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Sample records for bouguer gravity anomalies

  1. Optimization schemes for the inversion of Bouguer gravity anomalies

    NASA Astrophysics Data System (ADS)

    Zamora, Azucena

    associated with structural changes [16]; therefore, it complements those geophysical methods with the same depth resolution that sample a different physical property (e.g. electromagnetic surveys sampling electric conductivity) or even those with different depth resolution sampling an alternative physical property (e.g. large scale seismic reflection surveys imaging the crust and top upper mantle using seismic velocity fields). In order to improve the resolution of Bouguer gravity anomalies, and reduce their ambiguity and uncertainty for the modeling of the shallow crust, we propose the implementation of primal-dual interior point methods for the optimization of density structure models through the introduction of physical constraints for transitional areas obtained from previously acquired geophysical data sets. This dissertation presents in Chapter 2 an initial forward model implementation for the calculation of Bouguer gravity anomalies in the Porphyry Copper-Molybdenum (Cu-Mo) Copper Flat Mine region located in Sierra County, New Mexico. In Chapter 3, we present a constrained optimization framework (using interior-point methods) for the inversion of 2-D models of Earth structures delineating density contrasts of anomalous bodies in uniform regions and/or boundaries between layers in layered environments. We implement the proposed algorithm using three different synthetic gravitational data sets with varying complexity. Specifically, we improve the 2-dimensional density structure models by getting rid of unacceptable solutions (geologically unfeasible models or those not satisfying the required constraints) given the reduction of the solution space. Chapter 4 shows the results from the implementation of our algorithm for the inversion of gravitational data obtained from the area surrounding the Porphyry Cu-Mo Cooper Flat Mine in Sierra County, NM. Information obtained from previous induced polarization surveys and core samples served as physical constraints for the

  2. World Gravity Map: a set of global complete spherical Bouguer and isostatic anomaly maps and grids

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Balmino, G.; Briais, A.; Kuhn, M.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

    2012-04-01

    We present here a set of digital maps of the Earth's gravity anomalies (surface free air, Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW) with support of UNESCO and other institutions. The Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, 2011). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy-Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial

  3. A simple Bouguer gravity anomaly map of southwestern Saudi Arabia and an initial interpretation

    USGS Publications Warehouse

    Gettings, M.E.

    1983-01-01

    Approximately 2,200 gravity stations on a 10-km2 grid were used to construct a simple Bouguer gravity anomaly map at 1:2,000,000 scale along a 150-km-wide by 850-km-long strip of the Arabian Peninsula from Sanam, southwest of Ar Riyad, through the Farasan Islands and including offshore islands, the coastal plain, and the Hijaz-Asir escarpment from Jiddah to the Yemen border. On the Precambrian Arabian Shield, local positive gravity anomalies are associated with greenstone belts, gneiss domes, and the Najd fault zones. Local negative gravity anomalies correlate with granitic plutonic rocks. A steep gravity gradient of as much as 4 mgal-km-1 marks the continental margin on the coastal plain near the southwestern end of the strip. Bouguer gravity anomaly values range from -10 to +40 mgal southwest of this gradient and from -170 to -100 mgal in a 300-km-wide gravity minimum northeast of the gradient. Farther northeast, the minimum is terminated by a regional gradient of about 0.1 mgal-km-1 that increases toward the Arabian Gulf. The regional gravity anomaly pattern has been modeled by using seismic refraction and Raleigh wave studies, heat-flow measurements, and isostatic considerations as constraints. The model is consistent with the hypothesis of upwelling of hot mantle material beneath the Red Sea and lateral mantle flow beneath the Arabian plate. The model yields best-fitting average crustal densities of 2.80 g-cm-3 (0-20 km depth) and 3.00 g-cm-3 (20-40 km depth) southwest of the Nabitah suture zone and 2.74 g-cm-3 (0-20 km depth) and 2.94 g-cm-3 (20-40 km depth) northeast of the suture zone. The gravity model requires that the crust be about 20 km thick at the continental margin and that the lower crust between the margin and Bishah (lat 20? N., long 42.5? E.) be somewhat denser than the lower crust to the northeast. Detailed correlations between 1:250,000- and 1:500,000-scale geologic maps and the gravity anomaly map suggest that the greenstone belts associated

  4. Principal facts and a discussion of terrain correction methods for the complete Bouguer gravity anomaly map of the Cascade Mountains, Washington

    SciTech Connect

    Danes, Z.F.; Phillips, W.M.

    1983-02-01

    Since 1974, the Division of Geology and Earth Resources, in conjunction with the US Department of Energy, has supported gravity studies in the Cascade Mountains of Washington State. Results of the Cascade gravity project are summarized graphically as a complete Bouguer gravity anomaly map of the Cascade Mountains, Washington (Danes and Phillips, 1983). This report provides supplementary data and documentation for the complete Bouguer gravity anomaly map. Presented are principal gravity facts, simple Bouguer and Free-air gravity anomalies, computational methods, error analysis and a discussion of terrain corrections.

  5. Bouguer gravity anomaly and isostatic residual gravity maps of the Tonopah 1 degree by 2 degrees Quadrangle, central Nevada

    USGS Publications Warehouse

    Plouff, Donald

    1992-01-01

    A residual isostatic gravity map (sheet 2) was prepared so that the regional effect of isostatic compensation present on the Bouguer gravity anomaly map (sheet 1) would be minimized. Isostatic corrections based on the Airy-Heiskanen system (Heiskanen and Vening Meinesz, 1958, p. 135-137) were estimated by using 3-minute topographic digitization and applying the method of Jachens and Roberts (1981). Parameters selected for the isostatic model were 25 km for the normal crustal thickness at sea level, 2.67 g/cm3 for the density of the crust, and 0.4 g/cm3 for the contrast in density between the crust and the upper mantle. These parameters were selected so that the isostatic residual gravity map would be consistent with isostatic residual gravity maps of the adjacent Walker Lake quadrangle (Plouff, 1987) and the state of Nevada (Saltus, 1988c).

  6. Data reduction and tying in regional gravity surveys—results from a new gravity base station network and the Bouguer gravity anomaly map for northeastern Mexico

    NASA Astrophysics Data System (ADS)

    Hurtado-Cardador, Manuel; Urrutia-Fucugauchi, Jaime

    2006-12-01

    Since 1947 Petroleos Mexicanos (Pemex) has conducted oil exploration projects using potential field methods. Geophysical exploration companies under contracts with Pemex carried out gravity anomaly surveys that were referred to different floating data. Each survey comprises observations of gravity stations along highways, roads and trails at intervals of about 500 m. At present, 265 separate gravimeter surveys that cover 60% of the Mexican territory (mainly in the oil producing regions of Mexico) are available. This gravity database represents the largest, highest spatial resolution information, and consequently has been used in the geophysical data compilations for the Mexico and North America gravity anomaly maps. Regional integration of gravimeter surveys generates gradients and spurious anomalies in the Bouguer anomaly maps at the boundaries of the connected surveys due to the different gravity base stations utilized. The main objective of this study is to refer all gravimeter surveys from Pemex to a single new first-order gravity base station network, in order to eliminate problems of gradients and spurious anomalies. A second objective is to establish a network of permanent gravity base stations (BGP), referred to a single base from the World Gravity System. Four regional loops of BGP covering eight States of Mexico were established to support the tie of local gravity base stations from each of the gravimeter surveys located in the vicinity of these loops. The third objective is to add the gravity constants, measured and calculated, for each of the 265 gravimeter surveys to their corresponding files in the Pemex and Instituto Mexicano del Petroleo database. The gravity base used as the common datum is the station SILAG 9135-49 (Latin American System of Gravity) located in the National Observatory of Tacubaya in Mexico City. We present the results of the installation of a new gravity base network in northeastern Mexico, reference of the 43 gravimeter surveys

  7. GTeC-A versatile MATLAB® tool for a detailed computation of the terrain correction and Bouguer gravity anomalies

    NASA Astrophysics Data System (ADS)

    Cella, Federico

    2015-11-01

    Gravity Terrain Correction (GTeC) is a versatile MATLAB® code for terrain correction aimed to this purpose and capable of going beyond the limits of other public domain codes targeted to this aim. It runs with input gravity data (absolute measurements or free air anomalies) at the land/sea surface and with one or more DTMs (indifferently gridded or scattered) at different detail levels. Each of them can be used to calculate the gravity contribution of a concentric terrain zone around the point station with increasing resolution toward the center. The user can choose between two alternative algorithms for terrain modeling. The simplest one considers each grid point as the flat top of a squared prism. For areas closer to the point station a second algorithm can be chosen to better approximate the relief, with respect to others formulas, by means of a tessellation based network formed by triangular prisms. A more precise terrain correction is therefore achieved, especially in presence of high topographic gradients or just outside the sea/land boundaries. In the last case a suitable algorithm was expressly devised to fit the tessellation based network to the irregular trend of the coastline. GTeC calculates also free air anomalies and both plate and curvature corrections, providing also a complete graphic output including topography, free air anomalies, plate correction, total terrain correction, Bouguer anomalies and the terrain effect due to each computational zone. GTeC speeds up CPU times taking advantage from the parallel computing functions and from the vectorization code, both exploited in MATLAB®. Two code versions of GTeC (for normal or parallel computation), executable under MATLAB environment (pcode), are fully available as public domain software. The results of a synthetic case, of a real case at the regional scale and of a microgravity survey carried out at a short scale, are here presented.

  8. On the Optimization of the Inverse Problem for Bouguer Gravity Anomalies

    NASA Astrophysics Data System (ADS)

    Zamora, A.; Velasco, A. A.; Gutierrez, A. E.

    2013-12-01

    Inverse modeling of gravity data presents a very ill-posed mathematical problem, given that solutions are non-unique and small changes in parameters (position and density contrast of an anomalous body) can highly impact the resulting Earth's model. Although implementing 2- and 3-Dimensional gravitational inverse problems can determine the structural composition of the Earth, traditional inverse modeling approaches can be very unstable. A model of the shallow substructure is based on the density contrasts of anomalous bodies -with different densities with respect to a uniform region- or the boundaries between layers in a layered environment. We implement an interior-point method constrained optimization technique to improve the 2-D model of the Earth's structure through the use of known density constraints for transitional areas obtained from previous geological observations (e.g. core samples, seismic surveys, etc.). The proposed technique is applied to both synthetic data and gravitational data previously obtained from the Rio Grande Rift and the Cooper Flat Mine region located in Sierra County, New Mexico. We find improvements on the models obtained from this optimization scheme given that getting rid of geologically unacceptable models that would otherwise meet the required geophysical properties reduces the solution space.

  9. Worldwide complete spherical Bouguer and isostatic anomaly maps

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Balmino, G.; Briais, A.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

    2011-12-01

    We present here a set of digital maps of the Earth's gravity anomalies (surface "free air", Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW). The free air and Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, submitted). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial Intelligence Agency (NGA) (Pavlis

  10. Aeromagnetic and complete Bouguer gravity anomaly maps of the Hunter-Fryingpan Wilderness area, Pitkin County, Colorado

    USGS Publications Warehouse

    Campbell, D.L.

    1981-01-01

    Behrendt and others (1968) pointed out the close correlation between a belt of extreme gravity lows (Behrendt and Bajwa, 1974) and a zone of precious and base mineral deposits (Tweto and Simms, 1963, fig. 1).  Tweto and Case (1972) showed that this belt of gravity lows probably reflects a series of Laramide and post-Laramide intrusions of relatively low density which may have influenced the hydrothermal systems responsible for much of the mineralization in the Colorado Mineral Belt.

  11. Nature of the Levantine (eastern Mediterranean) crust from multiple-source Werner deconvolution of Bouguer gravity anomalies

    NASA Astrophysics Data System (ADS)

    Khair, Kamal; Tsokas, Gregory N.

    1999-11-01

    The nature of the Levantine (eastern Mediterranean) crust has been the subject of controversy for many years, revolving around two hypotheses: the continental crust hypothesis and the oceanic crust hypothesis. The proponents of the first hypothesis suggest that the Levantine (eastern Mediterranean) basin is characterized by a thick sedimentary succession overlying thinned crust of continental origin, through which a number of aborted Mesozoic rifts were etched. However, multiple-source Werner deconvolution (MSWD) estimates and other geophysical data, integrated with earlier geological and geophysical results, provide further support to the second hypothesis (oceanic crust) and lead to the following conclusions: (1) The depth to Moho ranges from about 20 km to about 28 km below sea level, with an average crustal thickness of about 22 km. (2) The large thickness (about 10 km) of Phanerozoic section leaves only about 12 km of thickness for the igneous/metamorphic (basement) complex. (3) The northern boundary of the Levantine (easternmost Mediterranean) lithosphere is delineated by an arcuate belt of seismic activities along the southern margin of Cyprus. (4) The formation of the Phoenician and Latakia basins and the Iskenderun Bay is probably controlled by the counterclockwise rotation of the lithospheric slices southeast of Cyprus. (5) The apparent absence of magnetic anomaly lineations (reversals) is due probably to the thick Phanerozoic cover, and/or the formation of the oceanic crust during a long magnetic chron.

  12. An updated Bouguer anomaly map of south-central West Africa

    USGS Publications Warehouse

    Hastings, David A.

    1983-01-01

    A new Bouguer gravity anomaly map compiled for western Africa adds data for Ghana, Guinea, and Liberia.The new data add detail to a key part of the Eburnean shield and assist in the development of a model of rifting at the time of the Eburnean orogeny, 2000 million years ago. This model includes a framework for the deposition of the region's mineral deposits. The model and existing field data can be used to guide future minerals exploration in the region.

  13. Seismic b-Values, Bouguer Gravity and Heat Flow Data Beneath Eastern Anatolia, Turkey: Tectonic Implications

    NASA Astrophysics Data System (ADS)

    Maden, Nafiz; Öztürk, Serkan

    2015-07-01

    In this paper, we analyze the relationships between the seismic b-values, Bouguer gravity and heat flow data in the Eastern Anatolia region of Turkey. For this purpose, spatial distributions of b-value, Bouguer gravity and heat flow have been presented for different depths and locations. In distinction to previous studies which have used only two parameters (gravity and seismic b-value or heat flow and seismic b-value), we have combined seismic b-values, Bouguer gravity and heat flow data to determine the new results on the active tectonics of the Eastern Anatolia region. Our analysis shows that there are significant and robust correlations amidst the heat flow data, Bouguer gravity anomaly and seismic b-values. The crustal structure is thick in areas where the large negative gravity anomalies and low b-values are observed. On the contrary, the regions with positive gravity anomalies and high b-values are likely to be associated with magma chambers or crustal low-velocity zones. We also provide some evidence suggesting that high b-values and high heat flow values can be related to the magmatic activities beneath the volcanic chain in the Eastern Pontide orogenic belt. Consequently, we have reached some conclusions for the Eastern Anatolia region: (1) The Moho to surface is rather thick and earthquakes are relatively smaller beneath the volcanic chain where the high heat flow values are observed, (2) a southward subduction model could have existed for the development of the Pontides during the late Mesozoic-Cenozoic era, (3) hot and unstable mantle lid zones or a lithosphere deprived of mantle under the study region is much more plausible, (4) a southward movement of the subduction plate and a northward extension of the Black Sea increase the state of stress along the trench axis and decrease the b-value, and (5) these movements may load the stress energy to the fault zones, thereby causing the catastrophic earthquakes in the Eastern Anatolia region.

  14. Gravity Anomalies of the Lunar Orientale Basin and the Mercurian Caloris Basin

    NASA Astrophysics Data System (ADS)

    Blair, D. M.; Johnson, B. C.; Freed, A. M.; Melosh, H. J.

    2013-08-01

    We model the formation and evolution of the lunar Orientale and mercurian Caloris basin gravity anomalies using a combination of hydrocode and finite-element methods, constrained by free-air and Bouguer gravity anomalies and basin topography.

  15. Spherical harmonic modelling to ultra-high degree of Bouguer and isostatic anomalies

    NASA Astrophysics Data System (ADS)

    Balmino, G.; Vales, N.; Bonvalot, S.; Briais, A.

    2012-07-01

    The availability of high-resolution global digital elevation data sets has raised a growing interest in the feasibility of obtaining their spherical harmonic representation at matching resolution, and from there in the modelling of induced gravity perturbations. We have therefore estimated spherical Bouguer and Airy isostatic anomalies whose spherical harmonic models are derived from the Earth's topography harmonic expansion. These spherical anomalies differ from the classical planar ones and may be used in the context of new applications. We succeeded in meeting a number of challenges to build spherical harmonic models with no theoretical limitation on the resolution. A specific algorithm was developed to enable the computation of associated Legendre functions to any degree and order. It was successfully tested up to degree 32,400. All analyses and syntheses were performed, in 64 bits arithmetic and with semi-empirical control of the significant terms to prevent from calculus underflows and overflows, according to IEEE limitations, also in preserving the speed of a specific regular grid processing scheme. Finally, the continuation from the reference ellipsoid's surface to the Earth's surface was performed by high-order Taylor expansion with all grids of required partial derivatives being computed in parallel. The main application was the production of a 1' × 1' equiangular global Bouguer anomaly grid which was computed by spherical harmonic analysis of the Earth's topography-bathymetry ETOPO1 data set up to degree and order 10,800, taking into account the precise boundaries and densities of major lakes and inner seas, with their own altitude, polar caps with bedrock information, and land areas below sea level. The harmonic coefficients for each entity were derived by analyzing the corresponding ETOPO1 part, and free surface data when required, at one arc minute resolution. The following approximations were made: the land, ocean and ice cap gravity spherical

  16. Fractal Characteristics of Geomorphology Units as Bouguer Anomaly Manifestations in Bumiayu, Central Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Agus Nur, Andi; Syafri, Ildrem; Muslim, Dicky; Hirnawan, Febri; Raditya, Pradnya P.; Sulastri, Murni; Abdulah, Fikri

    2016-01-01

    Bumiayu in Central Java, Indonesia, has a typical landform characteristics. Differences of topography on each geomorphological unit indicated by the value of fractal dimension. This research provides important information on the influence of geomorphology conditions and subsurface geological phenomenon of research area based on fractal application. This research methodology relies on laboratory analysis and field observation. Landform is a characteristics of Bouguer anomaly contour manifestation. It is indicated by occurences of significant correlation between the Bouguer anomaly countour and geological cross section as well topography contour slope and Bouguer anomaly contour slope. Based on spatial analysis, morphology of research area is dominated by very high steep hills (more than 60%). Result of Bouguer anomaly countour analysis also shows that research area dominated by very high steep hills (more than 55%). Statistical analysis between the fractal value of lineament in Digital Elevation Model and fractal value of lineament in Bouguer anomaly countour as well the fractal value of topography countour and fractal value of Bouguer anomaly countour shows that the relationship was not significant. Further, the entire result of this verified research shows clearly that geomorphology conditions represents subsurface geological phenomenon.

  17. Imaging subsurface density distribution beneath Montserrat (West Indies) from Bouguer gravity data

    NASA Astrophysics Data System (ADS)

    Hautmann, S.; Camacho, A. G.; Gottsmann, J.; Odbert, H. M.; Syers, T.

    2012-12-01

    High resolution static gravity data allow to resolve for spatial inhomogeneities in the Earth's gravity field by providing information on the density distribution in the shallow subsurface. Images of the subsurface density distribution and identification of structural discontinuities in the ground are of particular interest in active volcanic regions, as they bear implications for fluid migration, edifice stability and the subsurface transmission of volcanically induced stresses. Although the persistently active Soufrière Hills Volcano (SHV; Montserrat, West Indies) is currently one of the most extensively studied actively erupting stratovolcanos, a local Bouguer anomaly map of the volcano and the island of Montserrat is missing to date. In June/July 2012 we conducted a static gravity survey on Montserrat. Using a Scintrex CG-5 Autograv a total of 160 new gravity data were collected on the entire island. Site positions and elevations were obtained via a TOPCON Hiperpro dual frequency GNSS receiver/antenna. Our Bouguer gravity network provides a dense coverage (distance of 200 m between adjacent sites) of the accessible regions of the older volcanic complexes Silver Hills and Centre Hills, while (due to operator's safety) the network coverage around the active SHV is more sparse with about 1 km distance between adjacent sites. The recorded gravity data were corrected for Solid Earth Tides and ocean loading and reduced for the effect of benchmark elevation (free-air effect) and latitude. The correction for topographic effects was done via an automated algorithm based on a digital elevation model and bathymetric data. In order to model our data we performed a non-linear inversion using the inversion package GROWTH 2.0. The inversion is based on a 3-D aggregation of M parallelepiped cells, which are filled, in a growth process, by means of prescribed positive and/or negative density contrasts. This methodology provides, via an automatic approach, a free 3-D geometry

  18. Processing the Bouguer anomaly map of Biga and the surrounding area by the cellular neural network: application to the southwestern Marmara region

    NASA Astrophysics Data System (ADS)

    Aydogan, D.

    2007-04-01

    An image processing technique called the cellular neural network (CNN) approach is used in this study to locate geological features giving rise to gravity anomalies such as faults or the boundary of two geologic zones. CNN is a stochastic image processing technique based on template optimization using the neighborhood relationships of cells. These cells can be characterized by a functional block diagram that is typical of neural network theory. The functionality of CNN is described in its entirety by a number of small matrices (A, B and I) called the cloning template. CNN can also be considered to be a nonlinear convolution of these matrices. This template describes the strength of the nearest neighbor interconnections in the network. The recurrent perceptron learning algorithm (RPLA) is used in optimization of cloning template. The CNN and standard Canny algorithms were first tested on two sets of synthetic gravity data with the aim of checking the reliability of the proposed approach. The CNN method was compared with classical derivative techniques by applying the cross-correlation method (CC) to the same anomaly map as this latter approach can detect some features that are difficult to identify on the Bouguer anomaly maps. This approach was then applied to the Bouguer anomaly map of Biga and its surrounding area, in Turkey. Structural features in the area between Bandirma, Biga, Yenice and Gonen in the southwest Marmara region are investigated by applying the CNN and CC to the Bouguer anomaly map. Faults identified by these algorithms are generally in accordance with previously mapped surface faults. These examples show that the geologic boundaries can be detected from Bouguer anomaly maps using the cloning template approach. A visual evaluation of the outputs of the CNN and CC approaches is carried out, and the results are compared with each other. This approach provides quantitative solutions based on just a few assumptions, which makes the method more

  19. Imprint of Southern Red Sea Major Tectonic Zone In A New Bouguer Anomaly Map of Southern Yemen Margin

    NASA Astrophysics Data System (ADS)

    Blecha, V.

    A new Bouguer anomaly map of western part of southern Yemen margin has been compiled. Densities of rock samples from main geological units (Precambrian base- ment, Mesozoic sediments, Tertiary volcanites) have been measured and used for grav- ity modeling. Regional gravity map indicates decrease of thickness of continental crust from volcanites of the Yemen Trap Series towards the coast of the Gulf of Aden. Most remarkable feature in the map of residual anomalies is a positive anomaly over the Dhala graben. The Dhala graben is a prominent geological structure in the area of study trending parallel to the Red Sea axis. Gravity modeling on a profile across the Dhala graben presumes intrusive plutonic rocks beneath the graben. There are two other areas in the southwestern tip of Arabia, which have essentially the same struc- tural position as the Dhala graben: the Jabal Tirf volcanic rift zone in the southern Saudi Arabia and Jabal Hufash extensional zone in northern Yemen. All three areas extend along the line trending parallel to the Red Sea axis with length of about 500 km. The line coincides with the axis of Afar (Danakil) depression after Arabia is shifted and rotated back to Africa. These facts imply conclusion that the Oligocene - Early Miocene magmatic activity on the Jabal Tirf - Dhala lineament is related to the same original deep tectonic zone, forming present-day Afar depression and still active.

  20. Gravity anomaly and crustal density structure in Jilantai rift zone and its adjacent region

    NASA Astrophysics Data System (ADS)

    Wu, Guiju; Shen, Chongyang; Tan, Hongbo; Yang, Guangliang

    2016-08-01

    This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly ( G h ) and the crustal density structure reveal that (1) the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault (F4) and Helandonglu fault (F6), which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; (2) the main active faults correspond to the G h contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault ( F1) or the southeast boundary of Alxa block is in accord with the western change belt of G h , a belt about 10 km wide that extends to about 30 km; (3) Yinchuan-Pingluo fault ( F8) is the seismogenic structure of the Pingluo M earthquake, and its focal depth is about 15 km; (4) the Moho depth trend and Bouguer gravity anomaly variation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.

  1. Gravity anomaly and crustal density structure in Jilantai rift zone and its adjacent region

    NASA Astrophysics Data System (ADS)

    Wu, Guiju; Shen, Chongyang; Tan, Hongbo; Yang, Guangliang

    2016-08-01

    This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly (G h ) and the crustal density structure reveal that (1) the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault (F4) and Helandonglu fault (F6), which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; (2) the main active faults correspond to the G h contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault (F1) or the southeast boundary of Alxa block is in accord with the western change belt of G h , a belt about 10 km wide that extends to about 30 km; (3) Yinchuan-Pingluo fault (F8) is the seismogenic structure of the Pingluo M earthquake, and its focal depth is about 15 km; (4) the Moho depth trend and Bouguer gravity anomaly variation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.

  2. Bouguer gravity trends and crustal structure of the Palmyride Mountain belt and surrounding northern Arabian platform in Syria

    SciTech Connect

    Best, J.A.; Barazangi, M. ); Al-Saad, D.; Sawaf, T.; Gebran, A. )

    1990-12-01

    This study examines the crustal structure of the Palmyrides and the northern Arabian platform in Syria by two- and three-dimensional modeling of the Bouguer gravity anomalies. Results of the gravity modeling indicate that (1) western Syria is composed of at least two different crustal blocks, (2) the southern crustal block is penetrated by a series of crustal-scale, high-density intrusive complexes, and (3) short-wavelength gravity anomalies in the southwest part of the mountain belt are clearly related to basement structure. The crustal thickness in Syria, as modeled on the gravity profiles, is approximately 40{plus minus}4 km, which is similar to crustal thicknesses interpreted from refraction data in Jordan and Saudi Arabia. The different crustal blocks and large-scale mafic intrusions are best explained, though not uniquely, by Proterozoic convergence and suturing and early Paleozoic rifting, as interpreted in the exposed rocks of the Arabian shield. These two processes, combined with documented Mesozoic rifting and Cenozoic transpression, compose the crustal evolution of the northern Arabian platform beneath Syria.

  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. Gravity anomaly, lithospheric structure and seismicity of Western Himalayan Syntaxis

    NASA Astrophysics Data System (ADS)

    Tiwari, V. M.; Rajasekhar, R. P.; Mishra, D. C.

    2009-07-01

    A compiled gravity anomaly map of the Western Himalayan Syntaxis is analysed to understand the tectonics of the region around the epicentre of Kashmir earthquake of October 8, 2005 (Mw = 7.6). Isostatic gravity anomalies and effective elastic thickness (EET) of lithosphere are assessed from coherence analysis between Bouguer anomaly and topography. The isostatic residual gravity high and gravity low correspond to the two main seismic zones in this region, viz. Indus-Kohistan Seismic Zone (IKSZ) and Hindu Kush Seismic Zones (HKSZ), respectively, suggesting a connection between siesmicity and gravity anomalies. The gravity high originates from the high-density thrusted rocks along the syntaxial bend of the Main Boundary Thrust and coincides with the region of the crustal thrust earthquakes, including the Kashmir earthquake of 2005. The gravity low of HKSZ coincides with the region of intermediate-deep-focus earthquakes, where crustal rocks are underthrusting with a higher speed to create low density cold mantle. Comparable EET (˜55 km) to the focal depth of crustal earthquakes suggests that whole crust is seismogenic and brittle. An integrated lithospheric model along a profile provides the crustal structure of the boundary zones with crustal thickness of about 60 km under the Karakoram-Pamir regions and suggests continental subduction from either sides (Indian and Eurasian) leading to a complex compressional environment for large earthquakes.

  5. Sedimentary cover in the South Western Desert of Egypt as deduced from Bouguer gravity and drill-hole data

    NASA Astrophysics Data System (ADS)

    Senosy, M. M.; Youssef, M. M.; Abdel Zaher, M.

    2013-06-01

    The Western Desert, Egypt includes the major groundwater aquifer in the country. It is apart from the Major Sahara Nubian Aquifer which is present in Sudan, Chad, Egypt and Libya. Thickness of this aquifer is changed laterally from south to north and also from west to east. The changes may structurally or litheologicalley control. The present study is focused on using of Bouguer gravity anomaly mapped at a scale of 1:500,000 and the lithological logs of about 120 deep wells used to determine the thickness of the sedimentary sequence containing the main Nubian sandstone water aquifer in important area of Egypt. The area is located in the southern part of the Western Desert bounded by the latitudes 22°00'-26°30'N, and longitudes 28°30'-33°00'E. The predominant structures affecting the basement rocks and the sedimentary cover were traced and analyzed. The gravity stripping approach was applied to eliminate the gravity effects caused by sedimentary sequence and to separate density anomalies within the sedimentary fill from the influence of rocks at deeper levels in the crystalline crust. The study indicated that the surface of the basement rocks is highly rugged and mostly controlled by structures which have a direct effect on thickness variation of the sedimentary cover all over the area. Regionally the area is characterized by two major intracratonic basins (the Dahkla Basin and the Nile valley Basin) separated by a NE-SW trending swell of the Kharga uplift and bounded at the south by the Oweinat-Bir Safsaf-Aswan uplift. These major tectonic units are controlled by fault structures trending in N-S, E-W, NE-SW, NW-SE, which cut the basement rocks and extend upward in the sedimentary cover. The maximum thickness of sandstone formations is recorded at west Oweinat, west Kurkur, southwest of Aswan, Gramashin, Dakhla oasis and some localities west of Sohag and Qena towns. At these localities the thickness ranges between 600 and 900 m. As this formation is the main

  6. Constraints on the deep structure and dynamic processes beneath the Alps and adjacent regions from an analysis of gravity anomalies

    NASA Technical Reports Server (NTRS)

    Lyon-Caen, Helene; Molnar, Peter

    1989-01-01

    Gravity anomalies over the Alps and the Molasse Basin are examined, focusing on the relationship between the anomalies and the tectonic processes beneath the region. Bouguer gravity anomalies measured in France, Germany, Italy, and Switzerland are analyzed. No large isostatic anomalies are observed over the Alps and an elastic model is unable to account for gravity anomalies over the Molasse Basin. These results suggest that the dynamic processes that flexed the European plate down, forming the Molasse Basin and building the Alpine chain, have waned. It is proposed that the late Cenozoic uplift of the region may be due to a diminution or termination of downwelling of mantle material.

  7. Comparison of onshore Bouguer anomalies with GOCE Satellite Data in two sections of the Andes: at 29°S and at 39°S.

    NASA Astrophysics Data System (ADS)

    Alvarez, O.; Gimenez, M.; Braitenberg, C.; Martinez, P.

    2012-04-01

    In the present work we compare the Bouguer anomaly obtained from onshore measurements with the Bouguer anomaly obtained from satellite GOCE data along two well known sections of the Andes, at 29°18'S and at 38°45'S. The first gravimetric section, published by Martinez et al. (2006), describes a gravity and altimetric profile that extends over a distance surpassing 800km in Argentina, at 29°18'S. Using gravimetric inversion methods a crustal model was obtained which is in accordance with the main regional geologic structures. This model fits with a dominant collision mechanism that affected ancient blocks and is a two-layer crustal model with lateral density variations. The Chilenia, Cuyania, Famatina System, Pampia and River Plate cratons were detected. From the gravimetric signal we identify beyond doubt the suture zone between the Precordillera and the Famatina System Ranges, as well as the shear zone between the latter ranges and the Velasco Range. The maximum crustal thickness determined beneath the Andean Cordillera at this latitude is 69 km, whereas under the Famatina System and the Velasco Ranges the values obtained are, respectively, 56 km and 46.5 km. The second profile was published by Folguera et al., (2008). The western retroarc of the Southern Andes between 38° and 40°S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4-3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Normal crustal thickness at these latitudes is around 42km, whereas in this part of the retroarc the thickness is less than 32km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath South American plate, which is suggested by a westward shift and narrowing of the arc during the last 5Ma

  8. Gravity Anomalies and Depths of Sedimentary of Mekong Delta Area, South of Vietnam

    NASA Astrophysics Data System (ADS)

    Dang Van, L.

    2014-12-01

    The Mekong Delta is the region in the south of Vietnam with the total area of about 40.000 km2 and almost of this area is covered by water. Gravity measurement of this area was performed by Cuu Long Petroleum Agency (Vietnam) in 1980's and the Bouguer anomaly map of this area at the scale of 1/500.000 was established.We used the Bouguer anomaly map to study the geological structure of this area. This paper is divided into two parts. Firstly, we split the Mekong Delta area into two basins (CanTho-DongThap and TraCu basins) and two swells (Saigon and SocTrang swells) and delineated their boundaries by using the characteristics of Bouguer anomalies. Secondly, we used the second polynomial formula to separate the Bouger anomaly map into the regional and residual gravity anomaly maps. With this residual anomaly map, the 3D basemenf of Cenozoic-Mesozoic sediments of this area was computed by using the Parker-Oldenburg method.

  9. Upward Continuation Apply Newly to Process Gravity Anomaly Data in the East China Sea

    NASA Astrophysics Data System (ADS)

    Han, Bo; Zhang, Xunhua; Jiang, Jinyu

    2014-05-01

    The research area lies in the East China Sea and its adjacent area and the concrete is between 120-130 degree of east longitude and 20-30 degree of north latitude and it also lies between Eurasian Plate and Pacific Plate. The structures of the area transform differently and they are namely Uplifted Zone of Zhejiang-Fujian, East China Sea Shelf Basin, Okinawa Trough Back-arc Basin, Ryukyu Arc, Ryukyu trench and Philippine Sea from west to east. Bouguer gravity anomaly can reflect deep structure characters and it is help to judge deep structures. The bouguer gravity anomalies of the area change differently from west to east. The anomalies increase gradually from land to the middle of Okinawa trough and near land anomaly contour strike accords with coastline and the middle of Okinawa trough reflect the highest anomalies in this area. Gravity anomalies re-increase from Ryukyu fore-arc basin to trench and Ryukyu island arc appears the low anomalies. Philippine Sea appears high gravity anomalies background. Upward continuation method has been used to process original gravity anomaly as a common method and its destination is to weaken local anomaly and at last strengthen deep anomaly and it's important to deep structure study. Upward 5 km, 10 km and 20 km have been used to process data and the results been compared. However, the research area is very large and the deep structure is complex, it isn't suitable to use single height to upward continuation processing bouguer gravity anomaly. Then we propose multiple upward heights continuation to process gravity data respectively in different area. We use upward 20km to process data in the area from land to the slope and upward 10km from Okinawa trough to Ryukyu island arc and upward 5km from Ryukyu trench to Philippine Sea. At last we obtain multiple upward height result and the calculated result confirms that it is fit to use this method. Gravity anomalies contours become smoother than before and the deep structures become

  10. Interpretation of gravity anomalies in the northwest Adirondack lowlands, northern New York

    SciTech Connect

    Revetta, F.A.; O'Brian, B. . Geology Dept.)

    1993-03-01

    Twelve hundred gravity measurements were made in the Adirondack Highlands and northwest Adirondack Lowlands, New York between 44[degree]15 minutes and 44[degree]30 minutes N. Latitude and 75[degree]00 minutes W. Longitude. A Bouguer gravity map constructed from the gravity measurements includes the Carthage-Colton Mylonite Zone, a major structural boundary between the highlands and lowlands. The gravity map indicates the gravity contours trend parallel to the CCMZ along most of its length however in some areas the contours cross the boundary. No clear-cut relationships exists between the CCMZ and gravity contours. The Bouguer gravity map shows several prominent gravity anomalies which correlate with the geology seismicity and mineral deposits in the area. Gravity lows of 20 to 30 g.u. are centered over the Gouverneur, Hyde and Payne Lake Alaskite gneiss bodies. A gravity high of 20 g.u. occurs over the Pleasant Lake gabbro pluton. Gravity highs of 35 and 100 g.u. occur over the Sylvia Lake Zinc District and marble just north of the district. A gravity high at Russell, N.Y. coincides with a cluster of nine earthquake epicenters. Finally a steep gravity gradient separates high density rocks from lower density rocks along the Black Lake fault. Two-dimensional computer modeling of the geologic features is underway and quantitative models of the structures will be presented.

  11. 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

  12. 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.

  13. The decompensative gravity anomaly and deep structure of the region of the Rio Grande rift

    SciTech Connect

    Cordell, L. ); Zorin, Y.A. ); Keller, G.R. )

    1991-04-10

    An isostatic correction is commonly made to Bouguer anomaly gravity data to remove the gravity effect of isostatic compensation of topographic loads. In the USSR a decompensative correction has then been made to the isostatic gravity anomaly to remove the gravity effect of isostatic compensation of geologic loads as well. The authors employ here calculations in the wave number domain, leading to an efficient and exact solution. In a 1,200 {times} 1,200 km region centered on the Rio Grande rift the decompensative correction ranges from about {minus}35 to +25 mGal. The decompensative anomaly, highlights an arcuate gravity low and a system of gravity highs inferred to reflect prerift welts of mass concentration which have indirectly influenced the position of the rift and its segmentation and zones of accommodation. Under the assumptions made, if the decompensative anomaly is subtracted from the Bouguer anomaly, then the residual is the gravity anomaly field of deep structure, without gravity effects of shallow sources in the upper crust. Using available seismic data to (weakly) constrain the Moho surface, they invert the residual gravity field for topography of the base of the lithosphere. Lithosphere is found to be 200 km thick in the High Plains; 40-50 km in the eastern Great Basin; 75-100 km in the Colorado Plateau, and as thin as 40 km in the southern Rio Grande rift. In the area studied, the thickness of the lithospere is everwhere greater than that of the crust. The separation of gravity effects made possible by the decompensative correction shows how the rift is fundamentally controlled by thinning of the lithosphere, yet in detail is deflected by long-lived tectonic welts in the shallow, brittle crust.

  14. Bouguer Images of the North American Craton

    NASA Technical Reports Server (NTRS)

    Arvidson, R. E.; Bindschadler, D.; Bowring, S.; Eddy, M.; Guinness, E.; Leff, C.

    1985-01-01

    Processing of existing gravity and aeromagnetic data with modern methods is providing new insights into crustal and mantle structures for large parts of the United States and Canada. More than three-quarters of a million ground station readings of gravity are now available for this region. These data offer a wealth of information on crustal and mantle structures when reduced and displayed as Bouguer anomalies, where lateral variations are controlled by the size, shape and densities of underlying materials. Digital image processing techniques were used to generate Bouguer images that display more of the granularity inherent in the data as compared with existing contour maps. A dominant NW-SE linear trend of highs and lows can be seen extending from South Dakota, through Nebaska, and into Missouri. This trend is probably related to features created during an early and perhaps initial episode of crustal assembly by collisional processes. The younger granitic materials are probably a thin cover over an older crust.

  15. Analysis of gravity anomalies in Maio Island, Cape Verde.

    NASA Astrophysics Data System (ADS)

    Catalao, Joao; Represas, Patricia; Montesinos, Fuensanta; Antunes, Carlos; Madeira, José; Mata, João.

    2010-05-01

    was performed by a stabilized non-linear inversion methodology. A local average terrain density of 2200 kgm-3 was determined by applying a fractal analysis to the free-air anomaly. Topographic gravity effects were computed and the Bouguer anomaly for Maio Island was revealed. The global model was used to estimate the regional field. The resulting residual field shows a single positive anomaly, with a maximum value of 63 mGal. It has an elliptic shape, slightly off-centred with the island, and presenting a long axis trending N20W. A 3-D density contrast model was estimated from the Bouguer anomalies by means of a stabilized non-linear inversion methodology. This gravimetric inversion technique aims to determine the geometry of the sources of the observed gravity field, upon the adjustment of a three dimensional model of prismatic cells which adopt a priori values of density contrast (positive and negative). The density contrast assigned for each cell is determined using a combination of a process of accretion with a search of model changes to achieve a minimum residual between gravity data and model response. Results from the gravity inversion presents a good correlation with the geology of the island of Maio. The structural model obtained depicts a main high density body coinciding with the positive gravity anomaly which dominates the island. This body corresponds to the Basament Complex which is exposed in this area, where the plutonic bodies of essexite/pyroxenite crop out and thus reflect the highest density of those rocks relatively to mafic lava flows and accompanying sediments. The deepest sections of the model show the relation between this body and the earlier growth stage of the island.

  16. New Antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in Antarctica

    NASA Astrophysics Data System (ADS)

    Scheinert, M.; Ferraccioli, F.; Schwabe, J.; Bell, R.; Studinger, M.; Damaske, D.; Jokat, W.; Aleshkova, N.; Jordan, T.; Leitchenkov, G.; Blankenship, D. D.; Damiani, T. M.; Young, D.; Cochran, J. R.; Richter, T. D.

    2016-01-01

    Gravity surveying is challenging in Antarctica because of its hostile environment and inaccessibility. Nevertheless, many ground-based, airborne, and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s. We present the first modern Antarctic-wide gravity data compilation derived from 13 million data points covering an area of 10 million km2, which corresponds to 73% coverage of the continent. The remove-compute-restore technique was applied for gridding, which facilitated leveling of the different gravity data sets with respect to an Earth gravity model derived from satellite data alone. The resulting free-air and Bouguer gravity anomaly grids of 10 km resolution are publicly available. These grids will enable new high-resolution combined Earth gravity models to be derived and represent a major step forward toward solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica.

  17. Complete Bouguer gravity map of the Nevada Test Site and vicinity, Nevada

    SciTech Connect

    Healey, D.L.; Harris, R.N.; Ponce, D.A.; Oliver, H.W.

    1987-12-31

    About 15,000 gravity stations were used to create the gravity map. Gravity studies at the Nevada Test Site were undertaken to help locate geologically favorable areas for underground nuclear tests and to help characterize potential high-level nuclear waste storage sites. 48 refs. (TEM)

  18. Gravity anomalies along the East Scotia Ridge: Importance of magmatic and tectonic controls on crustal accretion

    NASA Astrophysics Data System (ADS)

    Nicholson, B. L.; Georgen, J. E.

    2010-12-01

    This study uses bathymetry and gravity data to infer upper mantle geodynamics in the eastern Scotia Sea region. The eastern Scotia Sea is comprised of an intermediate-rate back-arc spreading center known as the East Scotia Ridge (ESR) that forms the boundary between the Scotia and Sandwich plates. To the east of the ESR are the South Sandwich island arc and the South Sandwich Trench. The ESR is a relatively young feature, with spreading estimated to have begun ~20 Ma. Earlier studies examining trends in bathymetry and geochemistry along the north-south striking ESR (e.g., Livermore 2003) suggested that westward-directed flow from the Bouvet plume, located approximately 2000 km to the east, may affect ridge magmatic processes near the slab ends, particularly at the northern ridge-trench intersection. In this investigation mantle Bouguer anomaly (MBA) is calculated for the eastern Scotia Sea to evaluate the relative importance of magmatic and tectonic factors in controlling crustal accretion along the ESR. Bathymetric and free-air gravity anomaly data were obtained from global satellite-derived grids (Smith and Sandwell 1997; Sandwell and Smith 1997). In order to determine MBA, a mantle Bouguer anomaly correction term was calculated by assuming that a constant density and constant thickness crustal layer is present above a crust-mantle interface mimicking seafloor topography. To ensure the independence of the gravity and bathymetry data sets, only seafloor depths along shiptracks were used during the calculation of the mantle Bouguer anomaly correction. MBA was then determined by subtracting the mantle Bouguer anomaly correction from free-air anomaly data. Along the ESR, MBA is generally highest in the north and lowest in the south, with a long-wavelength decrease of approximately 25-50 mGal in a profile extracted along the ridge axis. Several segments in the central portion of the ridge have fairly well-developed MBA lows of approximately 15-20 mGal amplitude

  19. Consistent anomalies of the induced W gravities

    NASA Astrophysics Data System (ADS)

    Abud, Mario; Ader, Jean-Pierre; Cappiello, Luigi

    1996-02-01

    The BRST anomaly which may be present in the induced Wn gravity quantized on the light-cone is evaluated in the geometrical framework of Zucchini. The cocycles linked by the cohomology of the BRST operator to the anomaly are straightforwardly calculated thanks to the analogy between this formulation and the Yang-Mills theory. We give also a conformally covariant formulation of these quantities including the anomaly, which is valid on arbitrary Riemann surfaces. The example of the W3 theory is discussed and a comparison with other candidates for the anomaly available in the literature is presented.

  20. Gravity anomalies, spatial variation of flexural rigidity, and role of inherited crustal structure in the Aquitaine Basin

    NASA Astrophysics Data System (ADS)

    Angrand, Paul; Ford, Mary; Watts, Anthony; Bell, Rebecca E.

    2016-04-01

    The Aquitaine foreland basin developed from Campanian to Miocene by flexure of the upper (European) plate during the Pyrenean orogeny. The foreland basin forms a syn-orogenic sedimentary wedge up to 6 km thick in the south, thinning rapidly north and has a maximum width of 200 km in the west. The flexural basin was superimposed on a lithosphere previously affected by Apto-Albian hyper-extension. What are the effects of an inherited extremely weak and narrow rifted zone on the behavior of a superimposed flexural foreland basin? Coupled with surface and subsurface data, Bouguer gravity anomalies were used to determine the crustal structure of the northern Pyrenean retrowedge and the flexure of the European plate. In the centre, the basin shows a regional Bouguer anomaly pattern typical of foreland basins with the maximum of syn-orogenic deposits corresponding to a low and the forebulge to a high. However, south of the North Pyrenean Frontal Thrust (NPFT) this regional field is overprinted by strong positive Bouguer anomalies, which correspond to high density bodies (mantle or lower crust) transported along the NPFT. Stratigraphy shows that the central basin evolved as a series of narrow, laterally variable depocentres that migrated north. Shortening is accommodated mainly by thick skinned deformation and local reactivation of salt structures. In the east, the Toulouse Fault separates the central and eastern foreland. The eastern foreland shows a broader zone of negative Bouguer values. This foreland is salt-free and stratigraphy records higher subsidence. The easternmost basin is completely overprinted by the opening of the Gulf of Lion. In the west, the foreland does not show a typical regional gravity anomaly pattern due to overprinting by the opening of the Bay of Biscay. Instead, a major gravity high is centered on the northern Landes High, with a second high centered on the Labourd massif south of the NPFT. Neither the Parentis rift basin nor the salt

  1. Basement structure based on gravity anomaly in the northern Noto peninsula, Central Japan

    NASA Astrophysics Data System (ADS)

    Mizubayashi, T.; Sawada, A.; Hamada, M.; Hiramatsu, Y.; Honda, R.

    2012-12-01

    Upper crustal block structures are usually defined by using surface information, such as geological and morphological data. The northern Noto Peninsula, central Japan, is divided into four geological block structures from tectonic geomorphologic perspectives (Ota and Hirakawa, 1979). This division is based on the surface crustal movement. To image the geological blocks three-dimensionally, it is necessary to construct a subsurface structure model. Gravity survey can clarify the detailed subsurface structure with dense gravity measurement. From the detailed Bouguer anomalies in the northwestern Noto Peninsula, Honda et al. (2008) suggested that the rupture size of the 2007 Noto Hanto earthquake was constrained by the geological block structures. Hiramatsu et al. (2008) also suggested the active faults on the seafloor, such as the source fault of the 2007 Noto Hanto earthquake plays a major role for the formation of the geological block structures. In this study, we analyze subsurface density structure based on the Bouguer anomaly and estimate the distribution of basement depth in the northern Noto Peninsula. We focus the relationship among the basement depth, the block structures and the active faults on the seafloor and discuss the block movement in the northern Noto Peninsula. We compiled the data measured and published previously (Gravity Database of Southwest Japan, 2001; Geological survey of Japan, 2004; Geographical survey institute of Japan, 2006; The Gravity Research Group in Southwest Japan, 2001; Komazawa and Okuma, 2010; Hokuriku electric power Co. Ltd., undisclosed) and calculated Bouguer anomaly in the northern Noto Peninsula. Based on this Bouguer anomaly, we analyzed subsurface density structures along 13 northeastern-southwestern profiles and 35 northwestern-southeastern profiles with the interval of 2 km using the two dimensional Talwani's method (Talwani et al., 1959). In the analysis, we assumed a density structure with four layers: basement

  2. Negative gravity anomalies on the moon

    NASA Technical Reports Server (NTRS)

    Bowin, C.

    1975-01-01

    Two kinds of negative gravity anomalies on the moon are distinguished - those which show a correspondence to lunar topography and those which appear to be unrelated to surface topography. The former appear to be due to mass deficiencies caused by the cratering process, in large part probably by ejection of material from the crater. Anomalies on the far side which do not correspond to topography are thought to have resulted from irregularities in the thickness of the lunar crust. Localized large negative anomalies adjacent to mascons are considered. Although structures on the moon having a half-wavelength of 800 km or less and large negative or positive gravity anomalies are not in isostatic equilibrium, many of these features have mass loadings of about 1000 kg/sq cm which can be statically sustained on the moon.

  3. Newberry Combined Gravity 2016

    DOE Data Explorer

    Kelly Rose

    2016-01-22

    Newberry combined gravity from Zonge Int'l, processed for the EGS stimulation project at well 55-29. Includes data from both Davenport 2006 collection and for OSU/4D EGS monitoring 2012 collection. Locations are NAD83, UTM Zone 10 North, meters. Elevation is NAVD88. Gravity in milligals. Free air and observed gravity are included, along with simple Bouguer anomaly and terrain corrected Bouguer anomaly. SBA230 means simple Bouguer anomaly computed at 2.30 g/cc. CBA230 means terrain corrected Bouguer anomaly at 2.30 g/cc. This suite of densities are included (g/cc): 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.67.

  4. The Origin of the Rodrigues Depth Anomaly: New constraints from integrated gravity inversion

    NASA Astrophysics Data System (ADS)

    Minakov, Alexander; Gaina, Carmen; Faleide, Jan Inge

    2016-04-01

    This study is focused on the Western Indian Ocean including the Central Indian Ridge. The Rodrigues Ridge is a bathymetric feature (500 km -long and 20 km -wide) situated east of the Mascarene Plateau and Mauritius, with an oblique trend with respect to the underlying seafloor spreading fabric. The trend is also different from the fracture zone and hotspot tracks in this area. The region where the Rodrigues Ridge intersects the Central Indian Ridge is characterized by broad area being shallower than it should be according to standard age-depth relations for oceanic basement. With this contribution we aim to determine key factors controlling the formation of the Rodrigues Ridge and the development of the depth anomaly through time. In order to better constrain the nature and extent of the depth anomaly underlying the Rodrigues Ridge and surrounding region, we have carried out a 3D gravity and bathymetry data analysis. This analysis included an iterative gravity inversion approach linked to the computation of residual topography through the temperature and density model of the crust and upper mantle. We use a refined plate kinematic model of the study area for the time period ca. 30 Ma to the present. The refined kinematic model is an important element for temperature modelling at the ridge-transform intersection. Existing seismological data provide additional constraints for the gravity inversion. The results of the 3D gravity and bathymetry data analysis support the model of enhanced production of crust at the Central Indian Ridge adjacent to the Rodrigues Ridge. The depth anomaly is composed of abrupt Rodrigues Ridge edifice sitting on top a relatively smooth and broad anomaly characterized by crustal thickness between 8 and 13 km. These values are significantly higher than those typical for the crustal thickness generated by slow seafloor spreading at the Central Indian Ridge and other slow spreading ridges. This gives rise to a large negative residual mantle

  5. Evolution of gravity anomalies across collisional mountain belts: Clues to the amount of continental convergence and underthrusting

    NASA Astrophysics Data System (ADS)

    Lillie, Robert J.

    1991-08-01

    A series of density models illustrates the gross form of free air and Bouguer gravity anomalies anticipated during ocean basin closure and consequent development of collisional orogens. When compared to gravity anomalies observed across some mountain belts, the hypothetical anomalies provide a clue to the degree of under thrusting of crust associated with one lithospheric plate beneath crust of the opposing plate margin. The results of the study suggest very early stage collision in the Ouachita Mountains of Arkansas and the Sulaiman Range of Pakistan, with thin transitional or oceanic crust still intact on the lower plate. In contrast, the Himalaya of Pakistan represent a much more advanced stage of collision, where continental crust may have underthrust the mountains for 600 km.

  6. Trace anomaly and counterterms in designer gravity

    NASA Astrophysics Data System (ADS)

    Anabalón, Andrés; Astefanesei, Dumitru; Choque, David; Martínez, Cristián

    2016-03-01

    We construct concrete counterterms of the Balasubramanian-Kraus type for Einstein-scalar theories with designer gravity boundary conditions in AdS4, so that the total action is finite on-shell and satisfy a well defined variational principle. We focus on scalar fields with the conformal mass m 2 = -2 l -2 and show that the holographic mass matches the Hamiltonian mass for any boundary conditions. We compute the trace anomaly of the dual field theory in the generic case, as well as when there exist logarithmic branches of non-linear origin. As expected, the anomaly vanishes for the boundary conditions that are AdS invariant. When the anomaly does not vanish, the dual stress tensor describes a thermal gas with an equation of state related to the boundary conditions of the scalar field. In the case of a vanishing anomaly, we recover the dual theory of a massless thermal gas. As an application of the formalism, we consider a general family of exact hairy black hole solutions that, for some particular values of the parameters in the moduli potential, contains solutions of four-dimensional gauged {N}=8 supergravity and its ω-deformation. Using the AdS/CFT duality dictionary, they correspond to triple trace deformations of the dual field theory.

  7. Short-wavelength, high-amplitude gravity anomalies around the Banda Sea, and the collapse of the Sulawesi orogen

    NASA Astrophysics Data System (ADS)

    Milsom, J.; Sardjono; Susilo, A.

    2001-04-01

    In eastern Indonesia, high-density ophiolitic rocks outcropping on islands surrounding the Banda Sea are in many cases associated with strong gravity anomalies and steep gravity gradients. However, the relationships are not always straightforward. Bouguer gravity levels and gradients over the extensive East Sulawesi Ophiolite are generally relatively low, although short-wavelength, high amplitude anomalies indicate rapid changes in thickness of high-density rocks in a few places. In the Banda Arc, most local positive anomalies due to ophiolites are superimposed on a steep regional gravity gradient but in one case, in western Seram, there is a distinct and important spatial separation between the two. On Buru, west of Seram, a gradient of more than 10 mGal/km testifies to the presence of very dense rocks in the near subsurface, despite the absence of ophiolites in the outcrop. Gravity variations and ophiolite distribution around the Banda Sea are compatible with extension having occurred in the Sulawesi region following, and as a result of, Oligo-Miocene collision with an Australian-derived microcontinent. Similar histories have been proposed for many Mediterranean deep basins of similar size, shape and character, and emplacement of some of the high-density masses in the Banda Arc has probably resembled at least the later stages in the emplacement of peridotite massifs in the Rif-Betic belt. In both areas the present close association of the ultramafic rocks and their associated local anomalies with a strong regional gravity gradient is largely coincidental.

  8. Determination of mean gravity anomalies in the Taiwan Island

    NASA Technical Reports Server (NTRS)

    Chang, Ruey-Gang

    1989-01-01

    The fitting and proper regression coefficients were made of one hundred seventeen 10 x 10' blocks with observed gravity data and corresponding elevation in the Taiwan Island. To compare five different predicted models, and the proper one for the mean gravity anomalies were determined. The predicted gravity anomalies of the non-observed gravity blocks were decided when the coefficients obtained through the model with the weighted mean method. It was suggested that the mean gravity anomalies of 10 x 10' blocks should be made when comprehensive the observed and predicted data.

  9. GRAVITY STUDIES IN THE CASCADE RANGE.

    USGS Publications Warehouse

    Finn, Carol; Williams, David

    1983-01-01

    A compatible set of gravity data has been compiled for the entire Cascade Range. From this data set a series of interpretive color gravity maps have been prepared, including a free air anomaly map, Bouguer anomaly map at a principle, and an alternate reduction density, and filtered and derivative versions of the Bouguer anomaly map. The regional anomaly pattern and gradients outline the various geological provinces adjacent to the Cascade Range and delineate major structural elements in the range. The more local anomalies and gradients may delineate low density basin and caldera fill, faults, and shallow plutons. Refs.

  10. Spectral analysis of gravity anomalies and the architecture of tectonic wedging, NE Venezuela and Trinidad

    NASA Astrophysics Data System (ADS)

    Russo, R. M.; Speed, R. C.

    1994-06-01

    We have analyzed the spectral content of free air gravity anomalies in the Caribbean-South American plate boundary zone in order to determine better the near-surface (0-120 km) distribution of crustal and upper mantle elements which give rise to the unusual gravity field of this region. The plate boundary zone in northeastern Venezuela and Trinidad is the site of the world's sea level continental minimum of Bouguer gravity anomalies, yet the region is also one of mild topography (mean value 43 m, maximum 1200 m). We find the mean depths to interfaces of significant density contrast at a variety of depths for portions of the plate boundary zone. We interpret interfaces at 30-35 km and 32 km beneath the Guyana Shield and the Aves Ridge, respectively, to be the Moho. Other shallow interfaces (5-14 km) are most likely sediment cover-basement contacts in the Maturin foreland basin and southern Grenada Basin. Deeper interfaces (54-63 km) we associate with loaded and downwarped continental and oceanic South American lithosphere. The deepest boundaries, at depths of 89-120 km, may be related to detached or detaching oceanic lithosphere overridden by continental South America. We use our results to test the tectonic wedging model of the plate boundary zone recently published by Russo and Speed (1992). We find that the tectonic wedging model adequately describes many of the structural boundaries inferable from our analysis of gravity anomalies but that the model must be modified to include a thinner Guyana Shield crust.

  11. Isostatic Model and Isostatic Gravity Anomalies of the Arabian Plate and Surroundings

    NASA Astrophysics Data System (ADS)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2016-04-01

    The isostatic modeling represents one of the most useful "geological" reduction methods of the gravity field. With the isostatic correction, it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. Although there exist several isostatic compensation schemes, it is usually supposed that a choice of the model is not an important factor to first order, since the total weight of compensating masses remains the same. We compare two alternative models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also, the predicted "isostatic" Moho is very different from existing seismic observations. The second isostatic model includes the Moho, which is based on seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). According to this model, the upper mantle under the Arabian Shield is less dense than under the Platform. In the Arabian platform, the maximum density coincides with the Rub' al Khali, one of the richest oil basin in the world. This finding agrees with previous studies, showing that such basins are often underlain by dense mantle, possibly related to an eclogite layer that has caused their subsidence. The mantle density variations might be also a result of variations of the lithosphere thickness. With the combined isostatic model, it is possible to minimize regional anomalies over the Arabian plate. The residual local anomalies correspond well to tectonic structure of the plate. Still very significant anomalies, showing isostatic disturbances of the lithosphere, are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

  12. Principal facts for gravity stations in Paradise and Stagecoach valleys, Humboldt and Lyon counties, Nevada

    USGS Publications Warehouse

    Schaefer, D.H.; Duffrin, B.G.; Plume, R.W.

    1986-01-01

    Principal facts for 178 gravity stations in Paradise Valley and 117 stations in Stagecoach Valley, are tabulated; they consists of latitude, longitude, altitude, observed gravity, free-air anomaly, terrain correction, and Bouguer gravity anomaly values at a bedrock density of 2.67 grams per cubic centimeter. (USGS)

  13. Upgraded gravity anomaly base of the United States

    USGS Publications Warehouse

    Keller, Gordon R.; Hildenbrand, T.G.; Kucks, R.; Roman, D.; Hittelman, A.M.

    2002-01-01

    A concerted effort to compile an upgraded gravity anomaly database, grid, and map for the United States by the end of 2002 is under way. This effort can be considered as the first step in building a data system for gravity measurements, and it builds on existing collaborative efforts. This paper outlines the strategy for assembling the individual map and digital products related to the United States gravity database.

  14. Interpretation of Local Gravity Anomalies in Northern New York

    NASA Astrophysics Data System (ADS)

    Revetta, F. A.

    2004-05-01

    About 10,000 new gravity measurements at a station spacing of 1 to 2 Km were made in the Adirondack Mountains, Lake Champlain Valley, St. Lawrence River Valley and Tug Hill Plateau. These closely spaced gravity measurements were compiled to construct computer contoured gravity maps of the survey areas. The gravity measurements reveal local anomalies related to seismicity, faults, mineral resources and gas fields that are not seen in the regional gravity mapping. In northern New York gravity and seismicity maps indicate epicenters are concentrated in areas of the most pronounced gravity anomalies along steep gravity gradients. Zones of weakness along the contacts of these lithologies of different density could possibly account for the earthquakes in this high stress area. Also, a computer contoured gravity map of the 5.3 magnitude Au Sable Forks earthquake of April 20, 2002 indicates the epicenter lies along a north-south trending gravity gradient produced by a high angle fault structure separating a gravity low in the west from high gravity in the east. In the St. Lawrence Valley, the Carthage-Colton Mylonite Zone, a major northeast trending structural boundary between the Adirondack Highlands and Northwest Lowlands, is represented as a steep gravity gradient extending into the eastern shore of Lake Ontario. At Russell, New York near the CCMZ, a small circular shaped gravity high coincides with a cluster of earthquakes. The coincidence of the epicenters over the high may indicate stress amplification at the boundary of a gabbro pluton. The Morristown fault located in the Morristown Quadrangle in St. Lawrence County produces both gravity and magnetic anomalies due to Precambrian Basement faulting. This faulting indicates control of the Morristown fault in the overlying Paleozoics by the Precambrian faults. Gravity and magnetic anomalies also occur over proposed extensions of the Gloucester and Winchester Springs faults into northern New York. Gravity and magnetic

  15. 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.

  16. 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.

  17. Detailed gravity anomalies from GEOS-3 satellite altimetry data

    NASA Technical Reports Server (NTRS)

    Gopalapillai, G. S.; Mourad, A. G.

    1978-01-01

    A technique for deriving mean gravity anomalies from dense altimetry data was developed. A combination of both deterministic and statistical techniques was used. The basic mathematical model was based on the Stokes' equation which describes the analytical relationship between mean gravity anomalies and geoid undulations at a point; this undulation is a linear function of the altimetry data at that point. The overdetermined problem resulting from the excessive altimetry data available was solved using Least-Squares principles. These principles enable the simultaneous estimation of the associated standard deviations reflecting the internal consistency based on the accuracy estimates provided for the altimetry data as well as for the terrestrial anomaly data. Several test computations were made of the anomalies and their accuracy estimates using GOES-3 data.

