Venus gravity anomalies and their correlations with topography

NASA Technical Reports Server (NTRS)

Sjogren, W. L.; Bills, B. G.; Birkeland, P. W.; Esposito, P. B.; Konopliv, A. R.; Mottinger, N. A.; Ritke, S. J.; Phillips, R. J.

1983-01-01

This report provides a summary of the high-resolution gravity data obtained from the Pioneer Venus Orbiter radio tracking data. Gravity maps, covering a 70 deg latitude band through 360 deg of longitude, are displayed as line-of-sight and vertical gravity. Topography converted to gravity and Bouguer gravity maps are also shown in both systems. Topography to gravity ratios are made over several regions of the planet. There are markedly different ratios for the Aphrodite area as compared to the Beta and Atla areas.

Deconstructing the shallow internal structure of the Moon using GRAIL gravity and LOLA topography

NASA Astrophysics Data System (ADS)

Zuber, M. T.

2015-12-01

Globally-distributed, high-resolution gravity and topography observations of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) mission and Lunar Orbiter Laser Altimeter (LOLA) instrument aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft afford the unprecedented opportunity to explore the shallow internal structure of the Moon. Gravity and topography can be combined to produce Bouguer gravity that reveals the distribution of mass in the subsurface, with high degrees in the spherical harmonic expansion of the Bouguer anomalies sensitive to shallowest structure. For isolated regions of the lunar highlands and several basins we have deconstructed the gravity field and mapped the subsurface distribution of density anomalies. While specified spherical harmonic degree ranges can be used to estimate contributions at different depths, such analyses require considerable caution in interpretation. A comparison of filtered Bouguer gravity with forward models of disk masses with plausible densities illustrates the interdependencies of the gravitational power of density anomalies with depth and spatial scale. The results have implications regarding the limits of interpretation of lunar subsurface structure.

Detection and characterization of buried lunar craters with GRAIL data

NASA Astrophysics Data System (ADS)

Sood, Rohan; Chappaz, Loic; Melosh, Henry J.; Howell, Kathleen C.; Milbury, Colleen; Blair, David M.; Zuber, Maria T.

2017-06-01

We used gravity mapping observations from NASA's Gravity Recovery and Interior Laboratory (GRAIL) to detect, characterize and validate the presence of large impact craters buried beneath the lunar maria. In this paper we focus on two prominent anomalies detected in the GRAIL data using the gravity gradiometry technique. Our detection strategy is applied to both free-air and Bouguer gravity field observations to identify gravitational signatures that are similar to those observed over buried craters. The presence of buried craters is further supported by individual analysis of regional free-air gravity anomalies, Bouguer gravity anomaly maps, and forward modeling. Our best candidate, for which we propose the informal name of Earhart Crater, is approximately 200 km in diameter and forms part of the northwestern rim of Lacus Somniorum, The other candidate, for which we propose the informal name of Ashoka Anomaly, is approximately 160 km in diameter and lies completely buried beneath Mare Tranquillitatis. Other large, still unrecognized, craters undoubtedly underlie other portions of the Moon's vast mare lavas.

MX Siting Investigation Gravity Survey - Wah Wah Valley, Utah.

DTIC Science & Technology

1981-05-15

Bouguer Anomaly (see Section A1.4, Appendix A1.0). The Defense Mapping Agency Aerospace Center (DMAAC), St. Louis, Missouri, calculates outer zone...Utah .... 12 LIST OF DRAWINGS Drawing Number 1 Complete Bouguer Anomaly Contours In Pocket at 2 Deptn to Rock - Interpreted from End of Report...DMAHTC/GSS obtained the basic observations for the new stations and reduced them to Simple Bouguer Anomalies (SBA) as described in Appendix A1.0. Up to

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

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

Revetta, F.A.; O'Brian, B.

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 withmore » 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.« less

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

USGS Publications Warehouse

Gettings, M.E.

1983-01-01

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

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 powerful than the classical methods.

High resolution Slovak Bouguer gravity anomaly map and its enhanced derivative transformations: new possibilities for interpretation of anomalous gravity fields

NASA Astrophysics Data System (ADS)

Pašteka, Roman; Zahorec, Pavol; Kušnirák, David; Bošanský, Marián; Papčo, Juraj; Szalaiová, Viktória; Krajňák, Martin; Ivan, Marušiak; Mikuška, Ján; Bielik, Miroslav

2017-06-01

The paper deals with the revision and enrichment of the present gravimetric database of the Slovak Republic. The output of this process is a new version of the complete Bouguer anomaly (CBA) field on our territory. Thanks to the taking into account of more accurate terrain corrections, this field has significantly higher quality and higher resolution capabilities. The excellent features of this map will allow us to re-evaluate and improve the qualitative interpretation of the gravity field when researching the structural and tectonic geology of the Western Carpathian lithosphere. In the contribution we also analyse the field of the new CBA based on the properties of various transformed fields - in particular the horizontal gradient, which by its local maximums defines important density boundaries in the lateral direction. All original and new transformed maps make a significant contribution to improving the geological interpretation of the CBA field. Except for the horizontal gradient field, we are also interested in a new special transformation of TDXAS, which excellently separates various detected anomalies of gravity field and improves their lateral delimitation.

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.

A harmonic analysis of lunar gravity

NASA Technical Reports Server (NTRS)

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

1980-01-01

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.

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 is a complex composite basin with several major depocenters (Figures 15 and 16). Major depocenters are present in the south-central, east-central, and northeastern parts of the basin. The distribution of gravity anomalies suggests a complex pattern of faulting in the subsurface of the basin, with many fault terminations, step-overs, and accommodation zones. The pattern of faulting implies that other, previously undiscovered blind geothermal systems are likely in the Carson Sink. The gravity survey was completed near the end of this project. Thus, more thorough analysis of the data and potential locations of blind geothermal systems is planned for future work.

Topographic gravity modeling for global Bouguer maps to degree 2160: Validation of spectral and spatial domain forward modeling techniques at the 10 microGal level

NASA Astrophysics Data System (ADS)

Hirt, Christian; Reußner, Elisabeth; Rexer, Moritz; Kuhn, Michael

2016-09-01

Over the past years, spectral techniques have become a standard to model Earth's global gravity field to 10 km scales, with the EGM2008 geopotential model being a prominent example. For some geophysical applications of EGM2008, particularly Bouguer gravity computation with spectral techniques, a topographic potential model of adequate resolution is required. However, current topographic potential models have not yet been successfully validated to degree 2160, and notable discrepancies between spectral modeling and Newtonian (numerical) integration well beyond the 10 mGal level have been reported. Here we accurately compute and validate gravity implied by a degree 2160 model of Earth's topographic masses. Our experiments are based on two key strategies, both of which require advanced computational resources. First, we construct a spectrally complete model of the gravity field which is generated by the degree 2160 Earth topography model. This involves expansion of the topographic potential to the 15th integer power of the topography and modeling of short-scale gravity signals to ultrahigh degree of 21,600, translating into unprecedented fine scales of 1 km. Second, we apply Newtonian integration in the space domain with high spatial resolution to reduce discretization errors. Our numerical study demonstrates excellent agreement (8 μGgal RMS) between gravity from both forward modeling techniques and provides insight into the convergence process associated with spectral modeling of gravity signals at very short scales (few km). As key conclusion, our work successfully validates the spectral domain forward modeling technique for degree 2160 topography and increases the confidence in new high-resolution global Bouguer gravity maps.

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

NASA Astrophysics Data System (ADS)

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

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

Structure of the St. Francois Mountains and surrounding lead belt, S. E. Missouri: Inferences from thermal IR and other data sets

NASA Technical Reports Server (NTRS)

Arvidson, R. E. (Principal Investigator)

1981-01-01

Heat Capacity Mapping Mission (HCMM) in the form of an apparent thermal inertia image were merged with shaded relief maps and Bouguer gravity maps. The HCMM data show that the dominant structural grain in Missouri strikes in a northwesterly direction. The strike is the same as a major basement fault or flexure identified on the basis of gravity images.

Gravity domains and assembly of the North American continent by collisional tectonics

NASA Technical Reports Server (NTRS)

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

1988-01-01

A gravity trend map of North America, based on a horizontal Bouguer gravity gradient map produced from gravity data for Canada and the conterminous United States, is presented and used to define a continental mosaic of gravity trend domains akin to structural domains. Contrasting trend characteristics at gravity domain boundaries support the concept of outward growth of the continent primarily by accretionary tectonics. Gravity patterns, however, indicate a different style of tectonics dominated in the development of now-buried Proterozoic orogenic belts in the south-central United States, supporting a view that these belts formed along the leading edge of a southward-migrating Proterozoic continental margin.

Observational Constraints on the Identification of Shallow Lunar Magmatism: Insights from Floor-Fractured Craters

NASA Technical Reports Server (NTRS)

Jozwiak, L. M.; Head, J. W., III; Neumann, G. A.; Wilson, L.

2016-01-01

Floor-fractured craters are a class of lunar crater hypothesized to form in response to the emplacement of a shallow magmatic intrusion beneath the crater floor. The emplacement of a shallow magmatic body should result in a positive Bouguer anomaly relative to unaltered complex craters, a signal which is observed for the average Bouguer anomaly interior to the crater walls. We observe the Bouguer anomaly of floor-fractured craters on an individual basis using the unfiltered Bouguer gravity solution from GRAIL and also a degree 100-600 band-filtered Bouguer gravity solution. The low-magnitude of anomalies arising from shallow magmatic intrusions makes identification using unfiltered Bouguer gravity solutions inconclusive. The observed anomalies in the degree 100-600 Bouguer gravity solution are spatially heterogeneous, although there is spatial correlation between volcanic surface morphologies and positive Bouguer anomalies. We interpret these observations to mean that the spatial heterogeneity observed in the Bouguer signal is the result of variable degrees of magmatic degassing within the intrusions.

A Geological and Geophysical Information System for the Middle East and North Africa,

DTIC Science & Technology

1995-08-14

Saad, D., Sawaf, T., and Gebran, A., 1990, Bouguer gravity trends and crustal structure of the Palmyride Mountain belt and surrounding northern Arabian ...that occurred between 1977 and 1992 (Figure 2). We have finished compiling a crustal scale Bouguer gravity data for Syria, Israel and Lebanon (Figure...3). This Bouguer gravity database is a part of our attempt to form a uniform grided Bouguer gravity data set for the entire Middle East, which then

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.

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

Halliday, M.E.; Cook, K.L.

Regional gravity data were collected in portions of the Pavant Range, Tushar Mountains, northern Sevier Plateau, the Antelope Range, and throughout Sevier Valley approximately between the towns of Richfield and Junction, Utah. Additionally, detailed gravity and ground magnetic data were collected in the vicinity of hot springs in both the Monroe and Joseph Known Geothermal Resource Areas (KGRA's) and subsurface geologic models were constructed. The regional gravity data were terrain corrected out to a distance of 167 km from the station and 948 gravity station values were compiled into a complete Bouguer gravity anomaly map of the survey area. Thismore » map shows a strong correlation with most structural features mapped in the survey area. Four regional gravity profiles were modeled using two-dimensional formerd and inverse algorithms.« less

Venus spherical harmonic gravity model to degree and order 60

NASA Technical Reports Server (NTRS)

Konopliv, Alex S.; Sjogren, William L.

1994-01-01

The Magellan and Pioneer Venus Orbiter radiometric tracking data sets have been combined to produce a 60th degree and order spherical harmonic gravity field. The Magellan data include the high-precision X-band gravity tracking from September 1992 to May 1993 and post-aerobraking data up to January 5, 1994. Gravity models are presented from the application of Kaula's power rule for Venus and an alternative a priori method using surface accelerations. Results are given as vertical gravity acceleration at the reference surface, geoid, vertical Bouguer, and vertical isostatic maps with errors for the vertical gravity and geoid maps included. Correlation of the gravity with topography for the different models is also discussed.

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.

Mean Gravity Anomaly Prediction Techniques with a Comparative Analysis of the Accuracy and Economy of Selected Methods.

DTIC Science & Technology

1982-03-01

gravity anomaly values computed from measured gravity at discrete points (x,y) within the 10 x 10 area. If the Ag are Bouguer gravity anomalies, the Ag is...a 10 x 10 mean Bouguer anomaly. If the Ag are free-air gravity anomalies, the Ag is a 10 x 10 mean free-air gravity anomaly. Either anomaly form can...it requires less subjective judgment. Predictions in continental areas always are made using Bouguer gravity anomalies because this anomaly form is

Deer Lodge Valley investigations, western Montana

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

Wideman, C.J.; Sonderegger, J.; Crase, E.

1982-07-01

A review of the geothermal investigations conducted in the Deer Lodge Valley of Western Montana is briefly presented. Maps of the generalized geology and Bouguer gravity and graphs of selected geothermal gradients and resistivity sounding profiles are presented. (MJF)

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.

Lunar Gravity Studies from the Lunar Prospector Line-of-Sight Acceleration Data: Isostatic Compensation of Medium Sized Craters

NASA Astrophysics Data System (ADS)

Sugano, T.; Heki, K.

2002-12-01

Direct estimation of mass distribution on the lunar nearside surface using the Lunar Prospector (LP) line-of-sight (LOS) acceleration data has several merits over conventional methods to estimate Stokes' coefficients of the lunar gravity field, such as (1) high resolution gravity anomaly recovery without introducing Kaula's constraint, (2) fast inversion calculation by stepwise estimation of parameter sets enabled by small correlation between parameters sets. Resolution of the lunar free-air gravity anomaly map obtained here, is as high as a gravity model complete to degree/order 225, and yet less noisy than the recent models. Next we performed terrain correction for the raw LOS acceleration data using lunar topography model from the Clementine laser altimetry data and the average crustal density of 2.9 g/cm3. By conducting the same inversion for the data after the correction, we obtained the map of Bouguer gravity anomaly that mainly reflects the MOHO topography. By comparing maps we notice that signatures of medium-sized (80-300 km in diameter) craters visible as topographic depression and negative free air anomaly, disappear in the Bouguer anomaly. The absence of mass deficits in the Bouguer anomaly suggests that the MOHO beneath them is flat. Generally speaking, longer wavelength topographic features have to be supported by MOHO topography (Airy isostatic compensation) while small scale topographic features are supported by lithospheric strength. The boundary between these two modes constrains the lithosphere thickness, and hence thermal structure near the surface. Larger craters are known to have become Mascons; mantle plugs and high-density mare basalts cause positive gravity anomalies there. The smallest Mascon has diameters a little larger than 300 km (e.g. Schiller-Zuccius), and the boundary between the two compensation status seems to lie around 300 km. Thermal evolution history of the Moon suggests temporally increasing thickness of lithosphere over its entire history, and the lithosphere as thick as 50-100 km around 4.0 Ga. This is consistent with the isostatic compensation status of the craters studied here, and a model describing the degree of lithospheric supports for various wavelength topographies.

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.

Seismic b-values and its correlation with seismic moment and Bouguer gravity anomaly over Indo-Burma ranges of northeast India: Tectonic implications

NASA Astrophysics Data System (ADS)

Bora, Dipok K.; Borah, Kajaljyoti; Mahanta, Rinku; Borgohain, Jayanta Madhab

2018-03-01

b-value is one of the most significant seismic parameters for describing the seismicity of a given region at a definite time window. In this study, high-resolution map of the Gutenberg-Richter b-value, seismic moment-release, Bouguer gravity anomaly and fault-plane solutions containing faulting styles are analyzed in the Indo-Burma ranges of northeast India using the unified and homogeneous part of the seismicity record in the region (January 1964-December 2016). The study region is subdivided into few square grids of geographical window size 1° × 1° and b-values are calculated in each square grid. Our goal is to explore the spatial correlations and anomalous patterns between the b-value and parameters like seismic moment release, Bouguer gravity anomaly and faulting styles that can help us to better understand the seismotectonics and the state of present-day crustal stress within the Indo-Burma region. Most of the areas show an inverse correlation between b-value and seismic moment release as well as convergence rates. While estimating the b-value as a function of depth, a sudden increase of b-value at a depth of 50-60 km was found out and the receiver function modeling confirms that this depth corresponds to the crust-mantle transition beneath the study region. The region is also associated with negative Bouguer gravity anomalies and an inverse relation is found between Gravity anomaly and b-value. Comparing b-values with different faulting styles, reveal that the areas containing low b-values show thrust mechanism, while the areas associated with intermediate b-values show strike-slip mechanism. Those areas, where the events show thrust mechanism but containing a strike-slip component has the highest b-value.

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.

Delineation of The Sumatra Fault in The Central Part of West Sumatra based on Gravity Method

NASA Astrophysics Data System (ADS)

Saragih, R. D.; Brotopuspito, K. S.

2018-04-01

The Sumatra Fault System is elongated across the Sumatra Island, Indonesia, Southeast Asia including the central part of West Sumatra, Indonesia, Southeast Asia. The Sumatra Fault and subsurface structure on the Central Part of West Sumatra had been analyzed using gravity method. Bouguer anomaly data were obtained from GRDC (Geological Research and Development Centre) maps, Bandung, Indonesia (i.e. without terrain correction). In this study, terrain correction had been applied to these Bouguer data. Bouguer anomaly in a horizontal plane at 3000 meters high and equivalent depth of mass point 7000 meters were obtained using Dampney Method. Residual and regional anomalies were separated using upward continuation method at 8000 meters high. The result of the SVD on residual anomaly shows two negative anomalies on northwest – southeast. The zero miligal per meter square quantity coincides remarkably well with trace faults which is a part of the Sumatra Fault System. Two negative anomalies are located around the Sianok Segment and Sumani Segment.

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.

Lateral Variations in Geologic Structure and Tectonic Setting from Remote Sensing Data

DTIC Science & Technology

1983-05-01

bodies. Analogous magnetic anomaly patterns perhaps can be inferred, since regional lithologies are comparable with some volcanic bodies around the...32 14 Geologic map of the Katahdin Batholith . . . . . . . . . . . 34 15 Bouguer gravity map of Mai ne ... ............ . 36 16 Magnetic anomaly map... magnetic anomaly patterns perhaps can be inferred, since regional lithologies are comparable with some volcanic bodies around the plutons. Linear

Seismicity and gravimetric studies of Cyrenaica platform and adjacent regions, northeastern Libya

NASA Astrophysics Data System (ADS)

Ben Suleman, abdunnur

2013-04-01

Cyrenaica, located in northeastern Libya, consists of two distinct tectonic provinces; the tectonically unstable northern Cyrenaica and the more stable Cyernaican platform to the south. This study represents detailed investigations that aim to focus on the structure and tectonic setting through a detailed Seismicity and gravity analysis. Seismicity of northeastern Libya is documented back to 262 A.D. when an earthquake destroyed the city of Ceryne. The same area was destroyed by an earthquake in 365 A.D, The city of Al-Maraj was heavily damaged in 1963 by an earthquake measuring 5,3 in the Richter scale. Data collected by the recently established Libyan National Seismograph Network confirms that northeastern Libya is seismically active with most of the activity concentrates on the northern part particularly in the city of Al-Maraj area. Seismic activity is also noticeable in the offshore area. Focal mechanism studies for a number of earthquakes recorded by the Libyan National Seismograph Network suggest that normal faulting is predominant. A gravity data base collected from a variety of sources was compiled to generate a Bouguer gravity anomaly map that represents the basic map used in the overall interpretations, as well as in generating more specialized gravity maps used in the detailed investigations. The Bouguer gravity map demonstrates that the northern inverted basins of Cyrenaica and the coastal plain of Al-Jabal Al-Akhdar show a raped northward increase in gravity values to up to 130 Mgal. In addition a series of steep faults that separates the unstable Al-Jabal Al-Akhdar from the more stable Cyrenaica platform as well as other faults within the platform were well delineated.

Venus - Global gravity and topography

NASA Technical Reports Server (NTRS)

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

1993-01-01

A new gravity field determination that has been produced combines both the Pioneer Venus Orbiter (PVO) and the Magellan Doppler radio data. Comparisonsbetween 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.

The origin of lunar mascons - Analysis of the Bouguer gravity associated with Grimaldi

NASA Technical Reports Server (NTRS)

Phillips, R. J.; Dvorak, J.

1981-01-01

Grimaldi is a relatively small multi-ringed basin located on the western limb of the moon. Spacecraft free-air gravity data reveal a mascon associated with the inner ring of this structure, and the topographic correction to the local lunar gravity field indicates a maximum Bouguer anomaly of +90 milligals at an altitude of 70 kilometers. Approximately 20% of this positive Bouguer anomaly can be attributed to the mare material lying within the inner ring of this basin. From a consideration of the Bouguer gravity and structure of large lunar craters comparable in size to the central basin of Grimaldi, it is suggested that the remaining positive Bouguer anomaly is due to a centrally uplifted plug of lunar mantle material. The uplift was caused by inward crustal collapse which also resulted in the formation of the concentric outer scarp of Grimaldi. In addition, an annulus of low density material, probably a combination of ejecta and in situ breccia, is required to fully reproduce the Bouguer gravity signature across this basin. It is proposed that Grimaldi supplies a critical test in the theory of mascon formation: crustal collapse by ring faulting and central uplift to depths of the crust-mantle boundary are requisites

MX Siting Investigation. Gravity Survey - Southern Snake Valley (Ferguson Desert), Utah.

DTIC Science & Technology

1980-03-28

Topographic Center (DMAHTC), head- quartered in Cheyenne, Wyoming. DMAHTC reduces the data to Simple Bouguer Anomaly (see Section A1.4, Appendix Al.0...Valley, Utah . . . . . ......... . . . . . 3 3 Complete Bouguer Anomaly Contours 4 Interpreted Gravity Profile SE-3,4 5 Interpreted Gravity Profile SE...observations and reduced them to Simple Bouguer Anomalies (SBA) for each station as described in Appendix Al.0. Up to three levels of terrain corrections were

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.

Isostatic gravity map of the Nevada Test Site and vicinity, Nevada

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

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

1988-12-31

The isostatic gravity map of the Nevada Test Site (NTS) and vicinity is based on about 16,000 gravity stations. Principal facts of the gravity data were listed by Harris and others (1989) and their report included descriptions of base stations, high-precision and absolute gravity stations, and data accuracy. Observed gravity values were referenced to the International Gravity Standardization Net 1971 gravity datum described by Morelli (1974) and reduced using the Geodetic Reference System 1967 formula for the normal gravity on the ellipsoid (International Union of Geodesy and Geophysics, 1971). Free-air, Bouguer, curvature, and terrain corrections for a standard reduction densitymore » of 2.67 g/cm{sup 3} were made to compute complete Bouguer anomalies. Terrain corrections were made to a radial distance of 166.7 km from each station using a digital elevation model and a computer procedure by Plouff (1977) and, in general, include manually estimated inner-zone terrain corrections. Finally, isostatic corrections were made using a procedure by Simpson and others (1983) based on an Airy-Heiskanen model with local compensation (Heiskanen and Moritz, 1967) with an upper-crustal density of 2.67 g/cm{sup 3}, a crustal thickness of 25 km, and a density contrast between the lower-crust and upper-mantle of 0.4 g/cm{sup 3}. Isostatic corrections help remove the effects of long-wavelength anomalies related to topography and their compensating masses and, thus, enhance short- to moderate-wavelength anomalies caused by near surface geologic features. 6 refs.« less

Use of MAGSAT anomaly data for crustal structure and mineral resources in the US midcontinent

NASA Technical Reports Server (NTRS)

Carmichael, R. S. (Principal Investigator)

1982-01-01

Progress in the correlation of MAGSAT anomaly maps with geological and geophysical data sets is reported. An excerpt from Bouguer gravity map of the U.S. was filtered to retain wavelengths of 250 km, thus being physically somewhat analogous to MAGSAT data at 400 km height. Residual anomalies were extracted to compare with the satellite magnetics.

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

USGS Publications Warehouse

Ben-Avraham, Z.; ten Brink, Uri S.; 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.

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.

Elevation Difference and Bouguer Anomaly Analysis Tool (EDBAAT) User's Guide

USGS Publications Warehouse

Smittle, Aaron M.; Shoberg, Thomas G.

2017-06-16

This report describes a software tool that imports gravity anomaly point data from the Gravity Database of the United States (GDUS) of the National Geospatial-Intelligence Agency and University of Texas at El Paso along with elevation data from The National Map (TNM) of the U.S. Geological Survey that lie within a user-specified geographic area of interest. Further, the tool integrates these two sets of data spatially and analyzes the consistency of the elevation of each gravity station from the GDUS with TNM elevation data; it also evaluates the consistency of gravity anomaly data within the GDUS data repository. The tool bins the GDUS data based on user-defined criteria of elevation misfit between the GDUS and TNM elevation data. It also provides users with a list of points from the GDUS data, which have Bouguer anomaly values that are considered outliers (two standard deviations or greater) with respect to other nearby GDUS anomaly data. “Nearby” can be defined by the user at time of execution. These outputs should allow users to quickly and efficiently choose which points from the GDUS would be most useful in reconnaissance studies or in augmenting and extending the range of individual gravity studies.

Geologic interpretation of gravity data from the Date Creek basin and adjacent areas, west-central Arizona

USGS Publications Warehouse

Otton, James K.; Wynn, Jeffrey C.

1978-01-01

A gravity survey of the Date Creek Basin and adjacent areas was conducted in June 1977 to provide information for the interpretation of basin geology. A comparison of facies relations in the locally uraniferous Chapin Wash Formation and the position of the Anderson mine gravity anomaly in the Date Creek Basin suggested that a relationship between gravity lows and the development of thick lacustrine sections in the region might exist. A second-order residual gravity map derived from the complete Bouguer gravity map for the survey area (derived from survey data and pre-existing U.S. Department of Defense data) shows an excellent correspondence between gravity lows and sediment-filled basins and suggests considerable variation in basin-fill thickness. Using the Anderson mine anomaly as a model, gravity data and facies relations suggest that the southeastern flank of the Aguila Valley gravity low and the gravity low at the western end of the Hassayampa Plain are likely areas for finding thick sections of tuffaceous lacustrine rocks.

Seismic Waveform Analysis of Underground Nuclear Explosions

DTIC Science & Technology

1979-11-15

parameters to be discussed here are Bouguer gravity (Figure 18), and station elevation (Figure 19). Tn this simple comparison of various geophysical...noted the frequent strong correlation between Bouguer gravity and elevation. Indeed, many of the geophysical parameters discussed above are interrelated

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

NASA Astrophysics Data System (ADS)

Alrefaee, H. A.

2017-05-01

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

The gravity field of the Red Sea and East Africa

NASA Astrophysics Data System (ADS)

Makris, Jannis; Henke, Christian H.; Egloff, Frank; Akamaluk, Thomas

1991-11-01

Reevaluation of all gravity data from the Red Sea, the Gulf of Aden and East Africa permitted the compilation of a new Bouguer anomaly map. The intensity of the gravity field and its regional pattern correlate closely with the topographic features of the region. The maximum Bouguer values (> + 100 mGal) are located over the median troughs of the Red Sea and Gulf of Aden. Dense juvenile oceanic crust in these rifts and intruding magmas in stretched continental areas produce excess mass responsible for the anomaly highs. In the Red Sea the orientation of the gravity highs is NW-SE in the south, turning to NE-SW in the north, almost parallel to the Aqaba-Dead Sea strike. This pattern reveals that the present basin axis is not identical with that which formed the Tertiary coastal margins and the pre-Red Sea zones of crustal weakness. In the Gulf of Aden, new oceanic crust along the Tadjura Trench and its eastward extension is also expressed in the Bouguer anomaly map by gravity highs and a sharp bending of the isolines. A maximum of approx. +150 mGal is located over the central section of the Sheba Ridge. Bouguer gravity values over the East African and Yemen Plateaus are of the order of -180 to -240 mGal, indicating significant crustal thickening. On the Somali Plateau, the Marda Fault also has a strong gravity signature that can be traced towards Somalia. By constraining crustal thickness and structure with seismic data and density values from the velocity distribution by means of the Nafe-Drake and Birch relationships, we computed density models for the crust and upper mantle. The crustal thickness is of the order of 40 km beneath the plateaus and only 5 to 6 km at the oceanized parts in the central and southern portions of the Red Sea median trough. The flanks of the southern Red Sea and the corresponding Arabian side are underlain by 12 to 16 km thick stretched continental type crust. Oceanization offshore Sudan and Egypt is asymmetrical. The continental crust terminates abruptly at about 20 km off the coastline, followed by an oceanic crust of early Miocene age that was produced in pull-apart basins. By contrast, the eastern side of the Red Sea trough offshore Saudi Arabia is floored by stretched continental crust that extends far into the sea. Seafloor spreading and the generation of oceanic crust in organized spreading centres are limited to the median troughs off Sudan and the northern part of Ethiopia and commenced approx. 5 m.y. BP. They are absent in the northern Red Sea, where crustal fracturing occurs only in pull-apart basins of Dead Sea-Aqaba orientation distributed in en-echelon pattern.

MX Siting Investigation Gravity Survey - Ralston Valley, Nevada.

DTIC Science & Technology

1981-08-20

Center (DMAHTC), headquartered in Cheyenne. Wyoming. DMAHTC reduces the data to Simple Bouguer Anomaly (see Section A1.4, Appendix Al.0). The Defense...LIST OF DRAWINGS Drawing Number 1 Complete Bouguer Anomaly Contours In Pocket at 2 Depth to Rock - Interpreted from End of Report Gravity Data iv, I I...REDUCTION DMAHTC obtained the basic observations for the new stations and reduced them to Simple Bouguer Anomalies (SBA) as described in Appendix A1.0

Mars - Crustal structure inferred from Bouguer gravity anomalies.

NASA Technical Reports Server (NTRS)

Phillips, R. J.; Saunders, R. S.; Conel, J. E.

1973-01-01

Bouguer gravity has been computed for the equatorial region of Mars by differencing free air gravity and the gravity predicted from topographic variations. The free air gravity was generated from an eighth-order set of spherical harmonic coefficients. The gravity from topographic variations was generated by integrating a two-dimensional Green's function over each contour level. The Bouguer gravity indicates crustal inhomogeneities on Mars that are postulated to be variations in crustal thickness. The Tharsis ridge is a region of thick continental type crust. The gravity data, structural patterns, topography, and surface geology of this region lead to the interpretation of the Tharsis topographic high as a broad crustal upwarp possibly associated with local formation of lower-density crustal material and subsequent rise of a thicker crust. The Amazonis region is one of several basins of relatively thin crust, analogous to terrestrial ocean basins. The Libya and Hellas basins, which are probable impact features, are also underlain by thin crust and are possible regions of mantle upwelling.

Lunar Bouguer gravity anomalies - Imbrian age craters

NASA Technical Reports Server (NTRS)

Dvorak, J.; Phillips, R. J.

1978-01-01

The Bouguer gravity of mass anomalies associated with four Imbrian age craters, analyzed in the present paper, are found to differ considerably from the values of the mass anomalies associated with some young lunar craters. Of the Imbrian age craters, only Piccolomini exhibits a negative gravity anomaly (i.e., a low density region) which is characteristic of the young craters studied. The Bouguer gravity anomalies are zero for each of the remaining Imbrian age craters. Since, Piccolomini is younger, or at least less modified, than the other Imbrian age craters, it is suggested that the processes responsible for the post-impact modification of the Imbrian age craters may also be responsible for removing the negative mass anomalies initially associated with these features.

Gravity investigation of the Manson impact structure, Iowa

NASA Technical Reports Server (NTRS)

Plescia, J. B.

1993-01-01

The Manson crater, of probable Cretaceous/Tertiary age, is located in northwestern Iowa (center at 42 deg. 34.44 min N; 94 deg. 33.60 min W). A seismic reflection profile along an east west line across the crater and drill hole data indicate a crater about 35 km in diameter having the classic form for an impact crater, an uplifted central peak composed of uplifted Proterozoic crystalline bedrock, surrounded by a 'moat' filled with impact produced breccia and a ring graben zone composed of tilted fault blocks of the Proterozoic and Paleozoic country rocks. The structure has been significantly eroded. This geologic structure would be expected to produce a significant gravity signature and study of that signature would shed additional light on the details of the crater structure. A gravity study was undertaken to better resolve the crustal structure. The regional Bouguer gravity field is characterized by a southeastward decreasing field. To first order, the Bouguer gravity field can be understood in the context of the geology of the Precambrian basement. The high gravity at the southeast corner is associated with the mid-continent gravity high; the adjacent low to the northwest results from a basin containing low-density clastic sediments shed from the basement high. Modeling of a simple basin and adjacent high predicts much of the observed Bouguer gravity signature. A gravity signature due to structure associated with the Manson impact is not apparent in the Bouguer data. To resolve the gravity signature of the impact, a series of polynomial surfaces were fit to the Bouguer gravity field to isolate the small wavelength residual anomalies. The residual gravity obtained after subtracting a 5th- or 6th-order polynomial seems to remove most of the regional effects and isolate local anomalies. The pattern resolved in the residual gravity is one of a gravity high surrounded by gravity lows and in turn surrounded by isolated gravity highs. The central portion of the crater is characterized by two positive anomalies having amplitudes of about plus 4 mGal separated by a gentle saddle located approximately at the crater center.

United States crustal thickness

NASA Technical Reports Server (NTRS)

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

1983-01-01

The thickness of the crust, the thickness of the basal (intermediate or lower) crustal layer, and the average velocity at the top of the mantle have been mapped using all available deep-penetrating seismic-refraction profiles in the conterminous United States and surrounding border areas. These profiles are indexed to their literature data sources. The more significant long wavelength anomalies on the three maps are briefly discussed and analyzed. An attempt to use Bouguer gravity to validate mantle structure was inconclusive.

Geophysical Data (Gravity and Magnetic) from the Area Between Adana, Kahramanmaras and Hatay in the Eastern Mediterranean Region: Tectonic Implications

NASA Astrophysics Data System (ADS)

Over, Semir; Akin, Ugur; Sen, Rahime

2018-01-01

The gravity and magnetic maps of the area between Adana-Kahramanmaras-Hatay provinces were produced from a compilation of data gathered during the period between 1973 and 1989. Reduced to the pole (RTP) and pseudo-gravity transformation (PGT) methods were applied to the magnetic data, while derivative ratio (DR) processing was applied to both gravity and magnetic data, respectively. Bouguer, RTP and PGT maps show the image of a buried structure corresponding to ophiolites under undifferentiated Quaternary deposits in the Adana depression and Iskenderun Gulf. DR maps show two important faults which reflect the tectonic framework in the study area: (1) the Karatas-Osmaniye Fault extending from Osmaniye to Karatas in the south between Adana and Iskenderun depressions and (2) Amanos Fault (southern part of East Anatolian Fault) in the Hatay region running southward from Turkoglu to Amik Basin along Amanos Mountain forming the actual plate boundary between the Anatolian block (part of Eurasian plate) and Arabian plate.

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)

Horizontal gravity gradient - An aid to the definition of crustal structure in North America

NASA Technical Reports Server (NTRS)

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

1987-01-01

A map of the magnitude of the horizontal Bouguer gravity gradient over the North American continent is used to delineate lateral discontinuities in upper crustal density and/or thickness associated with such processes as suturing and rifting. The usefulness of gradient trends in mapping major structural boundaries, which are sometimes poorly exposed or completely buried, is demonstrated by examples such as the buried southward extension of the Grenville Front and buried boundaries of the Superior Province. Gradient trends also draw attention to poorly known structures, which may have major tectonic significance, and to a continent-wide structural fabric, which may provide a record of the tectonic growth of the North American continent.

The surface and interior of Venus

NASA Technical Reports Server (NTRS)

Masursky, H.; Kaula, W. M.; Russell, C. T.; Schubert, G.; Mcgill, G. E.; Pettengill, G. H.; Shapiro, I. I.; Phillips, R. J.

1977-01-01

The present knowledge of Venus is reviewed with discussions of the nature and history of both the surface, crust and interior. Instrumentation on board the Pioneer Venus Orbiter, including the radar mapper, radio tracking and the fluxgate magnetometer, is described. Topographic, geological, Bouguer gravity, magnetic, and crustal thickness maps will be constructed from Orbiter data. These maps should provide information on composition and thermal history, the major geological or geophysical provinces, the rate of past and present tectonic activity, and evidence of past or present MHD dynamos.

Petroleum system of Northwest Java basin based on gravity data analysis

NASA Astrophysics Data System (ADS)

Widianto, E.

2018-01-01

Energy management in the upstream oil and gas sector becomes very important for the country’s energy security. The renewal of energy resources and reserves becomes necessary and is a must. In the oil and gas industry, gravity data is usually used only for regional surveys, but with the development of instrumentation technology and gravity software development, this method can be used for assessing oil and gas survey stages from exploration to production. This study was conducted to evaluate aspects of petroleum system and exploration play concept in the part of Northwest Java Basin, covering source rock deposition regions (source kitchen area, migration direction), development of reservoirs, structural and stratigraphic trap, based on gravity data. This study uses data from Bouguer gravity anomaly map by filtering process to produce a residual map depicting sedimentation basin configuration. The mapping generated 20 sedimentary basins in Java Island with the total hydrocarbon resources of 113 BBOE (Billion Barrel of Oil Equivalent). The petroleum system analysis was conducted in the Northwest Basin section. The final map produced illustrates the condition of petroleum system and play concept that can be used as exploration direction, expectedly reducing the risk of drilling failure.

Integrating gravity and magnetic field data to delineate structurally controlled gold mineralization in the Sefwi Belt of Ghana

NASA Astrophysics Data System (ADS)

Konadu Amoah, Bernard; Dadzie, Isaac; Takyi-Kyeremeh, Kwaku

2018-08-01

Gravity and magnetic surveys were used to delineate potential gold mineralization zones in the Sefwi belt of Ghana. The study area is an intrusive dominated area that hosts pockets of small scale mining operations locally referred to as Galamsey. These Galamsey operations are not guided by a scientific approach to back the trend of gold mineralization which is conventionally mined. The study aimed at mapping lithological units, structural setting and relating Galamsey sites to delineate potential zones of gold mineralization. A Scintrex CG5 gravimeter and GEM’s Overhauser magnetometer were used for gravity and magnetic data acquisition respectively. The magnetic data were corrected and enhancing filters such as reduction to the pole (RTP), analytical signal and first vertical derivative were applied using Oasis montaj 7.1. Gravity data were also reduced to the geoid using the Oasis montaj software to produce a complete Bouguer anomaly map. The regional/residual separation technique produced a residual gravity map. The RTP and analytical signal filters from the magnetic data and residual gravity anomaly map from the gravity data helped in mapping belt type (Dixcove) Birimian granitoids and mafic intrusive unit, interpreted as gabbro. The first vertical derivative filter was useful in mapping NE/SW minor faults and crosscutting dykes largely concentrated in the belt type Birimian granitoids. All the three mapped Galamsey sites fell on a minor fault and are associated with the belt type granitoids which were used in delineating four potential zones of gold mineralization.

GEOPHYSICAL INVESTIGATIONS OF THE STRUCTURE OF THE EARTH’S CRUST IN THE ATLANTIC OCEAN REGION,

DTIC Science & Technology

50--100 mgal and then increase to +50--70mgal. The Bouguer isoanomaly lines are denser in the transition zone and a considerable gravity gradient...data has also become more abundent. Investigations to determine relation between Bouguer gravity anomalies and the thickness of the earth’s crust

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.

Indications of correlation between gravity measurements and isoseismal maps. A case study of Athens basin (Greece)

NASA Astrophysics Data System (ADS)

Dilalos, S.; Alexopoulos, J. D.

2017-05-01

In this paper, we discuss the correlation between isoseismal contour maps and gravity residual anomaly maps and how it might contribute to the characterization of vulnerable areas to earthquake damage, especially in urban areas, where the geophysical data collection is difficult. More specifically, we compare a couple of isoseismal maps that have been produced and published after the catastrophic earthquake of 7th September 1999 (5.9R) in Athens, the metropolis of Greece, with the residual map produced from the processing and data reduction of a gravity survey that has been carried out in the Athens basin recently. The geologic and tectonic regime of the Athens basin is quite complicated and it is still being updated with new elements. Basically it is comprised of four different geotectonic units, one of them considered as the autochthon. During the gravity investigation, 807 gravity stations were collected, based on a grid plan with spacing almost 1 km, covering the entire basin and supported by a newly established gravity base network comprised by thirteen bases. Differential DGPS technique was used for the accurate measurement of all the gravity stations and bases coordinates. After the appropriate data reduction and the construction of the Complete Bouguer Anomaly map, we applied FFT filtering in order to remove the regional component and produce the Residual Anomaly Map. The comparison of the Residual Anomaly Map with the isoseismal contours revealed that the areas with the most damage because of the earthquake were located in the areas with the minimum values of the Residual Anomaly Map.

Interpretation of recent gravity profiles over the ophiolite belt, Northern Oman Mountains, United Arab Emirates

NASA Astrophysics Data System (ADS)

Khattab, M. M.

1993-04-01

The compiled Bouguer gravity anomaly map over parts of the ophiolite rocks of the Northern Oman Mountains suggests the existence of three partially serpentinized nappes: two along the Gulf of Oman coast with axes near Dadnah, near Fujira and the third 17 km SSE of Masafi. Modeling of the subsurface geology, beneath two gravity profiles (Diba-Kalba and Masafi-Fujira), is based on the occurrence (field evidence) of multiphase low-angle thrusting of the members of the Tethyan lithosphere in northern and Oman Mountains. An assumed crustal model at the Arabian continental margin, beneath the Masafi-Fujira profile, is made to explain an intense gravity gradient. Gravity interpretation is not inconsistent with a gliding mechanism for obduction of the ophiolite on this part of the Arabian continental margin.

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.

TEM and Gravity Data for Roosevelt Hot Springs, Utah FORGE Site

DOE Data Explorer

Hardwick, Christian; Nash, Greg

2018-02-05

This submission includes a gravity data in text format and as a GIS point shapefile and transient electromagnetic (TEM) raw data. Each text file additionally contains location data (UTM Zone 12, NAD83) and elevation (meters) data for that station. The gravity data shapefile was in part downloaded from PACES, University of Texas at El Paso, http://gis.utep.edu/subpages/GMData.html, and in part collected by the Utah Geological Survey (UGS) as part of the DOE GTO supported Utah FORGE geothermal energy project near Milford, Utah. The PACES data were examined and scrubbed to eliminate any questionable data. A 2.67 g/cm^3 reduction density was used for the Bouguer correction. The attribute table column headers for the gravity data shapefile are explained below. There is also metadata attached to the GIS shapefile. name: the individual gravity station name. HAE: height above ellipsoid [meter] NGVD29: vertical datum for geoid [meter] obs: observed gravity ERRG: gravity measurement error [mGal] IZTC: inner zone terrain correction [mGal] OZTC: outer zone terrain correction [mGal] Gfa: free air gravity gSBGA: Bouguer horizontal slab sCBGA: Complete Bouguer anomaly

3D gravimetric investigation of the Cerro do Jarau structure, Rio Grande do Sul, Brazil

NASA Astrophysics Data System (ADS)

Giacomini, Bruno B.; Leite, Emilson P.; Crósta, Alvaro P.

2017-04-01

The Cerro do Jarau structure is possibly the third Brazilian basaltic crater formed in continental flood basalt of the Serra Geral Formation, Paraná Basin, a large igneous province (LIP) in southern Brazil. It is a nearly circular landform with a diameter of approximately 13 km that rises 200 m above the plains of the "pampas" in southern Brazil. In this work, Bouguer anomalies were calculated from gravity accelerations measured on the area of this structure. The residual Bouguer map shows a strong positive anomaly trending NE-SW, located in the northeastern part of the structure, a feature not commonly associated with impact structures. However, the negative anomaly present in its center and the circular positive anomaly surrounding the central portion are typical of impact structures. The residual Bouguer anomaly varies from -2 mGal to 8 mGal. The positive circular anomaly is not spatially coincident with the rim of the structure. Based on the interpretation of our gravimetric data, the estimated diameter of the structure is 12 km and the central portion has a diameter of approximately 5 km, both slightly smaller than previously suggested. The Bouguer anomaly map was inverted into a 3D density model using a constrained inversion method with a maximum density contrast of 0.5 g cm-3. This model was interpreted to associate densities with rock types, resulting in a geological model. This geological model is in accordance with the meteorite impact nature of Cerro do Jarau.

Mars topography harmonics and geophysical implications

NASA Technical Reports Server (NTRS)

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

1978-01-01

The paper describes an improved model of Martian global topography which has been obtained by fitting a sixteenth-degree harmonic series to occultation, radar, spectral, and photogrammetric measurements. Empirical elevation data based on photographic data are used to supplement the observations in areas without data. Values for the mean radius, the mean density, and the displacement of the center of the figure from the center of mass are presented. The reported geometric flattening is too great and the reported dynamic flattening is too small for Mars to be homogeneous and hydrostatic. Maps of the data distribution, global topography, and Bouguer gravity anomaly are interpreted in terms of a crustal thickness map which is consistent with gravity, topography, and recent preliminary Viking seismic results.

Geology and resource assessment of Costa Rica at 1:500,000 scale; a digital representation of maps of the U.S. Geological Survey's 1987 folio I-1865

USGS Publications Warehouse

Schruben, Paul G.

1997-01-01

This CD-ROM contains digital versions of the geology and resource assessment maps of Costa Rica originally published in USGS Folio I-1865 (U.S. Geological Survey, the Direccion General de Geologia, Minas e Hidrocarburos, and the Universidad de Costa Rica, 1987) at a scale of 1:500,000. The following layers are available on the CD-ROM: geology and faults; favorable domains for selected deposit types; Bouguer gravity data; isostatic gravity contours; mineral deposits, prospects, and occurrences; and rock geochemistry sample points. For DOS users, the CD-ROM contains MAPPER, a user-friendly map display program. Some of the maps are also provided in the following additional formats on the CD-ROM: (1) ArcView 1 and 3, (2) ARC/INFO 6.1.2 Export, (3) Digital Line Graph (DLG) Optional, and (4) Drawing Exchange File (DXF.)

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.

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.

Research in Seismology

DTIC Science & Technology

1975-01-01

edge of the Persian Gulf, isolatina the Arabian continental shelf from the subduction process. Slippage along this fault is Pleistocene and probably...Fault-plane solutions for these events (Fitch, 1970; Nowroozi, 1972) confirm the mechanisms to be shallow underthrusting. The Bouguer gravity anomaly...at 40 km behind the subduction zone. A Bouguer gravity anomaly has also been calculated for this model by assuming that the structure is flat and

A harmonic analysis of lunar topography

NASA Technical Reports Server (NTRS)

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

1977-01-01

A global lunar topographic map has been derived from existing earth-based and orbital observations supplemented in areas without data by a linear autocovariance predictor. Of 2592 bins, each 5 deg square, 1380 (64.7% by area) contain at least one measurement. A spherical harmonic analysis to degree 12 yields a mean radius of 1737.53 plus or minus 0.03 km (formal standard error) and an offset of the center of figure of 1.98 plus or minus 0.06 km toward (19 plus or minus 2) deg S, (194 plus or minus 1) deg E. A Bouguer gravity map, derived from a 12-degree free-air gravity model and the present topography data, is presented for an elevation of 100 km above the mean surface. It is confirmed that the low-degree gravity harmonics are determined primarily by surface height variations and only secondarily by lateral density variations.

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 harmonic coefficients were computed up to the third degree of the altitude, and the harmonics of the other, smaller parts up to the second degree. Their sum constitutes what we call ETOPG1, the Earth's TOPography derived Gravity model at 1' resolution (half-wavelength). The EGM2008 gravity field model and ETOPG1 were then used to rigorously compute 1' × 1' point values of surface gravity anomalies and disturbances, respectively, worldwide, at the real Earth's surface, i.e. at the lower limit of the atmosphere. The disturbance grid is the most interesting product of this study and can be used in various contexts. The surface gravity anomaly grid is an accurate product associated with EGM2008 and ETOPO1, but its gravity information contents are those of EGM2008. Our method was validated by comparison with a direct numerical integration approach applied to a test area in Morocco-South of Spain (Kuhn, private communication 2011) and the agreement was satisfactory. Finally isostatic corrections according to the Airy model, but in spherical geometry, with harmonic coefficients derived from the sets of the ETOPO1 different parts, were computed with a uniform depth of compensation of 30 km. The new world Bouguer and isostatic gravity maps and grids here produced will be made available through the Commission for the Geological Map of the World. Since gravity values are those of the EGM2008 model, geophysical interpretation from these products should not be done for spatial scales below 5 arc minutes (half-wavelength).

Imaging the Buried Chicxulub Crater with Gravity Gradients and Cenotes

NASA Astrophysics Data System (ADS)

Hildebrand, A. R.; Pilkington, M.; Halpenny, J. F.; Ortiz-Aleman, C.; Chavez, R. E.; Urrutia-Fucugauchi, J.; Connors, M.; Graniel-Castro, E.; Camara-Zi, A.; Vasquez, J.

1995-09-01

Differing interpretations of the Bouguer gravity anomaly over the Chicxulub crater, Yucatan Peninsula, Mexico, have yielded diameter estimates of 170 to 320 km. Knowing the crater's size is necessary to quantify the lethal perturbations to the Cretaceous environment associated with its formation. The crater's size (and internal structure) is revealed by the horizontal gradient of the Bouguer gravity anomaly over the structure, and by mapping the karst features of the Yucatan region. To improve our resolution of the crater's gravity signature we collected additional gravity measurements primarily along radial profiles, but also to fill in previously unsurveyed areas. Horizontal gradient analysis of Bouguer gravity data objectively highlights the lateral density contrasts of the impact lithologies and suppresses regional anomalies which may obscure the gravity signature of the Chicxulub crater lithologies. This gradient technique yields a striking circular structure with at least 6 concentric gradient features between 25 and 85 km radius. These features are most distinct in the southwest probably because of denser sampling of the gravity field. Our detailed profiles detected an additional feature and steeper gradients (up to 5 mGal/km) than the original survey. We interpret the outer four gradient maxima to represent concentric faults in the crater's zone of slumping as is also revealed by seismic reflection data. The inner two probably represent the margin of the central uplift and the peak ring and or collapsed transient cavity. Radial gradients in the SW quadrant over the inferred ~40 km-diameter central uplift (4) may represent structural "puckering" as revealed at eroded terrestrial craters. Gradient features related to regional gravity highs and lows are visible outside the crater, but no concentric gradient features are apparent at distances > 90 km radius. The marginal gradient features may be modelled by slump faults as observed in large complex craters on the other terrestrial planets. A modeled fault of 1.5 km displacement (slightly slumped block exterior and impact breccia interior) reproduces the steepest gradient feature. This model is incompatible with models that place these gradient features inside the collapsed transient cavity. Locations of the karst features of the northern Yucatan region were digitized from 1:50,000 topographic maps, which show most but not all the water-filled sinkholes (locally known as cenotes). A prominent ring of cenotes is visible over the crater that is spatially correlated to the outer steep gravity gradient feature. The mapped cenotes constitute an unbiased sampling of the region's karst surface features of >50 m diameter. The gradient maximum and the cenote ring both meander with amplitudes of up to 2 km. The wiggles in the gradient feature and the cenote distribution probably correspond to the "scalloping" observed at the headwall of terraces in large complex craters. A second partial cenote ring exterior to the southwest side of the main ring corresponds to a less-prominent gravity gradient feature. No concentric structure is observable in the distribution of karst features at radii >90 km. The cenote ring is bounded by the outer peripheral steep gradient feature and must be related to it; the slump faults must have been reactivated sufficiently to create fracturing in the overlying and much younger sediment. Long term subsidence, as found at other terrestrial craters is a possible mechanism for the reactivation. Such long term subsidence may be caused by differential compaction or thermal relaxation. Elevations acquired during gravity surveys show that the cenote ring also corresponds to a topographic low along some of its length that probably reflects preferential erosion.

The Lunar Crust: Global Structure and Signature of Major Basins

NASA Technical Reports Server (NTRS)

Neumann, Gregory A.; Zuber, Maria T.; Smith, David E.; Lemoine, Frank G.

1996-01-01

New lunar gravity and topography data from the Clementine Mission provide a global Bouguer anomaly map corrected for the gravitational attraction of mare fill in mascon basins. Most of the gravity signal remaining after corrections for the attraction of topography and mare fill can be attributed to variations in depth to the lunar Moho and therefore crustal thickness. The large range of global crustal thickness (approx. 20-120 km) is indicative of major spatial variations in melting of the lunar exterior and/or significant impact-related redistribution. The 6l-km average crustal thickness, constrained by a depth-to-Moho measured during the Apollo 12 and 14 missions, is preferentially distributed toward the farside, accounting for much of the offset in center-of-figure from the center-of-mass. While the average farside thickness is 12 km greater than the nearside, the distribution is nonuniform, with dramatic thinning beneath the farside, South Pole-Aitken basin. With the global crustal thickness map as a constraint, regional inversions of gravity and topography resolve the crustal structure of major mascon basins to half wavelengths of 150 km. In order to yield crustal thickness maps with the maximum horizontal resolution permitted by the data, the downward continuation of the Bouguer gravity is stabilized by a three- dimensional, minimum-slope and curvature algorithm. Both mare and non-mare basins are characterized by a central upwarped moho that is surrounded by rings of thickened crust lying mainly within the basin rims. The inferred relief at this density interface suggests a deep structural component to the surficial features of multiring lunar impact basins. For large (greater than 300 km diameter) basins, moho relief appears uncorrelated with diameter, but is negatively correlated with basin age. In several cases, it appears that the multiring structures were out of isostatic equilibrium prior to mare emplacement, suggesting that the lithosphere was strong enough to maintain their state of stress to the present.

GRAVITY DATA OBTAINED DURING CHAIN CRUISE NO. 70.

DTIC Science & Technology

Profiles, tabulations, and charts are presented of principal gravity facts, free-air gravity anomalies, and simple Bouguer gravity anomalies obtained in the western North Atlantic Ocean during R/V CHAIN cruise 70. (Author)

Integrated geophysical study of the northeastern margin of Tibetan Plateau

NASA Astrophysics Data System (ADS)

Shi, L.; Meng, X.; Guo, L.

2011-12-01

Tibetan Plateau, the so-called "Roof of the World", is a direct consequence of collision of the Indian plate with the Eurasian plate starting in the early Cenozoic time. The continent-continent collision is still going on. The northeastern margin of Tibetan Plateau is the front part of the Tibetan Plateau extends to mainland and favorable area for studying uplift and deformation of the Tibetan Plateau. In the past decades, a variety of geophysical methods were conducted to study geodynamics and geological tectonics of this region. We assembled satellite-derived free-air gravity anomalies with a resolution of one arc-minute from the Scripps Institution of Oceanography, and reduced them to obtain Complete Bouguer Gravity Anomalies. Then we gridded Complete Bouguer Gravity Anomalies on a regular grid, and subsequently processed them with the preferential continuation method to attenuate high-frequency noise and analyzed regional and residual anomalies. We also calculated tilt-angle derivative of Complete Bouguer Gravity Anomalies to derive clearer geological structures with more details. Then we calculated the depth distribution of the Moho discontinuity surface in this area by 3D density interface inversion. From the results of preliminary processing, we analyzed the main deep faults and geological tectonics in this region. We extracted seven important profiles' data of Complete Bouguer Gravity Anomalies in this area, and then did forward modeling and inversion on each profile with constraints of geological information and other geophysical data. In the future, we will perform 3D constrained inversion of Complete Bouguer Gravity Anomalies in this region for better understanding deep structure and tectonics of the northeastern margin of Tibetan Plateau. Acknowledgment: We acknowledge the financial support of the SinoProbe project (201011039), the Fundamental Research Funds for the Central Universities (2010ZY26 2011PY0184), and the National Natural Science Foundation of China (40904033).

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 oro-genic belts, the "Dome zone" of northern Tunisia is characterized by the juxtaposition of various structures that mainly controlled the long geody-namic 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.

Geology and resource assessment of Costa Rica at 1:500,000 scale; a digital representation of maps of the U.S. Geological Survey's 1987 Folio I-1865

USGS Publications Warehouse

Schruben, Paul G.

1996-01-01

This CD-ROM contains digital versions of the geology and resource assessment maps of Costa Rica originally published by the U.S. Geological Survey (USGS), the Direccion General de Geologia, Minas e Hidrocarburos, and the Universidad de Costa Rica in 1987 at a scale of 1:500,000 in USGS Folio I-1865. The following layers of the map are available on the CD-ROM: geology, favorable domains for selected deposit types, Bouguer gravity, isostatic gravity, mineral deposits, and rock geochemistry sample points. Some of the layers are provided in the following formats: ArcView 1 for Windows and UNIX, ARC/INFO 6.1.2 Export, Digital Line Graph (DLG) Optional, and Drawing Exchange File (DXF). This CD-ROM was produced in accordance with the ISO 9660 and Apple Computer's HFS standards.

The importance of bulk density determination in gravity data processing for structure interpretation

NASA Astrophysics Data System (ADS)

Wildan, D.; Akbar, A. M.; Novranza, K. M. S.; Sobirin, R.; Permadi, A. N.; Supriyanto

2017-07-01

Gravity method use rock density variation for determining subsurface lithology and geological structure. In the "green area" where measurement of rock density has not been done, an attemp to find density is usually performed by calculating using Parasnis method, or by using using the average of rock density in the earth's crust (2,67 gr/cm3) or by using theoritical value of dominant rock density in the survey area (2,90 gr/cm3). Those three values of densities are applied to gravity data analysis in the hilly "X" area. And we have compared all together in order to observed which value has represented the structure better. The result showed that the higher value of rock density, the more obvious structure in the Bouguer anomaly profile. It is due to the contrast of maximum and minimum value of Bouguer anomaly that will affect the exageration in distance vs Bouguer anomaly graphic.

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.

Lineaments in the Shamakhy-Gobustan and Absheron hydrocarbon containing areas using gravity data

NASA Astrophysics Data System (ADS)

Elmas, Ali; Karsli, Hakan; Kadirov, Fakhraddin A.

2017-12-01

In this study, we purposed to investigate the edge of geostructures and position of existing faults of the Shamakhy-Gobustan and Absheron hydrocarbon containing regions in Azerbaijan. For this purpose, the horizontal gradient, analytic signal, tilt angle, and hyperbolic of tilt angle methods were applied to the first vertical derivative of gravity data instead of Bouguer gravity data. We obtained the maps that show the previous lineaments which were designated by considering the maximum contours of horizontal gradient, analytic signal maps, and zero values of tilt angle, hyperbolic of tilt angle maps. The geometry of basement interface was also modeled utilizing the Parker-Oldenburg algorithm to understand the sediment thickness and coherency or incoherency between the gravity values and basement topography. The lineaments were held a candle to most current tectonic structure map of the study area. It was seen that the techniques used in this study are very effective to determine the old and new lineaments in the Shamakhy-Gobustan and Absheron regions. The epicenter distribution of earthquakes within the study area supports the new lineaments which are extracted by our interpretation. We concluded that better comprehension of Azerbaijan geostructures and its effect on the large scale works will be provided by means of this study.

Lineaments in the Shamakhy-Gobustan and Absheron hydrocarbon containing areas using gravity data

NASA Astrophysics Data System (ADS)

Elmas, Ali; Karsli, Hakan; Kadirov, Fakhraddin A.

2018-02-01

In this study, we purposed to investigate the edge of geostructures and position of existing faults of the Shamakhy-Gobustan and Absheron hydrocarbon containing regions in Azerbaijan. For this purpose, the horizontal gradient, analytic signal, tilt angle, and hyperbolic of tilt angle methods were applied to the first vertical derivative of gravity data instead of Bouguer gravity data. We obtained the maps that show the previous lineaments which were designated by considering the maximum contours of horizontal gradient, analytic signal maps, and zero values of tilt angle, hyperbolic of tilt angle maps. The geometry of basement interface was also modeled utilizing the Parker-Oldenburg algorithm to understand the sediment thickness and coherency or incoherency between the gravity values and basement topography. The lineaments were held a candle to most current tectonic structure map of the study area. It was seen that the techniques used in this study are very effective to determine the old and new lineaments in the Shamakhy-Gobustan and Absheron regions. The epicenter distribution of earthquakes within the study area supports the new lineaments which are extracted by our interpretation. We concluded that better comprehension of Azerbaijan geostructures and its effect on the large scale works will be provided by means of this study.

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.

GRAIL gravity observations of the transition from complex crater to peak-ring basin on the Moon: Implications for crustal structure and impact basin formation

NASA Astrophysics Data System (ADS)

Baker, David M. H.; Head, James W.; Phillips, Roger J.; Neumann, Gregory A.; Bierson, Carver J.; Smith, David E.; Zuber, Maria T.

2017-08-01

High-resolution gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) mission provide the opportunity to analyze the detailed gravity and crustal structure of impact features in the morphological transition from complex craters to peak-ring basins on the Moon. We calculate average radial profiles of free-air anomalies and Bouguer anomalies for peak-ring basins, protobasins, and the largest complex craters. Complex craters and protobasins have free-air anomalies that are positively correlated with surface topography, unlike the prominent lunar mascons (positive free-air anomalies in areas of low elevation) associated with large basins. The Bouguer gravity anomaly profiles of complex craters are highly irregular, with central positive anomalies that are generally absent or not clearly tied to interior morphology. In contrast, gravity profiles for peak-ring basins (∼200 km to 580 km) are much more regular and are highly correlated with surface morphology. A central positive Bouguer anomaly is confined within the peak ring and a negative Bouguer anomaly annulus extends from the edge of the positive anomaly outward to about the rim crest. A number of degraded basins lacking interior peak rings have diameters and gravity patterns similar to those of well-preserved peak-ring basins. If these structures represent degraded peak-ring basins, the number of peak-ring basins on the Moon would increase by more than a factor of two to 34. The gravity anomalies within basins are interpreted to be due to uplift of the mantle confined within the peak ring and an annulus of thickened crust between the peak ring and rim crest. We hypothesize that mantle uplift is influenced by interaction between the transient cavity and the mantle. Further, mascon formation is generally disconnected from the number of basin rings formed and occurs over a wide range of basin sizes. These observations have important implications for models of basin and mascon formation on the Moon and other planetary bodies.

Measuring and Modeling the Earth's Gravity - Introduction to Ground-Based Gravity Surveys and Analysis of Local Gravity Data

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

Rowe, Charlotte Anne

We can measure changes in gravity from place to place on the earth. These measurements require careful recording of location, elevation and time for each reading. These readings must be adjusted for known effects (such as elevation, latitude, tides) that can bias our data and mask the signal of interest. After making corrections to our data, we can remove regional trends to obtain local Bouguer anomalies. The Bouguer anomalies arise from variations in the subsurface density structure. We can build models to explain our observations, but these models must be consistent with what is known about the local geology. Combiningmore » gravity models with other information – geologic, seismic, electromagnetic, will improve confidence in the results.« less

Structure of the Saint Francois Mountains and surrounding lead belt, south east Missouri: Inferences from thermal IR and other data sets

NASA Technical Reports Server (NTRS)

Arvidson, R. E. (Principal Investigator); Guinness, E. A.; Bindschadler, D. L.

1983-01-01

Several digital data sets were registered to a common base map for southern Missouri. These registered data sets were examined in an attempt to improve our understanding of the crustal structure and the relationships between structure and Pb-Zn-Cu, Fe, Mn, and Ba ores in the area. Data included land station reading of gravity, geologic data, and Heat Capacity Mapping Mission (HCMM) images. The HCMM day infrared (IR) images of Missouri displayed linear features, which parallel a newly discovered NW-SE trending Bouguer gravity low. The structural pattern over the gravity low suggests vertical uplift of the low density crust via isostatic readjustment and consequent fracturing of the Paleozoic sedimentary cover. The presence of a gravity low is interesting because rifts are often sites of extensive mineralization. The HCMM thermal data were also examined in conjunction with digital topography, land use, and LANDSAT MSS data to understand the phenomena that produce linears on the HCMM day IR images. Finally, the kinds of information that can be extracted from day-night IR pairs are discussed.

Gravity field and shape of Ceres from Dawn

NASA Astrophysics Data System (ADS)

Park, Ryan; Konopliv, Alexander; Vaughan, Andrew; Bills, Bruce; Castillo-Rogez, Julie; Ermakov, Anton; Fu, Roger; Raymond, Carol; Russell, Chris; Zuber, Maria

2017-04-01

The Dawn gravity science investigation utilizes the DSN radio tracking of the spacecraft and on-board framing camera images to determine the gravity field and global shape of Ceres. The gravity science data collected during Approach, Survey, High-Altitude Mapping Orbit, and Low-Altitude Mapping Orbit phases were processed. The final gravity science solution yielded a degree and order 18 gravity field, called CERES18C, which is globally accurate to degree and order 14. Also, the final Ceres shape using the stereo-photoclinometry method is available with the height uncertainty better than 30 meters. The degree-2 gravity harmonics show that the rotation of Ceres is very nearly about a principal axis. Combining the gravity field and topography gives the bulk density of 2162.6±2.0 kg/m3. The estimated spin pole vector yields RA=(291.42744±0.00022)° and Dec=(66.76065±0.00022)° with the prime meridian and rotation rate of (170.374±0.012)° and (952.1532638±0.0000019)°/day, respectively. The low Bouguer gravity at high topographic areas, and vice versa, indicates that the topography of Ceres is compensated, which can be explained by a low-viscosity layer at depth. Further studies on Ceres interior show that low gravity-topography admittances are consistent with Airy isostasy and finite-element modeling require a decrease of viscosity with depth.

A gravity model for the Sudbury Structure along the Lithoprobe seismic line

NASA Astrophysics Data System (ADS)

McGrath, P. H.; Broome, H. J.

1994-05-01

Previous gravity models of the Sudbury Structure (1850 Ma) were constrained by surface geology, and by density measurements of surface and borehole rock samples. Recent high-resolution seismic reflection data provide additional constraints for modeling new gravity observations made along the Sudbury Lithoprobe transect. Results indicate, (1) density distributions constrained by the seismic data yield calculated gravity values matching the Bouguer gravity data, (2) the main sources of gravitational disturbance are external to the Sudbury Structure, (3) the positive gravity anomaly trend south of the Sudbury Structure is associated with mafic rocks of Proterozoic age, and (4) the large, ramplike, gravity anomaly paralleling the northwest margin of the Sudbury Structure is an expression of a northward dipping boundary within the Archean basement. The presence of a hidden mafic layer beneath the Sudbury Structure is not required to model the Bouguer gravity data. An enigma is an 8 mGal, positive, gravity anomaly over the south central Sudbury Structure.

Apollo 17 traverse gravimeter experiment /Preliminary results/

NASA Technical Reports Server (NTRS)

Talwani, M.; Kahle, H.-G.

1976-01-01

Preliminary results of the traverse gravimeter experiment successfully performed during the Apollo 17 mission are discussed. An earth-moon gravity tie was established. On the basis of several readings, a gravity value of 162,695 + or - 5 mgal was obtained at the lunar-module landing site in the Taurus-Littrow valley. Free-air and Bouguer corrections were applied to the gravity data. The resultant Bouguer anomaly, analyzed with a two-dimensional approximation, shows a relative gravity maximum of about 25 to 30 mgal over the Taurus-Littrow valley. This maximum is interpreted in terms of a 1-km-thick block of basalt flow with a positive density contrast of 0.8 g/cu cm relative to the highland material on either side.

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.

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

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

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)more » 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.« less

Lithologic boundaries from gravity and magnetic anomalies over Proterozoic Dalma volcanics

NASA Astrophysics Data System (ADS)

Yadav, Pramod Kumar; Adhikari, P. K.; Srivastava, Shalivahan; Maurya, Ved P.; Tripathi, Anurag; Singh, Shailendra; Singh, Roshan K.; Bage, Ashish K.

2018-03-01

Dalma volcanics (DVs) has intruded the older Singhbhum Group of Metapelites. Despite DVs being rich in mineralisation, its boundaries are not clearly demarcated. Gravity and magnetic surveys have been attempted for mapping the boundaries in DVs. These surveys were made in the northern fringe of the DVs over an area of ˜ 0.70 km2 along 13 parallel lines at 50 m spacing. The data was acquired at ˜ 25 m spacing. The surveys were taken for determination of lithological boundaries, depths and nature of causative source using Euler depth solutions and radially averaged power spectrum (RAPS). Residual anomaly maps of gravity and magnetic intensity show the same trend as that of Bouguer gravity anomaly and total magnetic intensity anomaly map indicating towards shallow sources. The magnetic map in general follows the same pattern as that of gravity anomaly maps. The map shows coincident high gravity and magnetic anomalies. These anomalies together with resistivity signatures confirm that the northern fringe of DVs hosts volcanogenic massive sulphide settings. The Euler depth solution delineated the lateral boundaries and nature of the source. It seems that the source is of spherical nature lying within a depth range of 25-40 m. The obtained lithological (vertical) units from RAPS are between Lower DVs, Upper DVs and Singhbhum Group Metapelites at depths of ˜ 15, ˜ 25 and ˜ 40 m, respectively. The metallogeny is associated with the Upper DVs and the corresponding delineated lithological (vertical) unit is indicative of the top of the ore body. Good agreement is observed with the geological succession from the drilling data and resistivity data. The findings suggest that the northern fringe of DVs could be a preferred target for drilling.

