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Sample records for 660-km seismic discontinuity

  1. Effect of water in depleted mantle on post-spinel transition and implication for 660 km seismic discontinuity

    NASA Astrophysics Data System (ADS)

    Ghosh, Sujoy; Ohtani, Eiji; Litasov, Konstantin D.; Suzuki, Akio; Dobson, David; Funakoshi, Kenichi

    2013-06-01

    We have determined the post-spinel transition boundary in anhydrous and hydrous Mg2SiO4 in a temperature range from 1173 to 2023 K at 19.3-25.4 GPa using synchrotron in situ X-ray diffraction measurements. The phase boundary in Mg2SiO4 is located at 22 GPa and 1800 K and 22.1 GPa and 1500 K, which is slightly lower (~0.3-0.5 GPa) than that determined in the previous in situ measurements using the same pressure scale [e.g. Katsura et al., 2003, Post-spinel transition in Mg2SiO4 determined by high P-Tin situ X-ray diffractometry. Phys. Earth Planet. Inter. 136, 11-24]. The Clapeyron slope of Mg2SiO4 was found to be gentle i.e. between -0.4 and -0.7 MPa/K, which is also consistent with previous in situ measurements, but inconsistent with diamond anvil cell experiments and theoretical estimations. The phase boundary in Mg2SiO4+2 wt% H2O which is relevant to Fe free-depleted harzburgitic composition is located between 23.4 and 23.6 GPa and 1500 K, which shifts the hydrous boundary to the higher pressures relative to anhydrous Mg2SiO4 from 1.3 to 1.0 GPa. The result for hydrous Mg2SiO4 shows steeper Clapeyron slope between -3.2 and -3.1 MPa/K compared with anhydrous Mg2SiO4 and hydrous pyrolite system. The present data suggest that water has a strong influence on 660 km discontinuity and the depressions observed at this boundary in several regions, especially related to subduction zones, can be explained by the presence of water in depleted harzburgite component.

  2. Phase relations in a harzburgite composition: implications for splitting of 660-km seismic discontinuity and seismic velocities in mantle transition zone

    NASA Astrophysics Data System (ADS)

    Nishiyama, N.; Kato, T.; Kinoshita, Y.; Irifune, T.

    2011-12-01

    density phase, Pv, and can cause the accumulation of harzburgite component at the base of MTZ. We calculated seismic velocities, Vp and Vs, of harzburgite using thermoelastic parameters determined in previous studies. Harzburgite is faster than pyrolite and 1D earth models, like PREM, at the lower half of MTZ (between 500 and 660 km depth) because of presence of St, Ak, and Pv in addition to the lower density caused by the low-Fe content. It has been demonstrated that pyrolite is slower than the 1D earth models in this region because of low velocity of majorite garnet. Mechanical mixture of pyrolite and harzgurgite can explain 1D earth models, which strongly indicates that harzburgite is accumulated and stagnant at the base of the MTZ. In addition, harzburgite can produce many seismic discontinuities in the non-olivine component, like Ak-Pv transition at 630 km depth, which are superimposed on phase transitions in olivine. Thus, presence of harzburgite in MTZ may explain regionally observed splitting of seismic discontinuities. The splitting of the seismic discontinuities may be caused by chemical heterogeneity, presence of harzburgite.

  3. Role of the transition zone and 660 km discontinuity in mantle dynamics

    NASA Astrophysics Data System (ADS)

    Ringwood, A. E.

    1994-10-01

    Recent seismic evidence suggests that subducted slabs experience resistance to further descent when they encounter the 660 km seismic discontinuity. Several possible causes of this resistance are evaluated. It is concluded that the chemical composition of the lower mantle is similar to that of the upper mantle, and that compositional change is therefore unlikely to be the cause of resistance to slab penetration. The proposal that a large increase of viscosity at the 660 km discontinuity impedes descending slabs is also rejected. However, three other factors are identified, each of which is capable of causing substantial resistance to descending slabs: (1) the negative slope of the transformation of silicate spinel to Mg-perovskite+magnesiowuestite; (2) differentiation of oceanic lithosphere into basaltic and depleted peridotitic layers, causing the slab to be buoyant compared with surrounding mantle pyrolite between depths of 660-800 km; (3) the accumulation of former oceanic crust to produce a gravitationally stable layer of garnetite (about 50 km thick) on top of the 660 km discontinuity. The combined effects of these sources of resistance provide a filter for subducted slabs. Those slabs with seismic zones extending below 600 km may possess sufficient negative buoyancy and strength to overcome the barriers and penetrate into the lower mantle. However, the resistance causes strong buckling and plastic thickening of these slabs, which accumulate to form huge blobs or 'megaliths' underneath the 660 km discontinuity. In contrast, slabs with seismic zones extending no deeper than 300 km possess much smaller degrees of negative buoyancy and strength and hence are unable to penetrate the 660 km discontinuity. Slabs of this type are recycled within the transition zone and upper mantle. Mixing and petrological homogenization processes are less efficient in the transition zone than in the upper mantle (above 400 km). The transition zone is composed mainly of ancient slabs

  4. Mantle seismic anisotropy beneath the 660km phase transition generated by subduction body force stresses.

    NASA Astrophysics Data System (ADS)

    Nippress, S.; Kusznir, N. J.; Kendall, M.

    2003-04-01

    Observations of seismic anisotropy can provide insights into the style of mantle dynamics near the 660km discontinuity. Wookey et al. (2002) report up to 7 seconds of shear wave splitting for rays generated by deep focus events from the Tonga subduction zone and recorded in Australia. The results suggest a transversely isotropic symmetry with the symmetry axis in the vertical plane, perpendicular to the ray direction. Thus, for horizontally travelling waves this would imply horizontally polarised shear waves (SH lead SV). They show that a topmost lower mantle model with anisotropy between 660-900km could produce theoretical shear wave splitting similar to that observed. Therefore, the seismic anisotropy observed by Wookey et al., can be explained by an anisotropic region between 660-900km, with only a minimal contribution from above the 660km phase transition. The goal of this study is to try to explain the observed shear wave splitting using geodynamical modelling. We use finite element (FE) modelling to calculate slab-induced models of fluid flow, total stress and deviatoric stress. A simple 2D subduction zone model with a prescribed viscosity structure and slab density is used. Large deviatoric stresses (maximum values ~ 40 MPa) are generated in the topmost lower mantle when the subducting slab encounters an increase in viscosity at the 660km phase transition. These stresses may induce mineral alignment in a broad region (lateral wavelength approximately » 800km) in the topmost lower mantle below the slab. Perovskite may therefore be aligned with a rotated symmetry axis conformal to the shape of this region of high deviatoric stress. Aligned Perovskite rotated more than 30 degrees predicts SH-waves faster than SV-waves for horizontally travelling S-waves. The formulation of McKenzie (1979) is used to calculate the finite strain accumulated by a mantle parcel as it propagates through the FE flow models. The computed strain ellipsoids align in a similar region

  5. The thermal influence of the subducting slab beneath South America from 410 and 660 km discontinuity observations

    NASA Astrophysics Data System (ADS)

    Collier, J. D.; Helffrich, G. R.

    2001-11-01

    Regional seismic network data from deep South American earthquakes to western United States and western European seismic arrays is slant stacked to detect weak near-source interactions with upper mantle discontinuities. These observations are complemented by an analysis of earlier work by Sacks & Snoke (1977) who observed S to P conversions from deep events to stations in South America, and similar observations from 1994-95 events using the BANJO and SEDA networks. Observations of the depth of the 410km discontinuity are made beneath central South America in the vicinity of the aseismic region of the subducting Nazca Plate. These results image the 410km discontinuity over a lateral extent of up to 850km perpendicular to the slab and over a distance of 2700km along the length of the slab. Away from the subducting slab the discontinuity is mainly seen near its global average depth, whilst inside the slab there is evidence for its elevation by up to around 60km but with significant scatter in the data. These results are consistent with the presence of a continuous slab through the aseismic region with a thermal anomaly of 900°C at 350km depth. This value is in good agreement with simple thermal models though our data are too sparse to accurately constrain them. Sparse observations of the 660km discontinuity agree with tomographic models suggesting penetration of the lower mantle by the slab in the north but stagnation at the base of the transition zone in the south. The geographical distribution of the data, however, does not allow us to rule out the possibility of slab stagnation at the base of the transition zone in the north. These observations, together with the presence of deep earthquakes, require more complicated thermal models than previously used to explain them, possibly including changes in slab dip and age with depth.

  6. Detection of the structure near the 410 km and 660 km discontinuities in Japan subduction zone from the waveform triplication

    NASA Astrophysics Data System (ADS)

    Cui, H.; Zhou, Y.

    2015-12-01

    Slab subduction plays an important role in the mantle material circulation [Stern, 2002], and can also affect the feature of the 410 km and 660 km seismic discontinuities (410 and 660) [Lebedev et al., 2002]. Japan subduction zone is a natural laboratory for studying the mantle composition and velocity structure associated with the deep subduction of the Pacific plate. In this study, triplicated waveforms of an intermediate-depth earthquake at the Hokkaido of Japan (2011/10/21, 08:02:37.62, 142.5315°E, 43.8729°N, Mb6.0, relocated depth: 188 km) are retrieved from the dense Chinese Digital Seismic Network (CDSN). P and S waveforms are filtered with the band of 0.05-1.0 Hz and 0.02-0.5 Hz, respectively, and then integrated into the displacement data. The relative traveltime and synthetic waveform fitting is applied to mapping the deep structure. The best fitting models are obtained through the trial and error tests. We find a 15 km uplift of the 410 and a 25 km depression of the 660, indicating the cold environment caused by the subduction slab; both the 410 and 660 show the sharp discontinuity, but a smaller velocity contrast than the IASP91 model [Kennett and Engdahl, 1991]. Atop the 410 and 660, there are high-velocity layers associated with the subduction (or stagnant) slab. We also find a low-velocity anomaly with the thickness of ~65 km below the 660, which may relate to the slab dehydration or the hot upwelling at the top of the lower mantle. The seismic velocity ratio (VP/VS) shows a lower zone at the depth of ~210-395 km, showing the consistency with the low Poisson's ratio signature of the oceanic plate; a higher zone at the depth of ~560-685 km, implying the hydrous mantle transition zone.

  7. Experimental Investigation of Strength Variation of Subducting Slabs Crossing the 660km Discontinuity and Its Implications for Deep-Focus Earthquakes

    NASA Astrophysics Data System (ADS)

    Zhao, S.; Green, H. W.; Jin, Z.; Zhang, J.

    2009-12-01

    The 660km seismic discontinuity corresponds, at least at lower temperatures, to the transition of the spinel phase of (Mg,Fe)2SiO4, ringwoodite, to (Mg,Fe)SiO3, perovskite (pv) + (Mg,Fe)O, magnesiowüstite (mw). The rheological properties of material above and below this discontinuity as well as the chemical/structural nature of the boundary itself play an important role for the understanding of deeply subducted slabs, the termination of deep earthquakes, mantle convection, post-glacial rebound, and other geodynamic processes. Although the rheology of olivine, the dominant upper-mantle mineral, has been extensively studied, knowledge about the rheological properties of the material near the 660km discontinuity, especially pv+mw is limited. It has been proposed (e.g. Ito and Sato, 1991; Karato et al, 1995) that decomposition of spinel to pv+mw leads to very fine-grained material that will be inherently weak and, making use of this kind of superplastic behavior, they interpreted the aseismicity, seismic anisotropy and other aspects of the lower mantle. However, the recent experimental results on a similar reaction (proxy reaction albite→jadeite+coesite) from Gleason & Green (2009) show that such decomposition reactions yield symplectites in which the apparent grain-size viewed in 2D is much smaller than the actual size of individual symplectites in which the two phases are complexly intergrown in 3D. They showed that such symplectites are in general not weak because the intergrown phases yield a strong composite material. Here we report a similar study in a more realistic analogue system: disproportionation of Co2TiO4 spinel into CoTiO3 ilmenite + CoO. We compare the strength of spinel with its dissociation product in detail through high pressure and temperature experiments in our 4 GPa piston-cylinder (Griggs) deformation apparatus in which the deformation can be well controlled, with accurate stress measurement. Our starting material, which is synthesized from

  8. A finite-frequency P-wave tomographic model: images of subducted slabs stagnant above, penetrating through and trapped below the 660-km discontinuity

    NASA Astrophysics Data System (ADS)

    Fukao, Y.; Obayashi, M.

    2012-12-01

    We constructed a new P-wave tomographic model of the mantle using more than ten millions of travel time data. The finite frequency effect of seismic ray was taken into account by calculating banana-donut kernels at 2 Hz for all the first arrival data and at 0.1 Hz for the broadband differential travel time data. Based on this model, a systematic survey was made for subducted slab images around the circum Pacific including Kurile, Honshu, Izu-Bonin, Mariana, Java, Tonga-Kermadec, southern and northern South America, and Central America. This survey clarified a progressive lateral variation of slab configuration along the arc or through the arc to arc, where a subducted slab is in general in one or two of the following four stages: I. slab stagnant above the 660, II. slab penetrating the 660, III. slab trapped in the uppermost lower mantle (660 to ˜1000 km in depth), and IV. slab descending well into the deep lower mantle. The majority of the slab images are either at stage I or III. We interpret I to IV as the successive stages of slab subduction through the transition region with the 660 at the middle, where I and III are relatively stable or neutral stages and II and IV are relatively unstable, transient stages. In particular, we emphasize III as a distinct stage of slab subduction, through which the slab once softened by the phase transition may progressively recover its hardness. Alternatively, the mantle viscosity may not increase stepwise across the 660 but increase gradually throughout the uppermost lower mantle. Plots of hypocentral distribution on tomographic slab images show that deep shocks at depths greater than ˜620 km are a good measure of slab penetration at stage either II or III.

  9. Seismic Structure of the Mantle Discontinuities beneath Northeast Asia

    NASA Astrophysics Data System (ADS)

    Li, J.; WANG, X.; Guo, G.

    2015-12-01

    Seismic structure of the upper mantle discontinuities is important for understanding the thermal structure, composition of the mantle, and scales of mantle circulation as well. Northeast Asia is located at the front edge of the subducting Pacific slab, which is an ideal place to study the interaction between the upper mantle discontinuities and the subducting slab. Seismic tomography images have revealed different morphologies of slabs in the deep mantle. A prominent stagnant slab is trapped in the MTZ beneath Japan Sea and southern Kuril trench; while the slabs penetrate into the lower mantle directly beneath the northern Kuril and southern Izu-Bonin trench. Due to the sparse distribution of seismic stations in the sea, investigation of the deep mantle structure beneath the broad sea regions is very limited. In this study, we applied the multiple-ScS reverberations analysis to waveforms recorded by the Chinese Regional Seismic Network and F-net. We took advantage of the dense distribution of stations and spatial clusters of intermediate and deep earthquakes occurred beneath Okhotsk Sea, Russia and Northeast China, and conducted a common-reflection-point (CRP) stacking to the data, that allows us to map the topography of the 410-km and 660-km discontinuities beneath Japan Sea, Kuril, and adjacent regions in detail. We also compiled previous results obtained from the high frequency receiver function and S-to-P converted wave analyzes, and compared the results in the overlapping island or continental margin regions. The comparison shows that the array stacking technique to long-period signals is effective in extracting the robust features of the upper mantle discontinuities. It can be used not only as a complimentary method to short-period waveform analysis, but also as an independent way which can be applied to regions with limited station coverage. This is the first time to show systematically a complete view of the topography of the 410-km and 660-km

  10. Body-wave imaging of Earth's mantle discontinuities from ambient seismic noise.

    PubMed

    Poli, P; Campillo, M; Pedersen, H

    2012-11-23

    Ambient seismic noise correlations are widely used for high-resolution surface-wave imaging of Earth's lithosphere. Similar observations of the seismic body waves that propagate through the interior of Earth would provide a window into the deep Earth. We report the observation of the mantle transition zone through noise correlations of P waves as they are reflected by the discontinuities associated with the top [410 kliometers (km)] and the bottom (660 km) of this zone. Our data demonstrate that high-resolution mapping of the mantle transition zone is possible without using earthquake sources.

  11. Mapping Upper Mantle Seismic Discontinuities Using Singular Spectrum Analysis

    NASA Astrophysics Data System (ADS)

    Gu, Y. J.; Dokht, R.; Sacchi, M. D.

    2015-12-01

    Seismic discontinuities are fundamental to the understanding of mantle composition and dynamics. Their depth and impedance are generally determined using secondary seismic phases, most commonly SS precursors and P-to-S converted waves. However, the analysis and interpretation using these approaches often suffer from incomplete data coverage, high noise levels and interfering seismic phases, especially near tectonically complex regions such as subduction zones and continental margins. To overcome these pitfalls, we apply Singular Spectrum Analysis (SSA) to remove random noise, reconstruct missing traces and enhance the robustness of SS precursors and P-to-S conversions from seismic discontinuities. Our method takes advantage of the predictability of time series in frequency-space domain and performs a rank reduction using a singular value decomposition of the trajectory matrix. We apply SSA to synthetic record sections as well as observations of 1) SS precursors beneath the northwestern Pacific subduction zones, and 2) P-to-S converted waves from the Western Canada Sedimentary Basin (WCSB). In comparison with raw or interpolated data, the SSA enhanced reflectivity maps show a greater resolution and a stronger negative correlation between the depths of the 410 and 660 km discontinuities. These effects can be attributed to the suppression of incoherent noise, which tends to reduce the signal amplitude during normal averaging procedures, through rank reduction and the emphasis of principle singular values. Our new results suggest a more laterally coherent 520 km reflection in the western Pacific regions. Similar improvements in data imaging are achieved in western Canada, where strong lateral variations in discontinuity topography are observed in the craton-Cordillera boundary zone. Improvements from SSA relative to conventional approaches are most notable in under-sampled regions.

  12. Upper-mantle seismic discontinuities and the thermal structure of subduction zones

    USGS Publications Warehouse

    Vidale, J.E.; Benz, H.M.

    1992-01-01

    The precise depths at which seismic velocities change abruptly in the upper mantle are revealed by the analysis of data from hundreds of seismometers across the western United States. The boundary near 410 km depth is locally elevated, that near 660 km depressed. The depths of these boundaries, which mark phase transitions, provide an in situ thermometer in subduction zones: the observed temperature contrasts require at least moderate thickening of the subducting slab near 660 km depth. In addition, a reflector near 210 km depth may mark the bottom of the aesthenosphere.

  13. Seismic Discontinuities within the Crust and Mantle Beneath Indonesia as Inferred from P Receiver Functions

    NASA Astrophysics Data System (ADS)

    Woelbern, I.; Rumpker, G.

    2015-12-01

    Indonesia is situated at the southern margin of SE Asia, which comprises an assemblage of Gondwana-derived continental terranes, suture zones and volcanic arcs. The formation of SE Asia is believed to have started in Early Devonian. Its complex history involves the opening and closure of three distinct Tethys oceans, each accompanied by the rifting of continental fragments. We apply the receiver function technique to data of the temporary MERAMEX network operated in Central Java from May to October 2004 by the GeoForschungsZentrum Potsdam. The network consisted of 112 mobile stations with a spacing of about 10 km covering the full width of the island between the southern and northern coast lines. The tectonic history is reflected in a complex crustal structure of Central Java exhibiting strong topography of the Moho discontinuity related to different tectonic units. A discontinuity of negative impedance contrast is observed throughout the mid-crust interpreted as the top of a low-velocity layer which shows no depth correlation with the Moho interface. Converted phases generated at greater depth beneath Indonesia indicate the existence of multiple seismic discontinuities within the upper mantle and even below. The strongest signal originates from the base of the mantle transition zone, i.e. the 660 km discontinuity. The phase related to the 410 km discontinuity is less pronounced, but clearly identifiable as well. The derived thickness of the mantle-transition zone is in good agreement with the IASP91 velocity model. Additional phases are observed at roughly 33 s and 90 s relative to the P onset, corresponding to about 300 km and 920 km, respectively. A signal of reversed polarity indicates the top of a low velocity layer at about 370 km depth overlying the mantle transition zone.

  14. A New Approach to Study the Upper-Mantle Seismic Discontinuities Based on Triplication Data: Application to the Kuril Subduction Zone Using Hi-net Array

    NASA Astrophysics Data System (ADS)

    Park, S.; Okeler, A.; Ishii, M.

    2015-12-01

    Constraining seismic properties of the 410- and 660-km discontinuities is crucial for understanding the mantle composition and dynamics. One approach to study the transition zone is to use the "triplicated" arrivals of seismic data. When a wavefield encounters an abrupt increase in wave speed with depth, three different phases, direct, reflected, and transmitted phases, result, and they can arrive at the same distance, producing the triplicated arrivals. Properties of the triplication pattern provide constraints on the depth and velocity jump of the discontinuities. One of the challenging aspects of using the triplication data, however, is to identify the three individual phases, since they arrive close in time and the waveforms often overlap. In order to separate the phases, we apply Radon transform to the data. Based on the transformed data, the caustics are identified, and the depth and the velocity jump of the discontinuities are obtained. This method is applied to study the Kuril subduction zone, beneath a region northeast of Japan. We take advantage of the High-Sensitivity Seismograph Network in Japan that consists of more than 700 stations, to capture the triplication pattern with dense sampling in distance. Given the distribution of the stations, deep and intermediate earthquakes in the Sea of Okhotsk region that are located within the triplication distance range are considered. We constrain the percentage velocity jump and depth of the 410- and 660-km discontinuities. The discontinuity depth estimates show significant deviations from the global average, but are, in general, comparable to the SS precursors and tomographic studies of the region.

  15. Thermodynamic properties of MgSiO3 majorite and phase transitions near 660 km depth in MgSiO3 and Mg2SiO4: A first principles study

    NASA Astrophysics Data System (ADS)

    Yu, Yonggang G.; Wentzcovitch, Renata M.; Vinograd, Victor L.; Angel, Ross J.

    2011-02-01

    Mg2SiO4 at conditions close to 660 km depth. This suggests that the large density discontinuity at 660 km depth as proposed by PREM (9.3%) might be accounted by a piclogite compositional model or marginally accounted by a pyrolite compositional model with, for example, 50 vol % ringwoodite, 45 vol % majorite, and 5 vol % other phases (such as calcium perovskite) at the bottom of the transition zone, provided that the density contrast between majorite and perovskite will not be greatly altered by the presence of other elements such as Fe, Al, Ca, and H. On the other hand, the smaller density discontinuity at 660 km depth as derived from impedance studies (4-6%) disfavors sharp contributions to seismic discontinuities from the majorite to perovskite transition.

  16. Receiver function analysis of mantle discontinuities beneath the Colorado Plateau and Colorado Rockies using the RISTRA and CREST seismic arrays teleseismic data

    NASA Astrophysics Data System (ADS)

    Zhang, Zhu

    Converted seismic waves (e.g. P-to-S) are sensitive to rapid velocity change and have been extensively used to characterize seismic discontinuities in the crust and mantle. A receiver function is a time series representing the Earth's responses and is conventionally estimated by deconvolving radial (or SV) component from vertical (or P) component with water-level. Two primary seismic discontinuities in the mantle, the 410- and 660-km discontinuities, are due to olivine phase changes. The region in between is termed as the mantle transition zone which separates the upper mantle from lower mantle. Thickness and topography of the two discontinuities contribute to understanding of mantle convection process, thermal anomaly and chemical composition. A 410-km low velocity layer atop the 410-km discontinuity has been identified regionally and globally. The low velocity layer is interpreted as partial melting and coherent with the prediction of the transition zone water filter model. Using receiver function analysis, I first study the mantle transition zone in the Colorado Plateau by the RISTRA array and find the 410-km low velocity layer is absent in high velocity regions about 410 km depth in P wave tomogram, and is present in low velocity regions. Our finding is consistent with a simple interpretation of the transition zone water filter model which predicts the production of a hydrous melt layer only where upflow of sufficiently hydrated transition zone mantle occurs. The second study is seismic imaging of mantle discontinuities beneath the Colorado Rockies by the CREST array combined with TA stations. The stacking images show a thinner than global averaged transition zone of 241 km, and existence of the 410-km low velocity layer. Those two findings suggest that the mantle is warm and upwelling in the region, which may provide partially uplift to the excess topography of the Colorado Rocky Mountains. A third finding is a negative polarity phase below the 410-km

  17. Unstructured discontinuous Galerkin for seismic inversion.

    SciTech Connect

    van Bloemen Waanders, Bart Gustaaf; Ober, Curtis Curry; Collis, Samuel Scott

    2010-04-01

    This abstract explores the potential advantages of discontinuous Galerkin (DG) methods for the time-domain inversion of media parameters within the earth's interior. In particular, DG methods enable local polynomial refinement to better capture localized geological features within an area of interest while also allowing the use of unstructured meshes that can accurately capture discontinuous material interfaces. This abstract describes our initial findings when using DG methods combined with Runge-Kutta time integration and adjoint-based optimization algorithms for full-waveform inversion. Our initial results suggest that DG methods allow great flexibility in matching the media characteristics (faults, ocean bottom and salt structures) while also providing higher fidelity representations in target regions. Time-domain inversion using discontinuous Galerkin on unstructured meshes and with local polynomial refinement is shown to better capture localized geological features and accurately capture discontinuous-material interfaces. These approaches provide the ability to surgically refine representations in order to improve predicted models for specific geological features. Our future work will entail automated extensions to directly incorporate local refinement and adaptive unstructured meshes within the inversion process.

  18. Discontinuity enhancement based on time-variant seismic image deblurring

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Lu, Wenkai

    2016-12-01

    Post-stack 3D seismic data is spatially blurred by the effects of migration operators with limited aperture widths, which is not conducive to discontinuity (such as fault, channel, etc.) detection. By approximating the migration blur with a time-invariant point spread function (TIPSF), seismic image deblurring methods have been used to obtain data with enhanced discontinuity. Better discontinuity detection results can be achieved on the deblurred data than on the original data. Since the migration blurs are always time-dependent, a time-variant PSF (TVPSF) estimation method is proposed in this paper to approximate these blurs. In our method, initial PSFs corresponding to each horizontal time slice (HTS) from a 3D seismic data are first obtained. Then, PSFs corresponding to adjacent time slices are divided into the same categories based on their similarities. With average PSFs calculated in each category, linear interpolation is performed to estimate PSFs for the whole data set. Finally, we perform seismic image deblurring HTS by HTS with these estimated PSFs. To suit different signal-to-noise ratios (SNR) in these HTSs of the 3D seismic data, the whitening factor of the Wiener filter for each HTS is adjusted adaptively. Using field dataset examples, we demonstrate that the performance of our proposed TVPSF method outperforms the TIPSF method.

  19. P-V-V p-V s-T measurements on wadsleyite to 7 GPa and 873 K: Implications for the 410-km seismic discontinuity

    NASA Astrophysics Data System (ADS)

    Li, Baosheng; Liebermann, Robert C.; Weidner, Donald J.

    2001-01-01

    The compressional (P) and shear wave (S) velocities for Mg2SiO4 wadsleyite have been measured to 7 GPa and 873 K using simultaneous ultrasonic interferometry and in situ X-ray diffraction techniques. From the velocity measurements we obtained the pressure and temperature derivatives for the elastic shear (G) and adiabatic bulk (KS) moduli, (∂G/∂P)T=1.5(1), (∂G/∂T)P=-0.017(1) GPa/K, KS=173(2) GPa, (∂Ks/∂P)T=4.2(1), and (∂Ks/∂T)P=-0.012(1) GPa/K; for the P and S waves, we obtained (∂Vs/∂P)T=0.021(1) (km/s)/GPa, (∂Vs/∂T)P=-0.035(2) (km/s)/K, (∂VP/∂P)T=0.065(2) (km/s)/GPa, and (∂VP/∂T)P = -0.038(2) (km/s)/K (values in parentheses are standard deviations, e.g., 1.5(1)=1.5±1). Independent equation of state analysis of P-V-T data provided an estimation of the temperature dependence for the isothermal bulk modulus of (∂KT/∂T)P=-0.022(12) GPa/K and thermal expansion (α=a+bT) coefficients of a=2×10-5 K-1 and b=2.5×10-8 K-2. Using these data along with elastic properties for other mantle phases, a velocity-depth profile for a pyrolite model to 670 km depth is constructed using a finite strain method along a 1673 K adiabat. In the transition zone the pyrolite model has a smaller gradient between 410 and 660 km than the body wave models from synthetic waveform analyses but converges with the seismic profiles at the bottom of the transition zone just above the 660-km discontinuity. The pyrolite model has velocity jumps of 6.9% and 7.9% for P and S waves, respectively, over a thickness of ˜10 km for the phase transformation from olivine to wadsleyite, which is in good agreement with short-period P wave reflection data and a recent fine structure model (C4) for both the velocity jumps and the thickness of the 410-km seismic discontinuity.

  20. Behaviour of mantle transition zone discontinuities beneath the Indian Ocean from PP and SS precursors

    NASA Astrophysics Data System (ADS)

    Reiss, Anne-Sophie; Thomas, Christine

    2015-04-01

    As part of the RHUM-RUM project we investigate the upwelling plume beneath the island La Réunion, located in the Indian Ocean 200 km east of Madagascar. This plume belongs to one of the most active hotspot regions in the world and is still active today. Understanding the depth origin and dimensions of such a plume helps to better understand mantle processes and the heat flux of the Earth. If the plume originates at the core-mantle boundary the Earth is cooled down differently compared with an indirect cooling of plumes originating in the upper mantle. Here we use underside reflections of PP and SS waves off the seismic discontinuities at 410 km and 660 km depth that arrive as precursors to the main phase in order to investigate the topography of these discontinuities that mark the top and bottom of the mantle transition zone. If hotter or colder material intersects the mantle transition zone, the discontinuities at 410 km and 660 km depth are deflected, hence the topography of the mantle transition zone can be an indicator for an upwelling plume. The 410 km discontinuity, which exists due to the phase change of olivine to spinel, should be depressed significantly in the presence of hot upwelling material. Because of the opposite Clapeyron slope of the phase change of spinel to magnesiowuestite and perovskite at 660 km depth, the topography of this discontinuity should be elevated. For this study we analyse over 200 events with Mw ≥ 5.8 and bounce points distributed over the entire Indian Ocean. Array seismology methods, such as vespagrams and slowness-backazimuth analysis, are used to enhance the signal-to-noise-ratio and detect and identify precursors. Using different source-receiver combinations enables us to get a dense coverage of bounce points of PP and SS waves in the Indian Ocean and especially around La Réunion, also with crossing ray paths. The differential travel times of PP and SS arrivals and their precursors of robust stacks are converted into

  1. Global seismic data reveal little water in the mantle transition zone

    NASA Astrophysics Data System (ADS)

    Houser, C.

    2016-08-01

    Knowledge of the Earth's present water content is necessary to constrain the amount of water and other volatiles the Earth acquired during its formation and the amount that is cycled back into the interior from the surface. This study compares 410 and 660 km discontinuity depth with shear wave tomography within the mantle transition zone to identify regions with seismic signals consistent with water. The depth of the 410 and 660 km discontinuities is determined from a large updated dataset of SS-S410S and SS-S660S differential travel times, known as SS precursors. The discontinuity depths measured from binning and stacking the SS precursor data are then compared to the shear velocity model HMSL-S06 in the transition zone. Mapping all the possible combinations, very few locations match the predictions from mineral physics for the effects of water on discontinuity depth and shear velocity. The predictions, although not yet measured at actual transition zone temperatures and pressures, are a shallow 410 km discontinuity, a deep 660 km discontinuity, and a slow shear velocity. Only 8% of the bins with high-quality data are consistent with these predictions, and the calculated average water content within these bins is around 0.6 wt.%. A few isolated locations have patterns of velocity/topography that are consistent with water, while there are large regional-scale patterns consistent with cold/hot temperature anomalies. Combining this global analysis of long period seismic data and the current mineral physics predictions for water in transition zone minerals, I find that the mantle transition zone is generally dry, containing less than one Earth ocean of water. Although subduction zones could be locally hydrated, the combined discontinuity and velocity data show no evidence that wadsleyite or ringwoodite have been globally hydrated by subduction or initial Earth conditions.

  2. A steeply dipping discontinuity in the lower mantle beneath Izu-Bonin

    NASA Astrophysics Data System (ADS)

    Castle, John C.; Creager, Kenneth C.

    1999-04-01

    We analyze the coda of teleseismic P waves to deterministically map seismic scatterers in a 1000 km on-a-side cube beneath the Izu-Bonin trench by migrating and stacking waveforms. This method was applied to several hundred short-period vertical-component western United States seismometer recordings of 17 deep-focus Izu-Bonin earthquakes. Except for isolated arrivals, the midmantle appears devoid of sharp discontinuities. S-to-P conversions at the 660-km discontinuity generated the largest signals; the 410-km discontinuity occasionally generated signals. Horizontal discontinuities poorly explain other signals; however, S-to-P conversions generated at a nearly north-south trending, steeply dipping discontinuity at 30°N, 145°E, and 1000 km beneath and parallel to the Izu-Bonin trench explain most additional signals. Observed coherent S-to-P conversions of 2-s period waves limit the width of a gradient zone to <7 km. Compressional and shear tomographic models [Grand et al., 1997; Widiyantoro, 1997] image a fast velocity structure at a similar depth and orientation extending southward from the middle of the Izu-Bonin trench to the Mariana trench. We interpret the sharp scattering surface as a subducted crust and the tomographically imaged structure as the cold thermal anomaly associated with an ancient slab. We observe neither the deep scatterer nor high-seismic wavespeeds north of 32°N. This feature is as much as 800 km east of recent deep earthquakes near 30°N and is at a latitude where the slab appears to extend horizontally on the 660-km discontinuity to the west of the seismicity. We suggest that this deep slab fragment was carried north 500-1000 km owing to oblique subduction. In this scenario, it would be associated with the near vertical subduction at the Mariana subduction zone.

  3. A Receiver Function Study of Mantle Transition Zone Discontinuities beneath Egypt and Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Liu, K. H.; Mohamed, A. A.; Gao, S. S.; Elsheikh, A. A.; Yu, Y.; Fat-Helbary, R. E.

    2014-12-01

    The dramatic asymmetry in terms of surface elevation, Cenozoic volcanisms, and earthquake activity across the Red Sea is an enigmatic issue in global tectonics, partially due to the unavailability of broadband seismic data on the African plate adjacent to the Red Sea. Here we report the first results from a receiver function study of the mantle transition zone (MTZ) discontinuities using data from the Egyptian National Seismic Network, and compare the resulting depths of the 410 and 660 km discontinuities (d410 and d660) with those observed on the Arabian side. Results using more than 6000 P-to-S receiver functions recorded at 49 broadband seismic stations in Egypt, Saudi Arabia and adjacent areas show that when the IASP91 Earth model is used for time-to-depth conversion, the resulting depth of the discontinuities increases systematically toward the axis of the Afro-Arabian Dome (AAD) from both the west and east. Relative to the westernmost area, the maximum depression of the 410-km discontinuity is about 30 km, and that of the 660-km discontinuity is about 45 km. Highly correlated d410 and d660 depths suggest that the observed apparent depth variations are mostly caused by lateral velocity anomalies in the upper mantle, while the 15 km additional depression of the d660 relative to the d410 requires either a colder-than-normal MTZ or the presence of water in the MTZ. We tested several models involving upper mantle and MTZ velocity anomalies and undulations of the MTZ discontinuities due to temperature anomalies and water content, and found that the observed systematic variations can best be explained by a model involving a hydrated MTZ and an upper-mantle low-velocity zone beneath the AAD (Mohamed et al., 2014, doi: 10.1093/gji/ggu284). Models invoking one or more mantle plumes originated from the MTZ or the lower-mantle beneath the study area are not consistent with the observations.

  4. Numerical model for the generation of the ensemble of lithospheric plates and their penetration through the 660-km boundary

    NASA Astrophysics Data System (ADS)

    Trubitsyn, V. P.; Trubitsyn, A. P.

    2014-11-01

    In the kinematic theory of lithospheric plate tectonics, the position and parameters of the plates are predetermined in the initial and boundary conditions. However, in the self-consistent dynamical theory, the properties of the oceanic plates (just as the structure of the mantle convection) should automatically result from the solution of differential equations for energy, mass, and momentum transfer in viscous fluid. Here, the viscosity of the mantle material as a function of temperature, pressure, shear stress, and chemical composition should be taken from the data of laboratory experiments. The aim of this study is to reproduce the generation of the ensemble of the lithospheric plates and to trace their behavior inside the mantle by numerically solving the convection equations with minimum a priori data. The models demonstrate how the rigid lithosphere can break up into the separate plates that dive into the mantle, how the sizes and the number of the plates change during the evolution of the convection, and how the ridges and subduction zones may migrate in this case. The models also demonstrate how the plates may bend and break up when passing the depth boundary of 660 km and how the plates and plumes may affect the structure of the convection. In contrast to the models of convection without lithospheric plates or regional models, the structure of the mantle flows is for the first time calculated in the entire mantle with quite a few plates. This model shows that the mantle material is transported to the mid-oceanic ridges by asthenospheric flows induced by the subducting plates rather than by the main vertical ascending flows rising from the lower mantle.

  5. Low-velocity zone atop the 410-km seismic discontinuity in the northwestern United States.

    PubMed

    Song, Teh-Ru Alex; Helmberger, Don V; Grand, Stephen P

    2004-02-05

    The seismic discontinuity at 410 km depth in the Earth's mantle is generally attributed to the phase transition of (Mg,Fe)2SiO4 (refs 1, 2) from the olivine to wadsleyite structure. Variation in the depth of this discontinuity is often taken as a proxy for mantle temperature owing to its response to thermal perturbations. For example, a cold anomaly would elevate the 410-km discontinuity, because of its positive Clapeyron slope, whereas a warm anomaly would depress the discontinuity. But trade-offs between seismic wave-speed heterogeneity and discontinuity topography often inhibit detailed analysis of these discontinuities, and structure often appears very complicated. Here we simultaneously model seismic refracted waves and scattered waves from the 410-km discontinuity in the western United States to constrain structure in the region. We find a low-velocity zone, with a shear-wave velocity drop of 5%, on top of the 410-km discontinuity beneath the northwestern United States, extending from southwestern Oregon to the northern Basin and Range province. This low-velocity zone has a thickness that varies from 20 to 90 km with rapid lateral variations. Its spatial extent coincides with both an anomalous composition of overlying volcanism and seismic 'receiver-function' observations observed above the region. We interpret the low-velocity zone as a compositional anomaly, possibly due to a dense partial-melt layer, which may be linked to prior subduction of the Farallon plate and back-arc extension. The existence of such a layer could be indicative of high water content in the Earth's transition zone.

  6. Seismic evidence for a tilted mantle plume and north-south mantle flow beneath Iceland

    USGS Publications Warehouse

    Shen, Y.; Solomon, S.C.; Bjarnason, I. Th; Nolet, G.; Morgan, W.J.; Allen, R.M.; Vogfjord, K.; Jakobsdottir, S.; Stefansson, R.; Julian, B.R.; Foulger, G.R.

    2002-01-01

    Shear waves converted from compressional waves at mantle discontinuities near 410- and 660-km depth recorded by two broadband seismic experiments in Iceland reveal that the center of an area of anomalously thin mantle transition zone lies at least 100 km south of the upper-mantle low-velocity anomaly imaged tomographically beneath the hotspot. This offset is evidence for a tilted plume conduit in the upper mantle, the result of either northward flow of the Icelandic asthenosphere or southward flow of the upper part of the lower mantle in a no-net-rotation reference frame. ?? 2002 Elsevier Science B.V. All rights reserved.

  7. The excitation of long period seismic waves by a source spanning a structural discontinuity

    NASA Astrophysics Data System (ADS)

    Woodhouse, J. H.

    Simple theoretical results are obtained for the excitation of seismic waves by an indigenous seismic source in the case that the source volume is intersected by a structural discontinuity. In the long wavelength approximation the seismic radiation is identical to that of a point source placed on one side of the discontinuity or of a different point source placed on the other side. The moment tensors of these two equivalent sources are related by a specific linear transformation and may differ appreciably both in magnitude and geometry. Either of these sources could be obtained by linear inversion of seismic data but the physical interpretation is more complicated than in the usual case. A source which involved no volume change would, for example, yield an isotropic component if, during inversion, it were assumed to lie on the wrong side of the discontinuity. The problem of determining the true moment tensor of the source is indeterminate unless further assumptions are made about the stress glut distribution; one way to resolve this indeterminancy is to assume proportionality between the integrated stress glut on each side of the discontinuity.

  8. Imaging Mantle Discontinuities Beneath North America Using ScS Reverberations

    NASA Astrophysics Data System (ADS)

    Griebel, K. A.; Schmerr, N. C.; Courtier, A. M.; Lekic, V.

    2015-12-01

    Seismic discontinuities are rapid changes in velocity and density over depth that arise from mechanisms such as changes in mineralogy, major element composition, melt content, volatile abundance, anisotropy, or a combination of the above. Seismic imaging of discontinuities complements information provided by seismic tomography and is important for understanding the dynamics and the structure of the mantle. For example, imaging variations in the depth and sharpness of discontinuities can trace underlying variations in temperature and composition in the mantle. We use ScSScS precursors and ScS postcursors (ScS reverberations) to map the depth and sharpness of upper- and mid- mantle discontinuities beneath North America. To observe the reverberations, we collected broadband data recordings of earthquakes with depth > 300 km, source moment magnitude ≥ 5.5, and location < 60 degrees of EarthScope USArray stations. Two primary source regions met our qualifications: earthquakes from the subduction of the Nazca plate beneath South America, and earthquakes from the subduction of the Pacific plate beneath the Sea of Okhotsk. Our dataset consists of ~15 deep focus earthquakes that have well defined ScS and ScSScS arrivals. We use array processing to generate vespagrams for detecting the ScS reverberations. Seismic energy falling at the appropriate slowness and travel time for reflections from upper- and mid- mantle discontinuities is migrated to depth. We use the resulting ScS reverberation derived reflectivity profiles to obtain estimates for discontinuity depth and impedance contrast in the regions falling between the source and array. We can use this information to image parts of the mantle under North America. Preliminary results indicate presence of multiple discontinuities in the upper mantle, including the 410 km discontinuity, a complex 660 km discontinuity, and intermittent mid-mantle discontinuities at 800-900 km depth.

  9. Seismic detection method for small-scale discontinuities based on dictionary learning and sparse representation

    NASA Astrophysics Data System (ADS)

    Yu, Caixia; Zhao, Jingtao; Wang, Yanfei

    2017-02-01

    Studying small-scale geologic discontinuities, such as faults, cavities and fractures, plays a vital role in analyzing the inner conditions of reservoirs, as these geologic structures and elements can provide storage spaces and migration pathways for petroleum. However, these geologic discontinuities have weak energy and are easily contaminated with noises, and therefore effectively extracting them from seismic data becomes a challenging problem. In this paper, a method for detecting small-scale discontinuities using dictionary learning and sparse representation is proposed that can dig up high-resolution information by sparse coding. A K-SVD (K-means clustering via Singular Value Decomposition) sparse representation model that contains two stage of iteration procedure: sparse coding and dictionary updating, is suggested for mathematically expressing these seismic small-scale discontinuities. Generally, the orthogonal matching pursuit (OMP) algorithm is employed for sparse coding. However, the method can only update one dictionary atom at one time. In order to improve calculation efficiency, a regularized version of OMP algorithm is presented for simultaneously updating a number of atoms at one time. Two numerical experiments demonstrate the validity of the developed method for clarifying and enhancing small-scale discontinuities. The field example of carbonate reservoirs further demonstrates its effectiveness in revealing masked tiny faults and small-scale cavities.

  10. Sharpness of upper-mantle discontinuities determined from high-frequency reflections

    USGS Publications Warehouse

    Benz, H.M.; Vidale, J.E.

    1993-01-01

    AN understanding of the nature of seismic discontinuities in the Earth's upper mantle is important for understanding mantle processes: in particular, the amplitude and sharpness of these discontinuities are critical for assessing models of upper-mantle phase changes and chemical layering. So far, seismic studies aimed at determining the thickness and lateral variability of upper-mantle discontinuities have yielded equivocal results, particularly for the discontinuity at 410km depth1,2. Here we present short-period (0.8-2.0 s) recordings of upper-mantle precursors to the seismic phase P???P??? (PKPPKP) from two South American earthquakes recorded by the ???700-station short-period array in California. Our results show that the 410- and 660-km discontinuities beneath the Indian Ocean are locally simple and sharp, corresponding to transi-tion zones of 4 km or less. These observations pose problems for mineral physics models3-5, which predict a transitional thickness greater than 6 km for the peridotite to ??-spinel phase transition. In contrast to the results of long-period studies6,7, we observe no short-period arrivals from near 520 km depth. ?? 1993 Nature Publishing Group.

  11. Sharpness of upper-mantle discontinuities determined from high-frequency reflections

    USGS Publications Warehouse

    Benz, H.M.; Vidale, J.E.

    1993-01-01

    AN understanding of the nature of seismic discontinuities in the Earth's upper mantle is important for understanding mantle processes: in particular, the amplitude and sharpness of these discontinuities are critical for assessing models of upper-mantle phase changes and chemical layering. So far, seismic studies aimed at determining the thickness and lateral variability of upper-mantle discontinuities have yielded equivocal results, particularly for the discontinuity at 410km depth1,2. Here we present short-period (0.8-2.0 s) recordings of upper-mantle precursors to the seismic phase P???P??? (PKPPKP) from two South American earthquakes recorded by the ???700-station short-period array in California. Our results show that the 410- and 660-km discontinuities beneath the Indian Ocean are locally simple and sharp, corresponding to transition zones of 4 km or less. These observations pose problems for mineral physics models3-5, which predict a transitional thickness greater than 6 km for the peridotite to ??-spinel phase transition. In contrast to the results of long-period studies6,7, we observe no short-period arrivals from near 520 km depth.

  12. Seismic imaging of a mid-lithospheric discontinuity beneath Ontong Java Plateau

    NASA Astrophysics Data System (ADS)

    Tharimena, Saikiran; Rychert, Catherine A.; Harmon, Nicholas

    2016-09-01

    Ontong Java Plateau (OJP) is a huge, completely submerged volcanic edifice that is hypothesized to have formed during large plume melting events ∼90 and 120 My ago. It is currently resisting subduction into the North Solomon trench. The size and buoyancy of the plateau along with its history of plume melting and current interaction with a subduction zone are all similar to the characteristics and hypothesized mechanisms of continent formation. However, the plateau is remote, and enigmatic, and its proto-continent potential is debated. We use SS precursors to image seismic discontinuity structure beneath Ontong Java Plateau. We image a velocity increase with depth at 28 ± 4 km consistent with the Moho. In addition, we image velocity decreases at 80 ± 5 km and 282 ± 7 km depth. Discontinuities at 60-100 km depth are frequently observed both beneath the oceans and the continents. However, the discontinuity at 282 km is anomalous in comparison to surrounding oceanic regions; in the context of previous results it may suggest a thick viscous root beneath OJP. If such a root exists, then the discontinuity at 80 km bears some similarity to the mid-lithospheric discontinuities (MLDs) observed beneath continents. One possibility is that plume melting events, similar to that which formed OJP, may cause discontinuities in the MLD depth range. Plume-plate interaction could be a mechanism for MLD formation in some continents in the Archean prior to the onset of subduction.

  13. Combination of the discontinuous Galerkin method with finite differences for simulation of seismic wave propagation

    SciTech Connect

    Lisitsa, Vadim; Tcheverda, Vladimir; Botter, Charlotte

    2016-04-15

    We present an algorithm for the numerical simulation of seismic wave propagation in models with a complex near surface part and free surface topography. The approach is based on the combination of finite differences with the discontinuous Galerkin method. The discontinuous Galerkin method can be used on polyhedral meshes; thus, it is easy to handle the complex surfaces in the models. However, this approach is computationally intense in comparison with finite differences. Finite differences are computationally efficient, but in general, they require rectangular grids, leading to the stair-step approximation of the interfaces, which causes strong diffraction of the wavefield. In this research we present a hybrid algorithm where the discontinuous Galerkin method is used in a relatively small upper part of the model and finite differences are applied to the main part of the model.

  14. The character and amplitude of 'discontinuous' bottom-simulating reflections in marine seismic data

    NASA Astrophysics Data System (ADS)

    Hillman, Jess I. T.; Cook, Ann E.; Sawyer, Derek E.; Küçük, H. Mert; Goldberg, David S.

    2017-02-01

    Bottom-simulating reflections (BSRs) identified in seismic data are well documented; and are commonly interpreted to indicate the presence of gas hydrates along continental margins, as well as to estimate regional volumes of gas hydrate. A BSR is defined as a reflection that sub-parallels the seafloor but is opposite in polarity and cross-cuts dipping sedimentary strata. BSRs form as a result of a strong negative acoustic impedance contrast. BSRs, however, are a diverse seismic phenomena that manifest in strikingly contrasting ways in different geological settings, and in different seismic data types. We investigate the characteristics of BSRs, using conventional and high resolution, 2D and 3D seismic data sets in three locations: the Terrebonne and Orca Basins in the Gulf of Mexico, and Blake Ridge on the US Atlantic Margin. The acquisition geometry and frequency content of the seismic data significantly impact the resultant character of BSRs, as observed with depth and amplitude maps of the BSRs. Furthermore, our amplitude maps reinforce the concept that the BSR represents a zone, over which the transition from hydrate to free gas occurs, as opposed to the conventional model of the BSR occurring at a single interface. Our results show that a BSR can be mapped in three dimensions but it is not spatially continuous, at least not at the basin scale. Rather, a BSR manifests itself as a discontinuous, or patchy, reflection and only at local scales is it continuous. We suggest the discontinuous nature of BSRs is the result of variable saturation and distribution of free gas and hydrate, acquisition geometry and frequency content of the recorded seismic data. The commonly accepted definition of a BSR should be broadened with careful consideration of these factors, to represent the uppermost extent of enhanced amplitude at the shallowest occurrence of free gas trapped by overlying hydrate-bearing sediments.

  15. Seismic imaging of transition zone discontinuities suggests hot mantle west of Hawaii.

    PubMed

    Cao, Q; van der Hilst, R D; de Hoop, M V; Shim, S-H

    2011-05-27

    The Hawaiian hotspot is often attributed to hot material rising from depth in the mantle, but efforts to detect a thermal plume seismically have been inconclusive. To investigate pertinent thermal anomalies, we imaged with inverse scattering of SS waves the depths to seismic discontinuities below the Central Pacific, which we explain with olivine and garnet transitions in a pyrolitic mantle. The presence of an 800- to 2000-kilometer-wide thermal anomaly (ΔT(max) ~300 to 400 kelvin) deep in the transition zone west of Hawaii suggests that hot material does not rise from the lower mantle through a narrow vertical plume but accumulates near the base of the transition zone before being entrained in flow toward Hawaii and, perhaps, other islands. This implies that geochemical trends in Hawaiian lavas cannot constrain lower mantle domains directly.

  16. Changes in seismic anisotropy shed light on the nature of the Gutenberg discontinuity.

    PubMed

    Beghein, Caroline; Yuan, Kaiqing; Schmerr, Nicholas; Xing, Zheng

    2014-03-14

    The boundary between the lithosphere and asthenosphere is associated with a platewide high-seismic velocity "lid" overlying lowered velocities, consistent with thermal models. Seismic body waves also intermittently detect a sharp velocity reduction at similar depths, the Gutenberg (G) discontinuity, which cannot be explained by temperature alone. We compared an anisotropic tomography model with detections of the G to evaluate their context and relation to the lithosphere-asthenosphere boundary (LAB). We find that the G is primarily associated with vertical changes in azimuthal anisotropy and lies above a thermally controlled LAB, implying that the two are not equivalent interfaces. The origin of the G is a result of frozen-in lithospheric structures, regional compositional variations of the mantle, or dynamically perturbed LAB.

  17. Mantle transition zone discontinuities beneath the contiguous United States

    NASA Astrophysics Data System (ADS)

    Gao, Stephen S.; Liu, Kelly H.

    2014-08-01

    Using over 310,000 high-quality radial receiver functions recorded by the USArray and other seismic stations in the contiguous United States, the depths of the 410 km and 660 km discontinuities (d410 and d660) are mapped in over 1,000 consecutive overlapping circles with a radius of 1°. The average mantle transition zone (MTZ) thickness for both the western and central/eastern U.S. is within 3 km from the global average of 250 km, suggesting an overall normal MTZ temperature beneath both areas. The Pacific Coast Ranges and the southern Basin and Range Province are underlain by a depressed d410, indicating higher-than-normal temperature in the upper MTZ. The proposed Yellowstone and Raton hot spots are not associated with clear undulations of the MTZ discontinuities, but d410 beneath another proposed hot spot, Bermuda, is depressed significantly and d660 has a normal depth. Low-temperature regions are found in the upper MTZ associated with the subducted Juan de Fuca slab beneath the northern Rocky Mountains and in two circular areas beneath the northern Basin and Range Province and the southern Colorado Plateau. Part of the Great Plains is characterized by a depressed d660. This observation, when combined with results from seismic tomography, suggests the existence of a cold region in the lower MTZ, probably associated with subducted Farallon slab segments.

  18. Seismic discontinuities beneath the southwestern United States from S receiver functions

    NASA Astrophysics Data System (ADS)

    Akanbi, Olufemi; Li, Aibing

    2016-05-01

    S-receiver functions along the Colorado Plateau-Rio Grande Rift-Great Plains Transect known as LA RISTRA in the southwestern United States have been utilized to map seismic discontinuities beneath this tectonically active region. Individual receiver functions were stacked according to ray piercing points with moveout corrections in order to improve the signal-to-noise ratio of the converted S-to-P phases. A mantle discontinuity, which is interpreted as the lithosphere-asthenosphere boundary (LAB), is observed along the profile with depth ranging from 80 km beneath the Rio Grande Rift (RGR) to 100 km beneath the Great Plains (GP) and 120-180 km beneath the Colorado Plateau (CP). The shallow LAB beneath the Rio Grande Rift is indicative of lithosphere extension and asthenosphere upwarp. The LAB deepens sharply at the RGR-CP and RGR-GP boundaries, providing evidence for edge-driven, small-scale mantle convection beneath LA RISTRA. Two local discontinuities beneath the southeastern Colorado Plateau are imaged at ~ 250 km and ~ 300 km and could be the top and base of the eroded lithosphere, respectively. The S receiver function images suggest that edge-driven, small-scale convection is probably the mantle source for recent extension and uplift in the Rio Grande Rift and the Colorado Plateau.

  19. A Study of the Link Between Seismic Anisotropy and the G Discontinuity Based on LPO Modeling in Oceanic Basins

    NASA Astrophysics Data System (ADS)

    Hedjazian, N.; Garel, F.; Davies, R.; Kaminski, E. C.

    2015-12-01

    Seismic anisotropy in oceanic basin inferred from surface waves shows a controversial discontinuity near the lithosphere-asthenosphere boundary (LAB). Radial anisotropy displays an age independent positive gradient, that may correspond to a shallow discontinuity at ~70km depth. This is at odds with the view of a mechanical and age dependent LAB, expected to roughly follow the isotherms. To model the development of seismic anisotropy in oceanic basins, and its potential implications for the interpretation of the G discontinuity, we use the model of lattice preferred orientation (LPO) evolution D-Rex, coupled with a two dimensional model of a plate-driven flow in a fluid with a viscosity depending mainly on stress and temperature. We perform a systematic investigation of the influence on seismic anisotropy of the parameters controlling olivine LPO development. We find that the fraction of deformation accommodated by dislocation creep relative to diffusion creep, the strength of the slip systems involved in plastic deformation, and the efficiency of dynamic recrystallization are key parameters for the production of seismic anisotropy. For a wide range of parameters, the predicted radial anisotropy displays an age independent positive gradient near the depth of the G discontinuity. We thus conclude that this is an ubiquitus characteristic of the seismic anisotropy produced by the 2-D plate driven flow in oceanic basins. If not excluded, no additional ingredients such as partial melting, or change in water content are thus required to explain the radial anisotropy pattern near the LAB.

  20. Seismic evidence for a wide-spread low velocity layer atop the 410-km discontinuity

    NASA Astrophysics Data System (ADS)

    Tauzin, B.; Debayle, E.; Wittlinger, G.

    2009-12-01

    The origin of a low seismic-velocity layer observed in a few regions in the world atop the upper boundary of the mantle transition zone (the 410-km seismic discontinuity) is debated. It has been attributed to the dehydration of subductions, the dehydration of water-bearing silicate beneath continental platforms in the vicinity of mantle plumes, or to dehydration-induced partial melting of ascending ambient mantle rising out of a high-water-solubility transition zone. These interpretations suggest the effect of water which reduces the solidus of mantle silicate rocks and favors partial melting. We present global multiple frequency observations of P-to-S receiver functions indicating that this low velocity layer is actually a wide-spread feature of the upper mantle. Its location is uncorrelated with any tectonic or geodynamic environment. The estimated layer thickness varies over short lateral wavelengths (~200 km) in a range 30 to 100 km. This complexity suggests a compositional origin with a lens-type lateral extension. Dehydration in the vicinity of subductions or mantle plumes cannot solely explain the observed layer implantation. (A) Synthetic receiver functions (RFs) obtained at four lower corner periods for different thicknesses of a low velocity layer (LVL) atop the "410". Steep downward increases of seismic velocities (e.g. the "410") show up as positive (white) amplitudes on the RFs. Steep downward velocity decreases (e.g. the top of the LVL) show up as negative (black) amplitudes. (B) Multiple-frequency RFs obtained at 42 seismic stations after alignment on the "410" waveform. The "410" waveform has a positive amplitude and is colored in white. Under these stations, the top of a LVL is visible. It shows up as a negative (black) amplitude and is emphasized with the small white crosses. The RFs have been ordered by increasing LVL thickness. (C) Synthetic RFs computed using the same LVL thickness distribution as observed on the data.

  1. Seismic structure of the western U.S. mantle and the origin of the Yellowstone hotspot

    NASA Astrophysics Data System (ADS)

    Schmandt, B.; Dueker, K.; Humphreys, E.; Hansen, S. M.

    2012-12-01

    As a result of EarthScope's Transportable Array and prior seismic deployments the quality of mantle imaging beneath Yellowstone is unparalleled among hotspots. P-to-s receiver functions mapped to depth through P and S body-wave tomography models image continuous 410 and 660 km discontinuities beneath the area covered by the TA prior to the middle of the year 2011. Mean depths to the 410 and 660 km discontinuities of 410 and 656 km imply a mantle transition zone that is about 4 km thicker than the global average and hence has a slightly cooler mean temperature and/or enhanced water content. Compared to the mean 660 depth beneath this ~2000 km wide area, the 660 beneath the Yellowstone hotspot is deflected upward by 12-18 km over an area about 200 km wide. This is the most anomalous shallowing of the 660 imaged and its horizontal extent is similar to the area where P and S tomography image low-velocity mantle extending from the top of the transition zone to about 900 km depth. Together, these results indicate a high-temperature, plume-like upwelling extending across the 660. The depth of 410 km discontinuity beneath the Yellowstone region is within 5 km of the mean depth implying the plume is vertically heterogeneous and possibly discontinuous. Tomography images a similar vertically heterogeneous thermal plume. The irregular plume structure may be intrinsic to the dynamics of upwelling through the transition zone, or distortion may be caused by subduction-induced mantle flow. Topography of the 410 and 660 confirm that subducted slabs beneath the western U.S. are highly segmented, as inferred from recent tomography studies. We find no evidence of regionally pervasive velocity discontinuities between 750 and 1400 km depth. The plume's depth of origin within the lower mantle remains uncertain.

  2. Seismic evidence for silicate melt atop the 410-km mantle discontinuity

    USGS Publications Warehouse

    Revenaugh, Justin; Sipkin, S.A.

    1994-01-01

    LABORATORY results demonstrating that basic to ultrabasic melts become denser than olivine-rich mantle at pressures above 6 GPa (refs 1-3) have important implications for basalt petrogenesis, mantle differentiation and the storage of volatiles deep in the Earth. A density cross-over between melt and solid in the extensively molten Archaean mantle has been inferred from komatiitic volcanism and major-element mass balances, but present-day evidence of dense melt below the seismic low-velocity zone is lacking. Here we present mantle shear-wave impedance profiles obtained from multiple-ScS reverberation mapping for corridors connecting western Pacific subduction zone earthquakes with digital seismograph stations in eastern China, imaging a ~5.8% impedance decrease roughly 330 km beneath the Sea of Japan, Yellow Sea and easternmost Asia. We propose that this represents the upper surface of a layer of negatively buoyant melt lying on top of the olivine ??? ??- phase transition (the 410-km seismic discontinuity). Volatile-rich fluids expelled from the partial melt zone as it freezes may migrate upwards, acting as metasomatic agents and perhaps as the deep 'proto-source' of kimberlites. The remaining, dense, crystalline fraction would then concentrate above 410 km, producing a garnet-rich layer that may flush into the transition zone.

  3. Seismic evidence for silicate melt atop the 410-km mantle discontinuity

    NASA Astrophysics Data System (ADS)

    Revenaugh, J.; Sipkin, S. A.

    1994-06-01

    LABORATORY results demonstrating that basic to ultrabasic melts become denser than olivine-rich mantle at pressures above 6 GPa (refs 1-3) have important implications for basalt petrogenesis, mantle differentiation and the storage of volatiles deep in the Earth. A density cross-over between melt and solid in the extensively molten Archaean mantle has been inferred from komatiitic volcanism4-6 and major-element mass balances7, but present-day evidence of dense melt below the seismic low-velocity zone is lacking. Here we present mantle shear-wave impedance profiles obtained from multiple-ScS reverberation mapping for corridors connecting western Pacific subduction zone earthquakes with digital seismograph stations in eastern China, imaging a ~5.8% impedance decrease roughly 330 km beneath the Sea of Japan, Yellow Sea and easternmost Asia. We propose that this represents the upper surface of a layer of negatively buoyant melt lying on top of the olivine-->β-phase transition (the 410-km seismic discontinuity). Volatile-rich fluids expelled from the partial melt zone as it freezes may migrate upwards, acting as metasomatic agents8,9 and perhaps as the deep 'proto-souree' of kimberlites10,11. The remaining, dense, crystalline fraction would then concentrate above 410 km, producing a garnet-rich layer that may flush into the transition zone.

  4. 3D Discontinuous Galerkin elastic seismic wave modeling based upon a grid injection method

    NASA Astrophysics Data System (ADS)

    Monteiller, V.

    2015-12-01

    Full waveform inversion (FWI) is a seismic imaging method that estimates thesub-surface physical properties with a spatial resolution of the order of thewavelength. FWI is generally recast as the iterative optimization of anobjective function that measures the distance between modeled and recordeddata. In the framework of local descent methods, FWI requires to perform atleast two seismic modelings per source and per FWI iteration.Due to the resulting computational burden, applications of elastic FWI have been usuallyrestricted to 2D geometries. Despite the continuous growth of high-performancecomputing facilities, application of 3D elastic FWI to real-scale problemsremain computationally too expensive. To perform elastic seismic modeling with a reasonable amount of time, weconsider a reduced computational domain embedded in a larger background modelin which seismic sources are located. Our aim is to compute repeatedly thefull wavefield in the targeted domain after model alteration, once theincident wavefield has been computed once for all in the background model. Toachieve this goal, we use a grid injection method referred to as the Total-Field/Scattered-Field (TF/SF) technique in theelectromagnetic community. We implemented the Total-Field/Scattered-Field approach in theDiscontinuous Galerkin Finite Element method (DG-FEM) that is used to performmodeling in the local domain. We show how to interface the DG-FEM with any modeling engine (analytical solution, finite difference or finite elements methods) that is suitable for the background simulation. One advantage of the Total-Field/Scattered-Field approach is related to thefact that the scattered wavefield instead of the full wavefield enter thePMLs, hence making more efficient the absorption of the outgoing waves at theouter edges of the computational domain. The domain reduction in which theDG-FEM is applied allows us to use modest computational resources opening theway for high-resolution imaging by full

  5. Upper Mantle Discontinuity Structure Beneath the Western Atlantic Ocean and Eastern North America from SS Precursors

    NASA Astrophysics Data System (ADS)

    Schmerr, N. C.; Beghein, C.; Kostic, D.; Baldridge, A. M.; West, J. D.; Nittler, L. R.; Bull, A. L.; Montesi, L.; Byrne, P. K.; Hummer, D. R.; Plescia, J. B.; Elkins-Tanton, L. T.; Lekic, V.; Schmidt, B. E.; Elkins, L. J.; Cooper, C. M.; ten Kate, I. L.; Van Hinsbergen, D. J. J.; Parai, R.; Glass, J. B.; Ni, J.; Fuji, N.; McCubbin, F. M.; Michalski, J. R.; Zhao, C.; Arevalo, R. D., Jr.; Koelemeijer, P.; Courtier, A. M.; Dalton, H.; Waszek, L.; Bahamonde, J.; Schmerr, B.; Gilpin, N.; Rosenshein, E.; Mach, K.; Ostrach, L. R.; Caracas, R.; Craddock, R. A.; Moore-Driskell, M. M.; Du Frane, W. L.; Kellogg, L. H.

    2015-12-01

    Seismic discontinuities within the mantle arise from a wide range of mechanisms, including changes in mineralogy, major element composition, melt content, volatile abundance, anisotropy, or a combination of the above. In particular, the depth and sharpness of upper mantle discontinuities at 410 and 660 km depth are attributed to solid-state phase changes sensitive to both mantle temperature and composition, where regions of thermal heterogeneity produce topography and chemical heterogeneity changes the impedance contrast across the discontinuity. Seismic mapping of this topography and sharpness thus provides constraint on the thermal and compositional state of the mantle. The EarthScope USArray is providing unprecedented access to a wide variety of new regions previously undersampled by the SS precursors. This includes the boundary between the oceanic plate in the western Atlantic Ocean and continental margin of eastern North America. Here we use a seismic array approach to image the depth, sharpness, and topography of the upper mantle discontinuities, as well as other possible upper mantle reflectors beneath this region. This array approach utilizes seismic waves that reflect off the underside of a mantle discontinuity and arrive several hundred seconds prior to the SS seismic phase as precursory energy. In this study, we collected high-quality broadband data SS precursors data from shallow focus (< 30 km deep), mid-Atlantic ridge earthquakes recorded by USArray seismometers in Alaska. We generated 4th root vespagrams to enhance the SS precursors and determine how they sample the mantle. Our data show detection of localized structure on the discontinuity boundaries as well as additional horizons, such as the X-discontinuity and a potential reflection from a discontinuity near the depth of the lithosphere-asthenosphere boundary. These structures are related to the transition from predominantly old ocean lithosphere to underlying continental lithosphere, as while

  6. A Numerical Study of Energy Balances and Flow Planforms in Earth's Mantle with Radioactive Heating, the 660 km-depth Phase Boundary and Continents

    NASA Astrophysics Data System (ADS)

    Sinha, Gunjan

    It is well established that the temperature gradients in the interiors of internally-heated mantle convection models are subadiabatic (e.g. Parmentier et al., 1994; Bunge et al., 1997, 2001). The subadiabatic gradients have been explained to arise due to a balance between vertical advection and internal heating, however, a detailed analysis of the energy balance in the subadiabatic regions has not been undertaken. In this research, I examine in detail the energy balance in a suite of two-dimensional convection calculations with mixed internal and basal heating, depth-dependent viscosity and continents. I find that there are three causes of subadiabatic gradients. One is the above-mentioned balance, which becomes significant when the ratio of internal heating to surface heat flux is large. The second mechanism involves the growth of the overshoot (maximum and minimum temperatures along a geotherm) of the geotherm near the lower boundary where the dominant balance is between vertical and horizontal advection. The latter mechanism is significant even in relatively weakly internally heated calculations. For time-dependent calculations, I find that local secular cooling can be a dominant term in the energy equation and can lead to subadiabaticity. However, it does not show its signature on the shape of the time-averaged geotherm. I also compare the basal heat flux with parameterized calculations based on the temperature drop at the core-mantle boundary, calculated both with and without taking the subadiabatic gradient into account and I find a significantly improved fit with its inclusion. I also explore a wide range of parameter space to investigate the dynamical interaction between effects due to surface boundary conditions representing continental and oceanic lithosphere and the endothermic phase boundary at 660 km-depth in two-dimensional Cartesian coordinate convection calculations. I find that phase boundary induced mantle layering is strongly affected by the

  7. Seismic Imaging of Mantle Plumes

    NASA Astrophysics Data System (ADS)

    Nataf, Henri-Claude

    The mantle plume hypothesis was proposed thirty years ago by Jason Morgan to explain hotspot volcanoes such as Hawaii. A thermal diapir (or plume) rises from the thermal boundary layer at the base of the mantle and produces a chain of volcanoes as a plate moves on top of it. The idea is very attractive, but direct evidence for actual plumes is weak, and many questions remain unanswered. With the great improvement of seismic imagery in the past ten years, new prospects have arisen. Mantle plumes are expected to be rather narrow, and their detection by seismic techniques requires specific developments as well as dedicated field experiments. Regional travel-time tomography has provided good evidence for plumes in the upper mantle beneath a few hotspots (Yellowstone, Massif Central, Iceland). Beneath Hawaii and Iceland, the plume can be detected in the transition zone because it deflects the seismic discontinuities at 410 and 660 km depths. In the lower mantle, plumes are very difficult to detect, so specific methods have been worked out for this purpose. There are hints of a plume beneath the weak Bowie hotspot, as well as intriguing observations for Hawaii. Beneath Iceland, high-resolution tomography has just revealed a wide and meandering plume-like structure extending from the core-mantle boundary up to the surface. Among the many phenomena that seem to take place in the lowermost mantle (or D''), there are also signs there of the presence of plumes. In this article I review the main results obtained so far from these studies and discuss their implications for plume dynamics. Seismic imaging of mantle plumes is still in its infancy but should soon become a turbulent teenager.