  18. Detailed gravity anomalies from Geos 3 satellite altimetry data

    NASA Technical Reports Server (NTRS)

    Gopalapillai, G. S.; Mourad, A. G.

    1979-01-01

    Detailed gravity anomalies are computed from a combination of Geos 3 satellite altimeter and terrestrial gravity data using least-squares principles. The mathematical model used is based on the Stokes' equation modified for a nonglobal solution. Using Geos 3 data in the calibration area, the effects of several anomaly parameter configurations and data densities/distributions on the anomalies and their accuracy estimates are studied. The accuracy estimates for 1 deg x 1 deg mean anomalies from low density altimetry data are of the order of 4 mgal. Comparison of these anomalies with the terrestrial data and also with Rapp's data derived using collocation techniques show rms differences of 7.2 and 4.9 mgal, respectively. Indications are that the anomaly accuracies can be improved to about 2 mgal with high density data. Estimation of 30 in. x 30 in. mean anomalies indicates accuracies of the order of 5 mgal. Proper verification of these results will be possible only when accurate ground truth data become available.

  19. Gravity Anomaly Assessment Using Ggms and Airborne Gravity Data Towards Bathymetry Estimation

    NASA Astrophysics Data System (ADS)

    Tugi, A.; Din, A. H. M.; Omar, K. M.; Mardi, A. S.; Som, Z. A. M.; Omar, A. H.; Yahaya, N. A. Z.; Yazid, N.

    2016-09-01

    The Earth's potential information is important for exploration of the Earth's gravity field. The techniques of measuring the Earth's gravity using the terrestrial and ship borne technique are time consuming and have limitation on the vast area. With the space-based measuring technique, these limitations can be overcome. The satellite gravity missions such as Challenging Mini-satellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), and Gravity-Field and Steady-State Ocean Circulation Explorer Mission (GOCE) has introduced a better way in providing the information on the Earth's gravity field. From these satellite gravity missions, the Global Geopotential Models (GGMs) has been produced from the spherical harmonics coefficient data type. The information of the gravity anomaly can be used to predict the bathymetry because the gravity anomaly and bathymetry have relationships between each other. There are many GGMs that have been published and each of the models gives a different value of the Earth's gravity field information. Therefore, this study is conducted to assess the most reliable GGM for the Malaysian Seas. This study covered the area of the marine area on the South China Sea at Sabah extent. Seven GGMs have been selected from the three satellite gravity missions. The gravity anomalies derived from the GGMs are compared with the airborne gravity anomaly, in order to figure out the correlation (R2) and the root mean square error (RMSE) of the data. From these assessments, the most suitable GGMs for the study area is GOCE model, GO_CONS_GCF_2_TIMR4 with the R2 and RMSE value of 0.7899 and 9.886 mGal, respectively. This selected model will be used in the estimating the bathymetry for Malaysian Seas in future.

  20. 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

  1. 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.

  2. Gravity anomalies without geomagnetic disturbances interfere with pigeon homing--a GPS tracking study.

    PubMed

    Blaser, Nicole; Guskov, Sergei I; Entin, Vladimir A; Wolfer, David P; Kanevskyi, Valeryi A; Lipp, Hans-Peter

    2014-11-15

    The gravity vector theory postulates that birds determine their position to set a home course by comparing the memorized gravity vector at the home loft with the local gravity vector at the release site, and that they should adjust their flight course to the gravity anomalies encountered. As gravity anomalies are often intermingled with geomagnetic anomalies, we released experienced pigeons from the center of a strong circular gravity anomaly (25 km diameter) not associated with magnetic anomalies and from a geophysical control site, equidistant from the home loft (91 km). After crossing the border zone of the anomaly--expected to be most critical for pigeon navigation--they dispersed significantly more than control birds, except for those having met a gravity anomaly en route. These data increase the credibility of the gravity vector hypothesis.

  3. Gravity anomalies without geomagnetic disturbances interfere with pigeon homing--a GPS tracking study.

    PubMed

    Blaser, Nicole; Guskov, Sergei I; Entin, Vladimir A; Wolfer, David P; Kanevskyi, Valeryi A; Lipp, Hans-Peter

    2014-11-15

    The gravity vector theory postulates that birds determine their position to set a home course by comparing the memorized gravity vector at the home loft with the local gravity vector at the release site, and that they should adjust their flight course to the gravity anomalies encountered. As gravity anomalies are often intermingled with geomagnetic anomalies, we released experienced pigeons from the center of a strong circular gravity anomaly (25 km diameter) not associated with magnetic anomalies and from a geophysical control site, equidistant from the home loft (91 km). After crossing the border zone of the anomaly--expected to be most critical for pigeon navigation--they dispersed significantly more than control birds, except for those having met a gravity anomaly en route. These data increase the credibility of the gravity vector hypothesis. PMID:25392461

  4. On global gravity anomalies and two-scale mantle convection

    NASA Technical Reports Server (NTRS)

    Marsh, B. D.; Marsh, J. G.

    1976-01-01

    The two-scale model of mantle convection developed by Richter and Parsons (1975) predicts that if the depth of the convective layer is about 600 km, then for a plate moving at 10 cm/yr, longitudinal convective rolls will be produced in about 50 million years, and the strike of these rolls indicates the direction of motion of the plate relative to the upper mantle. The paper tests these predictions by examining a new global free air gravity model complete to the 30th degree and order. The free air gravity map developed shows a series of linear positive and negative anomalies (with transverse wavelengths of about 2000 km) spanning the Pacific Ocean, crossing the Pacific rise and striking parallel to the Hawaiian seamounts. It is suggested that the pattern of these anomalies may indicate the presence of longitudinal convective rolls beneath the Pacific plates, a result which tends to support the predictions of Richter and Parsons.

  5. New analytic solutions for modeling vertical gravity gradient anomalies

    NASA Astrophysics Data System (ADS)

    Kim, Seung-Sep; Wessel, Paul

    2016-05-01

    Modern processing of satellite altimetry for use in marine gravimetry involves computing the along-track slopes of observed sea-surface heights, projecting them into east-west and north-south deflection of the vertical grids, and using Laplace's equation to algebraically obtain a grid of the vertical gravity gradient (VGG). The VGG grid is then integrated via overlapping, flat Earth Fourier transforms to yield a free-air anomaly grid. Because of this integration and associated edge effects, the VGG grid retains more short-wavelength information (e.g., fracture zone and seamount signatures) that is of particular importance for plate tectonic investigations. While modeling of gravity anomalies over arbitrary bodies has long been a standard undertaking, similar modeling of VGG anomalies over oceanic features is not commonplace yet. Here we derive analytic solutions for VGG anomalies over simple bodies and arbitrary 2-D and 3-D sources. We demonstrate their usability in determining mass excess and deficiency across the Mendocino fracture zone (a 2-D feature) and find the best bulk density estimate for Jasper seamount (a 3-D feature). The methodologies used herein are implemented in the Generic Mapping Tools, available from gmt.soest.hawaii.edu.

  6. Gravity anomalies in Silurian pinnacle reef trend, southwestern Indiana

    SciTech Connect

    Malinconico, L.L. Jr.; Gognat, T.A.; Scher, P.L. )

    1989-08-01

    Structures produced over the top or along the margins of Silurian Pinnacle reefs have proven to be the source of significant oil production in the eastern Illinois basin. The authors have been able to refine gravity methods that can assist in the exploration of such reef targets. A gravity/density model was developed by combining the 1980 work of Dana at the Wilfred pool (Sullivan County, Indiana) with other lithologic and log data in southwestern Indiana. This model includes the density differences between the reef facies and surrounding lithologies as well as density variations that are the result of compaction of the sedimentary sequence above the reef. The density models suggest that positive gravity anomalies with amplitude between 1.5 to 2.5 mgals might occur over the reefs.

  7. The gravity field and crustal structure of the northwestern Arabian Platform in Jordan

    NASA Astrophysics Data System (ADS)

    Batayneh, A. T.; Al-Zoubi, A. S.

    2001-01-01

    The Bouguer gravity field over the northwestern Arabian Platform in Jordan is dominated by large variations, ranging from -132 to +4 mGal. A study of the Bouguer anomaly map shows that the gravity field maintains a general north-northeasterly trend in the Wadi Araba-Dead Sea-Jordan Riff, Northern Highlands and Northeast Jordanian Limestone Area, while the remainder of the area shows north-northwesterly-trending gravity anomalies. Results of 2-D gravity modeling of the Bouguer gravity field indicate that the crustal thickness in Jordan is ˜ 38 km, which is similar to crustal thicknesses obtained from refraction data in northern Jordan and Saudi Arabia, and from gravity data in Syria.

  8. Gravity survey of the southwestern part of the sourthern Utah geothermal belt

    SciTech Connect

    Green, R.T.; Cook, K.L.

    1981-03-01

    A gravity survey covering an area of 6200 km/sup 2/ was made over the southwestern part of the southern Utah geothermal belt. The objective of the gravity survey is to delineate the geologic structures and assist in the understanding of the geothermal potential of the area. A total of 726 new gravity stations together with 205 existing gravity stations, are reduced to give: (1) a complete Bouguer gravity anomaly map, and (2) a fourth-order residual gravity anomaly map; both maps have a 2-mgal contour interval. The complete Bouguer gravity anomaly map shows an east-trending regional gravity belt with a total relief of about 70 mgal which crosses the central portion of the survey area. The gravity belt is attributed to a crustal lateral density variation of 0.1 gm/cc from a depth of 5 to 15 km.

  9. The quest for the perfect gravity anomaly: Part 2 - Mass effects and anomaly inversion

    USGS Publications Warehouse

    Keller, Gordon R.; Hildenbrand, T.G.; Hinze, W. J.; Li, X.; Ravat, D.; Webring, M.

    2006-01-01

    Gravity anomalies have become an important tool for geologic studies since the widespread use of high-precision gravimeters after the Second World War. More recently the development of instrumentation for airborne gravity observations, procedures for acquiring data from satellite platforms, the readily available Global Positioning System for precise vertical and horizontal control, improved global data bases, and enhancement of computational hardware and software have accelerated the use of the gravity method. As a result, efforts are being made to improve the gravity databases that are made available to the geoscience community by broadening their observational holdings and increasing the accuracy and precision of the included data. Currently the North American Gravity Database as well as the individual databases of Canada, Mexico, and the United States of America are being revised using new formats and standards. The objective of this paper is to describe the use of the revised standards for gravity data processing and modeling and there impact on geological interpretations. ?? 2005 Society of Exploration Geophysicists.

  10. Altered orientation and flight paths of pigeons reared on gravity anomalies: a GPS tracking study.

    PubMed

    Blaser, Nicole; Guskov, Sergei I; Meskenaite, Virginia; Kanevskyi, Valerii A; Lipp, Hans-Peter

    2013-01-01

    The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The "gravity vector" theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons, while reactivity to gravity gradients during flight was variable and appeared to depend on individual navigational strategies and frequency of position updates.

  11. Altered Orientation and Flight Paths of Pigeons Reared on Gravity Anomalies: A GPS Tracking Study

    PubMed Central

    Blaser, Nicole; Guskov, Sergei I.; Meskenaite, Virginia; Kanevskyi, Valerii A.; Lipp, Hans-Peter

    2013-01-01

    The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The “gravity vector” theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons, while reactivity to gravity gradients during flight was variable and appeared to depend on individual navigational strategies and frequency of position updates. PMID:24194860

  12. Gravity anomalies, forearc morphology and seismicity in subduction zones

    NASA Astrophysics Data System (ADS)

    Bassett, D.; Watts, A. B.; Das, S.

    2012-12-01

    We apply spectral averaging techniques to isolate and remove the long-wavelength large-amplitude trench-normal topographic and free-air gravity anomaly "high" and "low" associated with subduction zones. The residual grids generated illuminate the short-wavelength structure of the forearc. Systematic analysis of all subduction boundaries on Earth has enabled a classification of these grids with particular emphasis placed on topography and gravity anomalies observed in the region above the shallow seismogenic portion of the plate interface. The isostatic compensation of these anomalies is investigated using 3D calculations of the gravitational admittance and coherence. In the shallow region of the megathrust, typically within 100 km from the trench, isolated residual anomalies with amplitudes of up to 2.5 km and 125 mGal are generally interpreted as accreted/subducting relief in the form of seamounts and other bathymetric features. While most of these anomalies, which have radii < 50km, are correlated with areas of reduced seismicity, several in regions such as Japan and Java appear to have influenced the nucleation and/or propagation of large magnitude earthquakes. Long-wavelength (500 - >1000 km) trench-parallel forearc ridges with residual anomalies of up to 1.5 km and 150 mGal are identified in approximately one-third of the subduction zones analyzed. Despite great length along strike, these ridges are less than 100 km wide and several appear uncompensated. A high proportion of arc-normal structure and the truncation/morphological transition of trench-parallel forearc ridges is explained through the identification and tracking of pre-existing structure on the over-riding and subducting plates into the seismogenic portion of the plate boundary. Spatial correlations between regions with well-defined trench-parallel forearc ridges and the occurrence of large magnitude interplate earthquakes, in addition to the uncompensated state of these ridges, suggest links

  13. 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.

  14. A priori noise and regularization in least squares collocation of gravity anomalies

    NASA Astrophysics Data System (ADS)

    Jarmołowski, Wojciech

    2013-12-01

    The paper describes the estimation of covariance parameters in least squares collocation (LSC) by the cross-validation (CV) technique called leave-one-out (LOO). Two parameters of Gauss-Markov third order model (GM3) are estimated together with a priori noise standard deviation, which contributes significantly to the covariance matrix composed of the signal and noise. Numerical tests are performed using large set of Bouguer gravity anomalies located in the central part of the U.S. Around 103 000 gravity stations are available in the selected area. This dataset, together with regular grids generated from EGM2008 geopotential model, give an opportunity to work with various spatial resolutions of the data and heterogeneous variances of the signal and noise. This plays a crucial role in the numerical investigations, because the spatial resolution of the gravity data determines the number of gravity details that we may observe and model. This establishes a relation between the spatial resolution of the data and the resolution of the gravity field model. This relation is inspected in the article and compared to the regularization problem occurring frequently in data modeling. Artykuł opisuje estymację parametrów kowariancji w kolokacji najmniejszych kwadratów (LSC) przy pomocy techniki kroswalidacji nazywanej leave-one-out (LOO). Wyznaczane są dwa parametry modelu Gaussa-Markova trzeciego rzędu (GM3) wraz z odchyleniem standardowym szumu a priori, które ma znaczny wpływ na macierz kowariancji złożoną z sygnału i szumu. Testy numeryczne przeprowadzono na dużym zbiorze anomalii grawimetrycznych Bouguera z obszaru centralnej części USA. Obszar ten mieści około 103000 pomiarów grawimetrycznych. Dane te wraz z regularnymi siatkami wygenerowanymi z modelu geopotencjalnego EGM2008 pozwalają na pracę z różną rozdzielczością przestrzenną i różnymi wariancjami sygnału i szumu. Odgrywa to kluczową rolę w badaniach numerycznych, ponieważ rozdzielczo

  15. Global correlation of topographic heights and gravity anomalies

    NASA Technical Reports Server (NTRS)

    Roufosse, M. C.

    1977-01-01

    The short wavelength features were obtained by subtracting a calculated 24th-degree-and-order field from observed data written in 1 deg x 1 deg squares. The correlation between the two residual fields was examined by a program of linear regression. When run on a worldwide scale over oceans and continents separately, the program did not exhibit any correlation; this can be explained by the fact that the worldwide autocorrelation function for residual gravity anomalies falls off much faster as a function of distance than does that for residual topographic heights. The situation was different when the program was used in restricted areas, of the order of 5 deg x 5 deg square. For 30% of the world,fair-to-good correlations were observed, mostly over continents. The slopes of the regression lines are proportional to apparent densities, which offer a large spectrum of values that are being interpreted in terms of features in the upper mantle consistent with available heat-flow, gravity, and seismic data.

  16. Gravity anomalies of the active mud diapirs off southwest Taiwan

    NASA Astrophysics Data System (ADS)

    Doo, Wen-Bin; Hsu, Shu-Kun; Lo, Chung-Liang; Chen, Song-Chuen; Tsai, Ching-Hui; Lin, Jing-Yi; Huang, Yuan-Ping; Huang, Yin-Sheng; Chiu, Shye-Donq; Ma, Yu-Fang

    2015-12-01

    Overpressure and buoyant effect of underlying sediments are generally used to account for the upward motion or formation of submarine mud volcanoes and mud diapirs. In this study, we process and interpret the gravity anomalies associated with the active mud diapirs off SW Taiwan. Geologically, the mud diapirs are just formed and are still very active, thus we can better understand the initial process of the mud diapirs formation through the gravity analysis. Our results show that the density contrasts of the submarine mud diapirs with respect to the surroundings are generally positive. Because the study area is in a tectonically compressive regime and the gas plume venting from the submarine mud volcanoes is very active, we thus infer that mechanically the mud diapirs off SW Taiwan have been formed mainly due to the tectonic compression on the underlying sediments of high pore-fluid pressure, instead of the buoyancy of the buried sediments. The overpressured sediments and fluid are compressed and pushed upwards to pierce the overlying sediments and form the more compacted mud diapirs. The relatively denser material of the mud diapirs probably constrains the flowing courses of the submarine canyons off SW Taiwan, especially for the upper reaches of the Kaoping and Fangliao submarine canyons.

  17. Gravity anomalies, caldera structure, and subsurface geology in the Rotorua area, New Zealand

    SciTech Connect

    Hunt, T.M. )

    1992-04-01

    This paper discusses a re-examination of gravity which indicates that Rotorua Caldera does not have the circular, negative gravity anomaly typical of other rhyolitic calderas. New gravity measurements and residual gravity anomalies in Rotorua City are consistent with numerous rhyolite domes and ignimbrite sheets, interbedded with a thick sequence of poorly-compacted sediments. Within the city a gravity high extends from the shore of Lake Rotorua south to Whakarewarewa and is associated with a buried ridge, formed by the coalescing of two rhyolite domes. A gravity low centered near Linton Park suggests that rhyolites are thin or absent in this area and sediments extend to a depth of about 1 km. A quantitative analysis of the residual gravity anomalies was limited by insufficient information about the density, extent, and thickness of the material underlying the rhyolites, and the uncertainty in the distribution and density of silicification within the sediments.

  18. The quest for the perfect gravity anomaly: Part 1 - New calculation standards

    USGS Publications Warehouse

    Li, X.; Hildenbrand, T.G.; Hinze, W. J.; Keller, Gordon R.; Ravat, D.; Webring, M.

    2006-01-01

    The North American gravity database together with databases from Canada, Mexico, and the United States are being revised to improve their coverage, versatility, and accuracy. An important part of this effort is revision of procedures and standards for calculating gravity anomalies taking into account our enhanced computational power, modern satellite-based positioning technology, improved terrain databases, and increased interest in more accurately defining different anomaly components. The most striking revision is the use of one single internationally accepted reference ellipsoid for the horizontal and vertical datums of gravity stations as well as for the computation of the theoretical gravity. The new standards hardly impact the interpretation of local anomalies, but do improve regional anomalies. Most importantly, such new standards can be consistently applied to gravity database compilations of nations, continents, and even the entire world. ?? 2005 Society of Exploration Geophysicists.

  19. An Anzatz about Gravity, Cosmology, and the Pioneer Anomaly

    SciTech Connect

    Murad, Paul

    2010-01-28

    The Pulsar 1913+16 binary system may represent a 'young' binary system where previously it is claimed that the dynamics are due to either a third body or a gravitational vortex. Usually a binary system's trajectory could reside in a single ellipse or circular orbit; the double ellipse implies that the 1913+16 system may be starting to degenerate into a single elliptical trajectory. This could be validated only after a considerably long time period. In a majority of binary star systems, the weights of both stars are claimed by analysis to be the same. It may be feasible that the trajectory of the primary spinning star could demonstrate repulsive gravitational effects where the neutron star's high spin rate induces a repulsive gravitational source term that compensates for inertia. If true, then it provides evidence that angular momentum may be translated into linear momentum as a repulsive source that has propulsion implications. This also suggests mass differences may dictate the neutron star's spin rate as an artifact of a natural gravitational process. Moreover, the reduced matter required by the 'dark' mass hypothesis may not exist but these effects could be due to repulsive gravity residing in rotating celestial bodies.The Pioneer anomaly observed on five different deep-space spacecraft, is the appearance of a constant gravitational force directed toward the sun. Pioneer spacecraft data reveals that a vortex-like magnetic field exists emanating from the sun. The spiral arms of the Sun's magnetic vortex field may be causal to this constant acceleration. This may profoundly provide a possible experimental verification on a cosmic scale of Gertsenshtein's principle relating gravity to electromagnetism. Furthermore, the anomalous acceleration may disappear once the spacecraft passes out into a magnetic spiral furrow, which is something that needs to be observed in the future. Other effects offer an explanation from space-time geometry to the Yarkovsky thermal

  20. High-resolution airborne gravity imaging over James Ross Island (West Antarctica)

    USGS Publications Warehouse

    Jordan, T.A.; Ferraccioli, F.; Jones, P.C.; Smellie, J.L.; Ghidella, M.; Corr, H. F. J.; Zakrajsek, A.F.

    2007-01-01

    James Ross Island (JRI) exposes a Miocene-Recent alkaline basaltic volcanic complex that developed in a back-arc, east of the northern Antarctic Peninsula. JRI has been the focus of several geological studies because it provides a window on Neogene magmatic processes and paleoenvironments. However, little is known about its internal structure. New airborne gravity data were collected as part of the first high-resolution aerogeophysical survey flown over the island and reveal a prominent negative Bouguer gravity anomaly over Mt Haddington. This is intriguing as basaltic volcanoes are typically associated with positive Bouguer anomalies, linked to underlying mafic intrusions. The negative Bouguer anomaly may be associated with a hitherto unrecognised low-density sub-surface body, such as a breccia-filled caldera, or a partially molten magma chamber.

  1. Procedures and results related to the direct determination of gravity anomalies from satellite and terrestrial gravity data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1974-01-01

    The equations needed for the incorporation of gravity anomalies as unknown parameters in an orbit determination program are described. These equations were implemented in the Geodyn computer program which was used to process optical satellite observations. The arc dependent parameter unknowns, 184 unknown 15 deg and coordinates of 7 tracking stations were considered. Up to 39 arcs (5 to 7 days) involving 10 different satellites, were processed. An anomaly solution from the satellite data and a combination solution with 15 deg terrestrial anomalies were made. The limited data samples indicate that the method works. The 15 deg anomalies from various solutions and the potential coefficients implied by the different solutions are reported.

  2. Crustal structure and gravity anomalies beneath the Rif, northern Morocco: implications for the current tectonics of the Alboran region

    NASA Astrophysics Data System (ADS)

    Petit, Carole; Le Pourhiet, Laetitia; Scalabrino, Bruno; Corsini, Michel; Bonnin, Mickaël; Romagny, Adrien

    2015-07-01

    We analyse Bouguer anomaly data and previously published Moho depths estimated from receiver functions in order to determine the amount of isostatic compensation or uncompensation of the Rif topography in northern Morocco. We use Moho depth variations extracted from receiver function analyses to predict synthetic Bouguer anomalies that are then compared to observed Bouguer anomaly. We find that Moho depth variations due to isostatic compensation of topographic and/or intracrustal loads do not match Moho depth estimates obtained from receiver function analyses. The isostatic misfit map evidences excess crustal root as large as 10 km in the western part of the study area, whereas a `missing' crustal root of ˜5 km appears east of 4.3°E. This excess root/missing topography correlates with the presence of a dense mantle lid, the noticeable southwestward drift of the Western Rif area, and with a current surface uplift. We propose that a delaminated mantle lid progressively detaching westward or southwestward from the overlying crust is responsible for viscous flow of the ductile lower crust beneath the Rif area. This gives rise to isostatic uplift and westward drift due to viscous coupling at the upper/lower crust boundary. At the same time, the presence of this dense sinking mantle lid causes a negative dynamic topography, which explains why the observed topography is too low compared to the crustal thickness.

  3. On the ratio of dynamic topography and gravity anomalies in a dynamic Earth

    NASA Astrophysics Data System (ADS)

    Colli, L.; Ghelichkhan, S.; Bunge, H.-P.

    2016-03-01

    Growing evidence from a variety of geologic indicators points to significant topography maintained convectively by viscous stresses in the mantle. However, while gravity is sensitive to dynamically supported topography, there are only small free-air gravity anomalies (<30 mGal) associated with Earth's long-wavelength topography. This has been used to suggest that surface heights computed assuming a complete isostatic equilibrium provide a good approximation to observed topography. Here we show that the apparent paradox is resolved by the well-established formalism of global, self-gravitating, viscously stratified Earth models. The models predict a complex relation between dynamic topography, mass, and gravity anomalies that is not summarized by a constant admittance—i.e., ratio of gravity anomalies to surface deflections—as one would infer from analytic flow solutions formulated in a half-space. Our results suggest that sizable dynamic topography may exist without a corresponding gravity signal.

  4. Analysis of gravity anomaly over coral-reef oil field: Wilfred Pool, Sullivan County, Indiana

    SciTech Connect

    Dana, S.W.

    1980-03-01

    To compare the measured and theoretical gravity anomaly of a typical coral-reef oil field, data were collected from the wilfred Pool, Sullivan County, Indiana. Densities of available core samples from the field were determined and the anomaly was calculated, taking into account the lateral and vertical variation of density and the geologic structure known from core studies and drilling-log records of lithologic types penetrated by the wells. Comparison of the theoretical and actual anomalies indicated a rough correspondence except for several sharp negative anomalies on the flanks of the measured gravity anomaly. Further studies indicated that the negative anomalies are possibly due to fluvial erosion that produced, on the surface of the youngest Pennsylvanian sediments, channels which were later filled with glacial till of lower density than the sediments. 13 figures.

  5. Gravity anomalies, plate tectonics and the lateral growth of Precambrian North America

    NASA Technical Reports Server (NTRS)

    Thomas, M. D.; Grieve, R. A. F.; Sharpton, V. L.

    1988-01-01

    The widespread gravity coverage of North America provides a picture of the gross structural fabric of the continent via the trends of gravity anomalies. The structural picture so obtained reveals a mosaic of gravity trend domains, many of which correlate closely with structural provinces and orogenic terranes. The gravity trend map, interpreted in the light of plate-tectonic theory, thus provides a new perspective for examining the mode of assembly and growth of North America. Suture zones, palaeosubduction directions, and perhaps, contrasting tectonic histories may be identified using gravity patterns.

  6. 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.

  7. Gravity data from the San Pedro River Basin, Cochise County, Arizona

    USGS Publications Warehouse

    Kennedy, Jeffrey R.; Winester, Daniel

    2011-01-01

    The U.S. Geological Survey, Arizona Water Science Center in cooperation with the National Oceanic and Atmospheric Administration, National Geodetic Survey has collected relative and absolute gravity data at 321 stations in the San Pedro River Basin of southeastern Arizona since 2000. Data are of three types: observed gravity values and associated free-air, simple Bouguer, and complete Bouguer anomaly values, useful for subsurface-density modeling; high-precision relative-gravity surveys repeated over time, useful for aquifer-storage-change monitoring; and absolute-gravity values, useful as base stations for relative-gravity surveys and for monitoring gravity change over time. The data are compiled, without interpretation, in three spreadsheet files. Gravity values, GPS locations, and driving directions for absolute-gravity base stations are presented as National Geodetic Survey site descriptions.

  8. Regional gravity analysis of the crustal structure of Tunisia

    NASA Astrophysics Data System (ADS)

    Jallouli, Chokri; Mickus, Kevin

    2000-01-01

    Gravity data were integrated with seismic refraction/reflection data, well data and geological investigations to determine a general crustal structure of Tunisia. The gravity data analysis included the construction of a complete Bouguer gravity anomaly map, residual gravity anomaly maps, horizontal gravity gradient maps and a 2.5-D gravity model. Residual gravity anomaly maps illustrate crustal anomalies associated with various structural domains within Tunisia including the Sahel Block, Saharian Flexure, Erg Oriental Basin, Algerian Anticlinorium, Gafsa Trough, Tunisian Trough, Kasserine Platform and the Tell Mountains. Gravity anomalies associated with these features are interpreted to be caused either by thickening or thinning of Palæozoic and younger sediments or by crustal thinning. Analysis of the residual gravity anomaly and horizontal gravity gradient maps also determined a number of anomalies that may be associated with previously unknown structures. A north-south trending gravity model in general indicated similar subsurface bodies as a coincident seismic model. However, thinner Mesozoic sediments within the Tunisian Trough, thinner Palæozoic sediments in the Gafsa Trough, and a greater offset on the Saharian Flexure were required by the gravity data. Additionally, basement uplifts under the Kasserine Platform and Gafsa Trough, not imaged by seismic data, were required by the gravity data. The gravity model revealed two previously unknown basins north and south of the Algerian Anticlinorium (5 km), while the Erg Oriental Basin is composed of at least two sub-basins, each with a depth of 5 km.

  9. 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.

  10. 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.

  11. Global accuracy estimates of point and mean undulation differences obtained from gravity disturbances, gravity anomalies and potential coefficients

    NASA Technical Reports Server (NTRS)

    Jekeli, C.

    1979-01-01

    Through the method of truncation functions, the oceanic geoid undulation is divided into two constituents: an inner zone contribution expressed as an integral of surface gravity disturbances over a spherical cap; and an outer zone contribution derived from a finite set of potential harmonic coefficients. Global, average error estimates are formulated for undulation differences, thereby providing accuracies for a relative geoid. The error analysis focuses on the outer zone contribution for which the potential coefficient errors are modeled. The method of computing undulations based on gravity disturbance data for the inner zone is compared to the similar, conventional method which presupposes gravity anomaly data within this zone.

  12. GEOS 3 data processing for the recovery of geoid undulations and gravity anomalies

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1979-01-01

    The paper discusses the analysis of GEOS 3 altimeter data for the determination of geoid heights and point and mean gravity anomalies. Methods are presented for determining the mean anomalies and mean undulations from the GEOS 3 altimeter data available by the end of September 1977 without having a complete set of precise orbits. The editing of the data is extensive to remove questionable data, although no filtering of the data is carried out. An adjustment process is carried out to eliminate orbit error and altimeter bias. Representative point anomaly values are computed to investigate anomaly behavior across the Bonin Trench and over the Patton seamounts.

  13. Mantle origin of the Emeishan large igneous province from an analysis of residual gravity anomalies

    NASA Astrophysics Data System (ADS)

    Deng, Y.; Zhang, Z.; Mooney, W. D.; Fan, W.; Zhong, Q.; Badal, J.

    2013-12-01

    The Emeishan large igneous province (ELIP) is the only verified large igneous province in China. It covers an area of 250,000 km2 from the eastern margin of the Tibetan Plateau to the western margin of the Yangtze block. Most studies on ELIP are from geochemistry and tectonics, but the deep origin of the ELIP is still unclear. In this study, we investigate the residual gravity anomaly in South China and its relationship to the Emeishan large igneous province with constrains of lithospheric structure from deep seismic sounding profiles, deep seismic reflection surveys, and a variety of broadband seismic observations acquired in South China in the last several decades. Our working scheme consists of removing the respective gravitational effects due to: (1) the sediments, and undulations of the (2) crystalline basement, (3) upper crust; (4) Moho and (5) lithospheric thickness. We have thus obtained the residual gravity anomaly of the ELIP and surrounding region, striking positive residual anomaly with maximum value of 140 mGal is observed at the ELIP region. We use the conjugate gradient method to locate the deep origins of the residual gravity data. As a result, our preferred model consists of a positive cylindrical density anomaly that provides a fit to the residual gravity anomaly observed in ELIP. As the distance increases from the inner zone of the ELIP to the outer zone, the positive residual gravity decreases. Hence, in our model, the density anomaly decreases from about 0.06 g/cm3 beneath the inner zone to about 0.03 g/cm3 beneath the outer zone. The residual gravity and our preferred density anomaly provide new evidence, along with the seismic data and geochemical data, to confirm the domal structure of the Permian mantle plume that gave rise to the Emenshan Large Igneous Province.

  14. 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.

  15. South China Sea crustal thickness and lithosphere thinning from satellite gravity inversion incorporating a lithospheric thermal gravity anomaly correction

    NASA Astrophysics Data System (ADS)

    Kusznir, Nick; Gozzard, Simon; Alvey, Andy

    2016-04-01

    The distribution of ocean crust and lithosphere within the South China Sea (SCS) are controversial. Sea-floor spreading re-orientation and ridge jumps during the Oligocene-Miocene formation of the South China Sea led to the present complex distribution of oceanic crust, thinned continental crust, micro-continents and volcanic ridges. We determine Moho depth, crustal thickness and continental lithosphere thinning (1- 1/beta) for the South China Sea using a gravity inversion method which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir, 2008). The gravity inversion method provides a prediction of ocean-continent transition structure and continent-ocean boundary location which is independent of ocean isochron information. A correction is required for the lithosphere thermal gravity anomaly in order to determine Moho depth accurately from gravity inversion; the elevated lithosphere geotherm of the young oceanic and rifted continental margin lithosphere of the South China Sea produces a large lithosphere thermal gravity anomaly which in places exceeds -150 mGal. The gravity anomaly inversion is carried out in the 3D spectral domain (using Parker 1972) to determine 3D Moho geometry and invokes Smith's uniqueness theorem. The gravity anomaly contribution from sediments assumes a compaction controlled sediment density increase with depth. The gravity inversion includes a parameterization of the decompression melting model of White & McKenzie (1999) to predict volcanic addition generated during continental breakup lithosphere thinning and seafloor spreading. Public domain free air gravity anomaly, bathymetry and sediment thickness data are used in this gravity inversion. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we improve the determination of pre-breakup rifted margin conjugacy, rift orientation and sea-floor spreading trajectory. SCS conjugate margins

  16. Anomaly-free cosmological perturbations in effective canonical quantum gravity

    SciTech Connect

    Barrau, Aurelien; Calcagni, Gianluca; Grain, Julien E-mail: bojowald@gravity.psu.edu E-mail: julien.grain@ias.u-psud.fr

    2015-05-01

    This article lays out a complete framework for an effective theory of cosmological perturbations with corrections from canonical quantum gravity. Since several examples exist for quantum-gravity effects that change the structure of space-time, the classical perturbative treatment must be rethought carefully. The present discussion provides a unified picture of several previous works, together with new treatments of higher-order perturbations and the specification of initial states.

  17. Simulation gravity modeling to spacecraft-tracking data - Analysis and application

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Sjogren, W. L.; Abbott, E. A.; Zisk, S. H.

    1978-01-01

    It is proposed that line-of-sight gravity measurements derived from spacecraft-tracking data can be used for quantitative subsurface density modeling by suitable orbit simulation procedures. Such an approach avoids complex dynamic reductions and is analogous to the modeling of conventional surface gravity data. This procedure utilizes the vector calculations of a given gravity model in a simplified trajectory integration program that simulates the line-of-sight gravity. Solutions from an orbit simulation inversion and a dynamic inversion on Doppler observables compare well (within 1% in mass and size), and the error sources in the simulation approximation are shown to be quite small. An application of this technique is made to lunar crater gravity anomalies by simulating the complete Bouguer correction to several large young lunar craters. It is shown that the craters all have negative Bouguer anomalies.

  18. Investigation of urban faults in Shenzhen using wavelet multi-scale analysis and modeling of gravity observations

    NASA Astrophysics Data System (ADS)

    Xu, Chuang; Chen, Liang; Liu, Xi-kai

    2016-04-01

    Urban faults in Shenzhen are potential threat to the city security and sustainable development. To improve the knowledge of the Shenzhen fault zone, interpretation and inversion of gravity data were carried out. Bouguer gravity covering the whole Shenzhen city was calculated with a resolution of 1kmx1km. Wavelet multi-scale analysis (MSA) was applied to the Bouguer gravity data to obtain the multilayer residual anomalies corresponding to different depths. In addition, 2D gravity models were constructed along three profiles. The Bouguer gravity anomaly shows a NE-striking high-low-high pattern from northwest to southeast, strongly related to the main faults. According to the result of MSA, the correlation between gravity anomaly and faults is particularly significant from 4 to 12 km depth. The residual gravity with small amplitude in each layer indicates weak tectonic activity in the crust. In the upper layers, positive anomalies along most of faults reveal the upwelling of high-density materials during the past tectonic movements. The multilayer residual anomalies also implicate important information about the faults, such as the vertical extension and the dip direction. The maximum depth of the faults is about 20km. In general, NE-striking faults extend deeper than NW-striking Faults and have a larger dip angle. This study is supported by the National Natural Science Foundation of China (Grant No.41504015) and China Postdoctoral Science Foundation (Grant No.2015M572146).

  19. Gravity anomaly map of Mars and Moon and analysis of Venus gravity field: New analysis procedures

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The technique of harmonic splines allows direct estimation of a complete planetary gravity field (geoid, gravity, and gravity gradients) everywhere over the planet's surface. Harmonic spline results of Venus are presented as a series of maps at spacecraft and constant altitudes. Global (except for polar regions) and local relations of gravity to topography are described.

  20. On the recovery of gravity anomalies from high precision altimeter data

    NASA Technical Reports Server (NTRS)

    Lelgemann, D.

    1976-01-01

    A model for the recovery of gravity anomalies from high precision altimeter data is derived which consists of small correction terms to the inverse Stokes' formula. The influence of unknown sea surface topography in the case of meandering currents such as the Gulf Stream is discussed. A formula was derived in order to estimate the accuracy of the gravity anomalies from the known accuracy of the altimeter data. It is shown that for the case of known harmonic coefficients of lower order the range of integration in Stokes inverse formula can be reduced very much.

  1. Plumes in the mantle. [free air and isostatic gravity anomalies for geophysical interpretation

    NASA Technical Reports Server (NTRS)

    Khan, M. A.

    1973-01-01

    Free air and isostatic gravity anomalies for the purposes of geophysical interpretation are presented. Evidence for the existance of hotspots in the mantle is reviewed. The prosposed locations of these hotspots are not always associated with positive gravity anomalies. Theoretical analysis based on simplified flow models for the plumes indicates that unless the frictional viscosities are several orders of magnitude smaller than the present estimates of mantle viscosity or alternately, the vertical flows are reduced by about two orders of magnitude, the plume flow will generate implausibly high temperatures.

  2. Mafic and ultramafic rocks of the northwestern Brooks Range of Alaska produce nearly symmetric gravity anomalies

    SciTech Connect

    Morin, R.L. )

    1993-04-01

    An arc of mafic and ultramafic rocks is mapped from Asik Mountain to Siniktanneyak Mountain in the northwestern Brooks Range of Alaska. Gravity data, although not very detailed, have been collected over the region and show some very conspicuous circular or oval gravity highs over portions of the mapped mafic-ultramafic bodies. Bodies which have large associated gravity anomalies are Asik Mountain (80 mGal), Avon Hills (20 mGal), Misheguk Mountain (30 mGal), and Siniktanneyak Mountain (20 mGal). Gabbros of the Siniktanneyak Mountain complex, where the gravity coverage is best, have densities of about 3.0 g/cm[sup 3] while the densities of the surrounding sedimentary rocks are about 2.6 g/cm[sup 3]. Volcanic rocks in the area have average densities of about 2.7 g/cm[sup 3]. Three-dimensional modeling indicates that the largest anomaly, on the southwestern part of the complex, could be caused by a polygonal prism of gabbro with vertical sides, about 6 km across and about 4.5 km deep. A smaller lobe of the anomaly on the northeast of the complex could be caused by another oblong polygonal prism about 4 km long and 2 km wide trending northeast and about 1.5 km deep. Modeling this anomaly with densities lower than gabbro would require greater thicknesses to produce the same anomaly. Modeling each anomaly along this arc in 2 1/2-dimensions shows many possible solutions using different body shapes and different density contrasts. There are several other gravity anomalies in this vicinity which could represent unexposed high density rocks. One such anomaly is in the Maiyumerak Mountains northeast of Asik Mountain (30 mGal). Another anomaly is to the northwest of Asik Mountain (20 mGal). There is also an anomaly at Uchugrak (20 mGal) east of Avan Hills. Although many of the anomalies in this region are poorly controlled, an attempt has been made to interpret the data to show possible solutions.

  3. Detailed Gravity and Magnetic Survey of the Taylorsville Triassic Basin

    SciTech Connect

    Leftwich, John; Nowroozi, Ali, A.

    1999-10-01

    This work reports the progress on collecting existing gravity data in a rectangular area covering the Richmond and Taylorsville Basins and its vicinity. The area covers one-degree latitude and one degree longitude, starting at 37 North, 77 West and ending at 38 North, 78 West. Dr. David Daniels of the United State Geological Survey supplied us with more than 4900 Bouguer gravity anomalies in this area. The purpose of this report is to present the data in form of several maps and discuss its relation to the geology of the Triassic Basins and its vicinity. Johnson and others (1985) also presented a map of the Bouguer gravity anomaly of this area. However, their map covers a smaller area, and it is based on smaller number of observations.

  4. 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.

  5. Kerr metric, geodesic motion, and Flyby Anomaly in fourth-order Conformal Gravity

    NASA Astrophysics Data System (ADS)

    Varieschi, Gabriele U.

    2014-06-01

    In this paper we analyze the Kerr geometry in the context of Conformal Gravity, an alternative theory of gravitation, which is a direct extension of General Relativity (GR). Following previous studies in the literature, we introduce an explicit expression of the Kerr metric in Conformal Gravity, which naturally reduces to the standard GR Kerr geometry in the absence of Conformal Gravity effects. As in the standard case, we show that the Hamilton-Jacobi equation governing geodesic motion in a space-time based on this geometry is indeed separable and that a fourth constant of motion—similar to Carter's constant—can also be introduced in Conformal Gravity. Consequently, we derive the fundamental equations of geodesic motion and show that the problem of solving these equations can be reduced to one of quadratures. In particular, we study the resulting time-like geodesics in Conformal Gravity Kerr geometry by numerically integrating the equations of motion for Earth flyby trajectories of spacecraft. We then compare our results with the existing data of the Flyby Anomaly in order to ascertain whether Conformal Gravity corrections are possibly the origin of this gravitational anomaly. Although Conformal Gravity slightly affects the trajectories of geodesic motion around a rotating spherical object, we show that these corrections are minimal and are not expected to be the origin of the Flyby Anomaly, unless conformal parameters are drastically different from current estimates. Therefore, our results confirm previous analyses, showing that modifications due to Conformal Gravity are not likely to be detected at the Solar System level, but might affect gravity at the galactic or cosmological scale.

  6. 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.

  7. 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.

  8. Gravity and geoid anomalies of the Philippine Sea: Evidence on the depth of compensation for the negative residual water depth anomaly

    NASA Technical Reports Server (NTRS)

    Bowin, C.

    1982-01-01

    A negative free-air gravity anomaly which occurs in the central part of the Philippine Sea was examined to determine the distribution and nature of possible regional mass excesses or deficiencies. Geoid anomalies from GEOS-3 observation were positive. A negative residual geoid anomaly consistent with the area of negative free-air gravity anomalies were found. Theoretical gravity-topography and geoid-topography admittance functions indicated that high density mantle at about 60 km dept could account for the magnitudes of the gravity and residual geoid anomaly and the 1 km residual water depth anomaly in the Philippine Sea. The negative residual depth anomaly may be compensated for by excess density in the uppermost mantle, but the residual geoid and regional free-air gravity anomalies and a slow surface wave velocity structure might result from low-density warm upper mantle material lying beneath the zone of high-density uppermost mantle. From a horizontal disk approximation, the depth of the low-density warm mantle was estimated to be on the order of 200 km.

  9. The estimation of 550 km x 550 km mean gravity anomalies. [from free atmosphere gravimetry data

    NASA Technical Reports Server (NTRS)

    Williamson, M. R.; Gaposchkin, E. M.

    1975-01-01

    The calculation of 550 km X 550 km mean gravity anomalies from 1 degree X 1 degree mean free-air gravimetry data is discussed. The block estimate procedure developed by Kaula was used, and estimates for 1452 of the 1654 blocks were obtained.

  10. A major crustal feature in the southeastern United States inferred from the MAGSAT equivalent source anomaly field

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    The MAGSAT equivalent-source anomaly field evaluated at 325 km altitude depicts a prominent anomaly centered over southeast Georgia, which is adjacent to the high-amplitude positive Kentucky anomaly. To overcome the satellite resolution constraint in studying this anomaly, conventional geophysical data were included in analysis: Bouguer gravity, seismic reflection and refraction, aeromagnetic, and in-situ stress-strain measurements. This integrated geophysical approach, infers more specifically the nature and extent of the crustal and/or lithospheric source of the Georgia MAGSAT anomaly. Physical properties and tectonic evolution of the area are all important in the interpretation.

  11. Forward modeling: Gravity anomalies of two-dimensional bodies of arbitrary shape with hyperbolic and parabolic density functions

    NASA Astrophysics Data System (ADS)

    Visweswara Rao, C.; Chakravarthi, V.; Raju, M. L.

    1994-06-01

    Computer programs in FORTRAN 77 to compute the gravity anomaly of a two-dimensional (2-D) body of irregular cross section with hyperbolic and parabolic variations in density contrast are developed and presented. The gravity anomaly of San Jacinto Graben, California, using a hyperbolic function and that of Los Angeles Basin, California, using a parabolic function, are computed and compared with respective observed anomalies.

  12. Principal facts of gravity stations with gravity and magnetic profiles from the Southwest Nevada Test Site, Nye County, Nevada, as of January, 1982

    USGS Publications Warehouse

    Jansma, P.E.; Snyder, D.B.; Ponce, David A.

    1983-01-01

    Three gravity profiles and principal facts of 2,604 gravity stations in the southwest quadrant of the Nevada Test Site are documented in this data report. The residual gravity profiles show the gravity measurements and the smoothed curves derived from these points that were used in geophysical interpretations. The principal facts include station label, latitude, longitude, elevation, observed gravity value, and terrain correction for each station as well as the derived complete Bouguer and isostatic anomalies, reduced at 2.67 g/cm 3. Accuracy codes, where available, further document the data.

  13. Covariant anomaly and Hawking radiation from the modified black hole in the rainbow gravity theory

    NASA Astrophysics Data System (ADS)

    Peng, Jun-Jin; Wu, Shuang-Qing

    2008-12-01

    Recently, Banerjee and Kulkarni (R. Banerjee, S. Kulkarni, arXiv: 0707. 2449 [hep-th]) suggested that it is conceptually clean and economical to use only the covariant anomaly to derive Hawking radiation from a black hole. Based upon this simplified formalism, we apply the covariant anomaly cancellation method to investigate Hawking radiation from a modified Schwarzschild black hole in the theory of rainbow gravity. Hawking temperature of the gravity’s rainbow black hole is derived from the energy-momentum flux by requiring it to cancel the covariant gravitational anomaly at the horizon. We stress that this temperature is exactly the same as that calculated by the method of cancelling the consistent anomaly.

  14. Gravity Analysis of the Jeffera Basin, Tunisia

    NASA Astrophysics Data System (ADS)

    Mickus, K.; Gabtni, H.; Jallouli, C.

    2004-12-01

    Southern Tunisia consists of two main tectonic provinces: 1) the Saharan Platform and 2) the folded Atlasic domain, separated by the North Saharan Flexure. The Saharan Platform, which contains the Ghadames Basin and the Telemzane Arch, consists of gently dipping Paleozoic strata overlain by Triassic to Cretaceous sediments. The Atlasic domain consists of a thicker sequence of mainly Mesozoic and younger rock with less complete sequences of Paleozoic strata. Within the Atlasic domain are the still actively subsiding Chotts and Jeffera basins. The Jeffera basin, which occurs to the east of the Telemzane Arch contains at least eight kilometers of Paleozoic and younger sediment that were formed during numerous subsidence episodes since Carboniferous time. The Jeffera basin is dominated by tilted fault blocks that were formed during numerous tectonic episodes. Several unpublished seismic reflection profiles and well data exist for the Jeffera basin, however a deep structural analysis of the basin has not been published. We examined the existing gravity data in conjunction with available well and geologic data to determine structural features within the basin. The Bouguer gravity anomaly map shows that the Jeffera basin is dominated by a narrow northwest-trending gravity minimum. However, a more detailed analysis consisting of wavelength filtering and edge enhancements indicate that the structure of the basin is more complicated than indicated by the Bouguer gravity anomaly map. A residual gravity anomaly map indicates that the Jeffera basin consists of at least three and maybe four subbasins. Additionally, the Jeffera Fault marks the boundary between northwest-trending gravity anomalies to its northeast and east-trending anomalies over the Saharan Platform. The above observation is amplified by the construction of the enhanced horizontal derivatives (EHG) of both the complete Bouguer gravity and the residual gravity anomaly maps. The EHG maps highlight the lateral

  15. Oceanwide gravity anomalies from Geos-3, Seasat and Geosat altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, Richard H.; Basic, Tomislav

    1992-01-01

    Three kinds of satellite altimeter data have been combined, along with 5 x 5 arcmin bathymetric data, to calculate a 0.125 deg ocean wide gridded set of 2.3 x 10 exp 6 free-air gravity anomalies. The procedure used was least squares collocation that yields the predicted anomaly and standard deviation. The value of including the bathymetric data was shown in a test around the Dowd Seamount where the root mean square (rms) difference between ship gravity measurements decreased from +/- 40 mgal to +/- 20 mgal when the bathymetry was included. Comparisons between the predicted anomalies and ship gravity data is described in three cases. In the Banda Sea the rms differences were +/- 20 mgal for two lines. In the South Atlantic rms differences over lines of 2000 km in length were +/- 7 mgal. For cruise data in the Antarctica region the discrepancies were +/- 12 mgal. Comparisons of anomalies derived from the Geosat geodetic mission data by Marks and McAdoo (1992) with ship dta gave differences of +/- 6 mgal showing the value of the much denser Geosat geodetic mission altimeter data.

  16. The origin of the non-mare mascon gravity anomalies in lunar basins

    NASA Astrophysics Data System (ADS)

    Andrews-Hanna, Jeffrey C.

    2013-01-01

    Many lunar basins are characterized by prominent positive gravity anomalies over the basin interiors, referred to as mass concentrations or mascons. While a significant fraction of some near-side mascon anomalies can be explained as a result of the flexural support of the mare basalts within the basins, a number of basins, including Orientale, exhibit mascons in excess of those that can be plausibly ascribed to the mare. Some basins exhibit mascons but lack mare altogether. Lunar gravity and topography data are used to map the isostatic anomaly, or the height of the surface above or below its isostatic level. Orientale is representative of the majority of lunar basins, in which the super-isostatic basin center is surrounded by a sub-isostatic annulus of comparable magnitude but greater area. The basin structure as a whole is found to be strongly sub-isostatic. High-resolution crustal thickness models of Orientale confirm that it is surrounded by an annulus of thickened but sub-isostatic crust. It is proposed that the flexural uplift of the annulus causes the uplift and positive gravity anomalies within the basin center. Finite element models are used to examine the flexural uplift of the sub-isostatic annulus and the basin center for a range of lithosphere thicknesses both outside the basin and in the basin interior. The uplift of the basin center can exceed 2 km, increasing the central gravity anomaly by ˜200 mGal. This annular uplift explains a significant fraction of the Orientale mascon, and is likely a dominant cause of non-mare mascons globally.

  17. 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.

  18. Sub-surface Models of Long- and Short-wavelength Gravity Anomalies in Pennsylvania

    NASA Astrophysics Data System (ADS)

    Malinconico, L. L.; Morabito, J.; Hudacek, W.; Harhen, M.; McAtee, B.

    2008-12-01

    Over the past several years we have been collecting and compiling gravity data in various areas in Pennsylvania to complement existing data previously compiled by the National Image and Mapping Agency and GeoNet. Supported by the Pennsylvania Geological Survey, the aim of this project is to generate a gravity map for the state. This has involved the collection of approximately 4000 new observations and identification of previously acquired data from other sources that had not been included in the above listed data bases. While we are still in the process of cleaning up the data set, it is now possible to use the data to model subsurface density changes for both short and long-wavelength anomalies. An intriguing feature of the gravity map of Pennsylvania is the long-wavelength NE-SW-trending positive and negative anomalies that have little direct correlation with the observed surface geology. The negative anomalies range in amplitude from -12 to - 40 mgals, with wavelengths from 80 to 150 km, while the positive anomalies have amplitudes from 11 to 54 mgals and wavelengths between 100 and 135 km. We have modeled several of these using both wavelength analysis and simple two-dimensional modeling. The results suggest that, unlike previous interpretations that suggested shallow basins or intrusions, part of the cause of these anomalies may be as deep as topographic variations at the crust-mantle boundary. With well-constrained regional trends we have also been able to use these data to isolate and model short- wavelength anomalies. Within the Newark Basin in southeastern Pennsylvania one focus has been on the diabase intrusions. The gravity data demonstrate a remarkable special coincidence of 5 to 10 mgal positive anomalies with the known outcrop pattern of the sills, however there are also some areas where the sill is observed to outcrop, but where the gravity signature is minimal or does not exist. The density models of the sills range in thickness from .3 km to

  19. Crustal Structure beneath Northeastern Japan Derived from Explosion Seismology and Gravity Anomalies

    NASA Astrophysics Data System (ADS)

    HARA, H.; KONO, Y.

    2001-12-01

    In 1997, one of the most extensive explosion seismological investigation was conducted along the Kamaishi-Iwaki profile in the northern part of Honshu Island, Japan, and Iwasaki et al.(1999) presented a detailed P-wave crustal velocity structure in this region. Our group had about 35,000 gravity data points covering northeastern Japan, and now we added the gravity data along the Kamaishi-Iwaki profile. Using this data set, we constructed a detailed gravity profile along this line. We obtained a two dimensional crustal structures applying 2D-Talwani?s method as we describe below. As a starting model, we converted a P-wave velocity structure given by Iwasaki et al. (1999) into a density structure model employing an empirical relationship between seismic velocity and rock density (Nafe and Drake, 1957). This model, however, did not agree with the gravity anomalies. Therefore we modified the starting model in the following order: (a) we changed the depth of the Moho and the Conrad boundary in order to achive a better fit to the long wavelength component of gravity anomalies; (b) modify the density of the sedimentary rocks into heavier one. However we could not obtain consistent theoretical gravity anomalies over the Tono region where large granitic bodies is thought to have intruded during the Cretaceous period exist. Therefore we assume a granite pluton whose density is lighter than surrounding rocks?, 2.64 g/cc, and insert in an advanced model. In this model, the depth of the diapir-shaped granite pluton is considered to be no deeper than 8-10 kilometers. This model is consistent with epicenter distribution of earthquakes and geology in this region.

  20. Preparation of Residual Gravity Maps for the Southern Cascade Mountains, Washington Using Fourier Analysis

    SciTech Connect

    Dishberger, Debra McLean

    1983-04-01

    This report represents a continuation of gravity work in the Cascade Mountains of Washington supported by the Division of Geology and Earth Resources since 1974. The purpose of this research has been collection of baseline gravity data for use in geothermal resource evaluation. Results of the Division's gravity studies to date are given in Danes and Phillips (1983a, 1983b). One of the problems encountered when analyzing gravity data is distinguishing between those parts of the data that represent geologic structures of interest, and those that do not. In many cases, the features of interest are relatively small, near-surface features, such as those sought in mineral, petroleum, or geothermal exploration. Gravity anomalies caused by such structures may be distorted or masked by anomalies caused by larger, deeper geologic structures. Gravity anomalies caused by relatively shallow, small geologic structures are termed residual anomalies. Those due to broad, deep-seated features can be described as regional anomalies. The purpose of this report is to describe a Fourier analysis method for separating residual and regional gravity anomalies from a complete Bouguer gravity anomaly field. The technique has been applied to gravity data from the Southern Cascade Mountains, Washington. Residual gravity anomaly maps at a scale of 1:250,000 are presented for various regional wavelength filters, and a power spectrum of the frequency components in the South Cascade gravity data is displayed. No attempt is made to interpret the results of this study in terms of geologic structures.

  1. Anomalies and Hawking fluxes from the black holes of topologically massive gravity

    NASA Astrophysics Data System (ADS)

    Porfyriadis, Achilleas P.

    2009-05-01

    The anomaly cancelation method proposed by Wilczek et al. is applied to the black holes of topologically massive gravity (TMG) and topologically massive gravito-electrodynamics (TMGE). Thus the Hawking temperature and fluxes of the ACL and ACGL black holes are found. The Hawking temperatures obtained agree with the surface gravity formula. Both black holes are rotating and this gives rise to appropriate terms in the effective U (1) gauge field of the reduced (1 + 1)-dimensional theory. It is found that the terms in this U (1) gauge field correspond exactly to the correct angular velocities on the horizon of both black holes as well as the correct electrostatic potential of the ACGL black hole. So the results for the Hawking fluxes derived here from the anomaly cancelation method, are in complete agreement with the ones obtained from integrating the Planck distribution.

  2. Joint Inversion and Forward Modeling of Gravity and Magnetic Data in the Ismenius Region of Mars

    NASA Technical Reports Server (NTRS)

    Milbury, C. A.; Raymond, C. A.; Jewell, J. B.; Smrekar, S. E.; Schubert, G.

    2005-01-01

    The unexpected discovery of remanent crustal magnetism on Mars was one of the most intriguing results from the Mars Global Surveyor mission. The origin of the pattern of magnetization remains elusive. Correlations with gravity and geology have been examined to better understand the nature of the magnetic anomalies. In the area of the Martian dichotomy between 50 and 90 degrees E (here referred to as the Ismenius Area), we find that both the Bouguer and the isostatic gravity anomalies appear to correlate with the magnetic anomalies and a buried fault, and allow for a better constraint on the magnetized crust].

  3. Joint Interpretation of Bathymetric and Gravity Anomaly Maps Using Cross and Dot-Products.

    NASA Astrophysics Data System (ADS)

    Jilinski, Pavel; Fontes, Sergio Luiz

    2010-05-01

    0.1 Summary We present the results of joint map interpretation technique based on cross and dot-products applied to bathymetric and gravity anomaly gradients maps. According to the theory (Gallardo, Meju, 2004) joint interpretation of different gradient characteristics help to localize and empathize patterns unseen on one image interpretation and gives information about the correlation of different spatial data. Values of angles between gradients and their cross and dot-product were used. This technique helps to map unseen relations between bathymetric and gravity anomaly maps if they are analyzed separately. According to the method applied for the southern segment of Eastern-Brazilian coast bathymetrical and gravity anomaly gradients indicates a strong source-effect relation between them. The details of the method and the obtained results are discussed. 0.2 Introduction We applied this method to investigate the correlation between bathymetric and gravity anomalies at the southern segment of the Eastern-Brazilian coast. Gridded satellite global marine gravity data and bathymetrical data were used. The studied area is located at the Eastern- Brazilian coast between the 20° W and 30° W meridians and 15° S and 25° S parallels. The volcanic events responsible for the uncommon width of the continental shelf at the Abrolhos bank also were responsible for the formation of the Abrolhos islands and seamounts including the major Vitoria-Trindade chain. According to the literature this volcanic structures are expected to have a corresponding gravity anomaly (McKenzie, 1976, Zembruscki, S.G. 1979). The main objective of this study is to develop and test joint image interpretation method to compare spatial data and analyze its relations. 0.3 Theory and Method 0.3.1 Data sources The bathymetrical satellite data were derived bathymetry 2-minute grid of the ETOPO2v2 obtained from NOAA's National Geophysical Data Center (http://www.ngdc.noaa.gov). The satellite marine gravity 1

  4. Improved gravity anomaly fields from retracked multimission satellite radar altimetry observations over the Persian Gulf and the Caspian Sea

    NASA Astrophysics Data System (ADS)

    Khaki, M.; Forootan, E.; Sharifi, M. A.; Awange, J.; Kuhn, M.

    2015-09-01

    Satellite radar altimetry observations are used to derive short wavelength gravity anomaly fields over the Persian Gulf and the Caspian Sea, where in situ and ship-borne gravity measurements have limited spatial coverage. In this study the retracking algorithm `Extrema Retracking' (ExtR) was employed to improve sea surface height (SSH) measurements that are highly biased in the study regions due to land contaminations in the footprints of the satellite altimetry observations. ExtR was applied to the waveforms sampled by the five satellite radar altimetry missions: TOPEX/POSEIDON, JASON-1, JASON-2, GFO and ERS-1. Along-track slopes have been estimated from the improved SSH measurements and used in an iterative process to estimate deflections of the vertical, and subsequently, the desired gravity anomalies. The main steps of the gravity anomaly computations involve estimating improved SSH using the ExtR technique, computing deflections of the vertical from interpolated SSHs on a regular grid using a biharmonic spline interpolation and finally estimating gridded gravity anomalies. A remove-compute-restore algorithm, based on the fast Fourier transform, has been applied to convert deflections of the vertical into gravity anomalies. Finally, spline interpolation has been used to estimate regular gravity anomaly grids over the two study regions. Results were evaluated by comparing the estimated altimetry-derived gravity anomalies (with and without implementing the ExtR algorithm) with ship-borne free air gravity anomaly observations, and free air gravity anomalies from the Earth Gravitational Model 2008 (EGM2008). The comparison indicates a range of 3-5 mGal in the residuals, which were computed by taking the differences between the retracked altimetry-derived gravity anomaly and the ship-borne data. The comparison of retracked data with ship-borne data indicates a range in the root-mean-square-error (RMSE) between approximately 1.8 and 4.4 mGal and a bias between 0

  5. Gravity evidence for a shallow intrusion under Medicine Lake volcano, California.

    USGS Publications Warehouse

    Finn, C.; Williams, D.L.

