Science.gov

Sample records for magnetic spreading anomalies

  1. Numerical investigations of the spreading-rate dependence of anomalous skewness of marine magnetic anomalies due to seafloor spreading

    NASA Astrophysics Data System (ADS)

    Boswell, S. M.; Zheng, L.; Gordon, R. G.; Dyment, J.

    2011-12-01

    An improved understanding of the spreading-rate dependence of anomalous skewness from magnetic anomalies due to seafloor spreading will allow for better constraints on apparent polar wander paths, plate reconstructions, and the magnetic and thermal structure of oceanic lithosphere. Anomalous skewness, which is the difference between experimentally determined skewness and skewness expected from simple magnetization models with vertical reversal boundaries, has been observed to vary as a function of spreading rate, decreasing with increasing spreading rate and becoming negligible at spreading half-rates exceeding about 55 mm/a [Roest et al. 1992; Dyment et al. 1994]. In our analysis, we determine model-based estimates of anomalous skewness as a function of spreading rate for each anomaly. We do so by creating many synthetic profiles using the model of Dyment and Arkani-Hamed (1995), which was specifically constructed to produce anomalies with anomalous skewness consistent with observed anomalies. We experimentally determine the phase shift that causes the resulting synthetic magnetic anomaly to best match a profile produced from a "standard" model for anomalies due to seafloor spreading that assumes simple vertical reversal boundaries. We present results for those anomalies between 12r and 33r from which reliable paleomagnetic poles may potentially be determined. Differences in anomalous skewness for different anomalies determined at the same spreading rate can be attributed to the sequence effect, that is, the effect on the shape of a magnetic anomaly above seafloor of a single polarity chron of the magnetization of neighboring blocks of lithosphere magnetized during other chrons. We find that the sequence effect is smaller than we expected with the largest difference being between the results for anomaly 25r and those for anomaly 33r, for which the difference is 14 degrees at a 10 mm/a half-rate. Results for other anomalies lie between these two. We also infer a

  2. Toward Quantifying the Spreading-Rate Dependence of Anomalous Skewness of Marine Magnetic Anomalies due to Seafloor Spreading

    NASA Astrophysics Data System (ADS)

    Boswell, S. M.; Zheng, L.; Gordon, R. G.; Dyment, J.

    2010-12-01

    In past work, reliable paleomagnetic poles have been determined from skewness data by solving for a single additional adjustable parameter, anomalous skewness, assumed to be independent of spreading rate [Petronotis et al. 1992, 1994; Petronotis & Gordon 1999]. Nonetheless, analysis of anomalies in several ocean basins indicate that anomalous skewness depends on spreading rate for spreading half rates less than ≈50 mm/yr [Roest et al., 1992; Dyment et al. 1994]. To facilitate investigation of the influence of spreading-rate dependent anomalous skewness on the determination of paleomagnetic poles determined from skewness, we build on the model for marine magnetic anomalies due to seafloor spreading of Dyment and Arkani-Hamed [1995]. We use this model to estimate anomalous skewness as a function of spreading rate for many anomalies. Synthetic magnetic anomaly profiles for oceanic lithosphere with sloping curving reversal boundaries were produced by forward modeling. Anomalous skewness values for chrons 25n to 33r were visually determined at various spreading rates using two approaches: balancing the shoulders of an anomaly corresponding to a single chron and best matching an anomaly corresponding to a single chron to a synthetic anomaly determined assuming vertical reversal boundaries. The new results may facilitate the determination of paleomagnetic poles from less widely distributed crossings of a magnetic anomaly than were used before. Further implications for determination of paleomagnetic poles for the Pacific plate will be discussed.

  3. Seafloor spreading in the eastern Gulf of Mexico: New evidence for marine magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Eskamani, Philip K.

    Possible sea-floor spreading anomalies are indentified in marine magnetic surveys conducted in the eastern Gulf of Mexico. A symmetric pattern of lineated anomalies can be correlated with the geomagnetic time scale using previously proposed opening histories for the Gulf of Mexico basin. Lineated magnetic anomalies are characterized by amplitudes of up to 30 nT and wavelengths of 45-55 km, and are correlatable across 12 different ship tracks spanning a combined distance of 6,712 km. The magnetic lineations are orientated in a NW-SE direction with 3 distinct positive lineations on either side of the inferred spreading ridge anomalies. The magnetic anomalies were forward modeled with a 2 km thick magnetic crust composed of vertically bounded blocks of normal and reverse polarity at a model source depth of 10 km. Remnant magnetization intensity and inclination are 1.6 A m-1 and 0.2° respectively, chosen to best fit the magnetic observed amplitudes and, for inclination, in accord with the nearly equatorial position of the Gulf of Mexico during Jurassic seafloor spreading. The current magnetic field is modeled with declination and inclination of and 0.65° and 20° respectively. Using a full seafloor spreading rate of 1.7 cm/yr, the anomalies correlate with magnetic chrons M21 to M10. The inferred spreading direction is consistent with previous suggestions of a North-East to South-West direction of sea-floor spreading off the west coast of Florida beginning 149 Ma (M21) and ending 134 Ma (M10). The opening direction is also consistent with the counter-clockwise rotation of Yucatan proposed in past models.

  4. Contribution of oceanic gabbros to sea-floor spreading magnetic anomalies.

    PubMed

    Kikawa, E; Ozawa, K

    1992-10-30

    The contribution of oceanic gabbros, representative rocks for layer 3 of the oceanic crust, to sea-floor spreading magnetic anomalies has been controversial because of the large variation in magnetic properties. Ocean Drilling Program (ODP) Leg 118 contains a continuous 500.7-meter section of oceanic gabbro that allows the relations between magnetization and petrologic characteristics, such as the degree of metamorphism and the magmatic evolution, to be clarified. The data suggest that oceanic gabbros, together with the effects of metamorphism and of magmatic evolution, account for a significant part of the marine magnetic anomalies.

  5. Contribution of oceanic gabbros to sea-floor spreading magnetic anomalies.

    PubMed

    Kikawa, E; Ozawa, K

    1992-10-30

    The contribution of oceanic gabbros, representative rocks for layer 3 of the oceanic crust, to sea-floor spreading magnetic anomalies has been controversial because of the large variation in magnetic properties. Ocean Drilling Program (ODP) Leg 118 contains a continuous 500.7-meter section of oceanic gabbro that allows the relations between magnetization and petrologic characteristics, such as the degree of metamorphism and the magmatic evolution, to be clarified. The data suggest that oceanic gabbros, together with the effects of metamorphism and of magmatic evolution, account for a significant part of the marine magnetic anomalies. PMID:17777035

  6. Magnetic and gravity anomalies of the slow-spreading system in the Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Nakanishi, M.; Fujimoto, H.; Tamaki, K.; Okino, K.

    2002-12-01

    The spreading system in the Gulf of Aden between Somalia, NE Africa, and Arabia has an ENE-WSW trend and its half spreading rate is about 1.0 cm/yr (e.g., Jestin et al., 1994). Previous studies (e.g., Tamsett and Searle, 1988) provided the general morphology of the spreading system. To reveal detailed morphology and tectonics of the spreading system in the Gulf of Aden, geophysical investigation was conducted along the spreading system between 45°30OE and 50°20OE by the R/V Hakuho-maru from December 2000 to January 2001. Bathymetric data were collected using an echo sounder SEA BEAM 2120 aboard R/V Hakuho-maru. Magnetic and gravity data were collected by towed proton magnetometer and shipboard gravimeter, respectively. The strike of the spreading centers east of 46°30OE is N65°W. The topographic expression of the spreading centers east of N46°30OE is an axial rift valley offset by transform faults siilar to that observed at slow spreading centers in other areas. The bathymetric feature of the spreading centers between 45°50OE and 46°30OE with a strike N80°E is N65°W trending en-echelon basins. The spreading center west of 45°50OE with a strike E-W is bouned by linear ridges and its bathymetric expression is N65°W trending en-echelon ridges. The axial rift valley west of N46°30OE is not offset by any prominent transform faults. Negative magnetic anomaly is dominant over the axial valleys. Its amplitude is about 500 nT and the wavelength is about 30 km. Prominent linear negative magnetic anomaly, which is more than 1000 nT, exists west of N46°30OE. The strike of the linear magnetic anomaly correlates with that of axial valleys west of N46°30OE. Mantle Bouguer gravity anomaly of the spreading centers increases eastward. This trend correlates with the eastward deepening of spreading centers.

  7. Investigation of spreading center ecolution by joint inversion of seafloor magnetic anomaly and tectonic fabric data

    NASA Technical Reports Server (NTRS)

    Shoberg, Tom; Stein, Seth

    1994-01-01

    Spreading center segments that have experienced a complex tectonic history including rift propagation may have a complicated signature in bathymetric and magnetic anomaly data. To gain insight into the history of such regions, we have developed techniques in which both the magnetic anomaly patterns and seafloor fabric trends are predicted theoretically, and the combined predictions are compared numerically with the data to estimate best fitting parameters for the propagation history. Fitting functions are constructed to help determine which model best matches the digitized fabric and magnetic anomaly data. Such functions offer statistical criteria for choosing the best fit model. We use this approach to resolve the propagation history of the Cobb Offset along the Juan de Fuca ridge. In this example, the magnetic anomaly data prove more useful in defining the geometry of the propagation events, while the fabric, with its greater temporal resolution, is more useful for constraining the rate of propagation. It thus appears that joint inversion of magnetic and seafloor fabric data can be valuable in tectonic analyses.

  8. Magnetic anomalies and seafloor spreading rates in the northern South Atlantic.

    PubMed

    van Andel, T H; Moore, T C

    1970-04-25

    A geomagnetic profile across the northern South Atlantic yields spreading rates for the last 70 m.y. which vary from 1.6 to 2.0 cm/year. There is evidence for three regional discontinuities in the spreading history of the South Atlantic.

  9. Magnetic anomalies and seafloor spreading rates in the northern South Atlantic.

    PubMed

    van Andel, T H; Moore, T C

    1970-04-25

    A geomagnetic profile across the northern South Atlantic yields spreading rates for the last 70 m.y. which vary from 1.6 to 2.0 cm/year. There is evidence for three regional discontinuities in the spreading history of the South Atlantic. PMID:16057239

  10. Opening of the Gulf of Mexico and the Nature of the Crust in the Deep Gulf: New Evidence from Seafloor Spreading Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Harry, D. L.; Eskamani, P. K.

    2013-12-01

    The seafloor spreading history in the Gulf of Mexico is poorly constrained due to a lack of recognized seafloor spreading magnetic anomalies, a paucity of deep penetrating seismic data, and absence of drilling to constrain crystalline ocean floor composition and ages. We have identified lineated magnetic anomalies in the eastern Gulf on profiles collected during the Woods Hole R/V Farnella FRNL85-2 cruise that correlate with magnetic chrons M21R to M10. Forward modeling shows that these anomalies formed during creation of weakly magnetized new seafloor in the eastern Gulf between 149-134 Ma at an average half-spreading rate of 3.2 cm/yr. The oldest anomalies are located against stretched continental crust beneath the western Florida shelf on the east and the Yucatan shelf on the west. The youngest anomalies form a juxtaposed conjugate pair that mark the location of an extinct spreading ridge between Yucatan and Florida. Seismic velocities of the crust in the eastern Gulf and the amplitude of the magnetic anomalies are similar to the Iberian and Newfoundland rifted margins, where the early stages of continental breakup were accommodated by exhumation of subcontinental lithosphere rather than creation of new basaltic oceanic crust. We infer that the eastern Gulf of Mexico is underlain by exhumed sub-continental peridotitic mantle intruded by lesser volumes of basaltic igneous rocks generated by decompression melting of the asthenosphere during the late stages of opening of the Gulf. The long wavelength characteristics of the magnetic and gravity fields in the eastern Gulf, as well as the seismic velocity structure of the crust, differ from those in the central and western Gulf, which are more similar to typical magmatic rifted margins. This suggests that the character of the Gulf changes along strike, from a magmatic western portion to an amagmatic eastern portion. Paleogeographic restoration of the lineated magnetic anomaly pattern suggests a 4-phase model for

  11. Magnetic anomalies. [Magsat studies

    NASA Technical Reports Server (NTRS)

    Harrison, C. G. A.

    1983-01-01

    The implications and accuracy of anomaly maps produced using Magsat data on the scalar and vector magnetic field of the earth are discussed. Comparisons have been made between the satellite maps and aeromagnetic survey maps, showing smoother data from the satellite maps and larger anomalies in the aircraft data. The maps are being applied to characterize the structure and tectonics of the underlying regions. Investigations are still needed regarding the directions of magnetization within the crust and to generate further correlations between anomaly features and large scale geological structures. Furthermore, an increased data base is recommended for the Pacific Ocean basin in order to develop a better starting model for Pacific tectonic movements. The Pacific basin was large farther backwards in time and subduction zones surround the basin, thereby causing difficulties for describing the complex break-up scenario for Gondwanaland.

  12. Magnetic Anomalies over Iceland.

    PubMed

    Serson, P H; Hannaford, W; Haines, G V

    1968-10-18

    An aeromagnetic survey of Iceland reveals broad anomalies of large amplitude over zones of recent volcanic activity. The source of the anomalies is ascribed to large masses of basalt that have been coherently remagnetized by intrusive heating. A simple correlation of the Icelandic anomalies with those of the ocean floor therefore appears unjustified.

  13. Pacific plate apparent polar wander between 67 Ma and 44 Ma determined from the analysis of the skewness of both vector and scalar magnetic anomalies due to seafloor spreading

    NASA Astrophysics Data System (ADS)

    Zheng, L.; Gordon, R. G.; Horner-Johnson, B. C.

    2011-12-01

    Pacific plate apparent polar wander between 67 Ma and 44 Ma determined from the analysis of the skewness of both vector and scalar magnetic anomalies due to seafloor spreading The apparent polar wander (APW) path for the Pacific plate is important to the study of Pacific plate motions and their relation to circum-Pacific tectonics. It can be used to discriminate between alternative plate motion circuits, determine the motion of Pacific hotspots relative to the paleomagnetic axis, and test the fixed hotspot hypothesis. The pioneering investigations of Jean Francheteau and his colleagues of Pacific plate APW through the analysis of magnetic anomalies over seamounts helped to demonstrate that the Pacific plate has had substantial northward motion relative to the spin axis since Cretaceous time. We also investigate the APW of the Pacific plate through analysis of magnetic anomalies. Instead of anomalies over seamounts, however, we investigate the skewness (asymmetry) of magnetic anomalies due to seafloor spreading. In prior work, skewness analysis of shipboard magnetic profiles has been used to determine Pacific paleomagnetic poles for chron 25r (57 Ma B.P.; Petronotis et al., 1994), chron 27r to 31n (62 to 69 Ma B.P.; Acton and Gordon, 1991) and chron 32n (72 Ma B.P.; Petronotis and Gordon, 1999). Recently, vector aeromagnetic data from low paleolatitudes, combined with shipboard profiles from low paleolatitudes, were used to determine a paleomagnetic pole with compact confidence limits for anomaly 12r (32 Ma B.P.; Horner-Johnson and Gordon, 2010). Here we use the low-paleolatitude shipboard- and vector aero-magnetic profiles to determine new paleomagnetic poles for the Pacific plate. A new feature of our analysis is a correction for the spreading-rate dependence of anomalous skewness (Koivisto et al. 2011). We estimate anomalous skewness as a function of spreading rate for each anomaly by creating many synthetic profiles using the model of Dyment and Arkani

  14. Methods used to identify seafloor spreading magnetic anomalies and to establish their relationship with the top of the basement topography in the Argentine continental margin between 35° S and 48° S

    NASA Astrophysics Data System (ADS)

    Abraham, D. A.; Ghidella, M. E.; Tassone, A.; Paterlini, M.; Ancarola, M.

    2013-05-01

    This paper discusses some methods for better identification of the spreading seafloor magnetic anomalies in the region between 35° S and 48° S at the outer edge of the continental margin of Argentina. In the area of Rio de la Plata craton and Patagonia Argentina, there is an extensional volcanic passive margin. This segment of the Atlantic continental margin is characterized by the existence of seismic reflectors sequences that lean toward the sea (seaward dipping reflectors - SDRs). These sequences of seismic reflectors, located in the transitional-continental basement wedge, are portrayed in seismic profiles as an interference pattern interpreted as basalt flows intercalated with sedimentary layers, and its origin is ascribed to volcanism occurred during the Early Cretaceous. The magnetic response of SDRs is in the area of the magnetic anomaly G (Rabinowitz and LaBrecque, 1979). Magnetic alignments are highlighted on a map by superimposing total field anomaly semitransparent layer of calculated numerical curvature. This method allows a regional identification of the most prominent alignments. It is convenient to calculate the curvature in the direction perpendicular to the magnetic alignments. The identification of seafloor spreading magnetic anomalies located in the eastern margin helps in the knowledge of the history of the Atlantic Ocean opening. M series magnetic alignments: M5n, M3n M0r (between 132 and 120 Ma) were identified in the analyzed area. The roughness of the top of the oceanic basement presents a contrast of amplitudes, in a wavelength range between about 4 km and 6 km, with the corresponding amplitudes in the area of the transitional crust. This contrast of amplitudes can be detected using spectral methods, especially short Fourier transform. The quantitative evaluation of the spectral energy density allowed the identification of wave numbers characterizing oceanic basement area and thus perform subsequent filtering of the signal with

  15. Magnetic Anomalies in the Enderby Basin, the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nogi, Y.; Sato, T.; Hanyu, T.

    2013-12-01

    Magnetic anomalies in the Southern indian Ocean are vital to understanding initial breakup process of Gondwana. However, seafloor age estimated from magnetic anomalies still remain less well-defined because of the sparse observations in this area. To understand the seafloor spreading history related to the initial breakup process of Gondwana, vector magnetic anomaly data as well as total intensity magnetic anomaly data obtained by the R/V Hakuho-maru and the icebreaker Shirase in the Enderby Basin, Southern Indian Ocean, are used. The strikes of magnetic structures are deduced from the vector magnetic anomalies. Magnetic anomaly signals, most likely indicating Mesozoic magnetic anomaly sequence, are obtained almost parallel to the west of WNW-ESE trending lineaments just to the south of Conrad Rise inferred from satellite gravity anomalies. Most of the strikes of magnetic structures indicate NNE-SSW trends, and are almost perpendicular to the WNW-ESE trending lineaments. Mesozoic sequence magnetic anomalies with mostly WNW-ESE strikes are also observed along the NNE-SSW trending lineaments between the south of the Conrad Rise and Gunnerus Ridge. Magnetic anomalies originated from Cretaceous normal polarity superchron are found in these profiles, although magnetic anomaly C34 has been identified just to the north of the Conrad Rise. However Mesozoic sequence magnetic anomalies are only observed in the west side of the WNW-ESE trending lineaments just to the south of Conrad Rise and not detected to the east of Cretaceous normal superchron signals. These results show that counter part of Mesozoic sequence magnetic anomalies in the south of Conrad Rise would be found in the East Enderby Basin, off East Antarctica. NNE-SSW trending magnetic structures, which are similar to those obtained just to the south of Conrad Rise, are found off East Antarctica in the East Enderby Basin. However, some of the strikes show almost E-W orientations. These suggest complicated ridge

  16. Magnetic Anomalies over the Pacific-Antarctic Ridge.

    PubMed

    Pitman, W C; Heirtzler, J R

    1966-12-01

    Four magnetic profiles across the Pacific-Antarctic Ridge reveal magnetic anomalies that show trends parallel with the ridge axis and symmetry about the ridge axis. The distribution of bodies that could cause these anomalies supports the Vine and Matthews hypothesis for the generation of patterns of magnetic anomalies associated with the midocean ridge system. The geometry of the bodies accords with the known reversals of the geomagnetic field during the last 3.4 million years, indicating a spreading rate of the ocean floor of 4.5 centimeters per year. If one assume that the spreading rate within 500 kilometers of the ridge axis has been constant, reversals of the geomagnetic field during the last 10.0 million years can be determined. This new, detailed history of field reversals accords with observed anomalies over Reykjanes Ridge in the North Atlantic if a spreading rate of 1 centimeter per year is assumed there.

  17. Magnetic Anomaly Lineations in the Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Noguchi, Y.; Nakanishi, M.; Tamaki, K.; Fujimoto, H.; Huchon, P.; Leroy, S.; Styles, P.

    2012-12-01

    We present the magnetic anomaly lineations in the Gulf of Aden to expose the seafloor spreading history. The Gulf of Aden is a young ocean basin formed by the rifting of Arabia Plate away from Somalia Plate. The Arabian plate moves away from Somalia Plate in an NE direction, at a rate of about 2 cm/yr. The rifting started from Oligocene (Bosworth et al., 2005). Seafloor spreading started at about 20 Ma in the eastern part of the Gulf of Aden (Fournier et al., 2010) and propagated westward into the Arabia-Africa continent (Manighetti et al., 1997). It reached the Afar hotspot area about 10 Ma (Audin et al., 2001). The spreading system continues to interact with the hotspot up to the present. Tamsett and Searle (1988) exposed that strike of segmentations of the spreading centers in the Gulf of Aden is NW-SE, although the trend of the spreading system is ENE. We examined magnetic anomaly data collected in the cruises by R/V L'Atalante in 1995 and R/V Hakuho-maru from 2000 to 2001 as well as those collected in other cruises. Elongated negative magnetic anomalies, which amplitude are more than 500 nT, are observed over the spreading centers. Most of the elongated anomalies are parallel with the spreading centers. The elongated magnetic anomalies west of 46 30'E have an E-W trend around the spreading centers. Several discontinuities in the magnetic anomaly contour map illustrate the position of the fracture zones concealed by sediments. Most of magnetic anomaly lineations east of 46 30'E have an N60-65 W strike. Our identification of magnetic anomaly lineations indicates a symmetric seafloor spreading with a spreading rate of about 1.0 cm/yr, although Leroy et al. (2004) showed an asymmetric seafloor spreading of the Sheba Ridge, east of our study area. The kinematics of the Arabia plate changed about 5 Ma, but our results did not show any coeval change in spreading rates of the spreading system in the Gulf of Aden.

  18. Magnetic Anomaly Lineations in the Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Noguchi, Y.; Nakanishi, M.; Tamaki, K.; Fujimoto, H.; Huchon, P.; Leroy, S. D.; Styles, P.

    2014-12-01

    We present the magnetic anomaly lineations in the Gulf of Aden. The Gulf of Aden has slow spreading ridges between the Arabia Plate and Somalia Plate. The Arabian plate moves away from Somalia Plate in an NE direction, at a rate of about 2 cm/yr. Previous works indicates that seafloor spreading started about 20 Ma in the eastern part of the Gulf of Aden and propagated westward. The spreading axis has a E-W trend west of 46 E and that east of 46 E has a N60 W trend. We examined magnetic data acquired in the cruises by R/V L'Atalante in 1995, R/V Hakuho-maru from 2000 to 2001, R/V Maurice Ewing in 2001, and Shackleton in 1975 and 1979. We also used data obtained from National Geophysical Data Center, NOAA. We calculated magnetic anomalies using the latest Internation Geomagnetic Reference Field. Elongated negative magnetic anomalies, which amplitude are more than 500 nT, observed over the spreading centers. Most of the elongated anomalies are parallel with the spreading centers. The elongated magnetic anomalies west of 46 30'E have an E-W trend around the spreading centers. Several discontinuities in the magnetic anomaly contour map illustrate the position of the fracture zones concealed by sediments. We identified magnetic lineations from 43 E to 52 E. Most of magnetic lineations west and east of 46 30'E have N-E and N60-65 W strikes, respectively. The oldest lineations are C3r (5.48~5.74 Ma) between 43 10'E and 44 E and C5Ar (12.4~12.7 Ma) east of 44 E. Our identification of magnetic anomaly lineations indicates a symmetric seafloor spreading with a spreading rate of about 1.0 cm/yr, although Leroy et al. (2004) showed an asymmetric seafloor spreading of the Sheba Ridge, east of our study area. The kinematics of the Arabia plate changed about 5 Ma, but our results did not show any coeval change in spreading rates of the spreading system in the Gulf of Aden.

  19. Spreading rate dependence of gravity anomalies along oceanic transform faults.

    PubMed

    Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montési, Laurent G J

    2007-07-12

    Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults. PMID:17625563

  20. Spreading rate dependence of gravity anomalies along oceanic transform faults.

    PubMed

    Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montési, Laurent G J

    2007-07-12

    Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults.

  1. Interpretation of magnetic anomalies over the Grenada Basin

    NASA Astrophysics Data System (ADS)

    Bird, Dale E.; Hall, Stuart A.; Casey, John F.; Millegan, Patrick S.

    1993-10-01

    The Grenada Basin is a back arc basin located near the eastern border of the Caribbean Plate. The basin is bounded on the west by the north-south trending Aves Ridge (a remnant island arc) and on the east by the active Lesser Antilles island arc. Although this physiography suggests that east-west extension formed the basin, magnetic anomalies over the basin exhibit predominantly east-west trends. If the observed magnetic anomalies over the basin are produced by seafloor spreading, then the orientation of extension is complex. Extension in back arc basins is roughly normal to the trench, although some basins exhibit oblique extension. Present models for the formation of the Grenada Basin vary from north-south extension through northeast-southwest extension to east-west extension. An interpretation of magnetic anomalies over the Grenada Basin supports basin development by nearly east-west extension. Low amplitude magnetic anomaly trends subparallel to the island arc magnetic anomaly trends over the southern part of the basin and the results of forward three-dimensional (3-D) magnetic modeling are consistent with this conclusion. Late Cenozoic tectonic movements may have been responsible for disrupting the magnetic signature over the northern part of the basin. On the basis of our 3-D analysis, we attribute the prominent east-west trending anomalies of the Grenada Basin to fracture zones formed during seafloor spreading at low latitude. This east-west trend is not interpreted as indicating north-south extension of the basin.

  2. Crustal structure interpreted from magnetic anomalies

    NASA Technical Reports Server (NTRS)

    Phillips, Jeffrey D.; Reynolds, Richard L.; Frey, Herbert

    1991-01-01

    This review, discusses publications during the last quadrennium (1987-1990) that used aeromagnetic data, marine magnetic data, satellite magnetic data, and rock magnetic and petrologic data to provide information on the sources of magnetic anomalies. The publications reviewed reflect increased integration of rock magnetic property and petrologic studies with magnetic anomaly interpretation studies, particularly in deep crustal magnetization, exploration for hydrocarbons, and inversion of marine magnetic anomalies. Interpretations of aeromagnetic data featuring image display techniques and using the horizontal gradient method for locating magnetization boundaries became standard.

  3. Spectral Methods for Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Parker, R. L.; Gee, J. S.

    2013-12-01

    Spectral methods, that is, those based in the Fourier transform, have long been employed in the analysis of magnetic anomalies. For example, Schouten and MaCamy's Earth filter is used extensively to map patterns to the pole, and Parker's Fourier transform series facilitates forward modeling and provides an efficient algorithm for inversion of profiles and surveys. From a different, and perhaps less familiar perspective, magnetic anomalies can be represented as the realization of a stationary stochastic process and then statistical theory can be brought to bear. It is vital to incorporate the full 2-D power spectrum, even when discussing profile data. For example, early analysis of long profiles failed to discover the small-wavenumber peak in the power spectrum predicted by one-dimensional theory. The long-wavelength excess is the result of spatial aliasing, when energy leaks into the along-track spectrum from the cross-track components of the 2-D spectrum. Spectral techniques may be used to improve interpolation and downward continuation of survey data. They can also evaluate the reliability of sub-track magnetization models both across and and along strike. Along-strike profiles turn out to be surprisingly good indicators of the magnetization directly under them; there is high coherence between the magnetic anomaly and the magnetization over a wide band. In contrast, coherence is weak at long wavelengths on across-strike lines, which is naturally the favored orientation for most studies. When vector (or multiple level) measurements are available, cross-spectral analysis can reveal the wavenumber interval where the geophysical signal resides, and where noise dominates. One powerful diagnostic is that the phase spectrum between the vertical and along-path components of the field must be constant 90 degrees. To illustrate, it was found that on some very long Project Magnetic lines, only the lowest 10% of the wavenumber band contain useful geophysical signal. In this

  4. Satellite Magnetic Anomalies of Africa and Europe

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator); Olivier, R.

    1984-01-01

    Preliminary MAGSAT scalar magnetic anomaly data of Africa, Europe, and adjacent marine areas were reduced to the pole assuming a constant inducing Earth's magnetic field of 60,000 nT. This process leads to a consistent anomaly data set free from marked variations in directional and intensity effects of the Earth's magnetic field over this extensive region. The resulting data are correlated with long wave length-pass filtered free-air gravity anomalies; regional heat flow, and tectonic data to investigate magatectonic elements and the region's geologic history. Magnetic anomalies are related to both ancient as well as more recent Cenozoic structural features.

  5. An impactor origin for lunar magnetic anomalies.

    PubMed

    Wieczorek, Mark A; Weiss, Benjamin P; Stewart, Sarah T

    2012-03-01

    The Moon possesses strong magnetic anomalies that are enigmatic given the weak magnetism of lunar rocks. We show that the most prominent grouping of anomalies can be explained by highly magnetic extralunar materials from the projectile that formed the largest and oldest impact crater on the Moon: the South Pole-Aitken basin. The distribution of projectile materials from a model oblique impact coincides with the distribution of magnetic anomalies surrounding this basin, and the magnetic properties of these materials can account for the intensity of the observed anomalies if they were magnetized in a core dynamo field. Distal ejecta from this event can explain the origin of isolated magnetic anomalies far from this basin.

  6. Northern east Pacific rise: Magnetic anomaly and bathymetric framework

    SciTech Connect

    Klitgord, K.D.; Mammerickx, J.

    1982-08-10

    The oceanic crust in the eastern Pacific between 7/sup 0/N and 30/sup 0/N and east of 127/sup 0/W contains a fairly complete history of the spreading centers associated with the East Pacific Rise since 25 m.y. B.P. (late Oligocene). In this paper, we have summarized the seafloor spreading magnetic-anomaly data and the bathymetric data that reflect the record of this technique history. The well-defined magnetic lineations north of the Clarion fracture zone, in the mouth of the Gulf of California, and on the east flank of the East Pacific Rise (EPR) are carefully examined and used to provide a guide for interpreting the spreading pattern between the Clarion and Clipperton fracture zones, southward of the Rivera fracture zone over the Mathematician Ridge, and over the entire EPR east of the Mathematician Ridge between the Rivera and Siqueiros fracture zones. The bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas. The fracture zone bathymetry and the seafloor spreading magnetc lineations on the EPR south of the Rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations. All these data provide a good record of the plate reorganizations in the middle Miocene at magnetic anomaly 5A time (12.5 to 11 m.y. B.P.), in the late Miocene at a magnetic anomaly 3'--4 time (6.5 m.y. B.P.), and in the Pliocene at magnetic anomaly 2'--3 time (3.5 m.y.B.P.). Several abandoned spreading centers, including the Mathematician Ridge, were left behind as a result of these reorganizations. The Mathematician Ridge is shown to be a set of ridges and trough whose origin is related to the tectonics activity associated with each of the above mentioned reorganizations since anomaly 5A.

  7. Regional magnetic anomaly constraints on continental rifting

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

    1985-01-01

    Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

  8. US Aeromagnetic and Satellite Magnetic Anomaly Comparisons

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W. (Principal Investigator); Sexton, J. L.

    1984-01-01

    Scalar aeromagnetic data obtained by the U.S. Naval Oceanographic Office (NOO) Vector Magnetic Survey of the conterminous U.S. were screened for periods of intense diurnal magnetic activity and reduced to anomaly form, filtered, and continued upward. A number of correlations between the NOO, POGO and preliminary MAGSAT data are evident at satellite elevations, including a prominent transcontinental magnetic high which extends from the Anadarko Basin to the Cincinnati Arch. The transcontinental magnetic high is breached by negative anomalies located over the Rio Grande Rift and Mississippi River Aulacogen. Differentially reduced-to-pole NOO and POGO magnetic anomaly data show that the transcontinental magnetic high corresponds to a well-defined regional trend of negative free-air gravity and enhanced crustal thickness anomalies.

  9. The magnetic anomaly of the Ivreazone

    NASA Technical Reports Server (NTRS)

    Albert, G.

    1979-01-01

    A magnetic field survey was made in the Ivreazone in 1969/70. The results were: significant anomaly of the vertical intensity is found. It follows the basic main part of the Ivrea-Verbano zone and continues to the south. The width of the anomaly is about 10 km, the maximum measures about +800 gamma. The model interpretation shows that possibly the anomaly belongs to an amphibolitic body, which in connection with the Ivrea-body was found by deep seismic sounding. Therefore, the magnetic anomaly provides further evidence for the conception that the Ivrea-body has to be regarded as a chip of earthmantle material pushed upward by tectonic processes.

  10. Marine Magnetic Anomalies and the Reconstruction of the World

    NASA Technical Reports Server (NTRS)

    Heirtzler, James R.; Smith, David E. (Technical Monitor)

    2000-01-01

    Until the middle of the 20th century little was known about magnetic anomalies in the oceans. Then it was discovered that there are relatively large anomalies in most of the oceans and they were unrelated to any geological structure known at that time. In the early 1950's large anomalies had been found over the Mid-Atlantic Ridge, and linear anomalies over the eastern continental shelf of North America and, shortly after that, off the west coast. A survey of the ridge south of Iceland showed that the anomalies were linear, parallel to the ridge axis, and symmetrical about the axis. Using the theory that the anomalies were caused by geomagnetic field reversals and seafloor spreading it was possible to greatly extend the time scale of geomagnetic reversals, to determine the velocity of seafloor spreading and estimate the time of opening of the North Atlantic. Lamont had a world-wide collection of marine magnetic profiles. These were used, systematically, to determine the positions of most of the land masses of the world since the beginnings of the world's present oceans.

  11. Global magnetic anomaly and aurora of Neptune

    SciTech Connect

    Cheng, A.F. )

    1990-09-01

    The large offset and tilt of Neptune's dipole magnetic field combine to create a global magnetic anomaly, analogous to but much more important than Earth's South Atlantic Anomaly. Energetic particle precipitation loss within the Neptune anomaly creates atmospheric drift shadows within which particle fluxes are greatly reduced. The energetic particle dropout observed by Voyager near closest approach occurred near the predicted times when Voyager passed within the atmospheric drift shadow. Extremely soft, structured bursts of ions and electrons within the drift shadow may result from plasma wave-induced pitch angle scattering of trapped particles confined near the magnetic equator. The dropout does not necessarily imply that Voyager passed through an Earth-like discrete auroral zone, as earlier reported. The ion and electron fluxes observed within the dropout period correspond to particles that must precipitate to Neptune's atmosphere within the anomaly region. This anomaly precipitation can account for a major portion of the ultraviolet emissions previously identified as Neptune aurora.

  12. Sources of Near Side Lunar Magnetic Anomalies

    NASA Technical Reports Server (NTRS)

    Richmond, Nicola C.; Hood, Lon L.; Halekas, J. S.; Mitchell, D. L.; Lin, R. P.; Acuna, M. H.; Binder, A.B.

    2002-01-01

    Lunar Prospector magnetometer data has been used to identify a number of nearside magnetic anomalies. Some of the features identified appear to correlate with impact ejecta, supporting a basin ejecta origin to the nearside anomalies. Additional information is contained in the original extended abstract.

  13. Understanding Magnetic Anomalies and Their Significance.

    ERIC Educational Resources Information Center

    Shea, James H.

    1988-01-01

    Describes a laboratory exercise testing the Vine-Matthews-Morley hypothesis of plate tectonics. Includes 14 questions with explanations using graphs and charts. Provides a historical account of the current plate tectonic and magnetic anomaly theory. (MVL)

  14. Regional magnetic anomaly constraints on continental breakup

    SciTech Connect

    von Frese, R.R.B.; Hinze, W.J.; Olivier, R.; Bentley, C.R.

    1986-01-01

    Continental lithosphere magnetic anomalies mapped by the Magsat satellite are related to tectonic features associated with regional compositional variations of the crust and upper mantle and crustal thickness and thermal perturbations. These continental-scale anomaly patterns when corrected for varying observation elevation and the global change in the direction and intensity of the geomagnetic field show remarkable correlation of regional lithospheric magnetic sources across rifted continental margins when plotted on a reconstruction of Pangea. Accordingly, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans.

  15. Martian magnetic anomalies and ionosphere escape rate.

    NASA Astrophysics Data System (ADS)

    Fedorov, A.; Barabash, S.; Sauvaud, J.-A.

    2012-04-01

    Looking forward to the MAVEN mission, it seems very useful to return to Mars Express data to refresh an important problem of Martian atmosphere escape: what role the crustal magnetic field may play in this process? There are several publications on this topic with completely opposite conclusions. The last hybrid simulations show that the magnetic anomalies significantly reduce the ion loss rate during solar minimum. We are trying to use a new approach to Mars Express IMA data analysis to check how it is possible.On the base of a statistical study of the ion distributions in the Martian magnetotail we show that the characteristic accelerated ions are not associated with the magnetic anomalies but only with interplanetary magnetic field clock angle. Moreover the magnetic anomalies screen and deviate the escaping flow leading to reducing of the total loss rate. Finally the observed heavy ions escaping rate is in a fantastic agreement with simulation results.

  16. The mineralogy of global magnetic anomalies

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E. (Principal Investigator)

    1984-01-01

    Experimental and analytical data on magnetic mineralogy was provided as an aid to the interpretation of magnetic anomaly maps. An integrated program, ranging from the chemistry of materials from 100 or more km depth within the Earth, to an examination of the MAGSAT anomaly maps at about 400 km above the Earth's surface, was undertaken. Within this framework, a detailed picture of the pertinent mineralogical and magnetic relationships for the region of West Africa was provided. Efforts were directed toward: (1) examining the geochemistry, mineralogy, magnetic properties, and phases relations of magnetic oxides and metal alloys in rocks demonstrated to have originated in the lower crust of upper mantle, (2) examining the assumption that these rocks portray the nature of their source regions; and (3) examining the regional geology, tectonics, gravity field and the MAGSAT anomaly maps for West Africa.

  17. Continental magnetic anomaly constraints on continental reconstruction

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

    1985-01-01

    Crustal magnetic anomalies mapped by the MAGSAT satellite for North and South America, Europe, Africa, India, Australia and Antarctica and adjacent marine areas were adjusted to a common elevation of 400 km and differentially reduced to the radial pole of intensity 60,000 nT. These radially polarized anomalies are normalized for differential inclination, declination and intensity effects of the geomagnetic field, so that in principle they directly reflected the geometric and magnetic polarization attributes of sources which include regional petrologic variations of the crust and upper mantle, and crustal thickness and thermal perturbations. Continental anomalies demonstrate remarkably detailed correlation of regional magnetic sources across rifted margins when plotted on a reconstruction of Pangea. Accordingly, they suggest further fundamental constraints on the geologic evolution of the continents and their reconstructions.

  18. CHAMP Magnetic Anomalies of the Antarctic Crust

    NASA Technical Reports Server (NTRS)

    Kim, Hyung Rae; Gaya-Pique, Luis R.; vonFrese, Ralph R. B.; Taylor, Patrick T.; Kim, Jeong Woo

    2003-01-01

    Regional magnetic signals of the crust are strongly masked by the core field and its secular variations components and hence difficult to isolate in the satellite measurements. In particular, the un-modeled effects of the strong auroral external fields and the complicated- behavior of the core field near the geomagnetic poles conspire to greatly reduce the crustal magnetic signal-to-noise ratio in the polar regions relative to the rest of the Earth. We can, however, use spectral correlation theory to filter the static lithospheric and core field components from the dynamic external field effects. To help isolate regional lithospheric from core field components, the correlations between CHAMP magnetic anomalies and the pseudo magnetic effects inferred from gravity-derived crustal thickness variations can also be exploited.. Employing these procedures, we processed the CHAMP magnetic observations for an improved magnetic anomaly map of the Antarctic crust. Relative to the much higher altitude Orsted and noisier Magsat observations, the CHAMP magnetic anomalies at 400 km altitude reveal new details on the effects of intracrustal magnetic features and crustal thickness variations of the Antarctic.

  19. Geological reasons for change in intensity of linear magnetic anomalies of the Kursk magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Zhavoronkin, I. A.; Kopayev, V. V.

    1985-01-01

    The geological reasons for fluctuations in the anomalous field intensity along the polar axes were examined. The Kursk magnetic anomaly is used as the basis for the study. A geological-geophysical section was constructed which used the results of the interpretation of gravimagnetic anomalies.

  20. Explanation of the nature of stripe magnetic anomalies without inversions

    NASA Astrophysics Data System (ADS)

    Melikhov, Vjacheslav; Lygin, Ivan; Sokolova, Tatiana

    2014-05-01

    Several scientists of different branches express doubts on the validity of the Earth's geomagnetic field inversions hypothesis [Vine F.J., Matthews D.H, 1963]. Presently a lot of information allows to link the appearance of stripe magnetic anomalies of both signs with the spreading fracture structure (horizontal segmentation of intrusions and sills, breaks in the strong crust, vertical movements of blocks), remagnetization near the borders of the blocks, hydrothermal activity. Non-inversion mechanism of origin of linear stripe magnetic anomalies in the oceans could be explained as follows. Ascending asthenospheric flows have been enrich with volatile components, become thinner, pressure on the walls of the lithospheric plates grows and part them. When it approaches the surface: - horizontal tensile pressure grows, - lithostatic pressure in the vertical column of rocks decreases, - crust strong upper layer flakes away and begins to move horizontally. It is important that thin magmatic and magnetic layers (further layers) of the newly formed strong upper crust move away from the ridge axis. The structure of such layers forms by horizontal stresses and so consist of the hills and depressions sequences or updiped and downdiped blocks heaped each other. This layer is the main source of the magnetic field and cannot be approximated by a horizontal homogeneous plate as it proved before. In the mid-ocean ridges (MOR) the folding periods of layer depend on its thickness and rigidity and horizontal velocity of spreading. The higher velocity - the longer periods of roughness are and contrary. Same pattern is observed for the stripe magnetic anomalies distribution. The magnetic field of the MOR forms there due to young lava flows which get thermoremanent magnetization according the current direction of geomagnetic field. Partial destruction of the relief, overlaying and creation of the new shapes occur when new magma penetrates the moved magnetic layer. The process entails

  1. Band Iron Formations and Satellite Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Nazarova, K. A.; Wasilewski, P.

    2005-05-01

    Band Iron Formations (BIF) are mainly Precambrian (2.5-1.8 Ga) sedimentary deposits and are composed of alternating layers of iron rich material and silica (chert). Precambrian BIF mark growth in the level of free oxygen in the atmosphere and the ocean which happened about 2.2 Ga. Distribution of main BIF includes Hamersley Range, Australia; Transvaal-Griquatown, South Africa; Minas Gerais, Brazil; Labrador Trough, Canada, and Kursk-Krivoi Rog (Russia). Together these five very large BIF deposits constitute about 90 percent of Earth's total estimated BIF (5.76*10 14 ). On each continent these ancient rocks usually metamorphosed and crystallized include what are variously described as hematite-quartzites, banded iron formations, banded jaspers or calico-rocks. West African, Hudson Bay and Western Australian Satellite Magnetic Anomalies coincide with distribution BIF deposits. The Kursk Satellite Magnetic Anomaly (KMA) (about 22 nT at the altitude=400km, centered at 51o N, 37o E) also was identified by ground and aeromagnetic observations and is recognized as one of the largest magnetic anomaly on the Earth. Magnetic modeling shows that immense Precambrian iron ore deposits (iron bands) of Voronezh uplift are the main source of KMA. Magnetic properties of 10000 BIF samples outcropped in the KMA area have been measured and analyzed (Krutikhovskaya et al., 1964) Rockmag BIF dataset is presented at: http://core2.gsfc.nasa.gov/MPDB/datasets.html. Mean NRM value is about 42 A/M, Qn about 1.4. Demagnetization tests suggest that hard and stable NRM component is caused by hematite occurring in BIF in different forms and grain sizes. Hematite deposits discovered on Mars in western equatorial area with layered topography of Aram Chaos and Sinus Meridiani could be of hydrothermal origin and may be formed similar to hematite precipitated in BIF on Earth.

  2. Magnetic anomalies northeast of Cape Adare, northern Victoria Land (Antarctica), and their relation to onshore structures

    USGS Publications Warehouse

    Damaske, D.; Läufer, A.L.; Goldmann, F.; Möller, H.-D.; Lisker, F.

    2007-01-01

    An aeromagnetic survey was flown over the offshore region northeast of Cape Adare and the magnetic anomalies compared to onshore structures between Pennell Coast and Tucker Glacier. The magnetic anomalies show two nearly orthogonal major trends. NNW-SSE trending anomalies northeast of Cape Adare represent seafloor spreading within the Adare Trough. A connection of these anomalies to the Northern Basin of the Ross Sea is not clear. Onshore faults are closely aligned to offshore anomalies. Main trends are NW-SE to NNW-SSE and NE-SW to NNESSW. NNW-SSE oriented dextral-transtensional to extensional faults parallel the Adare Peninsula and Adare Trough anomalies. NE-SW trending normal faults appear to segment the main Hallett volcanic bodies.

  3. Paleo-Pole Positions from Martian Magnetic Anomaly Data

    NASA Technical Reports Server (NTRS)

    Frawley, James J.; Taylor, Patrick T.

    2004-01-01

    Magnetic component anomaly maps were made from five mapping cycles of the Mars Global Surveyor's magnetometer data. Our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body. From these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization. We found nine suitable anomaly pairs and from these we computed paleo-poles that were nearly equally divided between north, south and mid-latitudes. These results suggest that during the existence of the martian main magnetic field it experienced several reversals and excursions.

  4. Paleo-Pole Positions from Martian Magnetic Anomaly Data

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; Frawley, James J.

    2003-01-01

    Magnetic component anomaly maps were made from five mapping cycles of the Mars Global Surveyor s magnetometer data. Our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body. From these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization. We found nine suitable anomaly pairs and from these we computed four North and 3 South poles with two at approximately 60 degrees north latitude. These results suggest that during the existence of the Martian main magnetic field it experienced several reversals.

  5. A global magnetic anomaly map. [obtained from POGO satellite data

    NASA Technical Reports Server (NTRS)

    Regan, R. D.; Davis, W. M.; Cain, J. C.

    1974-01-01

    A subset of POGO satellite magnetometer data has been formed that is suitable for analysis of crustal magnetic anomalies. Using a thirteenth order field model, fit to these data, magnetic residuals have been calculated over the world to latitude limits of plus 50 deg. These residuals averaged over one degree latitude-longitude blocks represent a detailed global magnetic anomaly map derived solely from satellite data. Preliminary analysis of the map indicates that the anomalies are real and of geological origin.

  6. Current thinking about Jupiter's magnetic anomaly

    NASA Astrophysics Data System (ADS)

    Grodent, D.; Gerard, J.-C.; Gustin, J.; Clarke, J. T.; Connerney, J. E.

    Repeated imaging of Jupiter's aurora has shown that the northern main oval has a distorted 'kidney bean' shape in the general range of 90-150o System III longitude, which appears unchanged since 1994. While it is more difficult to observe the conjugate regions in the southern aurora, no corresponding distortion appears in the south. Recent improved accuracy in locating the auroral footprint emission of Io has provided new information about the geometry of Jupiter's magnetic field in this and other areas. The persistent pattern of the main oval implies a disturbance of the local magnetic field, and the increased latitudinal separation of the locus of the Io footprint from the main oval implies a locally weaker field strength. The most recent images obtained with the Hubble Space Telescope Advance Camera for Surveys (ACS) allow us to complement previous observations with the location of the auroral footprints of Io, Europa, and Ganymede in the region of interest. Their footpaths vary in parallel and form a kink in the 90-150° S3 sector which strongly suggests the presence of a magnetic anomaly in this region.

  7. Anomaly induced effects in a magnetic field

    NASA Astrophysics Data System (ADS)

    Antoniadis, Ignatios; Boyarsky, Alexey; Ruchayskiy, Oleg

    2008-04-01

    We consider a modification of electrodynamics by an additional light massive vector field, interacting with the photon via Chern-Simons-like coupling. This theory predicts observable effects for the experiments studying the propagation of light in an external magnetic field, very similar to those, predicted by theories of axion and axion-like particles. We discuss a possible microscopic origin of this theory from a theory with non-trivial gauge anomaly cancellation between massive and light particles (including, for example, millicharged fermions). Due to the conservation of the gauge current, the production of the new vector field is suppressed at high energies. As a result, this theory can avoid both stellar bounds (which exist for axions) and the bounds from CMB considered recently, allowing for positive results in experiments like ALPS, LIPPS, OSQAR, PVLAS-2, BMV, Q&A, etc.

  8. Continental and oceanic magnetic anomalies: Enhancement through GRM

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.

    1985-01-01

    In contrast to the POGO and MAGSAT satellites, the Geopotential Research Mission (GRM) satellite system will orbit at a minimum elevation to provide significantly better resolved lithospheric magnetic anomalies for more detailed and improved geologic analysis. In addition, GRM will measure corresponding gravity anomalies to enhance our understanding of the gravity field for vast regions of the Earth which are largely inaccessible to more conventional surface mapping. Crustal studies will greatly benefit from the dual data sets as modeling has shown that lithospheric sources of long wavelength magnetic anomalies frequently involve density variations which may produce detectable gravity anomalies at satellite elevations. Furthermore, GRM will provide an important replication of lithospheric magnetic anomalies as an aid to identifying and extracting these anomalies from satellite magnetic measurements. The potential benefits to the study of the origin and characterization of the continents and oceans, that may result from the increased GRM resolution are examined.

  9. A model of ocean basin crustal magnetization appropriate for satellite elevation anomalies

    NASA Technical Reports Server (NTRS)

    Thomas, Herman H.

    1987-01-01

    A model of ocean basin crustal magnetization measured at satellite altitudes is developed which will serve both as background to which anomalous magnetizations can be contrasted and as a beginning point for studies of tectonic modification of normal ocean crust. The model is based on published data concerned with the petrology and magnetization of the ocean crust and consists of viscous magnetization and induced magnetization estimated for individual crustal layers. Thermal remanent magnetization and chemical remanent magnetization are excluded from the model because seafloor spreading anomalies are too short in wavelength to be resolved at satellite altitudes. The exception to this generalization is found at the oceanic magnetic quiet zones where thermal remanent magnetization and chemical remanent magnetization must be considered along with viscous magnetization and induced magnetization.

  10. Improving the geological interpretation of magnetic and gravity satellite anomalies

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W. (Principal Investigator); Vonfrese, R. R. B.

    1985-01-01

    Current limitations in the quantitative interpretation of satellite-elevation geopotential field data and magnetic anomaly data were investigated along with techniques to overcome them. A major result was the preparation of an improved scalar magnetic anomaly map of South America and adjacent marine areas directly from the original MAGSAT data. In addition, comparisons of South American and Euro-African data show a strong correlation of anomalies along the Atlantic rifted margins of the continents.

  11. New Magnetic Anomaly Compilation Illuminates the Formation of the Aleutian Basin

    NASA Astrophysics Data System (ADS)

    Scheirer, D. S.; Barth, G. A.; Scholl, D. W.; Stern, R. J.

    2013-12-01

    Aleutian Basin crust is deeply buried beneath 2 to 5 km of sediment, so magnetic data provide valuable insights into its structure and origin. A new compilation of marine magnetic anomalies, derived from one recent cruise (2011) and re-analysis of dozens of legacy cruises (primarily 1970's to 1980's), provides both a refined view of the magnetic field in the Bering Sea area and insights into the formation of the deep-water Aleutian and Bowers Basins. In the Aleutian Basin, the magnetic fabric can be divided into two similar-sized areas of distinct types. Type 1 magnetic fabric is characterized by north-south-oriented lineations in the southern Aleutian Basin. The lineations have irregular spacing, reminiscent of seafloor spreading stripes, and the amplitudes of the anomalies are also consistent with a magnetic source formed at spreading centers. Seismic reflection data show that the strongest magnetic lineations in the Type 1 area are not associated with basement relief, supporting an origin from remanent magnetization variations and consistent with their formation by seafloor spreading. This interpretation is consistent with OBS refraction results indicating that this is mafic crust ~8 km thick. The pattern of anomalies does not show an obvious symmetry about a possible fossil spreading axis, and attempts to assign the sequence of lineaments to the geomagnetic polarity timescale are not definitive. Thus, we cannot rule out either of the two hypotheses for the formation of the Aleutian Basin, as a Paleogene back-arc basin or as captured (old) plate trapped by formation of the Aleutian subduction zone at ~50 Ma. Type 2 magnetic fabric is characterized by higher-amplitude and more heterogeneous magnetic anomalies than Type 1 fabric, and it is located around the margins of the Aleutian Basin, to the north and west of the lineated fabric. Some features of the basement (e.g. Sounder Ridge) have corresponding magnetic anomalies in Type 2 areas, but other anomalies with

  12. Study of gravity and magnetic anomalies using MAGSAT data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1981-01-01

    The results of modeling satellite-elevation magnetic and gravity data using the constraints imposed by near surface data and seismic evidence shows that the magnetic minimum can be accounted for by either an intracrustal lithologic variation or by an upwarp of the Curie point isotherm. The long wavelength anomalies of the NOO's-vector magnetic survey of the conterminous U.S. were contoured and processed by various frequency filters to enhance particular characteristics. A preliminary inversion of the data was completed and the anomaly field calculated at 450 km from the equivalent magnet sources to compare with the POGO satellite data. Considerable progress was made in studing the satellite magnetic data of South America and adjacent marine areas. Preliminary versions of the 1 deg free-air gravity anomaly map (20 m gal contour interval) and the high cut (lambda approximately 8 deg) filtered anomaly maps are included.

  13. The south-central United States magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Starich, P. J.

    1985-01-01

    The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free-air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced-to-pole and derivative maps provide additional constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the anomaly, but are rather indicative of a crustal zone which was disturbed during a Middle Proterozoic thermal event which enriched magnetic material deep in the crust.

  14. The south-central United States magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W. (Principal Investigator); Starich, P. J.

    1984-01-01

    The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced to pole and derivative maps provide constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the anomaly, but are rather indicative of a crustal zone which was disturbed during a Middle Proterozoic thermal event which enriched magnetic material deep in the crust.

  15. Do Satellite Magnetic Anomaly Data Accurately Portray the Crustal Component?

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J. (Principal Investigator)

    1984-01-01

    Scalar aeromagnetic data obtained during the U.S. Naval Oceanographic Office (NOO)-Vector Magnetic Survey of the conterminous United States were upward continued by equivalent point source inversion and compared with POGO satellite magnetic anomaly and preliminary scalar MAGSAT data. Initial comparisons indicate that the upward continued NOO data is dominated by long wavelength (approximately equal to 1000 to 3000 km) anomalies which are not present in the satellite anomaly data. Thus, the comparison of the data sets is poor. Several possible sources for these differences are present in the data analysis chain. However, upon removal of these long wavelengths from the upward continued NOO data, a close comparison observed between the anomalies verifies that satellite magnetic anomaly data do portray the crustal component within a range of wavelengths from roughly 1000 km down to the resolution limit of the observations.

  16. Magnetic anomalies and tectonic fabric of marginal basins North of New Zealand

    SciTech Connect

    Malahoff, A.; Feden, R.H.; Fleming, H.S.

    1982-05-10

    Detailed airborne magnetic studies conducted over the region of the S. W. Pacific marginal basins extending from the Solomon Islands to New Zealand suggest that three major phases of basin formation and island arc development have occurred in this region. Development of the Tasman Sea took place during the Late Cretaceous-Paleocene. Development of the basins to the east of the Tasman Sea occurred predominantly during the Oligocene as well as during the Upper Miocene to Recent. The South Fuji Basin, consisting of the Kupe and Minerva Abyssal Plains, is marked by the presence of possibly two RRR triple junction spreading centers that were active between the times of anomalies 13 to 7 (36--25.5 m.y.). The Kupe Abyssal Plain shows the presence of residual magnetic anomalies 7 to 13 of the eastern limb of the proposed spreading center. The western limb appears to have been subducted beneath the present site of the Three Kings Rise. This seafloor spreading phase (calculated half-spreading rate of 35 mm/yr) was coincident with the overthrusting phase of the New Caledonia ultramafic rocks. During that period, active volcanism along the then continuous Solomons-New Hebrides-Fiji-Lau Island arc was taking place. Magnetic anomalies from 1 to 4 (0--8 m.y. B. P.) are seen to extend along a clearly defined lineation pattern over the North Fuji Basin.

  17. Alternative explanation for intermediate--wavelength magnetic anomalies

    SciTech Connect

    Shure, L.; Parker, R.L.

    1981-12-10

    Harrison and Carle and others have examined very long profiles of the magnetic field and have calculated one-dimensional power spectra. In these they expect to see, but do not find, a minimum in power at intermediate wavelengths, between 65 and 150 km. Conventional one-dimensional models of the field predict very little power in this band, which lies between the spectral peaks arising from sources in the crust and the core. Mantle sources or high-intensity, long-wavelength magnetizations have been proposed to account for the observations. An alternative, more plausible explanation is that one-dimensional spectra of two-dimensional fields contain contributions from wavenumbers in the perpendicular (i.e., nonsampled) direction. Unless the seafloor spreading anomalies are perfectly lineated at right angles to the profile, some low-wavenumber energy must be attributed to this effect; we propose that such directional aliasing is a major factor in the power spectra. To support this idea we discuss theoretical models and analyze a large-scale marine survey.

  18. Macquarie island and the cause of oceanic linear magnetic anomalies.

    PubMed

    Varne, R; Gee, R D; Quilty, P G

    1969-10-10

    Macquarie Islands is formed of probably Pliocene oceanic crust. Intruded into pillow lavas is a belt of harzburgite and layered gabbro mnasses cut by dike swarms. Similar belt-like structures may cause the linear magnetic anomalies of the ocean.

  19. Hematite Versus Magnetite as the Signature for Planetary Magnetic Anomalies?

    NASA Technical Reports Server (NTRS)

    Kletetshka, Gunther; Taylor, Patrick T.; Wasilewski, Peter J.

    1999-01-01

    Crustal magnetic anomalies are the result of adjacent geologic units having contrasting magnetization. This magnetization arises from induction and/or remanence. In a planetary context we now know that Mars has significant crustal magnetic anomalies due to remanent magnetization, while the Earth has some anomalies where remanence can be shown to be important. This picture, however, is less clear because of the nature and the magnitude of the geomagnetic field which is responsible for superimposed induced magnetization. Induced magnetization assumes a magnetite source, because of its much greater magnetic susceptibility when compared with other magnetic minerals. We investigated the TRM (thermoremanent magnetization) acquisition of hematite, in weak magnetic fields up to 1 mT, to determine if the remanent and induced magnetization of hematite could compete with magnetite. TRM acquisition curves of magnetite and hematite show that multi-domain hematite reaches TRM saturation (0.3 - 0.4 A sq m/kg) in fields as low as 100 microT. However, multi-domain magnetite reaches only a few percent of its TRM saturation in a field of 100 microT (0.02 - 0.06 A sq m/kg). These results suggest that a mineral such as hematite and, perhaps, other minerals with significant remanence and minor induced magnetization may play an important role in providing requisite magnetization contrast. Perhaps, and especially for the Mars case, we should reevaluate where hematite and other minerals, with efficient remanence acquisition, exist in significant concentration, allowing a more comprehensive explanation of Martian anomalies and better insight into the role of remanent magnetization in terrestrial crustal magnetic anomalies.

  20. Distribution of Narrow-Width Magnetic Anomalies in Antarctica.

    PubMed

    Behrendt, J C

    1964-05-22

    Data for aeromagnetic profiles obtained in Antarctica during the 1963-64 austral summer were used together with earlier results to construct a map showing the areal distribution of narrow-width magnetic anomalies. Numerous anomalies are associated with known volcanic mountains in western Antarctica. A large area of few anomalies is probably a result of an extension of the thick metasedimentary section observed in the Ellsworth Mountains. Portions of the Trans-Antarctic Mountains have associated anomalies which are probably caused by late Cenozoic volcanic rocks.

  1. Distribution of narrow-width magnetic anomalies in Antarctica

    USGS Publications Warehouse

    Behrendt, John C.

    1964-01-01

    Data for aeromagnetic profiles obtained in Antarctica during the 1963-64 austral summer were used together with earlier results to construct a map showing the areal distribution of narrow-width magnetic anomalies. Numerous anomalies are associated with known volcanic mountains in western Antarctica. A large area of few anomalies is probably a result of an extension of the thick metasedimentary section observed in the Ellsworth Mountains. Portions of the Trans-Antarctic Mountains have associated anomalies which are probably caused by late Cenozoic volcanic rocks.

  2. Distribution of Narrow-Width Magnetic Anomalies in Antarctica.

    PubMed

    Behrendt, J C

    1964-05-22

    Data for aeromagnetic profiles obtained in Antarctica during the 1963-64 austral summer were used together with earlier results to construct a map showing the areal distribution of narrow-width magnetic anomalies. Numerous anomalies are associated with known volcanic mountains in western Antarctica. A large area of few anomalies is probably a result of an extension of the thick metasedimentary section observed in the Ellsworth Mountains. Portions of the Trans-Antarctic Mountains have associated anomalies which are probably caused by late Cenozoic volcanic rocks. PMID:17811603

  3. Petrophysical correlation of Fennoscandian magnetic and gravity anomalies

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

    Magnetic anomaly, Bouguer-anomaly and petrophysical grids of the Fennoscandian shield and adjoining area have been compiled as a joint venture between Finland, Norway, Sweden and Russia, and with contribution of Denmark, Estonia, Latvia and Lithuania. Maps have been printed on a scale of 1:2 million. The aim was to provide an overall view of the anomaly structure of the area, and especially assist in correlating Precambrian geological formations across seas, state borders and areas covered by younger formations. Insert maps on a scale of 1:15 million are aimed to correlate anomaly components in different source scales: pseudogravimetric anomaly with Bouguer anomaly, DGRF-65 anomaly with pseudomagnetic anomaly, magnetic vertical derivative with second derivative of Bouguer anomaly. Data on bulk density, total magnetisation, Q-value and lithology of samples have been presented as scatter diagrams and average distribution maps to delineate variation and evolution trends of properties in space and time. Major anomalies of the Bouguer-anomaly map are due to Caledonian and Belomorian zones, Rapakivi granites and high metamorphic blocks in central area of the shield. Magnetic positive regional anomalies are due to granite areas in the north and west and to high-grade rocks in south. The central magnetic low is associated with rocks of supracrustal origin. Bouguer anomaly and depth-integrated magnetisation were compared with average bulk density and total magnetisation to find information on depth extent of exposed anomaly sources. The source magnetisation of the north Fennoscandian magnetic high is interpreted to reach 10 km in depth. The source area extends to the west under the Caledonian cover and to the east under the granite area of Central Finnish Lapland. The thickness of the latter is a few km only, as interpreted by density -- gravity correlation. In SE Fennoscandia the thickness of Wiborg rapakivi is c. 10 km by bulk density, and thickness of North Estonian

  4. Near-seafloor magnetic field observations at the Mariana Trough back-arc spreading center

    NASA Astrophysics Data System (ADS)

    Fujiwara, Toshiya; Asada, Miho; Umino, Susumu; Koike, Yuki; Kanamatsu, Toshiya

    2010-05-01

    We surveyed the Mariana Trough back-arc basin in the western Pacific with the Japanese submersible Shinkai 6500 to understand detailed crustal formation process at the 17° N segment [Fujiwara et al., 2008]. The 17° N segment is suggested to be in vigorous magmatic stage. Sheet lava flows, suggesting a high rate of eruption, occupy the seafloor of the segment even the slow spreading with a full-rate of ~3 cm/yr [Deschamps et al., 2005; Asada et al., 2007]. The objective of magnetic field measurements is to investigate magnetization of lava flows at the seafloor. Near-seafloor observations provide us high-resolution magnetic anomaly that is valuable for the studies of the detailed magnetization structure of ocean crust and paleointensity recorded in the ocean crust. Magnetization intensities relate to age of lava, therefore deep-sea magnetic data may provide geophysical evidence for discussion of relative age differences of the lava flows. Three submersible dives were made in the axial valley situated in the spreading center. One of the dives traversed the axial valley a distance of ~2 km from the center of the valley toward off-axis, roughly parallel to the spreading direction. We observed magnetic anomalies with large-amplitude (up to 5000 nT) and short-wavelength (several tens of meters). We evaluated fine-scale across-axis magnetic structure along the dive path from the anomalies. High magnetization intensity (up to 50 A/m) was estimated at the center of the axial valley, and therefore the lava flows in the area was likely young in age. The magnetization intensity decreased toward the off-axis. The result suggests the seafloor age increases toward the off-axis. However the detailed variation of the magnetization distribution does not show simple seafloor age increment in proportion to distance from the spreading center. It implies the complexity of the crustal formation process. There is no clear correlation between the distribution of magnetization intensity

  5. The south-central United States magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Starich, P. J.; Hinze, W. J.; Braile, L. W.

    1985-01-01

    A positive magnetic anomaly, which dominates the MAGSAT scalar field over the south-central United States, results from the superposition of magnetic effects from several geologic sources and tectonic structures in the crust. The highly magnetic basement rocks of this region show good correlation with increased crustal thickness, above average crustal velocity and predominantly negative free-air gravity anomalies, all of which are useful constraints for modeling the magnetic sources. The positive anomaly is composed of two primary elements. The western-most segment is related to middle Proterozoic granite intrusions, rhyolite flows and interspersed metamorphic basement rocks in the Texas panhandle and eastern New Mexico. The anomaly and the magnetic crust are bounded to the west by the north-south striking Rio Grande Rift. The anomaly extends eastward over the Grenville age basement rocks of central Texas, and is terminated to the south and east by the buried extension of the Ouachita System. The northern segment of the anomaly extends eastward across Oklahoma and Arkansas to the Mississippi Embayment. It corresponds to a general positive magnetic region associated with the Wichita Mountains igneous complex in south-central Oklahoma and 1.2 to 1.5 Ga. felsic terrane to the north.

  6. The mineralogy of global magnetic anomalies

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E. (Principal Investigator)

    1982-01-01

    The Curie Balance was brought to operational stage and is producing data of a preliminary nature. Substantial problems experienced in the assembly and initial operation of the instrument were, for the most part, rectified, but certain problems still exist. Relationships between the geology and the gravity and MAGSAT anomalies of West Africa are reexamined in the context of a partial reconstruction of Gondwanaland.

  7. Lunar magnetic anomaly concentrations at the antipodal regions

    NASA Astrophysics Data System (ADS)

    Hemant Singh, Kumar; Kuang, Weijia; Singh, Raghav

    2014-05-01

    The high resolution lunar-wide magnetic anomaly map derived from Lunar Prospector (LP) vector magnetometer data has revealed weak anomalies over the nearside large impact basins flooded by mare basalts. Stronger anomaly features are observed over many of the Nectarian and Pre-Nectarian aged lunar highlands. In particular, regions antipodal to some of the largest basin-forming impact craters show strong magnetic anomaly concentrations. Of the 43 basins investigated here, antipodal regions of 9 basins show these anomalous features with strengths in excess of 1-18 nT at LP's mapping altitude (30 km). These distinct anomalous concentrations were previously known to occur only at the antipodes of Imbrium, Orientale, Serenitatis, Crisium and Nectaris basins. The mean magnetic anomaly strength within each antipodal region, when plotted against increasing age of the antipodes, shows two age groupings with similar magnetic behavior. The first age grouping - (Imbrium, Orientale, Serenitatis, Crisium and Nectaris) is of Imbrium to Nectarian in age. This grouping is correlative with peak magnetic field enhancements between 3.6 and 3.9 Gyr, inferred from paleomagnetic data from the returned Apollo samples. The second age grouping (Lorentz, Coulomb-Sarton, Tranquillitatis and Cognitum) is of Mid to Early Pre-Nectarian age. This grouping has not been correlated to any known global magnetic field enhancement event, and needs further investigation to ascertain the origin of the anomalies. Although spatially adjacent, the magnetic field signatures of the Serenitatis and Imbrium antipodes exhibit distinct features, supporting the antipodal hypothesis. The absence of appreciable field enhancements at 34 other antipodes, however, indicates the importance of other processes, and superposition effects, that have operated on the Moon during its history.

  8. SEISMIC DISCRIMINATION OF THERMAL AND MAGNETIC ANOMALIES IN SUNSPOT UMBRAE

    SciTech Connect

    Lindsey, C.; Cally, P. S.; Rempel, M.

    2010-08-20

    Efforts to model sunspots based on helioseismic signatures need to discriminate between the effects of (1) a strong magnetic field that introduces time-irreversible, vantage-dependent phase shifts, apparently connected to fast- and slow-mode coupling and wave absorption and (2) a thermal anomaly that includes cool gas extending an indefinite depth beneath the photosphere. Helioseismic observations of sunspots show travel times considerably reduced with respect to equivalent quiet-Sun signatures. Simulations by Moradi and Cally of waves skipping across sunspots with photospheric magnetic fields of order 3 kG show travel times that respond strongly to the magnetic field and relatively weakly to the thermal anomaly by itself. We note that waves propagating vertically in a vertical magnetic field are relatively insensitive to the magnetic field, while remaining highly responsive to the attendant thermal anomaly. Travel-time measurements for waves with large skip distances into the centers of axially symmetric sunspots are therefore a crucial resource for discrimination of the thermal anomaly beneath sunspot umbrae from the magnetic anomaly. One-dimensional models of sunspot umbrae based on compressible-radiative-magnetic-convective simulations such as by Rempel et al. can be fashioned to fit observed helioseismic travel-time spectra in the centers of sunspot umbrae. These models are based on cooling of the upper 2-4 Mm of the umbral subphotosphere with no significant anomaly beneath 4.5 Mm. The travel-time reductions characteristic of these models are primarily a consequence of a Wilson depression resulting from a strong downward buoyancy of the cooled umbral medium.

  9. The magnetic anomalies significantrly reduce the Martian ionospheric escape rate

    NASA Astrophysics Data System (ADS)

    Fedorov, A.; Barabash, S.; Sauvaud, J.-A.

    2012-09-01

    Looking forward to the MAVEN mission, it seems very useful to return to Mars Express data to refresh an important problem of Martian atmosphere escape: what role the crustal magnetic field may play in this process? There are several publications on this topic with completely opposite conclusions. The last hybrid simulations show that the magnetic anomalies significantly reduce the ion loss rate during solar minimum. We are trying to use a new approach to Mars Express IMA data analysis to check how it is possible. On the base of a statistical study of the ion distributions in the Martian magnetotail we show that the characteristic accelerated ions are not associated with the magnetic anomalies but only with interplanetary magnetic field clock angle. Moreover the magnetic anomalies screen and deviate the escaping flow leading to reducing of the total loss rate. We have calculated a "quasiexperimental" escaping rate in an assumption of the total absence of the magnetic anomalies. We are comparing this value with a real measured escape rate.

  10. Optimizing depth estimates from magnetic anomalies using spatial analysis tools

    NASA Astrophysics Data System (ADS)

    Curto, Julia B.; Diniz, Tatiana; Vidotti, Roberta M.; Blakely, Richard J.; Fuck, Reinhardt A.

    2015-11-01

    We offer a methodology to analyze the spatial and statistical properties of the tilt derivative of magnetic anomalies, thus facilitating the mapping of the location and depth of concealed magnetic sources. This methodology uses commonly available graphical information system (GIS) software to estimate and interpolate horizontal distances between key attributes of the tilt derivative, which then are used to estimate depth and location of causative bodies. Application of the method to synthetic data illustrates its reliability to determine depths to magnetic contacts. We also achieved consistent depth results using real data from the northwest portion of the Paraná Basin, Brazil, where magnetic anomaly interpretations are complicated by low geomagnetic inclinations and rocks with remanent magnetization. The tilt-derivative method provides more continuous and higher resolution contact information than the 3D Euler deconvolution technique.

  11. First high-resolution near-seafloor survey of magnetic anomalies of the South China Sea

    NASA Astrophysics Data System (ADS)

    Lin, J.; Xu, X.; Li, C.; Sun, Z.; Zhu, J.; Zhou, Z.; Qiu, N.

    2013-12-01

    -wavelength anomalies were unrecognized in sea surface measurements. (3) Preliminary results showed that the study regions might have experienced several episodes of magnetic reversal events that were not recognized in existing models. (4) We are currently investigating the geomagnetic timing of these relatively short-duration events to determine the detailed spreading history of the sub-basins of the SCS. These high-resolution near-seafloor magnetic survey lines are located close to the planned drilling sites of IODP Expedition 349 scheduled for January-March 2014.