  8. Mantle Transition Zone Discontinuities beneath the Contiguous United States

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The depths of the 410 km (d410) and 660 km (d660) discontinuities are robust indicators of in-situ temperature in the upper and lower boundary, respectively, of the mantle transition zone (MTZ), and thus can provide critical constraints on the depth extent of major tectonic features. Using over 310,000 high-quality radial receiver functions recorded by the USArray and other seismic stations in the contiguous United States, the depths of the d410 and d660 are mapped in over 1000 consecutive overlapping circles with a radius of 1 degree. The average MTZ thickness for both the western and central/eastern US is within 3 km from the global average of 250 km, suggesting an overall normal MTZ temperature beneath both areas. The Pacific Coast Ranges and the southern Basin and Range Province are underlain by a depressed d410, indicating higher-than-normal temperature in the upper MTZ. The proposed Yellowstone and Raton hotspots are not associated with clear undulations of the MTZ discontinuities, but d410 beneath another proposed hotspot, Bermuda, is depressed significantly and d660 has a normal depth. Low-temperature regions are found in the upper MTZ associated with the subducted Juan de Fuca slab beneath the northern Rocky Mountains, and in two circular areas beneath the northern Basin and Range Province and the southern Colorado Plateau. Part of the Great Plains is characterized by a depressed d660. This observation, when combined with results from seismic tomography, suggests the existence of a cold region in the lower MTZ, probably associated with subducted Farallon slab segments.

  9. An upper mantle seismic discontinuity beneath the Galápagos Archipelago and its implications for studies of the lithosphere-asthenosphere boundary

    NASA Astrophysics Data System (ADS)

    Byrnes, Joseph S.; Hooft, Emilie E. E.; Toomey, Douglas R.; Villagómez, Darwin R.; Geist, Dennis J.; Solomon, Sean C.

    2015-04-01

    An upper mantle seismic discontinuity (the Gutenberg or G discontinuity), at which shear wave velocity decreases with depth, has been mapped from S-to-p conversions in radial receiver functions recorded across the Galápagos Archipelago. The mean depth of the discontinuity is 91 ± 8 km beneath the southeastern archipelago and 72 ± 5 km beneath surrounding regions. The discontinuity appears deeper beneath the portion of the Nazca plate that we infer passed over the Galápagos mantle plume than elsewhere in the region. We equate the depth of the G discontinuity to the maximum depth extent of anhydrous melting, which forms an overlying layer of dehydrated and depleted mantle. We attribute areas of shallow discontinuity depth to the formation of the dehydrated layer near the Galápagos Spreading Center and areas of greater discontinuity depth to its modification over a mantle plume with an excess temperature of 115 ± 30°C. The G discontinuity lies within a high-seismic-velocity anomaly that we conclude forms by partial dehydration and a gradual but steady increase in seismic velocity with decreasing depth after upwelling mantle first encounters the solidus for volatile-bearing mantle material. At the depth of the solidus for anhydrous mantle material, removal of remaining water creates a sharp decrease in velocity with depth; this discontinuity may also mark a site of melt accumulation. Results from seismic imaging, the compositions of Galápagos lavas, and rare-earth-element concentrations across the archipelago require that mantle upwelling and partial melting occur over a broad region within the dehydrated and depleted layer. We conclude that the G discontinuity beneath the archipelago does not mark the boundary between rigid lithosphere and convecting asthenosphere.

  10. Seismic evidence for very deep roots of continents

    NASA Astrophysics Data System (ADS)

    Gossler, Jürgen; Kind, Rainer

    1996-02-01

    A major problem in geodynamics with seismic data is discussed: How deeply do the continents penetrate into the mantle? Differential travel times of underside reflections from mantle discontinuities that appear as precursors to SS, in large parts of the globe, show a clear correlation with oceans and continents. They are significantly larger beneath the Asian and North American continents than underneath the neighbouring Pacific. From this observation we conclude that the Asian and North American continents affect the mantle well below 410 km. Changes in the thickness of the transition zone can explain our observations, which are in agreement with the hypothesis of petrological phase changes causing the 410 km and 660 km seismic discontinuities. Average thickness of the transition zone underneath continents is about 14 kim thicker than beneath oceans. Moreover, our findings imply temperature variations about 100-200 K in the mantle transition zone. Weak reflections from 520 km depth corresponding to an impedance contrast of about 2% can be observed only in some areas of the Earth, while observations from other locations definitively show no signal from this depth. Therefore, we propose that the 520 km reflector is only a regional feature.

  11. Investigation of global variations in the in amplitude and frequency content of the PdP, SdS and Pds phases from common upper mantle discontinuities

    NASA Astrophysics Data System (ADS)

    Ainiwaer, A.; Gurrola, H.; Zou, Z.

    2013-12-01

    The global existence of transition zone discontinuities at 410 km and 660 km depths and both almost universally observed in PdP, SdS and Pds data but the 520 and 660 are usually not observed in PdP data.. Discontinuities at approximately 220 km and 520 km depth are observed in these types of data at many regions. The discontinuities at 410, 520 and 660 km are believed to be the polymorphic phase transition zone in olivine. At 410 km discontinuity, α-olivine transforms to β-wadsleyite while γ-ringwoodite decomposes into wusite and provskite at 660 discontinuity while the 220 is usually considered to be the LAB and caused by partial melt. The contrast of elastic properties and the thickness of discontinuity can be estimated by investigating the amplitude of reflected or converted seismic waves. Recent progress in our ability to image these discontinuities in PP and SS data have made it possible to image these PdP and SdS phases to a much as 4 Hz. This will make it possible to investigate the frequency response of these phases to frequencies previously not possible; analysis of which makes it possible add new insight as to the nature of these boundaries. For example beneath the regions beneath the Line Island and the Aleutian Trench The PdP phase has amplitudes of 0.04 to 0.08, which is significantly higher than beneath Hawaii(0.02-0.04) and the region near the Nazca Plate and South American subduction zone Plate where the PdP phase has amplitudes of 0.02-0.04. We interpret that the difference of reflection amplitudes is the result of variations in the impedance between layers due to variations in the velocity and density contrast and the sharpness thereof. For example in most region investigated the P510P is not present in our data but is present in some regions such as the Line Islands. But the phase change expected for the 520 is usually considered to occur over a wide range of depths in which case it should not be visible anywhere at such high frequencies

  12. Simultaneous inversion for mantle shear velocity and the topography of transition zone discontinuities

    NASA Astrophysics Data System (ADS)

    Gu, Y. J.; Dziewonski, A. M.

    2001-05-01

    A method is presented for the simultaneous inversions of shear velocity in the mantle and the topography of transition zone discontinuities. Each travel time residual, corrected for crust and free surface topography, is modeled as resulting from contributions from three-dimensional shear velocity perturbations to a spherical Earth model and boundary undulations to the 410 and 660 km discontinuities. This approach minimizes tradeoffs between velocity and topography. We expand the lateral variations in velocity and the topography of each discontinuity using 362 spherical B-splines; we expand the radial variations using 14 cubic B-splines. To increase the reliability of the measurements, particularly in the undersampled southern hemisphere, we re-examine the topography of the 410- and 660 km discontinuities from more than 21,000 SH-component records. This new data set is significantly larger than those used earlier studies of SS precursors. The long-wavelength features of our new topography maps of the 410- and 660-km discontinuities are compatible with results of earlier studies: the large-scale patterns are dominated by low degree spherical harmonics, particularly at degrees 1 and 2. We also include an independent measurement of the global transition zone thickness for additional constraints on the structure in the transition zone. The best-fit model from the joint inversion reduces the variance of the absolute and differential travel times of S, SS and ScS by 40 to 70 %, and the differential travel times of SS precursors by up to 90%.

  13. The Mohorovičić discontinuity beneath the continental crust: An overview of seismic constraints

    NASA Astrophysics Data System (ADS)

    Carbonell, Ramon; Levander, Alan; Kind, Rainer

    2013-12-01

    The seismic signature of the Moho from which geologic and tectonic evolution hypotheses are derived is to a large degree a result of the seismic methodology which has been used to obtain the image. Seismic data of different types, passive source (earthquake) broad-band recordings, and controlled source seismic refraction, densely recorded wide-angle deep seismic reflection, and normal incidence reflection (using VibroseisTM, explosives, or airguns), have contributed to the description of the Moho as a relatively complex transition zone. Of critical importance for the quality and resolution of the seismic image are the acquisition parameters, used in the imaging experiments. A variety of signatures have been obtained for the Moho at different scales generally dependent upon bandwidth of the seismic source. This variety prevents the development of a single universally applicable interpretation. In this way source frequency content, and source and sensor spacing determine the vertical and lateral resolution of the images, respectively. In most cases the different seismic probes provide complementary data that gives a fuller picture of the physical structure of the Moho, and its relationship to a petrologic crust-mantle transition. In regional seismic studies carried out using passive source recordings the Moho is a relatively well defined structure with marked lateral continuity. The characteristics of this boundary change depending on the geology and tectonic evolution of the targeted area. Refraction and wide-angle studies suggest the Moho to be often a relatively sharp velocity contrast, whereas the Moho in coincident high quality seismic reflection images is often seen as the abrupt downward decrease in seismic reflectivity. The origin of the Moho and its relation to the crust-mantle boundary is probably better constrained by careful analysis of its internal details, which can be complex and geographically varied. Unlike the oceanic Moho which is formed in a

  14. NEXD: A Software Package for High Order Simulation of Seismic Waves using the Nodal Discontinuous Galerkin Method

    NASA Astrophysics Data System (ADS)

    Schumacher, F.; Lambrecht, L.; Friederich, W.

    2015-12-01

    In geophysics numerical simulations are a key tool to understand the processes of earth. For example, global simulations of seismic waves excited by earthquakes are essential to infer the velocity structure within the earth. Furthermore, numerical investigations can be helpful on local scales in order to find and characterize oil and gas reservoirs. Moreover, simulations enable a better understanding of wave propagation in borehole and tunnel seismic applications. Even on microscopic scales, numerical simulations of elastic waves can help to increase knowledge about the behaviour of materials, e.g. to understand the mechanism of crack propagation in rocks. To deal with highly complex heterogeneous models, here the Nodal Discontinuous Galerkin Method (NDG) is used to calculate synthetic seismograms. The advantage of this method is that complex mesh geometries can be computed by using triangular or tetrahedral elements for domain discretization together with a high order spatial approximation of the wave field. The simulation tool NEXD is presented which has the capability of simulating elastic and anelastic wave fields for seismic experiments for one-, two- and three- dimensional settings. The implementation of poroelasticity and simulation of slip interfaces are currently in progress and are working for the one dimensional part. External models provided by e.g. Trelis/Cubit can be used for parallelized computations on triangular or tetrahedral meshes. For absorbing boundary conditions either a fluxes based approach or a Nearly Perfectly Matched Layer (NPML) can be used. Examples are presented to validate the method and to show the capability of the software for complex models such as the simulation of a tunnel seismic experiment.

  15. Correlation of the 410 km Discontinuity Low Velocity Layer with Tomographic Wavespeed Variations

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Dueker, K. G.

    2010-12-01

    The transition zone water-filter model predicts that a hydrous melt layer at the 410-km discontinuity is only actively produced in upwelling region, and does not exist in downwelling region (Bercovici and Karato, 2003). This prediction has been tested by stacking of P-S receiver functions using the RISTRA linear array which crosses west-Texas, New Mexico and Utah. The receiver functions are binned into the NW, SE, SW azimuthal quadrants and stacked to produce well-resolved images of the 410- and 660-km discontinuities. The three receiver function quadrant stack images find a correlation between the occurrence of negative polarity 410-km low velocity layer arrival and the teleseismic body wave velocity tomogram of Schmandt and Humphreys (2010); the 410 low velocity layer arrival is absent where the velocities about the 410 km discontinuity are relatively high and present where the velocities are low. Our finding is consistent with a simple interpretation of the transition zone water filter model which predicts the production of a hydrous melt layer where upflow of sufficiently hydrated transition zone mantle occurs and destruction of a hydrous melt layer where there is downflow. We test this prediction by analyzing the Colorado Rockies Experiment and Seismic Transects (CREST) seismic data which was collected in 2008-2009. This 15 month deployment of 59 CREST stations in tandem with 31 Transportable Array stations yields a total of 161 Mb>5.5 events at 30°-95° distances. The P-S receiver functions are calculated using a multi-channel deconvolution methodology and filtered with a 30-3 s post-deconvolution filter. The receiver function dataset contains about 1800 SV components after RMS, cross-correlation, and visual data quality culling. Common conversion point images are constructed using Pds timing correction from a 3-D upper mantle tomography model (McCarthy and Aster, pers. com.) to account for lateral P/S velocity heterogeneity.

  16. Toward a comprehensive understanding of transition zone seismic discontinuities: A new constraint near the stagnant slab region beneath China

    NASA Astrophysics Data System (ADS)

    Song, T. R. A.; Shen, X.; Stixrude, L. P.; Lithgow-Bertelloni, C. R.

    2015-12-01

    Plate tectonics and subduction operating over much of the Earth's history can induce mantle mixing, chemical heterogeneities and recycle volatiles into the mantle. Some slabs are penetrating into the deep lower mantle, but others are stagnated near the transition zone (TZ). Presumably, the thermochemical state of the TZ is a consequence of delicate balance and feedback between the short-term and long-term mixing. Near the stagnant slab, what's the thermochemical state of the TZ? what's the degree of hydration in the TZ? TZ seismic discontinuities hold the key to resolve the mystery of mass and heat transport in the Earth's mantle as well as the composition of the Earth's interior. But deciphering discontinuity properties are not trivial. Data were typically limited to either mantle triplications, converted waves (P-to-S or S-to-P) or mantle reflections (e.g. SS precursors, ScS reverberations). These observations place constraints on the velocity gradient near the discontinuity as well as discontinuity reflectivity, but hardly offer independent information on the density jump or/and density gradient. In few cases where multiple datasets are jointly analysed to resolve the density jump, the region of sensitivity (or the fresnel zone) of different dataset does not necessarily coincide. Finally, the use of short period (~1 Hz) data (e.g., P'P' precursors) or long period (~> 0.1 Hz) data (e.g., SS precursors) does not allow us to simultaneously address the transition width and the gradient near the discontinuity. We advocate a simple and effective strategy. Specifically, we involve broadband direct converted waves (e.g., P410s, P660s) and the topside reflections (the multiples, e.g., PpP410s, PpP660s) in the context of P wave receiver function technique. Such a tactic not only minimizes tradeoffs between velocity and density jumps, but allows self-consistent estimates of the shear velocity jump, the density jump, the transition width and the velocity/density gradient

  17. Evidence from three-dimensional seismic reflectivity images for enhanced melt supply beneath mid-ocean-ridge discontinuities

    PubMed

    Kent; Singh; Harding; Sinha; Orcutt; Barton; White; Bazin; Hobbs; Tong; Pye

    2000-08-10

    Quantifying the melt distribution and crustal structure across ridge-axis discontinuities is essential for understanding the relationship between magmatic, tectonic and petrologic segmentation of mid-ocean-ridge spreading centres. The geometry and continuity of magma bodies beneath features such as overlapping spreading centres can strongly influence the composition of erupted lavas and may give insight into the underlying pattern of mantle flow. Here we present three-dimensional images of seismic reflectivity beneath a mid-ocean ridge to investigate the nature of melt distribution across a ridge-axis discontinuity. Reflectivity slices through the 9 degrees 03' N overlapping spreading centre on East Pacific Rise suggest that it has a robust magma supply, with melt bodies underlying both limbs and ponding of melt beneath large areas of the overlap basin. The geometry of melt distribution beneath this offset is inconsistent with large-scale, crustal redistribution of melt away from centres of upwelling. The complex distribution of melt seems instead to be caused by a combination of vertical melt transport from the underlying mantle and subsequent focusing of melt beneath a magma freezing boundary in the mid-crust.

  18. Seismic Discontinuities beneath the Southwestern United States from S Receiver Functions

    NASA Astrophysics Data System (ADS)

    Akanbi, O. E.; Li, A.

    2015-12-01

    S- Receiver functions along the Colorado Plateau-Rio Grande Rift-Great Plains Transect known as La RISTRA in the southwestern United States have been utilized to map the Moho and lithosphere-asthenosphere boundary (LAB) beneath this tectonically active region. The receiver functions were stacked according to ray piercing points with moveout corrections in order to improve the signal-to-noise ratio of converted S-to-P phases. The Moho appears at 30-40 km beneath the Rio Grande Rift (RGR) and deepens to 35-45 km beneath the Great Plains (GP) and the Colorado Plateau (CP). A sharp discontinuity is observed along the profile with the average depth of 80 km beneath the RGR, 100 km beneath the GP, and 160 km beneath the CP. This discontinuity is consistent with the top of a low velocity zone in a shear wave model beneath the array and is interpreted as the LAB. Strong phases imaged at ~90 km beneath the CP and GP could be a combination of side-lobes of the Moho conversions and primary Sp phases from a mid-lithosphere discontinuity (MLD). The relatively shallow Moho and LAB beneath the Rio Grande Rift is indicative of lithosphere extension and asthenosphere upwarp. In addition, the LAB shows depth-step depressions at the RGR-CP and RGR-GP boundaries, providing evidence for mantle downwelling. The variation of the lithospheric depth across the RISTRA array supports that edge-driven, small-scale mantle convection is largely responsible for the recent extension and uplift in the Rio Grande Rift and the Colorado Plateau.

  19. Mantle transition zone beneath a normal seafloor in the northwestern Pacific: Electrical conductivity, seismic discontinuity, and water content

    NASA Astrophysics Data System (ADS)

    Matsuno, Tetsuo; Suetsugu, Daisuke; Utada, Hisashi; Baba, Kiyoshi; Tada, Noriko; Shimizu, Hisayoshi; Shiobara, Hajime; Isse, Takehi; Sugioka, Hiroko; Ito, Aki

    2016-04-01

    We conducted a joint electromagnetic and seismic field experiment to probe water content reserved in the mantle transition zone (MTZ) beneath a normal seafloor around the Shatsky Rise in the northwestern Pacific. Specifically for the investigation of the MTZ structure, we developed new ocean bottom instruments for providing higher S/N ratio data and having higher mobility in field experiment than ever. We installed our state-of-the-art instruments in two arrays to the north and south of the Shatsky Rise for 5 years from 2010 to 2015. We first analyzed data obtained in our and previous studies to elucidate an electrical conductivity structure through the magnetotelluric and geomagnetic depth sounding methods and seismic discontinuity depths or thickness of the MTZ through the P-wave receiver function method. An electrical conductivity structure beneath two observational arrays is represented well by an average 1-D model beneath the northern Pacific. A MTZ thickness beneath the north array is thicker than a global average of MTZ thickness by 22 km, and that beneath the south array is similar to the average. For estimating water content in the MTZ, we implemented a series of forward modeling of the electromagnetic responses based on the average 1-D electrical conductivity model, temperature profiles of the MTZ involving temperature anomalies estimated from the MTZ thickness perturbations, and electrical conductivities of dry and hydrous MTZ materials (wadsleyite and ringwoodite). A result of the forward modeling indicates that the maximum water content in the MTZ beneath the north array is 0.5 wt.%.

  20. Mid-mantle deformation inferred from seismic anisotropy.

    PubMed

    Wookey, James; Kendall, J-Michael; Barruol, Guilhem

    2002-02-14

    With time, convective processes in the Earth's mantle will tend to align crystals, grains and inclusions. This mantle fabric is detectable seismologically, as it produces an anisotropy in material properties--in particular, a directional dependence in seismic-wave velocity. This alignment is enhanced at the boundaries of the mantle where there are rapid changes in the direction and magnitude of mantle flow, and therefore most observations of anisotropy are confined to the uppermost mantle or lithosphere and the lowermost-mantle analogue of the lithosphere, the D" region. Here we present evidence from shear-wave splitting measurements for mid-mantle anisotropy in the vicinity of the 660-km discontinuity, the boundary between the upper and lower mantle. Deep-focus earthquakes in the Tonga-Kermadec and New Hebrides subduction zones recorded at Australian seismograph stations record some of the largest values of shear-wave splitting hitherto reported. The results suggest that, at least locally, there may exist a mid-mantle boundary layer, which could indicate the impediment of flow between the upper and lower mantle in this region.

  1. Seismic tomography of the Pacific slab edge under Kamchatka

    NASA Astrophysics Data System (ADS)

    Jiang, Guoming; Zhao, Dapeng; Zhang, Guibin

    2009-02-01

    We determine a 3-D P-wave velocity structure of the mantle down to 700 km depth under the Kamchatka peninsula using 678 P-wave arrival times collected from digital seismograms of 75 teleseismic events recorded by 15 portable seismic stations and 1 permanent station in Kamchatka. The subducting Pacific slab is imaged clearly that is visible in the upper mantle and extends below the 660-km discontinuity under southern Kamchatka, while it shortens toward the north and terminates near the Aleutian-Kamchatka junction. Low-velocity anomalies are visible beneath northern Kamchatka and under the junction, which are interpreted as asthenospheric flow. A gap model without remnant slab fragment is proposed to interpret the main feature of high-V anomalies. Combining our tomographic results with other geological and geophysical evidences, we consider that the slab loss may be induced by the friction with surrounding asthenosphere as the Pacific plate rotated clockwise at about 30 Ma ago, and then it was enlarged by the slab-edge pinch-off by the asthenospheric flow and the presence of Meiji seamounts. As a result, the slab loss and the subducted Meiji seamounts have jointly caused the Pacific plate to subduct under Kamchatka with a lower dip angle near the junction, which made the Sheveluch and Klyuchevskoy volcanoes shift westward.

  2. Structure of the Crust and Mantle Lithosphere underneath NW Namibia Revealed by the WALPASS Seismic Experiment

    NASA Astrophysics Data System (ADS)

    Yuan, X.; Jokat, W.; Weber, M. H.; Geissler, W.; Heit, B.; Eken, T.; Pandey, S.; Lushetile, B.; Hoffmann, K.

    2013-12-01

    The amphibian Walvis Ridge Passive-Source Seismic Experiment (WALPASS) have been operated for a period of two years from 2010 to 2012 in the area where the Walvis Ridge intersects the continental margin of northwestern Namibia. The deployment was intended to study the lithospheric and upper mantle structure in the ocean-continent transition area beneath the passive continental margin. The main idea is to find seismic anomalies related to the postulated hotspot track from the continent to the ocean along the Walvis Ridge that links the Etendeka continental flood-basalt province to the Tristan da Cunha hotspot in the mid Atlantic ocean. This could provide clues of the role of plume-lithosphere interaction during the continental break-up. We present here seismic structures of the crustal and mantle lithosphere in this geophysically little studied region using seismic methods including P and S receiver functions and shear wave splitting. The average crustal thickness in the continental Namibia is ~35 km with a relatively low Vp/Vs ratio of 1.7. Underneath the NE extension of the Walvis Ridge the crust is the thickest (45 km) with a high Vp/Vs ratio (>1.80). The thick crust and high Vp/Vs ratio beneath the Walvis Ridge are consistent with high Vp derived by controlled source seismics, implying a magmatic underplating. A low velocity zone in the mantle is observed at depths of 60-120 km, possibly representing the base of the lithosphere. The P-to-S converted phases at the 410 and 660 km discontinuities arrive 2-3 s earlier, indicating higher upper mantle velocities (+5%). Seismic anisotropy in the mantle derived by the SKS splitting exhibits a pattern of the plume and plate interaction.

  3. Passive rifting of thick lithosphere in the southern East African Rift: Evidence from mantle transition zone discontinuity topography

    NASA Astrophysics Data System (ADS)

    Reed, Cory A.; Liu, Kelly H.; Chindandali, Patrick R. N.; Massingue, Belarmino; Mdala, Hassan; Mutamina, Daniel; Yu, Youqiang; Gao, Stephen S.

    2016-11-01

    To investigate the mechanisms for the initiation and early-stage evolution of the nonvolcanic southernmost segments of the East African Rift System (EARS), we installed and operated 35 broadband seismic stations across the Malawi and Luangwa rift zones over a 2 year period from mid-2012 to mid-2014. Stacking of over 1900 high-quality receiver functions provides the first regional-scale image of the 410 and 660 km seismic discontinuities bounding the mantle transition zone (MTZ) within the vicinity of the rift zones. When a 1-D standard Earth model is used for time-depth conversion, a normal MTZ thickness of 250 km is found beneath most of the study area. In addition, the apparent depths of both discontinuities are shallower than normal with a maximum apparent uplift of 20 km, suggesting widespread upper mantle high-velocity anomalies. These findings suggest that it is unlikely for a low-velocity province to reside within the upper mantle or MTZ beneath the nonvolcanic southern EARS. They also support the existence of relatively thick and strong lithosphere corresponding to the widest section of the Malawi rift zone, an observation that is consistent with strain localization models and fault polarity and geometry observations. We postulate that the Malawi rift is driven primarily by passive extension within the lithosphere attributed to the divergent rotation of the Rovuma microplate relative to the Nubian plate, and that contributions of thermal upwelling from the lower mantle are insignificant in the initiation and early-stage development of rift zones in southern Africa.

  4. Control Effect of a Large Geological Discontinuity on the Seismic Response and Stability of Underground Rock Caverns: A Case Study of the Baihetan #1 Surge Chamber

    NASA Astrophysics Data System (ADS)

    Cui, Zhen; Sheng, Qian; Leng, Xianlun

    2016-06-01

    In this paper, the seismic stability of the #1 surge chamber of the Baihetan hydropower plant, which is influenced by a large dominating geological discontinuity [the interlayer shear weakness zone (ISWZ) C2)], is studied. An advanced, nonlinear, continuously yielding (CY) model was adopted to describe the complex mechanical properties of ISWZ C2. This model considers a power function type, normal stress dependent behavior and the progressive damage that occurred during shear tests. The applicability of the CY model is proved via a comparison with field test results and the theoretical solution. Verification work was conducted in 3DEC code to show that the 3DEC software is suitable for implementing this model. Three ground motion waveforms were utilized to conduct a seismic analysis of the #1 surge chamber after a special response spectrum matching process. The seismic analysis confirmed the control effect of ISWZ C2 on the seismic stability of the cavern. The majority of the cavern's seismic displacement consists of elastic body movement, while the plastic deformation is relatively limited. Further, most of the deformations were caused by the contact deformation of C2. For the contact deformation of C2, the magnitude of permanent shear deformation is larger than that of the normal deformation. The magnitude of permanent shear deformation is more notable along the strike direction of C2, and the permanent normal displacement n of C2 mainly occurs along the dip direction of C2. Finally, the seismic stability of the cavern is assessed via the overload method. The seismic safety factor of the cavern is approximately 2-3.

  5. Effect of H2O on Upper Mantle Phase Transitions in MgSiO3: is the Seismic X-discontinuity an Indicator of Mantle Water Content

    SciTech Connect

    S Jacobsen; Z Liu; T Boffa Ballaran; E Littlefield; L Ehm; R Hemley

    2011-12-31

    The mantle X-discontinuity, usually assigned to positive seismic velocity reflectors in the 260-330 km depth range, has proved difficult to explain in terms of a single mineralogical phase transformation in part because of its depth variability. The coesite to stishovite transition of SiO{sub 2} matches deeper X-discontinuity depths but requires 5-10% free silica in the mantle to match observed impedance contrast. The orthoenstatite (OEn) to high-pressure clinoenstatite (HPCen) transformation of MgSiO{sub 3} also broadly coincides with depths of the X but requires chemically depleted and orthoenstatite-rich lithology at 300 km depth in order to match observed seismic impedance contrast. On the basis of high-pressure infrared spectroscopy, X-ray diffraction, and Raman spectroscopy, we show that 1300 ppm variation of H{sub 2}O content in MgSiO{sub 3} can displace the transition of low-pressure clinoenstatite (LPCen) to HPCen by up to 2 GPa, similar to previous quench experiments on the OEn to HPCen phase transition, where about 30-45 km (1.0-1.5 GPa) of deflection could occur per 0.1 wt% H{sub 2}O. If the mantle X-discontinuity results from pyroxene transitions in a depleted harzburgite layer, because of the strong influence of minor amounts of water on the transformation boundary, the depth of the mantle X-discontinuity could serve as a potentially sensitive indicator of water content in the uppermantle.

  6. Seismic structure and heterogeneity in the upper mantle

    NASA Astrophysics Data System (ADS)

    Kenntt, B. L. N.

    The earliest models of the seismic velocity structure of the upper mantle were smooth. But, since the introduction of strong gradients near 400 km depth by Jeffreys to explain the '20° discontinuity" in observed travel times, there has been a steady accumulation of detail in mantle structure. For a particular region, a smoothed and averaged representation of the seismic structure in the upper mantle can be derived from long-period body wave and higher mode surface wave observations. The vertical resolving power of such techniques is limited by the relatively long wavelengths. In contrast short-period observations offer potential resolution, but are susceptible to the influence of lateral heterogeneity. Fortunately the major features of the upper mantle can be discerned but important questions for structural processes such as the detailed nature ofthe transitions near 410 and 660 km are generally inaccessible. There is a natural tendency to overweight those observations on which particularly clear features are seen (as compared with the statistical anonymity of less spectacular data) which can lead to unwarranted generalizationsof specific results. To reconcile different views of mantle structure requires us to address the purpose for which the mantle structures are to be used. For example, fine detail in a velocity model which is insignificant for travel time studies can have a profound effect on amplitudes and short-period seismic waveforms. The variability in the patterns of body wave observations, especially atshort periods, provides strong evidence for 1-2 per cent heterogeneity on scales around 200 km in the upper mantle. Such features are superimposed on larger scale and larger amplitude lateral variations which can be mapped using surface wave studies. Much of the pattern of lateral variability in the upper mantle is likely to be due to thermal processes both directly by the influence of temperature and indirectly by compositional effects induced by flow

  7. The nature of the 660-kilometer discontinuity in Earth's mantle from global seismic observations of PP precursors.

    PubMed

    Deuss, Arwen; Redfern, Simon A T; Chambers, Kit; Woodhouse, John H

    2006-01-13

    The 660-kilometer discontinuity, which separates Earth's upper and lower mantle, has been detected routinely on a global scale in underside reflections of precursors to SS shear waves. Here, we report observations of this discontinuity in many different regions, using precursors to compressional PP waves. The apparent absence of such precursors in previous studies had posed major problems for models of mantle composition. We find a complicated structure, showing single and double reflections ranging in depth from 640 to 720 kilometers, that requires the existence of multiple phase transitions at the base of the transition zone. The results are consistent with a pyrolite mantle composition.

  8. Seismic interrogation of two highly dynamical earth boundaries: The 410-km discontinuity low-velocity layer and the inner-outer core boundary

    NASA Astrophysics Data System (ADS)

    Jasbinsek, John J.

    Recently, the Transition Zone Water Filter (TZWF) hypothesis of Bercovici and Karato, 2003, highlighted the importance of the 410-km discontinuity in interpreting the Earth's chemical dynamics. This model hypothesizes a localized layer of hydrous melt atop the density increase associated with the 410 km discontinuity. The hydrous melting is predicted to result from a water solubility contrast between the transition zone mineral assemblage dominated by wadsleyite and the upper mantle olivine-dominated mineral assemblage. Thermodynamic calculations and experiments suggest that the hydrous solidus of the olivine dominated assemblage would be exceeded when transition zone material having >1.0% weight percent water is fluxed upwards across the 410 km phase transformation. This hydrous melting thus partitions and sequesters incompatible elements into a melt layer that ponds atop the 410, leaving the upwelling residuum MORB-like with respect to its trace-element inventory. In this model, the geochemical surface observables (mi-oceand ridge basalt and ocean-island basalt geochemistry) are linked to the chemical dynamics at the 410-km discontinuity. If the melt layer is thick enough, it may be detected as a layer of lowered seismic velocity. In Chapters one and two, I test the melt-layer prediction of the TZWF model by searching for lowered seismic velocities atop the 410 beneath four seismic broad-band arrays in the Rocky Mountain region. Aside from available dense seismic arrays, 150 million years of Farallon slab subduction beneath North America provides (1) a possible mechanism to hydrate the transition zone, and (2) downward flow which may provide enhanced upwelling rates in the study region. Both conditions are necessary for operation of the TZWF; thus the western United States is a natural location to test the TZWF model. Low-velocity layers are found by isolating P-S converted waves, and layer thicknesses and velocity reductions are robustly characterized by a

  9. Accelerating the discontinuous Galerkin method for seismic wave propagation simulations using the graphic processing unit (GPU)—single-GPU implementation

    NASA Astrophysics Data System (ADS)

    Mu, Dawei; Chen, Po; Wang, Liqiang

    2013-02-01

    We have successfully ported an arbitrary high-order discontinuous Galerkin (ADER-DG) method for solving the three-dimensional elastic seismic wave equation on unstructured tetrahedral meshes to an Nvidia Tesla C2075 GPU using the Nvidia CUDA programming model. On average our implementation obtained a speedup factor of about 24.3 for the single-precision version of our GPU code and a speedup factor of about 12.8 for the double-precision version of our GPU code when compared with the double precision serial CPU code running on one Intel Xeon W5880 core. When compared with the parallel CPU code running on two, four and eight cores, the speedup factor of our single-precision GPU code is around 12.9, 6.8 and 3.6, respectively. In this article, we give a brief summary of the ADER-DG method, a short introduction to the CUDA programming model and a description of our CUDA implementation and optimization of the ADER-DG method on the GPU. To our knowledge, this is the first study that explores the potential of accelerating the ADER-DG method for seismic wave-propagation simulations using a GPU.

  10. Toward a Comprehensive Understanding of Transition Zone Seismic Discontinuities: Part I. New Constraints from Receiver Function Forward and Backward Scattering Waves

    NASA Astrophysics Data System (ADS)

    Shen, X.; Song, T. R. A.; Yuan, X.

    2014-12-01

    Transition zone discontinuities, among all, hold the key to resolve the mystery of mass and heat transport in the Earth's mantle and the composition of the Earth's interior. In previous efforts, the data are limited to either upper mantle triplications, converted waves or mantle reflections (e.g. SS precursors, ScS reverberations). When multiple datasets are jointly analyzed, they are often restrained at relatively long period (~ 0.1 Hz). To complement previous efforts, we advocate a simple and effective strategy to tackle a number of seismic observables altogether. Specifically, we involve broadband direct converted waves (e.g., P410s, P660s) and the topside reflections (the multiples, e.g., PpP410s, PpP660s) in the context of P wave receiver function technique. Such a tactic not only minimizes tradeoffs between velocity and density jumps, but also allows a superior resolution on the sharpness of the boundary and a detailed description of transition zone discontinuities. Here we summarize our first attempt in the region of stagnant slab beneath Chinese continent. We processed waveforms from 1000 stations of the Chinese seismic array using an automatic scheme to remove noisy waveforms and retained close to ~300,000 high quality receiver functions in the L-Q-T coordinate system. While avoiding interferences from other mantle waves, we perform slowness stacking of direct converted waves and the multiples, respectively, at several discrete frequency bands between 0.05 Hz and 1Hz and obtain amplitude estimates and uncertainties through the bootstrap method. To properly calibrate the amplitudes of receiver functions, we take into account the effect of incoherent stacking due to discontinuity topography and frequency-dependent attenuation. Our findings indicate that the 410 is a sharp boundary with a small density jump (<< 5 km, ΔVs=5-6%, Δρ=1.5-2%), but there is no significant gradient near the sharp transition. While the 660 is best described by a sharp boundary and

  11. Self-consistent Synthetic Mantle Discontinuities From Joint Modeling of Geodynamics and Mineral Physics and Their Effects on the 3D Global Wave Field

    NASA Astrophysics Data System (ADS)

    Schuberth, B.; Piazzoni, A.; Bunge, H.; Igel, H.; Steinle-Neumann, G.; Moder, C.; Oeser, J.

    2007-12-01

    Our current understanding of mantle structure and dynamics is to a large part based on inversion of seismic data resulting in tomographic images and on direct analysis of a wide range of seismic phases such as Pdiff, PcP, ScS SdS etc. For solving inverse problems, forward modeling is needed to obtain a synthetic dataset for a given set of model parameters. In this respect, great progress has been made over the last years in the developement of sophisticated numerical full waveform modeling tools. However, the main limitation in the application of this new class of techniques for the forward problem of seismology is the lack of accurate predictions of mantle heterogeneity that allow us to test hypotheses about Earth's mantle. Such predictive models should be based on geodynamic and mineralogical considerations and derived independently of seismological observations. Here, we demonstrate the feasibility of joining forward simulations from geodynamics, mineral physics and seismology to obtain earth-like seismograms. 3D global wave propagation is simulated for dynamically consistent thermal structures derived from 3D mantle circulation modeling (e.g. Bunge et al. 2002), for which the temperatures are converted to seismic velocities using a recently published, thermodynamically self-consistent mineral physics approach (Piazzoni et al. 2007). Assuming a certain, fixed mantle composition (e.g. pyrolite) our mineralogic modeling algorithm computes the stable phases at mantle pressures for a wide range of temperatures by system Gibbs free energy minimization. Through the same equations of state that model the Gibbs free energy, we compute elastic moduli and density for each stable phase assemblage at the same P-T conditions. One straightforward application of this approach is the study of the seismic signature of synthetic mantle discontinuities arising in such models, as the temperature dependent phase transformations occuring at around 410 Km and 660 Km depth are

  12. Mantle transition zone structure beneath the Changbai volcano: Insight into deep slab dehydration and hot upwelling near the 410 km discontinuity

    NASA Astrophysics Data System (ADS)

    Tian, You; Zhu, Hongxiang; Zhao, Dapeng; Liu, Cai; Feng, Xuan; Liu, Ting; Ma, Jincheng

    2016-08-01

    We study the detailed mantle transition zone structure beneath the active Changbai intraplate volcano in Northeast China by using a receiver-function method. A total of 3005 teleseismic receiver functions recorded by 70 broadband stations are obtained by using a common-conversion-point stacking method. For conducting the time-to-depth conversion, we use a three-dimensional velocity model of the study region so as to take into account the influence of structural heterogeneities. Our results reveal significant depth variations of the 410, 520, and 660 km discontinuities. A broad depression of the 410 km discontinuity and a low-velocity anomaly are revealed beneath the Changbai volcano, which may reflect a large-scale hot mantle upwelling around the 410 km discontinuity with a positive Clapeyron slope. The 520 km discontinuity is identified clearly, and its uplift occurs above the stagnant Pacific slab. We also find a prominent depression of the 660 km discontinuity, which is elongated along the trend of deep earthquake clusters in a range of 39°N-44°N latitude, and the depression area has a lateral extent of about 400 km. Because the 520 and 660 km discontinuities correspond to positive and negative Clapeyron slopes, respectively, we think that the 520 uplift and the 660 depression are caused by the cold subducting Pacific slab. A part of the Pacific slab may have penetrated into the lower mantle and so caused the large-scale 660 depression in front of the deep earthquake clusters. Our results also reveal a part of the upper boundary of the subducting Pacific slab in the mantle transition zone.

  13. Accelerating the discontinuous Galerkin method for seismic wave propagation simulations using multiple GPUs with CUDA and MPI

    NASA Astrophysics Data System (ADS)

    Mu, Dawei; Chen, Po; Wang, Liqiang

    2013-12-01

    We have successfully ported an arbitrary high-order discontinuous Galerkin method for solving the three-dimensional isotropic elastic wave equation on unstructured tetrahedral meshes to multiple Graphic Processing Units (GPUs) using the Compute Unified Device Architecture (CUDA) of NVIDIA and Message Passing Interface (MPI) and obtained a speedup factor of about 28.3 for the single-precision version of our codes and a speedup factor of about 14.9 for the double-precision version. The GPU used in the comparisons is NVIDIA Tesla C2070 Fermi, and the CPU used is Intel Xeon W5660. To effectively overlap inter-process communication with computation, we separate the elements on each subdomain into inner and outer elements and complete the computation on outer elements and fill the MPI buffer first. While the MPI messages travel across the network, the GPU performs computation on inner elements, and all other calculations that do not use information of outer elements from neighboring subdomains. A significant portion of the speedup also comes from a customized matrix-matrix multiplication kernel, which is used extensively throughout our program. Preliminary performance analysis on our parallel GPU codes shows favorable strong and weak scalabilities.

  14. Grain size evolution in the mantle and its effect on geodynamics, seismic velocities and attenuation

    NASA Astrophysics Data System (ADS)

    Dannberg, Juliane; Eilon, Zach; Gassmoeller, Rene; Moulik, Pritwiraj; Myhill, Robert; Faul, Ulrich; Asimow, Paul

    2015-04-01

    viscosities than their cores. Dynamic recrystallisation in subducting slabs results in lower seismic velocities and Q than would be predicted from purely thermal models. A change in physical parameters such as activation volume is required across the 660 km discontinuity to match the higher Q observed seismically in the lower mantle. The very slow grain growth in the lower mantle predicted by high pressure experiments produces unrealistically large travel time delays (>20 s) and t* values (>4 s) in our synthetic calculations with our current constitutive relationships for deriving Vs and Q. Benchmarking our dynamic models against seismic observations will involve further adjustments to the grain size evolution in the lower mantle as well as the tuning of these constitutive relationships.

  15. Seismic structure of the lithosphere beneath NW Namibia: Impact of the Tristan da Cunha mantle plume

    NASA Astrophysics Data System (ADS)

    Yuan, Xiaohui; Heit, Benjamin; Brune, Sascha; Steinberger, Bernhard; Geissler, Wolfram H.; Jokat, Wilfried; Weber, Michael

    2017-01-01

    Northwestern Namibia, at the landfall of the Walvis Ridge, was affected by the Tristan da Cunha mantle plume during continental rupture between Africa and South America, as evidenced by the presence of the Etendeka continental flood basalts. Here we use data from a passive-source seismological network to investigate the upper mantle structure and to elucidate the Cretaceous mantle plume-lithosphere interaction. Receiver functions reveal an interface associated with a negative velocity contrast within the lithosphere at an average depth of 80 km. We interpret this interface as the relic of the lithosphere-asthenosphere boundary (LAB) formed during the Mesozoic by interaction of the Tristan da Cunha plume head with the pre-existing lithosphere. The velocity contrast might be explained by stagnated and "frozen" melts beneath an intensively depleted and dehydrated peridotitic mantle. The present-day LAB is poorly visible with converted waves, indicating a gradual impedance contrast. Beneath much of the study area, converted phases of the 410 and 660 km mantle transition zone discontinuities arrive 1.5 s earlier than in the landward plume-unaffected continental interior, suggesting high velocities in the upper mantle caused by a thick lithosphere. This indicates that after lithospheric thinning during continental breakup, the lithosphere has increased in thickness during the last 132 Myr. Thermal cooling of the continental lithosphere alone cannot produce the lithospheric thickness required here. We propose that the remnant plume material, which has a higher seismic velocity than the ambient mantle due to melt depletion and dehydration, significantly contributed to the thickening of the mantle lithosphere.

  16. Effect of H2O on Upper Phase Transitions in MgSiO3: Is the Depth of the Seismic X-Discontinuity an Indicator of Mangle Water Content?

    SciTech Connect

    Jacobsen, S.D.; Ehm, L.; Liu, Z.; Ballaran T.B.; Littlefield, E.F.; Hemley, R.J.

    2010-06-29

    The mantle X-discontinuity, usually assigned to positive seismic velocity reflectors in the 260-330 km depth range, has proved difficult to explain in terms of a single mineralogical phase transformation in part because of its depth variability. The coesite to stishovite transition of SiO{sub 2} matches deeper X-discontinuity depths but requires 5-10% free silica in the mantle to match observed impedance contrast. The orthoenstatite (OEn) to high-pressure clinoenstatite (HPCen) transformation of MgSiO{sub 3} also broadly coincides with depths of the X but requires chemically depleted and orthoenstatite-rich lithology at 300 km depth in order to match observed seismic impedance contrast. On the basis of high-pressure infrared spectroscopy, X-ray diffraction, and Raman spectroscopy, we show that 1300 ppm variation of H{sub 2}O content in MgSiO{sub 3} can displace the transition of low-pressure clinoenstatite (LPCen) to HPCen by up to 2 GPa, similar to previous quench experiments on the OEn to HPCen phase transition, where about 30-45 km (1.0-1.5 GPa) of deflection could occur per 0.1 wt% H{sub 2}O. If the mantle X-discontinuity results from pyroxene transitions in a depleted harzburgite layer, because of the strong influence of minor amounts of water on the transformation boundary, the depth of the mantle X-discontinuity could serve as a potentially sensitive indicator of water content in the upper mantle.

  17. The contribution of the seismic component of Topo-Iberia to the imaging of the deep structure of the Iberian Peninsula and North Morocco

    NASA Astrophysics Data System (ADS)

    Diaz, Jordi; Gallart, Josep; de Lis Mancilla, Flor; Villaseñor, Antonio; Bonatto, Luciana; Schimmel, Martin; Harnafi, Mimoun; El Moudnib, Lahcen

    2015-04-01

    Topo-Iberia has been a large-scale Spanish project running from 2007 to 2013 that integrated more than 150 researchers on Earth Sciences. One of its key assets was the management of an observatory platform, named IberArray, aimed to provide new geophysical datasets (seismic, GPS, MT) to constrain the structure of Iberia with unprecedented resolution. The IberArray seismic pool was composed by 70+ BB stations, covering the study area in 3 deployments with a site-density of 60km x 60km. The data base holds ~300 sites, including the permanent networks in the area. Hence it forms a unique seismic database in Europe that allows for multiple analyses to constrain the complex geodinamics of the Western Mediterranean. A summary of new results coming from different techniques is presented here. The SKS splitting analysis has provided a spectacular image of the rotation of the fast velocity direction along the Gibraltar Arc. In central and northern Iberia, the fast polarization directions are close to EW, consistently with global mantle flow models considering contributions of surface plate motion, density variations and net lithosphere rotation. Those results suggest an asthenospheric origin of the observed anisotropy related to present-day mantle flow. Receiver functions have revealed the crustal thickness variations beneath the Atlas, Rif and southern Iberia, evidencing a relevant crustal root beneath the Rif, in agreement with recent, high-density active seismic experiments. The Variscan Iberian massif shows a flat Moho discontinuity, while the areas reworked in the Alpine orogeny show a slightly thicker crust. Beneath N Iberia, the imbrication of the Iberian and Eurasian crusts results in complex receiver functions. Depths exceeding 45 km are observed along the Pyrenean range, while the crust thins to values of 26-28 km close to the Atlantic coasts. The geometry of the 410-km and 660-km discontinuities has been investigated using novel cross

  18. Plume's buoyancy and heat fluxes from the deep mantle estimated by an instantaneous mantle flow simulation based on the S40RTS global seismic tomography model

    NASA Astrophysics Data System (ADS)

    Yoshida, Masaki

    2012-11-01

    It is still an open question as to how much heat is transported from the deep mantle to the upper mantle by mantle upwelling plumes, which would impose a strong constraint on models of the thermal evolution of the earth. Here I perform numerical computations of instantaneous mantle flow based on a recent highly resolved global seismic tomography model (S40RTS), apply new simple fluid dynamics theories to the plume's radius and velocity, considering a Poiseuille flow assumption and a power-law relationship between the boundary layer thickness and Rayleigh number, and estimate the plume's buoyancy and heat fluxes from the deep lower mantle under varying plume viscosity. The results show that for some major mantle upwelling plumes with localized strong ascent velocity under the South Pacific and Africa, the buoyancy fluxes of each plume beneath the ringwoodite to perovskite + magnesiowüstite ("660-km") phase decomposition boundary are comparable to those inferred from observed hotspot swell volumes on the earth, i.e., on the order of 1 Mg s-1, when the plume viscosity is 1019-1020 Pa s. This result, together with previous numerical simulations of mantle convection and the gentle Clausius-Clapeyron slope for the 660-km phase decomposition derived from recent high-pressure measurements under dehydrated/hydrated conditions in the mantle transition zone, implies that mantle upwelling plumes in the lower mantle penetrate the 660-km phase decomposition boundary without significant loss in thermal buoyancy because of the weak thermal barrier at the 660-km boundary. The total plume heat flux under the South Pacific is estimated to be about 1 TW beneath the 660-km boundary, which is significantly smaller than the core-mantle boundary heat flux. Previously published scaling laws for the plume's radius and velocity based on a plume spacing theory, which explains well plume dynamics in three-dimensional time-dependent mantle convection, suggest that these plume fluxes depend

  19. Diffractional Imaging of Mantle Transition Zone Discontinuities Using SdS-SS Traveltimes

    NASA Astrophysics Data System (ADS)

    Guo, Z.; Zhou, Y.

    2015-12-01

    The mantle transition zone is characterized by two discontinuities at depths of about 410 and 660 km. Mineral physics studies suggest that wavespeed and density jumps across the discontinuities are associated with olivine phase transformations and the depths at which the phase transformations occur are strongly dependent on temperature. Imaging lateral variations of the discontinuity depths is important for constraining thermal structure in the mid mantle. SS precursors (SdS) are waves reflected at the underside of the discontinuities and arrive beforethe SS phase. Their traveltime measurements at teleseismic distances can be used to map the discontinuities at a global scale. In this study, we measure frequency-dependent SS precursors traveltimes using seismograms recorded at GSN stations for earthquakes occurred between 2000 and 2015. The measurements were made using cosine tapers and multitapers and the traveltimes show significant dispersion. We calculate finite-frequency sensitivity kernels for SdS-SS differential measurements based on traveling-wave mode summation, which account for complete wave interactions within the measurement window. We will discuss preliminary results from finite-frequency imaging using SdS-SS dispersion measurements and the effects of 3-D crustal structure and mantle wavespeed structure.

  20. The IberArray BB seismic network of Topo-Iberia: new constraints revealing the deep structure of the Iberian Peninsula and North Morocco

    NASA Astrophysics Data System (ADS)

    Gallart, J.; Diaz Cusi, J.; Villasenor, A.; Mancilla, F. D. L.; Bonatto, L.; Schimmel, M.; El moudnib, L.

    2014-12-01

    Topo-Iberia has been a large-scale Spanish project running from 2007 to 2013 that integrated more than 150 researchers on Earth Sciences. One of its key assets was the management of an observatory platform, named IberArray, aimed to provide new geophysical datasets (seismic, GPS, MT) to constrain the structure of Iberia with unprecedented resolution. The IberArray seismic pool was composed by 70+ BB stations, covering the study area in 3 deployments with a site-density of 60km x 60km. The data base holds ~300 sites, including the permanent networks in the area. Hence it forms a unique seismic database in Europe that allow for multiple analyses to constrain the complex geodinamics of the Western Mediterranean. A summary of new results coming from different techniques is presented here. The SKS splitting analysis has provided a spectacular image of the rotation of the fast velocity direction along the Gibraltar Arc. In central and northern Iberia, the fast polarization directions are close to EW, consistently with global mantle flow models considering contributions of surface plate motion, density variations and net lithosphere rotation. Those results suggest an asthenospheric origin of the observed anisotropy related to present-day mantle flow. Receiver functions have revealed the crustal thickness variations beneath the Rif and southern Iberia, including a crustal root beneath the Rif. The Variscan Iberian massif shows a flat Moho discontinuity, while the areas reworked in the Alpine orogeny show a slightly thicker crust. Beneath N Iberia, the imbrication of the Iberian and Eurasian crusts results in complex receiver functions. Depths exceeding 45 km are observed along the Pyrenean range, while the crust thins to values of 26-28 km close to the Atlantic coasts. The geometry of the 410-km and 660-km discontinuities has been investigated using novel cross-correlation/stacking techniques. Ambient noise tomography allows to identify the main sedimentary basins and to

  1. The amount of water reserved in a "normal" oceanic mantle transition zone beneath the northwestern Pacific, inferred from data of coincident ocean bottom electromagnetic and seismic observations

    NASA Astrophysics Data System (ADS)

    Matsuno, T.; Suetsugu, D.; Utada, H.; Baba, K.; Tada, N.; Shimizu, H.; Shiobara, H.; Isse, T.; Sugioka, H.; Ito, A.

    2015-12-01

    "Is the mantle transition zone (MTZ) a major water reservoir of the Earth?" To answer this question, we have inferred the amount of water reserved in a "normal" oceanic MTZ beneath the northwestern Pacific from electrical and seismic structures. The field experiment was conducted with arrays of ocean bottom electromagnetometers and broadband ocean bottom seismometers in 2010-2014. Our innovative ocean bottom instruments, Earth's electric field observation system was used to measure time-variations of electric field with high S/N ratio at periods of >105s where the electromagnetic field is sensitive to the MTZ, and broadband ocean bottom seismometer of the next generation was used to record the earth motion with as low noise level as land stations. Electromagnetic data were first analyzed to derive MT and GDS response functions at periods of >105s. Then, model responses were numerically obtained from electrical conductivity models overlain by earth-surface land-ocean heterogeneity. Comparison between the observation and the prediction suggested that a MTZ electrical conductivity structure beneath the northwestern Pacific is similar to an averaged 1-D structure of the north Pacific [Shimizu et al., 2010]. Seismic data were analyzed through a P-wave receiver function method. Depths of 410 and 660 km discontinuities and thickness of the MTZ were variable by areas. The MTZ thickness beneath the southern part of Area A (northwest to the Shatsky Rise), 270 km, is larger a global average of 243 km [e.g., Flanagan & Shearer, 1989], while those beneath Area B (southeast to the Shatsky Rise), 241 and 248 km, are comparable to the average. The water content and a thermal structure in the MTZ beneath Area A were inferred from the data. First, a temperature perturbation was determined to -70~-150 K from the thickness perturbation of the MTZ. Then, a thermal structure for Area A is assumed to a structure [Katsura et al., 2010] with the temperature perturbation. Electrical

  2. Seismically imaging the Afar plume

    NASA Astrophysics Data System (ADS)

    Hammond, J. O.; Kendall, J. M.; Bastow, I. D.; Stuart, G. W.; Keir, D.; Ayele, A.; Ogubazghi, G.; Ebinger, C. J.; Belachew, M.

    2011-12-01

    Plume related flood basalt volcanism in Ethiopia has long been cited to have instigated continental breakup in northeast Africa. However, to date seismic images of the mantle beneath the region have not produced conclusive evidence of a plume-like structure. As a result the nature and even existence of a plume in the region and its role in rift initiation and continental rupture are debated. Previous seismic studies using regional deployments of sensors in East-Africa show that low seismic velocities underlie northeast Africa, but their resolution is limited to the top 200-300km of the Earth. Thus, the connection between the low velocities in the uppermost mantle and those imaged in global studies in the lower mantle is unclear. We have combined new data from Afar, Ethiopia with 6 other regional experiments and global network stations across Ethiopia, Eritrea, Djibouti and Yemen, to produce high-resolution models of upper mantle P- and S- wave velocities to the base of the transition zone. Relative travel time tomographic inversions show that the top 100km is dominated by focussed low velocity zones, likely associated with melt in the lithosphere/uppermost asthenosphere. Below these depths a broad SW-NE oriented sheet like upwelling extends down to the top of the transition zone. Within the transition zone two focussed sharp-sided low velocity regions exist: one beneath the Western Ethiopian plateau outside the rift valley, and the other beneath the Afar depression. The nature of the transition zone anomalies suggests that small upwellings may rise from a broader low velocity plume-like feature in the lower mantle. This interpretation is supported by numerical and analogue experiments that suggest the 660km phase change and viscosity jump may impede flow from the lower to upper mantle creating a thermal boundary layer at the base of the transition zone. This allows smaller, secondary upwellings to initiate and rise to the surface. Our images of secondary upwellings

  3. Mantle discontinuities under southern Africa from precursors to P′ P′df

    USGS Publications Warehouse

    Xu, Fei; Vidale, John E.; Earle, Paul S.; Benz, Harley M.

    1998-01-01

    We investigate the reflection properties of upper-mantle discontinuities beneath southern Africa using precursors to the df branch of PKPPKP (P′ P′). The P′ P′df branch is weaker than the ab and bc branches, but it does not have the complication of a caustic and appears across a wider distance range. Stacks from hundreds of short-period seismograms recorded in California from the March 9, 1994 Tonga earthquake (Mw = 7.6) show an ∼5% reflection (at 3.5 s dominate period) from 660-km depth indicating a sharp “660” under southern Africa. A 3.5 s period reflection from 410-km depth is also visible in these stacks, but only ∼2% the strength of P′ P′df. This result contrasts with the observation of the “410” and the “660” reflecting comparable amounts of high-frequency energy under the Indian Ocean [Benz and Vidale, 1993a], indicating either a diffuse “410” boundary under southern Africa or global variations in the impedance change across the “410”. A 1.5 s period reflection may indicate the existence of fine-scale heterogeneity near 320-km depth. Reflectivity synthetic seismograms also show that a previously claimed reflection from 785-km depth has the more likely explanation as PcPPKP.

  4. Variations of Hales Discontinuity beneath South India

    NASA Astrophysics Data System (ADS)

    Goyal, Ayush; Kosre, Goukaran Kumar; Borah, Kajaljyoti

    2016-04-01

    Thermodynamic studies show the spinel-garnet transition in fertile and hot mantle should be relatively narrow and should show up in the seismological studies as a discontinuity. The evidence for a shallow lithospheric mantle discontinuity was first proposed by Hales (1969) based on seismological travel time measurement from the Early Rise experiment in the Central United States, where a ~4% increase in the S-wave velocity at a depth of 75 km was observed. The recent studies show, in cratonic blocks with colder geotherms, that it appears at greater depths and over broader intervals, that is, from the Moho to 150 km depth. Different studies interpreted that Hales discontinuity may be due to seismic anisotropy or pervasive partial melts or cation ordering in mantle olivine. In the present study an attempt is made to model the Hales discontinuity in the South Indian shield, by jointly inverting group velocity dispersion and receiver functions, calculated from teleseismic earthquakes recorded at 20 broadband seismograph locations in the study region. South Indian shield is an amalgamation of several crustal blocks, namely, Eastern Dharwar Craton (EDC), Western Dharwar Craton (WDC), Southern Granulite Terrain (SGT) etc. Inversion modeling results show deeper Hales discontinuity (~104-110 km depth) in the south of WDC and SGT, while in the north of Western Dharwar Craton and Eastern Dharwar Craton it varies from ~70-80 km. It is also observed that the Hales Discontinuity is present at greater depth in the western part of Dharwar Craton, compared to the eastern part. Details of the depth, thickness, and the cause of the Hales discontinuity are also investigated. Keywords: Hales Discontinuity, South Indian Shield, Receiver Function, Craton, Inversion modeling.

  5. Estimation of discontinuous coefficients and boundary parameters for hyperbolic systems

    NASA Technical Reports Server (NTRS)

    Lamm, P. K.; Murphy, K. A.

    1986-01-01

    The problem of estimating discontinuous coefficients, including locations of discontinuities, that occur in second order hyperbolic systems typical of those arising in I-D surface seismic problems is discussed. In addition, the problem of identifying unknown parameters that appear in boundary conditions for the system is treated. A spline-based approximation theory is presented, together with related convergence findings and representative numerical examples.

  6. Seismic evidence for water deep in Earth's upper mantle.

    PubMed

    van der Meijde, Mark; Marone, Federica; Giardini, Domenico; van der Lee, Suzan

    2003-06-06

    Water in the deep upper mantle can influence the properties of seismic discontinuities in the mantle transition zone. Observations of converted seismic waves provide evidence of a 20- to 35-kilometer-thick discontinuity near a depth of 410 kilometers, most likely explained by as much as 700 parts per million of water by weight.

  7. Mapping the Hawaiian plume conduit with converted seismic waves

    PubMed

    Li; Kind; Priestley; Sobolev; Tilmann; Yuan; Weber

    2000-06-22

    The volcanic edifice of the Hawaiian islands and seamounts, as well as the surrounding area of shallow sea floor known as the Hawaiian swell, are believed to result from the passage of the oceanic lithosphere over a mantle hotspot. Although geochemical and gravity observations indicate the existence of a mantle thermal plume beneath Hawaii, no direct seismic evidence for such a plume in the upper mantle has yet been found. Here we present an analysis of compressional-to-shear (P-to-S) converted seismic phases, recorded on seismograph stations on the Hawaiian islands, that indicate a zone of very low shear-wave velocity (< 4 km s(-1)) starting at 130-140 km depth beneath the central part of the island of Hawaii and extending deeper into the upper mantle. We also find that the upper-mantle transition zone (410-660 km depth) appears to be thinned by up to 40-50 km to the south-southwest of the island of Hawaii. We interpret these observations as localized effects of the Hawaiian plume conduit in the asthenosphere and mantle transition zone with excess temperature of approximately 300 degrees C. Large variations in the transition-zone thickness suggest a lower-mantle origin of the Hawaiian plume similar to the Iceland plume, but our results indicate a 100 degrees C higher temperature for the Hawaiian plume.

  8. Interactions between magnetohydrodynamical discontinuities

    SciTech Connect

    Dai, W.; Woodward, P.R. )

    1994-11-01

    Interactions between magnetohydrodynamical (MHD) discontinuities are studied through numerical simulations for the set of one-dimensional MHD equations. The interactions include the impact of a shock on a contact discontinuity, the collision of two shocks, and the catchup of a shock over another shock. The shocks involved in the interactions may be very strong. Each shock in an interaction may be either a fast or a slow shock.

  9. Wave field features of shallow vertical discontinuity and their application in non-destructive detection

    USGS Publications Warehouse

    Liu, J.; Xia, J.; Luo, Y.; Chen, C.; Li, X.; Huang, Y.

    2007-01-01

    The geotechnical integrity of critical infrastructure can be seriously compromised by the presence of fractures or crevices. Non-destructive techniques to accurately detect fractures in critical infrastructure such as dams and highways could be of significant benefit to the geotechnical industry. This paper investigates the application of shallow seismic and georadar methods to the detection of a vertical discontinuity using numerical simulations. The objective is to address the kinematical analysis of a vertical discontinuity, determine the resulting wave field characteristics, and provide the basis for determining the existence of vertical discontinuities based on the recorded signals. Simulation results demonstrate that: (1) A reflection from a vertical discontinuity produces a hyperbolic feature on a seismic or georadar profile; (2) In order for a reflection from a vertical discontinuity to be produced, a reflecting horizon below the discontinuity must exist, the offset between source and receiver (x0) must be non-zero, on the same side of the vertical discontinuity; (3) The range of distances from the vertical discontinuity where a reflection event is observed is proportional to its length and to x0; (4) Should the vertical crevice (or fracture) pass through a reflecting horizon, dual hyperbolic features can be observed on the records, and this can be used as a determining factor that the vertical crevice passes through the interface; and (5) diffractions from the edges of the discontinuity can be recorded with relatively smaller amplitude than reflections and their ranges are not constrained by the length of discontinuity. If the length of discontinuity is short enough, diffractions are the dominant feature. Real-world examples show that the shallow seismic reflection method and the georadar method are capable of recording the hyperbolic feature, which can be interpreted as vertical discontinuity. Thus, these methods show some promise as effective non

  10. Modern Regression Discontinuity Analysis

    ERIC Educational Resources Information Center

    Bloom, Howard S.

    2012-01-01

    This article provides a detailed discussion of the theory and practice of modern regression discontinuity (RD) analysis for estimating the effects of interventions or treatments. Part 1 briefly chronicles the history of RD analysis and summarizes its past applications. Part 2 explains how in theory an RD analysis can identify an average effect of…

  11. A sporadic low-velocity layer atop the western U.S. mantle transition zone and short-wavelength variations in transition zone discontinuities

    NASA Astrophysics Data System (ADS)

    Schmandt, B.; Dueker, K. G.; Hansen, S. M.; Jasbinsek, J. J.; Zhang, Z.

    2011-08-01

    Teleseismic receiver function analysis of data from six dense arrays in the western U.S. is used to investigate mantle transition zone (MTZ) discontinuities and the prevalence of a low-velocity layer atop the 410 km discontinuity (410-LVL). Negative polarity Ps arrivals indicative of a low-velocity layer with a top 25-60 km above the 410 are identified in 8-11 out of 18 stacks of receiver functions from highly sampled back azimuth corridors. The 410-LVL is interpreted as partial melt resulting from upwelling of hydrated mantle across a water solubility contrast at the 410. The 669 km mean depth of the 660 km discontinuity (660) and the magnitude of 660 topography suggest variable hydration, locally approaching saturation, in addition to >150 K lateral temperature variations beneath five arrays. Mean amplitudes of P410s and P660s increase monotonically with period from 2 to 10 s; however, greater variations are observed in the frequency dependence of P410s compared to P660s implying 410 thickness is more heterogeneous. Variable 410 thickness is attributed to changes in hydration modulating the width of the olivine-to-wadsleyite transition interval. Frequency dependence of P660s amplitudes suggests a broad velocity gradient consistent with multivariate phase changes in the olivine and garnet systems. Sporadic detection of the 410-LVL, the magnitude and length scales of MTZ discontinuity topography, and inferred variations in hydration support the occurrence of vigorous small-scale convection in the western U.S. mantle. Comparison of receiver functions with body wave tomography suggests small-scale convection driven by sinking slab segments and lithospheric instabilities contributes to the intermittent nature of the 410-LVL.

  12. An aripiprazole discontinuation syndrome.

    PubMed

    Philip, Noah S

    2013-02-01

    Major depression is a common and debilitating illness. Over recent years, new pharmacologic treatments have been approved for this disorder, including the atypical antipsychotics. One of the benefits of these medications is their significant efficacy as augmenting agents for unipolar, nonpsychotic major depressive disorder (MDD).Aripiprazole (marketed as Abilify, Bristol-Myers Squibb/ Otsuka Pharmaceuticals) was the first medication of this class approved for adjunctive treatment of MDD, and is the 5th most commonly prescribed medication in the United States in 2010. However, despite the frequency of its use, little has been described regarding events surrounding aripiprazole discontinuation. Here I describe what is, to my knowledge, the first reported case of an aripiprazole discontinuation syndrome. While directly relevant to psychiatrists and behavioral specialists, the symptoms described here are pertinent for internists and neurologists who may encounter this medication in their clinical practice.

  13. Mingus Discontinuous Multiphysics

    SciTech Connect

    Pat Notz, Dan Turner

    2014-05-13

    Mingus provides hybrid coupled local/non-local mechanics analysis capabilities that extend several traditional methods to applications with inherent discontinuities. Its primary features include adaptations of solid mechanics, fluid dynamics and digital image correlation that naturally accommodate dijointed data or irregular solution fields by assimilating a variety of discretizations (such as control volume finite elements, peridynamics and meshless control point clouds). The goal of this software is to provide an analysis framework form multiphysics engineering problems with an integrated image correlation capability that can be used for experimental validation and model

  14. Discontinuous ephemeral streams

    NASA Astrophysics Data System (ADS)

    Bull, William B.