    1982-01-01

    A positive gravity anomaly is associated with Medicine Lake volcano, California. Trials with different Bouguer reduction densities indicate that this positive anomaly cannot be explained by an inappropriate choice of Bouguer reduction density but must be caused by a subvolcanic body. After separating the Medicine Lake gravity high from the regional field, we were able to fit the 27mgal positive residual anomaly with a large, shallow body of high density contrast (+0.41g/cm3) and a thickness of 2.5km. We interpret this body to be an intrusion of dense material emplaced within the several-kilometres-thick older volcanic layer that probably underlies Medicine Lake volcano.-Authors

  6. Mean gravity anomalies and sea surface heights derived from GEOS-3 altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1978-01-01

    Approximately 2000 GEOS-3 altimeter arcs were analyzed to improve knowledge of the geoid and gravity field. An adjustment procedure was used to fit the sea surface heights (geoid undulations) in an adjustment process that incorporated cross-over constraints. The error model used for the fit was a one or two parameter model which was designed to remove altimeter bias and orbit error. The undulations on the adjusted arcs were used to produce geoid maps in 20 regions. The adjusted data was used to derive 301 5 degree equal area anomalies and 9995 1 x 1 degree anomalies in areas where the altimeter data was most dense, using least squares collocation techniques. Also emphasized was the ability of the altimeter data to imply rapid anomaly changes of up to 240 mgals in adjacent 1 x 1 degree blocks.

  7. 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.

  8. 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.

  9. 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.

  10. Vertical and Horizontal Analysis of Crustal Structure of Southeastern Mediterranean and the Egyptian Coastal Zone, from Bouguer and Satellite Mission Data

    NASA Astrophysics Data System (ADS)

    Saleh, Salah

    2016-07-01

    The present Tectonic system of Southeastern Mediterranean is driven by the collision of the African and Eurasian plates, the Arabian Eurasian convergence and the displacement of the Anatolian Aegean microplate, which generally represents the characteristic of lithospheric structure of the region. In the scope of this study, Bouguer and the satellite gravity (satellite altimetry) anomalies of southeastern Mediterranean and North Eastern part of Egypt were used for investigating the lithospheric structures. Second order trend analyses were applied firstly to Bouguer and satellite altimetry data for examining the characteristic of the anomaly. Later, the vertical and horizontal derivatives applications were applied to the same data. Generally, the purpose of the applying derivative methods is determining the vertical and horizontal borders of the structure. According to the results of derivatives maps, the study area could mainly divided into important four tectonic subzones depending on basement and Moho depth maps. These subzones are distributed from south to the north as: Nile delta-northern Sinai zone, north Egyptian coastal zone, Levantine basin zone and northern thrusting (Cyprus and its surroundings) zone. These zones are separated from each other by horizontal tectonic boundaries and/or near-vertical faults that display the block-faulting tectonic style of this belt. Finally, the gravity studies were evaluated together with the seismic activity of the region. Consequently, the geodynamical structure of the region is examined with the previous studies done in the region. Thus, the current study indicates that satellite gravity mission data is a valuable source of data in understanding the tectonic boundary behavior of the studied region and that satellite gravity data is an important modern source of data in the geodynamical studies.

  11. 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.

  12. Lunar floor-fractured craters as magmatic intrusions: Geometry, modes of emplacement, associated tectonic and volcanic features, and implications for gravity anomalies

    NASA Astrophysics Data System (ADS)

    Jozwiak, Lauren M.; Head, James W.; Wilson, Lionel

    2015-03-01

    , the intrusion concentrates bending primarily at the periphery, resulting in a flat, tabular intrusion. We predict that this process will result in concentric fractures over the region of greatest bending. This location is close to the crater wall in large, flat-floored craters, as observed in the crater Humboldt, and interior to the crater over the domed floor in smaller craters, as observed in the crater Vitello. A variety of volcanic features are predicted to be associated with the solidification and degassing of the intrusion; these include: (1) surface lava flows associated with concentric fractures (e.g., in the crater Humboldt); (2) vents with no associated pyroclastic material, from the deflation of under-pressurized magmatic foam (e.g., the crater Damoiseau); and (3) vents with associated pyroclastic deposits from vulcanian eruptions of highly pressurized magmatic foam (e.g., the crater Alphonsus). The intrusion of basaltic magma beneath the crater is predicted to contribute a positive component to the Bouguer gravity anomaly; we assess the predicted Bouguer anomalies associated with FFCs and outline a process for their future interpretation. We conclude that our proposed mechanism serves as a viable formation process for FFCs and accurately predicts numerous morphologic, morphometric, and geophysical features associated with FFCs. These predictions can be further tested using GRAIL (Gravity Recovery and Interior Laboratory) data.

  13. Longwavelength gravity anomalies and the deep thermal structure of the Baikal rift

    SciTech Connect

    Diament, M. ); Kogan, M.G. )

    1990-10-01

    The analysis of the gravity field over the Baikal rift area has been carried out in order: (1) to detect the amount of the deep hot material, and (2) to constrain the flexural rigidity of the lithosphere. The authors removed a few first harmonics of the global field and the gravity effects due to the crust from the observed field and found a residual anomaly which is aligned with the rift. This residual, which they attribute to the mantle, shows a minimum of about 15 mgal in amplitude and 900 km width, which is superimposed over a wider minimum with smaller amplitude. A model involving a simple stretching of the lithosphere with diffusion of heat predicts the right order of magnitude for both the amplitude and the wavelength of the 900-km anomaly. Results confirm that the stretching factor is of the order of 1.2 to 1.5. Interpretation of the coherence function computed between gravity and topography shows that the lithosphere in the area has a significant equivalent elastic thickness of about 30 km (i.e. flexural rigidity about 2.3 10{sup 23} N.m.).

  14. Gravity Survey of the Carson Sink - Data and Maps

    DOE Data Explorer

    Faulds, James E.

    2013-12-31

    A detailed gravity survey was carried out for the entire Carson Sink in western Nevada (Figure 1) through a subcontract to Zonge Engineering, Inc. The Carson Sink is a large composite basin containing three known, blind high‐temperature geothermal systems (Fallon Airbase, Stillwater, and Soda Lake). This area was chosen for a detailed gravity survey in order to characterize the gravity signature of the known geothermal systems and to identify other potential blind systems based on the structural setting indicated by the gravity data. Data: Data were acquired at approximately 400, 800, and 1600 meter intervals for a total of 1,243 stations. The project location and station location points are presented in Figure 14. The station distribution for this survey was designed to complete regional gravity coverage in the Carson Sink area without duplication of available public and private gravity coverage. Gravity data were acquired using a Scintrex CG‐5 gravimeter and a LaCoste and Romberg (L&R) Model‐G gravimeter. The CG‐5 gravity meter has a reading resolution of 0.001 milligals and a typical repeatability of less than 0.005 milligals. The L&R gravity meter has a reading resolution of 0.01 milligals and a typical repeatability of 0.02 milligals. The basic processing of gravimeter readings to calculate through to the Complete Bouguer Anomaly was made using the Gravity and Terrain Correction software version 7.1 for Oasis Montaj by Geosoft LTD. Results: The gravity survey of the Carson Sink yielded the following products. Project location and station location map (Figure 14). Complete Bouguer Anomaly @ 2.67 gm/cc reduction density. Gravity Complete Bouguer Anomaly at 2.50 g/cc Contour Map (Figure 15). Gravity Horizontal Gradient Magnitude Shaded Color Contour Map. Gravity 1st Vertical Derivative Color Contour Map. Interpreted Depth to Mesozoic Basement (Figure 16), incorporating drill‐hole intercept values. Preliminary Interpretation of Results: The Carson Sink

  15. 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,…

  16. Gravity anomalies and the structure of western Tibet and the southern Tarim Basin

    NASA Technical Reports Server (NTRS)

    Lyon-Caen, H.; Molnar, P.

    1984-01-01

    Gravity anomalies across the western part of the Tarim Basin and the Kunlun mountain belt show that this area is not in local isostatic equilibrium. These data can be explained if a strong plate underlying the Tarim Basin extends southwestward beneath the belt at least 80 km and supports part of the topography of northwest Tibet. This corroborates Norin's inference that late Tertiary crustal shortening has occurred in this area by southward underthrusting of the Tarim Basin beneath the Kunlun. This study places a lower bound on the amount of underthrusting.

  17. Crustal structure beneath the southern Appalachians: nonuniqueness of gravity modeling

    USGS Publications Warehouse

    Hutchinson, Deborah R.; Grow, John A.; Klitgord, Kim D.

    1983-01-01

    Gravity models computed for a profile across the long-wavelength paired negative-positive Bouguer anomalies of the southern Appalachian Mountains show that the large negative anomaly can be explained by a crustal root zone, whereas the steep gradient and positive anomaly east of the root may be explained equally well by three different geometries: a suture zone, a mantle upwarp, or a shallow body. Seismic data support the existence of a mountain root but are inadequate to resolve differences among the three possible geometries for the positive anomaly. The presence of outcropping mafic and ultramafic rocks in the southern Appalachians and the inferred tectonic history of the Appalachian orogen are most consistent with the suture-zone model. Crust similar to continental crust probably exists beneath the Coastal Plain and inner continental shelf where the gravity anomalies return to near-zero values.

  18. Subsurface structure of Teboursouk and El Krib plains (dome zone, northern Tunisia) by gravity analysis

    NASA Astrophysics Data System (ADS)

    Hadhemi, Balti; Fatma, Hachani; Ali, Kadri; Mohamed, Gasmi

    2016-07-01

    Gravity data was used to investigate sub-surface structure of the Teboursouk and El Krib plains belonging to the dome zone in the Northwest of Tunisia. Analysis of the gravity data included the computation of the Bouguer anomaly, the horizontal and vertical gravity gradients, the upward continuations, Euler deconvolution and analytic signal of high-resolution. The Bouguer anomaly map (d = 2.4 g cm-3) has provided information on the variation of the underground density and shown contrasting anomalous zones. The treatments applied to the Bouguer anomaly map have detected new deep faults and provided details on their dips and depths (exceeding 1500 m per places). Statistical analysis of the gravity data filtering shows that the study area is divided by four major faults with NW-SE, NE-SW, E-W and N-S trends. These faults have contributed to the structuring of the area. The results provide confirmation of some faults already recognized or inferred from the previous structural studies, and specify their depths and dips. While large number of new faults that remained undetected until now, have been highlighted.

  19. Subsurface structure of Teboursouk and El Krib plains (dome zone, northern Tunisia) by gravity analysis

    NASA Astrophysics Data System (ADS)

    Hadhemi, Balti; Fatma, Hachani; Ali, Kadri; Mohamed, Gasmi

    2016-07-01

    Gravity data was used to investigate sub-surface structure of the Teboursouk and El Krib plains belonging to the dome zone in the Northwest of Tunisia. Analysis of the gravity data included the computation of the Bouguer anomaly, the horizontal and vertical gravity gradients, the upward continuations, Euler deconvolution and analytic signal of high-resolution. The Bouguer anomaly map (d = 2.4 g cm-3) has provided information on the variation of the underground density and shown contrasting anomalous zones. The treatments applied to the Bouguer anomaly map have detected new deep faults and provided details on their dips and depths (exceeding 1500 m per places). Statistical analysis of the gravity data filtering shows that the study area is divided by four major faults with NW-SE, NE-SW, E-W and N-S trends. These faults have contributed to the structuring of the area. The results provide confirmation of some faults already recognized or inferred from the previous structural studies, and specify their depths and dips. While large number of new faults that remained undetected until now, have been highlighted.

  20. Modeling of shallow structures in the Cappadocia region using gravity and aeromagnetic anomalies

    NASA Astrophysics Data System (ADS)

    Kosaroglu, Sinan; Buyuksarac, Aydin; Aydemir, Attila

    2016-07-01

    In this study, shallow structures and bodies creating gravity and magnetic anomalies in the Cappadocia Volcanic Complex region in central Anatolia were investigated in order to determine the tectonic origin and structural setting of young volcanic units. The shallow geological structures in the region are depressions filled with mainly low-density, loose volcano-clastics and ignimbrite sheets associated with the continental Neogene deposits. These units together with other volcanic products are originated from the large Neogene and Quaternary volcanoes of the central Anatolia, particularly in the Cappadocia region. At first, spectral analysis to obtain the cut-off frequencies for the high-pass filter was performed in this investigation. Then, gravity and magnetic data were high-pass filtered to remove the deep and regional effects on anomalies and to unveil only shallow structures' effects. Subsequently, upward and downward continuations were carried out to determine how these shallow structures influence the total anomalies and their contribution in the confining total potential field. In addition, three and two dimensional gravity models (3D and 2D) of the study area were also constructed to obtain the bottom depth of shallow bodies. According to spectral analysis results, shallow structures could be separated into two groups from the power spectrums and bottom depth of deeper structure was commonly determined about 2 km in gravity and magnetic spectrum, both. More shallow structure is at the depth around 0.317 km according to the gravity power spectrum. Obviously, 3D and 2D models are consistent with the spectral analysis results for the deeper unit depth. A circular, large depression (70 × 50 km2) surrounds Mount Melendiz with a 1-2.7 km depth range (2 km in average). Because the depressions around the central volcanoes of Mount Melendiz and Mount Hasan cover very large areas in the basin scale, the shallow and low-density volcanic units can hardly be claimed

  1. Genesis of the largest Amazonian wetland in northern Brazil inferred by morphology and gravity anomalies

    NASA Astrophysics Data System (ADS)

    Rossetti, Dilce de Fátima; Cassola Molina, Eder; Cremon, Édipo Henrique

    2016-08-01

    The Pantanal Setentrional (PS) is the second largest wetland in Brazil, occurring in a region of northern Amazonia previously regarded as part of the intracratonic Solimões Basin. However, while Paleozoic to Neogene strata are recorded in this basin, the PS constitutes a broad region with an expressive record of only Late Pleistocene and Holocene deposits. The hypothesis investigated in the present work is if these younger deposits were formed within a sedimentary basin having a geological history separated from the Solimões Basin. Due to the location in a remote region of low accessibility, the sedimentary fill of the PS wetland remains largely unknown in subsurface. In the present work, we combine geomorphological and gravity data acquired on a global basis by several satellite gravity missions to approach the geological context of this region. The results revealed a wetland characterized in surface by a low-lying terrain with wedge shape and concave-up geometry that is in sharp contact with highland areas of Precambrian rocks of the Guiana Shield. Such contact is defined by a series of mainly NE- or NW-trending straight lineaments that eventually extend into both the Guiana Shield and the PS wetland. Also of relevance is that a great part of the PS wetland sedimentary cover consists of dominantly sandy deposits preserved as residual paleo-landforms with triangular shapes previously related to megafan depositional systems. These are distributed radially at the northern margin of the PS, with axis toward basement rocks and fringes toward the wetland's center, the latter containing the largest megafan landform. The analysis of gravity anomaly data revealed a main NNE-trending chain ∼500 km in length defined by high gravity values (i.e., up to 60 mGal); these are bounded by negative anomalies as low as -90 mGal. The chain with positive gravity anomaly marks the center of a subsiding area having a geological evolution that differs from the adjacent intracratonic

  2. A harmonic analysis of lunar gravity

    NASA Astrophysics Data System (ADS)

    Bills, B. G.; Ferrari, A. J.

    1980-02-01

    An improved model of lunar global gravity has been obtained by fitting a sixteenth-degree harmonic series to a combination of Doppler tracking data from Apollo missions 8, 12, 15, and 16, and Lunar Orbiters 1, 2, 3, 4, and 5, and laser ranging data to the lunar surface. To compensate for the irregular selenographic distribution of these data, the solution algorithm has also incorporated a semi-empirical a priori covariance function. Maps of the free-air gravity disturbance and its formal error are presented, as are free-air anomaly and Bouguer anomaly maps. The lunar gravitational variance spectrum has the form V(G; n) = O(n to the -4th power), as do the corresponding terrestrial and martian spectra. The variance spectra of the Bouguer corrections (topography converted to equivalent gravity) for these bodies have the same basic form as the observed gravity; and, in fact, the spectral ratios are nearly constant throughout the observed spectral range for each body. Despite this spectral compatibility, the correlation between gravity and topography is generally quite poor on a global scale.

  3. Crustal thickness anomalies in the North Atlantic Ocean basin from gravity analysis

    NASA Astrophysics Data System (ADS)

    Wang, Tingting; Lin, Jian; Tucholke, Brian; Chen, Yongshun John

    2011-03-01

    Gravity-derived crustal thickness models were calculated for the North Atlantic Ocean between 76°N and the Chain Fracture Zone and calibrated using seismically determined crustal thickness. About 7% of the ocean crust is <4 km thick (designated as thin crust), and 58% is 4-7 km thick (normal crust); the remaining 35% is >7 km thick and is interpreted to have been affected by excess magmatism. Thin crust probably reflects reduced melt production from relatively cold or refractory mantle at scales of up to hundreds of kilometers along the spreading axis. By far the most prominent thick crust anomaly is associated with Iceland and adjacent areas, which accounts for 57% of total crustal volume in excess of 7 km. Much smaller anomalies include the Azores (8%), Cape Verde Islands (6%), Canary Islands (5%), Madeira (<4%), and New England-Great Meteor Seamount chain (2%), all of which appear to be associated with hot spots. Hot spot-related crustal thickening is largely intermittent, suggesting that melt production is episodic on time scales of tens of millions of years. Thickened crust shows both symmetrical and asymmetrical patterns about the Mid-Atlantic Ridge (MAR) axis, reflecting whether melt anomalies were or were not centered on the MAR axis, respectively. Thickened crust at the Bermuda and Cape Verde rises appears to have been formed by isolated melt anomalies over periods of only ˜20-25 Myr. Crustal thickness anomalies on the African plate generally are larger than those on the North American plate; this most likely results from slower absolute plate speed of the African plate over relatively fixed hot spots.

  4. Massive torsion modes, chiral gravity and the Adler-Bell-Jackiw anomaly

    NASA Astrophysics Data System (ADS)

    Chang, Lay Nam; Soo, Chopin

    2003-04-01

    Regularization of quantum field theories introduces a mass scale which breaks axial rotational and scaling invariances. We demonstrate from first principles that axial torsion and torsion trace modes have non-transverse vacuum polarization tensors, and become massive as a result. The underlying reasons are similar to those responsible for the Adler-Bell-Jackiw (ABJ) and scaling anomalies. Since these are the only torsion components that can couple minimally to spin-½ particles, the anomalous generation of masses for these modes, naturally of the order of the regulator scale, may help to explain why torsion and its associated effects, including CPT violation in chiral gravity, have so far escaped detection. As a simpler manifestation of the reasons underpinning the ABJ anomaly than triangle diagrams, the vacuum polarization demonstration is also pedagogically useful. In addition, it is shown that the teleparallel limit of a Weyl fermion theory coupled only to the left-handed spin connection leads to a counter term which is the Samuel-Jacobson-Smolin action of chiral gravity in four dimensions.

  5. Principal facts for gravity stations in the Elko, Steptoe Valley, Coyote Spring Valley, and Sheep Range areas, eastern and southern Nevada

    USGS Publications Warehouse

    Berger, D.L.; Schaefer, D.H.; Frick, E.A.

    1990-01-01

    Principal facts for 537 gravity stations in the carbonate-rock province of eastern and southern Nevada are tabulated and presented. The gravity data were collected in support of groundwater studies in several valleys. The study areas include the Elko area, northern Steptoe Valley, Coyote Spring Valley, and the western Sheep Range area. The data for each site include values for latitude, longitude, altitude, observed gravity, free- air anomaly, terrain correction, and Bouguer anomaly (calculated at a bedrock density of 2.67 g/cu cm. (USGS)

  6. 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.

  7. 3D free-air gravity anomaly modeling for the Southeast Indian Ridge

    NASA Astrophysics Data System (ADS)

    Girolami, Chiara; Heyde, Ingo; Rinaldo Barchi, Massimiliano; Pauselli, Cristina

    2016-04-01

    In this study we analyzed the free-air gravity anomalies measured on the northwestern part of the Southeast Indian Ridge (hereafter SEIR) during the BGR cruise INDEX2012 with RV FUGRO GAUSS. The survey area covered the ridge from the Rodriguez Triple Junction along about 500 km towards the SSE direction. Gravity and magnetic data were measured along 65 profiles with a mean length of 60 km running approximately perpendicular to the ridge axis. The final gravity data were evaluated every 20 seconds along each profile. This results in a sampling interval of about 100 m. The mean spacing of the profiles is about 7 km. Together with the geophysical data also the bathymetry was measured along all profiles with a Kongsberg Simrad EM122 multibeam echosounder system. Previous studies reveal that the part of the ridge covered by the high resolution profiles is characterized by young geologic events (the oldest one dates back to 1 Ma) and that the SEIR is an intermediate spreading ridge. We extended the length of each profile to the area outside the ridge, integrating INDEX2012 high resolution gravity and bathymetric data with low resolution data derived from satellite radar altimeter measurements. The 3D forward gravity modeling made it possible to reconstruct a rough crustal density model for an extended area (about 250000 km2) of the SEIR. We analyzed the gravity signal along those 2D sections which cross particular geological features (uplifted areas, accommodation zones, hydrothermal fields and areas with hints for extensional processes e.g. OCCs) in order to establish a correlation between the gravity anomaly signal and the surface geology. We started with a simple "layer-cake" geologic model consisting of four density bodies which represent the sea, upper oceanic crust, lower oceanic crust and the upper mantle. Considering that in the study area the oceanic crust is young, we did not include the sediment layer. We assumed the density values of these bodies considering

  8. Principal facts for gravity stations for the Central Arizona Project

    USGS Publications Warehouse

    Peterson, Donald L.

    1972-01-01

    Observed gravity values, station locations, terrain corrections, and Bouguer gravity data are provided in tabular form for approximately 2460 gravity observations in south-central Arizona. "These data were used in preparation of -- Peterson, Donald L., 1968, Bouguer gravity map of parts of Maricopa, Pima, Pinal, and Yuma Counties, Arizona: U.S. Geol. Survey Geonhvs. Inv. Map GP-615.

  9. Comparison of different gravity field implied density models of the topography

    NASA Astrophysics Data System (ADS)

    Sedighi, Morteza; Tabatabaee, Seied; Najafi-Alamdari, Mehdi

    2009-06-01

    Density within the Earth crust varies between 1.0 and 3.0 g/cm3. The Bouguer gravity field measured in south Iran is analyzed using four different regional-residual separation techniques to obtain a residual map of the gravity field suitable for density modeling of topography. A density model of topography with radial and lateral distribution of density is required for an accurate determination of the geoid, e.g., in the Stokes-Helmert approach. The apparent density mapping technique is used to convert the four residual Bouguer anomaly fields into the corresponding four gravity im-plied subsurface density (GRADEN) models. Although all four density models showed good correlation with the geological density (GEODEN) model of the region, the GRADEN models obtained by high-pass filter-ing and GGM high-pass filtering show better numerical correlation with GEODEN model than the other models.

  10. Venus - Global gravity and topography

    NASA Astrophysics Data System (ADS)

    McNamee, J. B.; Borderies, N. J.; Sjogren, W. L.

    1993-05-01

    A new gravity field determination that has been produced combines both the Pioneer Venus Orbiter (PVO) and the Magellan Doppler radio data. Comparisons between this estimate, a spherical harmonic model of degree and order 21, and previous models show that significant improvements have been made. Results are displayed as gravity contours overlaying a topographic map. We also calculate a new spherical harmonic model of topography based on Magellan altimetry, with PVO altimetry included where gaps exist in the Magellan data. This model is also of degree and order 21, so in conjunction with the gravity model, Bouguer and isostatic anomaly maps can be produced. These results are very consistent with previous results, but reveal more spatial resolution in the higher latitudes.

  11. Implications of new gravity data for Baikal Rift zone structure

    NASA Technical Reports Server (NTRS)

    Ruppel, C.; Kogan, M. G.; Mcnutt, M. K.

    1993-01-01

    Newly available, 2D Bouguer gravity anomaly data from the Baikal Rift zone, Siberia, indicate that this discrete, intracontinental rift system is regionally compensated by an elastic plate about 50 km thick. However, spectral and spatial domain analyses and isostatic anomaly calculations show that simple elastic plate theory does not offer an adequate explanation for compensation in the rift zone, probably because of significant lateral variations in plate strength and the presence of subsurface loads. Our results and other geophysical observations support the interpretation that the Baikal Rift zone is colder than either the East African or Rio Grande rift.

  12. Gravity anomalies, flexure and mantle rheology seaward of Circum-Pacific trenches

    NASA Astrophysics Data System (ADS)

    Hunter, J.; Watts, A. B.

    2016-07-01

    We have used ensemble averages of satellite-derived free-air gravity anomaly data, together with inverse modelling techniques, to determine the effective elastic thickness, Te, of circum-Pacific subducting oceanic lithosphere and its relationship to plate age. Synthetic modelling tests show that Te can be recovered best using gravity anomaly, rather than bathymetry, data and profiles that are at least 750 km long. Inverse modeling based on a uniform Te elastic plate suggests that Te increases with age of the subducting oceanic lithosphere and is given approximately by the depth to the 390 ± 10°C oceanic isotherm based on a cooling plate model. Misfits between the observed and calculated gravity anomalies are significantly improved if a mechanically weak zone is included between the trench axis and the outer rise. This weak zone is coincident with observations of bend-faulting and seismicity. Inverse modelling shows that Te landward of the outer rise is generally 40-65% less than the Te seaward of the outer rise. Both landward and seaward Te increases with age of the lithosphere and are given by the depth to the 342-349°C and 671-714°C oceanic isotherm respectively. A dependence of Te on age is consistent with models for the cooling of oceanic lithosphere as it moves away from a mid-ocean ridge and the temperature-dependent ductile creep of oceanic lithospheric minerals such as olivine. By comparing the observed Te to the predicted Te based on laboratory-derived yield strength envelopes and an assumption of elastic-perfectly plastic deformation, we have attempted to constrain the rheology of oceanic lithosphere. Regardless of the assumed friction coefficient, the dry-olivine low-temperature plasticity flow laws of Goetze (1978), Evans & Goetze (1979), Raterron et al. (2004) and Mei et al. (2010) all provide quite a good fit to the observed Te at circum-Pacific subduction zones. This result contrasts with the Hawaiian Islands, where these flow laws are generally

  13. Gravity anomalies, flexure and mantle rheology seaward of circum-Pacific trenches

    NASA Astrophysics Data System (ADS)

    Hunter, J.; Watts, A. B.

    2016-10-01

    We have used ensemble averages of satellite-derived free-air gravity anomaly data, together with inverse modelling techniques, to determine the effective elastic thickness, Te, of circum-Pacific subducting oceanic lithosphere and its relationship to plate age. Synthetic modelling tests show that Te can be recovered best using gravity anomaly, rather than bathymetry, data and profiles that are at least 750 km long. Inverse modelling based on a uniform Te elastic plate suggests that Te increases with age of the subducting oceanic lithosphere and is given approximately by the depth to the 390 ± 10 °C oceanic isotherm based on a cooling plate model. Misfits between the observed and calculated gravity anomalies are significantly improved if a mechanically weak zone is included between the trench axis and the outer rise. This weak zone is coincident with observations of bend-faulting and seismicity. Inverse modelling shows that Te landward of the outer rise is generally 40-65 per cent less than the Te seaward of the outer rise. Both landward and seaward Te increases with age of the lithosphere and are given by the depth to the 342-349 °C and 671-714 °C oceanic isotherm, respectively. A dependence of Te on age is consistent with models for the cooling of oceanic lithosphere as it moves away from a mid-ocean ridge and the temperature-dependent ductile creep of oceanic lithospheric minerals such as olivine. By comparing the observed Te to the predicted Te based on laboratory-derived yield strength envelopes and an assumption of elastic-perfectly plastic deformation, we have attempted to constrain the rheology of oceanic lithosphere. Regardless of the assumed friction coefficient, the dry-olivine low-temperature plasticity flow laws of Goetze, Evans & Goetze, Raterron et al. and Mei et al. all provide quite a good fit to the observed Te at circum-Pacific subduction zones. This result contrasts with the Hawaiian Islands, where these flow laws are generally too strong to

  14. 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

  15. The effect of spatial truncation error on variance of gravity anomalies derived from inversion of satellite orbital and gradiometric data

    NASA Astrophysics Data System (ADS)

    Eshagh, Mehdi; Ghorbannia, Morteza

    2014-07-01

    The spatial truncation error (STE) is a significant systematic error in the integral inversion of satellite gradiometric and orbital data to gravity anomalies at sea level. In order to reduce the effect of STE, a larger area than the desired one is considered in the inversion process, but the anomalies located in its central part are selected as the final results. The STE influences the variance of the results as well because the residual vector, which is contaminated with STE, is used for its estimation. The situation is even more complicated in variance component estimation because of its iterative nature. In this paper, we present a strategy to reduce the effect of STE on the a posteriori variance factor and the variance components for inversion of satellite orbital and gradiometric data to gravity anomalies at sea level. The idea is to define two windowing matrices for reducing this error from the estimated residuals and anomalies. Our simulation studies over Fennoscandia show that the differences between the 0.5°×0.5° gravity anomalies obtained from orbital data and an existing gravity model have standard deviation (STD) and root mean squared error (RMSE) of 10.9 and 12.1 mGal, respectively, and those obtained from gradiometric data have 7.9 and 10.1 in the same units. In the case that they are combined using windowed variance components the STD and RMSE become 6.1 and 8.4 mGal. Also, the mean value of the estimated RMSE after using the windowed variances is in agreement with the RMSE of the differences between the estimated anomalies and those obtained from the gravity model.

  16. Spectral analysis of GEOS-3 altimeter data and frequency domain collocation. [to estimate gravity anomalies

    NASA Technical Reports Server (NTRS)

    Eren, K.

    1980-01-01

    The mathematical background in spectral analysis as applied to geodetic applications is summarized. The resolution (cut-off frequency) of the GEOS 3 altimeter data is examined by determining the shortest wavelength (corresponding to the cut-off frequency) recoverable. The data from some 18 profiles are used. The total power (variance) in the sea surface topography with respect to the reference ellipsoid as well as with respect to the GEM-9 surface is computed. A fast inversion algorithm for matrices of simple and block Toeplitz matrices and its application to least squares collocation is explained. This algorithm yields a considerable gain in computer time and storage in comparison with conventional least squares collocation. Frequency domain least squares collocation techniques are also introduced and applied to estimating gravity anomalies from GEOS 3 altimeter data. These techniques substantially reduce the computer time and requirements in storage associated with the conventional least squares collocation. Numerical examples given demonstrate the efficiency and speed of these techniques.

  17. Flexure and gravity anomalies of the oceanic lithosphere beneath the Louisville seamount

    NASA Astrophysics Data System (ADS)

    Hwang, Gyuha; Kim, Seung-Sep

    2016-08-01

    We have calculated the elastic thickness (Te), flexural deflection, and gravity anomaly of the oceanic crust beneath the Louisville seamount (LSC-03), near the Kermadec trench. A regional-residual separation of the bathymetry was performed to remove the effect of other geologic features (e.g., the trench). We used the uniform density and dense core models to approximate the total mass of the seamount, which was defined as the surface load required for flexural deformation. From the flexure modeling results, we found that more flexural depression was predicted by the uniform density model than by the dense core model. However, the uniform density model predicted a significantly smaller gravity anomaly than observed, whereas the dense core model minimized the prediction misfits reasonably. The best flexure model was found with a Te of 16 km for the uniform density model and 6 km for the dense core model. The flexure computed with the dense core model was consistent with the seismically detected Moho. The flexure modeling for LSC-03, thus, indicates that the dense core model better approximates the inner structure of the LSC-03. Based on the crustal age and geochronology of the given seamount, the age of the oceanic crust at the time of seamount formation (Δt) is 20 Ma. If this is the case, however, the Te estimates from both flexure models require some degree of lithospheric reheating by Louisville hotspot activity. Alternatively, considering the tectonic plate motion of the Osbourn Trough, Δt becomes approximately 4 Ma. This younger lithosphere model is more consistent with the observed flexural deformation and the Te estimate from the dense core model. Therefore, the time that the seamount-induced lithospheric deformation occurred may be far earlier than the age-dated volcanism.

  18. Implications of the Utopia Gravity Anomaly for the Resurfacing of the Northern Plains of Mars

    NASA Technical Reports Server (NTRS)

    Banerdt, W. B.

    2004-01-01

    Whereas the surface units of the northern plain of Mars generally exhibit ages ranging from late Hesperian to Amazonian, interpretation of precise topographic measurements indicate that the age of the underlying "basement" is early Noachian, or almost as old as the southern highlands. This suggests that widespread but relatively superficial resurfacing has occurred throughout the northern plains since the end of early heavy bombardment. In this abstract I examine some of the possible implications of the subsurface structure inferred for the Utopia basin from gravity data on the nature of this resurfacing. The large, shallow, circular depression in Utopia Planitia has been identified as a huge impact basin, based on both geological evidence and detailed analysis of MOLA topography. Its diameter (approx. 3000 km) is equivalent to that of the Hellas basin, as is its inferred age (early Noachian). However, whereas Hellas is extremely deep with rough terrain and large slopes, the Utopia basin is a smooth, shallow, almost imperceptible bowl. Conversely, Utopia displays one of the largest (non-Tharsis-related) positive geoid anomalies on Mars, in contrast to a much more subdued negative anomaly over Hellas.

  19. Fluid/Gravity Correspondence, Second Order Transport and Gravitational Anomaly***

    NASA Astrophysics Data System (ADS)

    Megías, Eugenio; Pena-Benitez, Francisco

    2014-03-01

    We study the transport properties of a relativistic fluid affected by chiral and gauge-gravitational anomalies. The computation is performed in the framework of the fluid/gravity correspondence for a 5 dim holographic model with Chern-Simons terms in the action. We find new anomalous and non anomalous transport coefficients, as well as new contributions to the existing ones coming from the mixed gauge-gravitational anomaly. Consequences for the shear waves dispersion relation are analyzed. Talk given by E. Megías at the International Nuclear Physics Conference INPC 2013, 2-7 June 2013, Firenze, Italy.Supported by Plan Nacional de Altas Energías (FPA2009-07908, FPA2011-25948), Spanish MICINN Consolider-Ingenio 2010 Programme CPAN (CSD2007-00042), Comunidad de Madrid HEP-HACOS S2009/ESP-1473, Spanish MINECO's Centro de Excelencia Severo Ochoa Program (SEV-2012-0234, SEV-2012-0249), and the Juan de la Cierva Program.

  20. 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.

  1. 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.

  2. Segmentation of the Himalayas as revealed by arc-parallel gravity anomalies

    PubMed Central

    Hetényi, György; Cattin, Rodolphe; Berthet, Théo; Le Moigne, Nicolas; Chophel, Jamyang; Lechmann, Sarah; Hammer, Paul; Drukpa, Dowchu; Sapkota, Soma Nath; Gautier, Stéphanie; Thinley, Kinzang

    2016-01-01

    Lateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen’s segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal & India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes. PMID:27649782

  3. Segmentation of the Himalayas as revealed by arc-parallel gravity anomalies.

    PubMed

    Hetényi, György; Cattin, Rodolphe; Berthet, Théo; Le Moigne, Nicolas; Chophel, Jamyang; Lechmann, Sarah; Hammer, Paul; Drukpa, Dowchu; Sapkota, Soma Nath; Gautier, Stéphanie; Thinley, Kinzang

    2016-01-01

    Lateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen's segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal &India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes. PMID:27649782

  4. Segmentation of the Himalayas as revealed by arc-parallel gravity anomalies

    NASA Astrophysics Data System (ADS)

    Hetényi, György; Cattin, Rodolphe; Berthet, Théo; Le Moigne, Nicolas; Chophel, Jamyang; Lechmann, Sarah; Hammer, Paul; Drukpa, Dowchu; Sapkota, Soma Nath; Gautier, Stéphanie; Thinley, Kinzang

    2016-09-01

    Lateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen’s segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal & India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes.

  5. Segmentation of the Himalayas as revealed by arc-parallel gravity anomalies.

    PubMed

    Hetényi, György; Cattin, Rodolphe; Berthet, Théo; Le Moigne, Nicolas; Chophel, Jamyang; Lechmann, Sarah; Hammer, Paul; Drukpa, Dowchu; Sapkota, Soma Nath; Gautier, Stéphanie; Thinley, Kinzang

    2016-09-21

    Lateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen's segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal &India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes.

  6. Detailed Gravity and Magnetic Survey of the Taylorsville Triassic Basin

    SciTech Connect

    Ali A. Nowroozi; John Leftwich

    1997-12-31

    Our research to date has involved the Interpretation of the Bouguer Gravity Anomaly Associated with the Richmond and Taylorsville Triassic Basins and its Vicinity. Continental rift basins around the world contain about 5% of the earth's sedimentary layers and produce about 20% of the total hydrocarbon production of the world (Ziegler (1983). Nearly 30 large basins of this type are reported by Manspeizer and Cousminer (1988) in eastern North America and northwestern Africa. There are eleven exposed basins of this type in the state of Virginia, from which nine are totally and two partially within the state's border. The number of unexposed basin's is not known. Exploration and drilling have been hampered largely because surface data are insufficient for even evaluation of those basins which are partly or completely exposed in the Piedmont Province. Generation of data through random exploratory drilling and seismic exploration is much too expensive and, therefore, these methods have not been widely used. In order to remedy this situation, we have used a geophysical method and completed a detailed and dense ground gravity surveys of the Richmond (Nowroozi and Wong, 1989, Daniels and Nowroozi, 1987). In this work we report our progress on collecting existing gravity data in a rectangular area covering the Richmond and Taylorsville Basins and its vicinity. The area covers one degree latitude and one degree longitude, starting at 37 North, 77 West and ending at 38 North, 78 West. Dr. David Daniels of the United State Geological Survey supplied us with more than 4900 Bouguer gravity anomalies in this area. The purpose of this progress report is to present the data in form of several maps and discuss its relation to the geology of the Triassic Basins and its vicinity. Johnson and others (1985) also presented a map of the Bouguer gravity anomaly of this area. However, their map covers a smaller area, and it is based on smaller number of observations.

  7. Detection of Characteristic Precipitation Anomaly Patterns of El Nino / La Nina in Time- variable Gravity Fields by GRACE

    NASA Astrophysics Data System (ADS)

    Heki, K.; Morishita, Y.

    2007-12-01

    GRACE (Gravity Recovery and Climate Experiment) satellites, launched in March 2002, have been mapping monthly gravity fields of the Earth, allowing us to infer changes in surface mass, e.g. water and ice. Past findings include the ice mass loss in southern Greenland (Luthcke et al., 2006) and its acceleration in 2004 (Velicogna and Wahr, 2006), crustal dilatation by the 2004 Sumatra Earthquake (Han et al., 2006) and the postseismic movement of water in mantle (Ogawa and Heki, 2007). ENSO (El Nino and Southern Oscillation) brings about global climate impacts, together with its opposite phenomenon, La Nina. Ropelewski and Halpert (1987) showed typical precipitation patterns in ENSO years; characteristic regional-scale precipitation anomalies occur in India, tropical and southern Africa and South America. Nearly opposite precipitation anomalies are shown to occur in La Nina years (Ropelewski and Halpert, 1988). Here we report the detection of such precipitation anomaly patterns in the GRACE monthly gravity data 2002 - 2007, which includes both La Nina (2005 fall - 2006 spring) and El Nino (2006 fall - 2007 spring) periods. We modeled the worldwide gravity time series with constant trends and seasonal changes, and extracted deviations of gravity values at two time epochs, i.e. February 2006 and 2007, and converted them into the changes in equivalent surface water mass. East Africa showed negative gravity deviation (-20.5 cm in water) in 2006 February (La Nina), which reversed to positive (18.7 cm) in 2007 February (El Nino). Northern and southern parts of South America also showed similar see-saw patterns. Such patterns closely resemble to those found meteorologically (Ropelewski and Halpert, 1987; 1988), suggesting the potential of GRACE as a sensor of inter-annual precipitation anomalies through changes in continental water storage. We performed numerical simulations of soil moisture changes at grid points in land area incorporating the CMAP precipitation data, NCEP

  8. Isostatic gravity map of the Monterey 30 x 60 minute quadrangle and adjacent areas, California

    USGS Publications Warehouse

    Langenheim, V.E.; Stiles, S.R.; Jachens, R.C.

    2002-01-01

    The digital dataset consists of one file (monterey_100k.iso) containing 2,385 gravity stations. The file, monterey_100k.iso, contains the principal facts of the gravity stations, with one point coded per line. The format of the data is described below. Each gravity station has a station name, location (latitude and longitude, NAD27 projection), elevation, and an observed gravity reading. The data are on the IGSN71 datum and the reference ellipsoid is the Geodetic Reference System 1967 (GRS67). The free-air gravity anomalies were calculated using standard formulas (Telford and others, 1976). The Bouguer, curvature, and terrain corrections were applied to the free-air anomaly at each station to determine the complete Bouguer gravity anomalies at a reduction density of 2.67 g/cc. An isostatic correction was then applied to remove the long-wavelength effect of deep crustal and/or upper mantle masses that isostatically support regional topography.

  9. The gravity anomaly field in the Gulf of Bothnia spatially characterized from satellite altimetry and in situ measurements

    NASA Astrophysics Data System (ADS)

    Noréus, J. P.; Nyborg, M. R.; Hayling, K. L.

    1997-06-01

    The gravity anomaly field in the Gulf of Bothnia has been investigated using (1) in situ high-precision measurements conducted on the sea ice during cold winters, and (2) gravity anomaly profiles computed from collinear satellite radar altimeter data from the Geosat ERM and the Topex/Poseidon missions. The in situ measurements were obtained from a collaboration between the Finnish Geodetic Institute, the Geological Survey of Sweden (SGU) and the National Survey of Sweden (LMV), and were processed with the geostatistical method called kriging. These data were used to calibrate the altimetric gravity. Altimetry generally resolves features of 20 km wavelength or longer, and in some cases detects shorter features when a sampling interval of 10 Hz is used. The precision of the along-track one-dimensional altimetric profiles corresponds to a gravity uncertainty of 2-3 mGal, and comparison with in situ measured gravity show 4 mGal discrepancy. The precision of the in situ measurements is better. However, depending on the sampling distance, the estimation uncertainty interior the in situ data areas may be up to 5 mGal between neighbouring data points. In regions with in situ data gaps, the estimation uncertainty of the in situ gravity measurements is rapidly increasing to a maximum of 9 mGal. An improved estimation uncertainty of 4-9 mGal was obtained in the same data gap regions with the support of satellite altimetry. Altimetric gravity is therefore used to estimate the gravity field in such regions, and to spatially characterize the gravity field in the Gulf of Bothnia.

  10. Evaluation Of The Potential Of Gravity Anomalies From Satellite Altimetry By Merging With Gravity Data From Various Sources - Application To Coastal Areas

    NASA Astrophysics Data System (ADS)

    Fernandes, M. J.; Bastos, L.; Tomé, P.

    The region of the Azores archipelago is a natural laboratory for gravity field studies, due to its peculiar geodynamic and oceanographic features, related to rough structures in the gravity field. As a consequence, gravity data from various sources have been collected in the scope of various observation campaigns. The available data set comprises marine, airborne and satellite derived gravity anoma- lies. The satellite data have been derived by altimetric inversion of satellite altimeter data (Topex/Poseidon and ERS), to which processing methods tuned for optimal data recovery in coastal areas have been applied. Marine and airborne data along coinci- dent profiles, some of them coincident with satellite tracks, were collected during an observation campaign that took place in the Azores in 1997, in the scope of the Eu- ropean Union project AGMASCO. In addition, gravity anomalies from an integrated GPS/INS system installed aboard an aircraft, have also been computed from the posi- tion and navigation data collected during the AGMASCO campaign. This paper presents a comparison study between all available data sets. In particular, the improvement of the satellite derived anomalies near the shoreline is assessed with respect to existing satellite derived models and with the high resolution geopotential model GPM98. The impact of these data sets in the regional geoid improvement will also be presented.

  11. Estimation of regional mass anomalies from Gravity Recovery and Climate Experiment (GRACE) over Himalayan region

    NASA Astrophysics Data System (ADS)

    Agrawal, R.; Singh, S. K.; Rajawat, A. S.; Ajai

    2014-11-01

    Time-variable gravity changes are caused by a combination of postglacial rebound, redistribution of water and snow/ice on land and as well as in the ocean. The Gravity Recovery and Climate Experiment (GRACE) satellite mission, launched in 2002, provides monthly average of the spherical harmonic co-efficient. These spherical harmonic co-efficient describe earth's gravity field with a resolution of few hundred kilometers. Time-variability of gravity field represents the change in mass over regional level with accuracies in cm in terms of Water Equivalent Height (WEH). The WEH reflects the changes in the integrated vertically store water including snow cover, surface water, ground water and soil moisture at regional scale. GRACE data are also sensitive towards interior strain variation, surface uplift and surface subsidence cover over a large area. GRACE data was extracted over the three major Indian River basins, Indus, Ganga and Brahmaputra, in the Himalayas which are perennial source of fresh water throughout the year in Northern Indian Plain. Time series analysis of the GRACE data was carried out from 2003-2012 over the study area. Trends and amplitudes of the regional mass anomalies in the region were estimated using level 3 GRACE data product with a spatial resolution at 10 by 10 grid provided by Center for Space Research (CSR), University of Texas at Austin. Indus basin has shown a subtle decreasing trend from 2003-2012 however it was observed to be statistically insignificant at 95 % confidence level. Ganga and Brahmaputra basins have shown a clear decreasing trend in WEH which was also observed to be statistically significant. The trend analysis over Ganga and Brahamputra basins have shown an average annual change of -1.28 cm and -1.06 cm in terms of WEH whereas Indus basin has shown a slight annual change of -0.07 cm. This analysis will be helpful to understand the loss of mass in terms of WEH over Indian Himalayas and will be crucial for hydrological and

  12. A gravity model for the Coso geothermal area, California

    SciTech Connect

    Feighner, M.A.; Goldstein, N.E.

    1990-08-01

    Two- and three-dimensional gravity modeling was done using gridded Bouguer gravity data covering a 45 {times} 45 km region over the Coso geothermal area in an effort to identify features related to the heat source and to seek possible evidence for an underlying magma chamber. Isostatic and terrain corrected Bouguer gravity data for about 1300 gravity stations were obtained from the US Geological Survey. After the data were checked, the gravity values were gridded at 1 km centers for the area of interest centered on the Coso volcanic field. Most of the gravity variations can be explained by two lithologic units: (1) low density wedges of Quarternary alluvium with interbedded thin basalts (2.4 g/cm{sup 3}) filling the Rose Valley and Coso Basin/Indian Wells Valley, and (2) low density cover of Tertiary volcanic rocks and intercalated Coso Formation (2.49 g/cm{sup 3}). A 3-D iterative approach was used to find the thicknesses of both units. The gravity anomaly remaining after effects from Units 1 and 2 are removed is a broad north-south-trending low whose major peak lies 5 km north of Sugarloaf Mountain, the largest of the less than 0.3 m.y. old rhyolite domes in the Coso Range. Most of this residual anomaly can be accounted for by a deep, low-density (2.47 g/cm{sup 3}) prismatic body extending from 8 to about 30 km below the surface. While some of this anomaly might be associated with fractured Sierran granitic rocks, its close correlation to a low-velocity zone with comparable geometry suggests that the residual anomaly is probably caused a large zone of partial melt underlying the rhyolite domes of the Coso Range. 12 refs., 9 figs.

  13. 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.

  14. Multifractal singular value decomposition (MSVD) for extraction of marine gravity anomaly

    NASA Astrophysics Data System (ADS)

    LYU, Wenchao; Zhu, Benduo; Qiu, Yan

    2015-04-01

    The concept of singularity is used for characterizing different types of nonlinear natural processes, including volcanic eruptions, faults, cloud formation, landslides, rainfall, hurricanes, flooding, earthquakes, wildfires, oil fields and mineralization. The singularity often results in anomalous amounts of energy release or material accumulation within a narrow spatial-temporal interval.The marine gravitation field has multi-fractal features, which show different scale invariant properties in region and local field. The SVD can be used in geophysical data processing for signal and noise separation, radar processing for enhancing weak signals in vertical seismic profiles (VSP). It has also been used in multi component seismic polarization filters and evaluating the amount of wavy reflections in ground-penetrating radar (GPR) images of base surge deposits. With the SVD, a matrix X can be decomposed to a series of eigenvalues. The eigenvalues conformed fractal or multi-fractal distribution described with the power-law function. The multi-fractal SVD can be used for feature extraction and anomaly identification for marine gravity investigation.This paper aims to analyze the marine gravitation data using the SVD and multifractal methods. This paper will also aim to more clearly define the spatial relationship between marine mineralization and the deep geological structures in the field by extracting the marine gravitation information at a particular frequency to provide valuable in depth evidence for predicting new deposits and deep tectonic.

  15. 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.

  16. Determining the COB location along the Iberian margin and Galicia Bank from gravity anomaly inversion, residual depth anomaly and subsidence analysis

    NASA Astrophysics Data System (ADS)

    Cowie, Leanne; Kusznir, Nick; Manatschal, Gianreto

    2015-11-01

    Knowledge and understanding of the ocean-continent transition (OCT) structure, continent-ocean boundary (COB) location and crustal type are of critical importance in evaluating rifted continental margin formation and evolution. OCT structure, COB location and magmatic type also have important implications for the understanding of the geodynamics of continental breakup and in the evaluation of petroleum systems in deep-water frontier oil and gas exploration at rifted continental margins. Mapping the distribution of thinned continental crust and lithosphere, its distal extent and the start of unequivocal oceanic crust and hence determining the OCT structure and COB location at rifted continental margins is therefore a generic global problem. In order to assist in the determination of the OCT structure and COB location, we present methodologies using gravity anomaly inversion, residual depth anomaly (RDA) analysis and subsidence analysis, which we apply to the west Iberian rifted continental margin. The west Iberian margin has one of the most complete data sets available for deep magma-poor rifted margins, so there is abundant data to which the results can be calibrated. Gravity anomaly inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning; subsidence analysis has been used to determine the distribution of continental lithosphere thinning; and RDAs have been used to investigate the OCT bathymetric anomalies with respect to expected oceanic bathymetries at rifted continental margins. These quantitative analytical techniques have been applied to the west Iberian rifted continental margin along profiles IAM9, Lusigal 12 (with the TGS-extension) and ISE-01. Our predictions of OCT structure, COB location and magmatic type (i.e. the volume of magmatic addition, whether the margin is `normal' magmatic, magma-starved or magma-rich) have been tested and validated using ODP wells (Legs 103, 149 and 173), which provide

  17. Principal facts for gravity stations in the Yuma, Arizona and Blythe, California areas

    USGS Publications Warehouse

    Peterson, Donald L.; Conradi, Arthur; Zohdy, Adel A.R.

    1972-01-01

    Observed gravity values, station locations, terrain corrections, and Bouguer gravity data are provided in tabular form for approximately 840 gravity observations in the Yuma, Arizona area and for approximately 225 gravity observations in the Blythe, California area.

  18. Gravity and fault structures, Long Valley caldera, California

    SciTech Connect

    Carle, S.F.; Goldstein, N.E.

    1987-07-01

    The main and catastrophic phase of eruption in Long Valley occurred 0.73 m.y. ago with the eruption of over 600 km/sup 3/ of rhyolitic magma. Subsequent collapse of the roof rocks produced a caldera which is now elliptical in shape, 32 km east-west by 17 km north-south. The caldera, like other large Quarternary silicic ash-flow volcanoes that have been studied by various workers, has a nearly coincident Bouguer gravity low. Earlier interpretations of the gravity anomaly have attributed the entire anomaly to lower density rocks filling the collapsed structure. However, on the basis of many additional gravity stations and supporting subsurface data from several new holes, a much more complex and accurate picture has emerged of caldera structure. From a three-dimensional inversion of the residual Bouguer gravity data we can resolve discontinuities that seem to correlate with extensions of pre-caldera faults into the caldera and faults associated with the ring fracture. Some of these faults are believed related to the present-day hydrothermal upflow zone and the zone of youngest volcanic activity within the caldera.

  19. Calculation of geoid undulations and gravity anomalies in the South China Sea by using the TOPEX/Poseidon and Geosat altimeter data

    NASA Astrophysics Data System (ADS)

    Zhang, Youguang; Zhang, Jie; Ji, Yonggang; Zhang, Huiqin

    2003-05-01

    In this paper, using TOPEX/Poseidon (9~346cycle) and Geosat/ERM(1~60cycle) altimeter data, the author applies combined adjustment model for calculating the South China Sea geoid undulations after data preprocessing. The difference between calculation result and OSU91A model is 30cm (spatial resolution is 22km). In addition, 12"x12" South China Sea gravity anomalies are calculated by using above geoid data and improved Stokes inverse formula. Contrasted with Scripps Institution of Oceanography gravity anomalies data, the accuracy of computation of gravity anomalies is 12´x10-5m/s2. These computations show that calculation speed is fast and calculation efficiency is high, so the method can calculate rapidly gravity anomalies in special sea area.

  20. Constraints on timing and magnitude of early global expansion of the Moon from topographic features in linear gravity anomaly areas

    NASA Astrophysics Data System (ADS)

    Sawada, Natsuki; Morota, Tomokatsu; Kato, Shinsuke; Ishihara, Yoshiaki; Hiramatsu, Yoshihiro

    2016-05-01

    Gravity data obtained from the Gravity Recovery and Interior Laboratory have revealed linear gravity anomalies (LGAs) formed by the early global expansion of the Moon and subsequent magma intrusion. In this study, using Lunar Orbiter Laser Altimeter topographic data, we investigated topographic profiles across LGAs to verify that they were formed by extensional tectonics. We found that 17 of the 20 LGAs investigated exhibited a valley structure, suggesting that they were formed by tensile stress. Assuming that these topographic depressions accompanied graben formation, the increase in the lunar radius is estimated to be on the order of several tens of meters. On the other hand, assuming that these topographic depressions accompanied flexure of elastic lithosphere due to the LGA load, the elastic thickness during the LGA formation is estimated as ~10 km. The crater frequencies in the vicinity of LGAs indicate that the peak tectonic activity occurred before the basin-forming epoch.

  1. Evaluation of low-temperature geothermal potential in Utah and Goshen Valleys and adjacent areas, Utah. Part I. Gravity survey

    SciTech Connect

    Davis, D.A.; Cook, K.L.

    1983-04-01

    During 1980 and 1981 a total of 569 new gravity stations were taken in Utah and Goshen Valleys and adjacent areas, Utah. The new stations were combined with 530 other gravity stations taken in previous surveys which resulted in a compilation of 1099 stations which were used in this study. The additional surveys were undertaken to assist in the evaluation of the area for the possible development of geothermal resources by providing an interpreted structural framework by delineating faults, structural trends, intrusions, thickness of valley fill, and increased density of host rock. The gravity data are presented as (1) a complete Bouguer gravity anomaly map with a 2 mgal contour interval on a scale of 1:100,000 and (2) five generally east-trending gravity profiles. A geologic interpretation of the study area was made from the gravity map and from the interpretive geologic cross sections which were modeled along the gravity profiles.

  2. Gravity anomalies, crustal structure, and seismicity at subduction zones: 1. Seafloor roughness and subducting relief

    NASA Astrophysics Data System (ADS)

    Bassett, Dan; Watts, Anthony B.

    2015-05-01

    An ensemble averaging technique is used to remove the long-wavelength topography and gravity field from subduction zones. >200 residual bathymetric and gravimetric anomalies are interpreted within fore arcs, many of which are attributed to the tectonic structure of the subducting plate. The residual-gravimetric expression of subducting fracture zones extends >200 km landward of the trench axis. The bathymetric expression of subducting seamounts with height ≥1 km and area ≥500 km2 (N=36), and aseismic ridges (N>10), is largest near the trench (within 70 km) and above shallow subducting slab depths (SLAB1.0 <17 km). Subducting seamounts are similar in wavelength, amplitude, and morphology to unsubducted seamounts. Morphology, spatial distributions, and reduced levels of seismicity are considered inconsistent with mechanical models proposing wholesale decapitation, and the association of subducting seamounts with large-earthquakes. Subducting aseismic ridges are associated with uplift and steepening of the outer fore arc, a gradual reduction in residual bathymetric expression across the inner fore arc, and a local increase in the width and elevation of the volcanic-arc/orogen. These contrasting expressions reflect the influence of margin-normal variations in rigidity on where and how the upper plate deforms, both to accommodate subducting relief and in response to stresses transmitted across the plate interface. The outer fore arc and arc have lower rigidity due to fracturing and thermal weakening, respectively. Similar associations with complex earthquakes and fault creep suggest aseismic ridge subduction may also be accommodated by the development and evolution of a broad fracture network, the geometrical strength of which may exceed the locking strength of a smooth fault.

  3. A New Search for Lunar Mascon Basins using Detrended Kaguya (SELENE) Gravity: Implications for GRAIL

    NASA Astrophysics Data System (ADS)

    Dombard, A. J.; Hauck, S. A.; Balcerski, J.

    2012-12-01

    The collection of GRAIL data and imminent release of its first gravity models will revolutionize understanding of the lunar interior, which motivates an assessment of the current state of knowledge. A primary goal of the GRAIL mission is to understand better mascon basins, large impact craters that display significant positive free-air and Bouguer gravity anomalies. Discovered in a handful of nearside basins during preparations for the Apollo landings and recently expanded by the global Kaguya (SELENE) gravity models, an important question is why is not every large crater a mascon basin, as less than half of the 41 impact basins > 300 km in diameter (minus South Pole-Aitken) have been previously determined to be mascons. An issue not generally considered in the identification of mascons is that the topography, and hence Bouguer gravity, display long-wavelength regional signals that might mask some mascons. Here, we use the SGM100i Kaguya gravity model and LRO's LOLA shape model to examine the free-air, topographic (arising solely from topography), and Bouguer gravity, detrended by omitting the first 5 spherical harmonic degrees from our expansions. In contrast to past studies, we find that most large basins (28 of 41) display characteristics of mascons (e.g., a strong positive Bouguer anomaly generally narrower than the surface rim). Negative annuli surrounding the central highs in the free-air gravity do not exist in the Bouguer gravity, with only 2 definitive exceptions. The fact that the majority of the Bouguer anomalies are narrower than the basin rim and that the negative free-air annulus appears to be a product of the surface topography has implications for the formation of the basins. We propose that beneath a forming large basin, the mantle uplifts in response to the large isostatic imbalance with the transient crater, while the surface topography forms from not only upward but inward collapse of the transient crater's rim wall and adjustment of the melt

  4. The Moho relief and the tectonic implications in North Vietnam using gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    Hsieh, H.; Yen, H.; Toan, D.

    2010-12-01

    The Red River fault system in Vietnam is considered as a complex rupture zone by the South China platform and the Indochina plate. There are some complex structures problems unsolved. The geophysical data are easily to explore the first step investigation. In this study, we combined the Bouguer gravity anomaly on land and the free-air gravity anomaly from satellite in ocean area to obtain the complete gravity anomaly of North Vietnam. We applied the FFT method to analyze the gravity effects from shallow and deeper structures. After remove the possible effects, the Moho topography is simulated from 3D inversion method. The magnetic anomaly usually indicates the igneous minerals distribution beneath the area. In Vietnam, we try to estimate the magnetic basement depth and Curie point depth from the magnetic anomaly. After numerical modeling for two potential fields, we have obtained preliminary results beneath the Red River fault zone and its vicinity. The residual gravity anomaly map is parallel the trend of faults distributions. The Moho depth beneath the Red River fault zone is about 30-40km. From magnetic anomaly map, the distributions of intrusive and igneous rocks were easily distinguished. The Curie point depth map is also shown the lower boundary of igneous rocks.

  5. Basin ring faults and giant dikes on the Moon revealed by GRAIL gravity gradiometry

    NASA Astrophysics Data System (ADS)

    Andrews-Hanna, J. C.; Zuber, M. T.; Smith, D. E.; Melosh, H. J.; Neumann, G. A.; Phillips, R. J.; Solomon, S. C.; Wieczorek, M. A.

    2012-12-01

    Gravity gradiometry makes use of the second spatial derivatives of the potential field (the first derivatives of the acceleration), which can be directly measured by surface, aerial, or satellite-based gradiometers or can be derived from the potential field itself. Gravity gradiometry is particularly well suited for identifying discrete structures in the subsurface such as faults cutting across density interfaces and dikes of different density from the host rock. With new high-resolution gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) mission, gravity gradiometry techniques can now be applied to the Moon. We here use the second horizontal derivatives of the lunar potential field derived from GRAIL to investigate the structure of lunar multiring basins. The potential is first separated into surface (terrain, derived from the topography) and subsurface (Bouguer) components. The horizontal gradient tensor is then used to calculate the eigenvalues and eigenvectors, from which the local radial and azimuthal gradients around the basins are calculated. The gradients of the terrain component of the potential field are dominated by the surface expression of the rings, whereas the gradients of the Bouguer component of the potential reveal the presence of ring faults in the subsurface. These subsurface anomalies may arise at the intersection of the faults with either the Moho or an intracrustal density interface separating the upper and lower crust. In many instances, the subsurface expressions of the ring structures in the Bouguer gradients are more prominent than the surface expressions in the terrain gradients. For the Orientale basin, the subsurface expression of ring faults is detected in association with both the Outer Rook and Cordillera rings, supporting a tectonic origin for both rings. The subsurface manifestations of the rings are displaced inward toward the basin center relative to their surface expressions, consistent with the expectation

  6. Gravity anomalies and lithospheric flexure around the Longmen Shan deduced from combinations of in situ observations and EGM2008 data

    NASA Astrophysics Data System (ADS)

    She, Yawen; Fu, Guangyu; Wang, Zhuohua; Liu, Tai; Xu, Changyi; Jin, Honglin

    2016-10-01

    The current work describes the combined data of three field campaigns, spanning 2009-2013. Their joint gravity and GPS observations thoroughly cover the sites of lithospheric flexure between the Sichuan Basin and the Eastern Tibetan Plateau. The study area's free-air gravity anomalies (FGAs) are updated by using a remove-and-restore algorithm which merges EGM2008 data with in situ observations. These new FGAs show pairs of positive and negative anomalies along the eastern edges of the Tibetan Plateau. The FGAs are used to calculate effective elastic thickness ( T e) and load ratios ( F) of the lithosphere. Admittance analysis indicates the T e of Longmen Shan (LMS) to be 6 km, and profile analysis indicates that the T e of the Sichuan Basin excesses 30 km. The load ratio ( F 1 = 1) confirms that the lithospheric flexure of the LMS area can be attributed solely to the surface load of the crust. [Figure not available: see fulltext. Caption: The current work describes the combined data of three field campaigns, spanning 2009-2013. Their joint gravity and GPS observations thoroughly cover the sites of lithospheric flexure between the Sichuan Basin and the Eastern Tibetan Plateau. The study area's free-air gravity anomalies (FGAs) are updated by using a remove-and-restore algorithm which merges EGM2008 data with in situ observations. With the new FGAs data, the lithospheric strength of the study area is studied by the authors, and they also give a combined model to illustrate the uplift mechanism of this area.