Integration of satellite gravity data with ground-based geophysical data for a better understanding of the structural control of groundwater flow in the Nubian Sandstone Aquifer System

NASA Astrophysics Data System (ADS)

Fathy, K.; Sultan, M.; Bettadpur, S. V.; Save, H.; Ahmed, M.; Zahran, K. H.; Emil, M. K.; Helaly, A.; Abotalib, A. Z.; Ismaiel, A.

2016-12-01

The Nubian Sandstone Aquifer System (NSAS) extends beyond Egypt's political boundaries to cover eastern Libya, northern and central Sudan and northeast Chad. The optimum utilization of this resource requires a better understanding of the connectivity of the NSAS sub-basins and the structural control on groundwater flow throughout the system. We provide an integrated (geophysics, remote sensing and field) approach to address these issues. Firstly, we evaluated GOCE-based global Geopotential models (GGMs) compared to the terrestrial gravity anomalies for 21262 sites to select the optimum model for deriving Bouguer gravity datasets. The Eigen-6C4 was found to have the lowest deviation from the terrestrial gravity anomalies. Secondly, structures and uplifts were mapped on the surface and in the sub-surface. Extensive N-S to NW-SE trending grabens were delineated in areas proximal to the Nile Valley using Palsar-derived DEMs, and hill shade maps; these depressions are here interpreted as basement structures that were reactivated during the opening of the Red Sea and the Gulf of Suez. The sinistral E-W trending faults and shear zones of the Syrian Arc were mapped in northern Egypt from Sinai and across the Eastern and Western Deserts. These structures were mapped on the surface using hill shade images and their extension in the subsurface was successfully detected from Eigen-6C4 model-derived Bouguer and TDR maps. The E-W trending basement uplift (Uweinat-Aswan uplift) was mapped in southern Egypt and the N-S trending Uweinat-Howar uplift was delineated in western Sudan and eastern Chad using TDR maps. Thirdly, hydrological analysis was conducted using GRACE spherical harmonic solutions (RL05), and CSR 0.5° X 0.5°, and JPL Mascon solutions. These showed: (1) pronounced TWS depletion over the Dakhla basin (average of three solutions: -3.03 mm/yr); (2) the south to north groundwater flow from Sudan to Egypt is impeded by the E-W trending Uweinat-Aswan basement uplift, yet the southwest to northeast flow from Chad into Sudan is not obstructed by the Uweinat-Howar uplift, (3) the E-W trending faults and shear zones impede groundwater flow to the north and act as conduits for deep-seated groundwater discharge on the surface in natural depressions (e.g., Qattara) and in the overlying layers.

Old torsion Balance Observations - too old for modern Exploration?

NASA Astrophysics Data System (ADS)

Götze, H.-J.

2003-04-01

Gravity gradiometry is a new gravity measurement technology that could fundamentally change the game of subsurface modelling and enhance geological interpretations: at fully inertial stabilized platforms they provide observed components of the E&{uml;o}tv&{uml;o}s tensor for 3D interpretations in mining and oil exploration and other fields of pure and applied geophysics. Although gravity gradiometry was among the first geophysical methods used successfully in applied Geophysics (E&{uml;o}tv&{uml;o}s torsion balance), the technology fell from favour in the 1930s. From this time measurements, done by torsion balances (Drehwaagen), are presented here which were observed to detect salt domes in the Northwest German basin. The data were digitized from old copies, then reprocessed and recalculated to draw Bouguer anomaly maps. However, the second derivatives of the gravity potential provide also independent data which can be used to constrain forward modelling. 3D modelling of Vxz, Vyz and other components of the E&{uml;o}tv&{uml;o}s tensor provide better insight into the geometry of the salt dome structure than modelling of the Bouguer gravity field. In addition to this first example results from gravity data processing by applying curvature techniques and again 3D forward modelling of second derivatives of the potential of density domains in the uppermost crust in the area of the Dead Sea Transform (Jordan) is presented here. The 3D modelling is conducted by the program package IGMAS which supply possibilities to calculate potential, gravity, its components and the Eötvös tensor components. Based on results so far one can conclude that the knowledge of the "second derivatives of the potential" could fundamentally change the role of gravity field measurements in the process of underground investigations not only for resource exploration but for investigations along large faults systems.

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.

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. The study suggests that the underplate was fundamental to the accretion process and may have played a role in compensating most of the plateau uplift and in localizing stresses.

Impact of GRM: New evidence from the Soviet Union

NASA Technical Reports Server (NTRS)

Mcnutt, M.

1985-01-01

Gravity information released by the Soviet Union allows the quantitative assessment of how the geopotential research mission (GRM) mission might effect the ability to use global gravity data for continental tectonic interpretation. The information is of an isostatic response spectra for eight individual tectonic units in the USSR. The regions examined include the Caroathians, Caucasus, Urals, Pamirs, Tien-Shan, Altal, Chersky Ridge, and East Siberian Platform. The 1 deg x 1 deg gravity data are used to calculate the admittances are used in two different sorts of tectonic studies of mountain belts in the USSR: (1) interpretation of isostatic responses in terms of plate models of compensation for mountainous terrain. Using geologic information concerning time of the orogeny, lithospheric plates involved, and polarity of subduction in collision zones, they convert the best-fitting flexural rigidity to an elastic plate thickness for the lithospheric plate inferred to underlie the mountains; the isostatic admittance functions is an attempt to directly model gravity and topography data for a few select regions in the Soviet Union. By knowing the value of the expected correlation between topography and gravity from the admittances, the Artemjev's map in mountainous areas can be calibrated, and the maps are converted back to Bouguer gravity. This procedure is applied to the Caucasus and southern Urals.

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

The frequency-domain approach for apparent density mapping

NASA Astrophysics Data System (ADS)

Tong, T.; Guo, L.

2017-12-01

Apparent density mapping is a technique to estimate density distribution in the subsurface layer from the observed gravity data. It has been widely applied for geologic mapping, tectonic study and mineral exploration for decades. Apparent density mapping usually models the density layer as a collection of vertical, juxtaposed prisms in both horizontal directions, whose top and bottom surfaces are assumed to be horizontal or variable-depth, and then inverts or deconvolves the gravity anomalies to determine the density of each prism. Conventionally, the frequency-domain approach, which assumes that both top and bottom surfaces of the layer are horizontal, is usually utilized for fast density mapping. However, such assumption is not always valid in the real world, since either the top surface or the bottom surface may be variable-depth. Here, we presented a frequency-domain approach for apparent density mapping, which permits both the top and bottom surfaces of the layer to be variable-depth. We first derived the formula for forward calculation of gravity anomalies caused by the density layer, whose top and bottom surfaces are variable-depth, and the formula for inversion of gravity anomalies for the density distribution. Then we proposed the procedure for density mapping based on both the formulas of inversion and forward calculation. We tested the approach on the synthetic data, which verified its effectiveness. We also tested the approach on the real Bouguer gravity anomalies data from the central South China. The top surface was assumed to be flat and was on the sea level, and the bottom surface was considered as the Moho surface. The result presented the crustal density distribution, which was coinciding well with the basic tectonic features in the study area.

Gravity observations and Bouguer anomaly values for eastern Tennessee

USGS Publications Warehouse

Watkins, J.S.; Yuval, Zvi

1971-01-01

Principal facts for gravity data in eastern Tennessee are presented in computer printout format. These data were used in preparation of Watkins, J. S., 1964, Regional geologic implications of the gravity and magnetic fields of a part of eastern Tennessee.

Response of Gravity, Magnetic, and Geoelectrical Resistivity Methods on Ngeni Southern Blitar Mineralization Zone

NASA Astrophysics Data System (ADS)

Sunaryo

2018-03-01

The research with entitle response of gravity, magnetic, and geoelectrical resistivity methods on Ngeni Southern Blitar mineralization zone has been done. This study aims to find the response of several geophysical methods of gravity, magnetic, and geoelectrical resistivity in an integrated manner. Gravity data acquisition was acquired 224 data which covers the whole region of Blitar district by using Gravity Meter La Coste & Romberg Model “G”, and magnetic data acquisition were acquired 195 data which covers the southern Blitar district only by using Proton Precession Magnetometer G-856. Meanwhile geoelectrical resistivity data only done in Ngeni village which is the location of phyropilite mining with the composition content of Fe, Si, Ca, S, Cu, and Mn by using ABEM Terrameter SAS 300C. Gravity data processing was performed to obtain the Bouguer anomaly value, which included unit conversion, tidal correction, drift correction, correction of tie point, base station correction, free air correction, and Bouguer correction. Magnetic data processing has been done by some corrections i.e daily, drift, and IGRF(International Geomagnetic Refference Field) to obtain the total magnetic anomaly. From gravity data processing has been obtained the simple Bouguer anomaly value in range from -10mGal until 115mGal. From this data processing has been obtained the total magnetic anomaly value in range from -650nT until 800nT. Meanwhile from geoelectrical resistivity 3.03Ωm until 11249.91 Ωm. There is a correlation between gravity anomaly, magnetic anomaly, and geoelectrical resistivity anomaly that are associated with deep anomaly, middle anomaly, and shallow anomaly.

Determination of the Basin Structure Beneath European Side of Istanbul

NASA Astrophysics Data System (ADS)

Karabulut, Savas; Cengiz Cinku, Mulla; Thomas, Michael; Lamontagne, Maurice

2016-04-01

Istanbul (near North Anatolian Fault Zone:NAFZ, Turkey) is located in northern part of Sea of Marmara, an area that has been influenced by possible Marmara Earthquakes. The general geology of Istanbul divided into two stratigraphic unit such as sedimentary (from Oligocene to Quaternary Deposits) and bedrock (Paleozoic and Eocene). The bedrock units consists of sand stone, clay stone to Paleozoic age and limestone to Eocene age and sedimentary unit consist of sand, clay, mil and gravel from Oligocene to Quaternary age. Earthquake disaster mitigation studies divided into two important phases, too. Firstly, earthquake, soil and engineering structure problems identify for investigation area, later on strategic emergency plan can prepare for these problems. Soil amplification play important role the disaster mitigation and the site effect analysis and basin structure is also a key parameter for determining of site effect. Some geophysical, geological and geotechnical measurements are requeired to defined this relationship. Istanbul Megacity has been waiting possible Marmara Earthquake and their related results. In order to defined to possible damage potential related to site effect, gravity measurements carried out for determining to geological structure, basin geometry and faults in Istanbul. Gravity data were collected at 640 sites by using a Scientrex CG-5 Autogravity meter Standard corrections applied to the gravity data include those for instrumental drift, Earth tides and latitude, and the free-air and Bouguer corrections. The corrected gravity data were imported into a Geosoft database to create a grid and map of the Bouguer gravity anomaly (grid cell size of 200 m). As a previously results, we determined some lineminants, faults and basins beneath Istanbul City. Especially, orientation of faults were NW-SE direction and some basin structures determined on between Buyukcekmece and Kucukcekmece Lake.

Gravimetric maps of the Central African Republic

NASA Technical Reports Server (NTRS)

Albouy, J.; Godivier, R. (Principal Investigator)

1982-01-01

Gravimetric maps of the Central African Republic are described including a map of Bouguer anomalies at 1/1,000,000 in two sections (eastern sheet, western sheet) and a map, in color, of Bouguer anomalies at 1/2,000,000. Instrumentation, data acquisition, calibration, and data correction procedures are discussed.

GRAIL Gravity Observations of the Transition from Complex Crater to Peak-Ring Basin on the Moon: Implications for Crustal Structure and Impact Basin Formation

NASA Technical Reports Server (NTRS)

Baker, David M. H.; Head, James W.; Phillips, Roger J.; Neumann, Gregory A.; Bierson, Carver J.; Smith, David E.; Zuber, Maria T.

2017-01-01

High-resolution gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) mission provide the opportunity to analyze the detailed gravity and crustal structure of impact features in the morphological transition from complex craters to peak-ring basins on the Moon. We calculate average radial profiles for free-air anomalies and Bouguer anomalies for peak-ring basins, proto-basins, and the largest complex craters. Complex craters and proto-basins have free-air anomalies that are positively correlated with surface topography, unlike the prominent lunar mascons (positive free-air anomalies in areas of low elevation) associated with large basins. The Bouguer gravity anomaly profiles of complex craters are highly irregular, with central positive anomalies that are generally absent or not clearly tied to interior morphology. In contrast, gravity profiles for peak-ring basins (approx. 200 km to 580 km) are much more regular and are highly correlated with surface morphology. A central positive Bouguer anomaly is confined within the peak ring and a negative Bouguer anomaly annulus extends from the edge of the positive anomaly outward to about the rim crest. A number of degraded basins lacking interior peak rings have diameters and gravity patterns similar to those of well-preserved peak-ring basins. If these structures represent degraded peak-ring basins, the number of peak-ring basins on the Moon would increase by more than a factor of two to 34. The gravity anomalies within basins are interpreted to be due to uplift of the mantle confined within the peak ring and an annulus of thickened crust between the peak ring and rim crest. We hypothesize that mantle uplift is influenced by interaction between the transient cavity and the mantle. Further, mascon formation is generally disconnected from the number of basin rings formed and occurs over a wide range of basin sizes. These observations have important implications for models of basin and mascon formation on the Moon and other planetary bodies.

Map showing drill-hole depths, lithologic intercepts, and partial isopachs of basin fill in the Winnemucca 1 degree by 2 degrees Quadrangle, Nevada

USGS Publications Warehouse

Moring, B.C.

1990-01-01

Wells logs used for this map of the Winnemucca quadrangle are from the following sources: (1) logs of more than 1,000 water wells reported to the State of Nevada Division of Water Resources, which are on file with them in Reno and at the with U.S. Geological Survey in Carson City, (2) 44 petroleum wells collected by the Nevada Bureau of Mines (Lintz, 1957; Schilling and Garside, 1968; Garside and Schilling, 1977, Garside and others, 1977; 1988), and (3) Two geothermal wells reported in Zoback (1979) and Flynn and others (1982). Data from isostatic residual and Bouguer gravity maps by Wagini (1985) contributed to the interpretation of basin configuration. Gravity models of Dixie Valley (Schaefer, 1982, and Speed, 1976) and Grass Valley (Grannell and Noble, 1977) and seismic profiles of Grass and Pine Valleys (Potter and others, 1987) helped refine basis interpretations in those areas. The geologic base map of Paleozoic and Mesozoic igneous and sedimentary rocks, Tertiary volcanic and sedimentary rocks, and Cenozoic structures was simplified from Stewart and Carlson (1976b).

2D Gravimetric Modeling of the Vargeão Impact Structure, Brazil

NASA Astrophysics Data System (ADS)

Giacomini, B. B.; Leite, E. P.; Ferreira, J. C.; Vasconcelos, M. A.; Crosta, A. P.

2013-05-01

Although common in other bodies of the solar system, impact craters formed in basaltic terrains are rare on Earth and only a few examples are known. One of the examples is the impact structure of Vargeão, south of Brazil, which was formed above the Paraná Basin. The impact origin of this structure was confirmed in 2009. This work focused on the construction of 2D subsurface geological models based on new ground gravimetric data obtained using a CG-5 gravity meter. These models were constrained by geological field data and one seismic section crossing the impact structure. Bouguer anomalies were calculated from gravity acceleration measured at 419 stations irregularly distributed on the area of the impact structure. The theoretical gravity acceleration at each station was calculated using the WGS84 reference ellipsoid. A regional component represented by a polynomial trend surface was extracted from the total Bouguer anomalies. The residual Bouguer map shows a well-defined circular negative anomaly on the central portion of the structure. Such gravity low can be associated with post-impact uplifting of sedimentary rocks, in this case the sandstones of Pirambóia and Botucatu Formations. The hypothesis of uplifting is supported by field observations of sandstone outcrops at the central portion of the structure. This is similar to the case of Steinheim structure in Germany. Although not spatially coincident with its edges, a strong positive anomaly surrounds its center and may be related to different levels of basalt fractures formed after the impact. Breccias near the center are more fractured leading to lower global densities. The density values of the clean and fractured basalts, sandstones and breccias were measured from rock samples and each average value was used for the gravimetric modeling. Edge structural features and a central uplift observed in the seismic section were included in the gravimetric models. The lateral extension of the uplifted sandstone in our models varies between 2000 m at the base and approximately 100 m at the top. The average thickness of the basalt layer in this region is 1000 m.

Basement-involved faults and deep structures in the West Philippine Basin: constrains from gravity field

NASA Astrophysics Data System (ADS)

Wang, Gang; Jiang, Suhua; Li, Sanzhong; Zhang, Huixuan; Lei, Jianping; Gao, Song; Zhao, Feiyu

2017-06-01

To reveal the basement-involved faults and deep structures of the West Philippine Basin (WPB), the gravitational responses caused by these faults are observed and analyzed based on the latest spherical gravity model: WGM2012 Model. By mapping the free-air and Bouguer gravity anomalies, several main faults and some other linear structures are located and observed in the WPB. Then, by conducting a 2D discrete multi-scale wavelet decomposition, the Bouguer anomalies are decomposed into the first- to eighth-order detail and approximation fields (the first- to eighth-order Details and Approximations). The first- to third-order Details reflect detailed and localized geological information of the crust at different depths, and of which the higher-order reflects gravity field of the deeper depth. The first- to fourth-order Approximations represent the regional gravity fields at different depths of the crust, respectively. The fourth-order Approximation represents the regional gravity fluctuation caused by the density inhomogeneity of Moho interface. Therefore, taking the fourth-order Approximation as input, and adopting Parker-Oldenburg interactive inversion, We calculated the depth of Moho interface in the WPB. Results show that the Moho interface depth in the WPB ranges approximately from 8 to 12 km, indicating that there is typical oceanic crust in the basin. In the Urdaneta Plateau and the Benham Rise, the Moho interface depths are about 14 and 16 km, respectively, which provides a piece of evidence to support that the Banham Rise could be a transitional crust caused by a large igneous province. The second-order vertical derivative and the horizontal derivatives in direction 0° and 90° are computed based on the data of the third-order Detail, and most of the basement-involved faults and structures in the WPB, such as the Central Basin Fault Zone, the Gagua Ridge, the Luzon-Okinawa Fault Zone, and the Mindanao Fault Zone are interpreted by the gravity derivatives.

Modeling and Inversion of three-dimensional crustal structures beneath the Pyrenees and their foreland basins based upon geological, gravimetric and seismological data

NASA Astrophysics Data System (ADS)

Spangenberg, Hannah; Chevrot, Sébastien; Courrioux, Gabriel; Guillen, Antonio

2017-04-01

Our goal is to obtain a three-dimensional (3D) model of mass density and seismic velocities beneath the Pyrenees and their foreland basins (Aquitaine and Ebro basins), which accounts for all the geological and geophysical information available for that region. This model covers the whole mountain range going from the Atlantic Ocean to the Mediterranean Sea, and from the Iberian range to the Massif Central. The model is described by different units: the lower, middle, and upper crusts, the accretionary prism, and the consolidated and unconsolidated sediment layers. Furthermore, a sub-continental, serpentinized European mantle is introduced to describe the exhumed mantle bodies which are responsible for the positive Bouguer gravity anomalies in the western Pyrenees. We build a first 3D model using all the geological information: drill-hole surveys, seismic sections, and the geological map. We use the potential field method implemented in Geomodeler to interpolate these geological data. However, these data are too sparse to build a model that explains seismic travel times or gravimetric data, especially the Labourd and the St. Gaudens Bouguer gravity anomalies. In addition, inconsistencies between the different data sets exist. We thus add by trial and error additional data points, comparing modeled and observed Bouguer gravimetric anomalies. The result of this procedure is a 3D geological model that respects the geological data and explains the measured Bouguer gravimetric anomalies. In a second step, we use this model to determine the average density and seismic velocities inside each geological unit assuming uniform layers. To constrain the seismic velocities we use travel time picks extracted from the bulletin of the Pyrenean seismicity released by the Observatoire Midi Pyrenées. In a third step, we use this 3D a priori model in a Monte Carlo inversion to invert jointly gravimetric data and seismic travel times from the bulletin. This probabilistic approach yields detailed information about the sedimentary foreland basins and the crustal structures beneath the Pyrenees. We will present and discuss different key steps of the construction of the 3D model of the Pyrenees. We will also compare selected cross-sections extracted from this model to the ECORS profiles, as well as CCP stacks of receiver functions along several PYROPE transects. Keywords: Pyrenees, 3D modeling, gravity, seismic tomography, joint inversion

Principal facts for gravity stations in the vicinity of San Bernardino, Southern California

USGS Publications Warehouse

Anderson, Megan L.; Roberts, Carter W.; Jachens, Robert C.

2000-01-01

New gravity measurements in the vicinity of San Bernardino, California were collected to help define the characteristics of the Rialto-Colton fault. The data were processed using standard reduction formulas and parameters. Rock properties such as lithology, magnetic susceptibility and density also were measured at several locations. Rock property measurements will be helpful for future modeling and density inversion calculations from the gravity data. On both the Bouguer and isostatic gravity maps, a prominent, 13-km long (8 mi), approximately 1-km (0.62 mi) wide gradient with an amplitude of 7 mGal, down to the northeast, is interpreted as the gravity expression of the Rialto-Colton fault. The gravity gradient strikes in a northwest direction and runs from the San Jacinto fault zone at its south end to San Sevine Canyon at the foot of the San Gabriel mountains at its north end. The Rialto-Colton fault has experienced both right-lateral strike-slip and normal fault motion that has offset basement rocks; therefore it is interpreted as a major, through-going fault.

Analysis of gravity data beneath Endut geothermal prospect using horizontal gradient and Euler deconvolution

NASA Astrophysics Data System (ADS)

Supriyanto, Noor, T.; Suhanto, E.

2017-07-01

The Endut geothermal prospect is located in Banten Province, Indonesia. The geological setting of the area is dominated by quaternary volcanic, tertiary sediments and tertiary rock intrusion. This area has been in the preliminary study phase of geology, geochemistry, and geophysics. As one of the geophysical study, the gravity data measurement has been carried out and analyzed in order to understand geological condition especially subsurface fault structure that control the geothermal system in Endut area. After precondition applied to gravity data, the complete Bouguer anomaly have been analyzed using advanced derivatives method such as Horizontal Gradient (HG) and Euler Deconvolution (ED) to clarify the existance of fault structures. These techniques detected boundaries of body anomalies and faults structure that were compared with the lithologies in the geology map. The analysis result will be useful in making a further realistic conceptual model of the Endut geothermal area.

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

The gravity anomaly of Mount Amiata; different approaches for understanding anomaly source distribution

NASA Astrophysics Data System (ADS)

Girolami, C.; Barchi, M. R.; Heyde, I.; Pauselli, C.; Vetere, F.; Cannata, A.

2017-11-01

In this work, the gravity anomaly signal beneath Mount Amiata and its surroundings have been analysed to reconstruct the subsurface setting. In particular, the work focuses on the investigation of the geological bodies responsible for the Bouguer gravity minimum observed in this area.

Decomposing Worldwide Complete Spherical Bouguer Gravity Anomaly Using 2-D Empirical Method

NASA Astrophysics Data System (ADS)

Firdaus, Ruhul; Mey Ekawati, Gestin

2017-04-01

Currently available worldwide gravity anomaly data provides a high-resolution (2’×2’) of Complete Spherical Bouguer Anomaly (CSBA) based on the available information of the Earth gravity field from surface and satellite measurements. The data has not only been provided and processed thoroughly but it also has been claimed to be appropriate for various geophysical applications. Therefore, the analysis of gravity anomaly is becoming increasingly significant for the earth sciences as a whole and assisting both shallow and deep geological problems. Earth gravity anomaly has to be analyzed carefully as it has very complex data due to anomaly mixing of the density masses spread over the Earth horizontally and vertically. The bigger the spatial coverage of data (e.g. global scale data), the more severe the data from anomaly mixing due to various wavelength. BEMD is an empirical method supposedly suitable with highly oscillation-mixing data. It can effectively isolate each local anomaly in details and is analogized as successively reverse moving average with local windowing. BEMD is designed to reduce multi-component, non-linear gravity field data to a series of single local anomaly contributions. Anomaly from a single body was assumed as a mono-component signal. The main advantage of BEMD processing techniques is to present the subtle details in the data which are not clearly identified in anomaly maps, without specifying any prior information about the nature of the source bodies. As the result, we have identified regional anomalies due to the drift of continental and oceanic masses considered as crust-regional anomaly (CRA). We remove the CRA from the CBA to provide surface-residual anomaly (SRA) where shallow geologic bodies reveal. Meanwhile, the CRA itself can be used as reference to reduce this high magnitude anomaly from any measurement data to exhibit only shallow body anomaly. Further analysis can be carried out to build a general understanding of the details and parameters of the shallower or deeper causative body distributions.

Isostasy, Stress and Gravitational Potential Energy in the Southern Atlantic - Insights from Satellite Gravity Observations

NASA Astrophysics Data System (ADS)

Goetze, H. J.; Klinge, L.; Scheck-Wenderoth, M.; Dressel, I.; Sippel, J.

2015-12-01

New satellite gravity fields e.g. EGM2008, GoCo3S and very recently EIGEN-6C4 (Förste et al., 2014) provide high-accuracy and globally uniform information of the Earth's gravity field and partly of its gradients. The main goal of this study is to investigate the impact of this new gravity field and its processed anomalies (Bouguer, Free-air and Vening-Meinesz residual fields) on lithospheric modelling of passive plate margins in the area of the Southern Atlantic. In an area fixed by the latitudes 20° N - 50° S and longitudes 70° W - 20° E we calculated station-complete Bouguer anomalies (bathymetry/topography corrected) both on- and offshore and compared them with the gravity effect of a velocity model which bases on S - waves tomography (Schaeffer and Lebedev, 2013). The corresponding maps provide more insight in the abnormal mass distribution of oceanic lithosphere and the ocean-continent transition zones on both sides of the Atlantic Ocean than Free-air anomalies which are masked by bathymetry. In a next step we calculated isostatic residual fields (Vening-Meinesz isostasy with regard to different lithospheric rigidities) to remove global components (long wavelengths) from the satellite gravity. The Isostatic residual field will be compared with the GPE (gravitational potential energy). GPE variations in the Southern Atlantic, relative to the reference state, were calculated as ΔGPE. Often the oceanic lithosphere is characterized by negative ΔGPE values indicating that the ocean basin is in compression. Differences from this observation will be compared with the state of stress in the area of the passive margins of South America and South Africa and the oceanic lithosphere in between. Schaeffer, A. J. and S. Lebedev, Global shear-speed structure of the upper mantle and transition zone. Geophys. J. Int., 194 (1), 417-449, 2013. doi:10.1093/gji/ggt095

Geologic map of the Sherbrooke-Lewiston area, Maine, New Hampshire, and Vermont, United States, and Quebec, Canada

USGS Publications Warehouse

Moench, R.H.; Boone, G.M.; Bothner, Wallace A.; Boudette, E.L.; Hatch, N.L.; Hussey, A. M.; Marvinney, R.G.

1995-01-01

This map is part of a folio of maps of the Lewiston 1° x 2° quadrangle, Maine, New Hampshire, and Vermont, and part of the Sherbrooke 1° x 2° quadrangle, Maine, New Hampshire, and Vermont, United States, and Quebec, Canada, prepared under the Conterminous United States Mineral Assessment Program (CUSMAP). Adjacent areas in Quebec are shown, in order to illustrate the geologic continuity between northwestern Maine and northern Vermont and New Hampshire. Other results of the project are contained in reports by Nowlan and others (1990a,b,c; stream sediment geochemistry), and Cox (1990; potential tin resources related to the White Mountain Plutonic-Volcanic Suite), Bothner and others (in press; complete Bouguer gravity and aeromagnetic maps), Moench and Boudette (in press, geologic synthesis and mineral occurrence map), and Moench (in press; metallic mineral resources).

Connected magma plumbing system between Cerro Negro and El Hoyo Complex, Nicaragua revealed by gravity survey

NASA Astrophysics Data System (ADS)

MacQueen, Patricia; Zurek, Jeffrey; Williams-Jones, Glyn

2016-11-01

Cerro Negro, near León, Nicaragua is a young, relatively small basaltic cinder cone volcano that has been unusually active during its short lifespan. Multiple explosive eruptions have deposited significant amounts of ash on León and the surrounding rural communities. While a number of studies investigate the geochemistry and stress regime of the volcano, subsurface structures have only been studied by diffuse soil gas surveys. These studies have raised several questions as to the proper classification of Cerro Negro and its relation to neighboring volcanic features. To address these questions, we collected 119 gravity measurements around Cerro Negro volcano in an attempt to delineate deep structures at the volcano. The resulting complete Bouguer anomaly map revealed local positive gravity anomalies (wavelength 0.5 to 2 km, magnitude +4 mGal) and regional positive (10 km wavelength, magnitudes +10 and +8 mGal) and negative (12 and 6 km wavelength, magnitudes -18 and -13 mGal) Bouguer anomalies. Further analysis of these gravity data through inversion has revealed both local and regional density anomalies that we interpret as intrusive complexes at Cerro Negro and in the Nicaraguan Volcanic Arc. The local density anomalies at Cerro Negro have a density of 2700 kg m-3 (basalt) and are located between -250 and -2000 m above sea level. The distribution of recovered density anomalies suggests that eruptions at Cerro Negro may be tapping an interconnected magma plumbing system beneath El Hoyo, Cerro La Mula, and Cerro Negro, and more than seven other proximal volcanic features, implying that Cerro Negro should be considered the newest cone of a Cerro Negro-El Hoyo volcanic complex.

Assessment of the Extent of Land Deformation Associated with Salt Domes within the Jazan City and Surroundings, Saudi Arabia

NASA Astrophysics Data System (ADS)

Pankratz, H. G.; Sultan, M.; Fathy, K.; AlMogren, S. M.; Harbi, H.; Sefry, S.; Emil, M.; Elkadiri, R.; Ahmed, M.; Othman, A.; Chouinard, K.

2016-12-01

The Jazan city in the Jazan Province of the Kingdom of Saudi Arabia is a vibrant and rapidly growing economic center and port. The old city of Jazan is centered over a salt dome (diaper) that crops out over an area, 3-4 km wide and 20 to 40 m above surroundings. The intrusion of the diaper into the overlying cap rock causes uneven surfaces, compromises building foundations, and causes infrastructural problems. Our study is aimed at the assessment of the salt dome-related land deformation. Using observations acquired over known locations of salt domes in Jazan and neighboring Farsan Islands, we identified criteria by which previously unidentified, near-surface salt domes, could be mapped. The selected criteria and/or applied methodologies included: (1) deformation over potential salt dome locations detected from Envisat, ERS-2, and Sentinel-1 scenes using the Stanford Method for Persistent Scatterers [StaMPs] and SARscape software. Uplift rates of about 3 mm/yr were observed over the salt dome outcrop in Jazan with increasing rates towards the center, indicating continuous rise of the salt diaper. (2) Local elevation highs over potential, near surface, salt dome intrusions observed in high spatial resolution (12.5 m), PALSAR digital elevation model (DEM). The elevation the Jazan dome is 45m high, whereas its surroundings are 15-30m high. (3) Negative Bouguer gravity anomalies over potential salt dome locations (Bouguer maps generated from 714 m interval airborne gravity data). Negative Bouguer anomalies were observed over the salt domes in Jazan (-3 mGal) and in Farsan (-30 mGal). (4) Boundaries of the potential salt domes extracted from zero tilt contour values on tilt derivative maps. (5) Shallow (< 2km) modeled depth to identified potential salt dome locations (software: Grav2dc 2-D modeling software). Zero contour values and 2-D modeling was used to identify the location and depth of the source anomaly (depth: Jazan = 0 m). (6) Spatial correlation (in a GIS platform) of observations extracted from remote sensing, geophysical, GPS, and DEM datasets (items 1 through 5). Eight previously unidentified locations of potential near-surface salt domes were identified along the Red Sea coastline within the scene extent, five of which were north of the salt dome outcrop and three to the south.

Structural Control and Groundwater Flow in the Nubian Aquifer

NASA Astrophysics Data System (ADS)

Fathy, K.; Sultan, M.; Ahmed, M.; Save, H.; Emil, M. K.; Elkaliouby, B.

2017-12-01

An integrated research approach (remote sensing, field, geophysics) was conducted to investigate the structural control on groundwater flow in large aquifers using the less studied Nubian Sandstone Aquifer System (NSAS) of NE Africa as a test site. The aquifer extends over 2.2 x 106 km2 in Egypt, Libya, Chad, and Sudan and consists of thick (> 3 kms), water-bearing, Paleozoic and Mesozoic sandstone with intercalations of Tertiary shale and clay. It is subdivided into three sub-basins (Northern Sudan Platform [NSP], Dakhla [DAS], and Kufra) that are separated by basement uplifts (e.g., E-W trending Uweinat-Aswan uplift that separates DAS from the NSP). Aquifer recharge occurs in the south (NSP and southern Kufra) where the aquifer is unconfined and precipitation is high (Average Annual Precipitation [AAP]: 117 mm/yr.) and discharge is concentrated in the north (DAS and northern Kufra). Our approach is a three-fold exercise. Firstly, we compared GOCE-based Global Geopotential Models (GGMs) to terrestrial gravity anomalies for 21262 sites to select the optimum model for deriving Bouguer gravity anomalies. Secondly, structures and uplifts were mapped using hill shade images and their extension in the subsurface were mapped using the Eigen_6C4 model-derived Bouguer anomalies and their Tilt Derivative products (TDR). Thirdly, hydrological analysis was conducted using GRACE CSR 1° x 1° mascon solutions to investigate the mass variations in relation to the mapped structures. Our findings include: (1) The Eigen-6C4 is the optimum model having the lowest deviation (9.122 mGal) from the terrestrial gravity anomalies; (2) the surface expressions of structures matched fairly well with their postulated extensions in the subsurface; (3) identified fault systems include: Red Sea rift-related N-S to NW-SE trending grabens formed by reactivating basement structures during Red Sea opening and Syrian arc-related NE-SW trending dextral shear systems; (4) TWS patterns are uniform throughout the length (hundreds of kilometers) of the identified shear systems but are dissimilar from those extracted in areas proximal to, but outside of, the shear zones; and (5) basement uplifts impede or redirect the groundwater flow.

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 either side of the fault are Proterozoic - Cretaceous metamorphic or/and plutonic rocks. Previous work based on geologic mapping hypothesized the existence of a shallow, low angle Abel Mountain Thrust in which crystalline rocks were thrust over Miocene sedimentary rocks, near Apache Saddle. However, gravity models indicate the crystalline rocks are vertically extensive and form a positive flower structure bounded by high angle faults. Also, based on the thickness of fault adjacent sedimentary cover, the gravity models suggest a minimum exhumation of 5-6 km for crystalline rocks in the south. Assuming exhumation began with the switch from the transtensional San Gabriel Fault to transpressional San Andreas Fault at approximately 5 Ma, this indicates exhumation rates of 1 km/Ma. Overall, the broad gravity highs observed along the southern transects are due to uplift of basement rocks in this area.

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

NASA Astrophysics Data System (ADS)

Best, John A.; Barazangi, Muawia; Al-Saad, Damen; Sawaf, Tarif; Gebran, Ali

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 ±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.

Gravity modelling of the Hellenic subduction zone — a regional study

NASA Astrophysics Data System (ADS)

Casten, U.; Snopek, K.

2006-05-01

The Hellenic subduction zone is clearly expressed in the arc-shaped distribution of earthquake epicenters and gravity anomalies, which connect the Peloponnesos with Crete and Anatolia. In this region, oceanic crust of the African plate collides northward with continental crust of the Aegean microplate, which itself is pushed apart to the south-west by the Anatolian plate and, at the same time, is characterised by crustal extension. The result is an overall collision rate of up to 4 cm/year and a retreating subduction process. Recent passive and active seismic studies on and around Crete gave first, but not in all details consistent, structural results useful for supporting gravity modelling. This was undertaken with the aim of presenting the first 3D density structure of the entire subduction zone. Gravity interpretation was based on a Bouguer map, newly compiled using data from land, marine and satellite sources. The anomalies range from + 170 mGal (Cretan Sea) to - 10 mGal (Mediterranean Ridge). 3D gravity modelling was done applying the modelling software IGMAS. The computed Bouguer map fits the low frequency part of the observed one, which is controlled by variations in Moho depth (less than 20 km below the Cretan Sea and extending 30 km below Crete) and the extremely thick sedimentary cover (partly up to 18 km) of the Mediterranean Ridge. The southernmost edge of the Eurasian plate, with its more triangular-shaped backstop area, was traced south off Crete. Only 50 to 100 km further to the south, the edge of the African continent was traced as well. In between these boundaries there is African oceanic crust, which has a clear arc-shaped detachment line situated at the Eurasian continental edge. The subduction arc is open towards the north, its slab separates hotter mantle material (lower density) below the updoming Moho of the Cretan Sea from colder one (higher density) in the south. Subjacent to the upper continental crust of Crete is a thickened layer of lower crust followed by the subducted oceanic crust with some mantle material as intermediate layer. The depth of the oceanic Moho below Crete is 50 km. The presence and structure of subducted or underplated sediments remains uncertain.

Geophysical investigation using gravity data in Kinigi geothermal field, northwest Rwanda

NASA Astrophysics Data System (ADS)

Uwiduhaye, Jean d.'Amour; Mizunaga, Hideki; Saibi, Hakim

2018-03-01

A land gravity survey was carried out in the Kinigi geothermal field, Northwest Rwanda using 184 gravity stations during August and September, 2015. The aim of the gravity survey was to understand the subsurface structure and its relation to the observed surface manifestations in the study area. The complete Bouguer Gravity anomaly was produced with a reduction density of 2.4 g/cm3. Bouguer anomalies ranging from -52 to -35 mGals were observed in the study area with relatively high anomalies in the east and northwest zones while low anomalies are observed in the southwest side of the studied area. A decrease of 17 mGals is observed in the southwestern part of the study area and caused by the low-density of the Tertiary rocks. Horizontal gradient, tilt angle and analytical signal methods were applied to the observed gravity data and showed that Mubona, Mpenge and Cyabararika surface springs are structurally controlled while Rubindi spring is not. The integrated results of gravity gradient interpretation methods delineated a dominant geological structure trending in the NW-SE, which is in agreement with the regional geological trend. The results of this gravity study will help aid future geothermal exploration and development in the Kinigi geothermal field.

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.

Investigation of Crustal Thickness in Eastern Anatolia Using Gravity, Magnetic and Topographic Data

NASA Astrophysics Data System (ADS)

Pamukçu, Oya Ankaya; Akçığ, Zafer; Demirbaş, Şevket; Zor, Ekrem

2007-12-01

The tectonic regime of Eastern Anatolia is determined by the Arabia-Eurasia continent-continent collision. Several dynamic models have been proposed to characterize the collision zone and its geodynamic structure. In this study, change in crustal thickness has been investigated using gravity, magnetic and topographic data of the region. In the first stage, two-dimensional low-pass filter and upward analytical continuation techniques were applied to the Bouguer gravity data of the region to investigate the behavior of the regional gravity anomalies. Next the moving window power spectrum method was used, and changes in the probable structural depths from 38 to 52 km were determined. The changes in crustal thickness where free air gravity and magnetic data have inversely correlated and the type of the anomaly resources were investigated applying the Euler deconvolution method to Bouguer gravity data. The obtained depth values are consistent with the results obtained using the power spectrum method. It was determined that the types of anomaly resources are different in the west and east of the 40° E longitude. Finally, using the obtained findings from this study and seismic velocity models proposed for this region by previous studies, a probable two-dimensional crust model was constituted.

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 within the ice shell) dominate the Bouguer gravity. Thus, gravity can be used to explore this interface. To test whether active volcanism can be detected, we scale gravity models for the terrestrial planets down to a body the size of Europa's silicate core and with a density contrast consistent with a rock-water interface. Here, Venus and Earth serve as proxies for volcanically active bodies, while the Moon and Mars are proxies for inactive bodies. Additionally, we create gravity from synthetic topography on the base of the ice shell. Maps of the Bouguer-gravity and geoid anomalies reveal that active volcanism is characterized by small amplitudes (a few mGal and a few meters). Large-scale topography on the base of the ice shell adds larger geoid anomalies (tens of meters) but still small gravity anomalies. The absence of volcanic activity on the rock-water interface is likely characterized by larger anomalies (tens of mGal and tens of meters), plausibly because the cooler thermal structure permits the rocky lithosphere to support larger mass-density anomalies. Thus, study of the gravity may illuminate the habitability of Europa, and gravity and topography experiments on any future mission (e.g., the Europa Clipper) should be given the highest scientific priority.

Tectonics of the Philippines and ambient regions from geophysical inversions

NASA Astrophysics Data System (ADS)

Liu, W.; Li, C.; Zhou, Z.; Fairhead, J. D.

2012-12-01

The geological study in the Philippines and ambient regions is relatively low so far for the rather scanty data and complex geological structure. Therefore it is a challenge to do the research with limited data. In this paper, an investigation of the Philippines and surrounding area has been carried out using regional magnetic and gravity anomalies. Owing to the difficulties and limitations in reduction to the pole at the low latitudes, analytical signal amplitudes of magnetic anomalies are calculated as the equivalent substitute. Application of the Parker-Oldenburg algorithm to Bouguer gravity anomalies yields a 3D Moho topography. Curie-point depths are estimated from the magnetic anomalies using a windowed wavenumber-domain algorithm. This paper aims to reveal the structure of the Manila subduction zone accurately, and moreover, to clarify the interplay between the magmatism and subduction in the Manila Trench and East Luzon Trough. On the basis of Bouguer gravity anomaly and AS(analytical signal) of magnetic anomaly, the positions of hydrated mantle wedge in the subduction zones of this area are identified in the areas charicterizd by the distribution of high-and low value of Bouguer gravity anomaly or the paralell high value of Bouguer gravity anomaly and AS. Using our inversion results together with some other published information, the boundaries of Palawan Block, Philippine Mobile Belt and Sulu-Celebes Block are defined and the collision history of PCB(Palawan continental block)-PMB (Philippine mobile belt) and PCB-Sulu Sea is also discussed. A "seismic gap" near the 14 degree north latitude on Manila Trench, mentioned in previous studies, is thought to be induced by the slab melting and plastic behavior due to the relatively high geothermal gradient. In the central Philippines, it is likely that an incipient collision-related rifting is proceeding. Furthermore, a possible new evolution model of Sulu Sea, in which the Cagayan Ridge area is thought to be the palaeo-subduction zone and volcanic arc and Palawan Trough is supposed to be a foredeep rather than an extinct trench, is presented. In addition, mantle serpentinization extent of this area is also estimated according to Curie point and Moho depths.

Interpretations of Complete Bouguer Gravity Anomalies from the GRAV-D Project in Alaska

NASA Astrophysics Data System (ADS)

Diehl, T. M.; Preaux, S. A.; Childers, V. A.

2010-12-01

The GRAV-D (Gravity for the Redefinition of the American Vertical Datum) Project of the U.S. National Geodetic Survey plans to collect airborne gravity data across the entire U.S. and its holdings over the next decade. The goal of the project is to create a gravimetric geoid model to use as the vertical datum for the U.S. by 2021. Airborne gravity survey work began more than two years ago, with Alaska as a high priority for new data collection. Data collection there is underway and will be ongoing for several more years, but two roughly 400 km x 400 km surveys have been completed: in 2008 (centered over Cook Inlet near Anchorage) and in 2009 (centered over the Interior, to the north of the Alaska Range and west of Fairbanks). The gravity data for both surveys was collected with a MicroG LaCoste TAGS system but each survey utilized a different aircraft and survey layout. The 2008 survey was flown at 35,000 ft with the NOAA Cessna Citation jet, with 10 km data line spacing and 60 km cross lines spacing. The 2009 survey was flown at 12,500 ft with the Naval Research Lab King Air (RC-12) turboprop, with 7.5 km data line spacing and 37.5 cross line spacing. The 2008 data reveal the > 20 km resolution gravity effects of all the near-trench features (from accretionary prism to volcanic arc) for a 400 km stretch of the active plate boundary. In comparison, the 2009 gravity data allow a slightly better resolution (> 15 km) view of the distal deformation to the north of the Alaska Range. The free-air gravity disturbances for each survey were computed and then complete (terrain-corrected) Bouguer gravity anomalies were calculated with Gauss-Legendre Quadrature integration (von Frese, et al., 1999) using standard density assumptions. Topography used to calculate the corrections came from the freely-available GTOPO30 (USGS, online) and bathymetry from the Smith and Sandwell (1997) altimetry-derived data. Interpretations of the complete Bouguer gravity anomalies will be made in the context of the tectonic activity in southern Alaska.

Geophysical Characterization of Some Terranes and the Geophysical Modeling of Candidate Suture Zones

NASA Technical Reports Server (NTRS)

Ravat, D.

1997-01-01

Indian participation in this project was terminated during the last year by a sudden withdrawal of support by the Department of Science and Technology, India, to the Indian Institute of Geomagnetism, Bombay. As a result, significant changes in the project focus had to be undertaken. Much of the work carried out at Southern Illinois University at Carbondale during the first year of the project anticipated the Indian participation and included development of computer programs to be used on gravity and magnetic data from the Indian subcontinent and preparations for fieldwork, tutorials, and workshops in India. Despite these setbacks, which were beyond our control, a number of significant tasks have been accomplished during the project period. These include: (1) Completion of digitization of the regional Bouguer gravity anomaly map of India and the regional ground total intensity magnetic anomaly map of India at an overdetermined spacing of 0.05 degrees. (2) We investigated and assessed the limitations of the Euler method using environmental examples because detailed aeromagnetic maps of parts of India were not available for interpretation by this method. (3) We also undertook an assessment of a suture zone between the Nyaza Craton (Archean) and the Mozambique Belt (Pan African) in the Kenya Rift, Africa, using gravity anomalies and the lithospheric seismological models. (4) We studied Magsat and high-altitude (approx. 4 km) aeromagnetic data over Canada.

Geologic Map of Central (Interior) Alaska

USGS Publications Warehouse

Wilson, Frederic H.; Dover, James H.; Bradley, Dwight C.; Weber, Florence R.; Bundtzen, Thomas K.; Haeussler, Peter J.

1998-01-01

Introduction: This map and associated digital databases are the result of a compilation and reinterpretation of published and unpublished 1:250,000- and limited 1:125,000- and 1:63,360-scale mapping. The map area covers approximately 416,000 sq km (134,000 sq mi) and encompasses 25 1:250,000-scale quadrangles in central Alaska. The compilation was done as part of the U.S. Geological Survey National Surveys and Analysis project, whose goal is nationwide assemble geologic, geochemical, geophysical, and other data. This map is an early product of an effort that will eventually encompass all of Alaska, and is the result of an agreement with the Alaska Department of Natural Resources, Division of Oil And Gas, to provide data on interior basins in Alaska. A paper version of the three map sheets has been published as USGS Open-File Report 98-133. Two geophysical maps that cover the identical area have been published earlier: 'Bouguer gravity map of Interior Alaska' (Meyer and others, 1996); and 'Merged aeromagnetic map of Interior Alaska' (Meyer and Saltus, 1995). These two publications are supplied in the 'geophys' directory of this report.

Contribution de la gravimétrie à l'étude de la structure du bassin de Tadla (Maroc) : Implications hydrogéologiques

NASA Astrophysics Data System (ADS)

Najine, Abdessamad; Jaffal, Mohammed; Khammari, Kamal El; Aïfa, Tahar; Khattach, Driss; Himi, Mahjoub; Casas, Albert; Badrane, Said; Aqil, Hicham

2006-08-01

This study is based on the analysis and the interpretation of the gravity data of the Tadla basin. Its purpose is to increase the knowledge of this basin structure. A residual anomaly map was first calculated from the Bouguer anomaly data witch are strongly affected by a regional gradient. The computed map provides information on the ground density variation but it does not bring enough of new elements. Data filtering allows us to emphasize the structures affecting the basin. We chose the horizontal gradient coupled to the upward continuation techniques that permit to highlight news structures and to give information on their dip. The elaborated structural map of the study area constitutes a useful document for rationalizing the future groundwater exploration in the Tadla basin. To cite this article: A. Najine et al., C. R. Geoscience 338 (2006).

Eastern US crustal thickness estimates from spectral analysis and inversion of onshore Bouguer gravity anaomalies

NASA Astrophysics Data System (ADS)

Dybus, W.; Benoit, M. H.; Ebinger, C. J.

2011-12-01

The crustal thickness beneath much of the eastern half of the US is largely unconstrained. Though there have been several controlled source seismic surveys of the region, many of these studies suffer from rays that turn in the crust above the Moho, resulting in somewhat ambiguous crustal thickness values. Furthermore, the broadband seismic station coverage east of the Mississippi has been limited, and most of the region remains largely understudied. In this study, we estimated the depth to the Moho using both spectral analysis and inversion of Bouguer gravity anomalies. We systematically estimated depths to lithospheric density contrasts from radial power spectra of Bouguer gravity within 100 km X 100 km windows eastward from the Mississippi River to the Atlantic Coast, and northward from North Carolina to Maine. The slopes and slope breaks in the radial power spectra were computed using an automated algorithm. The slope values for each window were visually inspected and then used to estimate the depth to the Moho and other lithospheric density contrasts beneath each windowed region. Additionally, we performed a standard Oldenburg-Parker inversion for lithospheric density contrasts using various reference depths and density contrasts that are realistic for the different physiographic provinces in the Eastern US. Our preliminary results suggest that the gravity-derived Moho depths are similar to those found using seismic data, and that the crust is relatively thinner (~28-33 km) than expected in beneath the Piedmont region (~35-40 km). Given the relative paucity of seismic data in the eastern US, analysis of onshore gravity data is a valuable tool for interpolating between seismic stations.

Gravity data of Nevada

USGS Publications Warehouse

Ponce, David A.

1997-01-01

Gravity data for the entire state of Nevada and adjacent parts of California, Utah, and Arizona are available on this CD-ROM. About 80,000 gravity stations were compiled primarily from the National Geophysical Data Center and the U.S. Geological Survey. Gravity data was reduced to the Geodetic Reference System of 1967 and adjusted to the Gravity Standardization Net 1971 gravity datum. Data were processed to complete Bouguer and isostatic gravity anomalies by applying standard gravity corrections including terrain and isostatic corrections. Selected principal fact references and a list of sources for data from the National Geophysical Data Center are included.

Principal Facts for Gravity Data Collected in Wisconsin: A Web Site and CD-ROM for Distribution of Data

USGS Publications Warehouse

Snyder, Stephen L.; Geister, Daniel W.; Daniels, David L.; Ervin, C. Patrick

2004-01-01

Principal facts for 40,488 gravity stations covering the entire state of Wisconsin are presented here in digital form. This is a compilation of previously published data collected between 1948 and 1992 from numerous sources, along with over 10,000 new gravity stations collected by the USGS since 1999. Also included are 550 gravity stations from previously unpublished sources. Observed gravity and complete-Bouguer gravity anomaly data for this statewide compilation are included here. Altogether, 14 individual surveys are presented here.

Clarifying the interplate main tectonic elements of Western Anatolia, Turkey by using GNSS velocities and Bouguer gravity anomalies

NASA Astrophysics Data System (ADS)

Çırmık, Ayça; Pamukçu, Oya

2017-10-01

In this study, the GNSS and gravity data were processed and compared together for examining the continental structures of the Western Anatolia region which has very complicated tectonism. The GNSS data of three national projects were processed and GNSS velocities were found as approximately 25 mm per year towards southwest with respect to the Eurasia fixed frame. In order to investigate the interplate motions of the region, the Anatolian and Aegean block solutions were calculated and the differences in directions and amplitudes of velocities were observed particularly in the Anatolian block solution. Due to the Anatolian block solutions, the study area was grouped into three regions and compared with the tectonic structures as the first time for Western Anatolia by this study. Additionally, W-E and N-S relative GNSS solutions were obtained for observing the possible tectonic borders of the study area. Besides, 2nd order horizontal derivative and low-pass filter methods were applied to Bouguer gravity anomalies and the results of the gravity applications and the changes on crustal-mantle interface were compared with the GNSS horizontal velocities.

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

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.

Along-axis steps in Ethiopian rift Bouguer gravity anomalies: Implications for crustal thinning and melt emplacement prior to breakup

NASA Astrophysics Data System (ADS)

Ebinger, C. J.; Tiberi, C.; Fowler, M. R.; Hunegnaw, A.

2001-12-01

The southern Afar depression, Africa, is virtually the only area worldwide where the transition from continental rifting to seafloor spreading is exposed onshore. During mid-Miocene to Pleistocene time the rift valley was segmented along its length by long normal faults; since Pleistocene time, faulting and magmatism have jumped to a narrow ca. 60 km-long volcanic mound marked by small faults. These magmatic segments are structurally similar to slow-spreading mid-ocean ridges, yet the rift is floored by continental crust. As part of the Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE), we examine new and existing Bouguer gravity anomaly data from the rift to study the modification of the lithosphere by extensional and magmatic processes. New and existing Bouguer gravity anomaly data also show an along-axis segmentation of elongate relative positive anomalies that coincide with the magmatic segments. These anomalies are superposed on a regionally eastward increasing field as one approaches true seafloor spreading in the Gulf of Aden, and crustal thickness decreases. Quite remarkably, the magmatic segment boundaries, where data coverage is good, are marked by 15-25 mGal steps. The amplitude of the along-axis steps, as well as their across-axis characteristics, indicate that magmatic intrusion and ca. 2 km relief at the crust-mantle interface contribute to the steps. We use inverse and forward models of gravity data constrained by existing seismic and petrological data to evaluate models for the along-axis steps. EAGLE seismic data will be acquired across and along the magmatic segments to improve our understanding of breakup processes.

Stratigraphy and structure of eastern Syria across the Euphrates depression

NASA Astrophysics Data System (ADS)

Sawaf, Tarif; Al-Saad, Damen; Gebran, Ali; Barazangi, Muawia; Best, John A.; Chaimov, Thomas A.

1993-04-01

A N-S crustal-scale geotransect across the northern Arabian platform in eastern Syria reveals an alternating series of basement uplifts and basins separated by predominantly transpressional fault zones above an effectively uniform crust. Four major tectonic provinces are crossed along a 325 × 100 km corridor that extends from the Iraqi border in the south to the Turkish border in the north: the Rutbah uplift, the Euphrates depression, the Abd el Aziz structural zone, and the Qamichli uplift. These features are the manifestations of reactivated pre-Cenozoic structures that responded to forces acting along nearby Arabian plate boundaries, particularly Cenozoic convergence and collision along the margins of the northern Arabian platform i.e., the Bitlis suture and the East Anatolian fault in southern Turkey and the Zagros suture in Iran and Iraq. The database for this study consists of 3000 km of industry seismic reflection data, 28 exploratory wells, and geologic and Bouguer gravity maps. The deep crustal structure and, in part, the basement geometry along this transect are inferred from two-dimensional modeling of Bouguer gravity, whereas the shallow (about 8 km) structure is constrained primarily by well and seismic data. Features of the geotransect reveal: (1) A relatively uniform crustal column approximately 37 km thick with only minor crustal thinning beneath the Euphrates. Crustal thinning may be slightly more pronounced beneath the Euphrates (about 35 km) to the southeast of the transect where the Bouguer gravity anomaly is slightly higher. (2) Along the Euphrates depression, ongoing subsidence, which began during the Late Cretaceous, resulted in the deposition of at least 3 km of Late Cretaceous and Cenozoic rocks. The structural complexity of the Paleozoic and most of the Mesozoic sedimentary sections along the transect contrasts markedly with a relatively simple, flat-lying Cenozoic section along most of the transect. A notable exception is the Abd el Aziz uplift, where Cenozoic rocks are strongly deformed. (3) While Euphrates subsidence continued throughout the Cenozoic, the inversion of the E-W-trending Abd el Aziz structure into a fault-bounded tilted block began in the Miocene, perhaps as a response to the last episode of intense Miocene collision along the nearby Bitlis and Zagros suture zones.

Depth to bedrock in the upper San Pedro Valley, Cochise County, southeastern Arizona

USGS Publications Warehouse

Gettings, M.E.; Houser, Brenda B.

2000-01-01

The thickness, distribution, and character of alluvial sediments that were deposited in the structural subbasins of the upper San Pedro basin in southeastern Arizona during the late Cenozoic provide important constraints on ground-water availability of the area. Two sedimentary units are recognized; the Oligocene and Miocene Pantano(?) Formation and an unnamed upper Miocene through lower Pleistocene unit termed basin fill. The complete Bouguer gravity anomaly map shows that there are three major structural subbasins in the upper San Pedro basin north of the international border with Mexico. The Tombstone subbasin is north of Tombstone, and two more are located north and south of Sierra Vista, respectively. This report concentrates on the two subbasins north and south of Sierra Vista. The northern subbasin (termed the Huachuca City subbasin) extends from east of Huachuca City to northeast of Whetstone, and the southern subbasin (termed the Palominas subbasin) extends southward from a line between Nicksville and Hereford to the border. The locations and shapes of these subbasins, thickness of basin fill, and depth to bedrock were estimated using a procedure involving interpolation of (1) the density functions derived in this study, (2) stratigraphic data from water wells, and (3) a residual gravity anomaly grid obtained by subtracting the gravity effects of the bedrock ranges bordering the basin from the complete Bouguer gravity anomaly. This procedure indicates that the subbasins are shallow and contain significant thicknesses of the Pantano(?) Formation in addition to the overlying younger basin fill. The maximum depth to bedrock is about 1,700 m in the Palominas subbasin and 800m in the Huachuca City subbasin; the basin-fill unit occupies the upper 250-350 m in general with local thickenings exceeding 1,000 m in the Palominas subbasin. An east-west trending buried bedrock high beneath Fort Huachuca, Sierra Vista, and Charleston separates the subbasins. The depth to bedrock over this high is 200-500 m and the basin-fill unit ranges from 100 to 200 m thick there. A number of previously unrecognized faults were identified and the lengths of some of the known faults were extended based on reconnaissance geologic mapping, study of driller's logs, interpretation of aerial photographs and thematic mapper satellite images, and inspection of contoured gravity and aeromagnetic anomaly data. Many faults that segment the main San Pedro basin and shape the boundaries of the subbasins are apparently pre-existing faults that have been reactivated by Basin and Range extension.

Definition of the continent-ocean boundary of India and the surrounding oceanic regions from Magsat data

NASA Astrophysics Data System (ADS)

Singh, B. P.; Rajaram, Mita; Bapat, V. J.

1991-06-01

Magsat studies over the Indian region and adjoining areas show that the continental-oceanic contrasts appear more distinctly in the equivalent magnetization solution than in the anomaly maps. The vertical component ( Z) is found to be more useful for the equatorial regions. It is also noted that, in general, the continental crust has a higher magnetization than the oceanic crust. Further, the continental crust seems to extend into the Arabian Sea across a part of the west coast. A similar continuation is seen in the northern part of the Bay of Bengal. The west coast result is corroborated using land and marine Bouguer gravity anomalies.

Gravity study of the Middle Aterno Valley

NASA Astrophysics Data System (ADS)

di Nezza, Maria; di Filippo, Michele; Cesi, Claudio; Ferri, Fernando

2010-05-01

A gravity study was carried out to identify the geological and structural features of the Middle Aterno Valley, and intramontane depression in the central Appennines, which was targeted to assess the seismic hazard of the city of L'Aquila and surrounding areas, after the Abruzzo 2009 earthquake. Gravity anomalies have been used for the construction of a 3D model of the area, and gravity data for the construction of Bouguer and residual anomaly maps. These data, together with geological surface data allowed for the understanding of the Plio-quaternary tectonic setting of the basins. The study area has been differentiated into different domains with respect to structural and morphological features of different styles of faults. Geology and gravity data show that the local amplification phenomena are due to the fact that the historical center of L'Aquila was built on a coarse breccias (debris-flow deposits with decameter scale limestone blocks) overlying sandy and clayey lacustrine sediments. As these sediments have a low density, gravity prospecting very easily identifies them. Residual anomalies, showing a relative gravity low corresponding to the historical center of L'Aquila, and surrounding areas, indicated that these sediments are up to 250 m-thick. Gravity prospecting also revealed the uprooting of the reliefs which outcrop in the area of Coppito. These reliefs, practically outcrop in the middle of the basin. Here, the gravity anomalies are negative and not positive as would be expected from outcropping geological bedrock.

Detailed magnetic and gravity surveys around the hydrothermal area off Kumejima Island in the Mid-Okinawa Trough, southwestern Japan

NASA Astrophysics Data System (ADS)

Kitada, K.; Kasaya, T.; Iwamoto, H.; Nogi, Y.

2017-12-01

The Okinawa Trough is an active back-arc basin formed by the rifting associated with extension of the continental margin behind the Ryukyu trench. New hydrothermal sites were recently discovered off Kumejima Island in the Mid-Okinawa Trough and the hydrothermal mineral deposits were identified by seafloor surveys and rock samplings by ROV (e.g., JOGMEC, 2015). In order to characterize the sub-seafloor structures and the spatial distribution of the magmatic activity around the sites, we conducted the dense magnetic, gravity and bathymetric surveys with a line spacing of 0.5 nmi aboard the R/Vs Yokosuka and Kairei, operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in 2016. The geophysical data collected during the previous cruises in the area by JAMSTEC were additionally used for this study. Magnetic anomaly was calculated by subtracting the IGRF model and the magnetization intensity was estimated by the method of Parker and Huestis (1974). Free-air gravity anomaly was calculated with subtracting the normal gravity field and with corrections of the drift and of the Eötvös effect. Bouguer gravity anomaly was calculated based on the method of Parker (1972). The magnetization intensity and the Bouguer gravity anomaly reveal three characteristics of the hydrothermal area off Kumejima Island: 1) The distribution of magnetization around the hydrothermal sites shows two different types of sub-seafloor magnetic features. One is corresponded to the submarine knolls with a relatively high magnetization of 4 A/M. The other is an ENE-WSW trending magnetization distribution with relatively high and low intensities, which is consistent with the trend of the bathymetric lineament. These features are considered to be formed by magmatism associated with submarine volcanoes and back-arc rifting. 2) The reduced magnetization zone corresponding to the hydrothermal area probably attributes to hydrothermal alteration of the host rock. 3) The hydrothermal site is located on the area where the Bouguer gravity anomaly is steeply changed from 10 to 30 mGal, suggesting that the hydrothermal activity can be related to the change in crustal thickness associated with back-arc rifting.

The integration of gravity, magnetic and seismic data in delineating the sedimentary basins of northern Sinai and deducing their structural controls

NASA Astrophysics Data System (ADS)

Selim, El Sayed Ibrahim

2016-01-01

The Sinai Peninsula is a part of the Sinai sub-plate that located between the southeast Nubian-Arabian shield and the southeastern Mediterranean northward. The main objectives of this investigation are to deduce the main sedimentary basin and its subdivisions, identify the subsurface structural framework that affects the study area and determine the thickness of sedimentary cover of the basement surface. The total intensity magnetic map, Bouguer gravity map and seismic data were used to achieve the study aims. Structural interpretation of the gravity and magnetic data were done by applying advanced processing techniques. These techniques include; Reduce to the pole (RTP), Power spectrum, Tile derivative and Analytical Signal techniques were applied on gravity and magnetic data. Two dimensional gravity and magnetic modeling and interpretation of seismic sections were done to determine the thickness of sedimentary cover of the study area. The integration of our interpretation suggests that, the northern Sinai area consists of elongated troughs that contain many high structural trends. Four major structural trends have been identified, that, reflecting the influence of district regional tectonic movements. These trends are: (1) NE-SW trend; (2) NNW-SSE trend; (3) ENE-WSW trend and (4) WNW-ESE trend. There are also many minor trends, E-W, NW-SE and N-S structural trends. The main sedimentary basin of North Sinai is divided into four sub-basins; (1) Northern Maghara; (2) Northeastern Sinai; (3) Northwestern Sinai and (4) Central Sinai basin. The sedimentary cover ranges between 2 km and 7 km in the northern part of the study area.

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.

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.

Velocity Structure of the Iran Region Using Seismic and Gravity Observations

NASA Astrophysics Data System (ADS)

Syracuse, E. M.; Maceira, M.; Phillips, W. S.; Begnaud, M. L.; Nippress, S. E. J.; Bergman, E.; Zhang, H.

2015-12-01

We present a 3D Vp and Vs model of Iran generated using a joint inversion of body wave travel times, Rayleigh wave dispersion curves, and high-wavenumber filtered Bouguer gravity observations. Our work has two main goals: 1) To better understand the tectonics of a prominent example of continental collision, and 2) To assess the improvements in earthquake location possible as a result of joint inversion. The body wave dataset is mainly derived from previous work on location calibration and includes the first-arrival P and S phases of 2500 earthquakes whose initial locations qualify as GT25 or better. The surface wave dataset consists of Rayleigh wave group velocity measurements for regional earthquakes, which are inverted for a suite of period-dependent Rayleigh wave velocity maps prior to inclusion in the joint inversion for body wave velocities. We use gravity anomalies derived from the global gravity model EGM2008. To avoid mapping broad, possibly dynamic features in the gravity field intovariations in density and body wave velocity, we apply a high-pass wavenumber filter to the gravity measurements. We use a simple, approximate relationship between density and velocity so that the three datasets may be combined in a single inversion. The final optimized 3D Vp and Vs model allows us to explore how multi-parameter tomography addresses crustal heterogeneities in areas of limited coverage and improves travel time predictions. We compare earthquake locations from our models to independent locations obtained from InSAR analysis to assess the improvement in locations derived in a joint-inversion model in comparison to those derived in a more traditional body-wave-only velocity model.

The nature of the gravity anomalies associated with large young lunar craters

NASA Technical Reports Server (NTRS)

Dvorak, J.; Phillips, R. J.

1977-01-01

The negative Bouguer anomalies (i.e., mass deficiencies) associated with four young lunar craters are analyzed. Model calculations based on generalizations made from studies of terrestrial impact structures suggest that the major contribution to the Bouguer anomaly for these lunar craters is due to a lens of brecciated material confined within the present crater rim crest and extending vertically to at least a depth of one-third the crater rim diameter. Calculations also reveal a systematic variation in the magnitude of the mass deficiencies with the cube of the crater diameter.

Gravity Anomalies in the Northern Hawaiian Islands: Evidence for an Alternative Magma Chamber on Kauai and a Conjoined Niihau-Kauai Island

NASA Astrophysics Data System (ADS)

Flinders, A. F.; Ito, G.; Garcia, M.; Kim, S.; Appelgate, B.

2008-12-01

The shield stage evolution of the islands of Kauai and Niihau are poorly understood. Previous land-based gravity surveys provide only a coarse constraint on the observed gravitational field. Questions as to whether the island of Kauai was formed by a single or multiple shields and the developmental relationship between these neighboring islands are still debated. Our new land-based gravity survey of Kauai and ship-board gravity surveys around both islands identified large complete Bouguer gravitational anomalies under Kauai's Lihue Basin and offshore in the Kaulakahi Channel, a 30-km-long bathymetric ridge connecting the two islands. These gravitational highs are consistent in size and magnitude with those of other Hawaiian islands and imply local zones of high density crust, most likely attributed to magmatic intrusions; e.g. former magma chambers, or rift zones. The Lihue Basin anomaly observed is offset 20 km east from the geologically mapped caldera region. This offset implies either the unlikely case that the shield stage plumbing system connecting the magma chamber and caldera could have been inclined by up to 75 degrees from the vertical, or that the currently mapped caldera is a late feature, unrelated to shield volcanism. The location of the gravitational anomaly, in the Kaulakahi Channel, 20 km east of Niihau is consistent with geologic mapping, which indicates that Niihau is a remnant of an ancient shield volcano centered east of the island. The proximity of the Niihau gravitational anomaly 10 km from the western edge of Kauai supports the hypothesis that the two volcanoes were part of the same island.

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.

Mars - Hellas Planitia gravity analysis

NASA Technical Reports Server (NTRS)

Sjogren, W. L.; Wimberley, R. N.

1981-01-01

Doppler radio tracking data from Viking Orbiter 1 has provided new detailed observations of gravity variations over Hellas Planitia. Line-of-sight Bouguer gravity definitely indicates that isostatic adjustment has occurred. Two theoretical models were tested to obtain fits to the gravity data. Results for a surface deficit model, and a model with a surface deficit and a mass excess at depth are displayed. The mass-at-depth model produced very marked improvement in the data fit as compared to the surface deficit model. The optimum depth for the mass excess is 130 km.

The Crustal Structure of the North-South Earthquake Belt in China Revealed from Deep Seismic Soundings and Gravity Data

NASA Astrophysics Data System (ADS)

Zhao, Yang; Guo, Lianghui; Shi, Lei; Li, Yonghua

2018-01-01

The North-South earthquake belt (NSEB) is one of the major earthquake regions in China. The studies of crustal structure play a great role in understanding tectonic evolution and in evaluating earthquake hazards in this region. However, some fundamental crustal parameters, especially crustal interface structure, are not clear in this region. In this paper, we reconstructed the crustal interface structure around the NSEB based on both the deep seismic sounding (DSS) data and the gravity data. We firstly reconstructed the crustal structure of crystalline basement (interface G), interface between upper and lower crusts (interface C) and Moho in the study area by compiling the results of 38 DSS profiles published previously. Then, we forwardly calculated the gravity anomalies caused by the interfaces G and C, and then subtracted them from the complete Bouguer gravity anomalies, yielding the regional gravity anomalies mainly due to the Moho interface. We then utilized a lateral-variable density interface inversion technique with constraints of the DSS data to invert the regional anomalies for the Moho depth model in the study area. The reliability of our Moho depth model was evaluated by comparing with other Moho depth models derived from other gravity inversion technique and receiver function analysis. Based on our Moho depth model, we mapped the crustal apparent density distribution in the study area for better understanding the geodynamics around the NSEB.