    1997-07-01

    Many ephemeral streams in western North America flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos. These inherently unstable streams of semiarid regions are sensitive to short-term climatic changes, and to human impacts, because hillslopes supply abundant sediment to infrequent large streamflow events. Discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation; either aggradation or degradation may become dominant. Attainment of equilibrium conditions is brief. Disequilibrium is promoted by channel entrenchment that causes the fall of local base level, and by deposition of channel fans that causes the rise of local base level. These opposing base-level processes in adjacent reaches are maintained by self-enhancing feedback mechanisms. The threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream. Extension of entrenched reaches into channel fans tends to create continuous arroyos. Upvalley migration of fan apexes tends to create depositional valley floors with few stream channels. Less than 100 years is required for arroyo cutting, but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors. Discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers. The sequence changes from degradation to aggradation — headcuts concentrate sheetflow, a single trunk channel conveys flow to the apex of a channel fan, braided distributary channels end in an area of diverging sheetflow, and converging sheetflow drains to headcuts. The sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams. Lithologic controls on the response of discontinuous ephemeral streams include: (1

  15. Seismic assessment for offshore pipelines

    SciTech Connect

    Bruschi, R.; Gudmestad, O.T.; Blaker, F.; Nadim, F.

    1995-12-31

    An international consensus on seismic design criteria for onshore pipelines has been established during the last thirty years. The need to assess seismic design for offshore pipelines has not been similarly recognized. In this paper, the geotechnical hazard for a pipeline routed across steep slopes and irregular terrains affected by earthquakes, is discussed. The integrity of both natural and artificial load bearing supports is assessed.d The response of the pipeline to direct excitation from soil or through discontinuous, sparsely distributed natural or artificial supports, is commented.

  16. Martian seismicity

    NASA Technical Reports Server (NTRS)

    Phillips, Roger J.; Grimm, Robert E.

    1991-01-01

    The design and ultimate success of network seismology experiments on Mars depends on the present level of Martian seismicity. Volcanic and tectonic landforms observed from imaging experiments show that Mars must have been a seismically active planet in the past and there is no reason to discount the notion that Mars is seismically active today but at a lower level of activity. Models are explored for present day Mars seismicity. Depending on the sensitivity and geometry of a seismic network and the attenuation and scattering properties of the interior, it appears that a reasonable number of Martian seismic events would be detected over the period of a decade. The thermoelastic cooling mechanism as estimated is surely a lower bound, and a more refined estimate would take into account specifically the regional cooling of Tharsis and lead to a higher frequency of seismic events.

  17. Academic Advising during Program Discontinuance

    ERIC Educational Resources Information Center

    Maher, Michelle A.

    2006-01-01

    Academic program closure is explored and student advising needs that emerged in 3 stages of program decline and discontinuation are identified. Data from interviews and advising communication of 20 graduate students enrolled in a master of education program targeted for discontinuation were qualitatively analyzed within a framework of an…

  18. A detailed map of the 660-kilometer discontinuity beneath the izu-bonin subduction zone.

    PubMed

    Wicks, C W; Richards, M A

    1993-09-10

    Dynamical processes in the Earth's mantle, such as cold downwelling at subduction zones, cause deformations of the solid-state phase change that produces a seismic discontinuity near a depth of 660 kilometers. Observations of short-period, shear-to-compressional wave conversions produced at the discontinuity yield a detailed map of deformation beneath the Izu-Bonin subduction zone. The discontinuity is depressed by about 60 kilometers beneath the coldest part of the subducted slab, with a deformation profile consistent with the expected thermal signature of the slab, the experimentally determined Clapeyron slope of the phase transition, and the regional tectonic history.

  19. A multiscale discontinuous Galerkin method.

    SciTech Connect

    Bochev, Pavel Blagoveston; Scovazzi, Guglielmo; Hughes, Thomas J. R.

    2005-04-01

    We propose a new class of Discontinuous Galerkin (DG) methods based on variational multiscale ideas. Our approach begins with an additive decomposition of the discontinuous finite element space into continuous (coarse) and discontinuous (fine) components. Variational multiscale analysis is used to define an interscale transfer operator that associates coarse and fine scale functions. Composition of this operator with a donor DG method yields a new formulation that combines the advantages of DG methods with the attractive and more efficient computational structure of a continuous Galerkin method. The new class of DG methods is illustrated for a scalar advection-diffusion problem.

  20. Multichannel seismic-reflection profiling on the R/V Maurice Ewing during the Los Angeles Region Seismic Experiment (LARSE), California

    USGS Publications Warehouse

    Brocher, Thomas M.; Clayton, Robert W.; Klitgord, Kim D.; Bohannon, Robert G.; Sliter, Ray; McRaney, John K.; Gardner, James V.; Keene, J.B.

    1995-01-01

    This report describes the acquisition of deep-crustal multichannel seismic-reflection data in the Inner California Borderland aboard the R/V Maurice Ewing, conducted in October 1994 as part of the Los Angeles Regional Seismic Experiment (LARSE). LARSE is a cooperative study of the crustal structure of southern California involving earth scientists from the U.S. Geological Survey, Caltech, the University of Southern California, the University of California Los Angeles, and the Southern California Earthquake Center (SCEC). During LARSE, the R/V Ewing's 20- element air gun array, totaling 137.7 liters (8470 cu. in.), was used as the primary seismic source for wide-angle recording along three main onshore-offshore lines centered on the Los Angeles basin and the epicenters of the 1933 Long Beach and 1994 Northridge earthquakes. The LARSE onshore-offshore lines were each 200-250 km long, with the offshore portions being between 90 and 150 km long. The nearly 24,000 air gun signals generated by the Ewing were recorded by an array of 170 PASSCAL REFTEK recorders deployed at 2 km intervals along all three of the onshore lines and 9 ocean bottom seismometers (OBSs) deployed along two of the lines. Separate passes over the OBS-deployment lines were performed with a long air gun repetition rate (60 and 90 seconds) to minimize acoustic-wave interference from previous shots in the OBS data. The Ewing's 4.2-km, 160-channel, digital streamer was also used to record approximately 1250 km of 40-fold multichannel seismic-reflection data. To enhance the fold of the wide-angle data recorded onshore, mitigating against cultural and wind noise in the Los Angeles basin, the entire ship track was repeated at least once resulting in fewer than about 660 km of unique trackline coverage in the Inner Borderland. Portions of the seismic-reflection lines were repeated up to 6 times. A variety of other geophysical data were also continuously recorded, including 3.5 kHz bathymetry, multi

  1. Spectral methods for discontinuous problems

    NASA Technical Reports Server (NTRS)

    Abarbanel, S.; Gottlieb, D.; Tadmor, E.

    1985-01-01

    Spectral methods yield high-order accuracy even when applied to problems with discontinuities, though not in the sense of pointwise accuracy. Two different procedures are presented which recover pointwise accurate approximations from the spectral calculations.

  2. [Discontinuation syndrome after SSRI antidepressants].

    PubMed

    Lykkegaard, Lotte Amalie Kai; Videbech, Poul

    2014-02-03

    Discontinuation symptoms are described for almost all major groups of antidepressants. Crucial differences between discontinuation symptoms and symptoms after withdrawal of benzodiazepines are pointed out. Furthermore, it is important to discern from relapse of depression in order to manage the symptoms in primary care where the use of selective serotonin re-uptake inhibitors (SSRI) is substantial. In this paper we inform of the key symptoms after SSRI, present tools for understanding and recognizing the condition and suggest initiatives to manage it rationally.

  3. The Gutenberg discontinuity: melt at the lithosphere-asthenosphere boundary.

    PubMed

    Schmerr, Nicholas

    2012-03-23

    The lithosphere-asthenosphere boundary (LAB) beneath ocean basins separates the upper thermal boundary layer of rigid, conductively cooling plates from the underlying ductile, convecting mantle. The origin of a seismic discontinuity associated with this interface, known as the Gutenberg discontinuity (G), remains enigmatic. High-frequency SS precursors sampling below the Pacific plate intermittently detect the G as a sharp, negative velocity contrast at 40- to 75-kilometer depth. These observations lie near the depth of the LAB in regions associated with recent surface volcanism and mantle melt production and are consistent with an intermittent layer of asthenospheric partial melt residing at the lithospheric base. I propose that the G reflectivity is regionally enhanced by dynamical processes that produce melt, including hot mantle upwellings, small-scale convection, and fluid release during subduction.

  4. Multiscale seismic attributes: source-corrected wavelet response and application to high-resolution seismic data

    NASA Astrophysics Data System (ADS)

    Ker, Stephan; Le Gonidec, Yves; Gibert, Dominique

    2012-09-01

    A wavelet-based method was presented in a previous work to introduce multiscale seismic attributes for high-resolution seismic data. Because of the limited frequency bandwidth of the seismic source, we observed distortions in the seismic attributes based on the wavelet response of the subsurface discontinuities (Le Gonidec et al.). In this paper, we go further in the seismic source-correction by considering Lévy alpha-stable distributions introduced in the formalism of the continuous wavelet transform (CWT). The wavelets are Gaussian derivative functions (GDF), characterized by a derivative order. We show that a high-resolution seismic source, after a classical signature processing, can be taken into account with a GDF. We demonstrate that in the framework of the Born approximation, the CWT of a seismic trace involving such a finite frequency bandwidth can be made equivalent to the CWT of the impulse response of the subsurface and is defined for a reduced range of dilations. We apply the method for the SYSIF seismic device (Marsset et al.; Ker et al.) and show that the source-corrections allow to define seismic attributes for layer thicknesses in the range [24; 115 cm]. We present the analysis for two seismic reflectors identified on a SYSIF profile, and we show that the source-corrected multiscale analysis quantifies their complex geometries.

  5. Management applications of discontinuity theory

    USGS Publications Warehouse

    Angeler, David G.; Allen, Craig R.; Barichievy, Chris; Eason, Tarsha; Garmestani, Ahjond S.; Graham, Nicholas A.J.; Granholm, Dean; Gunderson, Lance H.; Knutson, Melinda; Nash, Kirsty L.; Nelson, R. John; Nystrom, Magnus; Spanbauer, Trisha; Stow, Craig A.; Sundstrom, Shana M.

    2015-01-01

    Human impacts on the environment are multifaceted and can occur across distinct spatiotemporal scales. Ecological responses to environmental change are therefore difficult to predict, and entail large degrees of uncertainty. Such uncertainty requires robust tools for management to sustain ecosystem goods and services and maintain resilient ecosystems.We propose an approach based on discontinuity theory that accounts for patterns and processes at distinct spatial and temporal scales, an inherent property of ecological systems. Discontinuity theory has not been applied in natural resource management and could therefore improve ecosystem management because it explicitly accounts for ecological complexity.Synthesis and applications. We highlight the application of discontinuity approaches for meeting management goals. Specifically, discontinuity approaches have significant potential to measure and thus understand the resilience of ecosystems, to objectively identify critical scales of space and time in ecological systems at which human impact might be most severe, to provide warning indicators of regime change, to help predict and understand biological invasions and extinctions and to focus monitoring efforts. Discontinuity theory can complement current approaches, providing a broader paradigm for ecological management and conservation.

  6. Seismic Discrimination

    DTIC Science & Technology

    1981-03-31

    for second-order Sturm - Liouville boundary-value problems, such a count of eigenvalues may be established in terms of the number of zero crossings of...will be operational during the next six months. Section 11 describes a series of activities in the development and imple- mentation of the seismic...element of seismic research. with emphasis on those areas directly related to tho operations of the SDC. Substantial progress has been made in the

  7. Seismic seiches

    USGS Publications Warehouse

    McGarr, Arthur; Gupta, Harsh K.

    2011-01-01

    Seismic seiche is a term first used by Kvale (1955) to discuss oscillations of lake levels in Norway and England caused by the Assam earthquake of August 15, 1950. This definition has since been generalized to apply to standing waves set up in closed, or partially closed, bodies of water including rivers, shipping channels, lakes, swimming pools and tanks due to the passage of seismic waves from an earthquake.

  8. Characterization and Petrological Constraints of the Midlithospheric Discontinuity

    NASA Astrophysics Data System (ADS)

    Rader, Erika; Emry, Erica; Schmerr, Nicholas; Frost, Daniel; Cheng, Cheng; Menard, Julie; Yu, Chun-Quan; Geist, Dennis

    2015-10-01

    Within continental lithosphere, widespread seismic evidence suggests a sharp discontinuous downward decrease in seismic velocity at 60-160 km depth. This midlithospheric discontinuity (MLD) may be due to anisotropy, melt, hydration, and/or mantle metasomatism. We survey global seismologic observations of the MLD, including observed depths, velocity contrasts, gradients, and locales across multiple seismic techniques. The MLD is primarily found in regions of thick continental lithosphere and is a decrease in seismic shear velocity (2-7% over 10-20 km) at 60-160 km depth, the majority of observations clustering at 80-100 km. Of xenoliths in online databases, 25% of amphibole-bearing xenoliths, 90% of phlogopite-bearing xenoliths, and none of carbonate-bearing xenoliths were formed at pressures associated with these depth (2-5 GPa). We used Perple_X modeling to evaluate the elastic moduli and densities of multiple petrologies to test if the MLD is a layer of crystallized melt. The fractional addition of 5-10% phlogopite, 10-15% carbonate, or 45-100% pyroxenite produce a 2-7% velocity decrease. We postulate this layer of crystallized melt would originate at active margins of continents and crystallize in place as the lithosphere cools. The concentration of mildly incompatible elements (Y, Ho, Er, Yb, and Lu) in xenoliths near the MLD is consistent with higher degrees of melting. Thus, we postulate that the MLD is the seismological signature of a chemical interface related to the paleointersection of a volatile-rich solidus and progressively cooling lithosphere. Furthermore, the MLD may represent a remnant chemical tracer of the lithosphere-asthenosphere boundary (LAB) from when the lithosphere was active and young.

  9. Physico-chemical constraints on cratonic lithosphere discontinuities

    NASA Astrophysics Data System (ADS)

    Aulbach, Sonja; Rondenay, Stéphane; Huismans, Ritske

    2014-05-01

    The origins of the mid-lithospheric discontinuity (MLD) and lithosphere-asthenosphere boundary (LAB) have received much attention over the recent years. Peculiarities of cratonic lithosphere construction - compositional and rheological stratification due to thickening in collisional settings or by plume subcretion, multiple metasomatic overprints due to longevity - offer a variety of possibilities for the generation of discontinuities. Interconnected small degrees of conductive partial melt (carbonate-rich melts, such as carbonatites and kimberlites, or highly alkaline melts) at the cratonic LAB, which produce seismic discontinuities, may be generated in the presence of volatiles. These depress the peridotite solidus sufficiently to intersect the mantle adiabat at depths near the cratonic LAB at ~160-220 km, i.e. above the depth of metal saturation where carbonatite becomes unstable. The absence of agreement between the different seismic and magnetotelluric estimates for the depth of the LAB beneath Kaapvaal may be due to impingement of a plume, leading to a pervasively, but heterogeneously metasomatised ('asthenospherised') hot and deep root. Such a root and hot sublithosphere may yield conflicting seismic-thermal-geochemical depths for the LAB. The question arises whether the chemical boundary layer should be defined as above or below the asthenospherised part of the SCLM, which has preserved isotopic, compositional (non-primitive olivine forsterite content) and physical evidence (e.g. from teleseismic tomography and receiver functions) for a cratonic heritage and which therefore is still distinguishable from the asthenospheric mantle. If cratonic lithosphere overlies anomalously hot mantle for extended periods of time, the LAB may be significantly thinned, aided by penetration of relatively high-degree Fe-rich partial melts, as has occurred beneath the Tanzanian craton. Xenoliths from the deep Slave craton show little evidence for 'asthenospherisation'. Its root

  10. The Morphosyntax of Discontinuous Exponence

    ERIC Educational Resources Information Center

    Campbell, Amy Melissa

    2012-01-01

    This thesis offers a systematic treatment of discontinuous exponence, a pattern of inflection in which a single feature or a set of features bundled in syntax is expressed by multiple, distinct morphemes. This pattern is interesting and theoretically relevant because it represents a deviation from the expected one-to-one relationship between…

  11. Technological Discontinuities and Organizational Environments.

    ERIC Educational Resources Information Center

    Tushman, Michael L.; Anderson, Philip

    1986-01-01

    Technological effects on environmental conditions are analyzed using longitudinal data from the minicomputer, cement, and airline industries. Technology evolves through periods of incremental change punctuated by breakthroughs that enhance or destroy the competence of firms. Competence-destroying discontinuities increase environmental turbulence;…

  12. Seismicity on the area of the Waste Isolation Pilot Plant (WIPP)

    SciTech Connect

    Sanford, A.; Sanford, S.; Wallace, T.; Barrows, L.; Sheldon, J.; Ward, R.; Johansen, S.; Merritt, L.

    1980-05-01

    Since April 1974, New Mexico Institute of Mining and Technology (NMIMT) has operated a short-period vertical-component seismograph 7 km from the center of the WIPP site. Peak magnifications ranged from 405 K to 1400 K. In the time period from April 1974 to February 1979, approximately 500 earthquakes were recorded by the instrument to distances as great as 660 km. With the aid of readings from stations operated by other organizations, epicenters and magnitudes for 159 earthquakes within about 300 km of the WIPP site were obtained. The greatest concentration of seismic activity is centered on the Central Basin Platform. This zone of activity, approximately 120 km in a NS direction and 100 km in an EW direction, approaches to within 60 km of the site. Other significant clusters of earthquakes occur near Synder, Big Springs and Valentine, Texas. Comparable levels of earthquake activity are observed within 100, 200, and 300 km of the site. Most reported Quaternary faulting lies to the west of 104.3/sup 0/W longitude. Comparable levels of activity were observed to the east and west of this longitude indicating the observed distribution of earthquake activity is probably not representative of the long-term (500,000 years) seismicity of the region. Several lines of evidence suggest that most earthquakes from the Delaware Basin eastward are induced by the production of hydrocarbons, but absolutely convincing proof is lacking. If due to natural tectonic forces, an extrapolation of the observed earthquake-frequency relation indicates an earthquake of magnitude 5 1/2 is possible somewhere within 300 km of the site each 100 years.

  13. Seismic Studies

    SciTech Connect

    R. Quittmeyer

    2006-09-25

    This technical work plan (TWP) describes the efforts to develop and confirm seismic ground motion inputs used for preclosure design and probabilistic safety 'analyses and to assess the postclosure performance of a repository at Yucca Mountain, Nevada. As part of the effort to develop seismic inputs, the TWP covers testing and analyses that provide the technical basis for inputs to the seismic ground-motion site-response model. The TWP also addresses preparation of a seismic methodology report for submission to the U.S. Nuclear Regulatory Commission (NRC). The activities discussed in this TWP are planned for fiscal years (FY) 2006 through 2008. Some of the work enhances the technical basis for previously developed seismic inputs and reduces uncertainties and conservatism used in previous analyses and modeling. These activities support the defense of a license application. Other activities provide new results that will support development of the preclosure, safety case; these results directly support and will be included in the license application. Table 1 indicates which activities support the license application and which support licensing defense. The activities are listed in Section 1.2; the methods and approaches used to implement them are discussed in more detail in Section 2.2. Technical and performance objectives of this work scope are: (1) For annual ground motion exceedance probabilities appropriate for preclosure design analyses, provide site-specific seismic design acceleration response spectra for a range of damping values; strain-compatible soil properties; peak motions, strains, and curvatures as a function of depth; and time histories (acceleration, velocity, and displacement). Provide seismic design inputs for the waste emplacement level and for surface sites. Results should be consistent with the probabilistic seismic hazard analysis (PSHA) for Yucca Mountain and reflect, as appropriate, available knowledge on the limits to extreme ground motion at

  14. Bursts in discontinuous Aeolian saltation

    PubMed Central

    Carneiro, M. V.; Rasmussen, K. R.; Herrmann, H. J.

    2015-01-01

    Close to the onset of Aeolian particle transport through saltation we find in wind tunnel experiments a regime of discontinuous flux characterized by bursts of activity. Scaling laws are observed in the time delay between each burst and in the measurements of the wind fluctuations at the fluid threshold Shields number θc. The time delay between each burst decreases on average with the increase of the Shields number until sand flux becomes continuous. A numerical model for saltation including the wind-entrainment from the turbulent fluctuations can reproduce these observations and gives insight about their origin. We present here also for the first time measurements showing that with feeding it becomes possible to sustain discontinuous flux even below the fluid threshold. PMID:26073305

  15. Factors Affecting Seismic Velocity in Alluvium

    NASA Astrophysics Data System (ADS)

    Huckins-Gang, H.; Mercadante, J.; Prothro, L.

    2015-12-01

    Yucca Flat at the Nevada National Security Site has been selected as the Source Physics Experiment (SPE) Dry Alluvium Geology Phase II site. The alluvium in this part of Yucca Flat is typical of desert basin fill, with discontinuous beds that are highly variable in clast size and provenance. Detailed understanding of the subsurface geology will be needed for interpretation of the SPE seismic data. A 3D seismic velocity model, created for Yucca Flat using interval seismic velocity data, shows variations in velocity within alluvium near the SPE Phase II site beyond the usual gradual increase of density with depth due to compaction. In this study we examined borehole lithologic logs, geophysical logs, downhole videos, and laboratory analyses of sidewall core samples to understand which characteristics of the alluvium are related to these variations in seismic velocity. Seismic velocity of alluvium is generally related to its density, which can be affected by sediment provenance, clast size, gravel percentage, and matrix properties, in addition to compaction. This study presents a preliminary subdivision of the alluvial strata in the SPE Phase II area into mappable units expected to be significant to seismic modeling. Further refinements of the alluvial units may be possible when seismic data are obtained from SPE Phase II tests. This work was done by National Security Technologies, LLC, under Contract No. DE-AC52-06NA25946 with the U.S. Department of Energy.

  16. The Hales discontinuity and upper mantle anisotropy beneath cratons

    NASA Astrophysics Data System (ADS)

    Musacchio, G.; White, D. J.; Thomson, C. J.

    2003-04-01

    Seismic velocity discontinuities are commonly found within the upper 100 km of the mantle lithosphere, with great variability in their depth, lateral extent, and the polarity of velocity jump. Among the more commonly observed is the Hales discontinuity, identified in a variety of tectonic environments, and commonly associated with a high-velocity, highly reflective and sometimes anisotropic layer. In the Archean Western Superior Province of the Canadian Shield, long range R/WAR profiling gives a high-resolution estimate of the mantle V_P in the shallow upper mantle, providing a more certain determination of the nature of the Hales dicontinuity. Ray-based travel-time inversion of the data, have shown that Vp in the uppermost mantle is 8.0-8.3 km/s. A 15-20 km thick layer (layer-H) with >6% seismic anisotropy (N-S V_P of 8.3 km/s and E-W V_P of 8.8 km/s) dips northward at ˜10^o from a minimum depth of 48-50 km. The attitude of layer-H is consistent with the general tectonic strike; its depth range (50-75 km) falls within that of the Hales discontinuity. If a link between the Hales discontinuity and layer-H can be drawn, observations strengthen the objection that the estimated velocity contrast (0.2 to 0.4 km/s depending on the direction of wave propagation) is relatively high if layer-H represents a phase transition, and thus (re)opens the debate on the nature of shallow upper-mantle boundaries beneath continents. The high V_P and intermediate anisotropy of upper-mantle layer-H requires a harzburgite peridotitic composition with the a-axis of olivine aligned E-W. Layer-H might have emplaced during accretion (2.7 Ga Kenoran orogeny) of the North American proto-craton and be relic oceanic lithosphere. The Hales discontinuity might be an expression of continents accretion and map relic slabs in the shallow upper mantle.

  17. Reinforced ceramics employing discontinuous phases

    SciTech Connect

    Becher, P.F.

    1990-01-01

    The fracture toughness of ceramics can be improved by the incorporation of a variety of discontinuous reinforcing phases and microstructures. Observations of crack paths in these systems indicate that these reinforcing phases bridge the crack tip wake region. Recent developments in micromechanics toughening models applicable to such systems are discussed and compared with experimental observations. Because material parameters and microstructural characteristics are considered, the crack bridging models provide a means to optimize the toughening effects. 18 refs., 2 figs.

  18. The discontinuity theory of immunity

    PubMed Central

    Pradeu, Thomas; Vivier, Eric

    2017-01-01

    Some biological systems detect the rate of change in a stimulus rather than the stimulus itself only. We suggest that the immune system works in this way. According to the discontinuity theory of immunity, the immune system responds to sudden changes in antigenic stimulation and is rendered tolerant by slow or continuous stimulation. This basic principle, which is supported by recent data on immune checkpoints in viral infections, cancers, and allergies, can be seen as a unifying framework for diverse immune responses.

  19. Discontinuous Mixed Covolume Methods for Parabolic Problems

    PubMed Central

    Zhu, Ailing

    2014-01-01

    We present the semidiscrete and the backward Euler fully discrete discontinuous mixed covolume schemes for parabolic problems on triangular meshes. We give the error analysis of the discontinuous mixed covolume schemes and obtain optimal order error estimates in discontinuous H(div) and first-order error estimate in L2. PMID:24983008

  20. 40 CFR 159.167 - Discontinued studies.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 24 2011-07-01 2011-07-01 false Discontinued studies. 159.167 Section... Discontinued studies. The fact that a study has been discontinued before the planned termination must be reported to EPA, with the reason for termination, if submission of information concerning the study is,...

  1. 40 CFR 159.167 - Discontinued studies.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 25 2013-07-01 2013-07-01 false Discontinued studies. 159.167 Section... Discontinued studies. The fact that a study has been discontinued before the planned termination must be reported to EPA, with the reason for termination, if submission of information concerning the study is,...

  2. 40 CFR 159.167 - Discontinued studies.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 25 2012-07-01 2012-07-01 false Discontinued studies. 159.167 Section... Discontinued studies. The fact that a study has been discontinued before the planned termination must be reported to EPA, with the reason for termination, if submission of information concerning the study is,...

  3. 40 CFR 159.167 - Discontinued studies.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 24 2014-07-01 2014-07-01 false Discontinued studies. 159.167 Section... Discontinued studies. The fact that a study has been discontinued before the planned termination must be reported to EPA, with the reason for termination, if submission of information concerning the study is,...

  4. 40 CFR 159.167 - Discontinued studies.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 23 2010-07-01 2010-07-01 false Discontinued studies. 159.167 Section... Discontinued studies. The fact that a study has been discontinued before the planned termination must be reported to EPA, with the reason for termination, if submission of information concerning the study is,...

  5. Receiver function images of the mantle transition zone beneath NE China: New constraints on intraplate volcanism, deep subduction and their potential link

    NASA Astrophysics Data System (ADS)

    Liu, Zheng; Niu, Fenglin; Chen, Yongshun John; Grand, Steve; Kawakatsu, Hitoshi; Ning, Jieyuan; Tanaka, Satoru; Obayashi, Masayuki; Ni, James

    2015-02-01

    In order to better understand the deep subduction geometry of the Pacific plate and genesis of intraplate volcanism in northeast China (NE China), we computed a total of 45,505 receiver functions from 788 teleseismic events recorded by 255 stations (NECESSArray temporal and permanent stations) in NE China. We used a common-conversion-point stacking (CCP) method to generate a 3D reflectivity volume beneath the study area. To position the P-to-S conversions to the correct depths, we employed 3D crustal and mantle models as references to make time to depth conversion. The 3D reflectivity volume was generated in an area between 115°-135°E and 40°-49°N, in the depth range of 300 to 800 km. We found significant topographic relief on the 660-km discontinuity across the study area. In particular, in a westward Pacific plate subduction section between 40°N and ∼45.5°N, the 660-km discontinuity is depressed by as much as ∼30-40 km along the western extension of the deep seismicity. The depression is elongated along the strike of the deep seismicity and is confined to a 200-300 km region in the E-W direction of subduction. To the west of this depression the 660-km discontinuity is uplifted by 5-10 km in a rectangular area of ∼100 km by 200 km centered at about 125°E and 43°N. In the north, the 660-km discontinuity is moderately depressed (∼20 km) in a broad area that extends further west. The high and low regions in the 660-km topographic map correlate, respectively, with low- and high-velocity anomalies in the P- and S-wave tomographic velocity images at the same depth. Our results suggest that slab stagnation might not be occurring in the southern part of the NE China, where the Changbaishan volcanic complex is located, thus the magmatism is unlikely caused by dehydration of the flat-lying Pacific slab in the transition zone. The low velocity mantle upwelling arising from a gap of stagnant slabs is a likely source that feeds the volcanic complex in NE China.

  6. Seismic Discrimination

    DTIC Science & Technology

    1975-12-31

    dyn-cm. It can be seen that there is a wide range of the potential con- tribution of different seismic zones to excitation of the Chandler wobble ...Correction to the Excitation of the Chandler Wobble by Earthquakes," Geophys. J. R. Astron. Soc. 32, 203-217 (1973). 22. S. C. Solomon, N. H. Sleep

  7. Seismic Tomography.

    ERIC Educational Resources Information Center

    Anderson, Don L.; Dziewonski, Adam M.

    1984-01-01

    Describes how seismic tomography is used to analyze the waves produced by earthquakes. The information obtained from the procedure can then be used to map the earth's mantle in three dimensions. The resulting maps are then studied to determine such information as the convective flow that propels the crustal plates. (JN)

  8. High Resolution Seismic Study of the Holocene Infill of the Elkhorn Slough, Central California

    EPA Science Inventory

    The seismic analysis of the sedimentary infill of the Elkhorn Slough, central California, reveals a succession of three main seismic units: U1, U2, U3, with their correspondent discontinuities d2, d3. These units are deposited over a paleorelief representing the channel location ...

  9. Seismic Symphonies

    NASA Astrophysics Data System (ADS)

    Strinna, Elisa; Ferrari, Graziano

    2015-04-01

    The project started in 2008 as a sound installation, a collaboration between an artist, a barrel organ builder and a seismologist. The work differs from other attempts of sound transposition of seismic records. In this case seismic frequencies are not converted automatically into the "sound of the earthquake." However, it has been studied a musical translation system that, based on the organ tonal scale, generates a totally unexpected sequence of sounds which is intended to evoke the emotions aroused by the earthquake. The symphonies proposed in the project have somewhat peculiar origins: they in fact come to life from the translation of graphic tracks into a sound track. The graphic tracks in question are made up by copies of seismograms recorded during some earthquakes that have taken place around the world. Seismograms are translated into music by a sculpture-instrument, half a seismograph and half a barrel organ. The organ plays through holes practiced on paper. Adapting the documents to the instrument score, holes have been drilled on the waves' peaks. The organ covers about three tonal scales, starting from heavy and deep sounds it reaches up to high and jarring notes. The translation of the seismic records is based on a criterion that does match the highest sounds to larger amplitudes with lower ones to minors. Translating the seismogram in the organ score, the larger the amplitude of recorded waves, the more the seismogram covers the full tonal scale played by the barrel organ and the notes arouse an intense emotional response in the listener. Elisa Strinna's Seismic Symphonies installation becomes an unprecedented tool for emotional involvement, through which can be revived the memory of the greatest disasters of over a century of seismic history of the Earth. A bridge between art and science. Seismic Symphonies is also a symbolic inversion: the instrument of the organ is most commonly used in churches, and its sounds are derived from the heavens and

  10. Seismic Discrimination

    DTIC Science & Technology

    1977-03-31

    Determining Phase and Group Velocities of Surface Seismic Waves 21 B. Group-Velocity Measurements Across Eurasia from Mashad SRO 22 C. Group-Velocity...Albuquerque), MAIO ( Mashad ), GUMO (Guam), NWAO (Australia), SNZO (New Zealand), and TATO (Taiwan). Fairly extensive data are now a|ailable for the...include a new rapid algorithm for the determination of group and phase velocity, a series of observations of Rayleigh-wave dispersion at the Mashad

  11. Seismic testing

    SciTech Connect

    Knott, S.

    1981-10-01

    Electric Power Research Institute (EPRI) research programs in seismic testing to improve earthquake design guidelines lowers the safety-design costs of nuclear power plants. Explosive tests that simulate earthquakes help to determine how structures respond to ground motion and how these are related to soil and geologic conditions at a specific site. Explosive tests develop data for simulation using several computer codes. Photographs illustrate testing techniques. 6 references. (DCK)

  12. Refined seismic stratigraphy in prograding carbonates

    SciTech Connect

    Pomar, L. )

    1991-03-01

    Complete exposure of the upper Miocene Reef Complex in the sea cliffs of Mallorca (Spain) allows for a more refined interpretation of seismic lines with similar progradational patterns. A 6 km long high-resolution cross section in the direction of reef progradation displays four hierarchical orders of accretional units. Although all these units are of higher order, they all exhibit similar characteristics as a third order depositional sequence and can likewise be interpreted as the result of high order sea-level cycles. The accretional units are composed of lagoonal horizontal beds, reefal sigmoids and gently dipping slope deposits. They are bounded by erosion surfaces at the top and basinwards by their correlative conformities. These architectural patterns are similar to progradational sequences seen on seismic lines. On seismic lines, the progradational pattern often shows the following geometrical details: (1) discontinuous climbing high-energy reflectors, (2) truncation of clinoforms by these high-energy reflectors with seaward dips, (3) transparent areas intercalated between clinoforms. Based on facies distribution in the outcrops of Mallorca the high-energy reflectors are interpreted as sectors where the erosion surfaces truncated the reef wall and are overlain by lagoonal sediments deposited during the following sealevel rise. The more transparent zones seem to correspond with areas of superposition of undifferentiated lagoonal beds. Offlapping geometries can also be detected in highest quality seismic lines. The comparison between seismic and outcrop data provides a more accurate prediction of lithologies, facies distribution, and reservoir properties on seismic profiles.

  13. Geodynamics of the Yellowstone hotspot and mantle plume: Seismic and GPS imaging, kinematics, and mantle flow

    NASA Astrophysics Data System (ADS)

    Smith, Robert B.; Jordan, Michael; Steinberger, Bernhard; Puskas, Christine M.; Farrell, Jamie; Waite, Gregory P.; Husen, Stephan; Chang, Wu-Lung; O'Connell, Richard

    2009-11-01

    Integration of geophysical and geological data show that the Yellowstone hotspot resulted from a mantle plume interacting with the overriding North America plate, a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16-17 Ma, 700-km-long Yellowstone-Snake River Plain (YSRP) silicic volcanic system. Accessibility of the YSRP allowed large-scale geophysical projects to seismically image the hotspot and evaluate its kinematic properties using geodetic measurements. Seismic tomography reveals a crustal magma reservoir of 8% to 15% melt, 6 km to 16 km deep, beneath the Yellowstone caldera. An upper-mantle low-P-wave-velocity body extends vertically from 80 km to 250 km beneath Yellowstone, but the anomalous body tilts 60 °WNW and extends to 660 km depth into the mantle transition zone. We interpret this conduit-shaped low-velocity body as a plume of up to - 3.5% Vp and - 5.5% Vs perturbation that corresponds to a 1-2% partial melt. Models of whole mantle convection reveal eastward upper-mantle flow beneath Yellowstone at relatively high rates of 5 cm/yr that deflects the ascending plume into its west-tilted geometry. A geodynamic model of the Yellowstone plume constrained by Vp and Vs velocities and attenuation parameters suggests low excess temperatures of up to 120 K, corresponding to a maximum 2.5% melt, and a small buoyancy flux of 0.25 Mg/s, i.e., properties of a cool, weak plume. The buoyancy flux is many times smaller than for oceanic plumes, nonetheless, plume buoyancy has produced a ~ 400-km-wide, ~ 500-m-high topographic swell centered on the Yellowstone Plateau. Contemporary deformation derived from GPS measurements reveals SW extension of 2-3 mm/yr across the Yellowstone Plateau, one-fourth of the total Basin-Range opening rate, which we consider to be part of Basin-Range intraplate extension. Locally, decadal episodes of subsidence and uplift, averaging ~ 2 cm/yr, characterize the 80-year

  14. Mantle transition zone beneath northeast China from P-receiver function

    NASA Astrophysics Data System (ADS)

    Zhang, R.; Wu, Q.

    2015-12-01

    We used receiver functions to examine lateral topographical variations on the 410- and 660-km beneath northeast China and particularly the Kuril-Japan arc junctions. Compared to other receiver functions studies, our analysis was based on greater station coverage of higher density by combining all recent seismic arrays so far deployed in northeast China. Our image shows that the 410-km is featured by a ~10-20 km uplift extending in the NNE direction beneath some areas of the Quaternary basaltic rocks distributed at Abaga and at Wudalianchi. The Clapeyron slope of the olivine phase transiton at 410-km suggests that the uplift is compatible with a negative thermal anomaly. We also confirm a significant depression of the 660 from the Changbai volcanism in the north to Korea in the south along the NW-SE direction. The depression is also accompanied by an uplift of the 660 to the west. The shallow 660-km discontinuity is also particularly detected beneath the Kuril-Japan arc junctions, while it was not detected before. The thermal anomaly at 410 km depth is most likely a remnant of a detached mantle lithosphere that recently sank to depth, thus providing robust evidence for the source and evolution of these basalts. The depression of the 660-km discontinuity may support that the subducting Pacific slab bends sharply and becomes stagnant when it meets strong resistance at a depth of about 670 km. After accumulation to a great extent the stagnant slab finally penetrates into the lower mantle. Combined with the previous triplicated studies, the shallow 660-km may suggest that descending Pacific slab at its leading and junction edges might be accommodated by a tearing near a depth of 660 km. Acknowledgements. Two liner seismic arrays were deployed by the Institute of Geophysics, China Earthquake Administration. The data of the permanent stations were provided by the Data Management Centre of China, National Seismic Network at the Institute of Geophysics, China Earthquake

  15. Observations of double discontinuities in the magnetotail

    NASA Astrophysics Data System (ADS)

    Whang, Y. C.; Fairfield, D.; Smith, E. J.; Lepping, R. P.; Kokubun, S.; Saito, Y.

    Observations of slow shocks in the Earth's magnetotail at the plasma sheet-lobe boundaries have been well documented. We restudy the magnetic field data of two slow shocks: one was observed from Geotail on January 17, 1994 at XGSE = -92 RE, and another was observed from ISEE-3 on February 2, 1983 at XGSE = -220 RE. In both cases, the slow shock layer was followed by an adjoining rotational discontinuity layer on the postshock side. Compound structures each composed of a slow shock layer and an adjoining rotational discontinuity layer have been recently observed in interplanetary space from Wind, Geotail and Imp-8. Because the two successive discontinuities are very close to each other, the compound structure looks like a new kind of MHD discontinuity. It may be called a double discontinuity. Since double discontinuities exist not only in interplanetary space but also in the magnetotail region, they could be a general MHD structure in space plasma.

  16. Forward modeling the perovskite-postperovskite transition in seismically anisotropic models beneath a slab

    NASA Astrophysics Data System (ADS)

    Cottaar, S.; Li, M.; Miyagi, L. M.; McNamara, A. K.; Romanowicz, B. A.; Wenk, H.

    2012-12-01

    Seismic observations of the lowermost mantle in subduction regions show strong seismic anisotropy as well as a seismic discontinuity. Both observations appear consistent with a perovskite to post-perovskite phase transition. The single crystal velocities of the post-perovksite phase are both faster and more anisotropic. How the seismic discontinuity appears in reflection studies will depend on the retainment of texturing across the phase transitions. In this study we test the texturing across the phase transition and its seismic detectability by forward modeling through a combination of geodynamics and mineral physics tools. Tracers in a 3D geodynamical model with a subducting slab (constrained at the surface) track the velocity gradient tensor along the slab. This information is fed into a viscoplastic polycrystal plasticity model along with major mineral components and different assumptions for their active slip systems and elastic properties. We include a perovskite to post-perovskite phase transition. We assume different models converting from perovskite to post-perovskite textured material, of which the simplest is a total randomization. Away from the discontinuity, the strong texturing towards the CMB will overprint the signature of any of these assumptions. Here we present radially anisotropic models expressed in terms of seismic SH and SV velocities, illustrating the seismic sensitivity to the texture conversion within the transition. Our geodynamical model has a large number of tracers that track different areas in the subducting slab and represent lateral variations in deformation. These variations result in a family of modeled seismic discontinuities, representing the spread in depth and sharpness of the discontinuity measured by seismic ScS precursor studies.

  17. Seismic waveform sensitivity to global boundary topography

    NASA Astrophysics Data System (ADS)

    Colombi, Andrea; Nissen-Meyer, Tarje; Boschi, Lapo; Giardini, Domenico

    2012-09-01

    We investigate the implications of lateral variations in the topography of global seismic discontinuities, in the framework of high-resolution forward modelling and seismic imaging. We run 3-D wave-propagation simulations accurate at periods of 10 s and longer, with Earth models including core-mantle boundary topography anomalies of ˜1000 km spatial wavelength and up to 10 km height. We obtain very different waveform signatures for PcP (reflected) and Pdiff (diffracted) phases, supporting the theoretical expectation that the latter are sensitive primarily to large-scale structure, whereas the former only to small scale, where large and small are relative to the frequency. PcP at 10 s seems to be well suited to map such a small-scale perturbation, whereas Pdiff at the same frequency carries faint signatures that do not allow any tomographic reconstruction. Only at higher frequency, the signature becomes stronger. We present a new algorithm to compute sensitivity kernels relating seismic traveltimes (measured by cross-correlation of observed and theoretical seismograms) to the topography of seismic discontinuities at any depth in the Earth using full 3-D wave propagation. Calculation of accurate finite-frequency sensitivity kernels is notoriously expensive, but we reduce computational costs drastically by limiting ourselves to spherically symmetric reference models, and exploiting the axial symmetry of the resulting propagating wavefield that collapses to a 2-D numerical domain. We compute and analyse a suite of kernels for upper and lower mantle discontinuities that can be used for finite-frequency waveform inversion. The PcP and Pdiff sensitivity footprints are in good agreement with the result obtained cross-correlating perturbed and unperturbed seismogram, validating our approach against full 3-D modelling to invert for such structures.

  18. Discontinuities in welds--cause and effect

    SciTech Connect

    Lundin, C.D.

    1983-12-01

    The prime reason for the rejection or failure of weldments is the presence of defects or discontinuities produced during welding. The generation or introduction of the discontinuities in a welded structure can result when the delicate balance of welding variables is upset. Of more importance is the determination of the effect of weld discontinuities. Will the discontinuity influence the weldment in its intended service and thus be termed a defect. Or can we ''live with'' a particular discontinuity, since it does not influence the future service of the weldment. These questions are asked over and over again and the answers, although sometimes difficult to obtain, are becoming available. Unfortunately, the terminology concerning weld discontinuities and/or weld defects grew without rigorous definition. Terms such as crack, fissure, porosity, shrinkage, void, flaw, defect, discontinuity, defective weld, acceptable weld, and others had not been officially defined by the AWS until recently. It is with some wonder we have progressed this far without hard definitions. Many have called attention to the connotation of the word defect that is normally applied to discontinuities of the type encountered in welds. They proposed the use of the term discontinuity in order to avoid the natural conclusion by the uninitiated to consider a weld defective if it contains ''defects,'' a prejudice certainly not intended even by the least knowledgeable individuals in the welding field. Over the last several years a series of definitions applies the word discontinuity to all interruptions of the typical structure of a weldment until the nature or accumulated effect of the discontinuities renders the part or product unable to meet acceptance standards or specifications. Then, the term defect applied. The cascading series of definitions is published in AWS A 3.0--''Terms and Definitions.''

  19. Discontinuity Detection in Multivariate Space for Stochastic Simulations

    SciTech Connect

    Archibald, Richard K; Gelb, Anne; Saxena, Rishu; Xiu, Dongbin

    2009-01-01

    Edge detection has traditionally been associated with detecting physical space jump discontinuities in one dimension, e.g. seismic signals, and two dimensions, e.g. digital images. Hence most of the research on edge detection algorithms is restricted to these contexts. High dimension edge detection can be of significant importance, however. For instance, stochastic variants of classical differential equations not only have variables in space/time dimensions, but additional dimensions are often introduced to the problem by the nature of the random inputs. The stochastic solutions to such problems sometimes contain discontinuities in the corresponding random space and a prior knowledge of jump locations can be very helpful in increasing the accuracy of the final solution. Traditional edge detection methods typically require uniform grid point distribution. They also often involve the computation of gradients and/or Laplacians, which can become very complicated to compute as the number of dimensions increases. The polynomial annihilation edge detection method, on the other hand, is more flexible in terms of its geometric specifications and is furthermore relatively easy to apply. This paper discusses the numerical implementation of the polynomial annihilation edge detection method to high dimensional functions that arise when solving stochastic partial differential equations.

  20. Mid-lithosphere discontinuities beneath the western and central North China Craton

    NASA Astrophysics Data System (ADS)

    Sun, Weijia; Kennett, B. L. N.

    2017-02-01

    By analyzing P reflectivity extracted from stacked autocorrelograms for teleseismic events on a dense seismic profile, we obtain a detailed image of the mid-lithosphere discontinuity (MLD) beneath western and central North China Craton (NCC). This seismic daylight imaging exploits a broad high-frequency band (0.5-4 Hz) to reveal the fine-scale component of multi-scale lithospheric heterogeneity. The depth of the MLD beneath the western and central parts of the NCC ranges 80-120 km, with a good match to the transition to negative S velocity gradient with depth from Rayleigh wave tomography. The MLD inferred from seismic daylight imaging also has good correspondence with the transition from conductive to convective regimes estimated from heat flow data indicating likely thermal control within the seismological lithosphere.

  1. A Practical Guide to Regression Discontinuity

    ERIC Educational Resources Information Center

    Jacob, Robin; Zhu, Pei; Somers, Marie-Andrée; Bloom, Howard

    2012-01-01

    Regression discontinuity (RD) analysis is a rigorous nonexperimental approach that can be used to estimate program impacts in situations in which candidates are selected for treatment based on whether their value for a numeric rating exceeds a designated threshold or cut-point. Over the last two decades, the regression discontinuity approach has…

  2. Discontinuous Galerkin Methods: Theory, Computation and Applications

    SciTech Connect

    Cockburn, B.; Karniadakis, G. E.; Shu, C-W

    2000-12-31

    This volume contains a survey article for Discontinuous Galerkin Methods (DGM) by the editors as well as 16 papers by invited speakers and 32 papers by contributed speakers of the First International Symposium on Discontinuous Galerkin Methods. It covers theory, applications, and implementation aspects of DGM.

  3. Student Discontinuations: Is the System Failing?

    ERIC Educational Resources Information Center

    McSherry, Wilfred; Marland, Glenn R.

    1999-01-01

    Discusses factors associated with fairness and equity in relation to student discontinuation in nursing education. Shows how discontinuation is an integral part of higher education quality reviews. Promotes pre-exit counseling, monitoring of attrition, and review of academic and professional standards. (SK)

  4. Discontinuation among University Students in Southern Thailand

    ERIC Educational Resources Information Center

    Sittichai, Ruthaychonnee; Tongkumchum, Phattrawan; McNeil, Nittaya

    2009-01-01

    This study uses a statistical model to account for the pattern of discontinuation of university study at Pattani campus of Prince of Songkla University (PSU) in southern Thailand. University records for 11,408 bachelor degree students enrolled between 1999 and 2006 were used. Discontinuation rates were analyzed by using a logistic regression model…

  5. Comparing the Gibraltar and Calabrian subduction zones (central western Mediterranean) based on seismic tomography

    NASA Astrophysics Data System (ADS)

    Argnani, Andrea; Battista Cimini, Giovanni; Frugoni, Francesco; Monna, Stephen; Montuori, Caterina

    2016-04-01

    The Central Western Mediterranean (CWM) was shaped by a complex tectonic and geodynamic evolution. Deep seismicity and tomographic studies point to the existence, under the Alboran and Tyrrhenian Seas, of lithospheric slabs extending down to the bottom of the mantle transition zone, at 660 km depth. Two narrow arcs correspond to the two slabs, the Gibraltar and Calabrian Arcs (e.g., Monna et al., 2013; Montuori et al., 2007). Similarities in the tectonic and mantle structure of the two areas have been explained by a common subduction and roll-back mechanism for the opening of the CWM, in which the two arcs are symmetrical end products. In spite of this unifying model, a wide amount of literature from different disciplines shows that many aspects of the two areas are still controversial. We present a new 3-D tomographic model at mantle scale for the Calabrian Arc and compare it with a recently published 3-D tomographic model for the Gibraltar Arc by Monna et al (2013). The two models are based on non-linear inversion of teleseismic phase arrivals, and have scale and parametrization that allow for a direct comparison. Unlike previous studies the tomographic models here presented include Ocean Bottom Seismometer broadband data, which improved the resolution of the mantle structures in the marine areas surrounding the arcs. We focus on key features of the two models that constrain reconstructions of the geodynamic evolution of the CWM (e.g., Monna et al., 2015). At Tortonian time the opening of the Tyrrhenian basin was in its initial stage, and the Calabrian arc formed subsequently; on the contrary, the Gibraltar arc was almost completely defined. We hypothesize that the complexity of the continental margin approaching the subduction zone played a key role during the final stages of the arc formation. References Monna, S., G. B. Cimini, C. Montuori, L. Matias, W. H. Geissler, and P. Favali (2013), New insights from seismic tomography on the complex geodynamic evolution

  6. Seismic sources

    DOEpatents

    Green, M.A.; Cook, N.G.W.; McEvilly, T.V.; Majer, E.L.; Witherspoon, P.A.

    1987-04-20

    Apparatus is described for placement in a borehole in the earth, which enables the generation of closely controlled seismic waves from the borehole. Pure torsional shear waves are generated by an apparatus which includes a stator element fixed to the borehole walls and a rotor element which is electrically driven to rapidly oscillate on the stator element to cause reaction forces transmitted through the borehole walls to the surrounding earth. Longitudinal shear waves are generated by an armature that is driven to rapidly oscillate along the axis of the borehole, to cause reaction forces transmitted to the surrounding earth. Pressure waves are generated by electrically driving pistons that press against opposite ends of a hydraulic reservoir that fills the borehole. High power is generated by energizing the elements for more than about one minute. 9 figs.

  7. Medical factors associated with early IVF discontinuation.

    PubMed

    Troude, Pénélope; Guibert, Juliette; Bouyer, Jean; de La Rochebrochard, Elise

    2014-03-01

    Even when IVF is reimbursed by the social insurance system, as in France, high discontinuation rates have been reported and some patients drop out as soon as the first failed IVF cycle. This study aims to investigate medical factors associated with treatment discontinuation in an IVF centre after the first unsuccessful cycle. The study included 5135 couples recruited in eight French IVF centres and who had had an unsuccessful first IVF cycle in these centres in 2000-2002 (i.e. no live birth). Of these couples with a first failed IVF, 1337 did not have a second IVF in the centre (26%, 'early discontinuation group') and 3798 continued treatment with a second IVF in the centre. The characteristics of couples who discontinued IVF treatment were compared with those who continued using logistic regressions. Older women, women with duration of infertility >5years, with female factor or unexplained infertility, with 0 or 1 oocyte retrieved and no embryo transfer during the first IVF were more likely to discontinue treatment early. Risk of early discontinuation was associated with medical factors that are also well known to be associated with impaired chance of successful IVF. Even when IVF is reimbursed by the social insurance system, as in France, high discontinuation rates have been reported and some patients drop out as soon as the first failed IVF cycle. This study aims to investigate medical factors associated with treatment discontinuation in an IVF centre after the first unsuccessful cycle. The study included 5135 couples recruited in eight French IVF centres who had had an unsuccessful first IVF cycle in these centres in 2000-2002 (i.e. who remained childless after a first cycle). Of these couples with a first failed IVF, 1337 did not have a second IVF in the centre and 3798 continued treatment with a second IVF in the centre. The characteristics of couples who discontinued IVF treatment were compared with those who continued. After a first failed IVF cycle, more

  8. Detection of a new sub-lithospheric discontinuity in Central Europe with S-receiver functions

    NASA Astrophysics Data System (ADS)

    Kind, Rainer; Handy, Mark R.; Yuan, Xiaohui; Meier, Thomas; Kämpf, Horst; Soomro, Riaz

    2017-03-01

    We used S-receiver functions (i.e. S-to-P converted signals) to study seismic discontinuities in the upper mantle between the Moho and the 410 km discontinuity beneath central Europe. This was done by using c. 49,000 S-receiver functions from c. 700 permanent and temporary broadband stations made available by the open EIDA Archives. Below Phanerozoic Europe we observed expected discontinuities like the Moho, the lithosphere-asthenosphere boundary (LAB), the Lehmann discontinuity and the 410 km discontinuity with an additional overlying low velocity zone. Below the East European Craton (EEC), we observed the Mid-Lithospheric Discontinuity (MLD) at c. 100 km depth as well as the controversial cratonic LAB at c. 200 km depth. At the boundary of the EEC but still below the Phanerozoic surface, we observed downward velocity reductions below the LAB in the following regions: the North German-Polish Plain at about 200 km depth; the Bohemian Massive, north-west dipping from 200 to 300 km depth; the Pannonian Basin, north-east dipping from 150 to 200 km depth underneath the western Carpathians and the EEC. We named this newly observed structure Sub-Lithospheric Discontinuity (SLD). At the northern edge of the Bohemian Massive, we see a sharp vertical step of about 100 km between the SLD below the Bohemian Massive and the North German-Polish Plain. This step follows the surface trace of the Rheic Suture between the continental Saxo-Thuringian and Rheno-Herzynian zones of the Variscan orogen. A preliminary interpretation of these features is that a prong of the cratonic mantle lithosphere penetrated the Phanerozoic asthenosphere during the continental collision at the western and south-western edges of the EEC.

  9. On the origin of the D'' discontinuity: Combining seismological observations with mineral physics

    NASA Astrophysics Data System (ADS)

    Cobden, L. J.; Thomas, C.

    2013-12-01

    The D'' region is one of the most seismologically complex and intriguing parts of the Earth. Many independent studies have observed reflections of both P and/or S waves from structures located c. 100-400 km above the CMB. These structures are often assumed to demarcate the top of the D'' layer and loosely referred to as 'the D'' discontinuity'. Unlike the major discontinuities of the upper mantle, which appear readily in global seismic inversions of 1-D structure but may be absent in regional seismic datasets, the D'' discontinuity is typically absent from 1-D reference models yet readily observed in regional seismic datasets. Furthermore, significant lateral variations are seen in the amplitude, polarity and timing of P and S wave reflections, both within and between different studies, and in some regions no reflections are detected. It is thus not clear if D'' reflections represent a globally ubiquitous discontinuity, or arise from local to regional scale heterogeneity. Most recently, a popular hypothesis is that the D'' discontinuity represents the phase change from perovskite to post-perovskite. This hypothesis is based on a consistency between the seismic properties of D'' reflections in the Caribbean region (where typically strong S-wave reflections are accompanied by weaker P-wave reflections) and the experimentally-inferred transformation pressure and velocity contrast of the phase change. However, it becomes more difficult to explain D'' reflections in terms of the pv-ppv transformation in regions such as Siberia, where strong reflections are seen in both P and S waves. Accordingly, we consider the possibility that D'' reflections may be generated by a range of alternative thermochemical phenomena. We compile observations of D'' reflections from several locations around the globe, and quantitatively assess how well different thermochemical models fit the seismic properties of the reflections at each location. Our compilation includes both published seismic

  10. Seismic facies analysis of lacustrine system: Paleocene upper Fort Union Formation, Wind River basin, Wyoming

    SciTech Connect

    Liro, L.M.; Pardus, Y.C.

    1989-03-01

    The authors interpreted seismic reflection data, supported by well control, to reconstruct the stratigraphic development of Paleocene Lake Waltman in the Wind River basin of Wyoming. After dividing the upper Fort Union into eight seismic sequences, the authors mapped seismic attributes (amplitude, continuity, and frequency) within each sequence. Interpretation of the variation in seismic attributes allowed them to detail delta development and encroachment into Lake Waltman during deposition of the upper Fort Union Formation. These deltas are interpreted as high-energy, well-differentiated lobate forms with distinct clinoform morphology on seismic data. Prograding delta-front facies are easily identified on seismic data as higher amplitude, continuous events within the clinoforms. Seismic data clearly demonstrate the time-Transgressive nature of this facies. Downdip of these clinoforms, homogeneous shales, as evidenced by low-amplitude, generally continuous seismic events, accumulated in an interpreted quiet, areally extensive lacustrine setting. Seismic definition of the lateral extent of this lacustrine facies is excellent, allowing them to effectively delineate changes in the lake morphology during deposition of the upper Fort Union Formation. Encasing the upper Fort Union lacustrine deposits are fluvial-alluvial deposits, interpreted from discontinuous, variable-amplitude seismic facies. The authors highlight the correlation of seismic facies data and interpretation to well log data in the Frenchie Draw field to emphasize the accuracy of depositional environment prediction from seismic data.

  11. Seismic sources

    DOEpatents

    Green, Michael A.; Cook, Neville G. W.; McEvilly, Thomas V.; Majer, Ernest L.; Witherspoon, Paul A.

    1992-01-01

    Apparatus is described for placement in a borehole in the earth, which enables the generation of closely controlled seismic waves from the borehole. Pure torsional shear waves are generated by an apparatus which includes a stator element fixed to the borehole walls and a rotor element which is electrically driven to rapidly oscillate on the stator element to cause reaction forces transmitted through the borehole walls to the surrounding earth. Logitudinal shear waves are generated by an armature that is driven to rapidly oscillate along the axis of the borehole relative to a stator that is clamped to the borehole, to cause reaction forces transmitted to the surrounding earth. Pressure waves are generated by electrically driving pistons that press against opposite ends of a hydraulic reservoir that fills the borehole. High power is generated by energizing the elements at a power level that causes heating to over 150.degree. C. within one minute of operation, but energizing the elements for no more than about one minute.

  12. Discontinuous Spirals of Stable Periodic Oscillations

    PubMed Central

    Sack, Achim; Freire, Joana G.; Lindberg, Erik; Pöschel, Thorsten; Gallas, Jason A. C.

    2013-01-01

    We report the experimental discovery of a remarkable organization of the set of self-generated periodic oscillations in the parameter space of a nonlinear electronic circuit. When control parameters are suitably tuned, the wave pattern complexity of the periodic oscillations is found to increase orderly without bound. Such complex patterns emerge forming self-similar discontinuous phases that combine in an artful way to produce large discontinuous spirals of stability. This unanticipated discrete accumulation of stability phases was detected experimentally and numerically in a Duffing-like proxy specially designed to bypass noisy spectra conspicuously present in driven oscillators. Discontinuous spirals organize the dynamics over extended parameter intervals around a focal point. They are useful to optimize locking into desired oscillatory modes and to control complex systems. The organization of oscillations into discontinuous spirals is expected to be generic for a class of nonlinear oscillators. PMID:24284508

  13. Discontinuity stresses in metallic pressure vessels

    NASA Technical Reports Server (NTRS)

    1971-01-01

    The state of the art, criteria, and recommended practices for the theoretical and experimental analyses of discontinuity stresses and their distribution in metallic pressure vessels for space vehicles are outlined. The applicable types of pressure vessels include propellant tanks ranging from main load-carrying integral tank structure to small auxiliary tanks, storage tanks, solid propellant motor cases, high pressure gas bottles, and pressurized cabins. The major sources of discontinuity stresses are discussed, including deviations in geometry, material properties, loads, and temperature. The advantages, limitations, and disadvantages of various theoretical and experimental discontinuity analysis methods are summarized. Guides are presented for evaluating discontinuity stresses so that pressure vessel performance will not fall below acceptable levels.

  14. Active seismic experiment

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    The Apollo 16 active seismic experiment (ASE) was designed to generate and monitor seismic waves for the study of the lunar near-surface structure. Several seismic energy sources are used: an astronaut-activated thumper device, a mortar package that contains rocket-launched grenades, and the impulse produced by the lunar module ascent. Analysis of some seismic signals recorded by the ASE has provided data concerning the near-surface structure at the Descartes landing site. Two compressional seismic velocities have so far been recognized in the seismic data. The deployment of the ASE is described, and the significant results obtained are discussed.

  15. Revealing small-scale diffracting discontinuities by an optimization inversion algorithm

    NASA Astrophysics Data System (ADS)

    Yu, Caixia; Zhao, Jingtao; Wang, Yanfei

    2017-02-01

    Small-scale diffracting geologic discontinuities play a significant role in studying carbonate reservoirs. The seismic responses of them are coded in diffracted/scattered waves. However, compared with reflections, the energy of these valuable diffractions is generally one or even two orders of magnitude weaker. This means that the information of diffractions is strongly masked by reflections in the seismic images. Detecting the small-scale cavities and tiny faults from the deep carbonate reservoirs, mainly over 6 km, poses an even bigger challenge to seismic diffractions, as the signals of seismic surveyed data are weak and have a low signal-to-noise ratio (SNR). After analyzing the mechanism of the Kirchhoff migration method, the residual of prestack diffractions located in the neighborhood of the first Fresnel aperture is found to remain in the image space. Therefore, a strategy for extracting diffractions in the image space is proposed and a regularized L 2-norm model with a smooth constraint to the local slopes is suggested for predicting reflections. According to the focusing conditions of residual diffractions in the image space, two approaches are provided for extracting diffractions. Diffraction extraction can be directly accomplished by subtracting the predicted reflections from seismic imaging data if the residual diffractions are focused. Otherwise, a diffraction velocity analysis will be performed for refocusing residual diffractions. Two synthetic examples and one field application demonstrate the feasibility and efficiency of the two proposed methods in detecting the small-scale geologic scatterers, tiny faults and cavities.

  16. Observations of oceanic crust and mantle structures at a deep ocean seismic array in the Eastern Mid Atlantic

    NASA Astrophysics Data System (ADS)

    Hannemann, Katrin; Krüger, Frank; Dahm, Torsten

    2016-04-01

    In 2011, twelve ocean bottom stations (OBS) were installed approximately 100 km North of the Gloria Fault during the DOCTAR project (Deep OCean Test ARray). This fault marks the plate boundary between the Eurasian and African plate in the North Eastern Mid Atlantic. The experiment took place in water depth of 4-6 km, 800 km West of the Portuguese coast. The stations were equipped with broad band seismometers which recorded for ten months. We employ P and S receiver functions (RF) to have a closer look at the structure of crust and mantle. The ocean is a quite noisy environment, therefore the number of usable events is low (around 20) compared to RF studies on land. We use several quality criteria (e.g. signal to noise ratio, relative spike position) to select proper processing parameters for the calculation of the RF and carefully reviewed all later on used RF. Despite the low number of events, the usage of an array of OBS with an aperture of 75 km allows us to investigate deeper discontinuities (e.g. in 410 and 660 km depth) compared to single station approaches which are usually employed for OBS. Furthermore, we increase the number of usable events by applying array methods. We use move out corrected and stacked RF to have a closer look at the mantle transition zone, and estimate average depth values for the Moho, the lithosphere asthenosphere boundary (LAB) and the base of the asthenosphere. The Moho lies at depth of 7 km, the LAB at approximately 50 km and the asthenosphere has an approximated thickness of 110 km. We observe a slight increase in the time difference of the mantle discontinuity conversion times compared to PREM. RF give just information regarding the impedance contrast at a discontinuity instead of velocities. We additionally use P wave polarization of teleseismic events to estimate absolute S velocities beneath the single stations. All in all, we use the information gained by the RF analysis, and the analysis of the P wave polarization to

  17. Discontinuities of multi-Regge amplitudes

    NASA Astrophysics Data System (ADS)

    Fadin, V. S.

    2015-04-01

    In the BFKL approach, discontinuities of multiple production amplitudes in invariant masses of produced particles are discussed. It turns out that they are in evident contradiction with the BDS ansatz for n-gluon amplitudes in the planar N = 4 SYM at n ≥ 6. An explicit expression for the NLO discontinuity of the two-to-four amplitude in the invariant mass of two produced gluons is is presented.

  18. Discontinuous splenogonadal fusion diagnosed on computed tomography

    PubMed Central

    Jakkani, Ravikanth; Alhajri, Fayzah A; Alteriki, Abdullattif; Almuteri, Meshari F; Athyal, Reji P; Hashem, Khaled Z

    2016-01-01

    Splenogonadal fusion is a very rare congenital anomaly which often manifests as a scrotal mass and rarely as cryptorchidism. It can be of continuous and discontinuous type based on the presence of a band of connecting splenic tissue. We report a rare case of discontinuous type of splenogonadal fusion in an adolescent male presenting as cryptorchidism. We emphasize the computed tomographic findings, which helped us in preoperative diagnosis and aided in appropriate management. PMID:28104947

  19. Discontinuous structure transition in a Debye cluster

    SciTech Connect

    Sheridan, T. E.

    2012-05-15

    We consider the structural phases of a cluster of identical particles confined in a two-dimensional biharmonic well and interacting through a screened Coulomb (Yukawa) potential (e.g., dusty plasma). For n = 6 particles, we show that there are one discontinuous and three continuous structure transitions, giving five structure phases. Two of these phases, the straight line and zigzag configurations, have previously been studied experimentally. We experimentally verify the discontinuous transition and observe the remaining three phases.

  20. Management applications of discontinuity theory | Science ...

    EPA Pesticide Factsheets

    1.Human impacts on the environment are multifaceted and can occur across distinct spatiotemporal scales. Ecological responses to environmental change are therefore difficult to predict, and entail large degrees of uncertainty. Such uncertainty requires robust tools for management to sustain ecosystem goods and services and maintain resilient ecosystems. 2.We propose an approach based on discontinuity theory that accounts for patterns and processes at distinct spatial and temporal scales, an inherent property of ecological systems. Discontinuity theory has not been applied in natural resource management and could therefore improve ecosystem management because it explicitly accounts for ecological complexity. 3.Synthesis and applications. We highlight the application of discontinuity approaches for meeting management goals. Specifically, discontinuity approaches have significant potential to measure and thus understand the resilience of ecosystems, to objectively identify critical scales of space and time in ecological systems at which human impact might be most severe, to provide warning indicators of regime change, to help predict and understand biological invasions and extinctions and to focus monitoring efforts. Discontinuity theory can complement current approaches, providing a broader paradigm for ecological management and conservation This manuscript provides insight on using discontinuity approaches to aid in managing complex ecological systems. In partic

  1. Seismic Receiver Functions and the Lithosphere-Asthenosphere Boundary

    NASA Astrophysics Data System (ADS)

    Kind, R.; Yuan, X.; Kumar, P.

    2012-12-01

    The lower boundary of the lithospheric plates has remained as an enigmatic boundary for seismologists, since it is relatively poorly observed by seismic means. There is traditionally a broad consensus that the asthenosphere is observable as a low velocity zone by seismic surface waves. Seismic techniques which use shorter period P-to-S or S-to-P converted body waves are now far enough developed to be successful in observing such a low velocity zone with a higher resolution. The principle of this technique (the so-called receiver function technique) is that a strong teleseismic mother phase (e.g. P, S, PP or SKS) incident from below on any seismic discontinuity beneath a station produces a converted phase (Ps or Sp) which indicates its depth and properties. We discuss details of this technique. A sufficient number of such observations exist already to indicate that the top of the low velocity zone is a globally observable discontinuity and it is sharper than previously thought. An intriguing observation is that in some cratons the new seismic data indicate that the low velocity zone exists already at shallower depths than obtained from surface waves. This confirms earlier results from controlled source observations (Thybo and Perchuc 1997). We discuss possible interpretations of this shallow low velocity zone in cratonic regions.

  2. Seismic receiver functions and the lithosphere-asthenosphere boundary

    NASA Astrophysics Data System (ADS)

    Kind, Rainer; Yuan, Xiaohui; Kumar, Prakash

    2012-04-01

    The lower boundary of the lithospheric plates has remained as an enigmatic boundary for seismologists, since it is relatively poorly observed by seismic means. There is traditionally a broad consensus that the asthenosphere is observable as a low velocity zone by seismic surface waves. Seismic techniques which use shorter period P-to-S or S-to-P converted body waves are now far enough developed to be successful in observing such a low velocity zone with a higher resolution. The principle of this technique (the so-called receiver function technique) is that a strong teleseismic mother phase (e.g. P, S, PP or SKS) incident from below on any seismic discontinuity beneath a station produces a converted phase (Ps or Sp) which indicates its depth and properties. We discuss details of this technique. A sufficient number of such observations exist already to indicate that the top of the low velocity zone is a globally observable discontinuity and it is sharper than previously thought. An intriguing observation is that in some cratons the new seismic data indicate that the low velocity zone exists already at shallower depths than obtained from surface waves. This confirms earlier results from controlled source observations (Thybo and Perchuc, 1997). We discuss possible interpretations of this shallow low velocity zone in cratonic regions.

