and trace gas analysis. The results were as follows: water vapor, 4.0 (+1.3 or - 0.9) ppmV; methane, 0.37 + or - 0.01 ppmV; molecular hydrogen, 0.47 + or - 0.02 ppmV; carbon monoxide, 0.05 + or - 0.01 ppmV; carbon dioxide, 316.2 + or - 2.8 ppmV; and nitrous oxide, 3 + or - 7 ppb.

Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

USGS Publications Warehouse

Han, Liang; Hole, John; Stock, Joann; Fuis, Gary S.; Williams, Colin F.; Delph, Jonathan; Davenport, Kathy; Livers, Amanda

2016-01-01

Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65–90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ∼7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from ∼1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at ∼3 km depth in most of the valley, but at only ∼1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the ≥2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7–8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust.

Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

NASA Astrophysics Data System (ADS)

Han, Liang; Hole, John A.; Stock, Joann M.; Fuis, Gary S.; Williams, Colin F.; Delph, Jonathan R.; Davenport, Kathy K.; Livers, Amanda J.

2016-11-01

Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65-90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ˜7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from ˜1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at ˜3 km depth in most of the valley, but at only ˜1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the ≥2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7-8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust.

Retrieval of temperature profiles from CHAMP for climate monitoring: intercomparison with Envisat MIPAS and GOMOS and different atmospheric analyses

NASA Astrophysics Data System (ADS)

Gobiet, A.; Kirchengast, G.; Manney, G. L.; Borsche, M.; Retscher, C.; Stiller, G.

2007-07-01

This study describes and evaluates a Global Navigation Satellite System (GNSS) radio occultation (RO) retrieval scheme particularly aimed at delivering bias-free atmospheric parameters for climate monitoring and research. The focus of the retrieval is on the sensible use of a priori information for careful high-altitude initialisation in order to maximise the usable altitude range. The RO retrieval scheme has been meanwhile applied to more than five years of data (September 2001 to present) from the German CHAllenging Minisatellite Payload for geoscientific research (CHAMP) satellite. In this study it was validated against various correlative datasets including the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and the Global Ozone Monitoring for Occultation of Stars (GOMOS) sensors on Envisat, five different atmospheric analyses, and the operational CHAMP retrieval product from GeoForschungsZentrum (GFZ) Potsdam. In the global mean within 10 to 30 km altitude we find that the present validation observationally constrains the potential RO temperature bias to be <0.2 K. Latitudinally resolved analyses show biases to be observationally constrained to <0.2-0.5 K up to 35 km in most cases, and up to 30 km in any case, even if severely biased (about 10 K or more) a priori information is used in the high altitude initialisation of the retrieval. No evidence is found for the 10-35 km altitude range of residual RO bias sources other than those potentially propagated downward from initialisation, indicating that the widely quoted RO promise of "unbiasedness and long-term stability due to intrinsic self-calibration" can indeed be realised given care in the data processing to strictly limit structural uncertainty. The results thus reinforce that adequate high-altitude initialisation is crucial for accurate stratospheric RO retrievals. The common method of initialising, at some altitude in the upper stratosphere, the hydrostatic integral with an upper boundary temperature or pressure value derived from meteorological analyses is prone to introduce biases from the upper boundary down to below 25 km. Also above 30 to 35 km, GNSS RO delivers a considerable amount of observed information up to around 40 km, which is particularly interesting for numerical weather prediction (NWP) systems, where direct assimilation of non-initialised observed RO bending angles (free of a priori) is thus the method of choice. The results underline the value of RO for climate applications.

Search for OH 18 cm Radio Emission from 1I/2017 U1 with the Green Bank Telescope

NASA Astrophysics Data System (ADS)

Park, Ryan S.; Pisano, D. J.; Lazio, T. Joseph W.; Chodas, Paul W.; Naidu, Shantanu P.