PROBLEM ON IRREGULAR 3-DIMENSIONAL DENSITY DISCONTINUITY SURFACES.

DTIC Science & Technology

method. The result is used to analyze the relation of linear correlation between the crustal thickness and the local Bouguer gravity anomaly, and good agreement is obtained in comparison with the actual statistical data. (Author)

Integrated study of basins in the Four Corners region

NASA Astrophysics Data System (ADS)

Fagbola, Olamide Olawumi

2007-12-01

This dissertation is an integrated study of basins in the four corners area of the central part of the Colorado Plateau. The Colorado Plateau is a structurally unique part of the Rocky Mountain region because it has only been moderately deformed when compared to the more intensely deformed areas around it. The Colorado Plateau covers a portion of Utah, Colorado, New Mexico and Arizona. The study area extends from latitude 34°N-40°N to longitude 106°W-111W° encompassing a series of major basins and uplifts: the San Juan, Black Mesa, Paradox, and the Blanding basins; and the Zuni, Defiance, Four Corners, Monument uplifts and the San Juan dome and volcanic field. An analysis of gravity anomalies, basement and crustal structure for basins in the four corners region was carried out. This involved using gravity, magnetic, well, outcrop, seismic estimates of crustal thickness, and geologic data in an integrated fashion. Six filtered gravity and three filtered magnetic maps were generated to aid in the interpretation of the gravity and magnetic anomalies in the study area. A detailed comparison of these maps was carried out. The results show a deep seated mafic structure in the basement acting as a crustal boundary separating the high gravity anomalies from the low. These maps also show that the sources of these anomalies are quite shallow resulting from the upper crust in the study area. The structures in the study area are characterized by northwest and northeast trends which correspond to the Precambrian and the Late Paleozoic structures, respectively. A crustal thickness map of the area was also constructed from seismic estimates of crustal thickness. A comparison was done between the crustal thickness map and the 45 km upward continuation Bouguer anomaly map. The result of this comparison shows that areas of thicker ix crust corresponded to low gravity while areas of thinner crust means mantle material is closer to the surface, thereby producing a high gravity anomaly. The thinnest crust encountered is about 32 km while the thickest crust is about 50 km. Seven gravity models were constructed and these include three crustal-scale profiles crisscrossing the study area and four local profiles. The gravity profiles were modeled using well data, structural thickness maps, cross section data, geologic maps and previous gravity models as constraints. Basement inhomogeneities beneath the basins and the uplifts were delineated by the gravity modeling. One of results from this study reveals that the basement beneath the Four Corners area is highly inhomogeneous. This study reveals that there is a high density deep seated mafic intrusion present in the basement which is responsible for the high gravity and magnetic anomaly in A. This dissertation has also shown that the Four Corners region does not possess a single crustal signature as shown by the different crustal trends in San Juan basin trending northeast and the east-west trending Uncompahgre uplift. The 45 km upward continuation gravity map was also found to correlate with seismic estimates of crustal thickness. The Precambrian basement in this region is also not homogeneous as shown by the necessity of inserting exotic bodies into the basement to compensate for high gravity anomalies and lastly an attempt was made to better define Tweto's (1980) outline of geologic features in the study area. On integrating gravity, magnetics, well and outcrop data, the relief of the Defiance uplift is not as high as delineated by Tweto's (1980) outline.

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

Brumbaugh, William D.; Cook, Kenneth L.

During the summers of 1975 and 1976, a gravity survey was conducted in the Cove Fort - Sulphurdale KGRA and north Mineral Mountains area, Millard and Beaver counties, Utah. The survey consisted of 671 gravity stations covering an area of about 1300 km{sup 2}, and included two orthogonal gravity profiles traversing the area. The gravity data are presented as a terrain-corrected Bouguer gravity anomaly map with a contour interval of 1 mgal and as an isometric three-dimensional gravity anomaly surface. Selected anomaly separation techniques were applied to the hand-digitized gravity data (at 1-km intervals on the Universal Transverse Mercator grid)more » in both the frequency and space domains, including Fourier decomposition, second vertical derivative, strike-filter, and polynomial fitting analysis, respectively. Residual gravity gradients of 0.5 to 8.0 mgal/km across north-trending gravity contours observed through the Cove Fort area, the Sulphurdale area, and the areas east of the East Mineral Mountains, along the west flanks of the Tushar Mountains, and on both the east and west flanks of the north Mineral Mountains, were attributed to north-trending Basin and Range high-angle faults. Gravity highs exist over the community of Black Rock area, the north Mineral Mountains, the Paleozoic outcrops in the east Cove Creek-Dog Valley-White Sage Flats areas, the sedimentary thrust zone of the southern Payant Range, and the East Mineral Mountains. The gravity lows over north Milford Valley, southern Black Rock Desert, Cunningham Wash, and northern Beaver Valley are separated from the above gravity highs by steep gravity gradients attributed to a combination of crustal warping and faulting. A gravity low with a closure of 2 mgal corresponds with Sulphur Cove, a circular topographic features containing sulphur deposits.« less

Geological-Seismological Evaluation of Earthquake Hazards at Prompton and Francis E. Walter Damsites, Pennsylvania.

DTIC Science & Technology

1986-09-01

gravity anomalies for the study area were prepared by 15 Wa *~~~.. A *-S A J~ V Hildreth (1979) and are shown in Figure 8. Magnetic anomalies for...the gravity and the magnetic anomalies reflect the patterns of the folded strata and the associated faulting. The magnetic anomalies are in- dicative...BOUGUER GRAVITY ANOMALY 5 C- -- I5 CONTOUR INTERVAL 0 20 40 60 80 100 120 26 - -KM 2 AND 5 MILLIGALS BOUNDARY FOR EARTHQUAKE /: I SOURCE

Subsurface structures of buried features in the lunar Procellarum region

NASA Astrophysics Data System (ADS)

Wang, Wenrui; Heki, Kosuke

2017-07-01

The Gravity Recovery and Interior Laboratory (GRAIL) mission unraveled numbers of features showing strong gravity anomalies without prominent topographic signatures in the lunar Procellarum region. These features, located in different geologic units, are considered to have complex subsurface structures reflecting different evolution processes. By using the GRAIL level-1 data, we estimated the free-air and Bouguer gravity anomalies in several selected regions including such intriguing features. With the three-dimensional inversion technique, we recovered subsurface density structures in these regions.

On the impact of topography and building mask on time varying gravity due to local hydrology

NASA Astrophysics Data System (ADS)

Deville, S.; Jacob, T.; Chéry, J.; Champollion, C.

2013-01-01

We use 3 yr of surface absolute gravity measurements at three sites on the Larzac plateau (France) to quantify the changes induced by topography and the building on gravity time-series, with respect to an idealized infinite slab approximation. Indeed, local topography and buildings housing ground-based gravity measurement have an effect on the distribution of water storage changes, therefore affecting the associated gravity signal. We first calculate the effects of surrounding topography and building dimensions on the gravity attraction for a uniform layer of water. We show that a gravimetric interpretation of water storage change using an infinite slab, the so-called Bouguer approximation, is generally not suitable. We propose to split the time varying gravity signal in two parts (1) a surface component including topographic and building effects (2) a deep component associated to underground water transfer. A reservoir modelling scheme is herein presented to remove the local site effects and to invert for the effective hydrological properties of the unsaturated zone. We show that effective time constants associated to water transfer vary greatly from site to site. We propose that our modelling scheme can be used to correct for the local site effects on gravity at any site presenting a departure from a flat topography. Depending on sites, the corrected signal can exceed measured values by 5-15 μGal, corresponding to 120-380 mm of water using the Bouguer slab formula. Our approach only requires the knowledge of daily precipitation corrected for evapotranspiration. Therefore, it can be a useful tool to correct any kind of gravimetric time-series data.

Principal facts for gravity data collected in South Dakota: a web site for distribution of data

USGS Publications Warehouse

Kucks, Robert P.; Zawislak, Ronald L.

2001-01-01

Principal facts for 12266 new gravity stations and 2880 stations previously released in paper form (Klasner and Kucks, 1988) for the state of South Dakota are presented. These data were contracted to fill a gap in existing data coverage for the state. Observed and Bouguer anomaly data for this regional compilation are available here in digital form.

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)

Bouguer gravity and crustal structure of the Dead Sea transform fault and adjacent mountain belts in Lebanon

NASA Astrophysics Data System (ADS)

Kamal; Khawlie, Mohamad; Haddad, Fuad; Barazangi, Muawia; Seber, Dogan; Chaimov, Thomas

1993-08-01

The northern extension of the Dead Sea transform fault in southern Lebanon bifurcates into several faults that cross Lebanon from south to north. The main strand, the Yammouneh fault, marks the boundary between the Levantine (eastern Mediterranean) and Arabian plates and separates the western mountain range (Mount Lebanon) from the eastern mountain range (Anti-Lebanon). Bouguer gravity contours in Lebanon approximately follow topographic contours; i.e., positive Bouguer anomalies are associated with the Mount Lebanon and Anti-Lebanon ranges. This suggests that the region is not in simple isostatic compensation. Gravity observations based on 2.5-dimensional modeling and other available geological and geophysical information have produced the following interpretations. (1) The crust of Lebanon thins from ˜35 km beneath the Anti-Lebanon range, near the Syrian border, to ˜27 km beneath the Lebanese coast. No crustal roots exist beneath the Lebanese ranges. (2) The depth to basement is ˜3.5-6 km below sea level under the ranges and is ˜8-10 km beneath the Bekaa depression. (3) The Yammouneh fault bifurcates northward into two branches; one passes beneath the Yammouneh Lake through the eastern part of Mount Lebanon and another bisects the northern part of the Bekaa Valley (i.e., Mid-Bekaa fault). The Lebanese mountain ranges and the Bekaa depression were formed as a result of transtension and later transpression associated with the relative motion of a few crustal blocks in response to the northward movement of the Arabian plate relative to the Levantine plate.

Tectonics and crustal structure of the Saurashtra peninsula: based on Gravity and Magnetic data

NASA Astrophysics Data System (ADS)

Mishra, A. K.; Singh, A.; Singh, U. K.

2016-12-01

The Saurashtra peninsula is located at the North Western margin of the Indian shield which occurs as a horst block between the rifts namely as Kachchh, Cambay and Narmada. It is important because of occurrence of moderate earthquake and presence of mesozoic sediments below the Deccan trap. The maps of bouguer gravity anomaly and the total intensity magnetic anomalies of Saurashtra have delineated six circular gravity highs of magnitudes 40-60 mGal and 800-1000 nT respectively. In order to understand the location, structure and depth of the source body, methods like continuous wavelet transform (CWT), Euler deconvolution and power spectrum analysis have been implemented in the potential field data. The CWT and Euler deconvolution give 16-18 km average depth of volcanic plug in Junagadh and Rajula region. From the power spectrum analysis, it is found that average Moho depth in the Saurashtra is about 36-38 km. Keeping the constraints obtained from geophysical studies like borehole, deep seismic survey, receiver function analysis and geological information, combined gravity and magnetic modeling have been performed. Detailed crustal structure of the Saurashtra region has been delineated along two profiles which pass from prominent geological features Junagadh and Rajula volcanic plugs respectively.

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)

Paleomagnetic determinations on Lanzarote from magnetic and gravity anomalies: Implications for the early history of the Canary Islands

NASA Astrophysics Data System (ADS)

Blanco-Montenegro, I.; Montesinos, F. G.; GarcíA, A.; Vieira, R.; VillalaíN, J. J.

2005-12-01

The Bouguer and aeromagnetic anomaly maps of Lanzarote show a gravity high and a dipolar magnetic anomaly over the central part of the island, indicating one isolated source. Assuming that the structure responsible for both anomalies is the same, a methodology has been designed to estimate the total magnetization vector of the source, which is interpreted as a large intrusive body (mafic core) positioned as a result of magma rising to the surface during the early stages of growth of Lanzarote. Considering its geometry to be known from a previous three-dimensional (3-D) gravity model, the approach proposed in this paper is based on the delineation of magnetic contacts through analysis of the horizontal gradient of the reduced-to-the-pole anomaly map, comparison between the gravity and the pseudogravity anomalies, and 3-D forward magnetic modeling. The total magnetization vector obtained by this method is defined by a module of 4.5 A m-1 and a direction D = -20° and I = 30°. Comparing the paleomagnetic pole, obtained from this direction, with the apparent polar wander path of Africa for the last 160 Myr, it is concluded that the main component of the total magnetization vector is probably a primary natural remanent magnetization (NRM) which could have been acquired between 60 and 100 Ma. This result suggests that the emplacement of magmas at shallow depths linked to the beginning of volcanism in Lanzarote took place during the Upper Cretaceous, thus providing the first evidence of a timeline for the early formative stages of this volcanic island.

Estimating crustal thickness and Vp/Vs ratio with joint constraints of receiver function and gravity data

NASA Astrophysics Data System (ADS)

Shi, Lei; Guo, Lianghui; Ma, Yawei; Li, Yonghua; Wang, Weilai

2018-05-01

The technique of teleseismic receiver function H-κ stacking is popular for estimating the crustal thickness and Vp/Vs ratio. However, it has large uncertainty or ambiguity when the Moho multiples in receiver function are not easy to be identified. We present an improved technique to estimate the crustal thickness and Vp/Vs ratio by joint constraints of receiver function and gravity data. The complete Bouguer gravity anomalies, composed of the anomalies due to the relief of the Moho interface and the heterogeneous density distribution within the crust, are associated with the crustal thickness, density and Vp/Vs ratio. According to their relationship formulae presented by Lowry and Pérez-Gussinyé, we invert the complete Bouguer gravity anomalies by using a common algorithm of likelihood estimation to obtain the crustal thickness and Vp/Vs ratio, and then utilize them to constrain the receiver function H-κ stacking result. We verified the improved technique on three synthetic crustal models and evaluated the influence of selected parameters, the results of which demonstrated that the novel technique could reduce the ambiguity and enhance the accuracy of estimation. Real data test at two given stations in the NE margin of Tibetan Plateau illustrated that the improved technique provided reliable estimations of crustal thickness and Vp/Vs ratio.

Geophysical investigation of an upper tertiary subbasin in the southern Egyptian Red Sea shelf and its bearing on oil exploration

NASA Astrophysics Data System (ADS)

Khattab, M. M.

Several narrow, elongate and Red Sea-trending gravity lows, suggested recently as due to depositional troughs, are shown on the Egyptian Red Sea shelf Bouguer map. Few drilling data and poor reflectivity below the Pliocene-Miocene uncorformity hinder subsurface evaluation. A 1 mgal anomaly (25 km north of Ras Benas Peninsula) was analysed along a crossing sessmic reflection line. The interpretation was aided by: lithology at an off-shore well, seismic data above the unconformity and aeromagnetic data in the southerly-located Foul Bay. The best fit of computed to observed gravity was for a three-layers model (water, post-evaporites and evaporites) where maximum sediment thickness was 3.8 km of which layers 2 and 3 constittted 1.6 and 2.2 km. The subbasin configuration was found to be controlled by Quaternary (similar to that mapped at Egyptian and Saudi Arabian coastal provinces) and pre-middle Miocence (affecting only middle Miocene evaprites beneath a reflection line at the western margin of the main trough near latitude 24°N) faulting which supports the conceot of Red Sea arching and subsequent faulting at marginal shelves. This subbasin is found associated, in part, with a sea--floor trough and with part of Foul Bay magnetic lineations (interpreted recently as caused by oceanic crust) which, in turn, are shown to constitute continuation of mapped onshore tholeiitic dikes.

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 mountains, suggesting that valleys are filled with low density sediments. Spectral analysis between 14 selected northwest-southeast trending airborne profiles and topography in the western Afghanistan mountains shows that the computed admittance is best fit to a theoretical isostatic compensation model of topographic loads including buried loading at bottom of the crust of 22 km with Young's modulus, 1.0x1011 Nm-2; effective elastic thickness, 5 km; crust and mantle densities of 2670 kg/m3 and 3330 kg/m3, respectively; and the ratio between surface and subsurface loading is set to 1, i.e., gravity effects from surface topography and subsurface loads are equal.

Fault structures in the focal area of the 2016 Kumamoto earthquake revealed by derivatives and structure parameters of a gravity gradient tensor

NASA Astrophysics Data System (ADS)

Hiramatsu, Y.; Matsumoto, N.; Sawada, A.

2016-12-01

We analyze gravity anomalies in the focal area of the 2016 Kumamoto earthquake, evaluate the continuity, segmentation and faulting type of the active fault zones, and discuss relationships between those features and the aftershock distribution. We compile the gravity data published by the Gravity Research Group in Southwest Japan (2001), the Geographical Survey Institute (2006), Yamamoto et al. (2011), Honda et al. (2012), and the Geological Survey of Japan, AIST (2013). We apply terrain corrections with 10 m DEM and a low-pass filter, then remove a linear trend to obtain Bouguer anomalies. We calculate the first horizontal derivative (HD), the first vertical derivative (VD), the normalized total horizontal derivative (TDX) (Cooper and Cowan, 2006), the dimensionality index (Di) (Beki and Pedersen, 2010), and dip angle (β) (Beki, 2013) from a gravity gradient tensor. The HD, VD and TDX show the existence of the continuous fault structure along the Futagawa fault zone, extending from the Uto peninsula to the Beppu Bay except Mt. Aso area. Aftershocks are distributed along this structural boundary from the confluence of the Futagawa and the Hinagu fault zones to the east end of the Aso volcano. The distribution of dip angle β along the Futagawa fault zone implies a normal faulting, which corresponds to the coseismic faulting estimated geologically and geomorphologically. We observe the S-shaped distribution of the Bouguer anomalies around the southern part of the Hinagu segment, indicating a right lateral faulting. The VD and TDX support the existence of the fault structure along the segment but it is not so clear. We can recognize no clear structural boundaries along the Takano-Shirahata segment. TDX implies the existence of a structural boundary with a NW-SE trend around the boundary between the Hinagu and Takano-Shirahata segments. The Di shows that this boundary has a 3D-like structure rather than a 2D-like one, suggesting the discontinuity of 2D-like fault structure along the fault zone. A geological map indicates that this structure boundary corresponds to a boundary between the metamorphic rock and the sedimentary rock. The active area of the aftershocks does not extend to the south beyond this structure boundary, implying that the spatial extent of the source fault is controlled by this boundary.

Principal facts for gravity data collected in the southern Albuquerque Basin area and a regional compilation, central New Mexico

USGS Publications Warehouse

Gillespie, Cindy L.; Grauch, V.J.S.; Oshetski, Kim; Keller, Gordon R.

2000-01-01

Principal facts for 156 new gravity stations in the southern Albuquerque basin are presented. These data fill a gap in existing data coverage. The compilation of the new data and two existing data sets into a regional data set of 5562 stations that cover the Albuquerque basin and vicinity is also described. Bouguer anomaly and isostatic residual gravity data for this regional compilation are available in digital form from ftp://greenwood.cr.usgs.gov/pub/openfile- reports/ofr-00-490.

A three-dimensional model of the Pyrenees and their foreland basins from geological and gravimetric data

NASA Astrophysics Data System (ADS)

Wehr, H.; Chevrot, S.; Courrioux, G.; Guillen, A.

2018-06-01

We construct a three-dimensional geological model of the Pyrenees and their foreland basins with the Geomodeller. This model, which accounts for different sources of geological and geophysical informations, covers the whole Pyrenees, from the Atlantic Ocean to the Mediterranean Sea, and from the Iberian range to the Massif Central, down to 70 km depth. We model the geological structure with a stratigraphic column composed of a superposition of layers representing the mantle, lower, middle, and upper crusts. The sedimentary basins are described by two layers which allow us to make the distinction between Mesozoic and Cenozoic sediments, which are characterized by markedly different densities and seismic velocities. Since the Pyrenees result from the convergence between the Iberian and European plates, we ascribe to each plate its own stratigraphic column in order to be able to model the imbrication of Iberian and European crusts along this fossile plate boundary. We also introduce two additional units which describe the orogenic prism and the water column in the Bay of Biscay and in the Mediterranean Sea. The last ingredient is a unit that represents bodies of shallow exhumed and partly serpentinized lithospheric mantle, which are assumed to produce the positive Bouguer gravity anomalies in the North Pyrenean Zone. A first 3D model is built using only the geological information coming from geological maps, drill-holes, and seismic sections. We use the potential field method implemented in Geomodeller to interpolate these geological data. This model is then refined in order to better explain the observed Bouguer anomalies by adding new constraints on the main crustal interfaces. The final model explains the observed Bouguer anomalies with a standard deviation less than 3.4 mGal, and reveals anomalous deep structures beneath the eastern Pyrenees.

Crustal structure along the DESERT 2000 Transect inferred from 3-D gravity modelling

NASA Astrophysics Data System (ADS)

El-Kelani, R.; Goetze, H.; Rybakov, M.; Hassouneh, M.; Schmidt, S.

2003-12-01

A three-dimensional interpretation of the newly compiled Bouguer anomaly map is part of the DESERT 2000 Transect. That is multi-disciplinary and multinational project studying for first time the Dead Sea Transform (DST) fault system (DST) from the Mediterranean Sea to Saudi Arabia across the international border in the NW-SE direction. The negative Bouguer anomalies (with magnitude reached "C130 mGal), located into transform valley, are caused by the internal sedimentary basins filled by the light density young sediments (­Y10 km). A high-resolution 3-D model constrained with the seismic results reveals a possible crustal thickness and density distribution beneath the DST valley. The inferred zone of intrusion coincides with the maximum gravity anomaly over the eastern flank of the DST. The intrusion is displaced at different sectors along the NW-SE direction. The zone of the maximum crustal thinning (­30 km) is attained in the western sector at the Mediterranean. The southeastern plateau, on the other hand, shows by far the largest crustal thickness in the region (38-42 km). Linked to the left lateral movement of ~ 105 km at the boundary between the African and Arabian plate, and constrained with the DESERT 2000 seismic data, a small asymmetric topography of the Moho beneath the DST was modelled. The thickness and density of the crust suggest that a continental crust underlies the DST. The deep basins, the relatively large nature of the intrusion and the asymmetric topography of the Moho lead to the conclusion that a small-scale asthenospheric upwelling(?) might be responsible for the thinning of the crust and subsequent rifting of the Dead Sea graben during the left lateral movement.

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 ground topographic corrections over the highest mountains, results in significantly reducing the differences between airborne and ground upward-continued Bouguer anomalies, which shows that some of the misfit stems from errors in the ground data.

Geophysical Investigations of Magma Plumbing Systems at Cerro Negro Volcano, Nicaragua

NASA Astrophysics Data System (ADS)

MacQueen, Patricia Grace

Cerro Negro near Leon, Nicaragua is a very young (163 years), relatively small basaltic cinder cone volcano that has been unusually active during its short lifespan (recurrence interval 6--7 years), presenting a significant hazard to nearby communities. Previous studies have raised several questions as to the proper classification of Cerro Negro and its relation to neighboring Las Pilas-El Hoyo volcano. Analysis of Bouguer gravity data collected at Cerro Negro has revealed connected positive density anomalies beneath Cerro Negro and Las Pilas-El Hoyo. These findings suggest that eruptions at Cerro Negro may be tapping a large magma reservoir beneath Las Pilas-El Hoyo, implying that Cerro Negro should be considered the newest vent on the Las Pilas-El Hoyo volcanic complex. As such, it is possible that the intensity of volcanic hazards at Cerro Negro may eventually increase in the future to resemble those pertaining to a stratovolcano. Keywords: Cerro Negro; Las Pilas-El Hoyo; Bouguer gravity; magmatic plumbing systems; potential fields; volcano.

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 project on Volcanism and Crustal Deformation, supervised by L. C. Pakiser of the U.S. Geological Survey. Professor Rodgers of the Geophysics Department of the Colorado School of Mines acted as an advisor.

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 (density is 2670kg/m3), Neocene volcanic rock (density is 2400kg/m3, or 2550kg/m3), Neocene sedimentary rock (density is 2200kg/m3), and Quaternary sedimentary rock (density is 1800kg/m3, or 1500kg/m3) (Honda et al., 2008). To compare our basement model to the geological block structures, we focus on a transition zone of the basement depth. We recognize that two of three geological block boundaries correspond to the transition zones. These boundaries also correspond to the boundary of active fault segments on the seafloor. Therefore, based on the relationship between the source fault of the 2007 Noto Hanto earthquake and the geological block, we suggest that the movement of those geological blocks is possibly controlled by the corresponding active fault segments. However, we find that the other block boundary doesn't correspond to the transition zone.

Gravimetry contributions to the study of the complex western Haouz aquifer (Morocco): Structural and hydrogeological implications

NASA Astrophysics Data System (ADS)

Chouikri, Ibtissam; el Mandour, Abdennabi; Jaffal, Mohammed; Baudron, Paul; García-Aróstegui, José-Luis; Manar, Ahmed; Casas, Albert

2016-03-01

This study provides new elements that illustrate the benefits of combining gravity, structural, stratigraphic and piezometric data for hydrogeological purposes. A combined methodology was applied to the western Haouz aquifer (Morocco), one of the main sources of water for irrigation and human consumption in the Marrakech region. First, a residual anomaly map was calculated from the Bouguer anomaly data. The computed map provided information on the ground density variation, revealing a strong control by a regional gradient. We then used various filtering techniques to delineate the major geological structures such as faults and basins: vertical and horizontal derivatives and upward continuation. This technique highlighted news structures and provided information on their dip. The gravity anomalies perfectly delineated the basement uplifts and the sedimentary thickening in depressions and grabens. The interpretation of gravimetric filtering, geological and hydrogeological data then highlighted two types of groundwater reservoirs, an unconfined aquifer hosted in conglomeratic mio-pliocene and quaternary rocks, covering the entire western Haouz and a deep confined aquifer contained in cenomanian-turonian limestone and eocene dolomitic formations in the south. Combining piezometric and residual anomaly maps revealed that groundwater flow and storage was in perfect agreement with the structures showing a negative anomaly, while structures with positive anomalies corresponded to groundwater divides. The study of gravity gradient zones by contact analysis enhanced the existing structural pattern of the study area and highlighted new structures, mainly oriented N70 and N130. The results of this study present a common framework and provide a notable step forward in the knowledge of the geometry and the groundwater flow pattern of the western Haouz aquifer, and will serve as a solid basis for a better water resource management.

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, and Freundlich-Sharonov basins have a broad peak of which magnitude in free-air anomalies is 20 to 60 % smaller than the one in Bouguer anomalies. We call the former basins Type I and the latter Type II. The central gravity high of Type I basins in Bouguer anomalies suggests the existence of excess mass below the center. Because mare fill is absent from Type I basins, the central gravity high is most likely a manifestation of mantle uplift beneath the basin. The peak height of positive Bouguer anomalies of Type II ranges from 400 to 900 mGal in comparison to those in free-air anomalies from 250 to 500 mGal. This difference can be attributed to local compensation at the center of the Type II basins. We propose a brittle deformation resulting from a load of uplifted mantle. Little relation between the class and formation age is found. On the other hand, there are fewer large lunar basins on the far side. It is unlikely that large impacts concentrated on one side of the Moon and smaller impacts on the other side, as crater diameter depends mostly on impacting energy and momentum, not the properties of the target [6]. A plausible hypothesis is that the primary mascon basins on the near side have deformed more after their initial formation. References: [1] A. S. Konopliv et al., Icarus, 150, 1 (2001). [2] T. Iwata et al., JGSJ, 47, 558 (2001). [3] F. G. Lemoine et al., JGR, 102, 16,339, (1997). [4] H. Araki et al., submitted to Science (2009). [5] N. Namiki et al., accepted by Science (2009). [6] H. J. Melosh, Impact Cratering: A Geologic Process (1989).

Imaging the density distributions at the regional scale using full waveform and gravity data inversion - Application to the Pyrenees

NASA Astrophysics Data System (ADS)

Martin, Roland; Chevrot, Sébastien; Wang, Yi; Spangenberg, Hannah; Goubet, Marie; Monteiller, Vadim; Komatitsch, Dimitri; Seoane, Lucia; Dufréchou, Grégory

2017-04-01

We present a hybrid inversion method that allows us to image density distributions at the regional scale using both seismic and gravity data. One main goal is to obtain densities and seismic wave velocities (P and S) in the lithosphere with a fine resolution to get important constraints on the mineralogic composition and thermal state of the lithosphere. In the context of the Pyrenees (located between Spain and France), accurate Vp and Vs seismic velocity models are computed first on a 3D spectral element grid at the scale of the Pyrenees by inverting teleseismic full waveforms. In a second step, Vp velocities are mapped to densities using empirical relations to build an a priori density model. BGI and BRGM Bouguer gravity anomaly data sets are then inverted on the same 3D spectral element grid as the Vp model at a resolution of 1-2 km by using high-order numerical integration formulae. Solutions are compared to those obtained using classical semi-analytical techniques. This procedure opens the possibility to invert both teleseismic and gravity data on the same finite-element grid. It can handle topography of the free surface in the same spectral-element distorted mesh that is used to solve the wave equation, without performing extra interpolations between different grids and models. WGS84 curvature, SRTM or ETOPO1 topographies are used.

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.

Recent crustal movements and seismicity in the western coastal region of peninsular India

NASA Astrophysics Data System (ADS)

Kailasam, L. N.

1983-09-01

Recent crustal movements, tectonics and seismicity of the western coastal region of peninsular India have been studied in detail in the very recent past. Prominent geomorphic features and large-scale manifestation of Holocene deformation and crustal movements have been noticed and studied over this coastal region from the Gulf of Cambay to the southernmost parts of Kerala, evidence for which is afforded in the form of Recent and sub-Recent raised beaches, sandbars, raised old terraces, pebble beds, etc. The sedimentary formations in this narrow coastal belt include Neogene and Quaternary sediments. The Bouguer gravity map of the western coastal tract shows some prominent gravity features extending into the offshore regions, suggestive of some significant tectonic and structural features. The seismic data in the offshore regions bring out some prominent roughly northwest-southeast as well as east-west faults and shears, in addition to prominent structural "highs" off the Bombay and Ratnagiri coast which have proved oil. The seismicity in this coastal tract as well as the faulted western margin of the western continental shelf in the Arabian Sea is generally of magnitude 3-6.

GOCE observations for Mineral exploration in Africa and across continents

NASA Astrophysics Data System (ADS)

Braitenberg, Carla

2014-05-01

The gravity anomaly field over the whole Earth obtained by the GOCE satellite is a revolutionary tool to reveal geologic information on a continental scale for the large areas where conventional gravity measurements have yet to be made (e.g. Alvarez et al., 2012). It is, however, necessary to isolate the near-surface geologic signal from the contributions of thickness variations in the crust and lithosphere and the isostatic compensation of surface relief (e.g. Mariani et al., 2013) . Here Africa is studied with particular emphasis on selected geological features which are expected to appear as density inhomogeneities. These include cratons and fold belts in the Precambrian basement, the overlying sedimentary basins and magmatism, as well as the continental margins. Regression analysis between gravity and topography shows coefficients that are consistently positive for the free air gravity anomaly and negative for the Bouguer gravity anomaly (Braitenberg et al., 2013; 2014). The error and scatter on the regression is smallest in oceanic areas, where it is a possible tool for identifying changes in crustal type. The regression analysis allows the large gradient in the Bouguer anomaly signal across continental margins to be removed. After subtracting the predicted effect of known topography from the original Bouguer anomaly field, the residual field shows a continent-wide pattern of anomalies that can be attributed to regional geological structures. A few of these are highlighted, such as those representing Karoo magmatism, the Kibalian foldbelt, the Zimbabwe Craton, the Cameroon and Tibesti volcanic deposits, the Benue Trough and the Luangwa Rift. A reconstruction of the pre-break up position of Africa, South and North America is made for the residual GOCE gravity field obtaining today's gravity field of the plates forming West Gondwana. The reconstruction allows the positive and negative anomalies to be compared across the continental fragments, and so helps identify common geologic units that extend across both the now-separate continents. Tracing the geologic units is important for mineral exploration, which is demonstrated with the analysis of correlations of the gravity signal with selected classes of mineral occurrences, for instance those associated to Greenstone belts. Alvarez, O., Gimenez M., Braitenberg C., Folguera, A. (2012) GOCE Satellite derived Gravity and Gravity gradient corrected for topographic effect in the South Central Andes Region. Geophysical Journal International, 190, 941-959, doi: 10.1111/j.1365-246X.2012.05556.x Braitenberg C., Mariani P., De Min A. (2013) The European Alps and nearby orogenic belts sensed by GOCE, Boll. Bollettino di Geofisica Teorica ed Applicata, doi:10.4430/bgta0105 Braitenberg C. (2014) Exploration of tectonic structures with GOCE in Africa and across-continents, J.of Applied Earth Observation and Geoinformation (in Review). Mariani P., Braitenberg C., Ussami N. (2013). Explaining the thick crust in Parana' basin, Brazil, with satellite GOCE-gravity observations. Journal of South American Earth Sciences, 45, 209-223, doi:10.1016/j.jsames.2013.03.008.

An analysis of methods for gravity determination and their utilization for the calculation of geopotential numbers in the Slovak national levelling network

NASA Astrophysics Data System (ADS)

Majkráková, Miroslava; Papčo, Juraj; Zahorec, Pavol; Droščák, Branislav; Mikuška, Ján; Marušiak, Ivan

2016-09-01

The vertical reference system in the Slovak Republic is realized by the National Levelling Network (NLN). The normal heights according to Molodensky have been introduced as reference heights in the NLN in 1957. Since then, the gravity correction, which is necessary to determine the reference heights in the NLN, has been obtained by an interpolation either from the simple or complete Bouguer anomalies. We refer to this method as the "original". Currently, the method based on geopotential numbers is the preferred way to unify the European levelling networks. The core of this article is an analysis of different ways to the gravity determination and their application for the calculation of geopotential numbers at the points of the NLN. The first method is based on the calculation of gravity at levelling points from the interpolated values of the complete Bouguer anomaly using the CBA2G_SK software. The second method is based on the global geopotential model EGM2008 improved by the Residual Terrain Model (RTM) approach. The calculated gravity is used to determine the normal heights according to Molodensky along parts of the levelling lines around the EVRF2007 datum point EH-V. Pitelová (UELN-1905325) and the levelling line of the 2nd order NLN to Kráľova hoľa Mountain (the highest point measured by levelling). The results from our analysis illustrate that the method based on the interpolated value of gravity is a better method for gravity determination when we do not know the measured gravity. It was shown that this method is suitable for the determination of geopotential numbers and reference heights in the Slovak national levelling network at the points in which the gravity is not observed directly. We also demonstrated the necessity of using the precise RTM for the refinement of the results derived solely from the EGM2008.

Geoacoustic Models for the Straits of Sicily and Sardinia-Tunisia.

DTIC Science & Technology

1982-04-01

basin have Bouguer gravity anomalies in excess of +200 milligals, indicating relatively thin crust (Allen and Morelli, 1971). Magnetic anomalies...E. L. and R. T. Bachman (1979a). Geoacoustic Models of the Sea Floor: Gulf of Oman, Arabian Sea, and Somali Basin. Naval Ocean Systems Center Tech

Profiles of gamma-ray and magnetic data from aerial surveys over the conterminous United States

USGS Publications Warehouse

Duval, Joseph S.; Riggle, Frederic E.

1999-01-01

This publication contains images for the conterminous U.S. generated from geophysical data, software for displaying and analyzing the images, and software for displaying and examining the profile data from the aerial surveys flown as part of the National Uranium Resource Evaluation (NURE) Program of the U.S. Department of Energy. The images included are of gamma-ray data (uranium, thorium, and potassium channels), Bouguer gravity data, isostatic residual gravity data, aeromagnetic anomalies, topography, and topography with bathymetry.

3-D lithospheric structure and regional/residual Bouguer anomalies in the Arabia-Eurasia collision (Iran)

NASA Astrophysics Data System (ADS)

Jiménez-Munt, I.; Fernãndez, M.; Saura, E.; Vergés, J.; Garcia-Castellanos, D.

2012-09-01

The aim of this work is to propose a first-order estimate of the crustal and lithospheric mantle geometry of the Arabia-Eurasia collision zone and to separate the measured Bouguer anomaly into its regional and local components. The crustal and lithospheric mantle structure is calculated from the geoid height and elevation data combined with thermal analysis. Our results show that Moho depth varies from ˜42 km at the Mesopotamian-Persian Gulf foreland basin to ˜60 km below the High Zagros. The lithosphere is thicker beneath the foreland basin (˜200 km) and thinner underneath the High Zagros and Central Iran (˜140 km). Most of this lithospheric mantle thinning is accommodated under the Zagros mountain belt coinciding with the suture between two different mantle domains on the Sanandaj-Sirjan Zone. The regional gravity field is obtained by calculating the gravimetric response of the 3-D crustal and lithospheric mantle structure obtained by combining elevation and geoid data. The calculated regional Bouguer anomaly differs noticeably from those obtained by filtering or just isostatic methods. The residual gravity anomaly, obtained by subtraction of the regional components to the measured field, is analyzed in terms of the dominating upper crustal structures. Deep basins and areas with salt deposits are characterized by negative values (˜-20 mGal), whereas the positive values are related to igneous and ophiolite complexes and shallow basement depths (˜20 mGal).

Crustal structure between Lake Mead, Nevada, and Mono Lake, California

USGS Publications Warehouse

Johnson, Lane R.

1964-01-01

Interpretation of a reversed seismic-refraction profile between Lake Mead, Nevada, and Mono Lake, California, indicates velocities of 6.15 km/sec for the upper layer of the crust, 7.10 km/sec for an intermediate layer, and 7.80 km/sec for the uppermost mantle. Phases interpreted to be reflections from the top of the intermediate layer and the Mohorovicic discontinuity were used with the refraction data to calculate depths. The depth to the Moho increases from about 30 km near Lake Mead to about 40 km near Mono Lake. Variations in arrival times provide evidence for fairly sharp flexures in the Moho. Offsets in the Moho of 4 km at one point and 2 1/2 km at another correspond to large faults at the surface, and it is suggested that fracture zones in the upper crust may displace the Moho and extend into the upper mantle. The phase P appears to be an extension of the reflection from the top of the intermediate layer beyond the critical angle. Bouguer gravity, computed for the seismic model of the crust, is in good agreement with the measured Bouguer gravity. Thus a model of the crustal structure is presented which is consistent with three semi-independent sources of geophysical data: seismic-refraction, seismic-reflection, and gravity.

A global reference model of Moho depths based on WGM2012

NASA Astrophysics Data System (ADS)

Zhou, D.; Li, C.

2017-12-01

The crust-mantle boundary (Moho discontinuity) represents the largest density contrast in the lithosphere, which can be detected by Bouguer gravity anomaly. We present our recent inversion of global Moho depths from World Gravity Map 2012. Because oceanic lithospheres increase in density as they cool, we perform thermal correction based on the plate cooling model. We adopt a temperature Tm=1300°C at the bottom of lithosphere. The plate thickness is tested by varying by 5 km from 90 to 140 km, and taken as 130 km that gives a best-fit crustal thickness constrained by seismic crustal thickness profiles. We obtain the residual Bouguer gravity anomalies by subtracting the thermal correction from WGM2012, and then estimate Moho depths based on the Parker-Oldenburg algorithm. Taking the global model Crust1.0 as a priori constraint, we adopt Moho density contrasts of 0.43 and 0.4 g/cm3 , and initial mean Moho depths of 37 and 20 km in the continental and oceanic domains, respectively. The number of iterations in the inversion is set to be 150, which is large enough to obtain an error lower than a pre-assigned convergence criterion. The estimated Moho depths range between 0 76 km, and are averaged at 36 and 15 km in continental and oceanic domain, respectively. Our results correlate very well with Crust1.0 with differences mostly within ±5.0 km. Compared to the low resolution of Crust1.0 in oceanic domain, our results have a much larger depth range reflecting diverse structures such as ridges, seamounts, volcanic chains and subduction zones. Base on this model, we find that young(<5 Ma) oceanic crust thicknesses show dependence on spreading rates: (1) From ultraslow (<4mm/yr) to slow (4 45mm/yr) spreading ridges, the thicknesses increase dramatically; (2)From slow to fast (45 95mm/yr) spreading ridges , the thickness decreases slightly; (3) For the super-fast ridges (>95mm/yr) we observe relatively thicker crust. Conductive cooling of lithosphere may constrain the melting of the mantle at ultraslow spreading centers. Lower mantle temperatures indicated by deeper Curie depths at slow and fast spreading ridges may decrease the volume of magmatism and crustal thickness. This new global model of gravity-derived Moho depth, combined with geochemical and Curie point depth, can be used to investigate thermal evolution of lithosphere.

An Interactive GIS Procedure for Building and Basement Corrections in Urban Microgravity Surveys

NASA Astrophysics Data System (ADS)

Chasseriau, P.; Olivier, R.

2007-12-01

Construction of a new underground railway in Lausanne, a highly-urbanized city in Switzerland, was an opportunity to test the feasibility and reliability of microgravity surveys in urban environments. The goal of our microgravity survey was to determine the depth-to-bedrock along the project corridor. Available drilling information allowed us verify the density model obtained. The geophysical results also provided spatially exhaustive subsurface information that could not be obtained with drilling methods alone. Gravimetry is one of the rare geophysical methods that can be used in noisy urban environments. An inevitable constraint of this method is terrain correction. It is not easy to obtain a simple and accurate digital elevation model (DEM) of an urban environment considering that buildings and basements are not included. However, these structures significantly influence gravity measurements. We calculate, with software that we have developed, the influence of buildings and basements in order to correct our gravity data. Our procedure permits the integration of gravity measurements, cadastral information (building typology and geometry) and basement geometry in an Access database that allows interactive determination of the Bouguer anomaly. A geographic information system (GIS) is used to extract building geometries based on cadastral information and to correct the influence of each building using a simplified architectural style. Basement voids are then introduced in the final DEM using building outlines given by cadastral maps. The depths and altitudes of the basements are measured by visiting them, and then linking the results to a regional topographic map. All of these corrections can be calculated before the gravity acquisition has begun in order to optimize the design of the survey. The surveys are executed late at night so as to minimize the effects of traffic noise. 160 gravity measurements were carried out before and after digging of the underground tunnel. The difference between gravimetric values of both surveys permitted validation of our modelling code.

Optimization schemes for the inversion of Bouguer gravity anomalies

NASA Astrophysics Data System (ADS)

Zamora, Azucena

Data sets obtained from measurable physical properties of the Earth structure have helped advance the understanding of its tectonic and structural processes and constitute key elements for resource prospecting. 2-Dimensional (2-D) and 3-D models obtained from the inversion of geophysical data sets are widely used to represent the structural composition of the Earth based on physical properties such as density, seismic wave velocities, magnetic susceptibility, conductivity, and resistivity. The inversion of each one of these data sets provides structural models whose consistency depends on the data collection process, methodology, and overall assumptions made in their individual mathematical processes. Although sampling the same medium, seismic and non-seismic methods often provide inconsistent final structural models of the Earth with varying accuracy, sensitivity, and resolution. Taking two or more geophysical data sets with complementary characteristics (e.g. having higher resolution at different depths) and combining their individual strengths to create a new improved structural model can help achieve higher accuracy and resolution power with respect to its original components while reducing their ambiguity and uncertainty effects. Gravity surveying constitutes a cheap, non-invasive, and non-destructive passive remote sensing method that helps to delineate variations in the gravity field. These variations can originate from regional anomalies due to deep density variations or from residual anomalies related to shallow density variations [41]. Since gravity anomaly inversions suffer from significant non-uniqueness (allowing two or more distinct density structures to have the same gravity signature) and small changes in parameters can highly impact the resulting model, the inversion of gravity data represents an ill-posed mathematical problem. However, gravity studies have demonstrated the effectiveness of this method to trace shallow subsurface density variations 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 inversion parameters. Finally, in order to achieve higher resolution, Chapter 5 introduces a 3-D theoretical framework for the joint inversion of Bouguer gravity anomalies and surface wave dispersion using interior-point methods. Through this work, we expect to contribute to the creation of additional tools for the development of 2- and 3-D models depicting the Earth's geological processes and to the widespread use of constrained optimization techniques for the inversion of geophysical data sets.

Structural control of monogenetic volcanism in the Garrotxa volcanic field (Northeastern Spain) from gravity and self-potential measurements

NASA Astrophysics Data System (ADS)

Barde-Cabusson, S.; Gottsmann, J.; Martí, J.; Bolós, X.; Camacho, A. G.; Geyer, A.; Planagumà, Ll.; Ronchin, E.; Sánchez, A.

2014-01-01

We report new geophysical observations on the distribution of subsurface structures associated with monogenetic volcanism in the Garrotxa volcanic field (Northern Spain). As part of the Catalan Volcanic Zone, this Quaternary volcanic field is associated with the European rifts system. It contains the most recent and best preserved volcanic edifices of the Catalan Volcanic Zone with 38 monogenetic volcanoes identified in the Garrotxa Natural Park. We conducted new gravimetric and self-potential surveys to enhance our understanding of the relationship between the local geology and the spatial distribution of the monogenetic volcanoes. The main finding of this study is that the central part of the volcanic field is dominated by a broad negative Bouguer anomaly of around -0.5 mGal, within which a series of gravity minima are found with amplitudes of up to -2.3 mGal. Inverse modelling of the Bouguer data suggests that surficial low-density material dominates the volcanic field, most likely associated with effusive and explosive surface deposits. In contrast, an arcuate cluster of gravity minima to the NW of the Croscat volcano, the youngest volcano of this zone, is modelled by vertically extended low-density bodies, which we interpret as a complex ensemble of fault damage zones and the roots of young scoria cones. A ground-water infiltration zone identified by a self-potential anomaly is associated with a steep horizontal Bouguer gravity gradient and interpreted as a fault zone and/or magmatic fissure, which fed the most recent volcanic activity in the Garrotxa. Gravimetric and self-potential data are well correlated and indicate a control on the locations of scoria cones by NNE-SSW and NNW-SSE striking tectonic features, which intersect the main structural boundaries of the study area to the north and south. Our interpretation of the data is that faults facilitated magma ascent to the surface. Our findings have major implications for understanding the relationship between subsurface structures and potential future volcanic activity in the Garrotxa volcanic field.

Principal facts for a gravity survey of the Gerlach Extension Known Geothermal Resource Area, Pershing County, Nevada

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

Peterson, D.L.; Kaufmann, H.E.

1978-01-01

During July 1977, fifty-one gravity stations were obtained in the Gerlach Extension Known Geothermal Resource Area and vicinity, northwestern Nevada. The gravity observations were made with a Worden gravimeter having a scale factor of about 0.5 milligal per division. No terrain corrections have been applied to these data. The earth tide correction was not used in drift reduction. The Geodetic Reference System 1967 formula (International Association of Geodesy, 1967) was used to compute theoretical gravity. Observed gravity is referenced to a base station in Gerlach, Nevada, having a value based on the Potsdam System of 1930. A density of 2.67more » g per cm/sup 3/ was used in computing the Bouguer anomaly.« less

Principal facts for a gravity survey of the Fly Ranch Extension Known Geothermal Resource Area, Pershing County, Nevada

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

Peterson, D.L.; Kaufmann, H.E.

1978-01-01

During July 1977, forty-four gravity stations were obtained in the Fly Ranch Extension Known Geothermal Resource Area and vicinity, northwestern Nevada. The gravity observations were made with a Worden gravimeter having a scale factor of about 0.5 milligal per division. No terrain corrections have been applied to these data. The earth tide correction was not used in drift reduction. The Geodetic Reference System 1967 formula (International Association of Geodesy, 1967) was used to compute theoretical gravity. Observed gravity is referenced to a base station in Gerlach, Nevada, having a value based on the Potsdam System of 1930 (fig. 1). Amore » density of 2.67 g per cm/sup 3/ was used in computing the Bouguer anomaly.« less

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].

Thermomechanical modeling of the Colorado Plateau-Basin and range transition zone

NASA Technical Reports Server (NTRS)

Londe, M. D.

1985-01-01

The Colorado Plateau (CP) basin and range (B & R) boundary is marked by a transition zone on the order of 75 to 150 km in width. As one moves westward across this transition from the CP interior to the B & R there is a variation in the surface topography, surface heat flow, Bouguer gravity, seismicity, and crustal structure. This transition extends eastward into the western CP from the Wastach-Hurricane fault line and is largely coincident with the high plateaus of Utah and the Wasatch Mountains. It has been suggested that this transition zone marks a thermal and tectonic encroachment of the CP by the B & R. A simple two dimensional numerical model of the thermal regime for the transition zone was constructed to test the hypothesis that the observed geophysical signatures across the transition are due to lateral heat conduction from steady state uniform extension within the B & R lithosphere. Surface heat flow, uplift due to flexure from thermal buoyant loading, and regional Bouguer gravity are computed for various extension rates, crustal structures, and compensation depths.

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.

Crustal Structure Picture of Deception Island [western Bransfield Strait] From Gravimetric and Magnetic Data.

NASA Astrophysics Data System (ADS)

Catalán, M.; Carbó, A.; Martín, Davila; Muñoz, A.; Agudo, L.

Bransfield Strait constitutes a marginal basin that separates the South Shetland archipielago from the Antarctic Peninsula. Since the beginning of its geological record, due to the presence of several submarine and above sea surface volcanoes, eruptions could be appointed easily. All these aspects turn the area as one of the most active at Antarctic region. During 1999 austral summer a seismic crisis was developed. It caused the organisation of a geophysical campaign called DECVOL, where several Spanish scientific institutions participated. Along this, several kinds of studies were carried out. Onland: geodesic GPS and gravity measurements, sampling and gases analysis, continuous seismic recording and geomagnetic measurements. Additionally a geophysical marine campaign [inside and outside Deception island] was carried out. Bathymetry and geopotential information [earth gravity field and geomagnetis m data] were acquired. The multi-disciplinar campaign goal was to perform a fast geophysical evaluation of the volcanic risk. This aspect was important particularly, because the emplacement of Spanish and Argentinean semi -permanent stations around its inner bay. In this study, potential field data recorded along this cruise have been used, together with satellite borne altimetry derived data for gravity, seismic bibliography information of the area, and finally magnetic data compiled in previous campaigns, that were processed until homogeneity could be guaranteed. All these gives a deep detail vision of the structure of the crust at Deception surroundings. In this communication the Bouguer gravity anomaly and scalar magnetic maps are presented, compared and discussed, as well as three gravity and magnetic marine profiles are 2D 1/2 modelled.

Investigation of lunar maria structure from cross-analysis of GRAIL gravity and Kaguya radar data

NASA Astrophysics Data System (ADS)

Zuber, M. T.; Ermakov, A.; Smith, D. E.; Mastroguiseppe, M.; Raguso, M.

2016-12-01

The Lunar Radar Sounder (LRS) on JAXA's Kaguya spacecraft investigated the subsurface structure of the Moon to a depth of a few km. GRAIL gravity models are potentially sensitive to subsurface structure at such depths. GRAIL gravity and LRS radar data are complementary since both are sensitive to density/compositional heterogeneities. Cross-correlation of GRAIL and LRS data has the potential to produce new constraints on the structure and evolution of the lunar maria. Originally, subsurface reflections within the lunar maria were detected with Lunar Sounder Experiment aboard Apollo 17. Subsurface layering was attributed to multiple episodes of volcanism. Later, Kaguya's LRS produced similar measurements but with global-scale coverage. Laboratory measurements show that density variations among mare basalts can be up to 200 kg m-3 or 7%. The LRS measurements have detected subsurface reflection in the upper 1 km of the crust. Combining these two estimates and using the Bouguer slab approximation, we estimate that anomalies of order 1-10 mGal are expected due to potentially varying density of surface and/or subsurface horizons. This accuracy is achievable with the latest GRAIL gravity models. The LRS surface backscattering power is indicative of surface and near sub-surface dielectric properties, which are sensitive to target density and roughness. We investigate the northwestern part of the Procellarum basin because it is the region with the strongest signal-to-noise ratios in gravity models within maria. To examine shallow subsurface structure, we map the surface received power by tracking the first return of radar echoes and compare it with gravity gradients, which are particularly sensitive to small-scale structures.

Gravity survey of the Nevada Test Site and vicinity, Nye, Lincoln, and Clark Counties, Nevada--interim report

USGS Publications Warehouse

Healy, D.L.; Miller, C.H.

1962-01-01

The gravity survey of the Nevada Test Site and contiguous areas of southern Nevada and southeastern California (fig. 1) has been made by the U.S. Geological Survey on behalf of the U.S. Atomic Energy Commission.The objective of this study is to delineate and interpret gravity anomalies and regional trends so that the configuration and depth of the buried erosional surface of the Paleozoic rocks may be determined. This buried surface is of utmost importance in understanding the geologic history of the Nevada Test Site region, the thickness and distribution of the overlying volcanic rocks and alluvium, and the movement of ground water. The Paleozoic rocks cause positive gravity anomalies where they outcrop or occur near the surface and negative anomalies where they are buried in valleys or capped by low-density Tertiary volcanic rocks. Gravity trends which extend over the entire area provide a basis for computing the regional gravity gradient. The regional gravity gradient must be removed from the data for geologic interpretation of the paleotopographic surface in any limited area. Knowledge of the thickness of low-density material overlying the paleotopographic surface is useful in several ways. Proposed underground test sites, such as drill holes and tunnels, may be evaluated in terms of rock unit thickness and alluvial cover requirements. Recent work by the Water Resources Division of the U.S. Geological Survey has demonstrated ground-water movement through the Paleozoic rocks in the vicinity of the Nevada Test Site. Therefore, knowledge of the position of buried Paleozoic rocks is important in evaluating (a) the rate and direction of flow of the ground water, (b) ground-water supplies for domestic and industrial uses, and (c) the possibility of radioactive contamination of ground water. Finally, regional gravity trends and paleotopography are useful in working out the structural history of the area in connection with geologic studies now in progress. The purpose of this interim report is to present the major part of the gravity data obtained as of December 31, 1961. The data are presented as a complete Bouguer gravity anomaly map. Although the gravity contours are somewhat generalized because the map has a scale of 1:250,000 and a contour interval of 5 milligals, the largest anomalies are adequately delineated. Preliminary results of this gravity survey have been reported by Wilmarth and others, 1960, and by Diment and others, 1959 and 1960.

New Antarctic Gravity Anomaly Grid for Enhanced Geodetic and Geophysical Studies in Antarctica

PubMed Central

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.

2018-01-01

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 levelling of the different gravity datasets 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 towards solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica. PMID:29326484

New Antarctic Gravity Anomaly Grid for Enhanced Geodetic and Geophysical Studies in Antarctica

NASA Technical Reports Server (NTRS)

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

New Antarctic Gravity Anomaly Grid for Enhanced Geodetic and Geophysical Studies in Antarctica.

PubMed

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

2016-01-28

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 km 2 , which corresponds to 73% coverage of the continent. The remove-compute-restore technique was applied for gridding, which facilitated levelling of the different gravity datasets 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 towards solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica.

Crustal Thickness on the Mid-Atlantic Ridge: Bull's-Eye Gravity Anomalies and Focused Accretion.

PubMed

Tolstoy, M; Harding, A J; Orcutt, J A

1993-10-29

Spreading segments of the Mid-Atlantic Ridge show negative bull's-eye anomalies in the mantle Bouguer gravity field. Seismic refraction results from 33 degrees S indicate that these anomalies can be accounted for by variations in crustal thickness along a segment. The crust is thicker in the center and thinner at the end of the spreading segment, and these changes are attributable to variations in the thickness of layer 3. The results show that accretion is focused at a slow-spreading ridge, that axial valley depth reflects the thickness of the underlying crust, and that along-axis density variations should be considered in the interpretation of gravity data.

Inner structure of the Puy de Dôme volcano: cross-comparison of geophysical models (ERT, Gravimetry, Muonic Imagery)

NASA Astrophysics Data System (ADS)

Portal, A.; Béné, S.; Boivin, P.; Busato, E.; Cârloganu, C.; Combaret, C.; Dupieux, P.; Fehr, F.; Gay, P.; Labazuy, P.; Laktineh, I.; Lénat, J.-F.; Miallier, D.; Mirabito, L.; Niess, V.; Vulpescu, B.

2012-09-01

Muon imagery of volcanoes and geological structures are presently and actively developed by several groups in the world. It has the potential to provide a 2-D or 3-D density distribution with an accuracy of a few percent. However, at this stage of the development of the method, comparisons with the results from established geophysical methods are necessary to validate its results. An experiment is currently carried out at the Puy de Dôme volcano involving the concurrent acquisition of muon imagery, electrical resistivity (2-D tomography) and gravity survey. Here, we present the preliminary results for the last two methods. North-south and east-west resistivity sections have been obtained in June 2011 and May 2012. These electric data allow to model of the distribution of the resistivity values down to the base of the dome. The dome and its surroundings are now mapped with more than 300 gravity stations measured during a detailed gravity survey carried out in March and May 2012. The computed Bouguer anomaly can be interpreted by models of the density distribution within the dome. This will be directly comparable with the results from the muon imagery. Our ultimate goal is to derive a model of the dome using the joint interpretation of all the sets of data.

Subsurface architecture of a strike-slip collapse structure: insights from Ilopango caldera, El Salvador

NASA Astrophysics Data System (ADS)

Saxby, Jennifer; Gottsmann, Joachim; Cashman, Katherine; Gutierrez, Eduardo

2016-04-01

While most calderas are created by roof collapse along ring-like faults into an emptying magma reservoir during a large and violent explosive eruption, an additional condition for caldera formation may be tectonically induced extensional stresses. Here we provide geophysical insights into the shallow sub-volcanic plumbing system of a collapse caldera in a major strike-slip tectonic setting by inverting Bouguer gravity data from the Ilopango caldera in El Salvador. Despite a long history of catastrophic eruptions with the most recent in 500 A.D., the internal architecture of the caldera has not been investigated, although studies of the most recent eruption have not identified the ring faults commonly associated with caldera collapse. The gravity data show that low-density material aligned along the principal stress orientations of the El Salvador Fault Zone (ESFZ) forms a pronounced gravity low beneath the caldera. Extending to around 6 km depth, the low density structure likely maps a complex stacked shallow plumbing system composed of magmatic and fractured hydrothermal reservoirs. A substantial volume of the plumbing system must be composed of a vapour phase to explain the modeled negative density contrasts. We use these constraints to map the possible multi-phase parameter space contributing to the subsurface architecture of the caldera and propose that the local extension along the complex ESFZ controls accumulation, ascent and eruption of magma at Ilopango. The data further suggest that future eruptions at Ilopango could be facilitated by rapid rise of magma along conjugate fault damage zones through a mechanically weak crust under tension. This may explain the absence of clear ring fault structures at the caldera.

Gravimetric 3D Subsurface Modelling of the Cerro Do Jarau Structure, Rio Grande Do Sul, Brazil.

NASA Astrophysics Data System (ADS)

Giacomini, B. B.

2014-12-01

Although common in other bodies of the solar system, impact craters formed in basaltic terrains are rare on Earth and only a few examples are known. Two of these craters are located south of Brazil, the Vargeão and Vista Alegre impact craters. The Cerro do Jarau structure is not confirmed, but is a possible third Brazilian basaltic crater, formed above the Serra Geral basalt floods of the Paraná Basin like the other two. Cerro do Jarau is a 13 km circular landform that rises over 200 meters above the plains of the "pampas" in southern Brazil. The name, meaning "Jarau hills", is given after the crests of silicified and deformed Botucatu sandstones, which form a semiring of elevated hills in the northern part of the structure. This work focused on the construction of a 3D subsurface geological model that could explain a new set of ground gravimetric data. Bouguer anomalies were calculated from gravity acceleration measured at 313 stations irregularly distributed on the area of the impact structure. A regional component represented by a polynomial trend surface was extracted from the total Bouguer anomalies. The residual Bouguer map (fig. 1) shows a strong positive anomaly with a NE-SW trend, located in the northeastern part of the structure. This gravity feature is not common in other impact structures, being possibly related to a dike intrusion. However, the negative anomaly present in the center of the structure and the circular positive anomaly surrounding the central part of the structure could be related to an impact structure. The positive circular anomaly is not spatially coincident with the edges of the structure, a feature that is also observed at the Vargeão and Vista Alegre impact structures. Density values of basalts, sandstones and breccias were measured from rock samples and each average value were used as constraints for the 3D model developed with the Geosoft® VOXI Earth modelling.This model provided a better understanding of the subsurface design of the structure. The impact crater hypothesis still remain the best hypothesis, but our results suggest that there was a post-impact dike intrusion and deep erosion processes that removed most of the impact breccia and a possible central uplift. The remaining of the uplifted rocks is observed as the silicified sandstone that forms the crests of the Jarau hills.

The T-Reflection and the deep crustal structure of the Vøring Margin offshore Mid-Norway

NASA Astrophysics Data System (ADS)

Abdelmalak, M. M.; Faleide, J. I.; Planke, S.; Gernigon, L.; Zastrozhnov, D.; Shephard, G. E.; Myklebust, R.

2017-12-01

Volcanic passive margins are characterized by massive occurrence of mafic extrusive and intrusive rocks, before and during plate breakup, playing major role in determining the evolution pattern and the deep structure of magma-rich margins. Deep seismic reflection data frequently provide imaging of strong continuous reflections in the middle/lower crust. In this context, we have completed a detailed 2D seismic interpretation of the deep crustal structure of the Vøring volcanic margin, offshore mid-Norway, where high-quality seismic data allow the identification of high-amplitude reflections, locally referred to as the T-Reflection (TR). Using the dense seismic grid we have mapped the top of the TR in order to compare it with filtered Bouguer gravity anomalies and seismic refraction data. The TR is identified between 7 and 10 s. Sometimes it consists of one single smooth reflection. However, it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries, amplitude and contact relationships. The TR seems to be connected to deep sill networks and locally located at the continuation of basement high structures or terminates over fractures and faults. The spatial correlation between the filtered positive Bouguer gravity anomalies and the TR indicates that the latter represents a high impedance boundary contrast associated with a high-density/velocity body. Within an uncertainty of ± 2.5 km, the depth of the mapped TR is found to correspond to the depth of the top of the Lower Crustal Body (LCB), characterized by high P-wave velocities (>7 km/s), in 50% of the outer Vøring Margin areas, whereas different depths between the TR and the top LCB are estimated for the remaining areas. We present a tectonic scenario, where a large part of the deep structure could be composed of preserved upper continental basement and middle to lower crustal lenses of inherited and intruded high-grade metamorphic rocks. Deep intrusions into the faulted crustal blocks are responsible for the rough character of the TR, whereas intrusions into the lower crust and detachment faults are likely responsible for its smoother appearance. Deep magma intrusions can be responsible for metamorphic processes leading to an increased velocity of the lower crust of more than 7 km/s.

Broadscale postseismic gravity change following the 2011 Tohoku-Oki earthquake and implication for deformation by viscoelastic relaxation and afterslip.

PubMed

Han, Shin-Chan; Sauber, Jeanne; Pollitz, Fred

2014-08-28

The analysis of GRACE gravity data revealed postseismic gravity increase by 6 μGal over a 500 km scale within a couple of years after the 2011 Tohoku-Oki earthquake, which is nearly 40-50% of the coseismic gravity change. It originates mostly from changes in the isotropic component corresponding to the M rr moment tensor element. The exponential decay with rapid change in a year and gradual change afterward is a characteristic temporal pattern. Both viscoelastic relaxation and afterslip models produce reasonable agreement with the GRACE free-air gravity observation, while their Bouguer gravity patterns and seafloor vertical deformations are distinctly different. The postseismic gravity variation is best modeled by the biviscous relaxation with a transient and steady state viscosity of 10 18 and 10 19  Pa s, respectively, for the asthenosphere. Our calculated higher-resolution viscoelastic relaxation model, underlying the partially ruptured elastic lithosphere, yields the localized postseismic subsidence above the hypocenter reported from the GPS-acoustic seafloor surveying.

Broadscale postseismic gravity change following the 2011 Tohoku-Oki earthquake and implication for deformation by viscoelastic relaxation and afterslip

PubMed Central

Han, Shin-Chan; Sauber, Jeanne; Pollitz, Fred

2014-01-01

The analysis of GRACE gravity data revealed postseismic gravity increase by 6 μGal over a 500 km scale within a couple of years after the 2011 Tohoku-Oki earthquake, which is nearly 40–50% of the coseismic gravity change. It originates mostly from changes in the isotropic component corresponding to the Mrr moment tensor element. The exponential decay with rapid change in a year and gradual change afterward is a characteristic temporal pattern. Both viscoelastic relaxation and afterslip models produce reasonable agreement with the GRACE free-air gravity observation, while their Bouguer gravity patterns and seafloor vertical deformations are distinctly different. The postseismic gravity variation is best modeled by the biviscous relaxation with a transient and steady state viscosity of 1018 and 1019 Pa s, respectively, for the asthenosphere. Our calculated higher-resolution viscoelastic relaxation model, underlying the partially ruptured elastic lithosphere, yields the localized postseismic subsidence above the hypocenter reported from the GPS-acoustic seafloor surveying. PMID:25821272

A gravity study along a profile across the Sichuan Basin, the Qinling Mountains and the Ordos Basin (central China): Density, isostasy and dynamics

NASA Astrophysics Data System (ADS)

Zhang, Yongqian; Teng, Jiwen; Wang, Qianshen; Lü, Qingtian; Si, Xiang; Xu, Tao; Badal, José; Yan, Jiayong; Hao, Zhaobing

2017-10-01

In order to investigate the structure of the crust beneath the Middle Qinling Mountains (MQL) and neighboring areas in the North China Block and South China Block, a north-south gravity profile from Yuquan in the Sichuan Basin to Yulin in the Ordos Basin was conducted in 2011. The Bouguer gravity anomaly is determined from a high-quality gravity dataset collected between 31°N and 36°N of latitude, and varies between -200 and -110 mGal in the study region. Using accredited velocity density relationships, an initial crust-mantle density model is constructed for MQL and adjacent areas, which is later refined interactively to simulate the observed gravity anomaly. The present study reveals the features of the density and Bouguer gravity with respect to the tectonic units sampled by the profile. The lithosphere density model shows typical density values that depict a layered structure and allow differentiate the blocks that extend along the reference profile. The gravity field calculated by forward modeling from the final density distribution model correlates well with the measured gravity field within a standard deviation of 1.26 mGal. The density in the crystalline crust increases with depth from 2.65 g/cm3 up to the highest value of 2.95 g/cm3 near the bottom of the crust. The Conrad interface is identified as a density jump of about 0.05 g/cm3. The average density of the crust in MQL is clearly lower than the density in the formations on both sides. Starting from a combined Airy-Pratt isostatic compensation model, a partly compensated crust is found below MQL, suggesting future growth of the crust, unlike the Ordos and Sichuan basins that will remain stable. On the basis of the density and isostatic state of the crust and additional seismological research, such as the P-wave velocity model and Poisson's ratio, it is concluded that the lower crust delamination is a reasonable interpretation for the geophysical characteristics below the Qinling Orogen.

Structural-geophysical model of the basement complex of the Aden-Red Sea region

NASA Astrophysics Data System (ADS)

Isaev, E. N.

1987-11-01

A relief map of the basement complex underlying the volcanogenic sedimentary cover has been constructed on the basis of composite Bouguer anomaly maps and maps of magnetic anomalies ΔT. Seismic and geological data on the Gulf of Aden and the Red Sea as well as on adjacent areas of Africa and Arabia have also been used. The mid-Red Sea and mid-Aden uplifts (similar to the mid-oceanic ones) as well as the foredeep have been identified. The thickness of cover in the foredeeps is 6-8 km. A regional negative Bouguer anomaly crosses the Aden-Red Sea rift system and includes the area of young volcanism. Intensive linear magnetic anomalies are traceable only within the area of overlap of the rift system and the zone of young volcanism. Rift system apophyses have advanced into the continent and their nature is similar to that of the Afar triangle.

Marine Geophysical Characterization of the Chain Fracture Zone in the Equatorial Atlantic

NASA Astrophysics Data System (ADS)

Harmon, N.; Rychert, C.; Agius, M. R.; Tharimena, S.; Kendall, J. M.

2017-12-01

The Chain Fracture zone is part of a larger system of fracture zones along the Mid Atlantic Ridge that is thought to be one of the original zones of weakness during the break up of Pangea. It is over 300 km long and produces earthquakes as large as Mw 6.9 on segments of the active fault zone. Here we present the results of two marine geophysical mapping campaigns over the active part of the Chain Fracture zone as part of the PI-LAB (Passive Imaging of the Lithosphere-Asthenosphere Boundary) experiment. We collected swath bathymetry, backscatter imagery, gravity and total field magnetic anomaly. We mapped the fault scarps within the transform fault system using the 50 m resolution swath and backscatter imagery. In addition, a 30-40 mGal residual Mantle Bouguer Anomaly determined from gravity analysis suggests the crust is by up to 1.4-2.0 km beneath the Chain relative to the adjacent ridge segments. However, in the eastern 75 km of the active transform we find evidence for thicker crust. The active fault system cuts through the region of thicker crust and there is a cluster of MW > 6 earthquakes in this region. There is a cluster of similar sized earthquakes on the western end where thinner crust is inferred. This suggests that variations in melt production and crustal thickness at the mid ocean ridge systems may have only a minor effect on the seismicity and longevity of the transform fault system.