  3. Seismic Velocity Structure of the Mantle beneath the Hawaiian Hotspot and Geodynamic Perspectives

    NASA Astrophysics Data System (ADS)

    Wolfe, C. J.; Laske, G.; Ballmer, M. D.; Ito, G.; Collins, J. A.; Solomon, S. C.; Rychert, C. A.

    2012-12-01

    Data from the PLUME deployments of land and ocean bottom seismometers have provided unprecedented new constraints on regional seismic structure of the mantle beneath the Hawaiian Islands and motivated a new generation of geodynamic models for understanding hotspot origins. Three-dimensional finite-frequency body-wave tomographic images of S- and P-wave velocity structure reveal an upper-mantle low-velocity anomaly beneath Hawaii that is elongated in the direction of the island chain and surrounded by a high-velocity anomaly in the shallow upper mantle that is parabolic in map view. Low velocities continue downward to the mantle transition zone between 410 and 660 km depth and extend into the topmost lower mantle southeast of Hawaii. Upper mantle structure from both S and P waves is asymmetric about the island chain, with lower velocities just southwest of the island of Hawaii and higher velocities to the east. Independent Rayleigh-wave tomography displays a similarly asymmetric structure in the lower lithosphere and asthenosphere, and also reveals a low-velocity anomaly (with horizontal dimensions of 100 by 300 km across and along the chain, respectively) beneath the hotspot swell that reaches to depths of at least 140 km. Shear-wave splitting observations dominantly reflect fossil lithospheric anisotropy, although a signature of asthenospheric flow also may be resolvable. S-to-P receiver function imaging of the lithosphere-asthenosphere boundary suggests shoaling from 100 km west of Hawaii to 80 km beneath the island, a pattern consistent with results from Rayleigh wave imaging. In terms of mantle plume geodynamic models, the broad upper-mantle low-velocity region beneath the Hawaiian Islands may reflect the "diverging pancake" at the top of the upwelling zone; the surrounding region of high velocities could represent a downwelling curtain of relatively cool sublithospheric material; and the low-velocity anomalies southeast of Hawaii in the transition zone and

  4. New Madrid seismic zone recurrence intervals

    SciTech Connect

    Schweig, E.S. Center for Earthquake Research and Information, Memphis, TN ); Ellis, M.A. )

    1993-03-01

    Frequency-magnitude relations in the New Madrid seismic zone suggest that great earthquakes should occur every 700--1,200 yrs, implying relatively high strain rates. These estimates are supported by some geological and GPS results. Recurrence intervals of this order should have produced about 50 km of strike-slip offset since Miocene time. No subsurface evidence for such large displacements is known within the seismic zone. Moreover, the irregular fault pattern forming a compressive step that one sees today is not compatible with large displacements. There are at least three possible interpretations of the observations of short recurrence intervals and high strain rates, but apparently youthful fault geometry and lack of major post-Miocene deformation. One is that the seismological and geodetic evidence are misleading. A second possibility is that activity in the region is cyclic. That is, the geological and geodetic observations that suggest relatively short recurrence intervals reflect a time of high, but geologically temporary, pore-fluid pressure. Zoback and Zoback have suggested such a model for intraplate seismicity in general. Alternatively, the New Madrid seismic zone is geologically young feature that has been active for only the last few tens of thousands of years. In support of this, observe an irregular fault geometry associated with a unstable compressive step, a series of en echelon and discontinuous lineaments that may define the position of a youthful linking fault, and the general absence of significant post-Eocene faulting or topography.

  5. 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.

  6. Seismic intrusion detector system

    DOEpatents

    Hawk, Hervey L.; Hawley, James G.; Portlock, John M.; Scheibner, James E.

    1976-01-01

    A system for monitoring man-associated seismic movements within a control area including a geophone for generating an electrical signal in response to seismic movement, a bandpass amplifier and threshold detector for eliminating unwanted signals, pulse counting system for counting and storing the number of seismic movements within the area, and a monitoring system operable on command having a variable frequency oscillator generating an audio frequency signal proportional to the number of said seismic movements.

  7. 3D seismic image processing for interpretation

    NASA Astrophysics Data System (ADS)

    Wu, Xinming

    Extracting fault, unconformity, and horizon surfaces from a seismic image is useful for interpretation of geologic structures and stratigraphic features. Although interpretation of these surfaces has been automated to some extent by others, significant manual effort is still required for extracting each type of these geologic surfaces. I propose methods to automatically extract all the fault, unconformity, and horizon surfaces from a 3D seismic image. To a large degree, these methods just involve image processing or array processing which is achieved by efficiently solving partial differential equations. For fault interpretation, I propose a linked data structure, which is simpler than triangle or quad meshes, to represent a fault surface. In this simple data structure, each sample of a fault corresponds to exactly one image sample. Using this linked data structure, I extract complete and intersecting fault surfaces without holes from 3D seismic images. I use the same structure in subsequent processing to estimate fault slip vectors. I further propose two methods, using precomputed fault surfaces and slips, to undo faulting in seismic images by simultaneously moving fault blocks and faults themselves. For unconformity interpretation, I first propose a new method to compute a unconformity likelihood image that highlights both the termination areas and the corresponding parallel unconformities and correlative conformities. I then extract unconformity surfaces from the likelihood image and use these surfaces as constraints to more accurately estimate seismic normal vectors that are discontinuous near the unconformities. Finally, I use the estimated normal vectors and use the unconformities as constraints to compute a flattened image, in which seismic reflectors are all flat and vertical gaps correspond to the unconformities. Horizon extraction is straightforward after computing a map of image flattening; we can first extract horizontal slices in the flattened space

  8. 27 CFR 17.187 - Discontinuance of business.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Discontinuance of business... PRODUCTS Miscellaneous Provisions § 17.187 Discontinuance of business. The manufacturer shall notify TTB when business is to be discontinued. Upon discontinuance of business, a manufacturer's entire stock...

  9. 27 CFR 17.187 - Discontinuance of business.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2012-04-01 2012-04-01 false Discontinuance of business... PRODUCTS Miscellaneous Provisions § 17.187 Discontinuance of business. The manufacturer shall notify TTB when business is to be discontinued. Upon discontinuance of business, a manufacturer's entire stock...

  10. 27 CFR 478.57 - Discontinuance of business.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2014-04-01 2014-04-01 false Discontinuance of business... Licenses § 478.57 Discontinuance of business. (a) Where a firearm or ammunition business is either discontinued or succeeded by a new owner, the owner of the business discontinued or succeeded shall within...

  11. 27 CFR 478.127 - Discontinuance of business.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2014-04-01 2014-04-01 false Discontinuance of business... Records § 478.127 Discontinuance of business. Where a licensed business is discontinued and succeeded by a... be delivered to the successor. Where discontinuance of the business is absolute, the records shall...

  12. 27 CFR 478.127 - Discontinuance of business.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2010-04-01 2010-04-01 false Discontinuance of business... Records § 478.127 Discontinuance of business. Where a licensed business is discontinued and succeeded by a... be delivered to the successor. Where discontinuance of the business is absolute, the records shall...

  13. 27 CFR 478.57 - Discontinuance of business.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2010-04-01 2010-04-01 false Discontinuance of business... Licenses § 478.57 Discontinuance of business. (a) Where a firearm or ammunition business is either discontinued or succeeded by a new owner, the owner of the business discontinued or succeeded shall within...

  14. 27 CFR 478.57 - Discontinuance of business.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2013-04-01 2013-04-01 false Discontinuance of business... Licenses § 478.57 Discontinuance of business. (a) Where a firearm or ammunition business is either discontinued or succeeded by a new owner, the owner of the business discontinued or succeeded shall within...

  15. 27 CFR 478.127 - Discontinuance of business.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2013-04-01 2013-04-01 false Discontinuance of business... Records § 478.127 Discontinuance of business. Where a licensed business is discontinued and succeeded by a... be delivered to the successor. Where discontinuance of the business is absolute, the records shall...

  16. 27 CFR 555.128 - Discontinuance of business.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2013-04-01 2013-04-01 false Discontinuance of business... Discontinuance of business. Where an explosive materials business or operations is discontinued and succeeded by... such facts and shall be delivered to the successor. Where discontinuance of the business or...

  17. 27 CFR 555.128 - Discontinuance of business.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2014-04-01 2014-04-01 false Discontinuance of business... Discontinuance of business. Where an explosive materials business or operations is discontinued and succeeded by... such facts and shall be delivered to the successor. Where discontinuance of the business or...

  18. 27 CFR 555.128 - Discontinuance of business.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 3 2010-04-01 2010-04-01 false Discontinuance of business... Discontinuance of business. Where an explosive materials business or operations is discontinued and succeeded by... such facts and shall be delivered to the successor. Where discontinuance of the business or...

  19. Mid-lithospheric Discontinuity Beneath the Malawi Rift, Deduced from Gravity Studies and its Relation to the Rifting Process.

    NASA Astrophysics Data System (ADS)

    Njinju, E. A.; Atekwana, E. A.; Mickus, K. L.; Abdelsalam, M. G.; Atekwana, E. A.; Laó-Dávila, D. A.

    2015-12-01

    The World Gravity Map satellite gravity data were used to investigate the lithospheric structure beneath the Cenozoic-age Malawi Rift which forms the southern extension of the Western Branch of the East African Rift System. An analysis of the data using two-dimensional (2D) power spectrum methods indicates the two distinctive discontinuities at depths of 31‒44 km and 64‒124 km as defined by the two steepest slopes of the power spectrum curves. The shallower discontinuity corresponds to the crust-mantle boundary (Moho) and compares well with Moho depth determined from passive seismic studies. To understand the source of the deeper discontinuity, we applied the 2D power spectrum analysis to other rift segments of the Western Branch as well as regions with stable continental lithospheres where the lithospheric structure is well constrained through passive seismic studies. We found that the deeper discontinuity corresponds to a mid-lithospheric discontinuity (MLD), which is known to exist globally at depths between 60‒150 km and as determined by passive seismic studies. Our results show that beneath the Malawi Rift, there is no pattern of N-S elongated crustal thinning following the surface expression of the Malawi Rift. With the exception of a north-central region of crustal thinning (< 35 km), most of the southern part of the rift is underlain by thick crust (~40‒44 km). Different from the Moho, the MLD is shallower beneath the axis of the Malawi Rift forming a N-S trending zone with depths of 64‒80 km, showing a broad and gentle topography. We interpret the MLD as representing a sharp density contrast resulting from metasomatized lithosphere due to lateral migration along mobile belts of hot mantle melt or fluids from a distant plume and not from an ascending asthenosphere. These fluids weaken the lithosphere enhancing rift nucleation. The availability of satellite gravity worldwide makes gravity a promising technique for determining the MLD globally.

  20. Precise Comparison of Phase Relations in Pyrolite, MORB and Harzburgite Up To 28 GPa 1600-2200°C Using Multi-sample Cell Technique

    NASA Astrophysics Data System (ADS)

    Ishii, T.; Akaogi, M.; Kojitani, H.

    2015-12-01

    It is accepted that 410- and 660-km seismic discontinuities are attributed to phase transitions in pyrolite. MORB, harzburgite and pyrolite constitute a subducting slab, and pyrolite is also major hot plume material. Mantle tomography studies demonstrated that slabs are subducting down to the lower mantle and that some hot plumes are elevating from the deep lower mantle to the upper mantle. Therefore, phase relations of these mantle rocks provide important information to elucidate dynamics of heterogeneous components in the deep mantle. We performed high-pressure high-temperature quench experiments at 12-28 GPa and 1600-2200°C for 2-10 hours using a Kawai-type multianvil apparatus at Gakushuin University. Starting materials were prepared from the oxide mixtures of pyrolite, MORB and harzburgite compositions. The three samples were packed with pressure calibrants (MgSiO3 enstatite or pyrope) in a Re multi-sample capsule with four holes, and kept at the same P, T conditions to precisely compare the phase relations. Phases of the recovered samples were identified with a microfocus X ray diffractometer and a SEM-EDS. Using the measured compositions, phase proportions were calculated with mass-balance calculation, and densities of the rocks were obtained using thermoelastic data. The density profiles of three rock compositions show that MORB and harzburgite in slabs can subduct to the 660-km discontinuity because the post-spinel transition in pyrolite occurs at lower pressure than that in harzburgite and the post-garnet transition in MORB. Besides, in hot plumes, pyrolite has lower density than average pyrolitic mantle by not only its higher temperature but also different mineral assemblages from the average mantle due to decomposition of ringwoodite to garnet + ferropericlase at the depth around 660-km discontinuity.

  1. Mantle transition zone thickness beneath the Yellowstone hotspot

    NASA Astrophysics Data System (ADS)

    Zurek, B. D.; Dueker, K.

    2002-12-01

    The Yellowstone hotspot is one of the largest continental hotspots, however whether the hotspot actively derives from a lower mantle plume or an upper mantle convective instability is not constrained. The plume model is supported by the 2-3 cm/yr volcanic age progression approximately parallel to the absolute North American plate motion and an elevated He3/He4 signature. Correspondingly, evidence against a plume model derives from the lack of dynamic topographic uplift (Lowry et al., 1998), absence of a low velocity anomaly below 200 km depth (Dueker et al., 2001) and shear-wave splits that show no plume related flow anomalies (Waite et al., 2002). To better constrain the origin of the hotspot, The Yellowstone Intermountain Seismic Array (YISA) with 47 PASSCAL broad-band seismometers was deployed for one year covering a region 250 km in radius from the center of the Yellowstone hotspot. Here we present images of the mantle transition zone from receiver function common conversion point imaging. Lateral velocity heterogeneity corrections are applied to the receiver functions using the teleseismic P-times calculated from the array. The mantle transition zone is composed of the 410 and 660 km discontinuities, these discontinuities are generally regarded to derive from phase changes that have opposite Clapeyron slopes. Thus if the mantle is assumed to be compositional homogenous, >100 degree lateral thermal gradients are resolvable from transition zone thickness maps. Preliminary results show that the transition zone beneath the Yellowstone hotspot has a mean thickness of 245 km with 20 km of variation across the array. The mean values of the 410 and 660 km discontinuities are, 412 km and 660 km, with 16 and 14 km of topography, respectively. The processes that could produce this topography are the focus of our current research.

  2. A hybrid simulation of contact discontinuity

    NASA Technical Reports Server (NTRS)

    Wu, B. H.; Chao, J. K.; Tsai, W. H.; Lin, Y.; Lee, L. C.

    1994-01-01

    Contact discontinuities in a collisionless plasma are studied by hybrid simulations, in which ions are treated as particles and electrons are considered as a fluid. It is demonstrated that contact discontinuity with a stable density ramp can exist in cases with a finite electron temperature. An electron pressure gradient is present across the contact discontinuity, leading to the presence of a parallel electric field and hence field-aligned potential increase (Delta Phi (sub parallel)) in the transition region. By reflecting ions at the discontinuity, this parallel electric potential peak reduces the interpenetration between hot and cold ions and maintains a stable density ramp across the contact discontinuity. The ratio of the field-aligned electric potential energy to ion thermal energy, e(Delta) Phi(sub parallel)/kT(sub i), is found to be an increasing function of T(sub e)/T(sub i), where T(sub e) and T(sub i) are respectively the electron and ion temperature.

  3. Infrastructure and evolution of ocean-ridge discontinuities in Iceland

    NASA Astrophysics Data System (ADS)

    Gudmundsson, Agust

    2007-01-01

    There are two main ocean-ridge discontinuities in Iceland: the Tjörnes Fracture Zone (TFZ) and the South Iceland Seismic Zone (SISZ). The TFZ is a 120-km-long and as much as 70-km-wide WNW-trending zone of high seismicity. It has three main seismic lineaments: the Husavik-Flatey Fault (HFF), the Dalvik lineament, and the Grimsey lineament. The HFF, a dextral strike-slip fault and active as a transform fault for about 9 Ma, has a cumulative transform-parallel displacement of some 60 km. Offshore, the HFF is marked by a transform (fracture-zone) valley, 5-10 km wide and 3-4 km deep. Onshore the Flateyjarskagi Peninsula the HFF is marked by a 3-5-km-wide zone of intense crustal deformation with numerous strike-slip and normal faults, transform-parallel dykes, dense sets of mineral veins, and subzones of completely crushed rocks, that is, fault cores. Where the HFF comes on land on Tjörnes there is a similar, but much thinner, zone of crushed rocks. The seismic lineaments are located a few tens of kilometres south (Dalvik) and north (Grimsey) of, and run subparallel with, the HFF. Both lineaments are composed of sets of NNW-trending sinistral faults arranged en echelon. The SISZ is a 70-km-long and 10-20-km wide zone of almost continuous seismicity located between the overlapping West and East Volcanic Zones. It produces the largest earthquakes in Iceland, some of which exceed M7, during which the N-S width of the zone may be as great as 50-60 km. The SISZ is partly covered with Holocene lava flows where the seismogenic faults occur as dextral NNE-trending and sinistral ENE-trending conjugate arrays with push-ups between their nearby ends. The same fault-segment trends occur in the Pleistocene pile north of the Holocene lava flows. The HFF is neither perpendicular to the nearby ridge segments nor parallel with the spreading vector. As a consequence, the North Volcanic Zone has propagated to the north and the Kolbeinsey Ridge to the south during the past 1 Ma

  4. The Role of Orientation of Magnetic Fields in Contact Discontinuities

    NASA Astrophysics Data System (ADS)

    Tsai, T. C.; Hsieh, W. C.; Chao, J. K.

    2014-12-01

    Contact discontinuities are one type of the discontinuities in MHD plasma. Contact discontinuities are discontinuities with continuous magnetic fields but without plasma flows across a plasma density jump. Contact discontinuities are characterized by a remarkable plasma density jump but identical plasma bulk velocity, magnetic fields and thermal pressure on two sides of the discontinuity. Contact discontinuities are rarely observed in the nature. Due to a rapid diffusion of plasma along the continuous magnetic field lines across its surface, it is believed that contact discontinuities will rapidly broaden into a smooth transition then lose its identity. In this presentation, we study the effect of the orientation of magnetic field lines on the diffusion of plasma in contact discontinuities. With respect to the normal of a contact discontinuity, the cases of orientation of (1) parallel, (2) quasi-parallel, (3) perpendicular and (4) quasi-perpendicular magnetic fields are studied.

  5. High resolution upper mantle discontinuity images across the Pacific Ocean from SS precursors using local slant stack filters

    NASA Astrophysics Data System (ADS)

    Zheng, Zhao; Ventosa, Sergi; Romanowicz, Barbara

    2015-07-01

    SS precursor observations are a powerful tool to study the topography and character of transition zone discontinuities, especially in regions such as ocean basins where few seismic stations exist, precluding other high resolution approaches. Still, the available coverage is limited by the distribution of sources and stations, but also by the level of noise and by the fact that, in some distance ranges, interfering seismic phases mask the weak signal from the SS precursors. We introduce an array data processing tool, the local slant-stack filter, to address these challenges and clean up the otherwise noisy SS precursor record sections. We show that these filters are a powerful tool for extracting the weak yet coherent SS precursor signals while removing interfering seismic phases as well as random noise, yielding robust precursor traveltime measurements with spatial resolution higher than what can be achieved by the conventional common midpoint stacking method. The effectiveness of the filters are demonstrated by application to synthetic and real data. We systematically apply this filtering method to an SS precursor data set recorded by the U.S. Transportable Array that samples a vast region of the Pacific Ocean and its northwest margin, and present maps of 410 and 660 discontinuity topography. We discuss correlations observed between our discontinuity images and several fine-scale heterogeneities revealed by mantle shear wave tomography in the vicinity of Hawaii and the Pacific Superswell.

  6. Correlation between the shear-speed structure and thickness of the mantle transition zone

    NASA Astrophysics Data System (ADS)

    Lebedev, Sergei; Chevrot, Sébastien; van der Hilst, R. D.

    2003-04-01

    The 410 and 660 km seismic discontinuities that bound the mantle transition zone (TZ) are attributed to phase transformations in olivine structure. This implies that variations in TZ thickness ( HTZ) should correlate with those in TZ temperature. Pertinent seismic evidence has so far been ambiguous, however. We measure converted-wave ( Pd s) differential times tdiff= tP660 s- tP410 s in SE Asia and Australia and compare them with S-velocity ( βTZ) estimates from regional tomographic models. Both tdiff and βTZ vary on a scale of a few hundred kilometers. Inferred variations in HTZ are up to ±30 km over length scales larger than 500 km, implying ±200 K thermal heterogeneity if the effect of composition can be neglected. tdiff and βTZ correlate strongly; the linear dependence of HTZ on the average temperature within the TZ is consistent with olivine Clapeyron slopes. We also show that this relationship holds on a global-scale as well, provided that the scalelengths and uncertainties of the variations in tdiff and βTZ are taken into account. These results confirm that the transformations in olivine structure give rise to the 410 and 660 km discontinuities globally.

  7. Method for simulating discontinuous physical systems

    DOEpatents

    Baty, Roy S.; Vaughn, Mark R.

    2001-01-01

    The mathematical foundations of conventional numerical simulation of physical systems provide no consistent description of the behavior of such systems when subjected to discontinuous physical influences. As a result, the numerical simulation of such problems requires ad hoc encoding of specific experimental results in order to address the behavior of such discontinuous physical systems. In the present invention, these foundations are replaced by a new combination of generalized function theory and nonstandard analysis. The result is a class of new approaches to the numerical simulation of physical systems which allows the accurate and well-behaved simulation of discontinuous and other difficult physical systems, as well as simpler physical systems. Applications of this new class of numerical simulation techniques to process control, robotics, and apparatus design are outlined.

  8. Long-range Receiver Function Profile of Crustal and Mantle Discontinuities From the Aleutian Arc to Tierra del Fuego

    NASA Astrophysics Data System (ADS)

    Spieker, Kathrin; Rondenay, Stéphane; Sawade, Lucas

    2016-04-01

    The Circum-Pacific belt, also called the Pacific Ring of Fire, is the most seismically active region on Earth. Multiple plate boundaries form a zone characterized by frequent volcanic eruptions and seismicity. While convergent plate boundaries such as the Peru-Chile trench dominate the Circum-Pacific belt, divergent and transform boundaries are present as well. The eastern section of the Circum-Pacific belt extends from the Aleutian arc, through the Cascadia subduction zone, San Andreas Fault, middle America trench and the Andean margin down to Tierra del Fuego. Due to the significant hazards posed by this tectonic activity, the region has been densely instrumented by thousands of seismic stations deployed across fifteen countries, over a distance of more than 15000 km. Various seismological studies, including receiver function analyses, have been carried out to investigate the crustal and mantle structure beneath local segments of the eastern Circum-Pacific belt (i.e., at ~100-500 km scale). However, to the best of our knowledge, no study to date has ever attempted to combine all available seismic data from the eastern Circum-Pacific belt to generate a continuous profile of seismic discontinuities extending from the Aleutians to Tierra del Fuego. Here, we use results from the "Global Imaging using Earthquake Records" (GLImER) P-wave receiver function database to create a long-range profile of crustal and upper mantle discontinuities across the entire eastern portion of the Circum-Pacific belt. We image intermittent crustal and mantle discontinuities along the profile, and examine them with regard to their behaviour and properties across transitions between different tectonic regimes.

  9. Rockburst Generation in Discontinuous Rock Masses

    NASA Astrophysics Data System (ADS)

    He, Ben-Guo; Zelig, Ravit; Hatzor, Yossef H.; Feng, Xia-Ting

    2016-10-01

    We study rockburst generation in discontinuous rock masses using theoretical and numerical approaches. We begin by developing an analytical solution for the energy change due to tunneling in a continuous rock mass using linear elasticity. We show that the affected zone where most of the increase in elastic strain energy takes place is restricted to an annulus that extends to a distance of three diameters from the tunnel center, regardless of initial tunnel diameter, magnitude of in situ stress, and in situ stress ratio. By considering local elastic strain concentrations, we further delineate the Rockbursting Prone Zone found to be concentrated in an annulus that extends to one diameter from the tunnel center, regardless of original stress ratio, magnitude, and the stiffness of the rock mass. We proceed by arguing that in initially discontinuous rock masses shear stress amplification due to tunneling will inevitably trigger block displacements along preexisting discontinuities much before shear failure of intact rock elements will ensue, because of the lower shear strength of discontinuities with respect to intact rock elements, provided of course that the blocks are removable. We employ the numerical discrete element DDA method to obtain, quantitatively, the kinetic energy, the elastic strain energy, and the dissipated energy in the affected zone in a discontinuous rock due to tunneling. We show that the kinetic energy of ejected blocks due to strain relaxation increases with increasing initial stress and with decreasing frictional resistance of preexisting discontinuities. Finally, we demonstrate how controlled strain energy release by means of top heading and bench excavation methodology can assist in mitigating rockburst hazards due to stain relaxation.

  10. Pharmacologic strategies for discontinuing benzodiazepine treatment.

    PubMed

    Rickels, K; DeMartinis, N; Rynn, M; Mandos, L

    1999-12-01

    Benzodiazepines have been shown to have broad-spectrum activity, rapid onset of action, and a wide therapeutic window compared with other anxiolytic medications. Yet the use of benzodiazepines has been limited by concern regarding dependence, withdrawal, and abuse. Agents such as antidepressants, serotonergic anxiolytics, anticonvulsants, and beta-blockers have been used with varying degrees of success to help facilitate the tapering of benzodiazepines. Carbamazepine, imipramine, valproate, and trazodone have been beneficial in the management of benzodiazepine discontinuation, but not in decreasing the severity of benzodiazepine withdrawal. A stepwise approach to discontinuing benzodiazepines is offered.

  11. Discontinuous Buckling of Wide Beams and Metabeams.

    PubMed

    Coulais, Corentin; Overvelde, Johannes T B; Lubbers, Luuk A; Bertoldi, Katia; van Hecke, Martin

    2015-07-24

    We uncover how nonlinearities dramatically alter the buckling of elastic beams. First, we show experimentally that sufficiently wide ordinary elastic beams and specifically designed metabeams-beams made from a mechanical metamaterial-exhibit discontinuous buckling, an unstable form of buckling where the postbuckling stiffness is negative. Then we use simulations to uncover the crucial role of nonlinearities, and show that beams made from increasingly nonlinear materials exhibit an increasingly negative postbuckling slope. Finally, we demonstrate that for sufficiently strong nonlinearity, we can observe discontinuous buckling for metabeams as slender as 1% numerically and 5% experimentally.

  12. Evidence for back scattering of near-podal seismic P'P' waves from the 150-220 km zone in Earth's upper mantle

    SciTech Connect

    Tkalcic, H; Flanagan, M P; Cormier, V F

    2005-07-15

    The deepest and most inaccessible parts of Earth's interior--the core and core-mantle boundary regions can be studied from compressional waves that turn in the core and are routinely observed following large earthquakes at epicentral distances between 145{sup o} and 180{sup o} (also called P', PKIKP or PKP waves). P'P' (PKPPKP) are P' waves that travel from a hypocenter through the Earth's core, reflect from the free surface and travel back through the core to a recording station on the surface. P'P' waves are sometimes accompanied by precursors, which were reported first in the 1960s as small-amplitude arrivals on seismograms at epicentral distances of about 50{sup o}-70{sup o}. Most prominent of these observed precursors were explained by P'P' waves generated by earthquakes or explosions that did not reach the Earth's surface but were reflected from the underside of first order velocity discontinuities at 410 and 660 km in the upper mantle mantle. Here we report the discovery of hitherto unobserved near-podal P'P' waves (at epicentral distance less than 10{sup o}) and very prominent precursors preceding the main energy by as much as 55 seconds. We interpret these precursors as a back scattered energy from undocumented structure in the upper mantle, in a zone between 150 and 220 km depth beneath Earth's surface. From these observations, we identify a frequency dependence of Q (attenuation quality factor) in the lithosphere that can be modeled by a flat relaxation spectrum below about 0.05-0.1 Hz and increasing with as the first power of frequency above this value, confirming pioneering work by B. Gutenberg.

  13. Angola Seismicity MAP

    NASA Astrophysics Data System (ADS)

    Neto, F. A. P.; Franca, G.

    2014-12-01

    The purpose of this job was to study and document the Angola natural seismicity, establishment of the first database seismic data to facilitate consultation and search for information on seismic activity in the country. The study was conducted based on query reports produced by National Institute of Meteorology and Geophysics (INAMET) 1968 to 2014 with emphasis to the work presented by Moreira (1968), that defined six seismogenic zones from macro seismic data, with highlighting is Zone of Sá da Bandeira (Lubango)-Chibemba-Oncócua-Iona. This is the most important of Angola seismic zone, covering the epicentral Quihita and Iona regions, geologically characterized by transcontinental structure tectono-magmatic activation of the Mesozoic with the installation of a wide variety of intrusive rocks of ultrabasic-alkaline composition, basic and alkaline, kimberlites and carbonatites, strongly marked by intense tectonism, presenting with several faults and fractures (locally called corredor de Lucapa). The earthquake of May 9, 1948 reached intensity VI on the Mercalli-Sieberg scale (MCS) in the locality of Quihita, and seismic active of Iona January 15, 1964, the main shock hit the grade VI-VII. Although not having significant seismicity rate can not be neglected, the other five zone are: Cassongue-Ganda-Massano de Amorim; Lola-Quilengues-Caluquembe; Gago Coutinho-zone; Cuima-Cachingues-Cambândua; The Upper Zambezi zone. We also analyzed technical reports on the seismicity of the middle Kwanza produced by Hidroproekt (GAMEK) region as well as international seismic bulletins of the International Seismological Centre (ISC), United States Geological Survey (USGS), and these data served for instrumental location of the epicenters. All compiled information made possible the creation of the First datbase of seismic data for Angola, preparing the map of seismicity with the reconfirmation of the main seismic zones defined by Moreira (1968) and the identification of a new seismic

  14. In-process discontinuity detection during friction stir welding

    NASA Astrophysics Data System (ADS)

    Shrivastava, Amber

    The objective of this work is to develop a method for detecting the creation of discontinuities (e.g., voids) during friction stir welding. Friction stir welding is inherently cost-effective, however, the need for significant weld inspection can make the process cost-prohibitive. A new approach to weld inspection is required -- where an in-situ characterization of weld quality can be obtained, reducing the need for post-process inspection. Friction stir welds with discontinuity and without discontinuity were created. In this work, discontinuities are generated by reducing the friction stir tool rotation frequency and increasing the tool traverse speed in order to create "colder" welds. During the welds, forces are measured. Discontinuity sizes for welds are measured by computerized tomography. The relationship between the force transients and the discontinuity sizes indicate that the force measurement during friction stir welding can be effectively used for detecting discontinuities in friction stir welds. The normalized force transient data and normalized discontinuity size are correlated to develop a criterion for discontinuity detection. Additional welds are performed to validate the discontinuity detection method. The discontinuity sizes estimated by the force measurement based method are in good agreement with the discontinuity sizes measured by computerized tomography. These results show that the force measurement based discontinuity detection model method can be effectively used to detect discontinuities during friction stir welding.

  15. General practitioners' decisions about discontinuation of medication: an explorative study.

    PubMed

    Nixon, Michael Simon; Vendelø, Morten Thanning

    2016-06-20

    Purpose - The purpose of this paper is to investigate how general practitioners' (GPs) decisions about discontinuation of medication are influenced by their institutional context. Design/methodology/approach - In total, 24 GPs were interviewed, three practices were observed and documents were collected. The Gioia methodology was used to analyse data, drawing on a theoretical framework that integrate the sensemaking perspective and institutional theory. Findings - Most GPs, who actively consider discontinuation, are reluctant to discontinue medication, because the safest course of action for GPs is to continue prescriptions, rather than discontinue them. The authors conclude that this is in part due to the ambiguity about the appropriateness of discontinuing medication, experienced by the GPs, and in part because the clinical guidelines do not encourage discontinuation of medication, as they offer GPs a weak frame for discontinuation. Three reasons for this are identified: the guidelines provide dominating triggers for prescribing, they provide weak priming for discontinuation as an option, and they underscore a cognitive constraint against discontinuation. Originality/value - The analysis offers new insights about decision making when discontinuing medication. It also offers one of the first examinations of how the institutional context embedding GPs influences their decisions about discontinuation. For policymakers interested in the discontinuation of medication, the findings suggest that de-stigmatising discontinuation on an institutional level may be beneficial, allowing GPs to better justify discontinuation in light of the ambiguity they experience.

  16. 38 CFR 21.7135 - Discontinuance dates.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 38 Pensions, Bonuses, and Veterans' Relief 2 2011-07-01 2011-07-01 false Discontinuance dates. 21.7135 Section 21.7135 Pensions, Bonuses, and Veterans' Relief DEPARTMENT OF VETERANS AFFAIRS (CONTINUED) VOCATIONAL REHABILITATION AND EDUCATION All Volunteer Force Educational Assistance Program (Montgomery...

  17. 27 CFR 18.38 - Permanent discontinuance.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Permanent discontinuance. 18.38 Section 18.38 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE TREASURY LIQUORS PRODUCTION OF VOLATILE FRUIT-FLAVOR CONCENTRATE Qualification...

  18. 27 CFR 18.38 - Permanent discontinuance.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Permanent discontinuance. 18.38 Section 18.38 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE TREASURY LIQUORS PRODUCTION OF VOLATILE FRUIT-FLAVOR CONCENTRATE Qualification...

  19. 38 CFR 21.9635 - Discontinuance dates.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...) VOCATIONAL REHABILITATION AND EDUCATION Post-9/11 GI Bill Payments-Educational Assistance § 21.9635... individual dies while pursuing a program of education, the discontinuance date of educational assistance will.... (Authority: 38 U.S.C. 3323, 3680(a)) (d) Reduction in the rate of pursuit of a program of education. If...

  20. Finite-Frequency Tomography of USArray Receiver Functions

    NASA Astrophysics Data System (ADS)

    Zhou, Y.

    2014-12-01

    Seismic waves diffract around structure perturbations when the length scale of lateral heterogeneities is comparable to the size of the Fresnel zone. Our recent studies based on wave propagation simulations show that Born sensitivity kernels can be used in seismic tomography to account for diffractional effects in surface waves as well as body waves. In addition to direct seismic phases, teleseismic receiver functions which take advantage of secondary waves converted at seismic discontinuities can provides important constraints on discontinuity structures. In this study, we calculate finite-frequency sensitivity of receiver functions to perturbations in seismic discontinuities in the mantle transition zone. The boundary sensitivity kernels based on Born approximation are formulated in the framework of traveling-wave mode summation to account for complete wave interactions within the measurement window. The sensitivity kernels allow us to employ frequency-dependent receiver functions in tomographic inversions to map the topography of the 410-km and 660-km discontinuities. We will discuss preliminary results on the structure of mantle transition zone discontinuities beneath the continental US imaged from finite-frequency receiver-function tomography using seismograms recorded at USArray TA stations.

  1. Three-dimensional structure of Conrad and Moho discontinuities in Egypt

    NASA Astrophysics Data System (ADS)

    Abdelwahed, Mohamed F.; El-Khrepy, Sami; Qaddah, Atef

    2013-09-01

    The three-dimensional structures of Conrad and Moho discontinuities beneath Egypt are investigated by local earthquake travel time inversion. A number of 2513 events with 24,696 arrival time data recorded by the Egyptian National Seismic Network (ENSN) are used. The station corrections of P- and S-waves and the hypocentral parameters are simultaneously estimated with the Conrad and Moho depths. The results of this study show that the discontinuities form patterns of shallow and deep structures getting shallow toward the northern and eastern coast, and deeper toward western Desert and northeastern Sinai. The Conrad and Moho discontinuities are located within the depth range 9-17 km and 27-41 km, respectively. The depth ranges of Conrad and Moho discontinuities are respectively: 15-16 km and 31-33 km in greater Cairo and Dahshour; 15-18 km and 32-35 km in Sinai; 16-17 and 33-35 km along the Nile River; 9 and 30 km near the Red Sea coast; 15 and 39 km toward the western desert. The comprehensive comparison with previous crustal studies suggests that the main patterns of Moho undulations and the range of Moho depths are in good agreement with the previous crustal models in Egypt, as well as with the Bouguer gravity anomalies that well explain the Nile River sediments, Red Sea mountain belts and Western Desert depression and Oasis. The model of the Moho and Conrad discontinuities improves knowledge of the three dimensional structure of the crust beneath Egypt in wide areas where geophysical data is sparse.

  2. Excursions in fluvial (dis)continuity

    USGS Publications Warehouse

    Grant, Gordon E.; O'Connor, James E.; Safran, Elizabeth

    2017-01-01

    Lurking below the twin concepts of connectivity and disconnectivity are their first, and in some ways, richer cousins: continuity and discontinuity. In this paper we explore how continuity and discontinuity represent fundamental and complementary perspectives in fluvial geomorphology, and how these perspectives inform and underlie our conceptions of connectivity in landscapes and rivers. We examine the historical roots of continuum and discontinuum thinking, and how much of our understanding of geomorphology rests on contrasting views of continuity and discontinuity. By continuum thinking we refer to a conception of geomorphic processes as well as geomorphic features that are expressed along continuous gradients without abrupt changes, transitions, or thresholds. Balance of forces, graded streams, and hydraulic geometry are all examples of this perspective. The continuum view has played a prominent role in diverse disciplinary fields, including ecology, paleontology, and evolutionary biology, in large part because it allows us to treat complex phenomena as orderly progressions and invoke or assume equilibrium processes that introduce order and prediction into our sciences.In contrast the discontinuous view is a distinct though complementary conceptual framework that incorporates non-uniform, non-progressive, and non-equilibrium thinking into understanding geomorphic processes and landscapes. We distinguish and discuss examples of three different ways in which discontinuous thinking can be expressed: 1) discontinuous spatial arrangements or singular events; 2) specific process domains generally associated with thresholds, either intrinsic or extrinsic; and 3) physical dynamics or changes in state, again often threshold-linked. In moving beyond the continuous perspective, a fertile set of ideas comes into focus: thresholds, non-equilibrium states, heterogeneity, catastrophe. The range of phenomena that is thereby opened up to scientific exploration similarly expands

  3. Shallow subsurface applications of high-resolution seismic reflection

    NASA Astrophysics Data System (ADS)

    Steeples, Don

    2002-11-01

    Shallow seismic reflection surveys have been applied to a wide variety of problems. For example, in many geologic settings, variations and discontinuities on the surface of bedrock can influence the transport and eventual fate of contaminants introduced at or near the ground surface. Using seismic methods to determine the nature and location of anomalous bedrock can be an essential component of hydrologic characterization. Shallow seismic surveys can also be used to detect earthquake faults and to image underground voids. During the early 1980s, the advent of digital engineering seismographs designed for shallow, high-resolution surveying spurred significant improvements in engineering and environmental reflection seismology. Commonly, shallow seismic reflection methods are used in conjunction with other geophysical and geological methods, supported by a well-planned drilling-verification effort. To the extent that seismic reflection, refraction, and surface-wave methods can constrain shallow stratigraphy, geologic structure, engineering properties, and relative permeability, these methods are useful in civil-engineering applications and in characterizing environmental sites. Case histories from Kansas, California, and Texas illustrate how seismic reflection can be used to map bedrock beneath alluvium at hazardous waste sites, detect abandoned coal mines, follow the top of the saturated zone during an alluvial aquifer pumping test, and map shallow faults that serve as contaminant flowpaths.

  4. Numerical modelling of post-seismic rupture propagation after the Sumatra 26.12.2004 earthquake constrained by GRACE gravity data

    NASA Astrophysics Data System (ADS)

    Mikhailov, V.; Lyakhovsky, V.; Panet, I.; van Dinther, Y.; Diament, M.; Gerya, T.; deViron, O.; Timoshkina, E.

    2013-08-01

    In the last decades, the development of the surface and satellite geodetic and geophysical observations brought a new insights into the seismic cycle, documenting new features of inter-, co-, and post-seismic processes. In particular since 2002 satellite mission GRACE provides monthly models of the global gravity field with unprecedented accuracy showing temporal variations of the Earth's gravity field, including those caused by mass redistribution associated with earthquake processes. When combined with GPS measurements, these new data have allowed to assess the relative importance of afterslip and viscoelastic relaxation after the Sumatra 26.12.2004 earthquake. Indeed the observed post-seismic crustal displacements were fitted well by a viscoelastic relaxation model assuming Burgers body rheology for the asthenosphere (60-220 km deep) with a transient viscosity as low as 4 × 1017 Pas and constant ˜1019 Pas steady state viscosity in the 60-660-km depth range. However, even the low-viscosity asthenosphere provides the amplitude of strain which gravity effect does not exceed 50 per cent of the GRACE gravity variations, thus additional localized slip of about 1 m was suggested at downdip extension of the coseismic rupture. Post-seismic slip at coseismic rupture or its downdip extension has been suggested by several authors but the mechanism of the post-seismic fault propagation has never been investigated numerically. Depth and size of localized slip area as well as rate and time decay during the post-seismic stage were either assigned a priory or estimated by fitting real geodesy or gravity data. In this paper we investigate post-seismic rupture propagation by modelling two consequent stages. First, we run a long-term, geodynamic simulation to self-consistently produce the initial stress and temperature distribution. At the second stage, we simulate a seismic cycle using results of the first step as initial conditions. The second short-term simulation involves

  5. Seismic Migration Imaging of the Lithosphere beneath the Afar Rift System, East Africa

    NASA Astrophysics Data System (ADS)

    Lee, T. T. Y.; Chen, C. W.; Rychert, C.; Harmon, N.

    2015-12-01

    The Afar Rift system in east Africa is an ideal natural laboratory for investigating the incipient continental rifting, an essential component of plate tectonics. The Afar Rift is situated at the triple junction of three rifts, namely the southern Red Sea Rift, Gulf of Aden Rift and Main Ethiopian Rift (MER). The ongoing continental rifting at Afar transitions to seafloor spreading toward the southern Red Sea. The tectonic evolution of Afar is thought to be influenced by a mantle plume, but how the plume affects and interacts with the Afar lithosphere remains elusive. In this study, we use array seismic data to produce high-resolution migration images of the Afar lithosphere from scattered teleseismic wavefields to shed light on the lithospheric structure and associated tectonic processes. Our preliminary results indicate the presence of lithospheric seismic discontinuities with depth variation across the Afar region. Beneath the MER axis, we detect a pronounced discontinuity at 55 km depth, characterized by downward fast-to-slow velocity contrast, which appears to abruptly deepen to 75 km depth to the northern flank of MER. This discontinuity may be interpreted as the lithosphere-asthenosphere boundary. Beneath the Ethiopian Plateau, on the other hand, a dipping structure with velocity increase is identified at 70-90 km depth. Further synthesis of observations from seismic tomography, receiver functions, and seismic anisotropy in the Afar region will offer better understanding of tectonic significance of the lithospheric discontinuities.

  6. New Madrid Seismic Zone

    DTIC Science & Technology

    2007-11-02

    NEW MADRID SEISMIC ZONE BY COLONEL J.DAVID NORWOOD United States Army DISTRIBUTION STATEMENT A...mCTBB l USAWC STRATEGY RESEARCH PROJECT New Madrid Seismic Zone by J. David Norwood, COL, USA Michael A. Pearson, COL, USA Project Advisor The...ABSTRACT AUTHOR: J. David Norwood, Colonel, U.S. Army TITLE: New Madrid Seismic Zone FORMAT: Strategy Research Project DATE: 22 April 1998 . PAGES:

  7. Seismic Waveguide of Metamaterials

    NASA Astrophysics Data System (ADS)

    Kim, Sang-Hoon; Das, Mukunda P.

    We developed a new method of an earthquake-resistant design to support conventional aseismic system using acoustic metamaterials. The device is an attenuator of a seismic wave that reduces the amplitude of the wave exponentially. Constructing a cylindrical shell-type waveguide composed of many Helmholtz resonators that creates a stop-band for the seismic frequency range, we convert the seismic wave into an attenuated one without touching the building that we want to protect. It is a mechanical way to convert the seismic energy into sound and heat.

  8. Seismic Imaging and Monitoring

    SciTech Connect

    Huang, Lianjie

    2012-07-09

    I give an overview of LANL's capability in seismic imaging and monitoring. I present some seismic imaging and monitoring results, including imaging of complex structures, subsalt imaging of Gulf of Mexico, fault/fracture zone imaging for geothermal exploration at the Jemez pueblo, time-lapse imaging of a walkway vertical seismic profiling data for monitoring CO{sub 2} inject at SACROC, and microseismic event locations for monitoring CO{sub 2} injection at Aneth. These examples demonstrate LANL's high-resolution and high-fidelity seismic imaging and monitoring capabilities.

  9. Gran Canaria temporary broadband seismic network: an study of the seismicity and Earth structure

    NASA Astrophysics Data System (ADS)

    Almendros, Javier; de Lis Mancilla, Flor; Martinez-Arevalo, Carmen; Carmona, Enrique; Sanchez, Nieves; Heit, Benjamin; Garcia, Alicia; Martin-Leon, Rosa; Buontempo, Luisa; Yuan, Xiahoui

    2010-05-01

    The present project is a joint effort between different institutions to deploy a dense seismic network at Gran Canaria island (Canary Islands, Spain). The interstation distance is around 20 km. The broadband seismic network is composed of one permanent (Guralp CMG-3T 120 s) and five temporary stations (Guralp CMG-3ESP 60 s). The permanent station is a 120 s Guralp CMG-3T and belongs to the Canary Island Seismic Network, run by the Instituto Geográfico Nacional (IGN) of Spain. The temporary stations are 60 s Guralp CMG-3ESP, provided by the GFZ seismic pool. The deployment was carried out in December 2009. The stations will be recording during two years. The improvement of the seismic network allow us to tackle the following issues: the detection and analysis of any local seismicity of tectonic and/or volcanic origin at Gran Canaria island; to contribute to the understanding of the regional seismicity with special interest in the oceanic channel between Tenerife and Gran Canaria Island in collaboration with a project running a dense temporary seismic network in Tenerife; to study the crustal and upper mantle structure, under Gran Canaria to constrain the crustal structure, the source of the volcanism, and better sample the mantle discontinuities and anisotropy. To study the Earth structure, we use receiver function analysis, ambient seismic noise and SKS anisotropy techniques, This project is part of a long-term research of the crustal and the mantle structure of the Canary Islands, which has started with Gran Canaria and Tenerife Islands and will eventually continue with the rest of the archipelago. The origin of the Canary Islands is generally attributed to a broad mantle upwelling under a slow moving plate, resulting in spatially and temporally distributed volcanic activity and a large number of seamounts and islands. A controversial discussion has been going on about the factors that control the evolution of the volcanic edifices, the type of the melting

  10. 3-D seismic tomographic modelling of the crustal structure of northwestern Svalbard based on deep seismic soundings

    NASA Astrophysics Data System (ADS)

    Czuba, Wojciech

    2016-11-01

    Wide angle refraction and reflection measurements were carried out in the passive continental margin zone of the northwestern Svalbard during several expeditions in 1978-1999. Data from a set of 2-D archival and modern seismic profiles recorded in-line and off-line, and from an additional permanent seismic station, were altogether used for seismic modelling of the crustal structure of the study area. Seismic arrivals (airgun and chemical explosive sources) were recorded by land (onshore) seismic stations, ocean bottom seismometers (OBS), and ocean bottom hydrophone stations (OBH). Good quality refracted and reflected P waves have provided an excellent data base for a seismic modelling. Chemical explosive sources were recorded even up to 300 km distances. The 3-D tomographic inversion method was applied. The results are comparable to the earlier 2-D modelling. Additional off-line information allowed to develop a 3-D image of the crustal structure. The continental crust thins to the west and north. A minimum depth of about 6 km to the Moho interface was determined east of the Molloy Deep and in the Knipovich Ridge. The Moho discontinuity deepens down to about 30 km below the continental crust of Spitsbergen.

  11. 3-D seismic tomographic modelling of the crustal structure of northwestern Svalbard based on deep seismic soundings

    NASA Astrophysics Data System (ADS)

    Czuba, Wojciech

    2017-01-01

    Wide angle refraction and reflection measurements were carried out in the passive continental margin zone of the northwestern Svalbard during several expeditions in 1978-1999. Data from a set of 2-D archival and modern seismic profiles recorded in-line and off-line, and from an additional permanent seismic station, were altogether used for seismic modelling of the crustal structure of the study area. Seismic arrivals (airgun and chemical explosive sources) were recorded by land (onshore) seismic stations, ocean bottom seismometers (OBS), and ocean bottom hydrophone stations (OBH). Good quality refracted and reflected P waves have provided an excellent data base for a seismic modelling. Chemical explosive sources were recorded even up to 300 km distances. The 3-D tomographic inversion method was applied. The results are comparable to the earlier 2-D modelling. Additional off-line information allowed to develop a 3-D image of the crustal structure. The continental crust thins to the west and north. A minimum depth of about 6 km to the Moho interface was determined east of the Molloy Deep and in the Knipovich Ridge. The Moho discontinuity deepens down to about 30 km below the continental crust of Spitsbergen.

  12. Elastic wave propagation in variable media using a discontinuous Galerkin method.

    SciTech Connect

    Ober, Curtis Curry; Smith, Thomas Michael; Collis, Samuel Scott; Overfelt, James Robert; Schwaiger, Hans

    2010-04-01

    Motivated by the needs of seismic inversion and building on our prior experience for fluid-dynamics systems, we present a high-order discontinuous Galerkin (DG) Runge-Kutta method applied to isotropic, linearized elasto-dynamics. Unlike other DG methods recently presented in the literature, our method allows for inhomogeneous material variations within each element that enables representation of realistic earth models - a feature critical for future use in seismic inversion. Likewise, our method supports curved elements and hybrid meshes that include both simplicial and nonsimplicial elements. We demonstrate the capabilities of this method through a series of numerical experiments including hybrid mesh discretizations of the Marmousi2 model as well as a modified Marmousi2 model with a oscillatory ocean bottom that is exactly captured by our discretization. A discontinuous Galerkin method for solving the equations of linear isotropic elasticity has been presented. The formulation is designed to accommodate variation of media parameters within elements, curved elements and unstructured heterogeneous meshes. We have demonstrated that each of these important features of the formulation can produce results that are significantly different from formulations that do not possess these capabilities suggesting that each of these capabilities may be important for effective full waveform inversion of elastic medium.

  13. Swept Impact Seismic Technique (SIST)

    USGS Publications Warehouse

    Park, C.B.; Miller, R.D.; Steeples, D.W.; Black, R.A.

    1996-01-01

    A coded seismic technique is developed that can result in a higher signal-to-noise ratio than a conventional single-pulse method does. The technique is cost-effective and time-efficient and therefore well suited for shallow-reflection surveys where high resolution and cost-effectiveness are critical. A low-power impact source transmits a few to several hundred high-frequency broad-band seismic pulses during several seconds of recording time according to a deterministic coding scheme. The coding scheme consists of a time-encoded impact sequence in which the rate of impact (cycles/s) changes linearly with time providing a broad range of impact rates. Impact times used during the decoding process are recorded on one channel of the seismograph. The coding concept combines the vibroseis swept-frequency and the Mini-Sosie random impact concepts. The swept-frequency concept greatly improves the suppression of correlation noise with much fewer impacts than normally used in the Mini-Sosie technique. The impact concept makes the technique simple and efficient in generating high-resolution seismic data especially in the presence of noise. The transfer function of the impact sequence simulates a low-cut filter with the cutoff frequency the same as the lowest impact rate. This property can be used to attenuate low-frequency ground-roll noise without using an analog low-cut filter or a spatial source (or receiver) array as is necessary with a conventional single-pulse method. Because of the discontinuous coding scheme, the decoding process is accomplished by a "shift-and-stacking" method that is much simpler and quicker than cross-correlation. The simplicity of the coding allows the mechanical design of the source to remain simple. Several different types of mechanical systems could be adapted to generate a linear impact sweep. In addition, the simplicity of the coding also allows the technique to be used with conventional acquisition systems, with only minor modifications.

  14. Deep earthquakes beneath the Fiji Basin, SW Pacific: Earth's most intense deep seismicity in stagnant slabs

    USGS Publications Warehouse

    Okal, E.A.; Kirby, S.H.

    1998-01-01

    Previous work has suggested that many of the deep earthquakes beneath the Fiji Basin occur in slab material that has been detached and foundered to the bottom of the transition zone or has been laid down by trench migration in a similar recumbent position. Since nowhere else in the Earth do so many earthquakes occur in slabs stagnated in the transition zone, these earthquakes merit closer study. Accordingly, we have assembled from historical and modern data a comprehensive catalogue of the relocated hypocenters and focal mechanisms of well-located deep events in the geographic area between the bottoms of the main Vanuatu and Tonga Wadati-Benioff zones. Two regions of deep seismogenesis are recognized there: (i) 163 deep shocks have occurred north of 15??S in the Vityaz Group from 1949 to 1996. These seismological observations and the absence of other features characteristic of active subduction suggest that the Vityaz group represents deep failure in a detached slab that has foundered to a horizontal orientation near the bottom of the transition zone. (ii) Another group of nearly 50 'outboard' deep shocks occur between about 450 and 660 km depth, west of the complexly buckled and offset western edge of the Tonga Wadati-Benioff zone. Their geometry is in the form of two or possibly three small-circle arcs that roughly parallel the inferred motion of Tonga trench migration. Earthquakes in the southernmost of these arcs occur in a recumbent high-seismic-wavespeed slab anomaly that connects both to the main inclined Tonga anomaly to the east and a lower mantle anomaly to the west [Van der Hilst, R., 1995. Complex morphology of subducted lithosphere in the mantle beneath the Tonga trench. Nature, Vol. 374, pp. 154-157.]. Both groups show complexity in their focal mechanisms. The major question raised by these observations is the cause of this apparent temporary arrest in the descent of the Tonga slab into the lower mantle. We approach these questions by considering the

  15. Detecting and Monitoring for Induced Seismicity without a Local Seismic Network: Application to the Youngstown, Ohio Induced Seismic Sequence

    NASA Astrophysics Data System (ADS)

    Holtkamp, S. G.; Brudzinski, M. R.; Currie, B. S.

    2013-12-01

    and absolute relocation of earthquake hypocenters shows the first events occurring close to the injection well and propagating WSW (consistent with the focal mechanism of the largest earthquake in the sequence) at a rate of 1-2 km/y. Individual families of events show delay times of 1-6 days between injection volume fluctuations and seismicity rate variations, proportional to distance from the well, which we interpret to represent diffusivity in the now saturated fault zone. A change in apparent diffusivity after arrival of the triggering front suggests development of more fully integrated fault zone permeability though time. We envision that injection-related pore-fluid pressure increased in discontinuous permeable zones of the fault system, reduced effective normal stress and permitted fault slip to occur. Early displacement could promote fluid infiltration into adjacent, initially inaccessible regions of the fault, iteratively increasing the area of potential failure, consistent with the observation that the largest events (M>2) were uncommon until late in the sequence. Our study shows that it is possible to quickly and inexpensively assess potential cases of induced seismicity with only a regional backbone network, such as the 1-in-4 preservation of the EarthScope Transportable Array that has been proposed in the Eastern US.

  16. Seismic Catalogue and Seismic Network in Haiti

    NASA Astrophysics Data System (ADS)

    Belizaire, D.; Benito, B.; Carreño, E.; Meneses, C.; Huerfano, V.; Polanco, E.; McCormack, D.

    2013-05-01

    The destructive earthquake occurred on January 10, 2010 in Haiti, highlighted the lack of preparedness of the country to address seismic phenomena. At the moment of the earthquake, there was no seismic network operating in the country, and only a partial control of the past seismicity was possible, due to the absence of a national catalogue. After the 2010 earthquake, some advances began towards the installation of a national network and the elaboration of a seismic catalogue providing the necessary input for seismic Hazard Studies. This paper presents the state of the works carried out covering both aspects. First, a seismic catalogue has been built, compiling data of historical and instrumental events occurred in the Hispaniola Island and surroundings, in the frame of the SISMO-HAITI project, supported by the Technical University of Madrid (UPM) and Developed in cooperation with the Observatoire National de l'Environnement et de la Vulnérabilité of Haiti (ONEV). Data from different agencies all over the world were gathered, being relevant the role of the Dominican Republic and Puerto Rico seismological services which provides local data of their national networks. Almost 30000 events recorded in the area from 1551 till 2011 were compiled in a first catalogue, among them 7700 events with Mw ranges between 4.0 and 8.3. Since different magnitude scale were given by the different agencies (Ms, mb, MD, ML), this first catalogue was affected by important heterogeneity in the size parameter. Then it was homogenized to moment magnitude Mw using the empirical equations developed by Bonzoni et al (2011) for the eastern Caribbean. At present, this is the most exhaustive catalogue of the country, although it is difficult to assess its degree of completeness. Regarding the seismic network, 3 stations were installed just after the 2010 earthquake by the Canadian Government. The data were sent by telemetry thought the Canadian System CARINA. In 2012, the Spanish IGN together

  17. 27 CFR 25.277 - Discontinuance of operations.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... BUREAU, DEPARTMENT OF THE TREASURY LIQUORS BEER Pilot Brewing Plants § 25.277 Discontinuance of operations. When operations of a pilot brewing plant are to be discontinued, the operator shall notify...

  18. 27 CFR 25.277 - Discontinuance of operations.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... BUREAU, DEPARTMENT OF THE TREASURY LIQUORS BEER Pilot Brewing Plants § 25.277 Discontinuance of operations. When operations of a pilot brewing plant are to be discontinued, the operator shall notify...

  19. Seismic response of rock slopes: Numerical investigations on the role of internal structure

    NASA Astrophysics Data System (ADS)

    Arnold, L.; Applegate, K.; Gibson, M.; Wartman, J.; Adams, S.; Maclaughlin, M.; Smith, S.; Keefer, D. K.

    2013-12-01

    The stability of rock slopes is significantly influenced and often controlled by the internal structure of the slope created by such discontinuities as joints, shear zones, and faults. Under seismic conditions, these discontinuities influence both the resistance of a slope to failure and its response to dynamic loading. The dynamic response, which can be characterized by the slope's natural frequency and amplification of ground motion, governs the loading experienced by the slope in a seismic event and, therefore, influences the slope's stability. In support of the Network for Earthquake Engineering Simulation (NEES) project Seismically-Induced Rock Slope Failure: Mechanisms and Prediction (NEESROCK), we conducted a 2D numerical investigation using the discrete element method (DEM) coupled with simple discrete fracture networks (DFNs). The intact rock mass is simulated with a bonded assembly of discrete particles, commonly referred to as the bonded-particle model (BPM) for rock. Discontinuities in the BPM are formed by the insertion of smooth, unbonded contacts along specified planes. The influence of discontinuity spacing, orientation, and stiffness on slope natural frequency and amplification was investigated with the commercially available Particle Flow Code (PFC2D). Numerical results indicate that increased discontinuity spacing has a non-linear effect in decreasing the amplification and increasing the natural frequency of the slope. As discontinuity dip changes from sub-horizontal to sub-vertical, the slope's level of amplification increases while the natural frequency of the slope decreases. Increased joint stiffness decreases amplification and increases natural frequency. The results reveal that internal structure has a strong influence on rock slope dynamics that can significantly change the system's dynamic response and stability during seismic loading. Financial support for this research was provided by the United States National Science Foundation (NSF

  20. Archetypal oscillator for smooth and discontinuous dynamics.

    PubMed

    Cao, Qingjie; Wiercigroch, Marian; Pavlovskaia, Ekaterina E; Grebogi, Celso; Thompson, J Michael T

    2006-10-01

    We propose an archetypal system to investigate transitions from smooth to discontinuous dynamics. In the smooth regime, the system bears significant similarities to the Duffing oscillator, exhibiting the standard dynamics governed by the hyperbolic structure associated with the stationary state of the double well. At the discontinuous limit, however, there is a substantial departure in the dynamics from the standard one. In particular, the velocity flow suffers a jump in crossing from one well to another, caused by the loss of local hyperbolicity due to the collapse of the stable and unstable manifolds of the stationary state. In the presence of damping and external excitation, the system has coexisting attractors and also a chaotic saddle which becomes a chaotic attractor when a smoothness parameter drops to zero. This attractor can bifurcate to a high-period periodic attractor or a chaotic sea with islands of quasiperiodic attractors depending on the strength of damping.

  1. Bounded extremum seeking with discontinuous dithers

    SciTech Connect

    Scheinker, Alexander; Scheinker, David

    2016-03-21

    The analysis of discontinuous extremum seeking (ES) controllers, e.g. those applicable to digital systems, has historically been more complicated than that of continuous controllers. We establish a simple and general extension of a recently developed bounded form of ES to a general class of oscillatory functions, including functions discontinuous with respect to time, such as triangle or square waves with dead time. We establish our main results by combining a novel idea for oscillatory control with an extension of functional analytic techniques originally utilized by Kurzweil, Jarnik, Sussmann, and Liu in the late 80s and early 90s and recently studied by Durr et al. Lastly, we demonstrate the value of the result with an application to inverter switching control.

  2. Constant-force approach to discontinuous potentials.

    PubMed

    Orea, Pedro; Odriozola, Gerardo

    2013-06-07

    Aiming to approach the thermodynamical properties of hard-core systems by standard molecular dynamics simulation, we propose setting a repulsive constant-force for overlapping particles. That is, the discontinuity of the pair potential is replaced by a linear function with a large negative slope. Hence, the core-core repulsion, usually modeled with a power function of distance, yields a large force as soon as the cores slightly overlap. This leads to a quasi-hardcore behavior. The idea is tested for a triangle potential of short range. The results obtained by replica exchange molecular dynamics for several repulsive forces are contrasted with the ones obtained for the discontinuous potential and by means of replica exchange Monte Carlo. We found remarkable agreements for the vapor-liquid coexistence densities as well as for the surface tension.

  3. Parallel Implementation of the Discontinuous Galerkin Method

    NASA Technical Reports Server (NTRS)

    Baggag, Abdalkader; Atkins, Harold; Keyes, David

    1999-01-01

    This paper describes a parallel implementation of the discontinuous Galerkin method. Discontinuous Galerkin is a spatially compact method that retains its accuracy and robustness on non-smooth unstructured grids and is well suited for time dependent simulations. Several parallelization approaches are studied and evaluated. The most natural and symmetric of the approaches has been implemented in all object-oriented code used to simulate aeroacoustic scattering. The parallel implementation is MPI-based and has been tested on various parallel platforms such as the SGI Origin, IBM SP2, and clusters of SGI and Sun workstations. The scalability results presented for the SGI Origin show slightly superlinear speedup on a fixed-size problem due to cache effects.

  4. An adaptive pseudospectral method for discontinuous problems

    NASA Technical Reports Server (NTRS)

    Augenbaum, Jeffrey M.

    1988-01-01

    The accuracy of adaptively chosen, mapped polynomial approximations is studied for functions with steep gradients or discontinuities. It is shown that, for steep gradient functions, one can obtain spectral accuracy in the original coordinate system by using polynomial approximations in a transformed coordinate system with substantially fewer collocation points than are necessary using polynomial expansion directly in the original, physical, coordinate system. It is also shown that one can avoid the usual Gibbs oscillation associated with steep gradient solutions of hyperbolic pde's by approximation in suitably chosen coordinate systems. Continuous, high gradient solutions are computed with spectral accuracy (as measured in the physical coordinate system). Discontinuous solutions associated with nonlinear hyperbolic equations can be accurately computed by using an artificial viscosity chosen to smooth out the solution in the mapped, computational domain. Thus, shocks can be effectively resolved on a scale that is subgrid to the resolution available with collocation only in the physical domain. Examples with Fourier and Chebyshev collocation are given.

  5. Bounded extremum seeking with discontinuous dithers

    DOE PAGES

    Scheinker, Alexander; Scheinker, David

    2016-03-21

    The analysis of discontinuous extremum seeking (ES) controllers, e.g. those applicable to digital systems, has historically been more complicated than that of continuous controllers. We establish a simple and general extension of a recently developed bounded form of ES to a general class of oscillatory functions, including functions discontinuous with respect to time, such as triangle or square waves with dead time. We establish our main results by combining a novel idea for oscillatory control with an extension of functional analytic techniques originally utilized by Kurzweil, Jarnik, Sussmann, and Liu in the late 80s and early 90s and recently studiedmore » by Durr et al. Lastly, we demonstrate the value of the result with an application to inverter switching control.« less

  6. Adaptive Discontinuous Galerkin Methods in Multiwavelets Bases

    SciTech Connect

    Archibald, Richard K; Fann, George I; Shelton Jr, William Allison

    2011-01-01

    We use a multiwavelet basis with the Discontinuous Galerkin (DG) method to produce a multi-scale DG method. We apply this Multiwavelet DG method to convection and convection-diffusion problems in multiple dimensions. Merging the DG method with multiwavelets allows the adaptivity in the DG method to be resolved through manipulation of multiwavelet coefficients rather than grid manipulation. Additionally, the Multiwavelet DG method is tested on non-linear equations in one dimension and on the cubed sphere.

  7. North American lithospheric discontinuity structure imaged by Ps and Sp receiver functions

    NASA Astrophysics Data System (ADS)

    Abt, David L.; Fischer, Karen M.; French, Scott W.; Ford, Heather A.; Yuan, Huaiyu; Romanowicz, Barbara

    2010-09-01

    Sp and Ps converted seismic waves at 93 permanent seismic stations are used to image upper mantle velocity discontinuities across the contiguous United States and portions of southeast Canada and northwest Mexico. Receiver functions are calculated with frequency-domain deconvolution and migrated with 1D models that account for variations in crustal structure and mantle velocities between stations. Strong positive Ps phases from the Moho are observed and agree well with previous crustal thickness estimates. In the tectonically active western U.S., high amplitude, negative Sp phases are interpreted as the lithosphere-asthenosphere boundary (LAB) at depths of 51-104 km. These phases indicate a large and rapid LAB velocity gradient and are consistent with an anomalously hot asthenosphere that is rich in water or contains partial melt. In the regions of the Phanerozoic southern and eastern U.S where Sp phases are interpretable as the LAB, the discontinuity lies at depths of 75-111 km and is also too sharp to be explained by temperature alone. In contrast, no Sp phases are observed at depths comparable to the base of the thick high velocity lithosphere that lies beneath cratonic North America and certain portions of the Phanerozoic eastern U.S. At these stations, negative Sp phases occur at depths of 59-113 km and are interpreted as the top of a low velocity zone internal to the lithosphere. The absence of an observable LAB discontinuity in regions of thick lithosphere indicates that the LAB velocity gradient is distributed over more than 50-70 km in depth and is consistent with a purely thermal boundary.

  8. 4D seismic data acquisition method during coal mining

    NASA Astrophysics Data System (ADS)

    Du, Wen-Feng; Peng, Su-Ping

    2014-06-01

    In order to observe overburden media changes caused by mining processing, we take the fully-mechanized working face of the BLT coal mine in Shendong mine district as an example to develop a 4D seismic data acquisition methodology during coal mining. The 4D seismic data acquisition is implemented to collect 3D seismic data four times in different periods, such as before mining, during the mining process and after mining to observe the changes of the overburden layer during coal mining. The seismic data in the research area demonstrates that seismic waves are stronger in energy, higher in frequency and have better continuous reflectors before coal mining. However, all this is reversed after coal mining because the overburden layer has been mined, the seismic energy and frequency decrease, and reflections have more discontinuities. Comparing the records collected in the survey with those from newly mined areas and other records acquired in the same survey with the same geometry and with a long time for settling after mining, it clearly shows that the seismic reflections have stronger amplitudes and are more continuous because the media have recovered by overburden layer compaction after a long time of settling after mining. By 4D seismic acquisition, the original background investigation of the coal layers can be derived from the first records, then the layer structure changes can be monitored through the records of mining action and compaction action after mining. This method has laid the foundation for further research into the variation principles of the overburden layer under modern coal-mining conditions.