  12. Improved determination of vector lithospheric magnetic anomalies from MAGSAT data

    NASA Technical Reports Server (NTRS)

    Ravat, Dhananjay

    1993-01-01

    Scientific contributions made in developing new methods to isolate and map vector magnetic anomalies from measurements made by Magsat are described. In addition to the objective of the proposal, the isolation and mapping of equatorial vector lithospheric Magsat anomalies, isolation of polar ionospheric fields during the period were also studied. Significant progress was also made in isolation of polar delta(Z) component and scalar anomalies as well as integration and synthesis of various techniques of removing equatorial and polar ionospheric effects. The significant contributions of this research are: (1) development of empirical/analytical techniques in modeling ionospheric fields in Magsat data and their removal from uncorrected anomalies to obtain better estimates of lithospheric anomalies (this task was accomplished for equatorial delta(X), delta(Z), and delta(B) component and polar delta(Z) and delta(B) component measurements; (2) integration of important processing techniques developed during the last decade with the newly developed technologies of ionospheric field modeling into an optimum processing scheme; and (3) implementation of the above processing scheme to map the most robust magnetic anomalies of the lithosphere (components as well as scalar).

  13. The early break-up phase of the South Atlantic - magnetic anomalies, volcanism and kinematics

    NASA Astrophysics Data System (ADS)

    Koopmann, H.; Schreckenberger, B.; Franke, D.; Becker, K.; Schnabel, M.

    2013-12-01

    The South Atlantic has been generally recognized as a prime example for continental break-up with accompanying volcanic activity reflected today in massive seaward dipping reflector sequences (SDRS) in reflection as well as high velocity lower crust in refraction seismic data. The early history of the South Atlantic passive margin evolution is investigated in the view of interlaced magnetic anomalies related to seafloor spreading lineations and anomalies caused by seaward-dipping reflector sequences (SDRS). As the Atlantic opened from South to North, the magma-poor segments of the southernmost South Atlantic are also the oldest segments of the Ocean. Therefore, the magma-poor segments on the conjugated margins must be considered crucial in the understanding of the initial phase of spreading and rifting concluding in the opening of the South Atlantic. The interpretation of pre-M5n lineations define timing of the termination of excess breakup related volcanic activity and the transition to 'normal' seafloor spreading. Termination of magnetic anomalies within SDR wedges point towards a scissor-like succession in volcanic activity from south to north, following the opening of the South Atlantic. Reflection, refraction seismic and potential field data show that while the two conjugated margins share much of their structural features such as segmentation and abundant volcanism, they are by no means perfectly symmetrical. This is for example shown in shelf width, strength of the magnetic anomalies or orientation of break-up related sedimentary basins. From our data, we suggest changes in spreading and later rifting direction to be the cause of for these asymmetries. This directional change is also suggested to be responsible for the change in margin character from magma-poor to volcanic rather than solely a spontaneous change in crustal melt-generation. New models for the magnetic response of SDRS reveal a high variability within the wedges on either side of the Atlantic

  14. Identification of a magnetic anomaly at Jupiter from satellite footprints

    NASA Astrophysics Data System (ADS)

    Grodent, Denis

    2004-07-01

    Repeated imaging of Jupiter's aurora has shown that the northern main oval has a distorted 'kidney bean' shape in the general range of 90-140? System III longitude, which appears unchanged since 1994. While it is more difficult to observe the conjugate regions in the southern aurora, no corresponding distortion appears in the south. Recent improved accuracy in locating the satellite footprint auroral emissions has provided new information about the geometry of Jupiter's magnetic field in this and other areas. The study of the magnetic field provides us with insight into the state of matter and the dynamics deep down Jupiter. There is currently no other way to do this from orbit. The persistent pattern of the main oval implies a disturbance of the local magnetic field, and the increased latitudinal separation of the locus of satellite footprints from each other and from the main oval implies a locally weaker field strength. It is possible that these phenomena result from a magnetic anomaly in Jupiter's intrinsic magnetic field, as was proposed by A. Dessler in the 1970's. There is presently only limited evidence from the scarcity of auroral footprints observed in this longitude range. We propose to obtain HST UV images with specific observing geometries of Jupiter to determine the locations of the auroral footprints of Io, Europa, and Ganymede in cycle 13 to accurately determine the magnetic field geometry in the suggested anomaly region, and to either confirm or refute the suggestion of a local magnetic anomaly.

  15. Intermediate-wavelength magnetic anomalies over the central Pacific

    NASA Technical Reports Server (NTRS)

    Labrecque, J. L.; Cande, S. C.

    1984-01-01

    A technique to extract the intermediate wavelength anomaly field from random ship tracks has been developed and is applied to extract the field from marine survey data of the central Pacific in the band pass of 4000-400 km. The technique minimizes the effects of external field sources, secular variation, and strike aliasing. The derived data field is compared to the equivalent MAGSAT data set, and it is shown that anomalies observed in both fields are correlatable to geologic features within the oceanic lithosphere but differ in amplitude by a factor of two. Likely sources for this discrepancy are identified. It is also shown that remanent magnetization of the central Pacific seamounts produces negative magnetic anomalies which are observed at satellite altitude.

  16. Approximating edges of source bodies from magnetic or gravity anomalies.

    USGS Publications Warehouse

    Blakely, R.J.; Simpson, R.W.

    1986-01-01

    Cordell and Grauch (1982, 1985) discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks. The final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes. Attempts to automate their final step. The method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources. The method applies to both local surveys and to continent-wide compilations of magnetic and gravity data.-from Authors

  17. Plasma acceleration above martian magnetic anomalies.

    PubMed

    Lundin, R; Winningham, D; Barabash, S; Frahm, R; Holmström, M; Sauvaud, J-A; Fedorov, A; Asamura, K; Coates, A J; Soobiah, Y; Hsieh, K C; Grande, M; Koskinen, H; Kallio, E; Kozyra, J; Woch, J; Fraenz, M; Brain, D; Luhmann, J; McKenna-Lawler, S; Orsini, R S; Brandt, P; Wurz, P

    2006-02-17

    Auroras are caused by accelerated charged particles precipitating along magnetic field lines into a planetary atmosphere, the auroral brightness being roughly proportional to the precipitating particle energy flux. The Analyzer of Space Plasma and Energetic Atoms experiment on the Mars Express spacecraft has made a detailed study of acceleration processes on the nightside of Mars. We observed accelerated electrons and ions in the deep nightside high-altitude region of Mars that map geographically to interface/cleft regions associated with martian crustal magnetization regions. By integrating electron and ion acceleration energy down to the upper atmosphere, we saw energy fluxes in the range of 1 to 50 milliwatts per square meter per second. These conditions are similar to those producing bright discrete auroras above Earth. Discrete auroras at Mars are therefore expected to be associated with plasma acceleration in diverging magnetic flux tubes above crustal magnetization regions, the auroras being distributed geographically in a complex pattern by the many multipole magnetic field lines extending into space. PMID:16484488

  18. Plasma acceleration above martian magnetic anomalies.

    PubMed

    Lundin, R; Winningham, D; Barabash, S; Frahm, R; Holmström, M; Sauvaud, J-A; Fedorov, A; Asamura, K; Coates, A J; Soobiah, Y; Hsieh, K C; Grande, M; Koskinen, H; Kallio, E; Kozyra, J; Woch, J; Fraenz, M; Brain, D; Luhmann, J; McKenna-Lawler, S; Orsini, R S; Brandt, P; Wurz, P

    2006-02-17

    Auroras are caused by accelerated charged particles precipitating along magnetic field lines into a planetary atmosphere, the auroral brightness being roughly proportional to the precipitating particle energy flux. The Analyzer of Space Plasma and Energetic Atoms experiment on the Mars Express spacecraft has made a detailed study of acceleration processes on the nightside of Mars. We observed accelerated electrons and ions in the deep nightside high-altitude region of Mars that map geographically to interface/cleft regions associated with martian crustal magnetization regions. By integrating electron and ion acceleration energy down to the upper atmosphere, we saw energy fluxes in the range of 1 to 50 milliwatts per square meter per second. These conditions are similar to those producing bright discrete auroras above Earth. Discrete auroras at Mars are therefore expected to be associated with plasma acceleration in diverging magnetic flux tubes above crustal magnetization regions, the auroras being distributed geographically in a complex pattern by the many multipole magnetic field lines extending into space.

  19. Magnetic Anomalies over the Mid-Atlantic Ridge near 27{degrees}N.

    PubMed

    Phillips, J D

    1967-08-25

    Ten magnetic profiles across the mid-Atlantic ridge near 27 degrees N show trends that are parallel to the ridge axis and symmetrical about the ridge axis. The configuration of magnetic bodies that could account for the pattern supports the Vine and Matthews hypothesis for the origin of magnetic anomalies over oceanic ridges. A polarity-reversal time scale inferred from models for sea-floor spreading in the Pacific-Antarctic ridge and radiometrically dated reversals of the geomagnetic field indicates a spreading rate of 1.25 centimeters per year during the last 6 million years and a rate of 1.65 centimeters per year between 6 and 10 million years ago. A similar analysis of more limited data over the mid-Atlantic ridge near 22 degrees N also indicates a change in the spreading rate. Here a rate of 1.4 centimeters per year appears to have been in effect during the last 5 million years; between 5 and 9 million years ago, an increased rate of 1.7 centimeters per year is indicated. The time of occurrence and relative magnitude of these changes in the spreading rate, about 5 to 6 million years ago and 18 to 27 percent, respectively, accords with the spreading rate change implied for the Juan de Fuca ridge in the northeast Pacific.

  20. Magnetic Anomalies over the Mid-Atlantic Ridge near 27{degrees}N.

    PubMed

    Phillips, J D

    1967-08-25

    Ten magnetic profiles across the mid-Atlantic ridge near 27 degrees N show trends that are parallel to the ridge axis and symmetrical about the ridge axis. The configuration of magnetic bodies that could account for the pattern supports the Vine and Matthews hypothesis for the origin of magnetic anomalies over oceanic ridges. A polarity-reversal time scale inferred from models for sea-floor spreading in the Pacific-Antarctic ridge and radiometrically dated reversals of the geomagnetic field indicates a spreading rate of 1.25 centimeters per year during the last 6 million years and a rate of 1.65 centimeters per year between 6 and 10 million years ago. A similar analysis of more limited data over the mid-Atlantic ridge near 22 degrees N also indicates a change in the spreading rate. Here a rate of 1.4 centimeters per year appears to have been in effect during the last 5 million years; between 5 and 9 million years ago, an increased rate of 1.7 centimeters per year is indicated. The time of occurrence and relative magnitude of these changes in the spreading rate, about 5 to 6 million years ago and 18 to 27 percent, respectively, accords with the spreading rate change implied for the Juan de Fuca ridge in the northeast Pacific. PMID:17792827

  1. New magnetic anomaly map of East Antarctica and surrounding regions

    USGS Publications Warehouse

    Golynsky, A.; Blankenship, D.; Chiappini, M.; Damaske, D.; Ferraccioli, F.; Finn, C.; Golynsky, D.; Goncharov, A.; Ishihara, T.; Ivanov, S.; Jokat, W.; Kim, H.R.; König, M.; Masolov, V.; Nogi, Y.; Sand, M.; Studing, M.; ,

    2007-01-01

    community over East Antarctica and surrounding regions, significantly upgrade the Antarctic Digital Magnetic Anomaly Project (ADMAP) compilation and lead to substantial improvements in magnetic anomaly pattern recognition. New data have been matched in one inverse operation by minimizing the data differences for the areas of overlap. The aeromagnetic data show many previously unknown magnetic patterns, lineaments and trends, defining the spatial extent of Ferrar volcanics and plutonic Granite Harbour Intrusives in the Transantarctic Mountains and previously unknown tectonic trends of the East Antarctic craton. Regional aeromagnetic investigations have successfully delineated Early Paleozoic inherited crustal features along the flanks of the West Antarctic Rift System and the southern boundary of the Archean Ruker Terrane in the Prince Charles Mountains. Magnetic records along the East Antarctic continental margin provide new constraints on the breakup of Gondwana.

  2. The possibilities of paleomagnetic and geohistorical analyses of "tiny wiggles" short-period marine magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Ivanov, S. A.; Merkuryev, S. A.

    2016-05-01

    Marine magnetic anomalies of the tiny wiggles (TW) type can be used to solve geohistorical and paleomagnetic problems. The model fields corresponding to Paleocene-Eocene anomalies in the northwestern Indian Ocean, which were formed during the fast-spreading stage, were studied. For these fields, widely used interpretation methods were compared with a method proposed previously by the authors. The testing was performed with first the classical block model and then more complex models reflecting actual processes of oceanic accretion and magnetic field variations in the past. It was shown that the proposed method has advantages for this problem; it gives an error close to the minimum possible error and can adequately be used in interpretations. Spectral and statistical methods are used to estimate the magnetic anomaly resolving power and to study some factors that can exert a distorting influence. In addition, model examples have been used to indicate how the TW determination accuracy is affected by diurnal variations in the main magnetic field (MMF) and by ancient magnetization vector determination errors.

  3. Axial Anomaly, Dirac Sea, and the Chiral Magnetic Effect

    SciTech Connect

    Kharzeev, D.E.

    2010-05-26

    Gribov viewed the axial anomaly as a manifestation of the collective motion of Dirac fermions with arbitrarily high momenta in the vacuum. In the presence of an external magnetic field and a chirality imbalance, this collective motion becomes directly observable in the form of the electric current - this is the chiral magnetic effect (CME). I give an elementary introduction into the physics of CME, and discuss the experimental status and recent developments.

  4. Macquarie island and the cause of oceanic linear magnetic anomalies.

    PubMed

    Varne, R; Gee, R D; Quilty, P G

    1969-10-10

    Macquarie Islands is formed of probably Pliocene oceanic crust. Intruded into pillow lavas is a belt of harzburgite and layered gabbro mnasses cut by dike swarms. Similar belt-like structures may cause the linear magnetic anomalies of the ocean. PMID:17731490

  5. New digital magnetic anomaly database for North America

    USGS Publications Warehouse

    Finn, C.A.; Pilkington, M.; Cuevas, A.; Hernandez, I.; Urrutia, J.

    2001-01-01

    The Geological Survey of Canada (GSC), U.S. Geological Survey (USGS), and Consejo de Recursos Minerales of Mexico (CRM) are compiling an upgraded digital magnetic anomaly database and map for North America. This trinational project is expected to be completed by late 2002.

  6. Estimation of lower crust magnetization form satellite derived anomaly field

    NASA Technical Reports Server (NTRS)

    Schnetzler, C. C.; Allenby, R. J.

    1983-01-01

    Various lines of evidence point to the lower crust as the source of the long-wavelength magnetic anomaly field measured by the POGO and Magsat satellites. Using seismically determined lower crust thicknesses and equivalent source inversion of the satellite anomaly data, magnetization for the lower crust for much of the United States has been calculated. The average magnetization for two hundred sixty-six 150 x 150 km areas is 3.5 A/m with a standard deviation of 1.1 A/m. These values are consistent with laboratory measurements of mafic-ultramafic rocks expected in the lower crust, and in agreement with previous estimates of lower crust magnetization based on long-wavelength aeromagnetic data. Average lower crust thickness for the same areas is 18.2 km (sigma = 6.4). Thus, over large regions, it appears that variation in magnetization and variation in magnetic layer thickness contribute almost equally in causing the anomaly field variation at satellite altitude.

  7. Toward the World Digital Magnetic Anomaly Map (WDMAM)

    NASA Astrophysics Data System (ADS)

    Ravat, D.; Ghidella, M.; Korhonen, J.; Maus, S.; McLean, S.; Reeves, C.

    2003-12-01

    During the 2003 IUGG meeting in Sapporo, Japan, the IAGA working group on Geomagnetic Modeling rekindled the World Digital Magnetic Anomaly Map (WDMAM) project. Even though preparation of such a map may appear a daunting task, the bulk of it could be accomplished within a few years, taking advantage of many existing national to continent-scale and oceanic magnetic anomaly compilations. In addition, Project Magnet high altitude aeromagnetic surveys could be utilized where available and necessary to fill gaps. Similarly, the CHAMP satellite-derived magnetic anomaly field could be downward continued to provide wavelengths greater than 500 km in this magnetic anomaly map. There are a large number of data handling and processing issues that need to be addressed during the preparation of this map and we discuss some of them here: What should the data spacing be? Should the spacing be uneven according to the data availability? At what elevation should the fields be displayed? How to treat the areas of complete lack of near-surface (marine and airborne) magnetic field coverage? How should one treat the long-wavelength anomaly limitations of the near-surface data? What should be the main field model? What should be the techniques for data processing? What should be the techniques for data merging? The ultimate utility of this first generation map is manifold: ranging from geologic interpretation of features of a few km width to recognizing individual geologic provinces in continental assemblages, developing regional models of the bottom of the magnetic layer and/or the Curie isotherm, and plate tectonic reconstructions using magnetic anomalies. The global view and the ability to move the inferred source magnetizations along with the continents and oceanic areas back in time will also significantly aid in deciphering the origin and evolution of geologic provinces presently appearing unrelated due to their vast intervening distances. We recognize the WDMAM as the legacy of

  8. Petrologic and geophysical sources of long-wavelength crustal magnetic anomalies

    NASA Technical Reports Server (NTRS)

    Marsh, B. D.; Schlinger, C. M.

    1984-01-01

    The magnetic mineralogy and magnetic properties of the deep crust are studied as they pertain to the interpretation of long wavelength, or regional, crustal magnetic anomalies in satellite magnetic data and near surface magnetic data. The conclusions have relevance to the understanding of regional magnetic anomalies in magnetic field measuring satellite missions data. There are two separable studies: (1) a synthesis of available information of regional magnetic anomalies and the magnetization of metamorphic and igneous rocks, and (2) a detailed field, analytical, and experimental study of in situ and laboratory specimens from a terrain that offers exposures of high grade granlite facies rocks that have associated regional magnetic and gravity anomalies.

  9. Spectral and Magnetic Studies of Lesser-Known Lunar Magnetic and Albedo Anomalies

    NASA Astrophysics Data System (ADS)

    Hawke, B. R.; Blewett, D. T.; Coman, E. I.; Purucker, M. E.; Gillis-Davis, J. J.

    2009-12-01

    The origin of the lunar swirls is an outstanding puzzle in lunar geoscience. In addition, the swirls lie at the intersection of broader issues in planetary science, including planetary magnetism (e.g., the origin of the magnetized crust via core dynamo versus impact processes) and the relative importance of solar wind exposure versus micrometeoroid bombardment in producing the optical effects of space weathering. Many of the unusual high-albedo features known as lunar swirls are associated with crustal magnetic anomalies, and many of the magnetic anomalies are found near the antipodes of major impact basins. The leading hypotheses that have been advanced for the formation of the swirls are: (a) regolith disturbance caused by the relatively recent impact of a comet coma, cometary fragments or cometary meteor swarms; and (b) atypical space weathering as a result of the magnetic anomaly shielding the surface from solar wind ion bombardment. Apollo subsatellite instruments, whose coverage was limited to equatorial and mid-latitudes, first revealed the existence of lunar crustal magnetic anomalies. The Lunar Prospector (LP) mission provided global data and has led to the discovery of additional regions of magnetized crust. We have conducted a series of studies on lunar magnetic and albedo anomalies using LP magnetometer data and Clementine multispectral images. Three of these magnetic anomalies have only been recently identified. Newly discovered magnetic anomalies near the craters Abel, Stofler, and Hartwig do not appear to harbor unusual albedo markings. The magnetic anomaly near Rima Sirsalis has long been known from Apollo data. A small sinuous swirl to the northwest may be related to the Sirsalis magnetic anomaly or could be a southern extension of Reiner Gamma. Our examination of images for Rima Sirsalis has led to the identification of an additional loop-shaped marking on Oceanus Procellarum and some possible anomalous bright patches in the nearby highlands. Our

  10. [Fetal ocular anomalies: the advantages of prenatal magnetic resonance imaging].

    PubMed

    Brémond-Gignac, D; Copin, H; Elmaleh, M; Milazzo, S

    2010-05-01

    Congenital ocular malformations are uncommon and require prenatal diagnosis. Severe anomalies are more often detected by trained teams and minor anomalies are more difficult to identify and must be systematically sought, particularly when multiple malformations or a family and maternal history is known. The prenatal diagnosis-imaging tool most commonly used is ultrasound but it can be completed by magnetic resonance imaging (MRI), which contributes crucial information. Fetal dysmorphism can occur in various types of dysfunction and prenatal diagnosis must recognize fetal ocular anomalies. After systematic morphologic ultrasound imaging, different abnormalities detected by MRI are studied. Classical parameters such as binocular and interorbital measurements are used to detect hypotelorism and hypertelorism. Prenatal ocular anomalies such as cataract microphthalmia, anophthalmia, and coloboma have been described. Fetal MRI added to prenatal sonography is essential in detecting cerebral and general anomalies and can give more information on the size and morphology of the eyeball. Fetal abnormality detection includes a detailed family and maternal history, an amniotic fluid sample for karyotype, and other analyses for a better understanding of the images. Each pregnancy must be discussed with all specialists for genetic counseling. With severe malformations, termination of pregnancy is proposed because of risk of blindness and associated cerebral or systemic anomalies. Early prenatal diagnosis of ocular malformations can also detect associated abnormalities, taking congenital cataracts that need surgical treatment into account as early as possible. Finally, various associated syndromes need a pediatric check-up that could lead to emergency treatment.

  11. On the origin of the Bangui magnetic anomaly, central African empire

    NASA Technical Reports Server (NTRS)

    Marsh, B. D.

    1977-01-01

    A large magnetic anomaly was recognized in satellite magnetometer data over the Central African Empire in central Africa. They named this anomaly the Bangui magnetic anomaly due to its location near the capital city of Bangui, C.A.E. Because large crustal magnetic anomalies are uncommon, the origin of this anomaly has provoked some interest. The area of the anomaly was visited to make ground magnetic measurements, geologic observations, and in-situ magnetic susceptibility measurements. Some rock samples were also collected and chemically analyzed. The results of these investigations are presented.

  12. Lunar magnetic anomalies detected by the Apollo substatellite magnetometers

    USGS Publications Warehouse

    Hood, L.L.; Coleman, P.J.; Russell, C.T.; Wilhelms, D.E.

    1979-01-01

    Properties of lunar crustal magnetization thus far deduced from Apollo subsatellite magnetometer data are reviewed using two of the most accurate presently available magnetic anomaly maps - one covering a portion of the lunar near side and the other a part of the far side. The largest single anomaly found within the region of coverage on the near-side map correlates exactly with a conspicuous, light-colored marking in western Oceanus Procellarum called Reiner Gamma. This feature is interpreted as an unusual deposit of ejecta from secondary craters of the large nearby primary impact crater Cavalerius. An age for Cavalerius (and, by implication, for Reiner Gamma) of 3.2 ?? 0.2 ?? 109 y is estimated. The main (30 ?? 60 km) Reiner Gamma deposit is nearly uniformly magnetized in a single direction, with a minimum mean magnetization intensity of ???7 ?? 10-2 G cm3/g (assuming a density of 3 g/cm3), or about 700 times the stable magnetization component of the most magnetic returned samples. Additional medium-amplitude anomalies exist over the Fra Mauro Formation (Imbrium basin ejecta emplaced ???3.9 ?? 109 y ago) where it has not been flooded by mare basalt flows, but are nearly absent over the maria and over the craters Copernicus, Kepler, and Reiner and their encircling ejecta mantles. The mean altitude of the far-side anomaly gap is much higher than that of the near-side map and the surface geology is more complex, so individual anomaly sources have not yet been identified. However, it is clear that a concentration of especially strong sources exists in the vicinity of the craters Van de Graaff and Aitken. Numerical modeling of the associated fields reveals that the source locations do not correspond with the larger primary impact craters of the region and, by analogy with Reiner Gamma, may be less conspicuous secondary crater ejecta deposits. The reason for a special concentration of strong sources in the Van de Graaff-Aitken region is unknown, but may be indirectly

  13. The resolution of a magnetic anomaly map expected from GRM data

    NASA Technical Reports Server (NTRS)

    Strangway, D. W.; Arkani-Hamed, J.; Teskey, D. J.; Hood, P. J.

    1985-01-01

    Data from the MAGSAT mission were used to derive a global scalar magnetic anomaly map at an average altitude of about 400 km. It was possible to work with 2 data sets corresponding to dawn and dusk. The anomalies which were repeatable at dawn and at dusk was identified and the error limits of these anomalies were estimated. The repeatable anomalies were downward continued to about 10 km altitude. The anomalies over Canada were correlated quantitatively with bandpass filtered magnetic anomalies derived from aeromagnetic surveys. The close correlation indicates that the repeatable anomalies detected from orbit are due to geological causes. This correlation supports the geological significance of the global anomaly map.

  14. Matched filtering method for separating magnetic anomaly using fractal model

    NASA Astrophysics Data System (ADS)

    Chen, Guoxiong; Cheng, Qiuming; Zhang, Henglei

    2016-05-01

    Fractal/scaling distribution of magnetization in the crust has found with growing body of evidences from spectral analysis of borehole susceptibility logs and magnetic field data, and fractal properties of magnetic sources have already been considered in processing magnetic data such as the Spector and Grant method for depth determination. In this study, the fractal-based matched filtering method is presented for separating magnetic anomalies caused by fractal sources. We argue the benefits of considering fractal natures of source distribution for data processing in magnetic exploration: the first is that the depth determination can be improved by using multiscaling model to interpret the magnetic data power spectrum; the second is that the matched filtering can be reconstructed by employing the difference in scaling exponent together with the corrected depth and amplitude estimates. In the application of synthetic data obtained from fractal modeling and real aeromagnetic data from the Qikou district of China, the proposed fractal-based matched filtering method obtains more reliable depth estimations as well as improved separation between local anomalies (caused by volcanic rocks) and regional field (crystalline basement) in comparison with the conventional matched filtering method.

  15. [Magnetic resonance in the evaluation of Mullerian duct anomalies].

    PubMed

    Fischetti, S G; Politi, G; Lomeo, E; Garozzo, G

    1995-01-01

    Müllerian duct alterations in development or fusion in the embryo cause congenital uterine anomalies which may be responsible for decreased fertility or problems in carrying out a normal pregnancy. In this study, the MR findings in uterine agenesis (1 case), unicornuate (2 cases), didelphys (3 cases), bicornuate (3 cases), arcuate (6 cases) and septate uterus (8 cases) are described, together with the optimal section planes for their demonstration. The examinations were performed with an 0.5-T superconductive magnet, the spin-echo technique and mostly T2-weighted sequences. The anomalies were grouped according to Buttram and Gibbons classification, which is the most used in clinics. In particular, the bicornuate uterus was distinguished from the septate uterus, the latter associated with the highest spontaneous abortion rates, on the basis of external fundal outline appearance. In such anomalies, the muscular or fibrotic nature of any intracavitary septum was assessed based on septal thickness more than on signal intensity at this level. MR diagnostic accuracy in 23 patients with Müllerian anomalies, compared with surgical, hysteroscopic, laparotomic and laparoscopic findings, was 100%. Nevertheless, if Müllerian duct anomalies responsible for gynecologic-obstetric problems are known or suspected, MRI should always be used, on the basis of a close gynecologist-radiologist collaboration, for classification agreement and the evaluation of any intracavitary septum morpho-biometric appearance and possibly nature, to discuss treatment options.

  16. Tracking pigeons in a magnetic anomaly and in magnetically "quiet" terrain

    NASA Astrophysics Data System (ADS)

    Schiffner, Ingo; Fuhrmann, Patrick; Wiltschko, Roswitha

    2011-07-01

    Pigeons were released at two sites of equal distance from the loft, one within a magnetic anomaly, the other in magnetically quiet terrain, and their tracks were recorded with the help of GPS receivers. A comparison of the beginning of the tracks revealed striking differences: within the anomaly, the initial phase lasted longer, and the distance flown was longer, with the pigeons' headings considerably farther from the home direction. During the following departure phase, the birds were well homeward oriented at the magnetically quiet site, whereas they continued to be disoriented within the anomaly. Comparing the tracks in the anomaly with the underlying magnetic contours shows considerable differences between individuals, without a common pattern emerging. The differences in magnetic intensity along the pigeons' path do not differ from a random distribution of intensity differences around the release site, indicating that the magnetic contours do not directly affect the pigeons' routes. Within the anomaly, pigeons take longer until their flights are oriented, but 5 km from the release point, the birds, still within the anomaly, are also significantly oriented in the home direction. These findings support the assumption that magnetically anomalous conditions initially interfere with the pigeons' navigational processes, with birds showing rather individual responses in their attempts to overcome these problems.

  17. Manifestation of the petrogeneration zones of Northern and the Bering seas in ground magnetic anomalies and anomalies of satellite Champ

    NASA Astrophysics Data System (ADS)

    Litvinova, Tamara; Krasinsky, Egor; Petrova, Alevtina; Demina, Irina

    2010-05-01

    The purpose of this paper are showed results of studying of specificity of a deep structure of zones of petrogeneration Northern and the Bering seas on aeromagnetic and satellite magnetometric datas. Research lateral and vertical heterogeneitys an earth's crust of Northern sea is carried out on the basis of the analysis of measurements of satellite Champ at height of 100 km and the digital database created on materials of sea shooting of a geomagnetic field, executed on non-magnetic schooner "Zarya". On sea measurements in Northern sea through large oil fields and gas ( Frigg, Ekofisk, Forties trough, Leman, etc.). Geomagnetic sections for an interval of depths from 1 up to 30 km are constructed. It has allowed to study character of distribution of magnetization of breeds of a cover, horizontal lamination intracore layers of an earth's crust and to allocate in zones petrogeneration synvertical fluidoconduct zones the channels described by alternation of not magnetic and low-magnetic layers. They were showed on geomagnetic sections as permeable zones quasi- laminated structures with the lowered magnetic properties in an interval of depths from 8 up to 28 km. Comparison to a map of the magnetic anomalies measured at height of 100 km by satellite Champ, has shown, that areas of the greatest petrocongestions North Sea рифта at height of 100 km are dated for a zone of gradients and a minimum of northeast displacement of regional anomalies of western and east blocks of Northern sea. It corresponds to representations about an orientation of a fissuring zone and the increased size of a geothermal gradient North Sea rift and is corresponded position allocated on hydromagnetic structures deep fluidoconduct channels. Thus, distribution to water areas of deposits of deposits is emphasized not only low-magnetic areas in a thickness of a sedimentary cover where they are directly located, but also by not magnetic lenses in breeds of the base spreading it in intervals of

  18. Anomalies.

    ERIC Educational Resources Information Center

    Online-Offline, 1999

    1999-01-01

    This theme issue on anomalies includes Web sites, CD-ROMs and software, videos, books, and additional resources for elementary and junior high school students. Pertinent activities are suggested, and sidebars discuss UFOs, animal anomalies, and anomalies from nature; and resources covering unexplained phenonmenas like crop circles, Easter Island,…

  19. Apparatus for detecting a magnetic anomaly contiguous to remote location by SQUID gradiometer and magnetometer systems

    SciTech Connect

    Overton, W.C. Jr.; Steyert, W.A. Jr.

    1984-03-13

    A superconducting quantum interference device (SQUID) magnetic detection apparatus detects magnetic fields, signals, and anomalies at remote locations. Two remotely rotatable SQUID gradiometers may be housed in a cryogenic environment to search for and locate unambiguously magnetic anomalies. The SQUID magnetic detection apparatus can be used to determine the azimuth of a hydrofracture by first flooding the hydrofracture with a ferrofluid to create an artificial magnetic anomaly therein.

  20. Apparatus for detecting a magnetic anomaly contiguous to remote location by squid gradiometer and magnetometer systems

    DOEpatents

    Overton, Jr., William C.; Steyert, Jr., William A.

    1984-01-01

    A superconducting quantum interference device (SQUID) magnetic detection apparatus detects magnetic fields, signals, and anomalies at remote locations. Two remotely rotatable SQUID gradiometers may be housed in a cryogenic environment to search for and locate unambiguously magnetic anomalies. The SQUID magnetic detection apparatus can be used to determine the azimuth of a hydrofracture by first flooding the hydrofracture with a ferrofluid to create an artificial magnetic anomaly therein.

  1. A magnetic anomaly of possible economic significance in southeastern Minnesota

    USGS Publications Warehouse

    Zietz, Isidore

    1964-01-01

    An aeromagnetic survey in southeastern Minnesota by the U. S. Geological Survey in cooperation with the State of Minnesota has revealed a high-amplitude, linear, and narrow magnetic feature that suggests a possible source of Precambrian iron-formation of economic value. For the past few years the U. S. Geological Survey has been conducting detailed geophysical studies of the midcontinent gravity anomaly--a broad, high-amplitude feature that extends from Lake Superior through the States of Minnesota, Iowa, Nebraska, and part of Kansas. As part of this study an aeromagnetic survey of the southern part of the State was made in cooperation with the State of Minnesota during the summer of 1963, in which a linear high-amplitude anomaly of the order of 4,000 gammas was discovered. Because of the high amplitude, the linearity, and the narrowness of the magnetic feature, it is believed the source may be Precambrian iron-formation of possible economic value. The anomalous area is in Fillmore County, approximately between the towns of Lanesboro and Peterson in the extreme southeastern part of the State. (See figures 1 and 2.) At the site of the anomaly, Cambrian sedimentary rocks occur in the valley of the Root River, and Ordovician rocks (nearly flat lying) mantle the upland areas. The uplands are largely covered by glacial deposits, which are relatively thin (Paul K. Sims, written communication, 1964). Depths to the Precambrian are estimated to range from 500 feet to 1,000 feet below the surface. The aeromagnetic map shown in figure 2 was compiled from continuous magnetic profiles made along east-west flight lines 1,000 feet above ground, and spaced approximately 1 mile apart. Contour intervals of 20, 100, and 500 gammas were used depending on the intensity. The instrument for the survey was a flux-gate type magnetometer (AN/ASQ-3A) which measures total-field variations. The contour map displays variations in magnetic pattern which are typical of shallow Precambrian rocks

  2. The moon: Sources of the crustal magnetic anomalies

    USGS Publications Warehouse

    Hood, L.L.; Coleman, P.J.; Wilhelms, D.E.

    1979-01-01

    Previously unmapped Apollo 16 subsatellite magnetometer data collected at low altitudes over the lunar near side are presented. Medium-amplitude magnetic anomalies exist over the Fra Mauro and Cayley Formations (primary and secondary basin ejecta emplaced 3.8 to 4.0 billion years ago) but are nearly absent over the maria and over the craters Copernicus, Kepler, and Reiner and their encircling ejecta mantles. The largest observed anomaly (radial component ??? 21 gammas at an altitude of 20 kilometers) is exactly correlated with a conspicuous light-colored deposit on western Oceanus Procellarum known as Reiner ??. Assuming that the Reiner ?? deposit is the source body and estimating its maximum average thickness as 10 meters, a minimum mean magnetization level of 5.2 ?? 2.4 ?? 10-2 electromagnetic units per gram, or ??? 500 times the stable magnetization component of the most magnetic returned sample, is calculated. An age for its emplacement of ??? 2.9 billion years is inferred from photogeologic evidence, implying that magnetization of lunar crustal materials must have continued for a period exceeding 1 billion years. Copyright ?? 1979 AAAS.

  3. Low energy spread ion source with a coaxial magnetic filter

    DOEpatents

    Leung, Ka-Ngo; Lee, Yung-Hee Yvette

    2000-01-01

    Multicusp ion sources are capable of producing ions with low axial energy spread which are necessary in applications such as ion projection lithography (IPL) and radioactive ion beam production. The addition of a radially extending magnetic filter consisting of a pair of permanent magnets to the multicusp source reduces the energy spread considerably due to the improvement in the uniformity of the axial plasma potential distribution in the discharge region. A coaxial multicusp ion source designed to further reduce the energy spread utilizes a cylindrical magnetic filter to achieve a more uniform axial plasma potential distribution. The coaxial magnetic filter divides the source chamber into an outer annular discharge region in which the plasma is produced and a coaxial inner ion extraction region into which the ions radially diffuse but from which ionizing electrons are excluded. The energy spread in the coaxial source has been measured to be 0.6 eV. Unlike other ion sources, the coaxial source has the capability of adjusting the radial plasma potential distribution and therefore the transverse ion temperature (or beam emittance).

  4. Thermal Sensitivity of MD Hematite: Implication for Magnetic Anomalies

    NASA Technical Reports Server (NTRS)

    Kletetschka, Gunther; Wasilewski, Peter J.; Taylor, Patrick T.

    1999-01-01

    Magnetic remanence of crustal rocks can reside in three common rock-forming magnetic minerals: magnetite, pyrrhotite, and hematite. Thermoremanent magnetization (TRM) of magnetite and pyrrhotite is carried mostly by single domain (SD) grains. The TRM of hematite grains, however, is carried mostly by multidomain (NM) grains. This characteristic is illustrated by TRM acquisition curves for hematite of variable grainsizes. The transition between truly NM behavior and tendency towards SD behavior his been established between hematite grainsizes of 0. 1 and 0.05 mm. Coarse grainsize of lower crustal rocks and the large sensitivity of MD hematite grains to acquire TRM indicates that hematite could be a significant contributor to long-wavelength magnetic anomalies.

  5. Can remanent magnetization in the deep crust contribute to long wavelength magnetic anomalies

    SciTech Connect

    Shive, P.N. )

    1989-01-01

    Long wavelength aeromagnetic anomalies require sources in the deep crust that are far more magnetic than the measured induced magnetization of lower crustal rocks. Several scientists have suggested that remanence in the deep crust may provide the missing magnetization. This is not likely, either through stable and/or viscous remanence. Bodies large enough to contribute to surface anomalies and carrying stable remanence probably cooled slowly enough that they are subdivided into zones of alternating polarity. This subdivision sharply reduces the power in the long wavelength portion of the anomaly spectrum. On the other hand, if such a body carries a viscous remanence, the viscous component will be acquired in such a way as to bring the total magnetization of the body into equilibrium with the earth's field. This equilibrium total magnetization, not enough to explain the discrepancy.

  6. Petrological Explanations for the Magnetic Anomalies Detected on Mars

    NASA Technical Reports Server (NTRS)

    Weitz, C. M.; Rutherford, M. J.

    1999-01-01

    The discovery of crustal magnetization in some locations on Mars, particularly the southern highlands, has major implications for the early evolution of Mars. The east-west-trending linear features in the southern highlands with alternating polarity may be the result of an early seafloor spreading process similar to that seen on Earth today. The larger magnetization of the martian crust compared to the Earth can be attributed to its higher Fe content and the proposed minerals associated with this magnetization are multidomain hematite and pyrrhotite. In this study, we discuss the petrological evolution of basalts on Earth and Mars and suggest processes that may enhance crystallization of magnetic minerals in the martian rocks, thereby accounting for their intense magnetic properties.

  7. Numerical Simulations on Origin of Galilean Moons' Magnetic Anomalies

    NASA Technical Reports Server (NTRS)

    Jiao, LiQuo; Kuang, WeiJia; Ma, ShiZhuang

    2011-01-01

    Galileo mission detected the magnetic anomalies originated from Galilean moons. These anomalies are likely generated in the moons interiors, under the influence of a strong ambient Jovian field. Among various possible generation mechanisms of the anomalies, we focus on magneto-convection and dynamos in the interiors via numerical simulation. To mimic the electromagnetic environment of the moons, we introduce in our numerical model an external uniform magnetic field B(sub 0) with a fixed orientation but varying field strength. Our results show that a finite B(sub 0) can substantially alter the dynamo processes inside the core. When the ambient field strength B(sub 0) increases to approximately 40% of the field generated by the pure dynamo action, the convective state in the core changes significantly: the convective flow decreases by 80% in magnitude, but the differential rotation becomes stronger in much of the fluid layer, leading to a stronger field generated in the core. The field morphologies inside the core tend to align with the ambient field, while the flow patterns show the symmetry-breaking effect under the influence of B(sub 0). Furthermore, the generated field tends to be temporally more stable.

  8. Improving the geological interpretation of magnetic and gravity satellite anomalies

    NASA Technical Reports Server (NTRS)

    Hinze, William J.; Braile, Lawrence W.; Vonfrese, Ralph R. B.

    1987-01-01

    Quantitative analysis of the geologic component of observed satellite magnetic and gravity fields requires accurate isolation of the geologic component of the observations, theoretically sound and viable inversion techniques, and integration of collateral, constraining geologic and geophysical data. A number of significant contributions were made which make quantitative analysis more accurate. These include procedures for: screening and processing orbital data for lithospheric signals based on signal repeatability and wavelength analysis; producing accurate gridded anomaly values at constant elevations from the orbital data by three-dimensional least squares collocation; increasing the stability of equivalent point source inversion and criteria for the selection of the optimum damping parameter; enhancing inversion techniques through an iterative procedure based on the superposition theorem of potential fields; and modeling efficiently regional-scale lithospheric sources of satellite magnetic anomalies. In addition, these techniques were utilized to investigate regional anomaly sources of North and South America and India and to provide constraints to continental reconstruction. Since the inception of this research study, eleven papers were presented with associated published abstracts, three theses were completed, four papers were published or accepted for publication, and an additional manuscript was submitted for publication.

  9. Interpretation of Magnetic Phase Anomalies over 2D Tabular Bodies

    NASA Astrophysics Data System (ADS)

    Subrahmanyam, M.

    2016-05-01

    In this study, phase angle (inverse tangent of the ratio of the horizontal to vertical gradients of magnetic anomalies) profile over two-dimensional tabular bodies has been subjected to detailed analysis for determining the source parameters. Distances between certain characteristic positions on this phase curve are related to the parameters of two-dimensional tabular magnetic sources. In this paper, I have derived the mathematical expressions for these relations. It has been demonstrated here that for locating the origin of the 2D tabular source, knowledge on the type of the model (contact, sheet, dyke, and fault) is not necessary. A procedure is evolved to determine the location, depth, width and magnetization angle of the 2D sources from the mathematical expressions. The method is tested on real field data. The effect of the overlapping bodies is also discussed with two synthetic examples. The interpretation technique is developed for contact, sheet, dike and inclined fault bodies.

  10. Magnetic torque anomaly in the quantum limit of Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Moll, Philip J. W.; Potter, Andrew C.; Nair, Nityan L.; Ramshaw, B. J.; Modic, K. A.; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal J.; Bauer, Eric D.; Kealhofer, Robert; Ronning, Filip; Analytis, James G.

    2016-08-01

    Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems.

  11. Magnetic torque anomaly in the quantum limit of Weyl semimetals.

    PubMed

    Moll, Philip J W; Potter, Andrew C; Nair, Nityan L; Ramshaw, B J; Modic, K A; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal J; Bauer, Eric D; Kealhofer, Robert; Ronning, Filip; Analytis, James G

    2016-01-01

    Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems. PMID:27545105

  12. Magnetic torque anomaly in the quantum limit of Weyl semimetals

    PubMed Central

    Moll, Philip J. W.; Potter, Andrew C.; Nair, Nityan L.; Ramshaw, B. J.; Modic, K. A.; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal J.; Bauer, Eric D.; Kealhofer, Robert; Ronning, Filip; Analytis, James G.

    2016-01-01

    Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems. PMID:27545105

  13. Unique U.S. magnetic anomaly data base forthcoming

    NASA Astrophysics Data System (ADS)

    Hildenbrand, Thomas G.; Hinze, William J.; Keller, G. Randy; Labson, Victor; Roest, Walter R.

    The year 2004 will offer an exciting and cost-effective opportunity to acquire a new U.S. magnetic anomaly data base. High Altitude Mapping Missions Inc. (HAMM) is currently planning an airborne mission to collect high-resolution Interferometric Synthetic Aperture Radar (IFSAR) imagery at an altitude of about 15 km, with a flight-line spacing of about 14 km over the conterminous United States and Alaska. Total and vector magnetic field data will also be collected with a "piggy-back" magnetometer system as a secondary mission objective. Because HAMM would fund the main flight costs of the mission, the geomagnetic community would acquire invaluable magnetic data at a nominal cost. These unique data will provide new insights on fundamental tectonic and thermal processes and give a new view of the structural and lithologic framework of continental areas and offshore regions.

  14. Utility of Satellite Magnetic Observations for Estimating Near-Surface Magnetic Anomalies

    NASA Technical Reports Server (NTRS)

    Kim, Hyung Rae; vonFrese, Ralph R. B.; Taylor, Patrick T.; Kim, Jeong Woo; Park, Chan Hong

    2003-01-01

    Regional to continental scale magnetic anomaly maps are becoming increasingly available from airborne, shipborne, and terrestrial surveys. Satellite data are commonly considered to fill the coverage gaps in regional compilations of these near-surface surveys. For the near-surface Antarctic magnetic anomaly map being produced by the Antarctic Digital Magnetic Anomaly Project (ADMAP), we show that near-surface magnetic anomaly estimation is greatly enhanced by the joint inversion of the near-surface data with the satellite observations relative to the conventional technique such as minimum curvature. Orsted observations are especially advantageous relative to the Magsat data that have order-of-magnitude greater measurement errors, albeit at much lower orbital altitudes. CHAMP is observing the geomagnetic field with the same measurement accuracy as the Orsted mission, but at the lower orbital altitudes covered by Magsat. Hence, additional significant improvement in predicting near-surface magnetic anomalies can result as these CHAMP data are available. Our analysis also suggests that considerable new insights on the magnetic properties of the lithosphere may be revealed by a further order-of-magnitude improvement in the accuracy of the magnetometer measurements at minimum orbital altitude.

  15. The Russian contribution in WDMAM-2011 magnetic anomalies and anomalies of satellite Champ

    NASA Astrophysics Data System (ADS)

    Livinova, Tamara; Glebovsky, Vladimir

    2010-05-01

    In VSEGEI is created the renovated digital cartographical model of an anomalous magnetic field (AMF) of territory of Russia and adjacent aquatory of scale 1:2 500000 on the basis of the available base summary digital materials prepared at various times by two organizations: VSEGEI and VNIIOkeangeologia. For this purpose uniform technological rules which have provided satisfactory synthesis of digital data files of an anomalous magnetic field in scale 1:2 500000 have been developed and realized. As a result of processing digital data file AMF the divergences reached 200 нТл, have been eliminated. For inclusion in WDMAM-2011 the Russian side the digital model counted on height 1 km on a grid 5х5км is offered. Anomalous values are designed from normal field VSEGEI of an epoch of 1965. The magnetic grid (5x5 km) within the Russian continental shelf compiled in VNIIOkeangeologia was leveled, adjusted and merged with those created in VSEGEI on shore of Russian Federation. Data processing is made by software Geosoft. Russian magnetic database in the Arctic Ocean was created as a result of adjusting of all historical and recent magnetic data sets, collected several organizations during the period about 40 years. Within the deep part of the Arctic Ocean this information was leveled, adjusted and combined with all available US magnetic data sets under cooperative project between and US Naval Research Laboratory. A result of this compilation is presented by grid of magnetic anomalies (5x5 km) that was used in the CAMP-GM project.

  16. The Stand Locations of Ancient People Depending On The Intensity of Local Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Shatokhin, I. T.; Khramov, A. V.; Shumilov, O. I.; Kasatkina, E. A.; Raspopov, O. M.

    For analysis 235 ancient people stands in the region of Kursk magnetic anomaly (one of the strongest anomaly all over the world) were chosen. All stands were dated by radiocarbon method and are placed in the State List of Archaeological Monuments of Belgorod Region. The oldest stands were radiocarbon dated to 70,000-50,000 years before present (kyr BP). All stands are located along the 300 km valley of Oskol river, having got a homogeneous climatic conditions. At the half of the valley the intensity of local magnetic field is rather low (0-1000 nT), so the region should be considered as the most comfort area for human occupation. The distribution of human occupation at this site looks as follows: 100% at 50-10 kyr BP, 94% at 6-4 kyr BP, 87% at 4-2 kyr BP, 83% at 3-2 kyr BP and 64% at 2-1 kyr BP. At ancient time humans preferred to occupy the sites with low magnetic field intensity. The spreading of human occupation outside of the comfort zone (more than 34%) began at Iron Age (2-1 kyr BP). Thus it may be concluded that in Palaeolithic age (50-10 kyr BP) humans avoided the area with enhanced level of local magnetic field. This seems to be connected to bad influence of the factor on human health, lower level of orientation on the surface, may be to different plant distribution features, and state of ancient people anxiety. The spreading of human occupation out of the comfort zone at rather recent time seems to be caused by social-economic activity.

  17. Evolution Of The Alpha Ride, The Arctic Ocean, On The Basis Of The Geohistorical Analysis Of The Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Gurevich, N. I.; Merkouriev, S. A.

    2004-12-01

    A new magnetic anomaly map of the Amerasian Basin has been created owing to a joint reprocessing of the Russian and American aeromagnetic data [Glebovsky, Kovacs at all., 2000]. This model produced the base for the magnetic data interpretation on the more qualitative level. As a result three series of seafloor spreading-type magnetic anomalies have been identified within the area of the Alpha Ridge and the adjacent part of the Canada Basin [Gurevich et all, 2003]. Their sources were formed from three spreading centers (SC). Two spreading centers: the western and the eastern, are situated at the axial part of the Alpha Ridge, the third one - the southern, is located on the southern slope of the Alpha Ridge and on the adjacent part of the Canada Basin. The triple junction of these SC had been located in the central part of the recent Alpha Ridge. The geohistorical analysis of these magnetic anomalies is fulfilled using an original computer programs. In consequence of this analysis: the geochronological characteristics are specified; the kinematic characteristics of the oceanic floor movement are determined and the main stages of the area evolution are found. The magnetic anomalies M16r (140 Ma), which signify the position of all three SC, and pair anomalies M20r (146.5 Ma) and M23r (151.5 Ma) are identified enough sure for all three SC and pair anomalies M30r (157.5 Ma) - fore the eastern and the southern SC. Finite and differential Euler poles of the lithospheric plates rotation were calculated for all three SC from best-fit pair magnetic anomalies. All the poles are concentrated around the Nares strait and at the northeastern part of the Ellesmere island. Angle and linear spreading rates were calculated using Euler poles. The calculation has showed that all three SC had low spreading rates. Three stages of the area evolution are found on the basis of the plate tectonic reconstruction for the periods 146.5, 151.5 and 157.5 Ma ago. The first stage, slightly earlier

  18. Anomalies

    NASA Astrophysics Data System (ADS)

    Deo, Nivedita

    1988-12-01

    This thesis studies the structure of local and global anomalies in certain systems and examines the conditions for their cancellation. Gauge anomalies-abelian and non -albelian-antisymmetric tensor, and gravitational anomalies in simple spinor theories with background fields have been analyzed by perturbative methods and local counterterms have been constructed to cancel the anomalies wherever possible. Anomalies occurring in supersymmetric theories in (2 + 1)-dimensions have also been calculated using both perturbative and heat kernel techniques, here again counterterms have been constructed to cancel these parity violating anomalies for certain gauge field configurations. (i) For gauge theories in four dimensions which contain couplings of fermions to a non-abelian antisymmetric tensor field, the contribution of the later to anomalies in the non-abelian chiral Ward identity is computed. It is shown by explicit construction of suitable counterterms that these anomalies can all be cancelled. (ii) The gauge anomalies associated with the gravitational fields in abelian gauge theories can be completely removed provided torsion is nonzero. This is shown by constructing a counterterm associated with the gravitational Goldstone-Wilczek current which cancels the anomalous gravitational contribution to the chiral Ward identity without introducing anomalies in the Lorentz or Einstein Ward identities. (iii) Using perturbative BPHZ renormalization techniques the parity odd part of the effective action has been extracted and explicitly determined for abitrary non-abelian gauge superfields in odd dimensions and shown to be the supersymmetric Chern -Simons secondary topological invariant. (iv) Schwinger's proper time technique is generalized to supersymmetric theories in odd dimensions. The effective action for supersymmetric QED is exactly found for space-time constant superfield. The parity violating anomaly induced in the effective action can be cancelled by adding a local

  19. Comparison between the recent U.S. composite magnetic anomaly map and Magsat anomaly data

    NASA Technical Reports Server (NTRS)

    Schnetzler, C. C.; Taylor, P. T.; Langel, R. A.; Hinze, W. J.; Phillips, J. D.

    1985-01-01

    The present investigation is concerned with a comparison of Magsat data with a Composite Magnetic Anomaly Map (CMAM) of the conterminous U.S. reported by Zietz (1982). The investigation was initiated to test the validity of the satellite measurements, and to provide insights into error or problems in either data set. It is found that upward continuation of the digital CMAM data is not in qualitative agreement with the Magsat map. However, if a least squares fit polynomial surface is taken out prior to upward continuation, there is improved quantitative agreement between a residual CMAM and Magsat. Causes for the remaining differences between the residual, upward continued CMAM and the Magsat map are also considered.

  20. Comparison between the recent U.S. composite magnetic anomaly map and Magsat anomaly data

    NASA Astrophysics Data System (ADS)

    Schnetzler, C. C.; Taylor, P. T.; Langel, R. A.; Hinze, W. J.; Phillips, J. D.

    1985-02-01

    The present investigation is concerned with a comparison of Magsat data with a Composite Magnetic Anomaly Map (CMAM) of the conterminous U.S. reported by Zietz (1982). The investigation was initiated to test the validity of the satellite measurements, and to provide insights into error or problems in either data set. It is found that upward continuation of the digital CMAM data is not in qualitative agreement with the Magsat map. However, if a least squares fit polynomial surface is taken out prior to upward continuation, there is improved quantitative agreement between a residual CMAM and Magsat. Causes for the remaining differences between the residual, upward continued CMAM and the Magsat map are also considered.

  1. Solar wind interaction with the Reiner Gamma crustal magnetic anomaly: Connecting source magnetization to surface weathering

    NASA Astrophysics Data System (ADS)

    Poppe, Andrew R.; Fatemi, Shahab; Garrick-Bethell, Ian; Hemingway, Doug; Holmström, Mats

    2016-03-01

    Remanent magnetization has long been known to exist in the lunar crust, yet both the detailed topology and ultimate origin(s) of these fields remains uncertain. Some crustal magnetic fields coincide with surface albedo anomalies, known as lunar swirls, which are thought to be formed by differential surface weathering of the regolith underlying crustal fields due to deflection of incident solar wind protons. Here, we present results from a three-dimensional, self-consistent, plasma hybrid model of the solar wind interaction with two different possible source magnetizations for the Reiner Gamma anomaly. We characterize the plasma interaction with these fields and the resulting spatial distribution of charged-particle weathering of the surface and compare these results to optical albedo measurements of Reiner Gamma. The model results constrain the proposed source magnetizations for Reiner Gamma and suggest that vertical crustal magnetic fields are required to produce the observed "dark lanes."

  2. Underwater magnetic gradiometer for magnetic anomaly detection, localization, and tracking

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Sulzberger, G.; Bono, J.; Skvoretz, D.; Allen, G. I.; Clem, T. R.; Ebbert, M.; Bennett, S. L.; Ostrom, R. K.; Tzouris, A.

    2007-04-01

    GE Security and the Naval Surface Warfare Center, Panama City (NSWC-PC) have collaborated to develop a magnetic gradiometer, called the Real-time Tracking Gradiometer or RTG that is mounted inside an unmanned underwater vehicle (UUV). The RTG is part of a buried mine hunting platform being developed by the United States Navy. The RTG has been successfully used to make test runs on mine-like targets buried off the coast of Florida. We will present a general description of the system and latest results describing system performance. This system can be also potentially used for other applications including those in the area of Homeland Security.

  3. Reflected Charged Particle Populations around Dipolar Lunar Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Deca, Jan; Divin, Andrey

    2016-10-01

    In this work we analyze and compare the reflected particle populations for both a horizontal and a vertical dipole model embedded in the lunar surface, representing the solar wind interaction with two different lunar magnetic anomaly (LMA) structures. Using the 3D full-kinetic electromagnetic code iPic3D, in combination with a test-particle approach to generate particle trajectories, we focus on the ion and electron dynamics. Whereas the vertical model electrostatically reflects ions upward under both near-parallel and near-perpendicular angles with respect to the lunar surface, the horizontal model only has a significant shallow component. Characterizing the electron dynamics, we find that the interplay of the mini-magnetosphere electric and magnetic fields is capable of temporarily trapping low-energy electrons and possibly ejecting them upstream. Our results are in agreement with recent high-resolution observations. Low- to medium-altitude ion and electron observations might be excellent indicators to complement orbital magnetic field measurements and better uncover the underlying magnetic field structure. The latter is of particular importance in defining the correlation between LMAs and lunar swirls, and further testing the solar wind shielding hypothesis for albedo markings due to space weathering. Observing more reflected ions does not necessarily point to the existence of a mini-magnetosphere.

  4. On long-wavelength magnetic anomalies over Indian region

    NASA Technical Reports Server (NTRS)

    Srinivasan, S.; Carlo, L.; Rastogi, R. G.; Singh, B. P. (Principal Investigator)

    1983-01-01

    A data set composed of vector magnetic measurements obtained by MAGSAT and very accurate altitude determinations made using Sun sensors and star cameras was used to obtain data for very quiet days over the Indian region at 10 S to 40 N and 60 E to 110 E in an effort to determine the validity of quantitative estimates made from aeromagnetic data obtained by removing the core field. To further account for the external effects, the ring current contributions estimated using both X and Z variations were subtracted from the observed values. Before this, the core contribution was eliminated through a spherical harmonic expansion with terms up to N=13. Analysis of the residual measurements using Fast Fourier techniques indicates that the anomalies contain substantial power for wavelengths of about 1500 kms. Because the ring current effect has a spatial structure of this dimension over India, efforts are being made to exactly eliminate these two interfering effects from the data.

  5. Lunar Compass: A Rover Mission for Exploration of a Lunar Crustal Magnetic Anomaly

    NASA Astrophysics Data System (ADS)

    Blewett, D. T.; Hurley, D. M.; Denevi, B. W.; Cahill, J. T. S.; Klima, R. L.; Plescia, J. B.; Paranicas, C. P.; Greenhagen, B. T.; Anderson, B. A.; Korth, H.; Ho, G. C.; Nunez, J. I.; Zimmerman, M. I.; Brandt, P. C.

    2016-11-01

    We suggest that a rover mission to a lunar magnetic anomaly could answer key questions in several major fields of planetary science: planetary magnetism, space plasma physics, lunar geology, and space weathering.

  6. Absolute Magnetization Distribution on Back-arc Spreading Axis Hosting Hydrothermal Vents; Insight from Shinkai 6500 Magnetic Survey

    NASA Astrophysics Data System (ADS)

    Fujii, M.; Okino, K.; Honsho, C.; Mochizuki, N.; Szitkar, F.; Dyment, J.

    2013-12-01

    Near-bottom magnetic profiling using submersible, deep-tow, Remotely Operated Vehicle (ROV) and Autonomous Underwater Vehicle (AUV) make possible to conduct high-resolution surveys and depict detailed magnetic features reflecting, for instance, the presence of fresh lavas or hydrothermal alteration, or geomagnetic paleo-intensity variations. We conducted near-bottom three component magnetic measurements onboard submersible Shinkai 6500 in the Southern Mariana Trough, where five active hydrothermal vent fields (Snail, Yamanaka, Archean, Pica, and Urashima sites) have been found in both on- and off-axis areas of the active back-arc spreading center, to detect signals from hydrothermally altered rock and to distinguish old and new submarine lava flows. Fourteen dives were carried out at an altitude of 1-40 m during the R/V Yokosuka YK10-10 and YK10-11 cruises in 2010. We carefully corrected the effect of the induced and permanent magnetizations of the submersible by applying the correction method for the shipboard three-component magnetometer measurement modified for deep-sea measurement, and subtracted the IGRF values from the corrected data to obtain geomagnetic vector anomalies along the dive tracks. We then calculated the synthetic magnetic vector field produced by seafloor, assumed to be uniformly magnetized, using three dimensional forward modeling. Finally, values of the absolute magnetizations were estimated by using a linear transfer function in the Fourier domain from the observed and synthetic magnetic anomalies. The distribution of estimated absolute magnetization generally shows low values around the five hydrothermal vent sites. This result is consistent with the equivalent magnetization distribution obtained from previous AUV survey data. The areas of low magnetization are also consistent with hydrothermal deposits identified in video records. These results suggest that low magnetic signals are due to hydrothermal alteration zones where host rocks are

  7. Solar Wind Interaction with Lunar Magnetic Anomalies: Reiner Gamma

    NASA Astrophysics Data System (ADS)

    Deca, Jan; Divin, Andrey; Wang, Xu; Lembège, Bertrand; Markidis, Stefano; Lapenta, Giovanni; Horányi, Mihály

    2016-04-01

    Discovered by early astronomers during the Renaissance, the Reiner Gamma formation is one of the most peculiar lunar surface features. Observations have shown that the tadpole-shaped albedo marking, the so-called swirl, found on the Oceanus Procellarum is co-located with one of the strongest magnetic anomalies (LMA) on our Moon. In previous work, using a horizontal dipole model [Deca et al. 2014, 2015], we have described the formation of a mini-magnetosphere structure surrounding the swirl pattern, locally shielding the underlying lunar surface from the impinging solar wind, and hinting at a correlation with its main surface albedo brightness marking in a distinctive concentric oval shape. Using the observed magnetic field model [Tsunakawa et al. 2015] in our full-kinetic electromagnetic framework, iPic3D, we reproduce a surface weathering pattern closely resembling the details of the Reiner Gamma swirls. This work therefore provides strong evidence that the solar wind standoff theory for lunar swirl formation is the dominant process to explain the albedo markings of the Reiner Gamma region. This work was supported by NASA's SSSERVI/IMPACT and by the Swedish National Space Board, Grant No. 136/11. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. Test simulations utilised the Janus supercomputer, supported by NSF (CNS-0821794) and CU Boulder.

  8. Magnetic anomaly depth and structural index estimation using different height analytic signals data

    NASA Astrophysics Data System (ADS)

    Zhou, Shuai; Huang, Danian; Su, Chao

    2016-09-01

    This paper proposes a new semi-automatic inversion method for magnetic anomaly data interpretation that uses the combination of analytic signals of the anomaly at different heights to determine the depth and the structural index N of the sources. The new method utilizes analytic signals of the original anomaly at different height to effectively suppress the noise contained in the anomaly. Compared with the other high-order derivative calculation methods based on analytic signals, our method only computes first-order derivatives of the anomaly, which can be used to obtain more stable and accurate results. Tests on synthetic noise-free and noise-corrupted magnetic data indicate that the new method can estimate the depth and N efficiently. The technique is applied to a real measured magnetic anomaly in Southern Illinois caused by a known dike, and the result is in agreement with the drilling information and inversion results within acceptable calculation error.

  9. Determination Gradients of the Earth's Magnetic Field from the Measurements of the Satellites and Inversion of the Kursk Magnetic Anomaly

    NASA Technical Reports Server (NTRS)

    Karoly, Kis; Taylor, Patrick T.; Geza, Wittmann

    2014-01-01

    We computed magnetic field gradients at satellite altitude, over Europe with emphasis on the Kursk Magnetic Anomaly (KMA). They were calculated using the CHAMP satellite total magnetic anomalies. Our computations were done to determine how the magnetic anomaly data from the new ESA/Swarm satellites could be utilized to determine the structure of the magnetization of the Earths crust, especially in the region of the KMA. Since the ten years of 2 CHAMP data could be used to simulate the Swarm data. An initial East magnetic anomaly gradient map of Europe was computed and subsequently the North, East and Vertical magnetic gradients for the KMA region were calculated. The vertical gradient of the KMA was determined using Hilbert transforms. Inversion of the total KMA was derived using Simplex and Simulated Annealing algorithms. Our resulting inversion depth model is a horizontal quadrangle with upper 300-329 km and lower 331-339 km boundaries.

  10. Surveying the South Pole-Aitken basin magnetic anomaly for remnant impactor metallic iron

    USGS Publications Warehouse

    Cahill, Joshua T.S.; Hagerty, Justin J.; Lawrence, David M.; Klima, Rachel L.; Blewett, David T.

    2014-01-01

    The Moon has areas of magnetized crust ("magnetic anomalies"), the origins of which are poorly constrained. A magnetic anomaly near the northern rim of South Pole-Aitken (SPA) basin was recently postulated to originate from remnant metallic iron emplaced by the SPA basin-forming impactor. Here, we remotely examine the regolith of this SPA magnetic anomaly with a combination of Clementine and Lunar Prospector derived iron maps for any evidence of enhanced metallic iron content. We find that these data sets do not definitively detect the hypothesized remnant metallic iron within the upper tens of centimeters of the lunar regolith.

  11. Isotopic anomaly and stratification of Ca in magnetic Ap stars

    NASA Astrophysics Data System (ADS)

    Ryabchikova, T.; Kochukhov, O.; Bagnulo, S.

    2008-03-01

    Aims: We have completed an accurate investigation of the Ca isotopic composition and stratification in the atmospheres of 23 magnetic chemically peculiar (Ap) stars of different temperature and magnetic field strength. Methods: With the UVES spectrograph at the 8 m ESO VLT, we have obtained high-resolution spectra of Ap stars in the wavelength range 3000-10 000 Å. Using a detailed spectrum synthesis calculations, we have reproduced a variety of Ca lines in the optical and ultraviolet spectral regions, inferring the overall vertical distribution of Ca abundance, and have deduced the relative isotopic composition and its dependence on height using the profile of the IR-triplet Ca II line at λ8498 Å. Results: In 22 out of 23 studied stars, we found that Ca is strongly stratified, being usually overabundant by 1.0-1.5 dex below logτ5000≈ -1, and strongly depleted above logτ5000=-1.5. The IR-triplet Ca II line at λ8498 Å reveals a significant contribution of the heavy isotopes 46Ca and 48Ca, which represent less than 1 % of the terrestrial Ca isotopic mixture. We confirm our previous finding that the presence of heavy Ca isotopes is generally anticorrelated with the magnetic field strength. Moreover, we discover that in Ap stars with relatively small surface magnetic fields (≤4-5 kG), the light isotope 40Ca is concentrated close to the photosphere, while the heavy isotopes are dominant in the outer atmospheric layers. This vertical isotopic separation, observed for the first time for any metal in a stellar atmosphere, disappears in stars with magnetic field strength above 6-7 kG. Conclusions: We suggest that the overall Ca stratification and depth-dependent isotopic anomaly observed in Ap stars may be attributed to a combined action of the radiatively-driven diffusion and light-induced drift. Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO program No. 68.D-0254).

  12. Airborne detection of magnetic anomalies associated with soils on the Oak Ridge Reservation, Tennessee

    SciTech Connect

    Doll, W.E.; Beard, L.P.; Helm, J.M.

    1995-04-01

    Reconnaissance airborne geophysical data acquired over the 35,000-acre Oak Ridge Reservation (ORR), TN, show several magnetic anomalies over undisturbed areas mapped as Copper Ridge Dolomite (CRD). The anomalies of interest are most apparent in magnetic gradient maps where they exceed 0.06 nT/m and in some cases exceed 0.5 nT/m. Anomalies as large as 25nT are seen on maps. Some of the anomalies correlate with known or suspected karst, or with apparent conductivity anomalies calculated from electromagnetic data acquired contemporaneously with the magnetic data. Some of the anomalies have a strong correlation with topographic lows or closed depressions. Surface magnetic data have been acquired over some of these sites and have confirmed the existence of the anomalies. Ground inspections in the vicinity of several of the anomalies has not led to any discoveries of manmade surface materials of sufficient size to generate the observed anomalies. One would expect an anomaly of approximately 1 nT for a pickup truck from 200 ft altitude. Typical residual magnetic anomalies have magnitudes of 5--10 nT, and some are as large as 25nT. The absence of roads or other indications of culture (past or present) near the anomalies and the modeling of anomalies in data acquired with surface instruments indicate that man-made metallic objects are unlikely to be responsible for the anomaly. The authors show that observed anomalies in the CRD can reasonably be associated with thickening of the soil layer. The occurrence of the anomalies in areas where evidences of karstification are seen would follow because sediment deposition would occur in topographic lows. Linear groups of anomalies on the maps may be associated with fracture zones which were eroded more than adjacent rocks and were subsequently covered with a thicker blanket of sediment. This study indicates that airborne magnetic data may be of use in other sites where fracture zones or buried collapse structures are of interest.

  13. Contributions of cretaceus quiet zone natural remanent magnetization to Magsat anomalies in the Southwest Indian Ocean

    NASA Technical Reports Server (NTRS)

    Fullerton, Lawrence G.; Frey, Herbert V.; Roark, James H.; Thomas, Herman H.

    1994-01-01

    The Magsat magnetic anomalies over the Southwest Indian Ocean are modeled using a combination of induced plus viscous remanent magnetization (IM/VRM) and natural remanent magnetization (NRM). Two broad, roughly parallel, SW to NE trending triple-peaked positive anomalies dominate the region, one lying south of Africa and the other north of Antarctica. Although these anomaly peaks generally correspond with the Agulhas Plateau/Maud Rise, Mozambique Plateau/Astrid Ridge, and Madagascar Ridge/Conrad Rise conjugate pairs, the IM/VRM contribution from structural characteristics (i.e., crustal thickness) accounts for only about 20% of the anomaly amplitudes. A spatially variable but observationally constrained NRM contribution in Cretaceous Quiet Zone (KQZ) crust is required to account for the location, shape, and amplitude contrast of these anomalies. Many crustal features in the Southwest Indian Ocean near Antarctica have little geophysical data to constrain their structure but do hagve tectonic conjugates near Africa for which much more geophysical data are generally available. Using geophysical and geological constraints from one member to model the magnetization structure of its conjugate reproduces the observed Magsat reduced-to-pole anomalies over both structures very well. This suggests that no significant alteration in their magnetization structure has occurred since the features split. Models of these conjugate structures show that IM/VRM reproduces the Magsat anomalies associated with non-KQZ crust but that both IM/VRM and a dominant NRM component are required to explain the anomalies associated with KQZ crust.

  14. Inversion of gravity and magnetic anomalies of two-dimensional polygonal cross sections

    NASA Astrophysics Data System (ADS)

    Radhakrishna Murthy, I. V.; Rama Rao, P.

    1993-10-01

    Two computer programs GPOLYIN and TPOLYIN coded in FORTRAN 77 are presented to invert respectively gravity and magnetic anomalies of two-dimensional (2-D) bodies of polygonal cross section. The computer input consists of the observed anomalies, their distances relative to a convenient reference point and the density contrast or the dip and direction of magnetization, as well as the coordinates of the vertices of the initial model. The programs solve for increments to the initial values of the coordinates using Marquardt's optimization technique. The partial derivatives are calculated by numerical differentiation. The program TPOLYIN is valid for any magnetization and for anomalies in any component.

  15. Analyzing and modeling gravity and magnetic anomalies using the SPHERE program and Magsat data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1981-01-01

    Computer codes were completed, tested, and documented for analyzing magnetic anomaly vector components by equivalent point dipole inversion. The codes are intended for use in inverting the magnetic anomaly due to a spherical prism in a horizontal geomagnetic field and for recomputing the anomaly in a vertical geomagnetic field. Modeling of potential fields at satellite elevations that are derived from three dimensional sources by program SPHERE was made significantly more efficient by improving the input routines. A preliminary model of the Andean subduction zone was used to compute the anomaly at satellite elevations using both actual geomagnetic parameters and vertical polarization. Program SPHERE is also being used to calculate satellite level magnetic and gravity anomalies from the Amazon River Aulacogen.

  16. Magnetic Structure of Backarc Spreading Axis with Hydrothermal Vents; the Southern Mariana Trough

    NASA Astrophysics Data System (ADS)

    Fujii, M.; Okino, K.; Mochizuki, N.; Honsho, C.; Szitkar, F.; Dyment, J.; Nakamura, K.