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.

Underwater gravity meter survey of San Francisco and San Pablo bays, California, 1982

USGS Publications Warehouse

Childs, Jonathan R.; Beyer, L.A.; McCulloch, D.S.; McHendrie, G.A.; Steele, W.C.

1983-01-01

Seafloor gravity measurements were made at 281 bottom stations in San Francisco and San Pablo Bays, California, on a series of lines oriented approximately NNE.. Line spacing was approximately 2.8 km and stations along the lines mere spaced 0.5 to 1.5 km apart, between 0.5 and 1.5 km perpendicular to the axis. Sample Bouguer anomalies in the San Francisco Bay range from -15 to +15 mGals (?0.1 mgal), while anomalies in the San Pablo Bay are consistently negative, ranging from +4.0 to -40.0 mGal (?0.2 mGal).

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

NASA Astrophysics Data System (ADS)

Cady, John W.

1989-11-01

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, I have divided the province 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. Basalt of the Angayucham domain causes strong gravity highs and weak magnetic highs. The Kanuti domain is distinguished from the Angayucham domain by intense magnetic highs caused by cumulus mafic and ultramafic plutonic rocks, abundant ultramafic mantle tectonites, and magnetic syenite and monzonite. Long-wavelength, low-intensity magnetic highs and undulating gravity anomalies indicate an undulating basement surface of varied lithology beneath the Kobuk-Koyukuk and Lower Yukon basins. Modeling of gravity and magnetic anomalies shows that oceanic rocks of the Angayucham and Kanuti domains dip inward beneath the Kobuk-Koyukuk basin. 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. Plutons of the Brooks Range and the southern Ruby geanticline are nonmagnetic, ilmenite series, S-type granites that cause magnetic lows. Plutons of the northern Ruby geanticline are variable in their magnetic properties and cause both highs and lows. Plutons of both the eastern and western Yukon-Koyukuk province are variable in their magnetic expression but commonly cause magnetic lows in contrast to andesite.

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 constrain inversions of gravity data. The integration of MT and gravity data will provide an insight into the potential density distribution within the resistors associated with the granites and whether the granites, likely to have elevated heat-production (HP), are underlain by electrically resistive but denser, more mafic bodies, likely to be associated with lower HP.

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.

Spatial uncertainty of a geoid undulation model in Guayaquil, Ecuador

NASA Astrophysics Data System (ADS)

Chicaiza, E. G.; Leiva, C. A.; Arranz, J. J.; Buenańo, X. E.

2017-06-01

Geostatistics is a discipline that deals with the statistical analysis of regionalized variables. In this case study, geostatistics is used to estimate geoid undulation in the rural area of Guayaquil town in Ecuador. The geostatistical approach was chosen because the estimation error of prediction map is getting. Open source statistical software R and mainly geoR, gstat and RGeostats libraries were used. Exploratory data analysis (EDA), trend and structural analysis were carried out. An automatic model fitting by Iterative Least Squares and other fitting procedures were employed to fit the variogram. Finally, Kriging using gravity anomaly of Bouguer as external drift and Universal Kriging were used to get a detailed map of geoid undulation. The estimation uncertainty was reached in the interval [-0.5; +0.5] m for errors and a maximum estimation standard deviation of 2 mm in relation with the method of interpolation applied. The error distribution of the geoid undulation map obtained in this study provides a better result than Earth gravitational models publicly available for the study area according the comparison with independent validation points. The main goal of this paper is to confirm the feasibility to use geoid undulations from Global Navigation Satellite Systems and leveling field measurements and geostatistical techniques methods in order to use them in high-accuracy engineering projects.

Lithospheric structure of Africa: insights from its effective elastic thickness variations.

NASA Astrophysics Data System (ADS)

Pérez-Gussinyé, M.; Metois, M.; Fernández, M.; Vergés, J.; Fullea, J.

2009-04-01

Detailed images of lithospheric structure can help understand how surface deformation is related to Earth's deep structure. A proxy for lithospheric structure is its effective elastic thickness, Te, which mainly depends on its thermal state and composition. We present a new effective elastic thickness, Te, map of the African lithosphere estimated using the coherence function between topography and Bouguer anomaly. The Bouguer anomaly used in this study derives from the EGM 2008 model, which constitutes the highest resolution gravity database over Africa, allowing a significant improvement on lateral resolution in Te. Our map shows that Te is high > 100 km, in the West African, Congo, Kalahari and Tanzania cratons. Of these, the Kalahari presents the thinnest elastic thicknesses and, based on additional seismic and mineral physics studies, we suggest this may reflect modification of the lithosphere by anomalously hot mantle beneath the lithosphere. The effective elastic thickness is lowest beneath the Afar and Main Ethiopian rifts, where the maximum extension and thinnest lithosphere of Africa occur. The Tanzania craton appears as two rigid blocks separated by a relatively low Te area located southwest of lake Victoria. This coincides with the centre of seismic radial anisotropy beneath the craton, suggested to be the Victoria plume head by Weertrane et al. [2003]. Along the eastern branch of the East African rift Te is low and increases abruptly at 2 to 3 degrees South, coinciding with a deepening of earthquake depocenter and a change from narrow to wide rifting. These and other considerations suggest that the southern part of the eastern branch is underlain by thick, rigid cratonic lithosphere. Finally, the northern part of Africa is characterised by low Te on the Darfur, Tibesti, Hoggar and Cameroon line volcanic provinces, suggesting that the underlying lithospheric mantle has been thermally thinned. Corridors of low Te connect these volcanic provinces, supporting the idea that hot mantle flows between them. However, a thin corridor between these volcanic provinces and the Afar hot-spot is less obvious.

Gravity-height correlations for unrest at calderas

NASA Astrophysics Data System (ADS)

Berrino, G.; Rymer, H.; Brown, G. C.; Corrado, G.

1992-11-01

Calderas represent the sites of the world's most serious volcanic hazards. Although eruptions are not frequent at such structures on the scale of human lifetimes, there are nevertheless often physical changes at calderas that are measurable over periods of years or decades. Such calderas are said to be in a state of unrest, and it is by studying the nature of this unrest that we may begin to understand the dynamics of eruption precursors. Here we review combined gravity and elevation data from several restless calderas, and present new data on their characteristic signatures during periods of inflation and deflation. We find that unless the Bouguer gravity anomaly at a caldera is extremely small, the free-air gradient used to correct gravity data for observed elevation changes must be the measured or calculated gradient, and not the theoretical gradient, use of which may introduce significant errors. In general, there are two models that fit most of the available data. The first involves a Mogi-type point source, and the second is a Bouguer-type infinite horizontal plane source. The density of the deforming material (usually a magma chamber) is calculated from the gravity and ground deformation data, and the best fitting model is, to a first approximation, the one producing the most realistic density. No realistic density is obtained where there are real density changes, or where the data do not fit the point source or slab model. We find that a point source model fits most of the available data, and that most data are for periods of caldera inflation. The limited examples of deflation from large silicic calderas indicate that the amount of mass loss, or magma drainage, is usually much less than the mass gain during the preceding magma intrusion. In contrast, deflationary events at basaltic calderas formed in extensional tectonic environments are associated with more significant mass loss as magma is injected into the associated fissure swarms.

Gravity and magnetic anomalies of the Cyprus arc and tectonic implications

NASA Astrophysics Data System (ADS)

Ergün, M.; Okay, S.; Sari, C.; Oral, E. Z.

2003-04-01

In present day, eastern Mediterranean is controlled by the collision of the African and Eurasian plates and displacements of Arabian, Anatolian and Aegean micro-plates. The boundary between African and Eurasian plates is delineated by the Hellenic arc and Pliny-Strabo trench in the west and the Cyprus arc and a diffuse fault system of the Eastern Anatolian Fault zone in the east. The available gravity and magnetic data from the easternmost Mediterranean allow to subdivide this basin into three provinces: the northeastern Mediterranean north of the Cyprus Arc; the Levant Basin south of the Cyprus Arc and east of the line that roughly continues the Suez rift trend toward the Gulf of Antalya, between Cyprus and Anaximander Mountains; and the Mediterranean Ridge, Herodotus Basin west of this line. High anomalies observed in Cyprus and the sea region at the south is prominent in the gravity data. The Bouguer gravity anomaly reaches its maximum values over Cyprus, where it is most probably caused by high dense Troodos ophiolites. The uplifted oceanic crust causes high Bouguer anomaly also seen in the vicinity of Eratosthenes Seamount. Another result obtained from gravity data is that the crust under Herodotos and Rhodes basins is somehow oceanic and Anaximander, Eratosthenes and Cyprus are continental fragments. There are no linear magnetic anomalies in the Mediterranean. But there are magnetic anomalies over the Eratosthenes seamount and as well as from Cyprus to the Antalya basin due to the ophiolitic bodies. In Cyprus, the last compressional deformations were defined near the Miocene/Pliocene boundary. The extensional deformation associated with the Antalya basin appears to be separated by a zone of the Florence rise and Anaximander Mountains affected by differential tectonic movements. Eratosthenes Seamount is a positive crustal feature in the process of collision with Cyprus along an active margin; there is clearly a potential tectonic relationship to the onland geology of Cyprus. Eratosthenes is in the process of actively being underthrust both northwards and southwards under opposing margins.

Muographic mapping of the subsurface density structures in Miura, Boso and Izu peninsulas, Japan

NASA Astrophysics Data System (ADS)

Tanaka, Hiroyuki K. M.

2015-02-01

While the benefits of determining the bulk density distribution of a landmass are evident, established experimental techniques reliant on gravity measurements cannot uniquely determine the underground density distribution. We address this problem by taking advantage of traffic tunnels densely distributed throughout the country. Cosmic ray muon flux is measured in the tunnels to determine the average density of each rock overburden. After analyzing the data collected from 146 observation points in Miura, South-Boso and South-Izu Peninsula, Japan as an example, we mapped out the shallow density distribution of an area of 1340 km2. We find a good agreement between muographically determined density distribution and geologic features as described in existing geological studies. The average shallow density distribution below each peninsula was determined with a great accuracy (less than +/-0.8%). We also observed a significant reduction in density along fault lines and interpreted that as due to the presence of multiple cracks caused by mechanical stress during recurrent seismic events. We show that this new type of muography technique can be applied to estimate the terrain density and porosity distribution, thus determining more precise Bouguer reduction densities.

Muographic mapping of the subsurface density structures in Miura, Boso and Izu peninsulas, Japan

PubMed Central

Tanaka, Hiroyuki K. M.

2015-01-01

While the benefits of determining the bulk density distribution of a landmass are evident, established experimental techniques reliant on gravity measurements cannot uniquely determine the underground density distribution. We address this problem by taking advantage of traffic tunnels densely distributed throughout the country. Cosmic ray muon flux is measured in the tunnels to determine the average density of each rock overburden. After analyzing the data collected from 146 observation points in Miura, South-Boso and South-Izu Peninsula, Japan as an example, we mapped out the shallow density distribution of an area of 1340 km2. We find a good agreement between muographically determined density distribution and geologic features as described in existing geological studies. The average shallow density distribution below each peninsula was determined with a great accuracy (less than ±0.8%). We also observed a significant reduction in density along fault lines and interpreted that as due to the presence of multiple cracks caused by mechanical stress during recurrent seismic events. We show that this new type of muography technique can be applied to estimate the terrain density and porosity distribution, thus determining more precise Bouguer reduction densities. PMID:25660352

Muographic mapping of the subsurface density structures in Miura, Boso and Izu peninsulas, Japan.

PubMed

Tanaka, Hiroyuki K M

2015-02-09

While the benefits of determining the bulk density distribution of a landmass are evident, established experimental techniques reliant on gravity measurements cannot uniquely determine the underground density distribution. We address this problem by taking advantage of traffic tunnels densely distributed throughout the country. Cosmic ray muon flux is measured in the tunnels to determine the average density of each rock overburden. After analyzing the data collected from 146 observation points in Miura, South-Boso and South-Izu Peninsula, Japan as an example, we mapped out the shallow density distribution of an area of 1340 km(2). We find a good agreement between muographically determined density distribution and geologic features as described in existing geological studies. The average shallow density distribution below each peninsula was determined with a great accuracy (less than ±0.8%). We also observed a significant reduction in density along fault lines and interpreted that as due to the presence of multiple cracks caused by mechanical stress during recurrent seismic events. We show that this new type of muography technique can be applied to estimate the terrain density and porosity distribution, thus determining more precise Bouguer reduction densities.

Uplift in the Fiordland region, New Zealand: implications for incipient subduction.

PubMed

House, M A; Gurnis, M; Kamp, P J J; Sutherland, R

2002-09-20

Low-temperature thermochronometry reveals regional Late Cenozoic denudation in Fiordland, New Zealand, consistent with geodynamic models showing uplift of the overriding plate during incipient subduction. The data show a northward progression of exhumation in response to northward migration of the initiation of subduction. The locus of most recent uplift coincides with a large positive Bouguer gravity anomaly within Fiordland. Thermochronometrically deduced crustal thinning, anomalous gravity, and estimates of surface uplift are all consistent with approximately 2 kilometers of dynamic support. This amount of dynamic support is in accord with geodynamic predictions, suggesting that we have dated the initiation of subduction adjacent to Fiordland.

Chicxulub impact basin: Gravity characteristics and implications for basin morphology and deep structure

NASA Technical Reports Server (NTRS)

Sharpton, Virgil L.; Burke, Kevin; Hall, Stuart A.; Lee, Scott; Marin, Luis E.; Suarez, Gerardo; Quezada-Muneton, Juan Manuel; Urrutia-Fucugauchi, Jaime

1993-01-01

The K-T-aged Chicxulub Impact Structure is buried beneath the Tertiary carbonate rocks of the Northern Yucatan Platform. Consequently its morphology and structure are poorly understood. Reprocessed Bouguer (onshore) and Free Air (offshore) gravity data over Northern Yucatan reveal that Chicxulub may be a 200-km-diameter multi-ring impact basin with at least three concentric basin rings. The positions of these rings follow the square root of 2 spacing rule derived empirically from analysis of multi-ring basins on other planets indicating that these rings probably correspond to now-buried topographic basin rings. A forward model of the gravity data along a radial transect from the southwest margin of the structure indicates that the Chicxulub gravity signature is compatible with this interpretation. We estimate the basin rim diameter to be 204 +/- 16 km and the central peak ring diameter (D) is 104 +/- 6 km.

Broadscale Postseismic Gravity Change Following the 2011 Tohoku-Oki Earthquake and Implication for Deformation by Viscoelastic Relaxation and Afterslip

NASA Technical Reports Server (NTRS)

Han, Shin-Chan; Sauber, Jeanne; Pollitz, Fred

2014-01-01

The analysis of GRACE gravity data revealed post-seismic gravity increase by 6 micro-Gal over a 500 km scale within a couple of years after the 2011 Tohoku-Oki earthquake, which is nearly 40-50% of the co-seismic gravity change. It originates mostly from changes in the isotropic component corresponding to the M(sub rr) moment tensor element. The exponential decay with rapid change in a year and gradual change afterward is a characteristic temporal pattern. Both viscoelastic relaxation and afterslip models produce reasonable agreement with the GRACE free-air gravity observation, while their Bouguer gravity patterns and seafloor vertical deformations are distinctly different. The post-seismic gravity variation is best modeled by the bi-viscous relaxation with a transient and steady state viscosity of 10(exp 18) and 10(exp 19) Pa s, respectively, for the asthenosphere. Our calculated higher-resolution viscoelastic relaxation model, underlying the partially ruptured elastic lithosphere, yields the localized post-seismic subsidence above the hypocenter reported from the GPS-acoustic seafloor surveying.

Geothermal Exploration of the Winston Graben, Central New Mexico, USA

NASA Astrophysics Data System (ADS)

Sophy, M. J.; Kelley, S. A.

2011-12-01

We are assessing the geothermal potential of the Winston Graben of central New Mexico using borehole temperature logs and geophysical data. The Winston Graben is a late Cenozoic rift basin, part of the larger Rio Grande rift, which is 5 to 10 km wide and 56 km long with northern and southern termini occurring at accommodation zones that coincide with late Cenozoic volcanic lineaments. The graben is interpreted to be symmetric based on geologic mapping, with 2 km of stratigraphic offset on both the western and eastern margins. The graben is bordered by the Black Range to the west and is separated from the Rio Grande valley by the Sierra Cuchillo, a horst block made of Paleozoic rocks intruded by a laccolith. Geothermal and geophysical data, including water table measurements, well temperature logs, thermal conductivity samples, bottom hole temperatures, water chemistry, and gravity data have been extracted from the New Mexico Geothermal Database, part of the National Geothermal Database, and the Geonet Gravity and Magnetic Dataset Repository. Combined with existing geologic maps of the Winston Graben and surroundings, these data help to identify spatial relationships between geologic structures and groundwater parameters and distribution. Geothermal gradients from industry temperature-depth well profiles range from 20°C/km to 60°C/km with a spatial distribution of higher gradients located on the eastern side of the Sierra Cuchillo horst, which is where a mapped warm spring is located. Lower thermal gradients were observed to the west in the groundwater recharge area of the basin. Analysis of Bouguer gravity data indicate a gravity low coinciding with the center of the Winston Graben, which is attributed to be the deepest part of the basin, symetrically surrounded by gravity highs. Gravity highs coincide with the middle Cenozoic Morenci and Chise volcanic lineaments along the northern and southern ends of the graben. The mapped warm spring occurs at the intersection of basin bounding faults and the Chise lineament. Water table gradient information from phreatic aquifers less than 75 meters deep suggests both along axis and cross axis flow direction within the basin. Because the temperature anomalies trend east-west and water table gradients trend north-south, a two component hydrogeologic system may exist. The east-west trend may be the result of deep groundwater, heated along its flowpath beneath the basin and the Sierra Cuchillo, being forced to the surface at structural zones. Major rift bounding faults along the Sierra Cuchillo horst block serve as fluid pathways for the existing warm springs, and a low temperature geothermal resource may have formed as deep warm, and shallow cool waters interact. Planned work on this project includes collecting hydrogen and oxygen isotopic data of precipitation and groundwater which may show distinct water chemistries of a two component system, continued temperature logging of deeper wells in order to understand temperature distributions at depth, and an increased number of gravity measurements of the southern end of the Winston Graben to improve mapping of the southern accommodation zone relative to the hydrogeologic system.

Evidence Supporting an Early as Well as Late Heavy Bombardment on the Moon

NASA Technical Reports Server (NTRS)

Frey, Herbert

2015-01-01

Evidence supporting an intense early bombardment on the Moon in addition to the traditional Late Heavy Bombardment at approx. 4 BY ago include the distribution of N(50) Crater Retention Ages (CRAs) for candidate basins, a variety of absolute age scenarios for both a "young" and an "old" Nectaris age, and the decreasing contrasts in both topographic relief and Bouguer gravity with increasing CRA.

Gravity field and nature of continent-continent collision along the Himalaya

NASA Astrophysics Data System (ADS)

Verma, R. K.

Gravity field (Bouguer) in the Himalaya is characterised by large negative-values ranging from nearly -180 mGal to over -450 mGal in Naga-Parbat/Haramosh massif which go up to -550 mGal in the Karakoram region. The observed Bouguer anomaly in NW Himalaya has been interpreted along a profile passing from Gujranwala (located at the edge of the Indian shield) to the Haramosh massif in terms of Moho depth and density contrast between the crust and the mantle. The Moho depth is interpreted to increase from nearly 35 km near the edge of Indian shield to 75 km (below sea level) underneath the Haramosh massif. A similar model is applicable to a profile passing to the west of Nanga Parbat massif, from Gujranwala to Ghizar, through the Kohistan region. However, along this profile high density lower crustal rocks appear to have been emplaced in the upper part along the Main Mantle thrust. The gravityanomalies in the Nepal-Tibet region hasbeen interpreted in terms of a northward sloping Moho which down faulted by about 15 km to attain a depth of 65 km around Tingri which corresponds to explosion seismology data. The nature of isostatic compensation prevailing underneath the Himalaya has been discussed.

Identification of a precambrian rift through Missouri by digital image processing of geophysical and geological data

NASA Technical Reports Server (NTRS)

Guinness, E. A.; Arvidson, R. E.; Strebeck, J. W.; Schulz, K. J.; Davies, G. F.; Leff, C. E.

1982-01-01

A newly discovered feature in the midcontinent - a gravity low that begins at a break in the midcontinent gravity high in SE Nebraska, extends across Missouri in a NW-SE direction, and intersects the Mississippi Valley graben to form the Pascola arch - is discussed. The anomaly varies from 120 to 160 km in width, extends approximately 700 km, and is best expressed in southern Missouri, where it has a Bouguer amplitude of about -34 mGal. It is noted that the magnitude of the anomaly cannot be explained on the basis of a thickened section of Paleozoic sedimentary rock. The gravity data and the sparse seismic refraction data for the region are found to be consistent with an increased crustal thickness beneath the gravity low. It is thought that the gravity anomaly is probably the present expression of a failed arm of a rifting event, perhaps one associated with the spreading that led to or preceded formation of the granite and rhyolite terrain of southern Missouri.

Structure of the Saint Francois Mountains and surrounding lead belt, S.E. Missouri: Inference from thermal IR and other data sets

NASA Technical Reports Server (NTRS)

Arvidson, R. E. (Principal Investigator)

1982-01-01

Progress in the preparation of manuscripts on the discovery of a Precambrian rift running NW-SE through Missouri as seen in free air and Bouguer gravity anomalies and in HCMM data, and on digital image processing of potential field and topographic data on the rift is reported. Copies of the papers are attached. Contrast-enhanced HCMM images that have been transformed to Mercator projections are presented. Shaded relief map overlays of thermal and apparent thermal inertia images used as part of a masers thesis examining correlations between HCMM data products, linears, and geologic units are presented. Progress in examination of the difference in information content of daytime infrared, night time infrared, albedo, and thermal inertia images and their application to he identification of linears not directly controlled by topography is reported. Thermal infrared and albedo data were coded as hue, saturation and brightness values to generate a color display, which is included.

Geologic and isostatic map of the Nenana Basin area, central Alaska

USGS Publications Warehouse

Frost, G.M.; Barnes, D.F.; Stanley, R.G.

2002-01-01

Introduction The Nenana Basin area is a prospective petroleum province in central Alaska, and this geologic and isostatic gravity map is part of a petroleum resource assessment of the area. The geology was compiled from published sources (Chapman and others, 1971, 1975a, 1975b, 1982; Chapman and Yeend, 1981; Csejtey and others, 1986; Jones and others, 1983; Pewe and others, 1966; Reed, 1961; and Weber and others, 1992), as shown on the index map (map sheet). Map units are organized and presented according to the scheme of lithotectonic terranes proposed by Jones and others (1987) and Silberling and Jones (1984); we recognize, however, that this terrane scheme is controversial and likely to be revised in the future. In some cases, we combined certain terranes because we were unable to match the terrane boundaries given by Jones and others (1987) and Silberling and Jones (1984) with specific faults shown on existing geologic maps. Postaccretion cover deposits represent overlap assemblages that depositionally overlie accreted terranes. Plutonic igneous rocks shown on this map include several plutons that are clearly postaccretionary, based on isotopic ages and (or) field relations. It is possible that some of the plutons predate accretion, but this has not been demonstrated. According to Jones and others (1982), the terranes in the area of our map were assembled during late Mesozoic or earliest Cenozoic time. The gravity contours are derived from data used in earlier compilations (Barnes, 1961, 1977; Hackett, 1981; Valin and others, 1991; Frost and Stanley, 1991) that are supplemented by some National Oceanic and Atmospheric Administration data along the Alaska Pipeline level line (W.E. Strange, written commun., 1980). The earlier compilations were used for simple Bouguer maps, prepared primarily by non-digital methods, and are superseded by this map. The present map is the result of digital processing that includes the 1967 Geodetic Reference System, the IGSN-71 datum, digital terrain corrections, and conversion to isostatic gravity so that geologic structures on the margin of the Alaska Range are more clearly portrayed (Simpson and others, 1986). Computation procedures are described in part by Barnes (1972, 1984), Jachens and Roberts (1981), and Barnes and others (1994). The calculations used a crustal density of 2.67 g/cm 3 , a density contrast at the base of the isostatic root of 0.4 g/cm 3 , and a root thickness at sea level of 25 km. The distribution of data within the map area is uneven and locally controls the shape of the computer-generated contours. Altimetry was used for most of the elevation control and its inconsistency is responsible for many of the small contour irregularities. Ninety percent of the measurements are estimated to have an accuracy of about 1.5 mgal or about a quarter of the 5 mgal contour interval. Data collection and analysis were assisted by R.V. Allen, R.C. Jachens, M.A. Fisher, T.R. Bruns, J.G. Blank, J.W. Bader, Z.C. Valin, J.W. Cady, R.L. Morin, and P.V. Woodward. The most promising area for petroleum exploration is a prominent 25 mgal isostatic gravity low north of Nenana (T. 2 S., R. 8 W.). This gravity low probably corresponds to the deepest part of a sedimentary basin filled by Cenozoic strata that includes nonmarine fluvial and lacustrine deposits of the Eocene to Miocene Usibelli Group. Smaller gravity lows are associated with outcrops of these sedimentary rocks north of Suntrana (T. 12 S., R. 6-9 W.) and Sable Pass (T. 16 S., R. 11 W.). A broad low on the north flank of the Alaska Range east of the Wood River (T. 10 S., R. 1 E.) indicates another basin under the Tanana lowland that extends eastward off the map area towards Delta Junction, where its presence was confirmed by both gravity and seismic data (Barnes and others, 1991). Gravity modelling suggests that the base of the Usibelli Group in the area north of Nenana (T. 2 S., R. 8 W.) is about 3,000 to 3,350 m beneath t

Mercury's lithospheric thickness and crustal density, as inferred from MESSENGER observations

NASA Astrophysics Data System (ADS)

James, P. B.; Mazarico, E.; Genova, A.; Smith, D. E.; Neumann, G. A.; Solomon, S. C.

2015-12-01

The gravity field and topography of Mercury measured by the MESSENGER spacecraft have provided insights into the thickness of the planet's elastic lithosphere, Te. We localized the HgM006 free-air gravity anomaly and gtmes_125v03 shape datasets to search for theoretical elastic thickness solutions that best fit a variety of localized coherence spectra between Bouguer gravity anomaly and topography. We adopted a crustal density of ρcrust =2700 kg m-3 for the Bouguer gravity correction, but density uncertainty did not markedly affect the elastic thickness estimates. A best-fit solution in the northern smooth plains (NSP) gives an elastic thickness of Te =30-60 km at the time of formation of topography for a range of ratios of top to bottom loading from 1 to 5. For a mechanical lithosphere with a thickness of ~2Te and a temperature of 1600 °C at the base, this solution is consistent with a geothermal gradient of 9-18 K km-1. A similar coherence analysis exterior to the NSP produces an elastic thickness estimate of Te =20-50 km, albeit with a poorer fit. Coherence in the northern hemisphere as a whole does not approach zero at any wavelength, because of the presence of variations in crustal thickness that are unassociated with elastic loading. The ratios and correlations of gravity and topography at intermediate wavelengths (harmonic degree l between 30 and 50) also constrain regional crustal densities. We localized gravity and topography with a moving Slepian taper and calculated regionally averaged crustal densities with the approximation ρcrust=Zl/(2πG), where Zl is the localized admittance and G is the gravitational constant. The only regional density estimates greater than 2000 kg m-3 for l=30 correspond to the NSP. Density estimates outside of the NSP were unreasonably low, even for highly porous crust. We attribute these low densities to the confounding effects of crustal thickness variations and Kaula filtering of the gravity dataset at the highest harmonic degrees, both of which tend to introduce a downward bias to crustal density estimation. An alternative analysis—which corrected for crustal thickness variability and was restricted to regions with gravity/topography coherence greater than 0.6—yielded an aggregate crustal density of ρcrust=2602 ± 470 kg m-3 for Mercury's high northern latitudes.

Geology of the Smythii and Marginis Region of the Moon: Using Integrated Remotely Sensed Data

NASA Technical Reports Server (NTRS)

Gillis, Jeffrey J.; Spudis, Paul D.

2000-01-01

We characterized the diverse and complex geology of the eastern limb region of the Moon using a trio of remote-sensing data sets: Clementine, Lunar Prospector, and Apollo. On the basis of Clementine-derived iron and titanium maps we classify the highlands into low-iron (3-6 wt % FeO) and high-iron (6-9 wt % FeO) units. The association of the latter with basalt deposits west of Smythii basin suggests that the highland chemical variation is the result of mixing between basalt and highland lithologies. Mare Smythii and Mare Marginis soils are compositionally similar, containing moderate iron (15-18 wt % FeO) and titanium (2.5-3.5 wt % TiO2). Smythii basin, in addition to the basalt deposits, contains an older, moderate-albedo plains unit. Our investigation reveals that the dark basin plains unit has a distinct albedo, chemistry, and surface texture and formed as a result of impact-mixing between highland and mare lithologies in approximately equal proportions. Clementine iron and maturity maps show that swirls along the northern margin of Mare Marginis have the same iron composition as the surrounding nonswirl material and indicate that the swirl material is bright because of its low agglutinate content. Gravity data for the eastern limb show high, positive Bouguer gravity anomalies for areas of thin basalt cover (e.g., Smythii basin and complex craters Joliot, Lomonosov, and Neper). We deduce that the uplift of dense mantle material is the primary (and mare basaltic fill the secondary) source for generating the concentration of mass beneath large craters and basins.

Geophysical Constraints on the Hydrogeologic and Structural Settings of the Gulf of Suez Rift-Related Basins: Case Study from the El Qaa Plain, Sinai, Egypt

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

Ahmed, M; Sauck, William; Sultan, Mohamed

2013-11-09

Groundwater has been identified as one of the major freshwater sources that can potentially meet the growing demands of Egypt’s population. Gravity data (from 381 ground gravity stations) were collected, processed, and analyzed together with the available aeromagnetic (800 line-km) data to investigate the hydrogeologic and structural settings, areal distribution, geometry, and water storage of the aquifers in El Qaa coastal plain in the southwest Sinai Peninsula, and to assess their longevity given projected extraction rates. Findings include (1) complete Bouguer anomaly and total magnetic intensity maps show two connected sub-basins separated by a narrow saddle with an average basinmore » length of 43 km and an average width of 12 km; (2) two-dimensional modeling of both gravity and magnetic data indicates basin fill with a maximum thickness of 3.5 km; (3) using anomalous residual gravity, the volume of water in storage was estimated at 40–56 km3; and (4) progressive increases in extraction rates over time will deplete up to 40 % of the aquifers’ volume in 200–230 years and will cause the water quality to deteriorate due to seawater intrusion in 45 years. Similar geophysical exploration campaigns, if conducted over the entire coastal plains of the Red Sea and the Gulfs of Suez and Aqaba, could assist in the development of sound and sustainable management schemes for the freshwater resources in these areas. The adopted techniques could pave the way toward the establishment of sustainable utilization schemes for a much larger suite of similar aquifers worldwide.« less

Structure and evolution of the northern Oman margin: gravity and seismic constraints over the Zagros-Makran-Oman collision zone

NASA Astrophysics Data System (ADS)

Ravaut, P.; Bayer, R.; Hassani, R.; Rousset, D.; Yahya'ey, A. Al

1997-09-01

The obduction process in Oman during Late Cretaceous time, and continental-to-oceanic subduction along the Zagros-Makran region during the Tertiary are consequences of the Arabian-Eurasian collision, resulting in construction of complex structures composed of the Oman ophiolite belt, the Zagros continental mountain belt and the Makran subduction zone with its associated accretionary wedge. In this paper, we jointly interpret Bouguer anomaly and available petroleum seismic profiles in terms of crustal structures. We show that the gravity anomaly in northern Oman is characterized by a high-amplitude negative-positive couple. The negative anomaly is coincident with Late Cretaceous (Fiqa) and Tertiary (Pabdeh) foreland basins and with the Zagros-Oman mountain belts, whereas the positive anomaly is correlated to the ophiolite massifs. The Bouguer anomaly map indicates the presence of a post-Late Cretaceous sedimentary basin, the Sohar basin, centred north of the Batinah plain. We interpret the negative/positive couple in terms of loading of the elastic Arabian lithosphere. We estimate the different Cretaceous-to-Recent loads, including topography, ophiolite nappes, sedimentary fill and the accretionary prism of the Makran trench. A new method, using Mindlin's elastic plate theory, is proposed to model the 2D deflection of the heterogeneous elastic Arabian plate, taking into account boundary conditions at the ends of the subducted plate. We show that remnant ophiolites are isolated from Tethyan oceanic lithosphere in the Gulf of Oman by a continental basement ridge, a NW prolongation of the Saih-Hatat window. Loading the northward-limited ophiolite blocks explains the deflection of the Fiqa foredeep basin. West of the Musandam Peninsula, the Tertiary Pabdeh foredeep is probably related to the emplacement of a 8-km-thick tectonic prism located on the Musandam Peninsula and in the Strait of Hormuz. Final 2D density models along profiles through the Oman mountain belt and the Gulf of Oman are discussed in the framework of Late Cretaceous obduction of the Tethys and synchronous subduction and exhumation of the Oman margin.

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, closely spaced gravity data may reliably detect these units. If the high-quartz phase occurs only as relatively thin units, interbedded with low-quartz phase, borehole gravity surveying can be used much more effectively than equivalent surface gravity surveying.

The potential of quantum technology gravity sensors in civil engineering

NASA Astrophysics Data System (ADS)

Tuckwell, G.; Metje, N.; Boddice, D.; Usher, C.

2017-12-01

Potential field techniques have advantages over active geophysical techniques as they are not limited to the depth they can image features, provided the signals of interest are detectable amongst the other variations recorded by the instrument. A new generation of gravity instruments based on quantum technology promise greatly increased measurement sensitivity, but with this comes significant challenges in data processing and noise suppression. In the UK Innovate UK funded SIGMA project (http://www.rsksigma.co.uk/) the field of opportunity for a step change in gravity sensor accuracy has been evaluated by comparison with existing geophysical sensors, identifying the range of targets and depths of interest to commercial end users that are currently undetectable and might become visible. Forward modelling was used to quantify the potential of a Quantum Technology (QT) gravity and gravity gradiometer sensor. A substantive improvement in detectability of targets is predicted, which can be considered as a factor of 1.5 to 2 increase in the depth of detectability, or in the reduction of the size of the feature of interest. To take further advantage of new instrument sensitivity, new survey workflows are required. The accuracy of measured gravity maps is limited by environmental vibration noise, and by the accuracy with which tidal variations and terrain signals can be removed. It is still common practice in engineering scale surveys for gravity values to be reduced to Bouguer residuals. However, with a more sensitive instrument comes the need to measure the terrain more accurately. This can be achieved within a commercially viable workflow using a laser scanner for rapid data acquisition and advanced processing to produce an accurate DEM. Initial tests on 4 commercial sites have shown that an improvement of 10s of mGal can be achieved if applying a full digital terrain model correction to the microgravity data even on sites with very minor topographic height variations. At the same time, the new algorithms developed by the project can reduce the computational time by a factor of 20. This will have implications on the commercial viability of a QT gravity instrument.

The structure, isostasy and gravity field of the Levant continental margin and the southeast Mediterranean area

NASA Astrophysics Data System (ADS)

Segev, Amit; Rybakov, Michael; Lyakhovsky, Vladimir; Hofstetter, Avraham; Tibor, Gidon; Goldshmidt, Vladimir; Ben Avraham, Zvi

2006-10-01

A 3-D layered structure of the Levant and the southeastern Mediterranean lithospheric plates was constructed using interpretations of seismic measurements and borehole data. Structural maps of three principal interfaces, elevation, top basement and the Moho, were constructed for the area studied. This area includes the African, Sinai and Arabian plates, the Herodotus and the Levant marine basins and the Nile sedimentary cone. In addition, an isopach map of the Pliocene sediments, as well as the contemporaneous amount of denuded rock units, was prepared to enable setting up the structural map of the base Pliocene sediment. Variable density distributions are suggested for the sedimentary succession in accord with its composition and compaction. The spatial density distribution in the crystalline crust was calculated by weighting the thicknesses of the lower mafic and the upper felsic crustal layers, with densities of 2.9 g/cm 3 and 2.77 g/cm 3, respectively. Results of the local (Airy) isostatic modeling with compensation on the Moho interface show significant deviations from the local isostasy and require variable density distribution in the upper mantle. Moving the compensation level to the base of the lithosphere (˜ 100 km depth) and adopting density variations in the mantle lithosphere yielded isostatic compensation (± 200 m) over most of the area studied. The spatial pattern obtained of a density distribution with a range of ± 0.05 g/cm 3 is supported by a regional heat flux. Simulations of the flexure (Vening Meinesz) isostasy related to the Pliocene to Recent sedimentary loading and unloading revealed concentric oscillatory negative and positive anomalies mostly related to the Nile sedimentary cone. Such anomalies may explain the rapid subsidence in the Levant Basin and the arching in central Israel, northern Sinai and Egypt during Pliocene-Recent times. Comparison between the observed (Bouguer) gravity and the calculated gravity for the constructed 3-D lithospheric structure, which has variable density distributions, provided a good match and an independent constraint for the large-scale structure suggested and confirmed an oceanic nature for the Levant Basin lithosphere.

The T-Reflection and the Deep Crustal Structure of the Vøring Margin, Offshore mid-Norway

NASA Astrophysics Data System (ADS)

Abdelmalak, M. M.; Faleide, J. I.; Planke, S.; Gernigon, L.; Zastrozhnov, D.; Shephard, G. E.; Myklebust, R.

2017-11-01

Seismic reflection data along volcanic passive margins frequently provide imaging of strong and laterally continuous reflections in the middle and lower crust. We have completed a detailed 2-D seismic interpretation of the deep crustal structure of the Vøring Margin, offshore mid-Norway, where high-quality seismic data allow the identification of high-amplitude reflections, locally referred to as the T-Reflection. Using a dense seismic grid, we have mapped the geometry of the T-Reflection in order to compare it with filtered Bouguer gravity anomalies and seismic refraction data. The T-Reflection is identified between 7 and 10 s. Sometimes it consists of one single smooth reflection. However, it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries, amplitudes, and contact relationships. The T-Reflection seems to be connected to deep sill networks and is locally identified at the continuation of basement high structures or terminates over fractures and faults. The T-Reflection presents a low magnetic signal. The spatial correlation between the filtered positive Bouguer gravity anomalies and the deep dome-shaped reflections indicates that the latter represent a high-impedance boundary contrast associated with a high-density and high-velocity body. In 50% of the outer Vøring Margin, the depth of the mapped T-Reflection is found to correspond to the depth of the top of the Lower Crustal Body (LCB), which is characterized by high P wave velocities (>7 km/s). We present a tectonic scenario, where a large part of the deep crustal structure is composed of preserved upper continental crustal blocks and middle to lower crustal lenses of inherited high-grade metamorphic rocks. Deep intrusions into the faulted crustal blocks are responsible for the rough character of the T-Reflection, whereas intrusions into the ductile lower crust and detachment faults are likely responsible for its smoother character. Deep magma intrusions can be responsible for regional metamorphic processes leading to an increasing velocity of the lower crust to more than 7 km/s. The result is a heterogeneous LCB that likely represents a complex mixture of pre- to syn-breakup mafic and ultramafic rocks (cumulates and sills) and old metamorphic rocks such as granulites and eclogites. An increasing degree of melting toward the breakup axis is responsible for an increasing proportion of cumulates and sill intrusions in the lower crust.

Correlation of Aerogravity and BHT Data to Develop a Geothermal Gradient Map of the Northern Western Desert of Egypt using an Artificial Neural Network

NASA Astrophysics Data System (ADS)

Mohamed, Haby S.; Abdel Zaher, Mohamed; Senosy, Mahmoud M.; Saibi, Hakim; El Nouby, Mohamed; Fairhead, J. Derek

2015-06-01

The northern part of the Western Desert of Egypt represents the second most promising area of hydrocarbon potential after the Gulf of Suez province. An artificial neural network (ANN) approach was used to develop a new predictive model for calculation of the geothermal gradients in this region based on gravity and corrected bottom-hole temperature (BHT) data. The best training data set was obtained with an ANN architecture composed of seven neurons in the hidden layer, which made it possible to predict the geothermal gradient with satisfactory efficiency. The BHT records of 116 deep oil wells (2,000-4,500 m) were used to evaluate the geothermal resources in the northern Western Desert. Corrections were applied to the BHT data to obtain the true formation equilibrium temperatures, which can provide useful constraints on the subsurface thermal regime. On the basis of these corrected data, the thermal gradient was computed for the linear sections of the temperature-versus-depth data at each well. The calculated geothermal gradient using temperature log data was generally 30 °C/km, with a few local high geothermal gradients in the northwestern parts of the study area explained by potential local geothermal fields. The Bouguer gravity values from the study area ranged from -60 mGal in the southern parts to 120 mGal in the northern areas, and exhibited NE-SW and E-W trends associated with geological structures. Although the northern Western Desert of Egypt has low regional temperature gradients (30 °C/km), several potential local geothermal fields were found (>40 °C/km). The heat flow at each well was also computed by combining sets of temperature gradients and thermal conductivity data. Aerogravity data were used to delineate the subsurface structures and tectonic framework of the region. The result of this study is a new geothermal gradient map of the northern Western Desert developed from gravity and BHT log data.

Crustal structure of an exhumed IntraCONtinental Sag (ICONS): the Mekele Basin in Northern Ethiopia.

NASA Astrophysics Data System (ADS)

Alemu, T. B.; Abdelsalam, M. G.

2017-12-01

The Mekele Sedimentary Basin (MSB) in Ethiopia is a Paleozoic-Mesozoic IntraCONtinental Sag (ICONS) exposed due to Cenozoic domal and rift flank uplift associated with the Afar mantle plume and Afar Depression (AD). ICONS are formed over stable lithosphere, and in contrast to rift and foreland basins, show circular-elliptical shape in map view, saucer shaped in cross section, and concentric gravity minima. Surface geological features of the MSB have been shown to exhibit geologic characteristics similar to those of other ICONS. We used the World Gravity Map (WGM 2012) data to investigate subsurface-crustal structure of the MSB. We also used 2D power spectrum analysis and inversion of the gravity field to estimate the Moho depth. Our results show the Bouguer anomalies of the WGM 2012 ranges between 130 mGal and - 110 mGal with the highest values within the AD. Despite the effect of the AD on the gravity anomalies, the MSB is characterized by the presence of gravity low anomaly that reaches in places -110 mGal, especially in its western part. The Moho depth estimates, from both spectral analysis and inversion of the gravity data, is between 36 and 40 km depth over most of the western and southern margins of the MSB. However, as the AD is approached, in the eastern margins of the MSB, crustal thickness estimates are highly affected by the anomalously thin and magmatic segment of the AD, and the Moho depth range between 30 and 25 km. Our results are consistent with that of seismic studies in areas far from the MSB, but within the Northwestern Ethiopian Plateau where the MSB is located. Those studies have reported an abrupt decrease in Moho depth from 40 km beneath the Northwestern plateau, to 20 km in the adjacent AD. Though the MSB is small (100 kmX100 km) compared to other ICONS, and affected by the neighboring AD, it is characterized by elliptical gravity minima and a relatively thicker crust that gradually thickens away from the rift. In addition, seismic imaging of faster shear wave velocity beneath the southwestern MSB at 80 km depth by previous studies mimic the surface and shallow subsurface features that we interpret as indicative of major characteristics of ICONS. Due to their location away from active plate boundaries, most ICONS are buried since the time of their formation. The MSB represents a rare example of a completely exhumed ICONS.

Spanish economic exclusive zone (zeee) project: valencia trough and balearic sea (western mediterranean) results.

NASA Astrophysics Data System (ADS)

Pérez Carrillo, F.; Palomo, C.; Martín Davila, J.; Carbó, A.; Acosta, J.; Catalán, M.; Herranz, P.; Muñoz Martín, A.; Muñoz Recio, A.; Marín, J. A.

2003-04-01

On 1993, the Spanish Government decided to perform a systematic hydrographic/oceanographic study of the so called "Spanish Exclusive Economic Zone" (ZEEE), that is, the marine area surrounding Spanish coast within the 200 nm limit. To achieve it, the oceanographic ship "Hespérides" would be at disposal of the Defense Ministry during one moth a year. A "ZEEE-Plan" was established on 1994 with the main objective to improve cartography of the ZEEE zone and acquire different geophysical parameters to characterize it. A "ZEEE-group" was conformed by personnel coming from the Hydrographic Institute of the Spanish Navy (IHM) and the Spanish Oceanographic Institute (IEO), the Institutions responsible of the campaigns, as well as San Fernando Naval Observatory (ROA), University Complutense of Madrid (UCM), and others. From 1995 to 1997 systematic marine campaigns were carried out at the Valencia Trough and Balearic Sea (Western Mediterranean), complemented by two additional campaigns, carried out on 1999 and 2000. As a result of those campaigns maps of Bathymetry, Geomagnetic Anomalies and Free Air/Bouguer Gravity Anomalies have been published, six maps of 1:200.000 scale and one additional map, of 1:500.000 scale, for the whole area (the maps are available at IEO: Juan.acosta@md.ieo.es, fax: +34 914135597, and IHM: fax: +34 956599396). In this work the above mentioned results will be presented, together with the main characteristics of the surveys.

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 tests and field applications indicate that the adaptive terrain correction method can be adopted as a rapid and accurate tool of marine gravity data processing. References Davis, K. &Kass, M.A. & Li, Y., 2011. Rapid gravity and gravity gradiometry terrain corrections via an adaptive quadtree mesh discretization, EXPLOR GEOPHYS, 42, 88-97. Sandwell, D.T., Müller, R.D., Smith, W.H., Garcia, E. & Francis, R., 2014. New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure, SCIENCE, 346, 65-67. Tao, C., Li, H., Jin, X., Zhou, J., Wu, T., He, Y., Deng, X., Gu, C., Zhang, G. & Liu, W., 2014. Seafloor hydrothermal activity and polymetallic sulfide exploration on the southwest Indian ridge, CHINESE SCI BULL, 59, 2266-2276. Tsoulis, D., 2012. Analytical computation of the full gravity tensor of a homogeneous arbitrarily shaped polyhedral source using line integrals, GEOPHYSICS, 77, F1-F11.

Space-Wise approach for airborne gravity data modelling

NASA Astrophysics Data System (ADS)

Sampietro, D.; Capponi, M.; Mansi, A. H.; Gatti, A.; Marchetti, P.; Sansò, F.

2017-05-01

Regional gravity field modelling by means of remove-compute-restore procedure is nowadays widely applied in different contexts: it is the most used technique for regional gravimetric geoid determination, and it is also used in exploration geophysics to predict grids of gravity anomalies (Bouguer, free-air, isostatic, etc.), which are useful to understand and map geological structures in a specific region. Considering this last application, due to the required accuracy and resolution, airborne gravity observations are usually adopted. However, due to the relatively high acquisition velocity, presence of atmospheric turbulence, aircraft vibration, instrumental drift, etc., airborne data are usually contaminated by a very high observation error. For this reason, a proper procedure to filter the raw observations in both the low and high frequencies should be applied to recover valuable information. In this work, a software to filter and grid raw airborne observations is presented: the proposed solution consists in a combination of an along-track Wiener filter and a classical Least Squares Collocation technique. Basically, the proposed procedure is an adaptation to airborne gravimetry of the Space-Wise approach, developed by Politecnico di Milano to process data coming from the ESA satellite mission GOCE. Among the main differences with respect to the satellite application of this approach, there is the fact that, while in processing GOCE data the stochastic characteristics of the observation error can be considered a-priori well known, in airborne gravimetry, due to the complex environment in which the observations are acquired, these characteristics are unknown and should be retrieved from the dataset itself. The presented solution is suited for airborne data analysis in order to be able to quickly filter and grid gravity observations in an easy way. Some innovative theoretical aspects focusing in particular on the theoretical covariance modelling are presented too. In the end, the goodness of the procedure is evaluated by means of a test on real data retrieving the gravitational signal with a predicted accuracy of about 0.4 mGal.

Middle East and North Africa Database Development and Research to Populate the DOE Knowledge Base

DTIC Science & Technology

2000-09-01

strongly in the Arabian peninsula, except in the shield region. The two deep basins in the northern Arabian peninsula, in the Palmyrides and the Rutbah...eastern Mediterranean) crust from multiple-source Werner deconvolution of Bouguer gravity anomalies, J. Geophy. Res., 104, 25,469-25,478, 1999...discontinuities beneath the Arabian Shield, Geophysical Research Letters, 25, 2,873-2,876, 1998b. Sweeney, J., and B. Walter, Preliminary Definition of

Utah FORGE Gravity Data Shapefile

DOE Data Explorer

Joe Moore

2016-03-13

This is a zipped GIS compatible shapefile of gravity data points used in the Milford, Utah FORGE project as of March 21st, 2016. The shapefile is native to ArcGIS, but can be used with many GIS software packages. Additionally, there is a .dbf (dBase) file that contains the dataset which can be read with Microsoft Excel. The Data was downloaded from the PACES (Pan American Center for Earth and Environmental Studies) hosted by University of Texas El Paso (http://research.utep.edu/Default.aspx?alias=research.utep.edu/paces) Explanation:Source: data source code if available LatNAD83: latitude in NAD83 [decimal degrees] LonNAD83: longitude in NAD83 [decimal degrees]zWGS84: elevation in WGS84 (ellipsoidal) [m]OBSless976: observed gravity minus 976000 mGalIZTC: inner zone terrain correction [mGal]OZTC: outer zone terrain correction [mGal]FA: Free Air anomaly value [mGal]CBGA: Complete Bouguer gravity anomaly value [mGal

Contributions of gravity and field data on the structural scheme updating of the Tellian domain and its foreland (Nefza-Bizerte region, northern Tunisia)

NASA Astrophysics Data System (ADS)

Essid, El Mabrouk; Kadri, Ali; Balti, Hadhemi; Gasmi, Mohamed; Zargouni, Fouad

2018-03-01

The Nefza-Bizerte region, eastern part of the Tunisian Alpine chain, covers the thrust sheets domain called the Tell and its Atlassic foreland. The deep structures under the Tellian thrust sheets are not enough explored. The structural interpretation of magmatic rocks, Triassic outcrops and the depressions are still a subject of discussion. In this work, we intend to investigate deep faults and their eventual role in magmatism and Triassic salt setting up and to explain the depression genesis. Analysis of the Bouguer anomaly map and its derivatives reveals the main gravity lineaments, organized in major NE- and NW-trending systems. The NE-trending system, dipping towards the NW, is the main component of the structural scheme and has controlled the tectonic evolution of this area. After the immobilization of the Tellian thrust sheets during the uppermost Langhian, the Tell and its Atlassic foreland were affected by the Tortonian compressive event with a NW-trending maximum horizontal stress. The reverse kinematics of the NE-trending deep-seated faults created at their front continental environments filled later by post-nappes Neogene deposits. After the early Pleistocene, a NNW-directed compressional stress regime deformed the post-nappes Neogene series and generated NW-trending grabens. This coexistence of compression-extension continues until present day.

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.

Forward calculation of gravity and its gradient using polyhedral representation of density interfaces: an application of spherical or ellipsoidal topographic gravity effect

NASA Astrophysics Data System (ADS)

Zhang, Yi; Chen, Chao

2018-02-01

A density interface modeling method using polyhedral representation is proposed to construct 3-D models of spherical or ellipsoidal interfaces such as the terrain surface of the Earth and applied to forward calculating gravity effect of topography and bathymetry for regional or global applications. The method utilizes triangular facets to fit undulation of the target interface. The model maintains almost equal accuracy and resolution at different locations of the globe. Meanwhile, the exterior gravitational field of the model, including its gravity and gravity gradients, is obtained simultaneously using analytic solutions. Additionally, considering the effect of distant relief, an adaptive computation process is introduced to reduce the computational burden. Then features and errors of the method are analyzed. Subsequently, the method is applied to an area for the ellipsoidal Bouguer shell correction as an example and the result is compared to existing methods, which shows our method provides high accuracy and great computational efficiency. Suggestions for further developments and conclusions are drawn at last.

Analyses on Origin of positive gravity anomalies of sedimentary basins of the Ross Sea

NASA Astrophysics Data System (ADS)

Gao, Jinyao; Yang, Chunguo; Ji, Fei; Wang, Wei; Shen, Zhongyan

2017-04-01

We have adopted gridded products describing surface elevation, ice-thickness and the sea floor and subglacial bed elevation south of 60◦ S from Bedmap2 and north of 60◦ S from JGP95E to calculate Bouguer and isostatic gravity anomaly of the Ross Sea region based on the DTU10 free-air gravity anomaly.Taking a view of the free-air, Bouguer and isostatic gravity anomalies, it is unusual that high values overlay the Victoria Land Basin, Central Trough, Northern Basin and Northern Central Trough while basement highs are associated with low value. A number of studies have attributed the high gravity anomalies across the depocenters to high-density volcanics deep within the basins or magmatic intrusions within the region of the thinned crust or upper mantle (e. g., Edwards et al., 1987). According to the conclusion from Karner et al. (2005), the anticorrelation of gravity anomalies with sediment basement can be reproduced if the flexural strength of the lithosphere during the late Cretaceous rifting is significantly lower than the flexural strength of the lithosphere at the Oligocene and Neogene time of sedimentation. We note that the isostatic gravity anomalies are higher than the free-air gravity anomalies adjacent to the Transantarctic Mountains, and vice versa away from the Transantarctic Mountains. We may ignore the constraints offered by the tranditional isostasy in the local gravity studies of the Ross Sea basins, especially advancing the concept of high density material in the lower crust or upper mantle. In particular, the modeled gravity does not laterally integrate to zero, due to the existence of unbalanced forces induced by mantle. Along the outer shelf uplift zone surrouding Antarctica, the positive gravity belt has higher values in free-air gravity anomalies than those in isostatic gravity anomalies. Meanwhile, the positive gravity belt of isostatic gravity anomalies almost disappears in the background anomalies of 20 mGal to 10 mGal facing the Pacific ocean between 105°E and 70°W. Moreover, the lithosphere of Ross Sea and offshore Wilkes Land near the Pacific-Antarctic Ridge are intensively broken by transform faults, its strength becomes weak, and this favors a local equilibrium adjustment with the Airy isostatic model. Within the Ross Sea sector area, including its outer ocean, isostatic gravity anomalies are smoothly lowest in the entire region. These transform faults may cut through lithosphere to induce the mantle thermal turbulence, which further reduces the lithospheric strength and brings about an over-compensation phenomenon. If both the Ross Sea and the outer shelf uplift zone, the Transantartic Mountains or the Antarctic Ice Sheet are treated as one system, we may get rid of this dilemma. As the outer shelf uplift zone had been broken and the Transantartic Mountaisn or the Antarctic Ice Sheet had been developing, the local crust would gradually subside and its underlying anthenosphere would flow outwards. Along weak belts or faults at the depocenters or edges of basins of the Ross Sea, compressed magma were likely to upwell, stretching the crust and uplifting the Moho with high gravity anomalies in basins.

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.

Comparison of survey and photogrammetry methods to position gravity data, Yucca Mountain, Nevada

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

Ponce, D.A.; Wu, S.S.C.; Spielman, J.B.

1985-12-31

Locations of gravity stations at Yucca Mountain, Nevada, were determined by a survey using an electronic distance-measuring device and by a photogram-metric method. The data from both methods were compared to determine if horizontal and vertical coordinates developed from photogrammetry are sufficently accurate to position gravity data at the site. The results show that elevations from the photogrammetric data have a mean difference of 0.57 +- 0.70 m when compared with those of the surveyed data. Comparison of the horizontal control shows that the two methods agreed to within 0.01 minute. At a latitude of 45{sup 0}, an error ofmore » 0.01 minute (18 m) corresponds to a gravity anomaly error of 0.015 mGal. Bouguer gravity anomalies are most sensitive to errors in elevation, thus elevation is the determining factor for use of photogrammetric or survey methods to position gravity data. Because gravity station positions are difficult to locate on aerial photographs, photogrammetric positions are not always exactly at the gravity station; therefore, large disagreements may appear when comparing electronic and photogrammetric measurements. A mean photogrammetric elevation error of 0.57 m corresponds to a gravity anomaly error of 0.11 mGal. Errors of 0.11 mGal are too large for high-precision or detailed gravity measurements but acceptable for regional work. 1 ref. 2 figs., 4 tabs.« less

Development of multiple source data processing for structural analysis at a regional scale. [digital remote sensing in geology

NASA Technical Reports Server (NTRS)

Carrere, Veronique

1990-01-01

Various image processing techniques developed for enhancement and extraction of linear features, of interest to the structural geologist, from digital remote sensing, geologic, and gravity data, are presented. These techniques include: (1) automatic detection of linear features and construction of rose diagrams from Landsat MSS data; (2) enhancement of principal structural directions using selective filters on Landsat MSS, Spacelab panchromatic, and HCMM NIR data; (3) directional filtering of Spacelab panchromatic data using Fast Fourier Transform; (4) detection of linear/elongated zones of high thermal gradient from thermal infrared data; and (5) extraction of strong gravimetric gradients from digitized Bouguer anomaly maps. Processing results can be compared to each other through the use of a geocoded database to evaluate the structural importance of each lineament according to its depth: superficial structures in the sedimentary cover, or deeper ones affecting the basement. These image processing techniques were successfully applied to achieve a better understanding of the transition between Provence and the Pyrenees structural blocks, in southeastern France, for an improved structural interpretation of the Mediterranean region.

New geothermal heat flux map of Greenland and the Iceland hotspot track

NASA Astrophysics Data System (ADS)

Martos, Y. M.; Jordan, T. A.; Catalan, M.; Jordan, T. M.; Bamber, J. L.; Vaughan, D. G.

2017-12-01

Greenland is the second largest reservoir of water on Earth and about 80% of its surface is covered by ice. It is mainly composed of Archean blocks that collided during the Early Proterozoic. Indirect methods have been used to study its subglacial thermal conditions, geology and lithospheric structure. Numerous regions of basal melting are identified in the central and north Greenland but their relationship with geothermal heat flux is not yet clear. Crustal thickness derived by seismology and gravity data are consistent, showing no significant lateral variations, and providing average values of about 40 and 36 km respectively. Even though Greenland is considered a craton its crust has been affected by the presume passage of the Iceland hotspot since at least 100 Ma. Here we present the newest and highest resolution Curie Depth and geothermal heat flux maps for Greenland as well as their associated uncertainties. For estimating the Curie Depths we applied spectral methods to aeromagnetic data from the World Digital Magnetic Anomaly Map WDMAM2.0. Calculated Curie Depths vary from 25 to 50 km with shallower values located to the east. A thermal model is built based on the 1D heat conduction equation and considering steady state conditions. The thermal parameters are then optimized using local values derived from direct measurements, temperature profiles and more indirect methods such as radar imaging. The heat flux distribution shows higher spatial variability and a very different pattern than previously proposed and with values of 50-80 mW/m2. We identify a NW-SE high heat flux feature crossing Greenland which we correlate with the Iceland hotspot track. Additionally, to evaluate the lithospheric structure we calculate the Bouguer anomaly from GOCO5s satellite free air data and construct several gravity models across the proposed hotspot track. We show that a dense lower crust body in the same location the high heat flux trend is permissible from a gravimetric perspective, and extensive underplating due to the plume may have occurred. Finally, our new geothermal heat flux map and lithospheric structure models allow us to understand the history and the path of the Iceland hotspot path.

The Unicorn Cave, Southern Harz Mountains, Germany: From known passages to unknown extensions with the help of geophysical surveys

NASA Astrophysics Data System (ADS)

Kaufmann, Georg; Nielbock, Ralf; Romanov, Douchko

2015-12-01

In soluble rocks (limestone, dolomite, anhydrite, gypsum, …), fissures and bedding partings can be enlarged with time by both physical and chemical dissolution of the host rock. With time, larger cavities evolve, and a network of cave passages can evolve. If the enlarged cave voids are not too deep under the surface, geophysical measurements can be used to detect, identify and trace these karst structures, e.g.: (i) gravity revealing air- and sediment-filled cave voids through negative Bouguer anomalies, (ii) electrical resistivity imaging (ERI) mapping different infillings of cavities either as high resistivities from air-filled voids or dry soft sediments, or low resistivities from saturated sediments, and (iii) groundwater flow through electrical potential differences (SP) arising from dislocated ionic charges from the walls of the underground flow paths. We have used gravity, ERI, and SP methods both in and above the Unicorn Cave located in the southern Harz Mountains in Germany. The Unicorn Cave is a show cave developed in the Werra dolomite formation of the Permian Zechstein sequence, characterised by large trunk passages interrupted by larger rooms. The overburden of the cave is only around 15 m, and passages are filled with sediments reaching infill thicknesses up to 40 m. We present results from our geophysical surveys above the known cave and its northern and southern extension, and from the cave interior. We identify the cave geometry and its infill from gravity and ERI measurements, predict previously unknown parts of the cave, and subsequently confirm the existence of these new passages through drilling. From the wealth of geophysical data acquired we derive a three-dimensional structural model of the Unicorn Cave and its surrounding, especially the cave infill.

The Paleozoic - Mesozoic Mekele Sedimentary Basin in Ethiopia: An example of an exhumed IntraCONtinental Sag (ICONS) basin

NASA Astrophysics Data System (ADS)

Alemu, Tadesse; Abdelsalam, Mohamed G.; Dawit, Enkurie L.; Atnafu, Balemwal; Mickus, Kevin L.

2018-07-01

We investigated the evolution of the Mekele Sedimentary Basin (MSB) in northern Ethiopia using geologic field and gravity data. The depth to Moho and lithospheric structure beneath the basin was imaged using two-dimensional (2D) radially-averaged power spectral analysis, Lithoflex three-dimensional (3D) forward and inverse modeling, and 2D forward modeling of the Bouguer gravity anomalies. Previous studies proposed that the basin was formed as part of a multi-branched rift system related to the breakup of Gondwana. Our results show that the MSB: (1) is circular to elliptical in map view and saucer shaped in cross sectional view, (2) is filled with terrestrial and shallow marine sedimentary rocks, (3) does not significantly structurally control the sedimentation and the major faults are post-depositional, (4) is characterized by a concentric gravity minima, (5) is underlain by an unstretched crust (∼40 km thick) and thicker lithosphere (∼120 km thick). These features compare positively with a group of basins known as IntraCONtinental Sags (ICONS), especially those ICONS formed over accretionary orogenic terranes. Since the MSB is located above the Neoproterozoic accretionary orogenic terranes of the Arabian-Nubian Shield (ANS), we propose that the formation of the MSB to be related to cooling and thickening of a juvenile sub-continental lithospheric mantle beneath the ANS, which most probably provided negative buoyancy, and hence subsidence in the MSB, leading to its formation as an ICONS. The MSB could be used as an outcrop analog for information about the internal facies architecture of ICONS because it is completely exhumed due to tectonic uplift on the western flank of the Afar Depression.

Integrated geologic and geophysical studies of North American continental intraplate seismicity

USGS Publications Warehouse

Van Lanen, X.; Mooney, W.D.

2007-01-01

The origin of earthquakes within stable continental regions has been the subject of debate over the past thirty years. Here, we examine the correlation of North American stable continental region earthquakes using five geologic and geophysical data sets: (1) a newly compiled age-province map; (2) Bouguer gravity data; (3) aeromagnetic anomalies; (4) the tectonic stress field; and (5) crustal structure as revealed by deep seismic-reflection profiles. We find that: (1) Archean-age (3.8-2.5 Ga) North American crust is essentially aseismic, whereas post-Archean (less than 2.5 Ga) crust shows no clear correlation of crustal age and earthquake frequency or moment release; (2) seismicity is correlated with continental paleorifts; and (3) seismicity is correlated with the NE-SW structural grain of the crust of eastern North America, which in turn reflects the opening and closing of the proto- and modern Atlantic Ocean. This structural grain can be discerned as clear NE-SW lineaments in the Bouguer gravity and aeromagnetic anomaly maps. Stable continental region seismicity either: (1) follows the NE-SW lineaments; (2) is aligned at right angles to these lineaments; or (3) forms clusters at what have been termed stress concentrators (e.g., igneous intrusions and intersecting faults). Seismicity levels are very low to the west of the Grenville Front (i.e., in the Archean Superior craton). The correlation of seismicity with NE-SW-oriented lineaments implies that some stable continental region seismicity is related to the accretion and rifting processes that have formed the North American continental crust during the past 2 b.y. We further evaluate this hypothesis by correlating stable continental region seismicity with recently obtained deep seismic-reflection images of the Appalachian and Grenville crust of southern Canada. These images show numerous faults that penetrate deep (40 km) into the crust. An analysis of hypocentral depths for stable continental region earthquakes shows that the frequency and moment magnitude of events are nearly uniform for the entire 0-35 km depths over which crustal earthquakes extend. This is in contradiction with the hypothesis that larger events have deeper focal depths. We conclude that the deep structure of the crust, in particular the existence of deeply penetrating faults, is the controlling parameter, rather than lateral variations in temperature, rheology, or high pore pressure. The distribution of stable continental region earthquakes in eastern North America is consistent with the existence of deeply penetrating crustal faults that have been reactivated in the present stress field. We infer that future earthquakes may occur anywhere along the geophysical lineations that we have identified. This implies that seismic hazard is more widespread in central and eastern North America than indicated by the limited known historical distribution of seismicity. ?? 2007 The Geological Society of America.

Understanding the Geological Structures of North China By Analyzing Regional Gravity and Magnetic Data

NASA Astrophysics Data System (ADS)

Shi, L.; Guo, L.; Meng, X.; Yao, C.

2010-12-01

North China is one of the most tectonically important regions in the world to study important continent geodynamics issues such as intraplate earthquakes, volcanism and continent-continent collision. The North China Craton, covering most of North China, bounded by complicated fault systems and orogenic belts, is one of the oldest cratons on the Earth, and is unique in its tectonic reactivation in the Late Mesozoic and Cenozoic. In the past few decades, a variety of geophysical methods were conducted to study geological tectonics and evolution of North China. We analyzed the regional gravity and magnetic data of this region using new data enhancement techniques to understand the regional geological structures. The satellite-derived free-air gravity anomalies with a resolution of 1 arc-minute were assembled from the Scripps Institution of Oceanography, and were then reduced to obtain Complete Bouguer Gravity Anomalies (CBGA). The Magnetic Anomalies (MA) with a resolution of 2 arc-minutes were assembled from the World Digital Magnetic Anomaly Map. The CBGA and the MA were then gridded on a regular grid, the MA were subsequently reduced to the magnetic pole. Then the data were processed with standard techniques to attenuate the high-frequency noise and analyze the regional and residual anomalies. Specially, we calculated the tilt-angle derivatives of the data. We then calculated the directional horizontal derivatives of the tilt-angle derivatives along different directions. This special processing derived clearer geological structures with more details. From the results of the preliminary processing, we analyzed the main deep faults and tectonic units distributed in this region. In the future, the interpretation of the CBGA and the MA with constraints of other geophysical methods will be performed for better understanding the deep structure of this region. Acknowledgment: We acknowledge the financial support of SinoProbe-01-05, the Fundamental Research Funds for the Central Universities (2010ZY26), and the National Natural Science Foundation of China (40904033).

3D Structure of Iran and Surrounding Areas From The Simultaneous Inversion of Complementary Geophysical Observations

NASA Astrophysics Data System (ADS)

Ammon, C. J.; Maceira, M.; Cleveland, M.

2010-12-01

We present a three-dimensional seismic-structure model of the Arabian-Eurasian collision zone obtained via simultaneous, joint inversion of surface-wave dispersion measurements, teleseismic P-wave receiver functions, and gravity observations. We use a simple, approximate relationship between density and seismic velocities so that the three data sets may be combined in a single inversion. The sensitivity of the different data sets are well known: surface waves provide information on the smooth variations in elastic properties, receiver functions provide information on abrupt velocity contrasts, and gravity measurements provide information on broad-wavenumber shallow density variations and long-wavenumber components of deeper density structures. The combination of the data provides improved resolution of shallow-structure variations, which in turn help produce the smooth features at depth with less contamination from the strong heterogeneity often observed in the upper crust. We also explore geologically based smoothness constraints to help resolve sharp features in the underlying shallow 3D structure. Our focus is on the region surrounding Iran from east Turkey and Iraq in the west, to Pakistan and Afghanistan in the east. We use Bouguer gravity anomalies derived from the global gravity model extracted from the GRACE satellite mission. Surface-wave dispersion velocities in the period range between 7 and 150 s are taken from previously published tomographic maps for the region. Preliminary results show expected strong variations in the Caspian region as well as the deep sediment regions of the Persian Gulf. Regions constrained with receiver-function information generally show sharper crust-mantle boundary structure than that obtained by inversion of the surface waves alone (with thin layers and smoothing constraints). Final results of the simultaneous inversion will help us to better understand one of the most prominent examples of continental collision. Such models also provide an important starting model for time-consuming and fully 3D inversions.