  9. Field Discontinuities and the Memory Effect

    NASA Astrophysics Data System (ADS)

    Tolish, Alexander; Wald, Robert

    2017-01-01

    The ``memory effect,'' a permanent change in the separation of test particles after the passage of a pulse of gravitational radiation, is a well-defined and fairly well-understood phenomenon in spacetimes with a notion of null infinity. However, many valid questions remain unanswered. For example, how do we define memory in the absence of null infinity? Or, does memory depend on the precise details of the radiation source or just on the source's asymptotic behavior? We believe that such questions are best answered using a simplified, distributional model of memory. If we consider linearized gravity on fixed background spacetimes, we can study the scattering of point particles, which radiate metric perturbations with sharp, step-function wave fronts. These steps correspond to derivative-of-delta-function discontinuities in the curvature, and according to the geodesic deviation equation, it is these discontinuities (and these alone) that contribute to permanent, finite changes in test particle separation-i.e., memory. Using this analysis of field discontinuities (as well as scalar and electromagnetic analogues of gravitational memory) we can isolate the physics of the memory effect from other, background phenomena.

  10. Mohorovicic discontinuity depth analysis beneath North Patagonian Massif

    NASA Astrophysics Data System (ADS)

    Gómez Dacal, M. L.; Tocho, C.; Aragón, E.

    2013-05-01

    The North Patagonian Massif is a 100000 km2, sub-rectangular plateau that stands out 500 to 700 m higher in altitude than the surrounding topography. The creation of this plateau took place during the Oligocene through a sudden uplift without noticeable internal deformation. This quite different mechanical response between the massif and the surrounding back arc, the short time in which this process took place and a regional negative Bouguer anomaly in the massif area, raise the question about the isostatic compensation state of the previously mentioned massif. In the present work, a comparison between different results about the depth of the Mohorovicic discontinuity beneath the North Patagonian Massif and a later analysis is made. It has the objective to analyze the crustal thickness in the area to contribute in the determination of the isostatic balance and the better understanding of the Cenozoic evolution of the mentioned area. The comparison is made between four models; two of these were created with seismic information (Feng et al., 2006 and Bassin et al., 2000), another model with gravity information (Barzaghi et al., 2011) and the last one with a combination of both techniques (Tassara y Etchaurren, 2011). The latter was the result of the adaptation to the work area of a three-dimensional density model made with some additional information, mainly seismic, that constrain the surfaces. The work of restriction and adaptation of this model, the later analysis and comparison with the other three models and the combination of both seismic models to cover the lack of resolution in some areas, is presented here. According the different models, the crustal thickness of the study zone would be between 36 and 45 Km. and thicker than the surrounding areas. These results talk us about a crust thicker than normal and that could behave as a rigid and independent block. Moreover, it can be observed that there are noticeable differences between gravimetric and seismic

  11. 27 CFR 31.162 - Discontinuance of business.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Discontinuance of business... and Reports § 31.162 Discontinuance of business. When a wholesale dealer in liquors who is required, under § 31.160, to file a monthly summary report discontinues business, a monthly summary report...

  12. 27 CFR 22.68 - Notice of permanent discontinuance.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Notice of permanent discontinuance. 22.68 Section 22.68 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE... Permanent Discontinuance of Use of Tax-Free Alcohol § 22.68 Notice of permanent discontinuance. A...

  13. 14 CFR 221.300 - Discontinuation of electronic tariff system.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false Discontinuation of electronic tariff system... of electronic tariff system. In the event that the electronic tariff system is discontinued, or the source of the data is changed, or a filer discontinues its business, all electronic data records prior...

  14. Program Discontinuance: A Faculty Perspective Revisited. Adopted Fall 2012

    ERIC Educational Resources Information Center

    Academic Senate for California Community Colleges, 2012

    2012-01-01

    The 1998 Academic Senate for California Community Colleges paper Program Discontinuance: A Faculty Perspective presented issues of program discontinuance and addressed principles and key factors for effective faculty participation in the development of fair and equitable program discontinuance processes. In 2009, an Academic Senate resolution…

  15. 27 CFR 46.138 - Discontinuance of business.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 2 2012-04-01 2011-04-01 true Discontinuance of business. 46.138 Section 46.138 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU....138 Discontinuance of business. A dealer who for any reason discontinues business is not entitled to...

  16. 27 CFR 46.138 - Discontinuance of business.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 2 2014-04-01 2014-04-01 false Discontinuance of business. 46.138 Section 46.138 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU....138 Discontinuance of business. A dealer who for any reason discontinues business is not entitled to...

  17. 27 CFR 31.162 - Discontinuance of business.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2012-04-01 2012-04-01 false Discontinuance of business... and Reports § 31.162 Discontinuance of business. When a wholesale dealer in liquors who is required, under § 31.160, to file a monthly summary report discontinues business, a monthly summary report...

  18. 20 CFR 658.503 - Discontinuation of services.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false Discontinuation of services. 658.503 Section... PROVISIONS GOVERNING THE JOB SERVICE SYSTEM Discontinuation of Services to Employers by the Job Service System § 658.503 Discontinuation of services. (a) If the employer does not provide a...

  19. SOAR Telescope seismic performance II: seismic mitigation

    NASA Astrophysics Data System (ADS)

    Elias, Jonathan H.; Muñoz, Freddy; Warner, Michael; Rivera, Rossano; Martínez, Manuel

    2016-07-01

    We describe design modifications to the SOAR telescope intended to reduce the impact of future major earthquakes, based on the facility's experience during recent events, most notably the September 2015 Illapel earthquake. Specific modifications include a redesign of the encoder systems for both azimuth and elevation, seismic trigger for the emergency stop system, and additional protections for the telescope secondary mirror system. The secondary mirror protection may combine measures to reduce amplification of seismic vibration and "fail-safe" components within the assembly. The status of these upgrades is presented.

  20. Shallow Moho with aseismic upper crust and deep Moho with seismic lower crust beneath the Japanese Islands obtained by seismic tomography using data from dense seismic network

    NASA Astrophysics Data System (ADS)

    Matsubara, Makoto; Obara, Kazushige

    2015-04-01

    P-wave seismic velocity is well known to be up to 7.0 km/s and over 7.5 km/s in the lower crust and in the mantle, respectively. A large velocity gradient is the definition of the Moho discontinuity between the crust and mantle. In this paper, we investigates the configuration of Moho discontinuity defined as an isovelocity plane with large velocity gradient derived from our fine-scale three-dimensional seismic velocity structure beneath Japanese Islands using data obtained by dense seismic network with the tomographic method (Matsubara and Obara, 2011). Japanese Islands are mainly on the Eurasian and North American plates. The Philippine Sea and Pacific plates are subducting beneath these continental plates. We focus on the Moho discontinuity at the continental side. We calculate the P-wave velocity gradients between the vertical grid nodes since the grid inversion as our tomographic method does not produce velocity discontinuity. The largest velocity gradient is 0.078 (km/s)/km at velocities of 7.2 and 7.3 km/s. We define the iso-velocity plane of 7.2 km/s as the Moho discontinuity. We discuss the Moho discontinuity above the upper boundary of the subducting oceanic plates with consideration of configuration of plate boundaries of prior studies (Shiomi et al., 2008; Kita et al., 2010; Hirata et al, 2012) since the Moho depth derived from the iso-velocity plane denotes the oceanic Moho at the contact zones of the overriding continental plates and the subducting oceanic plates. The Moho discontinuity shallower than 30 km depth is distributed within the tension region like northern Kyushu and coastal line of the Pacific Ocean in the northeastern Japan and the tension region at the Cretaceous as the northeastern Kanto district. These regions have low seismicity within the upper crust. Positive Bouguer anomaly beneath the northeastern Kanto district indicates the ductile material with large density in lower crust at the shallower portion and the aseismic upper crust

  1. Origins of cratonic mantle discontinuities: A view from petrology, geochemistry and thermodynamic models

    NASA Astrophysics Data System (ADS)

    Aulbach, Sonja; Massuyeau, Malcolm; Gaillard, Fabrice

    2017-01-01

    Geophysically detectible mid-lithospheric discontinuities (MLD) and lithosphere-asthenosphere boundaries (LAB) beneath cratons have received much attention over recent years, but a consensus on their origin has not yet emerged. Cratonic lithosphere composition and origin is peculiar due to its ultra-depletion during plume or accretionary tectonics, cool present-day geothermal gradients, compositional and rheological stratification and multiple metasomatic overprints. Bearing this in mind, we integrate current knowledge on the physical properties, chemical composition, mineralogy and fabric of cratonic mantle with experimental and thermodynamic constraints on the formation and migration of melts, both below and within cratonic lithosphere, in order to find petrologically viable explanations for cratonic mantle discontinuities. LABs characterised by strong seismic velocity gradients and increased conductivity require the presence of melts, which can form beneath intact cratonic roots reaching to 200-250 km depth only in exceptionally warm and/or volatile-rich mantle, thus explaining the paucity of seismical LAB observations beneath cratons. When present, pervasive interaction of these - typically carbonated - melts with the deep lithosphere leads to densification and thermochemical erosion, which generates topography at the LAB and results in intermittent seismic LAB signals or conflicting seismic, petrologic and thermal LAB depths. In rare cases (e.g. Tanzanian craton), the tops of live melt percolation fronts may appear as MLDs and, after complete lithosphere rejuvenation, may be sites of future, shallower LABs (e.g. North China craton). Since intact cratons are presently tectonomagmatically quiescent, and since MLDs produce both positive and negative velocity gradients, in some cases with anisotropy, most MLDs may be best explained by accumulations (metasomes) of seismically slow minerals (pyroxenes, phlogopite, amphibole, carbonates) deposited during past

  2. Visualization, Extraction and Quantification of Discontinuities in Compressible Flows

    NASA Technical Reports Server (NTRS)

    Samtaney, Ravi; Morris, R. D.; Cheeseman, P.; Sunelyansky, V.; Maluf, D.; Wolf, D.

    2000-01-01

    Scientific visualizations of two-dimensional compressible flow of a gas with discontinuities are presented. The numerical analogue to experimental techniques such as schlieren imaging, shadowgraphs, and interferograms are discussed. Edge detection techniques are utilized to identify the discontinuities. In particular, the zero crossing of the Laplacian of a field (usually density) is recommended for extracting the discontinuities. An algorithm to extract and quantify the discontinuities is presented. To illustrate the methods developed in the report, the example chosen is that of an unsteady interaction of a shock wave with a contact discontinuity.

  3. Dynamic Rupture Modeling in Three Dimensions on Unstructured Meshes Using a Discontinuous Galerkin Method

    NASA Astrophysics Data System (ADS)

    Pelties, C.; Käser, M.

    2010-12-01

    We will present recent developments concerning the extensions of the ADER-DG method to solve three dimensional dynamic rupture problems on unstructured tetrahedral meshes. The simulation of earthquake rupture dynamics and seismic wave propagation using a discontinuous Galerkin (DG) method in 2D was recently presented by J. de la Puente et al. (2009). A considerable feature of this study regarding spontaneous rupture problems was the combination of the DG scheme and a time integration method using Arbitrarily high-order DERivatives (ADER) to provide high accuracy in space and time with the discretization on unstructured meshes. In the resulting discrete velocity-stress formulation of the elastic wave equations variables are naturally discontinuous at the interfaces between elements. The so-called Riemann problem can then be solved to obtain well defined values of the variables at the discontinuity itself. This is in particular valid for the fault at which a certain friction law has to be evaluated. Hence, the fault’s geometry is honored by the computational mesh. This way, complex fault planes can be modeled adequately with small elements while fast mesh coarsening is possible with increasing distance from the fault. Due to the strict locality of the scheme using only direct neighbor communication, excellent parallel behavior can be observed. A further advantage of the scheme is that it avoids spurious high-frequency contributions in the slip rate spectra and therefore does not require artificial Kelvin-Voigt damping or filtering of synthetic seismograms. In order to test the accuracy of the ADER-DG method the Southern California Earthquake Center (SCEC) benchmark for spontaneous rupture simulations was employed. Reference: J. de la Puente, J.-P. Ampuero, and M. Käser (2009), Dynamic rupture modeling on unstructured meshes using a discontinuous Galerkin method, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, B10302, doi:10.1029/2008JB006271

  4. Continuous-Discontinuous Model for Ductile Fracture

    SciTech Connect

    Seabra, Mariana R. R.; Cesar de Sa, Jose M. A.

    2010-06-15

    In this contribution, a continuum-dicontinuum model for ductile failure is presented. The degradation of material properties trough deformation is described by Continuum Damage Mechanics in a non-local integral formulation to avoid mesh dependence. In the final stage of failure, the damaged zone is replaced by a cohesive macro crack and subsequent traction-free macro crack for a more realistic representation of the phenomenon. The inclusion of the discontinuity surfaces is performed by the XFEM and Level Set Method and avoids the spurious damage growth typical of this class of models.

  5. Discontinuous Galerkin methods for extended hydrodynamics

    NASA Astrophysics Data System (ADS)

    Suzuki, Yoshifumi

    This dissertation presents a step towards high-order methods for continuum-transition flows. In order to achieve maximum accuracy and efficiency for numerical methods on a distorted mesh, it is desirable that both governing equations and corresponding numerical methods are in some sense compact. We argue our preference for a physical model described solely by first-order partial differential equations called hyperbolic-relaxation equations, and, among various numerical methods, for the discontinuous Galerkin method. Hyperbolic-relaxation equations can be generated as moments of the Boltzmann equation and can describe continuum-transition flows. Two challenging properties of hyperbolic-relaxation equations are the presence of a stiff source term, which drives the system towards equilibrium, and the accompanying change of eigenstructure. The first issue can be solved by an implicit treatment of the source term. To cope with the second difficulty, we develop a space-time discontinuous Galerkin method, based on Huynh's "upwind moment scheme." It is called the DG(1)--Hancock method. The DG(1)--Hancock method for one- and two-dimensional meshes is described, and Fourier analyses for both linear advection and linear hyperbolic-relaxation equations are conducted. The analyses show that the DG(1)--Hancock method is not only accurate but efficient in terms of turnaround time in comparison to other semi- and fully discrete finite-volume and discontinuous Galerkin methods. Numerical tests confirm the analyses, and also show the properties are preserved for nonlinear equations; the efficiency is superior by an order of magnitude. Subsequently, discontinuous Galerkin and finite-volume spatial discretizations are applied to more practical equations, in particular, to the set of 10-moment equations, which are gas dynamics equations that include a full pressure/temperature tensor among the flow variables. Results for flow around a micro-airfoil are compared to experimental data and

  6. General spline filters for discontinuous Galerkin solutions

    PubMed Central

    Peters, Jörg

    2015-01-01

    The discontinuous Galerkin (dG) method outputs a sequence of polynomial pieces. Post-processing the sequence by Smoothness-Increasing Accuracy-Conserving (SIAC) convolution not only increases the smoothness of the sequence but can also improve its accuracy and yield superconvergence. SIAC convolution is considered optimal if the SIAC kernels, in the form of a linear combination of B-splines of degree d, reproduce polynomials of degree 2d. This paper derives simple formulas for computing the optimal SIAC spline coefficients for the general case including non-uniform knots. PMID:26594090

  7. General spline filters for discontinuous Galerkin solutions.

    PubMed

    Peters, Jörg

    2015-09-01

    The discontinuous Galerkin (dG) method outputs a sequence of polynomial pieces. Post-processing the sequence by Smoothness-Increasing Accuracy-Conserving (SIAC) convolution not only increases the smoothness of the sequence but can also improve its accuracy and yield superconvergence. SIAC convolution is considered optimal if the SIAC kernels, in the form of a linear combination of B-splines of degree d, reproduce polynomials of degree 2d. This paper derives simple formulas for computing the optimal SIAC spline coefficients for the general case including non-uniform knots.

  8. Spacetime Discontinuous Galerkin FEM: Spectral Response

    NASA Astrophysics Data System (ADS)

    Abedi, R.; Omidi, O.; Clarke, P. L.

    2014-11-01

    Materials in nature demonstrate certain spectral shapes in terms of their material properties. Since successful experimental demonstrations in 2000, metamaterials have provided a means to engineer materials with desired spectral shapes for their material properties. Computational tools are employed in two different aspects for metamaterial modeling: 1. Mircoscale unit cell analysis to derive and possibly optimize material's spectral response; 2. macroscale to analyze their interaction with conventional material. We compare two different approaches of Time-Domain (TD) and Frequency Domain (FD) methods for metamaterial applications. Finally, we discuss advantages of the TD method of Spacetime Discontinuous Galerkin finite element method (FEM) for spectral analysis of metamaterials.

  9. Discontinuous Galerkin for Stiff Hyperbolic Systems

    SciTech Connect

    Lowrie, R.B.; Morel, J.E.

    1999-06-27

    A Discontinuous Galerkin (DG) method is applied to hyperbolic systems that contain stiff relaxation terms. We demonstrate that when the relaxation time is under-resolved, DG is accurate in the sense that the method accurately represents the system's Chapman-Enskog (or ''diffusion'') approximation. Moreover, we demonstrate that a high-resolution, finite-volume method using the same time-integration method as DG is very inaccurate in the diffusion limit. Results for DG are presented for the hyperbolic heat equation, the Broadwell model of gas kinetics, and coupled radiation-hydrodynamics.

  10. Method of migrating seismic records

    DOEpatents

    Ober, Curtis C.; Romero, Louis A.; Ghiglia, Dennis C.

    2000-01-01

    The present invention provides a method of migrating seismic records that retains the information in the seismic records and allows migration with significant reductions in computing cost. The present invention comprises phase encoding seismic records and combining the encoded seismic records before migration. Phase encoding can minimize the effect of unwanted cross terms while still allowing significant reductions in the cost to migrate a number of seismic records.

  11. Southern Africa seismic structure and source studies

    NASA Astrophysics Data System (ADS)

    Zhao, Ming

    1998-09-01

    The upper mantle seismic velocity structure beneath southern Africa is investigated using travel time and waveform data. Waveform and travel time data used in this study come mainly from a large mine tremor in South Africa (msb{b} 5.6) recorded on stations of the southern Africa and the Tanzania Broadband Seismic Experiment. Auxiliary data along similar profiles are obtained from other moderate events within eastern and southern Africa. The waveform data from the large tremor show upper mantle triplications for both the 400 and 670-km discontinuities between 18sp° and 27sp° distance. The most notable feature of the data is a large, late P phase that propagates to at least 27sp°. This phase is striking because of its late arrival time (as much as 15 seconds after direct P at 27sp°) and high amplitude relative to the first arrival. Travel times from all available stations are used to invert for the P wave velocity structure down to 800 km depth and S wave velocity structure down to 200 km using the Wiechert-Herglotz (W-H) inversion technique. The P wave velocities from the uppermost mantle down to 300 km are as much as 3% higher than the global average and are slightly slower than the global average between 300 and 400 km depths. The velocity gradient between 300 and 400 km is 0.0015 1/s. The S wave travel time data yield fast velocities above 200-km depth. The S wave velocity structure appears inconsistent with the P wave structure model indicating varying Poisson's ratio in the upper mantle. Little evidence is found for a pronounced upper mantle low velocity zone. Both sharp and gradual-change 400-km discontinuities are favored by the waveform data. The 670-km discontinuity appears as a gradual-change zone. The source mechanism of the mb 5.6 mining tremor itself is important for seismic discrimination and insight into mining tremor sources. Source parameters for this event as well as some other large mining tremors from the South African gold mines are studied

  12. Seismic attenuation in Florida

    SciTech Connect

    Bellini, J.J.; Bartolini, T.J.; Lord, K.M.; Smith, D.L. . Dept. of Geology)

    1993-03-01

    Seismic signals recorded by the expanded distribution of earthquake seismograph stations throughout Florida and data from a comprehensive review of record archives from stations GAI contribute to an initial seismic attenuation model for the Florida Plateau. Based on calculations of surface particle velocity, a pattern of attenuation exists that appears to deviate from that established for the remainder of the southeastern US. Most values suggest greater seismic attenuation within the Florida Plateau. However, a separate pattern may exist for those signals arising from the Gulf of Mexico. These results have important implications for seismic hazard assessments in Florida and may be indicative of the unique lithospheric identity of the Florida basement as an exotic terrane.

  13. The seismic design handbook

    SciTech Connect

    Naeim, F. )

    1989-01-01

    This book contains papers on the planning, analysis, and design of earthquake resistant building structures. Theories and concepts of earthquake resistant design and their implementation in seismic design practice are presented.

  14. BUILDING 341 Seismic Evaluation

    SciTech Connect

    Halle, J.

    2015-06-15

    The Seismic Evaluation of Building 341 located at Lawrence Livermore National Laboratory in Livermore, California has been completed. The subject building consists of a main building, Increment 1, and two smaller additions; Increments 2 and 3.

  15. Deepwater seismic acquisition technology

    SciTech Connect

    Caldwell, J.

    1996-09-01

    Although truly new technology is not required for successful acquisition of seismic data in deep Gulf of Mexico waters, it is helpful to review some basic aspects of these seismic surveys. Additionally, such surveys are likely to see early use of some emerging new technology which can improve data quality. Because such items as depth imaging, borehole seismic, 4-D and marine 3-component recording were mentioned in the May 1996 issue of World Oil, they are not discussed again here. However, these technologies will also play some role in the deepwater seismic activities. What is covered in this paper are some new considerations for: (1) longer data records needed in deeper water, (2) some pros and cons of very long steamer use, and (3) two new commercial systems for quantifying data quality.

  16. Subcell resolution in simplex stochastic collocation for spatial discontinuities

    NASA Astrophysics Data System (ADS)

    Witteveen, Jeroen A. S.; Iaccarino, Gianluca

    2013-10-01

    Subcell resolution has been used in the Finite Volume Method (FVM) to obtain accurate approximations of discontinuities in the physical space. Stochastic methods are usually based on local adaptivity for resolving discontinuities in the stochastic dimensions. However, the adaptive refinement in the probability space is ineffective in the non-intrusive uncertainty quantification framework, if the stochastic discontinuity is caused by a discontinuity in the physical space with a random location. The dependence of the discontinuity location in the probability space on the spatial coordinates then results in a staircase approximation of the statistics, which leads to first-order error convergence and an underprediction of the maximum standard deviation. To avoid these problems, we introduce subcell resolution into the Simplex Stochastic Collocation (SSC) method for obtaining a truly discontinuous representation of random spatial discontinuities in the interior of the cells discretizing the probability space. The presented SSC-SR method is based on resolving the discontinuity location in the probability space explicitly as function of the spatial coordinates and extending the stochastic response surface approximations up to the predicted discontinuity location. The applications to a linear advection problem, the inviscid Burgers' equation, a shock tube problem, and the transonic flow over the RAE 2822 airfoil show that SSC-SR resolves random spatial discontinuities with multiple stochastic and spatial dimensions accurately using a minimal number of samples.

  17. Discontinuous phase transitions via cooperative contagion

    NASA Astrophysics Data System (ADS)

    Ghanbarnejad, Fakhteh; Cai, Weiran; Chen, Li; Grassberger, Peter

    2015-03-01

    We study the spreading of two diseases that interact cooperatively (the presence of one helps the other one to spread) on different network topologies, and with two microscopic realizations, both of which are stochastic versions of an SIR type studied by us recently in mean field approximation. We had shown that cooperativity can lead to discontinuous transitions (DT). However, due to the rapid mixing implied by the mean field assumption, DTs were seen only when there were finite (non-zero) densities of sick individuals in the initial state.In this paper we find that the results for the stochastic model depend strongly on the underlying network. In particular, DTs are found when there are few short but many long loops: (i) No DTs exist on trees, due to the absence of loops; (ii) On 2-d lattices with local contacts there are no DTs either, but because of too many short loops; (iii) We do find DTs on Erdos-Renyi (ER) networks, on d-dimensional lattices with d >= 4 ,and on 2-d lattices with sufficiently long-ranged contacts; (iv) On 3-d lattices with local contacts the results depend on the microscopic details of the implementation. All found discontinuous transitions are of ``hybrid'' type, i.e. they display also scaling features usually associated with continuous transitions.

  18. Local discontinuous Galerkin approximations to Richards’ equation

    NASA Astrophysics Data System (ADS)

    Li, H.; Farthing, M. W.; Dawson, C. N.; Miller, C. T.

    2007-03-01

    We consider the numerical approximation to Richards' equation because of its hydrological significance and intrinsic merit as a nonlinear parabolic model that admits sharp fronts in space and time that pose a special challenge to conventional numerical methods. We combine a robust and established variable order, variable step-size backward difference method for time integration with an evolving spatial discretization approach based upon the local discontinuous Galerkin (LDG) method. We formulate the approximation using a method of lines approach to uncouple the time integration from the spatial discretization. The spatial discretization is formulated as a set of four differential algebraic equations, which includes a mass conservation constraint. We demonstrate how this system of equations can be reduced to the solution of a single coupled unknown in space and time and a series of local constraint equations. We examine a variety of approximations at discontinuous element boundaries, permeability approximations, and numerical quadrature schemes. We demonstrate an optimal rate of convergence for smooth problems, and compare accuracy and efficiency for a wide variety of approaches applied to a set of common test problems. We obtain robust and efficient results that improve upon existing methods, and we recommend a future path that should yield significant additional improvements.

  19. A Three - Dimensional Receiver Function Study of the Western United States

    NASA Astrophysics Data System (ADS)

    Lindsey, C.; Gurrola, H.

    2008-12-01

    The western United States has a complex geologic history and has been the focus of many regional scale PASSCAL seismic studies that investigate depth variations to the Moho, the 410 km discontinuity, and the 660 km discontinuities. Analysis of depth variations to the Moho in relation to topography is important in understanding the isostatic compensation depth, the thermal state of the upper mantle and boundaries between tectonic provinces. Analysis of the 410 and 660 km discontinuities allow us to determine variations in mantle temperature at these depths and facilitates comparison with tectonic boundaries. This abstract summarizes results from stacking Pds phases throughout the western US using data from all available previous PASSCAL studies in the western U.S. together with data from the EarthScope Transportable array. These data sets enable us to produce an image over the entire western US from the Pacific coast to the Rocky mountain front. Common conversion point stacking of Pds phases was performed by back projecting the data through a 3-D seismic velocity model (surface wave tomography model NA04 by Van der Lee). The images produced show large variations in Moho topography with an average depth of 39.6 kilometer over the western US with ± 7.2 km standard deviation in depth. As would be expected the Moho appears to be deepest beneath the Colorado Plateau and central Montana and shallowest throughout the Basin and Raange. The Moho also appears very shallow beneath eastern Washington. There is a band oof thick crust along the Yellowstone hot spot track. The 410 km discontinuity appears to have a mean depth of 427 km with a standard deviation in depth of ± 10.2 km. At this time the images are still very noisy but in a regional sense the 410 appears deepest beneath the southern part of the image and shallower to the north. Depths to the 660 km discontinuity appear to average 675 km with standard deviation of ± 9.8 km. The 660 does not appear to have a north

  20. Seismic offset balancing

    SciTech Connect

    Ross, C.P.; Beale, P.L.

    1994-01-01

    The ability to successfully predict lithology and fluid content from reflection seismic records using AVO techniques is contingent upon accurate pre-analysis conditioning of the seismic data. However, all too often, residual amplitude effects remain after the many offset-dependent processing steps are completed. Residual amplitude effects often represent a significant error when compared to the amplitude variation with offset (AVO) response that the authors are attempting to quantify. They propose a model-based, offset-dependent amplitude balancing method that attempts to correct for these residuals and other errors due to sub-optimal processing. Seismic offset balancing attempts to quantify the relationship between the offset response of back-ground seismic reflections and corresponding theoretical predictions for average lithologic interfaces thought to cause these background reflections. It is assumed that any deviation from the theoretical response is a result of residual processing phenomenon and/or suboptimal processing, and a simple offset-dependent scaling function is designed to correct for these differences. This function can then be applied to seismic data over both prospective and nonprospective zones within an area where the theoretical values are appropriate and the seismic characteristics are consistent. A conservative application of the above procedure results in an AVO response over both gas sands and wet sands that is much closer to theoretically expected values. A case history from the Gulf of Mexico Flexure Trend is presented as an example to demonstrate the offset balancing technique.

  1. Seismic Consequence Abstraction

    SciTech Connect

    M. Gross

    2004-10-25

    The primary purpose of this model report is to develop abstractions for the response of engineered barrier system (EBS) components to seismic hazards at a geologic repository at Yucca Mountain, Nevada, and to define the methodology for using these abstractions in a seismic scenario class for the Total System Performance Assessment - License Application (TSPA-LA). A secondary purpose of this model report is to provide information for criticality studies related to seismic hazards. The seismic hazards addressed herein are vibratory ground motion, fault displacement, and rockfall due to ground motion. The EBS components are the drip shield, the waste package, and the fuel cladding. The requirements for development of the abstractions and the associated algorithms for the seismic scenario class are defined in ''Technical Work Plan For: Regulatory Integration Modeling of Drift Degradation, Waste Package and Drip Shield Vibratory Motion and Seismic Consequences'' (BSC 2004 [DIRS 171520]). The development of these abstractions will provide a more complete representation of flow into and transport from the EBS under disruptive events. The results from this development will also address portions of integrated subissue ENG2, Mechanical Disruption of Engineered Barriers, including the acceptance criteria for this subissue defined in Section 2.2.1.3.2.3 of the ''Yucca Mountain Review Plan, Final Report'' (NRC 2003 [DIRS 163274]).

  2. Serotonin reuptake inhibitor discontinuation syndrome: a hypothetical definition. Discontinuation Consensus panel.

    PubMed

    Schatzberg, A F; Haddad, P; Kaplan, E M; Lejoyeux, M; Rosenbaum, J F; Young, A H; Zajecka, J

    1997-01-01

    Adverse events following discontinuation from serotonin reuptake inhibitors (SRIs) are being reported in the literature with increasing frequency; the frequency and severity of these symptoms appear to vary according to the half-life of the SRI, e.g., the incidence appears higher with the shorter half-life agents than with fluoxetine, which has an extended half-life. Yet, there have been no systematic studies of the phenomenon to date. Therefore, a group of experts convened in Phoenix, Arizona, to develop a clear description or definition of the phenomenon based on these reports. The SRI discontinuation syndrome, referred to as "withdrawal symptoms" in many anecdotal case reports, is distinctly different from the classic withdrawal syndrome associated with alcohol and barbiturates. Anti-depressants are not associated with dependence or drug-seeking behavior. SRI discontinuation symptoms tend to be short-lived and self-limiting, but can be troublesome. They may emerge when an SRI is abruptly discontinued, when doses are missed, and less frequently, during dosage reduction. In addition, the symptoms are not attributable to any other cause and can be reversed when the original agent is reinstituted, or one that is pharmacologically similar is substituted. SRI discontinuation symptoms, in most cases, may be minimized by slowly tapering antidepressant therapy, but there have been several case reports where symptoms occurred consistently even through repeated attempts to taper therapy. Physical symptoms include problems with balance, gastrointestinal and flu-like symptoms, and sensory and sleep disturbances. Psychological symptoms include anxiety and/or agitation, crying spells, and irritability. Further analyses of data bases and clinical studies are needed to define this proposed syndrome more clearly.

  3. Deep crustal fracture zones control fluid escape and the seismic cycle in the Cascadia subduction zone

    NASA Astrophysics Data System (ADS)

    Tauzin, Benoît; Reynard, Bruno; Perrillat, Jean-Philippe; Debayle, Eric; Bodin, Thomas

    2017-02-01

    Seismic activity and non-volcanic tremors are often associated with fluid circulation resulting from the dehydration of subducting plates. Tremors in the overriding continental crust of several subduction zones suggest fluid circulation at shallower depths, but potential fluid pathways are still poorly documented. Using receiver function analysis in the Cascadia subduction zone, we provide evidence for a seismic discontinuity near 15 km depth in the crust of the overriding North American plate. This interface is segmented, and its interruptions are spatially correlated with conductive regions of the forearc and shallow swarms of seismicity and non-volcanic tremors. These observations suggest that fluid circulation in the overriding plate is controlled by fault zones separating blocks of accreted terranes. These zones constitute fluid escape routes that may influence the seismic cycle by releasing fluid pressure from the megathrust.

  4. Deformation and seismicity of Taiwan.

    PubMed

    Vita-Finzi, C

    2000-10-10

    14C-dated Holocene coastal uplift, conventional and satellite geodetic measurements, and coseismic and aseismic fault slip reveal the pattern of distributed deformation at Taiwan resulting from convergence between the Philippine Sea plate and Eurasia; as in other subduction orogenic settings, the locus of strain release and accumulation is strongly influenced by changes in fault geometry across strike. Uplift evidence from the islands of Lutao and Lanhsu is consistent with progressive oblique collision between the Luzon arc and the Chinese continental margin. In the Coastal Range, geodetic and seismic records show that shortening is taken up serially by discontinuous slip on imbricate faults. The geodetic data point to net extension across the Central Range, but deformed Holocene shorelines in the Hengchun Peninsula at its southern extremity suggest that the extension is a superficial effect partly caused by blind reverse faulting. The fastest shortening rates indicated by geodesy are recorded on the Longitudinal Valley fault and across the Chukou fault within the fold-and-thrust belt. In the former, the strain is dissipated mainly as aseismic reverse and strike-slip displacement. In contrast, the fold-and-thrust belt has witnessed five earthquakes with magnitudes of 6.5 or above in the 20th century, including the 1999.9.21 Chi-Chi earthquake (magnitude approximately 7.6) on a branch of the Chukou fault. The neotectonic and geodetic data for Taiwan as a whole suggest that the fold-and-thrust belt will continue to host the majority of great earthquakes on the island.

  5. Seismic Safety Study

    SciTech Connect

    Tokarz, F J; Coats, D W

    2006-05-16

    During the past three decades, the Laboratory has been proactive in providing a seismically safe working environment for its employees and the general public. Completed seismic upgrades during this period have exceeded $30M with over 24 buildings structurally upgraded. Nevertheless, seismic questions still frequently arise regarding the safety of existing buildings. To address these issues, a comprehensive study was undertaken to develop an improved understanding of the seismic integrity of the Laboratory's entire building inventory at the Livermore Main Site and Site 300. The completed study of February 2005 extended the results from the 1998 seismic safety study per Presidential Executive Order 12941, which required each federal agency to develop an inventory of its buildings and to estimate the cost of mitigating unacceptable seismic risks. Degenkolb Engineers, who performed the first study, was recontracted to perform structural evaluations, rank order the buildings based on their level of seismic deficiencies, and to develop conceptual rehabilitation schemes for the most seriously deficient buildings. Their evaluation is based on screening procedures and guidelines as established by the Interagency Committee on Seismic Safety in Construction (ICSSC). Currently, there is an inventory of 635 buildings in the Laboratory's Facility Information Management System's (FIMS's) database, out of which 58 buildings were identified by Degenkolb Engineers that require seismic rehabilitation. The remaining 577 buildings were judged to be adequate from a seismic safety viewpoint. The basis for these evaluations followed the seismic safety performance objectives of DOE standard (DOE STD 1020) Performance Category 1 (PC1). The 58 buildings were ranked according to three risk-based priority classifications (A, B, and C) as shown in Figure 1-1 (all 58 buildings have structural deficiencies). Table 1-1 provides a brief description of their expected performance and damage state

  6. Exploring Patients’ Reasons for Discontinuance of Heart Medications

    PubMed Central

    Garavalia, Linda; Garavalia, Brian; Spertus, John A.; Decker, Carole

    2012-01-01

    Background Despite the importance of secondary prevention, non-adherence rates for myocardial infarction (MI) patients range from 13-60% for prescribed, evidence-based medicines. Although rates and consequences of discontinuance vary for different medications, the existing literature provides little insight into reasons for discontinuance. Objective To address this gap, we explored clopidogrel and cholesterol lowering therapy (CLT) discontinuance after an MI to understand patients’ reasons for stopping these two medications. Methods In this qualitative descriptive study, two groups of patients who stopped a heart medication – either clopidogrel or CLT – were recruited from a prospective MI registry. Patients who discontinued CLT (n=29) or clopidogrel (n=11) were interviewed within 18 months of hospitalization. Patients were recruited and interviewed until data saturation was achieved. The Health Belief Model (HBM) was used as an organizing framework in analyzing and coding the narrative data. The codes were then summarized for each group and compared to identify similarities and differences in reasons for CLT and clopidogrel discontinuance. Results and Conclusions The most common reason for CLT discontinuance was adverse side effects that were painful and interfered with daily life. Less common reasons for discontinuance were prescription confusion, cost, mistrust of medicines/health care system, and preference for alternative therapies. Reasons for clopidogrel discontinuance were duration confusion, side effects, and cost. Although doctors stopped patients’ clopidogrel in preparation for surgery, doctors conceded to discontinuance of CLT for patients who experienced side effects after trying 2 to 3 different CLTs. Patients who discontinued CLT were more likely to believe they did not need the treatment than patients who discontinued clopidogrel. Clinicians should be aware that reasons may vary across patients and medication class for prematurely stopping

  7. Intensity Based Seismic Hazard Map of Republic of Macedonia

    NASA Astrophysics Data System (ADS)

    Dojcinovski, Dragi; Dimiskovska, Biserka; Stojmanovska, Marta

    2016-04-01

    The territory of the Republic of Macedonia and the border terrains are among the most seismically active parts of the Balkan Peninsula belonging to the Mediterranean-Trans-Asian seismic belt. The seismological data on the R. Macedonia from the past 16 centuries point to occurrence of very strong catastrophic earthquakes. The hypocenters of the occurred earthquakes are located above the Mohorovicic discontinuity, most frequently, at a depth of 10-20 km. Accurate short -term prognosis of earthquake occurrence, i.e., simultaneous prognosis of time, place and intensity of their occurrence is still not possible. The present methods of seismic zoning have advanced to such an extent that it is with a great probability that they enable efficient protection against earthquake effects. The seismic hazard maps of the Republic of Macedonia are the result of analysis and synthesis of data from seismological, seismotectonic and other corresponding investigations necessary for definition of the expected level of seismic hazard for certain time periods. These should be amended, from time to time, with new data and scientific knowledge. The elaboration of this map does not completely solve all issues related to earthquakes, but it provides basic empirical data necessary for updating the existing regulations for construction of engineering structures in seismically active areas regulated by legal regulations and technical norms whose constituent part is the seismic hazard map. The map has been elaborated based on complex seismological and geophysical investigations of the considered area and synthesis of the results from these investigations. There were two phases of elaboration of the map. In the first phase, the map of focal zones characterized by maximum magnitudes of possible earthquakes has been elaborated. In the second phase, the intensities of expected earthquakes have been computed according to the MCS scale. The map is prognostic, i.e., it provides assessment of the

  8. Analysis of Waveguide Junction Discontinuities Using Finite Element Method

    NASA Technical Reports Server (NTRS)

    Deshpande, Manohar D.

    1997-01-01

    A Finite Element Method (FEM) is presented to determine reflection and transmission coefficients of rectangular waveguide junction discontinuities. An H-plane discontinuity, an E-plane ridge discontinuity, and a step discontinuity in a concentric rectangular waveguide junction are analyzed using the FEM procedure. Also, reflection and transmission coefficients due to presence of a gap between two sections of a rectangular waveguide are determined using the FEM. The numerical results obtained by the present method are in excellent agreement with the earlier published results. The numerical results obtained by the FEM are compared with the numerical results obtained using the Mode Matching Method (MMM) and also with the measured data.

  9. Effect of the woman's age on discontinuation of IVF treatment.

    PubMed

    Soullier, Noémie; Bouyer, Jean; Pouly, Jean-Luc; Guibert, Juliette; de La Rochebrochard, Elise

    2011-05-01

    Treatment discontinuations are an important issue in IVF programmes. In the French context, financial constraint does not intervene in discontinuation until older ages. This study examined treatment discontinuation in IVF programmes, according to the woman's age and when there is no financial burden for couples. Medical records were collected for 3037 women who began their IVF programme between 1998 and 2002 in two French IVF units. Up to four attempts were taken into consideration. Cumulative success (delivery) rates were calculated, as well as discontinuation rates. Multiple imputation was applied to estimate a theoretical cumulative success rate as if no woman discontinued treatment before the end of the IVF programme without delivering. Cumulative discontinuation rates at the end of the IVF programme increased with the woman's age (41% for age <35, 56% for age 35-39, 80% for age ⩾40). The benefit in terms of delivery rates of pursuing treatment would be smaller for older women (∼10% for age <35, 7% for age 35-39, 4% for age ⩾40). Even when treatment is reimbursed, the discontinuation rate is high for older women, suggesting that the strong decrease in success rate with age induces older women to discontinue. Treatment discontinuations are an important issue in IVF programmes. In the French context, financial constraint does not intervene in discontinuation until older ages. We aimed to examine treatment discontinuation in IVF programmes, according to the woman's age and when there is no financial burden for couples. Medical records were collected for 3037 women who began their IVF programme between 1998 and 2002 in two French IVF units. Up to four attempts were taken into consideration. Cumulative success (delivery) rates were calculated, as well as discontinuation rates. Multiple imputation was applied to estimate a theoretical cumulative success rate as if no woman discontinued treatment before the end of the IVF programme without delivering. Cumulative

  10. Experiencing antipsychotic discontinuation: results from a survey of Australian consumers.

    PubMed

    Salomon, C; Hamilton, B; Elsom, S

    2014-12-01

    Despite high reported rates of antipsychotic non-adherence, little is known about consumer experiences during discontinuation. This study was designed to increase understanding of antipsychotic discontinuation from consumer perspectives. In 2011-2012, 98 Australian consumers involved with participating organizations completed an anonymous survey detailing past antipsychotic discontinuation attempts. Of the 88 participants who reported at least one discontinuation attempt, over half (n = 47, 54.7%) reported stopping without clinician knowledge or support. This group was 35% (confidence interval 15.4-54.6%) more likely to stop abruptly than those (n = 41, 45.3%) stopping with clinician support (P = 0.002). Only 10 participants (23.3%) recalled being given information about discontinuation symptoms other than relapse; however, 68 participants (78.2%) reported experiencing a range of discontinuation symptoms including physical, cognitive, emotional, psychotic or sleep-related disturbances. Findings cannot be readily generalized because of sampling constraints. However, the significant number of participants who reported discontinuation symptoms, in addition to psychosis, is consistent with previous research. This study provides new insight into consumer motivations for discontinuation and possible problems in clinical communication that may contribute to frequent non-collaborative discontinuation attempts. Mental health nurses, who play a pivotal role in medication communication events, may benefit from increased awareness of consumer perspectives on this topic.

  11. From weak discontinuities to nondissipative shock waves

    SciTech Connect

    Garifullin, R. N. Suleimanov, B. I.

    2010-01-15

    An analysis is presented of the effect of weak dispersion on transitions from weak to strong discontinuities in inviscid fluid dynamics. In the neighborhoods of transition points, this effect is described by simultaneous solutions to the Korteweg-de Vries equation u{sub t}'+ uu{sub x}' + u{sub xxx}' = 0 and fifth-order nonautonomous ordinary differential equations. As x{sup 2} + t{sup 2} {yields}{infinity}, the asymptotic behavior of these simultaneous solutions in the zone of undamped oscillations is given by quasi-simple wave solutions to Whitham equations of the form r{sub i}(t, x) = tl{sub i} x/t{sup 2}.

  12. Discontinuous Galerkin Methods for Turbulence Simulation

    NASA Technical Reports Server (NTRS)

    Collis, S. Scott

    2002-01-01

    A discontinuous Galerkin (DG) method is formulated, implemented, and tested for simulation of compressible turbulent flows. The method is applied to turbulent channel flow at low Reynolds number, where it is found to successfully predict low-order statistics with fewer degrees of freedom than traditional numerical methods. This reduction is achieved by utilizing local hp-refinement such that the computational grid is refined simultaneously in all three spatial coordinates with decreasing distance from the wall. Another advantage of DG is that Dirichlet boundary conditions can be enforced weakly through integrals of the numerical fluxes. Both for a model advection-diffusion problem and for turbulent channel flow, weak enforcement of wall boundaries is found to improve results at low resolution. Such weak boundary conditions may play a pivotal role in wall modeling for large-eddy simulation.

  13. Weld stresses beyond elastic limit: Materials discontinuity

    NASA Technical Reports Server (NTRS)

    Verderaime, V.

    1989-01-01

    When welded structures depend on properties beyond the elastic limit to qualify their ultimate safety factor, and weld-parent materials abruptly change at the interface, then stress discontinuity is inevitable. The stress concentration is mildly sensitive to material relative strain hardening and acutely sensitive to applied stress fields. Peak stresses occur on the weld surface, at the interface, and dissipate within a 0.01-inch band. When the stress is intense, the weld will always fracture at the interface. The analysis incorporates a classical mechanics model to more sharply define stress spikes within the bandwidth, and suggests a relative material index and Poisson's ratio related to strain hardening. Implications are discussed which are applicable to industries of high performance structures.

  14. Bayesian Enrichment Strategies for Randomized Discontinuation Trials

    PubMed Central

    Trippa, Lorenzo; Rosner, Gary L.; Müller, Peter

    2013-01-01

    Summary We propose optimal choice of the design parameters for random discontinuation designs (RDD) using a Bayesian decision-theoretic approach. We consider applications of RDDs to oncology phase II studies evaluating activity of cytostatic agents. The design consists of two stages. The preliminary open-label stage treats all patients with the new agent and identifies a possibly sensitive subpopulation. The subsequent second stage randomizes, treats, follows, and compares outcomes among patients in the identified subgroup, with randomization to either the new or a control treatment. Several tuning parameters characterize the design: the number of patients in the trial, the duration of the preliminary stage, and the duration of follow-up after randomization. We define a probability model for tumor growth, specify a suitable utility function, and develop a computational procedure for selecting the optimal tuning parameters. PMID:21714780

  15. Low-index discontinuity terahertz waveguides

    NASA Astrophysics Data System (ADS)

    Nagel, Michael; Marchewka, Astrid; Kurz, Heinrich

    2006-10-01

    A new type of dielectric THz waveguide based on recent approaches in the field of integrated optics is presented with theoretical and experimental results. Although the guiding mechanism of the low-index discontinuity (LID) THz waveguide is total internal reflection, the THz wave is predominantly confined in the virtually lossless low-index air gap within a high-index dielectric waveguide due to the continuity of electric flux density at the dielectric interface. Attenuation, dispersion and single-mode confinement properties of two LID structures are discussed and compared with other THz waveguide solutions. The new approach provides an outstanding combination of high mode confinement and low transmission losses currently not realizable with any other metal-based or photonic crystal approach. These exceptional properties might enable the breakthrough of novel integrated THz systems or endoscopy applications with sub-wavelength resolution.

  16. Seismic evidence for an inner core transition zone

    PubMed

    Song; Helmberger

    1998-10-30

    Seismic waves that traverse Earth's inner core along north-south paths produce unusually broad pulse shapes at long periods (compared with waves along east-west paths) and reflections from below the inner core boundary at short periods. The observations provide compelling evidence for a seismic velocity discontinuity along north-south paths about 200 kilometers below the inner core boundary separating an isotropic upper inner core from an anisotropic lower inner core. The triplication associated with such a structure might be responsible for reported waveform complexity of short-period inner core arrivals along north-south paths and, if the depth of the boundary is laterally variable, their large travel-time variation.

  17. Mantle transition zone thickness in the Central South-American Subduction Zone

    NASA Astrophysics Data System (ADS)

    Braunmiller, Jochen; van der Lee, Suzan; Doermann, Lindsey

    We used receiver functions to determine lateral variations in mantle transition zone thickness and sharpness of the 410- and 660-km discontinuities in the presence of subducting lithosphere. The mantle beneath the central Andes of South America provides an ideal study site owing to its long-lived subduction history and the availability of broadband seismic data from the dense BANJO/SEDA temporary networks and the permanent station LPAZ. For LPAZ, we analyzed 26 earthquakes between 1993-2003 and stacked the depth-migrated receiver functions. For temporary stations operating for only about one year (1994-1995), station stacks were not robust. We thus stacked receiver functions for close-by stations forming five groups that span the subduction zone from west to east, each containing 12 to 25 events. We found signal significant at the 2σ level for several station groups from P to S conversions that originate near 520- and 850-900 km depth, but most prominently from the 410- and 660-km discontinuities. For the latter, the P to S converted signal is clear in stacks for western groups and LPAZ, lack of coherent signal for two eastern groups is possibly due to incoherent stacking and does not necessitate the absence of converted energy. The thickness of the mantle transition zone increases progressively from a near-normal 255 km at the Pacific coast to about 295 km beneath station LPAZ in the Eastern Cordillera. Beneath LPAZ, the 410-km discontinuity appears elevated by nearly 40 km, thus thickening the transition zone. We compared signal amplitudes from receiver function stacks calculated at different low-pass frequencies to study frequency dependence and possibly associated discontinuity sharpness of the P to S converted signals. We found that both the 410- and 660-km discontinuities exhibit amplitude increase with decreasing frequency. Synthetic receiver function calculations for discontinuity topography mimicking observed topography show that the observed steep

  18. Landslide seismic magnitude

    NASA Astrophysics Data System (ADS)

    Lin, C. H.; Jan, J. C.; Pu, H. C.; Tu, Y.; Chen, C. C.; Wu, Y. M.

    2015-11-01

    Landslides have become one of the most deadly natural disasters on earth, not only due to a significant increase in extreme climate change caused by global warming, but also rapid economic development in topographic relief areas. How to detect landslides using a real-time system has become an important question for reducing possible landslide impacts on human society. However, traditional detection of landslides, either through direct surveys in the field or remote sensing images obtained via aircraft or satellites, is highly time consuming. Here we analyze very long period seismic signals (20-50 s) generated by large landslides such as Typhoon Morakot, which passed though Taiwan in August 2009. In addition to successfully locating 109 large landslides, we define landslide seismic magnitude based on an empirical formula: Lm = log ⁡ (A) + 0.55 log ⁡ (Δ) + 2.44, where A is the maximum displacement (μm) recorded at one seismic station and Δ is its distance (km) from the landslide. We conclude that both the location and seismic magnitude of large landslides can be rapidly estimated from broadband seismic networks for both academic and applied purposes, similar to earthquake monitoring. We suggest a real-time algorithm be set up for routine monitoring of landslides in places where they pose a frequent threat.

  19. Singular spectrum analysis and its applications in mapping mantle seismic structure

    NASA Astrophysics Data System (ADS)

    Dokht, Ramin M. H.; Gu, Yu Jeffrey; Sacchi, Mauricio D.

    2017-03-01

    Seismic discontinuities are fundamental to the understanding of mantle composition and dynamics. Their depths and impedance contrasts are generally determined using secondary phases such as SS precursors and P-to-S converted waves. However, analysing and interpreting these weak signals often suffer from incomplete data coverage, high noise levels and interfering seismic arrivals, especially near tectonically complex regions such as subduction zones. To overcome these pitfalls, we adopt a singular spectrum analysis (SSA) method to remove random noise, reconstruct missing traces and enhance the robustness of SS precursors and P-to-S conversions from mantle seismic discontinuities. Our method takes advantage of the predictability of time series in the frequency-space domain and performs rank reduction using a singular value decomposition of the trajectory matrix. We apply SSA to synthetic record sections as well as the observations of (1) SS precursors beneath the northwestern Pacific subduction zones, and (2) P-to-S converted waves from southwestern Canada. In comparison with raw or interpolated data, the SSA enhanced seismic sections exhibit greater resolution due to the suppression of random noise (which reduces signal amplitude during standard averaging procedures) through rank reduction. SSA also enables an effective separation of the SS precursors from the postcursors of S-wave core diffractions. This method will greatly benefit future analyses of weak crustal and mantle seismic phases, especially when data coverages are less than ideal.

  20. High order discontinuous Galerkin discretizations with discontinuity resolution within the cell

    NASA Astrophysics Data System (ADS)

    Ekaterinaris, John; Panourgias, Konstantinos

    2016-11-01

    The nonlinear filter of Yee et al. and used for low dissipative well-balanced high order accurate finite-difference schemes is adapted to the finite element context of discontinuous Galerkin (DG) discretizations. The performance of the proposed nonlinear filter for DG discretizations is demonstrated for different orders of expansions for one- and multi-dimensional problems with exact solutions. It is shown that for higher order discretizations discontinuity resolution within the cell is achieved and the design order of accuracy is preserved. The filter is applied for inviscid and viscous flow test problems including strong shocks interactions to demonstrate that the proposed dissipative mechanism for DG discretizations yields superior results compared to the results obtained with the TVB limiter and high-order hierarchical limiting. The proposed approach is suitable for p-adaptivity in order to locally enhance resolution of three-dimensional flow simulations.

  1. Discontinuation of Buprenorphine Maintenance Therapy: Perspectives and Outcomes

    PubMed Central

    Bentzley, Brandon S.; Barth, Kelly S.; Back, Sudie E.; Book, Sarah W.

    2015-01-01

    Buprenorphine maintenance therapy (BMT) is increasingly the preferred opioid maintenance agent due to its reduced toxicity and availability in an office-based setting in the United States. Although BMT has been shown to be highly efficacious, it is often discontinued soon after initiation. No current systematic review has yet investigated providers’ or patients’ reasons for BMT discontinuation or the outcomes that follow. Hence, provider and patient perspectives associated with BMT discontinuation after a period of stable buprenorphine maintenance and the resultant outcomes were systematically reviewed with specific emphasis on pre-buprenorphine-taper parameters predictive of relapse following BMT discontinuation. Few identified studies address provider or patient perspectives associated with buprenorphine discontinuation. Within the studies reviewed providers with residency training in BMT were more likely to favor long term BMT instead of detoxification, and providers were likely to consider BMT discontinuation in the face of medication misuse. Patients often desired to remain on BMT because of fear of relapse to illicit opioid use if they were to discontinue BMT. The majority of patients who discontinued BMT did so involuntarily, often due to failure to follow strict program requirements, and 1 month following discontinuation, rates of relapse to illicit opioid use exceeded 50% in every study reviewed. Only lower buprenorphine maintenance dose, which may be a marker for attenuated addiction severity, predicted better outcomes across studies. Relaxed BMT program requirements and frequent counsel on the high probability of relapse if BMT is discontinued may improve retention in treatment and prevent the relapse to illicit opioid use that is likely to follow BMT discontinuation. PMID:25601365

  2. HANFORD DOUBLE SHELL TANK (DST) THERMAL & SEISMIC PROJECT SEISMIC ANALYSIS OF HANFORD DOUBLE SHELL TANKS

    SciTech Connect

    MACKEY, T.C.

    2006-03-17

    M&D Professional Services, Inc. (M&D) is under subcontract to Pacific Northwest National Laboratory (PNNL) to perform seismic analysis of the Hanford Site double-shell tanks (DSTs) in support of a project entitled ''Double-Shell Tank (DSV Integrity Project--DST Thermal and Seismic Analyses)''. The overall scope of the project is to complete an up-to-date comprehensive analysis of record of the DST system at Hanford in support of Tri-Party Agreement Milestone M-48-14, The work described herein was performed in support of the seismic analysis of the DSTs. The thermal and operating loads analysis of the DSTs is documented in Rinker et al. (2004). The work statement provided to M&D (PNNL 2003) required that the seismic analysis of the DSTs assess the impacts of potentially non-conservative assumptions in previous analyses and account for the additional soil mass due to the as-found soil density increase, the effects of material degradation, additional thermal profiles applied to the full structure including the soil-structure response with the footings, the non-rigid (low frequency) response of the tank roof, the asymmetric seismic-induced soil loading, the structural discontinuity between the concrete tank wall and the support footing and the sloshing of the tank waste. The seismic analysis considers the interaction of the tank with the surrounding soil and the effects of the primary tank contents. The DSTs and the surrounding soil are modeled as a system of finite elements. The depth and width of the soil incorporated into the analysis model are sufficient to obtain appropriately accurate analytical results. The analyses required to support the work statement differ from previous analysis of the DSTs in that the soil-structure interaction (SSI) model includes several (nonlinear) contact surfaces in the tank structure, and the contained waste must be modeled explicitly in order to capture the fluid-structure interaction behavior between the primary tank and contained

  3. Coherence estimation algorithm using Kendall's concordance measurement on seismic data

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Gao, Jing-Huai; Zhang, Bing; Wang, Da-Xing

    2016-09-01

    The coherence method is always used to describe the discontinuity and heterogeneity of seismic data. In traditional coherence methods, a linear correlation coefficient is always used to measure the relationship between two random variables (i.e., between two seismic traces). However, mathematically speaking, a linear correlation coefficient cannot be applied to describe nonlinear relationships between variables. In order to overcome this limitation of liner correlation coefficient. We proposed an improved concordance measurement algorithm based on Kendall's tau. That mainly concern the sensitivity of the liner correlation coefficient and concordance measurements on the waveform. Using two designed numerical models tests sensitivity of waveform similarity affected by these two factors. The analysis of both the numerical model results and real seismic data processing suggest that the proposed method, combining information divergence measurement, can not only precisely characterize the variations of waveform and the heterogeneity of an underground geological body, but also does so with high resolution. In addition, we verified its effectiveness by the actual application of real seismic data from the north of China.

  4. Neotectonics and seismicity of the Clearlake region in northern California

    SciTech Connect

    Burns, K.L.

    1996-04-01

    Geological, topographic, and seismic methods were used to locate faults in the vicinity of Clearlake in northern California. The geological method, which seeks faults as discontinuities in the lithotope, found faults in the Tertiary-Cretaceous rocks east of Burns Valley. The topographic method, which is used to produce Fault Evaluation Reports, found a very active fault zone, the Konocti Bay fault zone, south of Highlands arm. It also found some active faults north of Highlands arm, in the eastern part of Burns Valley and on the lakeshore near Oak Park. The seismic method is the most enduring of the three methods but is limited by location accuracy; the results improve as monitoring continues because of increases in the density of events and improvements in the crustal velocity model. The seismic method identified faulting along the valley at Borax Lake and possibly also on a line running northeast from the city of Clearlake. The latter may be associated with the Burns Valley fault or with the line of scoria domes which runs parallel to it. Seismic observations over longer periods at higher resolution will be required in order to determine the location of active faults near the city. 47 refs., 13 figs.

  5. Canadian Seismic Agreement

    SciTech Connect

    Wetmiller, R.J.; Lyons, J.A.; Shannon, W.E.; Munro, P.S.; Thomas, J.T.; Andrew, M.D.; Lapointe, S.P.; Lamontagne, M.; Wong, C.; Anglin, F.M.; Adams, J.; Cajka, M.G.; McNeil, W.; Drysdale, J.A. )

    1992-05-01

    This is a progress report of work carried out under the terms of a research agreement entitled the Canadian Seismic Agreement'' between the US Nuclear Regulatory Commission (USNRC), the Canadian Commercial Corporation and the Geophysics Division of the Geological Survey of Canada (GD/GSC) during the period from July 01, 1989 to June 30, 1990. The Canadian Seismic Agreement'' supports generally the operation of various seismograph stations in eastern Canada and the collection and analysis of earthquake data for the purpose of mitigating seismic hazards in eastern Canada and the northeastern US. The specific activities carried out in this one-year period are summarized below under four headings; Eastern Canada Telemetred Network and local network developments, Datalab developments, strong-motion network developments and earthquake activity. During this period the first surface fault unequivocably determined to have accompanied a historic earthquake in eastern North America, occurred in northern Quebec.

  6. Induced seismicity. Final report

    SciTech Connect

    Segall, P.

    1997-09-18

    The objective of this project has been to develop a fundamental understanding of seismicity associated with energy production. Earthquakes are known to be associated with oil, gas, and geothermal energy production. The intent is to develop physical models that predict when seismicity is likely to occur, and to determine to what extent these earthquakes can be used to infer conditions within energy reservoirs. Early work focused on earthquakes induced by oil and gas extraction. Just completed research has addressed earthquakes within geothermal fields, such as The Geysers in northern California, as well as the interactions of dilatancy, friction, and shear heating, on the generation of earthquakes. The former has involved modeling thermo- and poro-elastic effects of geothermal production and water injection. Global Positioning System (GPS) receivers are used to measure deformation associated with geothermal activity, and these measurements along with seismic data are used to test and constrain thermo-mechanical models.

  7. Unraveling Megathrust Seismicity

    NASA Astrophysics Data System (ADS)

    Funiciello, Francesca; Corbi, Fabio; van Dinther, Ylona; Heuret, Arnauld

    2013-12-01

    The majority of global seismicity originates at subduction zones, either within the converging plates or along the plate interface. In particular, events with Mw ≥ 8.0 usually occur at the subduction megathrust, which is the frictional interface between subducting and overriding plates. Consequently, seismicity at subduction megathrusts is responsible for most of the seismic energy globally released during the last century [Pacheco and Sykes, 1992]. What's more, during the last decade giant megathrust earthquakes occurred at an increased rate with respect to the last century [Ammon et al., 2010], often revealing unexpected characteristics and resulting in catastrophic effects. Determining the controlling factors of these events would have fundamental implications for earthquake and tsunami hazard assessment.

  8. 3-D Seismic Interpretation

    NASA Astrophysics Data System (ADS)

    Moore, Gregory F.

    2009-05-01

    This volume is a brief introduction aimed at those who wish to gain a basic and relatively quick understanding of the interpretation of three-dimensional (3-D) seismic reflection data. The book is well written, clearly illustrated, and easy to follow. Enough elementary mathematics are presented for a basic understanding of seismic methods, but more complex mathematical derivations are avoided. References are listed for readers interested in more advanced explanations. After a brief introduction, the book logically begins with a succinct chapter on modern 3-D seismic data acquisition and processing. Standard 3-D acquisition methods are presented, and an appendix expands on more recent acquisition techniques, such as multiple-azimuth and wide-azimuth acquisition. Although this chapter covers the basics of standard time processing quite well, there is only a single sentence about prestack depth imaging, and anisotropic processing is not mentioned at all, even though both techniques are now becoming standard.

  9. Controllable seismic source

    SciTech Connect

    Gomez, Antonio; DeRego, Paul Jeffrey; Ferrell, Patrick Andrew; Thom, Robert Anthony; Trujillo, Joshua J.; Herridge, Brian

    2015-09-29

    An apparatus for generating seismic waves includes a housing, a strike surface within the housing, and a hammer movably disposed within the housing. An actuator induces a striking motion in the hammer such that the hammer impacts the strike surface as part of the striking motion. The actuator is selectively adjustable to change characteristics of the striking motion and characteristics of seismic waves generated by the impact. The hammer may be modified to change the physical characteristics of the hammer, thereby changing characteristics of seismic waves generated by the hammer. The hammer may be disposed within a removable shock cavity, and the apparatus may include two hammers and two shock cavities positioned symmetrically about a center of the apparatus.

  10. Controllable seismic source

    SciTech Connect

    Gomez, Antonio; DeRego, Paul Jeffrey; Ferrel, Patrick Andrew; Thom, Robert Anthony; Trujillo, Joshua J.; Herridge, Brian

    2014-08-19

    An apparatus for generating seismic waves includes a housing, a strike surface within the housing, and a hammer movably disposed within the housing. An actuator induces a striking motion in the hammer such that the hammer impacts the strike surface as part of the striking motion. The actuator is selectively adjustable to change characteristics of the striking motion and characteristics of seismic waves generated by the impact. The hammer may be modified to change the physical characteristics of the hammer, thereby changing characteristics of seismic waves generated by the hammer. The hammer may be disposed within a removable shock cavity, and the apparatus may include two hammers and two shock cavities positioned symmetrically about a center of the apparatus.

  11. Seismic ruggedness of relays

    SciTech Connect

    Merz, K.L. )

    1991-08-01

    This report complements EPRI report NP-5223 Revision 1, February 1991, and presents additional information and analyses concerning generic seismic ruggedness of power plant relays. Existing and new test data have been used to construct Generic Equipment Ruggedness Spectra (GERS) which can be used in identifying rugged relays during seismic re-evaluation of nuclear power plants. This document is an EPRI tier 1 report. The results of relay fragility tests for both old and new relays are included in an EPRI tier 2 report with the same title. In addition to the presentation of relay GERS, the tier 2 report addresses the applicability of GERS to relays of older vintage, discusses the important identifying nomenclature for each relay type, and examines relay adjustment effects on seismic ruggedness. 9 refs., 3 figs, 1 tab.

  12. A nonlinear filter for high order discontinuous Galerkin discretizations with discontinuity resolution within the cell

    NASA Astrophysics Data System (ADS)

    Panourgias, Konstantinos T.; Ekaterinaris, John A.

    2016-12-01

    The nonlinear filter introduced by Yee et al. (1999) [27] and extensively used in the development of low dissipative well-balanced high order accurate finite-difference schemes is adapted to the finite element context of discontinuous Galerkin (DG) discretizations. The filter operator is constructed in the canonical computational domain for the standard cubical element where it is applied to the computed conservative variables in a direction per direction basis. Filtering becomes possible for all element types in unstructured meshes using collapsed coordinate transformations. The performance of the proposed nonlinear filter for DG discretizations is demonstrated and evaluated for different orders of expansions for one-dimensional and multidimensional problems with exact solutions. It is shown that for higher order discretizations discontinuity resolution within the cell is achieved and the design order of accuracy is preserved. The filter is applied for a number of standard inviscid flow test problems including strong shocks interactions to demonstrate that the proposed dissipative mechanism for DG discretizations yields superior results compared to the results obtained with the total variation bounded (TVB) limiter and high-order hierarchical limiting. The proposed approach is suitable for p-adaptivity in order to locally enhance resolution of three-dimensional flow simulations that include discontinuities and complex flow features.

  13. The utility of petroleum seismic exploration data in delineating structural features within salt anticlines

    USGS Publications Warehouse

    Stockton, S.L.; Balch, Alfred H.

    1978-01-01

    The Salt Valley anticline, in the Paradox Basin of southeastern Utah, is under investigation for use as a location for storage of solid nuclear waste. Delineation of thin, nonsalt interbeds within the upper reaches of the salt body is extremely important because the nature and character of any such fluid- or gas-saturated horizons would be critical to the mode of emplacement of wastes into the structure. Analysis of 50 km of conventional seismic-reflection data, in the vicinity of the anticline, indicates that mapping of thin beds at shallow depths may well be possible using a specially designed adaptation of state-of-the-art seismic oil-exploration procedures. Computer ray-trace modeling of thin beds in salt reveals that the frequency and spatial resolution required to map the details of interbeds at shallow depths (less than 750 m) may be on the order of 500 Hz, with surface-spread lengths of less than 350 m. Consideration should be given to the burial of sources and receivers in order to attenuate surface noise and to record the desired high frequencies. Correlation of the seismic-reflection data with available well data and surface geology reveals the complex, structurally initiated diapir, whose upward flow was maintained by rapid contemporaneous deposition of continental clastic sediments on its flanks. Severe collapse faulting near the crests of these structures has distorted the seismic response. Evidence exists, however, that intrasalt thin beds of anhydrite, dolomite, and black shale are mappable on seismic record sections either as short, discontinuous reflected events or as amplitude anomalies that result from focusing of the reflected seismic energy by the thin beds; computer modeling of the folded interbeds confirms both of these as possible causes of seismic response from within the salt diapir. Prediction of the seismic signatures of the interbeds can be made from computer-model studies. Petroleum seismic-reflection data are unsatisfactory for

  14. Interpolation of aliased seismic traces

    SciTech Connect

    Monk, D.J.; McBeath, R.G.; Wason, C.B.

    1993-08-10

    A method is described of interpolating seismic traces comprising the steps of: (a) processing seismic data to produce input seismic traces; (b) transforming the input seismic traces from the x, y, and time domain into the x-slope, y-slope and time domain (domains) by using a two dimensional power diversity slant stack; and (c) transforming the product of step (b) back into the x, y, and time domain using an inverse slant stack.

  15. Induced Seismicity Monitoring System

    NASA Astrophysics Data System (ADS)

    Taylor, S. R.; Jarpe, S.; Harben, P.