  7. Integrating stations from the North America Gravity Database into a local GPS-based land gravity survey

    USGS Publications Warehouse

    Shoberg, Thomas G.; Stoddard, Paul R.

    2013-01-01

    The ability to augment local gravity surveys with additional gravity stations from easily accessible national databases can greatly increase the areal coverage and spatial resolution of a survey. It is, however, necessary to integrate such data seamlessly with the local survey. One challenge to overcome in integrating data from national databases is that these data are typically of unknown quality. This study presents a procedure for the evaluation and seamless integration of gravity data of unknown quality from a national database with data from a local Global Positioning System (GPS)-based survey. The starting components include the latitude, longitude, elevation and observed gravity at each station location. Interpolated surfaces of the complete Bouguer anomaly are used as a means of quality control and comparison. The result is an integrated dataset of varying quality with many stations having GPS accuracy and other reliable stations of unknown origin, yielding a wider coverage and greater spatial resolution than either survey alone.

  8. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements.

    PubMed

    Neumann, Gregory A; Zuber, Maria T; Wieczorek, Mark A; Head, James W; Baker, David M H; Solomon, Sean C; Smith, David E; Lemoine, Frank G; Mazarico, Erwan; Sabaka, Terence J; Goossens, Sander J; Melosh, H Jay; Phillips, Roger J; Asmar, Sami W; Konopliv, Alexander S; Williams, James G; Sori, Michael M; Soderblom, Jason M; Miljković, Katarina; Andrews-Hanna, Jeffrey C; Nimmo, Francis; Kiefer, Walter S

    2015-10-01

    Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population. PMID:26601317

  9. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements.

    PubMed

    Neumann, Gregory A; Zuber, Maria T; Wieczorek, Mark A; Head, James W; Baker, David M H; Solomon, Sean C; Smith, David E; Lemoine, Frank G; Mazarico, Erwan; Sabaka, Terence J; Goossens, Sander J; Melosh, H Jay; Phillips, Roger J; Asmar, Sami W; Konopliv, Alexander S; Williams, James G; Sori, Michael M; Soderblom, Jason M; Miljković, Katarina; Andrews-Hanna, Jeffrey C; Nimmo, Francis; Kiefer, Walter S

    2015-10-01

    Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population.

  10. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements

    PubMed Central

    Neumann, Gregory A.; Zuber, Maria T.; Wieczorek, Mark A.; Head, James W.; Baker, David M. H.; Solomon, Sean C.; Smith, David E.; Lemoine, Frank G.; Mazarico, Erwan; Sabaka, Terence J.; Goossens, Sander J.; Melosh, H. Jay; Phillips, Roger J.; Asmar, Sami W.; Konopliv, Alexander S.; Williams, James G.; Sori, Michael M.; Soderblom, Jason M.; Miljković, Katarina; Andrews-Hanna, Jeffrey C.; Nimmo, Francis; Kiefer, Walter S.

    2015-01-01

    Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population. PMID:26601317

  11. Complete Bouguer gravity map of the Medicine Lake Quadrangle, California

    USGS Publications Warehouse

    Finn, C.

    1981-01-01

    A mathematical technique, called kriging, was programmed for a computer to interpolate hydrologic data based on a network of measured values in west-central Kansas. The computer program generated estimated values at the center of each 1-mile section in the Western Kansas Groundwater Management District No. 1 and facilitated contouring of selected values that are needed in the effective management of ground water for irrigation. The kriging technique produced objective and reproducible maps that illustrated hydrologic conditions in the Ogallala aquifer, the principal source of water in west-central Kansas. Maps of the aquifer, which use a 3-year average, included the 1978-80 water-table altitudes, which ranged from about 2,580 to 3,720 feet; the 1978-80 saturated thicknesses, which ranged from about 0 to 250 feet; and the percentage changes in saturated thickness from 1950 to 1978-80, which ranged from about a 50-percent increase to a 100-percent decrease. A map showing errors of estimate also was provided as a measure of reliability for the 1978-80 water-table altitudes. Errors of estimate ranged from 2 to 24 feet. (USGS)

  12. 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

  13. Model parameter estimations from residual gravity anomalies due to simple-shaped sources using Differential Evolution Algorithm

    NASA Astrophysics Data System (ADS)

    Ekinci, Yunus Levent; Balkaya, Çağlayan; Göktürkler, Gökhan; Turan, Seçil

    2016-06-01

    An efficient approach to estimate model parameters from residual gravity data based on differential evolution (DE), a stochastic vector-based metaheuristic algorithm, has been presented. We have showed the applicability and effectiveness of this algorithm on both synthetic and field anomalies. According to our knowledge, this is a first attempt of applying DE for the parameter estimations of residual gravity anomalies due to isolated causative sources embedded in the subsurface. The model parameters dealt with here are the amplitude coefficient (A), the depth and exact origin of causative source (zo and xo, respectively) and the shape factors (q and ƞ). The error energy maps generated for some parameter pairs have successfully revealed the nature of the parameter estimation problem under consideration. Noise-free and noisy synthetic single gravity anomalies have been evaluated with success via DE/best/1/bin, which is a widely used strategy in DE. Additionally some complicated gravity anomalies caused by multiple source bodies have been considered, and the results obtained have showed the efficiency of the algorithm. Then using the strategy applied in synthetic examples some field anomalies observed for various mineral explorations such as a chromite deposit (Camaguey district, Cuba), a manganese deposit (Nagpur, India) and a base metal sulphide deposit (Quebec, Canada) have been considered to estimate the model parameters of the ore bodies. Applications have exhibited that the obtained results such as the depths and shapes of the ore bodies are quite consistent with those published in the literature. Uncertainty in the solutions obtained from DE algorithm has been also investigated by Metropolis-Hastings (M-H) sampling algorithm based on simulated annealing without cooling schedule. Based on the resulting histogram reconstructions of both synthetic and field data examples the algorithm has provided reliable parameter estimations being within the sampling limits of

  14. Frozen subduction in the Yangtze block: insights from the deep seismic profiling and gravity anomaly in east Sichuan fold belt

    NASA Astrophysics Data System (ADS)

    Xiong, Xiaosong; Gao, Rui; Wang, Haiyan; Zhang, Jisheng; Guo, Lianghui

    2016-04-01

    The Sichuan basin is the main part of the middle-upper Yangtze block, which has been experienced a long-term tectonic evolution since Archean. The Yangtze block was regarded as a stable block until the collision with the Cathaysia block in late Neoproterozoic. A new deep seismic reflection profile conducted in the eastern Sichuan fold belt (ESFB) discovered a serials of south-dipping reflectors shown from lower crust to the mantle imply a frozen subduction zone within the Yangtze block. In order to prove the speculation, we also obtain the middle-lower crustal gravity anomalies by removing the gravity anomalies induced by the sedimentary rocks and the mantle beneath the Moho, which shows the mid-lower crustal structure of the Sichuan basin can be divided into eastern and western parts. Combined with the geochronology and Aeromagnetic anomalies, we speculated the Yangtze block was amalgamated by the West Sichuan and East Sichuan blocks separated by the Huayin-Chongqing line. The frozen subduction zone subsequently shifted to a shear zone accommodated the lower crustal shortening when the decollement at the base of the Nanhua system functioned in the upper plate.

  15. Gravity anomaly and geoid undulation results in local areas from GEOS-3 altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1979-01-01

    The adjusted GEOS-3 altimeter data, taken as averages within a data frame, have been used to construct free air anomaly and geoid undulation profiles and maps in areas of geophysical interest. Profiles were constructed across the Philippine Trench (at a latitude of 6 deg) and across the Bonin Trench (at a latitude of 28 deg). In the latter case an anomaly variation of 443 mgals in 143 km was derived from the altimeter data. These variations agreed reasonably with terrestrial estimates, considering the predicted point accuracy was about + or - 27 mgals. An area over the Patton Sea mounts was also investigated with the altimeter anomaly field agreeing well with the terrestrial data except for the point directly over the top of the sea mount. It is concluded that the GEOS-3 altimeter data is valuable not only for determining 5 deg and 1 deg x 1 deg mean anomalies, but also can be used to describe more local anomaly variations.

  16. Gravity anomalies, crustal structure, and seismicity at subduction zones: 2. Interrelationships between fore-arc structure and seismogenic behavior

    NASA Astrophysics Data System (ADS)

    Bassett, Dan; Watts, Anthony B.

    2015-05-01

    An ensemble-averaging technique is used to remove the long-wavelength topography and gravity field associated with subduction zones. Short-wavelength residual anomalies are attributed to the tectonic structure of subducting and overthrusting plates. A paired (positive-negative) fore-arc anomaly is observed consisting of a long (>1000 km), linear, trench-parallel ridge landward of the deep-sea-terrace basin. Ridges have amplitudes of 1500-3000 m and 160-240 mGal, wavelengths of 150-200 km, and high gravity anomaly to topography ratios (50-75 mGal km-1). The ridge crests correlate with the downdip limit of coseismic slip and strong interplate coupling and in Cascadia, the updip limit of tremor epicenters. The ridge crest may be interpreted as defining the boundary between the velocity-weakening and seismogenic region of the subduction interface and the downdip frictional transition zone. In Tonga-Kermadec, the Kuril Islands and Chile landward ridges are associated with extinct volcanic arcs. Paired anomalies are attributed to the preferential subduction erosion of the outer fore arc and a spatially varying combination of (a) lower crustal underplating beneath the inner fore arc, (b) the transformation of interseismic strain into permanent geologic strain via faulting, folding, or buckling of the inner fore arc, and (c) the relative trenchward migration of extinct volcanic arcs in regions operating with a net crustal deficit. Along-strike transitions in fore-arc morphology and seismogenic behavior are related to preexisting crustal structure of subducting and overthrusting plates. Fore arcs have the added potential of recording the time-integrated response of the upper plate to subduction processes, and fore-arc structure should be considered in tandem with seismological observations.

  17. The determination of gravity anomalies from geoid heights using the inverse Stokes' formula, Fourier transforms, and least squares collocation

    NASA Technical Reports Server (NTRS)

    Rummel, R.; Sjoeberg, L.; Rapp, R. H.

    1978-01-01

    A numerical method for the determination of gravity anomalies from geoid heights is described using the inverse Stokes formula. This discrete form of the inverse Stokes formula applies a numerical integration over the azimuth and an integration over a cubic interpolatory spline function which approximates the step function obtained from the numerical integration. The main disadvantage of the procedure is the lack of a reliable error measure. The method was applied on geoid heights derived from GEOS-3 altimeter measurements in the calibration area of the GEOS-3 satellite.

  18. 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.

  19. Small-scale gravity modeling of upper crustal structures in the Araba Valley along the Dead Sea Transform

    NASA Astrophysics Data System (ADS)

    TašáRová, Z.; GöTze, H.-J.; El-Kelani, R.; Ebbing, J.; Hassouneh, M.

    2006-09-01

    A detailed three-dimensional (3-D) gravity model of upper crustal structures was created for the Dead Sea Transform in the Araba/Arava Valley, located some 80 km south of the Dead Sea Basin. The density model covers an area of ˜30 × 30 km and incorporates results from several recent geophysical experiments performed in this region. The model presented is a local density model that focuses on the uppermost crustal layers to a depth of ˜5 km. Therefore, in order to separate the effect of regional structures (such as the crust-mantle boundary) from that of local structures within the crust, a residual anomaly was computed from a newly compiled Bouguer gravity anomaly database. In contrast to the Bouguer anomaly, which is negative across the entire study area, the residual gravity field contains both positive and negative values. The 3-D structural image of the upper crust reveals that the basement east and west of the Dead Sea Transform is vertically offset by 1.5 to 2.8 km. Considering the 105 km of sinistral displacement of the Dead Sea Transform, this result confirms the findings of other geophysical measurements that show an abrupt change in the physical parameters and geometry of the two lithological blocks that are juxtaposed along the Dead Sea Transform. Additionally, analysis of the calculated gravity gradients suggests that the Dead Sea Transform and the neighboring Zofar fault could be offset at depth with respect to the present-day traces at the surface.

  20. Geoid undulations and gravity anomalies over the Aral Sea, the Black Sea and the Caspian Sea from a combined GEOS-3/SEASAT/GEOSAT altimeter data set

    NASA Technical Reports Server (NTRS)

    Au, Andrew Y.; Brown, Richard D.; Welker, Jean E.

    1991-01-01

    Satellite-based altimetric data taken by GOES-3, SEASAT, and GEOSAT over the Aral Sea, the Black Sea, and the Caspian Sea are analyzed and a least squares collocation technique is used to predict the geoid undulations on a 0.25x0.25 deg. grid and to transform these geoid undulations to free air gravity anomalies. Rapp's 180x180 geopotential model is used as the reference surface for the collocation procedure. The result of geoid to gravity transformation is, however, sensitive to the information content of the reference geopotential model used. For example, considerable detailed surface gravity data were incorporated into the reference model over the Black Sea, resulting in a reference model with significant information content at short wavelengths. Thus, estimation of short wavelength gravity anomalies from gridded geoid heights is generally reliable over regions such as the Black Sea, using the conventional collocation technique with local empirical covariance functions. Over regions such as the Caspian Sea, where detailed surface data are generally not incorporated into the reference model, unconventional techniques are needed to obtain reliable gravity anomalies. Based on the predicted gravity anomalies over these inland seas, speculative tectonic structures are identified and geophysical processes are inferred.

  1. Principal facts for gravity stations in Dixie; Fairview, and Stingaree valleys, Churchill and Pershing counties, Nevada

    USGS Publications Warehouse

    Schaefer, D.H.; Thomas, J.M.; Duffrin, B.G.

    1984-01-01

    During March through July 1979, gravity measurements were made at 300 stations in Dixie Valley, Nevada. In December 1981, 45 additional stations were added--7 in Dixie Valley, 23 in Fairview Valley, and 15 in Stingaree Valley. Most altitudes were determined by using altimeters or topographic maps. The gravity observations were made with a Worden temperature-controlled gravimeter with an initial scale factor of 0.0965 milliGal/scale division. Principal facts for each of the 345 stations are tabulated; they consist of latitude, longitude, altitude, observed gravity, free-air anomaly, terrain correction, and Bouguer anomaly values at a bedrock density of 2.67 grams/cu cm. (Lantz-PTT)

  2. Accuracy of the determination of mean anomalies and mean geoid undulations from a satellite gravity field mapping mission

    NASA Technical Reports Server (NTRS)

    Jekeli, C.; Rapp, R. H.

    1980-01-01

    Improved knowledge of the Earth's gravity field was obtained from new and improved satellite measurements such as satellite to satellite tracking and gradiometry. This improvement was examined by estimating the accuracy of the determination of mean anomalies and mean undulations in various size blocks based on an assumed mission. In this report the accuracy is considered through a commission error due to measurement noise propagation and a truncation error due to unobservable higher degree terms in the geopotential. To do this the spectrum of the measurement was related to the spectrum of the disturbing potential of the Earth's gravity field. Equations were derived for a low-low (radial or horizontal separation) mission and a gradiometer mission. For a low-low mission of six month's duration, at an altitude of 160 km, with a data noise of plus or minus 1 micrometers sec for a four second integration time, we would expect to determine 1 deg x 1 deg mean anomalies to an accuracy of plus or minus 2.3 mgals and 1 deg x 1 deg mean geoid undulations to plus or minus 4.3 cm. A very fast Fortran program is available to study various mission configurations and block sizes.

  3. Analysis of converted S-waves and gravity anomaly along the Aegir Ridge: implications for crustal lithology

    NASA Astrophysics Data System (ADS)

    Rai, A. K.; Breivik, A. J.; Mjelde, R.; Hanan, B. B.; Ito, G.; Sayit, K.; Howell, S.; Vogt, P. R.; Pedersen, R.

    2012-12-01

    The Aegir Ridge is an extinct spreading ridge in North-East Atlantic ocean. A thinner than normal crust around the Aegir Ridge appears as a hole in the extensively magmatic surroundings. Its proximity to the Iceland hot-spot makes it particularly important for understanding the changing dynamics of hotspot-ridge interaction. An integrated seismic and dredging experiment was conduced during the summer of 2010 with the primary aim to understand the nature of magmatism along the ridge shortly before cessation of seafloor spreading through variations of sub-seafloor lithological properties. Here, we present results of analysis of converted shear-waves recorded on OBS-sesimic data, and ship-gravity data. The shear-wave study enables us to quantify the variation of Vp/Vs in the sediments, crust and the upper-most mantle. We also inverted the gravity data to determine the sub-seafloor density distribution. The P- to S- converted shear-waves were identified on 20 OBSs along a profile with a total length of 550 km parallel to the ridge-axis. The sedimentary section on top of the crystalline crust is well illuminated in the streamer data. The forward modelling of the OBS data reveals that the Vp/Vs ratio in sediments are as high as 4.8, decreasing rapidly to a value of 3.00, primarily due to compaction of sediments with depth. Identification of sufficient PnS and PSn phases enable us to model the crustal and upper-most mantle Vp/Vs. The upper crystalline crust requires a Vp/Vs value of 1.99 and 1.89 for the southern and the northern profiles respectively, to fit the observations. The lower crust and upper-most part of the mantle have a Vp/Vs of ~1.82 and 1.795 respectively. Slightly lower Vp and moderate increase in Vp/Vs in parts of the crust and upper mantle presumably indicate presence of faulting, fracturing in the crust and moderate degree of serpentinization of the upper mantle. A sub-seafloor density model is derived by non-linear inversion of the gravity anomaly. The

  4. Comparative study of compensation mechanism of lunar impact basins from new gravity field model of SELENE (Kaguya)

    NASA Astrophysics Data System (ADS)

    Namiki, N.; Sugita, S.; Matsumoto, K.; Goossens, S.; Ishihara, Y.; Noda, H.; Ssasaki, S.; Iwata, T.; Hanada, H.; Araki, H.

    2009-04-01

    The gravity field is a fundamental physical quantity for the study of the internal structure and the evolution of planetary bodies. The most significant problem of the previous lunar gravity models, however, is the lack of direct observations of the far side gravity signals [1]. We then developed a satellite-to-satellite Doppler tracking sub-system for SELENE [2]. In this study, we adopt our new gravity field model with nearly full coverage of the lunar far side to discuss dichotomy of the lunar basins. Because all the nearside impact basins are filled with extensive mare basalt deposits, it is difficult to estimate the subsurface structures, such as uplift of the Moho surface, from gravity measurements. In contrast, far-side impact basins have much less or no mare basalt coverage. This may allow us to investigate the internal structure underneath impact basins. Such knowledge will be important in understanding the response of a solid planetary body to large meteoritic impacts and also the thermal state of the Moon during the late heavy bombardment period. There are distinctive differences between the anomalies of the near side principal mascons and the far side basins. As shown previously [1, 3], the near side principal mascons have sharp shoulders with a gravity plateau and a weakly negative gravity anomaly in the surroundings. In contrast, the far side basins are characterized by concentric rings of positive and negative anomalies. The circular gravity highs agree well with the topographic rims of the basins revealed by SELENE topography model STM-359_grid-02 [4]. In our gravity model, Orientale, Mendel-Rydberg, Lorentz, and Humboldtianum show more affinity with the far side basins than the near side principal mascons [5]. Korolev, Mendeleev, Planck, and Lorentz basins have sharp central peaks of which magnitude in free-air anomalies is almost equivalent to the one in Bouguer anomalies. On the other hand, Orientale, Mendel-Rydberg, Humboldtianum, Moscoviense

  5. Dip distribution of Oita-Kumamoto Tectonic Line located in central Kyushu, Japan, estimated by eigenvectors of gravity gradient tensor

    NASA Astrophysics Data System (ADS)

    Kusumoto, Shigekazu

    2016-09-01

    We estimated the dip distribution of Oita-Kumamoto Tectonic Line located in central Kyushu, Japan, by using the dip of the maximum eigenvector of the gravity gradient tensor. A series of earthquakes in Kumamoto and Oita beginning on 14 April 2016 occurred along this tectonic line, the largest of which was M = 7.3. Because a gravity gradiometry survey has not been conducted in the study area, we calculated the gravity gradient tensor from the Bouguer gravity anomaly and employed it to the analysis. The general dip distribution of the Oita-Kumamoto Tectonic Line was found to be about 65° and tends to be higher towards its eastern end. In addition, we estimated the dip around the largest earthquake to be about 60° from the gravity gradient tensor. This result agrees with the dip of the earthquake source fault obtained by Global Navigation Satellite System data analysis.[Figure not available: see fulltext.

  6. Use of gravity potential field methods for defining a shallow magmatic intrusion: the Mt. Amiata case history (Tuscany, Central Italy)

    NASA Astrophysics Data System (ADS)

    Girolami, Chiara; Rinaldo Barchi, Massimiliano; Pauselli, Cristina; Heyde, Ingo

    2016-04-01

    We analyzed the Bouguer gravity anomaly signal beneath the Mt. Amiata area in order to reconstruct the subsurface setting. The study area is characterized by a pronounced gravity minimum, possibly correlated with the observed anomalous heat flow and hydrothermal activity. Using different approaches, previous authors defined a low density body (generally interpreted as a magmatic intrusion) beneath this area, which could explain the observed gravity anomaly minimum. However the proposed geologic models show different geometries and densities for the batholith. The gravity data used in this study (kindly provided by eni) were acquired from different institutions (eni, OGS, USDMA and Servizio Geologico d'Italia) and collected in a unique dataset, consisting of about 50000 stations, randomly distributed, which cover Central Italy, with a spacing of less than 1 km. For each station the elevation and the Bouguer gravity anomaly data are given. From this dataset, we created two maps of the Bouguer gravity anomaly and the topography, using the Minimum Curvature gridding method considering a grid cell size of 500m x 500m. The Bouguer gravity anomaly has been computed using a density of 2.67 g/cm3. From these maps we extracted a window of about 240 km2 (12x20 km) for the study area, which includes the Mt. Amiata region and the adjacent Radicofani sedimentary basin. The first part of this study was focused on calculating the first order vertical derivative and the power spectra analysis of the Bouguer gravity anomaly to enhance the effect of shallow bodies and estimating the source depth respectively. The second part of this study was focused on constructing a 3D geological density model of the subsurface setting of the studied area, implementing a forward modelling approach. The stratigraphy of the study area's upper crust schematically consists of six litho-mechanical units, whose density was derived from velocity data collected by active seismic surveys. A preliminary

  7. First application of airborne gravity to oil exploration in the Shengli oil province, eastern China

    NASA Astrophysics Data System (ADS)

    Li, Wenyong; Zhoud, Jianxin; Liu, Yanxu; Xu, Jianchun

    2015-07-01

    An airborne gravity survey was successfully conducted over the Dongying, Gudao and Gudong oilfields of Shengli oil province, eastern China. These survey areas cover onshore and offshore regions of the south-west Bohai Sea. The data were processed using the potential field transformation approach. The derived Bouguer gravity data correlate well with features such as known faults, swells and sags identified by earlier seismic survey and drilling data. The depth to the Cenozoic basement in the study area, including the Dongying, Gudao, and Gudong oilfields, was calculated by means of gravity inversion constrained by seismic and drilling data. The differences between the depths to the Cenozoic basement calculated from gravity anomaly and those determined by the earlier seismic and drilling data are less than 5%.

  8. Michigan Magnetic and Gravity Maps and Data: A Website for the Distribution of Data

    USGS Publications Warehouse

    Daniels, David L.; Kucks, Robert P.; Hill, Patricia L.; Snyder, Stephen L.

    2009-01-01

    This web site provides the best available, public-domain, aeromagnetic and gravity data in the State of Michigan and merges these data into composite grids that are available for downloading. The magnetic grid is compiled from 25 separate magnetic surveys that have been knit together to form a single composite digital grid and map. The magnetic survey grids have been continued to 305 meters (1,000 feet) above ground and merged together to form the State compilation. A separate map shows the location of the aeromagnetic surveys, color-coded to the survey flight-line spacing. In addition, a complete Bouguer gravity anomaly grid and map were generated from more than 20,000 gravity station measurements from 33 surveys. A table provides the facts about each gravity survey where known.

  9. Oregon Magnetic and Gravity Maps and Data: A Web Site for Distribution of Data

    USGS Publications Warehouse

    Roberts, Carter W.; Kucks, Robert P.; Hill, Patricia L.

    2008-01-01

    This web site gives the results of a USGS project to acquire the best available, public-domain, aeromagnetic and gravity data in the United States and merge these data into uniform, composite grids for each State. The results for the State of Oregon are presented here on this site. Files of aeromagnetic and gravity grids and images are available for these States for downloading. In Oregon, 49 magnetic surveys have been knit together to form a single digital grid and map. Also, a complete Bouguer gravity anomaly grid and map was generated from 40,665 gravity station measurements in and adjacent to Oregon. In addition, a map shows the location of the aeromagnetic surveys, color-coded to the survey flight-line spacing. This project was supported by the Mineral Resource Program of the USGS.

  10. Illinois, Indiana, and Ohio Magnetic and Gravity Maps and Data: A Website for Distribution of Data

    USGS Publications Warehouse

    Daniels, David L.; Kucks, Robert P.; Hill, Patricia L.

    2008-01-01

    This web site gives the results of a USGS project to acquire the best available, public-domain, aeromagnetic and gravity data in the United States and merge these data into uniform, composite grids for each state. The results for the three states, Illinois, Indiana, and Ohio are presented here in one site. Files of aeromagnetic and gravity grids and images are available for these states for downloading. In Illinois, Indiana, and Ohio, 19 magnetic surveys have been knit together to form a single digital grid and map. And, a complete Bouguer gravity anomaly grid and map was generated from 128,227 gravity station measurements in and adjacent to Illinois, Indiana, and Ohio. In addition, a map shows the location of the aeromagnetic surveys, color-coded to the survey flight-line spacing. This project was supported by the Mineral Resource Program of the USGS.

  11. Detailed gravity and aeromagnetic surveys in the Black Rock Desert Area, Utah. Topical report

    SciTech Connect

    Serpa, L.F.; Cook, K.L.

    1980-01-01

    Aeromagnetic and gravity surveys were conducted during 1978 in the Black Rock Desert, Utah over an area of about 2400 km/sup 2/ between the north-trending Pavant and Cricket Mountains. The surveys assisted in evaluating the geothermal resources in the Meadow-Hatton Known Geothermal Resource Area (KGRA) and vicinity by delineating geophysical characteristics of the subsurface. The gravity measurements from approximately 700 new stations were reduced to complete Bouguer gravity anomaly values with the aid of a computerized terrain-correction program and contoured at an interval of 1 milligal. The aeromagnetic survey was drape flown at an altitude of 305 m (1000 ft) and a total intensity residual aeromagnetic map with a contour interval of 20 gammas was produced. Two gravity and aeromagnetic east-west profiles and one north-south profile were modeled using a simultaneous 2 1/2-dimensional modeling technique to provide a single model satisfying both types of geophysical data.

  12. Application of high-pass filtering techniques on gravity and magnetic data of the eastern Qattara Depression area, Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Zahra, Hesham Shaker; Oweis, Hesham T.

    2016-06-01

    In this work, a reconnaissance study is presented to delineate the subsurface tectonics and lithological inferences of the eastern area of Qattara Depression using the Bouguer gravity and aeromagnetic data. To achieve this goal, several transformation techniques and filtering processes are accomplished on these maps. At first, the total intensity aeromagnetic map is processed through the application of reduction to the magnetic north pole technique. The fast Fourier transform is carried out on the gravity and RTP magnetic data for establishing and defining the residual (shallow) sources. The frequency high-pass filtering is used to enhance the anomaly wavelengths associated with the shallow sources. The used processing techniques are the polynomial surface fitting enhancement, Laplacian, Strike Filtering, Enhancement Utilization, Suppression Utilization, Butterworth Filtering Utilization, Butterworth high-pass filter, Euler's deconvolution and forward modeling. The equivalent depths of the isolated short wavelength anomalies are 0.759 and 0.340 km below the flight surface, and the depths of the intermediate wavelength anomalies are 1.28 and 2.00 km for the gravity and magnetic data, respectively. Finally, the quantitative interpretations of the Bouguer gravity and RTP magnetic maps of the study area, reflect the occurrence of the various types of structures and their components. The main tectonic deformations of the study area have NNW-SSE, NNE-SSW, NE-SW, NW-SE and E-W trends.

  13. 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

  14. Structure of the midcontinent basement. Topography, gravity, seismic, and remote sensing

    NASA Technical Reports Server (NTRS)

    Guinness, E. A.; Strebeck, J. W.; Arvidson, R. E.; Scholz, K.; Davies, G. F.

    1981-01-01

    Some 600,000 discrete Bouguer gravity estimates of the continental United States were spatially filtered to produce a continuous tone image. The filtered data were also digitally painted in color coded form onto a shaded relief map. The resultant image is a colored shaded relief map where the hue and saturation of a given image element is controlled by the value of the Bouguer anomaly. Major structural features (e.g., midcontinent gravity high) are readily discernible in these data, as are a number of subtle and previously unrecognized features. A linear gravity low that is approximately 120 to 150 km wide extends from southeastern Nebraska, at a break in the midcontinent gravity high, through the Ozark Plateau, and across the Mississippi embayment. The low is also aligned with the Lewis and Clark lineament (Montana to Washington), forming a linear feature of approximately 2800 km in length. In southeastern Missouri the gravity low has an amplitude of 30 milligals, a value that is too high to be explained by simple valley fill by sedimentary rocks.

  15. 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.

  16. 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.

  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. 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

  19. Geophysical investigations on the gravity and aeromagnetic anomalies of the region between Sapanca and Duzce, along the North Anatolian Fault, Turkey

    NASA Astrophysics Data System (ADS)

    Tigli, Cigdem Sendur; Ates, Abdullah; Aydemir, Attila

    2012-12-01

    In this paper, it is aimed to model subsurface structures to the east of the Gulf of Izmit through Duzce by using the gravity and aeromagnetic anomaly data. 1/500.000 scaled gravity anomaly map of the area was taken from the General Directorate of Mineral Research and Exploration (MTA) and it was digitized. The aeromagnetic anomaly data were obtained in the digital form. 3D and 2D models were constructed to reveal the subsurface structure in two different inset regions in the study area including most important negative and positive gravity anomalies. Seismic velocities obtained from the deep seismic recordings were converted to densities. In addition, density information from a previous research was also taken. These densities were used for construction of 3D and 2D gravity models where it was shown that there are narrow and long sedimentary basins and depressions with 0.5-3 km depths. These sedimentary basins with the shape of negative flower structures indicating pull-apart basins are controlled by the active fault segments of the North Anatolian Fault (NAF). Earthquake epicenter data were also correlated with the constructed models from the gravity anomalies. Positive gravity anomalies are also caused by very shallow (about 2 km) masses that are accepted as the crustal origin intrusions into the fractures of the NAF and, ophiolites and gabbro outcropping on the surface of the studied regions. These intrusives and remnants of the Tethys Ocean are located between the fault segments where the fault bifurcates and they also constitute barriers for straight extension of the NAF. Analytic signal method was applied to the aeromagnetic anomaly data to determine the locations and boundaries of the causative bodies. Those bodies are observed around Duzce, and to the E-SE of it, to the NW of Golyaka and a large mass between Adapazari and Sapanca. Shallow settlement of these magmatics was confirmed by the second vertical derivative of the aeromagnetic data. An anti

  20. Improved global prediction of 300 nautical mile mean free air anomalies

    NASA Technical Reports Server (NTRS)

    Cruz, J. Y.

    1982-01-01

    Current procedures used for the global prediction of 300nm mean anomalies starting from known values of 1 deg by 1 deg mean anomalies yield unreasonable prediction results when applied to 300nm blocks which have a rapidly varying gravity anomaly field and which contain relatively few observed 60nm blocks. Improvement of overall 300nm anomaly prediction is first achieved by using area-weighted as opposed to unweighted averaging of the 25 generated 60nm mean anomalies inside the 300nm block. Then, improvement of prediction over rough 300nm blocks is realized through the use of fully known 1 deg by 1 deg mean elevations, taking advantage of the correlation that locally exists between 60nm mean anomalies and 60nm mean elevations inside the 300nm block. An improved prediction model which adapts itself to the roughness of the local anomaly field is found to be the model of Least Squares Collocation with systematic parameters, the systematic parameter being the slope b which is a type of Bouguer slope expressing the correlation that locally exists between 60nm mean anomalies and 60nm mean elevations.

  1. 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.

  2. Preliminary isostatic residual gravity anomaly map of Paso Robles 30 x 60 minute quadrangle, California

    USGS Publications Warehouse

    McPhee, D.K.; Langenheim, V.E.; Watt, J.T.

    2011-01-01

    This isostatic residual gravity map is part of an effort to map the three-dimensional distribution of rocks in the central California Coast Ranges and will serve as a basis for modeling the shape of basins and for determining the location and geometry of faults within the Paso Robles quadrangle. Local spatial variations in the Earth\\'s gravity field, after accounting for variations caused by elevation, terrain, and deep crustal structure reflect the distribution of densities in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithological or structural boundaries. High-density rocks exposed within the central Coast Ranges include Mesozoic granitic rocks (exposed northwest of Paso Robles), Jurassic to Cretaceous marine strata of the Great Valley Sequence (exposed primarily northeast of the San Andreas fault), and Mesozoic sedimentary and volcanic rocks of the Franciscan Complex [exposed in the Santa Lucia Range and northeast of the San Andreas fault (SAF) near Parkfield, California]. Alluvial sediments and Tertiary sedimentary rocks are characterized by low densities; however, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of older basement rocks.

  3. Preliminary gravity investigations of the Wahmonie Site, Nevada Test Site, Nye County, Nevada

    SciTech Connect

    Ponce, D.A.

    1981-12-31

    A gravity survey of the southwest corner of the Nevada Test Site was completed during 1979 to 1980 as part of an effort to characterize a possible radioactive waste storage site in granitic rocks. The survey outlined a large, broad, and flat gravity high centered near Wahmonie Site. Combined geophysical data indicate that the anomalous area is underlain by a dense, magnetic, and possibly intrusive body. Gravity data show a +15 milligal Bouguer anomaly coincident with a large positive aeromagnetic anomaly. The data reveal a prominent fault at the west edge of the inferred intrusive. Both gravity and magnetic anomalous highs extend NNE over a horst composed predominantly of rhyodacite of the Tertiary Salyer Formation. Local aeromagnetic highs are closely associated with two granodiorite exposures on the eastern edge of the horst. A local gravity high of about +2 milligal is centered directly over the southern granodiorite exposure and another high is centered over the northern exposure. A steep gravity gradient outlining the gravity high coincides with the outer edge of a zone of hydrothermal alteration which surrounds the horst. The gravity gradient probably marks the approximate limit of an intrusive body.

  4. Structure of the southern Rio Grande rift from gravity interpretation

    NASA Technical Reports Server (NTRS)

    Daggett, P. H.; Keller, G. R.; Wen, C.-L.; Morgan, P.

    1986-01-01

    Regional Bouguer gravity anomalies in southern New Mexico have been analyzed by two-dimensional wave number filtering and poly-nomial trend surface analysis of the observed gravity field. A prominent, regional oval-shaped positive gravity anomaly was found to be associated with the southern Rio Grande rift. Computer modeling of three regional gravity profiles suggests that this anomaly is due to crustal thinning beneath the southern Rio Grande rift. These models indicate a 25 to 26-km minimum crustal thickness within the rift and suggest that the rift is underlain by a broad zone of anomalously low-density upper mantle. The southern terminus of the anomalous zone is approximately 50 km southwest of El Paso, Texas. A thinning of the rifted crust of 2-3 km relative to the adjacent Basin and Range province indicates an extension of about 9 percent during the formation of the modern southern Rio Grande rift. This extension estimate is consistent with estimates from other data sources. The crustal thinning and anomalous mantle is thought to result from magmatic activity related to surface volcanism and high heat flow in this area.

  5. 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

  6. Seismicity and tectonic relationships of the Nemaha Uplift and Midcontinent geophysical anomaly. Final project summary

    SciTech Connect

    Burchett, R.R.; Luza, K.V.; Van Eck, O.J.; Wilson, F.W.

    1983-02-01

    The geological surveys of Iowa, Nebraska, Kansas, and Oklahoma conducted a 4- to 6-year investigation of the seismicity and tectonic relationships of the Nemaha Uplift and associated geologic features in the Midcontinent. Regional geological, gravity, aeromagnetic, seismological, and topographic information were compiled on 1:1,000,000-scale base maps. The following maps were prepared: (1) relief, (2) earthquake epicenter and station location, (3) lineament, (4) geologic bedrock, (5) structure contour (base of Kansas City Group or older Pennsylvanian rock units), (6) Precambrian configuration, (7) Bouguer gravity anomaly, (8) aeromagnetic, and (9) Precambrian rock type. One correlation between earthquakes and tectonic structures was made. There appears to be recent as well as historical earthquake activity associated with the Humbolt Fault zone, southeastern Nebraska and northeastern Kansas.

  7. The alpine Swiss-French airborne gravity survey

    NASA Astrophysics Data System (ADS)

    Verdun, Jérôme; Klingelé, Emile E.; Bayer, Roger; Cocard, Marc; Geiger, Alain; Kahle, Hans-Gert

    2003-01-01

    In February 1998, a regional-scale, airborne gravity survey was carried out over the French Occidental Alps within the framework of the GéoFrance 3-D research program.The survey consisted of 18 NS and 16 EW oriented lines with a spacing of 10 and 20 km respectively, covering the whole of the Western French Alps (total area: 50 000 km2; total distance of lines flown: 10 000 km). The equipment was mounted in a medium-size aircraft (DeHavilland Twin Otter) flowing at a constant altitude of 5100 m a.s.l, and at a mean ground speed of about 280 km h-1. Gravity was measured using a LaCoste & Romberg relative, air/sea gravimeter (type SA) mounted on a laser gyro stabilized platform. Data from 5 GPS antennae located on fuselage and wings and 7 ground-based GPS reference stations were used to determine position and aircraft induced accelerations.The gravimeter passband was derived by comparing the vertical accelerations provided by the gravimeter with those estimated from the GPS positions. This comparison showed that the gravimeter is not sensitive to very short wavelength aircraft accelerations, and therefore a simplified formulation for computing airborne gravity measurements was developed. The intermediate and short wavelength, non-gravitational accelerations were eliminated by means of digital, exponential low-pass filters (cut-off wavelength: 16 km). An important issue in airborne gravimetry is the reliability of the airborne gravity surveys when compared to ground surveys. In our studied area, the differences between the airborne-acquired Bouguer anomaly and the ground upward-continued Bouguer anomaly of the Alps shows a good agreement: the rms of these differences is equal to 7.68 mGal for a spatial resolution of 8 km. However, in some areas with rugged topography, the amplitudes of those differences have a striking correlation with the topography. We then argue that the choice of an appropriate density (reduction by a factor of 10 per cent) for computing the

  8. MODTOHAFSD — A GUI based JAVA code for gravity analysis of strike limited sedimentary basins by means of growing bodies with exponential density contrast-depth variation: A space domain approach

    NASA Astrophysics Data System (ADS)

    Chakravarthi, V.; Sastry, S. Rajeswara; Ramamma, B.

    2013-07-01

    Based on the principles of modeling and inversion, two interpretation methods are developed in the space domain along with a GUI based JAVA code, MODTOHAFSD, to analyze the gravity anomalies of strike limited sedimentary basins using a prescribed exponential density contrast-depth function. A stack of vertical prisms all having equal widths, but each one possesses its own limited strike length and thickness, describes the structure of a sedimentary basin above the basement complex. The thicknesses of prisms represent the depths to the basement and are the unknown parameters to be estimated from the observed gravity anomalies. Forward modeling is realized in the space domain using a combination of analytical and numerical approaches. The algorithm estimates the initial depths of a sedimentary basin and improves them, iteratively, based on the differences between the observed and modeled gravity anomalies within the specified convergence criteria. The present code, works on Model-View-Controller (MVC) pattern, reads the Bouguer gravity anomalies, constructs/modifies regional gravity background in an interactive approach, estimates residual gravity anomalies and performs automatic modeling or inversion based on user specification for basement topography. Besides generating output in both ASCII and graphical forms, the code displays (i) the changes in the depth structure, (ii) nature of fit between the observed and modeled gravity anomalies, (iii) changes in misfit, and (iv) variation of density contrast with iteration in animated forms. The code is used to analyze both synthetic and real field gravity anomalies. The proposed technique yielded information that is consistent with the assumed parameters in case of synthetic structure and with available drilling depths in case of field example. The advantage of the code is that it can be used to analyze the gravity anomalies of sedimentary basins even when the profile along which the interpretation is intended fails to

  9. Gravity is the Key Experiment to Address the Habitability of the Ocean in Jupiter's Moon Europa

    NASA Astrophysics Data System (ADS)

    Sessa, A. M.; Dombard, A. J.

    2013-12-01

    Life requires three constituents: a liquid solvent (i.e., water), a chemical system that can form large molecules to record genetic information (e.g., carbon based) as well as chemical nutrients (e.g., nitrogen, phosphorous), and a chemical disequilibrium system that can provide metabolic energy. While it is believed that there is a saline water layer located between the rock and ice layers in Jupiter's moon Europa, which would satisfy the first requirement, it is unknown if the other conditions are currently met. The likelihood that Europa is a haven for life in our Solar System skyrockets, however, if there is currently active volcanism at the rock-water interface, much the same that volcanic processes enable the chemosynthetic life that forms the basis of deep sea-vent communities at the bottom of Earth's oceans. Exploring the volcanic activity on this interface is challenging, as direct observation via a submersible or high-resolution indirect observations via a dense global seismic network on the surface is at present technically (and fiscally!) untenable. Thus, gravity studies are the best way to explore currently the structure of this all-important interface. Though mostly a silicate body with only a relatively thin (~100 km) layer of water, Europa is different from the terrestrial planets in that this rock-water interface, and not the surface, represents the largest density contrast across the moon's near-surface layers, and thus topography on this interface could conceivably dominate the gravity. Here, we calculate the potential anomalies that arise from topography on the surface, the water-ice interface (at 20 km depth), and the rock-water interface, finding that the latter dominates the free-air gravity at the longest wavelengths (spherical harmonic degrees < 10) and the Bouguer gravity at intermediate wavelengths (degrees ~10-50), and only for the shortest wavelengths (degrees > 50) does the water-ice interface (and presumably mass-density anomalies

  10. Gravity survey of marine field: Case study for Silurian reef exploration

    SciTech Connect

    Heigold, P.C.; Whitaker, S.T. )

    1989-08-01

    A gravity survey conducted over and around Marine field in southwestern Illinois has been used as an example to show how measurement of the local gravity field can aid in the search for Silurian reefs in the Illinois basin. Acquisition parameters for gravity surveys over Silurian reefs should be calculated beforehand from simple models of the reef based on estimates of density contrasts, depths, and size. Residual and derivative mapping techniques generally enhance gravity anomalies and enable more accurate portrayals of the structural relief on buried reefs. The second vertical derivative map of the residual Bouguer gravity anomaly surface at Marine field compares very well with the structure of the reef as mapped from subsurface data. This study indicates that similar mapping techniques could be effective on other reefs throughout the Illinois basin. Although gravity mapping methods are potentially powerful exploration tools in themselves, the writers believe that their proper role is as a part of a more comprehensive exploration approach. Gravity surveys can be used effectively as an initial exploration method in reef-prone areas to define smaller, prospect-size areas in which more intensive exploration techniques can subsequently be focused.

  11. Gravity anomaly at a Pleistocene lake bed in NW Alaska interpreted by analogy with Greenland's Lake Taserssauq and its floating ice tongue

    USGS Publications Warehouse

    Barnes, D.F.

    1987-01-01

    A possible example of a very deep glacial excavation is provided by a distinctive gravity low located at the front of a valley glacier that once flowed into glacial Lake Aniuk (formerly Lake Noatak) in the western Brooks Range. Geologic and geophysical data suggest that sediments or ice filling a glacially excavated valley are the most probable cause of the 30-50 mGal anomaly. Reasonable choices of geometric models and density contrasts indicate that the former excavation is now filled with a buried-ice thickness of 700 m or sediment thicknesses greater than 1 km. No direct evidence of efficient excavation was observed in Greenland, but efficient glacial erosion behind a floating polar ice tongue could explain the excavation that caused the Alaskan gravity anomaly. -from Author

  12. Determining OCT structure and COB Location of the Omani Gulf of Aden Continental Margin from Gravity Inversion, Residual Depth Anomaly and Subsidence Analysis.

    NASA Astrophysics Data System (ADS)

    Cowie, Leanne; Kusznir, Nick; Leroy, Sylvie; Manatshal, Gianreto

    2013-04-01

    Knowledge and understanding of the ocean-continent transition (OCT) structure and continent-ocean boundary (COB) location, the distribution of thinned continental crust and lithosphere, its distal extent and the start of unequivocal oceanic crust are of critical importance in evaluating rifted continental margin formation and evolution. In order to determine the OCT structure and COB location for the eastern Gulf of Aden, along the Oman margin, we use a combination of gravity inversion, subsidence analysis and residual depth anomaly (RDA) analysis. Gravity inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning; subsidence analysis has been used to determine the distribution of continental lithosphere thinning; and RDAs have been used to investigate the OCT bathymetric anomalies with respect to expected oceanic bathymetries at rifted margins. The gravity inversion method, which is carried out in the 3D spectral domain, incorporates a lithosphere thermal gravity anomaly and includes a correction for volcanic addition due to decompression melting. Reference Moho depths used in the gravity inversion have been calibrated against seismic refraction Moho depths. RDAs have been calculated by comparing observed and age predicted oceanic bathymetries, using the thermal plate model predictions from Crosby and McKenzie (2009). RDAs have been computed along profiles and have been corrected for sediment loading using flexural back-stripping and decompaction. In addition, gravity inversion crustal basement thicknesses together with Airy isostasy have been used to predict a synthetic RDA. The RDA results show a change in RDA signature and may be used to estimate the distal extent of thinned continental crust and where oceanic crust begins. Continental lithosphere thinning has been determined using flexural back-stripping and subsidence analysis assuming the classical rift model of McKenzie (1978) with a correction for

  13. Compositional Density Structure of the Upper Mantle from Constrained 3-D Inversion of Gravity Anomaly: A Case Study of Southeast Asia

    NASA Astrophysics Data System (ADS)

    Liang, Q.; Chen, C.; Kaban, M. K.; Thomas, M.

    2014-12-01

    Mantle density structure is a key for tectonics. The density variations in the upper mantle are affected by temperature and composition. Seismic tomography method has been widely applied to obtain the P- and S-wave velocity structure in the mantle, which is then used to calculate the density perturbation. However, the velocity model is mainly due to the thermal effects but not the compositional effects. A method of 3-D inversion of gravity anomaly developed in spherical coordinates is used to image the large-scale density structure of upper mantle in Southeast Asia. The mantle gravity anomalies used in inversion are calculated by removing the crustal effects from the observed gravity. With constraints of thermal density model from seismic tomography, the integrative density structure is estimated from gravity inversion. Consequently, we obtain the compositional density by subtracting the thermal density from the integrative structure. The result of inversion shows the anisotropic composition of subduction zones, Cratons and plates boundary in Southeast Asia. In the shallow depth, the compositional density anomalies of large scales present uniform features in oceanic and continental mantle. In depth of 75-175 km, there are differences between the thermal and the compositional variations. The density anomalies at these depths are both affected by temperature and composition of the upper mantle. Below 175-km depth, the density anomalies are dominated by the compositional variations. Furthermore, comparing with high seismicity occurred at moderate-depth (50-300 km), we found that the compositional density variations is one of the factor that inducing earthquakes. The constrained inversion of mantle gravity anomaly has possibility to reveal the subduction which is not clearly seen from low-resolution tomography data, and may reveal the relation of seismicity and composition in the upper mantle. This study is supported by the Program of International Science and

  14. Deep structure study of the salt body of Jbel Rheouis (central tunisia) from geological and gravity data

    NASA Astrophysics Data System (ADS)

    Bouzid, Wajih; Abbes, Chedly; Gabtni, Hakim; Hassine, Mouna

    2016-04-01

    Jbel Rheouis situated in south west of Sidi Bouzid, central Tunisia, is a complex structure located at a tectonic node between N-S, NE-SW and NW-SE corridors. It was considered as a diapir containing the most complete series of The Upper Triassic formation in Central Tunisia. The good quality of preserved fossils markers especially at the limestone levels made it possible for Burollet (1952) to propose a lithostratigraphic description of the Rheouis Formation. This stratigraphy was clarified by Soussi and Abbes (2004) basing on new paleontological, palynological and outcrops detailed mapping data. Thus, they assigned the base of this outcrops series to Carnian and its top to Rhaetian. Using these geological and lithostratigraphic data we suspects that the base of the Rheouis formation formed by black limestone can be correlated to the Rehach limestone in the South of Tunisia where this level is laying on a clayey sandstones level identified as the Lower Triassic outcrops. In this concept, this study intend to investigate the Rheouis structure and to identify it's nature basing on the intra salt structures identification and the nature of the Lower Triassic sediments buried beneath the Black limestones, using a combination of geological, lithostratigraphic and geophysical (gravity) data. The gravity data used in this work were obtained from the ONM with a mesh of 1Km /1Km. All the data were merged and reduced using the 1967 International gravity formula. Free air and Bouguer gravity correction were made using sea level as a datum and 2.4 g/cm³ as a reduction density. The Bouguer anomaly map shows a variation in anomaly values range from -12.5 mGal to -4.5 mGal with a contrasted anomaly distribution. This map present 5 gravity maxima and 4 gravity minima where the major direction of those maxima and minima are N-S, NE-SW and NW-SE. The presence of a relative positive anomaly concentrated J.Rheouis can be explained by a mass excess probably due to the uplift of the

  15. Large-scale gravity anomaly in northern Norway: tectonic implications of shallow or deep source depth and a possible conjugate in northeast Greenland

    NASA Astrophysics Data System (ADS)

    Gradmann, Sofie; Ebbing, Jörg

    2015-12-01

    A prominent gravity and geoid low lies just south of the Lofoten peninsula in northern Norway, partly coinciding with the location of Proterozoic granites of the Transscandinavian Igneous Belt and being offset by ca. 100 km to the highest topography of northern Norway. The study area extends both onshore and offshore and lies at the transition between Archaean and Proterozoic lithosphere. The Palaeoproterozoic basement has been overthrusted by the Palaeozoic nappes of the Caledonian orogen and now forms the passive margin of the NE Atlantic. We investigate the gravity anomaly performing combined 3-D geophysical-petrological forward modelling of the lithosphere and sublithospheric upper mantle using the interactive modelling program LitMod3D. We include variations in thickness and composition of the lithospheric mantle in order to include the effects on the rifted margin adjoining the Baltic craton. We compare three possible origins of the anomaly: (i) a low-density upper crust, representing the northward extension of the Transscandinavian Igneous Belt, (ii) a lower crustal source formed by a Moho depression and (iii) a thick, depleted lithospheric mantle of possibly Archaean origin. A similar, yet wider and stronger gravity anomaly is found on the conjugate margin in northeastern Greenland. A shallow crustal source is most consistent with the geophysical data sets. A respective source of the granitic belt, however, is difficult to reconcile with the regional geology both in Fennoscandia and Greenland. An additional contribution form a deeper source is suggested.

  16. World Gravity Map (WGM) Project: Objectives and Status

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Briais, A.; Peyrefitte, A.; Biancale, R.; Gabalda, G.; Moreaux, G.; Sarrailh, M.; Fayard, T.

    2009-12-01

    The WGM project is a gravity mapping project undertaken under the aegis of the Commission for the Geological Map of the World (CGMW) to complement a set of global geological and geophysical digital maps published and updated by CGMW, such as the World Digital Magnetic Anomaly Map (WDMAM), released in 2007. This new global digital map aims to provide a high-resolution picture of the gravity anomalies of the world (free-air and topography-corrected Bouguer) based on the available information on the Earth gravity field, with the final objective to contribute to research and educational projects. The WGM project is conducted by the International Gravimetric Bureau (IGB), a center of the International Gravity Field Service (IGFS) of the International Association of Geodesy (IAG), with the support of the United Nations Educational Scientific and Cultural Organization (UNESCO). Major contributions to the WGM are provided by the EGM08 global model, recently released by the National Geospatial-Intelligence Agency (NGA, USA), as well as the new global marine gravity fields derived from satellite altimetry (DNSC08 computed at the Danish National Space Center, and V18.1 computed at Scripps Institution of Oceanography). The WGM also aims to improve the gravity anomalies at regional scale, using available products from recent regional compilations of land, marine and airborne surveys (possibly derived from BGI or other global or regional databases). As other geophysical maps published by CGMW, the WGM maps and digital products should be regularly updated according to the incoming gravity datasets. We present here the current status of the WGM project.

  17. Gravity field over the Sea of Galilee: Evidence for a composite basin along a transform fault

    USGS Publications Warehouse

    Ben-Avraham, Z.; ten Brink, U.; Bell, R.; Reznikov, M.

    1996-01-01

    The Sea of Galilee (Lake Kinneret) is located at the northern portion of the Kinneret-Bet Shean basin, in the northern Dead Sea transform. Three hundred kilometers of continuous marine gravity data were collected in the lake and integrated with land gravity data to a distance of more than 20 km around the lake. Analyses of the gravity data resulted in a free-air anomaly map, a variable density Bouguer anomaly map, and a horizontal first derivative map of the Bouguer anomaly. These maps, together with gravity models of profiles across the lake and the area south of it, were used to infer the geometry of the basins in this region and the main faults of the transform system. The Sea of Galilee can be divided into two units. The southern half is a pull-apart that extends to the Kinarot Valley, south of the lake, whereas the northern half was formed by rotational opening and transverse normal faults. The deepest part of the basinal area is located well south of the deepest bathymetric depression. This implies that the northeastern part of the lake, where the bathymetry is the deepest, is a young feature that is actively subsiding now. The pull-apart basin is almost symmetrical in the southern part of the lake and in the Kinarot Valley south of the lake. This suggests that the basin here is bounded by strike-slip faults on both sides. The eastern boundary fault extends to the northern part of the lake, while the western fault does not cross the northern part. The main factor controlling the structural complexity of this area is the interaction of the Dead Sea transform with a subperpendicular fault system and rotated blocks.

  18. OCT structure, COB location and magmatic type of the S Angolan & SE Brazilian margins from integrated quantitative analysis of deep seismic reflection and gravity anomaly data

    NASA Astrophysics Data System (ADS)

    Cowie, Leanne; Kusznir, Nick; Horn, Brian

    2014-05-01

    Integrated quantitative analysis using deep seismic reflection data and gravity inversion have been applied to the S Angolan and SE Brazilian margins to determine OCT structure, COB location and magmatic type. Knowledge of these margin parameters are of critical importance for understanding rifted continental margin formation processes and in evaluating petroleum systems in deep-water frontier oil and gas exploration. The OCT structure, COB location and magmatic type of the S Angolan and SE Brazilian rifted continental margins are much debated; exhumed and serpentinised mantle have been reported at these margins. Gravity anomaly inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. Residual Depth Anomaly (RDA) analysis has been used to investigate OCT bathymetric anomalies with respect to expected oceanic bathymetries and subsidence analysis has been used to determine the distribution of continental lithosphere thinning. These techniques have been validated for profiles Lusigal 12 and ISE-01 on the Iberian margin. In addition a joint inversion technique using deep seismic reflection and gravity anomaly data has been applied to the ION-GXT BS1-575 SE Brazil and ION-GXT CS1-2400 S Angola deep seismic reflection lines. The joint inversion method solves for coincident seismic and gravity Moho in the time domain and calculates the lateral variations in crustal basement densities and velocities along the seismic profiles. Gravity inversion, RDA and subsidence analysis along the ION-GXT BS1-575 profile, which crosses the Sao Paulo Plateau and Florianopolis Ridge of the SE Brazilian margin, predict the COB to be located SE of the Florianopolis Ridge. Integrated quantitative analysis shows no evidence for exhumed mantle on this margin profile. The joint inversion technique predicts oceanic crustal thicknesses of between 7 and 8 km thickness with

  19. Gravity survey in part of the Snake River Plain, Idaho - a preliminary report

    USGS Publications Warehouse

    Baldwin, Harry L.; Hill, David P.

    1960-01-01

    During the early summer of 1959, a total of 1,187 gravity stations were occupied on the western part of the Snake River plain in Idaho. An area of 2,000 square miles extending from Glenns Ferry, Idaho, to Caldwell, Idaho, was covered with a station density of one station per two square miles. An additional 1,200 square miles of surrounding area, mainly from Caldwell, Idaho, to the Oregon-Idaho state line, was covered with a density of one station per seven square miles. The mean reproducibility of the observed gravities of these stations was 0.05 milligal, with a maximum discrepancy of 0.2 milligal. Gravity data were reduced to simple Bouguer values using a combined free-air and Bouguer correction of 0.06 milligal per foot. The only anomalies found with closure in excess of 10 milligals are two elongated highs, orientated northwest-southeast, with the northwestern high offset to the northeast by 10 miles. The smaller of these highs extends from Meridian, Idaho, to Nyssa, Oregon, and the larger extends from Swan Falls, Idaho, to Glenns Ferry, Idaho. The maximum value recorded is a simple Bouguer value of -66.5 milligals with respect to the International Ellipsoid. Gradients on the sides of these highs are largest on the northeast sides, reaching six milligals per mile in places. Graticule interpretations of a profile across the southeastern high using a density contrast of 0.3 gm per cubic centimeter indicate an accumulation of lava reaching a thickness of at least 28,000 feet. The Snake River investigation was made for the purpose of searching out, defining, and interpreting gravity anomalies present on the western part of the Snake River lava plain in Idaho. In particular, it was desired to further define gradients associated with the gravity high shown by the regional work of Bonini and Lavin (1957). It was not planned to cover any specific area, but rather to let the observed anomalies determine the course of the field work. The study was undertaken as part of a

  20. New fast least-squares algorithm for estimating the best-fitting parameters due to simple geometric-structures from gravity anomalies

    PubMed Central

    Essa, Khalid S.

    2013-01-01

    A new fast least-squares method is developed to estimate the shape factor (q-parameter) of a buried structure using normalized residual anomalies obtained from gravity data. The problem of shape factor estimation is transformed into a problem of finding a solution of a non-linear equation of the form f(q) = 0 by defining the anomaly value at the origin and at different points on the profile (N-value). Procedures are also formulated to estimate the depth (z-parameter) and the amplitude coefficient (A-parameter) of the buried structure. The method is simple and rapid for estimating parameters that produced gravity anomalies. This technique is used for a class of geometrically simple anomalous bodies, including the semi-infinite vertical cylinder, the infinitely long horizontal cylinder, and the sphere. The technique is tested and verified on theoretical models with and without random errors. It is also successfully applied to real data sets from Senegal and India, and the inverted-parameters are in good agreement with the known actual values. PMID:25685472

  1. New fast least-squares algorithm for estimating the best-fitting parameters due to simple geometric-structures from gravity anomalies.

    PubMed

    Essa, Khalid S

    2014-01-01

    A new fast least-squares method is developed to estimate the shape factor (q-parameter) of a buried structure using normalized residual anomalies obtained from gravity data. The problem of shape factor estimation is transformed into a problem of finding a solution of a non-linear equation of the form f(q) = 0 by defining the anomaly value at the origin and at different points on the profile (N-value). Procedures are also formulated to estimate the depth (z-parameter) and the amplitude coefficient (A-parameter) of the buried structure. The method is simple and rapid for estimating parameters that produced gravity anomalies. This technique is used for a class of geometrically simple anomalous bodies, including the semi-infinite vertical cylinder, the infinitely long horizontal cylinder, and the sphere. The technique is tested and verified on theoretical models with and without random errors. It is also successfully applied to real data sets from Senegal and India, and the inverted-parameters are in good agreement with the known actual values.

  2. GRAIL Gravity Observations of Peak-Ring Basins on the Moon: Implications for Basin Formation

    NASA Astrophysics Data System (ADS)

    Baker, D. M.; Head, J. W.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2012-12-01

    Reassessment of the formation of peak-ring basins on the Moon using image and altimetry data from the Lunar Reconnaissance Orbiter has yielded a number of morphometric properties of these basin types that are helping to constrain the processes leading to their formation and the formation of larger multi-ring basins [1,2]. These analyses demonstrate the importance of the volume and depth of impact melting in modifying the interior morphology of large impact craters. At the onset diameter of peak-ring basins, the depth of the basin's melted zone approaches the depth of the transient crater, creating a strengthless interior melt cavity that facilitates gravitational collapse of the transient crater. The melt cavity suppresses central peak formation, and peak rings are formed outward from the melt zone boundary by the interaction of deep-seated rotational faults in the collapsing wall of the transient crater and huge vertical uplifts in the central portions of the basin. The final configuration of the peak-ring basin has a kilometers-thick slab of cooled residual impact melt resting on an uplifted mantle plug with little or no unmelted crustal material. Highly faulted and fractured, dilatant and possibly thickened crust should occur below and outward from the peak ring due to inward and upward translation of collapsed transient crater rim material. As a result of this configuration, the gravity structure should reflect an anomalously high density, uplifted impact melt plus mantle zone spatially confined to within the peak ring. Surrounding this should be a highly fractured, low density zone of possibly thickened crust. Bouguer gravity anomalies derived from Gravity Recovery and Interior Laboratoy (GRAIL) gravity data and Lunar Orbiter Laser Altimeter (LOLA) altimetry data show spatial patterns that are consistent with those predicted by the formation model briefly outlined above. Nearly all 17 peak-ring basins that have been cataloged on the Moon show positive Bouguer

  3. 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.

  4. Comparison of New Airborne Gravity Results and GRACE Anomalies in the Thwaites Glacier Catchment of the Amundsen Sea Embayment, West Antarctica

    NASA Astrophysics Data System (ADS)

    Diehl, T. M.; Holt, J. W.; Blankenship, D. D.; Richter, T. G.; Filina, I. Y.