Gravity anomalies and associated tectonic features over the Indian Peninsular Shield and adjoining ocean basins

NASA Astrophysics Data System (ADS)

Mishra, D. C.; Arora, K.; Tiwari, V. M.

2004-02-01

A combined gravity map over the Indian Peninsular Shield (IPS) and adjoining oceans brings out well the inter-relationships between the older tectonic features of the continent and the adjoining younger oceanic features. The NW-SE, NE-SW and N-S Precambrian trends of the IPS are reflected in the structural trends of the Arabian Sea and the Bay of Bengal suggesting their probable reactivation. The Simple Bouguer anomaly map shows consistent increase in gravity value from the continent to the deep ocean basins, which is attributed to isostatic compensation due to variations in the crustal thickness. A crustal density model computed along a profile across this region suggests a thick crust of 35-40 km under the continent, which reduces to 22/20-24 km under the Bay of Bengal with thick sediments of 8-10 km underlain by crustal layers of density 2720 and 2900/2840 kg/m 3. Large crustal thickness and trends of the gravity anomalies may suggest a transitional crust in the Bay of Bengal up to 150-200 km from the east coast. The crustal thickness under the Laxmi ridge and east of it in the Arabian Sea is 20 and 14 km, respectively, with 5-6 km thick Tertiary and Mesozoic sediments separated by a thin layer of Deccan Trap. Crustal layers of densities 2750 and 2950 kg/m 3 underlie sediments. The crustal density model in this part of the Arabian Sea (east of Laxmi ridge) and the structural trends similar to the Indian Peninsular Shield suggest a continent-ocean transitional crust (COTC). The COTC may represent down dropped and submerged parts of the Indian crust evolved at the time of break-up along the west coast of India and passage of Reunion hotspot over India during late Cretaceous. The crustal model under this part also shows an underplated lower crust and a low density upper mantle, extending over the continent across the west coast of India, which appears to be related to the Deccan volcanism. The crustal thickness under the western Arabian Sea (west of the Laxmi ridge) reduces to 8-9 km with crustal layers of densities 2650 and 2870 kg/m 3 representing an oceanic crust.

Gravity Anomalies and Isostasy Deduced From New Dense Gravimetry Around the Tsangpo Gorge, Tibet

NASA Astrophysics Data System (ADS)

Fu, Guangyu; She, Yawen

2017-10-01

We built the first dense gravity network including 107 stations around the Tsangpo Gorge, Tibet, one of the hardest places in the world to reach, and conducted a gravity and hybrid GPS observation campaign in 2016. We computed the Bouguer gravity anomalies (BGAs) and free-air gravity anomalies (FGAs) and increased the resolution of the FGAs by merging the in situ data with EIGEN-6C4 gravity model data. The BGAs around the Tsangpo Gorge are in general negative and gradually decrease from south (-360 mGal) to north (-480 mGal). They indicate a uniformly dipping Moho around the Tsangpo Gorge that sinks from south to north at an angle of 12°. We introduced a method to compute the vertical tectonic stress of the lithosphere, a quantitative expression of isostasy, using BGA and terrain data, and applied it to the area around the Tsangpo Gorge. We found that the lithosphere of the upstream of the Tsangpo Gorge is roughly in an isostatic state, but the lithosphere of the downstream exhibits vertical tectonic stress of 50 MPa, which indicates the loss of a large amount of surface material. This result does not support the deduction of the valley bottom before uplift of the Tsangpo Gorge by Wang et al. (2014).

High-resolution gravity and geoid models in Tahiti obtained from new airborne and land gravity observations: data fusion by spectral combination

NASA Astrophysics Data System (ADS)

Shih, Hsuan-Chang; Hwang, Cheinway; Barriot, Jean-Pierre; Mouyen, Maxime; Corréia, Pascal; Lequeux, Didier; Sichoix, Lydie

2015-08-01

For the first time, we carry out an airborne gravity survey and we collect new land gravity data over the islands of Tahiti and Moorea in French Polynesia located in the South Pacific Ocean. The new land gravity data are registered with GPS-derived coordinates, network-adjusted and outlier-edited, resulting in a mean standard error of 17 μGal. A crossover analysis of the airborne gravity data indicates a mean gravity accuracy of 1.7 mGal. New marine gravity around the two islands is derived from Geosat/GM, ERS-1/GM, Jason-1/GM, and Cryosat-2 altimeter data. A new 1-s digital topography model is constructed and is used to compute the topographic gravitational effects. To use EGM08 over Tahiti and Moorea, the optimal degree of spherical harmonic expansion is 1500. The fusion of the gravity datasets is made by the band-limited least-squares collocation, which best integrates datasets of different accuracies and spatial resolutions. The new high-resolution gravity and geoid grids are constructed on a 9-s grid. Assessments of the grids by measurements of ground gravity and geometric geoidal height result in RMS differences of 0.9 mGal and 0.4 cm, respectively. The geoid model allows 1-cm orthometric height determination by GPS and Lidar and yields a consistent height datum for Tahiti and Moorea. The new Bouguer anomalies show gravity highs and lows in the centers and land-sea zones of the two islands, allowing further studies of the density structure and volcanism in the region.

USSR and Eastern Europe Scientific Abstracts, Geophysics, Astronomy and Space, Number 395

DTIC Science & Technology

1977-04-15

of the air masses, wind condi- tions, cloudiness and precipitation in the eastern part of the Arabian Sea are related to the beginning of the monsoon...layer of the atmosphere which plays a large role in the air shifts near the earth’s surface. In the west- ern part of the Arabian Sea the "Yu. M...mod- el. Gravity anomalies can be used in both the Bouguer and in the Faye re- ductions. It is noted, in particular, that investigations of ocean

Morphological Indicators of a Mascon Beneath Ceres's Largest Crater, Kerwan

NASA Astrophysics Data System (ADS)

Bland, M. T.; Ermakov, A. I.; Raymond, C. A.; Williams, D. A.; Bowling, T. J.; Preusker, F.; Park, R. S.; Marchi, S.; Castillo-Rogez, J. C.; Fu, R. R.; Russell, C. T.

2018-02-01

Gravity data of Ceres returned by the National Aeronautics and Space Administration's Dawn spacecraft is consistent with a lower density crust of variable thickness overlying a higher density mantle. Crustal thickness variations can affect the long-term, postimpact modification of impact craters on Ceres. Here we show that the unusual morphology of the 280 km diameter crater Kerwan may result from viscous relaxation in an outer layer that thins substantially beneath the crater floor. We propose that such a structure is consistent with either impact-induced uplift of the high-density mantle beneath the crater or from volatile loss during the impact event. In either case, the subsurface structure inferred from the crater morphology is superisostatic, and the mass excess would result in a positive Bouguer anomaly beneath the crater, consistent with the highest-degree gravity data from Dawn. Ceres joins the Moon, Mars, and Mercury in having basin-associated gravity anomalies, although their origin may differ substantially.

Geophysical interpretation of the gneiss terrane of northern Washington and southern British Columbia, and its implications for uranium exploration

USGS Publications Warehouse

Cady, John W.; Fox, Kenneth F.

1984-01-01

The Omineca crystalline belt of northeastern Washington and southern British Columbia has a regional Bouguer gravity high, and individual gneiss domes within the terrane are marked by local gravity highs. Models of crustal structure that satisfy the limited available seismic-refraction data and explain the gravity high over the gneiss terrane permit the hypothesis that the core metamorphic complexes are the surface expression of a zone of dense infrastructure that makes up the upper 20 km (kilometers) of the crust within the crystalline belt. The Omineca crystalline belt is characterized regionally by low aeromagnetic relief. The gneiss domes and biotite- and biotite-muscovite granites are generally marked by low magnetic relief, whereas hornblende-biotite granites often cause magnetic highs. Exceptional magnetic highs mark zones of magnetic rock within the biotite- and biotite-muscovite granites and the gneiss domes; these areas are worthy of study, both to determine the origin and disposition of the magnetite and to explore the possible existence of uraniferous magnetite deposits.

Morphological indicators of a mascon beneath Ceres' largest crater, Kerwan

USGS Publications Warehouse

Bland, Michael T.; Ermakov, Anton; Raymond, Carol A.; Williams, David A.; Bowling, Tim J.; Preusker, F.; Park, Ryan S.; Marchi, Simone; Castillo-Rogez, Julie C.; Fu, R.R.; Russell, Christopher T.

2018-01-01

Gravity data of Ceres returned by the National Aeronautics and Space Administration's Dawn spacecraft is consistent with a lower density crust of variable thickness overlying a higher density mantle. Crustal thickness variations can affect the long‐term, postimpact modification of impact craters on Ceres. Here we show that the unusual morphology of the 280 km diameter crater Kerwan may result from viscous relaxation in an outer layer that thins substantially beneath the crater floor. We propose that such a structure is consistent with either impact‐induced uplift of the high‐density mantle beneath the crater or from volatile loss during the impact event. In either case, the subsurface structure inferred from the crater morphology is superisostatic, and the mass excess would result in a positive Bouguer anomaly beneath the crater, consistent with the highest‐degree gravity data from Dawn. Ceres joins the Moon, Mars, and Mercury in having basin‐associated gravity anomalies, although their origin may differ substantially.

Trench Parallel Bouguer Anomaly (TPBA): A robust measure for statically detecting asperities along the forearc of subduction zones

NASA Astrophysics Data System (ADS)

Raeesi, M.

2009-05-01

During 1970s some researchers noticed that large earthquakes occur repeatedly at the same locations. These observations led to the asperity hypothesis. At the same times some researchers noticed that there was a relationship between the location of great interplate earthquakes and the submarine structures, basins in particular, over the rupture area in the forearc regions. Despite these observations there was no comprehensive and reliable hypothesis explaining the relationship. There were numerous cons and pros to the various hypotheses given in this regard. In their pioneering study, Song and Simons (2003) approached the problem using gravity data. This was a turning point in seismology. Although their approach was correct, appropriate gravity anomaly had to be used in order to reveal the location and extent of the asperities. Following the method of Song and Simons (2003) but using the Bouguer gravity anomaly that we called "Trench Parallel Bouguer Anomaly", TPBA, we found strong, logical, and convincing relation between the TPBA-derived asperities and the slip distribution as well as earthquake distribution, foreshocks and aftershocks in particular. Various parameters with different levels of importance are known that affect the contact between the subducting and the overriding plates, We found that the TPBA can show which are the important factors. Because the TPBA-derived asperities are based on static physical properties (gravity and elevation), they do not suffer from instabilities due to the trade-offs, as it happens for asperities derived in dynamic studies such as waveform inversion. Comparison of the TPBA-derived asperities with rupture processes of the well-studied great earthquakes, reveals the high level of accuracy of the TPBA. This new measure opens a forensic viewpoint on the rupture process along the subduction zones. The TPBA reveals the reason behind 9+ earthquakes and it explains where and why they occur. The TPBA reveals the areas that can generate tsunami earthquakes. It gives a logical dimension to the foreshock and aftershock distributions. Using the TPBA, we can derive the scenarios for the early 20th century great earthquakes for which limited data is available. We present cases from Aleutian and South America subduction zones. The TPBA explains why there should be no great earthquake in the down-dip of Shumagin, but that there should be a major tsunami earthquake for its up-dip. Our evidences suggest that the process has already started. We give numerous examples for South America, Aleutian-Alaska, and Kurile-Kamchatka subduction zones and we also look at Cascadia. Despite the possible various applications of the new measure, here we draw the attention to its most important application - the detection of critical asperities. Supplied with this new measure, in addition to the available seismological data, seismologists should be able to detect the critical asperities and follow the evolving rupture process. This paves the way for revealing systematically the great interplate earthquakes.

A regional-scale network for geoid monitoring and satellite gravimetry validation

NASA Astrophysics Data System (ADS)

Winester, D.; Pool, D.; Kennedy, J.

2010-12-01

In the past two decades, improved measurements of acceleration due to gravity have allowed for accurate detection of temporal gravity change. Terrestrial absolute gravimeters (for example, Micro-g LaCoste FG5 or A-10) can sense changes of gravity induced by elevation or mass changes, including local effects that may bias regional studies. Satellite instrumentation (e.g. GRACE) can detect large scale mass changes on a regular basis. However, the Nyquist wave number for satellite observations is often much too small for the size of regional studies. Also, satellites are limited by their life of deployment. Both techniques are used to (in)validate change models generated from other geophysical observations including water storage(underground and glacial), geoid definition, isostatic adjustments and tectonic(magmatic and faulting)activity. The gap between terrestrial and satellite gravity observations (and between satellite missions) might be bridged by developing a terrestrial network of sites of various observation techniques that define a representative sample of a given, regional study area. This information could then be statistically extrapolated to the extent of the region. The Southern High Plains Aquifer is such a region, since it has widespread relatively uniform geology, has relatively flat topography, and is well monitored for groundwater levels and soil moisture. Each site would have extensive instrumentation for monitoring, at a minimum, gravity (periodic and continuous) using absolute and tidal gravimeters, soil moisture, precipitation, depths to water in wells, evapotranspiration, air pressure, and land surface (GPS). Where possible, the network would build upon existing, data collection infrastructure. Preferably, the region would also have seismic tomography or crustal seismic reflection observations to characterize Moho-depth mass changes and have regional Bouguer anomaly mapping. In addition to information on local hydrology and geology, data collection would allow for characterization of local seasonal corrections, earth tides, atmospheric loading and episodic slip. No test network has yet been funded, but cost and man-power can be estimated. Such a network would rely on co-operation between various federal, state, local and university groups.

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 sediments, micaschists and metagrauwackes have intermediate to low magnetization and density values. Detailed lithological attribution of geophysical anomalies was achieved separately for each geological sub-domain (in between 2 major structures). This methodology will be generalized at the scale of the entire Paris basin in order to propose a tectonic reconstruction of this segment of the Variscan belt, and provide guides for the exploration of hidden resources.

Effective elastic thickness along the conjugate passive margins of India, Madagascar and Antarctica: A re-evaluation using the Hermite multitaper Bouguer coherence application

NASA Astrophysics Data System (ADS)

Ratheesh-Kumar, R. T.; Xiao, Wenjiao

2018-05-01

Gondwana correlation studies had rationally positioned the western continental margin of India (WCMI) against the eastern continental margin of Madagascar (ECMM), and the eastern continental margin of India (ECMI) against the eastern Antarctica continental margin (EACM). This contribution computes the effective elastic thickness (Te) of the lithospheres of these once-conjugated continental margins using the multitaper Bouguer coherence method. The results reveal significantly low strength values (Te ∼ 2 km) in the central segment of the WCMI that correlate with consistently low Te values (2-3 km) obtained throughout the entire marginal length of the ECMM. This result is consistent with the previous Te estimates of these margins, and confirms the idea that the low-Te segments in the central part of the WCMI and along the ECMM represents paleo-rift inception points of the lithospheric margins that was thermally and mechanically weakened by the combined action of the Marion hotspot and lithospheric extension during the rifting. The uniformly low-Te value (∼2 km) along the EACM indicates a mechanically weak lithospheric margin, probably due to considerable stretching of the lithosphere, considering the fact that this margin remained almost stationary throughout its rift history. In contrast, the ECMI has comparatively high-Te variations (5-11 km) that lack any correlation with the regional tectonic setting. Using gravity forward and inversion applications, we find a leading order of influence of sediment load on the flexural properties of this marginal lithosphere. The study concludes that the thick pile of the Bengal Fan sediments in the ECMI masks and has erased the signal of the original load-induced topography, and its gravity effect has biased the long-wavelength part of the observed gravity signal. The hence uncorrelated flat topography and deep lithospheric flexure together contribute a bias in the flexure modeling, which likely accounts a relatively high Te estimate.

Effective elastic thicknesses of the lithosphere and mechanisms of isostatic compensation in Australia

NASA Technical Reports Server (NTRS)

Zuber, Maria T.; Bechtel, Timothy D.; Forsyth, Donald W.

1989-01-01

The isostatic compensation of Australia is investigated using an isostatic model for the Australian lithosphere that assumes regional compensation of an elastic plate which undergoes flexure in response to surface and subsurface loading. Using the coherence between Bouguer gravity and topography and two separate gravity/topography data sets, it was found that, for the continent as a whole, loads with wavelengths above 1500 km are locally compensated. Loads with wavelengths in the range 600-1500 km are partially supported by regional stresses, and loads with wavelengths less than 600 km are almost entirely supported by the strength of the lithosphere. It was found that the predicted coherence for a flexural model of a continuous elastic plate does not provide a good fit to the observed coherence of central Australia. The disagreement between model and observations is explained.

A deep structural ridge beneath central India

NASA Astrophysics Data System (ADS)

Agrawal, P. K.; Thakur, N. K.; Negi, J. G.

A joint-inversion of magnetic satellite (MAGSAT) and free air gravity data has been conducted to quantitatively investigate the cause for Bouguer gravity anomaly over Central Indian plateaus and possible fold consequences beside Himalayan zone in the Indian sub-continent due to collision between Indian and Eurasian plates. The appropriate inversion with 40 km crustal depth model has delineated after discriminating high density and magnetisation models, for the first time, about 1500 km long hidden ridge structure trending NW-SE. The structure is parallel to Himalayan fold axis and the Indian Ocean ridge in the Arabian Sea. A quantitative relief model across a representative anomaly profile confirms the ridge structure with its highest point nearly 6 km higher than the surrounding crustal level in peninsular India. The ridge structure finds visible support from the astro-geoidal contours.

Extent of Continental Crust Thickening Derived From Gravity Profile Leading From Aden Towards the Dhala Plateau in the Yemen Trap Series

NASA Astrophysics Data System (ADS)

Blecha, V.

2003-12-01

Gravity profile trends NNW from Aden and terminates at the Dhala plateau formed by Tertiary volcanics often referred to as the Yemen Trap Series. The length of profile is 120 km. Profile consists of 366 gravity stations with average distance of 300 m between stations. The mean square error of Bouguer anomalies is 0.06 mGal. This final error includes errors of gravity and altitude measurements and error in terrain corrections. Altitudes along profile are ranging from 0 m a.s.l. in the south to 1400 m a.s.l. at the northern side of profile. In the central part of the Gulf of Aden occurs juvenile oceanic crust. Stretched continental crust is assumed on the coast. Regional gravity field decreases from +38 mGal on the coast in Aden to -126 mGal at mountains of the Dhala plateau. According to gravity modeling the decrease of 164 mGal in gravity is caused by 8 km continental crust thickening over the distance of 120 km. Regional gravity field is accompanied by local anomalies with amplitudes of tens of mGal. Sources of local anomalies are from S to N: coastal sediments (negative), Tertiary intrusions and volcanics within the Dhala graben (positive), Mesozoic sediments (negative) and Tertiary volcanics of the Dhala plateau (positive). Gravity profile is most detailed and most precise regional gravity measurement carried out in the southern tip of Arabia and brings new information about geology of the area with scarce geophysical data.

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.

ON BOUGUER ANOMALIES IN THE OCEAN (Ob Anomaliyakh Buge na Okeanakh),

DTIC Science & Technology

The paper deals with the problems of the accepted interpretation of the Bouguer reduction for the sea. The only thing which to some extent could...justify the introduction of the Bouguer reduction at sea is a certain smoothing out of the effect exerted by the relief forms of the oceanic bottom in...the Bouguer reduction at sea is associated with the problem of specific processing of the material for its various types of interpretation. Bouguer

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

NASA Astrophysics Data System (ADS)

Syracuse, E. M.; Zhang, H.; Maceira, M.

2017-10-01

We present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body wave first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region. Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. Without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.

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

Crustal structure of the southeastern Tibetan Plateau from gravity data: New evidence for clockwise movement of the Chuan-Dian rhombic block

NASA Astrophysics Data System (ADS)

Xuan, Songbai; Shen, Chongyang; Shen, Wenbin; Wang, Jiapei; Li, Jianguo

2018-06-01

The crustal deformation beneath the Chuan-Dian rhombic block (CDB) and surrounding regions has been studied in geological and geodetic methods, and provide important insights into the kinematics and dynamics about the clockwise movement of this tectonic block. In this work, we present images of the normalized full gradient (NFG) of the Bouguer gravity anomalies from five gravity profiles across the boundary faults of the CDB measured in recent years, and investigate the distribution characteristics of the crustal anomalous bodies along the profiles. Firstly, an anomalous body with eastward dipping exist beneath the Xianshuihe fault, suggesting that crustal mass move to east. Secondly, near the Xiaojiang fault, two anomalous bodies dip westward with depth increasing. The inferred movement direction of the north one is from west to east, and the south one is from east to west. Thirdly, anomalous bodies on the northeast and southwest sides of the Red River fault suggest the directions of crustal movement is from northeast to southwest. These results are also consistent with GPS solutions, and provide gravity evidence for crustal deformation of the CDB with clockwise rotation.

Moho depth variations over the Maldive Ridge and adjoining Arabian and Central Indian Basins, Western Indian Ocean, from three dimensional inversion of gravity anomalies

NASA Astrophysics Data System (ADS)

Kunnummal, Priyesh; Anand, S. P.; Haritha, C.; Rama Rao, P.

2018-05-01

Analysis of high resolution satellite derived free air gravity data has been undertaken in the Greater Maldive Ridge (GMR) (Maldive Ridge, Deep Sea Channel, northern limit of Chagos Bank) segment of the Chagos Laccadive Ridge and the adjoining Arabian and Central Indian Basins. A Complete Bouguer Anomaly (CBA) map was generated from the Indian Ocean Geoidal Low removed Free Air Gravity (hereinafter referred to as "FAG-IOGL") data by incorporating Bullard A, B and C corrections. Using the Parker method, Moho topography was initially computed by inverting the CBA data. From the CBA the Mantle Residual Gravity Anomalies (MRGA) were computed by incorporating gravity effects of sediments and lithospheric temperature and pressure induced anomalies. Further, the MRGA was inverted to get Moho undulations from which the crustal thickness was also estimated. It was found that incorporating the lithospheric thermal and pressure anomaly correction has provided substantial improvement in the computed Moho depths especially in the oceanic areas. But along the GMR, there was not much variation in the Moho thickness computed with and without the thermal and pressure gravity correction implying that the crustal thickness of the ridge does not depend on the oceanic isochrones used for the thermal corrections. The estimated Moho depths in the study area ranges from 7 km to 28 km and the crustal thickness from 2 km to 27 km. The Moho depths are shallower in regions closer to Central Indian Ridge in the Arabian Basin i.e., the region to the west of the GMR is thinner compared to the region in the east (Central Indian Basin). The thickest crust and the deepest Moho are found below the N-S trending GMR segment of the Chagos-Laccadive Ridge. Along the GMR the crustal thickness decreases from north to south with thickness of 27 km below the Maldives Ridge reducing to ∼9 km at 3°S and further increasing towards Chagos Bank. Even though there are similarities in crustal thickness between Maldive Ridge and other regions like Mascarene Plateau which was recently interpreted as underlain by continental crust, much more geoscientific work including drilling has to be undertaken to finally confirm the exact nature of the ridge.

Three Least-Squares Minimization Approaches to Interpret Gravity Data Due to Dipping Faults

NASA Astrophysics Data System (ADS)

Abdelrahman, E. M.; Essa, K. S.

2015-02-01

We have developed three different least-squares minimization approaches to determine, successively, the depth, dip angle, and amplitude coefficient related to the thickness and density contrast of a buried dipping fault from first moving average residual gravity anomalies. By defining the zero-anomaly distance and the anomaly value at the origin of the moving average residual profile, the problem of depth determination is transformed into a constrained nonlinear gravity inversion. After estimating the depth of the fault, the dip angle is estimated by solving a nonlinear inverse problem. Finally, after estimating the depth and dip angle, the amplitude coefficient is determined using a linear equation. This method can be applied to residuals as well as to measured gravity data because it uses the moving average residual gravity anomalies to estimate the model parameters of the faulted structure. The proposed method was tested on noise-corrupted synthetic and real gravity data. In the case of the synthetic data, good results are obtained when errors are given in the zero-anomaly distance and the anomaly value at the origin, and even when the origin is determined approximately. In the case of practical data (Bouguer anomaly over Gazal fault, south Aswan, Egypt), the fault parameters obtained are in good agreement with the actual ones and with those given in the published literature.

Regional models of the gravity field from terrestrial gravity data of heterogeneous quality and density

NASA Astrophysics Data System (ADS)

Talvik, Silja; Oja, Tõnis; Ellmann, Artu; Jürgenson, Harli

2014-05-01

Gravity field models in a regional scale are needed for a number of applications, for example national geoid computation, processing of precise levelling data and geological modelling. Thus the methods applied for modelling the gravity field from surveyed gravimetric information need to be considered carefully. The influence of using different gridding methods, the inclusion of unit or realistic weights and indirect gridding of free air anomalies (FAA) are investigated in the study. Known gridding methods such as kriging (KRIG), least squares collocation (LSCO), continuous curvature (CCUR) and optimal Delaunay triangulation (ODET) are used for production of gridded gravity field surfaces. As the quality of data collected varies considerably depending on the methods and instruments available or used in surveying it is important to somehow weigh the input data. This puts additional demands on data maintenance as accuracy information needs to be available for each data point participating in the modelling which is complicated by older gravity datasets where the uncertainties of not only gravity values but also supplementary information such as survey point position are not always known very accurately. A number of gravity field applications (e.g. geoid computation) demand foran FAA model, the acquisition of which is also investigated. Instead of direct gridding it could be more appropriate to proceed with indirect FAA modelling using a Bouguer anomaly grid to reduce the effect of topography on the resulting FAA model (e.g. near terraced landforms). The inclusion of different gridding methods, weights and indirect FAA modelling helps to improve gravity field modelling methods. It becomes possible to estimate the impact of varying methodical approaches on the gravity field modelling as statistical output is compared. Such knowledge helps assess the accuracy of gravity field models and their effect on the aforementioned applications.

Results of pre-drilling potential field measurements at the Bosumtwi crater

NASA Astrophysics Data System (ADS)

Danuor, S. K.; Menyeh, A.

Gravity and magnetic measurements were carried out at the Bosumtwi crater to determine the geophysical signature of the crater. Land gravity data was acquired at 163 locations around the structure and on the shore of the lake. The separation between the gravity stations was 500 m for radial profiles, but 700-1000 m along roads and footpaths that ran parallel to the lake's shore. Additionally, a marine gravity survey was carried out along 14 north-south and 15 east-west profiles on the lake. Magnetic data was also acquired along 14 north-south profiles on the lake. In all marine surveys, the line spacing was 800 m, and navigation was provided by a Garmin 235 Echo Sounder/GPS. The gravity signature of the crater is characterized by a negative Bouguer anomaly with an amplitude of about -18 mgal. Using the seismic results as constraints, the gravity model obtained indicates the central uplift at a depth of 250 m. The negative anomaly is the contribution of the gravity deficiencies due to fractured and brecciated rocks in the rim area and below the crater floor, the impact breccias within the crater, and the sedimentary and water infilling of the lake. Magnetic modeling yielded a model for the causative body, which is located north of the central uplift: the model has a magnetic susceptibility of 0.03 S.I. and extends from a depth of 250 to 610 m. The causative bodies have been interpreted as impactites.

Backscattering and geophysical features of volcanic ridges offshore Santa Rosalia, Baja California Sur, Gulf of California, Mexico

NASA Astrophysics Data System (ADS)

Fabriol, Hubert; Delgado-Argote, Luis A.; Dañobeitia, Juan José; Córdoba, Diego; González, Antonio; García-Abdeslem, Juan; Bartolomé, Rafael; Martín-Atienza, Beatriz; Frias-Camacho, Víctor

1999-11-01

Volcanic ridges formed by series of volcanic edifices are identified in the central part of the Gulf of California, between Isla Tortuga and La Reforma Caldera-Santa Rosalía region. Isla Tortuga is part of the 40-km-long Tortuga Volcanic Ridge (TVR) that trends almost perpendicular to the spreading center of the Guaymas Basin. The Rosalía Volcanic Ridge (RVR), older than TVR, is characterized by volcanic structures oriented towards 310°, following a fracture zone extension and the peninsular slope. It is interpreted that most of the aligned submarine volcanic edifices are developed on continental crust while Isla Tortuga lies on oceanic-like crust of the Guaymas Basin. From a complete Bouguer anomaly map, it is observed that the alignments of gravity highs trending 310° and 290° support the volcanic and subvolcanic origin of the bathymetric highs. Volcanic curvilinear structures, lava flows and mounds were identified from backscattering images around Isla Tortuga and over a 400-m high (Vírgenes High), where the TVR and the RVR intersect. A refraction/wide-angle seismic profile crossing perpendicular to the Vírgenes High, together with gravity and magnetic data indicate the presence of shallow intrusive bodies presumably of basaltic or andesitic composition. It is inferred that most volcanic edifices along the ridges have similar internal structures. We suggest that the growth of different segments of the ridges have a volcano-tectonic origin. The older RVR lies along the extension of a fracture zone and it probably is associated with Pliocene NE-SW extension.

Crustal thickness inversions from recent Mars Reconnaissance Orbiter gravity solutions

NASA Astrophysics Data System (ADS)

Neumann, Gregory; Zuber, Maria T.; Lemoine, Frank; Neumann, Gregory A.; Smith, David E.

Recent Mars Reconnaissance Orbiter gravity solutions from low-altitude tracking of MRO, together with previous spacecraft, have dramatically improved correlation with MOLA topography at spherical harmonic degrees up to 95. We present several updated models of crustal thickness. These models are calculated to fit the Bouguer potential anomaly following the assumptions in Neumann et al. 2004, with much weaker a priori constraints applied to the topographic corrections and the downward continuation to the martian mantle. These models are available via anonymous ftp to "ftp://lepftp.gsfc.nasa.gov/pub/exports/tharsis/marscrust3". The higher-resolution models improve on those we produced in 2004-2005. They are appropriate for modeling impacts as small as 300 km diameter, and for processes related to the hemispheric dichotomy boundary. We discuss in particular the assumption of quasi-uniform crustal density and its likely failure in volcanic regions.

Magma storage in a strike-slip caldera

PubMed Central

Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

2016-01-01

Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions. PMID:27447932

Magma storage in a strike-slip caldera.

PubMed

Saxby, J; Gottsmann, J; Cashman, K; Gutiérrez, E

2016-07-22

Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.

The Presence of a Stable Block bounded by Active Zones (Mobile Belts) in the southwestern North American Proterozoic craton

NASA Astrophysics Data System (ADS)

Goodell, P.; Martinez P, C.; Mahar, M. A.

2014-12-01

Bouguer gravity data, initial Sr isotope values, zircon U-Pb, and multiple occurrences of felsic Proterozoic rocks, have revealed an elevated, less deformed, felsic cratonic block in the northern Mexico. The block is situated in western Chihuahua and is bounded by active zones or mobile belts on three sides, and is here referred to as the Western Chihuahua Cratonic Block (WCCB). Bouguer gravity data clearly indicate a region of a highly negative anomaly (< -200 mgal) in contrast to adjoining areas. The region is large and the anomaly is relatively smooth over broad areas; the WCCB appears as a smaller version of the Colorado Plateau. The block is characterized by high initial Sr isotope ratios (<0.706). Several occurrences of Proterozoic rocks are located within or next to the WCCB, and they reveal the character of the Bouguer anomaly. On the east, at Los Filtros, Proterozoic rocks crop out in a basement cored uplift interpreted to having been derived from the WCCB during the Ouachita orogeny. At Sierra La Mojina boulders of 1.1 Ga granites are found in Permian conglomerates. And at Basasiachic, xenoliths of 1.1 Ga granites are present in ash flow tuffs. Establishment of the Precambrian character of the WCCB is of importance, and these multiple occurrences are evidence. Prior studies of the Sierra Madre Occidental suggest that the region was uplifted because of a vast Cenozoic batholith presumed to lie under the SLIP (Silicic Large Igneous Province), the Upper Volcanic Series. The present study challenges that conclusion and maintains the SMO is underlain by Proterozoic silicic crust. The geology of age dated samples supports this. The WCCB is surrounded on three sides by Active Zones or Mobile Belts, which have been active extensional and translational zones periodically over a long period of time. On the east are the Paleozoic Pedrogosa Basin, Mesozoic Chihuahua Trough and Cenozoic Rio Grande Rift, the first two of which also continue around the northern border of the block. On the west are the Paleozoic Sonora embayment and Mesozoic Sahuaripa basin. A possible model for the origin of the WCCB is that it was an integral part of the North American Proterozoic craton but has been displaced from North America by multiple episodes of extension associated with the mobile belts.

A review of the regional geophysics of the Arizona Transition Zone

NASA Technical Reports Server (NTRS)

Hendricks, J. D.; Plescia, J. B.

1991-01-01

A review of existing geophysical information and new data presented in this special section indicate that major changes in crustal properties between the Basin and Range and Colorado Plateau occur in, or directly adjacent to, the region defined as the Arizona Transition Zone. Although this region was designated on a physiographic basis, studies indicate that it is also the geophysical transition between adjoining provinces. The Transition Zone displays anomalous crustal and upper mantle seismic properties, shallow Curie isotherms, high heat flow, and steep down-to-the-plateau Bouguer gravity gradients. Seismic and gravity studies suggest that the change in crustal thickness, from thin crust in the Basin and Range to thick crust in the Colorado Plateau, may occur as a series of steps rather than a planar surface. Anomalous P wave velocities, high heat flow, shallow Curie isotherms, and results of gravity modeling suggest that the upper mantle is heterogeneous in this region. A relatively shallow asthenosphere beneath the Basin and Range and Transition Zone contrasted with a thick lithosphere beneath the Colorado Plateau would be one explanation that would satisfy these geophysical observations.

Isostatic compensation of equatorial highlands on Venus

NASA Technical Reports Server (NTRS)

Kucinskas, Algis B.; Turcotte, Donald L.

1994-01-01

Spherical harmonic models for Venus' global topography and gravity incorporating Magellan data are used to test isostatic compensation models in five 30 deg x 30 deg regions representative of the main classes of equatorial highlands. The power spectral density for the harmonic models obeys a power-law scaling with spectral slope Beta approximately 2 (Brown noise) for the topography and Beta approximately 3 (Kaula's law) for the geoid, similar to what is observed for Earth. The Venus topography spectrum has lower amplitudes than Earth's which reflects the dominant lowland topography on Venus. Observed degree geoid to topography ratios (GTRs) on Venus are significantly smaller than degree GTRs for uncompensated topography, indicative of substantial compensation. Assuming a global Airy compensation, most of the topography is compensated at depths greater than 100 km, suggesting a thick lithosphere on Venus. For each region considered we obtain a regional degree of compensation C from a linear regression of Bouguer anomaly versus Bouguer gravity data. Geoid anomaly (N) versus topography variation (h) data for each sample were compared, in the least-squares sense, to theoretical correlations for Pratt, Airy, and thermal thinning isostasy models yielding regional GTR, zero-elevation crustal thickness (H), and zero elevation thermal lithosphere thickness (y(sub L(sub 0)), respectively. We find the regional compensation to be substantial (C approximately 52-80%), and the h, N data correlations in the chosen areas can be explained by isostasy models applicable on the Earth and involving variations in crustal thickness (Airy) and/or lithospheric (thermal thinning) thickness. However, a thick crust and lithosphere (y(sub L(sub 0)) approximately 300 km) must be assumed for Venus.

Fast inversion of gravity data using the symmetric successive over-relaxation (SSOR) preconditioned conjugate gradient algorithm

NASA Astrophysics Data System (ADS)

Meng, Zhaohai; Li, Fengting; Xu, Xuechun; Huang, Danian; Zhang, Dailei

2017-02-01

The subsurface three-dimensional (3D) model of density distribution is obtained by solving an under-determined linear equation that is established by gravity data. Here, we describe a new fast gravity inversion method to recover a 3D density model from gravity data. The subsurface will be divided into a large number of rectangular blocks, each with an unknown constant density. The gravity inversion method introduces a stabiliser model norm with a depth weighting function to produce smooth models. The depth weighting function is combined with the model norm to counteract the skin effect of the gravity potential field. As the numbers of density model parameters is NZ (the number of layers in the vertical subsurface domain) times greater than the observed gravity data parameters, the inverse density parameter is larger than the observed gravity data parameters. Solving the full set of gravity inversion equations is very time-consuming, and applying a new algorithm to estimate gravity inversion can significantly reduce the number of iterations and the computational time. In this paper, a new symmetric successive over-relaxation (SSOR) iterative conjugate gradient (CG) method is shown to be an appropriate algorithm to solve this Tikhonov cost function (gravity inversion equation). The new, faster method is applied on Gaussian noise-contaminated synthetic data to demonstrate its suitability for 3D gravity inversion. To demonstrate the performance of the new algorithm on actual gravity data, we provide a case study that includes ground-based measurement of residual Bouguer gravity anomalies over the Humble salt dome near Houston, Gulf Coast Basin, off the shore of Louisiana. A 3D distribution of salt rock concentration is used to evaluate the inversion results recovered by the new SSOR iterative method. In the test model, the density values in the constructed model coincide with the known location and depth of the salt dome.

Subsurface Density Structure of Taurus Littrow Valley Using Apollo 17 Gravity Data

NASA Astrophysics Data System (ADS)

Urbancic, N.; Ghent, R. R.; Johnson, C.; Stanley, S.; Hatch, D.; Carroll, K. A.; Williamson, M. C.; Garry, W. B.; Talwani, M.

2016-12-01

The Traverse Gravimeter Experiment (TGE) from the Apollo 17 mission was the first and only successful gravity survey on the surface of the Moon, revealing the local gravity field at Taurus Littrow Valley (TLV). Satellite surveys are resolution-limited due to their altitudes, making the TGE dataset a novel tool to probe the near-surface, fine-scale (<1 km) subsurface density structure of the Moon. TLV is hypothesized to be a basalt-filled graben oriented radial to Serenitatis basin. Talwani et al. [Apollo 17 Preliminary Science Report, 13 (1973)] used 2D correction and modelling techniques to derive a 1 km thickness for the subsurface basalt, assuming a rectangular geometry and densities derived from Apollo samples. We used modern 3D correction and modelling techniques and recent high-resolution Lunar Reconnaisance Orbiter topographic and image datasets to reinvestigate the subsurface structure of TLV, assuming a trapezoidal geometry for the valley. Updated topographic maps led to significant improvements in the accuracy of free-air, Bouguer and terrain corrections applied to the data. To determine the underlying geometry for TLV, we tested a range of possible thicknesses (T), dips (θ) and positions for the graben fill. We found that the thickness and position used by Talwani et al. represent the best fit to the data, but with walls that dip 30°. From sensitivity analyses we quantified the effect that different noise levels have on determining the correct model parameters. We found that less than 4 mgal noise in the gravity measurements is required to determine the valley position to within 1 km. At the noise level from the TGE data of ˜3.1 mgal, for an input model with θ=90° and a T=1 km, there will be a range in model dips and thicknesses, with θ=45-90° and T=0.9-1.1 km. Even for noise levels of 1 mgal, the range in parameters is θ=72-90° and T=0.95-1.05 km. These noise constraints are crucial for informing the design of future lunar gravimetry experiments.

Isostatic anomaly characteristics and dynamic environment of New Britain Ocean trenches and neighboring Area in Papua New Guinea

NASA Astrophysics Data System (ADS)

Yang, G.; Shen, C.; Wang, J.

2017-12-01

we calculated the Bouguer gravity anomaly and the Airy-Heiskanen isostatic anomaly in the New Britain ocean trenches and its surrounding areas of Papua New Guinea using the topography model and the gravity anomaly model from Scripps Institute of Oceanography, and analyzed the characteristics of isostatic anomaly and the earthquake dynamic environment of this region. The results show that there are obviously differences in the isostatic state between each block in the region, and the crustal tectonic movement is very intense in the regions with high positive or negative isostatic gravity anomalies; A number of sub-plates in this area is driven by the external tectonic action such as plate subduction and thrust of the Pacific plate, the Indian - Australian plate and the Eurasian plate. From the distribution of isostatic gravity anomaly, the tectonic action of anti-isostatic movement in this region is the main source of power; from the isostatic gravity and the spatial distribution of the earthquake, with the further contraction of the Indian-Australian plate, the southwestern part of the Solomon Haiya plate will become part of the Owen Stanley fold belt, the northern part will enter the lower part of the Bismarck plate, eastern part will enter the front of the Pacific plate, the huge earthquake will migrate to the north and east of the Solomon Haiya plate.

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.

Crustal Structure in the Southern Rockall Trough from Satellite Gravity Data: Evidence for Sea-floor Spreading

NASA Astrophysics Data System (ADS)

Chappell, A.; Kusznir, N. J.

2005-05-01

The southern Rockall Trough south of 57 N has previously been interpreted as either an intra-continental rift floored with highly extended continental crust, or a failed oceanic rift formed by Cretaceous sea floor spreading. Satellite gravity, bathymetry data and seismic estimates of sediment thickness are used to derive crustal basement thickness for the southern Rockall Trough and adjacent regions using a gravity inversion method incorporating a correction for the large negative thermal gravity component present in oceanic and stretched continental lithosphere. The marine Bouguer anomaly, derived from satellite free air gravity (Sandwell & Smith 1997) and Gebco 2003 bathymetry data, is inverted using the method of Oldenberg (1974), incorporating an iteratively applied thermal anomaly correction, to give Moho depth. For oceanic crust the thermal anomaly correction is calculated using isochron ages (Muller et al. 1997) and for continental crust from the beta stretching factors resulting from gravity derived crustal basement thickness and an assumed rift age. When sediment thickness and volcanic addition are assumed to be zero, the resulting upper bound of crustal thickness from the gravity inversion is as little as 10 km in the southern Rockall Trough. A segmented axial thickening of the crust at the centre of the Rockall Trough is predicted, between the Barra volcanic ridge and the Anton Dohrn seamount and is interpreted as having a volcanic origin. Inclusion of a sediment thickness correction in the gravity inversion further reduces predicted crustal thickness. A pseudo-sediment-thickness map has been constructed from the available wide-angle data and incorporated in the gravity inversion. The addition of up to 5.5 km of sediment in the gravity inversion reduces the upper bound of crustal thickness to less than 3 km in some locations. The segmented axial thickening and thin crust shown by the gravity inversion, the lack of intra-basinal faulting, and the volcanic origin for the axis shown by normal incidence seismic data, are consistent with a sea-floor spreading origin for the southern Rockall Trough and not formation by intra-continental rifting. We investigate the formation of the southern Rockall Trough using SfMargin, a new model of continental lithosphere thinning leading to continental breakup and sea-floor spreading initiation. Comparisons of the geometry of the southern Rockall Trough predicted by SfMargin with that observed are consistent with a short period (20Ma) of slow Cretaceous sea-floor spreading, followed by thermal subsidence to present day. This work forms part of the NERC Margins iSIMM project. iSIMM investigators are from Liverpool and Cambridge Universities, Badley Geoscience & Schlumberger Cambridge Research supported by the NERC, the DTI, Agip UK, BP, Amerada Hess Ltd, Anadarko, ConocoPhillips, Shell, Statoil and WesternGeco. The iSIMM team comprises NJ Kusznir, RS White, AM Roberts, PAF Christie, A Chappell, J Eccles, R Fletcher, D Healy, N Hurst, ZC Lunnon, CJ Parkin, AW Roberts, LK Smith, V Tymms & R Spitzer.

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

DOE PAGES

Syracuse, Ellen Marie; Zhang, Haijiang; Maceira, Monica

2017-07-11

Here, we present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body waves first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region.more » Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. In conclusion, without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.« less

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

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

Syracuse, Ellen Marie; Zhang, Haijiang; Maceira, Monica

Here, we present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body waves first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region.more » Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. In conclusion, without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.« less

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.

Gravity anomaly and crustal structure characteristics in North-South Seismic Belt of China

NASA Astrophysics Data System (ADS)

Shen, Chongyang; Xuan, Songtbai; Yang, Guangliang; Wu, Guiju

2017-04-01

The North-South Seismic Belt (NSSB) is the binary system boundary what is formed by the western Indian plate subduction pushing and the eastern west Pacific asthenosphere rising, and it is one of the three major seismic belts (Tianshan, Taiwan and NSSB) and mainly located between E102°and E107°. And it is mainly composed of topographic gradient zones, faults, cenozoic basins and strong earthquake zones, which form two distinct parts of tectonic and physical features in the west and east. The research results of geophysical and deep tectonic setting in the NSSB show that it is not only a gravity anomaly gradient zone, it is but also a belt of crustal thickness increasing sharply westward of abrupt change. Seismic tomography results show that the anomaly zone is deeper than hundreds of kilometers in the NSSB, and the composition and structure of the crust are more complex. We deployed multiple Gravity and GNSS synchronous detection profiles in the NSSB, and these profiles crossed the mainly faults structure and got thousands of points data. In the research, source analysis, density structure inversion, residual gravity related imaging and normalized full gradient methods were used, and analyzed gravity field, density and their structure features in different positions, finally obtained the crustal density structure section characteristics and depth structure differences. The research results showed that the gravity Bouguer anomaly is similar to the existing large scale result. The Bouguer anomaly is rising significantly from west to east, its trend variation coincides well with the trend change of Moho depth, which is agreeing with the material flows to the peripheral situation of the Tibetan plateau. The obvious difference changes of the residual anomaly is relative to the boundary of structure or main tectonics, it's also connected with the stop degree of the eurasian plate when the material migrates around. The density structure of the gravity profiles mainly reflects basic frame work of the regional crust structure. The earth's crust basically present three layer structure, nearly horizontally distributes, undulation of Moho is obvious, which is consistent with the results of seismic sounding and seismic array detection; in the local area, there are lower density layer zonal distribution in the earth's crust what accelerates the lateral movement in up and middle crust; when the substance of the Tibetan plateau spreads around, the integrity in up and middle crust is well, and it is basically a coupling movement together; in the lower crust, the thickness of the Tibetan plateau is outward gradually thinning, there is decoupling phenomenon in crust-mantle; The results of the gravity and the crustal density structure show that the research area can be divided into several part such as Qinghai-Tibet Plateau, Sichuan-Yunnan block, Ordos block and Alxa block, the transitional zones of the Qinghai-Tibet Plateau and Sichuan basin, and Alxa and Ordos are complex, and Moho slope is bigger, where is the part of strong tectonic activity and strong earthquakes occur easily. The research is of great significance for study the crustal deep structure, geodynamic evolution process and environment of earthquake gestation of the NSSB region.

The Conterminous United States Mineral Assessment Program; background information to accompany folio of geologic, geophysical, geochemical, mineral-occurrence, mineral-resource potential, and mineral-production maps of the Charlotte 1 degree x 2 degrees Quadrangle, North Carolina and South Carolina

USGS Publications Warehouse

Gair, Jacob Eugene; Goldsmith, Richard; Daniels, D.L.; Griffitts, W.R.; DeYoung, J.H.; Lee, M.P.

1986-01-01

This Circular and the folio of separately published maps described herein are part of a series of reports compiled under the Conterminous United States Mineral Assessment Program ICUSMAP). The folio on the Charlotte 1 degree ? 2 degree quadrangle, North Carolina and South Carolina, includes (1) a geologic map; (2) four geophysical maps; (3) geochemical maps for metamorphic heavy minerals, copper, lead and artifacts, zinc, gold, tin, beryllium, niobium, tungsten, molybdenum, titanium, cobalt, lithium, barium, antimony-arsenic-bismuth-cadmium, thorium-cerium-monazite, and limonite; (4) mineral-occurrence maps for kyanite-sillimanite-lithium-mica-feldspar-copper-lead-zinc, gold-quartz-barite-fluorite, iron-thorium-tin-niobium, and construction materials-gemstones; (5) mineral-resource potential maps for copper-lead-zinc-combined base metals, gold, tin-tungsten, beryllium-molybdenum-niobium, lithium-kyanite- sillimanitebarite, thorium (monazite)-uranium, and construction materials; and (6) mineral-production maps. The Charlotte quadrangle is mainly within the Piedmont physiographic province and extends from near the Coastal Plain on the southeast into the Blue Ridge province on the northwest for a short distance. Parts of six lithotectonic belts are present--the Blue Ridge, the Inner Piedmont, the Kings Mountain belt, the Charlotte belt, the Carolina slate belt, and the Wadesboro basin. Igneous, metamorphic, and sedimentary rocks are present and range in age from Proterozoic to Mesozoic; alluvial sediments of Quaternary age occur along rivers and larger streams. Rocks of the Blue Ridge include Middle Proterozoic granitoid gneiss intruded by Late Proterozoic granite; Late Proterozoic paragneiss, schist, and other metasedimentary and metavolcaniclastic rocks (Ashe and Grandfather Mountain Formations); Late Proterozoic and Early Cambrian metasedimentary rocks (Chilhowee Group); and Early Cambrian sedimentary rocks (Shady Dolomite). Paleozoic granites intrude the Proterozoic rocks. The Inner Piedmont contains noncarbonate metasedimentary rocks and amphibolite of medium to high metamorphic grades. These rocks are intruded by the Toluca Granite and Henderson Gneiss of Cambrian and Ordovician(?) age. The Charlotte belt consists largely of Late Proterozoic to Late Paleozoic granitic and gabbroic plutonic rocks and intervening enclaves of metasedimentary and metavolcanic rocks. The narrow Kings Mountain belt is located between the Charlotte and the Inner Piedmont belts and contains mainly Late Proterozoic metasedimentary rocks and plutonic rocks similar to those of the Charlotte belt. The Carolina slate belt, flanking the Charlotte belt on the east, contains weakly metamorphosed volcanic and sedimentary rocks. East of this belt, at the southeast corner of the quadrangle, is the Wadesboro basin, which has continental sedimentary rocks of Triassic age. Layered rocks westward from and in the Charlotte belt are complexly folded, are steeply dipping, and in the Blue Ridge and Inner Piedmont are contained within major thrust slices. Rocks of the Carolina slate belt are gently folded. Rocks of the Wadesboro basin occur in downfaulted blocks. The geophysical surveys of the Charlotte quadrangle consisted of Bouguer gravity, aeromagnetic, and aeroradioactivity surveys and used both newly obtained data and information from prior work. The gravity survey disclosed a distinct northeast-trending, northwest-decreasing gradient, which is part of the major gravity gradient that extends the length of the Appalachian Mountains. Granitic plutons of the Charlotte belt, in particular, are marked by gravity lows, and gabbro plutons, by highs. Several of the geologic belts display distinct magnetic character. The aeroradioactivity surveys showed a swath of consistently high gamma-ray intensities along the central part of the Inner Piedmont belt; these high intensities correspond to the so-called monazite belt. Oval patterns of high gamma-ray readi

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.

The origin of Mauna Loa's Nīnole Hills: Evidence of rift zone reorganization

USGS Publications Warehouse

Zurek, Jeffrey; Williams-Jones, Glyn; Trusdell, Frank A.; Martin, Simon

2015-01-01

In order to identify the origin of Mauna Loa volcano's Nīnole Hills, Bouguer gravity was used to delineate density contrasts within the edifice. Our survey identified two residual anomalies beneath the Southwest Rift Zone (SWRZ) and the Nīnole Hills. The Nīnole Hills anomaly is elongated, striking northeast, and in inversions both anomalies merge at approximately −7 km above sea level. The positive anomaly, modeled as a rock volume of ~1200 km3 beneath the Nīnole Hills, is associated with old eruptive vents. Based on the geologic and geophysical data, we propose that the gravity anomaly under the Nīnole Hills records an early SWRZ orientation, now abandoned due to geologically rapid rift-zone reorganization. Catastrophic submarine landslides from Mauna Loa's western flank are the most likely cause for the concurrent abandonment of the Nīnole Hills section of the SWRZ. Rift zone reorganization induced by mass wasting is likely more common than currently recognized.

Structure and State of Stress of the Chilean Subduction Zone from Terrestrial and Satellite-Derived Gravity and Gravity Gradient Data

NASA Astrophysics Data System (ADS)

Gutknecht, B. D.; Götze, H.-J.; Jahr, T.; Jentzsch, G.; Mahatsente, R.; Zeumann, St.

2014-11-01

It is well known that the quality of gravity modelling of the Earth's lithosphere is heavily dependent on the limited number of available terrestrial gravity data. More recently, however, interest has grown within the geoscientific community to utilise the homogeneously measured satellite gravity and gravity gradient data for lithospheric scale modelling. Here, we present an interdisciplinary approach to determine the state of stress and rate of deformation in the Central Andean subduction system. We employed gravity data from terrestrial, satellite-based and combined sources using multiple methods to constrain stress, strain and gravitational potential energy (GPE). Well-constrained 3D density models, which were partly optimised using the combined regional gravity model IMOSAGA01C (Hosse et al. in Surv Geophys, 2014, this issue), were used as bases for the computation of stress anomalies on the top of the subducting oceanic Nazca plate and GPE relative to the base of the lithosphere. The geometries and physical parameters of the 3D density models were used for the computation of stresses and uplift rates in the dynamic modelling. The stress distributions, as derived from the static and dynamic modelling, reveal distinct positive anomalies of up to 80 MPa along the coastal Jurassic batholith belt. The anomalies correlate well with major seismicity in the shallow parts of the subduction system. Moreover, the pattern of stress distributions in the Andean convergent zone varies both along the north-south and west-east directions, suggesting that the continental fore-arc is highly segmented. Estimates of GPE show that the high Central Andes might be in a state of horizontal deviatoric tension. Models of gravity gradients from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission were used to compute Bouguer-like gradient anomalies at 8 km above sea level. The analysis suggests that data from GOCE add significant value to the interpretation of lithospheric structures, given that the appropriate topographic correction is applied.

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 bisect the strike length.

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

Microgravity investigations are comparatively rarely used for searching of hidden ancient targets (e.g., Eppelbaum, 2013). It is caused mainly by small geometric size of the desired archaeological objects and various types of noise complicating the observed useful signal. At the same time, development of modern generation of field gravimetric equipment allows to register microGal (10-8 m/s2) anomalies that offer a new challenge in this direction. Correspondingly, an accuracy of gravity variometers (gradientometers) is also sharply increased. How we can improve the interpretation effectiveness and reliability? Undoubtedly, it must be a multi-stage process. I believe that we must begin since nonconventional methodologies for reducing topographic effect and terrain correction computation. Topographic effect reducing The possibilities of reducing topographic effects by grouping the points of additional gravimetric observations around the central point located on the survey network were demonstrated in (Khesin et al., 1996). A group of 4 to 8 additional points is located above and below along the relief approximately symmetrically and equidistant from the central point. The topographic effect is reduced to the obtained difference between the gravity field in the center of the group and its mean value for the whole group. Application of this methodology in the gold-pyrite deposit Gyzyl-Bulakh (Lesser Caucasus, western Azerbaijan) indicated its effectiveness. Computation of terrain correction Some geophysicists compare the new ideas in the field of terrain correction (TC) in gravimetry with the 'perpetuum mobile' invention. However, when we speak about very detailed gravity observations, the problem of most optimal computation of surrounding relief influence is of a great importance. Let us will consider two approaches applied earlier in ore geophysics. First approach A first method was applied in the Gyzyl-Bulakh gold-pyrite deposit situated in the Mekhmana ore region of 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, about 1000 characteristic points were used to describe the DTRM (most frequently points were focused in the center of the DTRM and more rarely - on the margins). Thus, in the interactive 3D ΔgB modeling (by the use of GSFC software) was computed effect not only from geological bodies occurring in this area, but also from surrounding DTRM. In the issue of this scheme application, two new ore bodies were discovered. Quantitative analysis of gravity anomalies The trivial formulas of quantitative analysis (based on simple relationships between the gravity field intensity and geometrical parameters of the anomalous body) are widely presented in the geophysical literature (e.g., Telford et al., 1993; Parasnis, 1997). However, absence of reliable information about the normal gravity field in the studied areas strongly limits practical application of these methods. Gravity field intensity F is expressed as F = - gradW, (1) where W is the gravity potential. For anomalous magnetic field Ua we can write (when magnetic susceptibility ≤ 0.1 SI unit) (Khesin et al., 1996): Ua = - gradV, (2) where V represents the magnetic potential. Let's consider analytical expressions of some typical models employed in magnetic and gravity fields (Table 1). Table 1. Comparison of some analytical expressions for magnetic and gravity fields Field Analytical expression MagneticThin bed (TB) z Zv = 2I2b-2--2 x + z (3) Point source (rod) mz Zv = ----3/2 (x2 + z2) (4) Gravity Horizontal Circular Cylinder (HCC) -z-- Δg = 2Gσ x2 + z2 (5) Sphere --z--- Δg = GM (x2 + z2)3/2 (6)

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.

Morphology and tectonics of the Mid-Atlantic Ridge, 7°-12°S

NASA Astrophysics Data System (ADS)

Bruguier, N. J.; Minshull, T. A.; Brozena, J. M.

2003-02-01

We present swath bathymetric, gravity, and magnetic data from the Mid-Atlantic Ridge between the Ascension and the Bode Verde fracture zones, where significant ridge-hot spot interaction has been inferred. The ridge axis in this region may be divided into four segments. The central two segments exhibit rifted axial highs, while the northernmost and southernmost segments have deep rift valleys typical of slow-spreading mid-ocean ridges. Bathymetric and magnetic data indicate that both central segments have experienced ridge jumps since ˜1 Ma. Mantle Bouguer anomalies (MBAs) derived from shipboard free air gravity and swath bathymetric data show deep subcircular lows centered on the new ridge axes, suggesting that mantle flow has been established beneath the new spreading centers for at least ˜1 Myr. Inversion of gravity data indicates that crustal thicknesses vary by ˜4 km along axis, with the thickest crust occurring beneath a large axial volcanic edifice. Once the effects of lithospheric aging have been removed, a model in which gravity variations are attributed entirely to crustal thickness variations is more consistent with data from an axis-parallel seismic line than a model that includes additional along-axis variations in mantle temperature. Both geophysical and geochemical data from the region may be explained by the melting of small (<200 km) mantle chemical heterogeneities rather than elevated temperatures. Therefore, there may be no Ascension/Circe plume.

Mechanisms of crustal shortening in the foreland of the central Andes, Argentina: insights from data-driven three-dimensional gravity, thermal and rheological modelling

NASA Astrophysics Data System (ADS)

Meeßen, Christian; Scheck-Wenderoth, Magdalena; Sippel, Judith; Strecker, Manfred

2017-04-01

Thin- and thick-skinned deformation styles in the foreland of the central Andes are the result of ongoing crustal shortening since the early Neogene. The mechanisms proposed for these different styles range from variations in subduction angle of the Nazca plate, lithospheric thickening to variations in temperature and strength of the crystalline crust. The latter hypothesis states a cold and strong lithosphere in the foreland of the Altiplano Plateau, facilitating thin-skinned shortening. In contrast, the foreland of the Puna plateau is proposed to be characterized by a warm lithosphere and strong upper crust, resulting in thick-skinned deformation. Whilst this hypothesis has been confirmed in numerical thermomechanical experiments, there is no evidence for this mechanism from data integrative modelling. We test this hypothesis by means of three-dimensional data integrative gravity, thermal and rheological modelling. Therefore, we constructed a lithospheric-scale density model of the foreland of northern Argentina and southern Bolivia using gravity forward modelling and inversion techniques. Into this density model we implemented sediment isopachs, data from receiver functions and densities from shear-wave velocities of the upper mantle. The model was verified using the observed Bouguer gravity anomaly. By assigning thermal and rheological properties to the modelled units we are able to quantify the strength of the lithosphere and test the predictions by the thermomechanical models.

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

2017-01-01

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.

Thermal structure, magmatism, and evolution of fast-spreading mid-ocean ridges

NASA Astrophysics Data System (ADS)

Shah, Anjana K.

2001-07-01

We use thin-plate flexural models and high-resolution magnetic field data to constrain magmatic and tectonic processes at fast-spreading mid-ocean ridges, and how these processes evolve over time. Models are constructed to predict axial high topography and gravity for a given thermal structure of the crust and mechanical structure of the lithosphere. Whereas previous models predicted the high is due to a narrow column of buoyant material extending to 10's of kilometers depth in the mantle, we find the high can also be produced by a narrow zone of crustal melt, and lithosphere which thickens rapidly with distance from the axis. We consider the effects of plastic weakening using a yield strength envelope to map bending stresses associated with deflections. Near-surface stresses are extensional at distances which closely resemble regions of normal fault growth at certain axial highs, suggesting bending stresses play a significant role in normal faulting at fast-spreading ridges. We further develop the model to simulate ridge jumps. We fit topography and gravity data of a plume-influenced region which has recently experienced a ridge jump. Steep sides of the new high are best modeled as constructional features. An abandoned ridge remains at the old axis due to plate strengthening associated with crustal cooling. By fitting more than one profile along-axis, we constrain the accretion history at the new ridge. We also predict than an inconsistency between bull's eye mantle Bouguer anomaly lows and a nearly constant along-axis depth can be resolved by assuming a low density zone below the axis widens near the bull's eye center. Finally, we study high-resolution magnetic field data at two regions of the East Pacific Rise with different eruptive histories. The anomalies are used to map relatively fresh pillow mounds, void space created by lava tubes and lobate flows, and dike complexes which extend along the length of recent fissure eruptions. The dikes suggest episodic eruptive histories in these regions, and have implications regarding the migration history of the area.

Structural Framework and Architecture of the Paleoproterozoic Bryah and Padbury Basins from Integrated Potential Field and Geological Datasets: Towards an Understanding of the Basin Evolution

NASA Astrophysics Data System (ADS)

Nigro R A Ramos, L.; Aitken, A.; Occhipinti, S.; Lindsay, M.

2017-12-01

The Bryah and Padbury Basins were developed along the northern margin of the Yilgarn Craton, in the southern portion of the Capricorn Orogen, which represents a Proterozoic tectonic zone that bounds the Yilgarn and Pilbara Cratons in Western Australia. These basins have been previously interpreted as developing in a rift, back-arc, and retro-arc foreland basins. Recent studies suggest that the Bryah Basin was deposited in a rift setting, while the overlying Padbury Basin evolved in a pro-foreland basin during the collision of the Yilgarn Craton and the Pilboyne block (formed by the Pilbara Craton and the Glenburgh Terrane), occurring in the Glenburgh Orogeny (2005-1960 Ma). This study focuses on characterizing the architecture and structural framework of the Bryah and Padbury Basins through analysis of geophysical and geological datasets, in order to better understand the different stages of the basins evolution. Gravity and magnetic data were used to define the main tectonic units and lithological boundaries, and to delineate major discontinuities in the upper and lower crust, as well as anomalies through a combination of map view interpretation and forward modelling. Geological mapping and drill core observations were linked with the geophysical interpretations. Fourteen magnetic domains are distinguished within the basins, while four main domains based on the Bouguer Anomaly are recognized. The highest gravity amplitude is related with an anomaly trending EW/NE-SW, which is coincident with the voluminous mafic rocks of the Bryah Basin, and may indicate the presence of an approximately 5km thick package of higher density mafic rocks. Magnetic depth estimations also indicate deep magnetic sources up to approximately 4,45km. These results can help to elucidate processes that occurred during the precursor rift of the early stages of the Bryah Basin, add information in relation to the basement control on sedimentation, allow the characterization of the varying thickness of the units from the Bryah and Padbury basins, and permit a synthesis describing basin evolution.

Bedrock morphology and structure, upper Santa Cruz Basin, south-central Arizona, with transient electromagnetic survey data

USGS Publications Warehouse

Bultman, Mark W.; Page, William R.

2016-10-31

The upper Santa Cruz Basin is an important groundwater basin containing the regional aquifer for the city of Nogales, Arizona. This report provides data and interpretations of data aimed at better understanding the bedrock morphology and structure of the upper Santa Cruz Basin study area which encompasses the Rio Rico and Nogales 1:24,000-scale U.S. Geological Survey quadrangles. Data used in this report include the Arizona Aeromagnetic and Gravity Maps and Data referred to here as the 1996 Patagonia Aeromagnetic survey, Bouguer gravity anomaly data, and conductivity-depth transforms (CDTs) from the 1998 Santa Cruz transient electromagnetic survey (whose data are included in appendixes 1 and 2 of this report).Analyses based on magnetic gradients worked well to identify the range-front faults along the Mt. Benedict horst block, the location of possibly fault-controlled canyons to the west of Mt. Benedict, the edges of buried lava flows, and numerous other concealed faults and contacts. Applying the 1996 Patagonia aeromagnetic survey data using the horizontal gradient method produced results that were most closely correlated with the observed geology.The 1996 Patagonia aeromagnetic survey was used to estimate depth to bedrock in the upper Santa Cruz Basin study area. Three different depth estimation methods were applied to the data: Euler deconvolution, horizontal gradient magnitude, and analytic signal. The final depth to bedrock map was produced by choosing the maximum depth from each of the three methods at a given location and combining all maximum depths. In locations of rocks with a known reversed natural remanent magnetic field, gravity based depth estimates from Gettings and Houser (1997) were used.The depth to bedrock map was supported by modeling aeromagnetic anomaly data along six profiles. These cross sectional models demonstrated that by using the depth to bedrock map generated in this study, known and concealed faults, measured and estimated magnetic susceptibilities of rocks found in the study area, and estimated natural remanent magnetic intensities and directions, reasonable geologic models can be built. This indicates that the depth to bedrock map is reason-able and geologically possible.Finally, CDTs derived from the 1998 Santa Cruz Basin transient electromagnetic survey were used to help identify basin structure and some physical properties of the basin fill in the study area. The CDTs also helped to confirm depth to bedrock estimates in the Santa Cruz Basin, in particular a region of elevated bedrock in the area of Potrero Canyon, and a deep basin in the location of the Arizona State Highway 82 microbasin. The CDTs identified many concealed faults in the study area and possibly indicate deep water-saturated clay-rich sediments in the west-central portion of the study area. These sediments grade to more sand-rich saturated sediments to the south with relatively thick, possibly unsaturated, sediments at the surface. Also, the CDTs may indicate deep saturated clay-rich sediments in the Highway 82 microbasin and in the Mount Benedict horst block from Proto Canyon south to the international border.

GOCE and Future Gravity Missions for Geothermal Energy Exploitation

NASA Astrophysics Data System (ADS)

Pastorutti, Alberto; Braitenberg, Carla; Pivetta, Tommaso; Mariani, Patrizia

2016-08-01

Geothermal energy is a valuable renewable energy source the exploitation of which contributes to the worldwide reduction of consumption of fossil fuels oil and gas. The exploitation of geothermal energy is facilitated where the thermal gradient is higher than average leading to increased surface heat flow. Apart from the hydrologic circulation properties which depend on rock fractures and are important due to the heat transportation from the hotter layers to the surface, essential properties that increase the thermal gradient are crustal thinning and radiogenic heat producing rocks. Crustal thickness and rock composition form the link to the exploration with the satellite derived gravity field, because both induce subsurface mass changes that generate observable gravity anomalies. The recognition of gravity as a useful investigation tool for geothermal energy lead to a cooperation with ESA and the International Renewable Energy Agency (IRENA) that included the GOCE derived gravity field in the online geothermal energy investigation tool of the IRENA database. The relation between the gravity field products as the free air gravity anomaly, the Bouguer and isostatic anomalies and the heat flow values is though not straightforward and has not a unique relationship. It is complicated by the fact that it depends on the geodynamical context, on the geologic context and the age of the crustal rocks. Globally the geological context and geodynamical history of an area is known close to everywhere, so that a specific known relationship between gravity and geothermal potential can be applied. In this study we show the results of a systematic analysis of the problem, including some simulations of the key factors. The study relies on the data of GOCE and the resolution and accuracy of this satellite. We also give conclusions on the improved exploration power of a gravity mission with higher spatial resolution and reduced data error, as could be achieved in principle by flying an atom interferometer sensor on board a satellite.

Lithospheric structure of a nascent spreading ridge inferred from gravity data: The western Gulf of Aden

NASA Astrophysics Data System (ADS)

HéBert, HéLèNe; Deplus, Christine; Huchon, Philippe; Khanbari, Khaled; Audin, Laurence

2001-11-01

The Aden spreading ridge (Somalia/Arabia plate boundary) does not connect directly to the Red Sea spreading ridge. It propagates toward the East African Rift through the Afar depression, where the presence of a hot spot has been postulated from seismological and geochemical evidence. The spreading direction (N37°E) is highly oblique to the overall trend (N90°E) of the ridge. We present and interpret new geophysical data gathered during the Tadjouraden cruise (R/V L'Atalante, 1995) in the Gulf of Aden west of 46°E. These data allow us to study the propagation of the ridge toward the Afar and to discuss the processes of the seafloor spreading initiation. We determine the lithospheric structure of the ridge using gravity data gathered during the cruise with the constraint of available refraction data. A striking Bouguer anomaly gradient together with the identification of magnetic anomalies defines the geographical extent of oceanic crust. The inversion of the Bouguer anomaly is performed in terms of variations of crustal thickness only and then discussed with respect to the expected thermal structure of the mantle lithosphere, which should depend not only on the seafloor spreading but also on the hot spot beneath East Africa. Our results allow us to define three distinct lithospheric domains in the western Gulf of Aden. East of 44°45'E the lithosphere displays an oceanic character (thermal subsidence recorded for the last 10 Ma and constant crustal thickness). Between 43°30'E and 44°10'E the lithosphere is of continental type but locally thinned beneath the axial valley. The central domain defined between 44°10'E and 44°45'E is characterized by a transitional lithosphere which can be seen as a stretched continental crust where thick blocks are mixed with thinned crust; it displays en echelon basins that are better interpreted as extension cells rather than accretion cells.