    2014-12-01

    There are many seismological aspects associated with monitoring of permanent storage of carbon dioxide (CO2) in geologic formations. Many of these include monitoring underground gas migration through detailed tomographic studies of rock properties, integrity of the cap rock and micro seismicity with time. These types of studies require expensive deployments of surface and borehole sensors in the vicinity of the CO2 injection wells. Another problem that may exist in CO2 sequestration fields is the potential for damaging induced seismicity associated with fluid injection into the geologic reservoir. Seismic hazard monitoring in CO2 sequestration fields requires a seismic network over a spatially larger region possibly having stations in remote settings. Expensive observatory-grade seismic systems are not necessary for seismic hazard deployments or small-scale tomographic studies. Hazard monitoring requires accurate location of induced seismicity to magnitude levels only slightly less than that which can be felt at the surface (e.g. magnitude 1), and the frequencies of interest for tomographic analysis are ~1 Hz and greater. We have developed a seismo/acoustic smart sensor system that can achieve the goals necessary for induced seismicity monitoring in CO2 sequestration fields. The unit is inexpensive, lightweight, easy to deploy, can operate remotely under harsh conditions and features 9 channels of recording (currently 3C 4.5 Hz geophone, MEMS accelerometer and microphone). An on-board processor allows for satellite transmission of parameter data to a processing center. Continuous or event-detected data is kept on two removable flash SD cards of up to 64+ Gbytes each. If available, data can be transmitted via cell phone modem or picked up via site visits. Low-power consumption allows for autonomous operation using only a 10 watt solar panel and a gel-cell battery. The system has been successfully tested for long-term (> 6 months) remote operations over a wide range

  16. A weighted Runge-Kutta discontinuous Galerkin method for wavefield modelling

    NASA Astrophysics Data System (ADS)

    He, Xijun; Yang, Dinghui; Wu, Hao

    2015-03-01

    In this paper, we propose a weighted Runge-Kutta (RK) discontinuous Galerkin (WRKDG) method for wavefield modelling. For this method, we first transform the seismic wave equations in 2-D heterogeneous anisotropic media into a first-order hyperbolic system, and then combine the discontinuous Galerkin method (DGM) with a weighted RK time discretization. The time discretization is based on an implicit diagonal RK method and an explicit technique, which changes the implicit RK method into an explicit one. In addition, we introduce a weighting factor in the process. Linear and quadratic polynomials for spatial basis functions are typically employed. We investigate the properties of the method in great detail, including the stability criteria and numerical dispersion relations for solving the 2-D acoustic equations. Our analysis indicates that the stability condition for the WRKDG method is more relaxed compared with the classic total variation diminishing (TVD) RK discontinuous Galerkin (RKDG) method, resulting in a 1.7 times superiority for P1 element and is about as efficient as TVD RKDG method for P2 element in computational efficiency. We also demonstrate that the WRKDG method can suppress numerical dispersion more efficiently than the staggered-grid (SG) method on the same grid. The WRKDG method is applied to simulate the wavefields in a large velocity contrast model, a 2-D homogeneous transversely isotropic (TI) model, a fluid-filled fracture model, and a 2-D SEG/EAGE salt dome model. Regular rectangular and irregular triangular elements are used. The numerical results show that the WRKDG method can effectively suppress numerical dispersion and provide accurate information on the wavefield on a coarse mesh. Therefore, the method evidently reduces the scale of the problem and increases computational efficiency. In addition, promising numerical tests show that the WRKDG method combines well with split perfectly matched layer boundary conditions.

  17. The Effect of Water on the 410-km Discontinuity

    NASA Astrophysics Data System (ADS)

    Smyth, J. R.; Frost, D. J.

    2001-12-01

    The H content of the Earth is one of the most poorly constrained compositional variables for the planet. The nominally anhydrous olivine and spinelloid phases thought to compose the bulk of the upper mantle and transition zone may contain many times the amount of H and O that reside in the hydrosphere. The discontinuity at 410 kilometers corresponds to the olivine-wadsleyite transition with an increase in both density and S-wave velocity of about five percent. Previous experiments and calculations in the anhydrous peridotite system indicate an olivine-wadsleyite two-phase interval that is from 10 to 18 km in width. Calculations indicate that the two-phase region would be significantly broader in a hydrous system. We have conducted a series of synthesis experiments in the multi-anvil press on hydrous and anhydrous peridotite compositions and characterized the products by electron microprobe and single-crystal X-ray diffraction. Six experiments were conducted in a hydrous peridotite system, and three in an anhydrous system. The results of our synthesis experiments are consistent with the prediction of Wood (1995) that the presence of H2O extends the stability of wadsleyite to 0.6 to 1.0 GPa lower pressure and would broaden the two-phase loop to as much as 30 km. In the hydrous runs containing both olivine and wadsleyite, there appears a sharp boundary between regions of olivine and regions of wadsleyite. The texture of the run thus does not appear to be a simple chemical equilibrium, but rather a diffusion-controlled boundary. Hydrogen is known to diffuse very rapidly in these materials, raising the possibility that diffusion of H might control the texture and may affect the sharpness of the boundary in the natural system. Hydrous wadsleyite is about five percent denser than anhydrous olivine. In a hypothetical two-phase region consisting of olivine and wadsleyite plus lesser amounts of garnet and clinopyroxene extending over a depth 20 km in a hydrous system

  18. 77 FR 18705 - Discontinuance of Form CO in Registration Practices

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-28

    ... Copyright Office 37 CFR Parts 201 and 202 Discontinuance of Form CO in Registration Practices AGENCY... amending its regulations in order to discontinue use of the Form CO application as an option for applying.... The removal of Form CO leaves applicants a choice of filing an application for...

  19. 27 CFR 31.138 - Discontinuance of business.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Discontinuance of business. 31.138 Section 31.138 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU... § 31.138 Discontinuance of business. A dealer going out of business must register that event within...

  20. 20 CFR 658.501 - Basis for discontinuation of services.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... (CONTINUED) ADMINISTRATIVE PROVISIONS GOVERNING THE JOB SERVICE SYSTEM Discontinuation of Services to Employers by the Job Service System § 658.501 Basis for discontinuation of services. (a) The State agency... alter or withdraw job orders containing specifications which are contrary to employment-related laws;...

  1. 20 CFR 658.501 - Basis for discontinuation of services.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... ADMINISTRATIVE PROVISIONS GOVERNING THE JOB SERVICE SYSTEM Discontinuation of Services to Employers by the Job... procedures for discontinuation of services to employers who: (1) Submit and refuse to alter or withdraw job orders containing specifications which are contrary to employment-related laws; (2) Submit job orders...

  2. 20 CFR 658.501 - Basis for discontinuation of services.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... (CONTINUED) ADMINISTRATIVE PROVISIONS GOVERNING THE JOB SERVICE SYSTEM Discontinuation of Services to Employers by the Job Service System § 658.501 Basis for discontinuation of services. (a) The State agency... alter or withdraw job orders containing specifications which are contrary to employment-related laws;...

  3. Discontinuities in Early Development of the Understanding of Physical Causality

    ERIC Educational Resources Information Center

    Aschersleben, Gisa; Henning, Anne; Daum, Moritz M.

    2013-01-01

    Research on early physical reasoning has shown surprising discontinuities in developmental trajectories. Infants possess some skills that seem to disappear and then re-emerge in childhood. It has been suggested that prediction skills required in search tasks might cause these discontinuities (Keen, 2003). We tested 3.5- to 5-year-olds'…

  4. EVALUATING DISCONTINUITIES IN COMPLEX SYSTEMS: TOWARD QUANTITATIVE MEASURE OF RESILIENCE

    EPA Science Inventory

    The textural discontinuity hypothesis (TDH) is based on the observation that animal body mass distributions exhibit discontinuities that may reflect the texture of the landscape available for exploitation. This idea has been extended to other complex systems, hinting that the ide...

  5. 27 CFR 21.3 - Stocks of discontinued formulas.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Stocks of discontinued..., DEPARTMENT OF THE TREASURY LIQUORS FORMULAS FOR DENATURED ALCOHOL AND RUM General Provisions § 21.3 Stocks of discontinued formulas. Denaturers, or specially denatured spirits dealers or users, having on hand stocks...

  6. 27 CFR 21.3 - Stocks of discontinued formulas.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2013-04-01 2013-04-01 false Stocks of discontinued..., DEPARTMENT OF THE TREASURY ALCOHOL FORMULAS FOR DENATURED ALCOHOL AND RUM General Provisions § 21.3 Stocks of discontinued formulas. Denaturers, or specially denatured spirits dealers or users, having on hand stocks...

  7. 27 CFR 21.3 - Stocks of discontinued formulas.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Stocks of discontinued..., DEPARTMENT OF THE TREASURY LIQUORS FORMULAS FOR DENATURED ALCOHOL AND RUM General Provisions § 21.3 Stocks of discontinued formulas. Denaturers, or specially denatured spirits dealers or users, having on hand stocks...

  8. 27 CFR 21.3 - Stocks of discontinued formulas.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2014-04-01 2014-04-01 false Stocks of discontinued..., DEPARTMENT OF THE TREASURY ALCOHOL FORMULAS FOR DENATURED ALCOHOL AND RUM General Provisions § 21.3 Stocks of discontinued formulas. Denaturers, or specially denatured spirits dealers or users, having on hand stocks...

  9. 27 CFR 21.3 - Stocks of discontinued formulas.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2012-04-01 2012-04-01 false Stocks of discontinued..., DEPARTMENT OF THE TREASURY LIQUORS FORMULAS FOR DENATURED ALCOHOL AND RUM General Provisions § 21.3 Stocks of discontinued formulas. Denaturers, or specially denatured spirits dealers or users, having on hand stocks...

  10. 47 CFR 90.157 - Discontinuance of station operation.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Discontinuance of station operation. 90.157 Section 90.157 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Applications and Authorizations § 90.157 Discontinuance...

  11. 47 CFR 90.157 - Discontinuance of station operation.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Discontinuance of station operation. 90.157 Section 90.157 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Applications and Authorizations § 90.157 Discontinuance...

  12. 27 CFR 72.37 - Discontinuance of administrative proceedings.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 2 2011-04-01 2011-04-01 false Discontinuance of administrative proceedings. 72.37 Section 72.37 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... to effect such sale or retention will be discontinued....

  13. 27 CFR 72.37 - Discontinuance of administrative proceedings.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 2 2012-04-01 2011-04-01 true Discontinuance of administrative proceedings. 72.37 Section 72.37 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... to effect such sale or retention will be discontinued....

  14. 27 CFR 72.37 - Discontinuance of administrative proceedings.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 2 2013-04-01 2013-04-01 false Discontinuance of administrative proceedings. 72.37 Section 72.37 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... to effect such sale or retention will be discontinued....

  15. 27 CFR 72.37 - Discontinuance of administrative proceedings.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 2 2010-04-01 2010-04-01 false Discontinuance of administrative proceedings. 72.37 Section 72.37 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... to effect such sale or retention will be discontinued....

  16. 27 CFR 72.37 - Discontinuance of administrative proceedings.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 2 2014-04-01 2014-04-01 false Discontinuance of administrative proceedings. 72.37 Section 72.37 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... to effect such sale or retention will be discontinued....

  17. 27 CFR 20.68 - Notice of permanent discontinuance.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Notice of permanent discontinuance. 20.68 Section 20.68 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE... Qualification of Dealers and Users Permanent Discontinuance of Business § 20.68 Notice of...

  18. 19 CFR 142.25 - Discontinuance of immediate delivery privileges.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 19 Customs Duties 2 2011-04-01 2011-04-01 false Discontinuance of immediate delivery privileges... SECURITY; DEPARTMENT OF THE TREASURY (CONTINUED) ENTRY PROCESS Special Permit for Immediate Delivery § 142.25 Discontinuance of immediate delivery privileges. (a) Authority of port director. The port...

  19. 19 CFR 142.25 - Discontinuance of immediate delivery privileges.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 2 2010-04-01 2010-04-01 false Discontinuance of immediate delivery privileges. 142.25 Section 142.25 Customs Duties U.S. CUSTOMS AND BORDER PROTECTION, DEPARTMENT OF HOMELAND SECURITY; DEPARTMENT OF THE TREASURY (CONTINUED) ENTRY PROCESS Special Permit for Immediate Delivery § 142.25 Discontinuance of immediate...

  20. 14 CFR 170.25 - LORAN-C discontinuance criteria.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 3 2011-01-01 2011-01-01 false LORAN-C discontinuance criteria. 170.25... SERVICES AND NAVIGATIONAL FACILITIES LORAN-C § 170.25 LORAN-C discontinuance criteria. A LORAN-C... costs (PVCM) of the LORAN-C approach exceed the present value of its remaining life-cycle benefits...

  1. 14 CFR 170.25 - LORAN-C discontinuance criteria.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false LORAN-C discontinuance criteria. 170.25... SERVICES AND NAVIGATIONAL FACILITIES LORAN-C § 170.25 LORAN-C discontinuance criteria. A LORAN-C... costs (PVCM) of the LORAN-C approach exceed the present value of its remaining life-cycle benefits...

  2. 14 CFR 170.25 - LORAN-C discontinuance criteria.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false LORAN-C discontinuance criteria. 170.25... SERVICES AND NAVIGATIONAL FACILITIES LORAN-C § 170.25 LORAN-C discontinuance criteria. A LORAN-C... costs (PVCM) of the LORAN-C approach exceed the present value of its remaining life-cycle benefits...

  3. 14 CFR 170.25 - LORAN-C discontinuance criteria.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false LORAN-C discontinuance criteria. 170.25... SERVICES AND NAVIGATIONAL FACILITIES LORAN-C § 170.25 LORAN-C discontinuance criteria. A LORAN-C... costs (PVCM) of the LORAN-C approach exceed the present value of its remaining life-cycle benefits...

  4. Auditory discontinuities interact with categorization: Implications for speech perception

    NASA Astrophysics Data System (ADS)

    Holt, Lori L.; Lotto, Andrew J.; Diehl, Randy L.

    2004-09-01

    Behavioral experiments with infants, adults, and nonhuman animals converge with neurophysiological findings to suggest that there is a discontinuity in auditory processing of stimulus components differing in onset time by about 20 ms. This discontinuity has been implicated as a basis for boundaries between speech categories distinguished by voice onset time (VOT). Here, it is investigated how this discontinuity interacts with the learning of novel perceptual categories. Adult listeners were trained to categorize nonspeech stimuli that mimicked certain temporal properties of VOT stimuli. One group of listeners learned categories with a boundary coincident with the perceptual discontinuity. Another group learned categories defined such that the perceptual discontinuity fell within a category. Listeners in the latter group required significantly more experience to reach criterion categorization performance. Evidence of interactions between the perceptual discontinuity and the learned categories extended to generalization tests as well. It has been hypothesized that languages make use of perceptual discontinuities to promote distinctiveness among sounds within a language inventory. The present data suggest that discontinuities interact with category learning. As such, ``learnability'' may play a predictive role in selection of language sound inventories.

  5. 25 CFR 175.21 - Discontinuance of service.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 25 Indians 1 2011-04-01 2011-04-01 false Discontinuance of service. 175.21 Section 175.21 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER INDIAN ELECTRIC POWER UTILITIES Utility Service Administration § 175.21 Discontinuance of service. Failure of customer(s) to comply...

  6. 25 CFR 175.21 - Discontinuance of service.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 25 Indians 1 2012-04-01 2011-04-01 true Discontinuance of service. 175.21 Section 175.21 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER INDIAN ELECTRIC POWER UTILITIES Utility Service Administration § 175.21 Discontinuance of service. Failure of customer(s) to comply...

  7. 25 CFR 175.21 - Discontinuance of service.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 25 Indians 1 2010-04-01 2010-04-01 false Discontinuance of service. 175.21 Section 175.21 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER INDIAN ELECTRIC POWER UTILITIES Utility Service Administration § 175.21 Discontinuance of service. Failure of customer(s) to comply...

  8. 25 CFR 175.21 - Discontinuance of service.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 25 Indians 1 2013-04-01 2013-04-01 false Discontinuance of service. 175.21 Section 175.21 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER INDIAN ELECTRIC POWER UTILITIES Utility Service Administration § 175.21 Discontinuance of service. Failure of customer(s) to comply...

  9. 25 CFR 175.21 - Discontinuance of service.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 25 Indians 1 2014-04-01 2014-04-01 false Discontinuance of service. 175.21 Section 175.21 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR LAND AND WATER INDIAN ELECTRIC POWER UTILITIES Utility Service Administration § 175.21 Discontinuance of service. Failure of customer(s) to comply...

  10. 47 CFR 90.157 - Discontinuance of station operation.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Discontinuance of station operation. 90.157 Section 90.157 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Applications and Authorizations § 90.157 Discontinuance...

  11. 47 CFR 90.157 - Discontinuance of station operation.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Discontinuance of station operation. 90.157 Section 90.157 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Applications and Authorizations § 90.157 Discontinuance...

  12. 47 CFR 90.157 - Discontinuance of station operation.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Discontinuance of station operation. 90.157 Section 90.157 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Applications and Authorizations § 90.157 Discontinuance...

  13. 27 CFR 31.138 - Discontinuance of business.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2012-04-01 2012-04-01 false Discontinuance of business. 31.138 Section 31.138 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU... § 31.138 Discontinuance of business. A dealer going out of business must register that event within...

  14. Adaptive Discontinuous Evolution Galerkin Method for Dry Atmospheric Flow

    DTIC Science & Technology

    2013-04-02

    standard one-dimensional approximate Riemann solver used for the flux integration demonstrate better stability, accuracy as well as reliability of the...discontinuous evolution Galerkin method for dry atmospheric convection. Comparisons with the standard one-dimensional approximate Riemann solver used...instead of a standard one- dimensional approximate Riemann solver, the flux integration within the discontinuous Galerkin method is now realized by

  15. Discontinuous deformation analysis of particulate media

    NASA Astrophysics Data System (ADS)

    Thomas, Patricia Ann

    Many geotechnical engineering problems involve the localization of deformations along distinct shear planes, such as the response of a layer of soil to displacement along an underlying bedrock fault. Understanding the process of deformation localization and the propagation of shear zones to the surface would aid in the siting of structures near faults, and in developing mitigation techniques. Discrete numerical methods are especially suited to this type of problem, because the discontinuous nature of soil and the kinematics of soil deformation are modeled directly. This research involves the development and validation of Discontinuous Deformation Analysis (DDA), a type of discrete numerical method, as a tool capable of modeling realistic soil behavior, thus providing the foundation for its application to complex soil mechanics problems, such as earthquake fault rupture propagation. First, a review of the two primary types of discrete numerical modeling, the Distinct Element Method (DEM) and DDA is presented along with a discussion of the key aspects of modeling particulate materials with these methods. Next, several extensions to the numerical program Discontinuous Deformation Analysis for Disks (DDAD), implemented during the process of developing DDAD as a tool for modeling particulate materials, were implemented. A flexible, stress-controlled boundary was incorporated, allows simulation of geotechnical biaxial shear tests that are commonly performed on specimens of granular soils. Using this boundary, the stress-strain and volumetric responses of simulated assemblies of particles were investigated. A new type of particle, the disk cluster, was developed and implemented. A disk cluster is a group of circular disks permanently attached to form a single particle. Disk clusters more accurately represent the nonspherical shape of particulate materials, minimize the problem of excessive rotation that occurs with perfectly circular elements, and retain the simplicity of

  16. Elastic properties of plagioclase aggregates and seismic velocities in the moon

    NASA Technical Reports Server (NTRS)

    Wang, H.; Todd, T.; Richter, D.; Simmons, G.

    1973-01-01

    The compressional velocities of Apollo 16 gabbroic anorthosites in which the cracks have been closed match the seismic velocity of 7 km/sec in the 25 to 65 km depth region of the moon beneath the Imbrium Basin. The intrinsic velocities of plagioclase aggregates indicate that a velocity of 7 km/sec in a highly calcic gabbroic anorthosite is consistent only with a very small pyroxene component. Because mare basalts and gabbroic-anorthosites both have intrinsic velocities of 7 km/sec, the laboratory velocity data do not require a compositional change from basalt to anorthosite at the 25 km discontinuity. The laboratory velocity data only imply that the 25 km seismic discontinuity is one of microcrack density. The physical rather than the chemical or mineralogical state is constrained.

  17. Seismic structure of the northwestern Japan convergent margin: A synthesis

    NASA Astrophysics Data System (ADS)

    Hasegawa, Akira; Horiuchi, Shigeki; Umino, Norihito

    1994-11-01

    Many studies recently made on the basis of seismic observations have revealed a detailed structure of the crust and the upper mantle beneath the northeastern Japan arc and its relationship to seismic and volcanic activity. Spatial distributions of the depths to the Conrad and the Moho discontinuities, estimated from shallow earthquake data and seismic explosion data, show that both discontinuities are deep in the middle of the land area and shallow toward the coastlines of the Japan Sea and the Pacific Ocean. The Pn velocity has a lateral variation; it is as low as approximately 7.5 km/s beneath the land area, while that beneath the Japan Sea and the Pacific Ocean is 8.0-8.2 km/s. It changes abruptly at the transition zones, which are located along the coastlines. Precise structure and location of the subducted Pacific plate beneath the land area is inferred from converted or reflected seismic waves at the top or bottom of the plate. The Pacific plate is composed of a thin (approximately 5 km) low-velocity upper layer and a thick high-velocity lower layer, its total thickness being 80-90 km. The upper plane seismicity of the double seismic zone is confined to the thin low-velocity upper layer, which probably corresponds to the subducted former oceanic crust. The lower plane seismicity lies at the middle of the high-velocity lower layer, and the lower half of the plate below it is incapable of generating earthquakes. The shallower portion of the upper surface of the plate beneath the Pacific Ocean, along which major seismicity with low-angle thrust faultings is actually occurring, is also located by seismic observations on land and in the sea. The Pacific plate subducts at an extremely low angle of approximately 5 deg for the first approximately 25-km depth, and then the dip steepens rather abruptly to approximately 30 deg. Normal-fault type events at the top of the plate have not been detected in the portion where the downward-bending is the largest, but have been

  18. The seismic analyzer: interpreting and illustrating 2D seismic data.

    PubMed

    Patel, Daniel; Giertsen, Christopher; Thurmond, John; Gjelberg, John; Gröller, M Eduard

    2008-01-01

    We present a toolbox for quickly interpreting and illustrating 2D slices of seismic volumetric reflection data. Searching for oil and gas involves creating a structural overview of seismic reflection data to identify hydrocarbon reservoirs. We improve the search of seismic structures by precalculating the horizon structures of the seismic data prior to interpretation. We improve the annotation of seismic structures by applying novel illustrative rendering algorithms tailored to seismic data, such as deformed texturing and line and texture transfer functions. The illustrative rendering results in multi-attribute and scale invariant visualizations where features are represented clearly in both highly zoomed in and zoomed out views. Thumbnail views in combination with interactive appearance control allows for a quick overview of the data before detailed interpretation takes place. These techniques help reduce the work of seismic illustrators and interpreters.

  19. Mobile seismic exploration

    NASA Astrophysics Data System (ADS)

    Dräbenstedt, A.; Cao, X.; Polom, U.; Pätzold, F.; Zeller, T.; Hecker, P.; Seyfried, V.; Rembe, C.

    2016-06-01

    Laser-Doppler-Vibrometry (LDV) is an established technique to measure vibrations in technical systems with picometer vibration-amplitude resolution. Especially good sensitivity and resolution can be achieved at an infrared wavelength of 1550 nm. High-resolution vibration measurements are possible over more than 100 m distance. This advancement of the LDV technique enables new applications. The detection of seismic waves is an application which has not been investigated so far because seismic waves outside laboratory scales are usually analyzed at low frequencies between approximately 1 Hz and 250 Hz and require velocity resolutions in the range below 1 nm/s/√Hz. Thermal displacements and air turbulence have critical influences to LDV measurements at this low-frequency range leading to noise levels of several 100 nm/√Hz. Commonly seismic waves are measured with highly sensitive inertial sensors (geophones or Micro Electro-Mechanical Sensors (MEMS)). Approaching a laser geophone based on LDV technique is the topic of this paper. We have assembled an actively vibration-isolated optical table in a minivan which provides a hole in its underbody. The laser-beam of an infrared LDV assembled on the optical table impinges the ground below the car through the hole. A reference geophone has detected remaining vibrations on the table. We present the results from the first successful experimental demonstration of contactless detection of seismic waves from a movable vehicle with a LDV as laser geophone.

  20. Hanford Seismic Network

    SciTech Connect

    Reidel, S.P.; Hartshorn, D.C.

    1997-05-01

    This report describes the Hanford Seismic Network. The network consists of two instrument arrays: seismometers and strong motion accelerometers. The seismometers determine the location and magnitude of earthquakes, and the strong motion accelerometers determine ground motion. Together these instruments arrays comply with the intent of DOE Order 5480.20, Natural Phenomena Hazards Mitigation.

  1. Nonstructural seismic restraint guidelines

    SciTech Connect

    Butler, D.M.; Czapinski, R.H.; Firneno, M.J.; Feemster, H.C.; Fornaciari, N.R.; Hillaire, R.G.; Kinzel, R.L.; Kirk, D.; McMahon, T.T.

    1993-08-01

    The Nonstructural Seismic Restraint Guidelines provide general information about how to secure or restrain items (such as material, equipment, furniture, and tools) in order to prevent injury and property, environmental, or programmatic damage during or following an earthquake. All SNL sites may experience earthquakes of magnitude 6.0 or higher on the Richter scale. Therefore, these guidelines are written for all SNL sites.

  2. Airborne electromagnetic imaging of discontinuous permafrost

    NASA Astrophysics Data System (ADS)

    Minsley, Burke J.; Abraham, Jared D.; Smith, Bruce D.; Cannia, James C.; Voss, Clifford I.; Jorgenson, M. Torre; Walvoord, Michelle A.; Wylie, Bruce K.; Anderson, Lesleigh; Ball, Lyndsay B.; Deszcz-Pan, Maryla; Wellman, Tristan P.; Ager, Thomas A.

    2012-01-01

    The evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes, climate, and ecosystems. Permafrost thawing has been linked to changes in wetland and lake areas, alteration of the groundwater contribution to streamflow, carbon release, and increased fire frequency. But detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma. Here, we present the results of a pioneering ˜1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past ˜4 million years and the configuration of permafrost to depths of ˜100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surface - groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past ˜1,000 years. This work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic, climatic, and ecological processes, and has significant implications for the stewardship of Arctic environments.

  3. Dynamics of Discontinuous Shear Thickening suspensions

    NASA Astrophysics Data System (ADS)

    Brown, Eric

    2015-03-01

    Concentrated suspensions of hard particles such as cornstarch in water exhibit Discontinuous Shear Thickening, in which an increasing shear rate drives a transition from liquid- to solid-like mechanical behavior. In steady-state shear this phenomena is a result of a dynamic version of jamming in which forces are transmitted along particle contact networks that span to system boundaries and repeatedly form and break up. Several dynamic phenomena observed in such suspensions have long been assumed to be a consequence of this shear thickening, but cannot be explained as a direct result of shear thickening; for example a uniquely strong impact response which allows a person to run on the fluid surface. We perform experiments in which a concentrated suspension is subjected to transient impact. We find that the strong impact response is due a short-lived jammed contact network spanning to the boundaries and a delay time required for this dynamically jammed region to propagate to the boundary. The resulting ability of this system-spanning solid-like region to support loads can explain the ability of a person to run on the surface of these fluids. This delay before a solid-like response may also explain several other dynamic phenomena observed in these fluids.

  4. Polar constellations design for discontinuous coverage

    NASA Astrophysics Data System (ADS)

    Sarno, Salvatore; Graziano, Maria Daniela; D'Errico, Marco

    2016-10-01

    A novel constellation design method is developed for discontinuous coverage of the globe and polar caps. It integrates and extends the applicability of the coverage regions and mitigates the limitations of the existing techniques based on streets-of-coverage (SOC) theory. In particular, the visibility conditions of the targets are mapped in the (Ω, u)-domain to identify the number of satellites per plane and the distance between successive orbits, whereas the planes are arranged around the equator exploiting satellites both in ascending and descending phase. The proposed approach is applied to design potential space segments in polar LEO supporting the existing maritime surveillance services over the globe and on the future polar routes. Results show they require a smaller total number of satellites with respect to the SOC-based configurations for revisit times less than one hour and wide range of swaths. In details, it is observed a reduction between 6% and 22% for global coverage and between 24% and 33% for the coverage of polar caps.

  5. Discontinuous Galerkin Methods for Neutrino Radiation Transport

    NASA Astrophysics Data System (ADS)

    Endeve, Eirik; Hauck, Cory; Xing, Yulong; Mezzacappa, Anthony

    2015-04-01

    We are developing new computational methods for simulation of neutrino transport in core-collapse supernovae, which is challenging since neutrinos evolve from being diffusive in the proto-neutron star to nearly free streaming in the critical neutrino heating region. To this end, we consider conservative formulations of the Boltzmann equation, and aim to develop robust, high-order accurate methods. Runge-Kutta discontinuous Galerkin (DG) methods, offer several attractive properties, including (i) high-order accuracy on a compact stencil and (ii) correct asymptotic behavior in the diffusion limit. We have recently developed a new DG method for the advection part for the transport solve, which is high-order accurate and strictly preserves the physical bounds of the distribution function; i.e., f ∈ [ 0 , 1 ] . We summarize the main ingredients of our bound-preserving DG method and discuss ongoing work to include neutrino-matter interactions in the scheme. Research sponsored in part by Oak Ridge National Laboratory, managed by UT-Battelle, LLC for the U. S. Department of Energy

  6. Stability of Dynamical Systems with Discontinuous Motions:

    NASA Astrophysics Data System (ADS)

    Michel, Anthony N.; Hou, Ling

    In this paper we present a stability theory for discontinuous dynamical systems (DDS): continuous-time systems whose motions are not necessarily continuous with respect to time. We show that this theory is not only applicable in the analysis of DDS, but also in the analysis of continuous dynamical systems (continuous-time systems whose motions are continuous with respect to time), discrete-time dynamical systems (systems whose motions are defined at discrete points in time) and hybrid dynamical systems (HDS) (systems whose descriptions involve simultaneously continuous-time and discrete-time). We show that the stability results for DDS are in general less conservative than the corresponding well-known classical Lyapunov results for continuous dynamical systems and discrete-time dynamical systems. Although the DDS stability results are applicable to general dynamical systems defined on metric spaces (divorced from any kind of description by differential equations, or any other kinds of equations), we confine ourselves to finite-dimensional dynamical systems defined by ordinary differential equations and difference equations, to make this paper as widely accessible as possible. We present only sample results, namely, results for uniform asymptotic stability in the large.

  7. Continuous and Discontinuous RNA Synthesis in Coronaviruses.

    PubMed

    Sola, Isabel; Almazán, Fernando; Zúñiga, Sonia; Enjuanes, Luis

    2015-11-01

    Replication of the coronavirus genome requires continuous RNA synthesis, whereas transcription is a discontinuous process unique among RNA viruses. Transcription includes a template switch during the synthesis of subgenomic negative-strand RNAs to add a copy of the leader sequence. Coronavirus transcription is regulated by multiple factors, including the extent of base-pairing between transcription-regulating sequences of positive and negative polarity, viral and cell protein-RNA binding, and high-order RNA-RNA interactions. Coronavirus RNA synthesis is performed by a replication-transcription complex that includes viral and cell proteins that recognize cis-acting RNA elements mainly located in the highly structured 5' and 3' untranslated regions. In addition to many viral nonstructural proteins, the presence of cell nuclear proteins and the viral nucleocapsid protein increases virus amplification efficacy. Coronavirus RNA synthesis is connected with the formation of double-membrane vesicles and convoluted membranes. Coronaviruses encode proofreading machinery, unique in the RNA virus world, to ensure the maintenance of their large genome size.

  8. Insects breathe discontinuously to avoid oxygen toxicity.

    PubMed

    Hetz, Stefan K; Bradley, Timothy J

    2005-02-03

    The respiratory organs of terrestrial insects consist of tracheal tubes with external spiracular valves that control gas exchange. Despite their relatively high metabolic rate, many insects have highly discontinuous patterns of gas exchange, including long periods when the spiracles are fully closed. Two explanations have previously been put forward to explain this behaviour: first, that this pattern serves to reduce respiratory water loss, and second, that the pattern may have initially evolved in underground insects as a way of dealing with hypoxic or hypercapnic conditions. Here we propose a third possible explanation based on the idea that oxygen is necessary for oxidative metabolism but also acts as a toxic chemical that can cause oxidative damage of tissues even at relatively low concentrations. At physiologically normal partial pressures of CO2, the rate of CO2 diffusion out of the insect respiratory system is slower than the rate of O2 entry; this leads to a build-up of intratracheal CO2. The spiracles must therefore be opened at intervals to rid the insect of accumulated CO2, a process that exposes the tissues to dangerously high levels of O2. We suggest that the cyclical pattern of open and closed spiracles observed in resting insects is a necessary consequence of the need to rid the respiratory system of accumulated CO2, followed by the need to reduce oxygen toxicity.

  9. Adaptive Discontinuous Galerkin Approximation to Richards' Equation

    NASA Astrophysics Data System (ADS)

    Li, H.; Farthing, M. W.; Miller, C. T.

    2006-12-01

    Due to the occurrence of large gradients in fluid pressure as a function of space and time resulting from nonlinearities in closure relations, numerical solutions to Richards' equations are notoriously difficult for certain media properties and auxiliary conditions that occur routinely in describing physical systems of interest. These difficulties have motivated a substantial amount of work aimed at improving numerical approximations to this physically important and mathematically rich model. In this work, we build upon recent advances in temporal and spatial discretization methods by developing spatially and temporally adaptive solution approaches based upon the local discontinuous Galerkin method in space and a higher order backward difference method in time. Spatial step-size adaption, h adaption, approaches are evaluated and a so-called hp-adaption strategy is considered as well, which adjusts both the step size and the order of the approximation. Solution algorithms are advanced and performance is evaluated. The spatially and temporally adaptive approaches are shown to be robust and offer significant increases in computational efficiency compared to similar state-of-the-art methods that adapt in time alone. In addition, we extend the proposed methods to two dimensions and provide preliminary numerical results.

  10. Capillary surface discontinuities above reentrant corners

    NASA Technical Reports Server (NTRS)

    Korevaar, H. J.

    1982-01-01

    A particular configuration of a vertical capillary tube for which S is the equilibrium interface between two fluids in the presence of a downward pointing gravitational field was investigated. S is the graph a function u whose domain is the (horizontal) cross section gamma of the tube. The mean curvature of S is proportional to its height above a fixed reference plane and lambda is a prescribed constant and may be taken between zero and pi/2. Domains gamma for which us is a bounded function but does not extend continuously to d gamma are sought. Simple domains are found and the behavior of u in those domains is studied. An important comparison principle that has been used in the literature to derive many of the results in capillarity is reviewed. It allows one to deduce the approximate shape of a capillary surface by constructing comparison surfaces with mean curvature and contact angle close to those of the (unknown) solution surface. In the context of nonparametric problems the comparison principle leads to height estimates above and below for the function u. An example from the literature where these height estimates have been used successfully is described. The promised domains for which the bounded u does not extend continuously to the boundary are constructed. The point on the boundary at which u has a jump discontinuity will be the vertext of a re-entrant corner having any interior angle theta pi. Using the comparison principle the behavior of u near this point is studied.

  11. Nodal discontinuous Galerkin methods on graphics processors

    NASA Astrophysics Data System (ADS)

    Klöckner, A.; Warburton, T.; Bridge, J.; Hesthaven, J. S.

    2009-11-01

    Discontinuous Galerkin (DG) methods for the numerical solution of partial differential equations have enjoyed considerable success because they are both flexible and robust: They allow arbitrary unstructured geometries and easy control of accuracy without compromising simulation stability. Lately, another property of DG has been growing in importance: The majority of a DG operator is applied in an element-local way, with weak penalty-based element-to-element coupling. The resulting locality in memory access is one of the factors that enables DG to run on off-the-shelf, massively parallel graphics processors (GPUs). In addition, DG's high-order nature lets it require fewer data points per represented wavelength and hence fewer memory accesses, in exchange for higher arithmetic intensity. Both of these factors work significantly in favor of a GPU implementation of DG. Using a single US$400 Nvidia GTX 280 GPU, we accelerate a solver for Maxwell's equations on a general 3D unstructured grid by a factor of around 50 relative to a serial computation on a current-generation CPU. In many cases, our algorithms exhibit full use of the device's available memory bandwidth. Example computations achieve and surpass 200 gigaflops/s of net application-level floating point work. In this article, we describe and derive the techniques used to reach this level of performance. In addition, we present comprehensive data on the accuracy and runtime behavior of the method.

  12. Airborne electromagnetic imaging of discontinuous permafrost

    USGS Publications Warehouse

    Minsley, B.J.; Abraham, J.D.; Smith, B.D.; Cannia, J.C.; Voss, C.I.; Jorgenson, M.T.; Walvoord, M.A.; Wylie, B.K.; Anderson, L.; Ball, L.B.; Deszcz-Pan, M.; Wellman, T.P.; Ager, T.A.

    2012-01-01

    The evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes, climate, and ecosystems. Permafrost thawing has been linked to changes in wetland and lake areas, alteration of the groundwater contribution to streamflow, carbon release, and increased fire frequency. But detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma. Here, we present the results of a pioneering ∼1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past ∼4 million years and the configuration of permafrost to depths of ∼100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surface – groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past ∼1,000 years. This work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic, climatic, and ecological processes, and has significant implications for the stewardship of Arctic environments.

  13. D″ shear velocity heterogeneity, anisotropy and discontinuity structure beneath the Caribbean and Central America

    NASA Astrophysics Data System (ADS)

    Garnero, Edward J.; Lay, Thorne

    2003-11-01

    The D″ region in the lowermost mantle beneath the Caribbean and Central America is investigated using shear waves from South American earthquakes recorded by seismic stations in North America. We present a large-scale, composite study of volumetric shear velocity heterogeneity, anisotropy, and the possible presence of a D″ discontinuity in the region. Our data set includes: 328 S( Sdiff)- SKS differential travel times, 300 ScS-S differential travel times, 125 S( Sdiff) and 120 ScS shear wave splitting measurements, and 297 seismograms inspected for Scd, the seismic phase refracted from a high-velocity D″ layer. Broadband digital data are augmented by high-quality digitized analog WWSSN data, providing extensive path coverage in our study area. In all, data from 61 events are utilized. In some cases, a given seismogram can be used for velocity heterogeneity, anisotropy, and discontinuity analyses. Significant mid-mantle structure, possibly associated with the ancient subducted Farallon slab, affects shear wave travel times and must be corrected for to prevent erroneous mapping of D″ shear velocity. All differential times are corrected for contributions from aspherical mantle structure above D″ using a high-resolution tomography model. Travel time analyses demonstrate the presence of pervasive high velocities in D″, with the highest velocities localized to a region beneath Central America, approximately 500-700 km in lateral dimension. Short wavelength variability overprints this general high-velocity background. Corrections are also made for lithospheric anisotropy beneath the receivers. Shear wave splitting analyses of the corrected waveforms reveal D″ anisotropy throughout the study area, with a general correlation with heterogeneity strength. Evidence for Scd arrivals is pervasive across the study area, consistent with earlier work, but there are a few localized regions (100-200 km) lacking clear Scd arrivals, which indicates heterogeneity in the

  14. Upper Mantle Qβ Structure beneath the East Pacific Rise from Shear Wave Triplicated Waveforms

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Grand, S. P.; Tang, Y.

    2012-12-01

    A consensus on how mantle flows in the transition zone region of the Earth has not been reached. Some propose a boundary to flow while others prefer a model with essentially no boundary to flow across the upper-lower mantle boundary. It is possible that an intermediate situation exists where flow is intermittent across the boundary. A situation where mantle flow is inhibited near the 660 km discontinuity will result in a thermal boundary layer at that depth and thus high temperature gradients. Such a high temperature gradient zone is difficult to detect using seismic velocities but may be detectable through measurements of Q since attenuation is highly sensitive to temperature. Models of seismic attenuation as a function of depth through the mantle are difficult to determine. Normal mode and surface waves have been used but use long wavelength waves and thus can only resolve broad scale structure. Body waves such as multiple ScS phases have been used for regional mantle attenuation studies but lack vertical resolution. S waves recorded from 15 to 28 degrees distance turn within the upper mantle and due to discontinuities near 410 and 660 km depth are triplicated with multiple arrivals sampling different depths arriving at the same station. The triplicated arrivals can also be seen in SS waves at double the distance and SSS waves at triple the distance …. Here we model dense profiles of broadband S, SS, SSS and SSSS waves recorded mainly by US-Array, Canadian seismic network and other surrounding stations in the North America. Earthquakes along the East Pacific Rise were recorded with the wave paths underneath oceanic crust younger than 15Ma. The distance range covered is from 15 to 105 degrees, consequently triplicated body waves sample the transition zone from S to SSSS. By modeling the relative amplitudes of the triplicated waveforms a model of Qβ (.01-.1 Hz) as a function of depth is determined focused on the mantle transition zone.

  15. Seismic signature of crustal magma and fluid from deep seismic sounding data across Tengchong volcanic area

    NASA Astrophysics Data System (ADS)

    Bai, Z. M.; Zhang, Z. Z.; Wang, C. Y.; Klemperer, S. L.

    2012-04-01

    . There are typical tectonic and deep origin mechanisms for the moderate-strong earthquakes nearby SP Tuantian, and precaution should be added on this area in case of the potential earthquake. Our fusion image also clearly revealed that there exist two remarkable positions on the Moho discontinuity through which the heat from the upper mantle was transmitted upward, and this is attributed to the widely distributed hot material within the crust and upper mantle. We acknowledge the financial support of the Ministry of Land and Resources of China (SinoProbe-02-02), and the National Nature Science Foundation of China (No. 41074033 and No. 40830315). Key Words: Seismic Signature, Magma, Tengchong Volcanic Area, Deep Seismic Sounding, Seismic Attribute Fusion Li, Chang, van der Hilst, D., Meltzer, A.S., Engdahl, E.R., 2008. Subduction of the Indian lithosphere beneath the Tibetan Plateau and Burma. Earth Planet. Sci. Lett. 274. doi:10.1016/j.epsl.2008.07.016. Lebedev, S., van der Hilst, R.D., 2008. Global upper-mantle tomography with the automated multi-mode surface and S waveforms. Geophys. J. Int. 173 (2), 505-518. Wang C.Y. and Huangfu G.. 2004. Crustal structure in Tengchong Volcano-Geothermal Area, western Yunnan, China. Tectonophysics, 380: 69-87.

  16. High Voltage Seismic Generator

    NASA Astrophysics Data System (ADS)

    Bogacz, Adrian; Pala, Damian; Knafel, Marcin

    2015-04-01

    This contribution describes the preliminary result of annual cooperation of three student research groups from AGH UST in Krakow, Poland. The aim of this cooperation was to develop and construct a high voltage seismic wave generator. Constructed device uses a high-energy electrical discharge to generate seismic wave in ground. This type of device can be applied in several different methods of seismic measurement, but because of its limited power it is mainly dedicated for engineering geophysics. The source operates on a basic physical principles. The energy is stored in capacitor bank, which is charged by two stage low to high voltage converter. Stored energy is then released in very short time through high voltage thyristor in spark gap. The whole appliance is powered from li-ion battery and controlled by ATmega microcontroller. It is possible to construct larger and more powerful device. In this contribution the structure of device with technical specifications is resented. As a part of the investigation the prototype was built and series of experiments conducted. System parameter was measured, on this basis specification of elements for the final device were chosen. First stage of the project was successful. It was possible to efficiently generate seismic waves with constructed device. Then the field test was conducted. Spark gap wasplaced in shallowborehole(0.5 m) filled with salt water. Geophones were placed on the ground in straight line. The comparison of signal registered with hammer source and sparker source was made. The results of the test measurements are presented and discussed. Analysis of the collected data shows that characteristic of generated seismic signal is very promising, thus confirms possibility of practical application of the new high voltage generator. The biggest advantage of presented device after signal characteristics is its size which is 0.5 x 0.25 x 0.2 m and weight approximately 7 kg. This features with small li-ion battery makes

  17. Long wavelength mantle transition zone structure beneath Europe as seen by Pds receiver functions

    NASA Astrophysics Data System (ADS)

    Cottaar, Sanne; Deuss, Arwen

    2015-04-01

    The mantle is delineated by seismic discontinuities between 300 and 800 km depth. Variations in topography, width and occurrence of the discontinuities indicate lateral variations in temperature, composition and water content, as these variations influence the mantle phase transitions. Seismic studies of the conversions of pressure to shear waves (Pds phases) are an important tool to observe lateral variations in these discontinuities. Here we collect a Pds data set across all European seismic stations since 2000 that are available through ORFEUS or IRIS; resulting in ~500,000 event-station pairs. We deconvolve the radial component by the vertical component - assumed to represent the source component- using the iterative deconvolution method to obtain receiver functions. We assess the quality of a receiver function by the signal-to-noise ratio and by evaluating how well the radial component is reproduced when reconvolving the receiver function with the vertical component. This results in ~45,000 high quality receiver functions across Europe. Here we present the large scale variations in the discontinuities around 410 and 660 km across Europe. The seismic discontinuities beneath the Eastern European craton show little topography and the mantle transition zone thickness is thinner compared to the thickness beneath the rest of Europe. Observing discontinuities within the mantle transition zone is complicated by arriving reverberations from strong shallow structure of the craton. The mantle transition zone around the Mediterranean is thicker and a lot more complexities are observed. The main discontinuities are generally weaker, and other discontinuities around 300 km and a negative jump around 600 km are observed.

  18. Seismic detection of folded, subducted lithosphere at the core-mantle boundary.

    PubMed

    Hutko, Alexander R; Lay, Thorne; Garnero, Edward J; Revenaugh, Justin

    2006-05-18

    Seismic tomography has been used to infer that some descending slabs of oceanic lithosphere plunge deep into the Earth's lower mantle. The fate of these slabs has remained unresolved, but it has been postulated that their ultimate destination is the lowermost few hundred kilometres of the mantle, known as the D'' region. Relatively cold slab material may account for high seismic velocities imaged in D'' beneath areas of long-lived plate subduction, and for reflections from a seismic velocity discontinuity just above the anomalously high wave speed regions. The D'' discontinuity itself is probably the result of a phase change in relatively low-temperature magnesium silicate perovskite. Here, we present images of the D'' region beneath the Cocos plate using Kirchhoff migration of horizontally polarized shear waves, and find a 100-km vertical step occurring over less than 100 km laterally in an otherwise flat D'' shear velocity discontinuity. Folding and piling of a cold slab that has reached the core-mantle boundary, as observed in numerical and experimental models, can account for the step by a 100-km elevation of the post-perovskite phase boundary due to a 700 degrees C lateral temperature reduction in the folded slab. We detect localized low velocities at the edge of the slab material, which may result from upwellings caused by the slab laterally displacing a thin hot thermal boundary layer.

  19. Magnetic discontinuities in magnetohydrodynamic turbulence and in the solar wind.

    PubMed

    Zhdankin, Vladimir; Boldyrev, Stanislav; Mason, Joanne; Perez, Jean Carlos

    2012-04-27

    Recent measurements of solar wind turbulence report the presence of intermittent, exponentially distributed angular discontinuities in the magnetic field. In this Letter, we study whether such discontinuities can be produced by magnetohydrodynamic (MHD) turbulence. We detect the discontinuities by measuring the fluctuations of the magnetic field direction, Δθ, across fixed spatial increments Δx in direct numerical simulations of MHD turbulence with an imposed uniform guide field B(0). A large region of the probability density function (pdf) for Δθ is found to follow an exponential decay, proportional to exp(-Δθ/θ(*)), with characteristic angle θ(*)≈(14°)(b(rms)/B(0))(0.65) for a broad range of guide-field strengths. We find that discontinuities observed in the solar wind can be reproduced by MHD turbulence with reasonable ratios of b(rms)/B(0). We also observe an excess of small angular discontinuities when Δx becomes small, possibly indicating an increasing statistical significance of dissipation-scale structures. The structure of the pdf in this case closely resembles the two-population pdf seen in the solar wind. We thus propose that strong discontinuities are associated with inertial-range MHD turbulence, while weak discontinuities emerge from dissipation-range turbulence. In addition, we find that the structure functions of the magnetic field direction exhibit anomalous scaling exponents, which indicates the existence of intermittent structures.

  20. Outcomes of patients with chronic lymphocytic leukemia after discontinuing ibrutinib.

    PubMed

    Jain, Preetesh; Keating, Michael; Wierda, William; Estrov, Zeev; Ferrajoli, Alessandra; Jain, Nitin; George, Binsah; James, Danelle; Kantarjian, Hagop; Burger, Jan; O'Brien, Susan

    2015-03-26

    Ibrutinib is a Bruton tyrosine kinase inhibitor approved for the treatment of patients with relapsed refractory chronic lymphocytic leukemia (RR-CLL). We describe the characteristics, causes of discontinuation, and outcomes in patients who discontinued treatment with ibrutinib. One hundred twenty-seven patients were enrolled in various clinical trials of ibrutinib, with or without rituximab, at our center. Thirty-three (26%) patients have discontinued ibrutinib to date. The majority of those patients had high-risk features: 94% with unmutated immunoglobulin heavy chain variable gene rearrangement, 58% with del(17p) by fluorescence in situ hybridization, and 54% with a complex karyotype. Causes of discontinuation were disease transformation (7), progressive CLL (7), stem cell transplantation (3), adverse events (11), serious adverse events/deaths (3), and miscellaneous reasons (2). Twenty five patients (76%) died after discontinuing ibrutinib; the median overall survival was 3.1 months after discontinuation. Most patients with RR-CLL who discontinued ibrutinib early were difficult to treat and had poor outcomes.

  1. Outcomes of patients with chronic lymphocytic leukemia after discontinuing ibrutinib

    PubMed Central

    Jain, Preetesh; Keating, Michael; Wierda, William; Estrov, Zeev; Ferrajoli, Alessandra; Jain, Nitin; George, Binsah; James, Danelle; Kantarjian, Hagop; Burger, Jan

    2015-01-01

    Ibrutinib is a Bruton tyrosine kinase inhibitor approved for the treatment of patients with relapsed refractory chronic lymphocytic leukemia (RR-CLL). We describe the characteristics, causes of discontinuation, and outcomes in patients who discontinued treatment with ibrutinib. One hundred twenty-seven patients were enrolled in various clinical trials of ibrutinib, with or without rituximab, at our center. Thirty-three (26%) patients have discontinued ibrutinib to date. The majority of those patients had high-risk features: 94% with unmutated immunoglobulin heavy chain variable gene rearrangement, 58% with del(17p) by fluorescence in situ hybridization, and 54% with a complex karyotype. Causes of discontinuation were disease transformation (7), progressive CLL (7), stem cell transplantation (3), adverse events (11), serious adverse events/deaths (3), and miscellaneous reasons (2). Twenty five patients (76%) died after discontinuing ibrutinib; the median overall survival was 3.1 months after discontinuation. Most patients with RR-CLL who discontinued ibrutinib early were difficult to treat and had poor outcomes. PMID:25573991

  2. [Discontinuation of immunosuppressive and immunomodulatory drugs in connective tissue diseases].

    PubMed

    Targońska-Stępniak, Bożena

    2015-01-01

    Remission in connective tissue diseases became a realistic goal of therapy nowadays. However, there is lack of recommendations on the management after achieving a remission. Chronic exposure to immunosuppressive or immunomodulatory drugs may be associated with adverse events, that is why temporal withdrawal or discontinuation of treatment is advisable. In patients with rheumatoid arthritis (RA) who achieve sustained remission lasting for 6-12 months, an attempt to withdraw biological disease modifying antirheumatic drugs (bDMARDs) may be considered. In most patients with established RA discontinuation of bDMARDs is accompanied by a disease flare, butthe risk of loss of good therapeutic response is lower in case of slowly tapering by expanding the interval between doses or reducing the dose of bDMARDs. Patients with early RA are more likely to have successful discontinuation of therapy. Discontinuation of conventional DMARDs (cDMARDs) is usually associated with a disease flare, that is why tapering of doses is advised rather than stopping cDMARDs. DMARDs free remission occurs relatively rare, more often in patients with seronegative RA and with early onset of modifying treatment. In lupus nephritis (LN) patients with persistent, long-term remission, progressive tapering of doses of immunosuppressive drugs and glucocorticoids is recommended, with treatment discontinuation as a goal. An attempt of treatment withdrawal may be taken in patients remaining in LN complete remission as a consequence of maintenance therapy for 3 years.The process of slow tapering of doses preceding discontinuation of drugs, may last several months. The therapy with antimalarial drugs may be helpful to maintain remission after the treatment discontinuation. There is few data on treatment discontinuation in patients with systemic lupus erythematosus (SLE) without kidney involvement. Immunosuppressive drugs withdrawal is usually performed in patients with stable serological and clinically

  3. EGLACOM project: seismic and oceanographic data integration

    NASA Astrophysics Data System (ADS)

    Petronio, L.; Lipizer, M.; Rebesco, M.; Deponte, D.; Ursella, L.; Fragiacomo, C.

    2009-04-01

    studies show that the AW inflow is variable in nature, both in terms of heat content and of transport intensity, therefore a detailed study of its structure is of particular importance. In order to study the thermohaline structure and the spatial extension of the AW inflow with a seismic oceanography approach, about 1000 Km of multichannel seismic reflection lines were acquired simultaneously with several types of oceanographic data. Seismic data interpretation is supported by 60 XBT (Expandable Bathy-Thermograph) profiles obtained concurrently during the seismic acquisition, 6 additional CTD (Conductivity-Temperature-Depth) casts carried out within 10 days from the XBT launches and sea-surface temperature and salinity measured continuously by a thermosalinograph installed on the vessel prow. In addition, Vessel-Mounted Acoustic Doppler Current Profiler (VM-ADCP) data were acquired during navigation to continuously monitor the velocity distribution in the upper water column. The velocity field, together with the sea-surface temperature data from the NOAA-18 satellite were used to obtain information on the dynamic in the area. The seismic data processing is still in progress as well as the elaboration of oceanographic data. The first results obtained display a good correlation between seismic reflectors and discontinuities in vertical temperature and salinity gradients. XBT sections and CTD profiles allow to recognise the spatial extension of the water masses of Atlantic and Arctic origin present in the area, and show the progressive cooling and shallowing of the warm and salty AW proceeding northwards. References: Holbrook W. S., P. Páramo, S. Pearse, and W. Schmitt, 2003, Thermohaline fine structure in an oceanographic front from seismic reflection profiling: Science, 301, 821-824. Jones S. M., R. J. J. Hardy, R. W. Hobbs, and D. Hardy, 2008, The new synergy between seismic reflection imaging and oceanography: First Break, 26, 51-57. Nakamura Y., T. Noguchi, T. Tsuji, S

  4. Characterizing the 410 km discontinuity low-velocity layer beneath the LA RISTRA array in the North American Southwest

    NASA Astrophysics Data System (ADS)

    Jasbinsek, John J.; Dueker, Ken G.; Hansen, Steven M.

    2010-03-01

    Receiver functions recorded by the 54-station 920 km long Program for Array Seismic Studies of the Continental Lithosphere-Incorporated Research Institutions for Seismology Colorado Plateau/Rio Grande Rift Seismic Transect Experiment (LA RISTRA) line array display a pervasive negative polarity P to S conversion (Pds) arrival preceding the positive polarity 410 km discontinuity arrival. These arrivals are modeled as a low-velocity layer atop the 410 km discontinuity (410-LVL) and are inverted for a velocity profile via a grid search using a five-parameter linear gradient velocity model. Model parameter likelihood and correlations are assessed via calculation of one- and two-dimensional marginal posterior probability distributions. The maximum likelihood model parameter values found are top velocity gradient thickness of 0.0 km with a 4.6% (-0.22 km/s) shear velocity reduction, a 19.8 km constant velocity layer, and bottom gradient thickness of 25.0 km with a 3.5% (+0.17 km/s) shear velocity increase. The estimated mean thickness of the 410-LVL is 32.3 km. The top gradient of the 410-LVL is sharp within vertical resolution limits of P to S conversion (<10 km), and the diffuse 410 km velocity gradient is consistent with hydration of the olivine-wadsleyite phase transformation. The 410-LVL is interpreted as a melt layer created by the Transition Zone Water Filter model. Two secondary observations are found: (1) the 410-LVL is absent from the SE end of the array and (2) an intermittent negative polarity P525s arrival is observed. We speculate that upper mantle shear velocity anomalies above the 410 km discontinuity may manifest Rayleigh-Taylor instabilities nucleated from the 410-LVL melt layer that are being shed upward on time scales of tens of millions of years.

  5. Anomalous Shear Properties of Coesite at High Pressure and Implications for the X-discontinuity in the Earth's Upper Mantle

    NASA Astrophysics Data System (ADS)

    Chen, T.; Gwanmesia, G. D.; Wang, X.; Zou, Y.; Liebermann, R. C.; Michaut, C.; Li, B.

    2013-12-01

    The X-discontinuity (250-350km) in the upper mantle has been revealed under some continental or oceanic plates by a number of seismic studies, at which depth the P and S wave velocities increase by about 2%. One possible cause for this discontinuity, as suggested in previous studies, is the coesite-stishovite phase transition. Although the compressional behavior of coesite was determined by a previous single crystal study, its shear properties at high pressure have not yet been assessed experimentally. In this study, we conducted ultrasonic interferometry measurements on polycrystalline coesite up to 12.5GPa at ambient temperature. The sample was hot-pressed at 6.5GPa and 920°C and confirmed to be single phased by X-ray diffraction. We find that while the P wave velocities of coesite continuously increase with pressure, the S wave velocities exhibit a monotonic decrease to the peak pressure of the current experiment followed by a reversible recovery upon release of pressure. By fitting to finite strain equations, the elastic bulk and shear moduli and their pressure derivatives are precisely determined using the data collected during compression and decompression. Comparing with stishovite, coesite has lower pressure derivatives for both the bulk and shear moduli that is especially pronounced for the shear modulus. The volume-pressure relations obtained in the current study are in excellent agreement with those from single crystal compression of coesite. These results indicate that the velocity and impedance contrasts of the coesite-stishovite transition will increase with pressure, and its seismic signatures will be greatly enhanced at the depths of the X-discontinuity.

  6. Discontinuity of cortical gradients reflects sensory impairment

    PubMed Central

    Saadon-Grosman, Noam; Tal, Zohar; Itshayek, Eyal; Amedi, Amir; Arzy, Shahar

    2015-01-01

    Topographic maps and their continuity constitute a fundamental principle of brain organization. In the somatosensory system, whole-body sensory impairment may be reflected either in cortical signal reduction or disorganization of the somatotopic map, such as disturbed continuity. Here we investigated the role of continuity in pathological states. We studied whole-body cortical representations in response to continuous sensory stimulation under functional MRI (fMRI) in two unique patient populations—patients with cervical sensory Brown-Séquard syndrome (injury to one side of the spinal cord) and patients before and after surgical repair of cervical disk protrusion—enabling us to compare whole-body representations in the same study subjects. We quantified the spatial gradient of cortical activation and evaluated the divergence from a continuous pattern. Gradient continuity was found to be disturbed at the primary somatosensory cortex (S1) and the supplementary motor area (SMA), in both patient populations: contralateral to the disturbed body side in the Brown-Séquard group and before repair in the surgical group, which was further improved after intervention. Results corresponding to the nondisturbed body side and after surgical repair were comparable with control subjects. No difference was found in the fMRI signal power between the different conditions in the two groups, as well as with respect to control subjects. These results suggest that decreased sensation in our patients is related to gradient discontinuity rather than signal reduction. Gradient continuity may be crucial for somatotopic and other topographical organization, and its disruption may characterize pathological processing. PMID:26655739

  7. Accountability Accentuates Interindividual-Intergroup Discontinuity by Enforcing Parochialism

    PubMed Central

    Wildschut, Tim; van Horen, Femke; Hart, Claire

    2015-01-01

    Interindividual-intergroup discontinuity is the tendency for relations between groups to be more competitive than relations between individuals. We examined whether the discontinuity effect arises in part because group members experience normative pressure to favor the ingroup (parochialism). Building on the notion that accountability enhances normative pressure, we hypothesized that the discontinuity effect would be larger when accountability is present (compared to absent). A prisoner’s dilemma game experiment supported this prediction. Specifically, intergroup (compared to interindividual) interaction activated an injunctive ingroup-favoring norm, and accountability enhanced the influence of this norm on competitive behavior. PMID:26635691

  8. Discontinuous Spectral Difference Method for Conservation Laws on Unstructured Grids

    NASA Technical Reports Server (NTRS)

    Liu, Yen; Vinokur, Marcel; Wang, Z. J.

    2004-01-01

    A new, high-order, conservative, and efficient method for conservation laws on unstructured grids is developed. The concept of discontinuous and high-order local representations to achieve conservation and high accuracy is utilized in a manner similar to the Discontinuous Galerkin (DG) and the Spectral Volume (SV) methods, but while these methods are based on the integrated forms of the equations, the new method is based on the differential form to attain a simpler formulation and higher efficiency. A discussion on the Discontinuous Spectral Difference (SD) Method, locations of the unknowns and flux points and numerical results are also presented.

  9. Discontinuous Galerkin computation of the Maxwell eigenvalues on simplicial meshes

    NASA Astrophysics Data System (ADS)

    Buffa, Annalisa; Houston, Paul; Perugia, Ilaria

    2007-07-01

    This paper is concerned with the discontinuous Galerkin approximation of the Maxwell eigenproblem. After reviewing the theory developed in [A. Buffa, I. Perugia, Discontinuous Galerkin approximation of the Maxwell eigenproblem, Technical Report 24-PV, IMATI-CNR, Pavia, Italy, 2005 ], we present a set of numerical experiments which both validate the theory, and provide further insight regarding the practical performance of discontinuous Galerkin methods, particularly in the case when non-conforming meshes, characterized by the presence of hanging nodes, are employed.

  10. Seismic random noise attenuation via 3D block matching

    NASA Astrophysics Data System (ADS)

    Amani, Sajjad; Gholami, Ali; Javaheri Niestanak, Alireza

    2017-01-01

    The lack of signal to noise ratio increases the final errors of seismic interpretation. In the present study, we apply a new non-local transform domain method called "3 Dimensional Block Matching (3DBM)" for seismic random noise attenuation. Basically, 3DBM uses the similarities through the data for retrieving the amplitude of signal in a specific point in the f-x domain, and because of this, it is able to preserve discontinuities in the data such as fractures and faults. 3DBM considers each seismic profile as an image and thus it can be applied to both pre-stack and post-stack seismic data. It uses the block matching clustering method to gather similar blocks contained in 2D data into 3D groups in order to enhance the level of correlation in each 3D array. By applying a 2D transform and 1D transform (instead of a 3D transform) on each array, we can effectively attenuate the noise by shrinkage of the transform coefficients. The subsequent inverse 2D transform and inverse 1D transform yield estimates of all matched blocks. Finally, the random noise attenuated data is computed using the weighted average of all block estimates. We applied 3DBM on both synthetic and real pre-stack and post-stack seismic data and compared it with a Curvelet transform based denoising method which is one of the most powerful methods in this area. The results show that 3DBM method eventuates in higher signal to noise ratio, lower execution time and higher visual quality.

  11. Why do patients discontinue fertility treatment? A systematic review of reasons and predictors of discontinuation in fertility treatment.

    PubMed

    Gameiro, S; Boivin, J; Peronace, L; Verhaak, C M

    2012-01-01

    BACKGROUND Chances of achieving parenthood are high for couples who undergo fertility treatment. However, many choose to discontinue before conceiving. A systematic review was conducted to investigate patients' stated reasons for and predictors of discontinuation at five fertility treatment stages. METHODS Six databases were systematically searched. Search-terms referred to fertility treatment and discontinuation. Studies reporting on patients' stated reasons for or predictors of treatment discontinuation were included. A list of all reasons for discontinuation presented in each study was made, different categories of reasons were defined and the percentage of selections of each category was calculated. For each predictor, it was noted how many studies investigated it and how many found a positive and/or negative association with discontinuation. RESULTS The review included 22 studies that sampled 21 453 patients from eight countries. The most selected reasons for discontinuation were: postponement of treatment (39.18%, postponement of treatment or unknown 19.17%), physical and psychological burden (19.07%, psychological burden 14%, physical burden 6.32%), relational and personal problems (16.67%, personal reasons 9.27%, relational problems 8.83%), treatment rejection (13.23%) and organizational (11.68%) and clinic (7.71%) problems. Some reasons were common across stages (e.g. psychological burden). Others were stage-specific (e.g. treatment rejection during workup). None of the predictors reported were consistently associated with discontinuation. CONCLUSIONS Much longitudinal and theory led research is required to explain discontinuation. Meanwhile, treatment burden should be addressed by better care organization and support for patients. Patients should be well informed, have the opportunity to discuss values and worries about treatment and receive advice to decide about continuing treatment.

  12. Seismic detection of tornadoes

    USGS Publications Warehouse

    Tatom, F. B.

    1993-01-01

    Tornadoes represent the most violent of all forms of atmospheric storms, each year resulting in hundreds of millions of dollars in property damage and approximately one hundred fatalities. In recent years, considerable success has been achieved in detecting tornadic storms by means of Doppler radar. However, radar systems cannot determine when a tornado is actually in contact with the ground, expect possibly at extremely close range. At the present time, human observation is the only truly reliable way of knowing that a tornado is actually on the ground. However, considerable evidence exists indicating that a tornado in contact with the ground produces a significant seismic signal. If such signals are generated, the seismic detection and warning of an imminent tornado can become a distinct possibility. 

  13. Canadian seismic agreement

    SciTech Connect

    Wetmiller, R.J.; Lyons, J.A.; Shannon, W.E.; Munro, P.S.; Thomas, J.T.; Andrew, M.D.; Lamontagne, M.; Wong, C.; Anglin, F.M.; Plouffe, M.; Adams, J.; Drysdale, J.A. . Geophysics Div.)

    1990-04-01

    During the period of this report, the contract resources were spent on operation and maintenance of the Eastern Canada Telemetred Network (ECTN), development of special purpose local network systems, servicing and maintenance of the strong-motion seismograph network in eastern Canada, operation of the Ottawa data lab and earthquake monitoring and reporting. Of special note in this period was the final completion of the Sudbury (SLTN) and Charlevoix (CLTN) local networks and the integration of their data processing and analysis requirements in the regular analysis stream for ECTN data. These networks now acquire high quality digital data for detailed analysis of seismic activity and source properties from these two areas, thus effectively doubling the amount of seismic data being received by the Ottawa data lab. 37 refs., 17 figs., 2 tabs.

  14. Albuquerque Basin seismic network

    USGS Publications Warehouse

    Jaksha, Lawrence H.; Locke, Jerry; Thompson, J.B.; Garcia, Alvin

    1977-01-01

    The U.S. Geological Survey has recently completed the installation of a seismic network around the Albuquerque Basin in New Mexico. The network consists of two seismometer arrays, a thirteen-station array monitoring an area of approximately 28,000 km 2 and an eight-element array monitoring the area immediately adjacent to the Albuquerque Seismological Laboratory. This report describes the instrumentation deployed in the network.

  15. 'Fracking', Induced Seismicity and the Critical Earth

    NASA Astrophysics Data System (ADS)

    Leary, P.; Malin, P. E.

    2012-12-01

    and ore body distributions can be managed by operating in a context which affords many small failures for a few large successes. In reverse view, 'fracking' and induced seismicity could be rationally managed in a context in which many small successes can afford a few large failures. However, just as there is every incentive to acquire information leading to higher rates of productive well drilling and ore body exploration, there are equal incentives for acquiring information leading to lower rates of 'fracking'-induced seismicity. Current industry practice of using an effective medium approach to reservoir rock creates an uncritical sense that property distributions in rock are essentially uniform. Well-log data show that the reverse is true: the larger the length scale the greater the deviation from uniformity. Applying the effective medium approach to large-scale rock formations thus appears to be unnecessarily hazardous. It promotes the notion that large scale fluid pressurization acts against weakly cohesive but essentially uniform rock to produce large-scale quasi-uniform tensile discontinuities. Indiscriminate hydrofacturing appears to be vastly more problematic in reality than as pictured by the effective medium hypothesis. The spatial complexity of rock, especially at large scales, provides ample reason to find more controlled pressurization strategies for enhancing in situ flow.

  16. Establishing seismic design criteria to achieve an acceptable seismic margin

    SciTech Connect

    Kennedy, R.P.

    1997-01-01

    In order to develop a risk based seismic design criteria the following four issues must be addressed: (1) What target annual probability of seismic induced unacceptable performance is acceptable? (2). What minimum seismic margin is acceptable? (3) Given the decisions made under Issues 1 and 2, at what annual frequency of exceedance should the Safe Shutdown Earthquake ground motion be defined? (4) What seismic design criteria should be established to reasonably achieve the seismic margin defined under Issue 2? The first issue is purely a policy decision and is not addressed in this paper. Each of the other three issues are addressed. Issues 2 and 3 are integrally tied together so that a very large number of possible combinations of responses to these two issues can be used to achieve the target goal defined under Issue 1. Section 2 lays out a combined approach to these two issues and presents three potentially attractive combined resolutions of these two issues which reasonably achieves the target goal. The remainder of the paper discusses an approach which can be used to develop seismic design criteria aimed at achieving the desired seismic margin defined in resolution of Issue 2. Suggestions for revising existing seismic design criteria to more consistently achieve the desired seismic margin are presented.