    2005-12-01

    The West Antarctic Ice Sheet is a marine ice sheet of which 75% is resting on bedrock below sea level. This situation is highly unstable and as the climate warms, the potential for rapid discharge of the ice sheet grows. Examining the areas of the ice sheet that are most likely to react to changing climate is essential. The Amundsen Sea Embayment contains two of the most important outlet glaciers in West Antarctica: Thwaites and Pine Island Glaciers. These two glaciers have among the highest discharge velocities in West Antarctica and they lack large protective ice shelves, making them susceptible to warming ocean waters. The area is currently a target of interest for both GRACE and GLAS, as well as future land- and air-based surveys. To date, we have conducted the only large-scale geophysical survey over the catchment of Thwaites Glacier: an airborne survey completed during the austral summer 2004-2005. Over 43,500 line-kilometers of data were collected with a geophysical platform that included ice-penetrating radar, gravity, magnetics, laser and pressure altimetry, and GPS. Free-air gravity, in conjunction with magnetics and radar-derived subglacial topography, is capable of delineating microplate and rift boundaries as well as basin and volcano locations. A free-air gravity map of these structures helps ascertain the contribution of subglacial geology to the ice sheet's decay in the Thwaites Glacier catchment. The acquisition, reduction, and initial results of the airborne gravity survey will be presented and then compared to GRACE gravity anomalies. Extreme relief in ice surface elevation across the survey area necessitated short, smooth vertical altitude changes at survey block boundaries to maintain adequate flight altitude for the onboard ice-penetrating radar systems. Weather conditions sometimes required additional elevation changes or course corrections, producing significant aircraft motion during data acquisition. The impacts of these aircraft motions

  5. Assessment Ground Safety Using Time Lap Vertical Gravity Gradient At The Subsidence Area

    NASA Astrophysics Data System (ADS)

    Rim, H. B.; Park, Y.; Lim, M.; Koo, S. B.; Kwon, B. D.

    2007-05-01

    We have carried out time-lap vertical gravity gradient (VGG) survey in order to assess the ground safety before and after grouting. The target area is new pavement through the rice field, and the area has subsidence problems because of excessive pumping for agricultural irrigation. Therefore, it has been reinforced with cement grouting avoiding subsidence. In this paper, we examined the change of subsurface density distribution due to cement grouting by means of VGG survey. VGG method is more sensitive to detect the change of near surface than gravity survey itself because VGG enhanced small variation of gravity anomaly. We gathered one line gravity data about 270m long at every 2m. VGG survey consisted of observations between the ground bottom and the top separated vertically about 1.5m with help of the ladder specially designed. According to result, VGG anomaly made the response of man-made waterway clearer than Bouguer anomaly in the middle part of the line. And VGG result showed changes of subsurface density distribution after grouting.

  6. The structural setting of the Ischia Island Caldera (Italy): first evidence from seismic and gravity data

    NASA Astrophysics Data System (ADS)

    Capuano, Paolo; De Matteis, Raffaella; Russo, Guido

    2015-09-01

    Ischia Island is one of the active volcanoes of the Neapolitan area (Italy). Hazard assessment of active, densely populated volcano is primarily based on knowledge of the volcano's past behaviour and of its present state. As a contribution to the definition of the present structural setting of Ischia Island, we constructed a new model of the shallow crust using geophysical data: seismic wave travel times and Bouguer anomaly data. We analysed these data sets through seismic tomography and gravity data inversion. The main results inferable from the 3D seismic and gravity images are the definition of the caldera rim along the perimeter of the island, as hypothesized by many authors, and the presence of a high velocity and density area inside the caldera consistent with extension of the resurgent block that characterizes the recent deformation of the island.

  7. Analysis of gravity data in Central Valleys, Oaxaca, southern, Mexico

    NASA Astrophysics Data System (ADS)

    Gonzalez, T.; Ferrusquia, I.

    2015-12-01

    The region known as Central Valleys is located in the state of Oaxaca, southern, Mexico (16.3o- 17.7 o N Lat. and 96 o - 97 o W Long.) In its central portion is settled the capital of the state. There are very few published detailed geological studies.. Geomorphological and geological features, indicates that Central Valleys and surrounding mountains conform a graben structure. Its shape is an inverted Y, centred on Oaxaca City. The study area was covered by a detailed gravity survey with a homogenous distribution of stations. The Bouguer gravity map is dominated by a large gravity low, oriented NW-SE. In order to know the characteristics of anomalies observed gravity, data transformations were used. The use of spectral methods has increased in recent years, especially for the estimation of the depth of the source. Analysis of the gravity data sheds light on the regional depth of the Graben basement and the spatial distribution of the volcanic rocks

  8. Estimates of Te for continental regions using GOCE gravity

    NASA Astrophysics Data System (ADS)

    McKenzie, Dan; Yi, Weiyong; Rummel, Reiner

    2015-10-01

    Satellite-only gravity fields and surface gravity obtained from altimetric measurements now agree well at wavelengths greater than ∼180 km. Satellite gravity fields can therefore be used to estimate the elastic thickness Te in regions where surface observations are sparse. They are used for this purpose in a number of continental regions, of India, Africa, and Antarctica, where the topography is sufficiently rough, and also in regions of the USA, China, Australia and Siberia, where there are surface measurements. Estimates of Te for Antarctica depend on measurements of ice thickness, which are now available for much of the continent. Values of Te are obtained using two methods: from the admittance between the free air gravity and the topography, and from the coherence between Bouguer gravity anomalies and the topography. The first, but not the second, gives values of Te that are everywhere less than the seismogenic thickness. Where there is sufficient topography, estimates of Te from PreCambrian shields are all greater than 10 km and do not correlate with the lithospheric thickness. They are probably are governed by variations in crustal heat generation rates. Values for regions strongly affected by Phanerozoic tectonics are all less than 7 km, and all such regions are underlain by thin lithosphere.

  9. Gravity anomalies, Quaternary vents, and Quaternary faults in the southern Cascade Range, Oregon and California: Implications for arc and backarc evolution

    USGS Publications Warehouse

    Blakely, R.J.; Christiansen, R.L.; Guffanti, M.; Wells, R.E.; Donnelly-Nolan, J. M.; Muffler, L.J. Patrick; Clynne, M.A.; Smith, James G.

    1997-01-01

    Isostatic residual gravity anomalies in the southern Cascade Range of northern California and southern Oregon are spatially correlated with broad zones of Quaternary magmatism as reflected by the total volume of Quaternary volcanic products, the distribution of Quaternary vents, and the anomalously low teleseismic P wave velocities in the upper 30 km of crust. The orientation of Quaternary faults also appears to be related to gravity anomalies and volcanism in this area, trending generally north-south within the magmatic regions and northwest-southeast as they enter the neighboring amagmatic zones to the north and south. The relationship between gravity anomalies, vent density, and fault orientations may indicate in a broad sense the strength of the middle and upper crust. The southern Cascade Range occupies a transition zone where horizontal stress is transferred from the northwest-southeast dextral shear of the Walker Lane belt to the east-west extension characteristic of the Cascade arc in central Oregon. Faulting along north-south strikes in the volcanically active areas indicates the east-west extensional stresses in thermally weakened crust, whereas northwest faulting between the volcanically active areas reflects the northwest trending, right lateral shear strain of the Walker Lane belt. The segmentation of the arc reflected in Quaternary magmatism may be caused by differential extension behind crustal blocks of the forearc rotating clockwise with respect to North America. In this view the volcanic centers at Mount Shasta, Medicine Lake volcano, and Lassen Peak in northern California are situated along the southern parts of the trailing edges of two distinct segments of the forearc where additional extension is implied by their differential clockwise rotation. U.S. copyright. Published in 1997 by the American Geophysical Union.

  10. Gravity anomalies, Quaternary vents, and Quaternary faults in the southern Cascade Range, Oregon and California: Implications for arc and backarc evolution

    NASA Astrophysics Data System (ADS)

    Blakely, Richard J.; Christiansen, Robert L.; Guffanti, Marianne; Wells, Ray E.; Donnelly-Nolan, Julie M.; Muffler, L. J. Patrick; Clynne, Michael A.; Smith, James G.

    1997-10-01

    Isostatic residual gravity anomalies in the southern Cascade Range of northern California and southern Oregon are spatially correlated with broad zones of Quaternary magmatism as reflected by the total volume of Quaternary volcanic products, the distribution of Quaternary vents, and the anomalously low teleseismic P wave velocities in the upper 30 km of crust. The orientation of Quaternary faults also appears to be related to gravity anomalies and volcanism in this area, trending generally north-south within the magmatic regions and northwest-southeast as they enter the neighboring amagmatic zones to the north and south. The relationship between gravity anomalies, vent density, and fault orientations may indicate in a broad sense the strength of the middle and upper crust. The southern Cascade Range occupies a transition zone where horizontal stress is transferred from the northwest-southeast dextral shear of the Walker Lane belt to the east-west extension characteristic of the Cascade arc in central Oregon. Faulting along north-south strikes in the volcanically active areas indicates the east-west extensional stresses in thermally weakened crust, whereas northwest faulting between the volcanically active areas reflects the northwest trending, right lateral shear strain of the Walker Lane belt. The segmentation of the arc reflected in Quaternary magmatism may be caused by differential extension behind crustal blocks of the forearc rotating clockwise with respect to North America. In this view the volcanic centers at Mount Shasta, Medicine Lake volcano, and Lassen Peak in northern California are situated along the southern parts of the trailing edges of two distinct segments of the forearc where additional extension is implied by their differential clockwise rotation.

  11. 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

  12. Geomodel constructs of the Earth's crust for water continuation of the Korotaikha depression from gravity and magnetic data for revealing promising areas of oil and gas accumulation

    NASA Astrophysics Data System (ADS)

    Litvinova, Tamara; Kudryavtsev, Ivan

    2016-04-01

    The paper considers the results of re-interpretation of geophysical data within the water continuation of the Korotaikha depression. To solve the issue of identifying promising areas of oil and gas accumulation in the region, magnetic and gravity materials were reprocessed: digital maps of potential fields at 1: 500 000 scale were compiled on a frame network of seismic lines (3 lines on land and 3 lines in water area) made by reflection-CDP, density models to a depth of 20 km by solving the direct problem of gravity prospecting in GM-SYS module (Geosoft) in 2D formulation were constructed. Deep reflection-CDP seismic sections specified according to the deep wells were used as starting models. Correctness of the selected density models was controlled by comparing the theoretical curve with the values interpolated on the profile line from the digital model of gravity anomaly (Bouguer, density of the intermediate layer of 2.67 g/cm3). Magnetic modeling was performed using geometry of blocks from the obtained density models to a depth of 20 km and is based on selection of local anomaly sources in the upper section (in the Triassic strata). Blocks of the Precambrian basement were used as sources of regional magnetic anomalies in the considered models. Modeling constructs show the defining role of the topography of terrigenous and carbonate complex boundary within the Paleozoic section as a source of gravity anomalies for the region under study. These findings are confirmed by comparison of gravity and seismic data (maps of local gravity anomalies and structural maps of reflecting horizons) and additionally substantiated by analysis of the nature of local magnetic anomalies distribution. The latter are associated with the Triassic basalt horizons at the top of the terrigenous complex and thus also reflect structures of the sedimentary cover, which are registered independently by gravity data.

  13. Modeling of Vesta's interior structure using gravity and shape models from the Dawn mission and hydrodynamic impact simulations

    NASA Astrophysics Data System (ADS)

    Ermakov, A.; Zuber, M. T.; Smith, D. E.; Raymond, C. A.; Balmino, G.; Ivanov, B.; Asphaug, E. I.; Jutzi, M.

    2012-12-01

    Observations from the Dawn spacecraft are used to determine the shape and gravity field of Vesta. Radio tracking data allowed an estimation of the gravity field of Vesta to spherical harmonic degree and order 20 (Asmar et al., 2011; Konolpiv et al., 2012). Images obtained by Dawn's Framing Camera (FC) have been used to produce shape models of Vesta using stereophotogrammetry and stereophotoclinometry methods (Preusker et al., 2011; Raymond et al., 2012). The data from the second High Altitude Mapping Orbit (HAMO 2) will be used to reconstruct the shape in the north pole region. In our study we represent the shape model as a spherical harmonic expansion. The topography power spectrum shows that the spectral slope of Vesta's topography is distinct from that of the terrestrial planets (Turcotte, 1987). The fractal dimension D of Vesta's topography on scales 10 - 1000 km is approximately equal to 1.28 (D=1.5 for Brownian noise topography). The spherical harmonic expansion of topography is used to compute gravity potential anomalies (Balmino, 1994); a three-layer interior structure model is computed by minimizing the power of the residual Bouguer gravity anomaly (Wieczorek and Philips, 1998). The densities of the core, mantle and crust are based on the constraints derived from the HED-meteorites (McSween el al., 2012; Zuber et al., 2012; Ruzicka et al., 1997). The center of mass - center of figure offset is compensated by offsetting the core center from the center of mass by 7-10 km, depending on assumed interior densities. We observe a significant contribution of non-zonal second-degree terms in the Bouguer gravity anomaly, which indicates spatial variability of the internal interfaces. The major positive gravity anomaly is observed in Vestalia Terra region. Results of hydrodynamic impact simulations of the Rheasilvia basin formation show a redistribution of crustal and mantle material within the basin (e.g. Ivanov el al., 2012; Jutzi and Asphaug, 2011). The regional

  14. Airborne Gravity Measurements using a Helicopter with Special Emphases on Delineating Local Gravity Anomalies Mainly for Detecting Active Seismic Faults (Invited)

    NASA Astrophysics Data System (ADS)

    Segawa, J.

    2010-12-01

    The first aerial gravity measurement in Japan started in 1998 using a Japanese airborne gravimeter ‘ Segawa-TKeiki airborne gravimeter Model FGA-1’. We lay emphasis on the measurement of detailed gravity structures at the land-to-sea border areas and mountainous areas. This is the reason why we use a helicopter and make surveys at low altitude and low speed. We have so far made measurement at twelve sites and the total flight amounts to 20,000km. The accuracy of measurement is 1.5 mgal and half-wavelength resolution is 1.5 km. The Japanese type gravimeter consists of a servo-accelerometer type gravity sensor, a horizontal platform controlled by an optical fiber gyro, GPS positioning system, and a data processing system. Helicopter movement has to be precisely monitored three-dimensionally to calculate the vehicle’s acceleration noises. The necessary accuracy of positioning of the vehicle must be better than 10 cm in positioning error. Our helicopter gravity measurement has a special target in Japan to investigate active seismic faults located across land-to-sea borderlines. In Japan, it is generally thought that gravity over most of the country has already been measured by the governmental surveys, leaving the land-sea border lines and mountainous zones unsurveyed as difficult-to-access areas. In addition the use of airplane or helicopter in Japan appeared disadvantageous because of the narrowness of the Japanese Islands. Under such situations the author thought there still remained a particular as well as unique need for aerial gravity measurement in Japan, i.e. the need for detailed and seamless knowledge of gravity structures across land-to-sea border lines to elucidate complicated crustal structures of the Japanese Islands as well as distribution of active seismic faults for disaster prevention. The results of gravity measurements we have conducted so far include those of 12 sites. In the following the brief logs of our measurements are listed. 1)April

  15. Importance of the Decompensative Correction of the Gravity Field for Study of the Upper Crust: Application to the Arabian Plate and Surroundings

    NASA Astrophysics Data System (ADS)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2016-08-01

    The isostatic correction represents one of the most useful "geological" reduction methods of the gravity field. With this correction it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. However, even this reduction does not show the full gravity effect of unknown anomalies in the upper crust since their impact is substantially reduced by the isostatic compensation. We analyze a so-called decompensative correction of the isostatic anomalies, which provides a possibility to separate these effects. It was demonstrated that this correction is very significant at the mid-range wavelengths and may exceed 100 m/s2 (mGal), therefore ignoring this effect would lead to wrong conclusions about the upper crust structure. At the same time, the decompensative correction is very sensitive to the compensation depth and effective elastic thickness of the lithosphere. Therefore, these parameters should be properly determined based on other studies. Based on this technique, we estimate the decompensative correction for the Arabian plate and surrounding regions. The amplitude of the decompensative anomalies reaches ±250 m/s2 10-5 (mGal), evidencing for both, large density anomalies of the upper crust (including sediments) and strong isostatic disturbances of the lithosphere. These results improve the knowledge about the crustal structure in the Middle East.

  16. 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

  17. Structure of the Tucson Basin, Arizona from gravity and aeromagnetic data

    USGS Publications Warehouse

    Rystrom, Victoria Louise

    2003-01-01

    Interpretation of gravity and high-resolution aeromagnetic data reveal the three-dimensional geometry of the Tuscson Basin, Arizona and the lithology of its basement. Limited drill hole and seismic data indicate that the maximum depth to the crystalline basement is approximately 3600 meters and that the sedimentary sequences in the upper ~2000 m of the basin were deposited during the most recent extensional episode that commenced about 13 Ma. The negative density contrasts between these upper Neogene and Quaternary sedimentary sequences and the adjacent country rock produce a Bouguer residual gravity low, whose steep gradients clearly define the lateral extent of the upper ~2000m of the basin. The aeromagnetic maps show large positive anomalies associated with deeply buried, late Cretaceous-early Tertiary and mid-Tertiary igneous rocks at and below the surface of the basin. These magnetic anomalies provide insight into the older (>13 Ma) and deeper structures of the basin. Simultaneous 2.5-dimensional modeling of both gravity and magnetic anomalies constrained by geologic and seismic data delineates the thickness of the basin and the dips of the buried faults that bound the basin. This geologic-based forward modeling approach to using geophysical data is shown to result in more information about the geologic and tectonic history of the basin as well as more accurate depth to basement determinations than using generalized geophysical inversion techniques.

  18. Imaging of subsurface lineaments in the southwestern part of the Thrace Basin from gravity data

    NASA Astrophysics Data System (ADS)

    Aydogan, D.; Pinar, A.; Elmas, A.; Bal, O. Tarhan; Yuksel, S.

    2013-04-01

    Linear anomalies, as an indicator of the structural features of some geological bodies, are very important for the interpretation of gravity and magnetic data. In this study, an image processing technique known as the Hough transform (HT) algorithm is described for determining invisible boundaries and extensions in gravity anomaly maps. The Hough function implements the Hough transform used to extract straight lines or circles within two-dimensional potential field images. It is defined as image and Hough space. In the Hough domain, this function transforms each nonzero point in the parameter domain to a sinusoid. In the image space, each point in the Hough space is transformed to a straight line or circle. Lineaments are depicted from these straight lines which are transformed in the image domain. An application of the Hough transform to the Bouguer anomaly map of the southwestern part of the Thrace Basin, NW Turkey, shows the effectiveness of the proposed approach. Based on geological data and gravity data, the structural features in the southwestern part of the Thrace Basin are investigated by applying the proposed approach and the Blakely and Simpson method. Lineaments identified by these approaches are generally in good accordance with previously-mapped surface faults.

  19. Gravity anomaly across the Yap Trench, Sorol Trough, and southernmost Parece Vela Basin and its implications for the flexural deformation of the lithosphere and regional isostasy

    NASA Astrophysics Data System (ADS)

    Kim, Y.; Lee, S.; Okino, K.; Koizumi, K.

    2005-12-01

    In June 2005, R/V Hakuho-maru (KH05-01-Leg 3) conducted a geological and geophysical survey of the southern tip of the Parece Vela Basin (PVB). The survey also profiled the Yap trench, the Yap arc and back-arc region, and Sorol Trough and collected multibeam bathymetry, gravity and magnetic data. In addition, one multichannel seismic reflection profiling across the Yap trench and two dredge rock samplings in the southwestern PVB were carried out. The shipboard free-air gravity field was measured by ZLS Dynamic Gravity Meter D-004 with calibration ties performed at Ocean Research Institute, University of Tokyo and at Apra Harbor in Guam. The shipboard gravity anomaly data show clear match with those derived from satellite altimetry. Also included in our analysis is the shipboard gravity data previously collected by R/V Onnuri. The Yap trench is unique in that it has a short trench-arc distance (approx. 50 km). This proximity has long been interpreted as feature resulting from a collision of over-thickened Caroline Ridge with the trench. In recent years, however, a new hypothesis has been put forward that such feature can be explained by initiation or rejuvenation of subduction, and that the style of subduction changes between north and south of the Sorol Trough. Our survey also revealed peculiar hook-shaped structures in the southernmost PVB and other evidences for large-scale, complex rotational deformation on the seafloor, whose origin remains unclear at this stage. To better understand the nature of these structures and features across Yap trench, Sorol Trough and in southernmost PVB, we examine the regional isostasy using the recently collected bathymetric and gravity data. The density information is deduced from studies conducted at other subduction systems, including Izu-Bonin Mariana trench, and from our own seismic experiment. Preliminary analysis shows that much of the features may be maintained by the flexural rigidity of the lithosphere, especially near

  20. Gravity evidence for a mafic intrusion beneath a mineralized zone in the Bondy gneiss complex, Grenville Province, Quebec - Exploration implications

    NASA Astrophysics Data System (ADS)

    Dufréchou, Grégory; Harris, Lyal B.; Corriveau, Louise; Antonoff, Vladimir

    2011-09-01

    A ground gravity survey over the Bondy gneiss complex and its mineralized iron oxide- and copper-rich hydrothermal system(s) in the Grenville Province of SW Quebec was undertaken to aid mineral exploration in mapping subsurface intrusions. Several kilometric-scale positive Bouguer anomalies were identified that coincide with outcropping mafic and intermediate intrusive rocks of the post peak-metamorphic, 1.17-1.16 Ga mafic to intermediate Chevreuil suite intrusions and a 1.09-1.07 Ga Rolleau ultramafic stock. An additional 4 × 3 kilometre positive gravity anomaly indicates a mafic body underlies part of the metamorphosed hydrothermal system in the area of magnetite, pyrite, pyrrhotite, and chalcopyrite mineralization. Advanced argilic alteration associated with sulphide enrichment here is however indicative of an epithermal system with a felsic intrusion fluid source. As a felsic intrusion cannot explain the positive Bouguer gravity anomaly both felsic and mafic bodies must be present beneath the mineralized zone. Our preferred interpretation based on integrating gravity data and 2D forward gravity modelling with the results of field and geochemical studies is that this anomaly corresponds to a ca. 500 m deep mafic 1.17-1.16 Ga Chevreuil suite pluton that may have provided the source for hydrothermal fluids associated with late ductile shear- and fault-related mineralization or remobilization of early mineralization associated with a felsic pluton into late structures. This interpretation is compatible with gabbro xenoliths in the 1.07 Ga Rivard lamprophyre dyke on the NW margin of the gravity anomaly that bear significant similarities with those of the Chevreuil intrusive suite. The presence of both early felsic and late mafic intrusions beneath a group of three mineral occurrences in the Bondy gneiss complex strengthens their prospectivity in comparison to other mineral occurrences in the area. That early, pre-metamorphic mineralization was upgraded late in the

  1. Gravity survey of the Escalante Desert and vicinity, in Iron and Washington Counties, Utah

    SciTech Connect

    Pe, W.; Cook, K.L.

    1980-08-01

    During the summers of 1978 and 1979, a total of 436 new gravity stations were taken in the southern part of the Escalante Desert and vicinity in Iron and Washington counties, Utah. The new stations were combined with 917 other stations taken in previous surveys, and a total of 1353 stations were used in this study, covering an area of about 2700 mi/sup 2/ (7000 km/sup 2/). The purpose of the study was to help evaluate the potential of geothermal resources within the survey area, which includes the Newcastle and Lund KGRA's. All the gravity data were terrain corrected out to a radial distance of 166.7 km from each station, using a computer terrain-correction program. The data were compiled and presented as a complete Bouguer gravity anomaly map with a 2-mgal contour interval. A geologic interpretation of the gravity data was made qualitatively from the gravity map and also quantitatively from four easterly trending gravity profiles taken across the area.

  2. Structure of the Presidio Bolson area, Texas, interpreted from gravity data

    SciTech Connect

    Mraz, J.R.; Keller, G.R.

    1980-01-01

    To obtain a better understanding of the structure and tectonism of the region, an integrated geophysical-geological study of the Presidio area, Texas, was undertaken using gravity measurements and deep drilling data. New gravity data were combined with existing data to construct simple Bouguer anomaly maps of the Presidio area, and two-dimensional computer modeling of gravity profiles was used to derive earth models. These data outline the major geologic features of the area that are dominated by the effects of Tertiary block faulting and volcanism. The main feature of interest was the Presidio Graben, which is approximately 1.5 km deep near Ruidosa, Texas. One motivation for this study was the collection of a part of the basic scientific data needed to assess the geothermal potential of the area, and the results obtained support the hypothesis that hot springs associated with the Presidio Graben derive their heat from deep circulation along its boundary faults. However, some gravity anomalies observed could be interpreted as indicating the presence of late Tertiary intrusions that could provide heat for the hot springs.

  3. 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.

  4. Gravity anomalies near the east Pacific rise with wavelengths shorter than 3300 km recovered from GEOS-3/ATS-6 satellite-to-satellite Doppler tracking data

    NASA Technical Reports Server (NTRS)

    Marsh, J. G.; Marsh, B. D.; Conrad, T. D.; Wells, W. T.; Williamson, R. G.

    1977-01-01

    The velocity of the GEOS-3 satellite measured by Doppler as a function of time from the ATS-6 satellite was used to recover gravity anomalies in the region of the East Pacific. The orbit GEOS-3 at an altitude of 840 km was perturbed by spatial changes in Earth's gravitational field. These perturbations were measured via ATS-6 which is in a synchronous orbit at an altitude of about 40,000 km. The range-rate data were reduced using a gravitational field model complete to the 12 degree and order. A simulation of the possible effects causing the remaining range-rate residuals relative to the 12, 12 field shows that in general the dominant effect is the neglect of the higher degree and order coefficients of the gravitational field model.

  5. Crustal Structure of the Flood Basalt Province of Ethiopia from Constrained 3-D Gravity Inversion

    NASA Astrophysics Data System (ADS)

    Mammo, Tilahun

    2013-12-01

    The Oligocene Afar mantle plume resulted in the eruption of a large volume of basaltic magma, including major sequences of rhyolitic ignimbrites, in a short span of time across Ethiopia. In order to assess the impact of these magmatic processes on the crust and to investigate the general crustal configuration beneath the Ethiopian plateau, northern part of the Main Ethiopian Rift and the Afar depression, analysis and modeling of the gravity field have been conducted. The Bouguer gravity map is dominated by long-wavelength anomalies that primarily arise from the isostatic compensation of the topography. Consequently, anomalies within the crust/upper mantle are masked and quantitative interpretation becomes difficult. The long-wavelength anomalies are approximated using admittance technique and subsequently removed from the Bouguer anomalies to obtain the residual isostatic anomalies. The residual map contains both short- and intermediate-wavelength anomalies related to geologic and tectonic features. The long-wavelength regional isostatic field is used to map the crust-mantle interface and the results are in good agreement with those determined by other geophysical methods. Seismic constrained gravity inversion was performed on the isostatic residual field and series of three-dimensional models have been constructed for the structures of the crust and upper mantle beneath the uplifted and rifted flood basalt province of northern Ethiopia. The inversion results have shown that the NW plateau has thick crust that rests on normal lithospheric mantle. Afar, On the other hand, is marked by thin stretched crust resting on a low-density upper mantle indicating a hotter thermal regime and partial melt. No lithospheric mantle is observed beneath Afar. The models further indicate the presence of an extensive sub-crustal thick (~12 km on average) and high-density (~3.06 gm/cc) mafic accreted igneous layer of fractionated cumulate (magmatic underplating) beneath the NW plateau

  6. Main crustal discontinuities of Morocco derived from gravity data

    NASA Astrophysics Data System (ADS)

    Khattach, D.; Houari, M. R.; Corchete, V.; Chourak, M.; El Gout, R.; Ghazala, H.

    2013-08-01

    Sharp linear gradients in maps of potential field data are generally assumed to result from sharp discontinuities or boundaries between rocks having different densities or magnetic susceptibilities and are usually associated with faults or other geological contacts. The computation of the horizontal gradients of the gravity field permits us to localize the limits of such blocks and then the fault locations. The horizontal derivative maxima of the Bouguer anomaly and its upward continuation at several heights show lineaments that could reflect the layout of faults and/or contacts and their dip directions. The application of this method to the Bouguer anomaly map of Morocco (with 19,571 points, using an average crustal density ρ = 2.67 g/cm3) allowed us to perform a multiscale analysis of the gravimetric lineaments of the country. The obtained structural map is consistent with several faults already identified in previous studies, and highlights five new major subsurface faults systems with location and dip: the Saghro fault system; Bou-Arfa Midelt fault system; Sidi Slimane Mezquitem fault; Ksar El Kebir-Chefchaouen fault and the Rifan West Mediterranean fault. In addition, this study suggests a new shape and localization for the Agadir-Oujda trans-Moroccan major fault with a NE-SW direction and 900 km length, subdividing Morocco into two main domains. The results of this study contribute to the improvement of the regional structural map of the north western part of Africa, which is situated within the convergence zone between Africa and Eurasia.

  7. Polyhedral shape model for terrain correction of gravity and gravity gradient data based on an adaptive mesh

    NASA Astrophysics Data System (ADS)

    Guo, Zhikui; Chen, Chao; Tao, Chunhui

    2016-04-01

    Since 2007, there are four China Da yang cruises (CDCs), which have been carried out to investigate polymetallic sulfides in the southwest Indian ridge (SWIR) and have acquired both gravity data and bathymetry data on the corresponding survey lines(Tao et al., 2014). Sandwell et al. (2014) published a new global marine gravity model including the free air gravity data and its first order vertical gradient (Vzz). Gravity data and its gradient can be used to extract unknown density structure information(e.g. crust thickness) under surface of the earth, but they contain all the mass effect under the observation point. Therefore, how to get accurate gravity and its gradient effect of the existing density structure (e.g. terrain) has been a key issue. Using the bathymetry data or ETOPO1 (http://www.ngdc.noaa.gov/mgg/global/global.html) model at a full resolution to calculate the terrain effect could spend too much computation time. We expect to develop an effective method that takes less time but can still yield the desired accuracy. In this study, a constant-density polyhedral model is used to calculate the gravity field and its vertical gradient, which is based on the work of Tsoulis (2012). According to gravity field attenuation with distance and variance of bathymetry, we present an adaptive mesh refinement and coarsening strategies to merge both global topography data and multi-beam bathymetry data. The local coarsening or size of mesh depends on user-defined accuracy and terrain variation (Davis et al., 2011). To depict terrain better, triangular surface element and rectangular surface element are used in fine and coarse mesh respectively. This strategy can also be applied to spherical coordinate in large region and global scale. Finally, we applied this method to calculate Bouguer gravity anomaly (BGA), mantle Bouguer anomaly(MBA) and their vertical gradient in SWIR. Further, we compared the result with previous results in the literature. Both synthetic model

  8. The contribution of gravity method in geothermal exploration of southern part of the Gulf of Suez-Sinai region, Egypt

    NASA Astrophysics Data System (ADS)

    Atef, H.; Abd El-Gawad, A. M. S.; Abdel Zaher, M.; Farag, K. S. I.

    2016-06-01

    The Gulf of Suez region represents the most promising area in Egypt for geothermal exploration which is characterized by superficial thermal manifestations represented by a cluster of hot springs with varying temperatures from 35 to 72 °C. The main purpose of the present study was to shed the light on the integration between gravity work and geothermal data in detecting the main subsurface structures in addition to expecting the geothermal sources in the area under consideration. Correction was applied on the bottom hole temperature data to obtain the true formation equilibrium temperatures that can provide useful information about the subsurface thermal regime. Based on these logging data, temperature gradient and heat flow values were computed at each well, and it is found that the mean geothermal gradient of the study area is 32 °C/km; nevertheless, some local geothermal potential fields were located with more than 40 °C/km. Also, heat flow values are ranging from 45 to 115 mW/m2. The Bouguer anomaly map of the study area was used for delineating the subsurface structures and tectonic trends that have resulted in a potential heat source. The gravity inversion revealed a good correlation between areas of high temperature gradients, high heat flow and positive gravity anomalies. The high temperature gradient and heat flow values suggested being associated with a noticeable hydrothermal source of heat anomaly located at relatively shallow depths which is expected to be due to the uplift of the basement in the area.

  9. Preliminary appraisal of gravity and magnetic data at Syncline Ridge, Western Yucca Flat, Nevada Test Site, Nye County, Nevada

    SciTech Connect

    Ponce, D.A.; Hanna, W.F.

    1982-12-31

    A gravity and magnetic study of the Syncline Ridge area was conducted as part of an investigation of argillite rocks of the Eleana Formation under consideration as a medium for the possible storage of high-level radioactive waste. Bouguer gravity anomaly, low-level aeromagnetic anomaly, density, and magnetization data collectively indicate the following, relative to the Eleana Formation, the principal target of the investigation: (1) in an area extending northwestward from Mine Mountain, through Syncline Ridge, to the Eleana Range, the Eleana Formation, where not exposed, occurs at depths of less than {similar_to}200 m, except for a small region of exposed older Paleozoic rocks; (2) in the region of shallowly buried Eleana Formation, occurrences of volcanic rock cover are delineated by low-level aeromagnetic anomaly data, which also discriminate normally polarized from reversely polarized tuff units; and (3) selective detection of high-quartz argillite relative to low-quartz argillite using surface gravity data is not feasible if the high-quartz and low-quartz varieties are intimately interbedded, as observed in boreholes. 4 figures, 2 tables.

  10. Software Analysis of New Space Gravity Data for Geophysics and Climate Research

    NASA Technical Reports Server (NTRS)

    Deese, Rupert; Ivins, Erik R.; Fielding, Eric J.

    2012-01-01

    Both the Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellites are returning rich data for the study of the solid earth, the oceans, and the climate. Current software analysis tools do not provide researchers with the ease and flexibility required to make full use of this data. We evaluate the capabilities and shortcomings of existing software tools including Mathematica, the GOCE User Toolbox, the ICGEM's (International Center for Global Earth Models) web server, and Tesseroids. Using existing tools as necessary, we design and implement software with the capability to produce gridded data and publication quality renderings from raw gravity data. The straight forward software interface marks an improvement over previously existing tools and makes new space gravity data more useful to researchers. Using the software we calculate Bouguer anomalies of the gravity tensor's vertical component in the Gulf of Mexico, Antarctica, and the 2010 Maule earthquake region. These maps identify promising areas of future research.

  11. The Lunar Crustal Thickness from Analysis of the Lunar Prospector Gravity and Clementine Topography Datasets

    NASA Technical Reports Server (NTRS)

    Asmar, S.; Schubert, G.; Konopliv, A.; Moore, W.

    1999-01-01

    The Lunar Prospector spacecraft has mapped the gravity field of the Moon to a level of resolution never achieved before, and a spherical harmonic representation to degree and order 100 is available. When combined with the topography dataset produced by the Clementine mission, the resulting Bouguer anomaly map is interpreted to model the thickness of the lunar crust. Such models are crucial to understanding the lunar thermal history and the formation of geological features such as mascon basins, several more of which have been newly discovered from this dataset. A two-layer planetary model was used to compute the variations of the depth to the lunar Moho. The thickness values ranged from near 0 to 120 km. There is significant agreement with previous work using the Clementine gravitational field data with differences in specific locations such as South Pole-Aitken Basin, for example.

  12. Lithospheric thickness jumps at the S-Atlantic continental margins from satellite gravity data and modelled isostatic anomalies

    NASA Astrophysics Data System (ADS)

    Shahraki, Meysam; Schmeling, Harro; Haas, Peter

    2016-04-01

    Isostatic equilibrium is a good approximation for passive continental margins. In these regions, geoid anomalies are proportional to the local dipole moment of density-depth distributions, which can be used to constrain the thickness of lithospheric jumps and corresponding tectonic stress. We analysed satellite derived geoid data and, after filtering, extracted typical averaged profiles across the Western and Eastern passive margins of the South Atlantic. They show geoid jumps of 8.1 m and 7.0 m for the Argentinian and African sides, respectively. Together with topography data and reasonable assumptions about densities these jumps are interpreted as isostatic geoid anomalies and yield best-fitting crustal and lithospheric thicknesses. They reveal a small asymmetry between the African and S-American crusts and lithospheres by a few kilometers. On both sides, the continental lithosphere is about 15 - 30km thicker than the oceanic lithosphere. To keep such geoid jumps stable over O(100Ma) fully dynamic models show that lithospheric viscosities must be of the order of 1e23 Pa s.

  13. 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.

  14. Wisconsin gravity minimum: Solution of a geologic and geophysical puzzle and implications for cratonic evolution

    SciTech Connect

    Allen, D.J.; Hinze, W.J. )

    1992-06-01

    An intense Bouguer gravity anomaly minimum extending across much of Wisconsin cannot be explained by the surface Phanerozoic sedimentary strata, the basement Precambrian geology, or the topography of the region. The most intense ({minus}100 mgal) part of the minimum coincides with the 1.47 Ga anorogenic granitic Wolf River batholith of northeastern Wisconsin. In southern Wisconsin, however, the densities of the Precambrian basement rocks, which are older than the batholith, provide no clue to the origin of the anomaly. The gradients of the minimum indicate that the source of the anomaly is in the upper crust. Furthermore, nearby deep seismic reflection data indicate that lower crustal structures do not significantly contribute to the gravity minimum. Thus, the minimum is appropriately interpreted as originating from the low-density Wolf River batholith that crops out only in northeastern Wisconsin but is buried beneath a veneer of older rocks in the southern and central parts of the state. Gravity modeling suggests that the batholith is at least 10 km thick and encompasses an area of {approximately}50,000 km{sup 2}. This interpretation provides an important clue to the origin of similar negative gravity anomalies of the Phanerozoic strata-covered craton. Also, the presence of this massive granitic body appears to have influenced the evolution of the craton - e.g., by controlling the location of the 1.1 Ga Midcontinent rift system and the Paleozoic Wisconsin arch. The fact that the Wolf River batholith is mostly buried suggests that central Wisconsin has been tectonically stable for the past 1.47 b.y. and that the Precambrian basement has been minimally eroded.

  15. Internal architecture of the Tuxtla volcanic field, Veracruz, Mexico, inferred from gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    Espindola, Juan Manuel; Lopez-Loera, Hector; Mena, Manuel; Zamora-Camacho, Araceli

    2016-09-01

    The Tuxtla Volcanic Field (TVF) is a basaltic volcanic field emerging from the plains of the western margin of the Gulf of Mexico in the Mexican State of Veracruz. Separated by hundreds of kilometers from the Trans-Mexican Volcanic Belt to the NW and the Chiapanecan Volcanic Arc to the SE, it stands detached not only in location but also in the composition of its rocks, which are predominantly alkaline. These characteristics make its origin somewhat puzzling. Furthermore, one of the large volcanoes of the field, San Martin Tuxtla, underwent an eruptive period in historical times (CE 1793). Such volcanic activity conveys particular importance to the study of the TVF from the perspective of volcanology and hazard assessment. Despite the above circumstances, few investigations about its internal structure have been reported. In this work, we present analyses of gravity and aeromagnetic data obtained from different sources. We present the complete Bouguer anomaly of the area and its separation into regional and residual components. The aeromagnetic data were processed to yield the reduction to the pole, the analytic signal, and the upward continuation to complete the interpretation of the gravity analyses. Three-dimensional density models of the regional and residual anomalies were obtained by inversion of the gravity signal adding the response of rectangular prisms at the nodes of a regular grid. We obtained a body with a somewhat flattened top at 16 km below sea level from the inversion of the regional. Three separate slender bodies with tops 6 km deep were obtained from the inversion of the residual. The gravity and magnetic anomalies, as well as the inferred source bodies that produce those geophysical anomalies, lie between the Sontecomapan and Catemaco faults, which are proposed as flower structures associated with an inferred deep-seated fault termed the Veracruz Fault. These fault systems along with magma intrusion at the lower crust are necessary features to

  16. Detailed gravity and aeromagnetic surveys of the Cove Fort-Sulphurdale KGRA and vicinity, Millard and Beaver Counties, Utah. Topical report

    SciTech Connect

    Cook, K.L.; Serpa, L.F.; Pe, W.

    1980-01-01

    A detailed gravity survey (comprising 231 stations over about 900 km/sup 2/) was made in the Cove Fort-Sulphurdale Known Geothermal Resource area (KGRA) and vicinity, Millard and Beaver counties, Utah to assist in the appraisal of the potential of this area as a geothermal resource. The survey reinforced the results and information obtained in the previous regional gravity surveys comprising 522 stations. The gravity data from about 700 stations were reduced and compiled as a terrain-corrected (out to 20 km) Bouguer gravity anomaly map with 1-mgal contour interval. In August 1975, an aeromagnetic survey was flown over part of the survey area at a constant barometric elevation of 12,000 ft (3660 m). These aeromagnetic data are used to supplement the interpretation of the gravity data. The aeromagnetic field intensity residual anomaly map and the second-order polynomial residual aeromagnetic map (obtained by removing a second-order polynomial surface) are presented with a 20-gamma contour interval. Two north-south profiles and one east-west profile were selected for magnetic interpretative modeling. The two north-south profiles were also stacked and averaged over 6-km-wide strips and modeled. The occurrences of hydrothermal alteration, hot spring deposits, and flowing hot springs coincide with inferred fault zones. No evidence of extensive alteration can be interpreted from the magnetic data.

  17. Structure and Evolution of the Lunar Procellarum Region as Revealed by GRAIL Gravity Data

    NASA Technical Reports Server (NTRS)

    Andrews-Hanna, Jeffrey C.; Besserer, Jonathan; Head, James W., III; Howett, Carly J. A.; Kiefer, Walter S.; Lucey, Paul J.; McGovern, Patrick J.; Melosh, H. Jay; Neumann, Gregory A.; Phillips, Roger J.; Schenk, Paul M.; Smith, David E.; Solomon, Sean C.; Zuber, Maria T.

    2014-01-01

    The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The Procellarum region has been interpreted as an ancient impact basin approximately 3200 km in diameter, though supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border the Procellarum region and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dikes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of quasi-rectangular border structures with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the elevated heat flux in the region.

  18. Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data

    NASA Astrophysics Data System (ADS)

    Andrews-Hanna, Jeffrey C.; Besserer, Jonathan; Head, James W., III; Howett, Carly J. A.; Kiefer, Walter S.; Lucey, Paul J.; McGovern, Patrick J.; Melosh, H. Jay; Neumann, Gregory A.; Phillips, Roger J.; Schenk, Paul M.; Smith, David E.; Solomon, Sean C.; Zuber, Maria T.

    2014-10-01

    The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The region has been interpreted as an ancient impact basin approximately 3,200 kilometres in diameter, although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border Procellarum and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the greater-than-average heat flux in the region.

  19. Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data.

    PubMed

    Andrews-Hanna, Jeffrey C; Besserer, Jonathan; Head, James W; Howett, Carly J A; Kiefer, Walter S; Lucey, Paul J; McGovern, Patrick J; Melosh, H Jay; Neumann, Gregory A; Phillips, Roger J; Schenk, Paul M; Smith, David E; Solomon, Sean C; Zuber, Maria T

    2014-10-01

    The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The region has been interpreted as an ancient impact basin approximately 3,200 kilometres in diameter, although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border Procellarum and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the greater-than-average heat flux in the region.

  20. Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data.

    PubMed

    Andrews-Hanna, Jeffrey C; Besserer, Jonathan; Head, James W; Howett, Carly J A; Kiefer, Walter S; Lucey, Paul J; McGovern, Patrick J; Melosh, H Jay; Neumann, Gregory A; Phillips, Roger J; Schenk, Paul M; Smith, David E; Solomon, Sean C; Zuber, Maria T

    2014-10-01

    The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The region has been interpreted as an ancient impact basin approximately 3,200 kilometres in diameter, although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border Procellarum and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the greater-than-average heat flux in the region. PMID:25279919

  1. Gravity and thermal models for the twin peaks silicic volcanic center, Southwestern Utah

    SciTech Connect

    Carrier, D.L.; Chapman, D.S.

    1981-11-10

    Gravity, heat flow, and surface geology observations have been used as constraints for a thermal model of a late Tertiary silicic volcanic center at Twin Peaks, Utah. Silicic Volcanism began in the area with the extrusion of the Coyote Hills rhyolite 2.74 +- 0.1 m.y. ago, followed by the Cudahy Mine obsidian, felsite, and volcanoclastics, and finally by a complex sequence of domes and flows that lasted until 2.3 +- 0.1 m.y. ago. Basalt sequence span the time 2.5 to 0.9 m.y. Terrain-corrected Bouguer gravity anomalies at Twin Peaks are shaped by three features of varying characteristic dimensions: (1) a major north-northeast trending --30 mGal gravity trough roughly 40 km wide caused by a thick sequence of Cenozoic sediments in the Black Rock Desert Valley, (2) a local roughly circular -7 mGal gravity low, 26 km across, probably related to an intrusive body in the basement, and (3) a series of narrow positive anomalies up to + 10 mGal produced by the major Twin Peaks volcanic domes. The intrusive bodies have been modeled as three-dimensional vertical cylinders; the total volume of intrusive material is estimated to be about 500 km/sup 3/. Simple models, assuming conductive heat transfer and using geometrical constraints from the gravity results, predict that a negligible thermal anomaly should exist 1 m.y. after emplacement of the intrusion. This prediction is consistent with an average heat flow of 96 mW m/sup -2/ for the area, not significantly different from eastern Basin and Range values elsewhere. Magmatic longevity of this system 2.7 to 2.3 m.y. for silicic volcanism of 2.5 to 0.9 m.y. for basaltic volcanism, does not seem to prolong the cooling of the system substantially beyond that predicted by conductive cooling.

  2. Local Gravity Field Determination On The Moon Using GRAIL Extended Mission Data

    NASA Astrophysics Data System (ADS)

    Goossens, S. J.; Lemoine, F. G.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2013-12-01

    The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft were launched on September 10, 2011, and conducted their primary mapping mission from March 1 until May 29, 2012 at an average altitude of 50 km. GRAIL's extended mission commenced on August 30 and was completed on December 14, 2012. The average altitude during the extended mission was 23 km above lunar surface. Both primary and extended mission data have been processed at NASA/GSFC using the GEODYN software, resulting in high-resolution (degree and order 900 in spherical harmonics) gravity field models of high accuracy. However, especially during low-altitude passes, Ka-band range-rate (KBRR) data residuals are still well above noise level. Here, we focus on methods to determine local gravity adjustments from KBRR data. We represent gravity in the area of interest as gravity anomaly adjustments with respect to the background spherical harmonics model. We use KBRR data only over the area of interest, and we then perform short-arc orbit determination. Our areas of focus are mainly the Mare Orientale area, where GRAIL achieved its lowest altitude above the lunar surface towards the end of the mission, and the south pole area, where naturally there is a confluence of orbit tracks. We investigate different grids and different smoothing constraints used in the estimation of the anomalies, numerical differentiation with respect to time of the KBRR data to localize its sensitivity further, and we evaluate the solutions in terms of Bouguer anomaly signatures, KBRR data fit, and correlations with local topography.

  3. A crustal model based mainly on gravity data in the area between the Bermejo Basin and the Sierras de Valle Fértil, Argentina

    NASA Astrophysics Data System (ADS)

    Gimenez, Mario E.; Martínez, M. Patricia; Introcaso, Antonio

    2000-07-01

    The Sierras Pampeanas ranges of central-western Argentina (26°00'S to 33°15'S, 63°30'W to 68°30'W; an area about 450 km wide and 800 km long) consists of a series of uplifted basement blocks bounded by deep sedimentary basins of relatively low relief and covered by modern sediments. The basement blocks of the Sierras Pampeanas are bounded by longitudinal faults that originated during or were reactivated by the Andean Orogeny, then uplifted by reverse faults during the late Tertiary and the Quaternary. Utilizing primarily gravity data, interpreted with the aid of geological information and seismological and seismic data, we developed models consistent with: (1) seismic data on the Moho, and (2) a significant regional gradient of "g" from west to east. In order to be consistent with (1), we took into account the gravimetric effects of the subhorizontal Nazca plate, whereas to be consistent with (2), it was necessary to wedge the Bermejo Basin sediments under very dense positive masses within the upper crust underlying the Sierra de Valle Fértil. Two crustal models were developed by inversion of the Bouguer anomaly. These fully fit the Bouguer anomaly and the geological data and reveal two zones of high density that are interpreted as paleosutures.

  4. Gravity anomalies, flexure, and deformation of the converging Indian lithosphere in Nepal and Sikkim-Darjeeling Himalayas

    NASA Astrophysics Data System (ADS)

    Ansari, Md. Afroz; Khan, Prosanta K.; Tiwari, Virendra M.; Banerjee, Jayashree

    2014-09-01

    Researchers ubiquitously noted that the common processes of partitioning oblique convergence in response to drag from the trench-hanging plate simultaneously produce radial slips, along-strike translation, and extension parallel to the deformation front. Here, we focus on the area between Nepal and Sikkim-Darjeeling Himalayas, and carry out gravity and finite-element stress modeling of the strike-orthogonal converging Indian lithosphere. We delineate the geometries of different layers and their interfaces through gravity modeling. The optimum model parameters along with rheological parameters of different layers are used for finite-element modeling. Finite-element modeling is done with boundary conditions of keeping the upper surface free and rigidly fixing the section of the northern boundary below the Main Himalayan Thrust. We impart on its frontal section an amount of 6 × 1012 N/m force, equivalent to resistive force of the Himalayan-Tibet system, and analyze the maximum and minimum compressive stress fields evolved in the lithosphere. We testify our observations with earthquake database and other geophysical and geological studies. We note that an increasing flexing of the Indian lithosphere beyond the Main Boundary Thrust becomes maxima between the Main Central Thrust and South Tibetan Detachment in both the areas; however, more steepening of the Moho boundary is identified in the Sikkim-Darjeeling Himalaya. This abrupt change in lithospheric geometry beneath the Greater Himalaya is likely correlated with the sharp elevation changes in the topography. Although the highest seismicity concentration is dominant in this zone, the Lesser and the Tethys Himalayas in Sikkim-Darjeeling area also record relatively fair seismic activity. More compressive stress field in different layers right within the sharp bending zone supports this observation. We thus propose that the sharp bending zone beneath the Greater Himalaya is suffering maximum deformation, and the

  5. High-resolution global and local lunar gravity field models using GRAIL mission data

    NASA Astrophysics Data System (ADS)

    Goossens, S. J.; Lemoine, F. G.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Neumann, G. A.; Loomis, B.; Chinn, D. S.; Smith, D. E.; Zuber, M. T.

    2014-12-01

    The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft were designed to map the structure of the Moon through high-precision global gravity mapping. The mission consisted of two spacecraft with Ka-band inter-satellite tracking complemented by tracking from Earth. The mission had two phases: (1) a primary mapping mission from March 1 until May 29, 2012 at an average altitude of 50 km; (2) an extended mission from August 30 until December 14, 2012, with an average altitude of 23 km before November 18, and between 11-20 km through December 14. Both the primary and the extended mission data have been processed into global models of the lunar gravity field at NASA/GSFC using the GEODYN software. Here we present our latest global model, an expansion in spherical harmonics of degree and order 1080. We discuss this new solution in terms of its power spectrum, its free-air and Bouguer anomalies, its associated error spectrum, and its correlations with topography-induced gravity. In addition to global models we also estimated local gravity adjustments in areas of particular interest such as Mare Orientale and the south pole area. We express gravity in terms of anomalies, and estimate them with respect to a global background model. We apply neighbor-smoothing in our estimation procedure. We present a local solution over the south pole area in a resolution of 1/6 by 1/6 of a degree, equivalent to degree and order 1080, and we compare this local solution to our global model.

  6. Analysis of Marine Gravity Anomalies in the Ulleung Basin (East Sea/Sea of Japan) and Its Implications for the Architecture of Rift-Dominated Backarc Basin

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Mook; Kim, Yoon-Mi

    2016-04-01

    Marginal basins locate between the continent and arc islands often exhibit diverse style of opening, from regions that appear to have formed by well-defined and localized spreading center (manifested by the presence of distinct seafloor magnetic anomaly patterns) to those with less obvious zones of extension and a broad magmatic emplacement most likely in the lower crust. Such difference in the style of back-arc basin formation may lead to marked difference in crustal structure in terms of its overall thickness and spatial variations. The Ulleung Basin, one of three major basins in the East Sea/Sea of Japan, is considered to represent a continental rifting end-member of back-arc opening. Although a great deal of work has been conducted on the sedimentary sections in the last several decades, the deep crustal sections have not been systematically investigated for long time, and thus the structure and characteristics of the crust remain poorly understood. This study examines the marine gravity anomalies of the Ulleung Basin in order to understand the crustal structure using crucial sediment-thickness information. Our analysis shows that the Moho depth in general varies from 16 km at the basin center to 22 km at the margins. However, within the basin center, the inferred thickness of the crust is more or less the same (10-12 km), thus by varying only about 10-20% of the total thickness, contrary to the previous impression. The almost-uniformly-thick crust that is thicker than a normal oceanic crust (~ 7 km) is consistent with previous observations using ocean bottom seismometers and recent deep seismic results from the nearby Yamato Basin. Another important finding is that small residual mantle gravity anomaly highs exist in the northern part of the basin. These highs are aligned in the NNE-SSW direction which correspond to the orientation of the major tectonic structures on the Korean Peninsula, raising the possibility that, though by a small degree, they are a

  7. Three-dimensional density structures of Taiwan and tectonic implications based on the analysis of gravity data

    NASA Astrophysics Data System (ADS)

    Hsieh, Hsien-Hsiang; Yen, Horng-Yuan

    2016-07-01

    Taiwan is located in a collision and subduction area and has a complex tectonic history. To better understand the complicated structure beneath Taiwan, gravity studies, in addition to seismic and geological studies, provide useful geophysical information for studying shallow depths. Previous gravity studies of Taiwan in the last 30 years focused on local regionalized explanations and 2-D profile modeling. This study is the first to complete a 3-D gravity inversion of Taiwan, and it provides a more comprehensive and large-scale tectonic analysis. Following 3-D gravity inversion using the least squares method, we sliced horizontal and vertical profiles from the 3-D density model to visualize tectonic changes. The low Bouguer anomaly was caused by thick sediment and crust layers. The high-density layers are located in special tectonic areas such as the Peikang and Kuanying basement highs. The deepest Moho depth beneath the middle of the Central Range is 45-50 km. The high gradient changes of the eastern section of the Moho relief are shown by the complex mechanism of plate collision. The geometry of plate subduction is apparent in northeastern Taiwan, and the oceanic crust is observable under eastern Taiwan, showing arc-collision boundaries. Our 3-D density model, when combined with updated gravity data and seismic tomography, offers better resolution for deep structures than the previous 2-D forward results and serves as a physical property reference to better understand the tectonic structure beneath Taiwan.

  8. Detailed gravity mapping of the Panther Mountain circular structure, Catskill Mountains, New York

    SciTech Connect

    Isachsen, Y.W. ); Revetta, F.A. )

    1993-03-01

    The Panther Mountain circular structure is located in the Catskill Mountains near the eastern edge of the Allegheny Plateau where depth through the sedimentary section to basement is about 3200 m. The structure is distinguished from the rest of the Plateau only by its physiography. It is a circular mountain mass, 10 km in diameter, defined by an anomalous annular drainage pattern formed by Esopus Creek and its tributary Woodland Creek. Because of pervasive fluvial cross bedding in the sedimentary pile, the authors were unable to determine whether the structure is slightly domical, sightly basinal, or unwarped. North-south and east-west gravity profiles were next made and modeled to look for a subsurface explanation for the structure. The only computed profiles that matched the measured values were those for a shallowly-buried meteorite crater with its underlying breccia lens, lying beneath the Panther Mountain. Renewed interest in the structure led them to make 125 new gravity measurements, in a study that is continuing. Gravity values are corrected using the International Gravity Formula of 1967 and densities of 2.67 and 2.50 gms/cm[sup 3]. Terrain corrections were computed using an inner radius of .895 km and an outer radius of 166.70 km. The complete Bouguer gravity anomaly was separated into its regional and residual components to obtain a third order residual gravity map for computer modeling. The residual gravity map confirms the earlier detected gravity low and leaves the buried meteorite crater model as a viable model.

  9. Gravity Data from the Teboursouk Area ("Diapirs Zone", Northern Tunisia): Characterization of Deep Structures and Updated Tectonic Pattern

    NASA Astrophysics Data System (ADS)

    Hachani, Fatma; Balti, Hadhemi; Kadri, Ali; Gasmi, Mohamed

    2016-04-01

    Located between eastern segments of the Atlas and Tell-Rif orogenic belts, the "Dome zone" of northern Tunisia is characterized by the juxtaposition of various structures that mainly controlled the long geodynamic history of this part of the south-Tethyan Margin. To better understand the organization and deep extension of these structures, gravity data from the Teboursouk key area are proposed. These data include the plotting of Bouguer anomaly map and related parameters such as vertical and horizontal gradients, upward continuation and Euler solution. Compared to geological and structural maps available, they allow the identification of new deep structures and greater precision regarding the characteristics and organization of known ones; consequently, an updated structural pattern is proposed.

  10. Complete Bouguer gravity and aeromagnetic maps of the Rattlesnake Roadless Area, Missoula County, Montana

    USGS Publications Warehouse

    Kulik, Dolores M.

    1986-01-01

    The rocks in the study area consist mainly of the Helena Formation and the Missoula Group of the Belt Supergroup (Proterozoic Y).  Rock units of less importance are diabase sills and dikes of probable Proterozoic Z age, Middle Cambrian rocks, and glacial deposits.  Structurally, the study area consists of the Rattlesnake thrust system in the south part and a parautochthonous area broken by vertical faults in the north part.

  11. Gravity and seismic study of crustal structure along the Juan de Fuca Ridge axis and across pseudofaults on the ridge flanks

    NASA Astrophysics Data System (ADS)

    Marjanović, Milena; Carbotte, Suzanne M.; Nedimović, Mladen R.; Canales, Juan Pablo

    2011-05-01

    Variations in topography and seismic structure are observed along the Juan de Fuca (JdF) Ridge axis and in the vicinity of pseudofaults on the ridge flanks left by former episodes of ridge propagation. Here we analyze gravity data coregistered with multichannel seismic data from the JdF Ridge and flanks in order to better understand the origin of crustal structure variations in this area. The data were collected along the ridge axis and along three ridge-perpendicular transects at the Endeavor, Northern Symmetric, and Cleft segments. Negative Mantle Bouguer anomalies of -21 to -28 mGal are observed at the axis of the three segments. Thicker crust at the Endeavor and Cleft segments is inferred from seismic data and can account for the small differences in axial gravity anomalies (3-7 mGal). Additional low densities/elevated temperatures within and/or below the axial crust are required to explain the remaining axial MBA low at all segments. Gravity models indicate that the region of low densities is wider beneath the Cleft segment. Gravity models for pseudofaults crossed along the three transects support the presence of thinner and denser crust within the pseudofault zones that we attribute to iron-enriched crust. On the young crust side of the pseudofaults, a 10-20 km wide zone of thicker crust is found. Reflection events interpreted as subcrustal sills underlie the zones of thicker crust and are the presumed source for the iron enrichment.

  12. Geologic implications of topographic, gravity, and aeromagnetic data in the northern Yukon-Koyukuk province and its borderlands, Alaska

    USGS Publications Warehouse

    Cady, J.W.

    1989-01-01

    The northern Yukon-Koyukuk province is characterized by low elevation and high Bouguer gravity and aeromagnetic anomalies in contrast to the adjacent Brooks Range and Ruby geanticline. Using newly compiled digital topographic, gravity, and aeromagnetic maps, the province is divided into three geophysical domains. The Koyukuk domain, which is nearly equivalent to the Koyukuk lithotectonic terrane, is a horseshoe-shaped area, open to the south, of low topography, high gravity, and high-amplitude magnetic anomalies caused by an intraoceanic magmatic arc. The Angayucham and Kanuti domains are geophysical subdivisions of the Angayucham lithotectonic terrane that occur along the northern and southeastern margins of the Yukon-Koyukuk province, where oceanic rocks have been thrust over continental rocks of the Brooks Range and Ruby geanticline. The modeling supports, but does not prove, the hypothesis that the crust of the Kobuk-Koyukuk basin is 32-35 km thick, consisting of a tectonically thickened section of Cretaceous volcanic and sedimentary rocks and older oceanic crust. -from Author

  13. Local Lunar Gravity Field Analysis over the South Pole-aitken Basin from SELENE Farside Tracking Data

    NASA Technical Reports Server (NTRS)

    Goossens, Sander Johannes; Ishihara, Yoshiaki; Matsumoto, Koji; Sasaki, Sho

    2012-01-01

    We present a method with which we determined the local lunar gravity field model over the South Pole-Aitken (SPA) basin on the farside of the Moon by estimating adjustments to a global lunar gravity field model using SELENE tracking data. Our adjustments are expressed in localized functions concentrated over the SPA region in a spherical cap with a radius of 45deg centered at (191.1 deg E, 53.2 deg S), and the resolution is equivalent to a 150th degree and order spherical harmonics expansion. The new solution over SPA was used in several applications of geophysical analysis. It shows an increased correlation with high-resolution lunar topography in the frequency band l = 40-70, and admittance values are slightly different and more leveled when compared to other, global gravity field models using the same data. The adjustments expressed in free-air anomalies and differences in Bouguer anomalies between the local solution and the a priori global solution correlate with topographic surface features. The Moho structure beneath the SPA basin is slightly modified in our solution, most notably at the southern rim of the Apollo basin and around the Zeeman crater

  14. Heat flow in the Oregon Cascade Range and its correlation with regional gravity, Curie point depths, and geology

    SciTech Connect

    Blackwell, D.D.; Steele, J.L. ); Frohme, M.K. ); Murphey, C.F. ); Priest, G.R.; Black, G.L. )

    1990-11-10

    Heat flow measurements from several deep wells (up to 2,500 m deep), as well as extensive new data from industry exploration efforts in the Breitenbush and the Santiam Pass-Belknap/Foley areas are described. The heat flow is about 100 mW m{sup {minus}2} in the High Cascade Range and at the eastern edge of the Western Cascade Range, and about 40-50 mW m{sup {minus}2} to the west in the outer arc block of the subduction zone. The gravity field in the Cascade Range has characteristics that can be closely related to the heat flow pattern. The relationship may be causal, and to examine the relationship in more detail, earlier two-dimensional modeling is extended to three dimensions. Consideration of the effects of a midcrustal density anomaly, such as might be associated with a region with at least areas of partial melt, as two major consequences. The first of these is that a high-frequency gravity gradient near the Western Cascade Range/High Cascade Range boundary is explained. Second, the negative gravity anomaly associated with the northeast/southwest striking regional Bouguer gravity anomaly associated with the north edge of the Blue Mountains becomes continuous across the Cascade Range with a similar feature along the north side of the Klamath Mountains. The correlation, or lack thereof, of the heat flow, depth to Curie point, gravity field, crustal electrical resistivity, crustal seismic velocity, and geology in the High/Western Cascade Ranges is summarized.