Regional methods for mapping major faults in areas of uniform low relief, as used in the London Basin, UK

NASA Astrophysics Data System (ADS)

Haslam, Richard; Aldiss, Donald

2013-04-01

Most of the London Basin, south-eastern UK, is underlain by the Palaeogene London Clay Formation, comprising a succession of rather uniform marine clay deposits up to 150 m thick, with widespread cover of Quaternary deposits and urban development. Therefore, in this area faults are difficult to delineate (or to detect) by conventional geological surveying methods in the field, and few are shown on the geological maps of the area. However, boreholes and excavations, especially those for civil engineering works, indicate that faults are probably widespread and numerous in the London area. A representative map of fault distribution and patterns of displacement is a pre-requisite for understanding the tectonic development of a region. Moreover, faulting is an important influence on the design and execution of civil engineering works, and on the hydrogeological characteristics of the ground. This paper reviews methods currently being used to map faults in the London Basin area. These are: the interpretation of persistent scatterer interferometry (PSI) data from time-series satellite-borne radar measurements; the interpretation of regional geophysical fields (Bouguer gravity anomaly and aeromagnetic), especially in combination with a digital elevation model; and the construction and interpretation of 3D geological models. Although these methods are generally not as accurate as large-scale geological field surveys, due to the availability of appropriate data in the London Basin they provide the means to recognise and delineate more faults, and with more confidence, than was possible using traditional geological mapping techniques. Together they reveal regional structures arising during Palaeogene crustal extension and subsidence in the North Sea, followed by inversion of a Mesozoic sedimentary basin in the south of the region, probably modified by strike-slip fault motion associated with the relative northward movement of the African Plate and the Alpine orogeny. This work is distributed under the Creative Commons Attribution 3.0 Unported License together with an NERC copyright. This license does not conflict with the regulations of the Crown Copyright.

Modelling airborne gravity data by means of adapted Space-Wise approach

NASA Astrophysics Data System (ADS)

Sampietro, Daniele; Capponi, Martina; Hamdi Mansi, Ahmed; Gatti, Andrea

2017-04-01

Regional gravity field modelling by means of remove - restore procedure is nowadays widely applied to predict grids of gravity anomalies (Bouguer, free-air, isostatic, etc.) in gravimetric geoid determination as well as in exploration geophysics. Considering this last application, due to the required accuracy and resolution, airborne gravity observations are generally adopted. However due to the relatively high acquisition velocity, presence of atmospheric turbulence, aircraft vibration, instrumental drift, etc. airborne data are contaminated by a very high observation error. For this reason, a proper procedure to filter the raw observations both in the low and high frequency should be applied to recover valuable information. In this work, a procedure to predict a grid or a set of filtered along track gravity anomalies, by merging GGM and airborne dataset, is presented. The proposed algorithm, like the Space-Wise approach developed by Politecnico di Milano in the framework of GOCE data analysis, is based on a combination of along track Wiener filter and Least Squares Collocation adjustment and properly considers the different altitudes of the gravity observations. Among the main differences with respect to the satellite application of the Space-Wise approach there is the fact that, while in processing GOCE data the stochastic characteristics of the observation error can be considered a-priori well known, in airborne gravimetry, due to the complex environment in which the observations are acquired, these characteristics are unknown and should be retrieved from the dataset itself. Some innovative theoretical aspects focusing in particular on the theoretical covariance modelling are presented too. In the end, the goodness of the procedure is evaluated by means of a test on real data recovering the gravitational signal with a predicted accuracy of about 0.25 mGal.

The major tectonic boundaries of the Northern Red Sea rift, Egypt derived from geophysical data analysis

NASA Astrophysics Data System (ADS)

Saleh, Salah; Pamukçu, Oya; Brimich, Ladislav

2017-09-01

In the present study, we have attempted to map the plate boundary between Arabia and Africa at the Northern Red Sea rift region including the Suez rift, Gulf of Aqaba-Dead Sea transform and southeastern Mediterranean region by using gravity data analysis. In the boundary analysis method which was used; low-pass filtered gravity anomalies of the Northern Red Sea rift region were computed. Different crustal types and thicknesses, sediment thicknesses and different heat flow anomalies were evaluated. According to the results, there are six subzones (crustal blocks) separated from each other by tectonic plate boundaries and/or lineaments. It seems that these tectonic boundaries reveal complex structural lineaments, which are mostly influenced by a predominant set of NNW-SSE to NW-SE trending lineaments bordering the Red Sea and Suez rift regions. On the other side, the E-W and N-S to NNE-SSW trended lineaments bordering the South-eastern Mediterranean, Northern Sinai and Aqaba-Dead Sea transform regions, respectively. The analysis of the low pass filtered Bouguer anomaly maps reveals that the positive regional anomaly over both the Red Sea rift and South-eastern Mediterranean basin subzones are considered to be caused by the high density of the oceanic crust and/or the anomalous upper mantle structures beneath these regions whereas, the broad medium anomalies along the western half of Central Sinai with the Suez rift and the Eastern Desert subzones are attributed to low-density sediments of the Suez rift and/or the thick upper continental crustal thickness below these zones. There are observable negative anomalies over the Northern Arabia subzone, particularly in the areas covered by Cenozoic volcanics. These negative anomalies may be attributed to both the low densities of the surface volcanics and/or to a very thick upper continental crust. On the contrary, the negative anomaly which belongs to the Gulf of Aqaba-Dead Sea transform zone is due to crustal thickening (with limited heat flow values) below this region. Additionally in this study, the crustal thinning was investigated with heat flow, magnetic and free air gravity anomalies in the Northern Red Sea rift region. In fact, the crustal thinning of the study area was also proportional to the regions of observable high heat flow values. Finally, our results were found to be well correlated with the topography, free air, aeromagnetic and heat flow dataset profiles crossing most of the study area.

Montana: Filling A Gap In The GeoSwath

NASA Astrophysics Data System (ADS)

Jensen, B.; Keller, G. R.

2010-12-01

The proposed Geoswath transect crosses southern Montana, and the swath of MT stations deployed as part of EarthScope cover all but a small portion of eastern Montana. USArray broadband stations of course cover the entire region. However, modern controlled-source seismic data are very sparse in this large state, and most of it dates from the 1960’s. In this study, we have taken an integrated approach to analyzing lithospheric structure by compiling and analyzing all the public domain geophysical results and data we could locate and combining them with industry seismic reflection data that were released for our study. This information was employed to interpret a suite of filtered regional maps gravity and magnetic data and to construct integrated gravity models of long profiles that reflect crustal structure and deeper features within the upper mantle of the region. Our analysis included previous seismic refraction/reflection results, EarthScope Automated Array receiver functions, new 2D seismic reflection data, seismic tomography, potential field data, and previous geological studies in order to investigate structural and compositional variations within the crust and upper mantle. Our targets included Precambrian structure and tectonics, Sevier and Laramide features, and Late Cenozoic extension. Our main conclusions are: 1) Receiver function and seismic refraction/reflection crustal thickness estimates show a W-E crustal thickening with thicknesses greater than 50 km in the central and eastern Montana; 2) Seismic reflection data reveal Laramide basement-involved structures as far east as central Montana. These structures also show that the western edge of the North American craton was affected by late Mesozoic to Cenozoic deformation and has thus been decratonized; 3) Potential field filtering methods revealed regional trends and tectonic province outlines. The tilt derivative of the reduced-to-pole magnetic data enhances crystalline basement patterns that reflect tectonic province boundary locations. The upward continuation of the complete Bouguer anomaly grid revealed a gravity high in the northeast portion of the region, which is interpreted to be associated with density variations in the upper mantle. This interpretation is consistent with seismic tomography that reveals a “wedge-like” zone fast material beneath the craton in this region.

Small-scale density variations in the lunar crust revealed by GRAIL

NASA Astrophysics Data System (ADS)

Jansen, J. C.; Andrews-Hanna, J. C.; Li, Y.; Lucey, P. G.; Taylor, G. J.; Goossens, S.; Lemoine, F. G.; Mazarico, E.; Head, J. W.; Milbury, C.; Kiefer, W. S.; Soderblom, J. M.; Zuber, M. T.

2017-07-01

Data from the Gravity Recovery and Interior Laboratory (GRAIL) mission have revealed that ∼98% of the power of the gravity signal of the Moon at high spherical harmonic degrees correlates with the topography. The remaining 2% of the signal, which cannot be explained by topography, contains information about density variations within the crust. These high-degree Bouguer gravity anomalies are likely caused by small-scale (10‧s of km) shallow density variations. Here we use gravity inversions to model the small-scale three-dimensional variations in the density of the lunar crust. Inversion results from three non-descript areas yield shallow density variations in the range of 100-200 kg/m3. Three end-member scenarios of variations in porosity, intrusions into the crust, and variations in bulk crustal composition were tested as possible sources of the density variations. We find that the density anomalies can be caused entirely by changes in porosity. Characteristics of density anomalies in the South Pole-Aitken basin also support porosity as a primary source of these variations. Mafic intrusions into the crust could explain many, but not all of the anomalies. Additionally, variations in crustal composition revealed by spectral data could only explain a small fraction of the density anomalies. Nevertheless, all three sources of density variations likely contribute. Collectively, results from this study of GRAIL gravity data, combined with other studies of remote sensing data and lunar samples, show that the lunar crust exhibits variations in density by ± 10% over scales ranging from centimeters to 100‧s of kilometers.

Small-Scale Density Variations in the Lunar Crust Revealed by GRAIL

NASA Technical Reports Server (NTRS)

Jansen, J. C.; Andrews-Hanna, J. C.; Li, Y.; Lucey, P. G.; Taylor, G. J.; Goossens, S.; Lemoine, F. G.; Mazarico, E.; Head, J. W., III; Milbury, C.;

Crustal surface wave velocity structure of the east Albany-Fraser Orogen, Western Australia, from ambient noise recordings

NASA Astrophysics Data System (ADS)

Sippl, C.; Kennett, B. L. N.; Tkalčić, H.; Gessner, K.; Spaggiari, C. V.

2017-09-01

Group and phase velocity maps in the period range 2-20 s for the Proterozoic east Albany-Fraser Orogen, Western Australia, are extracted from ambient seismic noise recorded with the 70-station ALFREX array. This 2 yr temporary installation provided detailed coverage across the orogen and the edge of the Neoarchean Yilgarn Craton, a region where no passive seismic studies of this scale have occurred to date. The surface wave velocities are rather high overall (>3 km s-1 nearly everywhere), as expected for exposed Proterozoic basement rocks. No clear signature of the transition between Yilgarn Craton and Albany-Fraser Orogen is observed, but several strong anomalies corresponding to more local geological features were obtained. A prominent, NE-elongated high-velocity anomaly in the northern part of the array is coincident with a Bouguer gravity high caused by the upper crustal metamorphic rocks of the Fraser Zone. This feature disappears towards longer periods, which hints at an exclusively upper crustal origin for this anomaly. Further east, the limestones of the Cenozoic Eucla Basin are clearly imaged as a pronounced low-velocity zone at short periods, but the prevalence of low velocities to periods of ≥5 s implies that the uppermost basement in this area is likewise slow. At longer periods, slightly above-average surface wave velocities are imaged below the Eucla Basin.

Accuracy of mapping the Earth's gravity field fine structure with a spaceborne gravity gradiometer mission

NASA Technical Reports Server (NTRS)

Kahn, W. D.

1984-01-01

The spaceborne gravity gradiometer is a potential sensor for mapping the fine structure of the Earth's gravity field. Error analyses were performed to investigate the accuracy of the determination of the Earth's gravity field from a gravity field satellite mission. The orbital height of the spacecraft is the dominating parameter as far as gravity field resolution and accuracies are concerned.

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.

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.

Lithospheric flexural strength and effective elastic thicknesses of the Eastern Anatolia (Turkey) and surrounding region

NASA Astrophysics Data System (ADS)

Oruç, Bülent; Gomez-Ortiz, David; Petit, Carole

2017-12-01

The Lithospheric structure of Eastern Anatolia and the surrounding region, including the northern part of the Arabian platform is investigated via the analysis and modeling of Bouguer anomalies from the Earth Gravitational Model EGM08. The effective elastic thickness of the lithosphere (EET) that corresponds to the mechanical cores of the crust and lithospheric mantle is determined from the spectral coherence between Bouguer anomalies and surface elevation data. Its average value is 18.7 km. From the logarithmic amplitude spectra of Bouguer anomalies, average depths of the lithosphere-asthenosphere boundary (LAB), Moho, Conrad and basement in the study area are constrained at 84 km, 39 km, 16 km and 7 km, respectively. The geometries of the LAB and Moho are then estimated using the Parker-Oldenburg inversion algorithm. We also present a lithospheric strength map obtained from the spatial variations of EET determined by Yield Stress Envelopes (YSE). The EET varies in the range of 12-23 km, which is in good agreement with the average value obtained from spectral analysis. Low EET values are interpreted as resulting from thermal and flexural lithospheric weakening. According to the lithospheric strength of the Eastern Anatolian region, the rheology model consists of a strong but brittle upper crust, a weak and ductile lower crust, and a weak lower part of the lithosphere. On the other hand, lithosphere strength corresponds to weak and ductile lower crust, a strong upper crust and a strong uppermost lithospheric mantle for the northern part of the Arabian platform.

Imaging the Chicxulub central crater zone from large scale seismic acoustic wave propagation and gravity modeling

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.

2017-12-01

Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments

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.;

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

2014-10-02

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.

Satellite-delivered gravimetry for the Vitória-Trindade Chain, Southeast Brazil, and its bearing on the volcanic seamount structure

NASA Astrophysics Data System (ADS)

Motoki, A.; Motoki, K. F.; Sichel, S. E.; Souza, K.; Bueno, G. V.; Poseidon

2013-05-01

The authors present gravimetric and geomorphologic analyses for the Vitória-Trindade volcanic seamount chain, State of Espírito Santo, Brazil. The seamounts are generally of 30 km in base diameter, 10 km in flat-top diameter, and 2500 to 4000 m in relative height. The flat-tops are constant in depth, without evidence of basement subsidence. The western half of the chain shows basement elevation of 2000 m, which took place before the eruptions. The size and frequency of the seamounts become smaller to the east. Most of them have conical form of central eruptions, and some large ones are of elongated form of fissure eruptions. The volcanic seamounts usually have Bouguer anomaly about 100 mGal lower than the adjacent area, showing funnel-shaped Bouguer depression. Large volcanoes show ring-like Bouguer structure composed of the central high and the marginal low. The marginal low is about 100 mGal lower than the adjacent abyssal plane and the central high is about 80 mGal higher than the marginal low. Very large volcanoes have bull's eye-like low Bouguer sites along the marginal low. On the foot of the volcanoes, there is the area with Bouguer anomaly 20 to 40 mGal higher, called peripheral high. These observations suggest the following growth history of the volcanic seamounts. At the initial stage, repeated central eruptions of lava flow construct the volcanic edifice. The weight of the volcano is sustained by mechanical firmness of the basement. The Bouguer anomaly is characterized by funnel-shaped depression. At the advanced stage, gabbroic radial dyke intrusion occurs along the central conduit in the upper level of the volcanic edifice, which is evidenced by the central Bouguer high. The seamount is supported mainly by mechanical firmness and partially by isostatic compensation of crustal down-buckling. At the highly advanced stage, the intrusion takes place into the lower level of the main volcanic edifice resulting lateral eruptions along its foot, which is shown by the bull's eye-like Bouguer lows. The crustal down-buckling and consequent isostatic compensation become relevant. The peripheral Bouguer high could be the rebound of the crustal down-buckling. The regional Bouguer anomaly suggests lithosphere thinning along the Vitória-Trindade Chain, which is relevant at the western end of the chain and becomes weak to east. The magmatism and tectonism of are strong at the western end of the chain and become less intense to the east.

Temporal sea-surface gravity changes observed near the source area prior to the 2011 Tohoku earthquake

NASA Astrophysics Data System (ADS)

Nakamura, T.; Tsuboi, S.

2013-12-01

Recent seismological studies suggested subsurface activities preceding the 2011 Tohoku earthquake; the occurrence of migration of seismicity (Kato et al., 2012) and slow slip events (Ito et al., 2013) in and around the source area one month before the mainshock. In this study, we investigated sea-surface gravity changes observed by the shipboard gravimeter mounted on research vessels before the mainshock. The vessels incidentally passed through the source area along almost the same cruise track twice, four months before and one month before the mainshock. Comparing the sea surface gravity in the former track with that in the latter after Bouguer correction, we find the gravity changes of approximately 7 mGal in coseismic slip areas near the trench axis during the three months. We find these gravity changes even in the crossing areas of the cruise tracks where seafloor topographies have no differences between the tracks. We also find that the topographic differences show positive changes but the gravity changes negative ones in other areas, which is a negative correlation inconsistent with the theoretical relationship between the topographic difference and the gravity change. These mean that the differences of seafloor topographies due to differences between the two cruise tracks are not main causes of the observed gravity changes there. The changes cannot also be explained by drifts of the gravimeter and geostrophic currents. Although we have not had any clear evidences, we speculate that the possible cause may be density increases around the seismogenic zone or uplifts of seafloor in order to explain the changes of this size. We estimate the density increases of 1.0 g/cm**3 in a disk with a radius of 40 km and a width of 200 m or the uplifts of several tens of meters in seafloor areas for the observed gravity changes. Our results indicate that sea-surface gravity observations may be one of valid approaches to monitor the approximate location of a possible great earthquake in offshore areas.

Free-Air Gravity Map of the Moon

NASA Image and Video Library

2014-06-27

This still image features a free-air gravity map of the Moon's southern latitudes developed by S. Goossens et al. from data returned by the Gravity Recovery and Interior Laboratory (GRAIL) mission. If the Moon were a perfectly smooth sphere of uniform density, the gravity map would be a single, featureless color, indicating that the force of gravity at a given elevation was the same everywhere. But like other rocky bodies in the solar system, including Earth, the Moon has both a bumpy surface and a lumpy interior. Spacecraft in orbit around the Moon experience slight variations in gravity caused by both of these irregularities. The free-air gravity map shows deviations from the mean gravity that a cueball Moon would have. The deviations are measured in milliGals, a unit of acceleration. On the map, purple is at the low end of the range, at around -400 mGals, and red is at the high end near +400 mGals. Yellow denotes the mean. The map shown here extends from the south pole of the Moon up to 50°S and reveals the gravity for that region in even finer detail than the global gravity maps published previously. The image illustrates the very good correlation between the gravity map and topographic features such as peaks and craters, as well as the mass concentration lying beneath the large Schrödinger basin in the center of the frame. The terrain in the image is based on Lunar Reconnaissance Orbiter (LRO) altimeter and camera data. Credit: NASA's Scientific Visualization Studio NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Characteristics of Marine Gravity Anomaly Reference Maps and Accuracy Analysis of Gravity Matching-Aided Navigation.

PubMed

Wang, Hubiao; Wu, Lin; Chai, Hua; Xiao, Yaofei; Hsu, Houtse; Wang, Yong

2017-08-10

The variation of a marine gravity anomaly reference map is one of the important factors that affect the location accuracy of INS/Gravity integrated navigation systems in underwater navigation. In this study, based on marine gravity anomaly reference maps, new characteristic parameters of the gravity anomaly were constructed. Those characteristic values were calculated for 13 zones (105°-145° E, 0°-40° N) in the Western Pacific area, and simulation experiments of gravity matching-aided navigation were run. The influence of gravity variations on the accuracy of gravity matching-aided navigation was analyzed, and location accuracy of gravity matching in different zones was determined. Studies indicate that the new parameters may better characterize the marine gravity anomaly. Given the precision of current gravimeters and the resolution and accuracy of reference maps, the location accuracy of gravity matching in China's Western Pacific area is ~1.0-4.0 nautical miles (n miles). In particular, accuracy in regions around the South China Sea and Sulu Sea was the highest, better than 1.5 n miles. The gravity characteristic parameters identified herein and characteristic values calculated in various zones provide a reference for the selection of navigation area and planning of sailing routes under conditions requiring certain navigational accuracy.

Characteristics of Marine Gravity Anomaly Reference Maps and Accuracy Analysis of Gravity Matching-Aided Navigation

PubMed Central

Wang, Hubiao; Chai, Hua; Xiao, Yaofei; Hsu, Houtse; Wang, Yong

2017-01-01

The variation of a marine gravity anomaly reference map is one of the important factors that affect the location accuracy of INS/Gravity integrated navigation systems in underwater navigation. In this study, based on marine gravity anomaly reference maps, new characteristic parameters of the gravity anomaly were constructed. Those characteristic values were calculated for 13 zones (105°–145° E, 0°–40° N) in the Western Pacific area, and simulation experiments of gravity matching-aided navigation were run. The influence of gravity variations on the accuracy of gravity matching-aided navigation was analyzed, and location accuracy of gravity matching in different zones was determined. Studies indicate that the new parameters may better characterize the marine gravity anomaly. Given the precision of current gravimeters and the resolution and accuracy of reference maps, the location accuracy of gravity matching in China’s Western Pacific area is ~1.0–4.0 nautical miles (n miles). In particular, accuracy in regions around the South China Sea and Sulu Sea was the highest, better than 1.5 n miles. The gravity characteristic parameters identified herein and characteristic values calculated in various zones provide a reference for the selection of navigation area and planning of sailing routes under conditions requiring certain navigational accuracy. PMID:28796158

Evaluation of using digital gravity field models for zoning map creation

NASA Astrophysics Data System (ADS)

Loginov, Dmitry

2018-05-01

At the present time the digital cartographic models of geophysical fields are taking a special significance into geo-physical mapping. One of the important directions to their application is the creation of zoning maps, which allow taking into account the morphology of geophysical field in the implementation automated choice of contour intervals. The purpose of this work is the comparative evaluation of various digital models in the creation of integrated gravity field zoning map. For comparison were chosen the digital model of gravity field of Russia, created by the analog map with scale of 1 : 2 500 000, and the open global model of gravity field of the Earth - WGM2012. As a result of experimental works the four integrated gravity field zoning maps were obtained with using raw and processed data on each gravity field model. The study demonstrates the possibility of open data use to create integrated zoning maps with the condition to eliminate noise component of model by processing in specialized software systems. In this case, for solving problem of contour intervals automated choice the open digital models aren't inferior to regional models of gravity field, created for individual countries. This fact allows asserting about universality and independence of integrated zoning maps creation regardless of detail of a digital cartographic model of geo-physical fields.

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 and Valdez on the northeast. This high coincides with the wide belt of greenstone and pillow basalt of the Orca Group and largely reflects the high density of these volcanic rocks. A large low in the east-central part of the sound is inferred to have a composite origin, and results from the combined effects of low-density sedimentary and granitic rocks. The Prince William Sound gravity high extends southwest-northeast without major horizontal offset for more than 100 miles. Thus the belt of volcanic rocks causing the high constitutes a major virtually continuous, geologic element of south-central Alaska.

Along-axis segmentation and isostasy in the Western rift, East Africa

NASA Astrophysics Data System (ADS)

Upcott, N. M.; Mukasa, R. K.; Ebinger, C. J.; Karner, G. D.

1996-02-01

Structural variations along the southern sectors of the Western rift, East Africa, have previously been described, but subsurface structures in the northern sector (Uganda, Zaire) are virtually unknown. Our aims are to investigate the along-axis segmentation of the northern sector, thereby adding to the structural picture of the Western rift, and to study the isostatic compensation of the varying rift morphology along the sector's length. This study describes the first gravity survey to be carried out on the shallow Lake Albert, forward models of these and existing gravity data, and the results from inverse modeling of existing aeromagnetic data designed to delimit border and transfer fault systems. Our tectonic model shows that the northern rift sector is segmented along-axis into five 25 to 65-km-wide, 80 to 100-km-long rift segments, characterized by closed-contour Bouguer anomaly lows, and bounded by steep gravity, aeromagnetic, and topographic/bathymetric gradients. Werner and Euler deconvolution results and gravity anomaly data reveal that some faulted basins are separated by structural highs and cross-rift ramps or faults and suggest sedimentary basin depths of 4-6 km. Forward modeling of structural and free-air gravity profiles across individual basins and flanks using a model that assumes flexural compensation also suggests sediment thicknesses of up to 5.5 km, similar to the estimates from magnetic data. The basin and flank morphology can be explained by 6-9 km of extension of a lithosphere with an effective elastic thickness (Te) of 25 km (equivalent to a flexural rigidity of 1.4 × 1023 N m), similar to results in other Western rift basins. Potential field data and lithospheric strength estimates in the Western rift system show small along-axis variations in lithospheric structure, regardless of the presence or absence of Cenozoic magmatism.

New Data Bases and Standards for Gravity Anomalies

NASA Astrophysics Data System (ADS)

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

2008-12-01

Ever since the use of high-precision gravimeters emerged in the 1950's, gravity surveys have been an important tool for geologic studies. Recent developments that make geologically useful measurements from airborne and satellite platforms, the ready availability of the Global Positioning System that provides precise vertical and horizontal control, improved global data bases, and the increased availability of processing and modeling software have accelerated the use of the gravity method. As a result, efforts are being made to improve the gravity databases publicly available to the geoscience community by expanding their holdings and increasing the accuracy and precision of the data in them. Specifically the North American Gravity Database as well as the individual databases of Canada, Mexico, and the United States are being revised using new formats and standards to improve their coverage, standardization, and accuracy. An important part of this effort is revision of procedures and standards for calculating gravity anomalies taking into account the enhanced computational power available, modern satellite-based positioning technology, improved terrain databases, and increased interest in more accurately defining the different components of gravity anomalies. 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 calculated value of theoretical gravity. The new standards hardly impact the interpretation of local anomalies, but do improve regional anomalies in that long wavelength artifacts are removed. Most importantly, such new standards can be consistently applied to gravity database compilations of nations, continents, and even the entire world. Although many types of gravity anomalies have been described, they fall into three main classes. The primary class incorporates planetary effects, which are analytically prescribed, to derive the predicted or modeled gravity, and thus, anomalies of this class are termed planetary. The most primitive version of a gravity anomaly is simply the difference between the value of gravity predicted by the effect of the reference ellipsoid and the observed gravity anomaly. When the height of the gravity station increases, the ellipsoidal gravity anomaly decreases because of the increased distance of measurement from the anomaly- producing masses. The two primary anomalies in geophysics, which are appropriately classified as planetary anomalies, are the Free-air and Bouguer gravity anomalies. They employ models that account for planetary effects on gravity including the topography of the earth. A second class of anomaly, geological anomalies, includes the modeled gravity effect of known or assumed masses leading to the predicted gravity by using geological data such as densities and crustal thickness. The third class of anomaly, filtered anomalies, removes arbitrary gravity effects of largely unknown sources that are empirically or analytically determined from the nature of the gravity anomalies by filtering.

Gravity at the Moon North Pole

NASA Image and Video Library

2013-03-19

This is a polar stereographic map of gravity of the north polar region of the moon from the Gravity Recovery and Interior Laboratory GRAIL mission. The map displays the region from latitude 60 north to the pole.

Contrasting modes of rifting: The Benue Trough and Cameroon Volcanic Line, West Africa

NASA Astrophysics Data System (ADS)

Okereke, C. S.

1988-08-01

The Benue trough of west Africa is commonly believed to be a rift feature that originated in the Cretaceous at about the time that Africa and South America began to separate. Bouguer gravity and available geological data in the trough indicate that its formation was probably the result of regional horizontal stresses in the lithosphere, causing crustal extension and surface subsidence. By contrast, the data for the adjoining Cameroon volcanic line suggests that the associated tensional stresses relate to mantle upwarp causing thinning of the lithosphere and regional crustal uplift similar to that associated with the Kenya rift. Thus the association of passive and active rifts seen in the Afro-Arabia rift system is also a feature of the Cretaceous rift system in west Africa.

Gravity and isostatic anomaly maps of Greece produced

NASA Astrophysics Data System (ADS)

Lagios, E.; Chailas, S.; Hipkin, R. G.

A gravity anomaly map of Greece was first compiled in the early 1970s [Makris and Stavrou, 1984] from all available gravity data collected by different Hellenic institutions. However, to compose this map the data had to be smoothed to the point that many of the smaller-wavelength gravity anomalies were lost. New work begun in 1987 has resulted in the publication of an updated map [Lagios et al., 1994] and an isostatic anomaly map derived from it.The gravity data cover the area between east longitudes 19° and 27° and north latitudes 32° and 42°, organized in files of 100-km squares and grouped in 10-km squares using UTM zone 34 coordinates. Most of the data on land come from the gravity observations of Makris and Stavrou [1984] with additional data from the Institute of Geology and Mining Exploration, the Public Oil Corporation of Greece, and Athens University. These data were checked using techniques similar to those used in compiling the gravity anomaly map of the United States, but the horizontal gradient was used as a check rather than the gravity difference. Marine data were digitized from the maps of Morelli et al. [1975a, 1975b]. All gravity anomaly values are referred to the IGSN-71 system, reduced with the standard Bouger density of 2.67 Mg/m3. We estimate the errors of the anomalies in the continental part of Greece to be ±0.9 mGal; this is expected to be smaller over fairly flat regions. For stations whose height has been determined by leveling, the error is only ±0.3 mGal. For the marine areas, the errors are about ±5 mGal [Morelli, 1990].

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.

Gravity Gradiometry and Map Matching: An Aid to Aircraft Inertial Navigation Systems

DTIC Science & Technology

2010-03-01

improve its performance. In all of these cases, because information from two or more different navigation systems feeds into a navigation solution...GRAVITY GRADIOMETRY AND MAP MATCHING: AN AID TO AIRCRAFT INERTIAL NAVIGATION SYSTEMS THESIS...M06 GRAVITY GRADIOMETRY AND MAP MATCHING: AN AID TO AIRCRAFT INERTIAL NAVIGATION SYSTEMS THESIS Presented to the Faculty Department of

New geological and geophysical antecedents at the Monturaqui Impact Crater, Chile

NASA Astrophysics Data System (ADS)

Ugalde, H.; Valenzuela, M.; Casas, E.; Milkereit, B.; Grandon, M.; Contreras, S.

2004-05-01

Impact structures are a common and important landform on planetary surfaces. Currently there are 168 confirmed impact structures in the Earth [1]. Out of those, the Monturaqui crater (<400 m diameter, 0.1 Ma [2]), located in the north of Chile, represents a grand opportunity for a detailed study of simple impact craters: it is accessible, well preserved and exposed. In December 2003 a field expedition accomplished detailed geological and geophysical mapping on it. The geology of the Monturaqui area is characterized by a basement of Paleozoic granites overlain by Pliocene ignimbrite units [3]. The granite outcrops mostly at the higher terrain in the crater rim, while the ignimbrites outcrop at lower levels filling the crater. Gravity, magnetic, differential GPS surveying and geological mapping built a detailed dataset of the crater. From the DGPS survey, its dimensions are 370 m EW, 350 m NS, and ~34 m deep. In the centre it has an uplift of 3 m approx, coincident with lime sediments. The northern edge of the crater exhibits magnetic anomalies with inverted polarization, presumably due to magnetic remanence. This could have been caused by post-impact alteration [4]. The Bouguer gravity anomaly shows a negative anomaly of ~1mGal at the centre, associated with fracturing and brecciation of the target rocks. Due to its lower competence than the granite, the shock wave fractured the ignimbrite instead of deforming it, building the regolith that presently fills the crater. Then the shock wave melted the basement locally. Breccia and melt were ejected hundreds of metres around the crater, and excavation raised the edges of the ignimbrite strata and granite. Late erosion was controlled mainly by mechanical weathering due to the extreme arid conditions of the area since the mid-Miocene [5]. References: [1] Earth Impact Database, www.unb.ca/passc/ImpactDatabase/, 2003; [2] Buchwald V. F. Handbook of Iron meteorites. University of California Press, v3, 1975; [3] Ramírez, C. y Gardeweg, M. Carta Geológica de Chile, Hoja Toconao. SERNAGEOMIN, 1982; [4] Ugalde, H. et. al., in GSA Special Volume, 2004 (Submitted); [5] Alpers, C. N. and G.H. Brimhall, Geolog. Soc. Of Am. Bull. 100, 1640-1656, 1988.

Isostatic gravity map with simplified geology of the Los Angeles 30 x 60 minute quadrangle

USGS Publications Warehouse

Wooley, R.J.; Yerkes, R.F.; Langenheim, V.E.; Chuang, F.C.

2003-01-01

This isostatic residual gravity map is part of the Southern California Areal Mapping Project (SCAMP) and is intended to promote further understanding of the geology in the Los Angeles 30 x 60 minute quadrangle, California, by serving as a basis for geophysical interpretations and by supporting both geological mapping and topical (especially earthquake) studies. Local spatial variations in the Earth's gravity field (after various corrections for elevation, terrain, and deep crustal structure explained below) reflect the lateral variation in density in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithologic boundaries. The map shows contours of isostatic gravity overlain on a simplified geology including faults and rock types. The map is draped over shaded-relief topography to show landforms.

Acoustic and gravity features of mud volcanoes along the seaward part of the Kumano forearc basin, Nankai region, central Japan

NASA Astrophysics Data System (ADS)

Asada, M.

2017-12-01

Mud volcanoes (MV) are geological features that are observed all over the world, especially along plate convergent margins. MVs bring fluid and sediment to the surface from depth. MVs around Japan are expected to transport of information from the shallow portions of the seismogenic zone. The Kumano forearc basin (FAB) in the Nankai region is the most studied area in Japan. It is bounded by a shelf on the north, and the Kumano Basin edge fault zone (KBEFZ) on the south. The Kumano FAB has 1-2 km of sediment and overlies the accretionary prism. There are at least 14 MVs in the Kumano Basin. Most of them are found over the northern basin floor, and at least one MV is at the KBEFZ. The MV at the KBEFZ is imaged on a 3D seismic data set as a small topographic feature on seafloor with a disrupted BSR below it. On high-resolution acoustic imagery, it is an 80 100m-high hill with a crater-like depression. It is characterized by a negative ph anomaly detected just above it. High-backscatter seafloor recognized around the MV suggests that harder seafloor exists in that area. To determine whether large subseafloor diapirs exist below active MVs, we try to detect the gravity contrast between the allochthonous materials and basin sediment. Gravity data were collected by research vessels over the area in 2012 2017. After corrections of drift and Etovos effects, absolute gravity, free-air and Bouguer gravity anomalies were calculated. The gravity data do not always show anomalies directly on MVs over the northern basin, thus suggesting that larger diapirs which have gravity contrast over a few milli-Gals do not exist below most of MVs in this basin. Instead, a large negative gravity anomaly is found at the northeastern end of the Kumano Basin. Localized positive anomalies exist along the KBEFZ in the area of theMV. The positive anomaly may suggest that an allochthonous high-density sediment body intrudes along the highly deformed, weak, fault zone.

Gravity anomalies and flexure of the lithosphere at the Middle Amazon Basin, Brazil

NASA Astrophysics Data System (ADS)

Nunn, Jeffrey A.; Aires, Jose R.

1988-01-01

The Middle Amazon Basin is a large Paleozoic sedimentary basin on the Amazonian craton in South America. It contains up to 7 km of mainly shallow water sediments. A chain of Bouguer gravity highs of approximately +40 to +90 mGals transects the basin roughly coincident with the axis of maximum thickness of sediment. The gravity highs are flanked on either side by gravity lows of approximately -40 mGals. The observed gravity anomalies can be explained by a steeply sided zone of high density in the lower crust varying in width from 100 to 200 km wide. Within this region, the continental crust has been intruded/replaced by more dense material to more than half its original thickness of 45-50 km. The much wider sedimentary basin results from regional compensation of the subsurface load and the subsequent load of accumulated sediments by flexure of the lithosphere. The observed geometry of the basin is consistent with an elastic lithosphere model with a mechanical thickness of 15-20 km. Although this value is lower than expected for a stable cratonic region of Early Proterozoic age, it is within the accepted range of effective elastic thicknesses for the earth. Rapid subsidence during the late Paleozoic may be evidence of a second tectonic event or lithospheric relaxation which could lower the effective mechanical thickness of the lithosphere. The high-density zone in the lower crust, as delineated by gravity and flexural modeling, has a complex sinuous geometry which is narrow and south of the axis of maximum sediment thickness on the east and west margins and wide and offset to the north in the center of the basin. The linear trough geometry of the basin itself is a result of smoothing by regional compensation of the load in the lower crust.

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.

Map showing free-air gravity anomalies off the western coast of Africa Senegal (south of 15° north latitude) to Sierra Leone

USGS Publications Warehouse

Folger, D.W.; Irwin, B.J.; McCullough, J.R.; Driscoll, G.R.; Polloni, C.F.

1990-01-01

This map is one of six in a series presenting marine gravity data off the western coast of Africa (fig. 1).  The data, collected by the U.S. Geological Survey (USGS) in 1987 in response to a request from the Defense Mapping Agency, are intended to improve gravity coverage where it has been insufficient or inadequate.  The information shown on this and the other three maps that cover the African coast represents a total of approximately 32,000 line kilometers of marine gravity data from Western Sahara south to Gabon.  This map includes data collected off the coasts of Senegal, Gambia, Guinea-Bissau, Guinea, and Sierra Leone from July 22 to August 20, 1987.

Present status of marine gravity

NASA Technical Reports Server (NTRS)

Watts, A. B.

1978-01-01

The technique of measuring gravity at sea was greatly improved by the development of spring-type surface-ship gravimeters which can be operated in a wide variety of sea conditions. A brief review of the most recent developments in marine gravity is presented. The extent of marine gravity data coverage is illustrated in a compilation map of the world's free-air gravity anomaly maps of the world's oceans. A brief discussion of some of the main results in the interpretation of marine gravity is given. Some comments made on recent determinations of the gravity field in oceanic regions using satellite radar altimeters are also presented.

Preliminary isostatic gravity map of the Grouse Creek and east part of the Jackpot 30 by 60 quadrangles, Box Elder County, Utah, and Cassia County, Idaho

USGS Publications Warehouse

Langenheim, Victoria; Willis, H.; Athens, N.D.; Chuchel, Bruce A.; Roza, J.; Hiscock, H.I.; Hardwick, C.L.; Kraushaar, S.M.; Knepprath, N.E.; Rosario, Jose J.

2013-01-01

A new isostatic residual gravity map of the northwest corner of Utah is based on compilation of preexisting data and new data collected by the Utah and United States Geological Surveys. Pronounced gravity lows occur over Junction, Grouse Creek, and upper Raft River Valleys, indicating significant thickness of low-density Tertiary sedimentary rocks and deposits. Gravity highs coincide with exposures of dense pre-Cenozoic rocks in the Raft River Mountains. Higher values in the eastern part of the map may be produced in part by deeper crustal density variations or crustal thinning. Steep linear gravity gradients coincide with mapped Neogene normal faults near Goose Creek and may define basin-bounding faults concealed beneath Junction and Upper Raft River Valleys.

The stochastic Beer-Lambert-Bouguer law for discontinuous vegetation canopies

NASA Astrophysics Data System (ADS)

Shabanov, N.; Gastellu-Etchegorry, J.-P.

2018-07-01

The 3D distribution of canopy foliage affects the radiation regime and retrievals of canopy biophysical parameters. The gap fraction is one primary indicator of a canopy structure. Historically the Beer-Lambert-Bouguer law and the linear mixture model have served as a basis for multiple technologies for retrievals of the gap (or vegetation) fraction and Leaf Area Index (LAI). The Beer-Lambert-Bouguer law is a form of the Radiative Transfer (RT) equation for homogeneous canopies, which was later adjusted for a correlation between fitoelements using concept of the clumping index. The Stochastic Radiative Transfer (SRT) approach has been developed specifically for heterogeneous canopies, however the approach lacks a proper model of the vegetation fraction. This study is focused on the implementation of the stochastic version of the Beer-Lambert-Bouguer law for heterogeneous canopies, featuring the following principles: 1) two mechanisms perform photon transport- transmission through the turbid medium of foliage crowns and direct streaming through canopy gaps, 2) the radiation field is influenced by a canopy structure (quantified by the statistical moments of a canopy structure) and a foliage density (quantified by the gap fraction as a function of LAI), 3) the notions of canopy transmittance and gap fraction are distinct. The derived stochastic Beer-Lambert-Bouguer law is consistent with the Geometrical Optical and Radiative Transfer (GORT) derivations. Analytical and numerical analysis of the stochastic Beer-Lambert-Bouguer law presented in this study provides the basis to reformulate widely used technologies for retrievals of the gap fraction and LAI from ground and satellite radiation measurements.

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.

High-resolution gravity model of Venus

NASA Technical Reports Server (NTRS)

Reasenberg, R. D.; Goldberg, Z. M.

1992-01-01

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 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 has been 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.

Interplate coupling along segments of the Central America Subduction zone

NASA Astrophysics Data System (ADS)

Zarifi, Zoya; Raeesi, Mohammad; Atakan, Kuvvet

2013-04-01

We analyzed 5 major earthquakes that occurred during 1992 to 2012 in a segment of the Central America subduction zone along the coasts of Guatemala and El Salvador. These events include 1992/09/02 (Mw 7.7), 1993/09/10 (Mw 7.2), 2001/01/13 (Mw 7.7), 2012/08/27 (Mw 7.3) and 2012/11/07 (Mw 7.3). We derived the asperities of these earthquakes using two completely independent methods of body-waveform inversion and a gravity-derived measure, Trench Parallel Bouguer Anomaly (TPBA). Using TPBA we discuss the status of interplate coupling along the segment and interpret each of the major earthquakes as a piece of the governing rupture process. We delineate the critical unbroken asperities along the segment that will likely generate great earthquake(s) in the future.

Results of Gravity Fieldwork Conducted in March 2008 in the Moapa Valley Region of Clark County, Nevada

USGS Publications Warehouse

Scheirer, Daniel S.; Andreasen, Arne Dossing

2008-01-01

In March 2008, we collected gravity data along 12 traverses across newly-mapped faults in the Moapa Valley region of Clark County, Nevada. In areas crossed by these faults, the traverses provide better definition of the gravity field and, thus, the density structure, than prior gravity observations. Access problems prohibited complete gravity coverage along all of the planned gravity traverses, and we added and adjusted the locations of traverses to maximize our data collection. Most of the traverses exhibit isostatic gravity anomalies that have gradients characteristic of exposed or buried faults, including several of the newly-mapped faults.

Isostatic gravity map of the Point Sur 30 x 60 quadrangle and adjacent areas, California

USGS Publications Warehouse

Watt, J.T.; Morin, R.L.; Langenheim, V.E.

2011-01-01

This isostatic residual gravity map is part of a regional effort to investigate the tectonics and water resources of the central Coast Range. This map serves as a basis for modeling the shape of basins and for determining the location and geometry of faults in the area. Local spatial variations in the Earth's gravity field (after removing variations caused by instrument drift, earth-tides, latitude, elevation, terrain, and deep crustal structure), as expressed by the isostatic anomaly, reflect the distribution of densities in the mid- to upper crust, which in turn can be related to rock type. Steep gradients in the isostatic gravity field often indicate lithologic or structural boundaries. Gravity highs reflect the Mesozoic granitic and Franciscan Complex basement rocks that comprise both the northwest-trending Santa Lucia and Gabilan Ranges, whereas gravity lows in Salinas Valley and the offshore basins reflect the thick accumulations of low-density alluvial and marine sediment. Gravity lows also occur where there are thick deposits of low-density Monterey Formation in the hills southeast of Arroyo Seco (>2 km, Marion, 1986). Within the map area, isostatic residual gravity values range from approximately -60 mGal offshore in the northern part of the Sur basin to approximately 22 mGal in the Santa Lucia Range.

Isostatic gravity map and principal facts for 694 gravity stations in Yellowstone National Park and vicinity, Wyoming, Montana, and Idaho

USGS Publications Warehouse

Carle, S.F.; Glen, J.M.; Langenheim, V.E.; Smith, R.B.; Oliver, H.W.

1990-01-01

The report presents the principal facts for gravity stations compiled for Yellowstone National Park and vicinity. The gravity data were compiled from three sources: Defense Mapping Agency, University of Utah, and U.S. Geological Survey. Part A of the report is a paper copy describing how the compilation was done and presenting the data in tabular format as well as a map; part B is a 5-1/4 inch floppy diskette containing only the data files in ASCII format. Requirements for part B: IBM PC or compatible, DOS v. 2.0 or higher. Files contained on this diskette: DOD.ISO -- File containing the principal facts of the 514 gravity stations obtained from the Defense Mapping Agency. The data are in Plouff format* (see file PFTAB.TEX). UTAH.ISO -- File containing the principal facts of 153 gravity stations obtained from the University of Utah. Data are in Plouff format. USGS.ISO -- File containing the principal facts of 27 gravity stations collected by the U.S. Geological Survey in July 1987. Data are in Plouff format. PFTAB.TXT -- File containing explanation of principal fact format. ACC.TXT -- File containing explanation of accuracy codes.

GOCE User Toolbox and Tutorial

NASA Astrophysics Data System (ADS)

Benveniste, Jérôme; Knudsen, Per

2016-07-01

The GOCE User Toolbox GUT is a compilation of tools for the utilisation and analysis of GOCE Level 2 products. GUT support applications in Geodesy, Oceanography and Solid Earth Physics. The GUT Tutorial provides information and guidance in how to use the toolbox for a variety of applications. GUT consists of a series of advanced computer routines that carry out the required computations. It may be used on Windows PCs, UNIX/Linux Workstations, and Mac. The toolbox is supported by The GUT Algorithm Description and User Guide and The GUT Install Guide. A set of a-priori data and models are made available as well. Without any doubt the development of the GOCE user toolbox have played a major role in paving the way to successful use of the GOCE data for oceanography. The GUT version 2.2 was released in April 2014 and beside some bug-fixes it adds the capability for the computation of Simple Bouguer Anomaly (Solid-Earth). During this fall a new GUT version 3 has been released. GUTv3 was further developed through a collaborative effort where the scientific communities participate aiming on an implementation of remaining functionalities facilitating a wider span of research in the fields of Geodesy, Oceanography and Solid earth studies. Accordingly, the GUT version 3 has: - An attractive and easy to use Graphic User Interface (GUI) for the toolbox, - Enhance the toolbox with some further software functionalities such as to facilitate the use of gradients, anisotropic diffusive filtering and computation of Bouguer and isostatic gravity anomalies. - An associated GUT VCM tool for analyzing the GOCE variance covariance matrices.

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 cracking models for the origin of gravity lineaments and associated volcanic ridges, favoring models with a dynamic mantle component such as small-scale convection or channelized asthenospheric return flow. Copyright 2006 by the American Geophysical Union.

Isostatic gravity map of Yukon Flats, east-central Alaska

USGS Publications Warehouse

Morin, Robert L.

2002-01-01

The gravity data used to make this map were collected between 1959 and 1984. The data were collected by automobile, aircraft, and watercraft. Most of the data were collected as part of a U.S. Geological Survey (USGS) regional gravity data collection project. Some of the data were collected as part of other USGS local projects. One data set was collected by the NGS (National Geodetic Survey). This map ranges from 65° to 68° N latitude and 141° to 152° W longitude. The names of the 12 1:250,000-scale U.S. Geological Survey quadrangle maps that make up this map are labeled on the map. The western edge of the map is 1 degree of longitude east of the edge of the three most western quadrangles.

Isostatic models and isostatic gravity anomalies of the Arabian plate and surroundings

NASA Astrophysics Data System (ADS)

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

2015-04-01

Isostaic anomalies represent one of the most useful "geological" reduction 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. This correction is based on the fact that a major part of the near-surface load is compensated by variations of the lithosphere boundaries (chiefly the Moho and LAB) and by density variations within the crust and upper mantle. It is usually supposed that it is less important to a first order, what is the actual compensation model when reducing the effect of compensating masses, since their total weight is exactly opposite to the near-surface load. We compare several compensating models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which can not be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also the predicted "isostatic" Moho is very different from the existing observations. The second group of the isostatic models includes the Moho, which is based on existing seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). In this way we minimize regional anomalies over the Arabian plate. The residual local anomalies well correspond to tectonic structure of the plate. Still very significant anomalies are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

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.

The thickness of cover sequences in the Western Desert of Iraq from a power spectrum analysis of gravity and magnetic data

NASA Astrophysics Data System (ADS)

Mousa, Ahmed; Mickus, Kevin; Al-Rahim, Ali

2017-05-01

The Western Desert of Iraq is part of the stable shelf region on the Arabian Plate where the subsurface structural makeup is relatively unknown due to the lack of cropping out rocks, deep drill holes and deep seismic refraction and reflection profiles. To remedy this situation, magnetic and gravity data were analyzed to determine the thickness of the Phanerozoic cover sequences. The 2-D power spectrum method was used to estimate the depth to density and magnetic susceptibility interfaces by using 0.5° square windows. Additionally, the gravity data were analyzed using isostatic residual and decompensative methods to isolate gravity anomalies due to upper crustal density sources. The decompensative gravity anomaly and the differentially reduced to the pole magnetic map indicate a series of mainly north-south and northwest-southeast trending maxima and minima anomalies related to Proterozoic basement lithologies and the varying thickness of cover sequences. The magnetic and gravity derived thickness of cover sequences maps indicate that these thicknesses range from 4.5 to 11.5 km. Both maps in general are in agreement but more detail in the cover thicknesses was determined by the gravity analysis. The gravity-based cover thickness maps indicates regions with shallower depths than the magnetic-based cover thickness t map which may be due to density differences between limestone and shale units within the Paleozoic sediments. The final thickness maps indicate that the Western Desert is a complicated region of basins and uplifts that are more complex than have been shown on previous structural maps of the Western Desert. These basins and uplifts may be related to Paleozoic compressional tectonic events and possibly to the opening of the Tethys Ocean. In addition, petroleum exploration could be extended to three basins outlined by our analysis within the relatively unexplored western portions of the Western Desert.

Towards the map of quantum gravity

NASA Astrophysics Data System (ADS)

Mielczarek, Jakub; Trześniewski, Tomasz

2018-06-01

In this paper we point out some possible links between different approaches to quantum gravity and theories of the Planck scale physics. In particular, connections between loop quantum gravity, causal dynamical triangulations, Hořava-Lifshitz gravity, asymptotic safety scenario, Quantum Graphity, deformations of relativistic symmetries and nonlinear phase space models are discussed. The main focus is on quantum deformations of the Hypersurface Deformations Algebra and Poincaré algebra, nonlinear structure of phase space, the running dimension of spacetime and nontrivial phase diagram of quantum gravity. We present an attempt to arrange the observed relations in the form of a graph, highlighting different aspects of quantum gravity. The analysis is performed in the spirit of a mind map, which represents the architectural approach to the studied theory, being a natural way to describe the properties of a complex system. We hope that the constructed graphs (maps) will turn out to be helpful in uncovering the global picture of quantum gravity as a particular complex system and serve as a useful guide for the researchers.

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, Kevin; 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.

USSR Report, Earth Sciences, No. 24

DTIC Science & Technology

1983-02-01

In investigating the gas and aerosol components of the atmosphere it is common to use the Bouguer method, employing the radiation flux in the...the direction to the sun and the relative error in determining the optical thickness of the atmosphere by the Bouguer method does not exceed 1

Using Gravity and Topography to Map Mars' Crustal Thickness

NASA Image and Video Library

2016-03-21

Newly detailed mapping of local variations in Mars' gravitational pull on orbiters (center), combined with topographical mapping of the planet's mountains and valleys (left) yields the best-yet mapping of Mars' crustal thickness (right). These three views of global mapping are centered at 90 degrees west longitude, showing portions of the planet that include tall volcanoes on the left and the deep Valles Marineris canyon system just right of center. Additional views of these global maps are available at http://svs.gsfc.nasa.gov/goto?4436. The new map of Mars' gravity (center) results from analysis of the planet's gravitational effects on orbiters passing over each location on the globe. The data come from many years of using NASA's Deep Space Network to track positions and velocities of NASA's Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter. If Mars were a perfectly smooth sphere of uniform density, the gravity experienced by the spacecraft would be exactly the same everywhere. But like other rocky bodies in the solar system, including Earth, Mars has both a bumpy surface and a lumpy interior. As the spacecraft fly in their orbits, they experience slight variations in gravity caused by both of these irregularities, variations which show up as small changes in the velocity and altitude of the three spacecraft. The "free-air" gravity map presents the results without any adjustment for the known bumpiness of Mars' surface. Local gravitational variations in acceleration are expressed in units called gals or galileos. The color-coding key beneath the center map indicates how colors on the map correspond to mGal (milligal) values. The map on the left shows the known bumpiness, or topography, of the Martian surface, using data from the Mars Orbiter Laser Altimeter (MOLA) instrument on Mars Global Surveyor. Mars has no actual "sea level," but does have a defined zero elevation level. The color-coding key beneath this map indicates how the colors correspond to elevations above or below zero, in kilometers. Analysis that subtracts effects of the surface topography from the free-air gravity mapping, combined with an assumption that crust material has a uniform density, leads to the derived mapping of crustal thickness -- or subsurface "lumpiness" -- on the right. Highs in gravity indicate places where the denser mantle material beneath the crust is closer to the surface, and hence where the crust is thinner. The color-coding key for this map indicates how the colors on the map correspond to the thickness of the crust, in kilometers. http://photojournal.jpl.nasa.gov/catalog/PIA20277

Multidisciplinary exploration of the Tendaho Graben geothermal fields

NASA Astrophysics Data System (ADS)

Armadillo, Egidio; Rizzello, Daniele; Verdoya, Massimo; Pasqua, Claudio; Marini, Luigi; Meqbel, Naser; Stimac, Jim; Kebede, Solomon; Mengiste, Andarge; Hailegiorgis, Getenesch; Abera, Fitsum; Mengesha, Kebede

2017-04-01

The NW-SE trending Tendaho Graben is the major extensional feature of the Afar, Ethiopia. Rifting and volcanic activity within the graben occurred mostly between 1.8 and 0.6 Ma, but extended to at least 0.2 Ma. Very recent (0.22- 0.03 Ma) activity is focused along the southern part of the younger and active Manda Hararo Rift, which is included in the north-western part of the graben. Extension gave rise to about 1600 m of vertical displacement (verified by drilling) of the basaltic Afar Stratoid sequence, over a crust with a mean thickness of about 23 km. The infill of graben, overlying the Stratoids, consists of volcanic and sedimentary deposits that have been drilled by six exploratory wells. Within the graben, two main geothermal fields have been explored by intensive geological, geochemical and geophysical surveys over an area that approximately covers a square sector of 40x40 km. Both new and existing data sets have been integrated. The Dubti-Ayrobera system is located along the central axis of the graben. Available data, acquired in the last three decades, comprise more than two thousands gravity and magnetic stations, 229 magnetotelluric stations and structural-geological and geochemical observations. The Alalobeda system is located along the SW flank of the graben, at about 25 km from the Dubti-Ayrobera system and has been very recently studied by means of gravimetric (300 stations), magnetotelluric and TDEM (140 stations) geological and geochemical surveys. The new residual magnetic anomaly map has been used to map the younger normal polarity basalt distribution and infer the location of the unknown main rift axis. The bedrock surface resulting by the 3D inversion of the new residual Bouguer anomaly enlightens the main normal faults hindered by sediments and the secondary structures represented by horsts and grabens. The three-dimensional resistivity models allow mapping the sedimentary infill of the graben, fracture zones in the Afar Stradoids bedrock and the dome-shape structure of the clay cap layer. The 2D and 3D gravimetric, magnetic and resistivity models have been integrated with the structural, geological and geochemical outcomings in order to get an updated conceptual model of the geothermal systems.

Chern-Simons expectation values and quantum horizons from loop quantum gravity and the Duflo map.

PubMed

Sahlmann, Hanno; Thiemann, Thomas

2012-03-16

We report on a new approach to the calculation of Chern-Simons theory expectation values, using the mathematical underpinnings of loop quantum gravity, as well as the Duflo map, a quantization map for functions on Lie algebras. These new developments can be used in the quantum theory for certain types of black hole horizons, and they may offer new insights for loop quantum gravity, Chern-Simons theory and the theory of quantum groups.

Tectonics at the Southeast Indian Ridge 79 to 99 E. Results from the GEISEIR cruises

NASA Astrophysics Data System (ADS)

Briais, A.; Hemond, C.; Maia, M. A.; Hanan, B. B.; Graham, D. W.; Geiseir Scientific Team; Geiseir2 Scientific Team

2011-12-01

During the GEISEIR (Géochimie Isotopique de la SEIR) and GEISEIR2 cruises on N/O Marion Dufresne in 2009 and 2010, we collected geophysical data, high-density wax-core or dredge basalt samples, and water column profiles along the Southeast Indian Ridge (SEIR) between 79E and 99E. This section of the intermediate-spreading SEIR is located between the St Paul-Amsterdam hotspot plateau and the Australia-Antarctic Discordance. We completed the multibeam bathymetry mapping of the axis and transform faults of the 79-88E and the 96-99E sections, and mapped the axial zone and discontinuities of the 88-96E section up to 800 kyr. These ridge sections were sampled at 20 km, 5 km and 10 km spacing, respectively. This presentation focusses on the results of a structural and geophysical analysis of the axial domain and the off-axis area up to 800 kyr. We merged the bathymetry data collected during the GEISEIR and GEISEIR2 cruises with those of the previous (Westward 9 and 10 and Boomerang 6) cruises. We also compiled the shipborne gravity data and estimated mantle Bouguer anomalies (MBA). The ridge displays large variations in axial depth and morphology, from a rifted axial high to an axial valley, at the scale of ridge segments. Ridge offsets vary in morphology from overlapping-spreading centers, to propagating rifts, to transform faults. Shalllow segments have pronounced axial MBA lows, probably resulting from a thicker ocean crust, and the presence of hotter mantle beneath the ridge axis. Water-column profiling at each wax-core sampling site reveals numerous moderate to strong signals of hydrothermal activity. The distribution of the hydrothermal vent signals does not always coincide with the magmatic robustness of the ridge axis, suggesting that tectonic activity also controls the vent setting. The recent evolution of the ridge discontinuities is marked by southeastward propagators at 92E and 95E, and by the eastward migration of the 96E transform fault. These areas correspond to relatively high MBA suggestive of thin crust. Some transform faults also appear to have changed orientation, and show intra-transform ridges suggestive of compressive deformation. The ridge flanks show large off-axis seamounts and seamount chains, clearly observed in the satellite-derived gravity maps. We mapped and sampled some of these seamounts. The ridge sections showing the most robust morphology are sometimes associated with off-axis seamounts, but some seamounts also occur close to relatively starved axial areas. These structural and geophysical observations of the SEIR suggest a much larger variety of ridge processes and discontinuity evolution than predicted from the intermediate-spreading rate quasi-constant along the surveyed axis. GEISEIR cruise scientific team: Claire Bassoulet, Dass Bissessur, Erwan Cambrai, Mathieu Clog, Céline Dantas, Ludovic Menjot, Emanuele Paganelli, Fabienne de Parseval, Marc Ulrich. GEISEIR2 cruise scientific team: Erwan Cambrai, Romain Chateau, Cédric Hamelin, Jabrane Labidi, Maximilliano Melchiorre, Ludovic Menjot, Emanuele Paganelli.

Venus gravity - Analysis of Beta Regio

NASA Technical Reports Server (NTRS)

Esposito, P. B.; Sjogren, W. L.; Mottinger, N. A.; Bills, B. G.; Abbott, E.

1982-01-01

Radio tracking data acquired over Beta Regio were analyzed to obtain a surface mass distribution from which a detailed vertical gravity field was derived. In addition, a corresponding vertical gravity field was evaluated solely from the topography of the Beta region. A comparison of these two maps confirms the strong correlation between gravity and topography which was previously seen in line-of-sight gravity maps. It also demonstrates that the observed gravity is a significant fraction of that predicted from the topography alone. The effective depth of complete isostatic compensation for the Beta region is estimated to be 330 km, which is somewhat deeper than that found for other areas of Venus.

Isostatic gravity map of the Death Valley ground-water model area, Nevada and California

USGS Publications Warehouse

Ponce, D.A.; Blakely, R.J.; Morin, R.L.; Mankinen, E.A.

2001-01-01

An isostatic gravity map of the Death Valley groundwater model area was prepared from over 40,0000 gravity stations as part of an interagency effort by the U.S. Geological Survey and the U.S. Department of Energy to help characterize the geology and hydrology of southwest Nevada and parts of California.

Feasibility of Shipboard Laser-Attenuation Measurements With a Portable Transmissometer.

DTIC Science & Technology

1979-02-26

Aerosol Extinction The transmittance of monochromatic, single-scattered light through aerosol is given by - S the Bouguer .-Beer law, (1) o where is the...of Applicability of the Bouguer Law in Scattering Media for Collimated Light Beams,” (English trans.), Izu. Atm. and Oceanic Phys. 3, 724-732 (1967

Spatial variations in isostatic compensation mechanisms of the Ninetyeast Ridge and their tectonic significance

NASA Astrophysics Data System (ADS)

Sreejith, K. M.; Krishna, K. S.

2013-10-01

Ninetyeast Ridge (NER), one of the longest linear volcanic features on the Earth, offers an excellent opportunity of understanding the isostatic response to the interactions of mantle plume with the migrating mid-ocean ridge. Bathymetry, geoid, and gravity (shipborne and satellite) data along 72 closely spaced transects and 17 overlapping grids on the NER are analyzed and modeled to determine the effective elastic thickness (Te) beneath the entire ridge. The results of 2-D and 3-D flexural modeling of the NER show large spatial variations in Te values ranging from 4 to 35 km, suggesting that the ridge was compensated along its length by different isostatic mechanisms. The southern (south of 22°S latitude) and northern (north of 2°N latitude) parts of the NER have Te values of >10 and >23 km, respectively, revealing that the southern part was emplaced on a lithosphere of intermediate strength possibly on flank of the Indian plate, whereas the northern part was emplaced in an intraplate setting. In contrast, in the central part of the NER (between latitudes 22°S and 2°N), highly variable Te values (4-22 km) are estimated. The scattered Te values in the central NER suggest that this part may have evolved due to the occurrence of frequent ridge jumps caused by the interaction of Kerguelen hot spot with rapid northward migration of the Wharton spreading ridge. Residual Mantle Bouguer Anomaly (RMBA) map of the NER and adjacent basins reveals that the entire length of the NER is associated with a significant negative anomaly up to 200 mGal, indicating the presence of thickened crust or less dense mantle beneath the ridge. 3-D crustal thickness map of the NER, generated by inversion of the RMBA data, shows a thick crust ranging from 15 to 19 km. The present study clearly shows that NER possesses a highly segmented isostatic pattern with the occurrence of subcrustal underplating or subsurface loading.

Isostatic Gravity Map with Geology of the Santa Ana 30' x 60' Quadrangle, Southern California

USGS Publications Warehouse

Langenheim, V.E.; Lee, Tien-Chang; Biehler, Shawn; Jachens, R.C.; Morton, D.M.

2006-01-01

This report presents an updated isostatic gravity map, with an accompanying discussion of the geologic significance of gravity anomalies in the Santa Ana 30 by 60 minute quadrangle, southern California. Comparison and analysis of the gravity field with mapped geology indicates the configuration of structures bounding the Los Angeles Basin, geometry of basins developed within the Elsinore and San Jacinto Fault zones, and a probable Pliocene drainage network carved into the bedrock of the Perris block. Total cumulative horizontal displacement on the Elsinore Fault derived from analysis of the length of strike-slip basins within the fault zone is about 5-12 km and is consistent with previously published estimates derived from other sources of information. This report also presents a map of density variations within pre-Cenozoic metamorphic and igneous basement rocks. Analysis of basement gravity patterns across the Elsinore Fault zone suggests 6-10 km of right-lateral displacement. A high-amplitude basement gravity high is present over the San Joaquin Hills and is most likely caused by Peninsular Ranges gabbro and/or Tertiary mafic intrusion. A major basement gravity gradient coincides with the San Jacinto Fault zone and marked magnetic, seismic-velocity, and isotopic gradients that reflect a discontinuity within the Peninsular Ranges batholith in the northeast corner of the quadrangle.

On the gravitational potential and field anomalies due to thin mass layers

NASA Technical Reports Server (NTRS)

Ockendon, J. R.; Turcotte, D. L.

1977-01-01

The gravitational potential and field anomalies for thin mass layers are derived using the technique of matched asymptotic expansions. An inner solution is obtained using an expansion in powers of the thickness and it is shown that the outer solution is given by a surface distribution of mass sources and dipoles. Coefficients are evaluated by matching the inner expansion of the outer solution with the outer expansion of the inner solution. The leading term in the inner expansion for the normal gravitational field gives the Bouguer formula. The leading term in the expansion for the gravitational potential gives an expression for the perturbation to the geoid. The predictions given by this term are compared with measurements by satellite altimetry. The second-order terms in the expansion for the gravitational field are required to predict the gravity anomaly at a continental margin. The results are compared with observations.

Magnetic and gravity anomalies in the Sierra del Padre and Sierra del Tala, San Luis Province, Argentina: evidence of buried mafic ultramafic rocks

NASA Astrophysics Data System (ADS)

Kostadinoff, José; Alfredo Bjerg, Ernesto; Gregori, Daniel; Delpino, Sergio; Dimieri, Luis; Raniolo, Ariel; Mogessie, Aberra; Hoinkes, Georg; Hauzenberger, Christoph; Felfernig, Anja

2001-07-01

This paper presents the results of a geophysical study of the southern portion of the Sierra Grande de San Luis, San Luis Province, Argentina. A 26 mGal amplitude Bouguer anomaly (Charlone anomaly), measuring 40 km long by 7 km wide, between Sierra de los Padres and Zanjitas reflects the presence of high-density rocks located at approximately 2000 m depth. Geophysical models based on more than 300 gravimetric, magnetometric, and geological field measurements and observations suggest that the mafic-ultramafic belt of Sierra Grande de San Luis continues south of San Luis. The low magnitude of the terrestrial magnetic field anomalies indicates that these mafic-ultramafic rocks do not carry a base metal sulfides (BMS) mineralization. The Charlone gravimetric anomaly is generated by a belt of mafic- ultramafic rocks whose amplitude is comparable with that responsible for the Virorco-Las Aguilas gravimetric anomaly.

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 surveys were conducted at the closed Benson Mines magnetite mine and the Zinc Mines at Balmat, New York. The gravity and magnetic anomalies at Benson Mines indicate that significant amounts of magnetite remain in the subsurface and the steep gradients indicate a shallow depth. A gravity high of 35 gravity units in the Sylvia Lake Zinc District at Balmat, New York occurs over the upper marble and a 100 gu anomaly occurs just northeast of the zinc district. Abandoned natural gas fields exist along the southern and southwestern boundary of the Tug Hill Plateau. Gravity surveys were conducted in the vicinity of three of these gas fields in the Tug Hill Plateau (Camden, Sandy Creek and Pulaski). The Tug Hill Plateau is thought to be an uplifted-fault-bounded block which, if correct, might account for the existence of those gas fields. The trends of the gravity contours on the gravity maps lends credence to the fault interpretation. Also gravity and magnetic traverses were conducted across faults in the Trenton-Black River. These traverses show gravity anomalies across the faults which indicate control by faulting in the Precambrian.

GRAIL Final Resting Spot

NASA Image and Video Library

2012-12-13

These maps of Earth moon highlight the region where the twin spacecraft of NASA Gravity Recovery and Interior Laboratory GRAIL mission will impact on Dec. 17, marking the end of its successful endeavor to map the moon gravity.

Ultrashort Laser Pulse Propagation in Water

DTIC Science & Technology

2011-09-30

Beer behavior ( It should be noted that the so called Lambert-Beer law was first discovered by Pierre Bouguer in his published work in 1729 titled...Essai d’optique sur la gradation de la lumiére and we will hereafter refer to it as the Bouguer -Lambert-Beer Law or BLB. The law is valid for

Ultrashort Laser Pulse Propagation in Water

DTIC Science & Technology

2009-01-01

It should be noted that the so called Lambert-Beer law was first discovered by Pierre Bouguer in his published work in 1729 titled Essai d’optique...sur la gradation de la lumiére and we will hereafter refer to it as the Bouguer -Lambert-Beer Law or BLB. The law is valid for monochromatic sources

Gravity and magnetic anomaly data analysis

NASA Technical Reports Server (NTRS)

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

1982-01-01

Progress on the analysis MAGSAT data is reported. The MAGSAT data from 40 deg S to 70 deg N latitude and 30 deg W to 60 E longitude was reduced to radial polarization. In addition, gravity anomaly data from this area were processed and a variety of filtered maps were prepared for combined interpretation of the gravity and magnetic data in conjunction with structural and tectonic maps of the area. The VERSATEC listings and cross-reference maps of variable and array names for the spherical Earth analysis programs NVERTSM, SMFLD, NVERTG, and GFLD were also prepared.

Application of isostatic gravity anomaly in the Yellow Sea area

NASA Astrophysics Data System (ADS)

Hao, Z.; Qin, J.; Huang, W.; Wu, X.