  17. Monitoring Seasonal Changes in Permafrost Using Seismic Interferometry

    NASA Astrophysics Data System (ADS)

    James, S. R.; Knox, H. A.; Abbott, R. E.

    2015-12-01

    The effects of climate change in polar regions and their incorporation in global climate models has recently become an area of great interest. Permafrost holds entrapped greenhouse gases, e.g. CO2 and CH4, which are released to the atmosphere upon thawing, creating a positive feedback mechanism. Knowledge of seasonal changes in active layer thickness as well as long term degradation of permafrost is critical to the management of high latitude infrastructures, hazard mitigation, and increasing the accuracy of climate predictions. Methods for effectively imaging the spatial extent, depth, thickness, and discontinuous nature of permafrost over large areas are needed. Furthermore, continuous monitoring of permafrost over annual time scales would provide valuable insight into permafrost degradation. Seismic interferometry using ambient seismic noise has proven effective for recording velocity changes within the subsurface for a variety of applications, but has yet to be applied to permafrost studies. To this end, we deployed 7 Nanometrics Trillium posthole broadband seismometers within Poker Flat Research Range, located 30 miles north of Fairbanks, Alaska in a zone of discontinuous permafrost. Approximately 2 years worth of nearly continuous ambient noise data was collected. Using the python package MSNoise, relative changes in velocity were calculated. Results show high amounts of variability throughout the study period. General trends of negative relative velocity shifts can be seen between August and October followed by a positive relative velocity shift between November and February. Differences in relative velocity changes with both frequency and spatial location are also observed, suggesting this technique is sensitive to permafrost variation with depth and extent. Overall, short and long term changes in shallow subsurface velocity can be recovered using this method proposing seismic interferometry is a promising new technique for permafrost monitoring. Sandia

  18. Seismic basement in Poland

    NASA Astrophysics Data System (ADS)

    Grad, Marek; Polkowski, Marcin

    2016-06-01

    The area of contact between Precambrian and Phanerozoic Europe in Poland has complicated structure of sedimentary cover and basement. The thinnest sedimentary cover in the Mazury-Belarus anteclize is only 0.3-1 km thick, increases to 7-8 km along the East European Craton margin, and 9-12 km in the Trans-European Suture Zone (TESZ). The Variscan domain is characterized by a 1- to 2-km-thick sedimentary cover, while the Carpathians are characterized by very thick sediments, up to c. 20 km. The map of the basement depth is created by combining data from geological boreholes with a set of regional seismic refraction profiles. These maps do not provide data about the basement depth in the central part of the TESZ and in the Carpathians. Therefore, the data set is supplemented by 32 models from deep seismic sounding profiles and a map of a high-resistivity (low-conductivity) layer from magnetotelluric soundings, identified as a basement. All of these data provide knowledge about the basement depth and of P-wave seismic velocities of the crystalline and consolidated type of basement for the whole area of Poland. Finally, the differentiation of the basement depth and velocity is discussed with respect to geophysical fields and the tectonic division of the area.

  19. Entropy-bounded discontinuous Galerkin scheme for Euler equations

    NASA Astrophysics Data System (ADS)

    Lv, Yu; Ihme, Matthias

    2015-08-01

    An entropy-bounded Discontinuous Galerkin (EBDG) scheme is proposed in which the solution is regularized by constraining the entropy. The resulting scheme is able to stabilize the solution in the vicinity of discontinuities and retains the optimal accuracy for smooth solutions. The properties of the limiting operator according to the entropy-minimum principle are proofed, and an optimal CFL-criterion is derived. We provide a rigorous description for locally imposing entropy constraints to capture multiple discontinuities. Significant advantages of the EBDG-scheme are the general applicability to arbitrary high-order elements and its simple implementation for multi-dimensional configurations. Numerical tests confirm the properties of the scheme, and particular focus is attributed to the robustness in treating discontinuities on arbitrary meshes.

  20. 38 CFR 8.17 - Discontinuance of premium waiver.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... SERVICE LIFE INSURANCE Premium Waivers and Total Disability § 8.17 Discontinuance of premium waiver. (a... address at which mail will reach him or her promptly shall not be grounds for a further extension of...

  1. 38 CFR 8.17 - Discontinuance of premium waiver.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... SERVICE LIFE INSURANCE Premium Waivers and Total Disability § 8.17 Discontinuance of premium waiver. (a... address at which mail will reach him or her promptly shall not be grounds for a further extension of...

  2. 38 CFR 8.17 - Discontinuance of premium waiver.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... SERVICE LIFE INSURANCE Premium Waivers and Total Disability § 8.17 Discontinuance of premium waiver. (a... address at which mail will reach him or her promptly shall not be grounds for a further extension of...

  3. 38 CFR 8.17 - Discontinuance of premium waiver.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... SERVICE LIFE INSURANCE Premium Waivers and Total Disability § 8.17 Discontinuance of premium waiver. (a... address at which mail will reach him or her promptly shall not be grounds for a further extension of...

  4. 47 CFR 5.81 - Discontinuance of station operation.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false Discontinuance of station operation. 5.81 Section 5.81 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL EXPERIMENTAL RADIO SERVICE (OTHER... Commission's Office of Engineering and Technology for cancellation....

  5. On cell entropy inequality for discontinuous Galerkin methods

    NASA Technical Reports Server (NTRS)

    Jiang, Guangshan; Shu, Chi-Wang

    1993-01-01

    We prove a cell entropy inequality for a class of high order discontinuous Galerkin finite element methods approximating conservation laws, which implies convergence for the one dimensional scalar convex case.

  6. Calculation of Accurate Hexagonal Discontinuity Factors for PARCS

    SciTech Connect

    Pounders. J., Bandini, B. R. , Xu, Y, and Downar, T. J.

    2007-11-01

    In this study we derive a methodology for calculating discontinuity factors consistent with the Triangle-based Polynomial Expansion Nodal (TPEN) method implemented in PARCS for hexagonal reactor geometries. The accuracy of coarse-mesh nodal methods is greatly enhanced by permitting flux discontinuities at node boundaries, but the practice of calculating discontinuity factors from infinite-medium (zero-current) single bundle calculations may not be sufficiently accurate for more challenging problems in which there is a large amount of internodal neutron streaming. The authors therefore derive a TPEN-based method for calculating discontinuity factors that are exact with respect to generalized equivalence theory. The method is validated by reproducing the reference solution for a small hexagonal core.

  7. 14 CFR 170.25 - LORAN-C discontinuance criteria.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... nonprecision approach may be subject to discontinuance when the present value of the continued maintenance costs (PVCM) of the LORAN-C approach exceed the present value of its remaining life-cycle benefits...

  8. 47 CFR 80.471 - Discontinuance or impairment of service.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... commercial mobile radio service providers, a public coast station must not discontinue or impair service unless authorized to do so by the Commission. Automated Systems ... Section 80.471 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL...

  9. Discontinuities, cross-scale patterns, and the organization of ecosystems

    USGS Publications Warehouse

    Nash, Kirsty L.; Allen, Craig R.; Angeler, David G.; Barichievy, Chris; Eason, Tarsha; Garmestani, Ahjond S.; Graham, Nicholas A.J.; Granholm, Dean; Knutson, Melinda; Nelson, R. John; Nystrom, Magnus; Stow, Craig A.; Sandstrom, Shana M.

    2014-01-01

    Ecological structures and processes occur at specific spatiotemporal scales, and interactions that occur across multiple scales mediate scale-specific (e.g., individual, community, local, or regional) responses to disturbance. Despite the importance of scale, explicitly incorporating a multi-scale perspective into research and management actions remains a challenge. The discontinuity hypothesis provides a fertile avenue for addressing this problem by linking measureable proxies to inherent scales of structure within ecosystems. Here we outline the conceptual framework underlying discontinuities and review the evidence supporting the discontinuity hypothesis in ecological systems. Next we explore the utility of this approach for understanding cross-scale patterns and the organization of ecosystems by describing recent advances for examining nonlinear responses to disturbance and phenomena such as extinctions, invasions, and resilience. To stimulate new research, we present methods for performing discontinuity analysis, detail outstanding knowledge gaps, and discuss potential approaches for addressing these gaps.

  10. Fixed point theorems and existence of equilibrium in discontinuous games

    NASA Astrophysics Data System (ADS)

    Messaoud, Deghdak

    2012-11-01

    In this paper, we generalize the existence of Berge's strong equilibrium in Deghdak (see [7]) to discontinuous games in infinite dimensional space of srategy. Moreover, we prove that most of Berge's strong games are essential.

  11. Discontinuous Galerkin finite element solution for poromechanics

    NASA Astrophysics Data System (ADS)

    Liu, Ruijie

    This dissertation focuses on applying discontinuous Galerkin (DG) methods to poromechanics problems. A few challenges have been presented in traditional and popular continuous Galerkin (CG) finite element methods for solving complex coupled thermal, flow and solid mechanics. For example, nonphysical pore pressure oscillations often occur in CG solutions for poroelasticity problems with low permeability. A robust and practical numerical scheme for removing or alleviating the oscillation is not available. In modeling thermoporoelastoplasticity, CG methods require the use of very small time steps to obtain a convergent solution. The temperature profile predicted by CG methods in the fine mesh zones is often seriously polluted by large errors produced in coarse mesh zones in the case where the convection dominates the thermal process. The nonphysical oscillations in pore pressure and temperature solutions induced by CG methods at very early time stages seriously corrupt the solutions at longer time. We propose DG methods to handle these challenges because they are physics driven, provide local conservation of mass and momentum, have high stability and robustness, are locking-free, and because of their meshing and implementation capabilities. We first apply a family of DG methods, including Oden-Babuska-Baumann (OBB), Nonsymmetric Interior Penalty Galerkin (NIPG), Symmetric Interior Penalty Galerkin (SIPG) and Incomplete Interior Penalty Galerkin (IIPG), to 3D linear elasticity problems. This family of DG methods is tested and evaluated by using a cantilever beam problem with nearly incompressible materials. It is shown that DG methods are simple, robust and locking-free in dealing with nearly incompressible materials. Based on the success of DG methods in elasticity, we extend the DG theory into plasticity problems. A DG formulation has been implemented for solving 3D poroelasticity problems with low permeability. Numerical examples solved by DG methods demonstrate

  12. Extrinsic toughening of discontinuously reinforced aluminum composites

    NASA Astrophysics Data System (ADS)

    Ellis, Lisa Yost

    Discontinuously reinforced aluminum (DRA) composites can exhibit desirable specific stiffness and strength properties as compared to monolithic aluminum alloys. Unfortunately, the addition of ceramic particulates to the aluminum matrix results in decreased fracture resistance. In this dissertation, DRA composites containing discrete regions of unreinforced aluminum (where these unreinforced aluminum regions are subsequently referred to as 'ductile phase' regions or DP regions) were studied with the objective of enhancing damage tolerance compared to the conventional DRA composite. The effects of 'ductile phase' size, shape and mechanical properties as well as the SiCp reinforcement distribution on crack initiation and growth were examined. The incorporation of properly selected DP regions can result in increased crack growth resistance of the DRA composite under monotonic loading conditions. In such cases, stable crack propagation (i.e. R-curve behavior) was observed in contrast to the behavior of the conventional DRA composite which failed catastrophically at about 20 MPasurdm. Increased size and ductility of the 'ductile phase' resulted in improved toughness over the range tested. For instance, materials with small DP regions (10-60 mum in thickness) did not show improvements in fracture toughness compared to the conventional composites while those materials containing large DP regions (80-400 mum in thickness) demonstrated stable crack propagation at elevated levels of stress intensity. The details of the R-curve as well as the dominant toughening mechanisms were also affected by test geometry (i.e. crack arrestor vs. crack divider). In the crack arrestor orientation, toughening was associated primarily with the renucleation of the crack across the DP regions, provided the DP regions possessed sufficient ductility. Apparent stress intensities of 30-50 MPasurdm resulted. In the crack divider orientation, rising R-curves resulted from the bridging action of

  13. Seismic upgrades of healthcare facilities.

    PubMed

    Yusuf, A

    1997-06-01

    Before 1989 seismic upgrading of hospital structures was not a primary consideration among hospital owners. However, after extensive earthquake damage to hospital buildings at Loma Prieta in Northern California in 1989 and then at Northridge in Southern California in 1994, hospital owners, legislators, and design teams become concerned about the need for seismic upgrading of existing facilities. Because the damage hospital structures sustained in the earthquakes was so severe and far-reaching, California has enacted laws that mandate seismic upgrading for existing facilities. Now hospital owners will have to upgrade buildings that do not conform to statewide seismic adequacy laws. By 2030, California expects all of its hospital structures to be sufficiently seismic-resistant. Slowly, regions in the Midwest and on the East Coast are following their example. This article outlines reasons and ways for seismic upgrading of existing facilities.

  14. Continuous seismic reflection profiling of hydrogeologic features beneath New River, Camp Lejeune, North Carolina

    USGS Publications Warehouse

    Cardinell, A.P.; Harned, D.A.; Berg, S.A.

    1990-01-01

    A medium-power, wide-frequency seismic system was used to collect more than 100 miles of continuous seismic reflection profiling data over a 4- day period along a 24-mile segment of the New River estuary and Intracoastal Waterway. The seismic reflection data were evaluated to determine the continuity of aquifer sediments and correlation with existing borehole geophysical well-log data at the Base. Results indicate that the Castle Hayne aquifer, the major source of freshwater for the military base and surrounding area, and deeper aquifers are continuous beds that gently dip to the southeast. However, immediately above the Castle Hayne aquifer, the survey showed that sediment beds are thin and discontinuous. This not only allows rainfall to more easily percolate and recharge the aquifer, but also makes the Castle Hayne more vulnerable to contamination.

  15. Heat exchanger containing a component capable of discontinuous movement

    DOEpatents

    Wilson, David Gordon

    2001-04-17

    Regenerative heat exchangers are described for transferring heat between hot and cold fluids. The heat exchangers have seal-leakage rates significantly less than those of conventional regenerative heat exchangers because the matrix is discontinuously moved and is releasably sealed while in a stationary position. Both rotary and modular heat exchangers are described. Also described are methods for transferring heat between a hot and cold fluid using the discontinuous movement of matrices.

  16. Heat exchanger containing a component capable of discontinuous movement

    DOEpatents

    Wilson, David Gordon

    2002-01-01

    Regenerative heat exchangers are described for transferring heat between hot and cold fluids. The heat exchangers have seal-leakage rates significantly less than those of conventional regenerative heat exchangers because the matrix is discontinuously moved and is releasably sealed while in a stationary position. Both rotary and modular heat exchangers are described. Also described are methods for transferring heat between a hot and cold fluid using the discontinuous movement of matrices.

  17. Heat exchanger containing a component capable of discontinuous movement

    DOEpatents

    Wilson, David G.

    1993-01-01

    Regenerative heat exchangers are described for transferring heat between hot and cold fluids. The heat exchangers have seal-leakage rates significantly less than those of conventional regenerative heat exchangers because the matrix is discontinuously moved and is releasably sealed while in a stationary position. Both rotary and modular heat exchangers are described. Also described are methods for transferring heat between a hot and cold fluid using the discontinuous movement of matrices.

  18. Determining the Locations and Discontinuities in the Derivatives of Functions

    SciTech Connect

    Archibald, Richard K; Gelb, Anne; Yoon, Jungho

    2007-01-01

    We introduce a method for detecting discontinuities in piecewise smooth functions and in their derivatives. The method is constructed from a local stencil of grid point values and is based on a polynomial annihilation technique. By varying the order of the method and the arrangement of the corresponding stencils, the jump discontinuities of a function and its derivatives can be identified with high order accuracy. The method is efficient and robust and can be applied to non-uniform distributions in one dimension.

  19. Heat exchanger containing a component capable of discontinuous movement

    DOEpatents

    Wilson, D.G.

    1993-11-09

    Regenerative heat exchangers are described for transferring heat between hot and cold fluids. The heat exchangers have seal-leakage rates significantly less than those of conventional regenerative heat exchangers because the matrix is discontinuously moved and is releasably sealed while in a stationary position. Both rotary and modular heat exchangers are described. Also described are methods for transferring heat between a hot and cold fluid using the discontinuous movement of matrices. 11 figures.

  20. Mantle transition zone thinning beneath eastern Africa: Evidence for a whole-mantle superplume structure

    NASA Astrophysics Data System (ADS)

    Mulibo, Gabriel D.; Nyblade, Andrew A.

    2013-07-01

    to S conversions from the 410 and 660 km discontinuities observed in receiver function stacks reveal a mantle transition zone that is ~30-40 km thinner than the global average in a region ~200-400 km wide extending in a SW-NE direction from central Zambia, across Tanzania and into Kenya. The thinning of the transition zone indicates a ~190-300 K thermal anomaly in the same location where seismic tomography models suggest that the lower mantle African superplume structure connects to thermally perturbed upper mantle beneath eastern Africa. This finding provides compelling evidence for the existence of a continuous thermal structure extending from the core-mantle boundary to the surface associated with the African superplume.

  1. Seismic Imager Space Telescope

    NASA Technical Reports Server (NTRS)

    Sidick, Erkin; Coste, Keith; Cunningham, J.; Sievers,Michael W.; Agnes, Gregory S.; Polanco, Otto R.; Green, Joseph J.; Cameron, Bruce A.; Redding, David C.; Avouac, Jean Philippe; Ampuero, Jean Paul; Leprince, Sebastien; Michel, Remi

    2012-01-01

    A concept has been developed for a geostationary seismic imager (GSI), a space telescope in geostationary orbit above the Pacific coast of the Americas that would provide movies of many large earthquakes occurring in the area from Southern Chile to Southern Alaska. The GSI movies would cover a field of view as long as 300 km, at a spatial resolution of 3 to 15 m and a temporal resolution of 1 to 2 Hz, which is sufficient for accurate measurement of surface displacements and photometric changes induced by seismic waves. Computer processing of the movie images would exploit these dynamic changes to accurately measure the rapidly evolving surface waves and surface ruptures as they happen. These measurements would provide key information to advance the understanding of the mechanisms governing earthquake ruptures, and the propagation and arrest of damaging seismic waves. GSI operational strategy is to react to earthquakes detected by ground seismometers, slewing the satellite to point at the epicenters of earthquakes above a certain magnitude. Some of these earthquakes will be foreshocks of larger earthquakes; these will be observed, as the spacecraft would have been pointed in the right direction. This strategy was tested against the historical record for the Pacific coast of the Americas, from 1973 until the present. Based on the seismicity recorded during this time period, a GSI mission with a lifetime of 10 years could have been in position to observe at least 13 (22 on average) earthquakes of magnitude larger than 6, and at least one (2 on average) earthquake of magnitude larger than 7. A GSI would provide data unprecedented in its extent and temporal and spatial resolution. It would provide this data for some of the world's most seismically active regions, and do so better and at a lower cost than could be done with ground-based instrumentation. A GSI would revolutionize the understanding of earthquake dynamics, perhaps leading ultimately to effective warning

  2. Minimizers with discontinuous velocities for the electromagnetic variational method

    SciTech Connect

    De Luca, Jayme

    2010-08-15

    The electromagnetic two-body problem has neutral differential delay equations of motion that, for generic boundary data, can have solutions with discontinuous derivatives. If one wants to use these neutral differential delay equations with arbitrary boundary data, solutions with discontinuous derivatives must be expected and allowed. Surprisingly, Wheeler-Feynman electrodynamics has a boundary value variational method for which minimizer trajectories with discontinuous derivatives are also expected, as we show here. The variational method defines continuous trajectories with piecewise defined velocities and accelerations, and electromagnetic fields defined by the Euler-Lagrange equations on trajectory points. Here we use the piecewise defined minimizers with the Lienard-Wierchert formulas to define generalized electromagnetic fields almost everywhere (but on sets of points of zero measure where the advanced/retarded velocities and/or accelerations are discontinuous). Along with this generalization we formulate the generalized absorber hypothesis that the far fields vanish asymptotically almost everywhere and show that localized orbits with far fields vanishing almost everywhere must have discontinuous velocities on sewing chains of breaking points. We give the general solution for localized orbits with vanishing far fields by solving a (linear) neutral differential delay equation for these far fields. We discuss the physics of orbits with discontinuous derivatives stressing the differences to the variational methods of classical mechanics and the existence of a spinorial four-current associated with the generalized variational electrodynamics.

  3. Hyperspherical Sparse Approximation Techniques for High-Dimensional Discontinuity Detection

    SciTech Connect

    Zhang, Guannan; Webster, Clayton G.; Gunzburger, Max; Burkardt, John

    2016-08-04

    This work proposes a hyperspherical sparse approximation framework for detecting jump discontinuities in functions in high-dimensional spaces. The need for a novel approach results from the theoretical and computational inefficiencies of well-known approaches, such as adaptive sparse grids, for discontinuity detection. Our approach constructs the hyperspherical coordinate representation of the discontinuity surface of a function. Then sparse approximations of the transformed function are built in the hyperspherical coordinate system, with values at each point estimated by solving a one-dimensional discontinuity detection problem. Due to the smoothness of the hypersurface, the new technique can identify jump discontinuities with significantly reduced computational cost, compared to existing methods. Several approaches are used to approximate the transformed discontinuity surface in the hyperspherical system, including adaptive sparse grid and radial basis function interpolation, discrete least squares projection, and compressed sensing approximation. Moreover, hierarchical acceleration techniques are also incorporated to further reduce the overall complexity. In conclusion, rigorous complexity analyses of the new methods are provided, as are several numerical examples that illustrate the effectiveness of our approach.

  4. Minimizers with discontinuous velocities for the electromagnetic variational method

    NASA Astrophysics Data System (ADS)

    de Luca, Jayme

    2010-08-01

    The electromagnetic two-body problem has neutral differential delay equations of motion that, for generic boundary data, can have solutions with discontinuous derivatives. If one wants to use these neutral differential delay equations with arbitrary boundary data, solutions with discontinuous derivatives must be expected and allowed. Surprisingly, Wheeler-Feynman electrodynamics has a boundary value variational method for which minimizer trajectories with discontinuous derivatives are also expected, as we show here. The variational method defines continuous trajectories with piecewise defined velocities and accelerations, and electromagnetic fields defined by the Euler-Lagrange equations on trajectory points. Here we use the piecewise defined minimizers with the Liénard-Wierchert formulas to define generalized electromagnetic fields almost everywhere (but on sets of points of zero measure where the advanced/retarded velocities and/or accelerations are discontinuous). Along with this generalization we formulate the generalized absorber hypothesis that the far fields vanish asymptotically almost everywhere and show that localized orbits with far fields vanishing almost everywhere must have discontinuous velocities on sewing chains of breaking points. We give the general solution for localized orbits with vanishing far fields by solving a (linear) neutral differential delay equation for these far fields. We discuss the physics of orbits with discontinuous derivatives stressing the differences to the variational methods of classical mechanics and the existence of a spinorial four-current associated with the generalized variational electrodynamics.

  5. Minimizers with discontinuous velocities for the electromagnetic variational method.

    PubMed

    De Luca, Jayme

    2010-08-01

    The electromagnetic two-body problem has neutral differential delay equations of motion that, for generic boundary data, can have solutions with discontinuous derivatives. If one wants to use these neutral differential delay equations with arbitrary boundary data, solutions with discontinuous derivatives must be expected and allowed. Surprisingly, Wheeler-Feynman electrodynamics has a boundary value variational method for which minimizer trajectories with discontinuous derivatives are also expected, as we show here. The variational method defines continuous trajectories with piecewise defined velocities and accelerations, and electromagnetic fields defined by the Euler-Lagrange equations on trajectory points. Here we use the piecewise defined minimizers with the Liénard-Wierchert formulas to define generalized electromagnetic fields almost everywhere (but on sets of points of zero measure where the advanced/retarded velocities and/or accelerations are discontinuous). Along with this generalization we formulate the generalized absorber hypothesis that the far fields vanish asymptotically almost everywhere and show that localized orbits with far fields vanishing almost everywhere must have discontinuous velocities on sewing chains of breaking points. We give the general solution for localized orbits with vanishing far fields by solving a (linear) neutral differential delay equation for these far fields. We discuss the physics of orbits with discontinuous derivatives stressing the differences to the variational methods of classical mechanics and the existence of a spinorial four-current associated with the generalized variational electrodynamics.

  6. Ionospheric mid-latitude response to solar wind discontinuities

    NASA Astrophysics Data System (ADS)

    Munteanu, Costel; Mosna, Zbysek; Kouba, Daniel; Echim, Marius

    2013-04-01

    We have compiled a database of 356 discontinuities detected by both the Advanced Composition Explorer ACE) and Cluster satellites in the solar wind between 2001-2012 and analyzed their ionospheric response. Each discontinuity of the data base is defined by a change of at least 5 nT in less than 5 min in one or more components of the interplanetary magnetic field (IMF). The discontinuities are observed in January-April every year, when Cluster enters the solar wind. The ionospheric effects of solar wind discontinuities are investigated by checking the variations of critical frequencies foF2, the heights of the F layer and the ionospheric plasma dynamics recorded using ground measurement with a time resolution of 15 minutes from mid-latitude digisondes located in Czech Republic. The time delay between solar wind input and the ionospheric response is analyzed using the characteristics and the shape of the ionograms. The geoeffectiveness of the solar wind discontinuities is expressed as correlation between key plasma parameters (e,g, the solar wind velocity, magnetic jump across the discontinuity) and the ionospheric variations. Solar cycle effects are also discussed.

  7. Hyperspherical Sparse Approximation Techniques for High-Dimensional Discontinuity Detection

    DOE PAGES

    Zhang, Guannan; Webster, Clayton G.; Gunzburger, Max; ...

    2016-08-04

    This work proposes a hyperspherical sparse approximation framework for detecting jump discontinuities in functions in high-dimensional spaces. The need for a novel approach results from the theoretical and computational inefficiencies of well-known approaches, such as adaptive sparse grids, for discontinuity detection. Our approach constructs the hyperspherical coordinate representation of the discontinuity surface of a function. Then sparse approximations of the transformed function are built in the hyperspherical coordinate system, with values at each point estimated by solving a one-dimensional discontinuity detection problem. Due to the smoothness of the hypersurface, the new technique can identify jump discontinuities with significantly reduced computationalmore » cost, compared to existing methods. Several approaches are used to approximate the transformed discontinuity surface in the hyperspherical system, including adaptive sparse grid and radial basis function interpolation, discrete least squares projection, and compressed sensing approximation. Moreover, hierarchical acceleration techniques are also incorporated to further reduce the overall complexity. In conclusion, rigorous complexity analyses of the new methods are provided, as are several numerical examples that illustrate the effectiveness of our approach.« less

  8. High Resolution Near Surface 3D Seismic Experiments: A Carbonate Platform vs. a Siliciclastic Sequence

    NASA Astrophysics Data System (ADS)

    Filippidou, N.; Drijkoningen, G.; Braaksma, H.; Verwer, K.; Kenter, J.

    2005-05-01

    Interest in high-resolution 3D seismic experiments for imaging shallow targets has increased over the past years. Many case studies presented, show that producing clear seismic images with this non-evasive method, is still a challenge. We use two test-sites where nearby outcrops are present so that an accurate geological model can be built and the seismic result validated. The first so-called natural field laboratory is located in Boulonnais (N. France). It is an upper Jurassic siliciclastic sequence; age equivalent of the source rock of N. Sea. The second one is located in Cap Blanc,to the southwest of the Mallorca island(Spain); depicting an excellent example of Miocene prograding reef platform (Llucmajor Platform); it is a textbook analog for carbonate reservoirs. In both cases, the multidisciplinary experiment included the use of multicomponent and quasi- or 3D seismic recordings. The target depth does not exceed 120m. Vertical and shear portable vibrators were used as source. In the center of the setups, boreholes were drilled and Vertical Seismic Profiles were shot, along with core and borehole measurements both in situ and in the laboratory. These two geologically different sites, with different seismic stratigraphy have provided us with exceptionally high resolution seismic images. In general seismic data was processed more or less following standard procedures, a few innovative techniques on the Mallorca data, as rotation of horizontal components, 3D F-K filter and addition of parallel profiles, have improved the seismic image. In this paper we discuss the basic differences as seen on the seismic sections. The Boulonnais data present highly continuous reflection patterns of extremenly high resolution. This facilitated a high resolution stratigraphic description. Results from the VSP showed substantial wave energy attenuation. However, the high-fold (330 traces ) Mallorca seismic experiment returned a rather discontinuous pattern of possible reflectors

  9. Modelling of NW Himalayan Seismicity

    NASA Astrophysics Data System (ADS)

    Bansal, A. R.; Dimri, V. P.

    2014-12-01

    The northwest Himalaya is seismicity active region due to the collision of Indian and Eurasian plates and experienced many large earthquakes in past. A systematic analysis of seismicity is useful for seismic hazard estimation of the region. We analyzed the seismicity of northwestern Himalaya since 1980. The magnitude of completeness of the catalogue is carried out using different methods and found as 3.0. A large difference in magnitude of completeness is found using different methods and a reliable value is obtained after testing the distribution of magnitudes with time. The region is prone to large earthquake and many studied have shown that seismic activation or quiescence takes place before large earthquakes. We studied such behavior of seismicity based on Epidemic Type Aftershock Sequence (ETAS) model and found that a stationary ETAS model is more suitable for modelling the seismicity of this region. The earthquake catalogue is de-clustered using stochasting approach to study behavior of background and triggered seismicity. The triggered seismicity is found to have shallower depths as compared to the background events.

  10. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    SciTech Connect

    Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin

    2003-04-01

    In this report we will show results of seismic and well log derived attenuation attributes from a deep water Gulf of Mexico data set. This data was contributed by Burlington Resources and Seitel Inc. The data consists of ten square kilometers of 3D seismic data and three well penetrations. We have computed anomalous seismic absorption attributes on the seismic data and have computed Q from the well log curves. The results show a good correlation between the anomalous absorption (attenuation) attributes and the presence of gas as indicated by well logs.

  11. Seismic hazard estimation of northern Iran using smoothed seismicity

    NASA Astrophysics Data System (ADS)

    Khoshnevis, Naeem; Taborda, Ricardo; Azizzadeh-Roodpish, Shima; Cramer, Chris H.

    2017-03-01

    This article presents a seismic hazard assessment for northern Iran, where a smoothed seismicity approach has been used in combination with an updated seismic catalog and a ground motion prediction equation recently found to yield good fit with data. We evaluate the hazard over a geographical area including the seismic zones of Azerbaijan, the Alborz Mountain Range, and Kopeh-Dagh, as well as parts of other neighboring seismic zones that fall within our region of interest. In the chosen approach, seismic events are not assigned to specific faults but assumed to be potential seismogenic sources distributed within regular grid cells. After performing the corresponding magnitude conversions, we decluster both historical and instrumental seismicity catalogs to obtain earthquake rates based on the number of events within each cell, and smooth the results to account for the uncertainty in the spatial distribution of future earthquakes. Seismicity parameters are computed for each seismic zone separately, and for the entire region of interest as a single uniform seismotectonic region. In the analysis, we consider uncertainties in the ground motion prediction equation, the seismicity parameters, and combine the resulting models using a logic tree. The results are presented in terms of expected peak ground acceleration (PGA) maps and hazard curves at selected locations, considering exceedance probabilities of 2 and 10% in 50 years for rock site conditions. According to our results, the highest levels of hazard are observed west of the North Tabriz and east of the North Alborz faults, where expected PGA values are between about 0.5 and 1 g for 10 and 2% probability of exceedance in 50 years, respectively. We analyze our results in light of similar estimates available in the literature and offer our perspective on the differences observed. We find our results to be helpful in understanding seismic hazard for northern Iran, but recognize that additional efforts are necessary to

  12. Seismic facies interpretation of Mesozoic sequences, Shiwandashan basin, China

    SciTech Connect

    Leu, Leikuang; Armentrout, J.M.; Faz, J.J. )

    1991-03-01

    Integration of outcrop and subsurface geologic data with seismic facies analysis identified three exploration plays in Shiwandashan basin, southeastern China: Triassic Submarine Fan: Elongate-mounded packages of variable amplitude, discontinuous, nonparallel reflections occur basinward of the slope and are downlapped by prograding slope clinoforms. This facies is undrilled. Basin modeling suggests the mounded seismic facies correlates with outcrops of Triassic marine siliclastic turbidites which grade laterally into basinal mudstone/limestone couplets. Triassic Shelf Carbonates: Localized, high amplitude parallel reflections occur in a retrograde succession at the top of the Triassic prograding clinoform. These high amplitude seismic facies are calibrated with drilled carbonate facies and are correlated with outcrops of upper Triassic shelf and shelf-edge reefs that contain two generations of migrated hydrocarbons. Jurassic Fan Deltas: Thick northeast-southwest bidirectional downlapping hummocks of variable amplitude reflections and intersecting northwest downlapping clinoforms form large mounds and grade laterally to moderately continuous parallel reflections. The hummocky-clinoform mound facies is calibrated by drilled, poorly sorted conglomerates and correlates with outcrops of a Jurassic synrift basin-fill succession. These Jurassic rocks are interpreted as fan-deltas grading laterally to sandy fluvial and shaley lacustrine facies. The geochemical data suggest a potential gas-prone play for the Triassic submarine fans and potential oil-prone play for the stratigraphically shallower Triassic shelf and shelf-edge reefs. The Jurassic fan delta play drilled tight with no hydrocarbons.

  13. Mapping bedrock beneath glacial till using CDP seismic reflection methods

    SciTech Connect

    Keiswetter, D.; Black, R.; Steeples, D.

    1994-03-01

    This paper is a case history demonstrating the applicability of the common depth point (CDP) seismic reflection method to image bedrock beneath glacial till in northwestern Iowa. Reflections from the base of the 40-m thick glacial till are clearly observable on field files at around 45 to 50 ms two-way traveltime and possess a dominant frequency of around 100 Hz. The bedrock reflection is confirmed by drill data. The seismic data are of sufficient quality to detect local bedrock topographic changes and to interpret discontinuities along the till-bedrock interface. Finite-difference synthetic seismograms substantiate the interpreted reflections and the diffraction signatures from faults observed on the field files. At some locations along the seismic line, intra-till reflections are apparent on the field files. These intra-till features are on the order of tens of meters in length along the line traverse and reflections from them are not enhanced by common depth point processing. Intra-till reflections could be indicative of gravels or other alluvial materials that may serve as local aquifers.

  14. Deep seismic reflection survey of Queen Charlotte basin

    SciTech Connect

    Rohr, K.; Dietrich, J. )

    1990-05-01

    One thousand kilometers of 14 sec marine seismic reflection data collected in the Queen Charlotte basin region in 1988 provide excellent images of Tertiary sedimentary basin fill as well as deep crustal structure. The Tertiary section is highly variable in thickness, with up to 6,500 m of strata occurring in the deepest depocenters in a complex array of subbasins and half-grabens. Widespread extensional deformation including normal faulting during basin development was followed later by compressional deformation in the northern half of the basin. Sediments have been compressed into open folds and flower structures; some normal faults have been reactivated as reverse faults. Seismic interpretations of structural features suggest that Tertiary extension and compression have developed in response to strike-slip tectonics. Crust under Hecate Strait is more reflective than under Queen Charlotte Sound; geological interpretation of these discontinuous and structurally variable crustal reflections requires further analysis. In some areas of the basin (e.g., near the Sockeye wells, Hecate Strait) coherent reflections occur directly beneath the Tertiary section and may be images of Mesozoic strata. Deep reflections damaged at times of 7.0 to 10.0 sec on many profiles, provide for the seismic differentiation between reflective lower crust and nonreflective upper mantle. Estimated crustal thicknesses of 18-21 km beneath Hecate Strait and Queen Charlotte Sound indicate significant coastal thinning beneath the Queen Charlotte basin.

  15. The crustal structure of the NW Moroccan continental margin from wide-angle and reflection seismic data

    NASA Astrophysics Data System (ADS)

    Contrucci, I.; Klingelhöfer, F.; Perrot, J.; Bartolome, R.; Gutscher, M.-A.; Sahabi, M.; Malod, J.; Rehault, J.-P.

    2004-10-01

    The Atlantic margin off Morocco with its neighbouring Jurassic oceanic crust is one of the oldest on earth. It is conjugate to the Nova Scotia margin of North America. The SISMAR marine seismic survey acquired deep reflection seismic data as well as wide-angle seismic profiles in order to image the deep structure of the margin, characterize the nature of the crust in the transitional domain and define the geometry of the synrift basins. We present results from the combined interpretation of the reflection seismic, wide-angle seismic and gravity data along a 440-km-long profile perpendicular to the margin at 33-34°N, extending from nearly normal oceanic crust in the vicinity of Coral Patch seamount to the coast at El Jadida and approximately 130 km inland. The shallow structure is well imaged by the reflection seismic data and shows a thick sedimentary cover that is locally perturbed by salt tectonics and reverse faulting. The sedimentary basin thickens from 1.5 km on the normal oceanic crust to a maximum thickness of 6 km at the base of the continental slope. Multichannel seismic (MCS) data image basement structures including a few tilted fault blocks and a transition zone to a thin crust. A strong discontinuous reflection at 12 s two-way travel-time (TWT) is interpreted as the Moho discontinuity. As a result of the good data quality, the deep crustal structure (depth and velocity field) is well constrained through the wide-angle seismic modelling. The crust thins from 35 km underneath the continent to approximately 7 km at the western end of the profile. The transitional region has a width of 150 km. Crustal velocities are lowest at the continental slope, probably as a result of faulting and fracturing of the upper crust. Upper-mantle velocities could be well defined from the ocean bottom seismometer (OBS) and land station data throughout the model.

  16. Validating induced seismicity forecast models—Induced Seismicity Test Bench

    NASA Astrophysics Data System (ADS)

    Király-Proag, Eszter; Zechar, J. Douglas; Gischig, Valentin; Wiemer, Stefan; Karvounis, Dimitrios; Doetsch, Joseph

    2016-08-01

    Induced earthquakes often accompany fluid injection, and the seismic hazard they pose threatens various underground engineering projects. Models to monitor and control induced seismic hazard with traffic light systems should be probabilistic, forward-looking, and updated as new data arrive. In this study, we propose an Induced Seismicity Test Bench to test and rank such models; this test bench can be used for model development, model selection, and ensemble model building. We apply the test bench to data from the Basel 2006 and Soultz-sous-Forêts 2004 geothermal stimulation projects, and we assess forecasts from two models: Shapiro and Smoothed Seismicity (SaSS) and Hydraulics and Seismics (HySei). These models incorporate a different mix of physics-based elements and stochastic representation of the induced sequences. Our results show that neither model is fully superior to the other. Generally, HySei forecasts the seismicity rate better after shut-in but is only mediocre at forecasting the spatial distribution. On the other hand, SaSS forecasts the spatial distribution better and gives better seismicity rate estimates before shut-in. The shut-in phase is a difficult moment for both models in both reservoirs: the models tend to underpredict the seismicity rate around, and shortly after, shut-in.

  17. Precise measurements of enthalpy of postspinel transition in Mg2SiO4 and application to the phase boundary calculation

    NASA Astrophysics Data System (ADS)

    Kojitani, Hiroshi; Inoue, Toru; Akaogi, Masaki

    2016-02-01

    Drop solution enthalpies (ΔH°d-s) of Mg2SiO4 ringwoodite, Mg2SiO4 forsterite, perovskite-type MgSiO3 (bridgmanite), and MgSiO3 enstatite were measured using a single batch of 2PbO · B2O3 solvent at 978 K. From the obtained ΔH°d-s values of Mg2SiO4 ringwoodite, MgSiO3 bridgmanite, and MgO, an enthalpy of the postspinel phase transition, Mg2SiO4 ringwoodite = MgSiO3 bridgmanite + MgO, was determined to be 78.54 ± 2.28 kJ/mol. Thermodynamic calculations using the obtained phase transition enthalpy and available thermochemical and thermoelastic data provided the phase transition pressure of 23.1 ± 1.4 GPa at 298 K. This value is comparable to those at about 2000 K determined by previous experimental and theoretical studies, implying a considerably gentle Clapeyron slope. Thermodynamic calculations of the postspinel boundary at high temperatures in the anhydrous condition by changing thermochemical and thermoelastic parameters within the uncertainties suggested that the postspinel transition pressure of Mg2SiO4 at high temperature is lower than the pressure corresponding to the global average depth of the "660 km" seismic discontinuity in the Earth's mantle (~23.5 GPa) estimated from one-dimensional reference Earth models and that a most likely Clapeyron slope is about -1 MPa/K. The postspinel transition in the hydrous condition with about 2 wt % H2O, which shows higher transition pressure and steeper Clapeyron slope than those in the anhydrous condition, gives a plausible explanation for seismic observations on the 660 km discontinuity, and therefore, hydrous mantle transition zone would be required.

  18. 3D dynamic rupture with anelastic wave propagation using an hp-adaptive Discontinuous Galerkin method

    NASA Astrophysics Data System (ADS)

    Tago, J.; Cruz-Atienza, V. M.; Etienne, V.; Virieux, J.; Benjemaa, M.; Sanchez-Sesma, F. J.

    2010-12-01

    Simulating any realistic seismic scenario requires incorporating physical basis into the model. Considering both the dynamics of the rupture process and the anelastic attenuation of seismic waves is essential to this purpose and, therefore, we choose to extend the hp-adaptive Discontinuous Galerkin finite-element method to integrate these physical aspects. The 3D elastodynamic equations in an unstructured tetrahedral mesh are solved with a second-order time marching approach in a high-performance computing environment. The first extension incorporates the viscoelastic rheology so that the intrinsic attenuation of the medium is considered in terms of frequency dependent quality factors (Q). On the other hand, the extension related to dynamic rupture is integrated through explicit boundary conditions over the crack surface. For this visco-elastodynamic formulation, we introduce an original discrete scheme that preserves the optimal code performance of the elastodynamic equations. A set of relaxation mechanisms describes the behavior of a generalized Maxwell body. We approximate almost constant Q in a wide frequency range by selecting both suitable relaxation frequencies and anelastic coefficients characterizing these mechanisms. In order to do so, we solve an optimization problem which is critical to minimize the amount of relaxation mechanisms. Two strategies are explored: 1) a least squares method and 2) a genetic algorithm (GA). We found that the improvement provided by the heuristic GA method is negligible. Both optimization strategies yield Q values within the 5% of the target constant Q mechanism. Anelastic functions (i.e. memory variables) are introduced to efficiently evaluate the time convolution terms involved in the constitutive equations and thus to minimize the computational cost. The incorporation of anelastic functions implies new terms with ordinary differential equations in the mathematical formulation. We solve these equations using the same order

  19. Seismic monitoring of Poland - temporary seismic project - first results

    NASA Astrophysics Data System (ADS)

    Trojanowski, J.; Plesiewicz, B.; Wiszniowski, J.; Suchcicki, J.; Tokarz, A.

    2012-04-01

    The aim of the project is to develop national database of seismic activity for seismic hazard assessment. Poland is known as a region of very low seismicity, however some earthquakes occur from time to time. The historical catalogue consists of less than one hundred earthquakes in the time span of almost one thousand years. Due to such a low occurrence rate, the study has been focussing on events at magnitudes lower than 2 which are more likely to occur during a few-year-long project. There are 24 mobile seismic stations involved in the project which are deployed in temporary locations close to humans neighbourhood. It causes a high level of noise and disturbances in recorded seismic signal. Moreover, the majority of Polish territory is covered by a thick sediments. It causes the problem of a reliable detection method for small seismic events in noisy data. The majority of algorithms is based on the concept of STA/LTA ratio and is designed for strong teleseismic events registered on many stations. Unfortunately they fail on the problem of weak events in the signal with noise and disturbances. It has been decided to apply Real Time Recurrent Neural Network (RTRN) to detect small natural seismic events from Poland. This method is able to assess relations of seismic signal in frequency domains as well as in time of seismic phases. The RTRN was taught by wide range of seismic signals - regional, teleseismic as well as blasts. The method is routinely used to analyse data from the project. In the firs two years of the project the seismic network was set in southern Poland, where relatively large seismicity in known. Since the mid-2010 the stations have been working in several regions of central and northern Poland where some minor historical earthquakes occurred. Over one hundred seismic events in magnitude range from 0.5 to 2.3 confirms the activity of Podhale region (Tatra Mountains, Carpathians), where an earthquake of magnitude 4.3 occurred in 2004. Initially three

  20. High-order Hybridized Discontinuous Galerkin (HDG) method for wave propagation simulation in complex geophysical media (elastic, acoustic and hydro-acoustic); an unifying framework to couple continuous Spectral Element and Discontinuous Galerkin Methods

    NASA Astrophysics Data System (ADS)

    Terrana, Sebastien; Vilotte, Jean-Pierre; Guillot, Laurent; Mariotti, Christian

    2015-04-01

    Today seismological observation systems combine broadband seismic receivers, hydrophones and micro-barometers antenna that provide complementary observations of source-radiated waves in heterogeneous and complex geophysical media. Exploiting these observations requires accurate and multi-physics - elastic, hydro-acoustic, infrasonic - wave simulation methods. A popular approach is the Spectral Element Method (SEM) (Chaljub et al, 2006) which is high-order accurate (low dispersion error), very flexible to parallelization and computationally attractive due to efficient sum factorization technique and diagonal mass matrix. However SEMs suffer from lack of flexibility in handling complex geometry and multi-physics wave propagation. High-order Discontinuous Galerkin Methods (DGMs), i.e. Dumbser et al (2006), Etienne et al. (2010), Wilcox et al (2010), are recent alternatives that can handle complex geometry, space-and-time adaptativity, and allow efficient multi-physics wave coupling at interfaces. However, DGMs are more memory demanding and less computationally attractive than SEMs, especially when explicit time stepping is used. We propose a new class of higher-order Hybridized Discontinuous Galerkin Spectral Elements (HDGSEM) methods for spatial discretization of wave equations, following the unifying framework for hybridization of Cockburn et al (2009) and Nguyen et al (2011), which allows for a single implementation of conforming and non-conforming SEMs. When used with energy conserving explicit time integration schemes, HDGSEM is flexible to handle complex geometry, computationally attractive and has significantly less degrees of freedom than classical DGMs, i.e., the only coupled unknowns are the single-valued numerical traces of the velocity field on the element's faces. The formulation can be extended to model fractional energy loss at interfaces between elastic, acoustic and hydro-acoustic media. Accuracy and performance of the HDGSEM are illustrated and

  1. Automating Shallow Seismic Imaging

    SciTech Connect

    Steeples, Don W.

    2004-12-09

    This seven-year, shallow-seismic reflection research project had the aim of improving geophysical imaging of possible contaminant flow paths. Thousands of chemically contaminated sites exist in the United States, including at least 3,700 at Department of Energy (DOE) facilities. Imaging technologies such as shallow seismic reflection (SSR) and ground-penetrating radar (GPR) sometimes are capable of identifying geologic conditions that might indicate preferential contaminant-flow paths. Historically, SSR has been used very little at depths shallower than 30 m, and even more rarely at depths of 10 m or less. Conversely, GPR is rarely useful at depths greater than 10 m, especially in areas where clay or other electrically conductive materials are present near the surface. Efforts to image the cone of depression around a pumping well using seismic methods were only partially successful (for complete references of all research results, see the full Final Technical Report, DOE/ER/14826-F), but peripheral results included development of SSR methods for depths shallower than one meter, a depth range that had not been achieved before. Imaging at such shallow depths, however, requires geophone intervals of the order of 10 cm or less, which makes such surveys very expensive in terms of human time and effort. We also showed that SSR and GPR could be used in a complementary fashion to image the same volume of earth at very shallow depths. The primary research focus of the second three-year period of funding was to develop and demonstrate an automated method of conducting two-dimensional (2D) shallow-seismic surveys with the goal of saving time, effort, and money. Tests involving the second generation of the hydraulic geophone-planting device dubbed the ''Autojuggie'' showed that large numbers of geophones can be placed quickly and automatically and can acquire high-quality data, although not under rough topographic conditions. In some easy-access environments, this device could

  2. Elastic-Wavefield Seismic Stratigraphy: A New Seismic Imaging Technology

    SciTech Connect

    Bob A. Hardage; Milo M. Backus; Michael V. DeAngelo; Sergey Fomel; Khaled Fouad; Robert J. Graebner; Paul E. Murray; Randy Remington; Diana Sava

    2006-07-31

    The purpose of our research has been to develop and demonstrate a seismic technology that will provide the oil and gas industry a better methodology for understanding reservoir and seal architectures and for improving interpretations of hydrocarbon systems. Our research goal was to expand the valuable science of seismic stratigraphy beyond the constraints of compressional (P-P) seismic data by using all modes (P-P, P-SV, SH-SH, SV-SV, SV-P) of a seismic elastic wavefield to define depositional sequences and facies. Our objective was to demonstrate that one or more modes of an elastic wavefield may image stratal surfaces across some stratigraphic intervals that are not seen by companion wave modes and thus provide different, but equally valid, information regarding depositional sequences and sedimentary facies within that interval. We use the term elastic wavefield stratigraphy to describe the methodology we use to integrate seismic sequences and seismic facies from all modes of an elastic wavefield into a seismic interpretation. We interpreted both onshore and marine multicomponent seismic surveys to select the data examples that we use to document the principles of elastic wavefield stratigraphy. We have also used examples from published papers that illustrate some concepts better than did the multicomponent seismic data that were available for our analysis. In each interpretation study, we used rock physics modeling to explain how and why certain geological conditions caused differences in P and S reflectivities that resulted in P-wave seismic sequences and facies being different from depth-equivalent S-wave sequences and facies across the targets we studied.

  3. Seismic risk perception test

    NASA Astrophysics Data System (ADS)

    Crescimbene, Massimo; La Longa, Federica; Camassi, Romano; Pino, Nicola Alessandro

    2013-04-01

    The perception of risks involves the process of collecting, selecting and interpreting signals about uncertain impacts of events, activities or technologies. In the natural sciences the term risk seems to be clearly defined, it means the probability distribution of adverse effects, but the everyday use of risk has different connotations (Renn, 2008). The two terms, hazards and risks, are often used interchangeably by the public. Knowledge, experience, values, attitudes and feelings all influence the thinking and judgement of people about the seriousness and acceptability of risks. Within the social sciences however the terminology of 'risk perception' has become the conventional standard (Slovic, 1987). The mental models and other psychological mechanisms which people use to judge risks (such as cognitive heuristics and risk images) are internalized through social and cultural learning and constantly moderated (reinforced, modified, amplified or attenuated) by media reports, peer influences and other communication processes (Morgan et al., 2001). Yet, a theory of risk perception that offers an integrative, as well as empirically valid, approach to understanding and explaining risk perception is still missing". To understand the perception of risk is necessary to consider several areas: social, psychological, cultural, and their interactions. Among the various research in an international context on the perception of natural hazards, it seemed promising the approach with the method of semantic differential (Osgood, C.E., Suci, G., & Tannenbaum, P. 1957, The measurement of meaning. Urbana, IL: University of Illinois Press). The test on seismic risk perception has been constructed by the method of the semantic differential. To compare opposite adjectives or terms has been used a Likert's scale to seven point. The test consists of an informative part and six sections respectively dedicated to: hazard; vulnerability (home and workplace); exposed value (with reference to

  4. Deep seismic exploration into the Arctic Lithosphere: Arctic-2012 Russian wide-angle seismic experiment

    NASA Astrophysics Data System (ADS)

    Kashubin, S.

    2013-12-01

    Integrated geological and geophysical studies of the Earth's crust and upper mantle (the Russian project 'Arctic-2012') were carried out in 2012 in the Mendeleev Rise, central Arctic. The set of studies included wide-angle seismic observations along the line crossing the Mendeleev Rise in its southern part. The DSS seismic survey was aimed at the determination of the Mendeleev Rise crust type. A high-power air gun (120 liters or 7320 cu.in) and ocean stations with multi-component recording (X, Y, Z geophone components and a hydrophone) were used for the DSS. The line was studied using a dense system of observation: bottom station spacing was from 10 to 20 km, excitation point spacing (seismic traces interval) was 315 m. Observation data were obtained in 27 location points of bottom stations, the distance between the first and the last stations was 480 km, the length of the excitation line was 740 km. In DSS wave fields, in the first and later arrivals, there are refracted and reflected waves associated with boundaries in the sedimentary cover, with the top of the basement, and with boundaries in the consolidated crust, including its bottom (Moho discontinuity). The waves could be traced for offsets up to 170-240 km. The DSS line coincides with the near-vertical CMP line worked out with the use of a 4500-m-long seismic streamer and with a 50 m shot point interval that allowed essential detalization of the upper part of the section and taking it into account in the construction of a deep crust model. The deep velocity model was constructed using ray-trace modeling of compressional, shear, and converted waves with the use of the SeisWide program. Estimates were obtained for Vp/Vs velocity ratios, which played an important role in determining the type of crust. The results of the interpretation show that the Mendeleev Rise section corresponds to sections of a thin continental crust of shelf seas and a thinned continental crust of submarine ridges and rises.

  5. A high-order discontinuous Galerkin method for wave propagation through coupled elastic-acoustic media

    NASA Astrophysics Data System (ADS)

    Wilcox, Lucas C.; Stadler, Georg; Burstedde, Carsten; Ghattas, Omar

    2010-12-01

    We introduce a high-order discontinuous Galerkin (dG) scheme for the numerical solution of three-dimensional (3D) wave propagation problems in coupled elastic-acoustic media. A velocity-strain formulation is used, which allows for the solution of the acoustic and elastic wave equations within the same unified framework. Careful attention is directed at the derivation of a numerical flux that preserves high-order accuracy in the presence of material discontinuities, including elastic-acoustic interfaces. Explicit expressions for the 3D upwind numerical flux, derived as an exact solution for the relevant Riemann problem, are provided. The method supports h-non-conforming meshes, which are particularly effective at allowing local adaptation of the mesh size to resolve strong contrasts in the local wavelength, as well as dynamic adaptivity to track solution features. The use of high-order elements controls numerical dispersion, enabling propagation over many wave periods. We prove consistency and stability of the proposed dG scheme. To study the numerical accuracy and convergence of the proposed method, we compare against analytical solutions for wave propagation problems with interfaces, including Rayleigh, Lamb, Scholte, and Stoneley waves as well as plane waves impinging on an elastic-acoustic interface. Spectral rates of convergence are demonstrated for these problems, which include a non-conforming mesh case. Finally, we present scalability results for a parallel implementation of the proposed high-order dG scheme for large-scale seismic wave propagation in a simplified earth model, demonstrating high parallel efficiency for strong scaling to the full size of the Jaguar Cray XT5 supercomputer.

  6. A high-order discontinuous Galerkin method for wave propagation through coupled elastic-acoustic media

    SciTech Connect

    Wilcox, Lucas C.; Stadler, Georg; Burstedde, Carsten; Ghattas, Omar

    2010-12-10

    We introduce a high-order discontinuous Galerkin (dG) scheme for the numerical solution of three-dimensional (3D) wave propagation problems in coupled elastic-acoustic media. A velocity-strain formulation is used, which allows for the solution of the acoustic and elastic wave equations within the same unified framework. Careful attention is directed at the derivation of a numerical flux that preserves high-order accuracy in the presence of material discontinuities, including elastic-acoustic interfaces. Explicit expressions for the 3D upwind numerical flux, derived as an exact solution for the relevant Riemann problem, are provided. The method supports h-non-conforming meshes, which are particularly effective at allowing local adaptation of the mesh size to resolve strong contrasts in the local wavelength, as well as dynamic adaptivity to track solution features. The use of high-order elements controls numerical dispersion, enabling propagation over many wave periods. We prove consistency and stability of the proposed dG scheme. To study the numerical accuracy and convergence of the proposed method, we compare against analytical solutions for wave propagation problems with interfaces, including Rayleigh, Lamb, Scholte, and Stoneley waves as well as plane waves impinging on an elastic-acoustic interface. Spectral rates of convergence are demonstrated for these problems, which include a non-conforming mesh case. Finally, we present scalability results for a parallel implementation of the proposed high-order dG scheme for large-scale seismic wave propagation in a simplified earth model, demonstrating high parallel efficiency for strong scaling to the full size of the Jaguar Cray XT5 supercomputer.

  7. Procedures for computing site seismicity

    NASA Astrophysics Data System (ADS)

    Ferritto, John

    1994-02-01

    This report was prepared as part of the Navy's Seismic Hazard Mitigation Program. The Navy has numerous bases located in seismically active regions throughout the world. Safe effective design of waterfront structures requires determining expected earthquake ground motion. The Navy's problem is further complicated by the presence of soft saturated marginal soils that can significantly amplify the levels of seismic shaking as evidenced in the 1989 Loma Prieta earthquake. The Naval Facilities Engineering Command's seismic design manual, NAVFAC P355.l, requires a probabilistic assessment of ground motion for design of essential structures. This report presents the basis for the Navy's Seismic Hazard Analysis procedure that was developed and is intended to be used with the Seismic Hazard Analysis computer program and user's manual. This report also presents data on geology and seismology to establish the background for the seismic hazard model developed. The procedure uses the historical epicenter data base and available geologic data, together with source models, recurrence models, and attenuation relationships to compute the probability distribution of site acceleration and an appropriate spectra. This report discusses the developed stochastic model for seismic hazard evaluation and the associated research.

  8. Weak localization of seismic waves.

    PubMed

    Larose, E; Margerin, L; Van Tiggelen, B A; Campillo, M

    2004-07-23

    We report the observation of weak localization of seismic waves in a natural environment. It emerges as a doubling of the seismic energy around the source within a spot of the width of a wavelength, which is several tens of meters in our case. The characteristic time for its onset is the scattering mean-free time that quantifies the internal heterogeneity.

  9. Seismic Data Gathering and Validation

    SciTech Connect

    Coleman, Justin

    2015-02-01

    Three recent earthquakes in the last seven years have exceeded their design basis earthquake values (so it is implied that damage to SSC’s should have occurred). These seismic events were recorded at North Anna (August 2011, detailed information provided in [Virginia Electric and Power Company Memo]), Fukushima Daichii and Daini (March 2011 [TEPCO 1]), and Kaswazaki-Kariwa (2007, [TEPCO 2]). However, seismic walk downs at some of these plants indicate that very little damage occurred to safety class systems and components due to the seismic motion. This report presents seismic data gathered for two of the three events mentioned above and recommends a path for using that data for two purposes. One purpose is to determine what margins exist in current industry standard seismic soil-structure interaction (SSI) tools. The second purpose is the use the data to validated seismic site response tools and SSI tools. The gathered data represents free field soil and in-structure acceleration time histories data. Gathered data also includes elastic and dynamic soil properties and structural drawings. Gathering data and comparing with existing models has potential to identify areas of uncertainty that should be removed from current seismic analysis and SPRA approaches. Removing uncertainty (to the extent possible) from SPRA’s will allow NPP owners to make decisions on where to reduce risk. Once a realistic understanding of seismic response is established for a nuclear power plant (NPP) then decisions on needed protective measures, such as SI, can be made.

  10. The effect of mechanical discontinuities on the growth of faults

    NASA Astrophysics Data System (ADS)

    Bonini, Lorenzo; Basili, Roberto; Bonanno, Emanuele; Toscani, Giovanni; Burrato, Pierfrancesco; Seno, Silvio; Valensise, Gianluca

    2016-04-01

    The growth of natural faults is controlled by several factors, including the nature of host rocks, the strain rate, the temperature, and the presence of fluids. In this work we focus on the mechanical characteristics of host rocks, and in particular on the role played by thin mechanical discontinuities on the upward propagation of faults and on associated secondary effects such as folding and fracturing. Our approach uses scaled, analogue models where natural rocks are simulated by wet clay (kaolin). A clay cake is placed above two rigid blocks in a hanging wall/footwall configuration on either side of a planar fault. Fault activity is simulated by motor-controlled movements of the hanging wall. We reproduce three types of faults: a 45°-dipping normal fault, a 45°-dipping reverse fault and a 30°-dipping reverse fault. These angles are selected as representative of most natural dip-slip faults. The analogues of the mechanical discontinuities are obtained by precutting the wet clay cake before starting the hanging wall movement. We monitor the experiments with high-resolution cameras and then obtain most of the data through the Digital Image Correlation method (D.I.C.). This technique accurately tracks the trajectories of the particles of the analogue material during the deformation process: this allows us to extract displacement field vectors plus the strain and shear rate distributions on the lateral side of the clay block, where the growth of new faults is best seen. Initially we run a series of isotropic experiments, i.e. experiments without discontinuities, to generate a reference model: then we introduce the discontinuities. For the extensional models they are cut at different dip angles, from horizontal to 45°-dipping, both synthetic and antithetic with respect to the master fault, whereas only horizontal discontinuities are introduced in the contractional models. Our experiments show that such discontinuities control: 1) the propagation rate of faults

  11. New Seismic Observables Constrain Structure within the Continental Lithosphere

    NASA Astrophysics Data System (ADS)

    Cunningham, E. E.; Lekic, V.

    2014-12-01

    The origin and stability of the continental lithosphere play a fundamental role in plate tectonics and enable the survival of Archean crust over billions of years. Recent advances in seismic data and imaging have revealed a velocity drop with depth within continental cratons too shallow to be interpreted as the lithosphere asthenosphere boundary (Rychert and Shearer 2009). The significance of this "mid lithospheric discontinuity" (MLD) - or multiple MLDs as suggested recently (Lekic & Fischer, 2013) - is not fully understood, and its implications for continental formation and stability are only beginning to be explored. Discrepancies call for both improving the constraints on the nature of the MLD, and relating these observations to tectonic setting and deformation history. The extensive coverage of the EarthScope USArray presents an unprecedented opportunity to systematically map the structure of the continental lithosphere. We use receiver functions (RFs) to isolate converted phases (Ps or Sp) produced across velocity discontinuities beneath a seismometer, and thereby constrain vertical density and seismic velocity variations. We show that at some stations, the apparent velocity contrast across the MLD demonstrates a dependence on seismic wave frequency, being greater at low frequencies than at high frequencies. This suggests that the MLD - at least in certain locations - is distributed across tens of kilometers in depth. The gradient of the MLD fingerprints physical process at play; a weak gradient indicates thermal origin, while an abrupt discontinuity implicates change in composition or partial melting. Furthermore, we map the strength, depth, and ratio of amplitudes of waves converted across the MLD and the Moho throughout the US. Because these receiver function based measurements only reveal relative velocity variations with depth, we combine them with frequency-dependent measurements of apparent incidence angles of P and S waves. Doing so allows us to

  12. Advances in Rotational Seismic Measurements

    SciTech Connect

    Pierson, Robert; Laughlin, Darren; Brune, Robert

    2016-10-19

    Rotational motion is increasingly understood to be a significant part of seismic wave motion. Rotations can be important in earthquake strong motion and in Induced Seismicity Monitoring. Rotational seismic data can also enable shear selectivity and improve wavefield sampling for vertical geophones in 3D surveys, among other applications. However, sensor technology has been a limiting factor to date. The US Department of Energy (DOE) and Applied Technology Associates (ATA) are funding a multi-year project that is now entering Phase 2 to develop and deploy a new generation of rotational sensors for validation of rotational seismic applications. Initial focus is on induced seismicity monitoring, particularly for Enhanced Geothermal Systems (EGS) with fracturing. The sensors employ Magnetohydrodynamic (MHD) principles with broadband response, improved noise floors, robustness, and repeatability. This paper presents a summary of Phase 1 results and Phase 2 status.

  13. Given enough choice, simple local rules percolate discontinuously

    NASA Astrophysics Data System (ADS)

    Waagen, Alex; D'Souza, Raissa M.

    2014-12-01

    There is still much to discover about the mechanisms and nature of discontinuous percolation transitions. Much of the past work considers graph evolution algorithms known as Achlioptas processes in which a single edge is added to the graph from a set of k randomly chosen candidate edges at each timestep until a giant component emerges. Several Achlioptas processes seem to yield a discontinuous percolation transition, but it was proven by Riordan and Warnke that the transition must be continuous in the thermodynamic limit. However, they also proved that if the number k(n) of candidate edges increases with the number of nodes, then the percolation transition may be discontinuous. Here we attempt to find the simplest such process which yields a discontinuous transition in the thermodynamic limit. We introduce a process which considers only the degree of candidate edges and not component size. We calculate the critical point tc = (1 - θ(1/k))n and rigorously show that the critical window is of size O(n/k(n)) . If k(n) grows very slowly, for example k(n) = log n, the critical window is barely sublinear and hence the phasetransition is discontinuous but appears continuous in finite systems. We also present arguments that Achlioptas processes with bounded size rules will always have continuous percolation transitions even with infinite choice.

  14. Solutions of the Wheeler-Feynman equations with discontinuous velocities

    NASA Astrophysics Data System (ADS)

    de Souza, Daniel Câmara; De Luca, Jayme

    2015-01-01

    We generalize Wheeler-Feynman electrodynamics with a variational boundary value problem for continuous boundary segments that might include velocity discontinuity points. Critical-point orbits must satisfy the Euler-Lagrange equations of the action functional at most points, which are neutral differential delay equations (the Wheeler-Feynman equations of motion). At velocity discontinuity points, critical-point orbits must satisfy the Weierstrass-Erdmann continuity conditions for the partial momenta and the partial energies. We study a special setup having the shortest time-separation between the (infinite-dimensional) boundary segments, for which case the critical-point orbit can be found using a two-point boundary problem for an ordinary differential equation. For this simplest setup, we prove that orbits can have discontinuous velocities. We construct a numerical method to solve the Wheeler-Feynman equations together with the Weierstrass-Erdmann conditions and calculate some numerical orbits with discontinuous velocities. We also prove that the variational boundary value problem has a unique solution depending continuously on boundary data, if the continuous boundary segments have velocity discontinuities along a reduced local space.

  15. Solutions of the Wheeler-Feynman equations with discontinuous velocities.

    PubMed

    de Souza, Daniel Câmara; De Luca, Jayme

    2015-01-01

    We generalize Wheeler-Feynman electrodynamics with a variational boundary value problem for continuous boundary segments that might include velocity discontinuity points. Critical-point orbits must satisfy the Euler-Lagrange equations of the action functional at most points, which are neutral differential delay equations (the Wheeler-Feynman equations of motion). At velocity discontinuity points, critical-point orbits must satisfy the Weierstrass-Erdmann continuity conditions for the partial momenta and the partial energies. We study a special setup having the shortest time-separation between the (infinite-dimensional) boundary segments, for which case the critical-point orbit can be found using a two-point boundary problem for an ordinary differential equation. For this simplest setup, we prove that orbits can have discontinuous velocities. We construct a numerical method to solve the Wheeler-Feynman equations together with the Weierstrass-Erdmann conditions and calculate some numerical orbits with discontinuous velocities. We also prove that the variational boundary value problem has a unique solution depending continuously on boundary data, if the continuous boundary segments have velocity discontinuities along a reduced local space.

  16. Discontinuous dual-primal mixed finite elements for elliptic problems

    NASA Technical Reports Server (NTRS)

    Bottasso, Carlo L.; Micheletti, Stefano; Sacco, Riccardo

    2000-01-01

    We propose a novel discontinuous mixed finite element formulation for the solution of second-order elliptic problems. Fully discontinuous piecewise polynomial finite element spaces are used for the trial and test functions. The discontinuous nature of the test functions at the element interfaces allows to introduce new boundary unknowns that, on the one hand enforce the weak continuity of the trial functions, and on the other avoid the need to define a priori algorithmic fluxes as in standard discontinuous Galerkin methods. Static condensation is performed at the element level, leading to a solution procedure based on the sole interface unknowns. The resulting family of discontinuous dual-primal mixed finite element methods is presented in the one and two-dimensional cases. In the one-dimensional case, we show the equivalence of the method with implicit Runge-Kutta schemes of the collocation type exhibiting optimal behavior. Numerical experiments in one and two dimensions demonstrate the order accuracy of the new method, confirming the results of the analysis.

  17. Discontinuous nonrigid registration using extended free-form deformations

    NASA Astrophysics Data System (ADS)

    Hua, Rui; Pozo, Jose M.; Taylor, Zeike A.; Frangi, Alejandro F.