    2012-12-01

    Seafloor hydrothermal systems are important in relation to global heat and chemical fluxes as well as habitat of microbial communities. The substantial variation of hydrothermal systems in various tectonic settings has important implications for the magnetic structure of oceanic crust. It has been very difficult to detect the geophysical signature of hydrothermal systems from sea-surface data because the small scale of hydrothermal systems is below the limit of resolution. The advance of near-bottom survey methods using a submersible, deep-tow, ROV and AUV has made possible high-resolution geophysical mapping around hydrothermal areas. Near-bottom magnetic surveys can provide direct information on the magnetization of the shallower oceanic crust, implying hydrothermal alteration both in active and fossil vent sites. Near-bottom three component magnetic measurements on submersible Shinkai 6500 were carried out at hydrothermal fields in the Southern Mariana Trough, a slow spreading backarc basin. Fourteen dive surveys were conducted during cruises YK11-10 and YK10-11. We investigated the magnetic structure of four hydrothermal systems located at on- and off-axis to clarify how the geophysical and geological setting controls the fluid circulation at small scale. Recent researches at slow spreading ridges showed a relationship between crustal magnetic structure and host rock around hydrothermal vents (e.g. Tivey and Dyment, 2010), but no observation at backarc spreading axis has been reported so far. We carefully corrected the effects of induced and permanent magnetizations of the submersible by applying the method of Isezaki [1986] with dumped least-square method (Honsho et al., 2009). After subtracting the IGRF from the corrected observed data, we obtained geomagnetic vector anomalies in geographical coordinate. For three transects of the axis, we applied three methods; 2D inversion technique (Parker and Huestis, 1972), 2D forward modeling technique (Honsho et al

  17. High-resolution magnetic signature of active hydrothermal systems in the back-arc spreading region of the southern Mariana Trough

    NASA Astrophysics Data System (ADS)

    Fujii, Masakazu; Okino, Kyoko; Honsho, Chie; Dyment, Jerome; Szitkar, Florent; Mochizuki, Nobutatsu; Asada, Miho

    2015-05-01

    High-resolution vector magnetic measurements were performed on five hydrothermal vent fields of the back-arc spreading region of the southern Mariana Trough using Shinkai 6500, a deep-sea manned submersible. A new 3-D forward scheme was applied that exploits the surrounding bathymetry and varying altitudes of the submersible to estimate absolute crustal magnetization. The results revealed that magnetic-anomaly-derived absolute magnetizations show a reasonable correlation with natural remanent magnetizations of rock samples collected from the seafloor of the same region. The distribution of magnetic-anomaly-derived absolute magnetization suggests that all five andesite-hosted hydrothermal fields are associated with a lack of magnetization, as is generally observed at basalt-hosted hydrothermal sites. Furthermore, both the Pika and Urashima sites were found to have their own distinct low-magnetization zones, which could not be distinguished in magnetic anomaly data collected at higher altitudes by autonomous underwater vehicle due to their limited extension. The spatial extent of the resulting low magnetization is approximately 10 times wider at off-axis sites than at on-axis sites, possibly reflecting larger accumulations of nonmagnetic sulfides, stockwork zones, and/or alteration zones at the off-axis sites.

  18. Long-wavelength magnetic and gravity anomaly correlations on Africa and Europe

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Olivier, R.; Hinze, W. J.

    1985-01-01

    Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.

  19. Long-wavelength Magnetic and Gravity Anomaly Correlations of Africa and Europe

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J. (Principal Investigator); Olivier, R.

    1984-01-01

    Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic Shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.

  20. Magnetic Anomalies of the Fennoscandian Shield on a 2km resolution grid

    NASA Astrophysics Data System (ADS)

    Korhonen, Juha V.; Aaro, Sven; Reidar Skilbrei, Jan; All, Tarmo

    2010-05-01

    Joint magnetic anomaly grid of the Fennoscandian Shield was released 2002, smoothed and used as data for the WDMAM2007. In comparison with MF5 this grid showed superior characteristics to other sets. The data will be released as a 2 km resolution grid for the WDMAM2011 with eventual updates of anomaly levels.

  1. Apparatus and method for detecting a magnetic anomaly contiguous to remote location by SQUID gradiometer and magnetometer systems

    DOEpatents

    Overton, W.C. Jr.; Steyert, W.A. Jr.

    1981-05-22

    A superconducting quantum interference device (SQUID) magnetic detection apparatus detects magnetic fields, signals, and anomalies at remote locations. Two remotely rotatable SQUID gradiometers may be housed in a cryogenic environment to search for and locate unambiguously magnetic anomalies. The SQUID magnetic detection apparatus can be used to determine the azimuth of a hydrofracture by first flooding the hydrofracture with a ferrofluid to create an artificial magnetic anomaly therein.

  2. Origin of the Eastern Galicia Magnetic Anomaly (NW Spain). Implications for the Origin of Magnetic Anomalies in the Central Iberian Arc

    NASA Astrophysics Data System (ADS)

    Ayarza, P.; Martinez-Catalan, J. R.; Villalain, J. J.; Alvarez Lobato, F.; Martin Paramio, M.; Rodriguez Gómez, S.; Sanz López, M.

    2015-12-01

    The aeromagnetic map of Iberia features outstanding anomalies that have been key to define the Central Iberian Arc, a late-orogenic orocline in the western part of the Variscan belt. The most studied of them is the EGMA (Eastern Galicia Magnetic Anomaly), which follows the Lugo-Sanabria extensional dome and is probably associated with it. Among the existing models of this anomaly, those relating it with magnetite-rich inhomogeneous granites and migmatites formed during late-Variscan extension seem to be more plausible ones. However, this and other interpretations involving deep-seated mafic/ultramafic bodies lack resolution as they are based on the aeromagnetic dataset. New ground magnetic data have been acquired in the northern part of the Xistral Tectonic Window, at the core of the Lugo dome where its deepest rocks crop out. The resulting maps show that the anomaly ranges ~1000 nT (vs. 190 nT on the aeromagnetic map) and that the most important maxima lie on top of extensional detachments located on high-grade metasediments or inhomogeneous granites. 2D forward modeling indicates that the magnetization is carried by upper Neoproterozoic and early Cambrian metasediments, partially melted during late-Variscan high-T and low-P metamorphic event linked to the extensional collapse. Furthermore, the anomaly maxima are spatially related with detachments, where the metasediments were strongly sheared. Therefore, the P-T, redox and fluid pressure conditions necessary for the formation of magnetite seem related with the extensional process and the dynamics of its structures. Many magnetic anomalies of the Central Iberian Arc lie on top of Variscan extensional domes and accordingly may have a similar origin. Special attention is paid to the Gredos Magnetic Anomaly, coincident with the batholith of the same name. Preliminary magnetic mapping and modeling indicate that the anomaly is previous to the intrusion of the Jurassic Alentejo-Plasencia dyke and to the tardi

  3. World Digital Magnetic Anomaly Map, development towards the Second Edition. (Invited)

    NASA Astrophysics Data System (ADS)

    Korhonen, J. V.

    2009-12-01

    Magnetic anomalies are small deviations in the Earth’s main magnetic field, caused by variation of magnetization in the uppermost lithosphere. Magnetic anomalies provide spatial key information for understanding the structure and evolution of the Earths crust. In practice these anomalies are used e.g. for assessment and prospecting of geological natural resources and planning of land use. A common way to calculate a magnetic anomaly value has been to subtract International Geomagnetic Reference Field (IGRF) from a total field measurement that is cleaned from short term variation of the Earth's magnetic field. World Digital Magnetic Anomaly Map (WDMAM) is a collaborative project between member organizations of International Association of Geomagnetism and Aeronomy (IAGA) and the Commission for Geological Map of the World (CGMW). The First Edition of the map was published in 2007. It consisted of a paper map 1:50 Million and a 3 minutes global grid of total field anomalies at an altitude of 5 km above the geoid. The First Edition was aimed to compile as much as possible available land and sea magnetic data, and homogenize it by comparing anomalies with a satellite magnetic lithospheric field model. This first version was prepared in a tight schedule, to show the usefulness of the map to the community and to form a basis for later development and future editions of the map. Hence, much was left to be improved for the second edition, including sparse coverage in two continents and all southern seas. The satellite models were understood to gain more detail in near future when the CHAMP-satellite would reach lower orbits, and hence higher resolution. The SWARM-satellite constellation was seen to produce even more suitable data in a few years thereafter. Ocean magnetic data sets required careful processing and leveling. The method of homogenization of anomalies included replacing long wavelength information by satellite model spectral data, and hence rejecting

  4. Calculation of gravity and magnetic anomalies along profiles with end corrections and inverse solutions for density and magnetization

    USGS Publications Warehouse

    Cady, John W.

    1977-01-01

    A computer program is presented which performs, for one or more bodies, along a profile perpendicular to strike, both forward calculations for the magnetic and gravity anomaly fields and independent gravity and magnetic inverse calculations for density and susceptibility or remanent magnetization.

  5. Reduction of ENA emission above the magnetic anomalies on Mars: MEX/ASPERA-3 result

    NASA Astrophysics Data System (ADS)

    Wang, X.-D.; Barabash, S.; Futaana, Y.

    2012-09-01

    We present the preliminary results of the effect of Martian magnetic anomalies (MAs) on the emission of energetic neutral atoms(ENAs) at Mars. It is demonstrated that the anomalies reduce ENA flux significantly. The explanation is that stronger magnetic field above the MAs elevates the induced magnetosphere boundary (IMB) so that only the higher and less dense part of Martian exosphere can interact with shocked solar wind. This is the first attempt to image Martian MAs with ENA remote sensing technique.

  6. Magnetic Resonance Imaging of Developmental Anomalies of the Uterus and the Vagina in Pediatric Patients.

    PubMed

    Gould, Sharon W; Epelman, Monica

    2015-08-01

    Developmental anomalies of the uterus and the vagina are associated with infertility and miscarriage and are most commonly detected in the postpubertal age-group. These conditions may also present in younger patients as a mass or pain owing to obstruction of the uterus or the vagina. Associated urinary tract anomalies are common, as well. Accurate diagnosis and thorough description of these anomalies is essential for appropriate management; however, evaluation may be difficult in an immature reproductive tract. Magnetic resonance imaging technique pertinent to imaging of the pediatric female reproductive tract is presented and illustrated along with the findings associated with various anomalies.

  7. Inhibition/Development of equatorial Spread F on magnetically disturbed days - A case study

    NASA Astrophysics Data System (ADS)

    Devasia, C. V.; Jyothi, N.; Pant, K. T.; Diwakar, T.; Sridharan, R.

    A case study of occurrence/ non-occurrence of Equatorial Spread F (ESF) events on several magnetically disturbed days over the magnetic equatorial location of Trivandrum (8.5°N; 77°E; dip 0.5°N) in India was conducted during March-April 1998. This study carried out under the ISTEP (Indian-STEP) program brought out some interesting aspects of the occurrence/non occurrence of ESF in relation to the nature of equatorial ionospheric response to the geomagnetic disturbance. The study indicated that the polarity and strength of the electric field disturbances which become active around noon hours on these days have an important role in modulating the development of Equatorial Ionization Anomaly (EIA). These electric field disturbances of larger timescales that are associated with ionospheric disturbance dynamo effects are shown to have a controlling effect on the F-region height rise, which in turn characterise the occurrence/ non- occurrence of ESF on different disturbed days. These aspects are discussed and presented.

  8. High-altitude structure of the magnetic anomalies using the gradient measurements in stratosphere

    NASA Astrophysics Data System (ADS)

    Tsvetkov, Yu.; Rotanova, N.; Belikova, M.

    2003-04-01

    HIGH-ALTITUDE STRUCTURE OF THE MAGNETIC ANOMALIES USING THE GRADIENT MEASUREMENTS IN STRATOSPHERE Yu. Tsvetkov, N. ROTANOVA, M. Belikova Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAS, Troitsk, Moscow Region, 142190, Russia rotanova@izmiran.rssi.ru/FAX: +7-095-3340124 Method of the recalculation of the anomaly magnetic field over the range of the altitudes of 20-40 km is suggested. Technique is based on the experimental data of the anomaly magnetic field, its vertical gradient and the gradient increment along vertical line, obtained from the aerostat gradient magnetic surveys in stratosphere. The high-altitude structure of the magnetic anomalies, obtained for the Baikal region has been constructed. These results were used to obtain the estimations of the deep magnetic sources. The numerous values of the low boundary of the sources are 30-35 km. These estimations of the depth coincide with the ones, obtained from the results of the spectral analysis of the same magnetic anomalies.

  9. Surface vector mapping of magnetic anomalies over the Moon using Kaguya and Lunar Prospector observations

    NASA Astrophysics Data System (ADS)

    Tsunakawa, Hideo; Takahashi, Futoshi; Shimizu, Hisayoshi; Shibuya, Hidetoshi; Matsushima, Masaki

    2015-06-01

    We have provided preliminary global maps of three components of the lunar magnetic anomaly on the surface applying the surface vector mapping (SVM) method. The data used in the present study consist of about 5 million observations of the lunar magnetic field at 10-45 km altitudes by Kaguya and Lunar Prospector. The lunar magnetic anomalies were mapped at 0.2° equi-distance points on the surface by the SVM method, showing the highest intensity of 718 nT in the Crisium antipodal region. Overall features on the SVM maps indicate that elongating magnetic anomalies are likely to be dominant on the Moon except for the young large basins with the impact demagnetization. Remarkable demagnetization features suggested by previous studies are also recognized at Hertzsprung and Kolorev craters on the farside. These features indicate that demagnetized areas extend to about 1-2 radii of the basins/craters. There are well-isolated central magnetic anomalies at four craters: Leibnitz, Aitken, Jules Verne, and Grimaldi craters. Their magnetic poles through the dipole source approximation suggest occurrence of the polar wander prior to 3.3-3.5 Ga. When compared with high-albedo markings at several magnetic anomalies such as the Reiner Gamma anomalies, three-dimensional structures of the magnetic field on/near the surface are well correlated with high-albedo areas. These results indicate that the global SVM maps are useful for the study of the lunar magnetic anomalies in comparison with various geological and geophysical data.

  10. Subduction-zone magnetic anomalies and implications for hydrated forearc mantle

    USGS Publications Warehouse

    Blakely, R.J.; Brocher, T.M.; Wells, R.E.

    2005-01-01

    Continental mantle in subduction zones is hydrated by release of water from the underlying oceanic plate. Magnetite is a significant byproduct of mantle hydration, and forearc mantle, cooled by subduction, should contribute to long-wavelength magnetic anomalies above subduction zones. We test this hypothesis with a quantitative model of the Cascadia convergent margin, based on gravity and aeromagnetic anomalies and constrained by seismic velocities, and find that hydrated mantle explains an important disparity in potential-field anomalies of Cascadia. A comparison with aeromagnetic data, thermal models, and earthquakes of Cascadia, Japan, and southern Alaska suggests that magnetic mantle may be common in forearc settings and thus magnetic anomalies may be useful in mapping hydrated mantle in convergent margins worldwide. ?? 2005 Geological Society of America.

  11. Magnetic Anomalies Within Lunar Impact Basins: Constraints on the History of the Lunar Dynamo

    NASA Astrophysics Data System (ADS)

    Richmond, N. C.; Hood, L. L.

    2011-12-01

    Previous work has shown that lunar crustal magnetization has a combination of origins including shock remanent magnetization in transient magnetic fields and thermoremanent magnetization in a steady core dynamo magnetic field (e.g., Hood and Artemieva, Icarus, 2008; Richmond and Hood, JGR, 2008; Garrick-Bethell et al., Science, 2009; Hood, Icarus, 2011). In particular, magnetic anomalies within the interiors of lunar impact basins and large craters provide a potentially valuable means of constraining the history of the former dynamo (Halekas et al., MAPS, 2003; Hood, 2011). These anomalies likely have a thermoremanent origin owing to high subsurface temperatures reached at the time of impact and therefore require a long-lived, steady magnetic field to explain their magnetization. Central anomalies have previously been confirmed to be present using Lunar Prospector magnetometer (LP MAG) data within several Nectarian-aged basins (Moscoviense, Mendel-Rydberg, Crisium, and Humboldtianum), implying that a dynamo existed during this lunar epoch (Hood, 2011). Here, we further analyze low altitude LP MAG data for several additional basins, ranging in age from Nectarian to Imbrian. Results indicate that magnetic anomalies with a probable basin-related origin are present within at least two additional Nectarian-aged basins (Serenitatis and Humorum) and one Imbrian-aged basin (Schrodinger). No discernible anomalies are present within the largest Imbrian-aged basins, Imbrium and Orientale. While there is uncertainty regarding the age of the Schrodinger basin, it has been reported to be slightly more recent than Imbrium (Wilhelms, 1984). Our initial interpretation is therefore that a dynamo likely existed during the Imbrian epoch. The absence of anomalies within Imbrium and Orientale can be explained by insufficient conditions for acquisition of strong magnetization (e.g., inadequate concentrations of efficient remanence carriers) following these relatively large impacts.

  12. Direct Observations of Magnetic Anomalies on the Lunar Surface under Varying Solar Wind Conditions

    NASA Astrophysics Data System (ADS)

    Vorburger, A.; Wurz, P.; Barabash, S.; Wieser, M.; Futaana, Y.; Holmström, M.; Bhardwaj, A.; Dhanya, M. B.; Sridharan, R.; Asamura, K.

    2012-04-01

    In contrast to Earth, the Moon does not have a global dipolar magnetic field. Since the first lunar landing with Apollo 11, we know, though, that localised magnetic fields exist on the lunar surface. Measurements conducted by the Lunar Prospector magnetometer and electron reflectometer suggested that these localised magnetic fields are able to deflect the impinging solar wind in favourable cases (Lin et al., Science 1998). Magnetohydrodynamic simulations support the implication that mini-magnetospheres are formed above the locations of strong localised magnetic fields and can hold off the impinging solar wind (Harnett and Winglee, JGR 2002). Analysis of magnetic field data from Lunar Prospector of the Reiner Gamma anomaly region showed that the distortion of the magnetic field of this anomaly strongly depends on the impinging solar wind parameters, which was interpreted that the size and shape of the mini-magnetosphere changed with the solar wind parametes (Kurata et al., GRL 2005). Wieser et al., GRL 2010 showed that SARA, the Sub-KeV Atom Analyzer on board Chandrayaan-1, is able to detect an ENA image of the mini-magnetosphere in the measured energetic neutral atom flux. Here we analysed all orbits where CENA, the Chandrayaan-1 Energetic Neutral Analyzer, recorded data when a magnetic anomaly was in CENA's field-of-view. Our goal was to determine if 1) a signature of the magnetic anomaly is always visible in the ENA signal and if 2) there is a correlation between the solar wind dynamic pressure, the solar wind magnetic field, the local magnetic field strength and the reduction in the reflected ENA flux. Our results show that for the simplest case, i.e., the Gerasimovich anomaly, there is indeed a clear correlation between the shielding efficiency, the magnetic field strength and the solar wind dynamic pressure. For the other observed magnetic anomalies, for which the magnetic fields are not only weaker but also spatially more variable than that of the

  13. Structure and segmentation of the eastern Gulf of Aden basin and the Sheba ridge from gravity, bathymetric and magnetic anomalies: implications for accretion processes

    NASA Astrophysics Data System (ADS)

    D'Acremont, E.; Leroy, S.; Maia, M.; Gente, P.; Autin, J.

    2007-12-01

    The eastern Gulf of Aden is a key place for investigating seafloor spreading processes and the evolution in space and time of the margin and ridge segmentation. The rifting of the Gulf that separated Arabia from Somalia started around 35 Ma ago followed by oceanic accretion from at least17.6 Ma. Bathymetric, gravity and magnetic data from the Encens-Sheba cruise are used to study the structure and segmentation of the eastern part of the basin and ridge, which have strong implications for accretion processes. The segmentation of the first oceanic spreading centre, which is dated at least 17.6 Ma by the magnetic anomaly (A5d) identification, seems to be directly related to the structural geometry of the margins. Then, magmatic processes governed the evolution of the segmentation. The segmentation of the oceanic crust evolved, by eastward propagation of the western segment, from three segments (from an5d to an5) to two segments (from an5). At 6 Ma (an3a) a third segment appeared by duplication of the Socotra transform fault, maybe due to a regional kinematics change. The Encens-Sheba oceanic domain is divided in two distinct areas trending NE-SW perpendicular to the Sheba ridge. (1) The Eastern area is characterized by a shorter wavelength variation of the axial segmentation with two spreading segments 30 to 40 km long, and by a thin crust particularly on the northern and southern ends of its flanks. (2) The Western zone, whose axial segment is more than 120 km long, is characterized by a thick crust and/or a hot mantle and no axial rift valley. This abnormal volcanic activity for a slow spreading ridge is emphasized by bathymetric highs with 5-10 km wide volcanic edifices, and by a negative anomaly of the MBA. These different results support the presence of an off-axis thermal anomaly located below the southern flank of the Sheba ridge. The magnetic anomalies and spreading asymmetry reveal that the location of this thermal anomaly might be relatively recent (~ 10 Ma

  14. Reduced to pole long-wavelength magnetic anomalies of Africa and Europe

    NASA Technical Reports Server (NTRS)

    Olivier, R.; Hinze, W. J.; Vonfrese, R. R. B.

    1985-01-01

    To facilitate analysis of the tectonic framework for Africa, Europe and adjacent marine areas, MAGSAT scalar anomaly data are differentially reduced to the pole and compared to regional geologic information and geophysical data including surface free-air gravity anomaly data upward continued to satellite elevation (350 km) on a spherical Earth. Comparative analysis shows magnetic anomalies correspond with both ancient as well as more recent Cenozoic structural features. Anomalies associated with ancient structures are primarily caused by intra-crustal lithologic variations such as the crustal disturbance associated with the Bangui anomaly in west-central Africa. Anomalies correlative with Cenozoic tectonic elements appear to be related to Curie isotherm perturbations. A possible example of the latter is the well-defined trend of magnetic minima that characterize the Alphine orogenic belt from the Atlas mountains to Eurasia. In contrast, a well-defined magnetic satellite minimum extends across the stable craton from Finland to the Ural mountains. Prominent magnetic maxima characterize the Arabian plate, Iceland, the Kursk region of the central Russian uplift, and generally the Precambrian shields of Africa.

  15. Reduced to Pole Long-wavelength Magnetic Anomalies of Africa and Europe

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator); Olivier, R.

    1984-01-01

    To facilitate analysis of the tectonic framework for Africa, Europe and adjacent marine areas, MAGSAT scalar anomaly data are differentially reduced to the pole and compared to regional geologic information and geophysical data including surface free-air gravity anomaly data upward continued to satellite elevation (350 km) on a spherical Earth. Comparative analysis shows magnetic anomalies correspond with both ancient as well as more recent Cenozoic structural features. Anomalies associated with ancient structures are primarily caused by intra-crustal lithologic variations such as the crustal disturbance associated with the Bangui anomaly in west-central Africa. Anomalies correlative with Cenozoic tectonic elements appear to be related to Curie isotherm perturbations. A possible example of the latter is the well-defined trend of magnetic minima that characterize the Alpine orogenic belt from the Atlas mountains to Eurasia. In contrast, a well-defined magnetic satellite minimum extends across the stable craton from Finland to the Ural mountains. Prominent magnetic maxima characterize the Arabian plate, Iceland, the Kursk region of the central Russian uplift, and generally the Precambrian shields of Africa.

  16. Satellite-Altitude Geopotential Study of the Kursk Magnetic Anomaly (KMA)

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; Kim, Hyung Rae; vonFrese, Ralph R. B.; Potts, Laramie V.; Frawley, James J.

    2003-01-01

    With the successful launch of the Orsted, SAC-C and CHAMP satellites we are able to make both magnetic and gravity anomaly maps of the Earth's crust; magnetic from all three missions and gravity with CHAMP. We have used these data to study the KMA area of Russia. This is an important region for several reasons: (1) we have already made satellite magnetic anomaly maps of this region and they can be integrated with the gravity data from CHAMP for a comprehensive interpretation; (2) KMA contains the largest know reserves of iron-ore in the world; and (3) there are significant ground truth data available for this region from aeromagnetic, balloon surveys and geophysical mapping, including extensive rock magnetic/paleo-magnetic and geologic studies. Utilizing the gravity observations, collocated with the magnetic data enabled us to make a joint interpretation. While there is a high amplitude magnetic anomaly recorded over the KMA the gravity anomaly at satellite altitude revealed by CHAMP is only around 3-6 mGal but is not centered on the magnetic high. This would indicate that despite the fact that in the region of the KMA the rocks have a higher percentage of iron than in the surrounding formations the entire area is Archean-Proterozoic in age and therefore very dense.

  17. Interpretation of the magnetic anomaly over the Omaha Oil Field, Gallatin County, Illinois

    SciTech Connect

    Sparlin, M.A. ); Lewis, R.D. . Waterways Experiment Station)

    1994-07-01

    A 40 nanoTesla (nT) magnetic anomaly identified in an aeromagnetic survey over southern Illinois contours as a localized magnetic high on the west flank of a regional magnetic low. This magnetic anomaly is generally coincident with the Omaha Oil Field in northwest Gallatin County, Illinois. It was initially assumed that cultural sources of steel associated with this oil field were the primary source of the magnetic feature; however, similar oil fields overflown by the survey do not exhibit magnetic anomalies in the data set. The Luther Rister et ux [number sign]1 well, drilled near the apex of the Omaha structural dome, encountered two zones of ultramafic intrusive rock containing 9.0% by volume magnetite. These intrusives were identified to be alnoeites which are a class of mantle-derived ultramafic rock that can be associated with the incipient stages of crustal rifting. A ground magnetic survey verified the presence of the anomaly, and provided detailed data for 3-D modeling of the source. Petrophysical evaluations, magnetic susceptibility measurements and thin section modal analysis were made on drill cuttings from the ultramafic intrusives encountered in the Luther Rister [number sign]1 well. These measurements were made to constrain the 3-D magnetic modeling by the petrophysical characteristics of the source. After removal of the regional magnetic field, the resulting 140 nT residual magnetic anomaly was successfully modeled using two ultramafic sills with an igneous feeder plug. The two igneous sills adequately account for the structural closure exhibited in the Omaha Oil Field and raise the interesting possibility of other hydrocarbon trapping structures generated by intrusives emplaced into the sedimentary section.

  18. Analysis of Marine Magnetic Field Anomaly Profiles of the West Philippine Basin to Infer Its Style of Opening

    NASA Astrophysics Data System (ADS)

    Choe, Hanjin; Lee, Sang-Mook

    2016-04-01

    The West Philippine Basin (WPB), located on the Philippine Sea Plate, is considered to have undergone a rapid opening during the Eocene. However, the detailed opening of the WPB and its relationship with surrounding basins were rather uncertain in the existing plate reconstruction models because of their sparse coverage. This study re-examines the opening using the sea surface marine magnetic anomaly data that were added to the database over the last several decades. Detailed rotation poles were computed different stages using Gplates program. According to our analysis, WPB started to open in NE-SW direction as early as the early Eocene (> 53 Ma) but changed gradually to N-S direction around 45 Ma. It appears that the spreading was not uniform, evidenced by jumps in the spreading axis and along-axis discontinuities with an average speed greater than previous reported. The spreading appears to have slowed down around 37 Ma and finally ceasing at around 25 Ma. The spreading was not symmetric between north and south, and this apparent asymmetry becomes notable towards the end of the opening.

  19. Weak extremely-low-frequency magnetic field-induced regeneration anomalies in the planarian, Dugesia tigrina

    SciTech Connect

    Jenrow, K.A.; Smith, C.H.; Liboff, A.R.

    1996-12-31

    The authors recently reported that cephalic regeneration in the planarian Dugesia tigrina was significantly delayed in populations exposed continuously to combined parallel DC and AC magnetic fields. This effect was consistent with hypotheses suggesting an underlying resonance phenomenon. The authors report here, in a parallel series of investigations on the same model system, that the incidence of regeneration anomalies presenting as tumor-like protuberances also increases significantly (P < .001) in association with exposure to weak 60 Hz magnetic fields, with peak intensities ranging between 1.0 and 80.0 {micro}T. These anomalies often culminate in the complete disaggregation of the organism. Similar to regeneration rate effects, the incidence of regeneration anomalies is specifically dependent upon the planaria possessing a fixed orientation with respect to the applied magnetic field vectors. However, unlike the regeneration rate effects, the AC magnetic field alone, in the absence of any measurable DC field, is capable of producing these anomalies. Moreover, the incidence of regeneration anomalies follows a clear dose-response relationship as a function of AC magnetic field intensity, with the threshold for induced electric field intensity estimated at 5 {micro} V/m. The addition of either 51.1 or 78.4 {micro}T DC magnetic fields, applied in parallel combination with the AC field, enhances the appearance of anomalies relative to the 60 Hz AC field alone, but only at certain AC field intensities. Thus, whereas the previous study of regeneration rate effects appeared to involve exclusively resonance interactions, the regeneration anomalies reported here appear to result primarily from Faraday induction coupling.

  20. Interaction of Solar Wind and Magnetic Anomalies - Modelling from Moon to Mars

    NASA Astrophysics Data System (ADS)

    Alho, Markku; Kallio, Esa; Wedlund, Cyril Simon; Wurz, Peter

    2015-04-01

    The crustal magnetic anomalies on both the Moon and Mars strongly affect the local plasma environment. On the Moon, the impinging solar wind is decelerated or deflected when interacting with the magnetic field anomaly, visible in the lunar surface as energetic neutral atom (ENA) emissions or as reflected protons, and may play a part in the space weathering of the lunar soil. At Mars, the crustal magnetic fields have been shown to be associated with, e.g., enhanced electron scale heights and modified convection of ionospheric plasma, resulting in the plasma environment being dominated by crustal magnetic fields up to altitudes of 400km. Our previous modelling work suggested that Hall currents are a dominant feature in a Moon-like magnetic anomaly interaction at scales at or below the proton inertial length. In this work we study the solar wind interaction with magnetic anomalies and compare the plasma environments of a Moon-like anomaly with a Mars-like anomaly by introducing an ionosphere and an exosphere to probe the transition from an atmosphere-less anomaly interaction to an ionospheric one. We utilize a 3D hybrid plasma model, in which ions are modelled as particles while electrons form a charge-neutralizing massless fluid. The hybrid model gives a full description of ion kinetics and associated plasma phenomena at the simulation region ranging from instabilities to possible reconnection. The model can thus be used to interpret both in-situ particle and field observations and remotely-sensed ENA emissions. A self-consistent ionosphere package for the model is additionally in development.

  1. Spherical earth gravity and magnetic anomaly analysis by equivalent point source inversion

    NASA Technical Reports Server (NTRS)

    Von Frese, R. R. B.; Hinze, W. J.; Braile, L. W.

    1981-01-01

    To facilitate geologic interpretation of satellite elevation potential field data, analysis techniques are developed and verified in the spherical domain that are commensurate with conventional flat earth methods of potential field interpretation. A powerful approach to the spherical earth problem relates potential field anomalies to a distribution of equivalent point sources by least squares matrix inversion. Linear transformations of the equivalent source field lead to corresponding geoidal anomalies, pseudo-anomalies, vector anomaly components, spatial derivatives, continuations, and differential magnetic pole reductions. A number of examples using 1 deg-averaged surface free-air gravity anomalies of POGO satellite magnetometer data for the United States, Mexico, and Central America illustrate the capabilities of the method.

  2. The mineralogy of global magnetic anomalies. [rock magnetic signatures and MAGSAT geological, and gravity correlations in West Africa

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E. (Principal Investigator)

    1982-01-01

    Problems with the Curie balance, which severely hindered the acquisition of data, were rectified. Chemical analytical activities are proceeding satisfactorily. The magnetization characteristics of metamorphic suites were analyzed and susceptibility data for a wide range of metamorphic and igneous rocks. These rock magnetic signatures are discussed as well as the relationships between geology, gravity and MAGSAT anomalies of West Africa.

  3. Application of Magsat lithospheric modeling in South America. Part 1: Processing and interpretation of magnetic and gravity anomaly data

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W.; Vonfrese, R. R. B. (Principal Investigator); Keller, G. R.; Lidiak, E. G.

    1984-01-01

    Scalar magnetic anomaly data from MAGSAT, reduced to vertical polarization and long wavelength pass filtered free air gravity anomaly data of South America and the Caribbean are compared to major crustal features. The continental shields generally are more magnetic than adjacent basins, oceans and orogenic belts. In contrast, the major aulacogens are characterized by negative anomalies. Spherical earth magnetic modeling of the Amazon River and Takatu aulacogens in northeastern South America indicates a less magnetic crust associated with the aulacogens. Spherical earth modeling of both positive gravity and negative magnetic anomalies observed over the Mississippi Embayment indicate the presence of a nonmagnetic zone of high density material within the lower crust associated with the aulacogen. The MAGSAT scalar magnetic anomaly data and available free air gravity anomalies over Euro-Africa indicate several similar relationships.

  4. Scalar magnetic anomaly maps of Earth derived from POGO and Magsat data

    NASA Technical Reports Server (NTRS)

    Arkani-Hamed, Jafar; Langel, Robert A.; Purucker, Mike

    1994-01-01

    A new Polar Orbit Geophysical Observatory (POGO) scalar magnetic anomaly map at 400 km altitude is presented which consists of spherical harmonics of degree 15-60. On the basis of the common features of this map with two new Magsat anomaly maps, dawn and dusk, two scalar magnetic anomaly maps of the Earth are presented using two selection criteria with different levels of stringency. These selection criteria suppress the noncrustal components of the original maps by different amounts. The more stringent selection criteria seek to eliminate as much contamination as possible, at the expense of suppressing some anomaly signal. This map is represented by spherical harmonics of degree 15-60. The less stringent selection criteria seek to retain as much crustal signal as possible, at the expense of also retaining some contaminating fields. This map is represented by spherical harmonics of degree 15-65. The resulting two maps are highly correlated with degree correlation coefficients greater than 0.8.

  5. Intermediate-wavelength magnetic anomaly field of the North Pacific and posible source distributions

    NASA Technical Reports Server (NTRS)

    Labrecque, J. L.; Cande, S. C.; Jarrard, R. D.

    1985-01-01

    A technique that eliminates external field sources and the effects of strike aliasing was used to extract from marine survey data the intermediate wavelength magnetic anomaly field for (B) in the North Pacific. A strong correlation exists between this field and the Magsat field although a directional sensitivity in the Magsat field can be detected. The intermediate wavelength field is correlated to tectonic features. Island arcs appear as positive anomalies of induced origin likely due to variations in crustal thickness. Seamount chains and oceanic plateaus also are manifested by strong anomalies. The primary contribution to many of these anomalies appears to be due to a remanent magnetization. The source parameters for the remainder of these features are presently unidentified ambiguous. Results indicate that the sea surface field is a valuable source of information for secular variation analysis and the resolution of intermediate wavelength source parameters.

  6. The intermediate wavelength magnetic anomaly field of the north Pacific and possible source distributions

    NASA Technical Reports Server (NTRS)

    Labrecque, J. L.; Cande, S. C.; Jarrard, R. D. (Principal Investigator)

    1983-01-01

    A technique that eliminates external field sources and the effects of strike aliasing was used to extract from marine survey data the intermediate wavelength magnetic anomaly field for (B) in the North Pacific. A strong correlation exists between this field and the MAGSAT field although a directional sensitivity in the MAGSAT field can be detected. The intermediate wavelength field is correlated to tectonic features. Island arcs appear as positive anomalies of induced origin likely due to variations in crustal thickness. Seamount chains and oceanic plateaus also are manifested by strong anomalies. The primary contribution to many of these anomalies appears to be due to a remanent magnetization. The source parameters for the remainder of these features are presently unidentified ambiguous. Results indicate that the sea surface field is a valuable source of information for secular variation analysis and the resolution of intermediate wavelength source parameters.

  7. Soil Magnetism and Magnetic Anomalies at the Marshall's Pen Archaeological Site, Mandeville, Jamaica

    NASA Astrophysics Data System (ADS)

    Figueroa, E.; Sternberg, R. S.; Delle, J. A.; Lawrence, N. D.; McAdoo, B. G.; Savina, M. E.

    2002-05-01

    Marshall's Pen, a 1000-acre parcel of land in Mandeville, Jamaica, underlain by limestone bedrock and bauxite soils, served as a coffee plantation in the early 19th century. Two to three hundred slaves of African descent worked the plantation from AD 1802 until slavery was abolished in Jamaica in 1838. The goal of the archaeological program at Marshall's Pen is to complement what little is known about Jamaican slave society from the historical record. Geophysical prospection was conducted at Marshall's Pen by ten undergraduate students as part of a Keck Geology Consortium project in the summer of 1999. In the slaves' village consisting of living and domestic labor areas, G858 cesium vapor magnetometer readings were taken every 0.1 seconds along 49 profiles, each 50 m long and spaced 1 meter apart, and magnetic susceptibility readings were taken at 1-meter intervals. Seven significant magnetic anomalies (up to 100 nT peak-to-peak) were detected in the village. Two of these were found to be caused by a buried machete and an iron woodworking tool. Three anomalies were associated with a large area of black, burned soil. Archaeological testing in this area produced partially carbonized seeds, charcoal, ceramics that were smudged after manufacture, and cutlery; this evidence suggests a domestic kitchen area. In situ susceptibility readings were zero on bedrock and low on the bauxite soils. Susceptibility readings generally correlated with the magnetics, to values as high as 50 (x 10-6, volume specific SI) in the ``kitchen'' area, suggesting a source in the susceptibility contrast for these magnetic anomalies. Soil samples were collected from the bauxite outside the village, and from the village area in the summer of 2001; ten village sites were sampled away from the kitchen area, and four from the kitchen area. Five samples from each site were boxed, weighed, and measured for laboratory susceptibility measurements. Eleven samples outide the village had a geometric mean

  8. Magnetic anomalies in east Pacific using MAGSAT data

    NASA Technical Reports Server (NTRS)

    Harrison, C. G. A. (Principal Investigator)

    1983-01-01

    Methods for solving problems encountered in separating the core field from the crustal field are summarized as well as those methods developed for inverting total magnetic field data to obtain source functions for oceanic areas. Accounting for magnetization contrasts and the magnetization values measured in rocks of marine origin are also discussed.

  9. MAGSAT investigation of crustal magnetic anomalies in the eastern Indian Ocean

    NASA Technical Reports Server (NTRS)

    Sailor, R. V.; Lazarewicz, A. R.

    1983-01-01

    Crustal magnetic anomalies in a region of the eastern Indian Ocean were studied using data from NASA's MAGSAT mission. The investigation region (0 deg to 50 deg South, 75 to 125 deg East) contains several important tectonic features, including the Broken Ridge, Java Trench, Ninetyeast Ridge, and Southeast Indian Ridge. A large positive magnetic anomaly is associated with the Broken Ridge and smaller positive anomalies correlate with the Ninetyeast Ridge and western Australia. Individual profiles of scalar data (computed from vector components) were considered to determine the overall data quality and resolution capability. A set of MAGSAT ""Quiet-Time'' data was used to compute an equivalent source crustal magnetic anomaly map of the study region. Maps of crustal magnetization and magnetic susceptibility were computed from the equivalent source dipoles. Gravity data were used to help interpretation, and a map of the ratio of magnetization to density contrasts was computed using Poisson's relation. The results are consistent with the hypothesis of induced magnetization of a crustal layer having varying thickness and composition.

  10. Why are There So Few Magnetic Anomalies in Martian Lowlands and Basins?

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.; Aharonson, Oded; Banerdt, W. Bruce; Dombard, Andrew J.; Frey, Herbert V.; Golombek, Matthew P.; Hauck, Steven A., II; Head, James W., III; Johnson, Catherine L.; McGovern, Patrick J.

    2003-01-01

    The discovery of large areas of strongly magnetized crust on Mars [1,2] provides important information on the timing of both crustal and deeper interior processes on that planet. Critical to an understanding of that timing, as well as to the processes that have contributed to the magnetization and demagnetization of crustal materials, is the geographical distribution of magnetic anomalies discernible from spacecraft orbit. The paucity of resolved magnetic anomalies in the northern lowlands and within and surrounding the best-preserved major impact basins has been noted since the crustal field was first globally mapped [1], but no straightforward explanation of that full pattern has yet been offered. Here we suggest that ancient hydrothermal alteration of magnetic carriers in Martian lowlands and basins may have contributed to the magnetization distribution observed today.

  11. Study on crustal magnetic anomalies and Curie surface in Southeast Tibet

    NASA Astrophysics Data System (ADS)

    Gao, Guoming; Kang, Guofa; Bai, Chunhua; Wen, Limin

    2015-01-01

    In this paper, the Potsdam model POMME-6.2 is used to investigate the distributions of crustal magnetic anomalies and Curie surface in Southeast Tibet. The Curie surface is compared with the regional heat flow, Bouguer anomaly, Moho depth, and seismicity. The results show that the magnetic anomalies and Curie surface are both consistent with the geological structure. Sichuan Basin exhibits a high positive anomaly, while orogenic belts such as the Longmenshan, northwestern Sichuan, and western Yunnan, exhibit weak positive or negative anomalies. The distribution of magnetic anomaly confirms that escape flow from east Tibet branches into northeastward part and southward part on west Sichuan Basin, due to resistance by the rigid basin. The depth of Curie surface ranges from 20 to 34 km. The Curie surface beneath the Longmenshan, Xiaojiang and Lijiang-Xiaojinhe faults is shallow, with the uplift strike consistent with the faults. The Curie surface beneath Sichuan Basin and the central Bayan Har massif is deep, with sheet-like depressions. Strong earthquakes primarily occurred in the areas with the uplift of Curie surface. The heat flow values near Tengchong, Lijiang, Dali and Kunming are high and the Curie surface there is shallow.

  12. Interpretations of gravity and magnetic anomalies in the Songliao Basin with Wavelet Multi-scale Decomposition

    NASA Astrophysics Data System (ADS)

    Li, Changbo; Wang, Liangshu; Sun, Bin; Feng, Runhai; Wu, Yongjing

    2015-09-01

    In this paper, we introduce the method of Wavelet Multi-scale Decomposition (WMD) combined with Power Spectrum Analysis (PSA) for the separation of regional gravity and magnetic anomalies. The Songliao Basin is situated between the Siberian Plate and the North China Plate, and its main structural trend of gravity and magnetic anomaly fields is NNE. The study area shows a significant feature of deep collage-type construction. According to the feature of gravity field, the region was divided into five sub-regions. The gravity and magnetic fields of the Songliao Basin were separated using WMD with a 4th order separation. The apparent depth of anomalies in each order was determined by Logarithmic PSA. Then, the shallow high-frequency anomalies were removed and the 2nd-4th order wavelet detail anomalies were used to study the basin's major faults. Twenty-six faults within the basement were recognized. The 4th order wavelet approximate anomalies were used for the inversion of the Moho discontinuity and the Curie isothermal surface.

  13. Ridge segmentation and the magnetic structure of the Southern Mid-Atlantic Ridge 26°S and 31°-35°S: Implications for magmatic processes at slow spreading centers

    NASA Astrophysics Data System (ADS)

    Weiland, Charles M.; MacDonald, Ken C.; Grindlay, Nancy R.

    1996-04-01

    Along-axis profiles of three-dimensional magnetic inversions for the Mid-Atlantic Ridge (MAR) 31°-35°S show low magnetization near the middle of ridge segments and high magnetization at the segment tips for three adjacent spreading segments; thus there is an inverse relation between axial magnetization and axial topography. The ridge segment at 26°S on the MAR has the same inverse relationship between magnetization and topography. The common occurrence of this relationship suggests that it reflects a fundamental process of crustal accretion at the MAR. We analyze the rock magnetic properties from 42 locations within the four ridge segments in the South Atlantic to constrain the inherent trade-off between source intensity and source thickness in the magnetization model. The natural remanent magnetization (NRM) intensities from the four ridge segments, averaged together, correlate with the magnetic inversion profiles. This finding implies that changes in the magnetization of the extrusives may account for much of the observed magnetic anomaly amplitude variation. A direct correlation of FeO content and magnetization suggests that magnetic anomaly amplitudes may be an indicator of FeTi-rich basalts at the slow spreading MAR, even though the iron content of the basalts from high magnetization areas is not as high as observed at Pacific spreading centers. Despite the different magma plumbing systematics of the Pacific spreading centers and the MAR, it appears that the segment-scale magma system of the MAR also results in segment-scale crustal magnetization variations. Further evidence that the axial magnetic variations result from source intensity variations is that older isochrons have higher intensities near the ridge-discontinuities, similar to the behavior on-axis. Between 0 and 5 Ma the decay in magnetization is ˜50% independent of location within a spreading segment.

  14. Gravity and magnetic anomaly modeling and correlation using the SPHERE program and Magsat data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J. (Principal Investigator); Vonfrese, R. R. B.

    1980-01-01

    The spherical Earth inversion, modeling, and contouring software were tested and modified for processing data in the Southern Hemisphere. Preliminary geologic/tectonic maps and selected cross sections for South and Central America and the Caribbean region are being compiled and as well as gravity and magnetic models for the major geological features of the area. A preliminary gravity model of the Andeas Beniff Zone was constructed so that the density columns east and west of the subducted plates are in approximate isostatic equilibrium. The magnetic anomaly for the corresponding magnetic model of the zone is being computed with the SPHERE program. A test tape containing global magnetic measurements was converted to a tape compatible with Purdue's CDC system. NOO data were screened for periods of high diurnal activity and reduced to anomaly form using the IGS-75 model. Magnetic intensity anomaly profiles were plotted on the conterminous U.S. map using the track lines as the anomaly base level. The transcontinental magnetic high seen in POGO and MAGSAT data is also represented in the NOO data.

  15. Craton vs. rift uppermost mantle contributions to magnetic anomalies in the United States interior

    NASA Astrophysics Data System (ADS)

    Friedman, S. A.; Feinberg, J. M.; Ferré, E. C.; Demory, F.; Martín-Hernández, F.; Conder, J. A.; Rochette, P.

    2014-06-01

    The interpretation of satellite magnetic information (Magsat, Oersted, CHAMP, Swarm) requires the understanding of the mineralogy of crustal and mantle sources. Also, spectral analysis of magnetic data over forearcs and cratons calls for upper mantle contribution. The prospect of such a contribution contradicts the view that the mantle is too hot and its magnetism is too weak to influence magnetic anomalies. Here we examine the rock magnetic properties of fresh mantle xenoliths from four settings across the United States: phlogopite-spinel dunites from the Bearpaw Mountains, Montana, and lherzolites/harzburgites from San Carlos, Arizona; Kilbourne Hole, New Mexico; and Knippa, Texas. Paleomagnetic results show single-component natural remanent magnetizations (NRMs), which, combined with optical and secondary electron microscopy support the lack of post-eruption alteration and absence of host-rock contamination. The NRM carriers include magnetite at Bearpaw Mountain and San Carlos, and pyrrhotite at Kilbourne Hole and Knippa. These four areas show continental crust of distinct thicknesses and various geotherms. The potential mantle contribution to magnetic anomalies is forward modeled using crustal thickness, current geotherm and average magnetic properties of xenoliths. The San Carlos and Kilbourne Hole mantle, situated near the Rio Grande Rift is too hot and its magnetism is too weak to contribute to anomalies. The sulfide-dominated assemblage at Knippa does not support magnetization at mantle depths. In contrast, the Bearpaw Mountains combine a relatively cold geotherm (craton) and abundance of magnetite formed at mantle depth. This cratonic mantle, metasomatized by fluids from the Farallon plate, may contribute to long wavelength magnetic anomalies.

  16. Processing and Analysis of Near-Seafloor Magnetic Anomalies around Futuna Island, SW Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Szitkar, F.; Dyment, J.; Fouquet, Y.; Choi, Y.

    2011-12-01

    In September 2010, cruise Futuna of R/V L'Atalante collected near-seafloor magnetic data with AUV Aster-X (70 m asf) and Deep-Sea Submersible (DSS) Nautile (2-20 m asf) on several volcanic systems around Futuna Island, SW Pacific Ocean. Here we present the data, the method of analysis, and a first geological interpretation. Unlike a ship, a submersible (or an AUV) cannot tow a magnetometer due to the close proximity of the seafloor. Instead, the magnetometer is rigidly fixed on the submersible, which magnetization affects the magnetic measurements. A vector magnetometer (i.e. three orthogonal fluxgate sensors) measures the field three components in a referential linked to the submarine, a requirement to determine and correct the magnetization of the submersible, The remanent magnetization vector (3 components) and the magnetic susceptibility tensor (9 coefficients) of the submersible are estimated by inverting magnetic data collected on calibration loops, far from both the ship and the seafloor, during the descent (ascent) of the submersible at the beginning (end) of the dives. For this estimation, the ambient field is assumed to be the IGRF, the departures from this assumption reflecting the magnetization of the submersible. The twelve coefficients are inverted from the loop data by a least square method, regularized by a dumping factor to account for the limited pitch and roll values sampled by the submersible. Once determined, these coefficients are used to reduce the magnetic data acquired during the whole dive for the magnetic effect of the submersible, the resulting three component anomalies being rotated to the geographic reference frame as well. The resulting anomalies acquired by the AUV on regularly-spaced tracks are gridded and reduced to the pole such as the resulting anomalies are located on the top of their causative sources. They are further inverted to equivalent magnetization using the high-resolution topography acquired by the AUV. The anomalies

  17. Lunar Ion Transport Near Magnetic Anomalies: Possible Implications for Swirl Formation

    NASA Technical Reports Server (NTRS)

    Keller, J. W.; Killen, R. M.; Stubbs, T. J.; Farrell, W. M.; Halekas, J. S.

    2011-01-01

    The bright swirling features on the lunar surface in areas around the Moon but most prominently at Reiner Gamma, have intrigued scientists for many years. After Apollo and later Lunar Prospector (LP} mapped the Lunar magnetic fields from orbit, it was observed that these features are generally associated with crustal magnetic anomalies. This led researchers to propose a number of explanations for the swirls that invoke these fields. Prominent among these include magnetic shielding in the form of a mini-magnetosphere which impedes space weathering by the solar wind, magnetically controlled dust transport, and cometary or asteroidal impacts that would result in shock magnetization with concomitant formation ofthe swirls. In this presentation, we will consider another possibility, that the ambient magnetic and electric fields can transport and channel secondary ions produced by micrometeorite or solar wind ion impacts. In this scenario, ions that are created in these impacts are under the influence of these fields and can drift for significant distances before encountering the magnetic anomalies when their trajectories are disrupted and concentrated onto nearby areas. These ions may then be responsible for chemical alteration of the surface leading either to a brightening effect or a disruption of space weathering processes. To test this hypothesis we have run ion trajectory simulations that show ions from regions about the magnetic anomalies can be channeled into very small areas near the anomalies and although questions remain as to nature of the mechanisms that could lead to brightening of the surface it appears that the channeling effect is consistent with the existence of the swirls.

  18. A tale of two anomalies: Depletion, dispersion, and the connection between the stellar lithium spread and inflated radii on the pre-main sequence

    SciTech Connect

    Somers, Garrett; Pinsonneault, Marc H. E-mail: pinsono@astronomy.ohio-state.edu

    2014-07-20

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T{sub eff} is nearly universal, and sets in by ∼200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  19. A Tale of Two Anomalies: Depletion, Dispersion, and the Connection between the Stellar Lithium Spread and Inflated Radii on the Pre-main Sequence

    NASA Astrophysics Data System (ADS)

    Somers, Garrett; Pinsonneault, Marc H.

    2014-07-01

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T eff is nearly universal, and sets in by ~200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  20. Hydrology in the Durius Valles Region: Evaluation of Possible Correlation with Volcanism and Magnetic Anomalies

    NASA Technical Reports Server (NTRS)

    Cabrol, Natalie A.; Marinangeli, Lucia; Grin, Edmond A.

    2000-01-01

    We envision the contribution of subglacial flows, hydrothermalism and sapping in the Durius Valles system and the consequences in term of climate on Mars in recent geological times. We evaluate the possible correlation of the hydrology with volcanism and magnetic anomalies.

  1. Curie isotherm map of Scotia Arc from near surface magnetic anomaly data

    NASA Astrophysics Data System (ADS)

    Catalán, Manuel

    2016-04-01

    The opening of the Drake Passage, situated between South America and Antarctica, represents the final stage of the fragmentation of Gondwana supercontinent. It led to the Scotia Arc formation, bordering the Scotia Sea, which is surrounded by fragments of the former continental connection. It is currently composed of Scotia and Sandwich Plates. Shackleton Fracture Zone constitutes its sinistral transpressive western boundary and it is a key structure that accommodates former Phoenix and Scotia Plates' differential movement. The formation of the Drake Passage and the Scotia Sea is considered of great importance to ocean circulation, as it allows the establishment of the Antarctic Circumpolar Current that isolated the Antarctic continent, with strong implications for climate and global changes. Thermal structure of the Earth's crust is one of the main parameters controlling geodynamic processes. There is few information regarding heat flow values on Scotia arc. These values are mainly located in its westernmost, southern and easternmost part, which are not enough to extract conclusions regarding lithospheric thickness variations and asthenospheric flow. Taking advantage of the World Digital Magnetic Anomaly Map Project's compilation we have extracted magnetic anomaly data which fall inside the Scotia Arc and surrounding areas. This magnetic anomaly picture provides the best representation of magnetic properties to date. We propose to use spectral methods on this regional magnetic compilation to obtain depth to the bottom of magnetic sources as a proxy to infer Curie depth and heat flow distribution in the Scotia Sea.

  2. Comparison of Magnetic Anomalies of Lithospheric Origin Measured by Satellite and Airborne Magnetometers over Western Canada

    NASA Technical Reports Server (NTRS)

    Langel, R. A.; Coles, R. L.; Mayhew, M. A.

    1979-01-01

    Crustal magnetic anomaly data from the OGO 2, 4 and 6 (Pogo) satellites are compared with upward-continued aeromagnetic data between 50 deg -85 deg N latitude and 220 deg - 260 deg E longitude. Agreement is good both in anomaly location and in amplitude, giving confidence that it is possible to proceed with the derivation and interpretation of satellite anomaly maps in all parts of the globe. The data contain a magnetic high over the Alpha ridge suggesting continental composition and a magnetic low over the southern Canada basin and northern Canadian Arctic islands (Sverdrup basin). The low in the Sverdrup basin corresponds to a region of high heat flow, suggesting a shallow Curie isotherm. A ridge of high field, with two distinct peaks in amplitude, is found over the northern portion of the platform deposits and a relative high is located in the central portion of the Churchill province. No features are present to indicate a magnetic boundary between Slave and Bear provinces, but a trend change is evident between Slave and Churchill provinces. South of 60 deg latitude a broad magnetic low is located over very thick (40-50 km) crust, interpreted to be a region of low magnetization.

  3. Three-dimensional inverse modelling of magnetic anomaly sources based on a genetic algorithm

    NASA Astrophysics Data System (ADS)

    Montesinos, Fuensanta G.; Blanco-Montenegro, Isabel; Arnoso, José

    2016-04-01

    We present a modelling method to estimate the 3-D geometry and location of homogeneously magnetized sources from magnetic anomaly data. As input information, the procedure needs the parameters defining the magnetization vector (intensity, inclination and declination) and the Earth's magnetic field direction. When these two vectors are expected to be different in direction, we propose to estimate the magnetization direction from the magnetic map. Then, using this information, we apply an inversion approach based on a genetic algorithm which finds the geometry of the sources by seeking the optimum solution from an initial population of models in successive iterations through an evolutionary process. The evolution consists of three genetic operators (selection, crossover and mutation), which act on each generation, and a smoothing operator, which looks for the best fit to the observed data and a solution consisting of plausible compact sources. The method allows the use of non-gridded, non-planar and inaccurate anomaly data and non-regular subsurface partitions. In addition, neither constraints for the depth to the top of the sources nor an initial model are necessary, although previous models can be incorporated into the process. We show the results of a test using two complex synthetic anomalies to demonstrate the efficiency of our inversion method. The application to real data is illustrated with aeromagnetic data of the volcanic island of Gran Canaria (Canary Islands).

  4. New Clues on the Source of the Central Magnetic Anomaly at Haughton Impact Structure, Canada

    NASA Astrophysics Data System (ADS)

    Quesnel, Y.; Rochette, P.; Gattacceca, J.; Osinski, G. R.

    2013-12-01

    The 23 km-diameter Haughton impact structure, located on Devon Island, Nunavut, Canada, is one of the best-preserved medium-size complex impact structures on Earth. The impact occurred ~39 Ma ago into a target formation composed of an ~2-km thick sequence of Lower Paleozoic sedimentary rocks of the Arctic Platform overlying Precambrian metamorphic basement of the Canadian Shield (Osinski et al., 2005). Clast-rich carbonate impact melt rocks fill the crater and impact-generated hydrothermal activity took place, but since then no significant geological event has affected the area. A 900 nT-amplitude magnetic anomaly with a wavelength of about 3 km is observed at the center of the crater (Pohl et al., 1988). Using high-resolution ground magnetic survey and magnetic property measurements on rock samples from inside and outside the structure, Quesnel et al. (2013) concluded that the source for this anomaly may correspond to uplifted and hydrothermally-aletered basement rocks. Hydrothermal activity can increase rock magnetization intensity by crystallization of magnetic minerals, such as magnetite and/or pyrrhotite. Here, we present the results of a new ground magnetic survey and electrical resistivity soundings conducted around the maximum of the magnetic anomaly. Drilling, with depths ranging from 5 m to 13 m was also conducted at three locations in the same area to ground truth the interpretation of geophysical data. The maximum of the magnetic anomaly is characterized by a ~50 m2 area of strong vertical magnetic gradient and low electrical resistivity, while the surroundings show weak gradient and large resistivity. Two drill holes into this localized area show about 6 m of sandy material with some more magnetic layers at about 5 m depth overlying a greenish impact melt breccia with very abundant and large clasts. Recovery in the first 9 meters is very poor, but down hole magnetic gradient measurement confirms the near 6 meter magnetic layer. A third hole was drilled

  5. Joint geophysical investigation of a small scale magnetic anomaly near Gotha, Germany

    NASA Astrophysics Data System (ADS)

    Queitsch, Matthias; Schiffler, Markus; Goepel, Andreas; Stolz, Ronny; Guenther, Thomas; Malz, Alexander; Meyer, Matthias; Meyer, Hans-Georg; Kukowski, Nina

    2014-05-01

    In the framework of the multidisciplinary project INFLUINS (INtegrated FLUid Dynamics IN Sedimentary Basins) several airborne surveys using a full tensor magnetic gradiometer (FTMG) system were conducted in and around the Thuringian basin (central Germany). These sensors are based on highly sensitive superconducting quantum interference devices (SQUIDs) with a planar-type gradiometer setup. One of the main goals was to map magnetic anomalies along major fault zones in this sedimentary basin. In most survey areas low signal amplitudes were observed caused by very low magnetization of subsurface rocks. Due to the high lateral resolution of a magnetic gradiometer system and a flight line spacing of only 50m, however, we were able to detect even small magnetic lineaments. Especially close to Gotha a NW-SE striking strong magnetic anomaly with a length of 1.5 km was detected, which cannot be explained by the structure of the Eichenberg-Gotha-Saalfeld (EGS) fault zone and the rock-physical properties (low susceptibilities). Therefore, we hypothesize that the source of the anomaly must be related to an anomalous magnetization in the fault plane. To test this hypothesis, here we focus on the results of the 3D inversion of the airborne magnetic data set and compare them with existing structural geological models. In addition, we conducted several ground based measurements such as electrical resistivity tomography (ERT) and frequency domain electromagnetics (FDEM) to locate the fault. Especially, the geoelectrical measurements were able to image the fault zone. The result of the 2D electrical resistivity tomography shows a lower resistivity in the fault zone. Joint interpretation of airborne magnetics, geoelectrical and geological information let us propose that the source of the magnetization may be a fluid-flow induced impregnation with iron-oxide bearing minerals in the vicinity of the EGS fault plane.

  6. Wave phenomena at the Moon: interaction of solar wind with magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Sadovski, Andrei; Skalsky, Alexander

    2016-07-01

    On the first sight the lunar plasma environment seems to be very simple matter but the interaction in Moon-plasma system shows that the physical processes are complex and varied. Moreover interactions have a kinetic nature and the kinetic theory is necessary for their studying. The solar wind interaction with Moon surface has received many attention last years. The regions of enhanced crustal magnetic field (magnetic anomalies), where a magnetic field may reach till several hundred nT were found. The observations of Kaguya and Chandrayaan revealed that significant deflected proton fluxes exist over magnetic anomalies at the lunar surface. Such proton fluxes allow to imply that the magnetic anomalies may act as magnetosphere-like obstacles (mini-magnetospheres), modifying the upstream plasma. The observations of energetic neutral atoms also confirm the existence of the enhanced fluxes of deflected particles. Variety of electric fluctuations was observed during the passage of Wind spacecraft across the lunar wake: langmuir waves, electrostatic modes above electron cyclotron frequency, whistlers. The investigations by Kuncic and Cairns (2004) revealed emissions on plasma frequency and its first harmonic. Electron reflection at quasi-shock at leading edge of magnetic anomaly could drive the electric field oscillations. The generation mechanism is similar to that known for foreshock of planetary bow shock.In KAGUYA and Lunar Prospector missions the monochromatic whistlers near the Moon were observed as narrow band magnetic fluctuations with frequencies close to 1 Hz, and are mostly left-hand polarized in the spacecraft frame. We review different mechanisms for wave generation in plasma environment near such mini-magnetosphere regions.

  7. Crustal modeling of \\O rsted, Magsat and Airborne magnetic anomalies of the Weddell Sea Province

    NASA Astrophysics Data System (ADS)

    Kim, H.; von Frese, R. R.; Kim, J.

    2001-05-01

    Magnetic anomaly data from the \\O rsted and Magsat satellite missions, as well as aeromagnetic surveys involve great altitude differences and provide vastly different perspectives on the crustal features of the Weddell Sea Province. These perspectives may be integrated into effective crustal models by joint inversions of the surveys. Joint inversion helps to differentiate crustal sources that are impossible to establish from the isolated analysis of either the aeromagnetic or satellite data sets. These data sets provide unique boundary conditions for qualitative and quantitative insight on the magnetic properties of the crust. For the Weddell Sea Province, a regional magnetic minimum at satellite altitude dominates the south-central portion of the area that may reflect extensive thinning of magnetic crust from the Dufek Massif northwards to Berkner Island. The Explora and Berkner Island Anomalies appear to be linked by deep-seated, strongly magnetic crustal sources that may rise significantly in the crust and die out southwards to the Dufek Massif. The airborne and satellite magnetic data characterize the southern extent of the Antarctic Peninsula Microplate as a region of anomalously thick magnetic crust. In addition, for the Haag Nunataks and Ellsworth Mountains, these data invoke positively magnetized crustal regions with effects that are constrained in effect to die out at altitudes of about 50 km or higher.

  8. Towards developing an analytical procedure of defining the equatorial electrojet for correcting satellite magnetic anomaly data

    NASA Technical Reports Server (NTRS)

    Ravat, Dhananjay; Hinze, William J.

    1991-01-01

    Analysis of the total magnetic intensity MAGSAT data has identified and characterized the variability of ionospheric current effects as reflected in the geomagnetic field as a function of longitude, elevation, and time (daily as well as monthly variations). This analysis verifies previous observations in POGO data and provides important boundary conditions for theoretical studies of ionospheric currents. Furthermore, the observations have led to a procedure to remove these temporal perturbations from lithospheric MAGSAT magnetic anomaly data based on 'along-the-dip-latitude' averages from dawn and dusk data sets grouped according to longitudes, time (months), and elevation. Using this method, high-resolution lithospheric magnetic anomaly maps have been prepared of the earth over a plus or minus 50 deg latitude band. These maps have proven useful in the study of the structures, nature, and processes of the lithosphere.

  9. Current Role of Fetal Magnetic Resonance Imaging in Neurologic Anomalies.

    PubMed

    Lyons, Karen; Cassady, Christopher; Jones, Jeremy; Paldino, Michael; Mehollin-Ray, Amy; Guimaraes, Carolina; Krishnamurthy, Rajesh

    2015-08-01

    Magnetic resonance imaging (MRI) is used increasingly to image the fetus when important questions remain unanswered after ultrasonography, which might occur particularly with abnormal amniotic fluid volumes, difficult fetal lie or position, and maternal obesity. Ultrasonography also has limitations due to sound attenuation by bone, such as within the cranium and spine, and therefore MRI has a real advantage in delineating potentially complex neuroanatomical relationships. This article outlines current MRI protocols for evaluation of the fetal neural axis, describes indications for the use of MRI in the fetal brain and spine, and provides examples to illustrate the uses of available fetal sequences. PMID:26296481

  10. Rock magnetic characterization of faulted sediments with associated magnetic anomalies in the Albuquerque Basin, Rio Grande rift, New Mexico

    USGS Publications Warehouse

    Hudson, M.R.; Grauch, V.J.S.; Minor, S.A.

    2008-01-01

    Variations in rock magnetic properties are responsible for the many linear, short-wavelength, low-amplitude magnetic anomalies that are spatially associated with faults that cut Neogene basin sediments in the Rio Grande rift, including the San Ysidro normal fault, which is well exposed in the northern part of the Albuquerque Basin. Magnetic-susceptibility measurements from 310 sites distributed through a 1200-m-thick composite section of rift-filling sediments of the Santa Fe Group and prerift Eocene and Cretaceous sedimentary rocks document large variations of magnetic properties juxtaposed by the San Ysidro fault. Mean volume magnetic susceptibilities generally increase upsection through eight map units: from 1.7 to 2.2E-4 in the prerift Eocene and Cretaceous rocks to 9.9E-4-1.2E-3 in three members of the Miocene Zia Formation of the Santa Fe Group to 1.5E-3-3.5E-3 in three members of the Miocene-Pleistocene Arroyo Ojito Formation of the Santa Fe Group. Rock magnetic measurements and petrography indicate that the amount of detrital magnetite and its variable oxidation to maghemite and hematite within the Santa Fe Group sediments are the predominant controls of their magnetic property variations. Magnetic susceptibility increases progressively with sediment grain size within the members of the Arroyo Ojito Formation (deposited in fluvial environments) but within members of the Zia Formation (deposited in mostly eolian environments) reaches highest values in fine to medium sands. Partial oxidation of detrital magnetite is spatially associated with calcite cementation in the Santa Fe Group. Both oxidation and cementation probably reflect past flow of groundwater through permeable zones. Magnetic models for geologic cross sections that incorporate mean magnetic susceptibilities for the different stratigraphic units mimic the aeromagnetic profiles across the San Ysidro fault and demonstrate that the stratigraphic level of dominant magnetic contrast changes with

  11. Marine Magnetic Anomalies of the Northern Part of the Gulf of Aqaba, Dead Sea Rift

    NASA Astrophysics Data System (ADS)

    Al-Zoubi, A.

    2009-04-01

    MARINE MAGNETIC ANOMALIES OF THE NORTHERN PART OF THE GULF OF AQABA, DEAD SEA RIFT Al-Zoubi (1), Z. Ben-Avraham (2), T. M. Niemi (3), E. Akawi (1), G. Tibor (4), R. Al-Rzouq (1), J.K. Hall (5), A. Abueladas (1), G. Hartman (2) (1) Surveying & Geomatics Department, Al-Balqa' Applied University, Salt, Jordan (2) Department of Geophysics & Planetary Sciences, Tel-Aviv University, Tel-Aviv, Israel (3) University of Missouri-Kansas City, USA. (4) Israel Oceanographic and Limnological Research, Haifa, Israel (5) Geological Survey of Israel, Jerusalem, Israel A high-resolution marine magnetic survey in the northern part of the Gulf of Aqaba, Dead Sea Rift was carried out during October and November 2006. The survey led by an international research group (Israel, Jordan, and USA) funded by MERC, USA and aims to provide the municipalities of Aqaba and Elat a base map of active faults for seismic hazard assessment. The total magnetic intensity at sea surface was measured by a proton precession magnetometer. Diurnal magnetic variation was corrected from the data by using the observation located in southern part of Israel during the survey period. The correction of the external field variation was carried out based on the continuous magnetic observations at a reference magnetic observatory close to the survey area. For calculations of the total intensity of magnetic anomaly, the IGRF model was used as the core field model in accordance with the recommendation of the IAGA. Geomagnetic total intensity anomaly map of the study area has been produced. The magnetic anomaly map shows that there are two major magnetic trends appear in the study area. These are the magnetic high across the northwest section of the Gulf and a magnetic low across the southeast section. These two general trends are divided by a northeast-trending boundary. The magnetic map reveals a complex faults system between the deep part of the Gulf as a pull-apart basin and the on land transform fault in the Araba

  12. Magnetic anomalies on Io and their relationship to the spatial distribution of volcanic centers

    NASA Astrophysics Data System (ADS)

    Knicely, J.; Everett, M. E.; Sparks, D. W.

    2014-12-01

    The analysis of terrestrial magnetic anomalies has long proved useful for constraining crustal structure and dynamics. Here, we study Jupiter's moon, Io, using magnetics. We conduct forward modeling to make predictions of the crustal magnetic anomaly distribution on Io. Io is the most volcanic body in the solar system due to tidal heating from its Laplace resonance with Europa and Ganymede, causing extensive sulfur and silicate volcanism. We assume the magnetic susceptibility, which controls the measured magnetic signal, is controlled by temperature. Continuous overturn of the crust controls the vertical temperature profile, and local volcanic centers give the lateral temperature structure. As non-magnetic sulfur volcanism occurs at cool temperatures beneath the Curie point, it should not greatly affect the planetary magnetism and consequently is ignored in this paper. We assume that the average crustal temperatures are determined by a model of continuous burial by newly erupted material (O'Reilly and Davies 1981, Geophysical Research Letters), which put the Curie isotherm at great depth. We use a cylindrically symmetric model of the thermal evolution of the crust around an isolated volcanic center to obtain the local deviations in the thickness of the magnetizable layer. The crustal rocks are presumed to be mafic or ultramafic in composition, based on their spectral signatures, the temperature of the silicate volcanic eruptions, and their rheology as inferred from flow structures. Analysis of the 1997 Pillan eruption suggests a composition similar to lunar mare basalt or komatiite. The magnetic and thermal properties of lunar mare basalt have been well studied since the Apollo missions. Unaltered terrestrial ultramafics have been studied sufficiently to constrain their properties. A common technique of discretizing the magnetized material into prisms and summing the magnetic field of each prism as per Blakely (1995) was used to obtain an estimate of the crustal

  13. Magnetic Anomalies and Rock Magnetic Properties Related to Deep Crustal Rocks of the Athabasca Granulite Terrane, Northern Canada

    NASA Astrophysics Data System (ADS)

    Brown, L. L.; Williams, M. L.

    2010-12-01

    The Athabasca granulite terrane in northernmost Saskatchewan, Canada is an exceptional exposure of lower crustal rocks having experienced several high temperature events (ca 800C) during a prolonged period of deep-crustal residence (ca 1.0 GPa) followed by uplift and exhumation. With little alteration since 1.8 Ga these rocks allow us to study ancient lower crustal lithologies. Aeromagnetic anomalies over this region are distinct and complex, and along with other geophysical measurements, define the Snowbird Tectonic zone, stretching NE-SW across northwestern Canada, separating the Churchill province into the Hearne (mid-crustal rocks, amphibolite facies) from the Rae (lower crust rocks, granulite facies). Distinct magnetic highs and lows appear to relate roughly to specific rock units, and are cut by mapped shear zones. Over fifty samples from this region, collected from the major rock types, mafic granulites, felsic granulites, granites, and dike swarms, as well as from regions of both high and low magnetic anomalies, are being used to investigate magnetic properties. The intention is to investigate what is magnetic in the lower crust and how it produces the anomalies observed from satellite measurements. The samples studied reveal a wide range of magnetic properties with natural remanent magnetization ranging from an isolated high of 38 A/m to lows of 1 mA/m. Susceptibilities also range over several orders of magnitude, from 1 to 1 x10-4 SI. Magnetite is identified in nearly all samples using both low and high temperature measurements, but concentrations are generally very low. Hysteresis properties on 41 samples reveal nearly equal numbers of samples represented by PSD and MD grains, with a few samples (N=6) plotting in or close to the SD region. Low temperature measurements indicate that most samples contain magnetite, showing a marked Verway transition around 120K. Also identified in nearly half of the samples is pyrrhotite, noted by low temperature

  14. Effects of sporadic E-layer characteristics on spread-F generation in the nighttime ionosphere near a northern equatorial anomaly crest during solar minimum

    NASA Astrophysics Data System (ADS)

    Lee, C. C.; Chen, W. S.

    2015-06-01

    This study is to know how the characteristics of sporadic E-layer (Es-layer) affect the generation of spread-F in the nighttime ionosphere near the crest of equatorial ionization anomaly during solar minimum. The data of Es-layer parameters and spread-F are obtained from the Chungli ionograms of 1996. The Es-layer parameters include foEs (critical frequency of Es-layer), fbEs (blanketing frequency of Es-layer), and Δf (≡foEs-fbEs). Results show that the nighttime variations of foEs and fbEs medians (Δf medians) are different from (similar to) that of the occurrence probabilities of spread-F. Because the total number of Es-layer events is greater than that of spread-F events, the comparison between the medians of Es-layer parameters and the occurrence probabilities of spread-F might have a shortfall. Further, we categorize the Es-layer and spread-F events into each frequency interval of Es-layer parameters. For the occurrence probabilities of spread-F versus foEs, an increasing trend is found in post-midnight of all three seasons. The increasing trend also exists in pre-midnight of the J-months and in post-midnight of all seasons, for the occurrence probabilities of spread-F versus Δf. These demonstrate that the spread-F occurrence increases with increasing foEs and/or Δf. Moreover, the increasing trends indicate that polarization electric fields generated in Es-layer assist to produce spread-F, through the electrodynamical coupling of Es-layer and F-region. Regarding the occurrence probabilities of spread-F versus fbEs, the significant trend only appears in post-midnight of the E-months. This implies that fbEs might not be a major factor for the spread-F formation.