2017-12-01

In order to study the deep crustal structure of the Yellow Sea area, we used the Airy-Heiskanen model to calculate the isostatic gravity anomaly of this area. Based on the Bouguer gravity anomaly and water depth data of this area, we chose the calculating parameters as standard crustal thickness 30 km, crust-mantle density difference 0.6g/cm3and grid spacing 0.1°×0.1°. This study reveals that there are six faults and four isostatic negative anomalies in the study area. The isostatic anomalies in much of Yellow Sea areas give priority to those with positive anomalies. The isostatic anomalies in North Yellow Sea are higher than South Yellow Sea with Jiashan-Xiangshui fault as the boundary. In the north of the study area, isostatic anomalies are characterized by large areas of positive anomaly. The change is relatively slow, and the trends give priority to the trend NE or NEE. In the middle of the north Yellow Sea basin, there is a local negative anomaly, arranged as a string of beads in NE to discontinuous distribution. Negative anomaly range is small, basically corresponds to the region's former Cenozoic sedimentary basin position. To the south of Jiashan-Xiangshui fault and west of Yellow Sea eastern margin fault, including most of the south Yellow Sea and Jiangsu province, the isostatic anomalies are lower. And the positive and negative anomalies are alternative distribution, and negative anomaly trap in extensive development. The trends give priority to NE, NEE, both to the NW. On the basis of the characteristics of isostatic gravity anomalies, it is concluded that the Yellow Sea belongs to continental crustal isostatic area whose isostatic anomalies is smooth and slow. ReferencesHeiskanen, W. A., F. A. V. Meinesz, and S. A. Korff (1958), The Earth and Its Gravity Field, McGraw-Hill, New York. Meng, X. J., X. H. Zhang, and J. Y. Yang (2014), Geophysical survey in eastern China seas and the characteristics of gravity and magnetic fields, Marine Geoglogy & Quaternary Geology, 34(6), 127-134.

An integrated geophysical study of north African and Mediterranean lithospheric structure

NASA Astrophysics Data System (ADS)

Dial, Paul Joseph

1998-07-01

This dissertation utilizes gravity and seismic waveform modeling techniques to: (1) determine models of lithospheric structure across northern African through gravity modeling and (2) determine lithospheric and crustal structure and seismic wave propagation characteristics across northern Africa and the Mediterranean region. The purpose of the gravity investigation was to construct models of lithospheric structure across northern Africa through the analysis of gravity data constrained by previous geological and geophysical studies. Three lithospheric models were constructed from Bouguer gravity data using computer modeling, and the gravity data was wavelength-filtered to investigate the relative depth and extent of the structures associated with the major anomalies. In the Atlas Mountains area, the resulting earth models showed slightly greater crustal thickness than those of previous studies if a low density mantle region is not included in the models. However, if a low density mantle region (density = 3.25 g/cm3) was included beneath the Atlas, the earth models showed little crustal thickening (38 km), in accord with previous seismic studies. The second portion of the research consisted of seismic waveform modeling of regional and teleseismic events to determine crustal and lithospheric structure across northern Africa and the Mediterranean. A total of 174 seismograms (145 at regional distances (200--1400 km) and 29 with epicentral distances exceeding 1900 km) were modeled using 1-D velocity models and a reflectivity code. At regional distances from four stations surrounding the western Mediterranean basin (MAL, TOL, PTO and AQU) and one station near the Red Sea (HLW), 1-D velocity models can satisfactorily model the relative amplitudes of both the Pnl and surface wave portions of the seismograms. Modeling of propagation paths greater than 1900 km was also conducted across northern Africa and the Mediterranean. The results indicate that the S-wave velocity model of Corchete et al. (1995) is more appropriate for the Iberian Peninsula, southwestern Mediterranean basin and northwest African coast than the other models tested. This model was better able to predict both the timing and amplitudes of the observed Sn and surface wave components on the observed seismograms. (Abstract shortened by UMI.)

Isostatic and Decompensative Gravity Anomalies of the Arabian Plate and Surrounding Regions: a Key for the Crustal Structure

NASA Astrophysics Data System (ADS)

Kaban, M. K.; El Khrepy, S.; Al-Arifi, N. S.

2016-12-01

The isostatic anomalies are often considered as one of the most useful correction of the gravity field for investigation of the upper crust structure in many practical applications. By applying this correction, a substantial part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomaly, can be removed. With this approach, it is not even necessary to know the deep density structure of the crust and upper mantle in details; it is sufficient to prescribe some type of compensation (regional vs. local) and a compensation depth. However, even when all the parameters are chosen correctly, this reduction of the gravity field does not show the full gravity effect of unknown anomalies in the crust. The last ones should be also compensated to some extent; therefore their impact is substantially reduced by the isostatic compensation. Long ago (Cordell et al., 1991), it was suggested a so-called decompensative correction of the isostatic anomalies, which provides a possibility to separate these effects. However, the decompensative correction is very sensitive to the parameters of the compensation scheme. In the present study we analyse the ways to choose these parameters and extend this approach by assuming a possibility for the regional compensation via elastic deformations of the lithosphere. Based on this technique, we estimate the isostatic and decompensative anomalies for the Arabian plate and surrounding regions. The parameters of the isostatic model are chosen based on previous studies. It was demonstrated that the decompensative correction is very significant at the mid-range wavelengths and may exceed 100 mGal, therefore ignoring this effect would lead to wrong conclusions about the upper crust structure. The total amplitude of the decompensative anomalies reaches ±250 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. Cordell, L., Zorin, Y. A., & Keller, G. R. (1991). The decompensative gravity anomaly and deep structure of the region of the Rio Grande rift. Journal of Geophysical Research: Solid Earth (1978-2012), 96(B4), 6557-6568.

Geophysical investigation of the Raton Basin

NASA Astrophysics Data System (ADS)

Cheney, R. S.

1982-05-01

This thesis correlates gravity, magnetic, and seismic data for the Raton Basin of Colorado and New Mexico. The gravity data suggest that the study area, and the region around it, is in isostatic equilibrium. The free air anomaly in the southern portion of the study area suggests lack of local compensation due to Quaternary volocanic rock. The volcanic rock thickness, calculated from the free air gravity data, is 180 m. The gravity data indicated a crustal thickness of about 45 km, and the crust thinned from west to east. A basement relief map was constructed from the Bouquer gravity data. Computer techniques were developed to calculate the depth to the basement surface and to plot a contour map of that surface. The Raton Basin magnetic map defined the same surface found on the basement relief map since the overlying sedimentary rocks have no magnetism; therefore, any magnetism present is caused by the basement rock. A seismic survey near capulin Mountain detected a high level of microseismicity that may be caused by adjustment along faults or dormant volcanic activity.

Integrated 3D density modelling and segmentation of the Dead Sea Transform

NASA Astrophysics Data System (ADS)

Götze, H.-J.; El-Kelani, R.; Schmidt, S.; Rybakov, M.; Hassouneh, M.; Förster, H.-J.; Ebbing, J.

2007-04-01

A 3D interpretation of the newly compiled Bouguer anomaly in the area of the “Dead Sea Rift” is presented. A high-resolution 3D model constrained with the seismic results reveals the crustal thickness and density distribution beneath the Arava/Araba Valley (AV), the region between the Dead Sea and the Gulf of Aqaba/Elat. The Bouguer anomalies along the axial portion of the AV, as deduced from the modelling results, are mainly caused by deep-seated sedimentary basins ( D > 10 km). An inferred zone of intrusion coincides with the maximum gravity anomaly on the eastern flank of the AV. The intrusion is displaced at different sectors along the NNW-SSE direction. The zone of maximum crustal thinning (depth 30 km) is attained in the western sector at the Mediterranean. The southeastern plateau, on the other hand, shows by far the largest crustal thickness of the region (38-42 km). Linked to the left lateral movement of approx. 105 km at the boundary between the African and Arabian plate, and constrained with recent seismic data, a small asymmetric topography of the Moho beneath the Dead Sea Transform (DST) was modelled. The thickness and density of the crust suggest that the AV is underlain by continental crust. The deep basins, the relatively large intrusion and the asymmetric topography of the Moho lead to the conclusion that a small-scale asthenospheric upwelling could be responsible for the thinning of the crust and subsequent creation of the Dead Sea basin during the left lateral movement. A clear segmentation along the strike of the DST was obtained by curvature analysis: the northern part in the neighbourhood of the Dead Sea is characterised by high curvature of the residual gravity field. Flexural rigidity calculations result in very low values of effective elastic lithospheric thickness ( t e < 5 km). This points to decoupling of crust in the Dead Sea area. In the central, AV the curvature is less pronounced and t e increases to approximately 10 km. Curvature is high again in the southernmost part near the Aqaba region. Solutions of Euler deconvolution were visualised together with modelled density bodies and fit very well into the density model structures.

Tectonic environments and local geologic controls of potential hydrothermal fields along the Southern Mid-Atlantic Ridge (12-14°S)

NASA Astrophysics Data System (ADS)

Li, Bing; Shi, Xuefa; Wang, Jixin; Yan, Quanshu; Liu, Chenguang; DY125-21 (Leg 3) Science Party; DY125-22 (Legs 2-5) Science Party; DY125-26 (Leg 3) Science Party

2018-05-01

Systematic hydrothermal exploration and multi-beam bathymetry mapping have been conducted along a 220-km-long section of the Southern Mid-Atlantic Ridge (SMAR) from 12°S (Bode Verde Fracture Zone) to 14°S (Cardno Fracture Zone), and previously reported deposits (Tao et al., 2011) are now being thoroughly investigated. Here, we present the characterization of three possible hydrothermal fields, a complete bathymetry data set of the ridge segment, gravity data, and the petrologic characteristics of collected rock samples. The magmatism characteristics, evolution of the ridge segment, and the local geological controls of the possible hydrothermal fields are then discussed. The studied segment can be divided into two segments by a Non-Transform Discontinuity (NTD). Our morphotectonic analysis shows significant along-axis heterogeneity in the surveyed segments: three distinctive cross-axis grabens were identified in the northern segment, and two were identified in the southern segment. Moreover, based on the gravity data (a relatively low spherical Bouguer anomaly) and petrologic data (low Mg# values and relatively low FeO and relatively high Al2O3 and CaO contents compared to nearby seafloor samples), a volcanic feature, the ZouYu seamount, on this segment is considered to be associated with strong magmatic activity, and the magmatic activity of the inside corner at the southern end of the segment has increased and decreased. The three possible hydrothermal fields occur in different local geological settings: a shallow magmatic seamount (ZouYu), an NTD (TaiJi), and an inside-corner high (CaiFan). These potential hydrothermal fields are significantly different from other fields in similar tectonic settings in terms of local geologic controls and products. The ZouYu field is primarily related to a newly formed cone, resulting in the production of sulfides, and differs from other fields on shallow magmatic seamounts. The TaiJi field is largely controlled by the tectonic evolution of the NTD and is based on mafic rocks. The inside corner containing the CaiFan field is a magmatic seamount rather than an Ocean Core Complex, making it strikingly different from other inside corner-related fields.

Geophysical reassessment of the role of ancient crustal structures on the development of western Laurentia and Selwyn Basin, Yukon and Northwest Territories, Canada.

NASA Astrophysics Data System (ADS)

Hayward, N.

2017-12-01

The structure of the western margin of the North American craton (Laurentia) in the northern Canadian Cordillera and its role in the development of the Neoproterozoic-Early Paleozoic Selwyn Basin are reassessed through 3D inversion of a new compilation of aeromagnetic data and archival Bouguer gravity data. The region's tectonic history is obscured by partial burial beneath Selwyn Basin, and a tectonic overprint that includes terrane accretion, regional plutonism, and strike-slip faults with displacements of 100s and perhaps 1000s of kilometers. Despite the implied complexity, preliminary geological and geophysical based interpretations of the structure of the western margin of Laurentia, have been adopted with few refinements in over two decades. Regionally continuous, NE-trending, crustal lineaments, including the Fort Norman line and Leith Ridge fault, were interpreted as having had long-standing influence on the craton development, its western margin, and overlapping sedimentary basin. New results reveal limited evidence for the regional continuity of the NE-trending lineaments. Instead, models suggest that the structure of the Laurentian margin is characterised by segmentation on numerous shorter structures of varied strike. The western margin of the craton and its structures are bound by a NW-trending structure that connects with the Richardson Trough to the north and may have been active during rifting of the Misty Creek embayment. This boundary also marks the easternmost limit of both granitic intrusions in Selwyn Basin, which gravity models suggest are of greater extent than reflected on geological maps, and SEDEX occurrences. An ENE-trending structure beneath northern Selwyn Basin is interpreted as marking the southern edge of a previously unidentified cratonic promontory, akin to the Liard line that marks a transfer fault that bounds the promontory of the Macdonald Platform, south of Selwyn Basin. The ENE-trending structure is traced from the Tintina fault in the west to near to the Great Bear magmatic zone. The structure's regional continuity also limits the interpretation of a post-Cretaceous structure, inboard of the Tintina fault that could be responsible for 1000's km of dextral strike-slip ascribed to the Baja-BC terrane translation model.

GOCE User Toolbox and Tutorial

NASA Astrophysics Data System (ADS)

Knudsen, Per; Benveniste, Jerome

2017-04-01

The GOCE User Toolbox GUT is a compilation of tools for the utilisation and analysis of GOCE Level 2 products.
GUT support applications in Geodesy, Oceanography and Solid Earth Physics. The GUT Tutorial provides information
and guidance in how to use the toolbox for a variety of applications. GUT consists of a series of advanced
computer routines that carry out the required computations. It may be used on Windows PCs, UNIX/Linux Workstations,
and Mac. The toolbox is supported by The GUT Algorithm Description and User Guide and The GUT
Install Guide. A set of a-priori data and models are made available as well. Without any doubt the development
of the GOCE user toolbox have played a major role in paving the way to successful use of the GOCE data for
oceanography. The GUT version 2.2 was released in April 2014 and beside some bug-fixes it adds the capability for the computation of Simple Bouguer Anomaly (Solid-Earth). During this fall a new GUT version 3 has been released. GUTv3 was further developed through a collaborative effort where the scientific communities participate aiming
on an implementation of remaining functionalities facilitating a wider span of research in the fields of Geodesy,
Oceanography and Solid earth studies.
Accordingly, the GUT version 3 has:
 - An attractive and easy to use Graphic User Interface (GUI) for the toolbox,
 - Enhance the toolbox with some further software functionalities such as to facilitate the use of gradients,
anisotropic diffusive filtering and computation of Bouguer and isostatic gravity anomalies.
 - An associated GUT VCM tool for analyzing the GOCE variance covariance matrices.

GOCE User Toolbox and Tutorial

NASA Astrophysics Data System (ADS)

Knudsen, Per; Benveniste, Jerome; Team Gut

2016-04-01

The GOCE User Toolbox GUT is a compilation of tools for the utilisation and analysis of GOCE Level 2 products.
GUT support applications in Geodesy, Oceanography and Solid Earth Physics. The GUT Tutorial provides information
and guidance in how to use the toolbox for a variety of applications. GUT consists of a series of advanced
computer routines that carry out the required computations. It may be used on Windows PCs, UNIX/Linux Workstations,
and Mac. The toolbox is supported by The GUT Algorithm Description and User Guide and The GUT
Install Guide. A set of a-priori data and models are made available as well. Without any doubt the development
of the GOCE user toolbox have played a major role in paving the way to successful use of the GOCE data for
oceanography. The GUT version 2.2 was released in April 2014 and beside some bug-fixes it adds the capability for the computation of Simple Bouguer Anomaly (Solid-Earth). During this fall a new GUT version 3 has been released. GUTv3 was further developed through a collaborative effort where the scientific communities participate aiming
on an implementation of remaining functionalities facilitating a wider span of research in the fields of Geodesy,
Oceanography and Solid earth studies.
Accordingly, the GUT version 3 has:
 - An attractive and easy to use Graphic User Interface (GUI) for the toolbox,
 - Enhance the toolbox with some further software functionalities such as to facilitate the use of gradients,
anisotropic diffusive filtering and computation of Bouguer and isostatic gravity anomalies.
 - An associated GUT VCM tool for analyzing the GOCE variance covariance matrices.

Contrasting styles of seafloor spreading in the Woodlark Basin: Indications of rift-induced secondary mantle convection

NASA Astrophysics Data System (ADS)

MartíNez, Fernando; Taylor, Brian; Goodliffe, Andrew M.

1999-06-01

The Woodlark Basin in the southwest Pacific is a young ocean basin which began forming by ˜6 Ma following the rifting of continental and arc lithosphere. The N-S striking Moresby Transform divides the oceanic basin into eastern and western parts which have contrasting characteristics. Seafloor spreading west of Moresby Transform began after ˜2 Ma, and although spreading rates decrease to the west, the western basin has faster spreading characteristics than the eastern basin. These include (1) ˜500 m shallower seafloor; (2) Bouguer gravity anomalies that are >30 mGals lower; (3) magnetic anomaly and modeled seafloor magnetization amplitudes that are higher; (4) a spreading center with an axial high in contrast to the axial valleys of the eastern basin; (5) smoother seafloor fabric; and (6) exclusively nontransform spreading center offsets in contrast to the eastern basin, which has transform faults and fracture zones that extend across most of the basin. Overall depth contrasts and Bouguer anomalies can be matched by end-member models of thicker crust (˜2 km) or thinner lithosphere (<1/3) in the western basin. Correlated with these contrasts, the surrounding rifted margins abruptly thicken westward of the longitude of Moresby Transform. We examine alternative explanations for these contrasts and propose that rift-induced secondary mantle convection driven by thicker western margin lithosphere is most consistent with the observations. Although rift-induced convection has been cited as a cause for the voluminous excess magmatism at some rifted margins, the observations in the Woodlark Basin suggest that this mechanism may significantly affect the morphology, structure, and geophysical characteristics of young ocean basins in alternate ways which resemble increased spreading rate.

Ultrashort Laser Pulse Propagation in Water

DTIC Science & Technology

2008-01-01

ANSI Std Z39-18 usual Lambert-Beer behavior ( It should be noted that the so called Lambert-Beer law was first discovered by Pierre Bouguer in his...published work in 1729 titled Essai d’optique sur la gradation de la lumiére and we will hereafter refer to it as the Bouguer -Lambert-Beer Law or BLB

Ultrashort Laser Pulse Propagation in Water

DTIC Science & Technology

2010-09-30

Lambert-Beer behavior ( It should be noted that the so called Lambert-Beer law was first discovered by Pierre Bouguer in his published work in 1729...titled Essai d’optique sur la gradation de la lumiére and we will hereafter refer to it as the Bouguer -Lambert-Beer Law or BLB. The law is valid for

Gravity Recovery and Interior Laboratory (GRAIL): Extended Mission and End-Game Status

NASA Technical Reports Server (NTRS)

Zuber, Maria T.; Smith, David E.; Wieczorek, Mark A.; Williams, James G.; Andrews-Hanna, Jeffrey C.; Head, James W.; Kiefer, Walter S.; Matsuyama, Isamu; McGovern, Patrick J.; Nimmo, Francis;

Subsurface density structure of Taurus-Littrow Valley using Apollo 17 gravity data

NASA Astrophysics Data System (ADS)

Urbancic, N.; Ghent, R.; Johnson, C. L.; Stanley, S.; Hatch, D.; Carroll, K. A.; Garry, W. B.; Talwani, M.

2017-06-01

The Traverse Gravimeter Experiment (TGE) from the Apollo 17 mission was the first and only successful gravity survey on the surface of the Moon, revealing the local gravity field at Taurus-Littrow Valley (TLV). TLV is hypothesized to be a basalt-filled graben, oriented radial to Serenitatis basin. We implemented modern 3-D modeling techniques using recent high-resolution Lunar Reconnaisance Orbiter topography and image data sets to reinvestigate the subsurface structure of TLV and constrain the volcanic and tectonic history of the region. Updated topography led to significant improvements in the accuracy of free-air, Bouguer, and terrain corrections. To determine the underlying geometry for TLV, we tested a range of possible thicknesses, dips, and wall positions for the graben fill. We found that the thickness and position previously determined by Talwani et al. (1973) represent our preferred model for the data, but with walls with dips of 30°, rather than 90°. We found large model misfits due to unmodeled 3-D structure and density anomalies, as well as parameter trade-offs. We performed a sensitivity analysis to quantify the parameter trade-offs in an ideal future survey, assuming dominantly 2-D geological structure. At the TGE survey noise level (2.5 mGal), the fill thickness was constrained to ±150 m, the wall angle to ±5∘20∘ and the wall positions to ±1 km of the preferred model. This information can be used to inform the design of future lunar gravimetry experiments in regions similar to TLV.

Modeling slow-slip segmentation in Cascadia subduction zone constrained by tremor locations and gravity anomalies

NASA Astrophysics Data System (ADS)

Li, Duo; Liu, Yajing

2017-04-01

Along-strike segmentation of slow-slip events (SSEs) and nonvolcanic tremors in Cascadia may reflect heterogeneities of the subducting slab or overlying continental lithosphere. However, the nature behind this segmentation is not fully understood. We develop a 3-D model for episodic SSEs in northern and central Cascadia, incorporating both seismological and gravitational observations to constrain the heterogeneities in the megathrust fault properties. The 6 year automatically detected tremors are used to constrain the rate-state friction parameters. The effective normal stress at SSE depths is constrained by along-margin free-air and Bouguer gravity anomalies. The along-strike variation in the long-term plate convergence rate is also taken into consideration. Simulation results show five segments of ˜Mw6.0 SSEs spontaneously appear along the strike, correlated to the distribution of tremor epicenters. Modeled SSE recurrence intervals are equally comparable to GPS observations using both types of gravity anomaly constraints. However, the model constrained by free-air anomaly does a better job in reproducing the cumulative slip as well as more consistent surface displacements with GPS observations. The modeled along-strike segmentation represents the averaged slip release over many SSE cycles, rather than permanent barriers. Individual slow-slip events can still propagate across the boundaries, which may cause interactions between adjacent SSEs, as observed in time-dependent GPS inversions. In addition, the moment-duration scaling is sensitive to the selection of velocity criteria for determining when SSEs occur. Hence, the detection ability of the current GPS network should be considered in the interpretation of slow earthquake source parameter scaling relations.

Preliminary Correlations of Gravity and Topography from Mars Global Surveyor

NASA Technical Reports Server (NTRS)

Zuber, M. T.; Tyler, G. L.; Smith, D. E.; Balmino, G. S.; Johnson, G. L.; Lemoine, F. G.; Neumann, G. A.; Phillips, R. J.; Sjogren, W. L.; Solomon, S. C.

1999-01-01

The Mars Global Surveyor (MGS) spacecraft is currently in a 400-km altitude polar mapping orbit and scheduled to begin global mapping of Mars in March of 1999. Doppler tracking data collected in this Gravity Calibration Orbit prior to the nominal mapping mission combined with observations from the MGS Science Phasing Orbit in Spring - Summer 1999 and the Viking and mariner 9 orbiters has led to preliminary high resolution gravity fields. Spherical harmonic expansions have been performed to degree and order 70 and are characterized by the first high spatial resolution coverage of high latitudes. Topographic mapping by the Mars Orbiter Laser Altimeter on MGS is providing measurements of the height of the martian surface with sub-meter vertical resolution and 5-30 m absolute accuracy. Data obtained during the circular mapping phase are expected to provide the first high resolution measurements of surface heights in the southern hemisphere. The combination of gravity and topography measurements provides information on the structure of the planetary interior, i.e. the rigidity and distribution of internal density. The observations can also be used to address the mechanisms of support of surface topography. Preliminary results of correlations of gravity and topography at long planetary wavelengths will be presented and the implications for internal structure will be addressed.

Evaluation of new GRACE time-variable gravity data over the ocean

NASA Astrophysics Data System (ADS)

Chambers, Don P.

2006-09-01

Monthly GRACE gravity field models from the three science processing centers (CSR, GFZ, and JPL) are analyzed for the period from February 2003 to April 2005 over the ocean. The data are used to estimate maps of the mass component of sea level at smoothing radii of 500 km and 750 km. In addition to using new gravity field models, a filter has been applied to estimate and remove systematic errors in the coefficients that cause erroneous patterns in the maps of equivalent water level. The filter is described and its effects are discussed. The GRACE maps have been evaluated using a residual analysis with maps of altimeter sea level from Jason-1 corrected for steric variations using the World Ocean Atlas 2001 monthly climatology. The mean uncertainty of GRACE maps determined from an average of data from all 3 processing centers is estimated to be less than 1.8 cm RMS at 750 km smoothing and 2.4 cm at 500 km smoothing, which is better than was found previously using the first generation GRACE gravity fields.

CryoSat-2 altimetry derived Arctic bathymetry map: first results and validation

NASA Astrophysics Data System (ADS)

Andersen, O. B.; Abulaitijiang, A.; Cancet, M.; Knudsen, P.

2017-12-01

The Technical University of Denmark (DTU), DTU Space has been developing high quality high resolution gravity fields including the new highly accurate CryoSat-2 radar altimetry satellite data which extends the global coverage of altimetry data up to latitude 88°. With its exceptional Synthetic Aperture Radar (SAR) mode being operating throughout the Arctic Ocean, leads, i.e., the ocean surface heights, is used to retrieve the sea surface height with centimeter-level range precision. Combined with the long repeat cycle ( 369 days), i.e., dense cross-track coverage, the high-resolution Arctic marine gravity can be modelled using the CryoSat-2 altimetry. Further, the polar gap can be filled by the available ArcGP product, thus yielding the complete map of the Arctic bathymetry map. In this presentation, we will make use of the most recent DTU17 marine gravity, to derive the arctic bathymetry map using inversion based on best available hydrographic maps. Through the support of ESA a recent evaluation of existing hydrographic models of the Arctic Ocean Bathymetry models (RTOPO, GEBCO, IBCAO etc) and various inconsistencies have been identified and means to rectify these inconsistencies have been taken prior to perform the inversion using altimetry. Simultaneously DTU Space has been placing great effort on the Arctic data screening, filtering, and de-noising using various altimetry retracking solutions and classifications. All the pre-processing contributed to the fine modelling of Actic gravity map. Thereafter, the arctic marine gravity grids will eventually be translated (downward continuation operation) to a new altimetry enhanced Arctic bathymetry map using appropriate band-pass filtering.

Earth's gravity field mapping requirements and concept. [using a supercooled gravity gradiometer

NASA Technical Reports Server (NTRS)

Vonbun, F. O.; Kahn, W. D.

1981-01-01

A future sensor is considered for mapping the Earth's gravity field to meet future scientific and practical requirements for earth and oceanic dynamics. These are approximately + or - 0.1 to 10 mgal over a block size of about 50 km and over land and an ocean geoid to 1 to 2 cm over a distance of about 50 km. To achieve these values requires a gravity gradiometer with a sensitivity of approximately 10 to the -4 power EU in a circular polar orbiting spacecraft with an orbital altitude ranging 160 km to 180 km.

Geophysical Interpretation of Venus Gravity Data

NASA Technical Reports Server (NTRS)

Reasenberg, R. D.

1985-01-01

The subsurface distribution of Venus was investigated through the analysis of the data from Pioneer Venus Orbiter (PVO). In particular, the Doppler tracking data were used to map the gravitational potential. These were compared to the topographic data from the PVO radar (ORAD). In order to obtain an unbiased comparison, the topography data obtained from the PVO-ORAD were filtered to introduce distortions which are the same as those of the gravity models. Both the gravity and filtered topography maps are derived by two stage processes with a common second stage. In the first stage, the topography was used to calculate a corresponding spacecraft acceleration under the assumptions that the topography has a uniform given density and no compensation. In the second stage, the acceleration measures found in the first stage were passed through a linear inverter to yield maps of gravity and topography. Because these maps are the result of the same inversion process, they contain the same distortion; a comparison between them is unbiased to first order.

Computer Programs to Display and Modify Data in Geographic Coordinates and Methods to Transfer Positions to and from Maps, with Applications to Gravity Data Processing, Global Positioning Systems, and 30-Meter Digital Elevation Models

USGS Publications Warehouse

Plouff, Donald

1998-01-01

Computer programs were written in the Fortran language to process and display gravity data with locations expressed in geographic coordinates. The programs and associated processes have been tested for gravity data in an area of about 125,000 square kilometers in northwest Nevada, southeast Oregon, and northeast California. This report discusses the geographic aspects of data processing. Utilization of the programs begins with application of a template (printed in PostScript format) to transfer locations obtained with Global Positioning Systems to and from field maps and includes a 5-digit geographic-based map naming convention for field maps. Computer programs, with source codes that can be copied, are used to display data values (printed in PostScript format) and data coverage, insert data into files, extract data from files, shift locations, test for redundancy, and organize data by map quadrangles. It is suggested that 30-meter Digital Elevation Models needed for gravity terrain corrections and other applications should be accessed in a file search by using the USGS 7.5-minute map name as a file name, for example, file '40117_B8.DEM' contains elevation data for the map with a southeast corner at lat 40? 07' 30' N. and lon 117? 52' 30' W.

Mapping Antarctic Crustal Thickness using Gravity Inversion and Comparison with Seismic Estimates

NASA Astrophysics Data System (ADS)

Kusznir, Nick; Ferraccioli, Fausto; Jordan, Tom

2017-04-01

Using gravity anomaly inversion, we produce comprehensive regional maps of crustal thickness and oceanic lithosphere distribution for Antarctica and the Southern Ocean. Crustal thicknesses derived from gravity inversion are consistent with seismic estimates. We determine Moho depth, crustal basement thickness, continental lithosphere thinning (1-1/β) and ocean-continent transition location using a 3D spectral domain gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir 2008). The gravity anomaly contribution from ice thickness is included in the gravity inversion, as is the contribution from sediments which assumes a compaction controlled sediment density increase with depth. Data used in the gravity inversion are elevation and bathymetry, free-air gravity anomaly, the Bedmap 2 ice thickness and bedrock topography compilation south of 60 degrees south and relatively sparse constraints on sediment thickness. Ocean isochrons are used to define the cooling age of oceanic lithosphere. Crustal thicknesses from gravity inversion are compared with independent seismic estimates, which are still relatively sparse over Antarctica. Our gravity inversion study predicts thick crust (> 45 km) under interior East Antarctica, which is penetrated by narrow continental rifts featuring relatively thinner crust. The largest crustal thicknesses predicted from gravity inversion lie in the region of the Gamburtsev Subglacial Mountains, and are consistent with seismic estimates. The East Antarctic Rift System (EARS), a major Permian to Cretaceous age rift system, is imaged by our inversion and appears to extend from the continental margin at the Lambert Rift to the South Pole region, a distance of 2500 km. Offshore an extensive region of either thick oceanic crust or highly thinned continental crust lies adjacent to Oates Land and north Victoria Land, and also off West Antarctica around the Amundsen Ridges. Thin crust is predicted under the Ross Sea and beneath the West Antarctic Ice Sheet and delineates the regional extent of the broad West Antarctic Rift System (WARS). Substantial regional uplift is required under Marie Byrd Land to reconcile gravity and seismic estimates. A mantle dynamic uplift origin of the uplift is preferred to a thermal anomaly from a very young rift. The new maps produced by this study support the hypothesis that one branch of the WARS links through to the De Gerlache sea-mounts and Peter I Island in the Bellingshausen Sea region, while another branch may link to the George V Sound Rift in the Antarctic Peninsula region. Crustal thickness and lithosphere thinning derived from gravity inversion also allows the determination of circum-Antarctic ocean-continent transition structure and the mapping of continent-ocean boundary location. Superposition of illuminated satellite gravity data onto crustal thickness maps from gravity inversion provides improved determination of Southern Ocean rift orientation, pre-breakup rifted margin conjugacy and continental breakup trajectory. The continental lithosphere thinning distribution, used to define the initial thermal model temperature perturbation, is derived from the gravity inversion and uses no a priori isochron information; as a consequence the gravity inversion method provides a prediction of ocean-continent transition location, which is independent of ocean isochron information.

Hydrogeological framework and geometry modeling via joint gravity and borehole parameters, the Nadhour-Sisseb-El Alem basin (central-eastern Tunisia)

NASA Astrophysics Data System (ADS)

Souei, Ali; Atawa, Mohamed; Zouaghi, Taher

2018-03-01

The Nadhour-Sisseb-El Alem basin, in the central-eastern part of Tunisia, is characterized by the scarcity of surface and subsurface water resources. Although the aquifer systems of this basin are not well understood, the scarce water resources are subject to a high rate of exploitation leading to a significant drop in the level of the water table. This work presents correlation of gravity data with hydrogeological data in order to improve the knowledge of the deep structures and aquifer systems. Various geophysical filtering techniques (e.g., residual anomaly, upward continuation, horizontal gradient, and Euler deconvolution) applied to the complete Bouguer anomaly, deduce the deep structures and geometry of the basin and highlight gravity lineaments that correspond to the tectonic features. The structural framework of the Nadhour-Sisseb-El Alem hydrogeological basin shows N-S to NNE-SSW and E-W oriented structures that should be related to tectonic deformations. In addition to the faults, previously recognized, new lineaments are highlighted by the present work. They correspond to NE-, NW-, E- and N- trending faults that have controlled structuring and geometry of the basin. 2D gravity forward modeling, based on the interpretation of geophysical, geological and hydrogeological data, led to a better understanding of the basin geometry and spatial distribution of the Campanian-Maastrichtian and Cenozoic potential aquifers. Three hydrogeological sub-basins identified include the Nadhour sub-basin in the north, the El Alem sub-Basin in the South and the Etrabelsia sub-Basin in the East. These sub-basins are marked by a thickening of deposits, are separated by the Sisseb-Fadeloun raised structure of Neogene and Quaternary thinned series. The results allow the determination of limit conditions for the basin hydrodynamic evolution and explain some anomalies on the quantity and quality of the groundwater. They provide a management guide for water resources prospection in Atlassic basins in North Africa.

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 development.

Arkansas and Louisiana Aeromagnetic and Gravity Maps and Data - A Website for Distribution of Data

USGS Publications Warehouse

Bankey, Viki; Daniels, David L.

2008-01-01

This report contains digital data, image files, and text files describing data formats for aeromagnetic and gravity data used to compile the State aeromagnetic and gravity maps of Arkansas and Louisiana. The digital files include grids, images, ArcInfo, and Geosoft compatible files. In some of the data folders, ASCII files with the extension 'txt' describe the format and contents of the data files. Read the 'txt' files before using the data files.

Gravity study of Libya;Evaluation and Integration with Geological Data

NASA Astrophysics Data System (ADS)

Ben Suleman, abdunnur; Saheel, Ahmed

2016-04-01

Libya is located on the Mediterranean foreland of the African Shield and covers an area of approximately 1.8 million square kilometers. Since Early Paleozoic time, Libya has been a site of deposition of large sheets of continental clastics and several transgressions and regressions by the seas with consequent accumulations of a wide variety of sedimentary rocks. Several tectonic cycles affected the area and shaped the geological setting of the country. However, the regional geology and the structural framework have been highly influenced by the Caledonian, Hercynian, and Alpine tectonic events. As a result, a total of seven sedimentary basins, namely Ghadames, Murzuq, Al Kufra, Al Butnan, Sirt, and the Offshore Pelagian Basin, were developed and were separated by intervening uplifts and platforms ( Gargaf, Tibesti, Nafusah and Cyrenaica platform). Apart from Sirt and the offshore basins, all the above mentioned basins are active since Early Paleozoic time and received several thousand feet of sediments. The capability of providing regional information on the structure of sedimentary basins makes gravity mapping, in conjunction with geological information, potentially powerful tools. In this study we used gravity mapping as our primary tool of investigation however, we also used all available geological information to better understand the regional tectonics. The gravity dataset that were used in the Gravity compilation project of Libya is not homogenous. As a result, some irregularities, apparent spikes or misties, and large shifts were obtained and were taken into consideration. Evaluation of gravity Maps of Libya and their integration with geological data provide a better understanding of the role that gravity mapping plays in the geological exploration of sedimentary basins. Results confirm the known Sirt Basin regional tectonic elements and the possible presence of NW-SE lateral wrench tectonics, crossing Ajdabiya Trough at the center of Sirt Basin. The residual gravity map supports new interpretation of the Sirwal Trough in Northern Cyrenaica. Results also indicate shallow crust along the present day coast line of Al Jabal Al Akhdar, steeply dipping toward the offshore. The depo-center of Ghadames Basin cannot be precisely defined due to the lack of gravity coverage. However, Murzuq Basin is well defined regionally, in spite of gravity gaps which make the overall coverage in the southern basins inadequate for precise interpretation.

Aerogeophysical evidence for complex subglacial geology below the Rutford drainage basin,WestAntarctica

NASA Astrophysics Data System (ADS)

Jones, P.; Ferraccioli, F.; Corr, H.; Smith, A. M.; King, E.; Vaughan, D.

2003-12-01

A significant part of the West Antarctic Ice Sheet appears to be imposed upon a complex and still largely unknown continental rift system, perhaps featuring sedimentary basins, thin crust and high heat flow. Subglacial geology has been postulated to strongly modulate the dynamics and stability of the ice sheet itself. Specifically, recent aerogeophysics collected over central West Antarctica at edge of the Whitmore Mountains crustal block show that narrow subglacial rift basins with thick sedimentary infill may control the onsets and lateral margins of ice streams. The British Antarctic Survey flew an aerogeophysical survey during the 2001-02 field season: the main aim was to investigate what factors control the location and dynamics of the onset region of the Rutford Ice stream. Airborne radar, aerogravity and aeromagnetic data were simultaneously collected over the drainage basin of the Rutford Ice Stream. The new bedrock elevation grid for the area shows that the Rutford Ice Stream is constrained by a deep bedrock trough with a N-S to NE-SW trend. The onset region appears however to lie within an E-W bedrock trough at the edge of the Ellsworth Mountains crustal block. Bouguer gravity maps do not reveal typical signatures for a coincident deep rift basin at this location. However, a sharp NE-SW trending gradient, likely separating crustal blocks with contrasting crustal thickness is revealed. Aeromagnetic data image NE-SW trends north of the Rutford Ice Stream. In the onset region, these trends appear to be truncated by a NNW-SSE trend, lying on strike with the Ellsworth Mountains. Hence, the new aerogeophysical data suggests greater complexity in the subglacial geology and structure of an onset region of an ice stream compared to previous investigations.

Profiles of gamma-ray and magnetic data for aerial surveys over parts of the Western United States from longitude 108 to 126 degrees W. and from latitude 34 to 49 degrees N.

USGS Publications Warehouse

Duval, Joseph S.

1995-01-01

This CD-ROM contains images generated from geophysical data, software for displaying and analyzing the images and software for displaying and examining profile data from aerial surveys flown as part of the National Uranium Resource Evaluation (NURE) Program of the U.S. Department of Energy. The images included are of gamma-ray data (uranium, thorium, and potassium channels), Bouguer gravity data, isostatic residual gravity data, aeromagnetic anomalies, topography, and topography with bathymetry. This publication contains image data for the conterminous United States and profile data for the conterminous United States within the area longitude 108 to 126 degrees W. and latitude 34 to 49 degrees N. The profile data include apparent surface concentrations of potassium, uranium, and thorium, the residual magnetic field, and the height above the ground. The images on this CD-ROM include graytone and color images of each data set, color shaded-relief images of the potential-field and topographic data, and color composite images of the gamma-ray data. The image display and analysis software can register images with geographic and geologic overlays. The profile display software permits the user to view the profiles as well as obtain data listings and export ASCII versions of data for selected flight lines.

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

USGS Publications Warehouse

Fliedner, M.M.; Ruppert, S.; Malin, P.E.; Park, S.K.; Jiracek, G.; Phinney, R.A.; Saleeby, J.B.; Wernicke, B.; Clayton, R.; Keller, Rebecca Hylton; Miller, K.; Jones, C.; Luetgert, J.H.; Mooney, W.D.; Oliver, H.; Klemperer, S.L.; Thompson, G.A.

1996-01-01

Traveltime data from the 1993 Southern Sierra Nevada Continental Dynamics seismic refraction experiment reveal low crustal 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.

First Gravity Traverse on the Martian Surface from the Curiosity Rover

NASA Astrophysics Data System (ADS)

Lewis, K. W.; Peters, S. F.; Gonter, K. A.; Vasavada, A. R.

2016-12-01

Orbital gravity surveys have been a key tool in understanding planetary interiors and shallow crustal structure, exemplified by recent missions such as GRAIL and Juno. However, due to the loss of spatial resolution with altitude, airborne and ground-based survey methods are typically employed on the Earth. Previously, the Lunar Traverse Gravimeter experiment on the Apollo 17 mission has been the only attempt to collect surface gravity measurements on another planetary body. We will describe the results of the first gravity survey on the Martian surface, using data from the Curiosity rover over its >10 km traverse across the floor of Gale crater and lower slopes of Mount Sharp. These results enable us to estimate bulk rock density, and to search for potential subsurface density anomalies. To measure local gravitational acceleration, we use one of the two onboard Rover Inertial Measurement Units (RIMU-A), designed for rover position and fine attitude determination. The IMU contains three-axis micro-electromechanical (MEMS) accelerometers and fiber-optic gyros, and is used for gyrocompassing by integrating data for several minutes on sols with no drive or arm motions (roughly 50% of sols to date). Raw acceleration data are calibrated for biases induced by temperature effects and rover orientation, along with rover elevation over the course of the mission using multiple regression. We use the best fit linear relationship between topographic height and gravitational acceleration to estimate a Bouguer correction for the observed change in magnitude over the mission as the rover has ascended over 100 meters up the lower slopes of Mount Sharp. We find a relatively low best-fit density of 1600 +/- 500 kg/m^3 for the rocks of Mount Sharp, consistent with rover-based measurements of thermal inertial, and potentially indicating pervasive fracturing, high porosity and/or low compaction within the original sediments at least to depths of order 100 meters. Future measurements will further refine this estimate as Curiosity continues to gain elevation. Although not originally intended as a science instrument, these results highlight the scientific potential of surface gravity and topography surveys for future planetary exploration missions.

Gravity evidence for shaping of the crustal structure of the Ameca graben (Jalisco block northern limit). Western Mexico

NASA Astrophysics Data System (ADS)

Alatorre-Zamora, Miguel Angel; Campos-Enríquez, José Oscar; Fregoso-Becerra, Emilia; Quintanar-Robles, Luis; Toscano-Fletes, Roberto; Rosas-Elguera, José

2018-03-01

The Ameca tectonic depression (ATD) is located at the NE of the Jalisco Block along the southwestern fringe of the NW-SE trending Tepic-Zacoalco Rift, in the west-central part of the Trans-Mexican Volcanic Belt, western Mexico. To characterize its shallow crustal structure, we conducted a gravity survey based on nine N-S gravity profiles across the western half of the Ameca Valley. The Bouguer residual anomalies are featured by a central low between two zones of positive gravity values with marked gravity gradients. These anomalies have a general NW-SE trend similar to the Tepic-Zacoalco Rift general trend. Basement topography along these profiles was obtained by means of: 1) a Tsuboi's type inverse modeling, and 2) forward modeling. Approximately northward dipping 10° slopes are modeled in the southern half, with south tilted down faulted blocks of the Cretaceous granitic basement and its volcano-sedimentary cover along sub-vertical and intermediate normal faults, whereas southward dipping slopes of almost 15° are observed at the northern half. According to features of the obtained models, this depression corresponds to a slight asymmetric graben. The Ameca Fault is part of the master fault system along its northern limit. The quantitative interpretation shows an approximately 500 to 1100 m thick volcano-sedimentary infill capped by alluvial products. This study has several implications concerning the limit between the Jalisco Block and the Tepic-Zacoalco Rift. The established shallow crustal structure points to the existence of a major listric fault with its detachment surface beneath the Tepic-Zacoalco Rift. The Ameca Fault is interpreted as a secondary listric fault. The models indicate the presence of granitic bodies of the Jalisco Block beneath the TMVB volcanic products of the Tepic-Zacoalco rift. This implies that the limit between these two regional structures is not simple but involves a complex transition zone. A generic model suggests that the extension related normal faulting has been operating as a mechanism in the evolution of this rift. Analysis of seismicity affecting the study area and neighborhood indicates the inferred faults are active.

Preliminary isostatic residual gravity map of the Newfoundland Mountains 30' by 60' quadrangle and east part of the Wells 30' by 60' quadrangle, Box Elder County, Utah

USGS Publications Warehouse

Langenheim, Victoria; Athens, N.D.; Churchel, B.A.; Willis, H.; Knepprath, N.E.; Rosario, Jose J.; Roza, J.; Kraushaar, S.M.; Hardwick, C.L.

2013-01-01

A new isostatic residual gravity map of the Newfoundland Mountains and east of the Wells 30×60 quadrangles of Utah is based on compilation of preexisting data and new data collected by the Utah and U.S. Geological Surveys. Pronounced gravity lows occur over Grouse Creek Valley and locally beneath the Great Salt Lake Desert, indicating significant thickness of low-density Tertiary sedimentary rocks and deposits. Gravity highs coincide with exposures of dense pre-Cenozoic rocks in the Newfoundland, Silver Island, and Little Pigeon Mountains. Gravity values measured on pre-Tertiary basement to the north in the Bovine and Hogup Mountains are as much as 10mGal lower. Steep, linear gravity gradients may define basin-bounding faults concealed along the margins of the Newfoundland, Silver Island, and Little Pigeon Mountains, Lemay Island and the Pilot Range.

Crustal structure and tectonics of the northern part of the Southern Granulite Terrane, India

USGS Publications Warehouse

Rao, V.V.; Sain, K.; Reddy, P.R.; Mooney, W.D.

2006-01-01

Deep seismic reflection studies investigating the exposed Archean lower continental crust of the Southern Granulite Terrane, India, yield important constraints on the nature and evolution of the deep crust, including the formation and exhumation of granulites. Seismic reflection images along the Kuppam-Bhavani profile reveal a band of reflections that dip southward from 10.5 to 15.0??s two-way-time (TWT), across a distance of 50??km. The bottom of these reflections beneath the Dharwar craton is interpreted as the Moho. Further south, another reflection band dipping northward is observed. These bands of reflectivity constitute a divergent reflection fabric that converges at the Moho boundary observed at the Mettur shear zone. Reflection fabrics that intersect at a steep angle are interpreted as a collisional signature due to the convergence of crustal blocks, which we infer resulted in crustal thickening and the formation of granulites. Anomalous gravity and magnetic signatures are also observed across the Mettur shear zone. The gravity model derived from the Bouguer gravity data corroborates seismic results. The tectonic regime and seismic reflection profiles are combined in a 3-D representation that illustrates our evidence for paleo-subduction at a collision zone. The structural dissimilarities and geophysical anomalies suggest that the Mettur shear zone is a suture between the Dharwar craton in the north and another crustal block in the south. This study contributes significantly to our understanding of the operation of Archean plate tectonics, here inferred to involve collision and subduction. Furthermore, it provides an important link between the Gondwanaland and global granulite evolution occurring throughout the late Archean. ?? 2006 Elsevier B.V. All rights reserved.

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.

Extension of continental lithosphere - A model for two scales of basin and range deformation

NASA Technical Reports Server (NTRS)

Zuber, M. T.; Parmentier, E. M.; Fletcher, R. C.

1986-01-01

The development of a model for deformation in an extending continental lithosphere that is stratified in density and strength is described. The lithosphere model demonstrates that the necking instabilities at two wavelengths originate due to a strong upper crust, a mantle layer, and a weak lower crust. It is observed that the dominant wavelengths of necking are controlled by layer thickness and the strength of the layers control the amplitude of the instabilities. The model is applied to the Basin and Range Province of the western U.S. where deformations in ranges and tile domains are detected. The relation between the Bouguer gravity anomaly and the deformations is studied. The data reveal that the horizontal scale of short wavelength necking correlates with the spacings of individual basins and ranges, and the longer wavelength corresponds to the width of tilt domains. The control of the Basin and Range deformation by two scales of extensional instability is proposed.

Research on the spatial analysis method of seismic hazard for island

NASA Astrophysics Data System (ADS)

Jia, Jing; Jiang, Jitong; Zheng, Qiuhong; Gao, Huiying

2017-05-01

Seismic hazard analysis(SHA) is a key component of earthquake disaster prevention field for island engineering, whose result could provide parameters for seismic design microscopically and also is the requisite work for the island conservation planning’s earthquake and comprehensive disaster prevention planning macroscopically, in the exploitation and construction process of both inhabited and uninhabited islands. The existing seismic hazard analysis methods are compared in their application, and their application and limitation for island is analysed. Then a specialized spatial analysis method of seismic hazard for island (SAMSHI) is given to support the further related work of earthquake disaster prevention planning, based on spatial analysis tools in GIS and fuzzy comprehensive evaluation model. The basic spatial database of SAMSHI includes faults data, historical earthquake record data, geological data and Bouguer gravity anomalies data, which are the data sources for the 11 indices of the fuzzy comprehensive evaluation model, and these indices are calculated by the spatial analysis model constructed in ArcGIS’s Model Builder platform.

Shield volcanism and lithospheric structure beneath the Tharsis plateau, Mars

NASA Technical Reports Server (NTRS)

Blasius, K. R.; Cutts, J. A.

1976-01-01

The heights of four great shield volcanoes, when interpreted as reflecting the local hydrostatic head on a common source of upwelling magma, provide significant constraints on models of lithospheric structure beneath the Tharsis plateau. If Bouguer gravity anomalies are modeled in terms of a variable thickness crust, and a two-component (crust/mantle) earth-like structure is assumed for the Martian lithosphere, the derived model lithosphere beneath the Tharsis plateau has the following properties: (1) the upper low-density 'crustal' component is thickened beneath the Tharsis plateau; (2) the lower high-density 'mantle' component is thinned beneath the Tharsis plateau; and (3) there is a net gradient on the base of the Martian lithosphere directed downward away from beneath the summit of the Tharsis plateau. A long history of magmatic intrusion is hypothesized to have been the cause of the updoming of the Tharsis plateau and the maintenance of the plateau in a state of only partial compensation.

Microelectromechanical system gravimeters as a new tool for gravity imaging.

PubMed

Middlemiss, Richard P; Bramsiepe, Steven G; Douglas, Rebecca; Hild, Stefan; Hough, James; Paul, Douglas J; Samarelli, Antonio; Rowan, Sheila; Hammond, Giles D

2018-05-28

A microelectromechanical system (MEMS) gravimeter has been manufactured with a sensitivity of 40 ppb in an integration time of 1 s. This sensor has been used to measure the Earth tides: the elastic deformation of the globe due to tidal forces. No such measurement has been demonstrated before now with a MEMS gravimeter. Since this measurement, the gravimeter has been miniaturized and tested in the field. Measurements of the free-air and Bouguer effects have been demonstrated by monitoring the change in gravitational acceleration measured while going up and down a lift shaft of 20.7 m, and up and down a local hill of 275 m. These tests demonstrate that the device has the potential to be a useful field-portable instrument. The development of an even smaller device is underway, with a total package size similar to that of a smartphone.This article is part of a discussion meeting issue 'The promises of gravitational-wave astronomy'. © 2018 The Author(s).

Microelectromechanical system gravimeters as a new tool for gravity imaging

NASA Astrophysics Data System (ADS)

Middlemiss, Richard P.; Bramsiepe, Steven G.; Douglas, Rebecca; Hild, Stefan; Hough, James; Paul, Douglas J.; Samarelli, Antonio; Rowan, Sheila; Hammond, Giles D.

2018-05-01

A microelectromechanical system (MEMS) gravimeter has been manufactured with a sensitivity of 40 ppb in an integration time of 1 s. This sensor has been used to measure the Earth tides: the elastic deformation of the globe due to tidal forces. No such measurement has been demonstrated before now with a MEMS gravimeter. Since this measurement, the gravimeter has been miniaturized and tested in the field. Measurements of the free-air and Bouguer effects have been demonstrated by monitoring the change in gravitational acceleration measured while going up and down a lift shaft of 20.7 m, and up and down a local hill of 275 m. These tests demonstrate that the device has the potential to be a useful field-portable instrument. The development of an even smaller device is underway, with a total package size similar to that of a smartphone. This article is part of a discussion meeting issue `The promises of gravitational-wave astronomy'.

An enhanced trend surface analysis equation for regional-residual separation of gravity data

NASA Astrophysics Data System (ADS)

Obasi, A. I.; Onwuemesi, A. G.; Romanus, O. M.

2016-12-01

Trend surface analysis is a geological term for a mathematical technique which separates a given map set into a regional component and a local component. This work has extended the steps for the derivation of the constants in the trend surface analysis equation from the popularly known matrix and simultaneous form to a more simplified and easily achievable format. To achieve this, matrix inversion was applied to the existing equations and the outcome was tested for suitability using a large volume of gravity data set acquired from the Anambra Basin, south-eastern Nigeria. Tabulation of the field data set was done using the Microsoft Excel spread sheet, while gravity maps were generated from the data set using Oasis Montaj software. A comparison of the residual gravity map produced using the new equations with its software derived counterpart has shown that the former has a higher enhancing capacity than the latter. This equation has shown strong suitability for application in the separation of gravity data sets into their regional and residual components.

Influence of the Density Structure of the Caribbean Plate Forearc on the Static Stress State and Asperity Distribution along the Costa Rican Seismogenic Zone

NASA Astrophysics Data System (ADS)

Lücke, O. H.; Gutknecht, B. D.

2014-12-01

Most of the forearc region along the Central American Subduction Zone shows a series of trench-parallel, positive gravity anomalies with corresponding gravity lows along the trench and toward the coast. These features extend from Guatemala to northern Nicaragua. However, the Costa Rican segment of the forearc does not follow this pattern. In this region, the along-trench gravity low is segmented, the coastal low is absent, and the forearc gravity high is located onshore at the Nicoya Peninsula which overlies the seismogenic zone. Geodetic and seismological studies along the Costa Rican Subduction Zone suggest the presence of coupled areas beneath the Nicoya Peninsula prior to the 2012, magnitude Mw 7.6 earthquake. These areas had previously been associated with asperities. Previous publications have proposed a mechanical model for the generation of asperities along the Chilean convergent margin based on the structure of the overriding plate above the seismogenic zone in which dense igneous bodies disturb the state of stress on the seismogenic zone and may influence seismogenic processes. In Costa Rica, surface geology and gravity data indicate the presence of dense basalt/gabbro crust overlying the seismogenic zone where the coupling is present. Bouguer anomaly values in this region reach up to 120×10-5 m/s2, which are the highest for Costa Rica. In this work, the state of stress on the Cocos-Caribbean plate interface is calculated based on the geometry and mass distribution of a 3D density model of the subduction zone as interpreted from gravity data from combined geopotential models. Results show a correlation between the coupled areas at the Nicoya Peninsula and the presence of stress anomalies on the plate interface. The stress anomalies are calculated for the normal component of the vertical stress on the seismogenic zone and are interpreted as being generated by the dense material which makes up the forearc in the area. The dense material of the Nicoya Complex mafic rocks and the topographic load of the peninsula on the seismogenic zone may play a role in the distribution of coupled areas and the seismic behavior of the region since the anomalous normal stress on the plate interface may increase the shear stress threshold for rupture.

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 longest wavelengths. We use the deal.ii finite-element library (Bangerth 2007) to compute relaxed topography spectra. In out future work, we plan to model viscous relaxation to constrain the viscosity profile and thermal evolution.

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 magnetotelluric survey may assist in confirming the results. However, lengths of the features were difficult to interpret as the wavelength filtering tends to truncate features in accordance with the bandpass window. Additional gravity measurements would aid in providing higher resolution for the identification and interpretation of features, particularly in the vicinity of the Humboldt House to the north and in an area located to the south of the study area where a large feature was identified in both the aeromagnetic and gravity surveys.

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 by the vertical movement of the partial melted magma chamber beneath the northern part of the Mt. Baekdu volcanic area, which is confirmed by vertical stress change calculation.

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 be explained by the vertical movement of the partial melted magma chamber beneath the northern part of the Mt. Baekdu volcanic area, which is confirmed by vertical stress calculation.

Feeling Gravity's Pull: Gravity Modeling. The Gravity Field of Mars

NASA Technical Reports Server (NTRS)

Lemoine, Frank; Smith, David; Rowlands, David; Zuber, Maria; Neumann, G.; Chinn, Douglas; Pavlis, D.

2000-01-01

Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly distributed within the planet. Changes in topography, such as glacial movement, an earthquake, or a rise in the ocean level, can subtly affect the gravity field. An accurate measurement of the Earth's gravity field helps us understand the distribution of mass beneath the surface. This insight can assist us in locating petroleum, mineral deposits, ground water, and other valuable substances. Gravity mapping can also help notice or verify changes in sea surface height and other ocean characteristics. Such changes may indicate climate change from polar ice melting and other phenomena. In addition, gravity mapping can indicate how land moves under the surface after earthquakes and other plate tectonic processes. Finally, changes in the Earth's gravity field might indicate a shift in water distribution that could affect agriculture, water supplies for population centers, and long-term weather prediction. Scientists can map out the Earth's gravity field by watching satellite orbits. When a satellite shifts in vertical position, it might be passing over an area where gravity changes in strength. Gravity is only one factor that may shape a satellite's orbital path. To derive a gravity measurement from satellite movement, scientists must remove other factors that might affect a satellite's position: 1. Drag from atmospheric friction. 2. Pressure from solar radiation as it heads toward Earth and. as it is reflected off the surface of the Earth 3. Gravitational pull from the Sun, the Moon, and other planets in the Solar System. 4. The effect of tides. 5. Relativistic effects. Scientists must also correct for the satellite tracking process. For example, the tracking signal must be corrected for refraction through the atmosphere of the Earth. Supercomputers can calculate the effect of gravity for specific locations in space following a mathematical process known as spherical harmonics, which quantifies the gravity field of a planetary body. The process is based on Laplace's fundamental differential equation of gravity. The accuracy of a spherical harmonic solution is rated by its degree and order. Minute variations in gravity are measured against the geoid, a surface of constant gravity acceleration at mean sea level. The geoid reference gravity model strength includes the central body gravitational attraction (9.8 m/sq s) and a geopotential variation in latitude partially caused by the rotation of the Earth. The rotational effect modifies the shape of the geoid to be more like an ellipsoid, rather than a perfect, circle. Variations of gravity strength from the ellipsoidal reference model are measured in units called milli-Galileos (mGals). One mGal equals 10(exp -5) m/sq s. Research projects have also measured the gravity fields of other planetary bodies, as noted in the user profile that follows. From this information, we may make inferences about our own planet's internal structure and evolution. Moreover, mapping the gravity fields of other planets can help scientists plot the most fuel-efficient course for spacecraft expeditions to those planets.

The active structure of the Dead Sea depression

NASA Astrophysics Data System (ADS)

Shamir, G.

2003-04-01

The ~220km long gravitational and structural Dead Sea Depression (DSD), situated along the southern section of the Dead Sea Transform (DST), is centered by the Dead Sea basin sensu strictu (DSB), which has been described since the 1960?s as a pull-apart basin over a presumed left-hand fault step. However, several observations, or their lack thereof, question this scheme, e.g. (i) It is not supported by recent seismological and geomorphic data; (ii) It does not explain the fault pattern and mixed sinistral and dextral offset along the DSB western boundary; (iii) It does not simply explain the presence of intense deformation outside the presumed fault step zone; (iv) It is inconsistent with the orientation of seismically active faults within the Dead Sea and Jericho Valley; (v); It is apparently inconsistent with the symmetrical structure of the DSD; (vi) The length of the DSB exceeds the total offset along the Dead Sea Transform, while its subsidence is about the age of the DST. Integration of newly acquired and analyzed data (high resolution and petroleum seismic reflection data, earthquake relocation and fault plane solutions) with previously published data (structural mapping, fracture orientation distribution, Bouguer anomaly maps, sinkhole distribution, geomorphic lineaments) now shows that the active upper crustal manifestation of the DSD is a broad shear zone dominated by internal fault systems oriented NNE and NNW. These fault systems are identified by earthquake activity, seismic reflection observations, alignment of recent sinkholes, and distribution of Bouguer anomaly gradients. Motion on the NNE system is normal-dextral, suggesting that counterclockwise rotation may have taken place within the shear zone. The overall sinistral motion between the Arabian and Israel-Sinai plates along the DSD is thus accommodated by distributed shear across the N-S extending DSD. The three-dimensionality of this motion at the DSD may be related to the rate of convergence between the two plates.

Detailed gravity survey to help seismic microzonation: Mapping the thickness of unconsolidated deposits in Ottawa, Canada

NASA Astrophysics Data System (ADS)

Lamontagne, M.; Thomas, M.; Silliker, J.; Jobin, D.

2011-11-01

In this study, measurements of gravity were made to map and model the thickness of Quaternary deposits (sand and clay) overlying Ordovician limestones in a suburb of Ottawa (Orléans, Ontario). Because ground motion amplification is partly related to the thickness of unconsolidated deposits, this work helps refine the assessment of the earthquake damage potential of the area. It also helps the mapping of clay basins, which can locally exceed 100 m in thickness, where ground motion amplification can occur. Previous work, including well log data and seismic methods, have yielded a wealth of information on near-surface geology in Orléans, thereby providing the necessary constraints to test the applicability of gravity modeling in other locations where other methods cannot always be used. Some 104 gravity stations were occupied in an 8 × 12 km test area in the Orléans. Stations were accurately located with differential GPS that provided centimetric accuracy in elevation. Densities of the unconsolidated Quaternary deposits (Champlain Sea clay) determined on core samples and densities determined on limestone samples from outcrops were used to constrain models of the clay layer overlying the higher density bedrock formations (limestone). The gravity anomaly map delineates areas where clay basins attain > 100 m depth. Assuming a realistic density for the Champlain Sea clays (1.9-2.1 g/cm 3), the thickness over the higher density bedrock formations (Ordovician carbonate rocks) was modeled and compared with well logs and two seismic reflection profiles. The models match quite well with the information determined from well logs and seismic methods. It was found that gravity and the thickness of unconsolidated deposits are correlated but the uncertainties in both data sets preclude the definition of a direct correlation between the two. We propose that gravity measurements at a local scale be used as an inexpensive means of mapping the thickness of unconsolidated deposits in low-density urban areas. To obtain meaningful results, three conditions must exist. Firstly, elevations of gravity stations must be measured accurately using differential GPS; secondly, that the regional gravity field must be well defined, and thirdly, that the local geology be simple enough to be realistically represented with a two-layer model.

Internal gravity wave contributions to global sea surface variability

NASA Astrophysics Data System (ADS)

Savage, A.; Arbic, B. K.; Richman, J. G.; Shriver, J. F.; Buijsman, M. C.; Zamudio, L.; Wallcraft, A. J.; Sharma, H.

2016-02-01

High-resolution (1/12th and 1/25th degree) 41-layer simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea-surface height (SSH). The HYCOM output has been separated into steric, non-steric, and total sea-surface height and the maps display variance in subtidal, tidal, and supertidal bands. Two of the global maps are of particular interest in planning for the upcoming Surface Water and Ocean Topography (SWOT) wide-swath satellite altimeter mission; (1) a map of the nonstationary tidal signal (estimated after removing the stationary tidal signal via harmonic analysis), and (2) a map of the steric supertidal contributions, which are dominated by the internal gravity wave continuum. Both of these maps display signals of order 1 cm2, the target accuracy for the SWOT mission. Therefore, both non-stationary internal tides and non-tidal internal gravity waves are likely to be important sources of "noise" that must be accurately removed before examination of lower-frequency phenomena can take place.

GRAIL Gravity Map of Orientale Basin

NASA Image and Video Library

2016-10-27

This color-coded map shows the strength of surface gravity around Orientale basin on Earth's moon, derived from data obtained by NASA's GRAIL mission. The GRAIL mission produced a very high-resolution map of gravity over the surface of the entire moon. This plot is zoomed in on the part of that map that features Orientale basin, where the two GRAIL spacecraft flew extremely low near the end of their mission. Their close proximity to the basin made the probes' measurements particularly sensitive to the gravitational acceleration there (due to the inverse squared law). The color scale plots the gravitational acceleration in units of "gals," where 1 gal is one centimeter per second squared, or about 1/1000th of the gravitational acceleration at Earth's surface. (The unit was devised in honor of the astronomer Galileo). Labels on the x and y axes represent latitude and longitude. http://photojournal.jpl.nasa.gov/catalog/PIA21050

Atom Interferometer Technologies in Space for Gravity Mapping and Gravity Science

NASA Astrophysics Data System (ADS)

Williams, Jason; Chiow, Sheng-Wey; Kellogg, James; Kohel, James; Yu, Nan

2015-05-01

Atom interferometers utilize the wave-nature of atomic gases for precision measurements of inertial forces, with potential applications ranging from gravity mapping for planetary science to unprecedented tests of fundamental physics with quantum gases. The high stability and sensitivity intrinsic to these devices already place them among the best terrestrial sensors available for measurements of gravitational accelerations, rotations, and gravity gradients, with the promise of several orders of magnitude improvement in their detection sensitivity in microgravity. Consequently, multiple precision atom-interferometer-based projects are under development at the Jet Propulsion Laboratory, including a dual-atomic-species interferometer that is to be integrated into the Cold Atom Laboratory onboard the International Space Station and a highly stable gravity gradiometer in a transportable design relevant for earth science measurements. We will present JPL's activities in the use of precision atom interferometry for gravity mapping and gravitational wave detection in space. Our recent progresses bringing the transportable JPL atom interferometer instrument to be competitive with the state of the art and simulations of the expected capabilities of a proposed flight project will also be discussed. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Relation of the lunar volcano complexes lying on the identical linear gravity anomaly

NASA Astrophysics Data System (ADS)

Yamamoto, K.; Haruyama, J.; Ohtake, M.; Iwata, T.; Ishihara, Y.

2015-12-01

There are several large-scale volcanic complexes, e.g., Marius Hills, Aristarchus Plateau, Rumker Hills, and Flamsteed area in western Oceanus Procellarum of the lunar nearside. For better understanding of the lunar thermal history, it is important to study these areas intensively. The magmatisms and volcanic eruption mechanisms of these volcanic complexes have been discussed from geophysical and geochemical perspectives using data sets acquired by lunar explorers. In these data sets, precise gravity field data obtained by Gravity Recovery and Interior Laboratory (GRAIL) gives information on mass anomalies below the lunar surface, and useful to estimate location and mass of the embedded magmas. Using GRAIL data, Andrews-Hanna et al. (2014) prepared gravity gradient map of the Moon. They discussed the origin of the quasi-rectangular pattern of narrow linear gravity gradient anomalies located along the border of Oceanus Procellarum and suggested that the underlying dikes played important roles in magma plumbing system. In the gravity gradient map, we found that there are also several small linear gravity gradient anomaly patterns in the inside of the large quasi-rectangular pattern, and that one of the linear anomalies runs through multiple gravity anomalies in the vicinity of Aristarchus, Marius and Flamstead volcano complexes. Our concern is whether the volcanisms of these complexes are caused by common factors or not. To clarify this, we firstly estimated the mass and depth of the embedded magmas as well as the directions of the linear gravity anomalies. The results were interpreted by comparing with the chronological and KREEP distribution maps on the lunar surface. We suggested providing mechanisms of the magma to these regions and finally discussed whether the volcanisms of these multiple volcano complex regions are related with each other or not.

Analyzing the Broken Ridge area of the Indian Ocean using magnetic and gravity anomaly maps and geoid undulation and bathymetry data

NASA Technical Reports Server (NTRS)

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

1982-01-01

A higher resolution anomaly map of the Broken Ridge area (2 degree dipole spacing) was produced and reduced to the pole using quiet time data for this area. The map was compared with equally scaled maps of gravity anomaly, geoid undulation, and bathymetry. The ESMAP results were compared with a NASA MAGSAT map derived by averaging data in two-degree bins. A survey simulation was developed to model the accuracy of MAGSAT anomaly maps as a function of satellite altitude, instrument noise level, external noise model, and crustal anomaly field model. A preliminary analysis of the geophysical structure of Broken Ridge is presented and unresolved questions are listed.

The geothermal gradient map of Central Tunisia: Comparison with structural, gravimetric and petroleum data

NASA Astrophysics Data System (ADS)

Dhia, Hamed Ben

1987-10-01

Five hundred and fifty temperature values, initially measured as either bottom-hole temperatures (BHT) or drill-stem tests (DST), from 98 selected petroleum exploration wells form the basis of a geothermal gradient map of central Tunisia. A "global-statistical" method was employed to correct the BHT measurements, using the DST as references. The geothermal gradient ranges from 23° to 49°C/km. Comparison of the geothermal gradient with structural, gravimetric and petroleum data indicates that: (1) the general trend of the geothermal gradient curves reflects the main structural directions of the region, (2) zones of low and high geothermal gradient are correlated with zones of negative and positive Bouguer anomalies and (3) the five most important oil fields of central Tunisia are located near the geothermal gradient curve of 40° C/km. Such associations could have practical importance in petroleum exploration, but their significance must first be established through further investigation and additional data.

Preliminary isostatic residual gravity map of the Tremonton 30' x 60' quadrangle, Box Elder and Cache Counties, Utah, and Franklin and Oneida Counties, Idaho

USGS Publications Warehouse

Langenheim, Victoria; Oaks, R.Q.; Willis, H.; Hiscock, A.I.; Chuchel, Bruce A.; Rosario, Jose J.; Hardwick, C.L.