  15. Improving the terrestial gravity dataset in South-Estonia

    NASA Astrophysics Data System (ADS)

    Oja, T.; Gruno, A.; Bloom, A.; Mäekivi, E.; Ellmann, A.; All, T.; Jürgenson, H.; Michelson, M.

    2009-04-01

    The only available gravity dataset covering the whole of Estonia has been observed from 1949 to 1958. This historic dataset has been used as a main input source for many applications including the geoid determination, the realization of the height system, the geological mapping. However, some recent studies have been indicated remarkable systematic biases in the dataset. For instance, a comparison of modern gravity control points with the historic data revealed unreasonable discrepancies in a large region in South-Estonia. However, the distribution of the gravity control was scarce, which did not allow to fully assess the quality of the historic data in the study area. In 2008 a pilot project was called out as a cooperation between Estonian Land Board, Geological Survey of Estonia, Tallinn University of Technology and Estonian University of Life Sciences to densify the detected problematic area (about 2000 km2) with new and reliable gravity data. Field work was carried out in October and November 2008, whereas GPS RTK and relative Scintrex gravimeter CG5 were used for precise positioning and gravity determinations, respectively. Altogether more than 140 new points were determined along the roads. Despite bad weather conditions and unstable observation base of the gravimeter (mostly on the bank of the road), uncertainty better than ±0.1 mGal (1 mGal = 10-5 m/s2) was estimated from the adjustment of gravimeter's readings. The separate gravity dataset of the Estonian Geological Survey were also incorporated into the gravity database of the project for further analysis. Those data were collected within several geological mapping projects in 1981-2007 and contain the data with uncertainty better than ±0.25 mGal. After the collection of new gravity data, a Kriging with proper variogram modeling was applied to form the Bouguer anomaly grids of the historic and the new datasets. The comparison of the resulting grids revealed biases up to -4 mGal at certain regions

  16. 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.

  17. Melt anomalies of the northern Atlantic Ocean basin

    NASA Astrophysics Data System (ADS)

    Wang, T.; Lin, J.; Tucholke, B. E.

    2009-12-01

    We investigated the melt anomalies and lithosphere dynamics of the northern Atlantic Ocean between 76°N and 8°S through combined analysis of seafloor bathymetry, shipboard and satellite-derived gravity, and sediment thickness. Residual mantle Bouguer anomaly (RMBA) was calculated by removing from free-air gravity anomaly the predicted attractions of water-sediment, sediment-crust, and crust-mantle interfaces as well as the effect of lithospheric plate cooling. Residual bathymetry anomaly (RBA) was obtained by subtracting from observed seafloor topography the predicted effects of plate cooling and the observed sediment load. Our analysis indicates that more than 50% of the seafloor has been affected by melt anomalies. The most prominent features that we observe include: (1) A pronounced negative RMBA associated with the Iceland hotspot, the Reykjanes Ridge, and the Mid-Atlantic Ridge (MAR) north of Iceland. The region of enhanced magma supply extends southward to the Charlie Gibbs F.Z., northward to the Jan Mayen F.Z., and to both the eastern and western basin margins. The strong negative RMBA associated with the submarine part of the Iceland hotspot reaches -450 mGal, corresponding to modeled crustal thickness of more than 22 km. (2) A widespread effect of the Azores hotspot on crustal accretion at the MAR since 40-50 Ma, as reflected in negative RMBA and positive RBA that extend southward to at least 26.5°N and northward to 44°N. The strongest RMBA anomaly associated with the Azores melt anomaly reaches about -230 mGal, corresponding to crustal thickening about half of that in Iceland. (3) A ~ 500 km wide corridor of negative RMBA is found along the west African margin between 40°N and 6°S, indicating that this region was influenced extensively by melt anomalies associated with the Horseshoe Seamounts, Madeira Islands, Canary Islands, and Cape Verde Islands. Negative RMBA of -100 to -180 mGal is also associated with the Bermuda Rise in the western Atlantic

  18. Geophysical Studies of Irish Granites Using Magnetotelluric and Gravity Data

    NASA Astrophysics Data System (ADS)

    Farrell, T. F.; Muller, M. R.; Rath, V.; Feely, M.; Hogg, C.

    2014-12-01

    We present results of on-going geophysical studies of Caledonian radiothermal granite bodies in Ireland, which are being undertaken to investigate the volumetric depth extent and structural features of these granites. During three field seasons, magnetotelluric (MT) and audio-magnetotelluric (AMT) data were acquired at 156 sites targeting three separate granite bodies. These studies will contribute to a crustal-scale investigation of the geothermal energy potential of the granites and their contribution to the thermal field of the Irish crust. Across the calc-alkaline Galway granite, located on the Irish west coast, MT and AMT data were acquired at 75 sites distributed in a grid. Preliminary 3D inversion reveals the presence of a resistor, thickest beneath the central block of the granite where it extends to depths of 11 - 12 km. The greater depth of the resistor beneath the central block is in contrast to previous thinking that proposed the central block granites to have shallower depth extent than those of the western block, based on Bouguer anomaly maps of the area in which the western block exhibited a more pronounced negative Bouguer anomaly than the central block. At the S-type Leinster granite, in eastern Ireland and to the south of Dublin, MT and AMT data were acquired along two profiles (LGN - 27 sites and LGS - 32 sites). Preliminary 1D inversions of AMT data along profile LGN show the Northern Units of the Leinster granite to extend to a depth of 4.5 km and the Lugnaquilla pluton extending to 2.5 km depth. MT and AMT data were acquired at 22 sites along a profile across the buried Kentstown granite, 35 km to the NW of Dublin. The Kentstown granite was intersected by two mineral exploration boreholes at depths of 492 m and 663 m. Preliminary 2D inversions do not yet satisfactorily resolve the top of the buried granite. Inversion of MT and AMT data is continuing, with the electrical conductivity structures revealed by these inversions being used to

  19. Gravity And Seismic Data Set Constraint On The Crust Structure Of Liyue Block, Northeast Of Nansha Area

    NASA Astrophysics Data System (ADS)

    Sun, Z.

    2011-12-01

    The Liyue Block is composed of two parts: Reed Bank and Liyue Basin. It is separated by Zhongnan Fault in west, Palawan Trough in southeast and fault scarp in the north of Nansha area. We make a systematic investigation on major tectonic and crust structure units in the Liyue Block basing on gravity and seismic data set. Multichannel seismic data can help to know the stratum and fault structure that locating upon the sediment basement. In the Reed Bank composed of reefs, the faults are undeveloped and the stratum is flat. In basin area, the early faults are developed and there two kinds of structures: tilted fault block and low relief anticline. The thickness of the Mesozoic strata in basin area decreases from SW to NE. But the rifting strata increases from SW to NE, which indicates the fault activity strength in the rift period increased from southwest to northeast. We have performed gravity inversion to understand the geometry of the MOHO surface and the crustal thicknesses beneath this area. The region is characterized by large positive Bouguer gravity anomaly (60 to 140 mgal), and the MOHO depth generally varies from 16-27km.We calculate the stretching factor of the research area, which ranging from 1.3 to 2.0, that indicates the local region is lowly stretched. In general, we can distinguish the crustal structures of the study area into the thinned continental crust. Key words: Liyue Block; Mesozoic stratum; Gravity inversion; Seismic profile; Crust structure

  20. Relation of Topography to Airborne Gravity in Afghanistan and the Tectonic Implications

    NASA Astrophysics Data System (ADS)

    Jung, W.; Brozena, J. M.; Peters, M. F.

    2012-12-01

    As part of a multi-sensor, multi-disciplinary aerogeophysical survey, the US Naval Research Laboratory collected airborne gravity over most of Afghanistan in 2006 (http://pubs.usgs.gov/of/2008/1089/Afghan_grv.html). The data were measured using a pair of ZLS Corporation air-sea gravimeters 7 km altitude above mean sea level aboard an NP-3D Orion aircraft operated by the US Navy's Scientific Development Squadron One (VXS-1). Aircraft positions were determined from kinematic GPS measurements in the aircraft relative to five base stations using differential interferometric techniques. Track spacing was set to 4 km over much of Afghanistan, but was increased to 8 km in the northern block of the survey area. Aircraft ground speed averaged between 300 and 380 knots, faster than ideal for high resolution gravity, but enabled approximately 113,000-km of data tracks to be flown in 220 flight hours, covering more than 330000 km2. In this presentation, we investigate the implications of the airborne gravity data for the tectonic development history of Afghanistan. Afghanistan is described as comprising three different platforms (Wheeler et al., 2005): 1) the north Afghanistan platform north of the Hari-Rud fault (HRF), a part of the Eurasian plate for 250-350 my; 2) the accreted terranes south of the HRF including low flats, formed as island arcs and fragments of continental and oceanic crust collided with the Eurasian plate during the closure of the Tethys Ocean in the past 250 my; and 3) the transpressional plate in the east, formed as the Indian plate moves northward since Cretaceous. The Bouguer anomaly map reveals elongated negative values along the east-west striking HRF, which seems to manifest different tectonic developmental histories across the boundary. Over the southern flats in the accreted terranes platform, the Bouguer anomaly map appears to show a continuation of alternating southwest-northeast trending highs and lows like those over the northern high

  1. Long Period Co-Seismic Gravity Modeling of Silent Slip Earthquakes Along the Cascadia Subduction Zone

    NASA Astrophysics Data System (ADS)

    Hayes, T. J.

    2004-05-01

    The Cascadia Subduction Zone (CSZ) is an area of large and potentially catastrophic seismic events which occur as large magnitude (Mm>8) events. The mitigation of such hazards within highly populated areas presents a difficult problem which is dependent upon such observations as plate motion and strain accumulation. Long period Bouguer anomalies may act as a proxy for permanent strain deformation at depth. To date there are no large scale models that successfully model the temporal gravity signal over extended spatial regions encompassing more than one fault. These deep slip events typically last for days to weeks which would generate a long period signal. The highly periodic (13--16 months) silent slip events along the Cascadia Subduction Zone (CSZ) present a ideal location for the observation of such long period signals. Models of co-seismic gravity changes based on the analytical solutions of Okada (1985) and Okubo (1992), which act as an upper limit, are in the range of 30 μ gals--800 μ gals. These amplitudes are well within the range of land based observations and potentially within the observable limits of several remote sensing satellites designed specifically for gravity data (e.g. GRACE, CHAMP, GEOS). This same technique should be applicable to any mechanism in which deformation occurs such as volcanic activity or glacial rebound.

  2. Investigation of the geologic and tectonic structures of Bafa Lake and Akbuk Gulf (terrestrial and marine areas) by means of gravity and magnetic methods

    NASA Astrophysics Data System (ADS)

    Edremit, Şüheda; Özel, Erdeniz

    2016-04-01

    Geologic units of Bafa Lake and Akbuk Gulf, which have very importance in point of geologic and tectonic structure, are generally are classified by high-grade metamorphic units of the Menderes Core Complex, Cycladic Complex (schist, marble, eclogite), Afyon zone meta sedimentary and Pan-African basement rocks, Neogene volcanic-sedimentary rocks and alluvium. As for tectonic structures of study areas are; Izmir-Balikesir Transfer Zone also affected the Buyuk Menderes Graben, Bornova Flysch Zone, Menderes Massif and Lycian Nappes. Regional researches were studied to reveal using Turkey Bouguer Anomaly and Turkey Aeromagnetic regional map with gravity method used for geologic structures analysis and magnetic method used to explain main structure, tectonic conditions of underground. General geologic structure and tectonic lineaments of region were examined and interpretated compatibility with gravity and magnetic values. When the geologic and tectonic structures on the terrestrial areas are generally investigated, graben systems and linearities are clearly seen on the Bouguer Anomaly map. Positive values are seen in the Bornova Flysch Zone and Menderes Massif areas at the north of study areas arising from high-density ophiolitic and metamorphic units. Graben areas in the Menderes Massif are observed negative gravity values on the low-density young alluviums. Positive gravity values are increased up to 50-60 mgal on the metamorphic rocks that are named Cycladic Complex located southwest of study areas. At the aeromagnetic regional magnetic map, gamma values about -100 observed on the Menderes Massif region are indicated metagranite rocks that are Paleozoic crystalline structure. Gamma values, which are changed between -100 and +100 at the transition areas granite with schists, are obviously revealed this transition region. Located northwest of study areas Upper Miocene-Pliocene aged from sedimentary rocks on the terrestrial carbonates and nonsegregated terrestrial

  3. Crustal thickness variation from a continental to an island arc terrane: Clues from the gravity signatures of the Central Philippines

    NASA Astrophysics Data System (ADS)

    Manalo, Pearlyn C.; Dimalanta, Carla B.; Faustino-Eslava, Decibel V.; Ramos, Noelynna T.; Queaño, Karlo L.; Yumul, Graciano P.

    2015-05-01

    Offshore and ground gravity data were utilized to estimate crustal thickness across the Central Philippines where a transition from continental to island arc terrane occurs. Significant differences in gravity anomalies were observed between the Palawan Microcontinental Block (PCB) and the Philippine Mobile Belt (PMB), two major terranes that came together through arc-continent collision. Islands of the PCB (Mindoro, Tablas, Romblon, Sibuyan and western Panay), made up of an assortment of continent-derived sedimentary and igneous rocks and slivers of ophiolitic bodies, register lower Bouguer anomalies compared to that displayed by Masbate Island in the PMB. The calculated crustal thickness of this region exhibits a complex Moho topography of non-uniform depth across the collision zone with the thickest parts (∼32 km) corresponding with ophiolitic units emplaced consequent to arc-continent collision. On the other hand, relatively thinner crust (∼21 km) within the collision zone coincides with areas surmised to have undergone attenuation following intra-arc rifting. The same characteristics are observed offshore of western Mindoro and within the Marinduque Basin, areas known to have experienced crustal thinning following regional tectonic rearrangements that triggered riftings and intra-basin openings.

  4. Incipient mantle delamination, active tectonics and crustal thickening in Northern Morocco: Insights from gravity data and numerical modeling

    NASA Astrophysics Data System (ADS)

    Baratin, Laura-May; Mazzotti, Stéphane; Chéry, Jean; Vernant, Philippe; Tahayt, Abdelilah; Mourabit, Taoufik

    2016-11-01

    The Betic-Rif orocline surrounding the Alboran Sea, the westernmost tip of the Mediterranean Sea, accommodates the NW-SE convergence between the Nubia and Eurasia plates. Recent GPS observations indicate a ∼4 mm/yr SW motion of the Rif Mountains, relative to stable Nubia, incompatible with a simple two-plate model. New gravity data acquired in this study define a pronounced negative Bouguer anomaly south of the Rif, interpreted as a ∼40 km-thick crust in a state of non-isostatic equilibrium. We study the correlation between these present-day kinematic and geodynamic processes using a finite-element code to model in 2-D the first-order behavior of a lithosphere affected by a downward normal traction (representing the pull of a high-density body in the upper mantle). We show that intermediate viscosities for the lower crust and uppermost mantle (1021-1022Pas) allow an efficient coupling between the mantle and the base of the brittle crust, thus enabling (1) the conversion of vertical movement, resulting from the downward traction, to horizontal movement and (2) shortening in the brittle upper crust. Our results show that incipient delamination of the Nubian continental lithosphere, linked to slab pull, can explain the present-day abnormal tectonics, contribute to the gravity anomaly observed in northern Morocco, and give insight into recent tectonics in the Western Mediterranean region.

  5. Gravity constraints on the geometry of the Big Bend of the San Andreas Fault in the southern Carrizo Plains and Pine Mountain egion

    NASA Astrophysics Data System (ADS)

    Altintas, Ali Can

    The goal of this project is to combine gravity measurements with geologic observations to better understand the "Big Bend" of the San Andreas Fault (SAF) and its role in producing hydrocarbon-bearing structures in the southern Central Valley of California. The SAF is the main plate boundary structure between the Pacific and North American plates and accommodates ?35 mm/yr of dextral motion. The SAF can be divided into three main parts: the northern, central and southern segments. The boundary between the central and southern segments is the "Big Bend", which is characterized by an ≈30°, eastward bend. This fault curvature led to the creation of a series of roughly east-west thrust faults and the transverse mountain ranges. Four high-resolution gravity transects were conducted across locations on either side of the bend. A total of 166 new gravity measurements were collected. Previous studies suggest significantly inclined dip angle for the San Andreas Fault in the Big Bend area. Yet, our models indicate that the San Andreas Fault is near vertical in the Big Bend area. Also gravity cross-section models suggest that flower structures occur on either side of the bend. These structures are dominated by sedimentary rocks in the north and igneous rocks in the south. The two northern transects in the Carrizo plains have an ≈-70 mgal Bouguer anomaly. The SAF has a strike of ≈315° near these transects. The northern transects are characterized by multiple fault strands which cut marine and terrestrial Miocene sedimentary rocks as well as Quaternary alluvial valley deposits. These fault strands are characterized by ?6 mgal short wavelength variations in the Bouguer gravity anomaly, which correspond to low density fault gouge and fault splays that juxtapose rocks of varying densities. The southern transects cross part of the SAF with a strike of 285°, have a Bouguer anomaly of ≈-50 mgal and are characterized by a broad 15 mgal high. At this location the rocks on

  6. Gravity and Magnetic Survey of the Oaxaca-Juarez Terrane Boundary (Oaxaca Fault), Southern Mexico: Evidence for three Half Grabens

    NASA Astrophysics Data System (ADS)

    Campos-Enriquez, J. O.; Belmonte-Jimenez, S. I.; Ortega-Gutierrez, F.; Keppie-Moorhouse, J. D.; Martinez-Silva, J.; Martinez-Serrano, R.

    2007-05-01

    A geophysical survey of the Oaxaca Fault boundary between the Oaxaca (Oaxaquia) (Zapoteco) and Juarez (Cuicateco) terranes along the Etla and Zaachila valleys area, southern Mexico shows a series of NW-SE Bouguer and magnetic anomalies with stronger gradients towards the east. The basement from the Oaxaca terrane has a high density (2.8 gr/cm3 ) and magnetic susceptibility of up to 0.0051 cgs units, which contrast with the Juarez basement that has a lower density (2.67 gr/cm3) and a higher magnetic susceptibility (values ranging between 0.0025 to 0.0045 cgs units). The magnetic susceptibility is similar south of the Donaji fault. Interpretation of six combined gravity and magnetic NE-SW profiles perpendicular to the valleys indicates the presence of a composite depression comprising three N-S sub-basins with the Etla and Zachila sub-basins located at the northern and southern portions, respectively, separated by a third sub-basin relatively displaced westwards. They are bounded on the east by the steeply W-dipping Oaxaca master fault, and on the west by the gently E-dipping Huitzo-Zimatlan fault. Two interpretations are suggested for the southward continuation of the Oaxaca Fault: 1) it continues southwards at depth with the same strike. Together the Bouguer and total field magnetic anomalies suggest that the Oaxaca fault is continuous from Etla via Oaxaca City and Ocotlán de Morelos probably to Miahuatlán de Porfirio Díaz, and 2) it continues with the same strike but is displaced eastwards ~20 km along a sinistral transfer fault, which forms the northern boundary of the Zaachila sub-basin.

  7. Analysis of gravity and topography in the GLIMPSE study region: Isostatic compensation and uplift of the Sojourn and Hotu Matua Ridge systems

    USGS Publications Warehouse

    Harmon, N.; Forsyth, D.W.; Scheirer, D.S.

    2006-01-01

    The Gravity Lieations Intraplate Melting Petrologic and Seismic Expedition (GLIMPSE) Experiment investigated the formation of a series of non-hot spot, intraplate volcanic ridges in the South Pacific and their relationship to cross-grain gravity lineaments detected by satellite altimetry. Using shipboard gravity measurements and a simple model of surface loading of a thin elastic plate, we estimate effective elastic thicknesses ranging from ???2 km beneath the Sojourn Ridge to a maximum of 10 km beneath the Southern Cross Seamount. These elastic thicknesses are lower than predicted for the 3-9 Ma seafloor on which the volcanoes lie, perhaps due to reheating and thinning of the plate during emplacement. Anomalously low apparent densities estimated for the Matua and Southern Cross seamounts 2050 and 2250 kg m-3, respectively, probably are artifacts caused by the assumption of only surface loading, ignoring the presence of subsurface loading in the form of underplated crust and/or low-density mantle. Using satellite free-air gravity and shipboard bathymetry, we calculate the age-detrended, residual mantle Bouguer anomaly (rMBA). The rMBA corrects the free-air anomaly for the direct effects of topography, including the thickening of the crust beneath the seamounts and volcanic ridges due to surface loading of the volcanic edifices. There are broad, negative rMBA anomalies along the Sojourn and Brown ridges and the Hotu Matua seamount chain that extend nearly to the East Pacific Rise. These negative rMBA anomalies connect to negative free-air anomalies in the western part of the study area that have been recognized previously as the beginnings of the cross-grain gravity lineaments. Subtracting the topographic effects of surface loading by the ridges and seamounts from the observed topography reveals that the ridges are built on broad bands of anomalously elevated seafloor. This swell topography and the negative rMBA anomalies contradict the predictions of lithospheric

  8. Gravity Survey of the Rye Patch KGRA, Rye Patch, Nevada

    NASA Astrophysics Data System (ADS)

    Mcdonald, M. R.; Gosnold, W. D.

    2011-12-01

    The Rye Patch Known Geothermal Resource Area (KGRA) is located in Pershing County Nevada on the west side of the Humboldt Range and east of the Rye Patch Reservoir approximately 200 km northeast of Reno, Nevada. Previous studies include an earlier gravity survey, 3-D seismic reflection, vertical seismic profiling (VSP) on a single well, 3-D seismic imaging, and a report of the integrated seismic studies. Recently, Presco Energy conducted an aeromagnetic survey and is currently in the process of applying 2-D VSP methods to target exploration and production wells at the site. These studies have indicated that geothermal fluid flow primarily occurs along faults and fractures and that two potential aquifers include a sandstone/siltstone member of the Triassic Natchez Pass Formation and a karst zone that occurs at the interface between Mesozoic limestone and Tertiary volcanics. We hypothesized that addition of a high-resolution gravity survey would better define the locations, trends, lengths, and dip angles of faults and possible solution cavity features. The gravity survey encompassed an area of approximately 78 km2 (30 mi2) within the boundary of the KGRA along with portions of 8 sections directly to the west and 8 sections directly to the east. The survey included 203 stations that were spaced at 400 m intervals. The simple Bouguer anomaly patterns were coincident with elevation, and those patterns remained after terrain corrections were performed. To remove this signal, the data were further processed using wave-length (bandpass) filtering techniques. The results of the filtering and comparison with the recent aeromagnetic survey indicate that the location and trend of major fault systems can be identified using this technique. Dip angles can be inferred by the anomaly contour gradients. By further reductions in the bandpass window, other features such as possible karst solution channels may also be recognizable. Drilling or other geophysical methods such as a

  9. Integrated Analysis on Gravity and Magnetic Fields of the Hailar Basin, NE China: Implications for Basement Structure and Deep Tectonics

    NASA Astrophysics Data System (ADS)

    Sun, Bin; Wang, Liangshu; Dong, Ping; Wu, YongJing; Li, Changbo; Hu, Bo; Wang, Chong

    2012-11-01

    The Hailar Basin is one of the typical basins among the NE China Basin Groups, which is situated in the east of East Asia Orogene between the Siberia Plate and the North China Plate. Based on the detailed analysis of magnetic, gravity, petrophysical, geothermal and seismological data, we separate the Gravity and Magnetic Anomalies (GMA) into four orders using Wavelet Multi-scale Decomposition (WMD). The apparent depths of causative sources were then assessed by Power Spectrum Analysis (PSA) of each order. Low-order wavelet detail anomalies were used to study the basin's basement structure such as major faults, the basement lithology, uplifts and depressions. High-order ones were used for the inversion of Moho and Curie discontinuities using the Parker method. The results show that the Moho uplifting area of the Hailar Basin is located at the NE part of the basin, the Curie uplifting area is at the NW part, and neither of them is consistent with the basin's sedimentary center. This indicates that the Hailar Basin may differ in basin building pattern from other middle and eastern basins of the basin groups, and the Hailar Basin might be of a passive type. When the Pacific Plate was subducting to NE China, the frontier of the plate lying on the mantle transition zone didn't pass through the Great Khingan Mountains region, so there is not an obvious magma upwelling or lithospheric extension in the Hailar Basin area. Finally, based on the seismological data and results of WMD, a probable 2D crust model is derived from an across-basin profile using the 2D forward modeling of the Bouguer gravity anomaly. The results agree with those from seismic inversion, suggesting WMD is suitable for identifying major crustal density interfaces.

  10. Investigating subglacial landscapes and crustal structure of the Gamburtsev Province in East Antarctica with the aid of new airborne gravity data

    NASA Astrophysics Data System (ADS)

    Jordan, T. A.; Ferraccioli, F.; Studinger, M.; Bell, R. E.; Damaske, D.; Elieff, S.; Finn, C.; Braaten, D. A.; Corr, H.

    2009-12-01

    The AGAP project was undertaken as part of the 2008\\09 field season and explored the Gamburtsev Subglacial Mountains (GSM) province in East Antarctica. AGAP collected >120, 000 line km of new airborne radar, aerogravity and aeromagnetic data. Here we focus on the airborne gravity part of the survey. The airborne gravity data were collected from two Twin Otters operating from remote field camps either side of Dome A. A high-resolution Sander Geophysics AIRGrav system was used for the first time in Antarctica and was mounted in the US plane. A more traditional L&R airborne gravity meter modified by ZLS was installed on the British Antarctic Survey aircraft. The AIRGrav system was flown in draped mode, which proved ideal for the simultaneous acquisition of radar and magnetic data, while the L&R system required flying along constant elevation survey blocks. The processed free-air gravity anomalies exhibit low cross-over errors of 1 mGal over the southern sector of the GSM, where the AIRGrav system was primarily used, and a spatial resolution of 3.5 km. Larger cross-over errors of 3.5 mGal and a coarser spatial resolution of 8 km characterise the northern part of the GSM and the adjacent Lambert Glacier, where the L&R meter was mainly flown. The merged free-air gravity anomaly grid primarily reflects the subglacial topography of the GSM province. The contrast between the Pensacola-Pole and Lambert Glacier basins and the rugged alpine-type relief of the GSM is clearly imaged. A dentritic system of subglacial valleys is mapped in the GSM, in good agreement with independent radar data. Inversion of the free-air gravity data assists in tracing the bedrock under several km-thick and fast-flowing crevassed ice of the Lambert Glacier. Using the ice thickness and bedrock topography data derived from airborne radar we compiled a new Bouguer anomaly map for the GSM province. The new gravity anomaly data can be used to estimate crustal thickness variations under the GSM and

  11. 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.

  12. A computer system for the storage and retrieval of gravity data, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Godson, Richard H.; Andreasen, Gordon H.

    1974-01-01

    A computer system has been developed for the systematic storage and retrieval of gravity data. All pertinent facts relating to gravity station measurements and computed Bouguer values may be retrieved either by project name or by geographical coordinates. Features of the system include visual display in the form of printer listings of gravity data and printer plots of station locations. The retrieved data format interfaces with the format of GEOPAC, a system of computer programs designed for the analysis of geophysical data.

  13. Effective photons in weakly absorptive dielectric media and the Beer-Lambert-Bouguer law

    NASA Astrophysics Data System (ADS)

    Judge, A. C.; Brownless, J. S.; Bhat, N. A. R.; Sipe, J. E.; Steel, M. J.; de Sterke, C. Martijn

    2014-04-01

    We derive effective photon modes that facilitate an intuitive and convenient picture of photon dynamics in a structured Kramers-Kronig dielectric in the limit of weak absorption. Each mode is associated with a mode field distribution that includes the effects of both material and structural dispersion, and an effective line-width that determines the temporal decay rate of the photon. These results are then applied to obtain an expression for the Beer-Lambert-Bouguer law absorption coefficient for unidirectional propagation in structured media consisting of dispersive, weakly absorptive dielectric materials.

  14. Bouguer images of the North American craton and its structural evolution

    NASA Technical Reports Server (NTRS)

    Arvidson, R. E.; Bowring, S.; Eddy, M.; Guinness, E.; Leff, C.; Bindschadler, D.

    1984-01-01

    Digital image processing techniques have been used to generate Bouguer images of the North American craton that diplay more of the granularity inherent in the data as compared with existing contour maps. A dominant NW-SE linear trend of highs and lows can be seen extending from South Dakota, through Nebraska, and into Missouri. The structural trend cuts across the major Precambrian boundary in Missouri, separating younger granites and rhyolites from older sheared granites and gneisses. This trend is probably related to features created during an early and perhaps initial episode of crustal assembly by collisional processes. The younger granitic materials are probably a thin cover over an older crust.

  15. High-Precise Gravity Observations at Archaeological Sites: How We Can Improve the Interpretation Effectiveness and Reliability?

    NASA Astrophysics Data System (ADS)

    Eppelbaum, Lev

    2015-04-01

    the Lesser Caucasus (western Azerbaijan) under conditions of rugged relief and complex geology. This deposit is well investigated by mining and drilling operations and therefore was used as a reference field polygon for testing this approach. A special scheme for obtaining the Bouguer anomalies has been employed to suppress the terrain relief effects dampening the anomaly effects from the objects of prospecting. The scheme is based on calculating the difference between the free-air anomaly and the gravity field determined from a 3D model of a uniform medium with a real topography. 3-D terrain relief model with an interval of its description of 80 km (the investigated 6 profiles of 800 m length are in the center of this interval) was employed to compute (by the use of GSFC software (Khesin et al., 1996)) the gravitational effect of the medium (σ = 2670 kg/m3). With applying such a scheme the Bouguer anomalies were obtained with accuracy in two times higher than that of TC received by the conventional methods. As a result, on the basis of the improved Bouguer gravity with the precise TC data, the geological structure of the deposit was defined (Khesin et al., 1996). Second approach Second approach was employed at the complex Katekh pyrite-polymetallic deposit, which is located at the southern slope of the Greater Caucasus (northern Azerbaijan). The main peculiarities of this area are very rugged topography of SW-NE trend, complex geology and severe tectonics. Despite the availability of conventional ΔgB (TC far zones were computed up to 200 km), for the enhanced calculation of surrounding terrain topography a digital terrain relief model was created (Eppelbaum and Khesin, 2004). The SW-NE regional topography trend in the area of the Katekh deposit occurrence was computed as a rectangular digital terrain relief model (DTRM) of 20 km long and 600 m wide (our interpretation profile with a length of 800 m was located in the geometrical center of the DTRM). As a whole

  16. 3D Geothermal Modelling Using Gravity Survey on Dolok Marawa, Simalungun District, North Sumatera

    NASA Astrophysics Data System (ADS)

    Rivandi, A.; Destawan, R.; Fajri, Z. R.; Hidayat, W.

    2016-01-01

    In North Sumatera, gravity method is applied to identify the geothermal model. This method measured the earth gravitational field. This research has 160 measurement points covering 9 square kilometers. We obtained complete Bouguer anomaly values ranging 85 mGal - 130.68 mGal interpreted as a heat source of andesitic igneous rocks that are affected by the presence of Mount Bahtopu magma chamber. We interpreted the values between 40 mGal - 80 mGal as reservoir and caprock. The 3D gravity inverse modelling conducted using Gravblox, and identifying the following lithologies; Toba Pyroclastic Fall (Qjt) with density 1.92 g/cm3, Toba Pyroclastic Flow (Qjt) with density 2.00 g/cm3, Mount Bahtopu Andesite (Qlb) with density 2.4 g/cm3, and 2.6 g/cm3 which is interpreted as heat source in form of andesitic rock and Mount Bahtopu magma chamber. This heat source is estimated to be at a depth of 1.45 km to 3.78 km below the surface.

  17. Three-dimensional crustal structure of the Vøring Margin (NE Atlantic): A combined seismic and gravity image

    NASA Astrophysics Data System (ADS)

    Torne, M.; Fernandez, M.; Wheeler, W.; Karpuz, R.

    2003-02-01

    The three-dimensional (3-D) crustal structure of the Vøring Margin is investigated by integrating results from reflection and wide-angle seismic data, well log data, and 3-D gravity modeling. The reduced "crustal" Bouguer anomaly, obtained after computing the gravity effects of the water layer and Cenozoic and Cretaceous sedimentary cover, displays an arcuate-shaped gravity high that coincides with the Cretaceous subbasins. The Pre-Cretaceous layer varies in thickness from 7 to 8 km below the Vøring Marginal High to <2 km in the Mesozoic depocenters and is overlying a relative "high-density" upper-middle crust (2850 kg m-3). Underlying the upper-middle crust, there is a "high-velocity/density" body, which is imaged along the Marginal High and western region of the Vøring Basin. The High Velocity Body shallows to <14 km depth in the western end of the Marginal High and thins out toward the eastern and southeastern regions of the basin. Regions of thick crust (˜24 km) are located in the eastern and southern parts of the basin and northern and central parts of the Marginal High, whereas thinner crust is observed at the southwest region of the study area (˜16 km) and in the Fenris Graben region and Utgard High (˜18 km). Residual gravity anomalies are related to the distribution of interbedded volcanics and to the presence of sedimentary subbasins under the Marginal High. Crustal thinning is not directly related to thickening of the HVB and/or the location of Cretaceous depocentres, indicating a major rejuvenation of the Cretaceous Moho related to the Maastritchian-Paleocene rifting episode and massive emplacement of igneous material during breakup.

  18. Basin-fill Aquifer Modeling with Terrestrial Gravity: Assessing Static Offsets in Bulk Datasets using MATLAB; Case Study of Bridgeport, CA

    NASA Astrophysics Data System (ADS)

    Mlawsky, E. T.; Louie, J. N.; Pohll, G.; Carlson, C. W.; Blakely, R. J.

    2015-12-01

    Understanding the potential availability of water resources in Eastern California aquifers is of critical importance to making water management policy decisions and determining best-use practices for California, as well as for downstream use in Nevada. Hydrologic well log data can provide valuable information on aquifer capacity, but is often proprietarily inaccessible or economically unfeasible to obtain in sufficient quantity. In the case of basin-fill aquifers, it is possible to make estimates of aquifer geometry and volume using geophysical surveys of gravity, constrained by additional geophysical and geological observations. We use terrestrial gravity data to model depth-to-basement about the Bridgeport, CA basin for application in preserving the Walker Lake biome. In constructing the model, we assess several hundred gravity observations, existing and newly collected. We regard these datasets as "bulk," as the data are compiled from multiple sources. Inconsistencies among datasets can result in "static offsets," or artificial bull's-eye contours, within the gradient. Amending suspect offsets requires the attention of the modeler; picking these offsets by hand can be a time-consuming process when modeling large-scale basin features. We develop a MATLAB script for interpolating the residual Bouguer anomaly about the basin using sparse observation points, and leveling offset points with a user-defined sensitivity. The script is also capable of plotting gravity profiles between any two endpoints within the map extent. The resulting anomaly map provides an efficient means of locating and removing static offsets in the data, while also providing a fast visual representation of a bulk dataset. Additionally, we obtain gridded basin gravity models with an open-source alternative to proprietary modeling tools.

  19. Basement and Basin Structures of the Northwest Paraná Basin, Brazil: Illuminated by Matched-Filter Analysis and 2D Modeling of Gravity and Magnetic Data

    NASA Astrophysics Data System (ADS)

    Curto, J. B.; Blakely, R. J.; Vidotti, R. M.; Fuck, R. A.

    2015-12-01

    The South American Platform includes two major geological components with common structural roots: the Transbrasiliano Lineament (LTB) and the Paraná Basin. Important relationships between the two components occur within the northwest Paraná Basin and concealed beneath sedimentary cover. We integrated all available airborne magnetic and gravity surveys and ground-based gravity data to produce consistent, digital magnetic and Bouguer anomaly maps. Data-processing and modeling techniques then were used in order to reveal principal crustal compartments and basin-basement structures at various depths. Three large magnetic discontinuities delineate crustal compartments in the area with N30°E, N60°E, and N70°E strike, from east to west, respectively. These magnetic lineaments bound regions with distinct gravity anomaly character. Robust matched-filter analysis applied to magnetic and gravity data yielded important depth estimates: (i) 2.5 km to the top of the Paraná Basin Neoproterozoic basement; (ii) 4-6 km to the top of a second group of basement units; (iii) 20 km, possibly associated with the upper-lower crust interface; and (iv) 33-39 and 43 km related to crustal thicknesses west and southeast of a major N30°E trending lineament, respectively. The 2D joint modeling of gravity and magnetic data sheds light on the asymmetric geometry of the basement beneath the Paraná basin, with at least three half-grabens formed by LTB reactivated structures. The central region of the study area is characterized by thinner crust and higher crustal weakness, where important structures have developed in the Mesozoic, including NW trending reactivations, linked to crustal uplift and evolution of small NE-aligned Cretaceous basins. Important depocenters occur to the north and east of the study area, with N70ºE and N30°E - NS strike, respectively.

  20. Mass Anomalies on Ganymede

    NASA Technical Reports Server (NTRS)

    Schubert, G.; Anderson, J. D.; Jacobson, R. A.; Lau, E. L.; Moore, W. B.; Palguta, J.

    2004-01-01

    Radio Doppler data from two Ganymede encounters (G1 and G2) on the first two orbits in the Galileo mission have been analyzed previously for gravity information . For a satellite in hydrostatic equilibrium, its gravitational field can be modeled adequately by a truncated spherical harmonic series of degree two. However, a fourth degree field is required in order to fit the second Galileo flyby (G2). This need for a higher degree field strongly suggests that Ganymede s gravitational field is perturbed by a gravity anomaly near the G2 closest approach point (79.29 latitude, 123.68 west longitude). In fact, a plot of the Doppler residuals , after removal of the best-fit model for the zero degree term (GM) and the second degree moments (J2 and C22), suggests that if an anomaly exists, it is located downtrack of the closest approach point, closer to the equator.

  1. On the link between particle size and deviations from the Beer-Lambert-Bouguer law for direct transmission

    NASA Astrophysics Data System (ADS)

    Larsen, Michael L.; Clark, Aaron S.

    2014-01-01

    Ballistic photon models of radiative transfer in discrete absorbing random media have demonstrated deviations from the Beer-Lambert-Bouguer law of exponential attenuation. A number of theoretical constructs to quantify the deviation from the Beer-Lambert-Bouguer law have appeared in the literature, several of which rely principally on a statistical measure related to the statistics of the absorber spatial positions alone. Here, we utilize a simple computational model to explore the interplay between the geometric size of the absorbing obstacles and the statistics governing the placement of the absorbers in the volume. We find that a description of the volume that depends on particle size and the spatial statistics of absorbers is not sufficient to fully characterize deviations from the Beer-Lambert-Bouguer law. Implications for future further theoretical and computational explorations of the problem are explored.

  2. Aeromagnetic, gravity anomaly, and derivative maps of the Craig and Dixon Entrance 1-degree by 3-degree quadrangles of southeastern Alaska

    USGS Publications Warehouse

    Wynn, Jeffrey C.; Kucks, R.P.; Grybeck, D.J.

    1999-01-01

    This CD-ROM contains aeromagnetic, gravity, geology, and topographic data as well as several derivative products, for the Craig and Dixon Entrance 1? ? 3? quadrangles of Southeastern Alaska. The data were collected by the U.S. Geological Survey directly and by means of several contract airborne surveys, through August 1991.

  3. Crustal structure in the vicinity of Las Vegas, Nevada, from seismic and gravity observations

    USGS Publications Warehouse

    Roller, John C.

    1963-01-01

    A seismic-refraction profile indicates that the crust of the Earth increases in thickness by as much as 5 km over a horizontal distance of less than 25 km northeast of Las Vegas, Nevada. This feature correlates with a decrease in the Bouguer anomaly and an increase in the average surface altitude.

  4. World gravity standards

    NASA Technical Reports Server (NTRS)

    Uotila, U. A.

    1978-01-01

    In order to use gravity anomalies in geodetic computations and geophysical interpretations, the observed gravity values from which anomalies are derived should be referred to one consistent world wide system. The International Gravity Standardization Net 1971 was adapted by the International Union of Geodesy and Geophysics at Moscow in 1971, the network was result of extensive cooperation by many organizations and individuals around the world. The network contains more than 1800 stations around the world. The data used in the adjustment included more than 25,000 gravimetry, pendulum and absolute measurements.

  5. Three-dimensional crustal structure of the southern Sierra Nevada from seismic fan profiles and gravity modeling

    SciTech Connect

    Fliedner, M.M.; Ruppert, S.; Park, S.K.; and others.

    1996-04-01

    Traveltime data from the 1993 Southern Sierra Nevada Continental Dynamics seismic refraction experiment reveal low velocities in the southern Sierra Nevada and Basin and Range province of California (6.0 to 6.6 km/s), as well as low upper mantle velocities (7.6 to 7.8 km/s). The crust thickens from southeast to northwest along the axis of the Sierra Nevada from 27 km in the Mojave Desert to 43 km near Fresno, California. A crustal welt is present beneath the Sierra Nevada, but the deepest Moho is found under the western slopes, not beneath the highest topography. A density model directly derived from the crustal velocity model but with constant mantle density satisfies the pronounced negative Bouguer anomaly associated with the Sierra Nevada, but shows large discrepancies of >50 mgal in the Great Valley and in the Basin and Range province. Matching the observed gravity with anomalies in the crust alone is not possible with geologically reasonable densities; we require a contribution from the upper mantle, either by lateral density variations or by a thinning of the lithosphere under the Sierra Nevada and the Basin and Range province. Such a model is consistent with the interpretation that the uplift of the present Sierra Nevada is caused and dynamically supported by asthenospheric upwelling or lithospheric thinning under the Basin and Range province and eastern Sierra Nevada. 20 refs., 4 figs.

  6. Correction to the Beer-Lambert-Bouguer law for optical absorption.

    PubMed

    Abitan, Haim; Bohr, Henrik; Buchhave, Preben

    2008-10-10

    The Beer-Lambert-Bouguer absorption law, known as Beer's law for absorption in an optical medium, is precise only at power densities lower than a few kW. At higher power densities this law fails because it neglects the processes of stimulated emission and spontaneous emission. In previous models that considered those processes, an analytical expression for the absorption law could not be obtained. We show here that by utilizing the Lambert W-function, the two-level energy rate equation model is solved analytically, and this leads into a general absorption law that is exact because it accounts for absorption as well as stimulated and spontaneous emission. The general absorption law reduces to Beer's law at low power densities. A criterion for its application is given along with experimental examples.

  7. Ocean gravity and geoid determination

    NASA Technical Reports Server (NTRS)

    Kahn, W. D.; Siry, J. W.; Brown, R. D.; Wells, W. T.

    1977-01-01

    Gravity anomalies have been recovered in the North Atlantic and the Indian Ocean regions. Comparisons of 63 2 deg x 2 deg mean free air gravity anomalies recovered in the North Atlantic area and 24 5 deg x 5 deg mean free air gravity anomalies in the Indian Ocean area with surface gravimetric measurements have shown agreement to + or - 8 mgals for both solutions. Geoids derived from the altimeter solutions are consistent with altimetric sea surface height data to within the precision of the data, about + or - 2 meters.

  8. 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.

  9. 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.

  10. Preliminary appraisal of gravity and magnetic data of Syncline Ridge, western Yucca Flat, Nevada Test Site, Nye County, Nevada

    USGS Publications Warehouse

    Ponce, David A.; Hanna, William F.

    1982-01-01

    A gravity and magnetic study of the Syncline Ridge area was conducted as part of an investigation of argillite rocks of the Eleana Formation under consideration as a medium for the possible storage of high-level radioactive waste. Bouguer gravity anomaly data, viewed in light of densities obtained by gamma-gamma logs and previous work of D. L. Healey (1968), delineate two regions of steep negative gradient where Cenozoic rocks and sediments are inferred to abruptly thicken: (1) the western third of the study area where Tertiary volcanic rocks are extensively exposed and (2) the northeast corner of the area where Quaternary alluvium is exposed and where volcanic rocks are inferred to occur at depth. In the remainder of the area, a region extending contiguously from Mine Mountain northwestward through Syncline Ridge to the Eleana Range, the gravity data indicate that the Eleana Formation, where not exposed, is buried at depths of less than about 200 m, except in a limited area of exposed older Paleozoic rocks on Mine Mountain. Quaternary alluvium and Tertiary volcanic rocks are inferred to occur in this region as veneers or shallow dishes of deposit on Tippipah Limestone or Eleana Formation. Low-level aeromagnetic anomaly data, covering the western two-thirds of the study area, delineate relatively magnetic tuff units within the Tertiary volcanic rocks and provide a very attractive means for distinguishing units of normal polarization from units of reversed polarization. If used in conjunction with results of previous magnetization studies of G. D. Bath (1968), the low-level survey may prove to be an effective tool for mapping specific tuff members in the volcanic terrane. The important question of the feasibility of discriminating high-quartz argillite from low-quartz argillite of the Eleana Formation using surface gravity data remains unresolved. If the more highly competent, denser, high-quartz phase should occur as stratigraphic units many tens of meters thick

  11. A new 3D Moho depth model for Iran based on the terrestrial gravity data and EGM2008 model

    NASA Astrophysics Data System (ADS)

    Kiamehr, R.; Gómez-Ortiz, D.

    2009-04-01

    Knowledge of the variation of crustal thickness is essential in many applications, such as forward dynamic modelling, numerical heat flow calculations and seismologic applications. Dehghani in 1984 estimated the first Moho depth model over the Iranian plateau using the simple profiling method and Bouguer gravity data. However, these data are high deficiencies and lack of coverage in most part of the region. To provide a basis for an accurate analysis of the region's lithospheric stresses, we develop an up to date three dimensional crustal thickness model of the Iranian Plateau using Parker-Oldenburg iterative method. This method is based on a relationship between the Fourier transform of the gravity anomaly and the sum of the Fourier transform of the interface topography. The new model is based on the new and most complete gravity database of Iran which is produced by Kiamehr for computation of the high resolution geoid model for Iran. Total number of 26125 gravity data were collected from different sources and used for generation an outlier-free 2x2 minutes gravity database for Iran. At the mean time, the Earth Gravitational Model (EGM2008) up to degree 2160 has been developed and published by National Geospatial Intelligence Agency. EGM2008 incorporates improved 5x5 minutes gravity anomalies and has benefited from the latest GRACE based satellite solutions. The major benefit of the EGM2008 is its ability to provide precise and uniform gravity data with global data coverage. Two different Moho depth models have been computed based on the terrestrial and EGM2008 datasets. The minimum and maximum Moho depths for land and EGM2008 models are 10.85-53.86 and 15.41-51.43 km, respectively. In general, we found a good agreement between the Moho geometry obtained using both land and EGM2008 datasets with the RMS of 2.7 km. Also, we had a comparison between these gravimetric Moho models versus global seismic crustal models CRUST 2.0. The differences between EGM2008 and land

  12. Gravity survey and regional geology of the Prince William Sound epicentral region, Alaska: Chapter C in The Alaska earthquake, March 27, 1964: regional effects

    USGS Publications Warehouse

    Case, J.E.; Barnes, D.F.; Plafker, George; Robbins, S.L.

    1966-01-01

    Sedimentary and volcanic rocks of Mesozoic and early Tertiary age form a roughly arcuate pattern in and around Prince William Sound, the epicentral region of the Alaska earthquake of 1964. These rocks include the Valdez Group, a predominantly slate and graywacke sequence of Jurassic and Cretaceous age, and the Orca Group, a younger sequence of early Tertiary age. The Orca consists of a lower unit of dense-average 2.87 g per cm3 (grams per cubic centimeter) pillow basalt and greenstone intercalated with sedimentary rocks and an upper unit of lithologically variable sandstone interbedded with siltstone or argillite. Densities of the clastic rocks in both the Valdez and Orca Groups average about 2.69 g per cm3. Granitic rocks of relatively low density (2.62 g per cm3) cut the Valdez and Orca Groups at several localities. Both the Valdez and the Orca Groups were complexly folded and extensively faulted during at least three major episodes of deformation: an early period of Cretaceous or early Tertiary orogeny, a second orogeny that probably culminated in late Eocene or early Oligocene time and was accompanied or closely followed by emplacement of granitic batholiths, and a third episode of deformation that began in late Cenozoic time and continued intermittently to the present. About 500 gravity stations were established in the Prince William Sound region in conjunction with postearthquake geologic investigations. Simple Bouguer anomaly contours trend approximately parallel to the arcuate geologic structure around the sound. Bouguer anomalies decrease northward from +40 mgal (milligals) at the southwestern end of Montague Island to -70 mgal at College and Harriman Fiords. Most of this change may be interpreted as a regional gradient caused by thickening of the continental crust. Superimposed on the gradient is a prominent gravity high of as much as 65 mgal that extends from Elrington Island on the southwest, across Knight and Glacier Islands to the Ellamar Peninsula

  13. A new method for extracting near-surface mass-density anomalies from land-based gravity data, based on a special case of Poisson's PDE at the Earth's surface: A case study of salt diapirs in the south of Iran

    NASA Astrophysics Data System (ADS)

    AllahTavakoli, Y.; Safari, A.; Ardalan, A.; Bahroudi, A.

    2015-12-01

    The current research provides a method for tracking near-surface mass-density anomalies via using only land-based gravity data, which is based on a special version of Poisson's Partial Differential Equation (PDE) of the gravitational field at Earth's surface. The research demonstrates how the Poisson's PDE can provide us with a capability to extract the near-surface mass-density anomalies from land-based gravity data. Herein, this version of the Poisson's PDE is mathematically introduced to the Earth's surface and then it is used to develop the new method for approximating the mass-density via derivatives of the Earth's gravitational field (i.e. via the gradient tensor). Herein, the author believes that the PDE can give us new knowledge about the behavior of the Earth's gravitational field at the Earth's surface which can be so useful for developing new methods of Earth's mass-density determination. In a case study, the proposed method is applied to a set of gravity stations located in the south of Iran. The results were numerically validated via certain knowledge about the geological structures in the area of the case study. Also, the method was compared with two standard methods of mass-density determination. All the numerical experiments show that the proposed approach is well-suited for tracking near-surface mass-density anomalies via using only the gravity data. Finally, the approach is also applied to some petroleum exploration studies of salt diapirs in the south of Iran.

  14. Geophysical Investigation of Australian-Antarctic Ridge Using High-Resolution Gravity and Bathymetry

    NASA Astrophysics Data System (ADS)

    Kim, S. S.; Lin, J.; Park, S. H.; Choi, H.

    2015-12-01

    Much of the Australian-Antarctic Ridge (AAR) has been remained uncharted until 2011 because of its remoteness and harsh weather conditions. From 2011, the multidisciplinary ridge program initiated by the Korea Polar Research Institute (KOPRI) surveyed the little-explored eastern ends of the AAR to characterize the tectonics, geochemistry, and hydrothermal activity of this intermediate spreading system. In this study, we present a detailed analysis of a 300-km-long supersegment of the AAR to quantify the spatial variations in ridge morphology and axial and off-axis volcanisms as constrained by high-resolution shipboard bathymetry and gravity. The ridge axis morphology alternates between rift valleys and axial highs within relatively short ridge segments. To obtain a geological proxy for regional variations in magma supply, we calculated residual mantle Bouguer gravity anomalies (RMBA), gravity-derived crustal thickness, and residual topography for neighboring seven sub-segments. The results of the analyses revealed that the southern flank of the AAR is associated with shallower seafloor, more negative RMBA, thicker crust, and/or less dense mantle in comparison to the conjugate northern flank. Furthermore, this north-south asymmetry becomes more prominent toward the KR1 supersegment of the AAR. The axial topography of the KR1 supersegment exhibits a sharp transition from axial highs at the western end to rift valleys at the eastern end, with regions of axial highs being associated with more robust magma supply as indicated by more negative RMBA. We also compare and contrast the characteristics of the AAR supersegment with that of other ridges of intermediate spreading rates, including the Juan de Fuca Ridge, Galápagos Spreading Center, and Southeast Indian Ridge west of the Australian-Antarctic Discordance, to investigate the influence of ridge-hotspot interaction on ridge magma supply and tectonics.

  15. Gravity Fields of the Moon Derived from GRAIL Primary and Extended Mission Data (Invited)

    NASA Astrophysics Data System (ADS)

    Lemoine, F. G.; Goossens, S. J.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Loomis, B.; Chinn, D. S.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2013-12-01

    The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft conducted the mapping of the gravity field of the Moon from March 1, 2012 to May 29, 2012, for the primary mission and from August 30, 2012 to December 14, 2012 for the extended mission and endgame. During both mission phases, the twin spacecraft acquired highly precise Ka-band range-rate (KBRR) intersatellite ranging data and Deep Space Network (DSN) data from altitudes of 2.3 to 98.2 km above the lunar surface. We have processed the GRAIL data using the NASA GSFC GEODYN orbit determination and geodetic parameter estimation program and used the supercomputers of the NASA Center for Climate Simulation (NCCS) at NASA GSFC to accumulate the SRIF arrays and derive the geopotential solutions. During the extended mission, the spacecraft orbits were maintained at a mean altitude of ~23 km, compared to ~50 km during the primary mission. In addition, from December 7 to December 14, 2012, data were acquired from a mean altitude of 11.5 km. With these data, we have derived solutions in spherical harmonics to degree 900. The new gravity solutions show improved correlations with LOLA-derived topography to very high degree and order and resolve many lunar features in the geopotential with a resolution of less than 15 km. We discuss the methods we used for the processing of the GRAIL data, and evaluate these solutions with respect to the derived power spectra, Bouguer anomalies, and fits with independent data (such as from the low-altitude phase of the Lunar Prospector mission).

  16. High-resolution Gravity Field Models of the Moon Using GRAIL mission Data

    NASA Astrophysics Data System (ADS)

    Lemoine, Frank G.; Goossens, Sander; Sabaka, Terrence J.; Nicholas, Joseph B.; Mazarico, Erwan; Rowlands, David D.; Loomis, Bryant D.; Chinn, Douglas S.; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

    2015-04-01

    The Gravity Recovery and Interior Laboratory (GRAIL) mission was designed to map the structure of the lunar interior from crust to core and to advance the understanding of the Moon's thermal evolution by producing a high-quality, high-resolution map of the gravitational field of the Moon. GRAIL consisted of two spacecraft, with Ka-band tracking between the two satellites as the single science instrument, with the addition of Earth-based tracking using the Deep Space Network. The science mission was divided into two phases: a primary mission from March 1, 2012 to May 29, 2012, and an extended mission from August 30, 2012 to December 14, 2012. The altitude varied from 3 km to 94 km above the lunar surface during both mission phases. Both the primary and the extended mission data have been processed into global models of the lunar gravity field at NASA/GSFC using the GEODYN software up to 1080 x 1080 in spherical harmonics. In addition to the high-resolution global models, local models have also been developed. Due to varying spacecraft altitude and ground track spacing, the actual resolution of the global models varies geographically. Information beyond the current resolution is still present in the data, as indicated by relatively higher fits in the last part of the extended mission, where the satellites achieved their lowest altitude above lunar surface. Local models of the lunar gravitational field at high resolution were thus estimated to accommodate this signal. Here, we present the current status of GRAIL gravity modeling at NASA/GSFC, for both global and local models. We discuss the methods we used for the processing of the GRAIL data, and evaluate these solutions with respect to the derived power spectra, Bouguer anomalies, and fits with independent data (such as from the low-altitude phase of the Lunar Prospector mission). We also evaluate the prospects for extending the resolution of our current models

  17. Relationship between surface and subsurface structures of the northern Atlas foreland of Tunisia deduced from regional gravity analysis

    NASA Astrophysics Data System (ADS)

    Frifita, N.; Arfaoui, M. S.; Zargouni, F.

    2016-08-01

    Gravity data were analyzed in the northern Atlas of Tunisia in order to identify the deep structures of the region and their relationship to the geological outcrop. The analysis based on the Bouguer gravity maps related to upward continuation at 1, 2, 4, 6, 10 and 12 km. The lineaments obtained by the horizontal gradient method were interpreted as deep faults with two global directions NE–SW and NW–SE related to major tectonic corridors. These lineaments were confirmed by the automatic estimation of depth solutions using the Euler deconvolution technique. By separation between the gravity anomaly bodies in different levels, it shows that almost all of the lineaments are oriented in NE–SW and NW–SE directions. The NW–SE-trending lineaments are related to deep faults and the NE–SW-oriented lineaments define the global direction of the surface, and they are related to shallow structures. 2.5D gravity modeling was used to improve the results obtained by the Maxima and the Euler deconvolution techniques. The 2.5D model points out the variation of depths of the NE–SW-trending major faults. In this study, we demonstrate the relationship between the NE–SW and the NW–SE directions. These two major sets of faults have been determined by the statistical study of the lineaments. This study confirms some faults already recognized or supposed by the classical geological studies, and it also detects a new deep fault masked in the surface, and gives information about major fault depths and the relation between different structures.

  18. Relationship between surface and subsurface structures of the northern Atlas foreland of Tunisia deduced from regional gravity analysis

    NASA Astrophysics Data System (ADS)

    Frifita, N.; Arfaoui, M. S.; Zargouni, F.

    2016-08-01

    Gravity data were analyzed in the northern Atlas of Tunisia in order to identify the deep structures of the region and their relationship to the geological outcrop. The analysis based on the Bouguer gravity maps related to upward continuation at 1, 2, 4, 6, 10 and 12 km. The lineaments obtained by the horizontal gradient method were interpreted as deep faults with two global directions NE-SW and NW-SE related to major tectonic corridors. These lineaments were confirmed by the automatic estimation of depth solutions using the Euler deconvolution technique. By separation between the gravity anomaly bodies in different levels, it shows that almost all of the lineaments are oriented in NE-SW and NW-SE directions. The NW-SE-trending lineaments are related to deep faults and the NE-SW-oriented lineaments define the global direction of the surface, and they are related to shallow structures. 2.5D gravity modeling was used to improve the results obtained by the Maxima and the Euler deconvolution techniques. The 2.5D model points out the variation of depths of the NE-SW-trending major faults. In this study, we demonstrate the relationship between the NE-SW and the NW-SE directions. These two major sets of faults have been determined by the statistical study of the lineaments. This study confirms some faults already recognized or supposed by the classical geological studies, and it also detects a new deep fault masked in the surface, and gives information about major fault depths and the relation between different structures.

  19. Spectral analysis of topography and gravity in the Basin and Range Province

    USGS Publications Warehouse

    Ricard, Y.; Froidevaux, C.; Simpson, R.

    1987-01-01

    A two-dimensional spectral analysis has been carried out for the topography and the Bouguer gravity anomaly of the Basin and Range Province in western North America. The aim was to investigate the possible presence of dominant wavelengths in the deformation pattern at the surface and at the depth of compensation. The results suggest that a 200-km wavelength in the deep compensating mass distribution has been inherited from an early tectonic phase of extension at an azimuth N65??E. The corresponding surface topography exhibits prominent overtones at wavelength of 100, 75, and possibly 45 km. It is argued that these characterize the non-linear rheology of the upper crust. The short wavelengths in the topography reflect the present phase of deformation, mixed with the results of the older deformations. These results point to a need to extend the physical models of lithospheric stretching beyond the presently available one-phase scenario. However, they show that the boudinage instability concept is consistent with the data. ?? 1987.

  20. Convergence of the Bouguer-Beer law for radiation extinction in particulate media

    NASA Astrophysics Data System (ADS)

    Frankel, A.; Iaccarino, G.; Mani, A.

    2016-10-01

    Radiation transport in particulate media is a common physical phenomenon in natural and industrial processes. Developing predictive models of these processes requires a detailed model of the interaction between the radiation and the particles. Resolving the interaction between the radiation and the individual particles in a very large system is impractical, whereas continuum-based representations of the particle field lend themselves to efficient numerical techniques based on the solution of the radiative transfer equation. We investigate radiation transport through discrete and continuum-based representations of a particle field. Exact solutions for radiation extinction are developed using a Monte Carlo model in different particle distributions. The particle distributions are then projected onto a concentration field with varying grid sizes, and the Bouguer-Beer law is applied by marching across the grid. We show that the continuum-based solution approaches the Monte Carlo solution under grid refinement, but quickly diverges as the grid size approaches the particle diameter. This divergence is attributed to the homogenization error of an individual particle across a whole grid cell. We remark that the concentration energy spectrum of a point-particle field does not approach zero, and thus the concentration variance must also diverge under infinite grid refinement, meaning that no grid-converged solution of the radiation transport is possible.

  1. Gravity study of the Central African Rift system: a model of continental disruption 2. The Darfur domal uplift and associated Cainozoic volcanism

    NASA Astrophysics Data System (ADS)

    Bermingham, P. M.; Fairhead, J. D.; Stuart, G. W.

    1983-05-01

    Gravity studies of the Darfur uplift, Western Sudan, show it to be associated with a circular negative Bouguer anomaly, 50 mGal in amplitude and 700 km across. A three-dimensional model interpretation of the Darfur anomaly, using constraints deduced from geophysical studies of similar but more evolved Kenya and Ethiopia domes, suggests either a low-density laccolithic body at mid-lithospheric depth (~ 60 km) or a thinned lithosphere with emplacement at high level of low-density asthenospheric material. The regional setting of the Darfur uplift is described in terms of it being an integral part of the Central African Rift System which is shown to be broadly equivalent to the early to middle Miocene stage in the development of the Afro-Arabian Rift System. Comparisons between these rift systems suggest that extensional tectonics and passive rifting, resulting in the subsiding sedimentary rift basins associated with the Ngaoundere, Abu Gabra, Red Sea and Gulf of Aden rifts, are more typical of the early stage development of passive continental margins than the active domal uplift and development of rifted features associated with the Darfur, Kenya and Ethiopia domes.