  15. Modeling of the Central Magnetic Anomaly at Haughton Impact Structure, Canada

    NASA Astrophysics Data System (ADS)

    Quesnel, Y.; Gattacceca, J.; Osinski, G. R.; Rochette, P.

    2011-12-01

    Located on Devon Island, Nunavut, Canada, the 23-km diameter Haughton impact structure is one of the best-preserved medium-size complex impact structures on Earth. The impact occurred ~39 Ma ago into a target formation composed of an ~2-km thick sequence of Lower Paleozoic sedimentary rocks of the Arctic Platform overlying Precambrian metamorphic basement of the Canadian Shield (Osinski et al., 2005). Clast-rich impact melt rocks line the crater and impact-induced hydrothermal activity took place, but since then no significant geological event has affected the area. In the 1980s, ground magnetic and gravity measurements were carried out within the central part of the crater (Pohl et al., 1988). A significant anomaly was discovered and coarsely modeled by a source body of simple geometry. More recently, an airborne magnetic survey delivered additional data that covered the whole crater but no modeling was done (Glass et al., 2002). Here, we present the results of a new ground magnetic survey accompanied by rock magnetic property measurements made on all samples of the crater. This has provided additional constraints to investigate the origin of this central magnetic anomaly. By conducting modeling, we have been able to reveal the geometry and volume of the source body as well as its magnetization properties. Our results suggest that the necessary magnetization intensity to account for this anomaly is too large to be associated with uplifted pre-impact target rocks. Therefore, we suggest that hydrothermal alteration could have enhanced the magnetization of the central part of this crater. References : Osinski, G. R. et al. 2005. MPS, 40:1759-1776 ; Pohl, J. et al. 1988. Meteoritics, 23:235-238 ; Glass, B. J. et al. 2002, Abstract #2008. 33th LPSC

  16. Central magnetic anomalies of Nectarian-aged lunar impact basins: Probable evidence for an early core dynamo

    NASA Astrophysics Data System (ADS)

    Hood, Lon L.

    2011-02-01

    A re-examination of all available low-altitude LP magnetometer data confirms that magnetic anomalies are present in at least four Nectarian-aged lunar basins: Moscoviense, Mendel-Rydberg, Humboldtianum, and Crisium. In three of the four cases, a single main anomaly is present near the basin center while, in the case of Crisium, anomalies are distributed in a semi-circular arc about the basin center. These distributions, together with a lack of other anomalies near the basins, indicate that the sources of the anomalies are genetically associated with the respective basin-forming events. These central basin anomalies are difficult to attribute to shock remanent magnetization of a shocked central uplift and most probably imply thermoremanent magnetization of impact melt rocks in a steady magnetizing field. Iterative forward modeling of the single strongest and most isolated anomaly, the northern Crisium anomaly, yields a paleomagnetic pole position at 81° ± 19°N, 143° ± 31°E, not far from the present rotational pole. Assuming no significant true polar wander since the Crisium impact, this position is consistent with that expected for a core dynamo magnetizing field. Further iterative forward modeling demonstrates that the remaining Crisium anomalies can be approximately simulated assuming a multiple source model with a single magnetization direction equal to that inferred for the northernmost anomaly. This result is most consistent with a steady, large-scale magnetizing field. The inferred mean magnetization intensity within the strongest basin sources is ˜1 A/m assuming a 1-km thickness for the source layer. Future low-altitude orbital and surface magnetometer measurements will more strongly constrain the depth and/or thicknesses of the sources.

  17. The satellite magnetic anomaly of Ahaggar - Evidence for African Plate motion

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Brown, C. R.

    1985-01-01

    The Ahaggar volcanic province of North Central Africa is considered a region of excess heat flow (hot spot) and hence elevated Curie isotherm. Using a modified version of the Parker FFT potential field representation, magnetic signals were calculated at Magsat altitudes for models in which the African Plate is both fixed and moving. The moving-plate model extends the Curie isotherm anomaly in the direction of plate motion and provides a satisfactory match to vertical component anomaly data when the magnitude of plate velocity is 0.75 cm/yr. Although the signal levels are marginal for the scalar component anomalies of this region, the same model provides an adequate match to this data set and is clearly preferable to a fixed-plate model.

  18. Initial Mapping of Mercury's Crustal Magnetic Anomalies: Relationship to the Caloris Impact Basin

    NASA Astrophysics Data System (ADS)

    Hood, L. L.

    2015-12-01

    78 low-altitude orbit passes of MESSENGER calibrated magnetometer data from August and September of 2014 have been applied to produce approximate maps of the crustal magnetic field covering latitudes of 50-80N and longitudes of 160-320E. Only anomalies with wavelengths < 215 km were mapped and amplitudes were adjusted for differences in spacecraft altitude using an equivalent source dipole technique. Maps of the radial field component show that the strongest large-scale anomalies are located in the western part of the mapped region just north and northeast of the 1550-km diameter Caloris impact basin centered at 164E, 30N. When adjusted to a common altitude of ~ 40 km, the strongest single anomaly (~170E, 60N; > 6 nT) lies over a smooth plains unit that extends north-northeastward from Caloris. A second anomaly (185E, 53N, > 5 nT) lies on the Odin Formation, interpreted as Caloris ejecta (e.g., Guest and Greeley, USGS, 1983). As previously reported by Johnson et al. (Science, 2015), a third anomaly (~ 212E, 61N, > 5 nT) also lies over a smooth plains unit, Suisse Planitia. Most smooth plains units on Mercury may have a volcanic origin (Denevi et al., JGR, 2013). However, as discussed by the latter authors, a subset of the smooth plains occur in an annulus around Caloris and could have an impact-related origin, involving fluidized basin ejecta deposition (Wilhelms, Icarus, 1976). A similar origin is widely accepted for the lunar Cayley smooth plains, which dominate the geology near the Apollo 16 landing site where the strongest surface magnetic fields were measured and which correlate best with orbital anomalies on the lunar near side (Halekas et al., JGR, 2001). Two of the remaining three anomalies (220E, 68N, > 4 nT; 234E, 77N, > 5 nT) lie over an older intermediate plains unit with an uncertain interpretation, possibly consisting of impact basin and crater ejecta as well as volcanic materials (Grolier and Boyce, USGS, 1984). In view of the proximity of the

  19. Magsat equivalent source anomalies over the southeastern United States - Implications for crustal magnetization

    NASA Technical Reports Server (NTRS)

    Ruder, M. E.; Alexander, S. S.

    1986-01-01

    The Magsat crustal anomaly field depicts a previously-unidentified long-wavelength negative anomaly centered over southeastern Georgia. Examination of Magsat ascending and descending passes clearly identifies the anomalous region, despite the high-frequency noise present in the data. Using ancillary seismic, electrical conductivity, Bouguer gravity, and aeromagnetic data, a preliminary model of crustal magnetization for the southern Appalachian region is presented. A lower crust characterized by a pervasive negative magnetization contrast extends from the New York-Alabama lineament southeast to the Fall Line. In southern Georgia and eastern Alabama (coincident with the Brunswick Terrane), the model calls for lower crustal magnetization contrast of -2.4 A/m; northern Georgia and the Carolinas are modeled with contrasts of -1.5 A/m. Large-scale blocks in the upper crust which correspond to the Blue Ridge, Charlotte belt, and Carolina Slate belt, are modeled with magnetization contrasts of -1.2 A/m, 1.2 A/m, and 1.2 A/m respectively. The model accurately reproduces the amplitude of the observed low in the equivalent source Magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass-filtered aeromagnetic map of the region.

  20. Magnetic anomalies concentrated near and within Mercury's impact basins: Early mapping and interpretation

    NASA Astrophysics Data System (ADS)

    Hood, L. L.

    2016-06-01

    Ninety-five low-altitude passes of MErcury Surface, Space ENvironment, GEochemistry, and Ranging magnetometer data from February, March, and April of 2015 have been applied to produce an approximate map of the crustal magnetic field at a constant altitude of 40 km covering latitudes of 35°-75°N and longitudes of 90°-270°E. Anomalies are concentrated near and within the Caloris impact basin. A smaller concentration occurs over and around Sobkou Planitia and an associated older large impact basin. The strongest anomalies are found within Caloris and are distributed in a semicircular arc that is roughly concentric with the basin rim. They imply the existence of a core dynamo at the time when Caloris formed (˜3.9 Gyr ago). Anomalies over high-reflectance volcanic plains are relatively weak while anomalies over low-reflectance material that has been reworked by impact processes are relatively strong. The latter characteristics are qualitatively consistent with the ejecta deposit model for anomaly sources.

  1. Deep crust vs shallow mantle: sources of long wavelength magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Ferre, E. C.; Friedman, S. A.; El Atrassi, F.; Conder, J. A.; Demory, F.; Feinberg, J. M.; Filiberto, J.; Khakhalova, E.; Knafelc, J.; Martín-Hernández, F.; Neal, C. R.; Rochette, P.; Till, J. L.; Walsh, K. B., Jr.

    2015-12-01

    Recent petromagnetic results on shallow mantle xenoliths suggest that the uppermost mantle is significantly more magnetic than previously thought, particularly in metasomatised or cold region. This magnetic mantle bears minute amounts of magnetite, a mineral indicative of higher oxygen fugacities. While the exact origin of this magnetite remains uncertain, its contribution to long wavelength magnetic anomalies adds to the potential contributions of crustal rocks. Here we present a compilation of rock magnetic and paleomagnetic data enabling the quantitification of the respective contributions in distinct tectonic settings including subduction zones and stable cratons. The magnetic properties of over 400 specimens of mantle xenoliths are compared to published data from hundreds of deep crustal xenoliths. The picture emerging from this comparison supports a layered distribution of oxidation state in the lithosphere reflecting both the tectonic setting and the degree of melt extraction.

  2. Magnetic Properties of Quaternary Deposits, Kenai Peninsula, Alaska -- Implications for Aeromagnetic Anomalies of Upper Cook Inlet

    USGS Publications Warehouse

    Saltus, R.W.; Haeussler, P.J.

    2004-01-01

    We measured magnetic susceptibilities of exposed Quaternary deposits on several beach cliffs and river banks on the Kenai Peninsula near Soldotna, Alaska. Data, descriptions, and photos from nine sites are included in this report. The mean susceptibility for Quaternary materials in this region is approximately 2.5 x 10-3 SI units. This is sufficiently magnetic to produce subtle aeromagnetic anomalies such as those observed to correlate with topographic features in the region of the measurements. The highest susceptibilities measured (greater than 20 x 10-3 SI units) may help, at least in part, to explain moderate amplitude aeromagnetic anomalies observed elsewhere in Cook Inlet, particularly those relating to structures showing Quaternary movement. Comparison of measured beach cliff susceptibility and susceptibility predicted from idealized formulas and two-dimensional cliff models suggests that measured susceptibilies underestimate true bulk susceptibility by 20 percent to 50 percent in this region.

  3. Bangui Anomaly

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.

    2004-01-01

    Bangui anomaly is the name given to one of the Earth s largest crustal magnetic anomalies and the largest over the African continent. It covers two-thirds of the Central African Republic and therefore the name derives from the capitol city-Bangui that is also near the center of this feature. From surface magnetic survey data Godivier and Le Donche (1962) were the first to describe this anomaly. Subsequently high-altitude world magnetic surveying by the U.S. Naval Oceanographic Office (Project Magnet) recorded a greater than 1000 nT dipolar, peak-to-trough anomaly with the major portion being negative (figure 1). Satellite observations (Cosmos 49) were first reported in 1964, these revealed a 40nT anomaly at 350 km altitude. Subsequently the higher altitude (417-499km) POGO (Polar Orbiting Geomagnetic Observatory) satellite data recorded peak-to-trough anomalies of 20 nT these data were added to Cosmos 49 measurements by Regan et al. (1975) for a regional satellite altitude map. In October 1979, with the launch of Magsat, a satellite designed to measure crustal magnetic anomalies, a more uniform satellite altitude magnetic map was obtained. These data, computed at 375 km altitude recorded a -22 nT anomaly (figure 2). This elliptically shaped anomaly is approximately 760 by 1000 km and is centered at 6%, 18%. The Bangui anomaly is composed of three segments; there are two positive anomalies lobes north and south of a large central negative field. This displays the classic pattern of a magnetic anomalous body being magnetized by induction in a zero inclination field. This is not surprising since the magnetic equator passes near the center of this body.

  4. Identification of magnetic anomalies based on ground magnetic data analysis using multifractal modelling: a case study in Qoja-Kandi, East Azerbaijan Province, Iran

    NASA Astrophysics Data System (ADS)

    Mansouri, E.; Feizi, F.; Karbalaei Ramezanali, A. A.

    2015-10-01

    Ground magnetic anomaly separation using the reduction-to-the-pole (RTP) technique and the fractal concentration-area (C-A) method has been applied to the Qoja-Kandi prospecting area in northwestern Iran. The geophysical survey resulting in the ground magnetic data was conducted for magnetic element exploration. Firstly, the RTP technique was applied to recognize underground magnetic anomalies. RTP anomalies were classified into different populations based on the current method. For this reason, drilling point area determination by the RTP technique was complicated for magnetic anomalies, which are in the center and north of the studied area. Next, the C-A method was applied to the RTP magnetic anomalies (RTP-MA) to demonstrate magnetic susceptibility concentrations. This identification was appropriate for increasing the resolution of the drilling point area determination and decreasing the drilling risk issue, due to the economic costs of underground prospecting. In this study, the results of C-A modelling on the RTP-MA are compared with 8 borehole data. The results show that there is a good correlation between anomalies derived via the C-A method and the log report of boreholes. Two boreholes were drilled in magnetic susceptibility concentrations, based on multifractal modelling data analyses, between 63 533.1 and 66 296 nT. Drilling results showed appropriate magnetite thickness with grades greater than 20 % Fe. The total associated with anomalies containing andesite units hosts iron mineralization.

  5. Remanent magnetization and 3-dimensional density model of the Kentucky anomaly region

    NASA Technical Reports Server (NTRS)

    Mayhew, M. A.; Estes, R. H.; Myers, D. M.

    1984-01-01

    A three-dimensional model of the Kentucky body was developed to fit surface gravity and long wavelength aeromagnetic data. Magnetization and density parameters for the model are much like those of Mayhew et al (1982). The magnetic anomaly due to the model at satellite altitude is shown to be much too small by itself to account for the anomaly measured by Magsat. It is demonstrated that the source region for the satellite anomaly is considerably more extensive than the Kentucky body sensu stricto. The extended source region is modeled first using prismatic model sources and then using dipole array sources. Magnetization directions for the source region found by inversion of various combinations of scalar and vector data are found to be close to the main field direction, implying the lack of a strong remanent component. It is shown by simulation that in a case (such as this) where the geometry of the source is known, if a strong remanent component is present its direction is readily detectable, but by scalar data as readily as vector data.

  6. Effects of edge magnetism on the Kohn anomalies of zigzag graphene nanoribbons.

    PubMed

    Culchac, F J; Capaz, Rodrigo B

    2016-02-12

    The effects of edge magnetism on the Kohn anomaly (KA) of the G-band phonons of zigzag graphene nanoribbons (ZGNRs) are studied using a combination of the tight-binding and mean-field Hubbard models. We show that the opening of an energy gap, induced by magnetic ordering, significantly changes the KA effects, particularly for narrow ribbons in which the gap is larger than the phonon energy. Therefore, the G-band phonon frequency and lifetime are altered for a magnetically-ordered edge state with respect to an unpolarized edge state. The effects of temperature, ZGNR width, doping and transverse electric fields are systematically investigated. We propose using this effect to probe the magnetic order of edge states in graphene nanoribbons using Raman spectroscopy.

  7. Chapter 3: Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic

    USGS Publications Warehouse

    Gaina, C.; Werner, S.C.; Saltus, R.; Maus, S.; Aaro, S.; Damaske, D.; Forsberg, R.; Glebovsky, V.; Johnson, K.; Jonberger, J.; Koren, T.; Korhonen, J.; Litvinova, T.; Oakey, G.; Olesen, O.; Petrov, O.; Pilkington, M.; Rasmussen, T.; Schreckenberger, B.; Smelror, M.

    2011-01-01

    New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain. ?? 2011 The Geological Society of London.

  8. Martian meteorites and Martian magnetic anomalies: a new perspective from NWA 7034 (Invited)

    NASA Astrophysics Data System (ADS)

    Gattacceca, J.; Rochette, P.; Scozelli, R. B.; Munayco, P.; Agee, C. B.; Quesnel, Y.; Cournede, C.; Geissman, J. W.

    2013-12-01

    The magnetic anomalies observed above the Martian Noachian crust [1] require strong crustal remanent magnetization in the 15-60 A/m range over a thickness of 20-50 km [2,3]. The Martian rocks available for study in the form of meteorites do contain magnetic minerals (magnetite and/or pyrrhotite) but in too small amount to account for such strong remanent magnetizations [4]. Even though this contradiction was easily explained by the fact that Martian meteorites (mostly nakhlites and shergottites) are not representative of the Noachian Martian crust, we were left with no satisfactory candidate lithology to account for the Martian magnetic anomalies. The discovery in the Sahara of a new type of Martian meteorite (NWA 7034 [5] and subsequent paired stones which are hydrothermalized volcanic breccia) shed a new light on this question as it contains a much larger amount of ferromagnetic minerals than any other Martian meteorite. We present here a study of the magnetic properties of NWA 7034, together with a review of the magnetic properties of thirty other Martian meteorites. Magnetic measurements (including high and low temperature behavior and Mössbauer spectroscopy) show that NWA 7034 contains about 15 wt.% of magnetite with various degrees of substitution and maghemitization up to pure maghemite, in the pseudo-single domain size range. Pyrrhotite, a common mineral in other Martian meteorites is not detected. Although it is superparamagnetic and cannot carry remanent magnetization, nanophase goethite is present in significant amounts confirming that NWA 7034 is the most oxidized Martian meteorite studied so far, as already indicated by the presence of maghemite (this study) and pyrite [5]. These magnetic properties show that a kilometric layer of a lithology similar to NWA 7034 magnetized in a dynamo field would be enough to account for the strongest Martian magnetic anomalies. Although the petrogenesis of NWA 7034 is still debated, as the brecciation could be either

  9. Effects of edge magnetism on the Kohn anomalies of zigzag graphene nanoribbons.

    PubMed

    Culchac, F J; Capaz, Rodrigo B

    2016-02-12

    The effects of edge magnetism on the Kohn anomaly (KA) of the G-band phonons of zigzag graphene nanoribbons (ZGNRs) are studied using a combination of the tight-binding and mean-field Hubbard models. We show that the opening of an energy gap, induced by magnetic ordering, significantly changes the KA effects, particularly for narrow ribbons in which the gap is larger than the phonon energy. Therefore, the G-band phonon frequency and lifetime are altered for a magnetically-ordered edge state with respect to an unpolarized edge state. The effects of temperature, ZGNR width, doping and transverse electric fields are systematically investigated. We propose using this effect to probe the magnetic order of edge states in graphene nanoribbons using Raman spectroscopy. PMID:26762781

  10. Spherical Earth analysis and modeling of lithospheric gravity and magnetic anomalies. Ph.D. Thesis - Purdue Univ.

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.

    1980-01-01

    A comprehensive approach to the lithospheric analysis of potential field anomalies in the spherical domain is provided. It has widespread application in the analysis and design of satellite gravity and magnetic surveys for geological investigation.

  11. Correlations Between In Situ and Remotely Sensed Magnetic Anomalies on the Lunar Prospector Mission

    NASA Astrophysics Data System (ADS)

    Delory, G. T.; Mitchell, D. L.; Halekas, J. S.; Lin, R. P.; Frey, S.

    2002-05-01

    The Lunar Prospector mission provides two complementary measurements of Lunar magnetic fields. The magnetometer (MAG) measures the vector magnetic field at the spacecraft position, while estimates of the magnetic field strength at the Lunar surface are derived remotely using the electron reflectometer (ER) measurements of the electron loss cone angle. In this work we study correlations between these two data sets with several goals in mind. First, since the ER instrument depends on some knowledge of the electron trajectories in order to determine the magnetic field footprint on the surface, we wish to assess the importance of strong magnetic field curvature in the determination of the location of the reflection points measured by the ER. Second, we wish to explore the utility of using the ER data as a lower boundary condition for models attempting to downward extend the magnetic field topology as measured by the MAG instrument on the spacecraft. Initial results using well isolated anomalies in areas such as Reiner Gamma and the Apollo 16 landing site indicate that for strong anomalies (~50 nT at 20-30 km altitude) corrections to the electron reflection points may be on the order of 1 degree in latitude or longitude at the surface. The magnetic fields of these sites and other similar examples were modeled using a simple magnetic dipole approximation. Sites with a more complex magnetic topology such as the Crisium antipode may be too difficult to model with a simple collection of dipoles as the run times for fitting routines increases dramatically. Spherical Cap Harmonic Analysis (SCHA) may be an appropriate tool to model these larger regional anomalies, and we discuss the possibility of using the ER data as a lower boundary condition at the surface for this technique. The end goal of our work is to remove at least some of the ambiguities inherent in any downward extension of orbital magnetometer data, using a synthesis of the in situ magnetic field data measured

  12. Origin of Strong Lunar Magnetic Anomalies: More Detailed Mapping in Regions Antipodal to Young Large Basins

    NASA Astrophysics Data System (ADS)

    Hood, L. L.; Richmond, N.; Spudis, P.

    2012-12-01

    Previous work has found evidence that the largest concentrations of strong lunar crustal magnetic fields are in regions antipodal to four young large lunar basins: Orientale, Imbrium, Crisium, and Serenitatis (Mitchell et al., Icarus, 2008; and references therein). A preliminary model for the production of lunar basin antipodal magnetic signatures has been developed (Hood and Artemieva, Icarus, 2008; Gattacceca et al., EPSL, 2010). The model involves shock magnetization of crustal materials in the presence of a transient magnetic field amplified by the expanding ionized vapor-melt cloud as it converges in the antipodal region. The model does not exclude a core dynamo; any ambient magnetic field (external solar wind or internal core dynamo) can be amplified in the antipodal zone. In this paper, we report further efforts to map in more detail Lunar Prospector magnetometer data in regions antipodal to young lunar basins. In addition to the four basins identified above, we also consider the polar Schrodinger basin, which is one of the three youngest lunar basins and which has not been previously considered in this context. We apply a direct mapping method (see Hood, Icarus, 2011 for details) to produce more complete maps of lunar magnetic anomalies at low altitudes over the central far side and over the north polar region. We also consider geologic data and spacecraft imagery to identify unusual modified terrain, which may be indicative of shock modification in the same basin antipodal zones. Previous work indicates the existence of such terrain antipodal to Imbrium, Orientale, and Serenitatis, as well as antipodal to the Caloris basin on Mercury. Results first confirm the concentrations of anomalies antipodal to Orientale, Imbrium, Crisium, and Orientale, and the occurrence of modified terrain in three of the four basin antipode zones (see, e.g., Richmond et al., JGR, 2005). In addition, we report here evidence for a large concentration of anomalies that is centered

  13. EMAG2: A 2-arc min resolution Earth Magnetic Anomaly Grid compiled from satellite, airborne, and marine magnetic measurements

    USGS Publications Warehouse

    Maus, S.; Barckhausen, U.; Berkenbosch, H.; Bournas, N.; Brozena, J.; Childers, V.; Dostaler, F.; Fairhead, J.D.; Finn, C.; von Frese, R.R.B; Gaina, C.; Golynsky, S.; Kucks, R.; Lu, Hai; Milligan, P.; Mogren, S.; Muller, R.D.; Olesen, O.; Pilkington, M.; Saltus, R.; Schreckenberger, B.; Thebault, E.; Tontini, F.C.

    2009-01-01

    A global Earth Magnetic Anomaly Grid (EMAG2) has been compiled from satellite, ship, and airborne magnetic measurements. EMAG2 is a significant update of our previous candidate grid for the World Digital Magnetic Anomaly Map. The resolution has been improved from 3 arc min to 2 arc min, and the altitude has been reduced from 5 km to 4 km above the geoid. Additional grid and track line data have been included, both over land and the oceans. Wherever available, the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids. Interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation, based on an oceanic crustal age model. The longest wavelengths (>330 km) were replaced with the latest CHAMP satellite magnetic field model MF6. EMAG2 is available at http://geomag.org/models/EMAG2 and for permanent archive at http://earthref.org/ cgi-bin/er.cgi?s=erda.cgi?n=970. ?? 2009 by the American Geophysical Union.

  14. True Polar Wander and Hotspot Fixity: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma B.P.) on the Pacific Plate

    NASA Astrophysics Data System (ADS)

    Gordon, R. G.; Horner-Johnson, B. C.

    2010-12-01

    Prior studies have shown that Pacific hotspots and Indo-Atlantic hotspots have moved in approximate unison relative to the spin axis since 65 Ma B.P. [Morgan, 1981; Gordon and Cape, 1981; Gordon, 1982] and since 56 Ma B.P. [Petronotis et al., 1994], which is most simply interpreted as true polar wander. In contrast, Pacific hotspots and Indo-Atlantic hotspots give conflicting results for 72 Ma B.P. and for 81 Ma B.P., which may indicate motion between Pacific hotspots and Indo-Atlantic hotspots [Tarduno and Cottrell, 1997; Petronotis et al., 1999; Tarduno et al., 2003]. Thus it is important to estimate Pacific plate apparent polar wander (APW) for more time intervals. From such estimates the APW of Pacific hotspots can be inferred and compared with that of Indo-Atlantic hotspots [e.g., Besse and Courtillot 2002]. Here we present a study of the skewness of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones. We chose this region for several reasons: First, numerical experiments, like those conducted by Acton and Gordon [1991], indicate that magnetic profiles between the Galapagos and Clarion fracture zones should contain the most information about the Pacific plate paleomagnetic pole for chron C12r (32 Ma B.P.). Second, in these two spreading rate corridors, spreading half rates range from 72 to 86 mm/a and therefore have negligible anomalous skewness, given that they exceed ≈50 mm/a [Roest et al., 1992; Dyment et al. 1994]. Third, vector aeromagnetic profiles are available for analysis. One of the challenges to interpreting magnetic anomalies in low latitudes where the anomalies strike nearly north-south is the very low amplitude of the signal relative to the noise, the latter of which can be especially intense near the present magnetic equator due to the amplification of diurnal variation by the equatorial electrojet. Previously we showed that vector aeromagnetic profiles record low-latitude Pacific plate

  15. Computed tomography and magnetic resonance imaging of the coronary sinus: anatomic variants and congenital anomalies.

    PubMed

    Chen, Yingming Amy; Nguyen, Elsie T; Dennie, Carole; Wald, Rachel M; Crean, Andrew M; Yoo, Shi-Joon; Jimenez-Juan, Laura

    2014-10-01

    The coronary sinus (CS) is an important vascular structure that allows for access into the coronary veins in multiple interventional cardiology procedures, including catheter ablation of arrhythmias, pacemaker implantation and retrograde cardioplegia. The success of these procedures is facilitated by the knowledge of the CS anatomy, in particular the recognition of its variants and anomalies. This pictorial essay reviews the spectrum of CS anomalies, with particular attention to the distinction between clinically benign variants and life-threatening defects. Emphasis will be placed on the important role of cardiac CT and cardiovascular magnetic resonance in providing detailed anatomic and functional information of the CS and its relationship to surrounding cardiac structures. Teaching Points • Cardiac CT and cardiovascular magnetic resonance offer 3D high-resolution mapping of the coronary sinus in pre-surgical planning.• Congenital coronary sinus enlargement occurs in the presence or absence of a left-to-right shunt.• Lack of recognition of coronary sinus anomalies can lead to adverse outcomes in cardiac procedures.• In coronary sinus ostial atresia, coronary venous drainage to the atria occurs via Thebesian or septal veins.• Coronary sinus diverticulum is a congenital outpouching of the coronary sinus and may predispose to cardiac arrhythmias.

  16. Magnetization models for the source of the 'Kentucky anomaly' observed by Magsat

    NASA Technical Reports Server (NTRS)

    Mayhew, M. A.; Estes, R. H.; Myers, D. M.

    1985-01-01

    Both the aeromagnetic data and magnetic anomaly data obtained by Magsat indicate the presence of a very magnetic source region within the crust beneath Kentucky and Tennessee. A source model was previously developed to fit surface gravity and long-wavelength aeromagnetic data, using limited seismic constraint. For the present study the model was further developed, and it is demonstrated that the source region for the satellite anomaly is considerably more extensive than the Kentucky body sensu stricto. The extended source region is modeled using both prismatic model sources and dipole array sources. Magnetization directions for the source region found by inversion of various combinations of scalar and vector data are found to be close to the main field direction, implying the lack of a strong remanent component. It is shown by simulation that in a case (such as this) where the geometry of the source is known, if a strong remanent component is present its direction is determinable, but by scalar data as readily as vector data. Magnetization magnitude for the extended source region is about 3 A/m if the vertical extent of the source includes the whole of the crust.

  17. Recognition of magnetic anomalies in Ground Conductivity Meter soil surveys: a high-resolution field experiment

    NASA Astrophysics Data System (ADS)

    Søe, Niels Emil; Bjergsted Pedersen, Jesper; Auken, Esben; Humlekrog Greve, Mogens; Nørgaard, Henrik; Tjelldén, Anna K. E.; Munch Kristiansen, Søren

    2013-04-01

    Ground conductivity measurements are widely used in soil surveys, where the objective is to map an element or property, which gives a strong conductive signal compared to the surroundings. It can be used in mapping of soil contamination, mineral exploration and soil mapping, where properties like porosity, clay-content and salinity of groundwater are explored. However, interpretations get poor, when too many variables, e.g. metals, affect the measurements. To improve interpretation of the GCM dataset, we investigated confounding signals from buried metals as magnetic anomalies by a magnetometer. The small field test site in Illerup Ådal, Denmark (2 ha) was situated on peat and clayey soil, where buried metal was expected due to previous archaeological investigations. Both GCM and magnetometer measurements were on-the-go behind an ATV and logged together with DGPS positioning. Instruments were a DUALEM-21 and a Geometrics G-858 Caesium magnetometer. Data were collected in separately runs, since close proximity of the instruments can affect the magnetometer data. Data were collected on 12 lines, which were spaced 5 m apart. The frequency of readings was 4 times s-1 at a speed of approximately 12 km h-1. A 1D multi-layer model was used for the inversion of EM data, providing detailed information of the resistivity structure in the upper 2-3 m of the soil. All 12 lines were driven in both directions during sampling of magnetic data, to check if measurements are influenced by the direction of the magnetometer. Time for collecting both datasets was 90 minutes. The combined dataset showed one area (200 m2) with a magnetic anomaly, which correlated with a relatively low apparent resistivity (approximately 27 Ohm m), while the adjacent areas had a higher apparent resistivity (>50 Ohm m). The inversion model showed that a relatively low resistivity (20-30 Ohm m) was present at all depths in the area with the magnetic anomaly. However, the model showed even lower resistivity

  18. Correlation between the Palaeozoic structures from West Iberian and Grand Banks margins using inversion of magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Silva, Elsa A.; Miranda, J. M.; Luis, J. F.; Galdeano, A.

    2000-05-01

    The Ibero-Armorican Arc (IAA) is a huge geological structure of Pre-Cambrian origin, tightened during hercynian times and deeply affected by the opening of the Atlantic Ocean and the Bay of Biscay. Its remnants now lie in Iberia, north-western France and the Canadian Grand Banks margins. The qualitative correlation between these three blocks has been attempted by several authors (e.g. Lefort, J.P., 1980. Un 'Fit' structural de l'Atlantique Nord: arguments geologiques pour correler les marqueurs geophysiques reconnus sur les deux marges. Mar. Geol. 37, 355-369; Lefort, J.P., 1983. A new geophysical criterion to correlate the Acadian and Hercynian orogenies of Western Europe and Eastern America. Mem. Geol. Soc. Am. 158, 3-18; Galdeano, A., Miranda, J.M., Matte, P., Mouge, P., Rossignol, C., 1990. Aeromagnetic data: A tool for studying the Variscan arc of Western Europe and its correlation with transatlantic structures. Tectonophysics 177, 293-305) using magnetic anomalies, mainly because they seem to preserve the hercynian zonation, in spite of the strong thermal and mechanical processes that took place during rifting and ocean spreading. In this paper, we present a new contribution to the study of the IAA structure based on the processing of a compilation of magnetic data from Iberia and Grand Banks margins. To interpret the magnetic signature, a Fourier-domain-based inversion technique was applied, considering a layer with a constant thickness of 10 km, and taking into account only the induced field. The digital terrain model was derived from ETOPO5 (ETOPO5, 1986. Relief map of the earth's surface. EOS 67, 121) and TerrainBase (TerrainBase, 1995. In: Row III, L.W., Hastings, D.A., Dunbar, P.K. (Eds.), Worldwide Digital Terrain Data, Documentation Manual, CD-ROM Release 1.0. GEODAS-NGDC Key to Geophysical Records. Documentation N. 30, April) databases. The pseudo-susceptibility distribution obtained was repositioned for the 156.5 Ma epoch, using the Srivastava and

  19. Spread F occurrence and drift under the crest of the equatorial ionization anomaly from continuous Doppler sounding and FORMOSAT-3/COSMIC scintillation data

    NASA Astrophysics Data System (ADS)

    Chum, Jaroslav; Liu, Jann-Yenq; Chen, Shih-Ping; Cabrera, Miguel Angel; Laštovička, Jan; Baše, Jiří; Burešová, Dalia; Fišer, Jiří; Hruška, František; Ezquer, Rodolfo

    2016-04-01

    A relatively new method based on measurements by multipoint continuous Doppler sounding is applied to study the occurrence rate, propagation velocities, and directions of spread F structures over Tucumán, Northern Argentina, and Taiwan, both of which were under the crest of the equatorial ionization anomaly in 2014. In addition, spread F is studied globally over the same time period from the S4 scintillation index measured onboard FORMOSAT-3/COSMIC (F3/C) satellite. It is shown that the continuous Doppler sounding gives results that are consistent with S4 data and with previous optical, global positioning system (GPS), and satellite measurements. Most of the spread F events were observed from September to March, i.e., during the local summer half of the year in Tucumán, whereas in Taiwan, the highest occurrence rate was observed around equinoxes. The occurrence rate in Tucumán was about four times higher than that in Taiwan. The propagation velocities and directions were estimated from the Doppler shift spectrograms. The spread structures related to spread F propagated roughly eastward at velocities from ~70 to ~200 m s-1 during nighttime hours. The mean observed horizontal velocity was 140 m s-1 over Tucumán and 107 m s-1 over Taiwan. The local times at which the highest velocities were observed roughly correspond to local times with highest values of scintillation index S4, at ~20 to 23 LT. In addition, a comparison of measured drift velocities with neutral wind velocities predicted by models is provided. The observed velocities usually exceeded the horizontal neutral wind velocities predicted by the HWM14 model for the locations and times of observations.

  20. Interpretation of gravity and magnetic anomalies at Lake Rotomahana: Geological and hydrothermal implications

    NASA Astrophysics Data System (ADS)

    Caratori Tontini, F.; de Ronde, C. E. J.; Scott, B. J.; Soengkono, S.; Stagpoole, V.; Timm, C.; Tivey, M.

    2016-03-01

    We investigate the geological and hydrothermal setting at Lake Rotomahana, using recently collected potential-field data, integrated with pre-existing regional gravity and aeromagnetic compilations. The lake is located on the southwest margin of the Okataina Volcanic Center (Haroharo caldera) and had well-known, pre-1886 Tarawera eruption hydrothermal manifestations (the famous Pink and White Terraces). Its present physiography was set by the caldera collapse during the 1886 eruption, together with the appearance of surface activities at the Waimangu Valley. Gravity models suggest that subsidence associated with the Haroharo caldera is wider than the previously mapped extent of the caldera margins. Magnetic anomalies closely correlate with heat-flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of Lake Rotomahana are characterized by a large, well-developed hydrothermal field. The field extends beyond the lake area with deep connections to the Waimangu area to the south. On the south, the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat-flux and bubble plumes which suggest hydrothermal activity occurring west of Patiti Island. The absence of a well-defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 Tarawera eruption. Locally confined intense magnetic anomalies on the north shore of Lake Rotomahana are interpreted as basalt dikes with high magnetization. Some appear to have been emplaced before the 1886 Tarawera eruption. A dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the Patiti geothermal system, and could have been originated from the 1886 Tarawera eruption.

  1. Anisotropic Solar Wind Sputtering of the Lunar Surface Induced by Crustal Magnetic Anomalies

    NASA Technical Reports Server (NTRS)

    Poppe, A. R.; Sarantos, M.; Halekas, J. S.; Delory, G. T.; Saito, Y.; Nishino, M.

    2014-01-01

    The lunar exosphere is generated by several processes each of which generates neutral distributions with different spatial and temporal variability. Solar wind sputtering of the lunar surface is a major process for many regolith-derived species and typically generates neutral distributions with a cosine dependence on solar zenith angle. Complicating this picture are remanent crustal magnetic anomalies on the lunar surface, which decelerate and partially reflect the solar wind before it strikes the surface. We use Kaguya maps of solar wind reflection efficiencies, Lunar Prospector maps of crustal field strengths, and published neutral sputtering yields to calculate anisotropic solar wind sputtering maps. We feed these maps to a Monte Carlo neutral exospheric model to explore three-dimensional exospheric anisotropies and find that significant anisotropies should be present in the neutral exosphere depending on selenographic location and solar wind conditions. Better understanding of solar wind/crustal anomaly interactions could potentially improve our results.

  2. An attempt to obtain a detailed declination chart from the United States magnetic anomaly map

    USGS Publications Warehouse

    Alldredge, L.R.

    1989-01-01

    Modern declination charts of the United States show almost no details. It was hoped that declination details could be derived from the information contained in the existing magnetic anomaly map of the United States. This could be realized only if all of the survey data were corrected to a common epoch, at which time a main-field vector model was known, before the anomaly values were computed. Because this was not done, accurate declination values cannot be determined. In spite of this conclusion, declination values were computed using a common main-field model for the entire United States to see how well they compared with observed values. The computed detailed declination values were found to compare less favourably with observed values of declination than declination values computed from the IGRF 1985 model itself. -from Author

  3. Magnetic anomaly map of North America south of 50 degrees north from Pogo data

    NASA Technical Reports Server (NTRS)

    Mayhew, M. A.

    1976-01-01

    A magnetic anomaly map produced from Pogo data for North America and adjacent ocean areas is presented. At satellite elevations anomalies have wavelengths measured in hundreds of kilometers, and reflect regional structures on a large scale. Prominent features of the map are: (1) a large east-west high through the mid-continent, breached at the Mississippi Embayment; (2) a broad low over the Gulf of Mexico; (3) a strong gradient separating these features, which follows the Southern Appalachian-Ouachita curvature; and (4) a high over the Antilles-Bahamas Platform which extends to northern Florida. A possible relationship between the high of the mid-continent and the 38th parallel lineament is noted.

  4. An equivalent source model of the satellite-altitude magnetic anomaly field over Australia

    NASA Technical Reports Server (NTRS)

    Mayhew, M. A.; Johnson, B. D.; Langel, R. A.

    1980-01-01

    The low-amplitude, long-wavelength magnetic anomaly field measured between 400 and 700 km elevation over Australia by the POGO satellites is modeled by means of the equivalent source technique. Magnetic dipole moments are computed for a latitude-longitude array of dipole sources on the earth's surface such that the dipoles collectively give rise to a field which makes a least squares best fit to that observed. The distribution of magnetic moments is converted to a model of apparent magnetization contrast in a layer of constant (40 km) thickness, which contains information equivalent to the lateral variation in the vertical integral of magnetization down to the Curie isotherm and can be transformed to a model of variable thickness magnetization. It is noted that the closest equivalent source spacing giving a stable solution is about 2.5 deg, corresponding to about half the mean data elevation, and that the magnetization distribution correlates well with some of the principle tectonic elements of Australia.

  5. Self-similar inverse cascade of magnetic helicity driven by the chiral anomaly

    DOE PAGES

    Hirono, Yuji; Kharzeev, Dmitri E.; Yin, Yi

    2015-12-28

    For systems with charged chiral fermions, the imbalance of chirality in the presence of magnetic field generates an electric current—this is the chiral magnetic effect (CME). We study the dynamical real-time evolution of electromagnetic fields coupled by the anomaly to the chiral charge density and the CME current by solving the Maxwell-Chern-Simons equations. We find that the CME induces the inverse cascade of magnetic helicity toward the large distances, and that at late times this cascade becomes self-similar, with universal exponents. We also find that in terms of gauge field topology the inverse cascade represents the transition from linked electricmore » and magnetic fields (Hopfions) to the knotted configuration of magnetic field (Chandrasekhar-Kendall states). The magnetic reconnections are accompanied by the pulses of the CME current directed along the magnetic field lines. In conclusion, we devise an experimental signature of these phenomena in heavy ion collisions, and speculate about implications for condensed matter systems.« less

  6. Self-similar inverse cascade of magnetic helicity driven by the chiral anomaly

    SciTech Connect

    Hirono, Yuji; Kharzeev, Dmitri E.; Yin, Yi

    2015-12-28

    For systems with charged chiral fermions, the imbalance of chirality in the presence of magnetic field generates an electric current—this is the chiral magnetic effect (CME). We study the dynamical real-time evolution of electromagnetic fields coupled by the anomaly to the chiral charge density and the CME current by solving the Maxwell-Chern-Simons equations. We find that the CME induces the inverse cascade of magnetic helicity toward the large distances, and that at late times this cascade becomes self-similar, with universal exponents. We also find that in terms of gauge field topology the inverse cascade represents the transition from linked electric and magnetic fields (Hopfions) to the knotted configuration of magnetic field (Chandrasekhar-Kendall states). The magnetic reconnections are accompanied by the pulses of the CME current directed along the magnetic field lines. In conclusion, we devise an experimental signature of these phenomena in heavy ion collisions, and speculate about implications for condensed matter systems.

  7. Implications of Depth Determination from Second Moving Average Residual Magnetic Anomalies on Mars

    NASA Astrophysics Data System (ADS)

    Essa, K. S.; Kletetschka, G.

    2014-12-01

    Mars total magnetic data obtained by Mars Global Surveyor mission from 400 km altitude were processed using a second moving average method (SMAM) to estimate the depth of the buried sources. Five profiles were chosen across major magnetic areas. Each profile was subjected to a separation technique using the SMAM. Second moving average residual anomalies (SMARA) were obtained from magnetic data using filters of successive spacing. The depth estimate is monitored by the standard deviation of the depths determined from all SMARA for various value of the shape factor (SF) that includes dike, cylinder, and sphere. The standard deviation along with depth estimate is considered to be a new criterion for determining the correct depth and shape of the buried structures on Mars.

  8. Magnetic Torque Anomaly in the Quantum Limit of Weyl and Dirac Semimetals

    NASA Astrophysics Data System (ADS)

    Nair, Nityan L.; Moll, Philip J. W.; Potter, Andrew C.; Ramshaw, Brad; Modic, Kimberly; Riggs, Scott; Zeng, Bin; Ghimire, Nirmal; Bauer, Eric; Kealhofer, Robert; Li, Zhenglu; Louie, Steven; Ronning, Filip; Analytis, James G.

    Three dimensional Dirac and Weyl semimetals, characterized by bulk quasiparticles that behave as massless, linearly dispersing Dirac or Weyl fermions, have excited physicists with their unique topological properties and potential for applications. The experimental signatures of Weyl or Dirac fermions, however, are often subtle and indirect, especially in systems where they coexist with trivial electrons. Here, we report a novel method by which these topological systems can be unambiguously experimentally identified. Magnetic torque measurements were performed on the Weyl semimetal NbAs in high magnetic field, showing a large anomaly upon entering the quantum limit. The torque exhibits a striking sign reversal, corresponding to a change in the magnetic anisotropy that is a direct result of the topological properties of the charge carriers. This result can be generalized to other Dirac and Weyl semimetal systems and establishes quantum limit torque measurements as a simple and direct experimental method of distinguishing topologically non-trivial Weyl and Dirac systems from trivial semiconductors.

  9. The magnetic anomaly model of the Jovian magnetosphere - Predictions for Voyager

    NASA Technical Reports Server (NTRS)

    Dessler, A. J.; Vasyliunas, V. M.

    1979-01-01

    The magnetic anomaly model, in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes, has been put forth to account for the various observed Jovian magnetospheric phenomena that show evidence of Jovian longitudinal asymmetry or planetary spin periodicity. From this model, normalized by empirical fitting to Pioneer 10 and 11 flyby data and to ground-based radio data, a series of predictions are made that are subject to test by the forthcoming flybys of Jupiter by Voyagers 1 and 2. These predictions cover: (1) the longitude range and time intervals of enhanced interaction between Io (and possibly Europa) and Jupiter's ionosphere, (2) plasma, energetic particle, and magnetic field periodicities in the outer magnetosphere, and (3) the sub-spacecraft System III longitude and the time, modulo 10 hours, of the first and subsequent magnetopause crossings.

  10. Mid-Atlantic Ridge at 13-14N: Evidence of Unstable Seafloor Spreading Processes From Deep-Towed Magnetic Measurements

    NASA Astrophysics Data System (ADS)

    Searle, R.; Mallows, C.; Cipcigan, F.; Party, J. S.

    2007-12-01

    During cruise JC007 in March-April 2007 we recorded total magnetic field anomalies over two active and one defunct oceanic core complex (OCC) and the intervening seafloor. Measurements were made by towed magnetometer at the sea surface, and by the TOBI deep-towed vehicle approximately 400 m above seafloor, along 13 E-W lines about 60 km long and spaced 3 to 6 km apart. Sea-surface data show a fairly coherent central anomaly on most lines, though on some it is significantly displaced from the spreading axis as indicated by bathymetry and side-scan sonar data. Modelling in terms of a standard, simple (but probably unrealistic), continuous reversal sequence requires total spreading rates ranging from about 15 to 40 km/Myr with offsets of the axis up to 20 km and highly asymmetric spreading. The deep-towed data were corrected for the heading-dependent magnetic effects of the TOBI vehicle before inversion to crustal magnetisation using the 2D Parker & Huestis (1974) procedure. These results were checked by comparing with inversions of the sea-surface field, which shows similar features at reduced resolution. The deep-towed inversion results show a rather incoherent magnetisation pattern. The central magnetisation high is nowhere more than 13 km wide, only 70% of the expected width of the Brunhes here, and several profiles yield apparently negative magnetisation over areas we expect to be of Brunhes age based on sonar and bathymetry data. This may due to a combination of destruction of magnetisation by faulting (Hussenoeder at al., 1996), departure from the 2D geometry assumed for the inversions, and departure (via tectonic rotation) from the assumed constant magnetisation direction. We are now carrying out fully 3D inversions and forward modelling guided by the structural evidence provided by sidescan and bathymetry. These results will be presented and discussed in relation to the seafloor spreading history and structure of the region.

  11. Magnetic anomalies in Bahia Esperanza: A window of magmatic arc intrusions and glacier erosion over the northeastern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Galindo-Zaldívar, Jesús; Ruiz-Constán, Ana; Pedrera, Antonio; Ghidella, Marta; Montes, Manuel; Nozal, Francisco; Rodríguez-Fernandez, Luis Roberto

    2013-02-01

    Bahia Esperanza, constituting the NE tip of the Antarctic Peninsula, is made up of Paleozoic clastic sedimentary rocks overlain by a Jurassic volcano-sedimentary series and intruded by Cretaceous gabbros and diorites. The area is located along the southern part of the Pacific Margin magnetic anomaly belt. Field magnetic researches during February 2010 contribute to determining the deep geometry of the intermediate and basic intrusive rocks. Moreover, the new field data help constrain the regional Pacific Margin Anomaly, characterized up to now only by aeromagnetic and marine data. Field magnetic susceptibility measurements of intrusive intermediate and basic rocks, responsible for magnetic anomalies, ranges from 0.5 × 10- 3 SI in diorites to values between 0.75 × 10- 3 SI and 1.3 × 10- 3 SI in gabbros. In addition, a significant remanent magnetism should also have contributed to the anomalies. The regional magnetic anomaly is characterized by a westward increase from 100 nT up to 750 nT, associated with large intrusive diorite bodies. They probably underlie most of the western slopes of Mount Flora. Gabbros in the Nobby Nunatak determine local residual rough anomalies that extend northwards and westwards, pointing to the irregular geometry of the top of the basic rocks bodies below the Pirámide Peak Glacier. However, the southern and eastern boundaries with the Buenos Aires Glacier are sharp related to deep glacier incision. As a result of the glacier dynamics, magnetic anomalies are also detected north of the Nobby Nunatak due to the extension of the anomalous body and the presence of gabbro blocks in the moraines. The Bahia Esperanza region is a key area where onshore field geological and magnetic research allows us to constrain the shape of the crustal igneous intrusions and the basement glacier geometry, providing accurate data that complete regional aeromagnetic research.

  12. Identification of magnetic anomalies based on ground magnetic data analysis using multifractal modeling: a case study in Qoja-Kandi, East Azerbaijan Province, Iran

    NASA Astrophysics Data System (ADS)

    Mansouri, E.; Feizi, F.; Karbalaei Ramezanali, A. A.

    2015-07-01

    Ground magnetic anomaly separation using reduction-to-the-pole (RTP) technique and the fractal concentration-area (C-A) method has been applied to the Qoja-Kandi prosepecting area in NW Iran. The geophysical survey that resulted in the ground magnetic data was conducted for magnetic elements exploration. Firstly, RTP technique was applied for recognizing underground magnetic anomalies. RTP anomalies was classified to different populations based on this method. For this reason, drilling points determination with RTP technique was complicated. Next, C-A method was applied on the RTP-Magnetic-Anomalies (RTP-MA) for demonstrating magnetic susceptibility concentration. This identification was appropriate for increasing the resolution of the drilling points determination and decreasing the drilling risk, due to the economic costs of underground prospecting. In this study, the results of C-A Modeling on the RTP-MA are compared with 8 borehole data. The results show there is good correlation between anomalies derived via C-A method and log report of boreholes. Two boreholes were drilled in magnetic susceptibility concentration, based on multifractal modeling data analyses, between 63 533.1 and 66 296 nT. Drilling results show appropriate magnetite thickness with the grades greater than 20 % Fe total. Also, anomalies associated with andesite units host iron mineralization.

  13. Fetal Central Nervous System Anomalies Detected by Magnetic Resonance Imaging: A Two-Year Experience

    PubMed Central

    Sefidbakht, Sepideh; Dehghani, Sakineh; Safari, Maryam; Vafaei, Homeira; Kasraeian, Maryam

    2016-01-01

    Background Magnetic resonance imaging (MRI) is gradually becoming more common for thorough visualization of the fetus than ultrasound (US), especially for neurological anomalies, which are the most common indications for fetal MRI and are a matter of concern for both families and society. Objectives We investigated fetal MRIs carried out in our center for frequency of central nervous system anomalies. This is the first such report in southern Iran. Materials and Methods One hundred and seven (107) pregnant women with suspicious fetal anomalies in prenatal ultrasound entered a cross-sectional retrospective study from 2011 to 2013. A 1.5 T Siemens Avanto scanner was employed for sequences, including T2 HASTE and Trufisp images in axial, coronal, and sagittal planes to mother’s body, T2 HASTE and Trufisp relative to the specific fetal body part being evaluated, and T1 flash images in at least one plane based on clinical indication. We investigated any abnormality in the central nervous system and performed descriptive analysis to achieve index of frequency. Results Mean gestational age ± standard deviation (SD) for fetuses was 25.54 ± 5.22 weeks, and mean maternal age ± SD was 28.38 ± 5.80 years Eighty out of 107 (74.7%) patients who were referred with initial impression of borderline ventriculomegaly. A total of 18 out of 107 (16.82%) patients were found to have fetuses with CNS anomalies and the remainder were neurologically normal. Detected anomalies were as follow: 3 (16.6%) fetuses each had the Dandy-Walker variant and Arnold-Chiari II (with myelomeningocele). Complete agenesis of corpus callosum, partial agenesis of corpus callosum, and aqueductal stenosis were each seen in 2 (11.1%) fetuses. Arnold-Chiari II without myelomeningocele, anterior spina bifida associated with neurenteric cyst, arachnoid cyst, lissencephaly, and isolated enlarged cisterna magna each presented in one (5.5%) fetus. One fetus had concomitant schizencephaly and complete agenesis of

  14. Spectral analysis of magnetic anomalies in and around the Philippine Sea

    NASA Astrophysics Data System (ADS)

    Tanaka, A.; Ishihara, T.

    2009-12-01

    Regional compilations of lithospheric structure from various methods and data and comparison among them are useful to understand lithospheric structure and the processes behind its formation and evolution. We present constraints on the regional variations of the magnetic thicknesses in and around the Philippine Sea. We used a new global magnetic anomaly data [Quesnel et al, 2009], which is CM4-corrected [Comprehensive Model 4; Sabaka et al., 2004], cleaned and leveled to clarify the three-dimensional crustal magnetic structure of the Philippine Sea. The Philippine Sea is one of the largest marginal seas of the world. The north-south-trending Kyushu-Palau Ridge divides it into two parts: the West Philippine Basin and the Daito Ridge province in the west and the Shikoku and Parece Vela Basins in the east. The age of the basins increases westward [Karig, 1971]. And, there are three ridges in the Daito Ridge province west of the Kyushu-Palau Ridge; the Oki-Daito, Daito Ridges and the Amami Plateau from south to north, and small basins among them. Two-dimensional spectral analysis of marine magnetic anomalies is used to estimate the centroid of magnetic sources (Zo) to constrain the lithospheric structure [Tanaka and Ishihara, 2008]. The method is based on that of Spector and Grant [1970]. Zo distribution of the Philippine Sea shows occurrence of shallow magnetic layer areas with approximately less than 10 km in the Shikoku Basin. It also shows variations in deep and shallow magnetic layer areas in the Amami-Daito Province. These patters correspond to spatial variations of the crustal thickness deduced from the three-dimensional gravity modeling [Ishihara and Koda, 2007] and acoustic basement structures [Higuchi et al., 2007]. These three spatial distributions are roughly consistent with each other, although they may contain some scatters and bias due to the different characteristics and errors. This two-dimensional spectral analysis method is based upon an assumption

  15. Building the second version of the World Digital Magnetic Anomaly Map (WDMAM)

    NASA Astrophysics Data System (ADS)

    Lesur, Vincent; Hamoudi, Mohamed; Choi, Yujin; Dyment, Jérôme; Thébault, Erwan

    2016-02-01

    The World Digital Anomaly Map (WDMAM) is a worldwide compilation of near-surface magnetic data. We present here a candidate for the second version of the WDMAM and its characteristics. This candidate has been evaluated by a group of independent reviewers and has been adopted as the official second version of the WDMAM during the 26th general assembly of the International Union of Geodesy and Geomagnetism (IUGG). The way this compilation has been built is described with some details. A global magnetic field model of the lithosphere contribution, parameterised by spherical harmonics, has been derived up to degree and order 800. The model information content has been evaluated by computing local spectra. Further, the compatibility of the anomaly field displayed by the WDMAM with a pure induced magnetisation is tested by comparison with the main field strength. These studies allowed an analysis of the compilation in terms of strength and wavelength content. They confirm the extremely smooth and weak contribution of the magnetic field generated in the lithosphere over Western Europe. This apparent weakness possibly extends to the Northern African continent. However, a global analysis remains difficult to achieve given the sparseness of good quality data over very large area of oceans and continents. The WDMAM and related information can be downloaded at http://www.wdmam.org/.

  16. Investigation of source location determination from Magsat magnetic anomalies: The Euler method approach

    NASA Technical Reports Server (NTRS)

    Ravat, Dhananjay

    1996-01-01

    The applicability of the Euler method of source location determination was investigated on several model situations pertinent to satellite-data scale situations as well as Magsat data of Europe. Our investigations enabled us to understand the end-member cases for which the Euler method will work with the present satellite magnetic data and also the cases for which the assumptions implicit in the Euler method will not be met by the present satellite magnetic data. These results have been presented in one invited lecture at the Indo-US workshop on Geomagnetism in Studies of the Earth's Interior in August 1994 in Pune, India, and at one presentation at the 21st General Assembly of the IUGG in July 1995 in Boulder, CO. A new method, called Anomaly Attenuation Rate (AAR) Method (based on the Euler method), was developed during this study. This method is scale-independent and is appropriate to locate centroids of semi-compact three dimensional sources of gravity and magnetic anomalies. The method was presented during 1996 Spring AGU meeting and a manuscript describing this method is being prepared for its submission to a high-ranking journal. The grant has resulted in 3 papers and presentations at national and international meetings and one manuscript of a paper (to be submitted shortly to a reputable journal).

  17. The Stardalur magnetic anomaly revisited—New insights into a complex cooling and alteration history

    NASA Astrophysics Data System (ADS)

    Vahle, C.; Kontny, A.; Gunnlaugsson, H. P.; Kristjansson, L.

    2007-10-01

    This study provides new rock magnetic and magneto-mineralogical data including Mössbauer spectroscopy of basaltic drill cores from the Stardalur volcanic complex, Iceland, in order to better understand the strong magnetic anomaly, which is caused by an extraordinary high natural remanent magnetization (NRM). NRM and magnetic susceptibility ( χ) display a positive linear correlation ( R2 = 0.81) and reach very high values up to 121 A/m and 148 × 10 -3 SI. Although a Curie temperature of 580 °C and a Verwey transition at about -160 °C is indicative of magnetite, χ- T heating experiments in argon and air atmosphere and thermal demagnetization measurements of NRM revealed a slight cation-deficiency. According to induced remanent magnetization experiments the remanence is carried solely by this low coercive phase. Minor titanomaghemite with a TC at about 340 °C only occurs in samples with larger oxide grains (20-80 μm). High vesicle abundances and the exsolution texture of Fe-Ti oxides suggest subaerial extrusion of the lava. A high oxygen fugacity (probably above the NNO buffer) and a low Ti/(Ti + Fe) ratio of the basaltic melt are suggested as a precondition for high concentration of magnetic minerals and therefore high primary TRM. During high temperature oxidation, ilmenite exsolution-lamellae, developed in titanomagnetite, and symplectic magnetite (+ pyroxene) formed by the breakdown of olivine. This secondary magnetite, grown at temperatures above the Curie temperature, increases the primary TRM. Early stage hydrothermal alteration (below about 375 °C) led to maghemitization of (titano)magnetite, clearly indicated by shrinkage cracks and irreversible χ- T curves. During later stage hydrothermal alteration, NRM intensity increased slightly due to the growth of secondary magnetite at lower temperatures (about 250-300 °C). This hydrothermally formed magnetite acquired only a low CRM but increased magnetic susceptibility significantly. According to our

  18. A semiclassical formulation of the chiral magnetic effect and chiral anomaly in even d + 1 dimensions

    NASA Astrophysics Data System (ADS)

    Dayi, Ömer F.; Elbistan, Mahmut

    2016-05-01

    In terms of the matrix valued Berry gauge field strength for the Weyl Hamiltonian in any even space-time dimensions a symplectic form whose elements are matrices in spin indices is introduced. Definition of the volume form is modified appropriately. A simple method of finding the path integral measure and the chiral current in the presence of external electromagnetic fields is presented. It is shown that within this new approach the chiral magnetic effect as well as the chiral anomaly in even d + 1 dimensions are accomplished straightforwardly.

  19. Polar Wander on the Moon Inferred from its Shape and Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Garrick-Bethell, I.

    2015-12-01

    The lunar shape can inform us about the Moon's early spin pole location, or history of true polar wander. This history is important for understanding the stability of polar ice deposits [1], and possible relationships between large-scale lunar features and the lunar orbit. Recently, Garrick-Bethell et al. [2] showed that when the effects of large basins are ignored, the Moon's early spin pole could be inferred from a tidal-rotational deformation that froze-in when the Moon was closer to the Earth. They also showed that the lunar shape is consistent with early tidal heating in the crust during the magma ocean epoch [3]. Here we will present some updates to this work, and discuss how the lunar spin pole may have evolved in time, as inferred from the progressive formation of large basins and components of the degree-2 gravity field that are not associated with basins. Separately, magnetic anomalies can address the problem of lunar polar wander, assuming the ancient dynamo that magnetized them was dominantly dipolar and aligned with the spin axis. However, recent surveys of magnetic anomalies reveal paleopole distributions that are quite complicated and inconsistent across different studies [4, 5]. Some reported paleopoles are consistent with the early spin pole inferred from the lunar shape [2], while others are not. These paleopoles imply either very large amounts of polar wander, or that the dynamo evolved with a complex field geometry. Some possible resolutions to these problems will be discussed, including secular variation of the magnetic field and difficulties with inversions for magnetic sources. References 1. Siegler, M. A. et al., 46th Lunar and Planetary Science Conference, LPI Contribution No. 1832, p. 2675 (2015). 2. Garrick-Bethell, I., et al., Nature 512, 181 (2014). 3. Garrick-Bethell, I., et al., Science 330, 949 (2010). 4. Arkani-Hamed, J. and Boutin, D., Icarus 237, 262 (2014). 5. Takahashi, F., et al., Nature Geoscience 7, 409 (2014).

  20. Calculation of the magnetic gradient tensor from total magnetic anomaly field based on regularized method in frequency domain

    NASA Astrophysics Data System (ADS)

    Yin, Gang; Zhang, Yingtang; Mi, Songlin; Fan, Hongbo; Li, Zhining

    2016-11-01

    To obtain accurate magnetic gradient tensor data, a fast and robust calculation method based on regularized method in frequency domain was proposed. Using the potential field theory, the transform formula in frequency domain was deduced in order to calculate the magnetic gradient tensor from the pre-existing total magnetic anomaly data. By analyzing the filter characteristics of the Vertical vector transform operator (VVTO) and Gradient tensor transform operator (GTTO), we proved that the conventional transform process was unstable which would zoom in the high-frequency part of the data in which measuring noise locate. Due to the existing unstable problem that led to a low signal-to-noise (SNR) for the calculated result, we introduced regularized method in this paper. By selecting the optimum regularization parameters of different transform phases using the C-norm approach, the high frequency noise was restrained and the SNR was improved effectively. Numerical analysis demonstrates that most value and characteristics of the calculated data by the proposed method compare favorably with reference magnetic gradient tensor data. In addition, calculated magnetic gradient tensor components form real aeromagnetic survey provided better resolution of the magnetic sources and original profile.

  1. Modeling of Magnetic Anomalies Associated with Magmatic Intrusions Away from the Guaymas Basin Rift, Gulf of California

    NASA Astrophysics Data System (ADS)

    Isunza, I.

    2015-12-01

    It is well known that continental breakup can be defined by the detection of magnetic anomalies caused by magma from a recently formed ridge. However in transitional continental-oceanic crust zones, special attention must be paid. These zones commonly present weak magnetic anomalies whose interpretation is debated, and the use of geophysical techniques is necessary. Guaymas basin in Gulf of California is one of the few known places in the world in which magmatic intrusions are intruding in rich-organic sediments. This is thought to cause the observed magnetic anomalies within the zone. In this work, magnetic and seismic data acquired during the GUAYMAS14 cruise, on board RV El Puma, are used to create a 2D forward model which describes structure geometry of the intrusions and their distribution outside the rift grabens.

  2. The Distorted Shape of Jupiter's North Auroral Oval - A Possible Magnetic Anomaly

    NASA Astrophysics Data System (ADS)

    Clarke, J. T.; D. Grodent Collaboration; J. Connerney Collaboration

    2002-09-01

    Repeated imaging of Jupiter's aurora has shown that the northern main oval has a distorted "kidney bean" shape in the general range of 40-100 deg magnetic longitude, which appears unchanged since 1994. More recently, improved accuracy in locating the satellite footprint auroral emissions has provided new information about the geometry of Jupiter's magnetic field in this and other areas. The persistent pattern of the main oval implies a disturbance of the local magnetic field, and the increased latitudinal separation of the locus of satellite footprints from each other and from the main oval implies a locally weaker field strength. It is possible that these phenomena result from a magnetic anomaly in Jupiter's intrinsic magnetic field, as was proposed by A. Dessler in the 1970's. There is presently only limited evidence from the scarcity of auroral footprints observed in this longitude range. Similarly, while it is difficult to observe the conjugate regions in the southern aurora, there does not appear to be any corresponding distortion in the south. We will present the observational evidence that we have accumulated to date, propose future observations to determine the nature of this disturbance, and speculate on its causes and implications.

  3. Coupled structural joint inversion and Euler deconvolution of isolated gravity and magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Fregoso, E.; Gallardo, L. A.; García-Abdeslem, J.

    2013-05-01

    The cross-gradient joint inversion is nowadays applied to a diversity of combinations of geophysical data in the search for structurally similar models that facilitate the interpretation of the subsurface characteristics. In line with these results, the cross-gradients joint inversion of gravity and magnetic data, in particular, has succeeded on finding commonly collocated density and magnetization structures. However, the inherent lack of depth resolution in the inversion of potential data still yields density and magnetization models with ambiguities at depth. In our work, we propose that the use of conceptually different interpretation strategies may help to resolve this difficulty and we performed some experiments incorporating the more conventional Euler deconvolution strategy in the joint inversion scheme. In this study we present a methodology to jointly invert potential field data incorporating Euler deconvolution for both magnetic and density sources characterized by the upper part of isolated tridimensional causative bodies. This information feeds, as a priori constraint, the cross-gradient joint 3D inversion methodology. Using synthetic and field data we demonstrate that the coupling of both methodologies generally produce more realistic density and magnetization models than when cross-gradient joint inversion is applied alone. Even though our experiments are performed on isolated anomalies, we suggest that the methodology may be suitable to regions described by sedimentary basins, faults, irregular sills, etc., in order to improve representative models of the true structures.

  4. Magnetic anomalies in East Antarctica: a window on major tectonic provinces and their boundaries

    USGS Publications Warehouse

    Golynsky, A.V.

    2007-01-01

    An analysis of aeromagnetic data compiled within the Antarctic Digital Magnetic Anomaly Project (ADMAP) yields significant new insight into major tectonic provinces of East Antarctica. Several previously unknown crustal blocks are imaged in the deep interior of the continent, which are interpreted as cratonic nuclei. These cratons are fringed by a large and continuous orogenic belt between Coats Land and Princess Elizabeth Land, with possible branches in the deeper interior of East Antarctica. Most of the crustal provinces and boundaries identified in this study are only in part exposed. More detailed analyses of these crustal provinces and their tectonic boundaries would require systematic acquisition of additional high-resolution magnetic data, because at present the ADMAP database is largely inadequate to address many remaining questions regarding Antarctica’s tectonic evolution.

  5. Energy Detection Based on Undecimated Discrete Wavelet Transform and Its Application in Magnetic Anomaly Detection

    PubMed Central

    Nie, Xinhua; Pan, Zhongming; Zhang, Dasha; Zhou, Han; Chen, Min; Zhang, Wenna

    2014-01-01

    Magnetic anomaly detection (MAD) is a passive approach for detection of a ferromagnetic target, and its performance is often limited by external noises. In consideration of one major noise source is the fractal noise (or called 1/f noise) with a power spectral density of 1/fa (0magnetic anomaly detection and UDWT are introduced in brief, while a possible detection system based on giant magneto-impedance (GMI) magnetic sensor is also given out. Then our proposed energy detection based on UDWT is described in detail, and the probabilities of false alarm and detection for given the detection threshold in theory are presented. It is noticeable that no a priori assumptions regarding the ferromagnetic target or the magnetic noise probability are necessary for our method, and different from the discrete wavelet transform (DWT), the UDWT is shift invariant. Finally, some simulations are performed and the results show that the detection performance of our proposed detector is better than that of the conventional energy detector even utilized in the Gaussian white noise, especially when the spectral parameter α is less than 1.0. In addition, a real-world experiment was done to demonstrate the advantages of the proposed method. PMID:25343484

  6. World Digital Magnetic Anomaly Map version 2 (WDMAM v.2) - released for research and education

    NASA Astrophysics Data System (ADS)

    CHOI-Dyment, Y.; Lesur, V.; Dyment, J.; Hamoudi, M.; Thebault, E.; Catalan, M.

    2015-12-01

    The World Digital Magnetic Anomaly Map is an international initiative carried out under the auspices of the International Association of Geomagnetism and Aeronomy (IAGA) and the Commission for the Geological Map of the World (CGMW). A first version of the map has been published and distributed eight years ago (WDMAM v1; Korhonen et al., 2007). We have produced a candidate which has been accepted as the second version of this map (WDMAM v2) at the International Union of Geophysics and Geodesy in Prag, in June 2015. On land, we adopted an alternative approach avoiding any unnecessary processing on existing aeromagnetic compilations. When available, we used the original aeromagnetic data. As a result the final compilation remains an acceptable representation of the national and international data grids. Over oceanic areas the marine data have been extended. In areas of insufficient data coverage, a model has been computed based on a modified digital grid of the oceanic lithosphere age, considering plate motions in the determination of magnetization vector directions. This model has been further adjusted to the available data, resulting in a better representation of the anomalies. The final grid will be periodically upgraded. Version 2.0 has been released and is available at wdmam.org to support both research and education projects. Colleagues willing to contribute data for future releases (and become a co-author of the map) should contact any of the authors or Jerome Dyment (chair of the WDMAM Task Force) at jdy@ipgp.fr .

  7. A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

    1999-01-01

    Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data are playing a major role in Arctic studies.

  8. A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

    1999-01-01

    Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While Magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and McAdoo, 1998) are playing a major role in Arctic studies.

  9. The analysis of ZTEM data across the Humble magnetic anomaly, Alaska

    NASA Astrophysics Data System (ADS)

    Sattel, Daniel; Witherly, Ken

    2015-09-01

    ZTEM data acquired across the Humble magnetic anomaly of almost 30 000 nT were analysed for the presence of a magnetic gradient response and the effects from elevated magnetic susceptibilities. Mag3D inversion of the magnetic data indicates magnetic susceptibility values as high as 2.0 (SI). The response of moving the receiver coil through the magnetic-field gradient peaks at 0.01 Hz and drops off strongly with frequency. Lacking information about the field strength at the base station precludes the comparison of amplitudes between computed gradient responses and the survey data, but the comparison of response shapes suggests that the gradient responses are too small to have a noticeable effect on the survey data. ZTEM responses were forward modelled with a 3D algorithm developed at the University of British Columbia Geophysical Inversion Facility (UBC-GIF) that takes into account electric conductivities σ and magnetic susceptibilities κ, in order to assess the impact of the elevated κ-values derived from the Mag3D inversion. Computing the ZTEM response for these κ-values combined with resistive half-spaces indicates that the response amplitudes and shapes strongly depend on the background resistivities. Ignoring the elevated κ-values during an inversion can result in patterns that resemble crop circles. The approximate conductivity structure of the survey area was derived with a UBC-GIF 3D ZTEM inversion, which models κ = 0. Forward-model results of these conductivities combined with the elevated κ-values derived from the Mag3D inversion indicate that the conductivities are underestimated with the κ = 0 assumption. For an environment such as Humble, with deep-seated zones of elevated κ-values, the shallow inverted conductivity structure appears to be reliable, but the deeper structure should be interpreted with caution.

  10. Interpretations of magnetic anomalies at a potential repository site located in the Yucca Mountain area, Nevada Test Site

    SciTech Connect

    Bath, G.D.; Jahren, C.E.

    1984-12-31

    In the Yucca Mountain area near the southwestern border of the Nevada Test Site, studies of the relation of magnetic properties to geologic features have provided structural information at and near a potential site for storage or radioactive waste. Interpreted features include a tabular mass of magnetized sedimentary rock beneath thick deposits of volcanic rock, and 11 major faults that strike generally northward and displace magnetized volcanic rock. A positive anomaly in a high-altitude aeromagnetic survey over exposures of strongly magnetized argillite of the Eleana Formation extends westward 20 km into the site area where interpretations indicate an argillite thickness of 800 m at a depth of 2.25 km. The high magnetite content of the argillite is not typical of the region, and was probably introduced by the heating effects of an underlying pluton. The basis for mapping traces of faults, and identifying their upthrown sides, was developed elsewhere at Yucca fault in the relatively simple volcanic terrains of Yucca Flat. In the site area, analyses of aeromagnetic anomalies from a low-altitude east-west aeromagnetic survey show the Topopah Spring Member of the Paintbrush Tuff as the primary source of anomalies from faulted sequences of volcanic rock. Faults related to belts of positive and negative anomalies surrounding the site have been identified. The possibility that an east-west pattern of anomalies is related to structure crossing the site was investigated by a recent aeromagnetic survey flown at low altitude in north-south directions. A significant reduction in amplitude of these anomalies resulted when effects of the deeply buried argillite were removed. The remaining anomalies over the site can be explained by a change in lateral extent, or magnetic properties, of volcanic units beneath the Topopah Spring Member. 37 references, 22 figures, 1 table.