    2015-03-01

    This paper presents a novel method to treat discontinuities in a 3D piece-wise non-rigid registration framework, coined as EXtended Free-Form Deformation (XFFD). Existing discontinuities in the image, such as sliding motion of the lungs or the cardiac boundary adjacent to the blood pool, should be handled to obtain physically plausible deformation fields for motion analysis. However, conventional Free-form deformations (FFDs) impose continuity over the whole image, introducing inaccuracy near discontinuity boundaries. The proposed method incorporates enrichment functions into the FFD formalism, inspired by the linear interpolation method in the EXtended Finite Element Method (XFEM). Enrichment functions enable B-splines to handle discontinuities with minimal increase of computational complexity, while avoiding boundary-matching problem. It retains all properties of the framework of FFDs yet seamlessly handles general discontinuities and can also coexist with other proposed improvements of the FFD formalism. The proposed method showed high performance on synthetic and 3D lung CT images. The target registration error on the CT images is comparable to the previous methods, while being a generic method without assuming any type of motion constraint. Therefore, it does not include any penalty term. However, any of these terms could be included to achieve higher accuracy for specific applications.

  18. Refined Local and Regional Seismic Velocity and Attenuation Models from Finite-Frequency Waveforms

    DTIC Science & Technology

    2008-09-30

    the velocities and quality factors of P and S waves specified on a l°xl ° horizontal grid and at 24 depths from 0 to 660 km. Figure 3 shows a few map...Technologies VPHf*"d VPh 0,a Xbr. dgo,u am 42SO 404 30 30 MW 3500 go am a’-s 42 5000 2 40 44o55 s50 0 45 s 6 o 4 35 4500 40 400 24 39 42 rNO 34400 am St

  19. An integrated exploration model for Council Run field analogs: Regional geology and seismic stratigraphy of Devonian 6th Elk sandstones

    SciTech Connect

    Kelleher, G.; Johnson, R. )

    1991-08-01

    A geologic study of the Devonian Lock Haven 6th Elk formation along the structural front of Pennsylvania and Maryland suggest that present-day structures were active at the time of deposition. These structures barred deposition to the west and helped to localize sands in a northeast-southwest fairway. The 6th Elk sandstones occur in two major depositional lobes (located in Centre and Somerset counties in Pennsylvania, and Garret County, Maryland) and were deposited on a shallow-marine shelf by turbidity currents and later modified by storm-generated currents. Deposition of 6th Elk sands may also have been influenced by cross-strike discontinuities. A seismic study of the Council Run field aids in subsurface identification of the 6th Elk. A high-amplitude seismic anomaly across the Council Run field is correlated with increasing san thickness. Two dimensional modeling suggests that the seismic response is extremely sensitive to specific acquisition and processing techniques including filter and phase variability. Additional attribute analysis integrates the seismic data with the forward models. This results in a predictive method for potentially identifying 6th Elk sandstone development from seismic data. Applying the results of the seismic modeling at Council Run field to a seismic grid across the previously defined 6th Elk depositional fairway has identified many exploratory prospects in Lycoming and Bradford counties, Pennsylvania. This area coincides with the site of a third, previously documented, Upper Devonian depositional lobe.

  20. Micromachined silicon seismic transducers

    SciTech Connect

    Barron, C.C.; Fleming, J.G.; Sniegowski, J.J.; Armour, D.L.; Fleming, R.P.

    1995-08-01

    Batch-fabricated silicon seismic transducers could revolutionize the discipline of CTBT monitoring by providing inexpensive, easily depolyable sensor arrays. Although our goal is to fabricate seismic sensors that provide the same performance level as the current state-of-the-art ``macro`` systems, if necessary one could deploy a larger number of these small sensors at closer proximity to the location being monitored in order to compensate for lower performance. We have chosen a modified pendulum design and are manufacturing prototypes in two different silicon micromachining fabrication technologies. The first set of prototypes, fabricated in our advanced surface- micromachining technology, are currently being packaged for testing in servo circuits -- we anticipate that these devices, which have masses in the 1--10 {mu}g range, will resolve sub-mG signals. Concurrently, we are developing a novel ``mold`` micromachining technology that promises to make proof masses in the 1--10 mg range possible -- our calculations indicate that devices made in this new technology will resolve down to at least sub-{mu}G signals, and may even approach to 10{sup {minus}10} G/{radical}Hz acceleration levels found in the low-earth-noise model.

  1. Community Seismic Network (CSN)

    NASA Astrophysics Data System (ADS)

    Clayton, R. W.; Heaton, T. H.; Kohler, M. D.; Chandy, M.; Krause, A.

    2010-12-01

    In collaboration with computer science and earthquake engineering, we are developing a dense network of low-cost accelerometers that send their data via the Internet to a cloud-based center. The goal is to make block-by-block measurements of ground shaking in urban areas, which will provide emergency response information in the case of large earthquakes, and an unprecedented high-frequency seismic array to study structure and the earthquake process with moderate shaking. When deployed in high-rise buildings they can be used to monitor the state of health of the structure. The sensors are capable of a resolution of approximately 80 micro-g, connect via USB ports to desktop computers, and cost about $100 each. The network will adapt to its environment by using network-wide machine learning to adjust the picking sensitivity. We are also looking into using other motion sensing devices such as cell phones. For a pilot project, we plan to deploy more than 1000 sensors in the greater Pasadena area. The system is easily adaptable to other seismically vulnerable urban areas.

  2. Seismic event classification system

    DOEpatents

    Dowla, Farid U.; Jarpe, Stephen P.; Maurer, William

    1994-01-01

    In the computer interpretation of seismic data, the critical first step is to identify the general class of an unknown event. For example, the classification might be: teleseismic, regional, local, vehicular, or noise. Self-organizing neural networks (SONNs) can be used for classifying such events. Both Kohonen and Adaptive Resonance Theory (ART) SONNs are useful for this purpose. Given the detection of a seismic event and the corresponding signal, computation is made of: the time-frequency distribution, its binary representation, and finally a shift-invariant representation, which is the magnitude of the two-dimensional Fourier transform (2-D FFT) of the binary time-frequency distribution. This pre-processed input is fed into the SONNs. These neural networks are able to group events that look similar. The ART SONN has an advantage in classifying the event because the types of cluster groups do not need to be pre-defined. The results from the SONNs together with an expert seismologist's classification are then used to derive event classification probabilities.

  3. Seismic moulin tremor

    NASA Astrophysics Data System (ADS)

    Roeoesli, Claudia; Walter, Fabian; Ampuero, Jean-Paul; Kissling, Edi

    2016-08-01

    Through glacial moulins, meltwater is routed from the glacier surface to its base. Moulins are a main feature feeding subglacial drainage systems and thus influencing basal motion and ice dynamics, but their geometry remains poorly known. Here we show that analysis of the seismic wavefield generated by water falling into a moulin can help constrain its geometry. We present modeling results of hour-long seimic tremors emitted from a vertical moulin shaft, observed with a seismometer array installed at the surface of the Greenland Ice Sheet. The tremor was triggered when the moulin water level exceeded a certain height, which we associate with the threshold for the waterfall to hit directly the surface of the moulin water column. The amplitude of the tremor signal changed over each tremor episode, in close relation to the amount of inflowing water. The tremor spectrum features multiple prominent peaks, whose characteristic frequencies are distributed like the resonant modes of a semiopen organ pipe and were found to depend on the moulin water level, consistent with a source composed of resonant tube waves (water pressure waves coupled to elastic deformation of the moulin walls) along the water-filled moulin pipe. Analysis of surface particle motions lends further support to this interpretation. The seismic wavefield was modeled as a superposition of sustained wave radiation by pressure sources on the side walls and at the bottom of the moulin. The former was found to dominate the wave field at close distance and the latter at large distance to the moulin.

  4. Seismic event classification system

    DOEpatents

    Dowla, F.U.; Jarpe, S.P.; Maurer, W.

    1994-12-13

    In the computer interpretation of seismic data, the critical first step is to identify the general class of an unknown event. For example, the classification might be: teleseismic, regional, local, vehicular, or noise. Self-organizing neural networks (SONNs) can be used for classifying such events. Both Kohonen and Adaptive Resonance Theory (ART) SONNs are useful for this purpose. Given the detection of a seismic event and the corresponding signal, computation is made of: the time-frequency distribution, its binary representation, and finally a shift-invariant representation, which is the magnitude of the two-dimensional Fourier transform (2-D FFT) of the binary time-frequency distribution. This pre-processed input is fed into the SONNs. These neural networks are able to group events that look similar. The ART SONN has an advantage in classifying the event because the types of cluster groups do not need to be pre-defined. The results from the SONNs together with an expert seismologist's classification are then used to derive event classification probabilities. 21 figures.

  5. The Mantle Seismic Heterogeneities Inferred by USArray Data

    NASA Astrophysics Data System (ADS)

    Ko, J. Y. T.; Zhan, Z.; Hung, S. H.; Li, D.; Helmberger, D. V.

    2015-12-01

    The detailed images of mantle seismic heterogeneities is establishing the link between modern mantle dynamics and past surface geological evolutions. The recent deployment of the USArray network of seismometers rolling from the west coast to the east coast of United States during 2004 to 2015 afford an extraordinary data set to investigate such mantle seismic heterogeneities. Here we first explored the D" structure beneath Caribbean region and found an east-to-west asymmetrical undulation of the D" discontinuity with a V-shaped depression of ~80-150 km over a lateral distance of 600 km, coinciding with a similar trend of shear wave velocity showing the most profound reduction of ~5% at the bottom of the thinnest D" layer. The strong correlation between the D" topography and velocity variations indicates lateral fluctuation in the D" temperature modulated by the reheated slab material has perturbed the phase transition boundary significantly and may reflect a transitional period of the proposed mega-plume scenario. Secondly, these emerging data not only shed light on the lowermost mantle structures but provide new constraints on the mid and upper mantle seismic velocity heterogeneities beneath the United States. We found that frequency-dependent traveltime residuals and amplitudes of S waves from South America events display considerable scatter patterns recorded by USArray stations which can be attributed to upper mantle heterogeneities beneath the U.S. and mid or lower mantle seismic anomalies along the raypaths. The analysis of waveform complexity is utilized in this work and gives complementary constraints on the location and geometry of these mantle heterogeneities such as possible slab remnants below Central and Eastern United States. We further exploited the newly developed 2D finite-difference method with various mantle heterogeneity models to better understand the possible geophysical features producing these anomalies.

  6. Non double couple seismic sources and its stress environment

    NASA Astrophysics Data System (ADS)

    Lutikov, A.; Yunga, S.

    2003-04-01

    Non double couple sources are considered in framework of the hypothesis that the process of seismic rupture can be viewed as a result of complicated fault geometry and its segmentation. The study focuses on the comparison of the deformation modes of the NDC sources with the states of stresses in its vicinity. The states of stresses are revealed using as a first approximation summation of seismic moment tensors. A measure of NDC part of moment tensor or deformation mode is described by angle parameter which correspond to characteristic equation of considered tensors. This parameter is of special interest as it cosine exhibit uniform distribution for sum of simulated random moment tensors series. Analytical approach is found to reveal reliability of NDC measure taking into consideration the values of seismic moment tensor errors. A tectonophysical interpretation of the numerical experiments is proposed to highlight the role played by stress factor in the local kinematics of structural discontinuities during the seismic rupture process. This technique, together with the construction of diagrams of principal axes, enables us to rapidly examine the stress-field pattern and further discuss the deformation modes of faulting and fracturing, which may take place at a small scale in earthquake focus and at regional scale in geological unit. An examination of angular measure of NDC part versus parameter of deformation mode in number of geodynamic regimes confirm the self-similarity assumption. But for the whole data set, in contradiction with this result, scaling relations do not verify self-similarity. This feature implies that second order factors, as the hydrothermal or magmatic pore fluids in rock, influence source characteristics and bring new complications in scaling relations. This work was partly supported by RFBR, grant 01-05-65340.

  7. Evaluating 1d Seismic Models of the Lunar Interior

    NASA Astrophysics Data System (ADS)

    Yao, Y.; Thorne, M. S.; Weber, R. C.; Schmerr, N. C.

    2012-12-01

    A four station seismic network was established on the Moon from 1969 to 1977 as part of the Apollo Lunar Surface Experiment Package (ALSEP). A total of nine 1D seismic velocity models were generated using a variety of different techniques. In spite of the fact that these models were generated from the same data set, significant differences exist between them. We evaluate these models by comparing predicted travel-times to published catalogs of lunar events. We generate synthetic waveform predictions for 1D lunar models using a modified version of the Green's Function of the Earth by Minor Integration (GEMINI) technique. Our results demonstrate that the mean square errors between predicted and measured P-wave travel times are smaller than those for S-wave travel times in all cases. Moreover, models fit travel times for artificial and meteoroid impacts better than for shallow and deep moonquakes. Overall, models presented by Nakamura [Nakamura, 1983] and Garcia et al. [Garcia et al., 2011] predicted the observed travel times better than all other models and were comparable in their explanation of travel-times. Nevertheless, significant waveform differences exist between these models. In particular, the seismic velocity structure of the lunar crust and regolith strongly affect the waveform characteristics predicted by these models. Further complexity is added by possible mantle discontinuity structure that exists in a subset of these models. We show synthetic waveform predictions for these models demonstrating the role that crustal structure has in generating long duration seismic coda inherent in the lunar waveforms.

  8. Seismic Gradiometry using Ambient Seismic Noise in an Anisotropic Earth

    NASA Astrophysics Data System (ADS)

    de Ridder, S. A. L.; Curtis, A.

    2017-02-01

    We introduce a wavefield gradiometry technique to estimate both isotropic and anisotropic local medium characteristics from short recordings of seismic signals by inverting a wave equation. The method exploits the information in the spatial gradients of a seismic wavefield that are calculated using dense deployments of seismic arrays. The application of the method uses the surface wave energy in the ambient seismic field. To estimate isotropic and anisotropic medium properties we invert an elliptically anisotropic wave equation. The spatial derivatives of the recorded wavefield are evaluated by calculating finite differences over nearby recordings, which introduces a systematic anisotropic error. A two step approach corrects this error: finite difference stencils are first calibrated, then the output of the wave-equation inversion is corrected using the linearized impulse response to the inverted velocity anomaly. We test the procedure on ambient seismic noise recorded in a large and dense ocean bottom cable array installed over Ekofisk field. The estimated azimuthal anisotropy forms a circular geometry around the production-induced subsidence bowl. This conforms with results from studies employing controlled sources, and with interferometry correlating long records of seismic noise. Yet in this example, the results where obtained using only a few minutes of ambient seismic noise.

  9. The impacts of mantle phase transitions and the iron spin crossover in ferropericlase on convective mixing—is the evidence for compositional convection definitive? New results from a Yin-Yang overset grid-based control volume model

    NASA Astrophysics Data System (ADS)

    Shahnas, M. H.; Peltier, W. R.

    2015-08-01

    High-resolution seismic tomographic images from several subduction zones provide evidence for the inhibition of the downwelling of subducting slabs at the level of the 660 km depth seismic discontinuity. Furthermore, the inference of old (~140 Myr) sinking slabs below fossil subduction zones in the lower mantle has yet to be explained. We employ a control volume methodology to develop a new anelastically compressible model of three-dimensional thermal convection in the "mantle" of a terrestrial planet that fully incorporates the influence of large variations in material properties. The model also incorporates the influence of (1) multiple solid-solid pressure-induced phase transitions, (2) transformational superplasticity at 660 km depth, and (3) the high spin-low spin iron spin transition in ferropericlase at midmantle pressures. The message passing interface-parallelized code is successfully tested against previously published benchmark results. The high-resolution control volume models exhibit the same degree of radial layering as previously shown to be characteristic of otherwise identical 2-D axisymmetric spherical models. The layering is enhanced by the presence of moderate transformational superplasticity, and in the presence of the spin crossover in ferropericlase, stagnation of cold downwellings occurs in the range of spin crossover depths (~1700 km). Although this electronic spin transition has been suggested to be invisible seismically, recent high-pressure ab initio calculations suggest it to have a clear signature in body wave velocities which could provide an isochemical explanation of a seismological signature involving the onset of decorrelation between Vp and Vs that has come to be interpreted as requiring compositional layering.

  10. A non-conventional discontinuous Lagrangian for viscous flow

    PubMed Central

    Marner, F.

    2017-01-01

    Drawing an analogy with quantum mechanics, a new Lagrangian is proposed for a variational formulation of the Navier–Stokes equations which to-date has remained elusive. A key feature is that the resulting Lagrangian is discontinuous in nature, posing additional challenges apropos the mathematical treatment of the related variational problem, all of which are resolvable. In addition to extending Lagrange's formalism to problems involving discontinuous behaviour, it is demonstrated that the associated equations of motion can self-consistently be interpreted within the framework of thermodynamics beyond local equilibrium, with the limiting case recovering the classical Navier–Stokes equations. Perspectives for applying the new formalism to discontinuous physical phenomena such as phase and grain boundaries, shock waves and flame fronts are provided. PMID:28386415

  11. Thermal inspection of discontinuities in bodies using contact thermochromic materials

    SciTech Connect

    Oleinik, A.S.

    1988-11-01

    The authors describes a method of thermal inspection of discontinuities in metallic compounds using contact thermochromic materials which can be used in instrument making and electronics. The aim of the work was to increase the sensitivity of the thermal inspection method. This was achieved by recording a new parameter, i.e., the time period from the start of thermal excitation of the inspected body to the start of variation of the color of the thermochromic material. The proposed nondestructive method increases the reliability of inspection and makes it possible to detect the discontinuities with a linear size of 0.1 mm whose depth is at least twice as large as the linear size of the discontinuity.

  12. On the structure of contact binaries. I - The contact discontinuity

    NASA Technical Reports Server (NTRS)

    Shu, F. H.; Lubow, S. H.; Anderson, L.

    1976-01-01

    The problem of the interior structure of contact binaries is reviewed, and a simple resolution of the difficulties which plague the theory is suggested. It is proposed that contact binaries contain a contact discontinuity between the lower surface of the common envelope and the Roche lobe of the cooler star. This discontinuity is maintained against thermal diffusion by fluid flow, and the transition layer is thin to the extent that the dynamical time scale is short in comparison with the thermal time scale. The idealization that the transition layer has infinitesimal thickness allows a simple formulation of the structure equations which are closed by appropriate jump conditions across the discontinuity. The further imposition of the standard boundary conditions suffices to define a unique model for the system once the chemical composition, the masses of the two stars, and the orbital separation are specified.

  13. Discontinuities of BFKL amplitudes and the BDS ansatz

    NASA Astrophysics Data System (ADS)

    Fadin, V. S.; Fiore, R.

    2015-12-01

    We perform an examination of discontinuities of multiple production amplitudes, which are required for further development of the BFKL approach. It turns out that the discontinuities of 2 → 2 + n amplitudes obtained in the BFKL approach contradict to the BDS ansatz for amplitudes with maximal helicity violation in N = 4 supersymmetric Yang-Mills theory with large number of colors starting with n = 2. Explicit expressions for the discontinuities of the 2 → 3 and 2 → 4 amplitudes in the invariant mass of pairs of produced gluons are obtained in the planar N = 4 SYM in the next-to-leading logarithmic approximation. These expressions can be used for checking the conjectured duality between the light-like Wilson loops and the MHV amplitudes.

  14. Fear conditioning to discontinuous auditory cues requires perirhinal cortical function.

    PubMed

    Kholodar-Smith, D B; Allen, T A; Brown, T H

    2008-10-01

    Pretraining lesions of rat perirhinal (PR) cortex impair fear conditioning to ultrasonic vocalizations (USVs) but have no effect on conditioning to continuous tones. This study attempted to deconstruct USVs into simpler stimulus features that cause fear conditioning to be PR-dependent. Rats were conditioned to one of three cues: a multicall 19-kHz USV, a 19-kHz discontinuous tone, and a 19-kHz continuous tone. The discontinuous tone duplicated the on/off pattern of the individual calls in the USV, but it lacked the characteristic frequency modulations. Well-localized neurotoxic PR lesions impaired conditioning to the USV, the discontinuous tone, and the training context. However, PR lesions had no effect on conditioning to the continuous tone. The authors suggest that the lesion effects on fear conditioning to both cues and contexts reflect the essential role of PR in binding stimulus elements together into unitary representations.

  15. A tessellated continuum approach to thermal analysis: discontinuity networks

    NASA Astrophysics Data System (ADS)

    Jiang, C.; Davey, K.; Prosser, R.

    2017-01-01

    Tessellated continuum mechanics is an approach for the representation of thermo-mechanical behaviour of porous media on tessellated continua. It involves the application of iteration function schemes using affine contraction and expansion maps, respectively, for the creation of porous fractal materials and associated tessellated continua. Highly complex geometries can be produced using a modest number of contraction mappings. The associated tessellations form the mesh in a numerical procedure. This paper tests the hypothesis that thermal analysis of porous structures can be achieved using a discontinuous Galerkin finite element method on a tessellation. Discontinuous behaviour is identified at a discontinuity network in a tessellation; its use is shown to provide a good representation of the physics relating to cellular heat exchanger designs. Results for different cellular designs (with corresponding tessellations) are contrasted against those obtained from direct analysis and very high accuracy is observed.

  16. A non-conventional discontinuous Lagrangian for viscous flow

    NASA Astrophysics Data System (ADS)

    Scholle, M.; Marner, F.

    2017-02-01

    Drawing an analogy with quantum mechanics, a new Lagrangian is proposed for a variational formulation of the Navier-Stokes equations which to-date has remained elusive. A key feature is that the resulting Lagrangian is discontinuous in nature, posing additional challenges apropos the mathematical treatment of the related variational problem, all of which are resolvable. In addition to extending Lagrange's formalism to problems involving discontinuous behaviour, it is demonstrated that the associated equations of motion can self-consistently be interpreted within the framework of thermodynamics beyond local equilibrium, with the limiting case recovering the classical Navier-Stokes equations. Perspectives for applying the new formalism to discontinuous physical phenomena such as phase and grain boundaries, shock waves and flame fronts are provided.

  17. Final Technical Report ''Double discontinuities in space plasma''

    SciTech Connect

    Yun Chow Whang

    2004-05-13

    This research used high-resolution magnetic field data to examine the interior structures of MHD shocks in interplanetary space and in the magnetotail; we discovered that a slow-mode shock is often followed by an adjoining rotational discontinuity layer on the postshock side. The thickness of each layer is of the order of a few ion inertial lengths. Such a compound structure is known as a double discontinuity. When the magnetic field rotates by several degrees per ion inertial length inside a thin layer, the Hall current term becomes important in the generalized Ohm's law. Steady state solutions based on the Hall-MHD theory have been obtained to show the merging of a rotational layer and a slow shock layer to form a compound structure like the observed double discontinuities.

  18. The effect of acute discontinuation of total parenteral nutrition.

    PubMed Central

    Wagman, L D; Newsome, H H; Miller, K B; Thomas, R B; Weir, G C

    1986-01-01

    The present study was undertaken to assess the impact of acute discontinuation (AD) of total parenteral nutrition (TPN) on serum glucose, insulin, and glucagon levels and on the generation of symptomatic hypoglycemia. Fifty studies were performed in 48 patients. In none of the 30 studies of 1 hour duration nor in the 20 studies of 8 hours duration was there a single episode of symptomatic hypoglycemia. One patient had a glucose below normal (60 mg/dl) during the first hour after AD. Glucose and insulin concentrations were elevated at the start of TPN discontinuation but returned to normal values within 60 minutes and remained there during the successive 7 hours of study. Although glucagon levels were slightly elevated at zero time, no significant decrease occurred. There was no evidence for counter-regulation based on the patterns of glucose and hormone levels. With some restrictions, acute discontinuation is a safe, rapid method of ending a prolonged TPN infusion. PMID:3094465

  19. Delta-Measure Perturbations of a Contact Discontinuity

    NASA Astrophysics Data System (ADS)

    Baty, Roy

    2012-11-01

    In this presentation, nonstandard analysis is applied to study generalized function perturbations of contact discontinuities in compressible, inviscid fluids. Nonstandard analysis is an area of modern mathematics that studies extensions of the real number system to nonstandard number systems that contain infinitely large and infinitely small numbers. Perturbations of a contact discontinuity are considered that represent one-dimensional analogs of the two-dimensional perturbations observed in the initial evolution of a Richtmyer-Meshkov instability on a density interface. Nonstandard predistributions of the Dirac delta measure and its derivatives are applied as the perturbations of a contact discontinuity. The one-dimensional Euler equations are used to model the flow field of a fluid containing a perturbed density interface and generalized solutions are constructed for the perturbed flow field.

  20. Passive seismic experiment and receiver functions analysis to determine crustal structure at the contact of the northern Dinarides and southwestern Pannonian Basin

    NASA Astrophysics Data System (ADS)

    Šumanovac, Franjo; Hegedűs, Endre; Orešković, Jasna; Kolar, Saša; Kovács, Attila C.; Dudjak, Darko; Kovács, István J.

    2016-06-01

    Passive seismic experiment was carried out at the SW contact of the Dinarides and Pannonian basin to determine the crustal structure and velocity discontinuities. The aim of the experiment was to define the relationship between the Adriatic microplate and the Pannonian segment as a part of the European plate. Most of the temporary seismic stations were deployed in Croatia along the Alp07 profile-a part of the active-source ALP 2002 project. About 300-km-long profile stretches from Istra peninsula to the Drava river, in a WSW-ESE direction. Teleseismic events recorded on 13 temporary seismic stations along the profile were analysed by P-receiver function method. Two types of characteristic receiver functions (RF) have been identified, belonging to Dinaridic and Pannonian crusts as defined on the Alp07 profile, while in transitional zone there are both types. Three major crustal discontinuities can be identified for the Dinaridic type: sedimentary basement, intracrustal discontinuity and Mohorovičić discontinuity, whereas the Pannonian type revealed only two discontinuities. The intracrustal discontinuity was not observed in the Pannonian type, thus pointing to a single-layered crust in the Pannonian basin. Two interpretation methods were applied: forward modelling of the receiver functions and H-κ stacking method, and the results were compared with the active-source seismic data at deep refraction profile Alp07. The receiver function modelling has given reliable results of the Moho depths that are in accordance with the seismic refraction results at the end of the Alp07 profile, that is in the area of Pannonian crust characterized by simple crustal structure and low seismic velocities (Vp between 5.9 and 6.2 km s-1). In the Dinarides and its peripheral parts, receiver function modelling regularly gives greater Moho depths, up to +15 per cent, due to more complex crustal structure. The depths of the Moho calculated by the H-κ stacking method vary within wide

  1. Active postoperative acromegaly: sustained remission after discontinuation of somatostatin analogues

    PubMed Central

    Cardenas-Salas, Jersy

    2016-01-01

    Summary In patients with active acromegaly after pituitary surgery, somatostatin analogues are effective in controlling the disease and can even be curative in some cases. After treatment discontinuation, the likelihood of disease recurrence is high. However, a small subset of patients remains symptom-free after discontinuation, with normalized growth hormone (GH) and insulin-like growth factor (IGF1) levels. The characteristics of patients most likely to achieve sustained remission after treatment discontinuation are not well understood, although limited evidence suggests that sustained remission is more likely in patients with lower GH and IGF1 levels before treatment withdrawal, in those who respond well to low-dose treatment, in those without evidence of adenoma on an MRI scan and/or in patients who receive long-term treatment. In this report, we describe the case of a 56-year-old female patient treated with lanreotide Autogel for 11 years. Treatment was successfully discontinued, and the patient is currently disease-free on all relevant parameters (clinical, biochemical and tumour status). The successful outcome in this case adds to the small body of literature suggesting that some well-selected patients who receive long-term treatment with somatostatin analogues may achieve sustained remission. Learning points: The probability of disease recurrence is high after discontinuation of treatment with somatostatin analogues. Current data indicate that remission after treatment discontinuation may be more likely in patients with low GH and IGF1 levels before treatment withdrawal, in those who respond well to low-dose treatment, in those without evidence of adenoma on MRI, and/or in patients receiving prolonged treatment. This case report suggests that prolonged treatment with somatostatin analogues can be curative in carefully selected patients. PMID:27933171

  2. Disparities in Discontinuing Rosiglitazone Following the 2007 FDA Safety Alert

    PubMed Central

    Qato, Danya M.; Trivedi, Amal N.; Mor, Vincent; Dore, David D.

    2016-01-01

    Background Responsiveness to the Food and Drug Administration (FDA) rosiglitazone safety alert, issued on May 21, 2007, has not been examined among vulnerable subpopulations of the elderly. Objective To compare time to discontinuation of rosiglitazone after the safety alert between black and white elderly persons, and across sociodemographic and economic subgroups. Research Design A cohort study. Subjects Medicare fee-for-service enrollees in 2007 who were established users of rosiglitazone identified from a 20% national sample of pharmacy claims. Measures Outcome of interest was time to discontinuation of rosiglitazone after the May alert. We modeled the number of days following the warning to the end of the days’ supply for the last rosiglitazone claim during the study period (May 21, 2007–December 31, 2007) using multivariable proportional hazards models. Results More than 67% of enrollees discontinued rosiglitazone within six months of the advisory. In adjusted analysis, white enrollees (hazard ratio = 0.90; 95% confidence interval, 0.86–0.94) discontinued rosiglitazone later than the comparison group of black enrollees. Enrollees with a history of low personal income also discontinued later than their comparison group (hazard ratio = 0.84; 95% confidence interval, 0.81–0.87). There were no observed differences across quintiles of area-level socioeconomic status. Conclusions White race and a history of low personal income modestly predicted later discontinuation of rosiglitazone after the FDA’s safety advisory in 2007. The impact of FDA advisories can vary among sociodemographic groups. Policymakers should continue to monitor whether risk management policies reach their intended populations. PMID:26978569

  3. Melange rheology, fluid pressure distribution, and seismic style (Invited)

    NASA Astrophysics Data System (ADS)

    Fagereng, A.; Sibson, R. H.

    2010-12-01

    Subduction megathrusts accommodate shear displacements in a range of seismic styles, including standard earthquakes, non-volcanic tremor, and continuous and transitory aseismic slip. Subduction channel shear zones, containing highly sheared, fluid-saturated trench-fill sediments intermingled with fragments of oceanic crust, are commonly inferred to occur along active subduction thrust interfaces. If this interpretation is correct, these plate boundary faults are not discrete planes, but may resemble the mélange shear zones commonly found in exhumed subduction-related rock assemblages. In such shear zones, deformation is accommodated by a mixture of continuous matrix flow and localized slip on numerous shear discontinuities. The dominant deformation mode in a mélange appears to depend critically on the ratio of competent to incompetent material, with shear discontinuities localized along lithological contacts or within competent domains, while matrix flow accommodates shearing by distributed strain. If the style of strain/displacement accommodation in a mélange reflects the partitioning between aseismic and seismic slip, the proportion of competent material seems likely to be a significant factor affecting seismic style within subduction channel shear zones. Along the Hikurangi margin, New Zealand, interseismic coupling varies from strong in the south to weak in the north. Variations in accretionary prism geometry indicate that the megathrust is mechanically stronger in the weakly coupled segment, than in the strongly coupled region. Thus, along this megathrust, weak coupling appears to occur on a relatively strong fault segment, while strong coupling relates to weak segments of the plate boundary. This may be caused by a fluid pressure difference, where frictional sliding is preferred in the strongly coupled, mechanically weak segment, where the incoming plate is relatively smooth and the overlying plate inferred to be relatively impermeable. In the weakly

  4. Micromechanics of Seismic Wave Propagation in Granular Rocks

    NASA Astrophysics Data System (ADS)

    Nihei, Kurt Toshimi

    1992-09-01

    This thesis investigates the details of seismic wave propagation in granular rocks by examining the micromechanical processes which take place at the grain level. Grain contacts are identified as the primary sites of attenuation in dry and fluid-saturated rocks. In many sedimentary rocks such as sandstones and limestones, the process of diagenesis leaves the grains only partially cemented together. When viewed at the micron scale, grain contacts are non-welded interfaces similar in nature to large scale joints and faults. Using a lumped properties approximation, the macroscopic properties of partially cemented grain contacts are modeled using a displacement-discontinuity boundary condition. This model is used to estimate the magnitude and the frequency dependence of the grain contact scattering attenuation for an idealized grain packing geometry. Ultrasonic P- and S-wave group velocity and attenuation measurements on sintered glass beads, alundum, and Berea sandstones were performed to determine the effects of stress, frequency, and pore fluid properties in granular materials with sintered and partially sintered grain contacts. P - and S-wave attenuation displayed the same overall trends for tests with n-decane, water, silicone oil, and glycerol. The magnitudes of the attenuation coefficients were, in general, higher for S-waves. The experimental measurements reveal that viscosity-dependent attenuation dominates in material with sintered grain contacts. Viscosity-dependent attenuation is also observed in Berea sandstone but only at hydrostatic stresses in excess of 15 MPa where the grain contacts are highly stiffened. Fluid surface chemistry-related attenuation was observed in Berea sandstone loaded uniaxially. These measurements suggest that attenuation in fluid-saturated rocks with partially cemented grain contacts is dependent on both the fluid properties and the state of stress at the grain contacts. A numerical method for simulating seismic wave propagation in

  5. A comparative study between shielded and open coplanar waveguide discontinuities

    NASA Technical Reports Server (NTRS)

    Dib, Nihad I.; Harokopus, W. P., Jr.; Ponchak, G. E.; Katehi, L. P. B.

    1993-01-01

    A comparative study between open and shielded coplanar waveguide (CPW) discontinuities is presented. The space domain integral equation method is used to characterize several discontinuities such as the open-end CPW and CPW series stubs. Two different geometries of CPW series stubs (straight and bent stubs) are compared with respect to resonant frequency and radiation loss. In addition, the encountered radiation loss due to different CPW shunt stubs is evaluated experimentally. The notion of forced radiation simulation is presented, and the results of such a simulation are compared to the actual radiation loss obtained rigorously. It is shown that such a simulation cannot give reliable results concerning radiation loss from printed circuits.

  6. Discontinuous Galerkin finite element methods for gradient plasticity.

    SciTech Connect

    Garikipati, Krishna.; Ostien, Jakob T.

    2010-10-01

    In this report we apply discontinuous Galerkin finite element methods to the equations of an incompatibility based formulation of gradient plasticity. The presentation is motivated with a brief overview of the description of dislocations within a crystal lattice. A tensor representing a measure of the incompatibility with the lattice is used in the formulation of a gradient plasticity model. This model is cast in a variational formulation, and discontinuous Galerkin machinery is employed to implement the formulation into a finite element code. Finally numerical examples of the model are shown.

  7. Discontinuous Galerkin schemes for nonstationary convection-diffusion problems

    NASA Astrophysics Data System (ADS)

    Dautov, R. Z.; Fedotov, E. M.

    2016-11-01

    In this paper we analyse an approximation of linear nonstationary convection- diffusion problem based on combination of discontinues Galerkin method for time discretisation in conjunction with hybridized discontinues Galerkin for spatial approximation. Such discrete schemes can be used for the solution of equations degenerating in the leading part and are formulated in term of solution of the problem, its gradient, the diffusional flux, and the restriction of the solution to the boundaries of elements. Conditions responsible for the solvability, stability and accuracy of the schemes are presented.

  8. Monotonicity Formula and Regularity for General Free Discontinuity Problems

    NASA Astrophysics Data System (ADS)

    Bucur, Dorin; Luckhaus, Stephan

    2014-02-01

    We give a general monotonicity formula for local minimizers of free discontinuity problems which have a critical deviation from minimality, of order d - 1. This result allows us to prove partial regularity results (that is closure and density estimates for the jump set) for a large class of free discontinuity problems involving general energies associated to the jump set, as for example free boundary problems with Robin conditions. In particular, we give a short proof to the De Giorgi-Carriero-Leaci result for the Mumford-Shah functional.

  9. Updated Colombian Seismic Hazard Map

    NASA Astrophysics Data System (ADS)

    Eraso, J.; Arcila, M.; Romero, J.; Dimate, C.; Bermúdez, M. L.; Alvarado, C.

    2013-05-01

    The Colombian seismic hazard map used by the National Building Code (NSR-98) in effect until 2009 was developed in 1996. Since then, the National Seismological Network of Colombia has improved in both coverage and technology providing fifteen years of additional seismic records. These improvements have allowed a better understanding of the regional geology and tectonics which in addition to the seismic activity in Colombia with destructive effects has motivated the interest and the need to develop a new seismic hazard assessment in this country. Taking advantage of new instrumental information sources such as new broad band stations of the National Seismological Network, new historical seismicity data, standardized global databases availability, and in general, of advances in models and techniques, a new Colombian seismic hazard map was developed. A PSHA model was applied. The use of the PSHA model is because it incorporates the effects of all seismic sources that may affect a particular site solving the uncertainties caused by the parameters and assumptions defined in this kind of studies. First, the seismic sources geometry and a complete and homogeneous seismic catalog were defined; the parameters of seismic rate of each one of the seismic sources occurrence were calculated establishing a national seismotectonic model. Several of attenuation-distance relationships were selected depending on the type of seismicity considered. The seismic hazard was estimated using the CRISIS2007 software created by the Engineering Institute of the Universidad Nacional Autónoma de México -UNAM (National Autonomous University of Mexico). A uniformly spaced grid each 0.1° was used to calculate the peak ground acceleration (PGA) and response spectral values at 0.1, 0.2, 0.3, 0.5, 0.75, 1, 1.5, 2, 2.5 and 3.0 seconds with return periods of 75, 225, 475, 975 and 2475 years. For each site, a uniform hazard spectrum and exceedance rate curves were calculated. With the results, it is

  10. 3D seismic attribute-assisted analysis of microseismic events in the Marcellus Shale

    NASA Astrophysics Data System (ADS)

    Hart, Ariel Kelton

    Microseismic monitoring is often used during the process of oil and gas exploitation to monitor seismicity that may be triggered by hydraulic fracturing, a common practice in the Appalachian Basin. Anthropogenically-induced minor upward fracture growth is not uncommon in the Marcellus shale; however, in the area of study, significant microseismic activity was registered above the target zone. In order to ascertain whether out-of-zone growth might have been predictable and identify which areas are more likely to experience brittle failure first, 3D seismic and microseismic data were analyzed with a focus on better understanding variations in the acoustic properties associated with unconventional naturally fractured reservoirs. Ant Tracking was used to identify areas of increased local seismic discontinuity, as these areas are generally more intensely deformed and may represent zones of increased fracture intensity. Ant Tracking results reveal discontinuities in the Marcellus are oriented approximately at N52E and N41W; discontinuities do not coincide with N25E trending folds apparent in the 3D seismic, but tend to follow deeper structural trends instead. These discontinuity orientations are interpreted to be a result of continued movement on deeper faults throughout the Paleozoic; these faults possibly acted as seed points for fractures further upsection and potentially led to the precipitation of the large N25E trending imbricate backthrusts seen in the 3D seismic. The reservoir's response to hydraulic fracturing also provided insights into local stress anisotropy and into optimal well and stage spacing needed to maximize drainage area and locate additional wells during the field development phase. Microseismic, well, and pump data used to gauge the reservoir's response to a hydraulic fracture treatment indicated that the number of stages, lateral length, total proppant volume, and fracture energy heavily influence how a well produces. SHmax in the area is oriented

  11. Crustal seismic anisotropy and structure from textural and seismic investigations in the Cycladic region, Greece

    NASA Astrophysics Data System (ADS)

    Cossette, Élise; Schneider, David; Audet, Pascal; Grasemann, Bernhard

    2016-04-01

    studies, and reveal an intra-crustal discontinuity at depth varying from 3 to 11 km, mostly observed in the south-central Aegean. Harmonic decomposition of the receiver functions further indicates layering of both shallow and deep crustal anisotropy related to crustal structures. We model synthetic receiver functions based on constraints from the in situ rock properties that we measured using the EBSD technique. Our results indicate that the shallow upper crustal layer is characterized by metapelites with ~5% anisotropy, underlain by a 20 km thick and anisotropic layer of possible high-pressure rocks comprising blueschist and eclogite and/or restitic crust as a consequence of Miocene magmatism. Seismic anisotropy models require a sub-vertical axis of hexagonal symmetry in the upper crust (i.e. radial anisotropy), consistent with in situ rock data. Finally, a thinned crust is likely caused by back-arc extension associated with elevated sub-crustal temperatures, in agreement with thermal isostasy models of back arcs. This study demonstrates the importance of integrating rock textural data with seismic velocity profiles in the interpretation of crustal architecture.

  12. Recent developments of seismic exploration in the Tannwald basin

    NASA Astrophysics Data System (ADS)

    Burschil, Thomas; Buness, Hermann; Gabriel, Gerald

    2016-04-01

    The ICDP proposal DOVE (Drilling Overdeepened Alpine Valleys) intends to examine the Quaternary glacial cycles in the Alpine region. The sediment succession of overdeepened valleys and basins will be analysed in a multidisciplinary way. Other objectives are related to groundwater supply and geohazards in Alpine valleys. In the context of DOVE, a DFG-funded project studies the benefit of modern multi-component reflection seismics. This project intends to characterize the structure and facies of the sedimentary fillings and to transfer methodological results to the DOVE drill sites. In 2014 and 2015 several reflection seismic surveys were carried out in the Tannwald basin, located about 50 km NE of Lake Constance. The basin constitutes a relict of one of the Rhine Glacier lobes in the Pleistocene. In total, we acquired five high-resolution profiles using P-waves, two profiles using horizontally polarized shear waves, and one profile using multi-component technique (SV- and SH-wave source, 3-component receivers) to explore the sedimentary filling of the basin. The P-wave profiles generally show strong heterogeneity and variations in the reflection pattern. Distinct reflections in depths between 100 m and 200 m are identified as basement, i.e. top Molasse, which is supported by a nearby research borehole. In particular, a ramp-like structure is prominent over a distance of 450 m and dips about 10°. Internal structures of the basin filling form discontinuous reflection segments, which are only visible in parts of the profile. The SH-wave profiles resolve both internal structures in detail and the basement. Since the location of the SH-wave profiles coincides with P-wave profiles, a detailed comparison of the structures gained from P-wave and SH-wave seismic exploration is possible. Moreover, Vp/Vs and Poisson ratio are calculated from P- and S-wave velocities received from refraction seismic tomography and the stack velocities, respectively. Further steps are

  13. Lithospheric structure of the Canadian Shield as characterised by its seismic anisotropy

    NASA Astrophysics Data System (ADS)

    Snyder, D. B.

    2011-12-01

    Distinct domains or layers of seismic anisotropy are increasingly recognized within Precambrian shields worldwide. Several relatively well-defined examples are now known from the Canadian Shield in North America. These benefit from a significantly large public suite of xenoliths produced during diamond exploration that provide calibration as to rock types found within these layers as well as increasingly resolved paleogeotherms. Independent parts of the seismic wave field provide consistent results; SKS, Ps conversions and Rayleigh waves were used to define sub-horizontal layers and to characterize deep lateral transitions associated with the edges of cratons previously defined by surface geological domain boundaries. The Slave and Rae cratons have received more intense study to date and can be shown to have formed by wedge tectonics that accreted smaller ancient blocks over time to first form the cratons in Archean times and the Canadian Shield in Proterozoic times. Differing mantle domains have distinct seismic anisotropy polarizations, inferred to represent both mineral fabrics (LPO) and larger scale dyke stockworks (SPO). Boundaries between these domains and layers appear as seismic discontinuities, primarily on sections constructed using transverse components of the seismic wavefield. This suggests that structures themselves, rather than greatly diverse physical properties and rock types, are key to imaging the sub-continental mantle lithosphere architecture and why gradual transitions such as the lithosphere-asthenosphere boundary may be difficult to characterize beneath shields.

  14. Seismic Structural Setting of Western Farallon Basin, Southern Gulf of California, Mexico.

    NASA Astrophysics Data System (ADS)

    Pinero-Lajas, D.; Gonzalez-Fernandez, A.; Lopez-Martinez, M.; Lonsdale, P.

    2007-05-01

    Data from a number of high resolution 2D multichannel seismic (MCS) lines were used to investigate the structure and stratigraphy of the western Farallon basin in the southern Gulf of California. A Generator-Injector air gun provided a clean seismic source shooting each 12 s at a velocity of 6 kts. Each signal was recorded during 6- 8 s, at a sampling interval of 1 ms, by a 600 m long digital streamer with 48 channels and a spacing of 12.5 m. The MCS system was installed aboard CICESE's (Centro de Investigacion Cientifica y de Educacion Superior de Ensenada) 28 m research vessel Francisco de Ulloa. MCS data were conventionally processed, to obtain post- stack time-migrated seismic sections. The MCS seismic sections show a very detailed image of the sub-bottom structure up to 2-3 s two-way travel time (aprox. 2 km). We present detailed images of faulting based on the high resolution and quality of these data. Our results show distributed faulting with many active and inactive faults. Our study also constrains the depth to basement near the southern Baja California eastern coast. The acoustic basement appears as a continuous feature in the western part of the study area and can be correlated with some granite outcrops located in the southern Gulf of California islands. To the East, near the center of the Farallon basin, the acoustic basement changes, it is more discontinuous, and the seismic sections show a number of diffracted waves.

  15. Seismic hazard assessment: Issues and alternatives

    USGS Publications Warehouse

    Wang, Z.

    2011-01-01

    Seismic hazard and risk are two very important concepts in engineering design and other policy considerations. Although seismic hazard and risk have often been used inter-changeably, they are fundamentally different. Furthermore, seismic risk is more important in engineering design and other policy considerations. Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space and to provide seismic hazard estimates for seismic risk assessment and other applications. Although seismic hazard assessment is more a scientific issue, it deserves special attention because of its significant implication to society. Two approaches, probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA), are commonly used for seismic hazard assessment. Although PSHA has been pro-claimed as the best approach for seismic hazard assessment, it is scientifically flawed (i.e., the physics and mathematics that PSHA is based on are not valid). Use of PSHA could lead to either unsafe or overly conservative engineering design or public policy, each of which has dire consequences to society. On the other hand, DSHA is a viable approach for seismic hazard assessment even though it has been labeled as unreliable. The biggest drawback of DSHA is that the temporal characteristics (i.e., earthquake frequency of occurrence and the associated uncertainty) are often neglected. An alternative, seismic hazard analysis (SHA), utilizes earthquake science and statistics directly and provides a seismic hazard estimate that can be readily used for seismic risk assessment and other applications. ?? 2010 Springer Basel AG.

  16. Seismic reflection characteristics of glacial and glacimarine sediment in the Gulf of Alaska and adjacent fjords

    USGS Publications Warehouse

    Carlson, P.R.

    1989-01-01

    Glaciation together with tectonism have been dominant factors affecting sedimentation in the Gulf of Alaska area from at least the late Miocene throughout the Quaternary. The effects of tectonism are apparent in high mountains that border the gulf, raised terraces of Middleton Island and the eastern gulf coastal zone, and numerous active faults and related earthquakes. Glacial evidence includes magnificent glaciers and their onshore deposits, spectacular fjords, large sea valleys incised in the continental shelf, submarine morainal ridges at mouths of bays and sea valleys, and thick glacimarine sedimentary sequences (diamicts) that are exposed onshore and at the sea floor along the outer shelf. Seismic-reflection profiling and sampling of the uppermost marine sedimentary sequences in the Gulf of Alaska and adjacent fjords and bays have allowed identification of three discrete glacially related stratigraphic units. These units were delineated on the basis of seismic signature, geometry, physiographic location, stratigraphic position, and sedimentologic characteristics. The oldest unit, a Quaternary diamict, is portrayed on seismic profiles by irregular, discontinuous reflections. This unit probably includes till, outwash and glacimarine sediment. A geographically restricted unit, one incorporating Holocene end moraines at bay mouths and associated with some sea valleys, consists of jumbled masses of discontinuous reflections and very irregular surface morphology. The youngest unit, a blanket of Holocene sand to clayey silt prograding as a sediment wedge across the shelf, contains nearly horizontal, parallel reflections except where disrupted by mass movement. Although seismic-reflection data alone cannot provide definitive proof of the presence of glacial sediment, when combined with sea-floor sampling, seismic profiling is a powerful tool for determining the continuity of marine sedimentary units and relationships to past and modern glaciers. ?? 1989.

  17. Seismic instrumentation of buildings

    USGS Publications Warehouse

    Çelebi, Mehmet

    2000-01-01

    The purpose of this report is to provide information on how and why we deploy seismic instruments in and around building structures. The recorded response data from buildings and other instrumented structures can be and are being primarily used to facilitate necessary studies to improve building codes and therefore reduce losses of life and property during damaging earthquakes. Other uses of such data can be in emergency response situations in large urban environments. The report discusses typical instrumentation schemes, existing instrumentation programs, the steps generally followed in instrumenting a structure, selection and type of instruments, installation and maintenance requirements and data retrieval and processing issues. In addition, a summary section on how recorded response data have been utilized is included. The benefits from instrumentation of structural systems are discussed.

  18. Downhole hydraulic seismic generator

    DOEpatents

    Gregory, Danny L.; Hardee, Harry C.; Smallwood, David O.

    1992-01-01

    A downhole hydraulic seismic generator system for transmitting energy wave vibrations into earth strata surrounding a borehole. The system contains an elongated, unitary housing operably connected to a well head aboveground by support and electrical cabling, and contains clamping apparatus for selectively clamping the housing to the walls of the borehole. The system further comprises a hydraulic oscillator containing a double-actuating piston whose movement is controlled by an electro-servovalve regulating a high pressure hydraulic fluid flow into and out of upper and lower chambers surrounding the piston. The spent hydraulic fluid from the hydraulic oscillator is stored and pumped back into the system to provide high pressure fluid for conducting another run at the same, or a different location within the borehole.

  19. SEISMIC-REFLECTOR DATABASE SOFTWARE.

    USGS Publications Warehouse

    Wright, Evelyn L.; Hosom, John-Paul; ,

    1986-01-01

    The seismic data analysis (SDA) software system facilitates generation of marine seismic reflector databases composed of reflector depths, travel times, root-mean-square and interval velocities, geographic coordinates, and identifying information. System processes include digitizing of seismic profiles and velocity semblance curves, merging of velocity and navigation data with profile travel-time data, calculation of reflector depths in meters, profile and map graphic displays, data editing and smoothing, and entry of finalized data into a comprehensive database. An overview of concepts, file structures, and programs is presented.

  20. Seismic Hazard and Public Safety

    NASA Astrophysics Data System (ADS)

    Marzocchi, Warner

    2013-07-01

    The recent destructive earthquakes in Wenchuan (China), L'Aquila (Italy), Port-au-Prince (Haiti), Christchurch (New Zealand), and Tohoku (Japan) have reignited the discussion over seismic safety. Several scientists [e.g., Stein et al., 2012; Wyss et al., 2012] have questioned the reliability of some seismic hazard maps based on the probabilistic seismic hazard analysis (PSHA)—a widely used probabilistic approach that estimates the likelihood of various levels of ground shaking occurring at a given location in a given future time period—raising an intense discussion on this specific point [Hanks et al., 2012; Frankel, 2013; Stein et al., 2013].

  1. SEISMIC ANALYSIS FOR PRECLOSURE SAFETY

    SciTech Connect

    E.N. Lindner

    2004-12-03

    The purpose of this seismic preclosure safety analysis is to identify the potential seismically-initiated event sequences associated with preclosure operations of the repository at Yucca Mountain and assign appropriate design bases to provide assurance of achieving the performance objectives specified in the Code of Federal Regulations (CFR) 10 CFR Part 63 for radiological consequences. This seismic preclosure safety analysis is performed in support of the License Application for the Yucca Mountain Project. In more detail, this analysis identifies the systems, structures, and components (SSCs) that are subject to seismic design bases. This analysis assigns one of two design basis ground motion (DBGM) levels, DBGM-1 or DBGM-2, to SSCs important to safety (ITS) that are credited in the prevention or mitigation of seismically-initiated event sequences. An application of seismic margins approach is also demonstrated for SSCs assigned to DBGM-2 by showing a high confidence of a low probability of failure at a higher ground acceleration value, termed a beyond-design basis ground motion (BDBGM) level. The objective of this analysis is to meet the performance requirements of 10 CFR 63.111(a) and 10 CFR 63.111(b) for offsite and worker doses. The results of this calculation are used as inputs to the following: (1) A classification analysis of SSCs ITS by identifying potential seismically-initiated failures (loss of safety function) that could lead to undesired consequences; (2) An assignment of either DBGM-1 or DBGM-2 to each SSC ITS credited in the prevention or mitigation of a seismically-initiated event sequence; and (3) A nuclear safety design basis report that will state the seismic design requirements that are credited in this analysis. The present analysis reflects the design information available as of October 2004 and is considered preliminary. The evolving design of the repository will be re-evaluated periodically to ensure that seismic hazards are properly

  2. Fractal features of seismic noise

    NASA Astrophysics Data System (ADS)

    Caserta, A.; Consolini, G.; Michelis, P. De

    2003-04-01

    We present experimental observations and data analysis concerning the fractal features of seismic noise in the frequency range from 1 Hz to 40 Hz. In detail, we investigate the 3D average squared soil displacement and the distribution function of its fluctuations for different near-surface geological structures. We found that the seismic noise is consistent with a persistent fractal brownian motion characterized by a Hurst exponent grather than 1/2. Moreover, a clear dependence of the fractal nature of the seismic noise on the near-surface local geology has been found.

  3. The seismic traffic footprint: Tracking trains, aircraft, and cars seismically

    NASA Astrophysics Data System (ADS)

    Riahi, Nima; Gerstoft, Peter

    2015-04-01

    Although naturally occurring vibrations have proven useful to probe the subsurface, the vibrations caused by traffic have not been explored much. Such data, however, are less sensitive to weather and low visibility compared to some common out-of-road traffic sensing systems. We study traffic-generated seismic noise measured by an array of 5200 geophones that covered a 7 × 10 km area in Long Beach (California, USA) with a receiver spacing of 100 m. This allows us to look into urban vibrations below the resolution of a typical city block. The spatiotemporal structure of the anthropogenic seismic noise intensity reveals the Blue Line Metro train activity, departing and landing aircraft in Long Beach Airport and their acceleration, and gives clues about traffic movement along the I-405 highway at night. As low-cost, stand-alone seismic sensors are becoming more common, these findings indicate that seismic data may be useful for traffic monitoring.

  4. Lithofacies and seismic-reflection interpretation of temperate glacimarine sedimentation in Tarr Inlet, Glacier Bay, Alaska

    USGS Publications Warehouse

    Cai, J.; Powell, R.D.; Cowan, E.A.; Carlson, P.R.

    1997-01-01

    High-resolution seismic-reflection profiles of sediment fill within Tart Inlet of Glacier Bay, Alaska, show seismic facies changes with increasing distance from the glacial termini. Five types of seismic facies are recognized from analysis of Huntec and minisparker records, and seven lithofacies are determined from detailed sedimentologic study of gravity-, vibro- and box-cores, and bottom grab samples. Lithofacies and seismic facies associations, and fjord-floor morphology allow us to divide the fjord into three sedimentary environments: ice-proximal, iceberg-zone and ice-distal. The ice-proximal environment, characterized by a morainal-bank depositional system, can be subdivided into bank-back, bank-core and bank-front subenvironments, each of which is characterized by a different depositional subsystem. A bank-back subsystem shows chaotic seismic facies with a mounded surface, which we infer consists mainly of unsorted diamicton and poorly sorted coarse-grained sediments. A bank-core depositional subsystem is a mixture of diamicton, rubble, gravel, sand and mud. Seismic-reflection records of this subsystem are characterized by chaotic seismic facies with abundant hyperbolic diffractions and a hummocky surface. A bank-front depositional subsystem consists of mainly stratified and massive sand, and is characterized by internal hummocky facies on seismic-reflection records with significant surface relief and sediment gravity flow channels. The depositional system formed in the iceberg-zone environment consists of rhythmically laminated mud interbedded with thin beds of weakly stratified diamicton and stratified or massive sand and silt. On seismic-reflection profiles, this depositional system is characterized by discontinuously stratified facies with multiple channels on the surface in the proximal zone and a single channel on the largely flat sediment surface in the distal zone. The depositional system formed in the ice-distal environment consists of interbedded

  5. Seismic imaging of deformation zones associated with normal fault-related folding

    NASA Astrophysics Data System (ADS)

    Lapadat, Alexandru; Imber, Jonathan; Iacopini, David; Hobbs, Richard

    2016-04-01

    Folds associated with normal faulting, which are mainly the result of fault propagation and linkage of normal fault segments, can exhibit complex deformation patterns, with multiple synthetic splay faults, reverse faults and small antithetic Riedel structures accommodating flexure of the beds. Their identification is critical in evaluating connectivity of potential hydrocarbon reservoirs and sealing capacity of faults. Previous research showed that seismic attributes can be successfully used to image complex structures and deformation distribution in submarine thrust folds. We use seismic trace and coherency attributes, a combination of instantaneous phase, tensor discontinuity and semblance attributes to identify deformation structures at the limit of seismic resolution, which accommodate seismic scale folding associated with normal faulting from Inner Moray Firth Basin, offshore Scotland. We identify synthetic splay faults and reverse faults adjacent to the master normal faults, which are localized in areas with highest fold amplitudes. This zone of small scale faulting is the widest in areas with highest fault throw / fold amplitude, or where a bend is present in the main fault surface. We also explore the possibility that changes in elastic properties of the rocks due to deformation can contribute to amplitude reductions in the fault damage zones. We analyse a pre-stack time-migrated 3D seismic data-set, where seismic reflections corresponding to a regionally-continuous and homogeneous carbonate layer display a positive correlation between strain distribution and amplitude variations adjacent to the faults. Seismic amplitude values are homogeneously distributed within the undeformed area of the footwall, with a minimum deviation from a mean amplitude value calculated for each seismic line. Meanwhile, the amplitude dimming zone is more pronounced (negative deviation increases) and widens within the relay zone, where sub-seismic scale faults, which accommodate

  6. Seismic hazard assessment in Central Asia using smoothed seismicity approaches

    NASA Astrophysics Data System (ADS)

    Ullah, Shahid; Bindi, Dino; Zuccolo, Elisa; Mikhailova, Natalia; Danciu, Laurentiu; Parolai, Stefano

    2014-05-01

    Central Asia has a long history of large to moderate frequent seismicity and is therefore considered one of the most seismically active regions with a high hazard level in the world. In the hazard map produced at global scale by GSHAP project in 1999( Giardini, 1999), Central Asia is characterized by peak ground accelerations with return period of 475 years as high as 4.8 m/s2. Therefore Central Asia was selected as a target area for EMCA project (Earthquake Model Central Asia), a regional project of GEM (Global Earthquake Model) for this area. In the framework of EMCA, a new generation of seismic hazard maps are foreseen in terms of macro-seismic intensity, in turn to be used to obtain seismic risk maps for the region. Therefore Intensity Prediction Equation (IPE) had been developed for the region based on the distribution of intensity data for different earthquakes occurred in Central Asia since the end of 19th century (Bindi et al. 2011). The same observed intensity distribution had been used to assess the seismic hazard following the site approach (Bindi et al. 2012). In this study, we present the probabilistic seismic hazard assessment of Central Asia in terms of MSK-64 based on two kernel estimation methods. We consider the smoothed seismicity approaches of Frankel (1995), modified for considering the adaptive kernel proposed by Stock and Smith (2002), and of Woo (1996), modified for considering a grid of sites and estimating a separate bandwidth for each site. The activity rate maps are shown from Frankel approach showing the effects of fixed and adaptive kernel. The hazard is estimated for rock site condition based on 10% probability of exceedance in 50 years. Maximum intensity of about 9 is observed in the Hindukush region.

  7. A nodal discontinuous Galerkin method for reverse-time migration on GPU clusters

    NASA Astrophysics Data System (ADS)

    Modave, A.; St-Cyr, A.; Mulder, W. A.; Warburton, T.

    2015-11-01

    Improving both accuracy and computational performance of numerical tools is a major challenge for seismic imaging and generally requires specialized implementations to make full use of modern parallel architectures. We present a computational strategy for reverse-time migration (RTM) with accelerator-aided clusters. A new imaging condition computed from the pressure and velocity fields is introduced. The model solver is based on a high-order discontinuous Galerkin time-domain (DGTD) method for the pressure-velocity system with unstructured meshes and multirate local time stepping. We adopted the MPI+X approach for distributed programming where X is a threaded programming model. In this work we chose OCCA, a unified framework that makes use of major multithreading languages (e.g. CUDA and OpenCL) and offers the flexibility to run on several hardware architectures. DGTD schemes are suitable for efficient computations with accelerators thanks to localized element-to-element coupling and the dense algebraic operations required for each element. Moreover, compared to high-order finite-difference schemes, the thin halo inherent to DGTD method reduces the amount of data to be exchanged between MPI processes and storage requirements for RTM procedures. The amount of data to be recorded during simulation is reduced by storing only boundary values in memory rather than on disk and recreating the forward wavefields. Computational results are presented that indicate that these methods are strong scalable up to at least 32 GPUs for a three-dimensional RTM case.

  8. Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere

    PubMed Central

    Qi, Chao; Warren, Jessica M.

    2016-01-01

    Tectonic plates are a key feature of Earth’s structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary. PMID:27606485

  9. Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere

    NASA Astrophysics Data System (ADS)

    Hansen, Lars N.; Qi, Chao; Warren, Jessica M.

    2016-09-01

    Tectonic plates are a key feature of Earth’s structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary.

  10. Validation of an Adaptive Triangular Discontinuous Galerkin Shallow Water Model for the 2011 Tohoku Tsunami

    NASA Astrophysics Data System (ADS)

    Vater, Stefan; Behrens, Jörn

    2016-04-01

    We apply a tsunami simulation framework, which is based on depth-integrated hydrodynamic model equations, to the 2011 Tohoku tsunami event. While this model has been previously validated for analytic test cases and laboratory experiments, here it is applied to earthquake sources which are based on seismic inversion. Simulated wave heights and runup at the coast are compared to actual measurements. The discretization is based on a second-order Runge-Kutta discontinuous Galerkin (RKDG) scheme on triangular grids and features a robust wetting and drying scheme for the simulation of inundation events at the coast. Adaptive mesh refinement enables the efficient computation of large domains, while at the same time it allows for high local resolution and geometric accuracy. This work is part of the ASCETE (Advanced Simulation of Coupled Earthquake and Tsunami Events) project, which aims at an improved understanding of the coupling between the earthquake and the generated tsunami event. In this course, a coupled simulation framework has been developed which couples physics-based rupture generation with the presented hydrodynamic tsunami propagation and inundation model.

  11. Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere.

    PubMed

    Hansen, Lars N; Qi, Chao; Warren, Jessica M

    2016-09-20

    Tectonic plates are a key feature of Earth's structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary.

  12. Progressive Seismic Failure, Seismic Gap, and Great Seismic Risk across the Densely Populated North China Basin

    NASA Astrophysics Data System (ADS)

    Yin, A.; Yu, X.; Shen, Z.

    2014-12-01

    Although the seismically active North China basin has the most complete written records of pre-instrumentation earthquakes in the world, this information has not been fully utilized for assessing potential earthquake hazards of this densely populated region that hosts ~200 million people. In this study, we use the historical records to document the earthquake migration pattern and the existence of a 180-km seismic gap along the 600-km long right-slip Tangshan-Hejian-Cixian (THC) fault zone that cuts across the North China basin. The newly recognized seismic gap, which is centered at Tianjin with a population of 11 million people and ~120 km from Beijing (22 million people) and Tangshan (7 million people), has not been ruptured in the past 1000 years by M≥6 earthquakes. The seismic migration pattern in the past millennium suggests that the epicenters of major earthquakes have shifted towards this seismic gap along the THC fault, which implies that the 180- km gap could be the site of the next great earthquake with M≈7.6 if it is ruptured by a single event. Alternatively, the seismic gap may be explained by aseismic creeping or seismic strain transfer between active faults.

  13. Fracture criteria for discontinuously reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Rack, H. J.; Goree, J. G.; Albritton, J.; Ratnaparkhi, P.

    1988-01-01

    Summarized is the progress achieved during the period September 16, 1987 to August 15, l988 on NASA Grant NAG1-724, Fracture Criteria for Discontinuously Reinforced Metal Matrix Composites. Appended are copies of three manuscripts prepared under NASA funding during the performance period.

  14. 77 FR 20988 - Discontinuance of Form CO in Registration Practices

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-09

    ... From the Federal Register Online via the Government Publishing Office LIBRARY OF CONGRESS Copyright Office 37 CFR Parts 201 and 202 Discontinuance of Form CO in Registration Practices Correction In rule document 2012-7429 appearing on pages 18705-18707 in the issue of March 28, 2012, make...

  15. 76 FR 60774 - Discontinuance of Form CO in Registration Practices

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-30

    ... Copyright Office 37 CFR Parts 201 and 202 Discontinuance of Form CO in Registration Practices AGENCY... the Form CO application as an option for applying for copyright registration; and remove the references to CON 1 and CON 2 sheets. Form CO applications comprise only a small percentage of...

  16. 29 CFR 2700.104 - Discontinuance of simplified proceedings.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...) Procedure. If it becomes apparent at any time that a case is not appropriate for Simplified Proceedings, the... Simplified Proceedings and order the case to continue under conventional rules. (b) Party motion. At any time... Simplified Proceedings be discontinued and that the matter continue under conventional procedures. A...

  17. 29 CFR 2700.104 - Discontinuance of simplified proceedings.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...) Procedure. If it becomes apparent at any time that a case is not appropriate for Simplified Proceedings, the... Simplified Proceedings and order the case to continue under conventional rules. (b) Party motion. At any time... Simplified Proceedings be discontinued and that the matter continue under conventional procedures. A...

  18. Derivative discontinuity with localized Hartree-Fock potential

    SciTech Connect

    Nazarov, V. U.; Vignale, G.

    2015-08-14

    The localized Hartree-Fock potential has proven to be a computationally efficient alternative to the optimized effective potential, preserving the numerical accuracy of the latter and respecting the exact properties of being self-interaction free and having the correct −1/r asymptotics. In this paper we extend the localized Hartree-Fock potential to fractional particle numbers and observe that it yields derivative discontinuities in the energy as required by the exact theory. The discontinuities are numerically close to those of the computationally more demanding Hartree-Fock method. Our potential enjoys a “direct-energy” property, whereby the energy of the system is given by the sum of the single-particle eigenvalues multiplied by the corresponding occupation numbers. The discontinuities c{sub ↑} and c{sub ↓} of the spin-components of the potential at integer particle numbers N{sub ↑} and N{sub ↓} satisfy the condition c{sub ↑}N{sub ↑} + c{sub ↓}N{sub ↓} = 0. Thus, joining the family of effective potentials which support a derivative discontinuity, but being considerably easier to implement, the localized Hartree-Fock potential becomes a powerful tool in the broad area of applications in which the fundamental gap is an issue.

  19. Effect of motion discontinuities on discrimination of periodic trajectories.

    PubMed

    Wilson, Hugh R; Fung, Jeffrey

    2016-01-01

    Many biologically important motions are described by periodic trajectories. Radial frequency (RF) trajectories are one example, in which the motion of a difference of Gaussians (DOG) target moves along a path described by a sinusoidal deviation of the radius from a perfect circle (Or, Thabet, Wilkinson, & Wilson, 2011). Here we explore the hypothesis that visual processing of RF trajectories involves global spatio-temporal processes that are disrupted by motion discontinuity. To test this hypothesis, RF trajectories were used that interspersed smooth, continuous motion with three or four discontinuous jumps to other portions of the trajectory. These jumps were arranged so that the entire trajectory was traversed in the same amount of time as in the continuous motion control condition. The motion discontinuities increased thresholds by a factor of approximately 2.1 relative to continuous motion. This result provides support for global spatio-temporal processing of RF motion trajectories. Comparison with previous results suggests that motion discontinuities erase memory for earlier parts of the trajectory, thereby causing thresholds to be based on only the final segment viewed. Finally, it is shown that RF trajectories obey the 1/3 power law characteristic of biological motion.

  20. 24 CFR 203.288 - Discontinuance of adjusted premium charge.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... HOUSING AND URBAN DEVELOPMENT MORTGAGE AND LOAN INSURANCE PROGRAMS UNDER NATIONAL HOUSING ACT AND OTHER... 24 Housing and Urban Development 2 2014-04-01 2014-04-01 false Discontinuance of adjusted premium charge. 203.288 Section 203.288 Housing and Urban Development Regulations Relating to Housing and...