  2. Point stability at shallow depths: experience from tilt measurements in the Lower Rhine Embayment, Germany, and implications for high-resolution GPS and gravity recordings

    NASA Astrophysics Data System (ADS)

    Kümpel, H.-J.; Lehmann, K.; Fabian, M.; Mentes, Gy.

    2001-09-01

    From 1996 to 1999, we have studied ground tilts at depths of between 2m and 5m at three sites in the Lower Rhine Embayment (LRE), western Germany. The LRE is a tectonically active extensional sedimentary basin roughly 50km×100km. The purpose of the tilt measurements was (a) to provide insight into the magnitude, nature and variability of background tilts and (b) to assess possible limitations of high-resolution GPS campaigns and microgravity surveys due to natural ground deformation. The tilt readings, sensed by biaxial borehole tiltmeters of baselength 0.85m, cover a frequency range from 10-8Hz to 10-2Hz (periods from minutes to years). Assuming that the tilt signals represent ground displacements on a scale typically not larger than several times the tiltmeters' baselength, and that tilt signals at shallow depth could in a simple geometric way be related to changes in surface elevation and gravity, we try to estimate the magnitude level of point movements and corresponding Bouguer gravity effects that is generally not surpassed. The largest tilt signals observed were some +/-50µradyr-1. If they were observable over a ground section of extension, e.g. 10m, the converted rates may correspond to about +/-0.5mm per 10myr-1 in vertical ground displacement, and +/-0.1µgalyr-1 in Bouguer gravity effect, respectively. Large signals are mostly related to seasonal effects, probably linked to thermomechanical strain. Other causes of ground deformation identified include seepage effects after rainfalls (order of +/-10µrad) and diurnal strains due to thermal heating and/or fluctuations in the water consumption of nearby trees (order of +/-1µrad). Episodic step-like tilt anomalies with amplitudes up to 22µrad at one of the observation sites might reflect creep events associated to a nearby active fault. Except for short-term ground deformation caused by the passage of seismic waves from distant earthquakes, amplitudes of non-identified tilt signals in the studied

  3. Gradients from GOCE reveal gravity changes before Pisagua Mw = 8.2 and Iquique Mw = 7.7 large megathrust earthquakes

    NASA Astrophysics Data System (ADS)

    Álvarez, Orlando; Nacif, Silvina; Spagnotto, Silvana; Folguera, Andres; Gimenez, Mario; Chlieh, Mohamed; Braitenberg, Carla

    2015-12-01

    Considerable improvements in the measurement of the Earth gravity field from GOCE satellite mission have provided global gravity field models with homogeneous coverage, high precision and good spatial resolution. In particular, the vertical gravity gradient (Tzz), in comparison to the classic Bouguer anomaly, defines more accurately superficial mass heterogeneities. Moreover, the correction of these satellite-derived data from the effect of Earth topographic masses by means of new techniques taking into account the Earth curvature, improves results in regional analyses. In a recent work we found a correlation between Tzz and slip distribution for the 2010 Maule Mw = 8.8 earthquake. In the present work, we derive the vertical gravity gradient from the last GOCE only model, corrected by the topographic effect and also by the sediments on depocenters of the offshore region at the Peru-Chile margin, in order to study a spatial relationship between different lobes of the gravity derived signal and the seismic sources of large megathrust earthquakes. In particular, we analyze this relation for the slip models of the 1996 Mw = 7.7 Nazca, 2001 Mw = 8.4 Arequipa, 2007 Mw = 8.0 Pisco events and for the slip models of the 2014 Mw = 8.2 Pisagua and Mw = 7.7 Iquique earthquakes from Schurr et al. (2014), including the previously analyzed 2010 Mw = 8.8 Maule event. Then we find a good correlation between vertical gravity gradients and main rupture zones, correlation that becomes even stronger as the event magnitude increases. Besides this, a gravity fall in the gravity gradient was noticed over the area of the main slip patches at least for the two years before 2014 Mw = 8.2 Pisagua and Mw = 7.7 Iquique earthquakes. Additionally, we found temporal variations of the gravity field after 2010 Mw = 8.8 Maule event, related to the main patches of the slip distribution, and coseismic deformation. Therefore, we analyzed vertical gravity gradient field variations as an indirect measure

  4. Crustal Accretion and Mantle Geodynamics at Microplates: Constraints from Gravity Analysis

    NASA Astrophysics Data System (ADS)

    Ames, K.; Georgen, J. E.; Dordevic, M. M.

    2013-12-01

    Oceanic crustal accretion occurs in a variety of locations, including mid-ocean ridges and back-arc spreading centers, and in unique settings within these systems, such as plate boundary triple junctions, intra-transform spreading centers, and microplates. This study focuses on crustal accretion and mantle geodynamics at microplates. The Easter and Juan Fernandez microplates are located in the South Pacific along the Pacific, Nazca and Antarctic plate boundaries. Both microplates formed 3-5 Ma and they are currently rotating clockwise at 15 deg/Ma and 9 deg/Ma respectively (e.g., Searle et al. J. Geol. Soc. Lond. 1993). The study area also encompasses the Easter/Sala y Gomez mantle plume and the Foundation seamount chain, both of which are located close to spreading centers. We calculate mantle Bouguer anomaly (MBA) from satellite gravity measurements and shipboard soundings in order to gain a better understanding of the thermal structure of these two oceanic microplates and to quantify the effect that melting anomalies may have on their boundaries. We assume a crustal thickness of 6.0 km, a 1.7 g/cm^3 density difference at the water/crust interface, and a 0.6 g/cm^3 density difference at the crust/mantle interface. The west rift of the Easter microplate has an MBA low ranging from approximately -50 to -100 mGal, while the east rift has slightly higher MBA values ranging from roughly 10 to -50 mGal. The west rift of the Juan Fernandez microplate has a maximum MBA low of about -100 mGal with a sharp increase to -20 mGal at -35 deg S. The east rift of the Juan Fernandez microplate is characterized by more variable MBA, ranging from 0 to -140 mGal. The MBA low associated with the Easter/Sala y Gomez mantle plume has a maximum amplitude about 150 mGal. Likewise, the Foundation seamounts show a gravity low of -140 to -150 mGal. These spatial variations in gravity, as well as published isotopic data and exploratory numerical models, are used to constrain upper mantle

  5. 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.

  6. A gravity survey of parts of quadrangles 26E, 26F, 27E, and 27F, northeastern Arabian Shield, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Miller, C.H.; Showail, A.A.; Kane, M.F.; Khoja, I.A.; Al Ghandi, S. A.

    1989-01-01

    The greatest complete Bouguer anomaly is associated with basaltic lava flows located in the northeastern part of the survey area. The thickness of the basalt in outcrop does not account for the anomalies with the highest amplitudes, but the latter may be due to the presence of a basalt-filled vent. Those anomalies that are present do not define the basalt flows well, but the largest free-air anomaly occurs over the southwestern margin of the Salma Caldera, located about 15 km from the basalt flows. The source of the free-air anomaly is unknown, but it may be related to another hidden basaltic vent.

  7. Gravity and crustal structure

    NASA Technical Reports Server (NTRS)

    Bowin, C. O.

    1976-01-01

    Lunar gravitational properties were analyzed along with the development of flat moon and curved moon computer models. Gravity anomalies and mascons were given particular attention. Geophysical and geological considerations were included, and comparisons were made between the gravitional fields of the Earth, Mars, and the Moon.

  8. 3-D density modeling of Mt. Paekdu (N Korea/China) stratovolcano and its evolution by a combination of EGM2008/terrestrial gravity field

    NASA Astrophysics Data System (ADS)

    Götze, Hans-Jürgen; Choi, Sungchan

    2015-04-01

    We combined the global gravity dataset EGM2008 and a local terrestrial gravity data survey to conduct constrained 3-D crustal density modeling of a strato-volcanic complex and the surrounding area located close to the border of North Korea and China. The independent geophysical (seismic, seismology, geochemistry) and petrological constraints will be presented together with the preprocessing of data base by curvature analysis and Euler deconvolution. The multiple data base is used to assist a general interpretation of the investigated area, and the 3D density model (modelled by the in-house IGMAS+ software). Mt. Paekdu is characterized by a low of Bouguer anomaly of some -110 × 10-5 m/s2, which is caused by the combined gravity effects of (1) Moho depth of about 40 km, (2) a zone with both lower P-wave velocity and density than the surrounding, (3) low density volcanic rocks at the surface, and (4) the presence of a magma chamber that has not previously been identified. The terrestrial gravity field measured along the seismic profile shows a remarkable anomaly descending from the southern- to the northern flank of the Mt. Paekdu volcano, which should be a typical anomaly pattern generally observed over the active volcanic area in the world (e.g. the Yellow Stone volcano). The trend is interpreted to be caused by a prominent density difference between a serious of high density mid crustal sill beneath the southern flank and a predicted partial melted zone locating in the northern flank. With the help of several geoscientific observations (seismic, electromagnetic, gravity and geochemistry) and the 3D density model we conclude that a high density sill was formed in Pliocene and early Pleistocene after pre-shield plateau-forming eruption. Since the Pliocene, volcanic activity in the Mt. Paekdu region might be migrated from the southeastern of North Korea to the northwest, following the path of NW-SE-trending faults. Recently observed seismic tremors can be explained

  9. 3-D Density Modeling of the Combined EGM2008/Terrestrial Gravity Field over the Mt. Paekdu (N Korea/China) Stratovolcano and Its Evolution

    NASA Astrophysics Data System (ADS)

    Goetze, H. J.; Choi, S.

    2014-12-01

    In the presentation we get use of the global gravity dataset EGM2008 and a local terrestrial gravity data survey for a constrained 3-D crustal density modeling of a stratovolcano and its surrounding area located close to the border of North Korea and China. The independent geophysical (seismic, seismology, geochemistry) and petrological constraints will be presented together with the preprocessing of data base by curvature analysis and Euler deconvolution. The multiple data base is used to assist a general interpretation of the investigated area in time, and the 3D density model (modelled by the inhouse IGMAS+ software). Mt. Paekdu is characterized by a low of Bouguer anomaly of some -110 ´ 10-5 m/s2, which is caused by the combined gravity effects of (1) Moho depth of about 40 km, (2) a zone with both lower P-wave velocity and density than the surrounding, (3) low density volcanic rocks at the surface, and (4) the presence of a magma chamber that has not previously been identified. The terrestrial gravity field measured along the seismic profile shows a remarkable anomaly descending from the southern- to the northern flank of the Mt. Paekdu volcano, which should be a typical anomaly pattern generally obsered over the active volcanic area in the world (e.g. the Yellow Stone volcano). The trend is interpreted to be caused by a prominent density difference between a serious of high density mid crustal sill beneath the southern flank and a predicted partial melted zone locating in the northern flank. With the help of several geoscientific observations (seismic, electromagnetic, gravity and geochemistry) and the 3D density model we conclude that a high density sill was formed in Pliocene and early Pleistocene after pre-shield plateau-forming eruption. Since the Pliocene, volcanic activity in the Mt. Paekdu region might be migrated from the southeastern of North Korea to the northwest, following the path of NW-SE-trending faults. Recently observed seismic tremors can

  10. 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)…

  11. 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

  12. Understanding Conspicuous Gravity Low Over the Koyna-Warna Seismogenic Region (Maharashtra, India) and Earthquake Nucleation: A Paradigm Shift

    NASA Astrophysics Data System (ADS)

    Vasanthi, A.; Satish Kumar, K.

    2016-06-01

    The continued seismicity in Koyna-Warna region of the western part of Maharastra (India) and its relationship with subsurface structures, concealed below thick volcanic sequences, are studied in detail using gravity field along with newly available deep scientific drilling results. This seismically active zone is marked by a large conspicuous negative gravity anomaly, the causes of which are yet to be fully understood. Recent findings from the boreholes drilled in the Koyna (G upta et al. in Int J Earth Sci 104:1511-1522, 2015) and Killari seismic zones, both of which penetrated the thick Deccan volcanic cover and the underlying Archean crystalline basement, have motivated us to revisit the Bouguer gravity field over this region, using a newly developed finite element method of regional-residual separation. Our study reveals the presence of two thick low-density/low-velocity crustal zones below the Koyna-Warna region, the shallower one between 5 and 13 km depth and the deeper one between 35 and 43 km depth just above the Moho. Both of these zones appear to contain mantle-metasomatised and fractionated magmatic material, respectively. Interestingly, the hypocenters of all M ≥ 5 Koyna earthquakes occur within the upper low-velocity/low-density zone. We also suggest high-order crustal exhumation below this region, which led to the removal of the entire sedimentary and granitic upper crustal column. This process has brought denser mid-crustal lithological facies close to the surface. Quaternary uplifting and movement of fault blocks along the old as well as newly created fault planes seem to be still continuing. A paleo-rift may have existed beneath this region below which Moho temperatures (~600 °C) and mantle heat flow (~31 mW/m2) are still high.

  13. Satellite Gravity Drilling the Earth

    NASA Technical Reports Server (NTRS)

    vonFrese, R. R. B.; Potts, L. V.; Leftwich, T. E.; Kim, H. R.; Han, S.-H.; Taylor, P. T.; Ashgharzadeh, M. F.

    2005-01-01

    Analysis of satellite-measured gravity and topography can provide crust-to-core mass variation models for new insi@t on the geologic evolution of the Earth. The internal structure of the Earth is mostly constrained by seismic observations and geochemical considerations. We suggest that these constraints may be augmented by gravity drilling that interprets satellite altitude free-air gravity observations for boundary undulations of the internal density layers related to mass flow. The approach involves separating the free-air anomalies into terrain-correlated and -decorrelated components based on the correlation spectrum between the anomalies and the gravity effects of the terrain. The terrain-decorrelated gravity anomalies are largely devoid of the long wavelength interfering effects of the terrain gravity and thus provide enhanced constraints for modeling mass variations of the mantle and core. For the Earth, subcrustal interpretations of the terrain-decorrelated anomalies are constrained by radially stratified densities inferred from seismic observations. These anomalies, with frequencies that clearly decrease as the density contrasts deepen, facilitate mapping mass flow patterns related to the thermodynamic state and evolution of the Earth's interior.

  14. Mapping of Basement Faults with Gravity and Magnetic Data at NE Mexico

    NASA Astrophysics Data System (ADS)

    Yutsis, V.; Krivosheya, K.; Tamez Ponce, A.

    2012-04-01

    Northeast Mexico is essentially the juncture of two distinctly different tectono-stratigraphic provinces, the eastern Gulf of Mexico (Coastal Plane, Sierra Madre Oriental) province and the western Pacific Mexico (Rivera plate, Meso-American trench, Sierra Madre Occidental) province (Goldhammer & Johnson, 2001). Tectonic evolution in northeast Mexico is dominated by divergent-margin development associated with the opening of the Gulf of Mexico and overprinted by non-igneous Laramide orogenic effects (Pindell et al., 1988). The structural grain of northeast Mexico consists of Triassic to Liassic fault-controlled basement blocks, the development of which reflects in part late Paleozoic orogenic patterns of metamorphism and igneous intrusion (Wilson, 1990). There are different tectonic provinces which are recognized interpreting the basement and sediment cover of this area: Coahuila block, La Popa sub-basin, Sabinas basin, Burgos basin, Sierra Madre Oriental (Monterrey trough), and Parras basin. Mojave-Sonora megashear and San Marcos fault (Chavez-Cabello et al., 2007) are two principal fault zones crossing the northeast Mexico in NW-SE direction. This paper is presented the integral analysis of the gravity and magnetic data in the northeast Mexico. Complementing with a Digital Model of Elevations (DME) that combined with the review of previous geological studies it serves to compare the surface structures and blocks of basement in this area. Also the separation of the most important tectonic blocks was done, and 2.5D geological-geophysical model was finally developed. This model represents in a general way the principal structural characteristics of northeast Mexico. Gravity and magnetic data analysis was used with purpose to study the structure of the substrata in order to allow modeling of the basement structure and its relation with the sedimentary cover features. The Bouguer gravity and the total field aeromagnetic data were supplied by Geological Survey of Mexico

  15. 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.

  16. Constraints on Ceres internal strcuture from the Dawn gravity and shape data

    NASA Astrophysics Data System (ADS)

    Ermakov, A.; Zuber, M. T.; Smith, D. E.; Fu, R. R.; Raymond, C. A.; Russell, C. T.; Park, R. S.

    2015-12-01

    Ceres is the largest body in the asteroid belt with a radius of approximately 470 km. It is large enough to attain a shape much closer to hydrostatic equilibrium than major asteroids. Pre-Dawn shape models of Ceres (e.g. Thomas et al., 2005; Carry et al., 2008) revealed that its shape is consistent with a hydrostatic ellipsoid. After the arrival of the Dawn spacecraft in Ceres orbit in March 2015, Framing Camera images were used to construct shape models of Ceres. Meanwhile, radio-tracking data are being used to develop gravity models. We use the Dawn-derived shape and gravity models to constrain Ceres' internal structure. These data for the first time allow estimation of the degree to which Ceres is hydrostatic. Observed non-hydrostatic effects include a 2.1 km triaxiality (difference between the two equatorial axes) as well as an 660-m center-of-mass - center-of-figure offset. The Dawn gravity data from the Survey orbit shows that Ceres has a central density concentration. Second-degree sectorial gravity coefficients are negatively correlated with topography indicating a peculiar interior structure. We compute the relative crustal thickness based on the observed Bouguer anomaly. Hydrostatic models show that Ceres appears more differentiated based on its gravity than on its shape. We expand the Ceres shape in spherical harmonics, observing that the power spectrum of topography deviates from the power law at low degrees (Fig. 1). We interpret the decrease of power at low degrees to be due to viscous relaxation. We suggest that relaxation happens on Ceres but, unlike modeled in Bland (2013), it is important only at the lowest degrees that correspond to scales of several hundreds of km. There are only a few features on Ceres of that size and at least one of them (an impact basin provisionally named Kerwan) appears relaxed. The simplest explanation is that Ceres's outer shell is not pure ice or pure rock but an ice-rock mixture that allows some relaxation at the

  17. Regional Geothermal Characterisation of East Anatolia from Aeromagnetic, Heat Flow and Gravity Data

    NASA Astrophysics Data System (ADS)

    Bektaş, Özcan; Ravat, Dhananjay; Büyüksaraç, Aydin; Bilim, Funda; Ateş, Abdullah

    2007-05-01

    East Anatolia is a region of high topography made up of a 2-km high plateau and Neogene and Quaternary volcanics overlying the subduction-accretion complex formed by the process of collision. The aeromagnetic and gravity data surveyed by the Mineral Research and Exploration (MTA) of Turkey have been used to interpret qualitatively the characteristics of the near-surface geology of the region. The residual aeromagnetic data were low-pass filtered and analyzed to produce the estimates of magnetic bottom using the centroid method and by forward modelling of spectra to evaluate the uncertainties in such estimates. The magnetic bottom estimates can be indicative of temperatures in the crust because magnetic minerals lose their spontaneous magnetization at the Curie temperature of the dominant magnetic minerals in the rocks and, thus, also are called Curie point depths (CPDs). The Curie point depths over the region of Eastern Anatolia vary from 12.9 to 22.6 km. Depths computed from forward modelling of spectra with 200 600 km window sizes suggest that the bottom depths from East Anatolia from the magnetic data may have errors exceeding 5 km; however, most of the obtained depths appear to lie in the above range and indicate that the lower crust is either demagnetized or non-magnetic. In the interpretation of the magnetic map, we also used reduction-to-pole (RTP) and amplitude of total gradient of high-pass filtered anomalies, which reduced dipolar orientation effects of induced aeromagnetic anomalies. However, the features of the RTP and the total gradient of the high-pass filtered aeromagnetic anomalies are not highly correlated to the hot spring water locations. On the other hand, many high-amplitude features seen on the total gradient map can be correlated with the ophiolitic rocks observed on the surface. This interpretation is supported by Bouguer gravity data. In this paper, we recommend that the sources of the widespread thermal activity seen in East Anatolia must

  18. On the tectonic problems of the southern East China Sea and adjacent regions: Evidence from gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    Shang, Luning; Zhang, Xunhua; Han, Bo; Du, Runlin

    2016-02-01

    In this paper, two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system: one data set was from the `Geological-geophysical map series of China Seas and adjacent areas' database and the other was newly collected by R/V Kexue III in 2011. Magnetic and gravity data were reorganized and processed using the software MMDP, MGDP and RGIS. In addition to the description of the anomaly patterns in different areas, deep and shallow structure studies were performed by using several kinds of calculation, including a spectrum analysis, upward-continuation of the Bouguer anomaly and horizontal derivatives of the total-field magnetic anomaly. The depth of the Moho and magnetic basement were calculated. Based on the above work, several controversial tectonic problems were discussed. Compared to the shelf area and Ryukyu Arc, the Okinawa Trough has an obviously thinned crust, with the thinnest area having thickness less than 14 km in the southern part. The Taiwan-Sinzi belt, which terminates to the south by the NW-SE trending Miyako fault belt, contains the relic volcanic arc formed by the splitting of the paleo Ryukyu volcanic arc as a result of the opening of the Okinawa Trough. As an important tectonic boundary, the strike-slip type Miyako fault belt extends northwestward into the shelf area and consists of several discontinuous segments. A forearc terrace composed of an exotic terrane collided with the Ryukyu Arc following the subduction of the Philippine Sea Plate. Mesozoic strata of varying thicknesses exist beneath the Cenozoic strata in the shelf basin and significantly influence the magnetic pattern of this area. The gravity and magnetic data support the existence of a Great East China Sea, which suggests that the entire southern East China Sea shelf area was a basin in the Mesozoic without alternatively arranged uplifts and depressions, and might have extended southwestward and connected with the

  19. A systematic analysis of the Mid-Atlantic Ridge morphology and gravity between 15°N and 40°N: Constraints of the thermal structure

    NASA Astrophysics Data System (ADS)

    Thibaud, RéMy; Gente, Pascal; Maia, MáRcia

    1998-10-01

    Multibeam bathymetry data obtained along a 2400 km long section of the Mid-Atlantic Ridge (MAR) from 15°N to the Azores platform (40°N) and satellite-derived gravity data were used to calculate the mantle Bouguer anomaly (MBA) along this portion of the MAR. Both data sets were used to determine the relations between gravity anomalies and topographic variations and discuss these in terms of thermal difference. A long-wavelength influence of the Azores hot spot is characterized by a gentle, continuous slope of the average ridge axial depth and a general gradient in the along-axis MBA profile. This thermal influence of the Azores hot spot controls a systematic southward propagation of the spreading segments at least to 26°30'N. South of 26°30'N, the direction of the segment propagation is controlled by the local difference in thermal state between adjacent segments. Except on the Azores platform, the systematic along-axis 11-90 km long wavelength segmentation is independent of the long-wavelength influence of the Azores. At the segment center, the axial morphology is linked to the thermal state of the segments between: (1) "Hotter segments" characterized by a smooth axial morphology, a well-defined shallow "inner valley", high ΔMBA and a long length;(2) "colder segments" which present a rough axial morphology with a deep, wide and well-defined rift valley, a low ΔMBA and a small length. For "hotter segments" the formation of the abyssal hills is mainly due to a magmato-tectonic cycle over periods of 0.3 to 1 Myr, whereas on "colder segments" the axial morphology is mainly controlled by a tectonic rift valley formation. We propose that these different segment types correspond to a temporal evolution of the rift valley morphology over periods of several million years.

  20. Quantum gravity and the large scale anomaly

    SciTech Connect

    Kamenshchik, Alexander Y.; Tronconi, Alessandro; Venturi, Giovanni E-mail: Alessandro.Tronconi@bo.infn.it

    2015-04-01

    The spectrum of primordial perturbations obtained by calculating the quantum gravitational corrections to the dynamics of scalar perturbations is compared with Planck 2013 and BICEP2/Keck Array public data. The quantum gravitational effects are calculated in the context of a Wheeler-De Witt approach and have quite distinctive features. We constrain the free parameters of the theory by comparison with observations.

  1. High-Precise Gravity Observations at Archaeological Sites: How We Can Improve the Interpretation Effectiveness and Reliability?

    NASA Astrophysics Data System (ADS)

    Eppelbaum, Lev

    2015-04-01

    the Lesser Caucasus (western Azerbaijan) under conditions of rugged relief and complex geology. This deposit is well investigated by mining and drilling operations and therefore was used as a reference field polygon for testing this approach. A special scheme for obtaining the Bouguer anomalies has been employed to suppress the terrain relief effects dampening the anomaly effects from the objects of prospecting. The scheme is based on calculating the difference between the free-air anomaly and the gravity field determined from a 3D model of a uniform medium with a real topography. 3-D terrain relief model with an interval of its description of 80 km (the investigated 6 profiles of 800 m length are in the center of this interval) was employed to compute (by the use of GSFC software (Khesin et al., 1996)) the gravitational effect of the medium (σ = 2670 kg/m3). With applying such a scheme the Bouguer anomalies were obtained with accuracy in two times higher than that of TC received by the conventional methods. As a result, on the basis of the improved Bouguer gravity with the precise TC data, the geological structure of the deposit was defined (Khesin et al., 1996). Second approach Second approach was employed at the complex Katekh pyrite-polymetallic deposit, which is located at the southern slope of the Greater Caucasus (northern Azerbaijan). The main peculiarities of this area are very rugged topography of SW-NE trend, complex geology and severe tectonics. Despite the availability of conventional ΔgB (TC far zones were computed up to 200 km), for the enhanced calculation of surrounding terrain topography a digital terrain relief model was created (Eppelbaum and Khesin, 2004). The SW-NE regional topography trend in the area of the Katekh deposit occurrence was computed as a rectangular digital terrain relief model (DTRM) of 20 km long and 600 m wide (our interpretation profile with a length of 800 m was located in the geometrical center of the DTRM). As a whole

  2. New standards for reducing gravity data: The North American gravity database

    USGS Publications Warehouse

    Hinze, W. J.; Aiken, C.; Brozena, J.; Coakley, B.; Dater, D.; Flanagan, G.; Forsberg, R.; Hildenbrand, T.; Keller, Gordon R.; Kellogg, J.; Kucks, R.; Li, X.; Mainville, A.; Morin, R.; Pilkington, M.; Plouff, D.; Ravat, D.; Roman, D.; Urrutia-Fucugauchi, J.; Veronneau, M.; Webring, M.; Winester, D.

    2005-01-01

    The North American gravity database as well as databases from Canada, Mexico, and the United States are being revised to improve their coverage, versatility, and accuracy. An important part of this effort is revising procedures for calculating gravity anomalies, taking into account our enhanced computational power, improved terrain databases and datums, and increased interest in more accurately defining long-wavelength anomaly components. Users of the databases may note minor differences between previous and revised database values as a result of these procedures. Generally, the differences do not impact the interpretation of local anomalies but do improve regional anomaly studies. The most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conventionally used geoid or sea level. Principal facts of gravity observations and anomalies based on both revised and previous procedures together with germane metadata will be available on an interactive Web-based data system as well as from national agencies and data centers. The use of the revised procedures is encouraged for gravity data reduction because of the widespread use of the global positioning system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with North American and national databases. Anomalies based on the revised standards should be preceded by the adjective "ellipsoidal" to differentiate anomalies calculated using heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid. ?? 2005 Society of Exploration Geophysicists. All rights reserved.

  3. The deep crustal structure of the mafic-ultramafic Seiland Igneous Province of Norway from 3D gravity modelling and geological implications

    NASA Astrophysics Data System (ADS)

    Pastore, Zeudia; Fichler, Christine; McEnroe, Suzanne A.

    2016-09-01

    The Seiland Igneous Province (SIP) is the largest complex of mafic and ultramafic intrusions in northern Fennoscandia intruded at ca. 580 - 560 Ma. The depth extent and the deep structure of the SIP are mainly unknown apart from three profiles modelled by gravity and refraction seismic data. Utilizing 3D gravity modelling, a complex model of the deep subsurface structure of the SIP has been developed. The structure is presented in a multi-profile model ranging from the surface to the Moho. The mafic/ultramafic rocks of the SIP are modelled with densities of 3100 and 3300 kg m-3, the surrounding rocks by densities of 2700 and 2900 kg m-3 for upper and lower crust, respectively. This density model explains the pronounced positive Bouguer gravity anomaly of up to 100 mGal above background. Its minimum volume is estimated from the subsurface model to 17000 km3 and as such we revise downwards the earlier estimations of 25000 km3. The new subsurface model suggests that most of the SIP has a thickness between 2 and 4 km. An area with roots in an annular pattern is found and two deep-reaching roots have been identified located below the islands of Seiland and Sørøy. The depth of these roots is estimated to approximatively 9 km. The SIP is presently interpreted to be in the Caledonian Kalak Nappe Complex and the roots depth constrains its minimum thickness which is larger than earlier estimated. Furthermore, the rather undisturbed shape of the annular root pattern indicates that the SIP has not been subjected to strong tectonic reworking during the Caledonian orogeny.

  4. New insight on the recent tectonic evolution and uplift of the southern Ecuadorian Andes from gravity and structural analysis of the Neogene-Quaternary intramontane basins

    NASA Astrophysics Data System (ADS)

    Tamay, J.; Galindo-Zaldívar, J.; Ruano, P.; Soto, J.; Lamas, F.; Azañón, J. M.

    2016-10-01

    The sedimentary basins of Loja, Malacatos-Vilcabamba and Catamayo belong to the Neogene-Quaternary synorogenic intramontane basins of South Ecuador. They were formed during uplift of the Andes since Middle-Late Miocene as a result of the Nazca plate subduction beneath the South American continental margin. This E-W compressional tectonic event allowed for the development of NNE-SSW oriented folds and faults, determining the pattern and thickness of sedimentary infill. New gravity measurements in the sedimentary basins indicate negative Bouguer anomalies reaching up to -292 mGal related to thick continental crust and sedimentary infill. 2D gravity models along profiles orthogonal to N-S elongated basins determine their deep structure. Loja Basin is asymmetrical, with a thickness of sedimentary infill reaching more than 1200 m in the eastern part, which coincides with a zone of most intense compressive deformation. The tectonic structures include N-S, NW-SE and NE-SW oriented folds and associated east-facing reverse faults. The presence of liquefaction structures strongly suggests the occurrence of large earthquakes just after the sedimentation. The basin of Malacatos-Vilcabamba has some folds with N-S orientation. However, both Catamayo and Malacatos-Vilcabamba basins are essentially dominated by N-S to NW-SE normal faults, producing a strong asymmetry in the Catamayo Basin area. The initial stages of compression developed folds, reverse faults and the relief uplift determining the high altitude of the Loja Basin. As a consequence of the crustal thickening and in association with the dismantling of the top of the Andes Cordillera, extensional events favored the development of normal faults that mainly affect the basins of Catamayo and Malacatos-Vilcabamba. Gravity research helps to constrain the geometry of the Neogene-Quaternary sedimentary infill, shedding some light on its relationship with tectonic events and geodynamic processes during intramontane basin

  5. Position from gravity

    NASA Technical Reports Server (NTRS)

    Mather, R. S.

    1973-01-01

    Procedures for obtaining position from surface gravity observations are reviewed and their relevance assessed in the context of the application of modern geodetic techniques to programs of Earth and ocean physics. Solutions based on the use of surface layer techniques, the discrete value approach, and the development from Green's theorem are stated in summary, the latter being extended to order e cubed in the height anomaly. The representation of the surface gravity field which is required in order that this accuracy may be achieved is discussed. Interim techniques which could be used in the absence of such a representation are also outlined.

  6. 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.

  7. Continuity, segmentation and faulting type of active fault zones of the 2016 Kumamoto earthquake inferred from analyses of a gravity gradient tensor

    NASA Astrophysics Data System (ADS)

    Matsumoto, Nayuta; Yoshihiro, Hiramatsu; Sawada, Akihiro

    2016-10-01

    We analyze Bouguer anomalies in/around the focal region of the 2016 Kumamoto earthquake to examine features, such as continuity, segmentation and faulting type, of the active fault zones related to the earthquake. Several derivatives and structural parameters calculated from a gravity gradient tensor are applied to highlight the features. First horizontal and vertical derivatives, as well as a normalized total horizontal derivative, characterize well the continuous subsurface fault structure along the Futagawa fault zone. On the other hand, the Hinagu fault zone is not clearly detected by these derivatives, especially in the case of the Takano-Shirahata segment, suggesting a difference of cumulative vertical displacement between the two fault zones. The normalized total horizontal derivative and the dimensionality index indicate a discontinuity of the subsurface structure of the Hinagu fault zone, that is, a segment boundary between the Takano-Shirahata and the Hinagu segments. The aftershock distribution does not extend beyond this segment boundary. In other words, this segment boundary controls the southern end of the rupture area of the foreshock. We also recognize normal fault structures dipping to the northwest in some areas of the fault zones from estimations of dip angles.[Figure not available: see fulltext.

  8. Environmental applications of gravity surveying

    SciTech Connect

    Barrows, L.J. ); Nesbit, L.C. ); Khan, W.A. )

    1994-04-01

    The Allis Park Sanitary Landfill Company developed a new landfill near Onway, Michigan in an area which has glacial alluvium and glacial till overlying limestone. There are several solution karst features in the region and some critics had maintained that a new karst collapse could rupture the liner system and allow escape of leachate into the groundwater. The gravity survey was conducted to determine the extent of any karst development at the site. The first portion of the survey was two profiles over some karst features located about five miles southeast of the proposed landfill. These showed negative gravity anomalies. The survey of the proposed landfill site resulted in a 50 microGal contour map of the area and also showed a negative anomaly. This could be due to either elevation variations on the till to limestone bedrock surface or to karst development within the limestone. Because there was no evidence of historic development of new karst features in the region, the gravity anomaly was not further investigated. In another gravity survey, a large retail department store had been remodeled and extended over an area previously occupied by an auto service center. The removal of a waste oil storage tank (UST) had not been documented and the environmental consultant (KEMRON, Inc.) proposed that a gravity survey be used to find the tank location. This proposal was based on calculations of the gravity effects of a UST. The survey resulted in a four-microGal contour map which showed a couple of anomalies which could be due to a tank or a backfilled tank excavation. During the survey, a store employee identified the previous location of the tank and explained that she had personally witnessed its removal. Based on the employee's eye-witness account of the tank removal and the coincidence of her indicated tank location with one of the gravity anomalies the authors recommended the site be granted clean closure.

  9. Combined magnetic and gravity analysis

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W.; Chandler, V. W.; Mazella, F. E.

    1975-01-01

    Efforts are made to identify methods of decreasing magnetic interpretation ambiguity by combined gravity and magnetic analysis, to evaluate these techniques in a preliminary manner, to consider the geologic and geophysical implications of correlation, and to recommend a course of action to evaluate methods of correlating gravity and magnetic anomalies. The major thrust of the study was a search and review of the literature. The literature of geophysics, geology, geography, and statistics was searched for articles dealing with spatial correlation of independent variables. An annotated bibliography referencing the Germane articles and books is presented. The methods of combined gravity and magnetic analysis techniques are identified and reviewed. A more comprehensive evaluation of two types of techniques is presented. Internal correspondence of anomaly amplitudes is examined and a combined analysis is done utilizing Poisson's theorem. The geologic and geophysical implications of gravity and magnetic correlation based on both theoretical and empirical relationships are discussed.

  10. It's All Gravity

    NASA Astrophysics Data System (ADS)

    Murad, P. A.

    2003-01-01

    Newtonian gravitation adequately predicts planet and satellite motion. Gravitational anomalies and the wish to travel at relativistic speeds, however, imply that gravity should be integrated within a unification framework that may include electricity and magnetism. Thus, new theories are needed that predict currently accepted phenomenon as well as anomalies to prepare the necessary groundwork for experimental validation needed for advanced technology propulsion schemes and far-term missions. A primary deficiency is that we are obviously limited within the confines of our own solar system and a different gravity model may be applicable elsewhere in the cosmos. The model proposed here follows previous ideas proposed by Murad, Dyatlov, and Jefimenko for a universal gravitation model with an intrinsic radial force term coupled with angular momentum. Including angular momentum may explain several spin symmetries seen in some anomalous gyroscopic experiments and throughout the universe regarding planets that orbit around the sun: moons that orbit larger planetary bodies: and the rotation about each planetary axis.

  11. Altimeter and gravity data analysis

    NASA Technical Reports Server (NTRS)

    Rapp, Richard H.

    1992-01-01

    The studies carried out under this grant fell into two broad areas. The first area was the analysis of surface gravity data with the ultimate goal of providing normal equations that could be used in combination with normal equations from the analysis of satellite orbit perturbations to obtain an optimal estimate of the gravitational potential coefficients of the Earth. The second main research activity was the estimation of gravity anomalies in ocean areas from satellite altimeter data. Such anomalies could enable the improved calibration of potential coefficient models derived solely from the analysis of orbital perturbation information. The studies in these two areas are discussed.

  12. 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.

  13. 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.

  14. Gravity over coronae and chasmata on Venus

    NASA Technical Reports Server (NTRS)

    Schubert, Gerald; Moore, William B.; Sandwell, David T.

    1994-01-01

    The global spherical harmonic model of Venus' gravity field MGNP60FSAAP, with horizontal resolution of about 600 km, shows that most coronae have little or no signature in the gravity field. Nevertheless, some coronae and some segments of chasmata are associated with distinct positive gravity anomalies. No corona has been found to have a negative gravity anomaly. The spatial coincidence of the gravity highs over four closely spaced 300- to 400-km-diameter coronae in Eastern Eistla Regio with the structures themselves is remarkable and argues for a near-surface or lithospheric origin of the gravity signals over such relatively small features. Apparent depths of compensation (ADCs) of the prominent gravity anomalies at Artemis, Latona, and Heng-o Coronae are about 150 to 200 km. The geoid/topography ratios (GTRs) at Artemis, Latona, and Heng-o Coronae lie in the range 32 to 35 m/km. The large ADCs and GTRs of Artemis, Latona, and Heng-o Coronae are consistent with topographically related gravity and a thick Venus lithosphere or shallowly compensated topography and deep positive mass anomalies due to subduction of underthrusting at these coronae. At arcuate segments of Hecate and Parga Chasmata ADCs are about 125 to 150 km, while those at Fauta Corona, four coronae in Eastern Eistla Regio, and an arcuate segment of Wester Parga Chasmata are about 75 km. The GTRs at Fauta Corona, the four coronae in eastern Eistla Regio, and the accurate segments of Hecate, Parga, and Western Parga Chasmata are about 12 to 21 m/km. By analogy with gravity anomalies of similar horizontal scale (600 km-several thousand kilometers) on the concave sides of terrestrial subduction zone arcs, which are due in large part to subducted lithosphere, it is inferred that the gravity anomalies on Venus are consistent with retrograde subduction at Artemis Chasma, along the northern and southern margins of Latona Coronam, and elsewhere along Parga and Hecate Chasmata.

  15. 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.

  16. 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.

  17. New Insights into the Tectonics of the Midcontintent of U.S.A. from EarthScope USArray Seismic, Gravity, Magnetic and Heat Flow Datasets

    NASA Astrophysics Data System (ADS)

    Ravat, D.; Zhang, H.; Newman, L. C. C.; Lowry, A. R.

    2015-12-01

    We examine crustal and upper mantle structure and physical parameters from EarthScope USArray receiver functions, seismic tomography, gravity, and magnetic anomaly data to understand the tectonic framework of the midcontinent of the U.S. (New Madrid Seismic Zone/Rift Complex, Illinois Basin, Tennessee-Illinois-Kentucky Lineament (TIKL), and Grenville Front). The neodymium (Nd) crustal formation boundary seen in geochemical and the long-wavelength magnetic anomaly data is not apparent in the crustal or mantle seismic parameters or density. This is not completely surprising since the Nd systematics and magnetization is controlled by accessory minerals rather than bulk physical parameters. The USArray station spacing is not sufficient to capture the density and corresponding magnetic variations associated with mafic plutons except where stations are located over the plutons themselves (e.g., the Bloomfield Pluton). With the standard Moho density contrasts, Vp/Vs based crustal densities, and mantle velocity-density relationships, significant long-wavelength residuals (misfit) between observed and modeled Bouguer gravity anomalies remain over the Illinois Basin, the TIKL, and the Grenville Front in Ohio, extending north into Lake Erie and New York. Jointly inverted USArray receiver functions and gravity based Vp/Vs and the crustal thickness suggest that the Moho in the western Illinois basin and the Grenville Front in Ohio are thicker than previously known (about 50 km). The bottom of the strong crustal magnetization layer is unusually thin (15-20 km) in the New Madrid Seismic Zone, which extends northward from there into Illinois, northern Missouri and Indiana. In the Rough Creek Graben, the magnetic layer thickness is about 40 km, which is consistent with the non-magmatic nature of that branch of the rift. These observation may also imply that the rift related basal crustal layer in the New Madrid Seismic Zone is non-magnetic or very weakly magnetic. The thinner

  18. 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.

  19. The Mystery of the Mars North Polar Gravity-Topography Correlation(Or Lack Thereof)

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Sjogren, W. L.; Johnson, C. L.

    1999-01-01

    Maps of moderately high resolution gravity data obtained from the Mars Global Surveyor (MGS) gravity calibration orbit campaign and high precision topography obtained from the Mars Orbiter Laser Altimeter (MOLA) experiment reveal relationships between gravity and topography in high northern latitudes of Mars. Figure 1 shows the results of a JPL spherical harmonic gravity model bandpass filtered between degrees 6 and 50 contoured over a MOLA topographic image. A positive gravity anomaly exists over the main North Polar cap, but there are at least six additional positive gravity anomalies, as well as a number of smaller negative anomalies, with no obvious correlation to topography. Additional information is contained in the original extended abstract.

  20. Global variations in gravity-derived oceanic crustal thickness: Implications on oceanic crustal accretion and hotspot-lithosphere interactions

    NASA Astrophysics Data System (ADS)

    Lin, J.; Zhu, J.

    2012-12-01

    We present a new global model of oceanic crustal thickness based on inversion of global oceanic gravity anomaly with constrains from seismic crustal thickness profiles. We first removed from the observed marine free-air gravity anomaly all gravitational effects that can be estimated and removed using independent constraints, including the effects of seafloor topography, marine sediment thickness, and the age-dependent thermal structure of the oceanic lithosphere. We then calculated models of gravity-derived crustal thickness through inversion of the residual mantle Bouguer anomaly using best-fitting gravity-modeling parameters obtained from comparison with seismically determined crustal thickness profiles. Modeling results show that about 5% of the global crustal volume (or 9% of the global oceanic surface area) is associated with model crustal thickness <5.2 km (designated as "thin" crust), while 56% of the crustal volume (or 65% of the surface area) is associated with crustal thickness of 5.2-8.6 km thick (designated as "normal" crust). The remaining 39% of the crustal volume (or 26% of the surface area) is associated with crustal thickness >8.6 km and is interpreted to have been affected by excess magmatism. The percentage of oceanic crustal volume that is associated with thick crustal thickness (>8.6 km) varies greatly among tectonic plates: Pacific (33%), Africa (50%), Antarctic (33%), Australia (30%), South America (34%), Nazca (23%), North America (47%), India (74%), Eurasia (68%), Cocos (20%), Philippine (26%), Scotia (41%), Caribbean (89%), Arabian (82%), and Juan de Fuca (21%). We also found that distribution of thickened oceanic crust (>8.6 km) seems to depend on spreading rate and lithospheric age: (1) On ocean basins younger than 5 Ma, regions of thickened crust are predominantly associated with slow and ultraslow spreading ridges. The relatively strong lithospheric plate at slow and ultraslow ridges might facilitate the loading of large magmatic

  1. Inversion for sources of crustal deformation and gravity change at the Yellowstone caldera

    SciTech Connect

    Vasco, D.W.; Taylor, C.L. ); Smith, R.B. )

    1990-11-10

    The Yellowstone caldera was formed in the latest of three explosive eruptions of rhyolites and ash flow tuffs totaling 3,700 km{sup 3} at 2, 1.2, and 0.6 m.y. before present. Its youthful volcanic history, widespread hydrothermal activity, intense seismicity, and extremely high heat flow, in excess of 30 times the continental average, marks the Yellowstone volcanic system as a giant caldera at unrest. Orthometric height increases of the caldera of up to 76 cm, measured from precise leveling surveys from 1923 to 1975-1977, were inverted to determine volume expansion source models for the caldera-wide deformation. For the 1923 to 1977 uplift episode, two regions of expansion were found: (1) in the northern part of the caldera near the Sour Creek resurgent dome of {approximately}0.37 km{sub 3}, and (2) in the southern part of the caldera, near the Mallard Lake resurgent dome of {approximately}0.41 km{sub 3}. Both bodies occur in the upper crust from near-surface depths to 6.0 km, but the largest volume expansions were found in the 3.0-6.0 km depth range. The southern caldera source volume, near the Mallard Lake dome, may extend down to 9.0 km. From 1976 to 1987, nearly simultaneous measurements of elevation and gravity changes were made on a profile across the northern caldera during a period of net uplift. Models of the temporal gravity variation infer that the volume increase for the northern caldera source must lie above 9.0 km and involved a density perturbation greater than +0.002 g/cm{sup 3}. The modeled volumetric sources are in the same general locations as bodies of low P wave velocities, high seismic attenuation, and large negative Bouguer gravity anomalies. It is likely that the modeled volumetric increases were caused by migration of magmas and/or the introduction of large volumes of hydrothermal fluids into the upper crust.

  2. 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.

  3. The gravity field in Taiwan Strait

    SciTech Connect

    Su Daquan; Chen Xue; Liu Zuhui )

    1990-06-01

    Gravity surveys have been carried out in the western part of Taiwan Strait by South China Sea Institute of Oceanology, Academia Sinica, from 1986 to 1989. More than 3,000 km of gravity profile data have been collected. The accuracy of the gravity is about {plus minus}2.5 mGal. Based on these data, gravity maps of Taiwan Strait (1:2,000,000) have been compiled, combined with the data from University of Tokyo, Lamont-Doherty geological observatory, and the USSR, which were collected from the east and southeast parts of Taiwan Strait. The interval of contour is 5 mGal. These maps cover part of East China Sea and South China Sea, where good gravity data have been gathered. Comparing the data from different sources in the same area, the authors think they are in very good agreement. These maps for the first time give detailed gravity information in the Taiwan Strait. It is very useful for the tectonic study and oil exploration in this area. The relationship between gravity anomalies and sedimentary basins has been studied in this area. Most of data show that the gravity low corresponds to the basin area and the gravity high is related to tectonic structure high. Xia-Peng depression, Wuqiuy depression, and Xinzhu depression, etc., show the gravity low. The relationship also can be seen in the gravity profiles clearly. The general tendency of gravity in the Taiwan Strait is that the gravity values gradually increase from the south part to the north part. It can be probably explained by deep geological structures. The relationship between gravity and geological structure units is also studied. They think the undulation of gravity anomalies is closely related to tectonic structures. Some main faults can be confirmed by the gravity maps.

  4. The Effect of Pre-Impact Porosity and Vertical Density Gradients on the Gravity Signature of Lunar Craters

    NASA Astrophysics Data System (ADS)

    Milbury, Colleen; Johnson, Brandon C.; Melosh, H. Jay; Collins, Gareth S.; Blair, David M.; Soderblom, Jason M.; Nimmo, Francis; Phillips, Roger J.; Bierson, Carver J.; Zuber, Maria T.

    2015-11-01

    As a result of NASA’s dual spacecraft Gravity Recovery And Interior Laboratory (GRAIL) mission [Zuber et al., 2013; doi:10.1126/science.1231507], we now know that the lunar crust is highly porous and that the porosity varies laterally [Wieczorek et al., 2013; doi:10.1126/science.1231530] and vertically [Besserer et al., 2014; doi:10.1002/2014GL060240]. Analysis of complex craters located within the lunar highlands reveals that: 1) craters larger than diameter D~210 have positive Bouguer Anomalies (BAs), 2) craters with D ≲ 100 km have both positive and negative BAs that vary about the (near 0) mean by approximately ± 25 mGal, and, 3) D and BA are anticorrelated for craters with D ≲ 100 km [Soderblom et al., 2015; doi:10.1002/2015GL065022]. Numerical modeling by Milbury et al. [2015, LPSC] shows that pre-impact porosity is the dominant influence on the gravity signature of complex craters with D ≲ 100 km, and mantle uplift dominates the gravity for those with D > 140 km. Phillips et al. [2015, LPSC] showed that complex craters located in the South Pole-Aitken (SPA) basin tend to have more-negative BAs than similar craters in the highlands. We use the iSALE hydrocode including pore space compaction [Wünnemann et al., 2006; doi:10.1016/j.icarus.2005.10.013] and dilatant bulking [Collins, 2014; doi:10.1002/2014JE004708] to understand how the gravity signature of impact craters develop. In this study we vary crustal porosity with depth. We find that simulations that have constant porosity with depth have a lower BA for a given crater diameter than those with the same mean porosity, but that vary with depth. We used two different mean porosities (7% and 14%) and found that the BA increases with increasing porosity, similar to simulations with constant porosity. We reproduce the observed anticorrelation between BA and D for D ≲ 100 km only for simulations where the pre-impact porosity is zero or low. Our results support the observation that SPA has lower

  5. 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)

  6. 3D gravity inversion and Euler deconvolution to delineate the hydro-tectonic regime in El-Arish area, northern Sinai Peninsula

    NASA Astrophysics Data System (ADS)

    Khalil, Mohamed A.; Santos, Fernando M.; Farzamian, Mohammad

    2014-04-01

    Sinai Peninsula occupies a part of the arid zone belt of northern Africa and southwestern Asia. The largest ephemeral stream in the Sinai Peninsula is called Wadi El-Arish, which winds down northward to the Mediterranean Sea. The delta of Wadi El-Arish has been built by the heavy floods of the Wadi. The Quaternary aquifer is the main water supply of the delta of Wadi El-Arish and its vicinities. The combined action of aridity and extensive pumping from the Quaternary aquifer led to a noticeable increase in groundwater salinity. The hydrochemistry and isotope hydrology confirm that the Quaternary aquifer is recharged by an old saline groundwater from the Pre-Quaternary. A hydrogeological connection between Quaternary and Pre-Quaternary aquifers in the form of fault(s) should exist to explain the hydro-tectonic regime of this area. The Bouguer gravity map shows the high gravity anomaly of the doubly plunging anticline of Risan Aniza Mountain to the south of El-Arish area, which is a part of the Syrian Arc System of northern Sinai Peninsula. A 3D density contrast model, 3D Euler deconvolution, horizontal derivative and least square separation have been performed. The findings showed that (1) two deep regional faults extending NE-SW, surround the Risan Aniza anticline, and (2) two deep local N-S faults are in the area of Delta Wadi El-Arish. These deep faults are proposed to bring the deep Cretaceous aquifer into contact with the shallow Quaternary aquifer and work as a hydrogeological connection between both aquifers. The present hypothesis has some geological evidences from the subsurface lithology of the nearby wells.

  7. A regional gravity survey of the Cuyuna Iron Range, Minnesota

    USGS Publications Warehouse

    Durfee, George Austin

    1957-01-01

    A regional gravity survey of the Cuyuna Iron Range, Minnesota, was conducted during the summer of 1955 by the U. S. Geological Survey. It was believed that gravity data would aid in the understanding of the major structures of the range. It was found that synclinal and steeply dipping structures produced positive gravity anomalies while anilclinal structures produced negative anomalies. This principle was noted in areas of well known geology and then applied to outlying areas of the district. The outstanding gravity feature is a narrow positive anomaly extending from south of Brainerd eastward through Aitkin, the axis of the anomaly being somewhat south of the South Range. This gives support to the theory that the Biwabik formation passes under the stratigraphically higher South Range member as a synclinal structure. However, this anomaly is also explained using one main iron formation and assuming an anticlinal structure between the North and South Ranges and a syncline between the South Range and Bay Lake. A large magnitude negative gravity anomaly north of Mille Lacs is postulated to result from an intrusive mass extending to the erosion surface. Aeromagnetics are used to strengthen the gravity interpretation. The need is realized for additional regional gravity coverage to the east of the area Included in this survey and a detailed gravity study of the area between the North and South Ranges.

  8. Gravity Waves

    Atmospheric Science Data Center

    2013-04-19

    article title:  Gravity Waves Ripple over Marine Stratocumulus Clouds ... Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar ... that occur when a pebble is thrown into a still pond, such "gravity waves" sometimes appear when the relatively stable and stratified air ...

  9. Combined Investigation of Vs and Density Structure Beneath the Colorado Plateau Based on Gravity, Receiver Function and Rayleigh Wave Phase Velocity Data

    NASA Astrophysics Data System (ADS)

    Bailey, I. W.; Miller, M. S.; Levander, A.; Liu, K.

    2010-12-01

    The uplift of the Colorado Plateau (>1.5 km over the last ~65 Ma) in the absence of large-scale tectonic deformation has been the subject of a number of recent geodynamical studies. Seismic observational constraints in those studies, if used, are generally based on pre-USArray data. A more detailed study of the subsurface structure can provide evidence with which to discriminate between differing geodynamical interpretations. We present results from a joint inversion of surface wave and receiver function data to compute Vs in the crust and upper mantle beneath the Colorado Plateau, then compare gravity observations with predictions based on the seismic results to constrain density or possible dynamic effects. We use the Computer Programs in Seismology (Herrmann & Ammon, 2002) for the joint inversion of 50 s P receiver function gathers and Rayleigh wave phase velocities computed from a two plane-wave approximation method, both using USArray data recorded between 2004 and 2010. The receiver functions are sensitive to sharp velocity contrasts while the Rayleigh wave data are more sensitive to absolute velocities. Jointly inverting these data simultaneously minimizes misfit between the two data sets and the Vs model predictions, and can therefore use the strengths of both to better constrain the discontinuities of interest. The inversions are performed for 30 layer 1-D Vs profiles centered on each receiver gather and subsequently interpolated for the 3-D structure. Our results show a sharp increase in crustal thickness on the western edge of the plateau that increases further towards the northeast. A high velocity anomaly is observed between 75 - 100 km below the plateau which also thickens to the northeast. The Bouguer anomaly from the US Gravity database shows a general correlation with the Vs structure for 30 - 50 km depth, and we use forward calculations based on density computed from a constant Vp/Vs and Birch’s law to iteratively adjust the seismic results

  10. Magnetotelluric deep soundings, gravity and geoid in the south São Francisco craton: Geophysical indicators of cratonic lithosphere rejuvenation and crustal underplating

    NASA Astrophysics Data System (ADS)

    Pinto, Luis Gustavo Rodrigues; de Pádua, Marcelo Banik; Ussami, Naomi; Vitorello, Ícaro; Padilha, Antonio Lopes; Braitenberg, Carla

    2010-09-01

    In the south São Francisco craton a circular and 8-m amplitude geoid anomaly coincides with the outcropping terrain of an Archean-Paleoproterozoic basement. Broadband magnetotelluric (MT) data inversions of two radial profiles within the positive geoid and Bouguer gravity anomaly yield geo-electrical crustal sections, whereby the lower crust is locally more conductive (10 to 100 Ωm) in spatial coincidence with a denser lower crust modeled by the gravity data. This anomalous lower crust may have resulted from magmatic underplating, associated with Mesoarchean and Proterozoic episodes of tholeiitic dike intrusion. Long-period MT soundings reveal a low electrical resistivity mantle (20 to 200 Ωm) from depths beyond 120 km. Forward geoid modeling, using the scope of the low electrical resistivity region within the mantle as a constraint, entails a density increase (40 to 50 kg/m 3) possibly due to Fe enrichment of mantle minerals. However, this factor alone does not explain the observed resistivity. A supplemented presence of small amounts of percolated carbonatite melting (~ 0.005 vol.%), dissolved water and enhanced oxygen fugacity within the peridotitic mantle are viable agents that could explain the less resistive upper mantle. We propose that metasomatic processes confined in the sub-continental lithospheric mantle foster the conditions for a low degree melting with variable CO 2, H 2O and Fe content. Even though the precise age of this metasomatism is unknown it might be older than the Early Cretaceous based on the evidence that a high-degree of melting in a lithospheric mantle impregnated with carbonatites originated the tholeiitic dike intrusions dispersed from the southeastern border of the São Francisco craton, during the onset of the lithosphere extension and break-up of the western Gondwana. The proxies are the NE Paraná and Espinhaço (130 Ma, Ar/Ar ages) tholeiitic dikes, which contain (~ 3%) carbonatites in their composition. The occurrence of a

  11. A wavelet transformation approach for multi-source gravity fusion: Applications and uncertainty tests

    NASA Astrophysics Data System (ADS)

    Bai, Yongliang; Dong, Dongdong; Wu, Shiguo; Liu, Zhan; Zhang, Guangxu; Xu, Kaijun

    2016-05-01

    Gravity anomalies detected by different measurement platforms have different characteristics and advantages. There are different kinds of gravity data fusion methods for generating single gravity anomaly map with a rich and accurate spectral content. Former studies using wavelet based gravity fusion method which is a newly developed approach did not pay more attention to the fusion uncertainties. In this paper, we firstly introduce the wavelet based gravity fusion method, and then apply this method to one synthetic model and also to the northern margin of the South China Sea. Wavelet type and the decomposition level are two input parameters for this fusion method, and the uncertainty tests show that fusion results are more sensitive to wavelet type than the decomposition level. The optimal application result of the fusion methodology on the synthetic model is closer to the true anomaly field than either of the simulated shipborne anomaly and altimetry-based anomaly grid. The best fusion result on the northern margin of the South China Sea is based on the 'rbio1.3' wavelet and four-level decomposition. The fusion result contains more accurate short-wavelength anomalies than the altimetry-based gravity anomalies along ship tracks, and it also has more accurate long wavelength characteristics than the shipborne gravity anomalies between ship tracks. The real application case shows that the fusion result has better correspondences to the seafloor topography variations and sub-surface structures than each of the two input gravity anomaly maps (shipborne based gravity anomaly map and altimetry based gravity anomaly map). Therefore, it is possible to map and detect more precise seafloor topography and geologic structures by the new gravity anomaly map.

  12. Three-dimensional gravity ideal body studies in rough terrain

    SciTech Connect

    Ander, M.E.; Huestis, S.P.

    1985-01-01

    An approach to the interpretation of potential field anomaly data is to maximize or minimize some non-linear scalar property of solutions fitting the data. As an example, a comparison of 2-D and 3-D gravity ideal body results from the Lucero Uplift, a westward-tilted fault block located on the western flank of the Rio Grande rift, is discussed. The anomaly was analyzed to obtain bounds on the density contrast, depth of burial, and minimum thickness of its sources. Based on a synthesis of the gravity data with structural analysis and geomorphology, a shallow mafic intrusion is proposed to account for the positive gravity anomaly. 12 refs. (ACR)

  13. 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

  14. 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.

  15. Basement interpretations from airborne magnetic and gravity data over the Lambert Rift region of East Antarctica

    NASA Astrophysics Data System (ADS)

    McLean, M. A.; Wilson, C. J. L.; Boger, S. D.; Betts, P. G.; Rawling, T. J.; Damaske, D.

    2009-06-01

    Geological exposures in the Lambert Rift region of East Antarctica comprise scattered coastal outcrops and inland nunataks sporadically protruding through the Antarctic ice sheet from Prydz Bay to the southernmost end of the Prince Charles Mountains. This study utilized airborne magnetic, gravity, and ice radar data to interpret the distribution and architecture of tectonic terranes that are largely buried beneath the thick ice sheet. Free-air and Bouguer gravity data are highly influenced by the subice and mantle topography, respectively. Gravity stripping facilitated the removal of the effect of ice and Moho, and the residual gravity data set thus obtained for the intermediate crustal level allowed a direct comparison with magnetic data. Interpretation of geophysical data also provided insight into the distribution and geometry of four tectonic blocks: namely, the Vestfold, Beaver, Mawson, and Gamburtsev domains. These tectonic domains are supported by surface observations such as rock descriptions, isotopic data sets, and structural mapping.

  16. 2006 Compilation of Alaska Gravity Data and Historical Reports

    USGS Publications Warehouse

    Saltus, Richard W.; Brown, Philip J.; Morin, Robert L.; Hill, Patricia L.

    2008-01-01

    Gravity anomalies provide fundamental geophysical information about Earth structure and dynamics. To increase geologic and geodynamic understanding of Alaska, the U.S. Geological Survey (USGS) has collected and processed Alaska gravity data for the past 50 years. This report introduces and describes an integrated, State-wide gravity database and provides accompanying gravity calculation tools to assist in its application. Additional information includes gravity base station descriptions and digital scans of historical USGS reports. The gravity calculation tools enable the user to reduce new gravity data in a consistent manner for combination with the existing database. This database has sufficient resolution to define the regional gravity anomalies of Alaska. Interpretation of regional gravity anomalies in parts of the State are hampered by the lack of local isostatic compensation in both southern and northern Alaska. However, when filtered appropriately, the Alaska gravity data show regional features having geologic significance. These features include gravity lows caused by low-density rocks of Cenozoic basins, flysch belts, and felsic intrusions, as well as many gravity highs associated with high-density mafic and ultramafic complexes.

  17. Spectral regularisation: induced gravity and the onset of inflation

    SciTech Connect

    Kurkov, Max A.; Sakellariadou, Mairi E-mail: mairi.sakellariadou@kcl.ac.uk

    2014-01-01

    Using spectral regularisation, we compute the Weyl anomaly and express the anomaly generating functional of the quantum effective action through a collective scalar degree of freedom of all quantum vacuum fluctuations. Such a formulation allows us to describe induced gravity on an equal footing with the anomaly-induced effective action, in a self-consistent way. We then show that requiring stability of the cosmological constant under loop quantum corrections, Sakharov's induced gravity and Starobinsky's anomaly-induced inflation are either both present or both absent, depending on the particle content of the theory.

  18. 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.

  19. Potential causes of absolute gravity changes in Taiwan over 2004-2014

    NASA Astrophysics Data System (ADS)

    Kao, R.; Hwang, C.; Kim, J. W.; Masson, F.; Mouyen, M.