  11. Magnetization anomaly of Nb3Al strands and instability of Nb3Al Rutherford cables

    SciTech Connect

    Yamada, Ryuji; Kikuchi, Akihiro; Wake, Masayoshi; /KEK, Tsukuba

    2006-08-01

    Using a Cu stabilized Nb{sub 3}Al strand with Nb matrix, a 30 meter long Nb{sub 3}Al Rutherford cable was made by a collaboration of Fermilab and NIMS. Recently the strand and cable were tested. In both cases instability was observed at around 1.5 Tesla. The magnetization of this Nb{sub 3}Al strand was measured first using a balanced coil magnetometer at 4.2 K. Strands showed an anomalously large magnetization behavior around at 1.6 T, which is much higher than the usual B{sub c2} {approx} 0.5 Tesla (4.2 K) of Nb matrix. This result is compared with the magnetization data of short strand samples using a SQUID magnetometer, in which a flux-jump signal was observed at 0.5 Tesla, but not at higher field. As a possible explanation for this magnetization anomaly, the interfilament coupling through the thin Nb films in the strands is suggested. The instability problem observed in low field tests of the Nb{sub 3}Al Rutherford cables is attributed to this effect.

  12. Observation of magnetic anomalies in one-step solvothermally synthesized nickel-cobalt ferrite nanoparticles.

    PubMed

    Datt, Gopal; Sen Bishwas, Mousumi; Manivel Raja, M; Abhyankar, A C

    2016-03-01

    Magnetic anomalies corresponding to the Verwey transition and reorientation of anisotropic vacancies are observed at 151 K and 306 K, respectively, in NiCoFe2O4 nanoparticles (NPs) synthesized by a modified-solvothermal method followed by annealing. Cationic disorder and spherical shape induced non-stoichiometry suppress the Verwey transition in the as-synthesized NPs. On the other hand, reorientation of anisotropic vacancies is quite robust. XRD and electron microscopy investigations confirm a single phase spinel structure and the surface morphology of the as-synthesized NPs changes from spherical to octahedral upon annealing. Rietveld analysis reveals that the Ni(2+) ions migrate from tetrahedral (A) to octahedral (B) sites upon annealing. The Mössbauer results show canted spins in both the NPs and the strength of superexchange is stronger in Co-O-Fe than Ni-O-Fe. Magnetic force images show that the as-synthesised NPs are single-domain whereas the annealed NPs are multi-domain octahedral particles. The FMR study reveals that both the NPs have a broad FMR line-width; and resonance properties are consistent with the random anisotropy model. The broad inhomogeneous FMR line-width, observation of the Verwey transition, tuning of the magnetic domain structure as well as the magnetic properties suggest that the NiCoFe2O4 ferrite NPs may be promising for future generation spintronics, magneto-electronics, and ultra-high-density recording media as well as for radar absorbing applications.

  13. Preparation of magnetic anomaly profile and contour maps from DOE-NURE aerial survey data. Volume I. Processing procedures

    SciTech Connect

    Tinnel, E.P.; Hinze, W.J.

    1981-09-01

    Total intensity magnetic anomaly data acquired as a supplement to radiometric data in the DOE National Uranium Resource Evaluation (NURE) Program are useful in preparing regional profile and contour maps. Survey-contractor-supplied magnetic anomaly data are subjected to a multiprocess, computer-based procedure which prepares these data for presentation. This procedure is used to produce the following machine plotted maps of National Topographic Map Series quadrangle units at a 1:250,000 scale: (1) profile map of contractor-supplied magnetic anomaly data, (2) profile map of high-cut filtered data with contour levels of each profile marked and annotated on the associated flight track, (3) profile map of critical-point data with contour levels indicated, and (4) contour map of filtered and selected data. These quadrangle maps are supplemented with a range of statistical measures of the data which are useful in quality evaluation.

  14. Deciphering tectonic phases of the Amundsen Sea Embayment shelf, West Antarctica, from a magnetic anomaly grid

    NASA Astrophysics Data System (ADS)

    Gohl, Karsten; Denk, Astrid; Eagles, Graeme; Wobbe, Florian

    2013-02-01

    The Amundsen Sea Embayment (ASE), with Pine Island Bay (PIB) in the eastern embayment, is a key location to understanding tectonic processes of the Pacific margin of West Antarctica. PIB has for a long time been suggested to contain the crustal boundary between the Thurston Island block and the Marie Byrd Land block. Plate tectonic reconstructions have shown that the initial rifting and breakup of New Zealand from West Antarctica occurred between Chatham Rise and the eastern Marie Byrd Land at the ASE. Recent concepts have discussed the possibility of PIB being the site of one of the eastern branches of the West Antarctic Rift System (WARS). About 30,000 km of aeromagnetic data - collected opportunistically by ship-based helicopter flights - and tracks of ship-borne magnetics were recorded over the ASE shelf during two RV Polarstern expeditions in 2006 and 2010. Grid processing, Euler deconvolution and 2D modelling were applied for the analysis of magnetic anomaly patterns, identification of structural lineaments and characterisation of magnetic source bodies. The grid clearly outlines the boundary zone between the inner shelf with outcropping basement rocks and the sedimentary basins of the middle to outer shelf. Distinct zones of anomaly patterns and lineaments can be associated with at least three tectonic phases from (1) magmatic emplacement zones of Cretaceous rifting and breakup (100-85 Ma), to (2) a southern distributed plate boundary zone of the Bellingshausen Plate (80-61 Ma) and (3) activities of the WARS indicated by NNE-SSW trending lineaments (55-30 Ma?). The analysis and interpretation are also used for constraining the directions of some of the flow paths of past grounded ice streams across the shelf.

  15. Insights into magmatic processes and hydrothermal alteration of in situ superfast spreading ocean crust at ODP/IODP site 1256 from a cluster analysis of rock magnetic properties

    NASA Astrophysics Data System (ADS)

    Dekkers, Mark J.; Heslop, David; Herrero-Bervera, Emilio; Acton, Gary; Krasa, David

    2014-08-01

    analyze magnetic properties from Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6°44.1' N, 91°56.1' W) on the Cocos Plate in ˜15.2 Ma oceanic crust generated by superfast seafloor spreading, the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Fuzzy c-means cluster analysis and nonlinear mapping are utilized to study down-hole trends in the ratio of the saturation remanent magnetization and the saturation magnetization, the coercive force, the ratio of the remanent coercive force and coercive force, the low-field magnetic susceptibility, and the Curie temperature, to evaluate the effects of magmatic and hydrothermal processes on magnetic properties. A statistically robust five cluster solution separates the data predominantly into three clusters that express increasing hydrothermal alteration of the lavas, which differ from two distinct clusters mainly representing the dikes and gabbros. Extensive alteration can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. Thus, the analysis complements interpretation based on electrofacies analysis. All clusters display rock magnetic characteristics compatible with an ability to retain a stable natural remanent magnetization suggesting that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Paleointensity determination is difficult because of the propensity of oxyexsolution during laboratory heating and/or the presence of intergrowths. The upper part of the extrusive sequence, the granoblastic dikes, and moderately altered gabbros may contain a comparatively uncontaminated thermoremanent magnetization.

  16. Circum-Arctic Magnetic Anomalies - Challenges of Compilation and the Value of Regional Interpretation in a Frontier Area

    NASA Astrophysics Data System (ADS)

    Saltus, R. W.; Gaina, C.; Brown, P. J.

    2007-12-01

    Important societal issues are driving increased attention to polar regions. The arctic, in particular, is the focus of scientific studies relating to climate change as well as resource exploration and territorial claims. The news and entertainment media are picking up on polar themes and driving interest within popular culture. Part of the attraction and mystique of the ends of the Earth lies in their relative inaccessibility and harsh environment. These same attributes make it difficult to conduct even basic scientific investigation, and therefore, the arctic remains a scientific frontier in many respects. Delineation of a robust tectonic framework for the top of the world is an essential prerequisite to resource assessment. The difficulty of making direct geologic observations beneath ice and sea requires remote measurement. Regional magnetic anomaly mapping provides important constraining information for the development of tectonic models for this structurally complex region. In addition to the obvious logistical challenges to detailed magnetic field measurement in the high arctic, noise and instability in the magnetic field itself at high latitudes presents difficulties. Nevertheless, regional magnetic anomaly data have been collected over the past 50 years for much of the arctic. The available surveys are diverse in vintage and survey design; the amplitude and frequency content of measured anomalies are widely variable. Availability of metadata and other documentation are also inconsistent for these surveys. This leads to significant challenges in constructing accurate regional magnetic anomaly maps. Preliminary maps from a new international cooperation effort (CAMP-GM, under the direction of Carmen Gaina, Geological Survey of Norway) provide the most consistent view yet of magnetic anomalies for the tectonically complex arctic basins and surrounding continents. Careful attention to digital compilation details allows the new grids to be mathematically filtered

  17. Investigation of the crust of the Pannonian Basin, Hungary using low-altitude CHAMP horizontal magnetic gradient anomalies

    NASA Astrophysics Data System (ADS)

    Taylor, P. T.; Kis, K. I.; Puszta, S.; Wittman, G.; Kim, H.; Toronyi, B.

    2011-12-01

    The Pannonian Basin is a deep intracontinental basin that formed as part of the Alpine orogeny. It is some 600 by 500 km in area and centered on Hungary. This region was chosen since it has one of the thinnest continental crusts in Europe and is the location of complex tectonic structures. In order to study the nature of the crustal basement we used the long-wavelength magnetic anomalies acquired by the CHAMP satellite. The SWARM constellation, scheduled to be launched next year, will have two lower altitude satellites flying abreast, with a separation of between ca. 150 to 200 km. to record the horizontal magnetic gradient. Since the CHAMP satellite has been in orbit for eight years and has obtained an extensive range of data, both vertically and horizontally there is a large enough data base to compute the horizontal magnetic gradients over the Pannonian Basin region using these many CHAMP orbits. We computed a satellite magnetic anomaly map, using the spherical-cap method of Haines (1985), the technique of Alsdorf et al. (1994) and from spherical harmonic coefficients of MF6 (Maus et al., 2008) employing recent and lowest altitude CHAMP data. We then computed the horizontal magnetic anomaly gradients (Kis and Puszta, 2006) in order to determine how these component data will improve our interpretation and to preview what the SWARM mission will reveal with reference to the horizontal gradient anomalies. The gradient amplitude of an 1000 km northeast-southwest profile through our horizontal component anomaly map varied from 0 to 0.025 nT/km with twin positive anomalies (0.025 and 0.023 nT/km) separated by a sharp V-shaped anomaly gradient to 0 nT/km between the two highs. Horizontal gradients indicate major magnetization boundaries in the crust (Dole and Jordan, 1978 and Cordell and Grauch, 1985). Our gradient anomaly was modeled with a two-dimensional body and this anomaly indicates a lateral variation of some 200 km. The model correlates with a 200 km area of

  18. Magnetic Properties of Rocks of the Kapuskasing Uplift (Ontario, Canada) and Origin of Long-Wavelength Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Dunlop, D. J.; Ozdemir, O.; Costanzo-Alvarez, V.

    2010-12-01

    The sources of long wavelength magnetic anomalies (LWA) in the crust are poorly understood. We have measured remanent and induced magnetizations of 210 samples of anorthosite, tonalite and mafic gneiss from the Kapuskasing uplift, an exposed partial crustal cross-section in northwestern Ontario, Canada. Anorthosites have generally high Q ratios of remanent/ induced magnetization, in the range 0.3-60, and their natural remanent magnetization (NRM) is resistant to both thermal and alternating-field (AF) demagnetization. However, anorthosite NRMs (0.001 to 0.3 A/m) are too weak to explain LWA amplitudes. Mafic gneisses also have relatively high Q ratios, peaking in the range 1-10, and the NRM is resistant to thermal and AF demagnetization. NRM and induced magnetization (IM) intensities are in the ranges 0.01-2 and 0.01-0.6 A/m, respectively. Tonalites have a bimodal distribution of magnetization. The more strongly magnetic group has both NRM and IM intensities in the range 0.1-5 A/m and wide-ranging Q values, from 0.1-10 approximately. Some tonalites could be an LWA source, although the long-term stability of their NRMs at high temperature in the crust is questionable because unblocking temperatures are broadly distributed from 100 to 600°C. In general, Q values measured at surface temperatures overestimate remanence at depth. In the deep crust, IM remains more or less constant but remanence decreases both reversibly and irreversibly, leading to Q ratios of <0.2-0.3 for multidomain grains and ≈1-3 for single-domain grains near their blocking temperatures. Thermoviscous magnetization over the Brunhes chron could add substantially to the effective induced magnetization. Typically induced + thermoviscous magnetization in the direction of the present Earth’s field will outweigh remanence in the direction of an ancient field as a source of LWA originating in the deepest crust. Remanence may play a larger role for mid-crustal sources where single-domain grains are well

  19. Magnetic properties of rocks of the Kapuskasing uplift (Ontario, Canada) and origin of long-wavelength magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Dunlop, David J.; Özdemir, Özden; Costanzo-Alvarez, Vincenzo

    2010-11-01

    The sources of long wavelength magnetic anomalies (LWA) in the crust are poorly understood. We have measured remanent and induced magnetizations of 210 samples of anorthosite, tonalite and mafic gneiss from the Kapuskasing uplift, an exposed partial crustal cross-section in northwestern Ontario, Canada. Anorthosites have generally high Q ratios of remanent/induced magnetization, in the range 0.3-60, and their natural remanent magnetization (NRM) is resistant to both thermal and alternating-field (AF) demagnetization. However, anorthosite NRMs (0.001-0.3 A m-1) are too weak to explain LWA amplitudes. Mafic gneisses also have relatively high Q ratios, peaking in the range 1-10, and the NRM is resistant to thermal and AF demagnetization. NRM and induced magnetization (IM) intensities are in the ranges 0.01-2 and 0.01-0.6 A m-1, respectively. Tonalites have a bimodal distribution of magnetization. The more strongly magnetic group has both NRM and IM intensities in the range 0.1-5 A m-1 and wide-ranging Q values, from 0.1 to 10 approximately. Some tonalites could be an LWA source, although the long-term stability of their NRMs at high temperature in the crust is questionable because unblocking temperatures are broadly distributed from 100 to 600°C. In general, Q values measured at surface temperatures overestimate remanence at depth. In the deep crust, IM remains more or less constant but remanence decreases both reversibly and irreversibly, leading to Q ratios of <0.2-0.3 for multidomain grains and ~1-3 for single-domain grains near their blocking temperatures. Thermoviscous magnetization over the Brunhes chron could add substantially to the effective induced magnetization. Typically induced + thermoviscous magnetization in the direction of the present Earth's field will outweigh remanence in the direction of an ancient field as a source of LWA originating in the deepest crust. Remanence may play a larger role for mid-crustal sources where single-domain grains are

  20. GRM crustal magnetic anomalies: Separating the Lord Howe Rise and Norfolk Ridge submarine structures

    NASA Technical Reports Server (NTRS)

    Frey, H.

    1985-01-01

    Multiple source bodies often lie within the resolution element of the MAGSAT and POGO data. Small weak sources lying near larger stronger sources will tend to be missed, although they do contribute to the total observed anomaly. Lower elevation magnetic anomaly surveys such as GRM alleviate this problem through the combined effects of significantly greater resolution and stronger signal amplitude. This permits the detection of smaller source bodies, and analysis of their structure and nature. The improvement a GRM will provide is demonstrated in the Lord Howe Rise/Norfolk Ridge area east of Australia, between the Tasman Sea and south Fiji Basin. The submarine features origin have important plate tectonic implications. The Lord Howe Rise (LHR) is a continental fragment broken off from Australia by the opening of the Tasman Sea. It is a wide, shallow structure lying between 160 and 165 deg longitude at 23 to 37 deg S latitude. Seismic refraction data show the LHR crust extending to depths in excess of 20 km.

  1. Electromagnetic particle-in-cell simulations of the solar wind interaction with lunar magnetic anomalies.

    PubMed

    Deca, J; Divin, A; Lapenta, G; Lembège, B; Markidis, S; Horányi, M

    2014-04-18

    We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier magnetohydrodynamics and hybrid simulations, the fully kinetic nature of iPic3D allows us to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe for the first time the interaction of a dipole model centered just below the lunar surface under plasma conditions such that only the electron population is magnetized. The fully kinetic treatment identifies electromagnetic modes that alter the magnetic field at scales determined by the electron physics. Driven by strong pressure anisotropies, the mini-magnetosphere is unstable over time, leading to only temporal shielding of the surface underneath. Future human exploration as well as lunar science in general therefore hinges on a better understanding of LMAs. PMID:24785022

  2. Electromagnetic particle-in-cell simulations of the solar wind interaction with lunar magnetic anomalies.

    PubMed

    Deca, J; Divin, A; Lapenta, G; Lembège, B; Markidis, S; Horányi, M

    2014-04-18

    We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier magnetohydrodynamics and hybrid simulations, the fully kinetic nature of iPic3D allows us to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe for the first time the interaction of a dipole model centered just below the lunar surface under plasma conditions such that only the electron population is magnetized. The fully kinetic treatment identifies electromagnetic modes that alter the magnetic field at scales determined by the electron physics. Driven by strong pressure anisotropies, the mini-magnetosphere is unstable over time, leading to only temporal shielding of the surface underneath. Future human exploration as well as lunar science in general therefore hinges on a better understanding of LMAs.

  3. Electromagnetic Particle-in-Cell Simulations of the Solar Wind Interaction with Lunar Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Deca, J.; Divin, A.; Lapenta, G.; Lembège, B.; Markidis, S.; Horányi, M.

    2014-04-01

    We present the first three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier magnetohydrodynamics and hybrid simulations, the fully kinetic nature of iPic3D allows us to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe for the first time the interaction of a dipole model centered just below the lunar surface under plasma conditions such that only the electron population is magnetized. The fully kinetic treatment identifies electromagnetic modes that alter the magnetic field at scales determined by the electron physics. Driven by strong pressure anisotropies, the mini-magnetosphere is unstable over time, leading to only temporal shielding of the surface underneath. Future human exploration as well as lunar science in general therefore hinges on a better understanding of LMAs.

  4. Hot flow anomaly formation by magnetic deflection. [regions of hot plasma in earth magnetosphere

    NASA Technical Reports Server (NTRS)

    Onsager, T. G.; Thomsen, M. F.; Winske, D.

    1990-01-01

    Hot flow anomalies (HFAs) are localized plasma structures observed in the solar wind and magnetosheath near the earth's quasi-parallel bow shock. This paper presents one-dimensional hybrid computer simulations illustrating a formation mechanism for HFAs in which the single hot ion population results from a spatial separation of two counterstreaming ion beams. The higher-density cooler regions are dominated by the background (solar wind) ions, and the lower-density hotter internal regions are dominated by the beam ions. The spatial separation of the beam and background is caused by the deflection of the ions in large-amplitude magnetic fields which are generated by ion/ion streaming instabilities.

  5. Investigating tectonic and bathymetric features of the Indian Ocean using MAGSAT magnetic anomaly data

    NASA Technical Reports Server (NTRS)

    Lazarewicz, A. R.; Sailor, R. V. (Principal Investigator)

    1982-01-01

    MAGSAT Investigator-B tapes were preprocessed by (1) removing all data points with obvious erroneous values and location errors; (2) removing smaller spikes (typically 15 nT or more), and deleting data tracks with fewer than 20 points; and (3) removing a linear trend from each track. The remaining data were recorded on tape for use by the equivalent source mapping (ESMAP) program which uses a least squares algorithm to fit the magnetization parameter of the grid of equivalent source dipoles in the crust to satellite data acquired at different times and locations. ESMAP was implemented on the TASC computing system and modified to read preprocessed MAGSAT tapes and interface with TASC plotting software. Some verification of the software was accomplished. Gridded 1-degree mean values of gravity anomaly and sea surface undulation computed from SEASAT radar altimeter were obtained and brought on line.

  6. A Hybrid Positive-and-Negative Curvature Approach for Detection of the Edges of Magnetic Anomalies, and Its Application in the South China Sea

    NASA Astrophysics Data System (ADS)

    Guo, Lianghui; Gao, Rui; Meng, Xiaohong; Zhang, Guoli

    2015-10-01

    In work discussed in this paper the characteristics of both the most positive and most negative curvatures of a magnetic anomaly were analyzed, and a new approach for detection of the edges of magnetic anomalies is proposed. The new approach, called the hybrid positive-and-negative curvature approach, combines the most positive and most negative curvatures into one curvature by formula adjustments and weighted summation, combining the advantages of the two curvatures to improve edge detection. This approach is suitable for vertically magnetized or reduction-to-pole anomalies, which avoids the complexity of magnetic anomalies caused by oblique magnetization. Testing on synthetic vertically magnetized magnetic anomalies data demonstrated that the hybrid approach traces the edges of magnetic source bodies effectively, discriminates between high and low magnetism intuitively, and is better than approaches based solely on use of the most positive or most negative curvature. Testing on reduced-to-pole magnetic anomalies data around the ocean basin of the South China Sea showed that the hybrid approach enables better edge detection than the most positive or most negative curvatures. On the basis of the features of the reduced-to-pole magnetic anomalies and their hybrid curvature, we suggest the tectonic boundary between the southwestern subbasin and the eastern subbasin of the South China Sea ranges from the northeastern edge of the Zhongsha Islands in the southeast direction to the northeastern edge of the Reed Bank.

  7. Geophysical Surveying of Shallow Magnetic Anomalies Using the iPhone Magnetometer

    NASA Astrophysics Data System (ADS)

    Opdyke, P.; Dudley, C.; Louie, J. N.

    2012-12-01

    This investigation examined whether the 3-axis Hall-effect magnetometer in the Apple iPhone 3GS can function as an effective shallow magnetic survey instrument. The xSensor Pro app from Crossbow Systems allows recoding of all three sensor components along with the GPS location, at a frequency of 1.0, 4.0, 16.0, and 32.0 Hz. If the iPhone proves successful in collecting useful magnetic data, then geophysicists and especially educators would have a new tool for high-density geophysical mapping. No-contract iPhones that can connect with WiFi can be obtained for about $400, allowing deployment of large numbers of instruments. iPhones with the xSensor Pro app surveyed in parallel with an Overhauser GEM system magnetometer (1 nT sensitivity) to test this idea. Anderson Bay, located on the Pyramid Lake Paiute Reservation, provided a rural survey location free from cultural interference. xSensor Pro, logged each component's intensity and the GPS location at a frequency of four measurements per second. Two Overhauser units functioned as a base unit and a roving unit. The roving unit collected total field at set points located with a handheld GPS. Comparing the total field computed from the iPhone components against that collected by the Overhauser establishes the level of anomalies that the iPhone can detect. iPhone total-field measurements commonly vary by 200 nT from point to point, so a spatial-temporal average over 25 seconds produces a smoothed signal for comparison. Preliminary analysis of the iPhone results show that the data do not accurately correlate to the total field collected by the Overhauser for any anomaly of less than 200 nT.

  8. Controls on Martian Hydrothermal Systems: Application to Valley Network and Magnetic Anomaly Formation

    NASA Technical Reports Server (NTRS)

    Harrison, Keith P.; Grimm, Robert E.

    2002-01-01

    Models of hydrothermal groundwater circulation can quantify limits to the role of hydrothermal activity in Martian crustal processes. We present here the results of numerical simulations of convection in a porous medium due to the presence of a hot intruded magma chamber. The parameter space includes magma chamber depth, volume, aspect ratio, and host rock permeability and porosity. A primary goal of the models is the computation of surface discharge. Discharge increases approximately linearly with chamber volume, decreases weakly with depth (at low geothermal gradients), and is maximized for equant-shaped chambers. Discharge increases linearly with permeability until limited by the energy available from the intrusion. Changes in the average porosity are balanced by changes in flow velocity and therefore have little effect. Water/rock ratios of approximately 0.1, obtained by other workers from models based on the mineralogy of the Shergotty meteorite, imply minimum permeabilities of 10(exp -16) sq m2 during hydrothermal alteration. If substantial vapor volumes are required for soil alteration, the permeability must exceed 10(exp -15) sq m. The principal application of our model is to test the viability of hydrothermal circulation as the primary process responsible for the broad spatial correlation of Martian valley networks with magnetic anomalies. For host rock permeabilities as low as 10(exp -17) sq m and intrusion volumes as low as 50 cu km, the total discharge due to intrusions building that part of the southern highlands crust associated with magnetic anomalies spans a comparable range as the inferred discharge from the overlying valley networks.

  9. The Effect of Dissipation Mechanism and Guide Field Strength on X-line Spreading in 3D Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Shepherd, Lucas; Cassak, P.; Drake, J.; Gosling, J.; Phan, T.; Shay, M. A.

    2013-07-01

    In two-ribbon flares, the fact that the ribbons separate in time is considered evidence of magnetic reconnection. However, in addition to the ribbons separating, they can also elongate (as seen in animations of, for example, the Bastille Day flare). The elongation is undoubtedly related to the reconnection spreading in the out-of-plane direction. Indeed, naturally occurring magnetic reconnection generally begins in a spatially localized region and spreads in the direction perpendicular to the reconnection plane as time progresses. For example, it was suggested that X-line spreading is necessary to explain the observation of X-lines extending more than 390 Earth radii (Phan et al., Nature, 404, 848, 2006), and has been seen in reconnection experiments. A sizeable out-of-plane (guide) magnetic field is present at flare sites and in the solar wind. Here, we study the effect of dissipation mechanism and the strength of the guide field has on X-line spreading. We present results from three-dimensional numerical simulations of magnetic reconnection, comparing spreading with the Hall term to spreading with anomalous resistivity. Applications to solar flares and magnetic reconnection in the solar wind will be discussed.

  10. Modelling Of The Contribution Of Upper Mantle Magnetism To The Magnetic Anomaly Map Observed On Earth's Surface: Analysis Of Different Tectonic Settings

    NASA Astrophysics Data System (ADS)

    Martin-Hernandez, F.; Ferre, E. C.; Friedman, S. A.

    2015-12-01

    Magnetic anomalies of the Geomagnetic Field have been increasing interest in recent years in particular with acquisition of new data from satellite missions. Traditionally, anomalies have been modelled from Earth's surface down to the crust-upper mantle boundary, considering the Moho as the magnetic-non magnetic interface. However, long wavelength magnetic anomalies appear as residuals not modelled in most global and large regional magnetic models. In the last years, several publications have proposed and analysed the magnetic signal from fresh upper mantle xenolith showing the presence of minor inclusions of magnetite that might be in ferrimagnetic state at those depths, depending on the particular geotherm of the geological setting. It has been modelled the effect on Earth surface of those magnetite inclusions taking into account the variation of magnetic intensity at depth, magnetic susceptibility and concentration of magnetite reported from mantle xenolith on different setting finding the effect of the inclusions can have measurable intensities at the surface. Results show that the effect of magnetite in the upper mantle could have a relevant effect when modelling magnetic signal from satellite missions.

  11. Evidence for Mini-Magnetospheres at four Lunar Magnetic Anomalies: Reiner-Gamma, Airy, Descartes and Crozier

    NASA Astrophysics Data System (ADS)

    Nayak, M.; Garrick-Bethell, I.; Hemingway, D.

    2014-12-01

    Lunar swirls are enigmatic high-albedo surface markings co-located with magnetic anomalies. The existence of mini-magnetospheres has been proposed as a formation mechanism, making small-scale magnetic field interactions with the solar wind of interest. Using data from the Lunar Prospector, Clementine, and Advanced Composition Explorer missions, we develop three metrics for the identification of mini-magnetospheres: 1) presence of coherent magnetism at low altitude for magnetic field measurements taken in the solar wind; 2) directional field distortions that are correlated with changes in incident solar wind azimuth; 3) intensification of total field strength. These metrics are applied to four lunar magnetic anomalies with various reflectances and magnetic field strengths, ranging from fully developed swirls (Reiner-Gamma, Airy) to diffuse albedo patches which may or may not be swirls (Descartes, Crozier). Specifically, we compare magnetic field measurements in the solar wind to source magnetization models constructed from observations in the lunar wake and Earth's magnetotail. By applying these criteria, we confirm previous findings of magnetosphere-like phenomena at Reiner-Gamma. We also find evidence of these phenomena at Descartes and Airy, and propose that mini-magnetospheres may exist here. At Airy, very large upwind distortions are observed, comparable to the length scale of the anomaly itself. At Reiner-Gamma and Descartes, this distortion is significantly smaller, yet the average field strengths are higher, implying that the scale of distortion is linked to the anomaly's field strength. Interestingly, at Crozier, the weakest anomaly considered, we do not observe this distortion. However, we do observe evidence of field intensification at high solar wind pressures (16 nPa). While Descartes and Reiner-Gamma are among the strongest anomalies on the Moon, and both exhibit magnetospheric properties, only Reiner-Gamma shows a well-developed swirl pattern

  12. Characterization of Lunar Swirls at Mare Ingenii: A Model for Space Weathering at Magnetic Anomalies

    NASA Technical Reports Server (NTRS)

    Kramer, Georgianna Y.; Combe, Jean-Philippe; Harnett, Erika M.; Hawke, Bernard Ray; Noble, Sarah K.; Blewett, David T.; McCord, Thomas B.; Giguere, Thomas A.

    2011-01-01

    Analysis of spectra from the Clementine ultraviolet-visible and near-infrared cameras of small, immature craters and surface soils both on and adjacent to the lunar swirls at Marc Ingenii has yielded the following conclusions about space weathering at a magnetic anomaly. (l) Despite having spectral characteristics of immaturity, the lunar swirls arc not freshly exposed surfaces. (2) The swirl surfaces arc regions of retarded weathering, while immediately adjacent regions experience accelerated weathering, (3) Weathering in the off-swirl regions darkens and flattens the spectrum with little to no reddening, which suggests that the production of larger (greater than 40 nm) nanophase iron dominates in these locations as a result of charged particle sorting by the magnetic field. Preliminaty analysis of two other lunar swirl regions, Reiner Gamma and Mare Marginis, is consistent with our observations at Mare Ingenii. Our results indicate that sputtering/vapor deposition, implanted solar wind hydrogen, and agglutination share responsibility for creating the range in npFe(sup 0) particle sizes responsible for the spectral effects of space weathering.

  13. Modelling the gravity and magnetic field anomalies of the Chicxulub crater

    NASA Technical Reports Server (NTRS)

    Aleman, C. Ortiz; Pilkington, M.; Hildebrand, A. R.; Roest, W. R.; Grieve, R. A. F.; Keating, P.

    1993-01-01

    The approximately 180-km-diameter Chicxulub crater lies buried by approximately 1 km of sediment on the northwestern corner of the Yucatan Peninsula, Mexico. Geophysical, stratigraphic and petrologic evidence support an impact origin for the structure and biostratigraphy suggests that a K/T age is possible for the impact. The crater's location is in agreement with constraints derived from proximal K/T impact-wave and ejecta deposits and its melt-rock is similar in composition to the K/T tektites. Radiometric dating of the melt rock reveals an age identical to that of the K/T tektites. The impact which produced the Chicxulub crater probably produced the K/T extinctions and understanding the now-buried crater will provide constraints on the impact's lethal effects. The outstanding preservation of the crater, the availability of detailed gravity and magnetic data sets, and the two-component target of carbonate/evaporites overlying silicate basement allow application of geophysical modeling techniques to explore the crater under most favorable circumstances. We have found that the main features of the gravity and magnetic field anomalies may be produced by the crater lithologies.

  14. Subsurface faults detection based on magnetic anomalies investigation: A field example at Taba protectorate, South Sinai

    NASA Astrophysics Data System (ADS)

    Khalil, Mohamed H.

    2016-08-01

    Quantitative interpretation of the magnetic data particularly in a complex dissected structure necessitates using of filtering techniques. In Taba protectorate, Sinai synthesis of different filtering algorithms was carried out to distinct and verifies the subsurface structure and estimates the depth of the causative magnetic sources. In order to separate the shallow-seated structure, filters of the vertical derivatives (VDR), Butterworth high-pass (BWHP), analytic signal (AS) amplitude, and total horizontal derivative of the tilt derivative (TDR_THDR) were conducted. While, filters of the apparent susceptibility and Butterworth low-pass (BWLP) were conducted to identify the deep-seated structure. The depths of the geological contacts and faults were calculated by the 3D Euler deconvolution. Noteworthy, TDR_THDR was independent of geomagnetic inclination, significantly less susceptible to noise, and more sensitive to the details of the shallow superimposed structures. Whereas, the BWLP proved high resolution capabilities in attenuating the shorter wavelength of the near surface anomalies and emphasizing the longer wavelength derived from deeper causative structure. 3D Euler deconvolution (SI = 0) was quite amenable to estimate the depths of superimposed subsurface structure. The pattern, location, and trend of the deduced shallow and deep faults were conformed remarkably to the addressed fault system.

  15. Characterization of lunar swirls at Mare Ingenii: A model for space weathering at magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Kramer, Georgiana Y.; Combe, Jean-Philippe; Harnett, Erika M.; Hawke, Bernard Ray; Noble, Sarah K.; Blewett, David T.; McCord, Thomas B.; Giguere, Thomas A.

    2011-04-01

    Analysis of spectra from the Clementine ultraviolet-visible and near-infrared cameras of small, immature craters and surface soils both on and adjacent to the lunar swirls at Mare Ingenii has yielded the following conclusions about space weathering at a magnetic anomaly. (1) Despite having spectral characteristics of immaturity, the lunar swirls are not freshly exposed surfaces. (2) The swirl surfaces are regions of retarded weathering, while immediately adjacent regions experience accelerated weathering. (3) Weathering in the off-swirl regions darkens and flattens the spectrum with little to no reddening, which suggests that the production of larger (>40 nm) nanophase iron dominates in these locations as a result of charged particle sorting by the magnetic field. Preliminary analysis of two other lunar swirl regions, Reiner Gamma and Mare Marginis, is consistent with our observations at Mare Ingenii. Our results indicate that sputtering/vapor deposition, implanted solar wind hydrogen, and agglutination share responsibility for creating the range in npFe0 particle sizes responsible for the spectral effects of space weathering.

  16. Inverse Dipolar Magnetic Anomaly Over the Volcanic Cone Linked to Reverse Polarity Magnetizations in Lavas and Tuffs - Implications for the Conduit System

    NASA Astrophysics Data System (ADS)

    Fucugauchi, J. U.; Perez-Cruz, L. L.; Trigo-Huesca, A.

    2012-12-01

    A combined magnetics and paleomagnetic study of Toluquilla monogenetic volcano and associated lavas and tuffs from Valsequillo basin in Central Mexico provides evidence on a magnetic link between lavas, ash tuffs and the underground volcanic conduit system. Paleomagnetic analyses show that lavas and ash tuffs carry reverse polarity magnetizations, which correlate with the inversely polarized dipolar magnetic anomaly over the volcano. The magnetizations in the lava and tuff show similar southward declinations and upward inclinations, supporting petrological inferences that the tuff was emplaced while still hot and indicating a temporal correlation for lava and tuff emplacement. Conduit geometry is one of the important controlling factors in eruptive dynamics of basaltic volcanoes. However volcanic conduits are often not, or only partly, exposed. Modeling of the dipolar anomaly gives a reverse polarity source magnetization associated with a vertical prismatic body with southward declination and upward inclination, which correlates with the reverse polarity magnetizations in the lava and tuff. The study documents a direct correlation of the paleomagnetic records with the underground magmatic conduit system of the monogenetic volcano. Time scale for cooling of the volcanic plumbing system involves a longer period than the one for the tuff and lava, suggesting that magnetization for the source of dipolar anomaly may represent a long time average as compared to the spot readings in the lava and tuff. The reverse polarity magnetizations in lava and tuff and in the underground source body for the magnetic anomaly are interpreted in terms of eruptive activity of Toluquilla volcano at about 1.3 Ma during the Matuyama reverse polarity C1r.2r chron.

  17. High-Resolution Ground-Based Magnetic Survey of a Buried Volcano: Anomaly B, Amargosa Desert, NV

    NASA Astrophysics Data System (ADS)

    McIlrath, J.; George, O.; Farrell, A. K.; Gallant, E.; Tavarez, S.; Downs, C. M.; Njoroge, M. W.; Wilson, J. A.; Connor, C.; Connor, L.; Kruse, S.

    2015-12-01

    Aeromagnetic surveys over the Amargosa Desert, Nevada, have revealed the presence of several magnetic anomalies that have been interpreted to be caused by buried volcanoes; many of these anomalies have been confirmed by drilling. We present data collected from a high-resolution, ground-based magnetic survey over Anomaly B, the largest of these anomalies, that reveal details about a buried crater and its associated lava flow, not previously observed in the aeromagnetic surveys. These details provide insight into the nature of the eruption and the volume of this buried volcano. Results from non-linear inversion demarcate a crater with a diameter of approximately 700 m and a base approximately 150 m below the ground surface. Coupled with well log data, the inversion results suggest a total volume for the Anomaly B crater area and associated lava flows of approximately 1.0 ± 0.4 km3, based on an estimated lava flow field area of 24 km2 and a lava thickness of 42 ± 15 m.

  18. Gulf Coast-East Coast magnetic anomaly I: Root of the main crustal decollement for the Appalachian-Ouachita orogen

    SciTech Connect

    Hall, D.J. )

    1990-09-01

    The Gulf Coast-East Coast magnetic anomaly extends for at least 4000 km from south-central Texas to offshore Newfoundland as one of the longest continuous tectonic features in North America and a major crustal element of the entire North Atlantic-Gulf Coast region. Analysis of 28 profiles spaced at 100km intervals and four computed models demonstrate that the anomaly may be explained by a thick zone of mafic and ultramafic rocks averaging 13-15 km in depth. The trend of the anomaly closely follows the trend of main Appalachian features: in the Gulf Coast of Louisiana, the anomaly is as far south of the Ouachita front as it is east of the western limit of deformation through the central Appalachians. Because the anomaly continues across well-known continental crust in northern Florida and onshore Texas, it cannot plausibly be ascribed to an edge effect at the boundary of oceanic with continental crustal compositions. The northwest-verging, deep-crustal events discovered in COCORP data from the Ouachitas and Appalachians suggest an analogy with the main suture of the Himalayan orogen in the Tibetan Plateau. In this paper the anomaly is identified with the late Paleozoic Alleghenian megasuture, in which the northwest-verging crustal-detachment surfaces ultimately root.

  19. 3D Electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Deca, J.; Lapenta, G.; Divin, A. V.; Lembege, B.; Markidis, S.

    2013-12-01

    Unlike the Earth and Mercury, our Moon has no global magnetic field and is therefore not shielded from the impinging solar wind by a magnetosphere. However, lunar magnetic field measurements made by the Apollo missions provided direct evidence that the Moon has regions of small-scale crustal magnetic fields, ranging up to a few 100km in scale size with surface magnetic field strengths up to hundreds of nanoTeslas. More recently, the Lunar Prospector spacecraft has provided high-resolution observations allowing to construct magnetic field maps of the entire Moon, confirming the earlier results from Apollo, but also showing that the lunar plasma environment is much richer than earlier believed. Typically the small-scale magnetic fields are non-dipolar and rather tiny compared to the lunar radius and mainly clustered on the far side of the moon. Using iPic3D we present the first 3D fully kinetic and electromagnetic Particle-in-Cell simulations of the solar wind interaction with lunar magnetic anomalies. We study the behaviour of a dipole model with variable surface magnetic field strength under changing solar wind conditions and confirm that lunar crustal magnetic fields may indeed be strong enough to stand off the solar wind and form a mini-magnetosphere, as suggested by MHD and hybrid simulations and spacecraft observations. 3D-PIC simulations reveal to be very helpful to analyze the diversion/braking of the particle flux and the characteristics of the resulting particles accumulation. The particle flux to the surface is significantly reduced at the magnetic anomaly, surrounded by a region of enhanced density due to the magnetic mirror effect. Second, the ability of iPic3D to resolve all plasma components (heavy ions, protons and electrons) allows to discuss in detail the electron physics leading to the highly non-adiabatic interactions expected as well as the implications for solar wind shielding of the lunar surface, depending on the scale size (solar wind protons

  20. Modelling magnetic anomalies of solid and fractal bodies with defined boundaries using the finite cube elements method

    NASA Astrophysics Data System (ADS)

    Mostafa, Mostafa E.

    2009-04-01

    The finite cube elements method (FCEM) is a numerical tool designed for modelling gravity anomalies and estimating structural index (SI) of solid and fractal bodies with defined boundaries, tilted or in normal position and with variable density contrast. In this work, we apply FCEM to modelling magnetic anomalies and estimating SI of bodies with non-uniform magnetization having variable magnitude and direction. In magnetics as in gravity, FCEM allows us to study the spatial distribution of SI of the modelled bodies on contour maps and profiles. We believe that this will impact the forward and inverse modelling of potential field data, especially Euler deconvolution. As far as the author knows, this is the first time that gravity and magnetic anomalies, as well as SI, of self similar fractal bodies such as Menger sponges and Sierpinsky triangles are calculated using FCEM. The SI patterns derived from different order sponges and triangles are perfectly overlapped. This is true for bodies having variable property distributions (susceptibility or density contrast) under different field conditions (in case of magnetics) regardless of their orientation and depth of burial. We therefore propose SI as a new universal fractal-order-invariant measure which can be used in addition to the fractal dimensions for formulating potential field theory of fractal objects.

  1. A Preliminary, Full Spectrum, Magnetic Anomaly Grid of the United States with Improved Long Wavelengths for Studying Continental Dynamics

    NASA Astrophysics Data System (ADS)

    Ravat, Dhananjay; Korhonen, Juha

    2010-05-01

    Under an initiative started by Thomas G. Hildenbrand of the U.S. Geological Survey, we have improved the long-wavelength (50-2,500 km) content of the regional magnetic anomaly compilation for the conterminous United States by utilizing a nearly homogeneous set of National Uranium Resource Evaluation (NURE) magnetic surveys flown from 1975 to 1981. The surveys were flown in quadrangles of 2° of longitude by 1° of latitude with east-west flight lines spaced 4.8 to 9.6 km apart, north-south tie lines variably spaced, and a nominal terrain clearance of 122 m. The NURE surveys were processed using the Comprehensive Magnetic Field Model (Sabaka et al. 2004) to remove the core field for the epochs of the surveys. Many of the surveys used base-station magnetometers to remove external field variations. This NURE magnetic anomaly field is merged with the short-wavelengths from the North American Magnetic Anomaly Map (ca. 2002) to create a full spectrum database called NURE_NAMAM2008. http://pubs.usgs.gov/of/2009/1258/

  2. An earthquake from space: detection of precursory magnetic anomalies from Swarm satellites before the 2015 M8 Nepal Earthquake

    NASA Astrophysics Data System (ADS)

    De Santis, A.; Balasis, G.; Pavón-Carrasco, F. J.; Cianchini, G.; Mandea, M.

    2015-12-01

    A large earthquake of around 8 magnitude occurred on 25 April 2015, 06:26 UTC, with epicenter in Nepal, causing more than 9000 fatalities and devastating destruction. The contemporary orbiting in the topside ionosphere of the three Swarm satellites by ESA makes it possible to look for possible pre-earthquake magnetic anomalous signals, likely due to some lithosphere-atmosphere-ionosphere (LAI) coupling. First, a wavelet analysis has been performed during the same day of the earthquake (from the external magnetic point of view, an exceptionally quiet day) with the result that a ULF anomalous and persisting signal (from around 3 to 6 UTC), is clearly detected before the earthquake. After this single-spot analysis, we performed a more extensive analysis for two months around the earthquake occurrence, to confirm or refute the cause-effect relationship. From the series of the detected magnetic anomalies (during night and magnetically quiet times) from Swarm satellites, we show that the cumulative numbers of anomalies follows the same typical power-law behavior of a critical system approaching its critical time, in our case, the large seismic event of 25 April, 2015, and then it recovers as the typical recovery phase after a large earthquake. The impressive similarity of this behavior with the analogous of seismic data analysis, provides strong support to the lithospheric origin of the satellite magnetic anomalies, as due to the LAI coupling during the preparation phase of the Nepal earthquake.

  3. Three-Dimensional Mapping of Magnetic Strata From Aeromagnetic Anomalies: The Deformed Neroly Formation South of Mt. Diablo, Northern California

    NASA Astrophysics Data System (ADS)

    Jachens, R. C.; Simpson, R. W.; Graymer, R. W.; Wentworth, C. M.

    2008-12-01

    We apply direct inversion of aeromagnetic anomalies to analyze the subsurface 3D shape of the highly magnetic Miocene Neroly Formation, which consists largely of medium to coarse-grained andesitic sandstones containing abundant magnetite. The Neroly Formation is widespread in the eastern San Francisco Bay region, and locally is tightly folded and disrupted by faulting in the compressional regime related to the left-stepping (restraining) connection between the strike-slip Greenville and Concord Faults. The inversion technique is based on the conversion of the anomalies produced by a magnetic layer to their equivalent magnetic potential (psuedogravity) anomalies, manipulation of these anomalies to produce anomalies that would result from a half-space with a variable-depth top having the shape of the top surface of the layer, and then inverting these pseudogravity anomalies for the shape of that top surface. Assumptions include a constant layer thickness, uniform magnetization which implies a constant pseudodensity contrast, and a surface that is single-valued (no recumbent folds or strata repeated with depth). Constraints on 3D position are applied where the layer crops out or is at a depth known from well or other information. Application of this inversion technique to aeromagnetic anomalies over the Neroly Formation yields a complex top surface characterized by elongate overlapping troughs and structural highs, including the well-known Tassajara anticline and adjacent Sycamore Valley syncline. Troughs are true synclinal lows whereas the structural highs may be fold crests, steep truncated strata, and/or fault duplicated strata. The strongest deformation is confined to within ~7 km of the near-vertical overturned Neroly beds that crop out along the NE margin of the valley, and is characterized by four laterally overlapping, margin parallel structural highs and intervening troughs, each between 10 and 20 km in length. A fifth possible structural high lies farther SW

  4. Negative magnetic anomaly over Mt. Resnik, a subaerially erupted volcanic peak beneath the West Antarctic Ice Sheet

    USGS Publications Warehouse

    Behrendt, John C.; Finn, C.; Morse, D.L.; Blankenship, D.D.

    2006-01-01

    Mt. Resnik is one of the previously reported 18 subaerially erupted volcanoes (in the West Antarctic rift system), which have high elevation and high bed relief beneath the WAIS in the Central West Antarctica (CWA) aerogeophysical survey. Mt. Resnik lies 300 m below the surface of the West Antarctic Ice Sheet (WAIS); it has 1.6 km topographic relief, and a conical form defined by radar ice-sounding of bed topography. It has an associated complex negative magnetic anomaly revealed by the CWA survey. We calculated and interpreted magnetic models fit to the Mt. Resnik anomaly as a volcanic source comprising both reversely and normally magnetized (in the present field direction) volcanic flows, 0.5-2.5-km thick, erupted subaerially during a time of magnetic field reversal. The Mt. Resnik 305-nT anomaly is part of an approximately 50- by 40-km positive anomaly complex extending about 30 km to the west of the Mt. Resnik peak, associated with an underlying source complex of about the same area, whose top is at the bed of the WAIS. The bed relief of this shallow source complex has a maximum of only about 400 m, whereas the modeled source is >3 km thick. From the spatial relationship we interpret that this source and Mt Resnik are approximately contemporaneous. Any subglacially (older?) erupted edifices comprising hyaloclastite or other volcanic debris, which formerly overlaid the source to the west, were removed by the moving WAIS into which they were injected as is the general case for the ???1000 volcanic centers at the base of the WAIS. The presence of the magnetic field reversal modeled for Mt. Resnik may represent the Bruhnes-Matayama reversal at 780 ka (or an earlier reversal). There are ???100 short-wavelength, steep-gradient, negative magnetic anomalies observed over the West Antarctic Ice Sheet (WAIS), or about 10% of the approximately 1000 short-wavelength, shallow-source, high-amplitude (50- >1000 nT) "volcanic" magnetic anomalies in the CWA survey. These

  5. Regional magnetic anomalies, crustal strength, and the location of the northern Cordilleran fold-and-thrust belt

    USGS Publications Warehouse

    Saltus, R.W.; Hudson, T.L.

    2007-01-01

    The northern Cordilleran fold-and-thrust belt in Canada and Alaska is at the boundary between the broad continental margin mobile belt and the stable North American craton. The fold-and-thrust belt is marked by several significant changes in geometry: cratonward extensions in the central Yukon Territory and northeastern Alaska are separated by marginward re-entrants. These geometric features of the Cordilleran mobile belt are controlled by relations between lithospheric strength and compressional tectonic forces developed along the continental margin. Regional magnetic anomalies indicate deep thermal and compositional characteristics that contribute to variations in crustal strength. Our detailed analysis of one such anomaly, the North Slope deep magnetic high, helps to explain the geometry of the fold-and-thrust front in northern Alaska. This large magnetic anomaly is inferred to reflect voluminous mafic magmatism in an old (Devonian?) extensional domain. The presence of massive amounts of malic material in the lower crust implies geochemical depletion of the underlying upper mantle, which serves to strengthen the lithosphere against thermal erosion by upper mantle convection. We infer that deep-source magnetic highs are an important indicator of strong lower crust and upper mantle. This stronger lithosphere forms buttresses that play an important role in the structural development of the northern Cordilleran fold-and-thrust belt. ?? 2007 The Geological Society of America.

  6. Middle atmospheric electrodynamic modification by particle precipitation at the South Atlantic magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Gonzalez, W. D.; Dutra, S. L. G.; Pinto, O., Jr.

    1987-01-01

    Evidence for a localized middle atmospheric electrodynamic modification at low latitudes (southern Brazilian coast) of the South Atlantic Magnetic Anomaly (SAMA), in association with enhanced geomagnetic activity, are presented in a unified way combining recent observational efforts and related numerical studies. They involve a distortion effect in the fair weather electric field at balloon altitudes. This effect is attributed to a local intensification of energetic electron precipitation through a related middle atmospheric ionization enhancement and is elucidated by numeric simulation. From the electric field measurements and the numeric simulation, the intensification of precipitation is considered to occur in fairly narrow regions at the observed low L values (around L = 1.13) of the SAMA, with horizontal extensions of the order of a few hundred kilometers. A physical mechanism that could be responsible for this sort of intensification is suggested. Furthermore, a comparison of the phenomenon of middle atmospheric electrodynamic modification at the SAMA with a similar one at auroral latitudes, in response to enhanced solar and geomagnetic activity, is also given.

  7. Analysis of the Nuevo Leon magnetic anomaly and its possible relation to the Cerro Prieto magmatic-hydrothermal system

    SciTech Connect

    Goldstein, N.E.; Wilt, M.J.; Corrigan, D.J.

    1982-10-01

    The broad dipolar magnetic anomaly whose positive peak is centered near Ejido Nuevo Leon, some 5 km east of the Cerro Prieto I Power Plant, has long been suspected to have a genetic relationship to the thermal source of the Cerro Prieto geothermal system. This suspicion was reinforced after several deep geothermal wells, drilled to depths of 3 to 3.5 km over the anomaly, intersected an apparent dike-sill complex consisting mainly of diabase but with minor rhyodacite. A detailed fit of the observed magnetic field to a computer model indicates that the source may be approximated by a tabular block 4 by 6 km in area, 3.7 km in depth, 2.3 km thick, and dipping slightly to the north. Mafic dike chips from one well, NL-1, were analyzed by means of electron microprobe analyses which showed tham to contain a titanomagnetite that is paramagnetic at in-situ temperature conditions. As the dike mineralogy does not account for the magnetic anomaly, the magnetic source is believed to be a deeper, magnetite-rich assemblage of peridotite-gabbro plutons. the suite of igneous rocks was probably passively emplaced at a shallow depth in response to crustal extension and thinning brought on by strike-slip faulting. The bottom of the magnetic source body, at an estimated depth of 6 km, is presumed to be at or near that of the Curie isotherm (575/sup 0/C) for magnetite, the principal ferromagnetic mineral in peridotitic-gabbroic rocks. The geological model derived from the magnetic study is generally supported by other geophysical data. In particular, earthquake data suggest dike injection is occurring at depths of 6 to 11 km in an area beneath the magnetic source. Thus, it is possible that heat for the geothermal field is being maintained by continuing crustal extension and magmatic activity.

  8. Analysis of the Nuevo Leon Magnetic Anomaly and its possible relation to the Cerro Prieto magmatic-hydrothermal system

    SciTech Connect

    Goldstein, N.E.; Corrigan, D.J.; Wilt, M.J.

    1984-01-01

    The broad dipolar magnetic anomaly whose positive peak is centered near Ejido Nuevo Leon, some 5 km east of the Cerro Prieto I power plant, has long been suspected to have a genetic relationship to the thermal source of the Cerro Prieto geothermal system. This suspicion was reinforced after several deep geothermal wells, drilled to depths of 3-3.5 km over the anomaly, intersected an apparent dike-sill complex consisting mainly of diabase but with minor rhyodacite. A detailed fit of the observed magnetic field to a computer model indicates that the source may be approximated by a tabular block 4 x 6 km in area, 3.7 km in depth, 2.3 km thick, and dipping slightly to the north. Mafic dike chips from one well, NL-1, were analysed by means of electron microprobe analyses which showed them to contain a titanomagnetite that is paramagnetic at in situ temperature conditions. As the dike mineralogy does not account for the magnetic anomaly, the magnetic source is believed to be a deeper, magnetite-rich assemblage of peridotite-gabbro plutons. The suite of igneous rocks was probably emplaced at a shallow depth in response to crustal extension and thinning brought on by en echelon strike-slip faulting. The bottom of the magnetic source body, at an estimated depth of 6 km, is presumed to be at or near that of the Curie isotherm (575/sup 0/C) for magnetite, the principal ferromagnetic mineral in peridotiticgabbroic rocks. The geological model derived from the magnetic study is generally supported by other geophysical data. In particular, earthquake data suggest dike injection is occurring at depths of 6-11 km in an area beneath the magnetic source. Thus, it is possible that heat for the geothermal field is being maintained by continuing crustal extension and magmatic activity.

  9. A four sphere model for calculating the magnetic field associated with spreading cortical depression.

    PubMed

    Wijesinghe, R S; Tepley, N

    1997-01-01

    In our previous model, we ascertained that the large amplitude waves (LAWs), reported by Barkley and coworkers (1990) in time series magnetoencephalography (MEG) recordings from migraine patients, could be simulated and compared with the recorded signals using a simple plane volume conductor model (Tepley and Wijesinghe 1996). In this paper, we model LAWs using the help of more complicated yet reliable four-sphere model. This mathematical model furthermore assumes that the LAWs arise from propagation of Spreading Cortical Depression (SCD) across a sulcus and these simulated signals are more similar to the recorded signals than the ones we obtained from our previous model. SCD propagates slowly across the cortex in all species in which it has been observed. In our model, current dipoles represent the excitable neurons in the cortex and magnetic fields created by these individual dipoles are calculated using a four-sphere model. The magnetic field arising from the excited area of cortex is obtained by summing the fields due to these individual dipoles. Sulci shapes are represented by simple mathematical formulae. PMID:9104830

  10. Regional gravity and magnetic anomalies related to a Proterozoic carbonatite terrane in the eastern Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Denton, K. M.; Ponce, D. A.; Miller, D. M.; Jernigan, C. T.

    2014-12-01

    One of the world's largest rare earth element carbonatite deposits is located at Mountain Pass in the eastern Mojave Desert, California. The 1.4 Ga carbonatite deposit is hosted by and intruded into 1.7 Ga gneiss and schist that occurs in a narrow north-northwest trending belt along the eastern parts of Clark Mountain Range, Mescal Range, and Ivanpah Mountains. The carbonatite is associated with an ultrapotassic intrusive suite that ranges from shonkinite through syenite and granite. Regional geophysical data reveal that the eastern Mojave carbonatite terrane occurs along the northeast edge of a prominent magnetic high and the western margin of a gravity high along the eastern Clark Mountain Range. To improve our understanding of the geophysical and structural framework of the eastern Mojave carbonatite terrane, we collected over 1900 gravity stations and over 600 physical rock property samples to augment existing geophysical data. Carbonatite intrusions typically have distinct gravity, magnetic, and radiometric signatures because these deposits are relatively dense, contain magnetite, and are enriched in thorium or uranium. However, our results show that the carbonatite is essentially nonmagnetic with an average susceptibility of 0.18 x 10-3 SI (n=31) and the associated ultrapotassic intrusive suite is very weakly magnetic with an average susceptibility of 2.0 x 10-3 SI (n=36). Although the carbonatite body is nonmagnetic, it occurs along a steep gradient of a prominent aeromagnetic anomaly. This anomaly may reflect moderately magnetic mafic intrusive rocks at depth. East of the ultrapotassic intrusive rocks, a prominent north trending magnetic anomaly occurs in the central part of Ivanpah Valley. Based on geologic mapping in the Ivanpah Mountains, this magnetic anomaly may reflect Paleoproterozoic mafic intrusive rocks related to the 1.7 Ga Ivanpah Orogeny. Physical property measurements indicate that exposed amphibolite along the eastern Ivanpah Mountains are

  11. Spreading of the ocean floor: new evidence.

    PubMed

    Vine, F J

    1966-12-16

    It is suggested that the entire history of the ocean basins, in terms of oceanfloor spreading,is contained frozen in the oceanic crust. Variations in the intensity and polarity of Earth's magnetic field are considered to be recorded in the remanent magnetism of the igneous rocks as they solidified and cooled through the Curie temperature at the crest of an oceanic ridge, and subsequently spread away from it at a steady rate. The hypothesis is supported by the extreme linearity and continuity of oceanic magnetic anomalies and their symmetry about the axes of ridges. If the proposed reversal time scale for the last 4 million years is combined with the model, computed anomaly profiles show remarkably good agreement with those observed, and one can deduce rates of spreading for all active parts of the midoceanic ridge system for which magnetic profilesor surveys are available. The rates obtained are in exact agreement with those needed to account for continental drift. An exceptionally high rate of spreading (approximately 4.5 cm/year) in the South Pacific enables one to deduce by extrapolation considerable details of the reversal time scale back to 11.5 million years ago. Again, this scale can be applied to other parts of the ridge system. Thus one isled to the suggestion that the crest of the East Pacific Rise in the northeast Pacific has been overridden and modified by the westward drift of North America, with the production of the anomalous width and unique features of the American cordillera in the western United States. The oceanicmagnetic anomalies also indicate that there was a change in derection of crustal spreading in this region during Pliocene time from eastwest to southeast-northwest. A profile from the crest to the boundary of the East Pacific Rise, and the difference between axial-zone and flank anomalies over ridges, suggest increase in the frequency of reversal of Earth's magnetic field, together, possibly, with decrease in its intensity

  12. High-resolution Measurement Of Magnetic Anomalies With An Unmanned Airship

    NASA Astrophysics Data System (ADS)

    Petzke, M.; Hofmeister, P.; Auster, H.; Hoerdt, A.; Glassmeier, K.

    2011-12-01

    High-resolution magnetic mapping of areas is a suitable way to determine location, geometry and physical parameters of disturbing objects that cause magnetic anomalies. Areas are often difficult to walk and handheld measurements can become costly. It can also be dangerous to enter areas where ordnance is suspected. In these cases it may be advantageous to use an aircraft to perform the measurement. We use a 6.5 m long unmanned airship. Compared to helicopters or gyrocopters, an advantage is that the damage in case of hazards is almost negligible. We made considerable efforts to construct a system that is easy to control without intense training under moderate wind conditions (up to 2 m/s wind speed). The airship has a mass of 10 kg and is powered by four electric motors with a maximum total power of 4.8 kW. Two of the rotors are used to control the altitude of the ship; the other two can be used to control direction and speed. The required energy is provided by four 4S1P Lithium-Polymer battery packs. Batteries are designed to provide a maximum of 125 A at 14.8 V. They have a capacity of 0.3 kWh and can be recharged in 20 minutes. The airship carries a differential GPS receiver that measures the position of the airship at 100 Hz with a precision of 10 cm. The distance to the ground is measured with ultrasonic sensors. A fluxgate magnetometer measures the magnetic field with an accuracy of 1 nT, also at 100 Hz. The flight path does not follow a rigid measuring grid but is a random walk, with roughly constant altitude to achieve a mean sensor position of 2 m above the ground. Thus, near-surface disturbing bodies are well resolved if their distance from each other is greater than 4 m. First measurements demonstrate the feasibility of the system. Future applications will be mid-scale measurements which are too large or too cumbersome for handheld measurements, and too small to justify the use of a manned helicopter.

  13. Energetic neutral atom imaging of the moon: Observation of a mini-magnetosphere above a lunar magnetic anomaly

    NASA Astrophysics Data System (ADS)

    Wieser, Martin; Barabash, Stas; Futaana, Yoshifumi; Holmström, Mats; Bhardwaj, Anil; Sridharan, R.; Dhanya, B.; Schaufelberger, Audrey; Wurz, Peter; Asamura, Kazushi

    The Sub-keV Atom Reecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 space-craft has resulted in a comprehensive data set about interaction of solar wind with the lunar surface. When solar wind hits the lunar surface, it is partly backscattered as energetic neutral atoms. The intensity of the backscattered energetic neutral atoms is a measure of the intensity of the solar wind reaching the surface. We report on the imaging of a lunar magnetic anomalies in backscattered neutral hydrogen atoms. At the example of the strong magnetic anomaly near the Crisium antipode on the lunar farside we show that a partial void of the solar wind, a mini-magnetosphere, is formed above the magnetic anomaly. The mini-magnetosphere is 360 km across at the surface and surrounded by a 300-km-thick region of enhanced plasma ux that results from the solar wind owing around the mini-magnetosphere. These observations demonstrate a new observational technique to study airless bodies, imaging in ackscattered neutral atoms, and its application to a new class of objects, mini-magnetospheres.

  14. Magnetic resonance imaging of retropharyngeal lymph node metastasis in nasopharyngeal carcinoma: Patterns of spread

    SciTech Connect

    Liu Lizhi; Zhang Guoyi; Xie Chuangmiao; Liu Xuewen; Cui Chunyan; Li Li . E-mail: lililixj@hotmail.com

    2006-11-01

    Purpose: To investigate the incidence, distribution, and spread pattern of retropharyngeal lymph node (RLN) involvement in patients with nasopharyngeal carcinoma (NPC) by using magnetic resonance imaging (MRI). Methods and Materials: The MR images of 275 patients with newly diagnosed NPC were reviewed retrospectively. Nodes were classified as metastatic based on size criteria, the presence of nodal necrosis, and extracapsular spread. Results: Retropharyngeal lymph node involvement was detected in 175 (63.6%) patients. Metastatic RLNs were seen at the following levels: occipital bone, 24 (9.6%) nodes; C1, 157 (62.5%) nodes; C1/2, 40 (15.9%) nodes; C2, 27 (10.8%) nodes; C2/3, 1 (0.4%) node; and C3, 2 (0.8%) nodes. The incidence of RLN involvement was equal to the incidence of cervical lymph node involvement (81.4% vs. 81.4%) in 215 patients with nodal metastases. A significantly higher incidence of metastatic RLNs was observed in the presence of oropharynx, prestyloid parapharyngeal space, post-styloid parapharyngeal space, longus colli muscle, medial pterygoid muscle, levator muscle of velum palatini, tensor muscle of velum palatini, Level II node, Level III node, and Level V node involvement. A significantly lower incidence of metastatic RLNs was found in T1, N0, and Stage I disease. Conversely, no significant difference in the incidence of metastatic RLNs was observed between T1, 2, and, 3; N2 and N3; or Stage II, III, and IV disease. Conclusions: There is an orderly decrease in the incidence of metastatic lateral RLNs from the C1 to C3 level. Metastatic RLNs associate well with involvement of certain structures in early stage primary tumors and lymph node metastases of the upper jugular chain (Level II, Level III nodes) and the posterior triangle (Level V nodes). Both RLNs and cervical Level II nodes appear to be the first-echelon nodes in NPC.

  15. Interpretation of the Total Magnetic Field Anomalies Measured by the CHAMP Satellite Over a Part of Europe and the Pannonian Basin

    NASA Technical Reports Server (NTRS)

    Kis, K. I.; Taylor, Patrick T.; Wittmann, G.; Toronyi, B.; Puszta, S.

    2012-01-01

    In this study we interpret the magnetic anomalies at satellite altitude over a part of Europe and the Pannonian Basin. These anomalies are derived from the total magnetic measurements from the CHAMP satellite. The anomalies reduced to an elevation of 324 km. An inversion method is used to interpret the total magnetic anomalies over the Pannonian Basin. A three dimensional triangular model is used in the inversion. Two parameter distributions: Laplacian and Gaussian are investigated. The regularized inversion is numerically calculated with the Simplex and Simulated Annealing methods and the anomalous source is located in the upper crust. A probable source of the magnetization is due to the exsolution of the hematite-ilmenite minerals.

  16. Airborne gamma-ray and magnetic anomaly signatures of serpentinite in relation to soil geochemistry, northern California

    USGS Publications Warehouse

    McCafferty, A.E.; Van Gosen, B. S.

    2009-01-01

    Serpentinized ultramafic rocks and associated soils in northern California are characterized by high concentrations of Cr and Ni, low levels of radioelements (K, Th, and U) and high amounts of ferrimagnetic minerals (primarily magnetite). Geophysical attributes over ultramafic rocks, which include airborne gamma-ray and magnetic anomaly data, are quantified and provide indirect measurements on the relative abundance of radioelements and magnetic minerals, respectively. Attributes are defined through a statistical modeling approach and the results are portrayed as probabilities in chart and map form. Two predictive models are presented, including one derived from the aeromagnetic anomaly data and one from a combination of the airborne K, Th and U gamma-ray data. Both models distinguish preferential values within the aerogeophysical data that coincide with mapped and potentially unmapped ultramafic rocks. The magnetic predictive model shows positive probabilities associated with magnetic anomaly highs and, to a lesser degree, anomaly lows, which accurately locate many known ultramafic outcrops, but more interestingly, locate potentially unmapped ultramafic rocks, possible extensions of ultramafic bodies that dip into the shallow subsurface, as well as prospective buried ultramafic rocks. The airborne radiometric model shows positive probabilities in association with anomalously low gamma radiation measurements over ultramafic rock, which is similar to that produced by gabbro, metavolcanic rock, and water bodies. All of these features share the characteristic of being depleted in K, Th and U. Gabbro is the only rock type in the study area that shares similar magnetic properties with the ultramafic rock. The aerogeophysical model results are compared to the distribution of ultramafic outcrops and to Cr, Ni, K, Th and U concentrations and magnetic susceptibility measurements from soil samples. Analysis of the soil data indicates high positive correlation between

  17. The location and nature of the Telemzan High Ghadames basin boundary in southern Tunisia based on gravity and magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Gabtni, H.; Jallouli, C.; Mickus, K. L.; Zouari, H.; Turki, M. M.

    2006-03-01

    Gravity and magnetic data were analyzed to add constraints on the location and nature of the Telemzan-Ghadames boundary (TGB) and structure of the Ghadames basin in southern Tunisia. TGB is the boundary between the thick sedimentary cover of the intracratonic Ghadames basin to the south and the thin sedimentary cover of the Saharan platform to the north. The upward continuation of the Bouguer gravity anomalies showed that the TGB is a regional geophysical feature that may have controlled the amount of sediment being deposited both north and south of the boundary and the tectonic environment in the region since Paleozoic time. To emphasize the shorter wavelength gravity and magnetic anomalies, a series of gray scale images of the directional horizontal gradients were constructed that determined a series of previously unknown east-west-trending gravity and magnetic anomalies south of 31.6°N that correspond to lineaments seen on a Landsat 7 image and the location of the TGB. Also, an edge-enhancement analysis illustrated the same linear gravity anomalies and showed the subbasins and uplifts within the Ghadames basin had source depths of between 0.5 and 3.4 km. A north-south trending gravity model showed that the TGB is a relatively gradual feature (possibly basement stepped down by relatively low-displacement faulting) controlling the subsidence of the main Ghadames basin and confirms the edge-enhancement analysis that subbasin S3 and uplift U1 are the main structural features within the Ghadames basin. The knowledge of basement architecture of the Ghadames basin is important for future petroleum exploration within this intracratonic basin.

  18. Analysis of the nature of excessive cosmic radiation in the area of the Brazilian magnetic anomaly at altitudes 250-500km, from Kosmos-225 satellite data

    NASA Technical Reports Server (NTRS)

    Raychenko, L. V.

    1974-01-01

    Results are presented from a study of the region of anomalous cosmic radiation in the area of the Brazilian magnetic anomaly at the altitudes 250-500 km, using data measurements taken on the Kosmos-225 satellite (14-29 June 1968). The existence of a stable intensity anomaly discovered in the experiments on the second and third Soviet spacecraft-satellites is confirmed. The total vector of the geomagnetic field at different altitudes was compared with isoline maps. An altitude profile of the South Atlantic anomaly of radiation intensity was obtained, using data from the same instrument. The nature of the anomalies in cosmic radiation intensity over the regions of negative magnetic anomalies is discussed.

  19. Investigation of feline brain anatomy for the detection of cortical spreading depression with magnetic resonance imaging.

    PubMed

    Smith, J M; James, M F; Bockhorst, K H; Smith, M I; Bradley, D P; Papadakis, N G; Carpenter, T A; Parsons, A A; Leslie, R A; Hall, L D; Huang, C L

    2001-05-01

    Cortical spreading depression (CSD) and peri-infarct depolarisation (PID) are related phenomena that have been associated with the human clinical syndromes of migraine (CSD), head injury and stroke (PID). Nevertheless the existence of CSD in man remains controversial, despite the detection of this phenomenon in the brains of most, if not all, other animal species investigated. This failure to unambiguously detect CSD clinically may be at least partly due to the anatomically complex, gyrencephalic structure of the human brain. This study was designed to establish conditions for the study of CSD in the brain of a gyrencephalic species using the noninvasive technique of magnetic resonance imaging (MRI). The 3-dimensional (3D) gyrencephalic anatomy of the cat brain was examined to determine the imaging conditions necessary to detect CSD events. Orthogonal transverse, sagittal and horizontal T1-weighted image slices showed that the marginal and suprasylvian gyri were the most appropriate cortical structures to study CSD. This was in view of (1) their simple geometry: (2) their lengthy extent of grey matter orientated rostrocaudally in the cortex: (3) their separation by a sulcus across which CSD spread could be studied and (4) the discontinuity in the grey matter in these regions between the right and left hemispheres dorsal to the corpus callosum. The structure suggested by the T1-weighted images was corroborated by systematic diffusion tensor imaging to map the fractional anisotropy and diffusion trace. Thus a single horizontal image plane could visualise the neighbouring suprasylvian and marginal gyri of both cerebral hemispheres, whereas its complex shape and position ruled out the ectosylvian gyrus for CSD studies. With the horizontal imaging plane, CSD events were reproducibly detected by animating successive diffusion-weighted MR images following local KCl stimulation of the cortical surface. In single image frames, CSD detection and characterisation required

  20. Middle proterozoic tectonic activity in west Texas and eastern New Mexico and analysis of gravity and magnetic anomalies

    SciTech Connect

    Adams, D.C.; Keller, G.R. )

    1994-03-01

    The Precambrian history of west Texas and eastern New Mexico is complex, consisting of four events: Early Proterozoic orogenic activity (16309-1800 Ma), formation of the western granite-rhyolite province (WGRP) (1340-1410 Ma), Grenville age tectonics (1116-1232 Ma), and middle Proterozoic extension possibly related to mid-continent rifting (1086-1109 Ma). Pre-Grenville tectonics, Grenville tectonics, and mid-continent rifting are represented in this area by the Abilene gravity minimum (AGM) and bimodal igneous rocks, which are probably younger. We have used gravity modeling and the comparison of gravity and magnetic anomalies with rock types reported from wells penetrating Precambrian basement to study the AGM and middle Proterozoic extension in this area. The AGM is an east-northeast-trending, 600 km long, gravity low, which extends from the Texas-Oklahoma border through the central basin platform (CBP) to the Delaware basin. This feature appears to predate formation of the mafic body in the CBP (1163 Ma) and is most likely related to Pre-Grenville tectonics, possibly representing a continental margin arc batholith. Evidence of middle Proterozoic extension is found in the form of igneous bodies in the CBP, the Van Horn uplift, the Franklin Mountains, and the Sacramento Mountains. Analysis of gravity and magnetic anomalies shows that paired gravity and magnetic highs are related to mafic intrusions in the upper crust. Mapping of middle Proterozoic igneous rocks and the paired anomalies outlines a 530 km diameter area of distributed east-west-oriented extension. The Debaca-Swisher terrain of shallow marine and clastic sedimentary rocks is age correlative with middle Proterozoic extension. These rocks may represent the lithology of possible Proterozoic exploration targets. Proterozoic structures were reactivated during the Paleozoic, affecting both the structure and deposition in the Permian basin.