2018-05-01

This paper reports the first OH 18 cm line observation of the first detected interstellar object 1I/2017 U1 (‘Oumuamua) using the Green Bank Telescope. We have observed the OH lines at 1665.402, 1667.359, and 1720.53 MHz frequencies with a spectral resolution of 357 Hz (approximately 0.06 km s‑1). At the time of the observation, ‘Oumuamua was at topocentric distance and velocity of 1.07 au and 63.4 km s‑1, respectively, or at heliocentric distance and velocity of 1.8 au and 39 km s‑1, respectively. Based on a detailed data reduction and an analogy-based inversion, our final results confirm the asteroidal origin of ‘Oumuamua with an upper bound OH production of Q[OH] < 0.17 × 1028 s‑1.

Gravity Recovery and Interior Laboratory (GRAIL): Extended Mission and End-Game Status

NASA Technical Reports Server (NTRS)

Zuber, Maria T.; Smith, David E.; Wieczorek, Mark A.; Williams, James G.; Andrews-Hanna, Jeffrey C.; Head, James W.; Kiefer, Walter S.; Matsuyama, Isamu; McGovern, Patrick J.; Nimmo, Francis;

Exploration of Venus with the Venera-15 IR Fourier spectrometer and the Venus Express planetary Fourier spectrometer

NASA Astrophysics Data System (ADS)

Zasova, L. V.; Moroz, V. I.; Formisano, V.; Ignatiev, N. I.; Khatuntsev, I. V.

2006-07-01

The infrared spectrometry of Venus in the range 6-45 μm allows one to sound the middle atmosphere of Venus in the altitude range 55-100 km and its cloud layer. This experiment was carried out onboard the Soviet automatic interplanetary Venera-15 station, where the Fourier spectrometer for this spectral range was installed. The measurements have shown that the main component of the cloud layer at all measured latitudes in the northern hemisphere is concentrated sulfuric acid (75-85%). The vertical profiles of temperature and aerosol were reconstructed in a self-consistent manner: the three-dimensional fields of temperature and zonal wind in the altitude range 55-100 km and aerosol at altitudes 55-70 km have been obtained, as well as vertical SO2 profiles and H2O concentration in the upper cloud layer. The solar-related waves at isobaric levels in the fields of temperature, zonal wind, and aerosol were investigated. This experiment has shown the efficiency of the method for investigation of the Venusian atmosphere. The Planetary Fourier Spectrometer has the spectral interval 0.9-45 μm and a spectral resolution of 1.8 cm-1. It will allow one to sound the middle atmosphere (55-100 km) of Venus and its cloud layer on the dayside, as well as the lower atmosphere and the planetary surface on the night side.

Geologic setting of Boulder 1, Station 2, Apollo 17 landing site

USGS Publications Warehouse

Wolfe, E.W.

1975-01-01

Boulder 1 at Station 2 is one of three boulders sampled by Apollo 17 at the base of the South Massif, which rises 2.3 km above the floor of a linear valley interpreted as a graben formed by deformation related to the southern Serenitatis impact. The boulders probably rolled from the upper part of the massif after emplacement of the light mantle. Orbital gravity data and photogeologic reinterpretation suggest that the Apollo 17 area is located approximately on the third ring of the southern Serenitatis basin, approximately 1.25 times larger than the analogous but fresher Orientale basin structure. The massif exposures are interpreted to represent the upper part of thick ejecta deposited by the southern Serenitatis impact near the rim of the transient cavity. Basin ring structure and the radial grabens that give the massifs definition were imposed on this ejecta at a slightly later stage in the basin-forming process. There is no clear-cut compositional, textural, or photogeologic evidence that Imbrium ejecta was collected at the Apollo 17 site. ?? 1975 D. Reidel Publishing Company, Dordrecht-Holland.

Gravity Waves and Mesospheric Clouds in the Summer Middle Atmosphere: A Comparison of Lidar Measurements and Ray Modeling of Gravity Waves Over Sondrestrom, Greenland

NASA Technical Reports Server (NTRS)

Gerrard, Andrew J.; Kane, Timothy J.; Eckermann, Stephen D.; Thayer, Jeffrey P.

2004-01-01

We conducted gravity wave ray-tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67N, 310 deg E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three-dimensional daily-varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi-vertically from 40-80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally-inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real-time runs with the model in 2001 using weather forecast data as a low-level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.