    2015-12-01

    We use absolute gravimeter (AG) and GPS observations collected from 2004 to 2014 in Taiwan to identify mass changes in connection to Moho deepening, volcanism, subsidence, earthquake and plate collision. The gravity observations are measured at sites of different geological settings under the AGTO and NGDS projects. The resulting gravity changes cannot be fully explained by vertical motions derived from GPS. Unlike previous AG gravity studies in Taiwan, we apply hydrology-induced gravity changes to raw gravity measurements using a simple model that estimates the Bouguer gravity effect due to rainfalls. Typhoon Morakot, occurring on August 8, 2009, results in torrential rainfalls and large debris flows in southern Taiwan. Morakot causes a gravity increase of 51.22 μGal near an AG site along the southern cross-island highway. The M7.0 Hengchun earthquake on December 26, 2006 causes a gravity rise of 2.32 μGal at the KDNG AG site near its epicenter. A Moho thickening rate (-0.81 μGal/yr) in central Taiwan and a deep-fault slip rate (-0.94 μGal/yr) in eastern Taiwan are postulated from the gravity changes. Other distinct gravity changes are potentially associated with the subsidence in Yunlin County (-2.73 μGal/yr), the magma coolings in Tatun Volcano Group (0.12 μGal/yr), Green Island (-2.95 μGal/yr) and Orchid Island (-0.97μGal/yr).

  20. Revisiting Gravitational Anomalies and a Potential Solution

    NASA Astrophysics Data System (ADS)

    Murad, P. A.

    2009-03-01

    Gravitational anomalies require investigation and resolution to understand the space environment if man is to travel beyond trans-lunar or trans-Mars region. This paper will provide a framework for further and more detailed evaluations. These anomalies include, a slight change in the sun's gravitational attraction observed by two Pioneer probes based upon trajectory deviations detected after being in flight for over a decade and, several events where other long-range spacecraft undergoing flybys of the Earth experience increases in velocity that could not be predicted by Newtonian gravitation. Moreover, the assumption of dark energy and dark matter supposedly explain some astronomical observations to include expansion of the cosmos on a scale of the order of galaxies, galaxy clusters and other celestial bodies at considerable distances from the Earth. If, however, gravitational waves exist, then gravity should obey a wavelike partial differential equation implying that gravity is a function of both spatial and temporal dimensions. If true, then gravity may grow or decay as a function of time in contrast to Newtonian gravitation, which has propulsion implications that may also provide a partial explanation to some of these anomalies.

  1. 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.

  2. Detailed petrophysical characterization enhances geological mapping of a buried substratum using aeromagnetic and gravity data; application to the southwestern Paris basin

    NASA Astrophysics Data System (ADS)

    Baptiste, Julien; Martelet, Guillaume; Faure, Michel; Beccaletto, Laurent; Chen, Yan; Reninger, Pierre-Alexandre

    2016-04-01

    Mapping the geometries (structure and lithology) of a buried basement is a key for targeting resources and for improving the regional geological knowledge. The Paris basin is a Mesozoic to Cenozoic intraplate basin set up on a Variscan substratum, which crops out in the surrounding massifs. We focus our study on the southwestern part of the Paris basin at its junction with the Aquitaine basin. This Mezo-Cenozoic cover separates the Armorican Massif and the Massif Central which compose of several litho-tectonic units bounded by crustal-scale shear zones. In spite of several lithological and structural correlations between various domains of the two massifs, their geological connection, hidden below the Paris basin sedimentary cover, is still largely debated. Potential field geophysics have proven effective for mapping buried basin/basement interfaces. In order to enhance the cartographic interpretation of these data, we have set up a detailed petrophysical library (field magnetic susceptibility data and density measurements on rock samples) of the Paleozoic rocks outcropping in the Variscan massifs. The combination of aeromagnetic and gravity data supported by the petrophysical signatures and field/borehole geological information, is carried out to propose a new map of the architecture of the Variscan substratum. The new synthetic map of geophysical signature of the Paris basin basement combines: i) the magnetic anomaly reduced to the pole, ii) the vertical gradient of the Bouguer anomaly and iii) the tilt derivative of the magnetic anomaly reduced to the pole. Based on this information, the Eastern extension of the major shear zones below the sedimentary cover is assessed. The petrophysical signatures were classified in three classes of magnetic susceptibility and density: low, intermediate and high. Basic rocks have high magnetization and density values whereas granite, migmatite and orthogneiss show low magnetization and density values, Proterozoic and Paleozoic

  3. 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.

  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. Venus gravity

    NASA Technical Reports Server (NTRS)

    Reasenberg, Robert D.

    1993-01-01

    The anomalous gravity field of Venus shows high correlation with surface features revealed by radar. We extract gravity models from the Doppler tracking data from the Pioneer Venus Orbiter (PVO) by means of a two-step process. In the first step, we solve the nonlinear spacecraft state estimation problem using a Kalman filter-smoother. The Kalman filter was evaluated through simulations. This evaluation and some unusual features of the filter are discussed. In the second step, we perform a geophysical inversion using a linear Bayesian estimator. To allow an unbiased comparison between gravity and topography, we use a simulation technique to smooth and distort the radar topographic data so as to yield maps having the same characteristics as our gravity maps. The maps presented cover 2/3 of the surface of Venus and display the strong topography-gravity correlation previously reported. The topography-gravity scatter plots show two distinct trends.

  6. The Effect of Pre-Impact Porosity and Vertical Density Gradients on the Gravity Signature of Lunar Craters as Seen by GRAIL

    NASA Astrophysics Data System (ADS)

    Milbury, C.; Johnson, B. C.; Melosh, H., IV; Collins, G. S.; Blair, D. M.; Soderblom, J. M.; Nimmo, F.; Bierson, C. J.; Phillips, R. J.; Zuber, M. T.

    2015-12-01

    As a result of NASA's dual spacecraft Gravity Recovery And Interior Laboratory (GRAIL) mission [Zuber et al., 2013; doi:10.1126/science.1231507], we now know that the lunar crust is highly porous and that the porosity varies laterally [Wieczorek et al., 2013; doi:10.1126/science.1231530] and vertically [Besserer et al., 2014; doi:10.1002/2014GL060240]. Analysis of complex craters located within the lunar highlands reveals that: 1) craters larger than diameter D~210 have positive Bouguer Anomalies (BAs), 2) craters with D ≲ 100 km have both positive and negative BAs that vary about the (near 0) mean by approximately ± 25 mGal, and, 3) D and BA are anticorrelated for craters with D ≲ 100 km [Soderblom et al., 2015; submitted]. Numerical modeling by Milbury et al. [2015, LPSC] shows that pre-impact porosity is the dominant influence on the gravity signature of complex craters with D ≲ 100 km, and mantle uplift dominates the gravity for those with D > 140 km. Phillips et al. [2015, LPSC] showed that complex craters located in the South Pole-Aitken (SPA) basin tend to have more-negative BAs than similar craters in the highlands. By including (pre-impact) vertical porosity/density gradients in our impact simulations, we reproduce the observed anticorrelation between BA and D for D ≲ 100 km, and the observed difference between the BAs of SPA and highland craters. We use the iSALE hydrocode including pore space compaction [Wünnemann et al., 2006; doi:10.1016/j.icarus.2005.10.013] and dilatant bulking [Collins, 2014; doi:10.1002/2014JE004708] to understand how the gravity signature of impact craters develop. In this study we vary density/porosity with depth. We find that simulations that have constant porosity with depth have a lower BA for a given crater diameter than those with varying porosity. We used two different mean porosities (7% and 14%) and found that the BA increases with increasing porosity, similar to simulations with constant porosity. Larger

  7. Gravity model studies of Newberry Volcano, Oregon

    SciTech Connect

    Gettings, M.E.; Griscom, A.

    1988-09-10

    Newberry, Volcano, a large Quaternary volcano located about 60 km east of the axis of the High Cascades volcanoes in central Oregon, has a coincident positive residual gravity anomaly of about 12 mGals. Model calculations of the gravity anomaly field suggest that the volcano is underlain by an intrusive complex of mafic composition of about 20-km diameter and 2-km thickness, at depths above 4 km below sea level. However, uplifted basement in a northwest trending ridge may form part of the underlying excess mass, thus reducing the volume of the subvolcanic intrusive. A ring dike of mafic composition is inferred to intrude to near-surface levels along the caldera ring fractures, and low-density fill of the caldera floor probably has a thickness of 0.7--0.9 km. The gravity anomaly attributable to the volcano is reduced to the east across a north-northwest trending gravity anomaly gradient through Newberry caldera and suggests that normal, perhaps extensional, faulting has occurred subsequent to caldera formation and may have controlled the location of some late-stage basaltic and rhyolitic eruptions. Significant amounts of felsic intrusive material may exist above the mafic intrusive zone but cannot be resolved by the gravity data.

  8. Gravity investigations

    SciTech Connect

    Healey, D.L.

    1983-12-31

    A large density contrast exists between the Paleozoic rocks (including the rocks of Climax stock) and less dense, Tertiary volcanic rocks and alluvium. This density contrast ranges widely, and herein for interpretive purposes, is assumed to average 0.85 Mg/m{sup 3} (megagrams per cubic meter). The large density contrast makes the gravity method a useful tool with which to study the interface between these rock types. However, little or no density contrast is discernible between the sedimentary Paleozoic rocks that surround the Climax stock and the intrusive rocks of the stock itself. Therefore the gravity method can not be used to define the configuration of the stock. Gravity highs coincide with outcrops of the dense Paleozoic rocks, and gravity lows overlie less-dense Tertiary volcanic rocks and Quaternary alluvium. The positions of three major faults (Boundary, Yucca, and Butte faults) are defined by steep gravity gradients. West of the Climax stock, the Tippinip fault has juxtaposed Paleozoic rocks of similar density, and consequently, has no expression in the gravity data in that area. The gravity station spacing, across Oak Spring Butte, is not sufficient to adequately define any gravity expression of the Tippinip fault. 18 refs., 5 figs.

  9. 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

  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. Hyperbolic Orbits and the Planetary Flylby Anomaly

    NASA Technical Reports Server (NTRS)

    Wilson, T.L.; Blome, H.J.

    2009-01-01

    Space probes in the Solar System have experienced unexpected changes in velocity known as the flyby anomaly [1], as well as shifts in acceleration referred to as the Pioneer anomaly [2-4]. In the case of Earth flybys, ESA s Rosetta spacecraft experienced the flyby effect and NASA s Galileo and NEAR satellites did the same, although MESSENGER did not possibly due to a latitudinal property of gravity assists. Measurements indicate that both anomalies exist, and explanations have varied from the unconventional to suggestions that new physics in the form of dark matter might be the cause of both [5]. Although dark matter has been studied for over 30 years, there is as yet no strong experimental evidence supporting it [6]. The existence of dark matter will certainly have a significant impact upon ideas regarding the origin of the Solar System. Hence, the subject is very relevant to planetary science. We will point out here that one of the fundamental problems in science, including planetary physics, is consistency. Using the well-known virial theorem in astrophysics, it will be shown that present-day concepts of orbital mechanics and cosmology are not consistent for reasons having to do with the flyby anomaly. Therefore, the basic solution regarding the anomalies should begin with addressing the inconsistencies first before introducing new physics.

  13. Geophysical investigations of a geothermal anomaly at Wadi Ghadir, eastern Egypt

    NASA Technical Reports Server (NTRS)

    Morgan, P.; Boulos, F. K.; Hennin, S. F.; El-Sherif, A. A.; El-Sayed, A. A.; Basta, N. Z.; Melek, Y. S.

    1984-01-01

    During regional heat flow studies a geothermal anomaly was discovered approximately 2 km from the Red Sea coast at Wadi Ghadir, in the Red Sea Hills of Eastern Egypt. A temperature gradient of 55 C/km was measured in a 150 m drillhole at this location, indicating a heat flow of approximately 175 mw/sqm, approximately four times the regional background heat flow for Egypt. Gravity and magnetic data were collected along Wadi Ghadir, and combined with offshore gravity data, to investigate the source of the thermal anomaly. Magnetic anomalies in the profile do not coincide with the thermal anomaly, but were observed to correlate with outcrops of basic rocks. Other regional heat flow and gravity data indicate that the transition from continental to oceanic type lithosphere occurs close to the Red Sea margin, and that the regional thermal anomaly is possibly related to the formation of the Red Sea.

  14. Standard model with gravity couplings

    NASA Astrophysics Data System (ADS)

    Chang, Lay Nam; Soo, Chopin

    1996-05-01

    In this paper we examine the coupling of matter fields to gravity within the framework of the standard model of particle physics. The coupling is described in terms of Weyl fermions of a definite chirality, and employs only (anti-)self-dual or left-handed spin connection fields. We review the general framework for introducing the coupling using these fields, and show that conditions ensuring the cancellation of perturbative chiral gauge anomalies are not disturbed. We also explore a global anomaly associated with the theory, and argue that its removal requires that the number of fundamental fermions in the theory must be multiples of 16. In addition, we investigate the behavior of the theory under discrete transformations P, C, and T, and discuss possible violations of these discrete symmetries, including CPT, in the presence of instantons and the Adler-Bell-Jackiw anomaly.

  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. A deterministic approach toward isostatic gravity residuals: A case study from South America

    SciTech Connect

    Chapin, D.A.

    1994-12-31

    Isostatic gravity residuals are based upon geologic models, therefore they provide a reasonable basis of comparison over large areas for reconnaissance studies. To help define the best isostatic model for South America, a new deterministic methodology overcomes the deficiencies of other empirically-based methods. The basis for the model was the Airy-Heiskanen (1958) isostatic model, which assumes that surface topography is supported by crustal thickening. The three key parameters -- (a) the crustal thickness at sea-level, (b) the surface reduction density, and (c) the density contrast between the crust and the mantle -- were determined directly from the elevation, free-air gravity, and Bouguer gravity datasets. The results of this work were not only an isostatic residual map, but methodology which cross-checks the data for quality control purposes. The final isostatic residual map can be used in confidence for basin evaluation throughout the continent of South America.

  17. Gravity and magnetic survey of the Oaxaca city region: Cenozoic horst-and-graben structure superimposed on the Oaxaca-Juarez terrane boundary, southern Mexico

    NASA Astrophysics Data System (ADS)

    Campos-Enríquez, J. O.; Belmonte-Jiménez, S. I.; Keppie, J. D.; Ortega-Gutiérrez, F.; Arzate, J. A.; Martínez-Silva, J.; Martínez-Serrano, R. G.

    2010-04-01

    A geophysical survey of the Oaxaca Fault along the north-trending Etla and Zaachila valleys area, southern Mexico, shows a series of NNW-SSE Bouguer and magnetic anomalies with steeper gradients towards the east. The Oaxaca Fault represents Tertiary extensional reactivation of the Juarez shear zone that constitutes the boundary between the Oaxaca and Juárez terranes. Cooperative interpretation of six combined gravity and magnetic NE-SW profiles perpendicular to the valleys indicates the presence of a composite depression comprising three N-S sub-basins: the northern Etla and southern Zaachila sub-basins separated by the Atzompa sub-basin. The Etla sub-basin is bounded by the moderately E-dipping, Etla Fault and the more steeply W-dipping Oaxaca Fault, which together constitute a graben that continues southwards into the Atzompa graben. The deeper Zaachila sub-basin, south of Oaxaca city, is a wide V-shaped graben with a horst in the middle. The new geophysical data suggest that the Oaxaca-Juarez terrane boundary is displaced sinistrally ca. 20 km along the E-W Donají Fault, which defines the northern boundary of the Zaachila sub-basin. On the other hand, the Oaxaca Fault may either continue unbroken southwards along the western margin of the horst in the Zaachila sub-basin or be offset along with the terrane boundary. The sinistral movement may have taken place either during the Late Mesozoic-Early Cenozoic, Laramide Orogeny as a lateral ramp in the thrust plane or under Miocene-Pliocene, NE-SW extension. The former suggests that the Donají Fault is a transcurrent fault, whereas the latter implies that it is a transfer fault. The models imply that originally the suture was continuous south of the Donaji Fault and provide a constraint for the accretion of the Oaxaca and Juarez terranes.

  18. Crustal influx, indentation, ductile thinning and gravity redistribution in a continental wedge: Building a Moldanubian mantled gneiss dome with underthrust Saxothuringian material (European Variscan belt)

    NASA Astrophysics Data System (ADS)

    Chopin, F.; Schulmann, K.; Skrzypek, E.; Lehmann, J.; Dujardin, J. R.; Martelat, J. E.; Lexa, O.; Corsini, M.; Edel, J. B.; Å TíPská, P.; Pitra, P.

    2012-02-01

    The contribution of lateral forces, vertical load, gravity redistribution and erosion to the origin of mantled gneiss domes in internal zones of orogens remains debated. In the Orlica-Śnieżnik dome (Moldanubian zone, European Variscan belt), the polyphase tectono-metamorphic history is initially characterized by the development of subhorizontal fabrics associated with medium- to high-grade metamorphic conditions in different levels of the crust. It reflects the eastward influx of a Saxothuringian-type passive margin sequence below a Teplá-Barrandian upper plate. The ongoing influx of continental crust creates a thick felsic orogenic root with HP rocks and migmatitic orthogneiss. The orogenic wedge is subsequently indented by the eastern Brunia microcontinent producing a multiscale folding of the orogenic infrastructure. The resulting kilometre-scale folding is associated with the variable burial of the middle crust in synforms and the exhumation of the lower crust in antiforms. These localized vertical exchanges of material and heat are coeval with a larger crustal-scale folding of the whole infrastructure generating a general uplift of the dome. It is exemplified by increasing metamorphic conditions and younging of 40Ar/39Ar cooling ages toward the extruded migmatitic subdomes cored by HP rocks. The vertical growth of the dome induces exhumation by pure shear-dominated ductile thinning laterally evolving to non-coaxial detachment faulting, while erosion feeds the surrounding sedimentary basins. Modeling of the Bouguer anomaly grid is compatible with crustal-scale mass transfers between a dense superstructure and a lighter infrastructure. The model implies that the Moldanubian Orlica-Śnieżnik mantled gneiss dome derives from polyphase recycling of Saxothuringian material.

  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. Gravity's overdrive

    NASA Astrophysics Data System (ADS)

    Reichhardt, Tony

    1994-03-01

    Mariner 10 traveled to Mercury by using Venus' gravity to bend its course in toward the sun, a correction that would otherwise required vast amounts of rocket fuel. For the first time, an interplanetary spacecraft changed course not with rocket fuel but by using a planet's gravitational field. That maneuver stands, along with the development of the rocket engine, as one of the keys that opened the solar system for exploration. The Pioneer, Voyager, and Galileo missions all used gravity assist, and in fact would not have been possible otherwise. Gravity assist is the most efficient form of space propulsion known. Various aspects of the developmental history of the gravity assist technique and the dispute over who should receive credit for inventing the technique are discussed.

  4. Gravity brake

    DOEpatents

    Lujan, Richard E.

    2001-01-01

    A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.

  5. Gravity waves

    NASA Technical Reports Server (NTRS)

    Fritts, David

    1987-01-01

    Gravity waves contributed to the establishment of the thermal structure, small scale (80 to 100 km) fluctuations in velocity (50 to 80 m/sec) and density (20 to 30%, 0 to peak). Dominant gravity wave spectrum in the middle atmosphere: x-scale, less than 100 km; z-scale, greater than 10 km; t-scale, less than 2 hr. Theorists are beginning to understand middle atmosphere motions. There are two classes: Planetary waves and equatorial motions, gravity waves and tidal motions. The former give rise to variability at large scales, which may alter apparent mean structure. Effects include density and velocity fluctuations, induced mean motions, and stratospheric warmings which lead to the breakup of the polar vortex and cooling of the mesosphere. On this scale are also equatorial quasi-biennial and semi-annual oscillations. Gravity wave and tidal motions produce large rms fluctuations in density and velocity. The magnitude of the density fluctuations compared to the mean density is of the order of the vertical wavelength, which grows with height. Relative density fluctuations are less than, or of the order of 30% below the mesopause. Such motions may cause significant and variable convection, and wind shear. There is a strong seasonal variation in gravity wave amplitude. Additional observations are needed to address and quantify mean and fluctuation statistics of both density and mean velocity, variability of the mean and fluctuations, and to identify dominant gravity wave scales and sources as well as causes of variability, both temporal and geographic.

  6. GRAIL Gravity Observations of Lunar Volcanic Complexes

    NASA Astrophysics Data System (ADS)

    Kiefer, W. S.; Zuber, M. T.; McGovern, P. J.; Head, J. W.

    2012-12-01

    Gravity observations by NASA's GRAIL mission are providing important new insights into the volcanic plumbing associated with major volcanic complexes on the Moon. The Marius Hills are the Moon's largest volcanic dome field, consisting of more than 250 basaltic domes and cones and 20 sinuous rilles. There are two distinct free-air gravity anomalies, with the larger anomaly (260 mGal) occurring close to the maximum concentration of volcanic domes in the northern part of the field. Much of the gravity anomaly in this area is due to buried, high density material, mapping out a sill complex with a spatial scale of 200 by 250 kilometers. For plausible choices of density contrast, the sill is more than 2 km thick in the north and 4 km thick in the south. The Aristarchus Plateau is the source for the Moon's largest pyroclastic eruption and numerous sinuous rilles. Most of the gravity anomaly on the plateau itself has relatively low amplitude (< 60 mGal) and is likely due to isostatic or flexurally supported topography. There is a significant gravity high (160 mGal) associated with the Cobra Head, which is the source region for Vallis Schröteri, the largest rille in the Aristarchus Plateau. Regions of high free-air gravity also occur in the plains wrapping around the south and east sides of the plateau and in the adjacent Harbinger Mountains/Prinz Crater volcanic field (150 mGal). These gravity highs are all likely due to buried, high density material, plausibly in the form of volcanic intrusions. The Cauchy volcanic dome complex in eastern Mare Tranquillitatis is a regional topographic high about 400 km across but a free-air gravity low (-90 mGal). Similarly, the Hortensius/Tobias Mayer volcanic field in Mare Insularum is also a free-air gravity low (-80 mGal) in its center. In both cases, this implies the presence of low density material at depth, possibly due to thicker than normal crust. The Rümker Hills in northern Oceanus Procellarum is a small basaltic dome complex

  7. Geological Features and Crustal Structure of the Cretaceous Middle Benue Trough, Nigeria: Insights from Detailed Analysis and Modelling of Magnetic and Gravity Data

    NASA Astrophysics Data System (ADS)

    Anudu, G. K.; Stephenson, R.; Macdonald, D.

    2015-12-01

    The middle Benue Trough is the middle (central) segment of the Nigerian Benue Trough, an intra-continental rift that developed during the second phase of rifting of the Gondwana supercontinent that resulted in the opening of the South Atlantic Ocean, Gulf of Guinea and separation of South America from Africa in the Late Jurassic to Early Cretaceous. Airborne magnetic and terrestrial gravity data from the area have been analysed and modelled in detail. Results obtained using a variety of edge enhancement (derivative) methods applied to high-resolution, airborne magnetic data reveal widespread magmatic intrusions (mainly volcanic/sub-volcanic rocks, with an areal extent greater than 12000 km2) and numerous geological structures. Rose (azimuth frequency) plots show that the geological structural trends are predominantly NE - SW, NW - SE and ESE - WNW with minor ENE -WSW/N - S trends and thus suggest that the area has undergone several phases of tectonic deformation at different geological times. Integrated two-dimensional (2-D) gravity and magnetic modelling along five profiles constrained by 2-D magnetic depth-to-source estimates and available seismological velocity models indicates the presence of a number of distinct crustal bodies and thin crust. Moho depth varies from ca. 21 - 29 km, while the crustal thickness ranges between ca. 19 and 29 km. Shallower Moho and thinner crust are observed along the trough axis. Results from the study also reveal that the amount of crustal thinning and crustal stretching factor (β) across the area varies from 3.3 - 14.5 km and 1.11 - 1.78, respectively. Broad positive to near positive Bouguer gravity anomalies in the region of the trough axis are due to the combined effects of dense (intermediate to basic) magmatic intrusions (both intra-sedimentary and intra-basement/crustal ones), shallow basement horsts (basement uplift zones) and thin crust replaced by dense abnormal upper mantle bodies. Reactivated intra-basement structures

  8. Evaluation of recent Earth's global gravity field models with terrestrial gravity data

    NASA Astrophysics Data System (ADS)

    Karpik, Alexander P.; Kanushin, Vadim F.; Ganagina, Irina G.; Goldobin, Denis N.; Kosarev, Nikolay S.; Kosareva, Alexandra M.

    2016-03-01

    In the context of the rapid development of environmental research technologies and techniques to solve scientific and practical problems in different fields of knowledge including geosciences, the study of Earth's gravity field models is still important today. The results of gravity anomaly modelling calculated by the current geopotential models data were compared with the independent terrestrial gravity data for the two territories located in West Siberia and Kazakhstan. Statistical characteristics of comparison results for the models under study were obtained. The results of investigations show that about 70% of the differences between the gravity anomaly values calculated by recent global geopotential models and those observed at the points in flat areas are within ±10 mGal, in mountainous areas are within ±20 mGal.

  9. Gravity field determination and error assessment techniques

    NASA Technical Reports Server (NTRS)

    Yuan, D. N.; Shum, C. K.; Tapley, B. D.

    1989-01-01

    Linear estimation theory, along with a new technique to compute relative data weights, was applied to the determination of the Earth's geopotential field and other geophysical model parameters using a combination of satellite ground-based tracking data, satellite altimetry data, and the surface gravimetry data. The relative data weights for the inhomogeneous data sets are estimated simultaneously with the gravity field and other geophysical and orbit parameters in a least squares approach to produce the University of Texas gravity field models. New techniques to perform calibration of the formal covariance matrix for the geopotential solution were developed to obtain a reliable gravity field error estimate. Different techniques, which include orbit residual analysis, surface gravity anomaly residual analysis, subset gravity solution comparisons and consider covariance analysis, were applied to investigate the reliability of the calibration.

  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. 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

  12. Holographic trace anomaly and local renormalization group

    NASA Astrophysics Data System (ADS)

    Rajagopal, Srivatsan; Stergiou, Andreas; Zhu, Yechao

    2015-11-01

    The Hamilton-Jacobi method in holography has produced important results both at a renormalization group (RG) fixed point and away from it. In this paper we use the Hamilton-Jacobi method to compute the holographic trace anomaly for four- and six-dimensional boundary conformal field theories (CFTs), assuming higher-derivative gravity and interactions of scalar fields in the bulk. The scalar field contributions to the anomaly appear in CFTs with exactly marginal operators. Moving away from the fixed point, we show that the Hamilton-Jacobi formalism provides a deep connection between the holographic and the local RG. We derive the local RG equation holographically, and verify explicitly that it satisfies Weyl consistency conditions stemming from the commutativity of Weyl scalings. We also consider massive scalar fields in the bulk corresponding to boundary relevant operators, and comment on their effects to the local RG equation.

  13. 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

  14. 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.

  15. 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

  16. 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.

  17. BF gravity

    NASA Astrophysics Data System (ADS)

    Celada, Mariano; González, Diego; Montesinos, Merced

    2016-11-01

    BF gravity comprises all the formulations of gravity that are based on deformations of BF theory. Such deformations consist of either constraints or potential terms added to the topological BF action that turn some of the gauge degrees of freedom into physical ones, particularly giving rise to general relativity. The BF formulations have provided new and deep insights into many classical and quantum aspects of the gravitational field, setting the foundations for the approach to quantum gravity known as spinfoam models. In this review, we present a self-contained and unified treatment of the BF formulations of D-dimensional general relativity and other related models, focusing on the classical aspects of them and including some new results.

  18. Gravity and magnetic evidence for a granitic intrusion near Wahmonie Site, Nevada Test Site, Nevada

    SciTech Connect

    Ponce, D.A.

    1984-10-10

    Gravity and magnetic data outline a broad anomaly near Wahmonie Site, Nye County, Nevada. A positive 15-mGal gravity anomaly with a steep western gradient and a broad magnetic anomaly coincident with the gravity high characterize the area. Two-dimensional computer models of the gravity data were made using magnetic, seismic, and electric data as independent constraints. The models indicate the presence of a shallow, relatively high density body of 2.65 kg m{sup -3} buried near Wahmonie Site. Aeromagnetic and ground magnetic data also indicate the presence of a large, shallow body. Two smaller local magnetic highs that occur along a magnetic prominence extending northward from the broad anomaly directly correlate to granodiorite outcrops. This indicates that the main anomaly is produced by a large shallow intrusion.

  19. 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.

  20. 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.

  1. Gravity settling

    DOEpatents

    Davis, Hyman R.; Long, R. H.; Simone, A. A.

    1979-01-01

    Solids are separated from a liquid in a gravity settler provided with inclined solid intercepting surfaces to intercept the solid settling path to coalesce the solids and increase the settling rate. The intercepting surfaces are inverted V-shaped plates, each formed from first and second downwardly inclined upwardly curved intersecting conical sections having their apices at the vessel wall.

  2. Simulating Gravity

    ERIC Educational Resources Information Center

    Pipinos, Savas

    2010-01-01

    This article describes one classroom activity in which the author simulates the Newtonian gravity, and employs the Euclidean Geometry with the use of new technologies (NT). The prerequisites for this activity were some knowledge of the formulae for a particle free fall in Physics and most certainly, a good understanding of the notion of similarity…

  3. Quantum Gravity

    NASA Astrophysics Data System (ADS)

    Goradia, Shantilal

    2009-11-01

    The continuing search for quantum gravity and never ending attempts to unify gravity with other forces of nature represent tremendous waste of public and private funds directing students' energy towards non-creative manipulative work instead of learning from the scientific creativity in Einstein's 1919 paper that unifies gravity with nuclear force. It reflects Einstein's 1919 jump beyond his own 1915 theory of gravity, including that of Newton as implicitly demanded by Newton in 1686. Einstein corrected and retracted his 1917 introduction of cosmological constant in 1919. Dislike of the fact that Einstein did not use quantum mechanics to prove his point has no real value now, because we will use key ingredients (Planck scale and probabilistic aspect) of quantum mechanics and show that they reach the same conclusion. Newton explained the solar system known after Kepler. Likewise, our quantum mechanical approach explains the strong coupling as well the solar system and shows new horizons, otherwise unexplained. Explanation of unexplained observations need no prediction per Hawking, and obviously otherwise.

  4. Massive gravity

    NASA Astrophysics Data System (ADS)

    Mukohyama, Shinji

    2013-09-01

    The concept of mass has been central in many areas of physics. Gravitation is not an exception, and it has been one of the long-standing questions whether the graviton, a spin-2 particle that mediates gravity, can have a non-vanishing mass or not. This question is relevant from not only theoretical but also phenomenological viewpoints, since a nonzero graviton mass may lead to late-time acceleration of the universe and thus may be considered as an alternative to dark energy. In 2010, de Rham, Gabadadze and Tolley proposed the first example of a fully nonlinear massive gravity theory and showed that the so called Boulware-Deser ghost, which had been one of the major obstacles against a stable nonlinear theory of massive gravity since 1972, can be removed by construction. Since then, nonlinear massive gravity has been attracting significant interest among physicists and cosmologists. The nonlinear theory of massive gravity provides a theoretical framework in which properties of the remaining five physical degrees of freedom of massive gravity can be studied. As always with any low-energy effective theories, one of the first tasks would be to identify good and bad backgrounds. Depending on the choice of backgrounds, some of the five degrees of freedom may become strongly coupled, may exhibit instantaneous propagation, or may lead to ghost/gradient instabilities. A related subject is to seek interesting solutions such as those relevant for astrophysical objects and those describing self-accelerating cosmology. Those solutions will allow us to study phenomenological and cosmological implications of the theory. Yet another important task would be to seek a possible (partial) UV completion that can be applied beyond the regime of validity of the low-energy effective theory that we currently know of. We invited articles to cover those important subjects in massive gravity. Given the recent rapid developments in the field, however, it must be noted that this focus issue

  5. Gravity inversion for modelling of subsurface structures associated to the volcanic evolution of La Gomera island (Canarian Archipelago, Spain)

    NASA Astrophysics Data System (ADS)

    Montesinos, F. G.; Arnoso, J.; Luque, T.; Benavent, T.; Vieira, R.

    2009-04-01

    basic and ultramafic complex could represent uplifted fragments of the deep crust or the upper mantle under the sea floor. The Basal Complex represents the submarine growth stage (the Submarine Edifice) and the hypabyssal roots of the different growth stages recorded in the island. Next, the first subaerial edifice was built up in two main stages. The first stage is represented by a large basaltic shield, of about 22 km in diameter, whose centre would be located near Vallehermoso Caldera (at the North of island) and would probably be extended some 5 km offshore the present northern coastline. Over the second growth stage an edifice of 25 km in diameter partly capped the earlier one. The second large edifice (the Young Edifice) emitted lava flows that covered up the central and southern areas of the island whilst they only filled deep ravines already excavated on the northern flank. The fact of La Gomera having an almost circular shape has traditionally been interpreted as the result of the built up of a single large volcanic edifice. However, the study of several authors about radial swarms of basic dikes shows that the island has gradually grown southwards but, because of the slow displacement of the magmatic focus, La Gomera does not display the N-S elongated shape which would be expected. In order to obtain a better knowledge about these volcanic and tectonic processes in the island, we have achieved a gravity survey to apply inversion techniques,which provide us a model of the crustal structures. The gravity data set, from the Institute of Astronomy and Geodesy (CSIC-UCM) and the Spanish National Geographic Institute, corresponds to 192 stations distributed over the whole island, although they are strongly conditioned by the sharp topography. Also, 899 marine gravity data from US Geological Survey have been used here. The obtained Bouguer anomaly map is analysed by means of a least squares prediction calculating a mean level of uncorrelated observational noise of 1

  6. 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.

  7. 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.

  8. Global gravity field recovery from the ARISTOTELES satellite mission

    NASA Astrophysics Data System (ADS)

    Visser, P. N. A. M.; Wakker, K. F.; Ambrosius, B. A. C.

    1994-02-01

    One of the primary objectives of the future ARISTOTELES satellite mission is to map Earth's gravity field with high resolution and accuracy. In order to achieve this objective, the ARISTOTELES satellite will be equipped with a gravity gradiometer and a Global Positioning System (GPS) receiver. Global gravity field error analyses have been performed for several combinations of gradiometer and GPS observations. These analyses indicated that the bandwidth limitation of the gradiometer prevents a stable high-accuracy, high-resolution gravity solution if no additional information is available. However, with the addition of high-accuracy GPS observations, a stable gravity field solution can be obtained. A combination of the measurements acquired by the high-quality GPS receiver and the bandwidth-limited gradiometer on board ARISTOTELES will yield a global gravity field model with a resolution of less than 100 km and with an accuracy of better than 5 mGal for gravity anomalies and 10 cm for geoid undulations.

  9. 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.

  10. Global detailed gravimetric geoid. [based on gravity model derived from satellite tracking and surface gravity data

    NASA Technical Reports Server (NTRS)

    Vincent, S.; Marsh, J. G.

    1973-01-01

    A global detailed gravimetric geoid has been computed by combining the Goddard Space Flight Center GEM-4 gravity model derived from satellite and surface gravity data and surface 1 deg-by-1 deg mean free air gravity anomaly data. The accuracy of the geoid is + or - 2 meters on continents, 5 to 7 meters in areas where surface gravity data are sparse, and 10 to 15 meters in areas where no surface gravity data are available. Comparisons have been made with the astrogeodetic data provided by Rice (United States), Bomford (Europe), and Mather (Australia). Comparisons have also been carried out with geoid heights derived from satellite solutions for geocentric station coordinates in North America, the Caribbean, Europe, and Australia.

  11. The Interpretation of Enceladus Gravity (Invited)

    NASA Astrophysics Data System (ADS)

    Stevenson, D. J.; Iess, L.; Parisi, M.; Ducci, M.; Asmar, S. W.

    2013-12-01

    The determination of the gravity field by Cassini is challenging because of the small mass and short duration of the gravitational interaction, even with data from three encounters. E19 data have been successfully integrated into the multiarc analysis, providing a stable and consistent gravity field. This required inclusion of the effect of atmospheric drag due to Enceladus' plumes. This presentation will deal only with the interpretation of these data. The dominant features of the non-central gravity are large values for the harmonic coefficients J2 and C22 and a much smaller but statistically significant negative J3. The value of J2/C22=3.55×0.05 is moderately in excess of the value of 10/3 that applies to a synchronously rotating body with no lateral variation in material properties. Given the obvious latitudinal variation of Enceladus' physical characteristics, primarily expressed by the activity centered on the South Pole, it is plausible that the deviation from 10/3 arises primarily because of a positive anomaly in J2 rather than any anomaly in C22. However, applying Radau-Darwin to the value of C22/q (where q is the usual dimensionless measure of the centrifugal effect on gravity) implies that the moment of inertia is about 0.34MR^2. The high heat output and indirect inference for liquid water suggests a fully differentiated Enceladus. For the known mean density and any plausible mantle density, this would require an unreasonably low core density of 2.5 g/cc or less. A more realistic interpretation is that both J2 and C22 are modestly non-hydrostatic, but that J2 is affected more because of a negative mass anomaly in the Southern hemisphere, consistent with the observed negative J3. One non-unique way to reconcile the observed gravity with a realistic MOI of 0.32 to 0.33MR^2 is to assume that the rocky core of Enceladus has retained some memory of a previous faster rotational state. Even if the ice shell is perfectly relaxed, this reconciles the data for a

  12. 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.

  13. Geochemical and geophysical anomalies in the western part of the Sheep Creek Range, Lander County, Nevada

    USGS Publications Warehouse

    Gott, Garland Bayard; Zablocki, Charles J.

    1968-01-01

    Extensive geochemical anomalies are present along the west side of the Sheep Creek Range in Lander County, Nev. Anomalous concentrations of zinc, arsenic, mercury, silver, copper, lead, and to some extent gold, molybdenum, and antimony occur in iron-rich material along fracture planes and in quartz veins in Paleozoic formations. A magnetic anomaly occurs over a pediment at the southern part of the range, close to one of the geochemical anomalies. Gravity and electrical resistivity measurements suggest that the magnetic anomaly is caused by an intrusive igneous mass rather than by a block of downfaulted basalt. A limited amount of shallow drilling would clarify the geochemical and geophysical data.

  14. Major results of gravity and magnetic studies at Yucca Mountain, Nevada

    USGS Publications Warehouse

    Oliver, H.W.; Ponce, D.A.; Sikora, R.F.; ,

    1991-01-01

    About 4,000 gravity stations have been obtained at Yucca Mountain and vicinity since the beginning of radioactive-waste studies there in 1978. These data have been integrated with data from about 29,000 stations previously obtained in the surrounding region to produce a series of Bouguer and isostatic-residual-gravity maps of the Nevada Test Site and southeastern Nevada. Yucca Mountain is characterized by a WNW-dipping gravity gradient whereby residual values of -10 mGal along the east edge of Yucca Mountain decrease to about -38 mGal over Crater Flat. Using these gravity data, two-dimensional modeling predicted the depth to pre-Cenozoic rocks near the proposed repository to be about 1,220??150 m, an estimate that was subsequently confirmed by drilling to be 1,244 m. Three-dimensional modeling of the gravity low over Crater Flat indicates the thickness of Cenozoic volcanic rocks and alluvial cover to be about 3,000 m. Gravity interpretations also identified the Silent Canyon caldera before geologic mapping of Pahute Mesa and provided an estimate of the thickness of the volcanic section there of nearly 5 km.

  15. Expanding Gravity

    NASA Astrophysics Data System (ADS)

    Aisenberg, Sol

    2005-04-01

    Newton's gravitational constant Gn and Laws of Gravity are based upon observations in our solar system. Mysteries appear when they are used far outside our solar system Apparently, Newton's gravitational constant can not be applied at large distances. Dark matter was needed to explain the observed flat rotational velocity curves of spiral galaxies (Rubin), and of groups of remote galaxies (Zwicky). Our expansion of Newton's gravitational constant Gn as a power series in distance r, is sufficient to explain these observations without using dark matter. This is different from the MOND theory of Milgrom involving acceleration. Also, our Expanded Gravitational Constant (EGC) can show the correct use of the red shift. In addition to the Doppler contribution, there are three other contributions and these depend only upon gravity. Thus, velocity observations only based on the red shift can not be used to support the concept of the expanding universe, the accelerating expansion, or dark energy. Our expanded gravity constant can predict and explain Olbers' paradox (dark sky), and the temperature of the CMB (cosmic microwave background). Thus, CMB may not support the big bang and inflation.

  16. Looking beneath Snake River Plain using gravity and magnetic methods Murari Khatiwada and G. Randy Keller, ConocoPhillips School of Geology and Geophysics, University of Oklahoma, Norman, OK 73069

    NASA Astrophysics Data System (ADS)

    Khatiwada, M.; Keller, G.

    2010-12-01

    Tectonic evolution and structural complexities of the Snake River Plain (SRP), the role of extension in its formation, and the effects of the YellowStone (YS) hotspot track have been a topic of scientific discussion for decades. In this research, we are addressing some of these issues by focusing on the Western Snake River Plain (WRSP) using a pre-existing gravity and magnetic database compiled through a community effort. These data are available at the Pan American Center for Environmental studies (http://research.utep.edu/paces). In the regional context of the SRP, the Complete Bouguer Anomaly (CBA) ranges by about 210 mGal with the highest value in the vicinity of the WRSP. We used upward continuation filters, bandpass filters, and directional derivative filters to delineate features by wavelength and trend. Total Magnetic Intensity (TMI) was also analyzed. The magnetic intensity ranges over 600 nT with much more complex and erratic magnetic signatures that arise from the shallow basalt and rhyolite deposits within the region. We used pseudogravity and tilt derivative filters for further processing of the magnetic data. We are able to identify the major structural components in the area using gravity and magnetic data and their processing. The bounding normal faults of the WSRP are well observed. We constructed an axial gravity profile along the SRP starting at Walla Walla, Washington and extending through Yellowstone to Reygate, Montana. CBA values along this profile show that the western and central sections of the SPR have higher gravity anomaly values than the eastern sections and the YS area. We used forward gravity modeling of the subsurface structures across the WSRP starting from the Basin and Range province on the southwest to the Atlanta Lobe of the Idaho Batholith on the northeast. From the model, we observed that the Moho depth increases northeastward and varies between 30 and 46 km along the profile. These results match with receiver function Moho

  17. Cosmological hints of modified gravity?

    NASA Astrophysics Data System (ADS)

    Di Valentino, Eleonora; Melchiorri, Alessandro; Silk, Joseph

    2016-01-01

    The recent measurements of cosmic microwave background (CMB) temperature and polarization anisotropies made by the Planck satellite have provided impressive confirmation of the Λ CDM cosmological model. However interesting hints of slight deviations from Λ CDM have been found, including a 95% C.L. preference for a "modified gravity" (MG) structure formation scenario. In this paper we confirm the preference for a modified gravity scenario from Planck 2015 data, find that modified gravity solves the so-called Alens anomaly in the CMB angular spectrum, and constrains the amplitude of matter density fluctuations to σ8=0.81 5-0.048+0.032 , in better agreement with weak lensing constraints. Moreover, we find a lower value for the reionization optical depth of τ =0.059 ±0.020 (to be compared with the value of τ =0.079 ±0.017 obtained in the standard scenario), more consistent with recent optical and UV data. We check the stability of this result by considering possible degeneracies with other parameters, including the neutrino effective number, the running of the spectral index and the amount of primordial helium. The indication for modified gravity is still present at about 95% C.L., and could become more significant if lower values of τ were to be further confirmed by future cosmological and astrophysical data. When the CMB lensing likelihood is included in the analysis the statistical significance for MG simply vanishes, indicating also the possibility of a systematic effect for this MG signal.

  18. Is nonrelativistic gravity possible?

    SciTech Connect

    Kocharyan, A. A.

    2009-07-15

    We study nonrelativistic gravity using the Hamiltonian formalism. For the dynamics of general relativity (relativistic gravity) the formalism is well known and called the Arnowitt-Deser-Misner (ADM) formalism. We show that if the lapse function is constrained correctly, then nonrelativistic gravity is described by a consistent Hamiltonian system. Surprisingly, nonrelativistic gravity can have solutions identical to relativistic gravity ones. In particular, (anti-)de Sitter black holes of Einstein gravity and IR limit of Horava gravity are locally identical.

  19. QCD trace anomaly

    SciTech Connect

    Andersen, Jens O.; Leganger, Lars E.; Strickland, Michael; Su, Nan

    2011-10-15

    In this brief report we compare the predictions of a recent next-to-next-to-leading order hard-thermal-loop perturbation theory (HTLpt) calculation of the QCD trace anomaly to available lattice data. We focus on the trace anomaly scaled by T{sup 2} in two cases: N{sub f}=0 and N{sub f}=3. When using the canonical value of {mu}=2{pi}T for the renormalization scale, we find that for Yang-Mills theory (N{sub f}=0) agreement between HTLpt and lattice data for the T{sup 2}-scaled trace anomaly begins at temperatures on the order of 8T{sub c}, while treating the subtracted piece as an interaction term when including quarks (N{sub f}=3) agreement begins already at temperatures above 2T{sub c}. In both cases we find that at very high temperatures the T{sup 2}-scaled trace anomaly increases with temperature in accordance with the predictions of HTLpt.

  20. 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.

  1. Weyl anomaly and initial singularity crossing

    NASA Astrophysics Data System (ADS)

    Awad, Adel

    2016-04-01

    We consider the role of quantum effects, mainly, Weyl anomaly in modifying Friedmann-Lemaitre-Robertson-Walker (FLRW) model singular behavior at early times. Weyl anomaly corrections to FLRW models have been considered in the past, here we reconsider this model and show the following: The singularity of this model is weak according to Tipler and Krolak, therefore, the spacetime might admit a geodesic extension. Weyl anomaly corrections change the nature of the initial singularity from a big bang singularity to a sudden singularity. The two branches of solutions consistent with the semiclassical treatment form a disconnected manifold. Joining these two parts at the singularity provides us with a C1 extension to nonspacelike geodesics and leaves the spacetime geodesically complete. Using Gauss-Codazzi equations one can derive generalized junction conditions for this higher-derivative gravity. The extended spacetime obeys Friedmann and Raychaudhuri equations and the junction conditions. The junction does not generate Dirac delta functions in matter sources which keeps the equation of state unchanged.

  2. Towards 3D multi-scale teleseismic and gravity data inversion using hybrid DSM/SPECFEM technique : application to the Pyrenees

    NASA Astrophysics Data System (ADS)

    Martin, Roland; Monteiller, Vadim; Chevrot, Sébastien; Wang, Yi; Komatitsch, Dimitri; Dufréchou, Grégory

    2015-04-01

    . The idea is to constrain the densities and the wave speeds simultaneously by a joint inversion of seismic waveforms and gravity data. The novelty of the approach is to improve tomographic images by using a full waveform inversion which provides finely resolved images of lithospheric structures, including the geometry of the main seismic interfaces such as the Moho. We take the spectral finite element SPECFEM3D package to model the wave propagation at the regional scale and we use MPI-based PRACE parallel platforms. This new tomographic approach has been applied to the Pyrenees, which thanks to the PYROPE and IBERARRAY experiments, has been densely covered by seismological probes. The gravimetric data come from the BGI. In this region, strong Bouguer gravity anomalies and strong constrasts in first P wave arrival time delays are observed. We have been able to identify, through reverse-time migration and also some first full waveform inversions using the adjoint theory, that strong Moho jumps from 25 down 60 kms depths can be detected at different locations around the France-Spain border.

  3. Predicting gravity and sediment thickness in Afghanistan

    NASA Astrophysics Data System (ADS)

    Jung, W.; Brozena, J.; Peters, M.

    2013-02-01

    The US Naval Research Laboratory conducted comprehensive high-altitude (7 km above mean sea level) aero-geophysical surveys over Afghanistan in 2006 (Rampant Lion I). The surveys were done in collaboration with the US Geological Survey and upon the request of Islamic Republic of Afghanistan Ministry of Mines. In this study, we show that a best fitting admittance between topography and airborne gravity in western Afghanistan can be used to predict airborne gravity for the no-data area of eastern Afghanistan where the mountains are too high to conduct airborne surveys, due to the threat of ground fire. The differences between the airborne and the predicted gravity along a tie-track through the no-data area were found to be within ±12 mGal range with rms difference 7.3 mGal, while those between the predicted gravity from a simple Airy model (with compensation depth of 32 km and crustal density of 2.67 g cm-3) and the airborne gravity were within ±22 mGal range with rms difference 10.3 mGal. A combined airborne free-air anomaly has been constructed by merging the predicted gravity with the airborne data. We also demonstrate that sediment thickness can be estimated for basin areas where surface topography and airborne free-air anomaly profiles do not show a correlation presumably because of thick sediments. In order to estimate sediment thickness, we first determine a simple linear relationship from a scatter plot of the airborne gravity points and the interpolated Shuttle Radar Topography Mission (SRTM) topography along the Rampant Lion I tracks, and computed corresponding quasi-topography tracks by multiplying the linear relationship with the airborne free-air anomalies. We then take the differences between the SRTM and quasi-topography as a first-order estimate of sediment thickness. A global gravity model (GOCO02S), upward continued to the same altitude (7 km above mean sea level) as the data collection, was compared with the low-pass filtered (with cutoff

  4. Gravity and Magnetic Surveys Over the Santa Rita Fault System, Southeastern Arizona

    USGS Publications Warehouse

    Hegmann, Mary

    2001-01-01

    Gravity and magnetic surveys were performed in the northeast portion of the Santa Rita Experimental Range, in southeastern Arizona, to identify faults and gain a better understanding of the subsurface geology. A total of 234 gravity stations were established, and numerous magnetic data were collected with portable and truck-mounted proton precession magnetometers. In addition, one line of very low frequency electromagnetic data was collected together with magnetic data. Gravity anomalies are used to identify two normal faults that project northward toward a previously identified fault. The gravity data also confirm the location of a second previously interpreted normal fault. Interpretation of magnetic anomaly data indicates the presence of a higher-susceptibility sedimentary unit located beneath lowersusceptibility surficial sediments. Magnetic anomaly data identify a 1-km-wide negative anomaly east of these faults caused by an unknown source and reveal the high variability of susceptibility in the Tertiary intrusive rocks in the area.

  5. Gravity changes in mid-west Greenland from GOCE gravity model and gradient data using ground and airborne gravity.

    NASA Astrophysics Data System (ADS)

    Tscherning, Carl Christian; Herceg, Matija

    2014-05-01

    GOCE (ESA's Gravity and Ocean Circulation Explorer) TRF (terrestrial reference frame) vertical anomalous gradients (Tzz) from the periods winter 2009 and summer 2012 have been used to determine gravity anomalies in mid-west Greenland, where a large mass-loss has been detected using GRACE. As additional data were used the GOCE DIR-3 model and ground gravity at the coast on solid rock, where no mass loss is expected. The methods of Least-Squares Collocation (LSC) and the Reduced Point Mass (RPM) methods have been used, however only LSC included the ground data. The latter method also permits the computation of error-estimates, which range from 3 mgal at the coast to 19 mgal 75 km from the coast in Eastern direction towards the ice-cap. The gravity anomaly differences vary from -30 mgal to 30 mgal. It is negative (showing mass loss) around the Jacobshavn Isbrae (latitude 69o15', longitude 49o W-50oW, where the yearly mass-loss has been estimated to correspond to -2 mgal, i.e. about -7 mgal for the period considered. The computed change range from 0 to -10 mgal in the area, with the error estimated to increase from 4 mgal to 15 mgal from West to East. This shows the capability of using GOCE Tzz and ground gravity to determine mass changes. The GOCE DIR-3 model was also used to evaluate gravity values in the points of the Greenland airborne gravity survey performed in 1991 and 1992. The differences had a mean value of 0.9 and a standard deviation of 17.3 mgal for all of Greenland. In the South-West area the mean of the differences was 0.15 and the standard deviation 7.14. This indicate that possibly no total mass loss has occurred in Greenland from 1992 to 2012.

  6. Vascular Anomalies and Airway Concerns

    PubMed Central

    Clarke, Caroline; Lee, Edward I.; Edmonds, Joseph

    2014-01-01

    Vascular anomalies, both tumors and malformations, can occur anywhere in the body, including the airway, often without any external manifestations. However, vascular anomalies involving the airway deserve special consideration as proper recognition and management can be lifesaving. In this article, the authors discuss vascular anomalies as they pertains to the airway, focusing on proper diagnosis, diagnostic modalities, and therapeutic options. PMID:25045336

  7. Anisotropy in Gravity and Holography

    NASA Astrophysics Data System (ADS)

    Melby-Thompson, Charles Milton

    the relationship between Hořava-Lifshitz gravity and holographic duals for anisotropic systems. A holographic correspondence is one that posits an equivalence between a theory of gravity on a given spacetime background and a field theory living on the "boundary" of that spacetime, which resides at infinite spatial separation from the interior. It is a non-trivial problem how to define this boundary, but in the case of relativistic boundary field theories, there is a well-known definition due to Penrose of the boundary which produces the geometric structure required to make sense of the correspondence. However, the proposed dual geometries to anisotropic quantum field theories have a Penrose boundary that is incompatible with the assumed correspondence. We generalize Penrose's approach, using concepts from Hořava-Lifshitz gravity, to spacetimes with anisotropic boundary conditions, thereby arriving at the concept of anisotropic conformal infinity that is compatible with the holographic correspondence in these spacetimes. We then apply this work to understanding the structure of holography for anisotropic systems in more detail. In particular, we examine the structure of divergences of a certain theory of gravity on Lifshitz space. We find, using our construction of anisotropic conformal infinity, that the appropriate geometric structure of the boundary is that of a foliated spacetime with an anisotropic metric complex. We then perform holographic renormalization in these spacetimes, yielding a computation of the divergent part of the effective action, and find that it exhibits precisely the structure of a Hořava-Lifshitz action. Moreover, we find that, for dynamical exponent z = 2, the logarithmic divergence gives rise to a conformal anomaly in 2+1 dimensions, whose general form is precisely that of conformal Hořava-Lifshitz gravity with detailed balance.

  8. 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.

  9. Could the Pioneer anomaly have a gravitational origin?

    SciTech Connect

    Tangen, Kjell

    2007-08-15

    If the Pioneer anomaly has a gravitational origin, it would, according to the equivalence principle, distort the motions of the planets in the Solar System. Since no anomalous motion of the planets has been detected, it is generally believed that the Pioneer anomaly can not originate from a gravitational source in the Solar System. However, this conclusion becomes less obvious when considering models that either imply modifications to gravity over long distances or gravitational sources localized to the outer Solar System, given the uncertainty in the orbital parameters of the outer planets. Following the general assumption that the Pioneer spacecraft move geodesically in a spherically symmetric space-time metric, we derive the metric disturbance that is needed in order to account for the Pioneer anomaly. We then analyze the residual effects on the astronomical observables of the three outer planets that would arise from this metric disturbance, given an arbitrary metric theory of gravity. Providing a method for comparing the computed residuals with actual residuals, our results imply that the presence of a perturbation to the gravitational field necessary to induce the Pioneer anomaly is in conflict with available data for the planets Uranus and Pluto, but not for Neptune. We therefore conclude that the motion of the Pioneer spacecraft must be nongeodesic. Since our results are model-independent within the class of metric theories of gravity, they can be applied to rule out any model of the Pioneer anomaly that implies that the Pioneer spacecraft move geodesically in a perturbed space-time metric, regardless of the origin of this metric disturbance.

  10. Digital Isostatic Gravity Map of the Nevada Test Site and Vicinity, Nye, Lincoln, and Clark Counties, Nevada, and Inyo County, California

    USGS Publications Warehouse

    Ponce, David A.; Mankinen, E.A.; Davidson, J.G.; Morin, R.L.; Blakely, R.J.

    2000-01-01

    An isostatic gravity map of the Nevada Test Site area was prepared from publicly available gravity data (Ponce, 1997) and from gravity data recently collected by the U.S. Geological Survey (Mankinen and others, 1999; Morin and Blakely, 1999). Gravity data were processed using standard gravity data reduction techniques. Southwest Nevada is characterized by gravity anomalies that reflect the distribution of pre-Cenozoic carbonate rocks, thick sequences of volcanic rocks, and thick alluvial basins. In addition, regional gravity data reveal the presence of linear features that reflect large-scale faults whereas detailed gravity data can indicate the presence of smaller-scale faults.

  11. Models for Near-Ridge Seamounts Constrained by Gravity Observations

    NASA Astrophysics Data System (ADS)

    Kostlan, M.; McClain, J. S.

    2009-12-01

    In an analysis of the seamount chain centered at 105°20’W, 9°05’N, west of the East Pacific Rise and south of the Clipperton transform fault, we compared measured free air gravity anomaly values with modeled gravity anomaly values. The seamount chain contains approximately ten seamounts trending roughly east-west, perpendicular to the mid-ocean ridge axis. They lie on lithosphere between 1.5 and 2.7 Ma in age. Based on its position and age, the seamount chain appears to be associated with the 9°03’N overlapping spreading center (OSC). This OSC includes several associated seamount chains, aligned generally east-west, and of varying ages. The observed data include both free air gravity anomalies and bathymetry of the seamount chain, provided by the National Geophysical Data Center (NGDC), and was selected because the gravity measurements are relatively well covered. We used a series of different structural models of the oceanic crust and mantle to generate gravity anomalies associated with the sea mounts. The models utilize Parker’s algorithm to generate these free air gravity anomalies. We compute a gravity residual by subtracting the calculated anomalies from the observed anomalies. The models include one with a crust of a constant thickness (6 km), while another introduces a constant-thickness Layer 2A. In contrast, a third model included a variable thickness crust, where the thickness is governed by Airy compensation. The calculations show that the seamounts must be partly compensated, because the constant-thickness models predict a high negative residual (or they produce an anomaly which is too high). In contrast, the Airy compensation model produces an anomaly that is too low at the longer wavelengths, indicating that the lithosphere must have some strength, and that flexure must be supporting part of the load of the seamount chain. This contrasts with earlier studies that indicate young, near-ridge seamounts do not result in flexure of the thin

  12. Waste Isolation Pilot Plant (WIPP) site gravity survey and interpretation

    SciTech Connect

    Barrows, L.J.; Fett, J.D.

    1983-04-01

    A portion of the WIPP site has been extensively surveyed with high-precision gravity. The main survey (in T22S, R31E) covered a rectangular area 2 by 4-1/3 mi encompassing all of WIPP site Zone II and part of the disturbed zone to the north of the site. Stations were at 293-ft intervals along 13 north-south lines 880 ft apart. The data are considered accurate to within a few hundredths of a milligal. Long-wavelength gravity anomalies correlate well with seismic time structures on horizons below the Castile Formation. Both the gravity anomalies and the seismic time structures are interpreted as resulting from related density and velocity variations within the Ochoan Series. Shorter wavelength negative gravity anomalies are interpreted as resulting from bulk density alteration in the vicinity of karst conduits. The WIPP gravity survey was unable to resolve low-amplitude, long-wavelength anomalies that should result from the geologic structures within the disturbed zone. It did indicate the degree and character of karst development within the surveyed area.

  13. Geopotential field anomalies and regional tectonic features - two case studies: southern Africa and Germany

    NASA Astrophysics Data System (ADS)

    Korte, Monika; Mandea, Mioara

    2016-05-01

    Maps of magnetic and gravity field anomalies provide information about physical properties of the Earth's crust and upper mantle, helpful in understanding geological conditions and tectonic structures. Depending on data availability, whether from the ground, airborne, or from satellites, potential field anomaly maps contain information on different ranges of spatial wavelengths, roughly corresponding to sources at different depths. Focussing on magnetic data, we compare amplitudes and characteristics of anomalies from maps based on various available data and as measured at geomagnetic repeat stations. Two cases are investigated: southern Africa, characterized by geologically old cratons and strong magnetic anomalies, and the smaller region of Germany with much younger crust and weaker anomalies. Estimating lithospheric magnetic anomaly values from the ground stations' time series (repeat station crustal biases) reveals magnetospheric field contributions causing time-varying offsets of several nT in the results. Similar influences might be one source of discrepancy when merging anomaly maps from different epochs. Moreover, we take advantage of recently developed satellite potential field models and compare magnetic and gravity gradient anomalies of ˜ 200 km resolution. Density and magnetization represent independent rock properties and thus provide complementary information on compositional and structural changes. 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 in the southern African region than the German region. This probably indicates stronger concordance between near-surface (down to at most a few km) and deeper (several kilometres down to Curie depth) structures in the former area, which can be seen to agree with a thicker lithosphere and a lower heat flux reported in the literature for the southern

  14. Gravity effect of sediment compaction: examples from the North Sea and the Rhine Graben

    NASA Astrophysics Data System (ADS)

    Cowie, Patience A.; Karner, Garry D.

    1990-07-01

    A Fourier domain expression for calculating the gravity effect of a continuously varying density structure is used to investigate the way in which sediment compaction modifies the shape of the gravity anomaly across a sedimentary basin. In general, sediment density increases with depth in a basin as the overburden thickness increases. The effect of the increase in sediment density is to reduce the gravity contribution from the density contrasts in the deeper parts of the basin relative to near surface contributions. For a theoretical uncompensated basin, the gravity effect of the sediments is calculated for a density-depth variation described by: (1) a simple exponential increase in sediment density with depth, and (2) an exponential modified to include a local density inversion representative of sediment overpressuring. It is shown that for both cases, the calculated gravity does not necessarily reflect the morphology of the sediment-basement interface. The gravity effect is most sensitive to the distribution of the youngest stratigraphic units within the basin. Results of modeling observed gravity anomalies across the Viking and Rhine Graben show that the small peak-to-trough amplitude of the gravity anomalies across these basins can be attributed to the increase in sediment density with depth rather than the compensation of the basin. For the Rhine Graben, it is further shown that the wavelength of the gravity anomaly is strongly controlled by the flexural strength of the lithosphere. Together these results suggest that while the amplitude of gravity anomalies across extensional basins may be primarily reflecting compaction of the sediment infill, the anomaly wavelength is more sensitive to the compensation mechanism.

  15. Artificial gravity.

    PubMed

    Scott, William B

    2005-04-25

    NASA's Artificial Gravity program consists of a team of researchers from Wyle Laboratories, NASA Johnson Space Center, and the University of Texas Medical Branch (UTMB). The short-radius centrifuge (SRC), built by Wyle Laboratories, will be integrated with UTMB's conducted bedrest studies, which mimic the detrimental effects of weightlessness (or microgravity). Bedrest subjects will be spun on the SRC at various accelerations and for various time periods, while being monitored medically. Parameters such as bone loss, muscle atrophy, balance control, and oxygen consumption will then be compared in order to research ways of mitigating the impact on astronauts' physiology. Other potential benefits from these studies extend to population groups on Earth, such as bedridden patients. PMID:15852559