  1. High-resolution near-bottom vector magnetic anomalies over Raven Hydrothermal Field, Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Tivey, Maurice A.; Johnson, H. Paul; Salmi, Marie S.; Hutnak, Michael

    2014-10-01

    High-resolution, near-bottom vector magnetic data were collected by remotely operated vehicle Jason over the Raven hydrothermal vent field (47°57.3'N 129°5.75'W) located north of Main Endeavour vent field on the Endeavour segment of the Juan de Fuca Ridge. The survey was part of a comprehensive heat flow study of the Raven site using innovative thermal blanket technology to map the heat flux and crustal fluid pathways around a solitary hydrothermal vent field. Raven hydrothermal activity is presently located along the western axial valley wall, while additional inactive hydrothermal deposits are found to the NW on the upper rift valley wall. Magnetic inversion results show discrete areas of reduced magnetization associated with both active and inactive hydrothermal vent deposits that also show high conductive heat flow. Higher spatial variability in the heat flow patterns compared to the magnetization is consistent with the heat flow reflecting the currently active but ephemeral thermal environment of fluid flow, while crustal magnetization is representative of the static time-averaged effect of hydrothermal alteration. A general NW to SE trend in reduced magnetization across the Raven area correlates closely with the distribution of hydrothermal deposits and heat flux patterns and suggests that the fluid circulation system at depth is likely controlled by local crustal structure and magma chamber geometry. Magnetic gradient tensor components computed from vector magnetic data improve the resolution of the magnetic anomaly source and indicate that the hydrothermally altered zone directly beneath the Raven site is approximately 15 × 106 m3 in volume.

  2. Modelling of the total electronic content and magnetic field anomalies generated by the 2011 Tohoku-Oki tsunami and associated acoustic-gravity waves

    NASA Astrophysics Data System (ADS)

    Kherani, E. A.; Lognonné, P.; Hébert, H.; Rolland, L.; Astafyeva, E.; Occhipinti, G.; Coïsson, P.; Walwer, D.; de Paula, E. R.

    2012-12-01

    In this work, numerical simulations of the atmospheric and ionospheric anomalies are performed for the Tohoku-Oki tsunami (2011 March 11). The Tsunami-Atmosphere-Ionosphere (TAI) coupling mechanism via acoustic gravity waves (AGWs) is explored theoretically using the TAI-coupled model. For the modelled tsunami wave as an input, the coupled model simulates the wind, density and temperature disturbances or anomalies in the atmosphere and electron density/magnetic anomalies in the F region of the ionosphere. Also presented are the GPS-total electron content (TEC) and ground-based magnetometer measurements during the first hour of tsunami and good agreements are found between modelled and observed anomalies. At first, within 6 min from the tsunami origin, the simulated wind anomaly at 250 km altitude and TEC anomaly appear as the dipole-shaped disturbances around the epicentre, then as the concentric circular wave fronts radially moving away from the epicentre with the horizontal velocity ˜800 m s-1 after 12 min followed by the slow moving (horizontal velocity ˜250 m s-1) wave disturbance after 30 min. The detailed vertical-horizontal propagation characteristics suggest that the anomalies appear before and after 30 min are associated with the acoustic and gravity waves, respectively. Similar propagation characteristics are found from the GPS-TEC and magnetic measurements presented here and also reported from recent studies. The modelled magnetic anomaly in the F region ionosphere is found to have similar temporal variations with respect to the epicentre distance as that of the magnetic anomaly registered from the ground-based magnetometers. The high-frequency component ˜10 min of the simulated wind, TEC and magnetic anomalies in the F region develops within 6-7 min after the initiation of the tsunami, suggesting the importance of monitoring the high-frequency atmospheric/ionospheric anomalies for the early warning. These anomalies are found to maximize across the

  3. Rock magnetic characteristics of faulted sediments with magnetic anomalies: A case study from the Albuquerque Basin, Rio Grande Rift, New Mexico (Invited)

    NASA Astrophysics Data System (ADS)

    Hudson, M. R.; Grauch, V. J.

    2009-12-01

    High-resolution airborne surveys in the Rio Grande rift have documented abundant short-wavelength, low-amplitude magnetic anomalies generated at faults within basin sediments. We present a rock magnetic study bearing on the source of a10-20-nT linear anomaly over the San Ysidro normal fault, which is well exposed in outcrop in the northern part of the Albuquerque Basin. Magnetic susceptibility (MS) values (SI vol) from 310 sites distributed through a 1200-m-thick composite section of rift-filling sediments of Santa Fe Group and pre-rift sedimentary rocks juxtaposed by the San Ysidro fault have lognormal distributions with well-defined means. These averages generally increase up section through eight map units: from 1.7E-4 to 2.2E-4 in the pre-rift Cretaceous and Eocene rocks, from 9.9E-4 to 1.2E-3 in three units of the Miocene Zia and Cerro Conejo Formations of the Santa Fe Group, and from 1.5E-3 to 3.5E-3 in three units of the Miocene-Pliocene Arroyo Ojito and Ceja Formations of the Santa Fe Group. Remanent magnetization is not important; Koenigsberger ratios are less than 0.3 for Santa Fe Group samples. Rock magnetic parameters (e.g., ARM/MS and S ratios) and petrography indicate that detrital magnetite content and its variable oxidation to maghemite and hematite are the predominant controls of magnetic property variations within the Santa Fe Group sediments. Magnetite is present in rounded detrital grains (including both homogeneous and subdivided types) and as fine inclusions in volcanic rock fragments. Santa Fe Group sediments with highest magnetic susceptibility have greatest magnetic-grain size as indicated by lowest ARM/MS ratios. Magnetic susceptibility increases progressively with sediment grain size to pebbly sand within the fluvial Arroyo Ojito Formation. In contrast, MS reaches highest values in fine to medium sands in eolian Zia Formation. Partial oxidation of detrital magnetite and resultant lower MS is spatially associated with calcite cementation

  4. Three axis fluxgate magnetometer with ring core development for studies and monitoring the South Atlantic Magnetic Anomaly - SAMA

    NASA Astrophysics Data System (ADS)

    Espindola Antunes, Cassio; Schuch, Nelson Jorge; de Siqueira, Josemar; Santos Silveira, Lucas; Babulal Trivedi, Nalin

    The Earth Magnetic Field variations are studied in different time scales classified as secular to diurnal variations and also micropulsations that have period smaller than 1000 seconds. The data acquisition for investigation of this phenomena can provide important information about the Magnetosphere, the Earth/Sun interaction, as well as events occurring in the Ionosphere which can, for instance, generate disturbances in telecommunications, small satellites or even in the space weather. In the area where there is observed the smallest intensity of the Earth's magnetic field on the Global' surface, the South Atlantic Magnetic Anomaly - SAMA, there frequently occur charged particle precipitations during magnetic storms. We have developed a three axis ring core fluxgate magnetometer at the Southern Regional Space Research Center - CRS/CIE/INPE-MCT in the south of Brazil to study the behavior and the geomagnetic process in the SAMA‘s proximities. The fluxgate magnetometer has its operation based on the iron magnetic properties of the high permeability ring-core. Varying the magnetic permeability of the nucleus through a high frequency excitation signal it is possible to obtain a response changing the magnetic saturation around the nucleus as in the (BxH) Hystereses curve. The sensor coil detects a signal with high harmonic content that has linear relation with the Earth's Magnetic Field variations in the observed local. This paper has the intention to show the way used to implement the sensor, the electric circuit and specially the preliminary data and conclusions about experiments performed at the Southern Space Observatory SSO/CRS/INPE - MCT which is located near the center of the SAMA in Brazil. This project also has the objective to develop this kind of low cost fluxgate magnetometers to install it at different points along the SAMA edge.

  5. Three-dimensional full-kinetic simulation of the solar wind interaction with a vertical dipolar lunar magnetic anomaly

    NASA Astrophysics Data System (ADS)

    Deca, Jan; Divin, Andrey; Wang, Xu; Lembège, Bertrand; Markidis, Stefano; Horányi, Mihály; Lapenta, Giovanni

    2016-05-01

    A detailed understanding of the solar wind interaction with lunar magnetic anomalies (LMAs) is essential to identify its implications for lunar exploration and to enhance our physical understanding of the particle dynamics in a magnetized plasma. We present the first three-dimensional full-kinetic electromagnetic simulation case study of the solar wind interaction with a vertical dipole, resembling a medium-size LMA. In contrast to a horizontal dipole, we show that a vertical dipole twists its field lines and cannot form a minimagnetosphere. Instead, it creates a ring-shaped weathering pattern and reflects up to 21% (four times more as compared to the horizontal case) of the incoming solar wind ions electrostatically through the normal electric field formed above the electron shielding region surrounding the cusp. This work delivers a vital piece to fully comprehend and interpret lunar observations, as we find the amount of reflected ions to be a tracer for the underlying field structure.

  6. Additions to Magnetic Trackline Archive For Improvements to Earth Magnetic Anomaly Grid (EMAG2) and Improvements to Data Dissemination at NGDC

    NASA Astrophysics Data System (ADS)

    Meyer, B.; Jencks, J.; Barckhausen, U.; Ishihara, T.; Campagnoli, J.

    2014-12-01

    The National Geophysical Data Center (NGDC) is the primary archive of marine geophysical data worldwide. However, it has been challenging for scientist to discover and access data due to variable data formats, non-digital data holdings, and transitioning data discovery portals. In 2014, NGDC made a concerted effort to identify, ingest, and archive all publicly available magnetic trackline data for access via a new Trackline Geophysical Data web-based interface. Non-digital data were digitized and added to the Global Geophysical Database and are now available for download in a common MGD77 format. All ancillary and analog data are accessible via the same interface, without having to navigate through multiple directories or prompts. The result is over 16.5 million miles of magnetic trackline data are now available, both through NGDC's improved user interface and as a web service for incorporation into other portals. This allows the geoscience community unprecedented access to global geophysical magnetic trackline data from a secure long-term archive. The addition of 6.5 million miles of magnetic trackline data to the database, since the previous release of the Earth Magnetic Anomaly Grid (EMAG2), will give NGDC the ability to improve the model coverage, especially in areas of low coverage, such as around the Eltanin Fracture Zone in the South Pacific. This poster will focus on some key data additions and how they will help us validate the accuracy of the ocean age model/directional gridding algorithm and improve the Earth Magnetic Anomaly Grid going forward.

  7. Detailed bathymetry and magnetic anomaly in the Central Ryukyu Arc, Japan: implications for a westward shift of the volcanic front after approximately 2.1 Ma

    NASA Astrophysics Data System (ADS)

    Sato, Taichi; Oda, Hirokuni; Ishizuka, Osamu; Arai, Kohsaku

    2014-12-01

    Detailed bathymetry and magnetic anomalies in the southern part of the Central Ryukyu Arc reveal recent volcanic structures in a southwestward extension of the active volcanic front of the Ryukyu Arc. A line of bathymetric highs running subparallel to this recent volcanic front was observed approximately 20 km to the east. A set of small, sharply defined magnetic anomalies extends southward from this line of bathymetric highs to the islands Kume-jima and Aguni-jima, suggesting the former existence of an ancient volcanic front. The ages of volcanic rocks from these islands indicate that magmatic activity along the ancient volcanic front continued until at least approximately 2.1 Ma. The presence of magnetic anomalies between the two volcanic fronts suggests that the volcanic front has moved gradually westward. This shift can be explained by the termination of asthenospheric upwelling and/or the rapid retreat of the Ryukyu Trench after its change in subduction direction.

  8. Detailed bathymetry and magnetic anomaly inthe Central Ryukyu Arc, Japan: implications for a westward shift of the volcanic front after ~2.1 Ma

    NASA Astrophysics Data System (ADS)

    Sato, T.; Oda, H.; Ishizuka, O.; Arai, K.

    2014-12-01

    Detailed bathymetry and magnetic anomalies in the southern part of the Central Ryukyu Arc reveal recent volcanic structures in a southwestward extension of the active volcanic front of the Ryukyu Arc. A line of bathymetric highs running subparallel to this recent volcanic front was observed ~20 km to the east. A set of small, sharply defined magnetic anomalies extends southward from this line of bathymetric highs to the islands Kume-jima and Aguni-jima, suggesting the former existence of an ancient volcanic front. The ages of volcanic rocks from these islands indicate that magmatic activity along the ancient volcanic front continued until at least ~2.1 Ma. The presence of magnetic anomalies between the two volcanic fronts suggests that the volcanic front has moved gradually westward. This shift can be explained by the termination of asthenospheric upwelling and/or the rapid retreat of the Ryukyu Trench after its change in subduction direction.

  9. Preparation of magnetic anomaly profile and contour maps from DOE-NURE aerial survey data. Volume I: processing procedures. [National Uranium Resource Evaluation

    SciTech Connect

    Tinnel, E.P.; Hinze, W.J.

    1981-09-01

    Total intensity magnetic anomaly data acquired as a supplement to radiometric data in the DOE National Uranium Resource Evaluation (NURE) Program are useful in preparing regional profile and contour maps. Survey-contractor-supplied magnetic anomaly data are subjected to a multiprocess, computer-based procedure which prepares these data for presentation. This procedure is used to produce the following machine plotted maps of National Topographic Map Series quadrangle units at a 1:250,000 scale: (1) profile map of contractor-supplied magnetic anomaly data, (2) profile map of high-cut filtered data with contour levels of each profile marked and annotated on the associated flight track, (3) profile map of critical-point data with contour levels indicated, and (4) contour map of filtered and selected data. These quadrangle maps are supplemented with a range of statistical measures of the data which are useful in quality evaluation.

  10. Deep magnetic anomaly sources interpreted as Otanmäki type Iron ore reserves

    NASA Astrophysics Data System (ADS)

    Korhonen, Juha; Kukkonen, Ilmo

    2013-04-01

    In Otanmäki ore province of Central Finland vertically integrated magnetization is estimated from two aeromagnetic coverages of different altitudes and by varying overall models of regional field. Petrophysically and geochemically determined magnetization of the mined deposits and correlation between it and ore concentration is used to evaluate iron ore reserves in the deeper part of known ore fields. Further, similar analysis is made to nearby magnetically anomalous areas covered by weakly magnetic metasediments, to estimate potential ore reserves at unexposed formations.

  11. Magnetic resonance imaging of cerebral anomalies in subjects with resistance to thyroid hormone

    SciTech Connect

    Leonard, C.M.; Hauser, P.; Weintraub, B.D. |

    1995-06-19

    Resistance to thyroid hormone (RTH) is an autosomal dominant disease caused by mutations in the human thyroid receptor beta gene on chromosome 3. Individuals with RTH have an increased incidence of attention deficit hyperactivity disorder (ADHD). The purpose of this study was to search for developmental brain malformations associated with RTH. Forty-three subjects (20 affected males [AM], 23 affected females [AF]) with resistance to thyroid hormone and 32 unaffected first degree relatives (18 unaffected males [UM], 14 unaffected females [UF]) underwent MRI brain scans with a volumetric acquisition that provided 90 contiguous 2 mm thick sagittal images. Films of six contiguous images beginning at a standard sagittal position lateral to the insula were analyzed by an investigator who was blind with respect to subject characteristics. The presence of extra or missing gyri in the parietal bank of the Sylvian fissure (multimodal association cortex) and multiple Heschl`s transverse gyri (primary auditory cortex) were noted. There was a significantly increased frequency of anomalous Sylvian fissures in the left hemisphere in males with RTH (AM: 70%; AF: 30%; UM: 28% UF: 28%). Also, there was an increased frequency of anomalous Sylvian fissures on the left combined with multiple Heschl`s gyri in either hemisphere in males with RTH (AM: 50%; AF: 9%; UM: 6%; UF: 0%). However, RTH subjects with anomalies did not have an increased frequency of ADHD as compared with RTH subjects with no anomalies. Abnormal thyroid hormone action in the male fetus early during brain development may be associated with grossly observable cerebral anomalies of the left hemisphere. The effects of mutations in the thyroid receptor beta gene provide a model system for studying the complex interaction of genetic and non-genetic factors on brain and behavioral development. 19 refs., 2 figs., 2 tabs.

  12. Southern Hemisphere Magnetic Variations Improved Coverage and South Atlantic Magnetic Anomaly (SAMA) Monitoring by the Installation of a Small Magnetometer Network on the Brazilian Territory

    NASA Astrophysics Data System (ADS)

    Fernandez, J. H.; et al.

    2006-11-01

    At the present time the magnetic planetary indices, specially the Kp (Ap) index, are basically North Hemisphere indices since the ample majority of the magnetic observatories that generate the indices are located above the Equator.The improving necessity in the coverage of the planetary indices leads to the installation of new and modern equipment in the Southern Hemisphere. Brazil has a special location in terms of being the site for the installation of such equipment. The South Atlantic Magnetic Anomaly (SAMA) is over the South Brazilian region at this moment and there are several groups from research institutes and universities, in Brazil, that can operate and maintain the equipments, carry out the data analysis and put the available data on the Internet. Space weather is a modern term to denote physical conditions in space around the Earth that are ultimately determined by solar activity. Space weather manifests itself through various physical phenomena such as enhanced intensity of hard radiation, increased strength of electric and magnetic fields and elevated magnitude of electric currents, to name only a few. A "magnetic storm", which may also be called a "space storm", is a rather violent phase of space weather and is often caused by solar outbursts such as flares and coronal mass ejections. Solar outbursts create disturbances of the solar wind that may impact the Earth environment with a delay of a few days after their eruption from the Sun. Also at the present time the Kp world network is composed of 13 magnetic observatories, 11 northern and two southern stations. The K indices are defined everywhere, but are most significant at sub-auroral latitudes. In the proposed project several magnetometers in the network could contribute to the generation of the planetary average giving a more realistic character to the index. Main scientific goals: - Improvement in the monitoring of the Southern Hemisphere magnetic variations - Local and continuous monitoring of

  13. Interpretation of Magnetic Anomalies in Salihli (Turkey) Geothermal Area Using 3-D Inversion and Edge Detection Techniques

    NASA Astrophysics Data System (ADS)

    Timur, Emre

    2016-04-01

    There are numerous geophysical methods used to investigate geothermal areas. The major purpose of this magnetic survey is to locate the boudaries of active hydrothermal system in the South of Gediz Graben in Salihli (Manisa/Turkey). The presence of the hydrothermal system had already been inferred from surface evidence of hydrothermal activity and drillings. Firstly, 3-D prismatic models were theoretically investigated and edge detection methods were utilized with an iterative inversion method to define the boundaries and the parameters of the structure. In the first step of the application, it was necessary to convert the total field anomaly into a pseudo-gravity anomaly map. Then the geometric boudaries of the structures were determined by applying a MATLAB based software with 3 different edge detection algorithms. The exact location of the structures were obtained by using these boundary coordinates as initial geometric parameters in the inversion process. In addition to these methods, reduction to pole and horizontal gradient methods were applied to the data to achieve more information about the location and shape of the possible reservoir. As a result, the edge detection methods were found to be successful, both in the field and as theoretical data sets for delineating the boundaries of the possible geothermal reservoir structure. The depth of the geothermal reservoir was determined as 2,4 km from 3-D inversion and 2,1 km from power spectrum methods.

  14. Low-temperature anomalies in the magnetic and thermal properties of molecular cryocrystals doped with oxygen impurity

    NASA Astrophysics Data System (ADS)

    Freiman, Yu. A.; Tretyak, S. M.; JeŻowski, A.

    2000-09-01

    The magnetic properties of oxygen pair clusters are investigated theoretically for different cluster geometries which can be realized by doping molecular cryomatrices with oxygen. Anomalous temperature and pressure behavior of the magnetic susceptibility, heat capacity, and entropy is predicted. It is proposed to use these anomalies for studying the parameters characterizing the oxygen clusters and the parameters of the host matrix: the effective spin-figure interaction constant D for the molecule in the matrix, the exchange parameter J, and the number of pair clusters Np, which can deviate markedly from the purely random value Np=6Nc2 (N is Avogadro's number, and c is the molar concentration of the impurity). The data on the magnetic susceptibility may be used to analyze the character of the positional and orientational short-range order in the solid solution. The value of D contains information about the orientational order parameter; the distance and angular dependence of the exchange interaction parameter are still subject to discussion in the literature. The temperature dependence of Np contains information about diffusion and clusterization processes in the system.

  15. 3D PIC Simulations of Collisionless Shocks at Lunar Magnetic Anomalies and Their Role in Forming Lunar Swirls

    NASA Astrophysics Data System (ADS)

    Bamford, R. A.; Alves, E. P.; Cruz, F.; Kellett, B. J.; Fonseca, R. A.; Silva, L. O.; Trines, R. M. G. M.; Halekas, J. S.; Kramer, G.; Harnett, E.; Cairns, R. A.; Bingham, R.

    2016-10-01

    Investigation of the lunar crustal magnetic anomalies offers a comprehensive long-term data set of observations of small-scale magnetic fields and their interaction with the solar wind. In this paper a review of the observations of lunar mini-magnetospheres is compared quantifiably with theoretical kinetic-scale plasma physics and 3D particle-in-cell simulations. The aim of this paper is to provide a complete picture of all the aspects of the phenomena and to show how the observations from all the different and international missions interrelate. The analysis shows that the simulations are consistent with the formation of miniature (smaller than the ion Larmor orbit) collisionless shocks and miniature magnetospheric cavities, which has not been demonstrated previously. The simulations reproduce the finesse and form of the differential proton patterns that are believed to be responsible for the creation of both the “lunar swirls” and “dark lanes.” Using a mature plasma physics code like OSIRIS allows us, for the first time, to make a side-by-side comparison between model and space observations. This is shown for all of the key plasma parameters observed to date by spacecraft, including the spectral imaging data of the lunar swirls. The analysis of miniature magnetic structures offers insight into multi-scale mechanisms and kinetic-scale aspects of planetary magnetospheres.

  16. Earth's magnetic field anomalies that precede the M6+ global seismic activity

    NASA Astrophysics Data System (ADS)

    Cataldi, Gabriele; Cataldi, Daniele; Straser, Valentino

    2014-05-01

    In this work has been analyzed the Earth's magnetic field variations and the M6+ global seismic activity to verify if M6+ earthquakes are preceded by a change of the Earth's magnetic field. The data of Earth's magnetic field used to conduct the study of correlation are provided by the induction magnetometer of Radio Emissions Project's station (Lat: 41°41'4.27"N, Long: 12°38'33,60"E, Albano Laziale, Rome, Italy), equipped with a ELF receiver prototype (with a vertically aligned coil antenna) capable to detect the variations of the intensity of the Earth's magnetic field on Z magnetic component. The M6+ global seismic activity data are provided in real-time by USGS, INGV and CSEM. The sample of data used to conduct the study refers to the period between 1 January 2012 and 31 December 2012. The Earth's magnetic field variations data set has been marked with the times (time markers) of M6+ earthquakes occurred on a global scale and has been verified the existence of disturbances of the Earth's geomagnetic field in the time interval that preceded the M6+ global seismic activity. The correlation study showed that all M6+ earthquakes recorded on 2012 were preceded by an increase of the Earth's magnetic field, detected in the Z magnetic component. The authors measured the time lag elapsed between the maximum increment of the Earth's magnetic field recorded before an earthquake M6+ and the date and time at which this occurred, and has been verified that the minimum time lag recorded between the Earth's magnetic field increase and the earthquake M6+ has been 1 minute (9 October 2012, Balleny Islands, M6,4); while, the maximum time lag recorded has been 3600 minutes (26 June 2012, China, M6,3). The average time lag has been 629.47 minutes. In addition, the average time lag is deflected in relation to the magnitude increase. Key words: Seismic Geomagnetic Precursor (SGP), Interplanetary Seismic Precursor (ISP), Earth's magnetic field variations, earthquakes, prevision.

  17. Tectonic history of the north portion of the San Andreas fault system, California, inferred from gravity and magnetic anomalies

    USGS Publications Warehouse

    Griscom, A.; Jachens, R.C.

    1989-01-01

    Geologic and geophysical data for the San Andreas fault system north of San Francisco suggest that the eastern boundary of the Pacific plate migrated eastward from its presumed original position at the base of the continental slope to its present position along the San Andreas transform fault by means of a series of eastward jumps of the Mendocino triple junction. These eastward jumps total a distance of about 150 km since 29 Ma. Correlation of right-laterally displaced gravity and magnetic anomalies that now have components at San Francisco and on the shelf north of Point Arena indicates that the presently active strand of the San Andreas fault north of the San Francisco peninsula formed recently at about 5 Ma when the triple junction jumped eastward a minimum of 100 km to its present location at the north end of the San Andreas fault. -from Authors

  18. Large-scale irregularities of electron concentration in the southern magnetic anomaly area according to Intercosmos 19 satellite data

    NASA Astrophysics Data System (ADS)

    Fligel', M. D.

    1992-02-01

    Using Intercosmos 19 satellite topside sounding data, a type of complex ionogram for which the lowest frequency of the radio-wave which has pased through the ionosphere is smaller than the greatest frequency of the radio-wave reflected from the ionosphere is considered. (Under normal conditions these frequencies are identically equal). A mechanism is suggested by which radio-waves transmitted by the satellite propagate over 3000 km in the topside ionosphere in the presence of inclined large-scale plasma structure, which can explain the main features of such ionograms. The space-time distribution of this phenomenon on a global scale is analyzed. It is shown that it manifests itself mainly in the local winter, in the daytime and in the Southern Hemisphere. It is hypothesized that these large-scale irregularities are formed in the vicinity of the South Atlantic magnetic anomaly, and then move westward.

  19. Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Boccato, Silvia; Sanson, Andrea; Kantor, Innokenty; Mathon, Olivier; Dyadkin, Vadim; Chernyshov, Dmitry; Carnera, Alberto; Pascarelli, Sakura

    2016-09-01

    The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom. No thermal anomalies have been detected from the current XRD data. On the contrary, an intriguing thermal anomaly at about 150 K, ascribed to a stiffening of the Fe–Fe bonds, was found by EXAFS.

  20. Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Boccato, Silvia; Sanson, Andrea; Kantor, Innokenty; Mathon, Olivier; Dyadkin, Vadim; Chernyshov, Dmitry; Carnera, Alberto; Pascarelli, Sakura

    2016-09-01

    The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom. No thermal anomalies have been detected from the current XRD data. On the contrary, an intriguing thermal anomaly at about 150 K, ascribed to a stiffening of the Fe-Fe bonds, was found by EXAFS.

  1. Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction.

    PubMed

    Boccato, Silvia; Sanson, Andrea; Kantor, Innokenty; Mathon, Olivier; Dyadkin, Vadim; Chernyshov, Dmitry; Carnera, Alberto; Pascarelli, Sakura

    2016-09-01

    The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom. No thermal anomalies have been detected from the current XRD data. On the contrary, an intriguing thermal anomaly at about 150 K, ascribed to a stiffening of the Fe-Fe bonds, was found by EXAFS.

  2. The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies

    NASA Astrophysics Data System (ADS)

    Blakely, Richard J.; Sherrod, Brian L.; Weaver, Craig S.; Wells, Ray E.; Rohay, Alan C.

    2014-06-01

    The Yakima fold and thrust belt (YFTB) in central Washington has accommodated regional, mostly north-directed, deformation of the Cascadia backarc since prior to emplacement of Miocene flood basalt of the Columbia River Basalt Group (CRBG). The YFTB consists of two structural domains. Northern folds of the YFTB strike eastward and terminate at the western margin of a 20-mGal negative gravity anomaly, the Pasco gravity low, straddling the North American continental margin. Southern folds of the YFTB strike southeastward, form part of the Olympic-Wallowa lineament (OWL), and pass south of the Pasco gravity low as the Wallula fault zone. An upper crustal model based on gravity and magnetic anomalies suggests that the Pasco gravity low is caused in part by an 8-km-deep Tertiary basin, the Pasco sub-basin, abutting the continental margin and concealed beneath CRBG. The Pasco sub-basin is crossed by north-northwest-striking magnetic anomalies caused by dikes of the 8.5 Ma Ice Harbor Member of the CRBG. At their northern end, dikes connect with the eastern terminus of the Saddle Mountains thrust of the YFTB. At their southern end, dikes are disrupted by the Wallula fault zone. The episode of NE-SW extension that promoted Ice Harbor dike injection apparently involved strike-slip displacement on the Saddle Mountains and Wallula faults. The amount of lateral shear on the OWL impacts the level of seismic hazard in the Cascadia region. Ice Harbor dikes, as mapped with aeromagnetic data, are dextrally offset by the Wallula fault zone a total of 6.9 km. Assuming that dike offsets are tectonic in origin, the Wallula fault zone has experienced an average dextral shear of 0.8 mm/y since dike emplacement 8.5 Ma, consistent with right-lateral stream offsets observed at other locations along the OWL. Southeastward, the Wallula fault transfers strain to the north-striking Hite fault, the possible location of the M 5.7 Milton-Freewater earthquake in 1936.

  3. The interpretation of magnetic anomalies by 3D inversion: A case study from Central Iran

    NASA Astrophysics Data System (ADS)

    Tavakoli, M.; Nejati Kalateh, A.; Ghomi, S.

    2016-03-01

    The thick sedimentary units in Central Iran contain structures that form oil traps and are underlain by a basaltic layer which is amenable for study using its magnetic susceptibility. The study and modeling of such sedimentary structures provide valuable exploratory information. In this study, we locate and interpret an underground magnetic susceptibility interface using 3D non-linear inverse modeling of magnetic data to make a better judgment in the context of hydrocarbon existence. The 3D structure is reconstructed by making it equal to a number of side by side rectangular hexahedrons or prisms and calculating their thicknesses such that the bottoms of the prisms are corresponding to the magnetic susceptibility interface. By one of the most important mathematical tool in computational science, Taylor series, the non-linear problem changes to a linear problem near to initial model. In many inverse problems, we often need to invert large size matrices. To find the inverse of these matrices we use Singular Value Decomposition (SVD) method. The algorithm by an iterative method comparing model response with actual data will modify the initial guess of model parameters. The efficiency of the method and subprograms, programmed in MATLAB, has been shown by inverse modeling of free noise and noise-contaminated synthetic data. Finally, we inverted magnetic field data from Garmsar area in Central Iran which the results were acceptable.

  4. Observation of a New Magnetic Anomaly Below the Ferromagnetic Curie Temperature in Yb14MnSb11

    SciTech Connect

    Srinath, S.; Poddar, P.; Srikanth, H.; Sales, Brian C; Mandrus, David

    2005-01-01

    Yb{sub 14}MnSb{sub 11} is an unusual ferromagnet with a Curie temperature of 52 {+-} 1 K. Recent optical, Hall, magnetic, and thermodynamic measurements indicate that Yb{sub 14}MnSb{sub 11} may be a rare example of an underscreened Kondo lattice. We report the first experimental observation of a new magnetic anomaly in this system at around 47 K, a few degrees below T{sub c}. Systematic investigations of the ac and dc susceptibilities of Yb{sub 14}MnSb{sub 11} single crystals reveal features associated with possible spin reorientation at this temperature. This new anomaly is extremely sensitive to the applied measurement field and is absent in temperature-dependent dc magnetization data for fields above 50 Oe. The origin of this could be due to decoupling of two distinct magnetic sublattices associated with MnSb{sub 4} tetrahedra.

  5. Global equivalent magnetization of the oceanic lithosphere

    NASA Astrophysics Data System (ADS)

    Dyment, J.; Choi, Y.; Hamoudi, M.; Lesur, V.; Thebault, E.

    2015-11-01

    As a by-product of the construction of a new World Digital Magnetic Anomaly Map over oceanic areas, we use an original approach based on the global forward modeling of seafloor spreading magnetic anomalies and their comparison to the available marine magnetic data to derive the first map of the equivalent magnetization over the World's ocean. This map reveals consistent patterns related to the age of the oceanic lithosphere, the spreading rate at which it was formed, and the presence of mantle thermal anomalies which affects seafloor spreading and the resulting lithosphere. As for the age, the equivalent magnetization decreases significantly during the first 10-15 Myr after its formation, probably due to the alteration of crustal magnetic minerals under pervasive hydrothermal alteration, then increases regularly between 20 and 70 Ma, reflecting variations in the field strength or source effects such as the acquisition of a secondary magnetization. As for the spreading rate, the equivalent magnetization is twice as strong in areas formed at fast rate than in those formed at slow rate, with a threshold at ∼40 km/Myr, in agreement with an independent global analysis of the amplitude of Anomaly 25. This result, combined with those from the study of the anomalous skewness of marine magnetic anomalies, allows building a unified model for the magnetic structure of normal oceanic lithosphere as a function of spreading rate. Finally, specific areas affected by thermal mantle anomalies at the time of their formation exhibit peculiar equivalent magnetization signatures, such as the cold Australian-Antarctic Discordance, marked by a lower magnetization, and several hotspots, marked by a high magnetization.

  6. Zeeman effect and magnetic anomalies in narrow-gap semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Prado, S. J.; Trallero-Giner, C.; López-Richard, V.; Alcalde, A. M.; Marques, G. E.

    2004-01-01

    We present a systematic theoretical study, based on the Kane-Weiler 8×8 k· p model, of the linear Zeeman splitting introduced by the interaction between the angular momentum and the magnetic field which can give a measure of the non-linear Zeeman effect associated with interband coupling and diamagnetic contributions. The conduction and valence bands g-factors are calculated for InSb spherical and semi-spherical quantum dots. The calculations of the g-factors showed an almost linear dependence, for the ground state, on the magnetic field. We have also found that the strong magnetic field dependence as well as the dependence on the dot size of the effective spin splitting can be unambiguously attributed to the strength of the inter-level mixing.

  7. Spherical-earth Gravity and Magnetic Anomaly Modeling by Gauss-legendre Quadrature Integration

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J. (Principal Investigator)

    1981-01-01

    The anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical Earth for an arbitrary body represented by an equivalent point source distribution of gravity poles or magnetic dipoles were calculated. The distribution of equivalent point sources was determined directly from the coordinate limits of the source volume. Variable integration limits for an arbitrarily shaped body are derived from interpolation of points which approximate the body's surface envelope. The versatility of the method is enhanced by the ability to treat physical property variations within the source volume and to consider variable magnetic fields over the source and observation surface. A number of examples verify and illustrate the capabilities of the technique, including preliminary modeling of potential field signatures for Mississippi embayment crustal structure at satellite elevations.

  8. Spherical-earth gravity and magnetic anomaly modeling by Gauss-Legendre quadrature integration

    NASA Technical Reports Server (NTRS)

    Von Frese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J.

    1981-01-01

    Gauss-Legendre quadrature integration is used to calculate the anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical earth. The procedure involves representation of the anomalous source as a distribution of equivalent point gravity poles or point magnetic dipoles. The distribution of equivalent point sources is determined directly from the volume limits of the anomalous body. The variable limits of integration for an arbitrarily shaped body are obtained from interpolations performed on a set of body points which approximate the body's surface envelope. The versatility of the method is shown by its ability to treat physical property variations within the source volume as well as variable magnetic fields over the source and observation surface. Examples are provided which illustrate the capabilities of the technique, including a preliminary modeling of potential field signatures for the Mississippi embayment crustal structure at 450 km.

  9. An annular high-current electron beam with an energy spread in a coaxial magnetically insulated diode

    SciTech Connect

    Grishkov, A. A. Pegel, I. V.

    2013-11-15

    An elementary theory of an annular high-current electron beam in a uniform transport channel and a coaxial magnetically insulated diode is generalized to the case of counterpropagating electron beams with a spread over kinetic energies. Expressions for the sum of the absolute values of the forward and backward currents in a uniform transport channel and for the flux of the longitudinal component of the generalized momentum in a coaxial magnetically insulated diode as functions of the maximum electron kinetic energy are derived for different values of the relative width of the energy distribution function. It is shown that, in a diode with an expanding transport channel and a virtual cathode limiting the extracted current, counterpropagating particle flows are established between the cathode and the virtual cathode within a certain time interval after the beginning of electron emission. The accumulation of electrons in these flows is accompanied by an increase in their spread over kinetic energies and the simultaneous decrease in the maximum kinetic energy. The developed model agrees with the results of particle-in-cell simulations performed using the KARAT and OOPIC-Pro codes.

  10. Calculation of gravity and magnetic anomalies of finite-length right polygonal prisms.

    USGS Publications Warehouse

    Cady, J.W.

    1980-01-01

    An equation is derived for the vertical gravity field due to a homogeneous body with polygonal cross‐section and finite strike‐length. The equation can be separated into the two‐dimensional (2-D) terms of Talwani et al. (1959) and exact terms for the contributions of the ends of the prism. Equations for the magnetic field due to a similar body were derived by Shuey and Pasquale (1973), who coined the term “two‐and‐a‐half dimensional” (2 1/2-D) to describe the geometry. Magnetic intensities are expressed as a vector sum, from which the common dot product formulation can be obtained by binomial expansion.

  11. Particle-In-Cell Simulations of the Solar Wind Interaction with Lunar Crustal Magnetic Anomalies: Magnetic Cusp Regions

    NASA Technical Reports Server (NTRS)

    Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.

    2012-01-01

    As the solar wind is incident upon the lunar surface, it will occasionally encounter lunar crustal remanent magnetic fields. These magnetic fields are small-scale, highly non-dipolar, have strengths up to hundreds of nanotesla, and typically interact with the solar wind in a kinetic fashion. Simulations, theoretical analyses, and spacecraft observations have shown that crustal fields can reflect solar wind protons via a combination of magnetic and electrostatic reflection; however, analyses of surface properties have suggested that protons may still access the lunar surface in the cusp regions of crustal magnetic fields. In this first report from a planned series of studies, we use a 1 1/2-dimensional, electrostatic particle-in-cell code to model the self-consistent interaction between the solar wind, the cusp regions of lunar crustal remanent magnetic fields, and the lunar surface. We describe the self-consistent electrostatic environment within crustal cusp regions and discuss the implications of this work for the role that crustal fields may play regulating space weathering of the lunar surface via proton bombardment.

  12. An Exercise on Magnetic-Anomaly Profiles and the Geomagnetic Polar-Reversal Time Scale.

    ERIC Educational Resources Information Center

    Shea, James Herbert

    1988-01-01

    Develops an exercise in which students use magnetic-profile data gathered in the South Pacific to test the Vine-Matthews-Morley hypothesis. Uses the Eltanin 19N and 20N profiles. Relates the exercise to 20 current geology texts. (MVL)

  13. The Mackenzie River magnetic anomaly, Yukon and Northwest Territories, Canada-Evidence for Early Proterozoic magmatic arc crust at the edge of the North American craton

    USGS Publications Warehouse

    Pilkington, M.; Saltus, R.W.

    2009-01-01

    We characterize the nature of the source of the high-amplitude, long-wavelength, Mackenzie River magnetic anomaly (MRA), Yukon and Northwest Territories, Canada, based on magnetic field data collected at three different altitudes: 300??m, 3.5??km and 400??km. The MRA is the largest amplitude (13??nT) satellite magnetic anomaly over Canada. Within the extent of the MRA, source depth estimates (8-12??km) from Euler deconvolution of low-altitude aeromagnetic data show coincidence with basement depths interpreted from reflection seismic data. Inversion of high-altitude (3.5??km) aeromagnetic data produces an average magnetization of 2.5??A/m within a 15- to 35-km deep layer, a value typical of magmatic arc complexes. Early Proterozoic magmatic arc rocks have been sampled to the southeast of the MRA, within the Fort Simpson magnetic anomaly. The MRA is one of several broad-scale magnetic highs that occur along the inboard margin of the Cordillera in Canada and Alaska, which are coincident with geometric changes in the thrust front transition from the mobile belt to stable cratonic North America. The inferred early Proterozoic magmatic arc complex along the western edge of the North American craton likely influenced later tectonic evolution, by acting as a buttress along the inboard margin of the Cordilleran fold-and-thrust belt. Crown Copyright ?? 2008.

  14. Lithology identification with gravity and magnetic anomalies for mine exploration in the China-Mongolia border

    NASA Astrophysics Data System (ADS)

    Meng, X.; Wang, J.

    2015-12-01

    China-Mongolia border is an important metallogenic province, its structural is complex and the study of it is of great significance for future detecting. In the last three years, we have conducted gravity and magnetic survey in the eastern segment of the China-Mongolia border along the profile, hoping to get a detailed characterization of the subsurface of this area. In this study, we conducted lithology identification in this area with measured gravity and magnetic data. In our work, topological calculations were performed on inversion data and physical property data for lithology identification. Our work can be summarized into the following steps: Firstly, the rock density and magnetic susceptibility near the survey profiles were summarized by field reconnaissance, and the lithology was divided into several types. Thus, a correspondence between lithology and physical properties was defined to some extent. Secondly, different mapping equations were established according to the physical properties for each lithology.Then, inversion of the gravity and magnetic data have been performed to get the physical properties (density and susceptibility) below the profile. Lastly, the lithology was identified through gravity and magnetic inversion result and the mapping equations mentioned above. In our study, the magmatic rocks within 50 km of the lower half space can be divided into four major types based on the identification result. The lithology varies significantly from north to south below this profile. Moreover, the lithology distribution trend and the formation age of the lower half space is summarized based on characteristics of the gravity and magnetic fields and the tectonic setting. For lithology identification with different types of data, we think that identify lithology information by one of the data can be conducted firstly, such as magnetic susceptibility, and then bring the results to lithology identification among the inversion of other data , which greatly

  15. Beam spreading and emittance oscillation of an intense magnetized beam in free space.

    SciTech Connect

    Wang, C.-x.; Kim, K.-J.; Zhang, J. G.; Accelerator Systems Division; IIT

    2006-01-01

    Intense beams with large angular momentum have important applications in electron cooling and in producing flat beams suitable for ultrafast x-ray generation, Smith-Purcell radiators, and possibly for a future linear collider. To gain a basic understanding of the influence of beam angular momentum in an otherwise space-charge-dominated beam, the behavior of such a beam in free space will be examined here, in particular, beam spreading due to space-charge force, as well as emittance oscillation. Drift space is an important part of a split photoinjector and plays a significant role in emitance compensation of a high-brightness photoinjector.

  16. Comparison of the dynamics and structure of Saturn and Jupiter magnetospheres: camshaft, magnetic anomalies and corotating convection models compared.

    NASA Astrophysics Data System (ADS)

    Southwood, D. J.; Kivelson, M. G.

    Scenarios are presented for the overall flux and mass circulation in the jovian and saturnian magnetospheres It is argued that similar fundamanetal processes underly the dynamical processes at both planets However the differences in parameter regime for the two systems leads to substantial resulting differences in morphology Transport is accomplished from the inner magnetosphere by interchange motion which then feeds into the outer magnetosphere where ballooning driven by centrifugal stress leads to field reconnection and plasma loss It seems likely that Jupiter loses much more material per rotation cycle than Saturn and is possibly much more symmetrically loaded in respect of planetary longitude Material loss and flux return at Jupiter have fixed orientations in local time early evening and morning sector respectively and newly returned flux is probably responsible for the morningside cushion region in the outer magnetosphere At Jupiter the dawn-dusk asymmetry in the current sheet thin in morning thick in afternoon is also a dominant feature At Saturn there seems no evidence of a cushion region flux return is thought to take place sporadically over much of the nightside Although definitive statements about the dusk plasma sheet await the orbit evolution of Cassini a fundamental observational feature in the Saturnian context is a planetary rotation induced magnetic field asymmetry which argues against major dawn-dusk asymmetry We propose the rotational feature could originate from a localized ionospheric magnetic anomaly The

  17. Gorringe Ridge gravity and magnetic anomalies are compatible with thrusting at a crustal scale

    NASA Astrophysics Data System (ADS)

    Galindo-Zaldívar, J.; Maldonado, A.; Schreider, A. A.

    2003-06-01

    The main features of the deep structure of the Gorringe Ridge are analysed on the basis of gravity and magnetic measurements, as well as seismic profiles, drill holes, rock dredges, submersible observations and seismicity data. The gravity and magnetic models of the Gettysburg and Ormonde seamounts, which form the Gorringe Ridge, suggest that the Moho is approximately flat and the upper part of the ridge corresponds to a northwestwards vergent fold. This structure is the result of a northwestward vergent thrust that deformed the oceanic crust, with a minimum slip of approximately 20 km. The activity of the thrust probably started 20 Myr, and produced the recent stages of seamount uplift. The seamount is mainly composed of gabbros of the oceanic crust, serpentinized rocks and alkaline basalts. The large antiform, located in the hangingwall of the thrust, is probably deformed by minor faults. This oceanic ridge is a consequence of the oblique convergence between the African Plate and the overlapping Eurasian Plate.

  18. Elastic anomalies at the magnetic phase transitions of TbTe3

    NASA Astrophysics Data System (ADS)

    Saint-Paul, M.; Guttin, C.; Lejay, P.; Leynaud, O.; Monceau, P.

    2016-08-01

    We report sound velocity and ultrasonic attenuation measurements in the vicinity of the successive magnetic phase transitions Tmag1~6.5 K, Tmag2~5.8 K and Tmag3~5.3 K in the charge density wave TbTe3 compound. A detailed investigation of the critical contributions to the temperature dependences of the sound velocity and ultrasonic attenuation is presented. Anisotropic stress dependences ∂Tmag1 / ∂σ found at the antiferromagnetic phase transition Tmag1 is associated with the layered structure of this compound. An abrupt step-like increase in the velocity and a sharp peak in the attenuation are observed with the longitudinal and shear modes at the lock-in magnetic phase transition Tmag3=5.3 K. The critical velocity and attenuation behaviors in the high temperature paramagnetic above Tmag1 are described in terms of a phenomenological dynamic scaling expression.

  19. Positive holes in magnesium oxide - Correlation between magnetic, electric, and dielectric anomalies

    NASA Technical Reports Server (NTRS)

    Batllo, F.; Leroy, R. C.; Parvin, K.; Freund, F.; Freund, M. M.

    1991-01-01

    The present magnetic susceptibility investigation of high purity MgO single crystals notes an anomally at 800 K which is associated with increasing electrical conductivity, a rise in static dielectric constant from 9 to 150, and the appearance of a pronounced positive surface charge. These phenomena can be accounted for in terms of peroxy defects which represent self-trapped, spin-paired positive holes at Mg(2+) vacancy sites. The holes begin to decouple their spins above 600 K.

  20. Aeromagnetic anomalies and discordant lineations beneath the Niger Delta: Implications for new fracture zones and multiple sea-floor spreading directions in the meso-Atlantic' Gulf of Guinea cul-de-sac

    SciTech Connect

    Babalola, O.O.; Gipson, M. Jr. )

    1991-06-01

    An aeromagnetic contour map compiled over shallow water and onshore portions of the Nigerian continental margin, shows several elongate, long-wavelength anomaly closures with some alternating polarity, separated by steep gradient, NE lineations. The lineations are interpreted as new fracture zones or extensions of previously mapped ones. The NE trend in the western delta region is concordant with the fracture zone trends of the deeper Gulf of Guinea. Aeromagnetic lineations of the SE Niger Delta Basin however, discordantly trend ENE. Their termination against the former, is interpreted as evidence of early sea-floor spreading in a ENE-WSW direction in addition to the well documented NE-SW spreading of the Gulf of Guinea and the rest of the meso-Atlantic sea-floor; The geophysical crustal structure indicate the existence of two Early Cretaceous triple junctions beneath the Niger Delta Basin. The two triple-junctions further support the hypothesis that the African continent was a multi-plate system (in the Niger Delta region) during the early opening of the Atlantic.

  1. Seeded growth of ferrite nanoparticles from Mn oxides: observation of anomalies in magnetic transitions.

    PubMed

    Song, Hyon-Min; Zink, Jeffrey I; Khashab, Niveen M

    2015-07-28

    A series of magnetically active ferrite nanoparticles (NPs) are prepared by using Mn oxide NPs as seeds. A Verwey transition is identified in Fe3O4 NPs with an average diameter of 14.5 nm at 96 K, where a sharp drop of magnetic susceptibility occurs. In MnFe2O4 NPs, a spin glass-like state is observed with the decrease in magnetization below the blocking temperature due to the disordered spins during the freezing process. From these MnFe2O4 NPs, MnFe2O4@Mn(x)Fe(1-x)O core-shell NPs are prepared by seeded growth. The structure of the core is cubic spinel (Fd3¯m), and the shell is composed of iron-manganese oxide (Mn(x)Fe(1-x)O) with a rock salt structure (Fm3¯m). Moiré fringes appear perpendicular to the 〈110〉 directions on the cubic shape NPs through the plane-matched epitaxial growth. These fringes are due to the difference in the lattice spacings between MnFe2O4 and Mn(x)Fe(1-x)O. Exchange bias is observed in these MnFe2O4@Mn(x)Fe(1-x)O core-shell NPs with an enhanced coercivity, as well as the shift of hysteresis along the field direction.

  2. Coronary artery anomalies.

    PubMed

    Earls, James P

    2006-12-01

    Coronary artery anomalies are uncommon findings but can be of significant clinical importance in a small number of individuals. Clinical presentation depends on the specific anomaly. Most coronary artery anomalies are benign and clinically insignificant, however, some anomalies are potentially significant and can lead to heart failure and even death. Noninvasive imaging has emerged as the preferred way to image coronary anomalies. Both electron beam computed tomography (EBCT) and magnetic resonance angiography (MRA) are useful for the diagnosis of anomalous coronary arteries. Recently, MDCT has also proven to be very useful in the detection and characterization of anomalous coronary arteries. This chapter will review the appearance of the most commonly encountered coronary anomalies on MDCT. PMID:17709086

  3. Curie isotherm surfaces inferred from high-altitude magnetic anomaly data

    NASA Technical Reports Server (NTRS)

    Mayhew, M. A.

    1985-01-01

    Two-dimensional Curie depth models along two sections across the western United States are derived using an equivalent layer magnetization model derived from Magsat data, and the results are used to constrain finite element thermal models developed by Mayhew and Majer (1980). Regional heat flow variations predicted by the models compare favorably with those inferred from direct measurements. The methodology is applied to upward-continued aeromagnetic data, and the results are found to be in good agreement with previous Curie depth estimates and average measured heat flow.

  4. Acoustic anomalies in UPt{3} at high magnetic fields and low temperatures.

    SciTech Connect

    Feller, J. R.; Ketterson, J. B.; Hinks, D. G.; Dasgupta, D.; Sarma, B. K.; Materials Science Division; Northwestern Univ.; Univ. of Wisconsin at Milwaukee

    2000-11-01

    Ultrasound velocity and attenuation measurements were performed on single crystals of the heavy fermion compound UPt{sub 3} in magnetic fields up to 33 T and at temperatures ranging from 2.4 K to below 0.1 K. With longitudinal sound propagated in the crystallographic basal plane, parallel to the applied field, the familiar elastic softening is observed at the metamagnetic transition field H-20.2 T. More complicated structure emerges at low temperatures, including quantum acoustic oscillations and a second velocity minimum at -21.6 T. A weak frequency dependence (dispersion) is observed in the velocity. The ultrasonic data are analyzed using the Landau-Khalatnikov formalism, from which temperature- and field-dependent relaxation times are deduced.

  5. FORTRAN codes to implement enhanced local wave number technique to determine the depth and location and shape of the causative source using magnetic anomaly

    NASA Astrophysics Data System (ADS)

    Agarwal, B. N. P.; Srivastava, Shalivahan

    2008-12-01

    The total field magnetic anomaly is analyzed to compute the depth and location and geometry of the causative source using two FORTRAN source codes, viz., FRCON1D and ELW. No assumption on the nature of source geometry, susceptibility contrast, etc. has been made. The source geometry is estimated by computing the structural index from previously determined depth and location. A detailed procedure is outlined for using these codes through a theoretical anomaly. The suppression of high-frequency noise in the observed data is tackled by designing a box-car window with cosine termination. The termination criterion is based on the peak position of the derivative operator computed for a pre-assumed depth of a shallow source below which the target is situated. The applicability of these codes has been demonstrated by analyzing a total field aeromagnetic anomaly of the Matheson area of northern Ontario, Canada.

  6. Oxfordian magnetostratigraphy of Poland and its correlation to Sub-Mediterranean ammonite zones and marine magnetic anomalies

    NASA Astrophysics Data System (ADS)

    Przybylski, P. A.; Głowniak, E.; Ogg, J. G.; Ziółkowski, P.; Sidorczuk, M.; Gutowski, J.; Lewandowski, M.

    2010-01-01

    A nearly continuous magnetostratigraphic polarity pattern was compiled from several ammonite-zoned carbonate successions of southern Poland and from a composite magnetostratigraphy from the Iberian Range of Spain. The array of sections spans the middle two-thirds of the Oxfordian within the Sub-Mediterranean Province (Cordatum through Bifurcatus ammonite zones). The average paleopole calculated from eight of these Polish sections is at 78.5°N, 184.9°E ( δp = 2.6°, δm = 3.5°). The Sub-Mediterranean polarity pattern is consistent with an independent polarity pattern derived from the Boreal-realm sections of the British Isles, and improves the inter-correlation between these faunal realms. Cycle stratigraphy published for these ammonite subzones from southern France enabled temporal scaling of the polarity pattern, thereby facilitating correlation to marine magnetic anomalies M28 through M33 as modeled from deep-tow magnetometer surveys in the Western Pacific. The bases of the Middle and Upper Oxfordian substages as defined in the Sub-Mediterranean zonation in Poland correspond approximately to chrons M33 and M29 of that Pacific M-sequence model.

  7. Recurrent cholangitis associated with biliary sludge and Phrygian cap anomaly diagnosed by magnetic resonance imaging and magnetic resonance cholangiopancreatography despite normal ultrasound and computed tomography.

    PubMed

    Basaranoglu, Metin; Balci, Numan Cem

    2005-06-01

    A 31-year-old woman presented with a one and half years' history of intermittent right upper quadrant (RUQ) pain, high fever and severely painful, warm and reddish swollen skin lesions on the fingers. Acute attack resolution occurred within 2 weeks after treatment with non-specific antibiotics. Low-grade fever (around 37.5 degrees C) and less painful swellings continued for 6 months after each attack. Abdominal ultrasound and computed tomography (CT) scans did not show any abnormality during the attacks. Biopsy of the skin lesions after the second attack revealed lymphocytic vasculitis. All laboratory studies including rheumatologic serology panel were normal. One month after the complete resolution of the second attack, the patient was observed to have high fever, the same skin lesions on the fingers as at the initial stage, nausea and marked abdominal pain in the RUQ. Routine laboratory studies including complete blood count, liver function tests and serum amylase and lipase levels were normal. An abdominal CT scan revealed a slight thickening of the gallbladder wall (3.9 mm). Two weeks later, abdominal magnetic resonance imaging (MRI) and magnetic resonance cholangiopancreatography (MRCP) were performed because of persistent abdominal pain. They revealed both biliary tract and pancreatic gland alterations consistent with past cholangitis and pancreatitis with coexisting Phrygian cap anomaly and biliary sludge on the neck of the gallbladder.

  8. Evaluation of seismo-electric anomalies using magnetic data in Taiwan

    NASA Astrophysics Data System (ADS)

    Chen, C. H.; Hsu, H. L.; Wen, S.; Yeh, T. K.; Chang, F. Y.; Wang, C. H.; Liu, J. Y.; Sun, Y. Y.; Hattori, K.; Yen, H. Y.; Han, P.

    2013-03-01

    The Parkinson vectors derived from 3-component geomagnetic data via the magnetic transfer function are discussed with respect to epicentre locations and hypocentre depths of 16 earthquakes (M ≥ 5.5) in Taiwan during a period of 2002-2005. To find out whether electric conductivity changes would happen particularly in the seismoactive depth ranges, i.e. in the vicinity of the earthquake foci, the frequency dependent penetration depth of the electromagnetic waves (skin effect) is taken into account. The background distributions involving the general conductivity structure and the coast effect at 20 particular depths are constructed using the Parkinson vectors during the entire study period. The background distributions are subtracted from the time-varying monitor distributions, which are computed using the Parkinson vectors within the 15-day moving window, to remove responses of the coast effect and underlying conductivity structure. Anomalous depth sections are identified by deviating distributions and agree with the hypocentre depths of 15 thrust and/or strike-slip earthquakes with only one exception of a normal fault event.

  9. Bahía de Banderas, Mexico: Morphology, Magnetic Anomalies and Shallow Structure

    NASA Astrophysics Data System (ADS)

    Mortera Gutiérrez, Carlos A.; Bandy, William L.; Ponce Núñez, Francisco; Pérez Calderón, Daniel A.

    2016-09-01

    The Bahía de Banderas lies within a tectonically complex area at the northern end of the Middle America Trench. The structure, morphology, subsurface geology and tectonic history of the bay are essential for unraveling the complex tectonic processes occurring in this area. With this focus, marine geophysical data (multi-beam bathymetry, high resolution seismic reflection and total field magnetic data) were collected within the bay and adjacent areas during four campaigns aboard the B.O. EL PUMA conducted in 2006 and 2009. These data image the detailed morphology of, and sedimentation patterns within, the Banderas Canyon (a prominent submarine canyon situated on the south side of the bay) as well as the shallow subsurface structure of the northern part of the bay and the submarine Marietas Ridge, which bounds the bay to the west. We find that the Marietas Ridge is presently a transtensional feature; the course of the Banderas Canyon is controlled by extensive turbidite fan sedimentation in its eastern extremity and by structural lineaments to the west; the canyon floor is filled by sediments and exhibits almost no evidence for recent tectonic movements; the southern canyon wall is quite steep and a few sediments are deposited as submarine fans at the base of the southern wall; and extensive turbidite fans form the lower part of the northern canyon wall, producing a gently sloping lower northern wall. We find no evidence for a regional east-west striking lineament between the bay and the Middle America Trench, which casts doubts on the previous assertion that the Banderas Canyon is unequivocally related to the presence of a regional half-graben. Finally, a N71°E oriented normal fault offsets the seafloor reflector by 15 m within the central part of the bay, suggesting that the bay is currently being subjected to NNW-SSE extension.

  10. Bahía de Banderas, Mexico: Morphology, Magnetic Anomalies and Shallow Structure

    NASA Astrophysics Data System (ADS)

    Mortera Gutiérrez, Carlos A.; Bandy, William L.; Ponce Núñez, Francisco; Pérez Calderón, Daniel A.

    2016-10-01

    The Bahía de Banderas lies within a tectonically complex area at the northern end of the Middle America Trench. The structure, morphology, subsurface geology and tectonic history of the bay are essential for unraveling the complex tectonic processes occurring in this area. With this focus, marine geophysical data (multi-beam bathymetry, high resolution seismic reflection and total field magnetic data) were collected within the bay and adjacent areas during four campaigns aboard the B.O. EL PUMA conducted in 2006 and 2009. These data image the detailed morphology of, and sedimentation patterns within, the Banderas Canyon (a prominent submarine canyon situated on the south side of the bay) as well as the shallow subsurface structure of the northern part of the bay and the submarine Marietas Ridge, which bounds the bay to the west. We find that the Marietas Ridge is presently a transtensional feature; the course of the Banderas Canyon is controlled by extensive turbidite fan sedimentation in its eastern extremity and by structural lineaments to the west; the canyon floor is filled by sediments and exhibits almost no evidence for recent tectonic movements; the southern canyon wall is quite steep and a few sediments are deposited as submarine fans at the base of the southern wall; and extensive turbidite fans form the lower part of the northern canyon wall, producing a gently sloping lower northern wall. We find no evidence for a regional east-west striking lineament between the bay and the Middle America Trench, which casts doubts on the previous assertion that the Banderas Canyon is unequivocally related to the presence of a regional half-graben. Finally, a N71°E oriented normal fault offsets the seafloor reflector by 15 m within the central part of the bay, suggesting that the bay is currently being subjected to NNW-SSE extension.

  11. Spread-F during the magnetic storm of 22 January 2004 at low latitudes: Effect of IMF-Bz in relation to local sunset time

    NASA Astrophysics Data System (ADS)

    Rastogi, R. G.; Chandra, H.; Janardhan, P.; Hoang, Thai Lan; Condori, Louis; Pant, T. K.; Prasad, D. S. V. V. D.; Reinisch, B.

    2014-08-01

    The paper describes the results of spread-F at low latitude stations around the world during the magnetic storm starting at 0130 UT on 22 January 2004. The storm can be divided into two phases, first phase up to 1000 UT when interplanetary magnetic field IMF-Bz was highly fluctuating around a small positive value and the second phase after a sudden large southward turning of IMF-Bz at 1030 UT. The first phase produced strong spread-F at Jicamarca, Sao Luis, and Ascension Island and caused complete inhibition of spread-F at Thumba and Waltair in India. It generated weak spread-F at Ho Chi Minh City in Vietnam and strong spread-F at Hainan and Chung Li. The strong spread-F at Hainan and Chung Li were caused by the positive IMF-Bz during the first phase of the storm and not by the negative pulse of IMF-Bz at 1000 UT.

  12. MAGSAT anomaly map and continental drift

    NASA Technical Reports Server (NTRS)

    Lemouel, J. L. (Principal Investigator); Galdeano, A.; Ducruix, J.

    1981-01-01

    Anomaly maps of high quality are needed to display unambiguously the so called long wave length anomalies. The anomalies were analyzed in terms of continental drift and the nature of their sources is discussed. The map presented confirms the thinness of the oceanic magnetized layer. Continental magnetic anomalies are characterized by elongated structures generally of east-west trend. Paleomagnetic reconstruction shows that the anomalies found in India, Australia, and Antarctic exhibit a fair consistency with the African anomalies. It is also shown that anomalies are locked under the continents and have a fixed geometry.

  13. THEOS-2 Orbit Design: Formation Flying in Equatorial Orbit and Damage Prevention Technique for the South Atlantic Magnetic Anomaly (SAMA)

    NASA Astrophysics Data System (ADS)

    Pimnoo, Ammarin

    2016-07-01

    Geo-Informatics and Space Technology Development Agency (GISTDA) has initiative THEOS-2 project after the THEOS-1 has been operated for more than 7 years which is over the lifetime already. THEOS-2 project requires not only the development of earth observation satellite(s), but also the development of the area-based decision making solution platform comprising of data, application systems, data processing and production system, IT infrastructure improvement and capacity building through development of satellites, engineering model, and infrastructures capable of supporting research in related fields. The developing satellites in THEOS-2 project are THAICHOTE-2 and THAICHOTE-3. This paper focuses the orbit design of THAICHOTE-2 & 3. It discusses the satellite orbit design for the second and third EOS of Thailand. In this paper, both THAICHOTE will be simulated in an equatorial orbit as a formation flying which will be compared the productive to THAICHOTE-1 (THEOS-1). We also consider a serious issue in equatorial orbit design, namely the issue of the geomagnetic field in the area of the eastern coast of South America, called the South Atlantic Magnetic Anomaly (SAMA). The high-energy particles of SAMA comprise a radiation environment which can travel through THAICHOTE-2 & 3 material and deposit kinetic energy. This process causes atomic displacement or leaves a stream of charged atoms in the incident particles' wake. It can cause damage to the satellite including reduction of power generated by solar arrays, failure of sensitive electronics, increased background noise in sensors, and exposure of the satellite devices to radiation. This paper demonstrates the loss of ionizing radiation damage and presents a technique to prevent damage from high-energy particles in the SAMA.

  14. Long periods (1 -10 mHz) geomagnetic pulsations variation with solar cycle in South Atlantic Magnetic Anomaly

    NASA Astrophysics Data System (ADS)

    Rigon Silva, Willian; Schuch, Nelson Jorge; Guimarães Dutra, Severino Luiz; Babulal Trivedi, Nalin; Claudir da Silva, Andirlei; Souza Savian, Fernando; Ronan Coelho Stekel, Tardelli; de Siqueira, Josemar; Espindola Antunes, Cassio

    The occurrence and intensity of the geomagnetic pulsations Pc-5 (2-7 mHz) and its relationship with the solar cycle in the South Atlantic Magnetic Anomaly -SAMA is presented. The study of geomagnetic pulsations is important to help the understanding of the physical processes that occurs in the magnetosphere region and help to predict geomagnetic storms. The fluxgate mag-netometers H, D and Z, three axis geomagnetic field data from the Southern Space Observatory -SSO/CRS/INPE -MCT, São Martinho da Serra (29.42° S, 53.87° W, 480m a.s.l.), RS, Brasil, a were analyzed and correlated with the solar wind parameters (speed, density and temperature) from the ACE and SOHO satellites. A digital filtering to enhance the 2-7 mHz geomagnetic pulsations was used. Five quiet days and five perturbed days in the solar minimum and in the solar maximum were selected for this analysis. The days were chosen based on the IAGA definition and on the Bartels Musical Diagrams (Kp index) for 2001 (solar maximum) and 2008 (solar minimum). The biggest Pc-5 amplitude averages differences between the H-component is 78,35 nT for the perturbed days and 1,60nT for the quiet days during the solar maximum. For perturbed days the average amplitude during the solar minimum is 8,32 nT, confirming a direct solar cycle influence in the geomagnetic pulsations intensity for long periods.

  15. Gravity and magnetic anomalies of the western Arctic ocean and its margins provide an imperfect window to a complex, multi-stage tectonic history (Invited)

    NASA Astrophysics Data System (ADS)

    Saltus, R. W.; Miller, E. L.; Gaina, C.

    2010-12-01

    Numerous scenarios are still in play for the tectonic development of the western Arctic. A wide range of kinematic models have been proposed for the opening of the Canadian basin. These models feature different combinations and geometries of extensional and transform motion and have informal descriptive names including the so-called ‘windshield wiper’, ‘railroad tracks’, ‘squeegee’, and ‘saloon door’ options. Another controversial issue is the timing and role of the gigantic Alpha-Mendeleev large igneous province relative to the tectonic stages. In our opinion, many current Arctic models have not adequately dealt with the mass and thermal fluxes implied by this huge province. Available data are extremely sparse for the circum-Arctic, although current political and economic interests are fueling accelerated data collection. Recent compilations of gravity and magnetic data are currently the best bets for synoptic imaging, however imprecise, of crustal composition and structure. Modeling and interpretation of regional geophysical anomalies provide some of the only available tests for scenario evaluation in the absence of more direct determinations of crustal structure and composition. Our goal in this talk is to review the key geophysical features of the western Arctic and relate these elements to the expectations of competing tectonic models. These key geophysical features include (1) contrasting Arctic domains of overall magnetic “thickness” and anomaly “fabric” (the domains correlate generally with broad tectonic categories); (2) cryptic sub-linear magnetic anomalies in the Canada basin (interpreted by some authors to be oceanic stripes); (3) a subtle but persistent gravity trough in the central Canada basin (inferred by some authors to represent an extensional trough); (4) spectacular “shelf edge” free-air gravity anomalies along the Canadian and Alaskan passive margins that show significant along-strike variation (which can be

  16. Origin of strong lunar magnetic anomalies: Further mapping and examinations of LROC imagery in regions antipodal to young large impact basins

    NASA Astrophysics Data System (ADS)

    Hood, Lon L.; Richmond, Nicola C.; Spudis, Paul D.

    2013-06-01

    The existence of magnetization signatures and landform modification antipodal to young lunar impact basins is investigated further by (a) producing more detailed regional crustal magnetic field maps at low altitudes using Lunar Prospector magnetometer data; and (b) examining Lunar Reconnaissance Orbiter Wide Angle Camera imagery. Of the eight youngest lunar basins, five are found to have concentrations of relatively strong magnetic anomalies centered within 10° of their antipodes. This includes the polar Schrödinger basin, which is one of the three youngest basins and has not previously been investigated in this context. Unusual terrain is also extensively present near the antipodes of the two largest basins (Orientale and Imbrium) while less pronounced manifestations of this terrain may be present near the antipodes of Serenitatis and Schrödinger. The area near the Imbrium antipode is characterized by enhanced surface thorium abundances, which may be a consequence of antipodal deposition of ejecta from Imbrium. The remaining three basins either have antipodal regions that have been heavily modified by later events (Hertzsprung and Bailly) or are not clearly recognized to be a true basin (Sikorsky-Rittenhouse). The most probable source of the Descartes anomaly, which is the strongest isolated magnetic anomaly, is the hilly and furrowed Descartes terrain near the Apollo 16 landing site, which has been inferred to consist of basin ejecta, probably from Imbrium according to one recent sample study. A model for the origin of both the modified landforms and the magnetization signatures near lunar basin antipodes involving shock effects of converging ejecta impacts is discussed.

  17. The seasonal and solar cycle variations of electron density gradient scale length during magnetically disturbed days: implications for Spread F

    NASA Astrophysics Data System (ADS)

    Manju, G.; Devasia, C. V.; Ravindran, S.

    2009-07-01

    The behaviour of electron density gradient scale length, L, around post-sunset hours during the magnetically disturbed days of the summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995) has been studied, using ionosonde data of Trivandrum (8.5°N, 76.5°E, dip = 0.5°N) in the Indian longitude sector. The results indicate a clear seasonal and solar cycle variation in L. Seasonal variations of the maximum vertical drift of the F layer were also examined on these days. In particular, the seasonal variation of the Equatorial Spread F (ESF) during this period is examined in terms of the relative roles of L and the vertical drift of the F layer in the triggering of the collisional Rayleigh-Taylor instability. Our results on the clear-cut seasonal and solar cycle variation in L for disturbed days and its control of ESF occurrence are presented and discussed.

  18. A source-depth separation filter: Using the Euler method on the derivatives of total intensity magnetic anomaly data

    USGS Publications Warehouse

    Ravat, D.; Kirkham, K.; Hildenbrand, T.G.

    2002-01-01

    An overview is given on the benefits of applying the Euler method on derivatives of anomalies to enhance the location of shallow and deep sources. Used properly, the method is suitable for characterizing sources from all potential-field data and/or their derivative, as long as the data can be regarded mathematically as "continuous". Furthermore, the reasons why the use of the Euler method on derivatives of anomalies is particularly helpful in the analysis and interpretation of shallow features are explained.

  19. The Effects of Magnetic Anomalies Discovered at Mars on the Structure of the Martian Ionosphere and the Solar Wind Interaction as Follows from Radio Occultation Experiments

    NASA Technical Reports Server (NTRS)

    Ness, N. F.; Acuna, M. H.; Connerney, J. E. P.; Cloutier, P.; Kliore, A. J.; Breus, T. K.; Krymskii, A. M.; Bauer, S. J.

    1999-01-01

    The electron density distribution in the ionosphere of nonmagnetic (or weakly magnetized) planet depends not only on the solar ultraviolet intensity, but also on the nature of the SW interaction with this planet. Two scenarios previously have been developed based on the observations of the bow shock crossings and on the electron density distribution within the ionosphere. According to one of them Mars has an intrinsic magnetosphere produced by a dipole magnetic field and the Martian ionosphere is protected from the SW flow except during "overpressure conditions, when the planetary magnetic field can not balance the SW dynamic pressure. In the second scenario the Martian intrinsic magnetic dipole field is so weak that Mars has mainly an induced magnetosphere and a Venus-like SW/ionosphere interaction. Today the possible existence of a sufficiently strong global magnetic field that participates in the SW/Mars interaction can no longer be supported. The results obtained by the Mars-Global-Surveyor (MGS) space-craft show the existence of highly variable, but also very localized magnetic fields of crustal origin at Mars as high as 400-1500 nT. The absence of the large-scale global magnetic field at Mars makes it similar to Venus, except for possible effects of the magnetic anomalies associated with the remnant crustal magnetization. However the previous results on the Martian ionosphere obtained mainly by the radio occultation methods show that there appears to be a permanent existence of a global horizontal magnetic field in the Martian ionosphere. Moreover the global induced magnetic field in the Venus ionosphere is not typical at the solar zenith angles explored by the radio occultation methods. Additional information is contained in the original extended abstract.

  20. M3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies

    USGS Publications Warehouse

    Kramer, G.Y.; Besse, S.; Dhingra, D.; Nettles, J.; Klima, R.; Garrick-Bethell, I.; Clark, R.N.; Combe, J.-P.; Head, J. W.; Taylor, L.A.; Pieters, C.M.; Boardman, J.; McCord, T.B.

    2011-01-01

    all three focus regions support the hypothesis that the magnetic anomalies deflect solar wind ions away from the swirls and onto off-swirl surfaces. Nanophase iron (npFe0) is largely responsible for the spectral characteristics we attribute to space weathering and maturation, and is created by vaporization/deposition by micrometeorite impacts and sputtering/reduction by solar wind ions. On the swirls, the decreased proton flux slows the spectral effects of space weathering (relative to nonswirl regions) by limiting the npFe0 production mechanism almost exclusively to micrometeoroid impact vaporization/deposition. Immediately adjacent to the swirls, maturation is accelerated by the increased flux of protons deflected from the swirls. Copyright 2011 by the American Geophysical Union.

  1. 3-D Full-kinetic Simulations of the Solar Wind Interaction with Lunar Magnetic Anomalies: Particle Behaviour

    NASA Astrophysics Data System (ADS)

    Deca, J.; Divin, A. V.; Wang, X.; Lembege, B.; Markidis, S.; Lapenta, G.; Horanyi, M.

    2015-12-01

    We present three-dimensional full-kinetic electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier MHD and hybrid simulations, the full-kinetic nature of iPic3D allows to self-consistently investigate space charge effects, and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe the general mechanism of the interaction of both a horizontal and vertical dipole model embedded just below the lunar surface focussing on the ion and electron kinetic behaviour of the system. It is shown that the configurations are largely dominated by electron motion, because the LMA scale size is small with respect to the gyro-radius of the solar wind ions. The formation of mini-magnetospheres is an electrostatic effect. Additionally, we discuss typical particle trajectories as well as complete particle distribution functions covering thermal and suprathermal energies, within the interaction region and on viable spacecraft altitudes. Our work opens new frontiers of research toward a deeper understanding of LMAs and is ideally suited to be compared with field or particle observations from spacecraft such as Kaguya (SELENE), Lunar Prospector or ARTEMIS. The ability to evaluate the implications for future lunar exploration as well as lunar science in general hinges on a better understanding of LMAs.This research has received funding from the European Commission's FP7 Program with the grant agreement EHEROES (project 284461, www.eheroes.eu). The simulations were conducted on the computational resources provided by the PRACE Tier-0 project 2013091928 (SuperMUC). This research was supported by the Swedish National Space Board

  2. Rock Magnetic Cyclostratigraphy and Magnetostratigraphy of the Rainstorm Member of the Neoproterozoic Johnnie Formation indicate a 2.5 Myr Duration for the Negative 13C Isotopic Anomaly

    NASA Astrophysics Data System (ADS)

    Kodama, K. P.; Hillhouse, J. W.

    2011-12-01

    The Rainstorm Member of the Neoproterozoic Johnnie Formation from Death Valley, CA, contains a negative 13C isotopic anomaly that records the oxidation of the oceans with the rise of atmospheric oxygen just before the appearance of multi-cellular life. Previously, the only estimate for the duration of the globally observed 13C anomaly, 50 myr, came from thermal subsidence modeling of rocks in Oman. In the southern Nopah Range, CA, we collected rock magnetic samples from 6 to 45 m above the Johnnie oolite marker bed to test for cyclostratigraphy in mudstone carbonates that correlate to the lower third of the carbon anomaly. Our objective was to independently determine the duration of the oxidation event by looking for evidence of orbital cycles in the rock magnetic properties. We also collected 8 horizons of three oriented samples each between 10 m and 40 m above the oolite for a magnetostratigraphy to constrain our interpretation of the rock magnetic cyclostratigraphy. After thermal demagnetization treatments, the remanent magnetization showed 4 chrons (R-N-R-N) in the 30 m interval with E (reversed)-W(normal) declinations and shallow inclinations (mean: D=262.8°, I=1.3°), similar to previous paleomagnetic determinations for an equivalent part of the Rainstorm Member in the Desert Range, Nevada (Van Alstine and Gillett , 1979) . Our rock magnetic cyclostratigraphy, sampled at 25 cm intervals, shows a well-defined 5 m wavelength for a measure of the goethite-to-hematite ratio that is interpreted to indicate climate variability (precipitation to aridity) in the Johnnie Formation source area. In addition to the 5 m cycle, a smaller amplitude cycle is observed in the data series with an average wavelength of 0.75 m. Multi-taper method (MTM) spectral analysis shows significant power (> than the 95% confidence limits above the robust red noise) at these frequencies, but also at harmonics of the 5 m waveform. If the 5 m cycle is assumed to be short eccentricity with a

  3. MAGSAT scalar and vector anomaly data analysis

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Efforts on the analysis of MAGSAT scalar anomaly data, the application of the scalar analysis results to three component vector data, and the comparison of MAGSAT data with corresponding MAGNET aeromagnetic and free air gravity anomaly data are briefly described.

  4. Reconstructing Coherent Networks from Electroencephalography and Magnetoencephalography with Reduced Contamination from Volume Conduction or Magnetic Field Spread

    PubMed Central

    Drakesmith, Mark; El-Deredy, Wael; Welbourne, Stephen

    2013-01-01

    Volume conduction (VC) and magnetic field spread (MFS) induce spurious correlations between EEG/MEG sensors, such that the estimation of functional networks from scalp recordings is inaccurate. Imaginary coherency [1] reduces VC/MFS artefacts between sensors by assuming that instantaneous interactions are caused predominantly by VC/MFS and do not contribute to the imaginary part of the cross-spectral densities (CSDs). We propose an adaptation of the dynamic imaging of coherent sources (DICS) [2] - a method for reconstructing the CSDs between sources, and subsequently inferring functional connectivity based on coherences between those sources. Firstly, we reformulate the principle of imaginary coherency by performing an eigenvector decomposition of the imaginary part of the CSD to estimate the power that only contributes to the non-zero phase-lagged (NZPL) interactions. Secondly, we construct an NZPL-optimised spatial filter with two a priori assumptions: (1) that only NZPL interactions exist at the source level and (2) the NZPL CSD at the sensor level is a good approximation of the projected source NZPL CSDs. We compare the performance of the NZPL method to the standard method by reconstructing a coherent network from simulated EEG/MEG recordings. We demonstrate that, as long as there are phase differences between the sources, the NZPL method reliably detects the underlying networks from EEG and MEG. We show that the method is also robust to very small phase lags, noise from phase jitter, and is less sensitive to regularisation parameters. The method is applied to a human dataset to infer parts of a coherent network underpinning face recognition. PMID:24349088

  5. MATLAB-based algorithm to estimate depths of isolated thin dike-like sources using higher-order horizontal derivatives of magnetic anomalies.

    PubMed

    Ekinci, Yunus Levent

    2016-01-01

    This paper presents an easy-to-use open source computer algorithm (code) for estimating the depths of isolated single thin dike-like source bodies by using numerical second-, third-, and fourth-order horizontal derivatives computed from observed magnetic anomalies. The approach does not require a priori information and uses some filters of successive graticule spacings. The computed higher-order horizontal derivative datasets are used to solve nonlinear equations for depth determination. The solutions are independent from the magnetization and ambient field directions. The practical usability of the developed code, designed in MATLAB R2012b (MathWorks Inc.), was successfully examined using some synthetic simulations with and without noise. The algorithm was then used to estimate the depths of some ore bodies buried in different regions (USA, Sweden, and Canada). Real data tests clearly indicated that the obtained depths are in good agreement with those of previous studies and drilling information. Additionally, a state-of-the-art inversion scheme based on particle swarm optimization produced comparable results to those of the higher-order horizontal derivative analyses in both synthetic and real anomaly cases. Accordingly, the proposed code is verified to be useful in interpreting isolated single thin dike-like magnetized bodies and may be an alternative processing technique. The open source code can be easily modified and adapted to suit the benefits of other researchers.

  6. MATLAB-based algorithm to estimate depths of isolated thin dike-like sources using higher-order horizontal derivatives of magnetic anomalies.

    PubMed

    Ekinci, Yunus Levent

    2016-01-01

    This paper presents an easy-to-use open source computer algorithm (code) for estimating the depths of isolated single thin dike-like source bodies by using numerical second-, third-, and fourth-order horizontal derivatives computed from observed magnetic anomalies. The approach does not require a priori information and uses some filters of successive graticule spacings. The computed higher-order horizontal derivative datasets are used to solve nonlinear equations for depth determination. The solutions are independent from the magnetization and ambient field directions. The practical usability of the developed code, designed in MATLAB R2012b (MathWorks Inc.), was successfully examined using some synthetic simulations with and without noise. The algorithm was then used to estimate the depths of some ore bodies buried in different regions (USA, Sweden, and Canada). Real data tests clearly indicated that the obtained depths are in good agreement with those of previous studies and drilling information. Additionally, a state-of-the-art inversion scheme based on particle swarm optimization produced comparable results to those of the higher-order horizontal derivative analyses in both synthetic and real anomaly cases. Accordingly, the proposed code is verified to be useful in interpreting isolated single thin dike-like magnetized bodies and may be an alternative processing technique. The open source code can be easily modified and adapted to suit the benefits of other researchers. PMID:27610303

  7. The Emerson Lake Body: A link between the Landers and Hector Mine earthquakes, southern California, as inferred from gravity and magnetic anomalies

    USGS Publications Warehouse

    Langenheim, V.E.; Jachens, R.C.

    2002-01-01

    Gravity and magnetic data indicate a mafic crustal heterogeneity that lies between the Hector Mine 16 October 1999 (Mw 7.1) and Landers 28 June 1992 (Mw 7.3) epicenters. The aftershocks and ruptures of these two events avoided the interior of the body. Two- and three-dimensional modeling of the potential-field anomalies shows that the source, here named the Emerson Lake body (ELB), extends to a depth of approximately 15 km. The source of the gravity and magnetic anomaly is most likely Jurassic diorite because exposures of these rocks coincide with both gravity and magnetic highs west of Emerson Lake. Seismic tomography also shows higher velocities within the region of the ELB. We propose that the ELB was an important influence on the rupture geometry of the Landers and Hector Mine ruptures and that the ELB may have played a role in transferring of stress from the Landers earthquake to the Hector Mine hypocenter. Seismicity before the Landers earthquake also tended to avoid the ELB, suggesting that the ELB affects how strain is distributed in this part of the Mojave Desert. Thus, faults within the body should have limited rupture sizes and lower seismic hazard than faults bounding or outside this mafic crustal heterogeneity.

  8. Manipulating Ce Valence in RE2Fe14B Tetragonal Compounds by La-Ce Co-doping: Resultant Crystallographic and Magnetic Anomaly.

    PubMed

    Jin, Jiaying; Zhang, Yujing; Bai, Guohua; Qian, Zeyu; Wu, Chen; Ma, Tianyu; Shen, Baogen; Yan, Mi

    2016-01-01

    Abundant and low-cost Ce has attracted considerable interest as a prospective alternative for those critically relied Nd/Pr/Dy/Tb in the 2:14:1-type permanent magnets. The (Nd, Ce)2Fe14B compound with inferior intrinsic magnetic properties to Nd2Fe14B, however, cannot provide an equivalent magnetic performance. Since Ce valence is sensitive to local steric environment, manipulating it towards the favorable trivalent state provides a way to enhance the magnetic properties. Here we report that such a desirable Ce valence can be induced by La-Ce co-doping into [(Pr, Nd)1-x(La, Ce)x]2.14Fe14B (0 ≤ x ≤ 0.5) compounds via strip casting. As verified by X-ray photoelectron spectroscopy results, Ce valence shifts towards the magnetically favorable Ce(3+) state in the composition range of x > 0.3, owing to the co-doping of large radius La(3+) into 2:14:1 phase lattice. As a result, both crystallographic and magnetic anomalies are observed in the same vicinity of x = 0.3, above which lattice parameters a and c, and saturation magnetization Ms increase simultaneously. Over the whole doping range, 2:14:1 tetragonal structure forms and keeps stable even at 1250 K. This finding may shed light on obtaining a favorable Ce valence via La-Ce co-doping, thus maintaining the intrinsic magnetic properties of 2:14:1-type permanent magnets. PMID:27457408

  9. Manipulating Ce Valence in RE2Fe14B Tetragonal Compounds by La-Ce Co-doping: Resultant Crystallographic and Magnetic Anomaly

    NASA Astrophysics Data System (ADS)

    Jin, Jiaying; Zhang, Yujing; Bai, Guohua; Qian, Zeyu; Wu, Chen; Ma, Tianyu; Shen, Baogen; Yan, Mi

    2016-07-01

    Abundant and low-cost Ce has attracted considerable interest as a prospective alternative for those critically relied Nd/Pr/Dy/Tb in the 2:14:1-type permanent magnets. The (Nd, Ce)2Fe14B compound with inferior intrinsic magnetic properties to Nd2Fe14B, however, cannot provide an equivalent magnetic performance. Since Ce valence is sensitive to local steric environment, manipulating it towards the favorable trivalent state provides a way to enhance the magnetic properties. Here we report that such a desirable Ce valence can be induced by La-Ce co-doping into [(Pr, Nd)1-x(La, Ce)x]2.14Fe14B (0 ≤ x ≤ 0.5) compounds via strip casting. As verified by X-ray photoelectron spectroscopy results, Ce valence shifts towards the magnetically favorable Ce3+ state in the composition range of x > 0.3, owing to the co-doping of large radius La3+ into 2:14:1 phase lattice. As a result, both crystallographic and magnetic anomalies are observed in the same vicinity of x = 0.3, above which lattice parameters a and c, and saturation magnetization Ms increase simultaneously. Over the whole doping range, 2:14:1 tetragonal structure forms and keeps stable even at 1250 K. This finding may shed light on obtaining a favorable Ce valence via La-Ce co-doping, thus maintaining the intrinsic magnetic properties of 2:14:1-type permanent magnets.

  10. Manipulating Ce Valence in RE2Fe14B Tetragonal Compounds by La-Ce Co-doping: Resultant Crystallographic and Magnetic Anomaly

    PubMed Central

    Jin, Jiaying; Zhang, Yujing; Bai, Guohua; Qian, Zeyu; Wu, Chen; Ma, Tianyu; Shen, Baogen; Yan, Mi

    2016-01-01

    Abundant and low-cost Ce has attracted considerable interest as a prospective alternative for those critically relied Nd/Pr/Dy/Tb in the 2:14:1-type permanent magnets. The (Nd, Ce)2Fe14B compound with inferior intrinsic magnetic properties to Nd2Fe14B, however, cannot provide an equivalent magnetic performance. Since Ce valence is sensitive to local steric environment, manipulating it towards the favorable trivalent state provides a way to enhance the magnetic properties. Here we report that such a desirable Ce valence can be induced by La-Ce co-doping into [(Pr, Nd)1−x(La, Ce)x]2.14Fe14B (0 ≤ x ≤ 0.5) compounds via strip casting. As verified by X-ray photoelectron spectroscopy results, Ce valence shifts towards the magnetically favorable Ce3+ state in the composition range of x > 0.3, owing to the co-doping of large radius La3+ into 2:14:1 phase lattice. As a result, both crystallographic and magnetic anomalies are observed in the same vicinity of x = 0.3, above which lattice parameters a and c, and saturation magnetization Ms increase simultaneously. Over the whole doping range, 2:14:1 tetragonal structure forms and keeps stable even at 1250 K. This finding may shed light on obtaining a favorable Ce valence via La-Ce co-doping, thus maintaining the intrinsic magnetic properties of 2:14:1-type permanent magnets. PMID:27457408

  11. Manipulating Ce Valence in RE2Fe14B Tetragonal Compounds by La-Ce Co-doping: Resultant Crystallographic and Magnetic Anomaly

    NASA Astrophysics Data System (ADS)

    Jin, Jiaying; Zhang, Yujing; Bai, Guohua; Qian, Zeyu; Wu, Chen; Ma, Tianyu; Shen, Baogen; Yan, Mi

    2016-07-01

    Abundant and low-cost Ce has attracted considerable interest as a prospective alternative for those critically relied Nd/Pr/Dy/Tb in the 2:14:1-type permanent magnets. The (Nd, Ce)2Fe14B compound with inferior intrinsic magnetic properties to Nd2Fe14B, however, cannot provide an equivalent magnetic performance. Since Ce valence is sensitive to local steric environment, manipulating it towards the favorable trivalent state provides a way to enhance the magnetic properties. Here we report that such a desirable Ce valence can be induced by La-Ce co-doping into [(Pr, Nd)1‑x(La, Ce)x]2.14Fe14B (0 ≤ x ≤ 0.5) compounds via strip casting. As verified by X-ray photoelectron spectroscopy results, Ce valence shifts towards the magnetically favorable Ce3+ state in the composition range of x > 0.3, owing to the co-doping of large radius La3+ into 2:14:1 phase lattice. As a result, both crystallographic and magnetic anomalies are observed in the same vicinity of x = 0.3, above which lattice parameters a and c, and saturation magnetization Ms increase simultaneously. Over the whole doping range, 2:14:1 tetragonal structure forms and keeps stable even at 1250 K. This finding may shed light on obtaining a favorable Ce valence via La-Ce co-doping, thus maintaining the intrinsic magnetic properties of 2:14:1-type permanent magnets.

  12. The reduction, verification and interpretation of MAGSAT magnetic data over Canada

    NASA Technical Reports Server (NTRS)

    Coles, R. L. (Principal Investigator); Haines, G. V.; Vanbeek, G. J.; Walker, J. K.; Newitt, L. R.; Nandi, A.

    1982-01-01

    Correlations between the MAGSAT scalar anomaly map produced at the Earth Physics ranch and other geophysical and geological data reveal relationships between high magnetic field and some metamorphic grade shields, as well as between low magnetic field and shield regions of lower metamorphic grade. An intriguing contrast exists between the broad low anomaly field over the Nasen-Gakkel Ridge (a spreading plate margin) and the high anomaly field over Iceland (part of a spreading margin). Both regions have high heat flow, and presumably thin magnetic crust. This indicates that Iceland is quite anomalous in its magnetic character, and possible similarities with the Alpha Ridge are suggested. Interesting correlations exist between MAGSAT anomalies around the North Atlantic, after reconstructing the fit of continents into a prerifting configuration. These correlations suggest that several orogenies in that region have not completely destroyed an ancient magnetization formed in high grade Precambrian rocks.

  13. Spreading-rate-dependent anomalous skewness and the estimate of the chron 32 palaeomagnetic pole for the Pacific plate

    NASA Astrophysics Data System (ADS)

    Koivisto, E.; Gordon, R.; Dyment, J.; Arkani-Hamed, J.

    2006-12-01

    Palaeomagnetic poles can be determined from asymmetry (skewness) of marine magnetic anomalies. Early works applying the skewness method were limited by the discovery of an apparently systematic error known as anomalous skewness (Cande 1976). Anomalous skewness can be thought of as the systematic difference between the observed skewness and the skewness predicted by a simple magnetization model with rectangular 2-D layer 2A prisms of alternating polarity separated by vertical boundaries. In the early works, anomalous skewness could be isolated for anomalies with counterparts across a mid-ocean ridge, but was much harder to estimate for anomalies with subducted counterparts, as is mostly the case in the Pacific plate. Petronotis et al. (1992) presented a solution to this problem by simultaneously estimating anomalous skewness and a best-fitting palaeomagnetic pole from skewness data from a single plate. In their approach, anomalous skewness is assumed to be identical for different crossings of the same plate and any spreading-rate dependence of anomalous skewness is neglected. Nonetheless, anomalous skewness of marine magnetic anomalies is observed to decrease with increasing spreading rate and become negligible above spreading rates of about 50 mm yr-1 (e.g. Roest et al. 1992; Dyment et al. 1994). Dyment &Arkani-Hamed (1995) proposed a model in which the magnetic structure of the oceanic lithosphere is dependent on spreading rate with parameters adjusted to fit the observed spreading- rate dependence of anomalous skewness for some key anomalies. Here we apply their model to determine a new Maastrichtian palaeomagnetic pole for the Pacific plate from skewness estimates of magnetic anomaly 32. Previously Petronotis &Gordon (1999) obtained a palaeopole assuming spreading-rate independent anomalous skewness for the same data used here. They also investigated the possible dependence of anomalous skewness on spreading rate and found it to have negligible effect on their

  14. Untangling Magmatic Processes and Hydrothermal Alteration of in situ Superfast Spreading Ocean Crust at ODP/IODP Site 1256 with Fuzzy c-means Cluster Analysis of Rock Magnetic Properties

    NASA Astrophysics Data System (ADS)

    Dekkers, M. J.; Heslop, D.; Herrero-Bervera, E.; Acton, G.; Krasa, D.

    2014-12-01

    Ocean Drilling Program (ODP)/Integrated ODP (IODP) Hole 1256D (6.44.1' N, 91.56.1' W) on the Cocos Plate occurs in 15.2 Ma oceanic crust generated by superfast seafloor spreading. Presently, it is the only drill hole that has sampled all three oceanic crust layers in a tectonically undisturbed setting. Here we interpret down-hole trends in several rock-magnetic parameters with fuzzy c-means cluster analysis, a multivariate statistical technique. The parameters include the magnetization ratio, the coercivity ratio, the coercive force, the low-field susceptibility, and the Curie temperature. By their combined, multivariate, analysis the effects of magmatic and hydrothermal processes can be evaluated. The optimal number of clusters - a key point in the analysis because there is no a priori information on this - was determined through a combination of approaches: by calculation of several cluster validity indices, by testing for coherent cluster distributions on non-linear-map plots, and importantly by testing for stability of the cluster solution from all possible starting points. Here, we consider a solution robust if the cluster allocation is independent of the starting configuration. The five-cluster solution appeared to be robust. Three clusters are distinguished in the extrusive segment of the Hole that express increasing hydrothermal alteration of the lavas. The sheeted dike and gabbro portions are characterized by two clusters, both with higher coercivities than in lava samples. Extensive alteration, however, can obliterate magnetic property differences between lavas, dikes, and gabbros. The imprint of thermochemical alteration on the iron-titanium oxides is only partially related to the porosity of the rocks. All clusters display rock magnetic characteristics in line with a stable NRM. This implies that the entire sampled sequence of ocean crust can contribute to marine magnetic anomalies. Determination of the absolute paleointensity with thermal techniques is

  15. A Preliminary, Full Spectrum, Magnetic Anomaly Grid of the United States with Improved Long Wavelengths for Studying Continental Dynamics: A Website for Distribution of Data

    USGS Publications Warehouse

    Ravat, D.; Finn, C.; Hill, P.; Kucks, R.; Phillips, J.; Blakely, R.; Bouligand, C.; Sabaka, T.; Elshayat, A.; Aref, A.; Elawadi, E.

    2009-01-01

    Under an initiative started by Thomas G. Hildenbrand of the U.S. Geological Survey, we have improved the long-wavelength (50-2,500 km) content of the regional magnetic anomaly compilation for the conterminous United States by utilizing a nearly homogeneous set of National Uranium Resource Evaluation (NURE) magnetic surveys flown from 1975 to 1981. The surveys were flown in quadrangles of 2 deg of longitude by 1 deg of latitude with east-west flight lines spaced 4.8 to 9.6 km apart, north-south tie lines variably spaced, and a nominal terrain clearance of 122 m. Many of the surveys used base-station magnetometers to remove external field variations.

  16. Imaging of facial anomalies.

    PubMed

    Castillo, M; Mukherji, S K

    1995-01-01

    Anomalies of the face may occur in its lower or middle segments. Anomalies of the lower face generally involve the derivatives of the branchial apparatus and therefore manifest as defects in the mandible, pinnae, external auditory canals, and portions of the middle ears. These anomalies are occasionally isolated, but most of them occur in combination with systemic syndromes. These anomalies generally do not occur with respiratory compromise. Anomalies of the midface may extend from the upper lip to the forehead, reflecting the complex embryology of this region. Most of these deformities are isolated, but some patients with facial clefts, notably the midline cleft syndrome and holoprosencephaly, have anomalies in other sites. This is important because these patients will require detailed imaging of the face and brain. Anomalies of the midface tend to involve the nose and its air-conducting passages. We prefer to divide these anomalies into those with and without respiratory obstruction. The most common anomalies that result in airway compromise include posterior choanal stenoses and atresias, bilateral cysts (mucoceles) of the distal lacrimal ducts, and stenosis of the pyriform (anterior) nasal aperture. These may be optimally evaluated with computed tomography (CT) and generally require immediate treatment to ensure adequate ventilation. Rare nasal anomalies that also result in airway obstruction are agenesis of the pharynx, agenesis of the nose, and hypoplasia of the nasal alae. Agenesis of the nasopharynx and nose are complex anomalies that require both CT and magnetic resonance imaging (MRI). The diagnosis of hypoplasia of the nasal alae is a clinical one; these anomalies do not require imaging studies. Besides facial clefts, anomalies of the nose without respiratory obstruction tend to be centered around the nasofrontal region. This is the site of the most common sincipital encephaloceles. Patients with frontonasal and nasoethmoidal encephaloceles require both

  17. Reliability of CHAMP Anomaly Continuations

    NASA Technical Reports Server (NTRS)

    vonFrese, Ralph R. B.; Kim, Hyung Rae; Taylor, Patrick T.; Asgharzadeh, Mohammad F.

    2003-01-01

    CHAMP is recording state-of-the-art magnetic and gravity field observations at altitudes ranging over roughly 300 - 550 km. However, anomaly continuation is severely limited by the non-uniqueness of the process and satellite anomaly errors. Indeed, our numerical anomaly simulations from satellite to airborne altitudes show that effective downward continuations of the CHAMP data are restricted to within approximately 50 km of the observation altitudes while upward continuations can be effective over a somewhat larger altitude range. The great unreliability of downward continuation requires that the satellite geopotential observations must be analyzed at satellite altitudes if the anomaly details are to be exploited most fully. Given current anomaly error levels, joint inversion of satellite and near- surface anomalies is the best approach for implementing satellite geopotential observations for subsurface studies. We demonstrate the power of this approach using a crustal model constrained by joint inversions of near-surface and satellite magnetic and gravity observations for Maude Rise, Antarctica, in the southwestern Indian Ocean. Our modeling suggests that the dominant satellite altitude magnetic anomalies are produced by crustal thickness variations and remanent magnetization of the normal polarity Cretaceous Quiet Zone.

  18. Origin of anomalies and phase competitions around magnetic transition temperature in Pr0.7Ca0.3MnO3

    NASA Astrophysics Data System (ADS)

    Shah, Matiullah; Nadeem, M.; Atif, M.

    2013-03-01

    A polycrystalline sample of Pr0.7Ca0.3MnO3 is synthesized by the conventional solid-state reaction method and the phase formation is confirmed by x-ray diffraction. In this work, we addressed the phase competition issues in the vicinity of magnetic transition temperature and also established its correlation with oxygen contents of domains, disorder effects and heterogeneity in the material. The appearance and disappearance of anomaly in the vicinity of TC (128 K) with magnetic field is discussed in terms of establishment of short- and long-range networks between Mn3+ and Mn4+. Switching behaviour of two competing phases is analysed qualitatively and quantitatively, using an equivalent circuit model and magnetization analysis. The issue of coexisting phases is further substantiated using a simple depression angle approach of impedance plane plots. variable range hopping is found to be a better model than polaronic for explaining the transport properties of both competing phases below the magnetic transition temperature, 128 K.

  19. Antipodal Magnetic Anomalies on the Moon, Contributions from Impact Induced Currents Due to Positive Holes and Flexoelectric Phenomina and Dynamo

    NASA Technical Reports Server (NTRS)

    Kletetschka, G.; Freund, F.; Wasilewski, P. J.; Mikula, V.; Kohout, Tomas

    2005-01-01

    Large impacts on the Moon generate large pressure pulses that penetrate the whole body. Several of these large impacts may have generated antipodal structure with anomalous magnetic intensity.These regions can be more than a thousand km across, with fields of the order of tens to hundreds of nT. This is the case of Orientale, Imbrium, Serenitatis, Crisium, and Nectaris impact basins. The production of large-scale magnetic fields and associated crustal magnetization due to lunar basin-forming impacts was hypothesized to have an origin in fields external to the impact plasma cloud that are produced by the magnetohydrodynamic interaction of the cloud with ambient magnetic fields and plasmas. During the period of compressed antipodal field amplification, seismic compressional waves from the impact converge at the antipode resulting in transient shock pressures that reach 2 GPa (20 kbar). This can produce conditions for shock magnetic acquisition of the crust antipodal to impact basins.

  20. Multiprobe in-situ measurement of magnetic field in a minefield via a distributed network of miniaturized low-power integrated sensor systems for detection of magnetic field anomalies

    NASA Astrophysics Data System (ADS)

    Javadi, Hamid H. S.; Bendrihem, David; Blaes, B.; Boykins, Kobe; Cardone, John; Cruzan, C.; Gibbs, J.; Goodman, W.; Lieneweg, U.; Michalik, H.; Narvaez, P.; Perrone, D.; Rademacher, Joel D.; Snare, R.; Spencer, Howard; Sue, Miles; Weese, J.

    1998-09-01

    Based on technologies developed for the Jet Propulsion Laboratory (JPL) Free-Flying-Magnetometer (FFM) concept, we propose to modify the present design of FFMs for detection of mines and arsenals with large magnetic signature. The result will be an integrated miniature sensor system capable of identifying local magnetic field anomaly caused by a magnetic dipole moment. Proposed integrated sensor system is in line with the JPL technology road-map for development of autonomous, intelligent, networked, integrated systems with a broad range of applications. In addition, advanced sensitive magnetic sensors (e.g., silicon micromachined magnetometer, laser pumped helium magnetometer) are being developed for future NASA space plasma probes. It is envisioned that a fleet of these Integrated Sensor Systems (ISS) units will be dispersed on a mine-field via an aerial vehicle (a low-flying airplane or helicopter). The number of such sensor systems in each fleet and the corresponding in-situ probe-grid cell size is based on the strength of magnetic anomaly of the target and ISS measurement resolution of magnetic field vector. After a specified time, ISS units will transmit the measured magnetic field and attitude data to an air-borne platform for further data processing. The cycle of data acquisition and transmission will be continued until batteries run out. Data analysis will allow a local deformation of the Earth's magnetic field vector by a magnetic dipole moment to be detected. Each ISS unit consists of miniaturized sensitive 3- axis magnetometer, high resolution analog-to-digital converter (ADC), Field Programmable Gate Array (FPGA)-based data subsystem, Li-batteries and power regulation circuitry, memory, S-band transmitter, single-patch antenna, and a sun angle sensor. ISS unit is packaged with non-magnetic components and the electronic design implements low-magnetic signature circuits. Care is undertaken to guarantee no corruption of magnetometer sensitivity as a result

  1. Enhancement of co-seismic piezomagnetic signals near the edges of magnetization anomalies in the Earth's crust

    NASA Astrophysics Data System (ADS)

    Yamazaki, K.

    2011-02-01

    A scheme is proposed for calculating the piezomagnetic fields that accompany the propagation of seismic waves through a non-uniformly magnetized crust. Examples of the calculations are provided. Generally, the calculation of the co-seismic piezomagnetic fields involves laborious three-dimensional volume integrals, even if the magnetization structure is two-dimensional. However, the calculation can be simplified by taking the Fourier transform of spatial distributions of the field into consideration. As an example, we have performed calculations for both the non-uniformly and uniformly magnetized crust with an intensity of 10 A/m. The incident seismic wave is considered to consist of Rayleigh waves with an amplitude of 5 cm. The amplitudes of the piezomagnetic signals arising from uniformly magnetized crust are up to 0.2 nT, whereas those arising from non-uniformly magnetized crust are as large as 0.5 nT. This result indicates that the piezomagnetic field may be a plausible mechanism of generating co-seismic changes in the magnetic field with detectable amplitudes for large earthquakes, provided that the observation site is located near the magnetization boundaries.

  2. General mechanism and dynamics of the solar wind interaction with lunar magnetic anomalies from 3-D particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Deca, Jan; Divin, Andrey; Lembège, Bertrand; Horányi, Mihály; Markidis, Stefano; Lapenta, Giovanni

    2015-08-01

    We present a general model of the solar wind interaction with a dipolar lunar crustal magnetic anomaly (LMA) using three-dimensional full-kinetic and electromagnetic simulations. We confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface, forming a so-called "minimagnetosphere," as suggested by spacecraft observations and theory. We show that the LMA configuration is driven by electron motion because its scale size is small with respect to the gyroradius of the solar wind ions. We identify a population of back-streaming ions, the deflection of magnetized electrons via the E × B drift motion, and the subsequent formation of a halo region of elevated density around the dipole source. Finally, it is shown that the presence and efficiency of the processes are heavily impacted by the upstream plasma conditions and, on their turn, influence the overall structure and evolution of the LMA system. Understanding the detailed physics of the solar wind interaction with LMAs, including magnetic shielding, particle dynamics and surface charging is vital to evaluate its implications for lunar exploration.

  3. DOWN'S ANOMALY.

    ERIC Educational Resources Information Center

    PENROSE, L.S.; SMITH, G.F.

    BOTH CLINICAL AND PATHOLOGICAL ASPECTS AND MATHEMATICAL ELABORATIONS OF DOWN'S ANOMALY, KNOWN ALSO AS MONGOLISM, ARE PRESENTED IN THIS REFERENCE MANUAL FOR PROFESSIONAL PERSONNEL. INFORMATION PROVIDED CONCERNS (1) HISTORICAL STUDIES, (2) PHYSICAL SIGNS, (3) BONES AND MUSCLES, (4) MENTAL DEVELOPMENT, (5) DERMATOGLYPHS, (6) HEMATOLOGY, (7)…

  4. Uhl's anomaly.

    PubMed Central

    Vecht, R J; Carmichael, D J; Gopal, R; Philip, G

    1979-01-01

    Uhl's anomaly of the heart is a rare condition. Another well-documented case is presented with a review of the published reports outlining the main clinical features and the bad overall prognosis. Right atriotomy should be avoided if closure of the atrial septal defect is attempted. Images PMID:465242

  5. Spreading History of a Segment of the Southern Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Stock, J. M.; Clayton, R. W.

    2001-12-01

    The Falkland-Agulhas fracture zone in the South Atlantic Ocean separates crust that records the entire Cenozoic history of South America-Africa spreading (on the north) from crust on the south that experienced a more complicated plate motion history including major ridge jumps, an additional plate (Malvinas), and plate reorganizations in early Cenozoic time. The Nathaniel B. Palmer cruise 01-02 in April 2001 measured gravity, magnetics, and swath bathymetry on a transit from Cape Town to Punta Arenas, including a survey line in Cenozoic crust on the north side of, and parallel to, the Falkland-Agulhas fracture zone. The objectives were to test previous models of Cenozoic plate motions for this region, and to examine the structure of the Falkland-Agulhas fracture zone by collection of limited single-channel seismic data. From 5° W to 3° W longitude, several seismic lines with accompanying SeaBeam data across the northern flank of the fracture zone reveal it to be a wide zone characterized by multiple parallel southward-facing fault scarps whose strike is 70-80° E of N. From chron 12 time to chron 6 time, the spreading history for this segment of the ridge was relatively simple, with slightly asymmetric spreading rates (more crust accreted to South America than to Africa), as has been previously noted for this part of the southern Mid-Atlantic Ridge. Between chron 5c and chron 2a, the magnetic anomalies are complex and disrupted, suggesting possible small-scale ridge jumps and continued asymmetric spreading. The modern ridge axis is 40 km east of the topographic high ("ridge crest"). The zones of disrupted magnetic anomalies may be due to the effects of pseudofault traces in the same spreading corridor, visible in satellite gravity data in younger seafloor north of the transit. We recorded late Cretaceous and younger magnetic anomalies (chrons 34y to 18) on the Africa plate to improve the distribution of known magnetic anomaly locations in this part of the South

  6. Seafloor spreading and microcontinent formation during Mesozoic breakup between Australia and Greater India

    NASA Astrophysics Data System (ADS)

    Williams, S.; Whittaker, J.; Müller, R.

    2012-12-01

    The Perth Abyssal Plain (PAP) formed at the nexus of rifting and breakup between three major continents within Gondwana - India, Australia and Antarctica. Oceanic crust within the PAP records the history of Mesozoic seafloor spreading as India moved away from Australia. However, despite the clear importance of the seafloor spreading history of the PAP in constraining the relative motions of these continents during the early stages of breakup, little attention has been paid to the PAP, and particularly its western flank largely due to a lack of new data in collected in this region. We present new observations to constrain the evolution of the PAP, collected during voyage ss2011/v06 of the Southern Surveyor in late 2011. The new data comprise magnetic anomaly profile data, swath bathymetry, and dredge samples collected from 7 sites. The most significant dredge results were obtained from the Batavia Knoll (BK) and Gulden Draak Knoll (GDK), two prominent bathymetric features located >1000 km west of the Australian continental margin. Previous tectonic reconstructions typically treat these bathymetric features as igneous plateaus emplaced on older oceanic crust. However, dredges carried out on the western flanks of each of these knolls recovered continental basement rocks, revealing that both knolls are continental fragments. Estimates of the depths to magnetic sources for shiptrack profiles across the knolls provide evidence for variations in sediment thickness within the knolls. We use forward modeling of shiptrack magnetic profiles combined with gravity anomalies derived from satellite altimetry to make first-order estimates of the extent and spatial variation in thickness of the continental crust. New magnetic anomaly profiles provide evidence for previously unidentified M-series anomalies in the western part of the Perth Abyssal Plain, east of the BK and GDK. These observations both support a reconstruction model in which the microcontinents rifted away from

  7. The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies

    SciTech Connect

    Blakely, Richard J.; Sherrod, Brian; Weaver, Craig; Wells, Ray E.; Rohay, Alan C.

    2013-11-13

    Magnetic and gravity data, collected in south-central Washington near the Yakima Fold and Thrust Belt (YFTB) are used to model upper crustal structure, the extent of the late Columbia River Basalt flow named the Ice Harbor member, the vertical conduits (dikes) that the Ice Harbor erupted from, and whether the dikes are offset or affected by faulting on the Wallula Fault zone.

  8. The SHEBA Ridge : a Particular Spreading Center or an End-member of the Slow Spreading Processes ?

    NASA Astrophysics Data System (ADS)

    GENTE, P.; LEROY, S.; BLAIS, A.; d'ACREMONT, E.; PATRIAT, P.; FLEURY, J.; MAIA, M.; PERROT, J.; FOURNIER, M.

    2001-12-01

    We analyze multibeam bathymetry, acoustic imagery, magnetic and gravity data collected during the Encens-Sheba cruise of the NO Marion Dufresne. The survey covered the axis and the flanks up to the continental margins of the Sheba Ridge between 52oE and 54o30'E, at the oriental extremity of the Aden gulf. The full spreading rate in this young oceanic basin is about 2 cmy since the continental rifting. Three second-order segments, one presenting an anomalously shallow axis, characterize this part of the Sheba ridge. The new bathymetry data reveal a particular fabric on the flanks and at the axis for the long (120 km) and shallow spreading center. The flanks, like the ridge axis, are marked by large, more or less circular, volcanic domes. They are built by a few large volcanoes (5-10 km diameter) and by several smaller (1-2 km diameter) edifices. Many of these volcanoes present a well-developed caldera. These volcanic constructions are well developed in the southern part of the axis. Close to the axis, the higher reliefs culminate at a depth of 1000 m. Tectonic scarps limit a deep axial valley at the extremities of this long segment. The deformation, diffuse at the ends, becomes more focused toward the center of this segment and is arranged in an hourglass pattern. A negative mantle Bouguer anomaly elongated in the spreading direction marks this segment. The differences in MBA (~70 mgals) and in depth (more than 2 km) between the center and the ends of this segment are the largest, highest of the slow spreading ridges. Acoustic imagery, axial magnetic and mantle Bouguer anomalies generally permit to precise the location of the spreading axis. In this segment, if the axial area is clearly defined, the neovolcanic zone is more difficult to localize. This suggests a diffuse volcanism at the center of the segment at the origin of the numerous small volcanoes. The other segments of the Sheba ridge present a more typical slow spreading axial valley. The discontinuities

  9. foF2 long-term trend linked to Earth's magnetic field secular variation at a station under the northern crest of the equatorial ionization anomaly

    NASA Astrophysics Data System (ADS)

    Pham Thi Thu, Hong; Amory-Mazaudier, Christine; Le Huy, Minh; Elias, Ana G.

    2016-01-01

    Long-term trend of the critical frequency of the F2 ionospheric region, foF2, at Phu Thuy station (21.03°N, 105.96°E), Vietnam, located under the northern crest of the equatorial ionization anomaly, EIA, is studied. Annual mean data are analyzed at 04 LT and 12 LT for the period 1962-2002 using monthly median values and monthly mean values during magnetically quiet days (am < 20). In both cases we obtain similar trends at 4 LT and 12 LT, which we interpret as an absence of geomagnetic activity effect over trends. The positive trends obtained are not consistent with the negative values expected from greenhouse gases effect at this layer of the upper atmosphere. The increasing trend observed at 12 LT is qualitatively in agreement with the expected effect of the secular displacement of the dip equator over the EIA latitudinal profile. At 04 LT, when the EIA is absent, the positive trend is in qualitative agreement with the secular variation of the Earth's magnetic field inclination, I, and the consequent increase of the sin(I)cos(I) factor at the corresponding location.

  10. Aeromagnetic anomalies over faulted strata

    USGS Publications Warehouse

    Grauch, V.J.S.; Hudson, Mark R.

    2011-01-01

    High-resolution aeromagnetic surveys are now an industry standard and they commonly detect anomalies that are attributed to faults within sedimentary basins. However, detailed studies identifying geologic sources of magnetic anomalies in sedimentary environments are rare in the literature. Opportunities to study these sources have come from well-exposed sedimentary basins of the Rio Grande rift in New Mexico and Colorado. High-resolution aeromagnetic data from these areas reveal numerous, curvilinear, low-amplitude (2–15 nT at 100-m terrain clearance) anomalies that consistently correspond to intrasedimentary normal faults (Figure 1). Detailed geophysical and rock-property studies provide evidence for the magnetic sources at several exposures of these faults in the central Rio Grande rift (summarized in Grauch and Hudson, 2007, and Hudson et al., 2008). A key result is that the aeromagnetic anomalies arise from the juxtaposition of magnetically differing strata at the faults as opposed to chemical processes acting at the fault zone. The studies also provide (1) guidelines for understanding and estimating the geophysical parameters controlling aeromagnetic anomalies at faulted strata (Grauch and Hudson), and (2) observations on key geologic factors that are favorable for developing similar sedimentary sources of aeromagnetic anomalies elsewhere (Hudson et al.).

  11. Interpretation of CHAMP Magnetic Anomaly Data over the Pannonian Basin Region Using Lower Altitude Horizontal Gradient Data

    NASA Technical Reports Server (NTRS)

    Taylor, P. T.; Kis, K. I.; Wittmann, G.

    2013-01-01

    The ESA SWARM mission will have three earth orbiting magnetometer bearing satellites one in a high orbit and two side-by-side in lower orbits. These latter satellites will record a horizontal magnetic gradient. In order to determine how we can use these gradient measurements for interpretation of large geologic units we used ten years of CHAMP data to compute a horizontal gradient map over a section of southeastern Europe with our goal to interpret these data over the Pannonian Basin of Hungary.

  12. Preliminary aeromagnetic anomaly map of California

    USGS Publications Warehouse

    Roberts, Carter W.; Jachens, Rober C.

    1999-01-01

    The magnetization in crustal rocks is the vector sum of induced in minerals by the Earth’s present main field and the remanent magnetization of minerals susceptible to magnetization (chiefly magnetite) (Blakely, 1995). The direction of remanent magnetization acquired during the rock’s history can be highly variable. Crystalline rocks generally contain sufficient magnetic minerals to cause variations in the Earth’s magnetic field that can be mapped by aeromagnetic surveys. Sedimentary rocks are generally weakly magnetized and consequently have a small effect on the magnetic field: thus a magnetic anomaly map can be used to “see through” the sedimentary rock cover and can convey information on lithologic contrasts and structural trends related to the underlying crystalline basement (see Nettleton,1971; Blakely, 1995). The magnetic anomaly map (fig. 2) provides a synoptic view of major anomalies and contributes to our understanding of the tectonic development of California. Reference fields, that approximate the Earth’s main (core) field, have been subtracted from the recorded magnetic data. The resulting map of the total magnetic anomalies exhibits anomaly patterns related to the distribution of magnetized crustal rocks at depths shallower than the Curie point isotherm (the surface within the Earth beneath which temperatures are so high that rocks lose their magnetic properties). The magnetic anomaly map has been compiled from existing digital data. Data obtained from aeromagnetic surveys that were made at different times, spacings and elevations, were merged by analytical continuation of each set onto a common surface 305 m (1000 ft) above terrain. Digital data in this compatible form allows application of analytical techniques (Blakley, 1995) that can be used to enhance anomaly characteristics (e.g., wavelength and trends) and provide new interpretive information.

  13. Phanerozoic stratigraphy of Northwind Ridge, magnetic anomalies in the Canada Basin, and the geometry and timing of rifting in the Amerasia Basin, Arctic Ocean

    USGS Publications Warehouse

    Grantz, A.; Clark, D.L.; Phillips, R.L.; Srivastava, S.P.; Blome, C.D.; Gray, L.-B.; Haga, H.; Mamet, B.L.; McIntyre, D.J.; McNeil, D.H.; Mickey, M.B.; Mullen, M.W.; Murchey, B.I.; Ross, C.A.; Stevens, C.H.; Silberling, Norman J.; Wall, J.H.; Willard, D.A.

    1998-01-01

    Cores from Northwind Ridge, a high-standing continental fragment in the Chukchi borderland of the oceanic Amerasia basin, Arctic Ocean, contain representatives of every Phanerozoic system except the Silurian and Devonian systems. Cambrian and Ordovician shallow-water marine carbonates in Northwind Ridge are similar to basement rocks beneath the Sverdrup basin of the Canadian Arctic Archipelago. Upper Mississippian(?) to Permian shelf carbonate and spicularite and Triassic turbidite and shelf lutite resemble coeval strata in the Sverdrup basin and the western Arctic Alaska basin (Hanna trough). These resemblances indicate that Triassic and older strata in southern Northwind Ridge were attached to both Arctic Canada and Arctic Alaska prior to the rifting that created the Amerasia basin. Late Jurassic marine lutite in Northwind Ridge was structurally isolated from coeval strata in the Sverdrup and Arctic Alaska basins by rift shoulder and grabens, and is interpreted to be a riftogenic deposit. This lutite may be the oldest deposit in the Canada basin. A cape of late Cenomanian or Turonian rhyodacite air-fall ash that lacks terrigenous material shows that Northwind Ridge was structurally isolated from the adjacent continental margins by earliest Late Cretaceous time. Closing Amerasia basin by conjoining seafloor magnetic anomalies beneath the Canada basin or by uniting the pre-Jurassic strata of Northwind Ridge with kindred sections in the Sverdrup basin and Hanna trough yield simular tectonic reconstructions. Together with the orientation and age of rift-marine structures, these data suggest that: 1) prior to opening of the Amerasia basin, both northern Alaska and continental ridges of the Chukchi borderland were part of North America, 2) the extension that created the Amerasia basin formed rift-margin graben beginning in Early Jurassic time and new oceanic crust probably beginning in Late Jurassic or early Neocomian time. Reconstruction of the Amerasia basin on the

  14. [The comparative role of computed tomography and magnetic resonance imaging in the diagnosis of extracapsular spread of malignant lymphomatous masses invading blood vessels].

    PubMed

    Dobrovolskiene, Laima; Griniûtë, Rasa

    2003-01-01

    Aim of the study was to search for an optimal method an of investigation in diagnosis of extracapsular spread of the malignant lymphomas and invading the blood vessels. In the period of 1998 to 2002, 81 patients with malignant lymphomas with coverage of neck and body areas were examined in the Department of Tomography of Kaunas University of Medicine Hospital. It was performed by computed tomography (CT) and magnetic resonance imaging (MRI), with or without iv. application of contrast media. The data were processed with SPSS 10.1 (Statistical package for Social Sciences 10.1 for Windows), including application of chi(2), t-test. Specificity, sensitivity and diagnostic accuracy of CT and MRI methods were calculated and compared according to recommendations by Gefland D. W. and Ott D. J., 1985. Diagnosis of extracapsular spread of the lymphomatous tissue and invading the blood vessels was best performed by MR method (specificity, sensitivity, accuracy in this case 91-95%). Bolus CT angiography because of low resolution in the range of soft tissues, insufficient opacification of blood vessels with contrast medium and differences in blood flow was not informative enough (specificity, sensitivity, accuracy in this case 80-85%).

  15. Aeromagnetic anomalies and discordant lineations beneath the Niger Delta - Implications for new fracture zones and multiple sea-floor spreading directions in the 'meso-Atlantic' Gulf of Guinea cul-de-sac

    NASA Astrophysics Data System (ADS)

    Babalola, Olufemi O.; Gipson, Mack, Jr.

    1991-06-01

    An aeromagnetic map eliminating data gaps in the Nigerian continental margin is presented, and the implications of the mapped fracture zone structure and the interpretation of two triple junctions beneath the Niger Delta Basin for its early tectonic history are discussed. Sea-floor spreading was found to occur in two different directions, and not only the well-documented NE-SW spreading in the 'meso-Atlantic' ocean. The existence of two triple junctions located where the Niger Delta Basin abuts the southern ends of the Abakaliki and Anambra troughs is shown. The two newly interpreted triple junctions beneath the Niger Delta demonstrate the previously recognized structural complexity of the region, necessitating a review of models for its early tectonic history.

  16. Equatorial Spread F Statistics in the American Longitudes: Some Problems Relevant to ESF Description in the IRI Scheme

    NASA Astrophysics Data System (ADS)

    Abdu, M. A.; Sobral, J. H. A.; Batista, I. S.

    Ground based ionograms (followed by radio wave scintillation and satellite in situ measurements) provide the most abundant data base for generating equatorial spread F (ESF) irregularity occurrence statistics. For practical purposes it is necessary that the statistics of the spread F occurrence distribution (from ionograms) be based, separately, on the range spreading and frequency spreading components of the spread F. The well known features of spread F include its day-to-day, seasonal and solar cycle variations. There seems to exist general consensus on the geomagnetic declination-, longitude- and solar- control of seasonal occurrence of spread F, whereas solar flux seems to produce superimposed effects, including the solar activity cycle in its occurrence features. The day-to-day variability is certainly the least understood of all the known spread F variabilities. Empirical description of the spread F occurrence statistics in the IRI (International Reference Ionosphere) prediction scheme requires detailed examination of the available statistics not only over the magnetic equator but necessarily also over low latitudes extending to equatorial anomaly location. We have produced, and are continuing to improve upon, such statistics based on spread F data covering the solar activity minimum and maximum years for the two Brazilian stations, Fortaleza and Cachoeira Paulista. In this paper we present a comparative study of these results with the published statistics available by other technique and for other longitude sectors, and discuss the findings in terms of their implications for formulating an empirical description of the ESF for possible incorporation into the IRI model

  17. Unique Aeromagnetic-radar Ice-sounding Survey over the West Antarctic Ice Sheet Allows Three Dimensional Definition of Sources of Magnetic Anomalies Caused by Subglacial Volcanic Sources at the Bed of the Ice

    NASA Astrophysics Data System (ADS)

    Behrendt, J. C.; Casertz; Soar Teams

    2011-12-01

    The West Antarctic Ice Sheet (WAIS) flows through the volcanically active West Antarctic Rift System (WARS). The aeromagnetic method has proven the most useful geophysical tool for studying subglacial volcanic rocks beneath the WAIS since early surveys in the 1950s. The Central West Antarctica (CWA) aerogeophysical survey covering ~354,000 km2 (about the area of Nevada and California combined) over the WAIS, consisting of a 5-km line-spaced, orthogonal set of aeromagnetic, radar ice-sounding and aerogravity measurements, is a unique Antarctic data set. This 1990-97 survey (CASERTZ and SOAR), still provides invaluable information on subglacial volcanic rocks, particularly when combined with widely spaced older aeromagnetic flight lines over a much greater area. These combined survey data indicate numerous high-amplitude (100->1000 nT), 5-50 km width, shallow-source, magnetic anomalies over a very extensive area (>1.2 x 106 km2) mostly resulting from subglacial volcanic eruptions. I interpreted the anomalies sampled in the CWA survey as defining ~1000 "volcanic centers" requiring high remanent normal magnetizations in the present field direction. About 400 of these anomaly sources (conservatively selected) are correlated with bed topography. The tops of >80% of these anomaly sources have <200 m relief at the bed of the WAIS. They appear modified by moving ice, requiring a younger age than the WAIS (~25 Ma). The 5 km by 5 km orthogonal flight line survey obviated aliasing of the magnetic and radar ice sounding data, because it is approximately equivalent to the flight elevation above the ice (1 km) surface plus the ice thickness (2-3 km); it reveals the magnetic anomalies and the tops of volcanic sources at its bed in three dimensions. Models (2 1/2 D) fit to a number of the magnetic anomalies, whose sources are at the bed of the ice sheet are constrained by topography measured by the radar ice sounding. Volcanoes in the WARS are <34 Ma, but at least four are active

  18. Concurrent observations at the magnetic equator of small-scale irregularities and large-scale depletions associated with equatorial spread F

    NASA Astrophysics Data System (ADS)

    Hickey, Dustin A.; Martinis, Carlos R.; Rodrigues, Fabiano S.; Varney, Roger H.; Milla, Marco A.; Nicolls, Michael J.; Strømme, Anja; Arratia, Juan F.

    2015-12-01

    In 2014 an all-sky imager (ASI) and an Advanced Modular Incoherent Scatter Radar consisting of 14 panels (AMISR-14) system were installed at the Jicamarca Radio Observatory. The ASI measures airglow depletions associated with large-scale equatorial spread F irregularities (10-500 km), while AMISR-14 detects small-scale irregularities (0.34 m). This study presents simultaneous observations of equatorial spread F (ESF) irregularities at 50-200 km scale sizes using the all-sky imager, at 3 m scale sizes using the JULIA (Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere) radar, and at 0.34 m scales using the AMISR-14 radar. We compare data from the three instruments on the night of 20-21 August 2014 by locating the radar scattering volume in the optical images. During this night no topside plumes were observed, and we only compare with bottomside ESF. AMISR-14 had five beams perpendicular to the magnetic field covering ~200 km in the east-west direction at 250 km altitude. Comparing the radar data with zenith ASI measurements, we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center, contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions. We attribute these differences to the occurrence of irregularities produced at submeter scales by the lower hybrid drift instability. Comparisons of the ASI observations with JULIA images show similar results to those found in the AMISR-14 and ASI comparison.

  19. Gauge anomalies, gravitational anomalies, and superstrings

    SciTech Connect

    Bardeen, W.A.

    1985-08-01

    The structure of gauge and gravitational anomalies will be reviewed. The impact of these anomalies on the construction, consistency, and application of the new superstring theories will be discussed. 25 refs.

  20. Method of Mapping Anomalies in Homogenous Material

    NASA Technical Reports Server (NTRS)

    Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor)

    2016-01-01

    An electrical conductor and antenna are positioned in a fixed relationship to one another. Relative lateral movement is generated between the electrical conductor and a homogenous material while maintaining the electrical conductor at a fixed distance from the homogenous material. The antenna supplies a time-varying magnetic field that causes the electrical conductor to resonate and generate harmonic electric and magnetic field responses. Disruptions in at least one of the electric and magnetic field responses during this lateral movement are indicative of a lateral location of a subsurface anomaly. Next, relative out-of-plane movement is generated between the electrical conductor and the homogenous material in the vicinity of the anomaly's lateral location. Disruptions in at least one of the electric and magnetic field responses during this out-of-plane movement are indicative of a depth location of the subsurface anomaly. A recording of the disruptions provides a mapping of the anomaly.

  1. ANOMALY STRUCTURE OF SUPERGRAVITY AND ANOMALY CANCELLATION

    SciTech Connect

    Butter, Daniel; Gaillard, Mary K.

    2009-06-10

    We display the full anomaly structure of supergravity, including new D-term contributions to the conformal anomaly. This expression has the super-Weyl and chiral U(1){sub K} transformation properties that are required for implementation of the Green-Schwarz mechanism for anomaly cancellation. We outline the procedure for full anomaly cancellation. Our results have implications for effective supergravity theories from the weakly coupled heterotic string theory.

  2. The elliptic anomaly

    NASA Technical Reports Server (NTRS)

    Janin, G.; Bond, V. R.

    1980-01-01

    An independent variable different from the time for elliptic orbit integration is used. Such a time transformation provides an analytical step-size regulation along the orbit. An intermediate anomaly (an anomaly intermediate between the eccentric and the true anomaly) is suggested for optimum performances. A particular case of an intermediate anomaly (the elliptic anomaly) is defined, and its relation with the other anomalies is developed.

  3. Equivalent magnetization over the World's Ocean

    NASA Astrophysics Data System (ADS)

    Dyment, J.; Choi, Y.; Hamoudi, M.; Erwan, T.; Lesur, V.

    2014-12-01

    As a by-product of our recent work to build a candidate model over the oceans for the World Digital Magnetic Anomaly Map (WDMAM) version 2, we derived global distributions of the equivalent magnetization in oceanic domains. In a first step, we use classic point source forward modeling on a spherical Earth to build a forward model of the marine magnetic anomalies at sea-surface. We estimate magnetization vectors using the age map of the ocean floor, the relative plate motions, the apparent polar wander path for Africa, and a geomagnetic reversal time scale. As magnetized source geometry, we assume 1 km-thick layer bearing a 10 A/m magnetization following the topography of the oceanic basement as defined by the bathymetry and sedimentary thickness. Adding a present-day geomagnetic field model allows the computation of our initial magnetic anomaly model. In a second step, we adjust this model to the existing marine magnetic anomaly data, in order to make it consistent with these data. To do so, we extract synthetic magnetic along the ship tracks for which real data are available and we compare quantitatively the measured and computed anomalies on 100, 200 or 400 km-long sliding windows (depending the spreading rate). Among the possible comparison criteria, we discard the maximal range - too dependent on local values - and the correlation and coherency - the geographical adjustment between model and data being not accurate enough - to favor the standard deviation around the mean value. The ratio between the standard deviations of data and model on each sliding window represent an estimate of the magnetization ratio causing the anomalies, which we interpolate to adjust the initial magnetic anomaly model to the data and therefore compute a final model to be included in our WDMAM candidate over the oceanic regions lacking data. The above ratio, after division by the magnetization of 10 A/m used in the model, represents an estimate of the equivalent magnetization under the

  4. Hotspot activity and plume pulses recorded by geometry of spreading axes

    NASA Astrophysics Data System (ADS)

    Abelson, Meir; Agnon, Amotz

    2001-06-01

    Anomalous plan view geometry (planform) of spreading axes is shown to be a faithful indicator of hotspot influence, possibly capable of detecting pulses of hotspot discharge. A planform anomaly (PA) occurs when the orientation of second-order ridge segments is prominently oblique to the spreading direction. PA is found in the vicinity of hotspots at shallow ridges (<1.5 km), suggesting hotspot influence. In places the PA and shallow bathymetry are accompanied by geochemical anomalies, corroborating hotspot influence. This linkage is best expressed in the western Gulf of Aden, where the extent of the PA from the Afar hotspot coincides with the extent of La/Sm and Sr isotopic anomalies. Using fracture mechanics we predict PA to reflect overpressurized melt that dominates the stresses in the crust, consistent with hotspot regime. Accordingly, the temporal variations of the planform previously inferred from magnetic anomalies around the Kolbeinsey Ridge (KR), north of Iceland, record episodes of interaction with the hotspot and major pulses of the plume. This suggestion is corroborated by temporal correlation of episodes showing PA north of Iceland with plume pulses previously inferred by the V-shaped ridges around the Reykjanes Ridge (RR), south of Iceland. In contrast to the RR, the temporal correlation suggests simultaneous incidence of the plume pulses at Iceland and KR, hundreds of kilometers to the north. A deep northward branch of the Iceland plume active during pulse-periods may explain these observations.

  5. Electromagnetic Particle-in-Cell Simulations of the Solar Wind Interaction with Lunar Magnetic Anomalies: Interaction Mechanisms Under Varying Solar Wind Conditions.

    NASA Astrophysics Data System (ADS)

    Deca, Jan; Divin, Andrey; Lapenta, Giovanni; Lembège, Bertrand; Markidis, Stefano; Horányi, Mihály

    2015-04-01

    We present three-dimensional fully kinetic and electromagnetic simulations of the solar wind interaction with lunar crustal magnetic anomalies (LMAs). Using the implicit particle-in-cell code iPic3D, we confirm that LMAs may indeed be strong enough to stand off the solar wind from directly impacting the lunar surface forming a mini-magnetosphere, as suggested by spacecraft observations and theory. In contrast to earlier MHD and hybrid simulations, the fully kinetic nature of iPic3D allows to investigate the space charge effects and in particular the electron dynamics dominating the near-surface lunar plasma environment. We describe the general picture of the interaction of a dipole model centered just below the lunar surface under various solar wind and plasma conditions, and focus afterwards on the ion and electron kinetic behavior of the system. It is shown that the configuration is dominated by electron motion, because the LMA scale size is small with respect to the gyroradius of the solar wind ions. We identify a population of backstreaming ions, the deflection of magnetized electrons via the ExB-drift motion and the subsequent formation of a halo region of elevated density around the dipole source. Finally, it is shown that the presence and efficiency of the latter mechanisms are heavily impacted by the upstream plasma conditions and, on their turn, influence the overall structure and evolution of the LMA system. Our work opens new frontiers of research toward a deeper understanding of LMAs and is ideally suited to be compared with field or particle observations from spacecraft such as Kaguya (SELENE), Lunar Prospector or ARTEMIS. The ability to evaluate the implications for future lunar exploration as well as lunar science in general hinges on a better understanding of LMAs. This research has received funding from the European Commission's FP7 Program with the grant agreement SWIFF (project 2633430, swiff.eu) and EHEROES (project 284461, www.eheroes.eu). The

  6. The seasonal and solar cycle variations of electron density gradient scale length, vertical drift and layer height during magnetically quiet days: Implications for Spread F over Trivandrum, India

    NASA Astrophysics Data System (ADS)

    Manju, G.; Devasia, C. V.; Ravindran, S.

    2009-12-01

    A study has been carried out on the behaviour of electron density gradient scale length, L, vertical drift and layer height, around post sunset hours, during the magnetically quiet days of summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995), using ionosonde data of Trivandrum (8.5°N, 76.5°E, dip = 0.5°N) in the Indian longitude sector. The results indicate a clear seasonal and solar cycle variation in all the three parameters. Further, the seasonal variation of equatorial Spread F (ESF) during the above period is examined in terms of the relative roles of L, the vertical drift and layer height (of the F layer) in the triggering of the collisional Rayleigh-Taylor instability. The results, show for the first time, that L also plays an important role, in controlling the quiet time seasonal and solar cycle variability of ESF; whereas in earlier studies this parameter had been taken to be constant. The detailed results are presented and discussed.

  7. Spreading behaviour of the Pacific-Farallon ridge system between 83 and 28 Ma

    NASA Astrophysics Data System (ADS)

    Rowan, C. J.; Rowley, D. B.

    2012-12-01

    At 83 Ma, the roughly N-S oriented Pacific-Farallon ridge extended more than 10,000 km from 51° N to 43° S. Despite substantial shortening of the ridge system since ~55 Ma, this ridge and its remnants (e.g., the East Pacific Rise/EPR) have produced as much as 45% of all the reconstructable oceanic lithosphere created in the Late Cretaceous and Cenozoic. Accurately reconstructing the past spreading history of the Pacific-Farallon ridge is therefore of paramount importance for determining possible variations in global spreading rates over geological time, which are the basis of suggested interactions between mantle dynamics, surface tectonics, sea-level rise and climate in the past 100 Myr. However, attempts to accurately determine Pacific-Farallon spreading face the twin challenges of extensive subduction of Farallon crust - which precludes reconstruction by fitting conjugate magnetic anomaly and fracture zone traces - and the well-established asymmetric spreading behaviour of the EPR and its ancestor ridges for at least the past 51 Myr. We present improved rotation poles for the Pacific-Farallon spreading system between geomagnetic chrons 34y (83 Ma) and 10y (28.28 Ma), complete with uncertainties that allow easier combination into global plate circuits. These poles are derived by combining magnetic anomaly and fracture zone data from both the northern and southern Pacific plate, maximising the data distribution along the original ridge length to average out local variations in spreading behaviour. We have calculated best fit 'half'-stage poles for Pacific-Farallon spreading between nine Pacific plate magnetic anomalies (34y, 33y, 29o, 24.3o, 20o, 18.2o, 17.1y, 13y and 10y). For poles younger than chron 24.3o, full stage poles have been calculated by using anomaly picks from yet-to-be subducted Farallon/Nazca crust in the south Pacific to determine spreading asymmetry. Characterisation of the variation in spreading asymmetry in the past 50 Ma also allows bounds

  8. Estimation of hydrothermal deposits location from magnetization distribution and magnetic properties in the North Fiji Basin

    NASA Astrophysics Data System (ADS)

    Choi, S.; Kim, C.; Park, C.; Kim, H.

    2013-12-01

    The North Fiji Basin is belong to one of the youngest basins of back-arc basins in the southwest Pacific (from 12 Ma ago). We performed the marine magnetic and the bathymetry survey in the North Fiji Basin for finding the submarine hydrothermal deposits in April 2012. We acquired magnetic and bathymetry datasets by using Multi-Beam Echo Sounder EM120 (Kongsberg Co.) and Overhouser Proton Magnetometer SeaSPY (Marine Magnetics Co.). We conducted the data processing to obtain detailed seabed topography, magnetic anomaly, reduce to the pole(RTP), analytic signal and magnetization. The study areas composed of the two areas(KF-1(longitude : 173.5 ~ 173.7 and latitude : -16.2 ~ -16.5) and KF-3(longitude : 173.4 ~ 173.6 and latitude : -18.7 ~ -19.1)) in Central Spreading Ridge(CSR) and one area(KF-2(longitude : 173.7 ~ 174 and latitude : -16.8 ~ -17.2)) in Triple Junction(TJ). The seabed topography of KF-1 existed thin horst in two grabens that trends NW-SE direction. The magnetic properties of KF-1 showed high magnetic anomalies in center part and magnetic lineament structure of trending E-W direction. In the magnetization distribution of KF-1, the low magnetization zone matches well with a strong analytic signal in the northeastern part. KF-2 area has TJ. The seabed topography formed like Y-shape and showed a high feature in the center of TJ. The magnetic properties of KF-2 displayed high magnetic anomalies in N-S spreading ridge center and northwestern part. In the magnetization distribution of KF-2, the low magnetization zone matches well with a strong analytic signal in the northeastern part. The seabed topography of KF-3 presented a flat and high topography like dome structure at center axis and some seamounts scattered around the axis. The magnetic properties of KF-3 showed high magnetic anomalies in N-S spreading ridge center part. In the magnetization of KF-2, the low magnetization zone mismatches to strong analytic signal in this area. The difference of KF-3

  9. Structure of the Hat Creek graben region: Implications for the structure of the Hat Creek graben and transfer of right-lateral shear from the Walker Lane north of Lassen Peak, northern California, from gravity and magnetic anomalies

    USGS Publications Warehouse

    Langenheim, Victoria; Jachens, Robert C.; Clynne, Michael A.; Muffler, L. J. Patrick

    2016-01-01

    Interpretation of magnetic and new gravity data provides constraints on the geometry of the Hat Creek Fault, the amount of right-lateral offset in the area between Mt. Shasta and Lassen Peak, and confirmation of the influence of pre-existing structure on Quaternary faulting. Neogene volcanic rocks coincide with short-wavelength magnetic anomalies of both normal and reversed polarity, whereas a markedly smoother magnetic field occurs over the Klamath Mountains and its Paleogene cover. Although the magnetic field over the Neogene volcanic rocks is complex, the Hat Creek Fault, which is one of the most prominent normal faults in the region and forms the eastern margin of the Hat Creek Valley, is marked by the eastern edge of a north-trending magnetic and gravity high 20-30 km long. Modeling of these anomalies indicates that the fault is a steeply dipping (~75-85°) structure. The spatial relationship of the fault as modeled by the potential-field data, the youngest strand of the fault, and relocated seismicity suggests that deformation continues to step westward across the valley, consistent with a component of right-lateral slip in an extensional environment. Filtered aeromagnetic data highlight a concealed magnetic body of Mesozoic or older age north of Hat Creek Valley. The body’s northwest margin strikes northeast and is linear over a distance of ~40 km. Within the resolution of the aeromagnetic data (1-2 km), we discern no right-lateral offset of this body. Furthermore, Quaternary faults change strike or appear to end, as if to avoid this concealed magnetic body and to pass along its southeast edge, suggesting that pre-existing crustal structure influenced younger faulting, as previously proposed based on gravity data.

  10. Spread Supersymmetry

    NASA Astrophysics Data System (ADS)

    Hall, Lawrence J.; Nomura, Yasunori

    2012-01-01

    In the multiverse the scale of supersymmetry breaking, widetilde{m} = {F_X}/{M_{ * }} ∗, may scan and environmental constraints on the dark matter density may exclude a large range of m from the reheating temperature after inflation down to values that yield a lightest supersymmetric particle (LSP) mass of order a TeV. After selection effects, for example from the cosmological constant, the distribution for widetilde{m} in the region that gives a TeV LSP may prefer larger values. A single environmental constraint from dark matter can then lead to multi-component dark matter, including both axions and the LSP, giving a TeV-scale LSP somewhat lighter than the corresponding value for single-component LSP dark matter. If supersymmetry breaking is mediated to the Standard Model sector at order X † X and higher, only squarks, sleptons and one Higgs doublet acquire masses of order widetilde{m} . The gravitino mass is lighter by a factor of M ∗ /M Pl and the gaugino masses are suppressed by a further loop factor. This Spread Supersymmetry spectrum has two versions, one with Higgsino masses arising from supergravity effects of order the gravitino mass giving a wino LSP, and another with the Higgsino masses generated radiatively from gaugino masses giving a Higgsino LSP. The environmental restriction on dark matter fixes the LSP mass to the TeV domain, so that the squark and slepton masses are order 103 TeV and 106 TeV in these two schemes. We study the spectrum, dark matter and collider signals of these two versions of Spread Supersymmetry. The Higgs boson is Standard Model-like and predicted to lie in the range 110-145 GeV; monochromatic photons in cosmic rays arise from dark matter annihilations in the halo; exotic short charged tracks occur at the LHC, at least for the wino LSP; and there are the eventual possibilities of direct detection of dark matter and detailed exploration of the TeV-scale states at a future linear collider. Gauge coupling unification is at

  11. Backarc Oceanic Core Complexes Formed During Initial Spreading in the Southern Shikoku Basin

    NASA Astrophysics Data System (ADS)

    Miura, R.; Coffin, M. F.; Nakamura, Y.; Nishizawa, A.; Koda, K.; Tokuyama, H.

    2007-12-01

    Seafloor spreading occurs in two distinct geodynamic environments, major ocean basins and backarc basins. Unusual magma-poor seafloor spreading has been identified at slow- and intermediate-rate spreading centers in major ocean basins, e.g., Mid-Atlantic Ridge, Southwest Indian Ridge, and Australia-Antarctica Discordance. Some of these spreading centers are characterized by corrugated bathymetry known as megamullions, and some by chaotic bathymetry. Serpentinized peridotite and altered gabbro have been sampled from megamullions, and the three-dimensional geological structures that form megamullions are known as oceanic core complexes. Oceanic core complexes have also been identified at extinct backarc spreading centers, e.g., Parece Vela Basin and Shikoku Basin. The Shikoku Basin formed in conjunction with subduction along the Izu- Bonin arc at the eastern edge of the Philippine Sea plate. Although the general spreading history of the basin is known from identification of magnetic lineations, the early tectonic history of Proto-Izu-Bonin arc breakup and subsequent initial backarc spreading is uncertain. We identify, describe, and interpret oceanic core complexes amid chaotic bathymetry of the southern Shikoku Basin just east of the Kyushu-Palau Ridge, the remnant arc of the Proto-Izu-Bonin arc, on the basis of marine geological and geophysical data including multichannel seismic reflection, seismic refraction, swath bathymetry, and gravity. Just west of the core complexes, the Kyushu-Palau Ridge has been dated as Oligocene in age (~25 Ma), and just to the east lies magnetic anomaly 6B (~23 Ma). Crustal structure derived from seismic and gravity data indicates that anomalously thin -less than 5 km thick- crust is located in the arc-ocean transition between the central Kyushu-Palau Ridge and southern Shikoku Basin, which suggests rift-related crustal thinning and low magma productivity during backarc spreading initiation. Near the core complexes, seamount fragments

  12. Geopotential field anomalies and regional tectonic features

    NASA Astrophysics Data System (ADS)

    Mandea, Mioara; Korte, Monika

    2016-07-01

    Maps of both gravity and magnetic field anomalies offer crucial information about physical properties of the Earth's crust and upper mantle, required in understanding geological settings and tectonic structures. Density and magnetization represent independent rock properties and thus provide complementary information on compositional and structural changes. Two regions are considered: southern Africa (encompassing South Africa, Namibia and Botswana) and Germany. This twofold choice is motivated firstly by the fact that these regions represent rather diverse geological and geophysical conditions (old Archean crust with strong magnetic anomalies in southern Africa, and much younger, weakly magnetized crust in central Europe) and secondly by our intimate knowledge of the magnetic vector ground data from these two regions. We take also advantage of the recently developed satellite potential field models and compare magnetic and gravity gradient anomalies of some 200 km resolution. Comparing short and long wavelength anomalies and the correlation of rather large scale magnetic and gravity anomalies, and relating them to known lithospheric structures, we generally find a better agreement over the southern African region than the German territory. This probably indicates a stronger concordance between near-surface and deeper structures in the former area, which can be perceived to agree with a thicker lithosphere.

  13. Accuracy and Internal Consistency of Cardiac Magnetic Resonance Imaging in Measuring Branch Pulmonary Artery Flows in Patients With Conotruncal Anomalies and Branch Pulmonary Artery Stents.

    PubMed

    Harris, Matthew A; Avitabile, Catherine M; Fu, Gregory L; Kim, Daniel W; Kim, Timothy S; Gillespie, Matthew J; Keller, Marc S; Fogel, Mark A; Whitehead, Kevin K

    2016-04-01

    Clinicians use branch pulmonary artery (BPA) blood flow distribution to help determine the need for intervention. Although phase-contrast magnetic resonance (PCMR) flow measurements are accurate, this has never been shown in the vicinity of a BPA ferromagnetic stent (FS) which produces significant susceptibility artifact. We retrospectively reviewed 49 consecutive PCMR studies performed from 2005 to 2012 on patients with repaired conotruncal anomalies and either left (n = 29) or right PA (n = 20) stents. Three methods of measuring the stented BPA flow were compared: (1) main PA (MPA) minus nonstented BPA, (2) direct PCMR of stented BPA away from the artifact, and (3) pulmonary venous flows (ipsilateral to stented BPA and derived pulmonary blood flow ratio from bilateral pulmonary venous flows). Internal consistency was tested with the Student t test, linear regression, Bland-Altman analysis, and intraclass correlation (ICC). The mean age was 11.7 ± 6.9 years with 5.8 ± 4.2 years between stent placement and CMR. There was good agreement without significant difference between MPA-derived stented BPA flow (method 1) and direct PCMR of stented BPA (method 2; 41 ± 19% vs 39 ± 19%, p = 0.59; R(2) = 0.84, p <0.001; ICC = 0.96). There was also good agreement between methods 1 and 2 compared to pulmonary venous flows, with the highest correlation occurring between method 2 and ipsilateral pulmonary venous flow (R(2) = 0.90, p <0.001; ICC = 0.97 for MPA-derived-stented BPA flow; R(2) = 0.94, p <0.001; ICC = 0.98 for direct PCMR of stented BPA). Eleven of the 49 patients (22%) underwent interventional catheterization after PCMR. In conclusion, in the vicinity of a BPA FS, accurate measurement of the net fractional pulmonary blood flow ratio is feasible. PCMR adjacent to the stent and ipsilateral pulmonary venous flows provide the most internally consistent data. These data underscore PCMR's utility in managing patients with implanted FS. PMID:26993977

  14. Chiral anomalies and differential geometry

    SciTech Connect

    Zumino, B.

    1983-10-01

    Some properties of chiral anomalies are described from a geometric point of view. Topics include chiral anomalies and differential forms, transformation properties of the anomalies, identification and use of the anomalies, and normalization of the anomalies. 22 references. (WHK)

  15. Tuning magnetofluidic spreading in microchannels

    NASA Astrophysics Data System (ADS)

    Wang, Zhaomeng; Varma, V. B.; Wang, Z. P.; Ramanujan, R. V.

    2015-12-01

    Magnetofluidic spreading (MFS) is a phenomenon in which a uniform magnetic field is used to induce spreading of a ferrofluid core cladded by diamagnetic fluidic streams in a three-stream channel. Applications of MFS include micromixing, cell sorting and novel microfluidic lab-on-a-chip design. However, the relative importance of the parameters which govern MFS is still unclear, leading to non-optimal control of MFS. Hence, in this work, the effect of various key parameters on MFS was experimentally and numerically studied. Our multi-physics model, which combines magnetic and fluidic analysis, showed excellent agreement between theory and experiment. It was found that spreading was mainly due to cross-sectional convection induced by magnetic forces, and can be enhanced by tuning various parameters. Smaller flow rate ratio, higher magnetic field, higher core stream or lower cladding stream dynamic viscosity, and larger magnetic particle size can increase MFS. These results can be used to tune magnetofluidic spreading in microchannels.

  16. Outstanding problems in the equatorial ionosphere-thermosphere electrodynamics relevant to spread F

    NASA Astrophysics Data System (ADS)

    Abdu, M. A.

    2001-01-01

    Dynamic coupling of the atmospheric regions involving upward energy transport coupled with the locally active thermal tidal modes establish the wind system of the thermosphere whose interaction with the magnetized conducting ionospheric layers produces the dynamo electric fields and currents that control the quiet time electrodynamic processes of the equatorial ionosphere-thermosphere system. The plasma fountain responsible for the ionization anomaly, the vertical and zonal plasma drifts of the post-sunset hours leading to plasma bubble//spread F irregularity generation, and the Hall electric field that drives the electrojet current system are among the most notable manifestations of the these processes. The electrodynamic processes to be discussed in this paper will concern mainly the equatorial spread F (ESF) irregularity generation and their variabilities. The key factors that control the ESF generation by generalized Rayleigh-Taylor instability process, such as the the prereversal enhancement electric field (vertical drift) that is controlled by post-sunset zonal wind and longitudinal conductivity gradients, meridional//transequatorial winds, flux tube integrated conducitvities, and the seed perturbations are discussed in some detail, focussing attention on the aspects of their seasonal, logitudinal and day-to-day variabilities. The role of the evening F layer vertical drift in the instability process leading to ESF has been the most extensively investigated experimentally so far. Recent theoretical and computational results have advanced greatly our understanding of the importance of the key factors in the development process of spread F. However, observational identification of the relative importance of some of the key control factors in a given spread F event or in its day-to-day variablity is still lacking, the main examples being that of the seed perturbation, meridional//transequatorial winds and integrated conductivities. However, some progress on

  17. Lymphatic Anomalies Registry

    ClinicalTrials.gov

    2016-07-26

    Lymphatic Malformation; Generalized Lymphatic Anomaly (GLA); Central Conducting Lymphatic Anomaly; CLOVES Syndrome; Gorham-Stout Disease ("Disappearing Bone Disease"); Blue Rubber Bleb Nevus Syndrome; Kaposiform Lymphangiomatosis; Kaposiform Hemangioendothelioma/Tufted Angioma; Klippel-Trenaunay Syndrome; Lymphangiomatosis

  18. Magnetosheath Flow Anomalies in 3-D

    NASA Technical Reports Server (NTRS)

    Vaisberg, O. L.; Burch, J. L.; Smirnov, V. N.; Avanov, L. A.; Moore, T. E.; Waite, J. H., Jr.; Skalsky, A. A.; Borodkova, N. L.; Coffey, V. N.; Gallagher, D. L.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    Measurements of the plasma and magnetic field with high temporal resolution on the Interball Tail probe reveal many flow anomalies in the magnetosheath. They are usually seen as flow direction and number density variations, accompanied by magnetic field discontinuities. Large flow anomalies with number density variations of factor of 2 or more and velocity variations of 100 km/s or more are seen with periodicity of about I per hour. The cases of flow anomalies following in succession are also observed, and suggest their decay while propagating through the magnetosheath. Some magnetospheric disturbances observed in the outer magnetosphere after the satellite has crossed the magnetopause on the inbound orbit suggest their association with magnetosheath flow anomalies observed in the magnetosheath prior to magnetopause crossing.

  19. Crustal Magnetization and Magnetic Petrology in Basalts - What Can We Learn from Scientific Drillings?

    NASA Astrophysics Data System (ADS)

    Kontny, A. M.

    2014-12-01

    Rock magnetic and magneto-mineralogical data from scientific drillings contribute to our understanding of the growth history and tectonic evolution of volcanic structures and allows for an improved interpretation of magnetic anomaly data. Such data are not only important for the magnetic structure of volcanic buildings and spreading ridges on Earth but may also provide basic data for the interpretation of extraterrestrial magnetic anomalies like on Mars. Crustal magnetization of basalts is well studied since decades and in general, the amplitude of magnetic anomalies is mainly related to the induced and remanent magnetization. Direct measurements of the magnetic field and measurements of magnetic properties of oceanic and continental crust have indicated that the crustal magnetization is very complex and depends on different factors like e.g. magma composition, cooling rate, age and hydrothermal alteration. Generally a high oxygen fugacity (above the NNO buffer) and a low Ti/(Ti+Fe) ratio of the basaltic melt are suggested as a precondition for high concentration of magnetic minerals and therefore high primary TRM. High temperature subsolidus reactions and hydrothermal alteration as e.g. observed in the strongly magnetic basalts from the Stardalur drill core, Iceland, seems to increase NRM intensity and magnetic susceptibility due to creation of small, secondary magnetite (Vahle et al. 2007). Probably the increase occurred after the extinction of the hydrothermal system because active high-temperature (>150 °C) geothermal areas like the Krafla caldera, NE-Iceland, often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity (Oliva-Urcia et al. 2011). The destruction explains the significant magnetization loss, which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like Iceland or Hawaii. Borehole and core magnetic susceptibility measurements in

  20. Spreading behaviour of the Pacific-Farallon ridge system since 83 Ma

    NASA Astrophysics Data System (ADS)

    Rowan, Christopher J.; Rowley, David B.

    2014-06-01

    We present improved rotations, complete with uncertainties, for the Pacific-Farallon Ridge (PFR) between geomagnetic chrons 34y (83 Ma) and 10y (28.28 Ma). Despite substantial shortening since ˜55 Ma, this ridge system and its remnants (e.g. the East Pacific Rise) have produced as much as 45 per cent of all oceanic lithosphere created since the Late Cretaceous, but reconstructions face the twin challenges of extensive subduction of Farallon crust-which precludes reconstruction by fitting conjugate magnetic anomaly and fracture zone (FZ) traces-and asymmetric spreading behaviour for at least the past 51 Myr. We have calculated best-fit `half'-angle stage rotations between nine geomagnetic chron boundaries (34y, 33y, 29o, 24.3o, 20o, 18.2o, 17.1y, 13y and 10y) using combined anomaly and FZ data from both the northern and southern Pacific Plate. For rotations younger than chron 24.3o, estimates for spreading asymmetry, derived using anomaly picks from yet-to-be subducted Farallon/Nazca crust in the south Pacific, allow full stage rotations to be calculated. Between 50 and 83 Ma, where no direct constraints on spreading asymmetry are possible, a `best-fit' full stage rotation was calculated based on the net Nazca:Pacific spreading asymmetry (Pacific spreading fraction fPAC = 0.44) over the past 50 Myr, with conservative lower and upper bounds, based on variability in the degree of spreading asymmetry over periods of <15 Myr, assuming fPACs of 0.5 and 0.36, respectively. Synthetic flowlines generated from our new stage rotation produce a better match to Pacific FZ trends than previously published rotations. With the exception of the chron 18o-20o rotation, the six stage poles for rotations between chrons 33y and 13y (74-33 Ma) all cluster tightly at 60-75°E, 60-68°N, consistent with the relatively constant trend of the major Pacific FZs. This stability spans at least one episode of Farallon Plate fragmentation caused by subduction of PFR segments beneath the Americas

  1. Spreading Rate versus Magma Supply in the Region of Mid-Atlantic Ridge at 16.5° N

    NASA Astrophysics Data System (ADS)

    Palmiotto, C.; Schouten, H.; Smith, D. K.; Cann, J. R.; Dick, H. J.; Parnell-Turner, R. E.

    2013-12-01

    The region of Mid-Atlantic Ridge (MAR) at 16.5° N is a slow spreading center characterized by several detachment faults and oceanic core complexes. This area is ideal to study the relationship between the formation and the evolution of detachment faults, the role of magma supply during detachment faulting, and its effect on the magnetization of the crust at a slow-spreading center. In May-June 2013, during cruise KN210-05 on RV Knorr, we acquired multibeam bathymetry and sea surface magnetic anomaly data to understand the spreading history of a section of the MAR near 16.5° N. Multibeam data acquired using a SeaBeam 3012 system show that the ridge axis can be divided into a northern segment, characterized by a 4500-m deep axial valley, and a southern segment, which is characterized by a robust and continuous axial volcanic ridge which reaches to 3200 m water depth. Both segments are bordered to the west by active detachment faults. Magnetic data were acquired with a Marine Magnetics SeaSPY system, and inverted for crustal magnetization. The inversion assumes a constant thickness source layer of 0.5 km whose upper bound is bathymetry. Isochrons were identified from the magnetization map. We found that spreading rate is symmetric, and have calculated a total spreading rate in this area of ~24 km/Ma for the last 4 Ma. The central anomaly (Brunhes, 0-0.78 Ma) in the southern segment, however, has only half the predicted width of ~ 20 km and is located exclusively east of the axis. No Brunhes normal magnetization is recorded in the rift valley floor west of the axis, which is the hanging wall of the detachment. This observation confirms predictions from ';asymmetric' spreading at oceanic core complexes where slip along long-lived detachment faults take up extension on one (western) side and magmatic accretion occurs exclusively to the other (eastern) of the axis; the hanging wall, bounded by detachment fault and axis, should be as old as the core complex and its

  2. Nolen-Schiffer anomaly

    SciTech Connect

    Pieper, S.C.; Wiringa, R.B.

    1995-08-01

    The Argonne v{sub 18} potential contains a detailed treatment of the pp, pn and nn electromagnetic potential, including Coulomb, vacuum polarization, Darwin Foldy and magnetic moment terms, all with suitable form factors and was fit to pp and pn data using the appropriate nuclear masses. In addition, it contains a nuclear charge-symmetry breaking (CSB) term adjusted to reproduce the difference in the experimental pp and nn scattering lengths. We have used these potential terms to compute differences in the binding energies of mirror isospin-1/2 nuclei (Nolen-Schiffer [NS] anomaly). Variational Monte Carlo calculations for the {sup 3}He-{sup 3}H system and cluster variational Monte Carlo for the {sup 15}O-{sup 15}N and {sup 17}F-{sup 17}O systems were made. In the first case, the best variational wave function for the A = 3 nuclei was used. However, because our {sup 16}O wave function does not reproduce accurately the {sup 16}O rms radius, to which the NS anomaly is very sensitive, we adjusted the A = 15 and A = 17 wave functions to reproduce the experimental density profiles. Our computed energy differences for these three systems are 0.757 {plus_minus} .001, 3.544 {plus_minus} .018 and 3.458 {plus_minus} .040 MeV respectively, which are to be compared with the experimental differences of 0.764, 3.537, and 3.544 MeV. Most of the theoretical uncertainties are due to uncertainties in the experimental rms radii. The nuclear CSB potential contributes 0.066, 0.188, and 0.090 MeV to these totals. We also attempted calculations for A = 39 and A = 41. However, in these cases, the experimental uncertainties in the rms radius make it impossible to extract useful information about the contribution of the nuclear CSB potential.

  3. Analysis of spacecraft anomalies

    NASA Technical Reports Server (NTRS)

    Bloomquist, C. E.; Graham, W. C.

    1976-01-01

    The anomalies from 316 spacecraft covering the entire U.S. space program were analyzed to determine if there were any experimental or technological programs which could be implemented to remove the anomalies from future space activity. Thirty specific categories of anomalies were found to cover nearly 85 percent of all observed anomalies. Thirteen experiments were defined to deal with 17 of these categories; nine additional experiments were identified to deal with other classes of observed and anticipated anomalies. Preliminary analyses indicate that all 22 experimental programs are both technically feasible and economically viable.

  4. Lifshitz scale anomalies

    NASA Astrophysics Data System (ADS)

    Arav, Igal; Chapman, Shira; Oz, Yaron

    2015-02-01

    We analyse scale anomalies in Lifshitz field theories, formulated as the relative cohomology of the scaling operator with respect to foliation preserving diffeomorphisms. We construct a detailed framework that enables us to calculate the anomalies for any number of spatial dimensions, and for any value of the dynamical exponent. We derive selection rules, and establish the anomaly structure in diverse universal sectors. We present the complete cohomologies for various examples in one, two and three space dimensions for several values of the dynamical exponent. Our calculations indicate that all the Lifshitz scale anomalies are trivial descents, called B-type in the terminology of conformal anomalies. However, not all the trivial descents are cohomologically non-trivial. We compare the conformal anomalies to Lifshitz scale anomalies with a dynamical exponent equal to one.

  5. Geophysical Investigation of Continental Margin Development, and Early Spreading History of the South Atlantic South of the Walvis Ridge/Rio Grande Rise.

    NASA Astrophysics Data System (ADS)

    Dragoi, D.; Hall, S.; Bird, D.

    2006-12-01

    Crustal models of the transition from continental (>30 km) to normal oceanic crust between 22°S and 32°S on the African side and from 28°S and 43°S on the S. American side have been constructed from extensive gravity and magnetic anomaly data together with more limited seismic reflection and refraction data. Offshore gravity highs related to major crustal thinning can be followed along each margin. A smaller, more seaward gravity high observed on the African side coincides with previously mapped magnetic anomaly M4 and appears to delineate the landward limit of normal oceanic crust. The transition zone width is relatively uniform ~320±30 km on the African margin but increases southward from ~300 km to >400 km on the S. American side. The zone of magmatic underplating beneath the thinned crust has a uniform width of ~200 km on the African side but is somewhat narrower (~130 km) and also decreases southwards on the S. American side. Seafloor spreading magnetic anomalies C31 to C34, and M0 to M4 have been identified on both sides. Distinctive C34 anomalies can be clearly correlated except where masked by large amplitude (~1000 nT) anomalies produced by seafloor topography of the Walvis Ridge. C34 spreading rates are slightly asymmetrical with 42 mm/yr on the S. American side compared with 38 mm/yr on the African side. M0 to M4 anomalies are more difficult to identify and reliably correlate over each margin. M0-M4 spreading appears to be asymmetric with more rapid spreading on the S. American side. The C34-M0 distance is noticeably larger on the S. American side suggesting that asymmetrical spreading may continue into the Cretaceous Quiet Zone. A more probable explanation for the asymmetry is that one or more ridge jumps occurred between 84 and 120 Ma. Residualized free air satellite gravity data have been used to delineate fracture zones (FZs) associated with the early opening. More than 10 flow lines determined from these FZs intersect the mapped C34, M0 and M4

  6. Magnetization of the oceanic crust: TRM or CRM?

    NASA Technical Reports Server (NTRS)

    Raymond, C. A.; Labrecque, J. L.

    1987-01-01

    A model was proposed in which chemical remanent magnetization (CRM) acquired within the first 20 Ma of crustal evolution may account for 80% of the bulk natural remanent magnetization (NRM) of older basalts. The CRM of the crust is acquired as the original thermoremanent magnetization (TRM) is lost through low temperature alteration. The CRM intensity and direction are controlled by the post-emplacement polarity history. This model explains several independent observations concerning the magnetization of the oceanic crust. The model accounts for amplitude and skewness discrepancies observed in both the intermediate wavelength satellite field and the short wavelength sea surface magnetic anomaly pattern. It also explains the decay of magnetization away from the spreading axis, and the enhanced magnetization of the Cretaceous Quiet Zones while predicting other systematic variations with age in the bulk magnetization of the oceanic crust. The model also explains discrepancies in the anomaly skewness parameter observed for anomalies of Cretaceous age. Further studies indicate varying rates of TRM decay in very young crust which depicts the advance of low temperature alteration through the magnetized layer.

  7. Magnetic investigations

    SciTech Connect

    Bath, G.D.; Jahren, C.E.; Rosenbaum, J.G.; Baldwin, M.J.

    1983-12-31

    Air and ground magnetic anomalies in the Climax stock area of the NTS help define the gross configuration of the stock and detailed configuration of magnetized rocks at the Boundary and Tippinip faults that border the stock. Magnetizations of geologic units were evaluated by measurements of magnetic properties of drill core, minimum estimates of magnetizations from ground magnetic anomalies for near surface rocks, and comparisons of measured anomalies with anomalies computed by a three-dimensional forward program. Alluvial deposits and most sedimentary rocks are nonmagnetic, but drill core measurements reveal large and irregular changes in magnetization for some quartzites and marbles. The magnetizations of quartz monzonite and granodiorite near the stock surface are weak, about 0.15 A/m, and increase at a rate of 0.00196 A/m/m to 1.55 A/m, at depths greater than 700 m (2300 ft). The volcanic rocks of the area are weakly magnetized. Aeromagnetic anomalies 850 m (2800 ft) above the stock are explained by a model consisting of five vertical prisms. Prisms 1, 2, and 3 represent the near surface outline of the stock, prism 4 is one of the models developed by Whitehill (1973), and prism 5 is modified from the model developed by Allingham and Zietz (1962). Most of the anomaly comes from unsampled and strongly-magnetized deep sources that could be either granite or metamorphosed sedimentary rocks. 48 refs., 23 figs., 3 tabs.

  8. Rifting to spreading in the southern Lau Basin: Variations within the transition zone

    NASA Astrophysics Data System (ADS)

    Watanabe, M.; Okino, K.; Kodera, T.

    2010-11-01

    The Lau Basin and Havre Trough are back-arc basins related to Pacific-Australian plate convergence. Seafloor spreading occurs in the Lau Basin whereas the Havre Trough is in a rifting stage. At present, the spreading propagator's tip lies at the southern end of the Valu Fa Ridge (VFR) at 22°40'S. Studying this propagation process provides an opportunity to characterize the evolution of rifting to the initiation of seafloor spreading which is fundamental to back-arc basin development. New geophysical data of the southern Lau Basin reveals that as spreading propagates south, it evolves in a discrete style south of 22°40'S. The propagation axis lies along the eastern margin of the basin, where the well defined, linear VFR loses its identifying morphology. Topography in this eastern zone is characterized by grabens separated by short narrow ridges. High backscatter intensity indicates tectonic and magmatic activity in this eastern area. Mantle Bouguer anomalies (MBA) increase southwards from the VFR to form an elevated MBA area extending west from the currently active area. This indicates eastward migration of active rifting, during which the arc crust was extremely thinned. High magnetization is observed in a left-stepping pattern south of the VFR. We interpret this pattern as discrete segments that characterize the initiation of the spreading stage. There is no evidence of a single, continuous spreading axis like that which characterizes the central and northern Lau Basin. The magnetization highs are discrete and are observed in areas where deformation and magmatism are focused. They are offset relative to the VFR, though they generally follow the same north-south trend as the VFR.

  9. Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift

    NASA Astrophysics Data System (ADS)

    Horst, A. J.; Varga, R. J.; Gee, J. S.; Karson, J. A.

    2011-12-01

    The uppermost oceanic crust produced at the superfast spreading (˜142 km Ma-1, full-spreading rate) southern East Pacific Rise (EPR) during the Gauss Chron is exposed in a tectonic window along the northeastern wall of the Pito Deep Rift. Paleomagnetic analysis of fully oriented dike (62) and gabbro (5) samples from two adjacent study areas yield bootstrapped mean remanence directions of 38.9° ± 8.1°, -16.7° ± 15.6°, n = 23 (Area A) and 30.4° ± 8.0°, -25.1° ± 12.9°, n = 44 (Area B), both are significantly distinct from the Geocentric Axial Dipole expected direction at 23° S. Regional tectonics and outcrop-scale structural data combined with bootstrapped remanence directions constrain models that involve a sequence of three rotations that result in dikes restored to subvertical orientations related to (1) inward-tilting of crustal blocks during spreading (Area A = 11°, Area B = 22°), (2) clockwise, vertical-axis rotation of the Easter Microplate (A = 46°, B = 44°), and (3) block tilting at Pito Deep Rift (A = 21°, B = 10°). These data support a structural model for accretion at the southern EPR in which outcrop-scale faulting and block rotation accommodates spreading-related subaxial subsidence that is generally less than that observed in crust generated at a fast spreading rate exposed at Hess Deep Rift. These data also support previous estimates for the clockwise rotation of crust adjacent to the Easter Microplate. Dike sample natural remanent magnetization (NRM) has an arithmetic mean of 5.96 A/m ± 3.76, which suggests that they significantly contribute to observed magnetic anomalies from fast- to superfast-spread crust.

  10. Familial Ebstein's anomaly.

    PubMed Central

    Rosenmann, A; Arad, I; Simcha, A; Schaap, T

    1976-01-01

    A family is described in which both a father and son are affected with Ebstein's anomaly, while several other family members manifest different cardiac malformations. Five additional instances of familial Ebstein's anomaly were found in the literature and compared with our family. Inspection of possible modes of inheritance in this group of families suggests that Ebstein's anomaly is probably inherited as a polygenic character with a threshold phenomenon. PMID:1018315

  11. Taussig-Bing Anomaly

    PubMed Central

    Konstantinov, Igor E.

    2009-01-01

    Taussig-Bing anomaly is a rare congenital heart malformation that was first described in 1949 by Helen B. Taussig (1898–1986) and Richard J. Bing (1909–). Although substantial improvement has since been achieved in surgical results of the repair of the anomaly, management of the Taussig-Bing anomaly remains challenging. A history of the original description of the anomaly, the life stories of the individuals who first described it, and the current outcomes of its surgical management are reviewed herein. PMID:20069085

  12. Aeromagnetic anomalies and perspective oil traps in China

    SciTech Connect

    Zhang, Y.X. )

    1994-10-01

    Based on analyses of aeromagnetic data from known oil and gas fields in China, aeromagnetic anomalies have been classified according to their genesis into three types: (1) structure-associated anomalies related to volcanic rocks, (2) anomalies related to magnetic basement fault blocks, and (3) structure-associated anomalies related to weakly magnetic sedimentary strata. The most successful applications of aeromagnetic data for locating favorable oil and gas structures are in the following kinds of areas: (1) areas where basement fault blocks of inhomogeneous lithology and magnetization are developed; (2) areas of weakly magnetic layered strata with a considerably thickness, either effusive or clastic deposits; and (3) areas where magnetic layers have undergone tectonic deformation with faulting and dip angles larger than 30 degrees. For reliable detection of such structures in sedimentary rocks and associated oil and gas traps, an integrated interpretation of geological and geophysical data is necessary.

  13. Characterization of potential sources of magnetic anomalies within the crust in a tectonically active region: Amphibolites and migmatites from Potrillo Maar, New Mexico

    NASA Technical Reports Server (NTRS)

    Spear, F. S.; Padovanni, E.

    1985-01-01

    The purpose was to characterize the oxide mineralogy and petrology of samples collected from Potrillo Maar, New Mexico with the goal of explaining the magnetic anamoly that is observed over this region from remote sensing. Potrillo Maar is a diatreme that has brought rocks from all depths in the crust to the surface almost instantaneously. The samples are therefore thought to be representative of the crust as it exists today below this portion of the Rio Grande Rift. It is generally believed that oxide minerals (magnetite, hematite, etc.) are responsible for the magnetic signature of the crust. The samples from Portillo Maar therefore offer a unique opportunity to examine the magnetic mineralogy of the entire crust. The results indicate that the magnetic anamoly observed over Rio Grande Rift may be consequence of the tectonic activity that caused mylonitization of the rocks and allowed the infiltration of oxidizing fluids.

  14. Developmental anomalies of the skin.

    PubMed

    Bellet, Jane Sanders

    2013-02-01

    This paper focuses on the diagnosis and management of developmental anomalies of the skin that may be seen early in life. Common locations include the head, nose, preauricular area of the face, neck, and spine. Those that occur in or near the midline can be more serious because of possible intracranial connections. Radiologic imaging of the areas of involvement is often important; computed tomography (CT) scans can delineate bony defects; whereas, magnetic resonance imaging (MRI) more clearly defines intracranial connections. Occult spinal dysraphism can be suspected when certain cutaneous signs are present.

  15. Hot Flow Anomalies at Venus

    NASA Technical Reports Server (NTRS)

    Collinson, G. A.; Sibeck, David Gary; Boardsen, Scott A.; Moore, Tom; Barabash, S.; Masters, A.; Shane, N.; Slavin, J.A.; Coates, A.J.; Zhang, T. L.; Sarantos, M.

    2012-01-01

    We present a multi-instrument study of a hot flow anomaly (HFA) observed by the Venus Express spacecraft in the Venusian foreshock, on 22 March 2008, incorporating both Venus Express Magnetometer and Analyzer of Space Plasmas and Energetic Atoms (ASPERA) plasma observations. Centered on an interplanetary magnetic field discontinuity with inward convective motional electric fields on both sides, with a decreased core field strength, ion observations consistent with a flow deflection, and bounded by compressive heated edges, the properties of this event are consistent with those of HFAs observed at other planets within the solar system.

  16. Splenic Anomalies of Shape, Size, and Location: Pictorial Essay

    PubMed Central

    Yildiz, Adalet Elcin; Ariyurek, Macit Orhan; Karcaaltincaba, Musturay

    2013-01-01

    Spleen can have a wide range of anomalies including its shape, location, number, and size. Although most of these anomalies are congenital, there are also acquired types. Congenital anomalies affecting the shape of spleen are lobulations, notches, and clefts; the fusion and location anomalies of spleen are accessory spleen, splenopancreatic fusion, and wandering spleen; polysplenia can be associated with a syndrome. Splenosis and small spleen are acquired anomalies which are caused by trauma and sickle cell disease, respectively. These anomalies can be detected easily by using different imaging modalities including ultrasonography, computed tomography, magnetic resonance imaging, and also Tc-99m scintigraphy. In this pictorial essay, we review the imaging findings of these anomalies which can cause diagnostic pitfalls and be interpreted as pathologic processes. PMID:23710135

  17. Magnetotransport phenomena related to the chiral anomaly in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Spivak, B. Z.; Andreev, A. V.

    2016-02-01

    We present a theory of magnetotransport phenomena related to the chiral anomaly in Weyl semimetals. We show that conductivity, thermal conductivity, thermoelectric, and the sound absorption coefficients exhibit strong and anisotropic magnetic field dependencies. We also discuss properties of magnetoplasmons and magnetopolaritons, whose existences are entirely determined by the chiral anomaly. Finally, we discuss the conditions of applicability of the quasiclassical description of electron transport phenomena related to the chiral anomaly.

  18. Characterization of the in situ magnetic architecture of oceanic crust (Hess Deep) using near-source vector magnetic data

    NASA Astrophysics Data System (ADS)

    Tominaga, Masako; Tivey, Maurice A.; MacLeod, Christopher J.; Morris, Antony; Lissenberg, C. Johan; Shillington, Donna J.; Ferrini, Vicki

    2016-06-01

    Marine magnetic anomalies are a powerful tool for detecting geomagnetic polarity reversals, lithological boundaries, topographic contrasts, and alteration fronts in the oceanic lithosphere. Our aim here is to detect lithological contacts in fast-spreading lower crust and shallow mantle by characterizing magnetic anomalies and investigating their origins. We conducted a high-resolution, near-bottom, vector magnetic survey of crust exposed in the Hess Deep "tectonic window" using the remotely operated vehicle (ROV) Isis during RRS James Cook cruise JC21 in 2008. Hess Deep is located at the western tip of the propagating rift of the Cocos-Nazca plate boundary near the East Pacific Rise (EPR) (2°15'N, 101°30'W). ROV Isis collected high-resolution bathymetry and near-bottom magnetic data as well as seafloor samples to determine the in situ lithostratigraphy and internal structure of a section of EPR lower crust and mantle exposed on the steep (~20°dipping) south facing slope just north of the Hess Deep nadir. Ten magnetic profiles were collected up the slope using a three-axis fluxgate magnetometer mounted on ROV Isis. We develop and extend the vertical magnetic profile (VMP) approach of Tivey (1996) by incorporating, for the first time, a three-dimensional vector analysis, leading to what we here termed as "vector vertical magnetic profiling" approach. We calculate the source magnetization distribution, the deviation from two dimensionality, and the strike of magnetic boundaries using both the total field Fourier-transform inversion approach and a modified differential vector magnetic analysis. Overall, coherent, long-wavelength total field anomalies are present with a strong magnetization contrast between the upper and lower parts of the slope. The total field anomalies indicate a coherently magnetized source at depth. The upper part of the slope is weakly magnetized and magnetic structure follows the underlying slope morphology, including a "bench" and lobe

  19. Competing Orders and Anomalies

    NASA Astrophysics Data System (ADS)

    Moon, Eun-Gook

    2016-08-01

    A conservation law is one of the most fundamental properties in nature, but a certain class of conservation “laws” could be spoiled by intrinsic quantum mechanical effects, so-called quantum anomalies. Profound properties of the anomalies have deepened our understanding in quantum many body systems. Here, we investigate quantum anomaly effects in quantum phase transitions between competing orders and striking consequences of their presence. We explicitly calculate topological nature of anomalies of non-linear sigma models (NLSMs) with the Wess-Zumino-Witten (WZW) terms. The non-perturbative nature is directly related with the ’t Hooft anomaly matching condition: anomalies are conserved in renormalization group flow. By applying the matching condition, we show massless excitations are enforced by the anomalies in a whole phase diagram in sharp contrast to the case of the Landau-Ginzburg-Wilson theory which only has massive excitations in symmetric phases. Furthermore, we find non-perturbative criteria to characterize quantum phase transitions between competing orders. For example, in 4D, we show the two competing order parameter theories, CP(1) and the NLSM with WZW, describe different universality class. Physical realizations and experimental implication of the anomalies are also discussed.

  20. Competing Orders and Anomalies.

    PubMed

    Moon, Eun-Gook

    2016-08-08

    A conservation law is one of the most fundamental properties in nature, but a certain class of conservation "laws" could be spoiled by intrinsic quantum mechanical effects, so-called quantum anomalies. Profound properties of the anomalies have deepened our understanding in quantum many body systems. Here, we investigate quantum anomaly effects in quantum phase transitions between competing orders and striking consequences of their presence. We explicitly calculate topological nature of anomalies of non-linear sigma models (NLSMs) with the Wess-Zumino-Witten (WZW) terms. The non-perturbative nature is directly related with the 't Hooft anomaly matching condition: anomalies are conserved in renormalization group flow. By applying the matching condition, we show massless excitations are enforced by the anomalies in a whole phase diagram in sharp contrast to the case of the Landau-Ginzburg-Wilson theory which only has massive excitations in symmetric phases. Furthermore, we find non-perturbative criteria to characterize quantum phase transitions between competing orders. For example, in 4D, we show the two competing order parameter theories, CP(1) and the NLSM with WZW, describe different universality class. Physical realizations and experimental implication of the anomalies are also discussed.

  1. Competing Orders and Anomalies.

    PubMed

    Moon, Eun-Gook

    2016-01-01

    A conservation law is one of the most fundamental properties in nature, but a certain class of conservation "laws" could be spoiled by intrinsic quantum mechanical effects, so-called quantum anomalies. Profound properties of the anomalies have deepened our understanding in quantum many body systems. Here, we investigate quantum anomaly effects in quantum phase transitions between competing orders and striking consequences of their presence. We explicitly calculate topological nature of anomalies of non-linear sigma models (NLSMs) with the Wess-Zumino-Witten (WZW) terms. The non-perturbative nature is directly related with the 't Hooft anomaly matching condition: anomalies are conserved in renormalization group flow. By applying the matching condition, we show massless excitations are enforced by the anomalies in a whole phase diagram in sharp contrast to the case of the Landau-Ginzburg-Wilson theory which only has massive excitations in symmetric phases. Furthermore, we find non-perturbative criteria to characterize quantum phase transitions between competing orders. For example, in 4D, we show the two competing order parameter theories, CP(1) and the NLSM with WZW, describe different universality class. Physical realizations and experimental implication of the anomalies are also discussed. PMID:27499184

  2. Competing Orders and Anomalies

    PubMed Central

    Moon, Eun-Gook

    2016-01-01

    A conservation law is one of the most fundamental properties in nature, but a certain class of conservation “laws” could be spoiled by intrinsic quantum mechanical effects, so-called quantum anomalies. Profound properties of the anomalies have deepened our understanding in quantum many body systems. Here, we investigate quantum anomaly effects in quantum phase transitions between competing orders and striking consequences of their presence. We explicitly calculate topological nature of anomalies of non-linear sigma models (NLSMs) with the Wess-Zumino-Witten (WZW) terms. The non-perturbative nature is directly related with the ’t Hooft anomaly matching condition: anomalies are conserved in renormalization group flow. By applying the matching condition, we show massless excitations are enforced by the anomalies in a whole phase diagram in sharp contrast to the case of the Landau-Ginzburg-Wilson theory which only has massive excitations in symmetric phases. Furthermore, we find non-perturbative criteria to characterize quantum phase transitions between competing orders. For example, in 4D, we show the two competing order parameter theories, CP(1) and the NLSM with WZW, describe different universality class. Physical realizations and experimental implication of the anomalies are also discussed. PMID:27499184

  3. The anomaly data base of screwworm information

    NASA Technical Reports Server (NTRS)

    Giddings, L. E.

    1976-01-01

    Standard statistical processing of anomaly data in the screwworm eradication data system is possible from data compiled on magnetic tapes with the Univac 1108 computer. The format and organization of the data in the data base, which is also available on dedicated disc storage, are described.

  4. Table of hyperfine anomaly in atomic systems

    SciTech Connect

    Persson, J.R.

    2013-01-15

    This table is a compilation of experimental values of magnetic hyperfine anomaly in atomic and ionic systems. The last extensive compilation was published in 1984 by Büttgenbach [S. Büttgenbach, Hyperfine Int. 20 (1984) 1] and the aim here is to make an up to date compilation. The literature search covers the period up to January 2011.

  5. Toward prediction of L band scintillations in the equatorial ionization anomaly region

    NASA Astrophysics Data System (ADS)

    Manju, G.; Sreeja, V.; Ravindran, Sudha; Thampi, Smitha V.

    2011-02-01

    The first observations of the duration and spread of equatorial spread F (ESF) at the magnetic equator and their relationship with the L band scintillations in the equatorial ionization anomaly (EIA) region have been presented here. The analysis is done for the equinoctial months of low solar activity period 2005-2006 and the moderate solar activity year 2004. Ionosonde and CRABEX data from Trivandrum and GPS data from four stations in the EIA region centered around 77°E meridian have been used for the study. The results show that the maximum scintillation index (s4) in the EIA region is linearly dependent on the spread of ESF traces for both the equinoxes. The corresponding duration of L band scintillations is also found to be linearly dependent on the duration of ESF at the magnetic equator. Further, the study for the first time reveals the plausible use of the ESF prediction parameter during 1600-1845 IST period for predicting L band scintillations and its inverse relationship with F10.7 cm flux.

  6. A physical model for the precursory magnetic anomalies of the M5.4 Alum Rock and M6.0 Parkfield earthquakes

    NASA Astrophysics Data System (ADS)

    Dologlou, Elizabeth

    2014-06-01

    Here, we propose an alternative physical model, based on the concept of criticality, for the explanation of the observed magnetic signals prior to the M6.0 Parkfield and the M5.4 Alum Rock earthquakes. Motivated by an analogous experience from major earthquakes in Greece, where both magnetic field variations and seismic electric signals were also recorded few weeks before the main shock, we suggest that in all these cases, similar dynamic processes characterized by critical behaviour should govern the corresponding pre-focal areas when the relevant precursory signals emerged.

  7. Quantum Spread Spectrum Communication

    SciTech Connect

    Humble, Travis S

    2011-01-01

    We show that communication of single-photon quantum states in a multi-user environment is improved by using spread spectrum communication techniques. We describe a framework for spreading, transmitting, despreading, and detecting single-photon spectral states that mimics conventional spread spectrum techniques. We show in the cases of inadvertent detection, unintentional interference, and multi-user management, that quantum spread spectrum communications may minimize receiver errors by managing quantum channel access.

  8. Anomalies in vortex lattice dynamics driven by induced ac currents in superconducting films with magnetic arrays of two-fold symmetry

    NASA Astrophysics Data System (ADS)

    Moreno, A. J.; Chiliotte, C. E.; Pasquini, G.; Bekeris, V.; Gomez, A.; del Valle, J.; Gonzalez, E. M.; Prieto, J. L.; Vicent, J. L.

    2015-01-01

    We study the dynamics of the vortex lattice driven by ac induced currents in the critical state regime, for T > 0.70 TC. The samples are superconducting films grown on top of two-fold symmetry array of magnetic dots. In these heterostructures, the induced ac currents flow parallel to the short and to the long side of the pinning array in different areas of the samples simultaneously. This behavior produces remarkable effects in the vortex lattice dynamics. First of all, periodic features are observed in the ac susceptibility versus applied magnetic field measurements which are related to matching effects between the vortex lattices and the magnetic array. However, the vortex lattice reconfiguration observed in magnetotransport experiments is absent. Some of these features are revealed as maxima instead of being minima, indicating higher mobility at certain matching fields. Competing unstable vortex configurations could lead to increase vortex mobility precluding the reconfiguration transition. At high temperatures, where the matching effects show up, the magnetic permeability of the dots is the mechanism that governs the JC(T) behavior. Moreover, the temperature dependence of the pinning force FP(T) shows a temperature crossover related to an unexpected enhancement in vortex mobility. Vortex-vortex interaction and the interplay between trapped and interstitial vortices are a hint to explain these phenomena.

  9. The role of time-resolved imaging of contrast kinetics (TRICKS) magnetic resonance angiography (MRA) in the evaluation of head–neck vascular anomalies: a preliminary experience

    PubMed Central

    Tavanti, F; Rossi Espagnet, M C; Terenzi, V; Cassoni, A; Suma, G; Boellis, A; Pierallini, A; Valentini, V; Bozzao, A

    2015-01-01

    Objectives: In this preliminary report, we describe our experience with time-resolved imaging of contrast kinetics–MR angiography (TRICKS-MRA) in the assessment of head–neck vascular anomalies (HNVAs). Methods: We prospectively studied six consecutive patients with clinically suspected or diagnosed HNVAs. All of them underwent TRICKS-MRA of the head and neck as part of the routine for treatment planning. A digital subtraction angiography (DSA) was also performed. Results: TRICKS-MRA could be achieved in all cases. Three subjects were treated based on TRICKS-MRA imaging findings and subsequent DSA examination. In all of them, DSA confirmed the vascular architecture of HNVAs shown by TRICKS-MRA. In the other three patients, a close follow up to assess the evolution of the suspected haemangioma was preferred. Conclusions: TRICKS sequences add important diagnostic information in cases of HNVAs, helpful for therapeutic decisions and post-treatment follow up. We recommend TRICKS-MRA use (if technically possible) as part of routine MRI protocol for HNVAs, representing a possible alternative imaging tool to conventional DSA. PMID:25410709

  10. Behavioral economics without anomalies.

    PubMed Central

    Rachlin, H

    1995-01-01

    Behavioral economics is often conceived as the study of anomalies superimposed on a rational system. As research has progressed, anomalies have multiplied until little is left of rationality. Another conception of behavioral economics is based on the axiom that value is always maximized. It incorporates so-called anomalies either as conflicts between temporal patterns of behavior and the individual acts comprising those patterns or as outcomes of nonexponential time discounting. This second conception of behavioral economics is both empirically based and internally consistent. PMID:8551195

  11. Development of oceanic detachment and asymmetric spreading at the Australian-Antarctic Discordance

    NASA Astrophysics Data System (ADS)

    Okino, Kyoko; Matsuda, Kohei; Christie, David M.; Nogi, Yoshifumi; Koizumi, Kin-Ichiro

    2004-12-01

    The largest known oceanic detachment terrains occur in Segment B3 of the Australian-Antarctic Discordance (AAD). Using newly collected bathymetry, magnetic, and gravity data, we show that Segment B3 is divided into two contrasting second-order segments. The western subsegment, B3W, is characterized by well-ordered, ridge parallel abyssal hills and low mantle Bouguer gravity anomalies. The eastern subsegment, B3E, displays rough, chaotic morphology and includes several megamullions characterized by high mantle Bouguer gravity anomaly values. The crust is estimated to be thinner by a maximum of 3 km in southern B3E. The combination of chaotic morphology with thinner crust supports the idea that the megamullions are exposed footwalls of oceanic detachments. Megamullion terrains are characterized by higher magnetization than adjacent terrains, most likely as a result of serpentinization of peridotite exposed at the detachment surfaces. Detachment surfaces constitute up to 70% of the total area of both ridge flanks younger than 2 Ma in B3E, indicating that oceanic detachments have played a major role in its development. Spreading in B3E has been extremely asymmetric, with higher apparent rates associated with the large detachment surfaces, where up to 75% of the total extension occurred. Similar asymmetric spreading on oceanic detachments is also recognized in Segment B4, suggesting that this is the dominant mode of extension associated with cold mantle and low magma supply in this deepest part of the AAD, where it is confined to a mere 100-km-long section of the AAD spreading axis.

  12. Octahedral distortion induced magnetic anomalies in LaMn{sub 0.5}Co{sub 0.5}O{sub 3} single crystals

    SciTech Connect

    Manna, Kaustuv Elizabeth, Suja; Anil Kumar, P. S.; Bhadram, Venkata Srinu; Narayana, Chandrabhas

    2014-07-28

    Single crystals of LaMn{sub 0.5}Co{sub 0.5}O{sub 3} belonging to the ferromagnetic-insulator and distorted perovskite class were grown using a four-mirror optical float zone furnace. The as-grown crystal crystallizes into an orthorhombic Pbnm structure. The spatially resolved 2D Raman scan reveals a strain-induced distribution of transition metal (TM)–oxygen (O) octahedral deformation in the as-grown crystal. A rigorous annealing process releases the strain, thereby generating homogeneous octahedral distortion. The octahedra tilt by reducing the bond angle TM-O-TM, resulting in a decline of the exchange energy in the annealed crystal. The critical behavior is investigated from the bulk magnetization. It is found that the ground state magnetic behavior assigned to the strain-free LaMn{sub 0.5}Co{sub 0.5}O{sub 3} crystal is of the 3D Heisenberg kind. Strain induces mean field-like interaction in some sites, and consequently, the critical exponents deviate from the 3D Heisenberg class in the as-grown crystal. The temperature-dependent Raman scattering study reveals strong spin-phonon coupling and the existence of two magnetic ground states in the same crystal.

  13. Slow to Ultraslow Seafloor Spreading in the Norway Basin Under Influence of the Iceland Hotspot

    NASA Astrophysics Data System (ADS)

    Breivik, A. J.; Mjelde, R.; Faleide, J. I.

    2005-12-01

    The Norway Basin was initiated by continental breakup between northern Europe and Greenland/Jan Mayen in the earliest Eocene (~54Ma). Being part of the North Atlantic Igneous Province, continental breakup and early seafloor spreading produced voluminous magmatism. An ocean bottom seismometer (OBS) profile acquired in the year 2000 from the Norwegian Moere margin to the extinct spreading axis of the Aegir Ridge, was used to estimate variations in magma productivity as the oceanic basin evolved. Due to low magnetic data coverage, a satellite derived gravity map proved suitable to reinterpret the East Jan Mayen Fracture Zone (EJMFZ) system, but none of the other proposed fracture zones within the Norway Basin could be identified along its ~500 km length. The revised EJMFZ trace was used to re-evaluate spreading direction in the Norway Basin, which is quite asymmetric as it is condensed mostly on the southwestern side. The magnetic track recorded along the OBS profile was used to identify magnetic seafloor spreading anomalies by forward modeling, and projected onto synthetic flow lines half spreading rates were derived along-profile. Maximum rate was above 3 cm/a between A24A and A24b, falling off to ~0.7 cm/a (ultra-slow) towards the mid-Oligocene (25-28 Ma) termination of seafloor spreading. Breakup magmatism created oceanic crust up to 10-11 km thick, tapering down to thin crust by C23 time (51.4 Ma), the increased melt potential was thus spent ~2.5 Ma after continental breakup. There is a conspicuous correlation between half spreading rate and oceanic crustal thickness. As this is not observed in a normal seafloor spreading environment at most rates observed here, both plate spreading and magma production should be governed by a common cause, presumably hot asthenosphere restricted to the continental rift zone. While Oceanic crust created during ultra-slow spreading is thin (4 km), crust created during slow spreading is also thinner than the world average (5 vs. 7

  14. Geomagnetic Polarity Reversal Model of Deeptow Magnetic Survey in the Southwest Subbasin of South China Sea Ridge

    NASA Astrophysics Data System (ADS)

    Qiu, N.; Sun, Z.; Lin, J.; Li, C. F.; Xu, X.

    2014-12-01

    South China Sea basin, which evolved from Cenozoic continental margin rifting and subsequent seafloor spreading, is a classic example of a marginal sea in Western Pacific. Since the early 1980's, several models have been proposed for the formation of this sea basin. The previous studies were based mainly on the distribution of magnetic anomaly lineation obtained from aerial and shipboard measurements. However, large water depth (over 4.5km) and thick sediment cover (up to 1km or more) make the magnetic anoamaly information not so well displayed in aerial and shipboard data. To better understand the evolution of the sea basin, we increased anomaly amplitudes by collecting magnetic data along deep-tow profiles over the magnetic lineations in the South China Sea oceanic area. The one across the southwest subsea basin was analyzed first. The total field magnetic measurements were processed through filtering, resampling, diurnal variation removal, continuation to a level datum, regional field correction, projection to a common azimuth, and deskewing. A magnetic polarity reversal timescale was constructed by matching deep-tow anomalies with a simple, rectangular block magnetization model with the expansion rate for oceanic crust. We analyzed the spreading duration, rate, asymmetry, and reversal events of Southwest subbasin, in reference to the recent GTS2012 geomagnetic polarity representative data and concluded that the Southwest subbasin opened from around 21.767 Ma and stopped around C5C at about 15.974Ma. The full spreading rate varied from 8 to 40 cm/yr. Spreading is usually asymmetric by showing alternate faster spreading rate in one slab than the other in different time periods. From the comparison, several small reversal were revealed in addition to the standard geomagnetic polarity. These findings helped to understand the evolution of the Southwest subbasin of South China Sea and will also help to establish new reversal discrimination.

  15. Dual diaphragmatic anomalies.

    PubMed

    Padmanabhan, Arjun; Thomas, Abin Varghese

    2016-01-01

    Although diaphragmatic anomalies such as an eventration and hiatus hernia are commonly encountered in incidental chest X-ray imaging, the presence of concomitant multiple anomalies is extremely rare. This is all the more true in adults. Herein, we present the case of a 75-year-old female, while undergoing a routine chest X-ray imaging, was found to have eventration of right hemidiaphragm along with a hiatus hernia as well. PMID:27625457

  16. Dual diaphragmatic anomalies

    PubMed Central

    Padmanabhan, Arjun; Thomas, Abin Varghese

    2016-01-01

    Although diaphragmatic anomalies such as an eventration and hiatus hernia are commonly encountered in incidental chest X-ray imaging, the presence of concomitant multiple anomalies is extremely rare. This is all the more true in adults. Herein, we present the case of a 75-year-old female, while undergoing a routine chest X-ray imaging, was found to have eventration of right hemidiaphragm along with a hiatus hernia as well.

  17. Dual diaphragmatic anomalies

    PubMed Central

    Padmanabhan, Arjun; Thomas, Abin Varghese

    2016-01-01

    Although diaphragmatic anomalies such as an eventration and hiatus hernia are commonly encountered in incidental chest X-ray imaging, the presence of concomitant multiple anomalies is extremely rare. This is all the more true in adults. Herein, we present the case of a 75-year-old female, while undergoing a routine chest X-ray imaging, was found to have eventration of right hemidiaphragm along with a hiatus hernia as well. PMID:27625457

  18. SADM potentiometer anomaly investigations

    NASA Astrophysics Data System (ADS)

    Wood, Brian; Mussett, David; Cattaldo, Olivier; Rohr, Thomas

    2005-07-01

    During the last 3 years Contraves Space have been developing a Low Power (1-2kW) Solar Array Drive Mechanism (SADM) aimed at small series production. The mechanism was subjected to two test programmes in order to qualify the SADM to acceptable levels. During the two test programmes, anomalies were experienced with the Potentiometers provided by Eurofarad SA and joint investigations were undertaken to resolve why these anomalies had occurred. This paper deals with the lessons learnt from the failure investigation on the two Eurofarad (rotary) Potentiometer anomaly. The Rotary Potentiometers that were used were fully redundant; using two back to back mounted "plastic tracks". It is a pancake configuration mounted directly to the shaft of the Slip Ring Assembly at the extreme in-board end of the SADM. It has no internal bearings. The anomaly initially manifested itself as a loss of performance in terms of linearity, which was first detected during Thermal Vacuum testing. A subsequent anomaly manifested itself by the complete failure of the redundant potentiometer again during thermal vacuum testing. This paper will follow and detail the chain of events following this anomaly and identifies corrective measures to be applied to the potentiometer design and assembly process.

  19. A statistical analysis of occurrence characteristics of Spread-F irregularities over Indian region

    NASA Astrophysics Data System (ADS)

    Upadhayaya, A. K.; Gupta, Sumedha

    2014-05-01

    We investigate the regularities of a change in Spread-F F probability during day-to-day, under varying solar variability, latitudinal behavior and their response to geomagnetic storm in equatorial and low-mid latitude stations. The occurrence characteristics of Spread-F irregularities, is obtained from daily hourly ionosonde data from a low-mid latitude station, Delhi (28.6°N, 77.2°E), for more than half a solar cycle (2001 to 2007). The latitudinal behavior of Spread-F is studied using ionosonde data from anomaly crest station, Ahmedabad (23.01°N, 72.36°E) and equatorial station, Kodaikanal (10.2°N, 77.5°E) for low, moderate and high solar activity periods. The maximum percentage occurrences of Spread-F were observed during the low solar activity year 2007, we believe, the low plasma and neutral density during 23/24 solar cycle minimum could be an important factor leading to the generation and propagation of TIDs and gravity waves. An anti-solar activity correlation to Spread-F occurrence is reported during all the seasons at different stations which are because of instability generated by the trans-equatorial meridional winds. There is a substantial variation during pre and post midnight hours in F region height from equatorial to low latitudes in response to magnetic disturbances. Concurrence was observed in the occurrence time of Spread-F to different storm events during different storm phases. The established irregularities and their behavior in Indian region are qualitatively interpreted and discussed.

  20. Z2 and Chiral Anomalies in Topological Dirac Semimetals

    NASA Astrophysics Data System (ADS)

    Burkov, Anton A.; Kim, Yong Baek

    2016-09-01

    We demonstrate that topological Dirac semimetals, which possess two Dirac nodes, separated in momentum space along a rotation axis and protected by rotational symmetry, exhibit an additional quantum anomaly, distinct from the chiral anomaly. This anomaly, which we call the Z2 anomaly, is a consequence of the fact that the Dirac nodes in topological Dirac semimetals carry a Z2 topological charge. The Z2 anomaly refers to nonconservation of this charge in the presence of external fields due to quantum effects and has observable consequences due to its interplay with the chiral anomaly. We discuss possible implications of this for the interpretation of magnetotransport experiments on topological Dirac semimetals. We also provide a possible explanation for the magnetic field dependent angular narrowing of the negative longitudinal magnetoresistance, observed in a recent experiment on Na3Bi .

  1. Off- and Along-Axis Slow Spreading Ridge Segment Characters: Insights From 3d Thermal Modeling

    NASA Astrophysics Data System (ADS)

    Gac, S.; Tisseau, C.; Dyment, J.

    2001-12-01

    Many observations along the Mid-Atlantic Ridge segments suggest a correlation between surface characters (length, axial morphology) and the thermal state of the segment. Thibaud et al. (1998) classify segments according to their thermal state: "colder" segments shorter than 30 km show a weak magmatic activity, and "hotter" segments as long as 90 km show a robust magmatic activity. The existence of such a correlation suggests that the thermal structure of a slow spreading ridge segment explains most of the surface observations. Here we test the physical coherence of such an integrated thermal model and evaluate it quantitatively. The different kinds of segment would constitute different phases in a segment evolution, the segment evolving progressively from a "colder" to a "hotter" so to a "colder" state. Here we test the consistency of such an evolution scheme. To test these hypotheses we have developed a 3D numerical model for the thermal structure and evolution of a slow spreading ridge segment. The thermal structure is controlled by the geometry and the dimensions of a permanently hot zone, imposed beneath the segment center, where is simulated the adiabatic ascent of magmatic material. To compare the model with the observations several geophysic quantities which depend on the thermal state are simulated: crustal thickness variations along axis, gravity anomalies (reflecting density variations) and earthquake maximum depth (corresponding to the 750° C isotherm depth). The thermal structure of a particular segment is constrained by comparing the simulated quantities to the real ones. Considering realistic magnetization parameters, the magnetic anomalies generated from the same thermal structure and evolution reproduce the observed magnetic anomaly amplitude variations along the segment. The thermal structures accounting for observations are determined for each kind of segment (from "colder" to "hotter"). The evolution of the thermal structure from the "colder" to

  2. How Leaky Are Seafloor Spreading Center Axes?

    NASA Astrophysics Data System (ADS)

    Baker, E. T.; Resing, J. A.; Martinez, F.; Haymon, R. M.; Nakamura, K.; Walker, S. L.; Ferrini, V.

    2013-12-01

    Some 500 active vent sites, both focused and diffuse, have now been located along spreading centers by either visual confirmation or instrumental detection of the discharging plume. Discovery of the large majority of these sites was made easier by high-volume discharge of particle-laden plumes. These observations led to estimates (as can be derived from the InterRidge Vents Database) of site frequency from ~0.5-5/100 km, generally increasing with spreading rate. Over the last decade, however, the increasing use of oxidation-reduction potential (ORP (mV)) (aka Eh) sensors capable of detecting minute concentrations of reduced hydrothermal chemicals (e.g., Fe+2, sulfides, Mn+2, H2, and others) suggests that these frequency estimates may be far too conservative. This hypothesis is consistent with earlier results from a few large-scale, high-resolution camera tows on some EPR segments. ORP data provide two important advantages for site identification not available with other commonly used continuously recording sensors: (1) detection of low-temperature, particle-scarce plumes, and (2) detection of reduced chemical species with very short residence times, thus increasing the location specificity of the discharge source. Here, we present high-resolution distributions of ORP anomalies observed in past plume surveys along the Eastern Lau Spreading Center (19.5°-22.5°S) in 2004 and 2008, the Galápagos Spreading Center (94.6°-86°W) in 2005/6 and 2011, as well as new data (2011) from the East Pacific Rise (9°-10°N). Except for the 2011 GSC data (a standard CTD tow-yo), all data were collected during continuous horizontal tows of ORP sensors at various depths <~120 m above the seafloor. We used two approaches to verify that ORP anomalies were authentic hydrothermal signals and not (especially in the case of small anomalies) produced by some other transient chemical anomaly. First, on the 2008 ELSC and 2011 EPR tows we compared temperature (ΔT) and ORP (ΔORP) data from

  3. Astrometric solar system anomalies

    SciTech Connect

    Nieto, Michael Martin; Anderson, John D

    2009-01-01

    There are at least four unexplained anomalies connected with astrometric data. perhaps the most disturbing is the fact that when a spacecraft on a flyby trajectory approaches the Earth within 2000 km or less, it often experiences a change in total orbital energy per unit mass. next, a secular change in the astronomical unit AU is definitely a concern. It is increasing by about 15 cm yr{sup -1}. The other two anomalies are perhaps less disturbing because of known sources of nongravitational acceleration. The first is an apparent slowing of the two Pioneer spacecraft as they exit the solar system in opposite directions. Some astronomers and physicists are convinced this effect is of concern, but many others are convinced it is produced by a nearly identical thermal emission from both spacecraft, in a direction away from the Sun, thereby producing acceleration toward the Sun. The fourth anomaly is a measured increase in the eccentricity of the Moon's orbit. Here again, an increase is expected from tidal friction in both the Earth and Moon. However, there is a reported unexplained increase that is significant at the three-sigma level. It is produent to suspect that all four anomalies have mundane explanations, or that one or more anomalies are a result of systematic error. Yet they might eventually be explained by new physics. For example, a slightly modified theory of gravitation is not ruled out, perhaps analogous to Einstein's 1916 explanation for the excess precession of Mercury's perihelion.

  4. Congenital Vascular Anomalies.

    PubMed

    Gravereaux, Edwin C.; Nguyen, Louis L.; Cunningham, Leslie D.

    2004-04-01

    Congenital vascular anomalies are rare. The cardiovascular specialist should nevertheless be aware of the more common types of vascular anomalies and understand the implications for patient treatment and the likelihood of associated morbidity. The presentation of congenital arteriovenous malformations can range from asymptomatic or cosmetic lesions, to those causing ischemia, ulceration, hemorrhage, or high-output congestive heart failure. Treatment of large, symptomatic arteriovenous malformations often requires catheter-directed embolization prior to the attempt at complete surgical excision. Later recurrence, due to collateral recruitment, is frequent. Graded compression stockings and leg elevation are the mainstays of treatment for the predominantly venous congenital vascular anomalies. Most congenital central venous disorders are clinically silent. An exception is the retrocaval ureter. Retroaortic left renal vein, circumaortic venous ring, and absent, left-sided or duplicated inferior vena cava are relevant when aortic or inferior vena cava procedures are planned. The treatment of the venous disorders is directed at prevention or management of symptoms. Persistent sciatic artery, popliteal entrapment syndrome, and aberrant right subclavian artery origin are congenital anomalies that are typically symptomatic at presentation. Because they mimic more common diseases, diagnosis is frequently delayed. Delay can result in significant morbidity for the patient. Failure to make the diagnosis of persistent sciatic artery and popliteal entrapment can result in critical limb ischemia and subsequent amputation. Unrecognized aberrant right subclavian artery origin associated with aneurysmal degeneration can rupture and result in death. The treatment options for large-vessel arterial anomalies are surgical, sometimes in combination with endovascular techniques.

  5. Statistical Anomaly Detection for Monitoring of Human Dynamics

    NASA Astrophysics Data System (ADS)

    Kamiya, K.; Fuse, T.

    2015-05-01

    Understanding of human dynamics has drawn attention to various areas. Due to the wide spread of positioning technologies that use GPS or public Wi-Fi, location information can be obtained with high spatial-temporal resolution as well as at low cost. By collecting set of individual location information in real time, monitoring of human dynamics is recently considered possible and is expected to lead to dynamic traffic control in the future. Although this monitoring focuses on detecting anomalous states of human dynamics, anomaly detection methods are developed ad hoc and not fully systematized. This research aims to define an anomaly detection problem of the human dynamics monitoring with gridded population data and develop an anomaly detection method based on the definition. According to the result of a review we have comprehensively conducted, we discussed the characteristics of the anomaly detection of human dynamics monitoring and categorized our problem to a semi-supervised anomaly detection problem that detects contextual anomalies behind time-series data. We developed an anomaly detection method based on a sticky HDP-HMM, which is able to estimate the number of hidden states according to input data. Results of the experiment with synthetic data showed that our proposed method has good fundamental performance with respect to the detection rate. Through the experiment with real gridded population data, an anomaly was detected when and where an actual social event had occurred.

  6. Conductivity Anomalies in Central Europe

    NASA Astrophysics Data System (ADS)

    Neska, Anne

    2016-01-01

    This paper is a review of studies which, by applying the magnetotelluric, geomagnetic deep sounding, and magnetovariational sounding methods (the latter refers to usage of the horizontal magnetic tensor), investigate Central Europe for zones of enhanced electrical conductivity. The study areas comprise the region of the Trans-European Suture Zone (i.e. the south Baltic region and Poland), the North German Basin, the German and Czech Variscides, the Pannonian Basin (Hungary), and the Polish, Slovakian, Ukrainian, and Romanian Carpathians. This part of the world is well investigated in terms of data coverage and of the density of published studies, whereas the certainty that the results lead to comprehensive interpretations varies within the reviewed literature. A comparison of spatially coincident or adjacent studies reveals the important role that the data coverage of a distinct conductivity anomaly plays for the consistency of results. The encountered conductivity anomalies are understood as linked to basin sediments, asthenospheric upwelling, large differences in lithospheric age, and—this concerns most of them, which all concentrate in the middle crust—tectonic boundaries that developed during all mountain building phases that have taken place on the continent.

  7. Multimodality imaging of vascular anomalies.

    PubMed

    Restrepo, Ricardo

    2013-03-01

    Vascular malformations and hemangiomas are common in children but remain a source of confusion during diagnosis, in part because of the lack of a uniform terminology. With the existing treatments for hemangiomas and vascular malformations, it is important to make the correct diagnosis initially to prevent adverse physical and emotional sequelae in not only the child but also the family. The diagnosis of vascular malformations is made primarily by the clinician and based on the physical exam. Imaging is carried out using predominantly ultrasound (US) and magnetic resonance imaging (MRI), which are complementary modalities. In most cases of vascular anomalies, US is the first line of imaging as it is readily available, less expensive, lacks ionizing radiation and does not require sedation. MRI is also of great help for further characterizing the lesions. Conventional arteriography is reserved for cases that require therapeutic intervention, more commonly for arteriovenous malformations. Radiographs usually play no role in diagnosing vascular anomalies in children. In this article, the author describes the terminology and types of hemangiomas and vascular malformations and their clinical, histological features, as well as the imaging approach and appearance.

  8. Correlation of Tectonic Provinces of South America and the Caribbean Region with MAGSAT Anomalies

    NASA Technical Reports Server (NTRS)

    Lidiak, E. G.; Hinze, W. J.; Keller, G. R. (Principal Investigator); Yuan, D. W.; Longacre, M. B.

    1984-01-01

    Intensities of MAGSAT scalar magnetic anomaly data correlate with the main tectonic provinces of South America and the Caribbean region. Magnetic anomalies of the continents generally have higher amplitudes than oceanic anomalies. This is particularly evident in Central America and in the shield areas of South America. The Caribbean Sea and Gulf of Mexico are underlain by prominent magnetic minima. Within these oceanic areas, linear magnetic highs correlate with topographic ridges which separate the Gulf of Mexico, the Colombian Basin, and the Venezuelan Basin. The boundaries of the Caribbean plate occur along magnetic gradients which are particularly sharp along the northern and western margins of the plate, but gradational along the southern margin where they merge with the Andean Cordillera. The anomalies along the western margin of the South American plate are also distinct and appear to be separate from those of the adjacent ocean basin. Eastern South America is characterized by magnetic anomalies which commonly extend into the Atlantic Ocean.

  9. Equivalent magnetization over the World Ocean

    NASA Astrophysics Data System (ADS)

    Dyment, J.; Hamoudi, M.; Choi, Y.; Thebault, E.; Quesnel, Y.; Roest, W. R.; Lesur, V.

    2012-12-01

    , the Mid-Atlantic Ridge displays a more uniform signature, although off-axis variations seem associated to the Tristan and St Helena hotspots. In the Indian Ocean, a strong equivalent magnetization characterizes areas of hotspot-ridge interaction such as the Gulf of Aden, the Central Indian Ridge near Rodrigues Island, the Southwest Indian Ridge near Marion Island, and the Southeast Indian Ridge near St Paul and Amsterdam Islands. A weaker one is observed in colder area, at the Australian-Antarctic Discordance and around the Rodrigues Triple Junction. The Pacific Ocean is characterized by a generally stronger equivalent magnetization, both near ridges and in abyssal plains. Time variations, i.e. along seafloor spreading flowlines, are apparent across the Mid-Atlantic and Pacific-Antarctic ridges, with highs near the ridge axis (younger than 10 Ma) and between ~83 and 60 Ma, just after the Cretaceous Normal Superchron and lows between ~60 and 10 Ma. The Mesozoic basins of the Pacific and Atlantic oceans show a weaker equivalent magnetization before ~155 Ma and a stronger one after. Basins covered by thick sediments such as the Bengal Bay, Great Australian Bight, Nova Scotia Basin, and Western Somali Basin show a very weak equivalent magnetization, reflecting both a deeper basement and a possible thermal demagnetization. Some of these variations coincide with satellite magnetic anomalies.

  10. Flame spread across liquids

    NASA Technical Reports Server (NTRS)

    Ross, Howard D.; Miller, Fletcher; Schiller, David; Sirignano, William

    1995-01-01

    Recent reviews of our understanding of flame spread across liquids show that there are many unresolved issues regarding the phenomenology and causal mechanisms affecting ignition susceptibility, flame spread characteristics, and flame spread rates. One area of discrepancy is the effect of buoyancy in both the uniform and pulsating spread regimes. The approach we have taken to resolving the importance of buoyancy for these flames is: (1) normal gravity (1g) and microgravity (micro g) experiments; and (2) numerical modeling at different gravitational levels. Of special interest to this work, as discussed at the previous workshop, is the determination of whether, and under what conditions, pulsating spread occurs in micro g. Microgravity offers a unique ability to modify and control the gas-phase flow pattern by utilizing a forced air flow over the pool surface.

  11. The spreading of disorder.

    PubMed

    Keizer, Kees; Lindenberg, Siegwart; Steg, Linda

    2008-12-12

    Imagine that the neighborhood you are living in is covered with graffiti, litter, and unreturned shopping carts. Would this reality cause you to litter more, trespass, or even steal? A thesis known as the broken windows theory suggests that signs of disorderly and petty criminal behavior trigger more disorderly and petty criminal behavior, thus causing the behavior to spread. This may cause neighborhoods to decay and the quality of life of its inhabitants to deteriorate. For a city government, this may be a vital policy issue. But does disorder really spread in neighborhoods? So far there has not been strong empirical support, and it is not clear what constitutes disorder and what may make it spread. We generated hypotheses about the spread of disorder and tested them in six field experiments. We found that, when people observe that others violated a certain social norm or legitimate rule, they are more likely to violate other norms or rules, which causes disorder to spread.

  12. New Constraints on the Age of the Opening of the South Atlantic Basin As Revealed By Recently Acquired Magnetic, Gravity and Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Hall, S. A.; Bird, D. E.; Danque, H. A.; Grant, J. V.; McLean, D. J.; Towle, P. J.

    2014-12-01

    Detailed, high quality, marine total field magnetic data has been recently acquired over parts of the South Atlantic ocean off the southwestern margin of South Africa. These data display a pattern of well-defined, NW-SE striking linear magnetic anomalies along the margin that can be traced with confidence over distances > 150 km. The anomalies are interpreted to be M-series seafloor spreading anomalies M9 to M11, which are consistent with the initiation of seafloor spreading around 135 Ma (Late Valanginian). Corresponding M-series anomalies M9 and M10 have previously been reported for the conjugate South American margin offshore Argentina, however the presence of the M11 series SE of the Cape Lineament suggests an earlier opening of the southern South Atlantic basin than previously recognized. Breaks in the continuity of the linear anomaly pattern, observed in map view, have generally NE-SW trends and are considered sites of possible fracture zones. One such discontinuity, which we have termed the "Cape Lineament" (CL), marks a significant change in crustal character and Cretaceous depositional history, as revealed by gravity data and seismic reflection data respectively. Crust NW of CL appears to be characterized by greater thicknesses and the presence of seaward dipping reflectors (SDRs), whereas crust SE of CL has more "normal" oceanic thicknesses and SDRs that are either absent or more limited in areal extent. Although linear magnetic anomalies are observed both NW and SE of CL, anomalies to the SE display a better correlation with those predicted by our seafloor spreading model.

  13. Euro-African MAGSAT anomaly-tectonic observations

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Olivier, R.; Vonfrese, R. R. B.

    1985-01-01

    Preliminary satellite (MAGSAT) scalar magnetic anomaly data are compiled and differentially reduced to radial polarization by equivalent point source inversion for comparison with tectonic data of Africa, Europe and adjacent marine areas. A number of associations are evident to constrain analyses of the tectonic features and history of the region. The Precambrian shields of Africa and Europe exhibit varied magnetic signatures. All shields are not magnetic highs and, in fact, the Baltic shield is a marked minimum. The reduced-to-the-pole magnetic map shows a marked tendency for northeasterly striking anomalies in the eastern Atlantic and adjacent Africa, which is coincident to the track of several hot spots for the past 100 million years. However, there is little consistency in the sign of the magnetic anomalies and the track of the hot spots. Comparison of the radially polarized anomalies of Africa and Europe with other reduced-to-the-pole magnetic satellite anomaly maps of the Western Hemisphere support the reconstruction of the continents prior to the origin of the present-day Atlantic Ocean in the Mesozoic Era.

  14. Euro-african MAGSAT Anomaly-tectonic Observations

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Vonfrese, R. R. B. (Principal Inv