2014-01-01

A new isostatic residual gravity map of the Tremonton 30' x 60' quadrangle of Utah is based on compilation of preexisting data and new data collected by the Utah and U.S. Geological Surveys. Pronounced gravity lows occur over North Bay, northwest of Brigham City, and Malad and Blue Creek Valleys, indicating significant thickness of low-density Tertiary sedimentary rocks and deposits. Gravity highs coincide with exposures of dense pre-Cenozoic rocks in the Promontory, Clarkston, and Wellsville Mountains. The highest gravity values are located in southern Curlew Valley and may be produced in part by deeper crustal density variations or crustal thinning. Steep, linear gravity gradients coincide with Quaternary faults bounding the Wellsville and Clarkston Mountains. Steep gradients also coincide with the margins of the Promontory Mountains, Little Mountain, West Hills, and the eastern margin of the North Promontory Mountains and may define concealed basin-bounding faults.

Middle Atmosphere Program. Handbook for MAP, volume 20

NASA Technical Reports Server (NTRS)

Bowhill, S. A. (Editor); Edwards, B. (Editor)

1986-01-01

Various topics related to investigations of the middle atmosphere are discussed. Numerical weather prediction, performance characteristics of weather profiling radars, determination of gravity wave and turbulence parameters, case studies of gravity-wave propagation, turbulence and diffusion due to gravity waves, the climatology of gravity waves, mesosphere-stratosphere-troposphere radar, antenna arrays, and data management techniques are among the topics discussed.

Seismic hazard of American Samoa and neighboring South Pacific Islands--methods, data, parameters, and results

USGS Publications Warehouse

Petersen, Mark D.; Harmsen, Stephen C.; Rukstales, Kenneth S.; Mueller, Charles S.; McNamara, Daniel E.; Luco, Nicolas; Walling, Melanie

2012-01-01

American Samoa and the neighboring islands of the South Pacific lie near active tectonic-plate boundaries that host many large earthquakes which can result in strong earthquake shaking and tsunamis. To mitigate earthquake risks from future ground shaking, the Federal Emergency Management Agency requested that the U.S. Geological Survey prepare seismic hazard maps that can be applied in building-design criteria. This Open-File Report describes the data, methods, and parameters used to calculate the seismic shaking hazard as well as the output hazard maps, curves, and deaggregation (disaggregation) information needed for building design. Spectral acceleration hazard for 1 Hertz having a 2-percent probability of exceedance on a firm rock site condition (Vs30=760 meters per second) is 0.12 acceleration of gravity (1 second, 1 Hertz) and 0.32 acceleration of gravity (0.2 seconds, 5 Hertz) on American Samoa, 0.72 acceleration of gravity (1 Hertz) and 2.54 acceleration of gravity (5 Hertz) on Tonga, 0.15 acceleration of gravity (1 Hertz) and 0.55 acceleration of gravity (5 Hertz) on Fiji, and 0.89 acceleration of gravity (1 Hertz) and 2.77 acceleration of gravity (5 Hertz) on the Vanuatu Islands.

High-resolution gravity field modeling using GRAIL mission data

NASA Astrophysics Data System (ADS)

Lemoine, F. G.; Goossens, S. J.; 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.

2015-12-01

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: a primary mapping mission from March 1 until May 29, 2012 at an average altitude of 50 km, and an extended mission from August 30 until December 14, 2012, with an average altitude of 23 km before November 18, and 20 and 11 km after. High-resolution gravity field models using both these data sets have been estimated, with the current resolution being degree and order 1080 in spherical harmonics. Here, we focus on aspects of the analysis of the GRAIL data: we investigate eclipse modeling, the influence of empirical accelerations on the results, and we discuss the inversion of large-scale systems. In addition to global models we also estimated local gravity adjustments in areas of particular interest such as Mare Orientale, the south pole area, and the farside. We investigate the use of Ka-band Range Rate (KBRR) data versus numerical derivatives of KBRR data, and show that the latter have the capability to locally improve correlations with topography.

Potential Geophysical Field Transformations and Combined 3D Modelling for Estimation the Seismic Site Effects on Example of Israel

NASA Astrophysics Data System (ADS)

Eppelbaum, Lev; Meirova, Tatiana

2015-04-01

It is well-known that the local seismic site effects may have a significant contribution to the intensity of damage and destruction (e.g., Hough et al., 1990; Regnier et al., 2000; Bonnefoy-Claudet et al., 2006; Haase et al., 2010). The thicknesses of sediments, which play a large role in amplification, usually are derived from seismic velocities. At the same time, thickness of sediments may be determined (or defined) on the basis of 3D combined gravity-magnetic modeling joined with available geological materials, seismic data and borehole section examination. Final result of such investigation is a 3D physical-geological model (PGM) reflecting main geological peculiarities of the area under study. Such a combined study needs in application of a reliable 3D mathematical algorithm of computation together with advanced methodology of 3D modeling. For this analysis the developed GSFC software was selected. The GSFC (Geological Space Field Calculation) program was developed for solving a direct 3-D gravity and magnetic prospecting problem under complex geological conditions (Khesin et al., 1996; Eppelbaum and Khesin, 2004). This program has been designed for computing the field of Δg (Bouguer, free-air or observed value anomalies), ΔZ, ΔX, ΔY , ΔT , as well as second derivatives of the gravitational potential under conditions of rugged relief and inclined magnetization. The geological space can be approximated by (1) three-dimensional, (2) semi-infinite bodies and (3) those infinite along the strike closed, L.H. non-closed, R.H. on-closed and open). Geological bodies are approximated by horizontal polygonal prisms. The program has the following main advantages (besides abovementioned ones): (1) Simultaneous computing of gravity and magnetic fields; (2) Description of the terrain relief by irregularly placed characteristic points; (3) Computation of the effect of the earth-air boundary by the method of selection directly in the process of interpretation; (4) Modeling of the selected profiles flowing over rugged relief or at various arbitrary levels (using characteristic points); (5) Simultaneous modeling of several profiles; (6) Description of a large number of geological bodies and fragments. The basic algorithm realized in the GSFC program is the solution of the direct 3-D problem of gravity and magnetic prospecting for horizontal polygonal prism limited in the strike direction. In the developed algorithm integration over a volume is realized on the surface limiting the anomalous body. It is necessary to note that when we apply a series of interpreting profiles, we can compile several detailed maps of thicknesses of sedimentary or intrusive associations for the area under study. Such an experience was obtained for Carmel and Maanit areas (Eppelbaum and Katz, 2012a). Taking into account that seismic site effects must have an obvious correlation with tectonic pattern (in regional, middle and detailed scales), satellite (gravity), airborne (magnetic measurements at 1 and 5 km levels) and land (both gravity and magnetic) data were processed by the use of different methodologies. For instance, it was shown that magnetic gradient computations from airborne magnetic observations (1 km level) enable to classify the region under study to areas with thick sedimentary cover and areas with shallow intrusive rock location. Self-adjusting and adaptive filtering of gravity satellite obtained and magnetic airborne (1 and 5 km) data enabled to reveal the areas with quasi-homogeneous characteristics. Satellite derived gravity data were processed by the use of numerous algorithms: entropy, adaptive filtering, wavelet, and information approach (Eppelbaum and Katz, 2015a, 2015b, Eppelbaum et al., 2014), and strike angle and virtual deformations (Klokočník et al., 2014). Application of these methods was effective not only for tectono-geological setting sharpening, but also for calculation of such parameters as 'dominant location of subsurface masses', areas of 'compression' and 'dilatation'. Land gravity and magnetic data were processed by the use of abovementioned algorithms including procedures of downward continuation and computation of third derivatives of gravitational potential. For this investigation was utilized the recently constructed map of the Neogene-Quaternary structural stage (indicating thicknesses of these deposits) of Israel and the eastern Mediterranean (Eppelbaum and Katz, 2014b). Results of other map compilation (Palaeogene, Late and Early Cretaceous, Jurassic and Triassic structural stages, hypsometric map of the base of the newest (Post-Jurassic) tectonic complex as well as map of Lower Mesozoic wells and outcrop locations) (Eppelbaum and Katz, 2011, 2012a, 2012b, 2014a, 2014b, 2015a, 2015b) were taken into consideration for 3D PGMs construction. Acknowledgements This research was carried out under grant No. 214-17-016 from the Ministry of Infrastructure, Energy and Water Resources of Israel. References Bonnefoy-Claudet, S., Cotton, F. and Bard, P.-Y., 2006. The nature of noise wavefield and its applications for site effects studies. A literature review. Earth Sciences Review, 79, 205-227. Eppelbaum, L. and Katz, Y., 2011. Tectonic-Geophysical Mapping of Israel and eastern Mediterranean: Implication for Hydrocarbon Prospecting. Positioning, 2, No. 1, doi: 10.4236/pos.2011.21004, 36-54. Eppelbaum, L.V., Katz, Y.I., 2012a. Mineral deposits in Israel: A contemporary view, In: (Eds. Ya'ari, A. and Zahavi, E.D.), Israel: Social, Economic and Political Developments, Nova Science Publ, NY, USA, 1-41. Eppelbaum, L.V. and Katz, Y.I., 2012b. Key Features of Seismo-Neotectonic Pattern of the Eastern Mediterranean. Izv. Acad. Sci. Azerb. Rep., Ser.: Earth Sciences, No. 3, 29-40. Eppelbaum, L.V. and Katz, Y.I., 2014a. First Paleomagnetic Map of the Easternmost Mediterranean Derived from Combined Geophysical-Geological Analysis. Trans. of the 10th EUG Meet., Geophysical Research Abstracts, Vol. 16, EGU2014-2424, Vienna, Austria, 1-5. Eppelbaum, L.V. and Katz, Y.I., 2014b. First Maps of Mesozoic and Cenozoic Structural-Sedimentation Floors of the Easternmost Mediterranean and their Relationship with the Deep Geophysical-Geological Zonation. Proceed. of the 19th Intern. Congress of Sedimentologists, Geneva, Switzerland, 1-3. Eppelbaum, L.V. and Katz, Yu.I., 2015a. Newly Developed Paleomagnetic Map of the Easternmost Mediterranean Unmasks Geodynamic History of this Region. Central European Jour. of Geosciences, 6, No. 4 (in Press). Eppelbaum, L.V. and Katz, Yu.I., 2015b. Application of Integrated Geological-Geophysical Analysis for Development of Paleomagnetic Maps of the Easternmost Mediterranean. In: (Eppelbaum L., Ed.), New Developments in Paleomagnetism Research, Nova Publisher, NY (in Press). Eppelbaum, L.V. and Khesin, B.E., 2004. Advanced 3-D modelling of gravity field unmasks reserves of a pyrite-polymetallic deposit: A case study from the Greater Caucasus. First Break, 22, No. 11, 53-56. Eppelbaum, L.V., Nikolaev, A.V. and Katz, Y.I., 2014. Space location of the Kiama paleomagnetic hyperzone of inverse polarity in the crust of the eastern Mediterranean. Doklady Earth Sciences (Springer), 457, No. 6, 710-714. Haase, J.S., Park, C.H., Nowack, R.L. and Hill, J.R., 2010. Probabilistic seismic hazard estimates incorporating site effects - An example from Indiana, U.S.A. Environmental and Engineering Geoscience, 16, No. 4, 369-388. Hough, S.E., Borcherdt, R. D., Friberg, P. A., Busby, R., Field, E. and Jacob, K. N., 1990. The role of sediment-induced amplification in the collapse of the Nimitz freeway. Nature, 344, 853-855. Khesin, B.E. Alexeyev, V.V. and Eppelbaum, L.V., 1996. Interpretation of Geophysical Fields in Complicated Environments. Kluwer Academic Publ., Ser.: Advanced Appr. in Geophysics, Dordrecht - London - Boston. Klokočník, J., Kostelecký, J., Eppelbaum, L. and Bezděk, A., 2014. Gravity Disturbances, the Marussi Tensor, Invariants and Other Functions of the Geopotential Represented by EGM 2008. Journal of Earth Science Research, 2, No. 3, 88-101. Regnier, M., Moris, S. Shapira, A., Malitzky, A. and Shorten, G., 2000. Microzonation of the expected seismic site effects across Port Vila, Vanuatu. Journal of Earthquake Engineering, 4, No. 2, 215-231.

3D Gravity Inversion by Growing Bodies and Shaping Layers at Mt. Vesuvius (Southern Italy)

NASA Astrophysics Data System (ADS)

Berrino, Giovanna; Camacho, Antonio G.

2008-06-01

To improve our knowledge of the structural pattern of Mt. Vesuvius and its magmatic system, which represents one of the three volcanoes located in the Neapolitan area (together with Campi Flegrei and Ischia; southern Italy), we analyze here the Bouguer gravity map that is already available through its interpretation by means of 2.5-dimensional modelling. We have carried out a three-dimensional interpretation using a new and original algorithm, known as ‘Layers’, that has been especially processed for this purpose. Layers works in an automatic and non-subjective way, and allows the definition of the structural settings in terms of several layers, each representing a specific geological formation. The same data are also interpreted in terms of isolated and shallow anomalous density bodies using a well tested algorithm known as ‘Growth’. We focus our inversions on the Mt. Vesuvius volcano, while globally analyzing the entire Neapolitan area, in order to investigate the deep structures, and in particular the deep extended ‘sill’ that has been revealed by seismic tomography. The final models generally confirm the global setting of the area as outlined by previous investigations, mainly for the shape and depth of the carbonate basement below Mt. Vesuvius. The presence of lateral density contrasts inside the volcano edifice is also shown, which was only hypothesized in the 2.5-dimensional inversion. Moreover, the models allow us to note a high density body that rises from the top of the carbonate basement and further elongates above sea level. This probably represents an uprising of the same basement, which is just below the volcano and which coincides with the VP and VP/VS anomalies detected under the crater. The three-dimensional results also reveal that the two inversion methods provide very similar models, where the high density isolated body in the Growth model can be associated with the rising high density anomaly in the Layers model. Taking into account the density of these modelled bodies, we would also suggest that they represent solidified magma bodies, as suggested by other studies. Finally, we did not clearly detect any deep anomalous body that can be associated with the sill that was suggested by seismic tomography.

Petrological and geophysical investigations of mafic rock properties in the Snake River Plain, in the Moscow-Pullman Aquifer, and in lunar impact craters

NASA Astrophysics Data System (ADS)

Piersol, Mark W.

2016-08-01

This dissertation is composed of three separate papers presented in three chapters. Although largely unrelated, the three papers all deal with mafic igneous rock. Chapter 1 is an investigation into the petrological properties of basalts found in the western and eastern Snake River plain of Idaho and the Saddle Mountain basalts of Washington and Idaho. Many of these basalts, separated by up to 600 km and spanning a period of over 12 Ma, appear to have been produced by a common mantle source. A tectonic model is proposed to explain their common origins. This paper was submitted to the journal Geosphere with co-author Professor Dennis J. Geist. Chapter 2 describes a geophysical model of the Kamiak Gap located in the basalt-hosted Moscow-Pullman aquifer of Idaho and Washington. Contrary to previous models, we conclude that there is indeed a hydrological connection between the southern and northern sections of the aquifer through the Kamiak Gap. This chapter is shown on the Palouse Basin Aquifer Committee Website http://www.webpages.uidaho.edu/pbac) and contributed, in part, to the publication of a separate hydrology oriented paper in the journal Resources (Piersol and Sprenke, 2015). Chapter 3 presents a geomorphometric model of impact craters on the Lunar highlands that is used in conjunction with published GRAIL Bouguer reduction density and residual Bouguer anomaly results to model the average bulk density of the mafic megaregolithic crust of the Moon. The currently visible craters in the lunar highlands are shown to have negative mass deficiencies, which correlate with elevation. The bulk density of the lunar megaregolith crust is found to be much lower than the generally used value found by minimizing the correlation between gravity and topography. This research has been published in part in a Lunar and Planetrary Science Institute meeting paper (Piersol and Sprenke, 2014) and is written in a form for future publication in the journal Icarus..

Establishment of National Gravity Base Network of Iran

NASA Astrophysics Data System (ADS)

Hatam Chavari, Y.; Bayer, R.; Hinderer, J.; Ghazavi, K.; Sedighi, M.; Luck, B.; Djamour, Y.; Le Moign, N.; Saadat, R.; Cheraghi, H.

2009-04-01

A gravity base network is supposed to be a set of benchmarks uniformly distributed across the country and the absolute gravity values at the benchmarks are known to the best accessible accuracy. The gravity at the benchmark stations are either measured directly with absolute devices or transferred by gravity difference measurements by gravimeters from known stations. To decrease the accumulation of random measuring errors arising from these transfers, the number of base stations distributed across the country should be as small as possible. This is feasible if the stations are selected near to the national airports long distances apart but faster accessible and measurable by a gravimeter carried in an airplane between the stations. To realize the importance of such a network, various applications of a gravity base network are firstly reviewed. A gravity base network is the required reference frame for establishing 1st , 2nd and 3rd order gravity networks. Such a gravity network is used for the following purposes: a. Mapping of the structure of upper crust in geology maps. The required accuracy for the measured gravity values is about 0.2 to 0.4 mGal. b. Oil and mineral explorations. The required accuracy for the measured gravity values is about 5 µGal. c. Geotechnical studies in mining areas for exploring the underground cavities as well as archeological studies. The required accuracy is about 5 µGal and better. d. Subsurface water resource explorations and mapping crustal layers which absorb it. An accuracy of the same level of previous applications is required here too. e. Studying the tectonics of the Earth's crust. Repeated precise gravity measurements at the gravity network stations can assist us in identifying systematic height changes. The accuracy of the order of 5 µGal and more is required. f. Studying volcanoes and their evolution. Repeated precise gravity measurements at the gravity network stations can provide valuable information on the gradual upward movement of lava. g. Producing precise mean gravity anomaly for precise geoid determination. Replacing precise spirit leveling by the GPS leveling using precise geoid model is one of the forth coming application of the precise geoid. A gravity base network of 28 stations established over Iran. The stations were built mainly at bedrocks. All stations were measured by an FG5 absolute gravimeter, at least 12 hours at each station, to obtain an accuracy of a few micro gals. Several stations were repeated several times during recent years to estimate the gravity changes.

Principal facts and an approach to collecting gravity data using near-real-time observations in the vicinity of Barstow, California

USGS Publications Warehouse

Phelps, G.; Cronkite-Ratcliff, C.; Klofas, L.

2013-01-01

A gravity survey was done in the vicinity of Barstow, California, in which data were processed and analyzed in the field. The purpose of the data collection was to investigate possible changes in gravity across mapped Quaternary faults and to improve regional gravity coverage, adding to the existing national gravity database. Data were collected, processed, analyzed, and interpreted in the field in order to make decisions about where to collect data for the remainder of the survey. Geological targets in the Barstow area included the Cady Fault, the Manix Fault, and the Yermo Hills. Upon interpreting initial results, additional data were collected to more completely define the fault targets, rather than collecting data to improve the regional gravity coverage in an adjacent area. Both the Manix and Cady Faults showed gravitational expression of the subsurface in the form of steep gravitational gradients that we interpret to represent down-dropped blocks. The gravitational expression of the Cady Fault is on trend with the linear projection of the mapped fault, and the gravitational expression of the Manix Fault is north of the current northernmost mapped strand of the fault. The relative gravitational low over the Yermo Hills was confirmed and better constrained, indicating a significant thickness of sediments at the junction of the Calico, Manix, and Tin Can Alley Faults.

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.

Exploring the Moon and Mars Using an Orbiting Superconducting Gravity Gradiometer

NASA Technical Reports Server (NTRS)

Paik, Ho Jung; Strayer, Donald M.

2004-01-01

Gravity measurement is fundamental to understanding the interior structure, dynamics, and evolution of planets. High-resolution gravity maps will also help locating natural resources, including subsurface water, and underground cavities for astronaut habitation on the Moon and Mars. Detecting the second spatial derivative of the potential, a gravity gradiometer mission tends to give the highest spatial resolution and has the advantage of requiring only a single satellite. We discuss gravity missions to the Moon and Mars using an orbiting Superconducting Gravity Gradiometer and discuss the instrument and spacecraft control requirements.

Integration of Full Tensor Gravity and Z-Axis Tipper Electromagnetic Passive Low Frequency EM Instruments for Simultaneous Data Acquisition - Final Technical Report

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

Wieberg, Scott

Ground gravity is a common and useful tool for geothermal exploration. Gravity surveys map density changes in the subsurface that may be caused by tectonic deformation such as faulting, fracturing, plutonism, volcanism, hydrothermal alteration, etc. Full Tensor Gravity Gradient (FTG) data has been used for over a decade in both petroleum and mining exploration to map changes in density associated with geologic structure. Measuring the gravity gradient, rather than the gravity field, provides significantly higher resolution data. Modeling studies have shown FTG data to be a viable tool for geothermal exploration, but no FTG data had been acquired for geothermalmore » applications to date. Electromagnetic methods have been used for geothermal exploration for some time. The Z-Axis Tipper Electromagnetic (ZTEM) was a newer technology that had found success in mapping deep conductivity changes for mining applications. ZTEM had also been used in limited tests for geothermal exploration. This newer technology provided the ability to cost effectively map large areas whilst detailing the electrical properties of the geological structures at depths. The ZTEM is passive and it uses naturally occurring audio frequency magnetic (AFMAG) signals as the electromagnetic triggering source. These geophysical methods were to be tested over a known geothermal site to determine whether or not the data provided the information required for accurately interpreting the subsurface geologic structure associated with a geothermal deposit. After successful acquisition and analysis of the known source area, an additional survey of a “greenfield” area was to be completed. The final step was to develop a combined interpretation model and determine if the combination produced a higher confident geophysical model compared to models developed using each of the technologies individually.« less

Madagascar's Escape from Africa: New Constraints and Understanding for Plate Tectonic Reconstructions

NASA Astrophysics Data System (ADS)

Phethean, J. J. J.; Davies, R. J.; Van Hunen, J.; Kalnins, L. M.; McCaffrey, K. J. W.

2015-12-01

We present a new plate tectonic reconstruction for the drift of Madagascar away from East Africa using the new Sandwell and Smith gravity dataset (V23.1). Detailed interpretation of free-air and Bouguer anomalies, together with gravity gradients, has allowed interpretation of the extinct mid ocean ridge and associated fracture zone lineaments from the Western Somali Basin. Combined with temporal constraints from previous ocean magnetic anomaly interpretations, this analysis produces a reconstruction that supports Reeves' (2014) tight fit of Gondwana fragments. Furthermore, it sheds light on the nature of the Davie Fracture Zone (DFZ) and the position of the continent-ocean boundary (COB) in the region. The model predicts that the COB lies along the Rovuma Basin; and that offshore Tanzania is most likely a segmented and obliquely rifted margin, not a transform continental margin along the DFZ as previously thought. This places the COB up to several hundred kilometres farther inboard than previous interpretations, which is supported by new seismic evidence of oceanic crust inboard of the DFZ. We show the DFZ to be a major ocean-ocean fracture zone formed by the coalescence of several smaller fracture zones during a change in plate motions as Madagascar escaped from Africa. This new geodynamical understanding has important implications for petroleum industry activities in East Africa, as the expected heat flow varies dramatically between oceanic and continental crust. Reeves, C., 2014. The position of Madagascar within Gondwana and its movements during Gondwana dispersal. J. Afr. Earth. Sci. 94, 45-57.

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-minute gridded data were obtained from the Satellite Geodesy at the Scripps Institution of Oceanography, Smith & Sandwell (1997; http://topex.ucsd.edu. Gravity anomaly data were re-gridded using the ETOPO2v2 grid. All calculations and maps were made using MatLab 2007 software. 0.3.2 Cross-Product Cross-product is the result of multiplication of bathymetric and gravity anomaly gradient magnitudes by the sine of the angle between them. According to the definition of gradient cross-product minimal values are expected to be found in points where the angle between gradients is close to zero or where one or both of the gradient magnitudes have values close to zero. It creates an ambiguity and a problem for data interpretation since there is no exact correspondence between bathymetric structures and gravity anomalies. 0.3.3 Dot-Product Dot-product is the result of multiplication of bathymetric and gravity anomaly magnitudes by the cosine on the angle between them. According to the definition of dot-product, values close to zero can be generated by near perpendicular orientation of the gradients or small magnitudes of one or both gradients. So, the results are mutually increased in areas with larger magnitudes or smaller angles between gradients. Due to this mutual amplification dot-products are less affected by the ambiguity of cross-product explained above. The same statistical separation of cross-product was used to support the conclusions. 0.3.4 Statistics and Significance Criteria Statistical analysis was made in order to sort the data into two groups to reduce ambiguity effect: first group - data with magnitudes that could be considered anomalous (where the main minimizing source is the angle between the gradients and the second group - data with magnitudes variations that could be considered as (non significant or background (where cross-product value is determined by the small magnitude). It was chosen to use the mean value and standard deviation (std) to sort the data in such two groups. These values were determined for bathymetric and gravity anomaly gradient magnitudes creating two data sets - one where one or both gradient magnitudes are one standard deviation larger than the mean value with a total of 7831 (anomalous) and a second one where both magnitudes differ smaller than one standard deviation from the mean value with 85584 (background ). Statistical analysis of distribution patterns for both groups was made. 0.4 Examples of Method Application 0.4.1 Map of Angles Between Gradients Figure 1 shows the map of angle values. The angle values were divided into 4 equal intervals. The statistical distribution of angles between gradient in the given intervals is the following (percents of the total): 0 to 60° - 51.39% of the values; 60° to 90° -12.08%; 90° to 120° -14.92%; 120° to 180° -21.18%. It can be seen that 51% of the gradients have a small angle between them, 72% of gradients can be considered as parallel (72%) with angles smaller than 60° or bigger than 120° between them. After statistical separation in the anomalous group almost 91% of the gradients have an angle smaller than 60° while in the background group just 48.6%. From these results we can make a conclusion that the majority of the bathymetric and gravity anomaly gradients are related. Regions with higher gradient magnitudes are characterized by cosine values close to 1 (indicating a small angle between them). The size of the areas characterized by small angles between gradients exceed the size of bathymetric and gravity anomaly isolines characterizing the area of influence of the structures and their effects. Regions with no significant anomalies show uncorrelated value spots. 0.4.2 Map of Cross-Product The resulting map shows small spots of higher cross-product magnitudes following magnitude isolines. About 90% of the values are close to minimum. As was mentioned before, we can presume that areas where bathymetry and gravity anomaly gradient cross-products have smallest magnitudes there is a good correspondence between them indicating a good correspondence between shapes. According to these results for the studied area the shapes and positions of bathymetric structures and gravity anomalies are well correlated suggesting strong correlation between source and its effect. 0.4.3 Map of Dot-Product The resulting map resembles bathymetric and gravity anomaly isolines. All the sea mounts, banks, continental slope and other notable geomorphologic structures and gravity anomalies are well delimitated in the dot-product map eliminating uncorrelated areas where gradient orientations can be considered as near perpendicular. The dot-product map of the studied area suggests a strong source-effect between bathymetry and gravity anomaly. 0.5 Conclusions The joint image interpretation technique uses three different criteria that are sensitive to different gradient properties. Angles between gradients are a good indicator of areas where data are related and it is not sensitive to the magnitudes of the gradients. Angles maps can be used to find areas with direct and inverse relation between mapped properties and contour areas of influence of anomalies unseen on gradient magnitude maps alone. Statistical measures of distribution of angles can be an indicator of relation between data sets as show using significance criteria. Cross-product map has a spotted character of contours. To reduce the effects of the ambiguity the separation into two groups proved to be useful. It helps to separate the cross-product values that are minimized due to gradient magnitudes from those that minimize due to sine values which is a measure of correlation between them. Dot-product values contour areas where gradients are correlated. According to joint image interpretation technique applied bathymetric structures especially the volcanic seamounts and banks in the southern part of East-Brazilian Coast are closely related to the observed gravity anomalies and can be interpreted as sources and effect. This technique also helps to evaluate the shape and dispersion of the gravitational effect from a bathymetrical source. 0.6 References Dehlinger P., Marine Gravity, Elsevier, 1978. Gallardo, L. A., and M. A. Meju., Joint 2D cross-gradient imaging of magnetotelluric and seismic travel-time data for structural and lithological classification, Geophys. J. Int., 169, 1261-1272. (2007) Gallardo, L.A., M. A. Meju (2004), Joint two-dimensional dc resistivity and seismic traveltime inversion with cross-gradients constraints, J. Geophys. Res., 109, B03311, doi:10.1029/2003JB002716 Jacoby, W., and Smilde P. L., Gravity Interpretation, Springer, 2009. McKenzie D. & Bowin C. 1976. The relationship between bathymetry and gravity in Atlantic Ocean. Journal of Geophysical Research, 81: 1903-1915. Roy. K. K., Potential Theory in Applied Geophysics, Springer, 2008. Smith, W. H. F., and D. T. Sandwell, Global seafloor topography from satellite altimetry and ship depth soundings, Science, v. 277, p. 1957-1962, 26 Sept., 1997. Sandwell, D. T., and W. H. F. Smith, Global marine gravity from retracked Geosat and ERS-1 altimetry: Ridge Segmentation versus spreading rate, J. Geophys. Res., 114, B01411, doi:10.1029/2008JB006008, 2009. Zembruscki, S.G. 1979. Geomorfologia da Margem Continental Sul Brasileira e das Bacias Oceânicas Adjacentes. In: Geomorfologia da margem continental brasileira e das áreas oceânicas adjacentes. Série Projeto REMAC, N° 7.

Principal Facts for 463 Gravity Stations in the Vicinity of Tangle Lakes, East-Central Alaska

USGS Publications Warehouse

Morin, Robert L.; Glen, Jonathan M.G.

2002-01-01

During the summer of 2001, a gravity survey was conducted in the vicinity of Tangle Lakes, east-central Alaska. Measurements of 87 gravity stations were made. The Tangle Lakes area is located about 25 km west of Paxson and north of the Denali Highway. The gravity survey is located on the southwest corner of the Mt. Hayes and the northwest corner of the Gulkana 1:250,000 scale USGS topographic maps. The boundaries of the study area are 62 deg 30' to 63 deg 30' N. latitude and 145 deg 30' to 147 deg 00' W. longitude. A map showing the location of the study area is shown in figure 1. One gravity base station was used for control for this survey. This base station, TLIN is located at the Tangle Lakes Inn. The observed gravity of this station was calculated based on multiple ties to base stations ANCU in Anchorage, PALH in Palmer, BD27 in Gulkana, and base stations D42, and D57 along the Denali Highway.

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

Lunar floor-fractured craters are a class of 170 lunar craters with anomalously shallow, fractured floors. Two end-member processes have been proposed for the floor formation: viscous relaxation, and subcrater magmatic intrusion and sill formation. Recent morphometric analysis with new Lunar Reconnaissance Orbiter Laser Altimeter (LOLA) and image (LROC) data supports an origin related to shallow magmatic intrusion and uplift. We find that the distribution and characteristics of the FFC population correlates strongly with crustal thickness and the predicted frequency distribution of overpressurization values of magmatic dikes. For a typical nearside lunar crustal thickness, dikes with high overpressurization values favor surface effusive eruptions, medium values favor intrusion and sill formation, and low values favor formation of solidified dikes concentrated lower in the crust. We develop a model for this process, make predictions for the morphologic, morphometric, volcanic, and geophysical consequences of the process and then compare these predictions with the population of observed floor-fractured craters. In our model, the process of magmatic intrusion and sill formation begins when a dike propagates vertically towards the surface; as the dike encounters the underdense brecciated region beneath the crater, the magmatic driving pressure is insufficient to continue vertical propagation, but pressure in the stalled dike exceeds the local lithostatic pressure. The dike then begins to propagate laterally forming a sill which does not propagate past the crater floor region because increased overburden pressure from the crater wall and rim crest pinch off the dike at this boundary; the sill then continues to inflate, further raising and fracturing the brittle crater floor. When the intrusion diameter to intrusion depth ratio is smaller than a critical value, the intrusion assumes a laccolith shape with a domed central region. When the ratio exceeds a critical value, 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.

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

NASA Technical Reports Server (NTRS)

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

2003-01-01

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

Hydro-gravimetry in West-Africa: First results from the Djougou (Benin) superconducting gravimeter

NASA Astrophysics Data System (ADS)

Hector, Basile; Hinderer, Jacques; Séguis, Luc; Boy, Jean-Paul; Calvo, Marta; Descloitres, Marc; Rosat, Séverine; Galle, Sylvie; Riccardi, Umberto

2014-10-01

The increasing number of hydro-gravimetry studies proves the rising interest of the hydrology community toward this monitoring method. The accuracy of superconducting gravimeters (SG) potentially allows the retrieval of small water storage changes (WSC) down to a few millimeters of equivalent water thickness. However, the importance of corrections applied to SG data to achieve such a precision in gravity residuals should be recalled. The Djougou permanent gravity station presented in this paper and located in northern Benin, West-Africa, provides a good opportunity to review these considerations. This station is equipped since July 2010 with the superconducting gravimeter SG-060 aimed at deriving WSC at different time-scales, daily to inter-annual. In this area, WSC are (1) part of the control system for evapotranspiration (ET) process, a key variable of the West-African monsoon cycle and (2) the state variable for resource management, a critical issue in storage-poor hard rock basement contexts such as in northern Benin. The potential for deriving WSC from time-lapse gravity data partly depends on environmental features such as topography and the instrument shelter. Therefore, this issue is addressed first, with the background idea that such sensitivity analysis should be undertaken before setting up any new instrument. In Djougou, local topography is quite flat leading to a theoretical straightforward relationship between gravity changes and WSC, close to the standard Bouguer value. However, the shelter plays a significant masking role, which is the principal limitation to the retrieval of fast hydrological processes such as ET following a rain event. Several issues concerning classical gravity corrections are also addressed in the paper. These include gap-filling procedures during rain-events and drift estimates for short time series. Special attention is provided to atmospheric corrections, and different approaches are tested: a simple scalar admittance, a filtered scalar admittance, a frequency-dependent admittance and direct atmospheric loading calculations. It is shown that the physically based approach of direct loading calculations performs better in both residual minimization and ET retrieval. Moreover, non-local hydrological effects are investigated and account for about 20% of the gravity residuals. Finally, gravity residuals are briefly analyzed at two distinct time scales: rapid (up to a few days) and seasonal. At the rapid time-scale, it is shown that ET retrieval is hardly achievable given shelter size and state-of-the-art atmospheric corrections. Still, mean values retrieved from this study are in accordance with known values of potential ET and lateral flow. Direct comparison of gravity changes with hydrological data (neutron probe monitoring and water table levels) show some discrepancies, particularly for the hydrological year of 2011, for which all hydrological data show a deficit, but SG and FG5 data do not. This preliminary analysis both provides a basis and call for further hydro-gravity modeling, to comprehensively investigate the water-cycle at the Djougou station.

ESA BRAT (Broadview Radar Altimetry Toolbox) and GUT (GOCE User Toolbox) toolboxes

NASA Astrophysics Data System (ADS)

Benveniste, J.; Ambrozio, A.; Restano, M.

2016-12-01

The Broadview Radar Altimetry Toolbox (BRAT) is a collection of tools designed to facilitate the processing of radar altimetry data from previous and current altimetry missions, including the upcoming Sentinel-3A L1 and L2 products. A tutorial is included providing plenty of use cases. BRAT's future release (4.0.0) is planned for September 2016. Based on the community feedback, the frontend has been further improved and simplified whereas the capability to use BRAT in conjunction with MATLAB/IDL or C/C++/Python/Fortran, allowing users to obtain desired data bypassing the data-formatting hassle, remains unchanged. Several kinds of computations can be done within BRAT involving the combination of data fields, that can be saved for future uses, either by using embedded formulas including those from oceanographic altimetry, or by implementing ad-hoc Python modules created by users to meet their needs. BRAT can also be used to quickly visualise data, or to translate data into other formats, e.g. from NetCDF to raster images. The GOCE User Toolbox (GUT) is a compilation of tools for the use and the analysis of GOCE gravity field models. It facilitates using, viewing and post-processing GOCE L2 data and allows gravity field data, in conjunction and consistently with any other auxiliary data set, to be pre-processed by beginners in gravity field processing, for oceanographic and hydrologic as well as for solid earth applications at both regional and global scales. Hence, GUT facilitates the extensive use of data acquired during GRACE and GOCE missions. In the current 3.0 version, GUT has been outfitted with a graphical user interface allowing users to visually program data processing workflows. Further enhancements aiming at facilitating the use of gradients, the anisotropic diffusive filtering, and the computation of Bouguer and isostatic gravity anomalies have been introduced. Packaged with GUT is also GUT's VCM (Variance-Covariance Matrix) tool for analysing GOCE's variance-covariance matrices. BRAT and GUT toolboxes can be freely downloaded, along with ancillary material, at https://earth.esa.int/brat and https://earth.esa.int/gut.

The BRAT and GUT Couple: Broadview Radar Altimetry and GOCE User Toolboxes

NASA Astrophysics Data System (ADS)

Benveniste, J.; Restano, M.; Ambrózio, A.

2017-12-01

The Broadview Radar Altimetry Toolbox (BRAT) is a collection of tools designed to facilitate the processing of radar altimetry data from previous and current altimetry missions, including Sentinel-3A L1 and L2 products. A tutorial is included providing plenty of use cases. BRAT's next release (4.2.0) is planned for October 2017. Based on the community feedback, the front-end has been further improved and simplified whereas the capability to use BRAT in conjunction with MATLAB/IDL or C/C++/Python/Fortran, allowing users to obtain desired data bypassing the data-formatting hassle, remains unchanged. Several kinds of computations can be done within BRAT involving the combination of data fields, that can be saved for future uses, either by using embedded formulas including those from oceanographic altimetry, or by implementing ad-hoc Python modules created by users to meet their needs. BRAT can also be used to quickly visualise data, or to translate data into other formats, e.g. from NetCDF to raster images. The GOCE User Toolbox (GUT) is a compilation of tools for the use and the analysis of GOCE gravity field models. It facilitates using, viewing and post-processing GOCE L2 data and allows gravity field data, in conjunction and consistently with any other auxiliary data set, to be pre-processed by beginners in gravity field processing, for oceanographic and hydrologic as well as for solid earth applications at both regional and global scales. Hence, GUT facilitates the extensive use of data acquired during GRACE and GOCE missions. In the current 3.1 version, GUT has been outfitted with a graphical user interface allowing users to visually program data processing workflows. Further enhancements aiming at facilitating the use of gradients, the anisotropic diffusive filtering, and the computation of Bouguer and isostatic gravity anomalies have been introduced. Packaged with GUT is also GUT's Variance-Covariance Matrix tool (VCM). BRAT and GUT toolboxes can be freely downloaded, along with ancillary material, at https://earth.esa.int/brat and https://earth.esa.int/gut.

Mantle wedge serpentinisation in a cold subduction setting: implications for slow-slip, subsidence, and large, negative, gravity anomalies

NASA Astrophysics Data System (ADS)

Stern, T. A.; Dimech, J.; Henrys, S.; Horgan, H. J.; Lamb, S. H.

2016-12-01

Seismic exploration of the crust in the behind-subduction region of New Zealand's southern Hikurangi margin provides new evidence for a link between serpentinization, megathrust slow slip events and large (-150 mgal) negative gravity anomalies. Our analysis focuses on a high resolution, crustal scale, migrated, seismic reflection data set collected with a 10-km-long streamer. A dominant feature of the data is a localized region of relatively bright reflectors, at a depth of 30 km where the overlying Australian plate Moho abuts the subducted Pacific plate. The reflectors are arched in a feature that resembles a hanging-wall anticline faulted. We interpret these features to image the top of a serpentinized mantle wedge, because: (1) a drop in the frequency content of reflections below the high amplitude reflectors indicates strong attenuation (Q 20±10) of seismic energy in the wedge; (2) there is a polarity/impedance contrast reversal implying a drop in seismic P-wave speed; and (3) large regions of Moho reflectivity adjacent to the bright reflectivity are weak or absent. We suggest that the mantle wedge in the southern portion of the Hikurangi margin is cold enough for peridotite to be hydrated and altered to antigorite, thereby giving rise to the observed seismic reflection characteristics and creating a lower viscosity mantle wedge. In the past 4 My, a roughly circular sedimentary basin, up to 4 km deep, has developed in the region, and this basin is associated with a -150 mgal free-air and Bouguer gravity anomaly. We propose that serpentinite is implicated in both the subsidence, due to induced pressure gradients as it undergoes corner flow above the subducted slab, and the strong negative gravity anomaly. Serpentinisation of 50% will lower the density of peridotite by about 300 kg/m3, and this could account for up to -100 mgal of the observed anomaly. Finally, the proximity of recently documented slow-slip events to the proposed zone of serpentinisation supports a causal link between the two phenomena.

Error Reduction Analysis and Optimization of Varying GRACE-Type Micro-Satellite Constellations

NASA Astrophysics Data System (ADS)

Widner, M. V., IV; Bettadpur, S. V.; Wang, F.; Yunck, T. P.

2017-12-01

The Gravity Recovery and Climate Experiment (GRACE) mission has been a principal contributor in the study and quantification of Earth's time-varying gravity field. Both GRACE and its successor, GRACE Follow-On, are limited by their paired satellite design which only provide a full map of Earth's gravity field approximately every thirty days and at large spatial resolutions of over 300 km. Micro-satellite technology has presented the feasibility of improving the architecture of future missions to address these issues with the implementation of a constellations of satellites having similar characteristics as GRACE. To optimize the constellation's architecture, several scenarios are evaluated to determine how implementing this configuration affects the resultant gravity field maps and characterize which instrument system errors improve, which do not, and how changes in constellation architecture affect these errors.

Short-Arc Analysis of Intersatellite Tracking Data in a Gravity Mapping Mission

NASA Technical Reports Server (NTRS)

Rowlands, David D.; Ray, Richard D.; Chinn, Douglas S.; Lemoine, Frank G.; Smith, David E. (Technical Monitor)

2001-01-01

A technique for the analysis of low-low intersatellite range-rate data in a gravity mapping mission is explored. The technique is based on standard tracking data analysis for orbit determination but uses a spherical coordinate representation of the 12 epoch state parameters describing the baseline between the two satellites. This representation of the state parameters is exploited to allow the intersatellite range-rate analysis to benefit from information provided by other tracking data types without large simultaneous multiple data type solutions. The technique appears especially valuable for estimating gravity from short arcs (e.g., less than 15 minutes) of data. Gravity recovery simulations which use short arcs are compared with those using arcs a day in length. For a high-inclination orbit, the short-arc analysis recovers low-order gravity coefficients remarkably well, although higher order terms, especially sectorial terms, are less accurate. Simulations suggest that either long or short arcs of GRACE data are likely to improve parts of the geopotential spectrum by orders of magnitude.

Lunar Prospector: overview.

PubMed

Binder, A B

1998-09-04

Lunar Prospector is providing a global map of the composition of the moon and analyzing the moon's gravity and magnetic fields. It has been in a polar orbit around the moon since 16 January 1998. Neutron flux data show that there is abundant H, and hence probably abundant water ice, in the lunar polar regions. Gamma-ray and neutron data reveal the distribution of Fe, Ti, and other major and trace elements on the moon. The data delineate the global distributions of a key trace element-rich component of lunar materials called KREEP and of the major rock types. Magnetic mapping shows that the lunar magnetic fields are strong antipodal to Mare Imbrium and Mare Serenitatis and has discovered the smallest known magnetosphere, magnetosheath, and bow shock complex in the solar system. Gravity mapping has delineated seven new gravity anomalies and shown that the moon has a small Fe-rich core of about 300 km radius.

Contribution of gravity data and Sentinel-1 image for structural mapping. Case of Beni Mellal Atlas and Beni Moussa plain (Morocco).

NASA Astrophysics Data System (ADS)

Boutirame, Ikram; Boukdir, Ahmed; Akhssas, Ahmed; Boutirame, Fatima; Manar, Ahmed; Aghzzaf, Brahim

2018-05-01

The present work is a combined study of gravity and Sentine-1 data for fracture mapping in the karstic massif of Beni Mellal Atlas and the adjacent plain of Beni Moussa. In order to locate the various faults that contribute to the study area structuring, the gravimetric contacts analysis method, based on the joint use of the horizontal gradient and the upward continuation at different altitudes, has been applied to the gravity data. To optimize the structural mapping in the study area, the gravimetric lineaments obtained were completed and correlated with the lineaments got from Sentinel-1 image. Four faults families of NE-SW; E-O; N-S and NWSE directions have been highlighted. There fault families are perfectly combined with the studied area's surface water network, moreover, they corroborate with the previous geological and structural studies.

Seismic expression of the Chesapeake Bay impact crater: Structural and morphologic refinements based on new seismic data

USGS Publications Warehouse

Poag, C. Wylie; Hutchinson, Deborah R.; Colman, Steve M.; Lee, Myung W.; Dressler, B.O.; Sharpton, V.L.

1999-01-01

This work refines previous interpretations of the structure and morphology of the Chesapeake Bay impact crater on the basis of more than 1,200 km of multichannel and single-channel seismic reflection profiles collected in the bay and on the adjacent continental shelf. The outer rim, formed in sedimentary rocks, is irregularly circular, with an average diameter of ~85 km. A 20–25-km-wide annular trough separates the outer rim from an ovate, crystalline peak ring of ~200 m of maximum relief. The inner basin is 35–40 km in diameter, and at least 1.26 km deep. A crystalline(?) central peak, approximately 1 km high, is faintly imaged on three profiles, and also is indicated by a small positive Bouguer gravity anomaly. These features classify the crater as a complex peak-ring/central peak crater. Chesapeake Bay Crater is most comparable to the Ries and Popigai Craters on Earth; to protobasins on Mars, Mercury, and the Moon; and to type D craters on Venus.

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.

V-GRAM: Magellan bulletin about Venus and the radar mapping mission

NASA Technical Reports Server (NTRS)

Jasnow, Mona (Editor)

1993-01-01

Papers on the following topics are presented: Magellan project update; summary of Magellan science findings; excerpt from 'Acquisition and Analysis of Magellan Gravity Data'; Magellan gravity; and Magellan stereo image data.

Shape and Gravity of Vesta South Pole

NASA Image and Video Library

2012-04-25

This set of images from NASA Dawn spacecraft shows topography of the southern hemisphere of the giant asteroid Vesta and a map of Vesta gravity variations that have been adjusted to account for Vesta shape.

Aeromagnetic signatures over western Marie Byrd Land provide insight into magmatic arc basement, mafic magmatism and structure of the Eastern Ross Sea Rift flank

NASA Astrophysics Data System (ADS)

Ferraccioli, F.; Bozzo, E.; Damaske, D.

2002-03-01

Aeromagnetic signatures over the Edward VII Peninsula (E7) provide new insight into the largely ice-covered and unexplored eastern flank of the Ross Sea Rift (RSR). Positive anomalies, 10-40 km in wavelength and with amplitudes ranging from 50 to 500 nT could reveal buried Late Devonian(?)-Early Carboniferous Ford Granodiorite plutons. This is suggested by similar magnetic signature over exposed, coeval Admiralty Intrusives of the Transantarctic Mountains (TAM). Geochemical data from mid-Cretaceous Byrd Coast Granite, contact metamorphic effects on Swanson Formation and hornblende-bearing granitoid dredge samples strengthen this magnetic interpretation, making alternative explanations less probable. These magnetic anomalies over formerly adjacent TAM and western Marie Byrd Land (wMBL) terranes resemble signatures typically observed over magnetite-rich magmatic arc plutons. Shorter wavelength (5 km) 150 nT anomalies could speculatively mark mid-Cretaceous mafic dikes of the E7, similar to those exposed over the adjacent Ford Ranges. Anomalies with amplitudes of 100-360 nT over the Sulzberger Bay and at the margin of the Sulzberger Ice Shelf likely reveal mafic Late Cenozoic(?) volcanic rocks emplaced along linear rift fabric trends. Buried volcanic rock at the margin of the interpreted half-graben-like "Sulzberger Ice Shelf Block" is modelled in the Kizer Island area. The volcanic rock is marked by a coincident positive Bouguer gravity anomaly. Late Cenozoic volcanic rocks over the TAM, in the RSR, and beneath the West Antarctic Ice Sheet exhibit comparable magnetic anomaly signature reflecting regional West Antarctic Rift fabric. Interpreted mafic magmatism of the E7 is likely related to mid-Cretaceous and Late Cenozoic regional crustal extension and possible mantle plume activity over wMBL. Magnetic lineaments of the E7 are enhanced in maximum horizontal gradient of pseudo-gravity, vertical derivative and 3D Euler Deconvolution maps. Apparent vertical offsets in magnetic basement at the location of the lineaments and spatially associated mafic dikes and volcanic rocks result from 2.5D magnetic modelling. A rift-related fault origin for the magnetic lineaments, segmenting the E7 region into horst and graben blocks, is proposed by comparison with offshore seismic reflection, marine gravity, on-land gravity, radio-echo sounding, apatite fission track data and structural geology. The NNW magnetic lineament, which we interpret to mark the eastern RSR shoulder, forms the western margin of the "Alexandra Mountains horst". This fundamental aeromagnetic feature lies on strike with the Colbeck Trough, a prominent NNW half-graben linked to Late Cretaceous(?) and Cenozoic(?) faulting in the eastern RSR. East-west and north-north-east to NE magnetic trends are also imaged. Magnetic trends, if interpreted as reflecting the signature of rift-related normal faults, would imply N-S to NE crustal extension followed by later northwest-southeast directed extension. NW-SE extension would be compatible with Cenozoic(?) oblique RSR rifting. Previous structural data from the Ford Ranges have, however, been interpreted to indicate that both Cretaceous and Cenozoic extensions were N-S to NE-SW directed.

Gravity and Aeromagnetic Gradients within the Yukon-Tanana Upland, Black Mountain Tectonic Zone, Big Delta Quadrangle, east-central Alaska

USGS Publications Warehouse

Saltus, R.W.; Day, W.C.

2006-01-01

The Yukon-Tanana Upland is a complex composite assemblage of variably metamorphosed crystalline rocks with strong North American affinities. At the broadest scale, the Upland has a relatively neutral magnetic character. More detailed examination, however, reveals a fundamental northeast-southwest-trending magnetic gradient, representing a 20-nT step (as measured at a flight height of 300 m) with higher values to the northwest, that extends from the Denali fault to the Tintina fault and bisects the Upland. This newly recognized geophysical gradient is parallel to, but about 100 km east of, the Shaw Creek fault. The Shaw Creek fault is mapped as a major left-lateral, strike-slip fault, but does not coincide with a geophysical boundary. A gravity gradient coincides loosely with the southwestern half of the magnetic gradient. This gravity gradient is the eastern boundary of a 30-mGal residual gravity high that occupies much of the western and central portions of the Big Delta quadrangle. The adjacent lower gravity values to the east correlate, at least in part, with mapped post-metamorphic granitic rocks. Ground-based gravity and physical property measurements were made in the southeastern- most section of the Big Delta quadrangle in 2004 to investigate these geophysical features. Preliminary geophysical models suggest that the magnetic boundary is deeper and more fundamental than the gravity boundary. The two geophysical boundaries coincide in and around the Tibbs Creek region, an area of interest to mineral exploration. A newly mapped tectonic zone (the Black Mountain tectonic zone of O'Neill and others, 2005) correlates with the coincident geophysical boundaries.

A no-hair theorem for black holes in f(R) gravity

NASA Astrophysics Data System (ADS)

Cañate, Pedro

2018-01-01

In this work we present a no-hair theorem which discards the existence of four-dimensional asymptotically flat, static and spherically symmetric or stationary axisymmetric, non-trivial black holes in the frame of f(R) gravity under metric formalism. Here we show that our no-hair theorem also can discard asymptotic de Sitter stationary and axisymmetric non-trivial black holes. The novelty is that this no-hair theorem is built without resorting to known mapping between f(R) gravity and scalar–tensor theory. Thus, an advantage will be that our no-hair theorem applies as well to metric f(R) models that cannot be mapped to scalar–tensor theory.

(abstract) Venus Gravity Field

NASA Technical Reports Server (NTRS)

Konopliv, A. S.; Sjogren, W. L.

1995-01-01

A global gravity field model of Venus to degree and order 75 (5772 spherical harmonic coefficients) has been estimated from Doppler radio tracking of the orbiting spacecraft Pioneer Venus Orbiter (1979-1992) and Magellan (1990-1994). After the successful aerobraking of Magellan, a near circular polar orbit was attained and relatively uniform gravity field resolution (approximately 200 km) was obtained with formal uncertainties of a few milligals. Detailed gravity for several highland features are displayed as gravity contours overlaying colored topography. The positive correlation of typography with gravity is very high being unlike that of the Earth, Moon, and Mars. The amplitudes are Earth-like, but have significantly different gravity-topography ratios for different features. Global gravity, geoid, and isostatic anomaly maps as well as the admittance function are displayed.

Preliminary Isostatic Gravity Map of Joshua Tree National Park and Vicinity, Southern California

USGS Publications Warehouse

Langenheim, V.E.; Biehler, Shawn; McPhee, D.K.; McCabe, C.A.; Watt, J.T.; Anderson, M.L.; Chuchel, B.A.; Stoffer, P.

2007-01-01

This isostatic residual gravity map is part of an effort to map the three-dimensional distribution of rocks in Joshua Tree National Park, southern California. This map will serve as a basis for modeling the shape of basins beneath the Park and in adjacent valleys and also for determining the location and geometry of faults within the area. 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 lithologic or structural boundaries. High-density basement rocks exposed within the Eastern Transverse Ranges include crystalline rocks that range in age from Proterozoic to Mesozoic and these rocks are generally present in the mountainous areas of the quadrangle. Alluvial sediments, usually located in the valleys, 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 basement rocks. Tertiary volcanic rocks are characterized by a wide range of densities, but, on average, are less dense than the pre-Cenozoic basement rocks. Basalt within the Park is as dense as crystalline basement, but is generally thin (less than 100 m thick; e.g., Powell, 2003). Isostatic residual gravity values within the map area range from about 44 mGal over Coachella Valley to about 8 mGal between the Mecca Hills and the Orocopia Mountains. Steep linear gravity gradients are coincident with the traces of several Quaternary strike-slip faults, most notably along the San Andreas Fault bounding the east side of Coachella Valley and east-west-striking, left-lateral faults, such as the Pinto Mountain, Blue Cut, and Chiriaco Faults (Fig. 1). Gravity gradients also define concealed basin-bounding faults, such as those beneath the Chuckwalla Valley (e.g. Rotstein and others, 1976). These gradients result from juxtaposing dense basement rocks against thick Cenozoic sedimentary rocks.

Proceedings of the Annual Gravity Gradiometer Conference (17th) Held in Hanscom AFB, Massachusetts on 12-13 October 1989

DTIC Science & Technology

1990-03-28

D’IC FILE COpY G---90-0067 ENVIRONMENTAL RESEARCH PAPERS , NO. 1059 AD-A223 568 PROCEEDINGS OF THE SEVENTEENTH ANNUAL GRAVITY GRADIOICET CONFERENCE 12...AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for Public Release; Distribution Unlimited 13. ABSTRACT (Maximu&m 200 words)/ Fourteen papers were...instrumentation * and applications. The technical papers covered test program results, applications to gravity field mapping, gravity signal processing

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.

Progress towards a space-borne quantum gravity gradiometer

NASA Technical Reports Server (NTRS)

Yu, Nan; Kohel, James M.; Ramerez-Serrano, Jaime; Kellogg, James R.; Lim, Lawrence; Maleki, Lute

2004-01-01

Quantum interferometer gravity gradiometer for 3D mapping is a project for developing the technology of atom interferometer-based gravity sensor in space. The atom interferometer utilizes atomic particles as free fall test masses to measure inertial forces with unprecedented sensitivity and precision. It also allows measurements of the gravity gradient tensor components for 3D mapping of subsurface mass distribution. The overall approach is based on recent advances of laser cooling and manipulation of atoms in atomic and optical physics. Atom interferometers have been demonstrated in research laboratories for gravity and gravity gradient measurements. In this approach, atoms are first laser cooled to micro-kelvin temperatures. Then they are allowed to freefall in vacuum as true drag-free test masses. During the free fall, a sequence of laser pulses is used to split and recombine the atom waves to realize the interferometric measurements. We have demonstrated atom interferometer operation in the Phase I period, and we are implementing the second generation for a complete gradiometer demonstration unit in the laboratory. Along with this development, we are developing technologies at component levels that will be more suited for realization of a space instrument. We will present an update of these developments and discuss the future directions of the quantum gravity gradiometer project.

Isostatic Gravity Map of the Battle Mountain 30 x 60 Minute Quadrangle, North Central Nevada

USGS Publications Warehouse

Ponce, D.A.; Morin, R.L.

2000-01-01

Introduction Gravity investigations of the Battle Mountain 30 x 60 minute quadrangle were begun as part of an interagency effort by the U.S. Geological Survey (USGS) and the Bureau of Land Management to help characterize the geology, mineral resources, hydrology, and ecology of the Humboldt River Basin in north-central Nevada. The Battle Mountain quadrangle is located between 40?30' and 41?N. lat. and 116? and 117?W. long. This isostatic gravity map of the Battle Mountain quadrangle was prepared from data from about 1,180 gravity stations. Most of these data are publicly available on a CD-ROM of gravity data of Nevada (Ponce, 1997) and in a published report (Jewel and others, 1997). Data from about 780 gravity stations were collected by the U.S. Geological Survey since 1996; data from about 245 of these are unpublished (USGS, unpub. data, 1998). Data collected from the 400 gravity stations prior to 1996 are a subset of a gravity data compilation of the Winnemucca 1:250,000-scale quadrangle described in great detail by Wagini (1985) and Sikora (1991). This detailed information includes gravity meters used, dates of collection, sources, descriptions of base stations, plots of data, and a list of principal facts. A digital version of the entire data set for the Battle Mountain quadrangle is available on the World Wide Web at: http://wrgis.wr.usgs.gov/docs/gump/gump.html

Japanese contributions to MAP

NASA Technical Reports Server (NTRS)

Kato, S.

1989-01-01

Japan contributed much to MAP in many branches. The MU (middle and upper atmosphere) radar, in operation during the MAP period, produced various novel possibilities in observations of middle atmosphere dynamics; possibilities which were fairly well realized. Gravity wave saturation and its spectrum in the mesosphere were observed successfully. Campaign observations by radars between Kyoto and Adelaide were especially significant in tidal and planetary wave observations. In Antarctica, middle atmosphere observation of the dramatic behavior of aerosols in winter is well elucidated together with the ozone hole. Theoretical and numerical studies have been progressing actively since a time much earlier than MAP. Now it is pointed out that gravity waves play an important role in producing the weak wind region in the stratosphere as well as the mesosphere.

Use of RADARSAT-1 satellite imagery and geophysical data for oil and kimberlite exploration

NASA Astrophysics Data System (ADS)

Paganelli, Flora

The synergy of RADARSAT-1 and seismic imagery interpretation has been applied in the Blackstone area of the Central Alberta Foothills in the Canadian Cordillera thrust and fold belt to map the continuity of geological structures, which are of importance for oil and gas exploration. The reconstruction of the continuity of thrust-fold related major structures known in the area has been successful. Transverse faults and lineaments with ENE-WSW, NE-SW, and NNE-SSW trends have been delineated on the radar images. The ENE-WSW transverse faults have an extensional character, cut across the inner and outer Foothills and are persistent at the regional scale. The NE-SW and NNE-SSW transverse faults are wrench type faults, which are mainly localized in the inner Foothills. These structures have been identified for the first time in the area and are possibly a third generation fault-play type for oil and gas exploration. Principal Component Analysis (PCA) of RADARSAT-1 images was applied in the Buffalo Head Hills area, in the Western Canada Sedimentary Basin (WCSB), to provide an enhanced image base for structural mapping. North- and NNE-trending lineaments bounding the eastern edge of the Buffalo Head Hills along the Loon River valley, a conjugate set of NW- and NE-trending lineaments, and ENE-trending lineaments identifying the latest features in the area were outlined. The development of these structures has been related to Precambrian terrane assemblage in the WCSB during the Early Proterozoic, the development of the Peace River Arch, and the Laramide Orogeny. In the Buffalo Head Hills area a weights of evidence statistical approach was used to determine the spatial relationship of NNE-, NE-, -NW, and ENE-trending lineaments to known kimberlite locations. This method outlined different degrees of spatial correlation between kimberlites and lineaments, with higher correlations defined for the NNE, NE, and ENE lineament datasets. A weights of evidence model was then constructed using the structural lineament maps, the Buffalo High and Buffalo Utikuma terrane boundary, Bouguer gravity data, and magnetic characteristics of the Buffalo High and Buffalo Utikuma terranes. The model reveals maximum favourability for kimberlite exploration along the Buffalo High and Buffalo Utikuma terrane boundary in correspondence with NNE-trending lineaments and their intersections with NE and ENE lineaments. The relationship of the kimberlite occurrences along the Buffalo High-Buffalo Utikuma terrane boundary and structural lineaments seems to favour an hypothesis of kimberlite emplacement through a major zone of weakness in the basement, here characterized by the boundary between the Buffalo High and Buffalo Utikuma terranes.

Detecting Taiwan's Shanchiao Active Fault Using AMT and Gravity Methods

NASA Astrophysics Data System (ADS)

Liu, H.-C.; Yang, C.-H.

2009-04-01

Taiwan's Shanchiao normal fault runs in a northeast-southwest direction and is located on the western edge of the Taipei Basin in northern Taiwan. The overburden of the fault is late Quaternary sediment with a thickness of approximately a few tenth of a meter to several hundred meters. No detailed studies of the western side of the Shanchiao fault are available. As Taiwan is located on the Neotectonic Belt in the western Pacific, detecting active faults near the Taipei metropolitan area will provide necessary information for further disaster prevention. It is the responsibility of geologists and geophysicists in Taiwan to perform this task. Examination of the resistivity and density contrasts of subsurface layers permits a mapping of the Shanchiao fault and the deformed Tertiary strata of the Taipei Basin. The audio-frequency magnetotelluric (AMT) method and gravity method were chosen for this study. Significant resistivity and gravity anomalies were observed in the suspected fault zone. The interpretation reveals a good correlation between the features of the Shanchiao fault and resistivity and density distribution at depth. In this observation, AMT and gravity methods provides a viable means for mapping the Shanchiao fault position and studying its features associated with the subsidence of the western side of the Taipei Basin. This study indicates the AMT and gravity methods' considerable potential for accurately mapping an active fault.

Geophysical Investigations on a Suspected Quarternary Volcanic Structure in North Eastern Bavaria, Germany

NASA Astrophysics Data System (ADS)

Geiss, E.; Rohrmüller, J.; Wassermann, J.; Hackl, M.; Kirscher, U.; Bachtadse, V.

2012-04-01

Recent geophysical studies on a small scale morphological depression northwest of the Zelezná hurka scoria cone (Eisenbühl, 49.99°N/12.45°E) near the village of Mytina (Czech Republic) revealed the presence of a maar-diatreme, filled with volcanic material and covered by alluvium. Reported Ar/Ar ages of 288 ± 17 ka imply that formation of the Mytina maar and emplacement of the Zelezná hurka might represent the youngest volcanic event in Central Europe, east of the volcanic Eifel province. If the interpretation that both the Mytina maar and the Zelezná hurka scoria cone are situated on the NW-SE striking Tachov Fault Zone south of the Cheb basin is correct, similar volcanic structures can be assumed to the west of the Czech-German border only a couple of km away from Mytina. Here we report the results of a combined gravity, magnetic, geoelectric and seismic survey carried out across a topographic depression situated along strike of the Tachov Fault Zone near the town of Neualbenreuth, eastern Bavaria. The local gravity field was determined at 120 data points covering roughly 10 square km. The Bouguer and topographically corrected gravity data show a very distinct isometric low of -2.84 mgals in an area of ~300x400m which coincides with the topographic depression in the center of the studied area. The resulting model of the density distribution in the underground is consistent with a maar-diatreme with rather low density rocks in the central vent. The structure has been modelled in 3D using IGMAS software. Geoelectrical measurements indicate low resistivity in the vent and higher porosity in the vent filling. However, magnetic data and seismic profiles across the postulated maar-diatreme do not strengthen our hypothesis and are inconclusive.

Chicxulub Impact Crater and Yucatan Carbonate Platform - PEMEX Oil Exploratory Wells Revisited

NASA Astrophysics Data System (ADS)

Pérez-Drago, G.; Gutierrez-Cirlos, A. G.; Pérez-Cruz, L.; Urrutia-Fucugauchi, J.

2008-12-01

Geophysical oil exploration surveys carried out by PEMEX in the 1940's revealed occurrence of an anomalous pattern of semi-circular concentric gravity anomalies. The Bouguer gravity anomalies covered an extensive area over the flat carbonate platform in the northwestern Yucatan Peninsula; strong density contrasts were suggestive of a buried igneous complex or basement uplift beneath the carbonates, which was referred as the Chicxulub structure. The exploration program carried out afterwards included a drilling program, starting with Chicxulub-1 well in 1952 and comprising eight deep boreholes through the 1970s. An aeromagnetic survey in late 1970's showed high amplitude anomalies in the gravity anomaly central sector. Thus, research showing Chicxulub as a large complex impact crater formed at the K/T boundary was built on the PEMEX decades-long exploration program. Despite frequent reference to PEMEX information and samples, original data and cores have not been openly available for detailed evaluation and integration with results from recent investigations. Core samples largely remain to be analyzed and interpreted in the context of recent marine, aerial and terrestrial geophysical surveys and the drilling/coring projects of UNAM and ICDP. In this presentation we report on the stratigraphy and paleontological data for PEMEX wells: Chicxulub- 1 (1582m), Sacapuc-1 (1530m), Yucatan-6 (1631m), Ticul-1 (3575m) Yucatan-4 (2398m), Yucatan-2 (3474m), Yucatan-5A (3003m) and Yucatan-1 (3221m). These wells remain the deepest drilled in Chicxulub, providing samples of impact lithologies, carbonate sequences and basement, which give information on post- and pre-impact stratigraphy and crystalline basement. We concentrate on stratigraphic columns, lateral correlations and integration with UNAM and ICDP borehole data. Current plans for deep drilling in Chicxulub crater target the peak ring and central sector, with offshore and onshore boreholes proposed to the IODP and ICDP programs.

Geophysical Characteristics of the Australian-Antarctic Ridge

NASA Astrophysics Data System (ADS)

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

2014-12-01

Between 2011 and 2013, the Korea Polar Research Institute (KOPRI) conducted three consecutive geologic surveys at the little explored eastern ends of the Australian-Antarctic Ridge (AAR) to characterize the tectonics, geochemistry, and hydrothermal activity of this intermediate spreading system. Using the Korean icebreaker R/V Araon, the multi-disciplinary research team collected bathymetry, gravity, magnetics, and rock and water column samples. In addition, Miniature Autonomous Plume Recorders (MAPRs) were deployed at wax-core rock sampling sites to detect the presence of active hydrothermal vents. Here we present a detailed analysis of a 300-km-long supersegment of the AAR to quantify the spatial variations in ridge morphology and robust axial and off-axis volcanisms. 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 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 than 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 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.

Crustal structure of an intraplate thrust belt: The Iberian Chain revealed by wide-angle seismic, magnetotelluric soundings and gravity data

NASA Astrophysics Data System (ADS)

Seillé, Hoël; Salas, Ramon; Pous, Jaume; Guimerà, Joan; Gallart, Josep; Torne, Montserrat; Romero-Ruiz, Ivan; Diaz, Jordi; Ruiz, Mario; Carbonell, Ramon; Mas, Ramón

2015-11-01

The Iberian Chain is a Cenozoic intraplate thrust belt located within the Iberian plate. Unlike other belts in the Iberia Peninsula, the scarcity of geophysical studies in this area results in a number of unknowns about its crustal structure. The Iberian Chain crust was investigated by means of a NE-SW refraction/wide-angle reflection seismic transect and two magnetotelluric profiles across the chain, oriented along the same direction. The seismic profile was designed to sample the crust by means of three shots designed to obtain a reversed profile. The resulting velocity-depth model shows a moderate thickening of the crust toward the central part of the profile, where crustal thickness reaches values above 40 km, thinning toward de SW Tajo and NE Ebro foreland basins. The crustal thickening is concentrated in the upper crust. The seismic results are in overall agreement with regional trends of Bouguer gravity anomaly and the main features of the seismic model were reproduced by gravity modeling. The magnetotelluric data consist of 39 sites grouped into two profiles, with periods ranging from 0.01 s to 1000 s. Dimensionality analyses show significant 3D effects in the resistivity structure and therefore we carried out a joint 3D inversion of the full impedance tensor and magnetic transfer functions. The Mesozoic and Cenozoic basins along the Chain are well characterized by shallow high conductive zones and low velocities. Elongated conductors reaching mid-crustal depths evidence the presence of major faults dominating the crustal structure. The results from the interpretation of these complementary geophysical data sets provided the first images of the crustal structure of the Iberian Chain. They are consistent with a Cenozoic shortening responsible of the upper crust thickening as well as of the uplift of the Iberian Chain and the generation of its present day topography.

New Views of Earth's Gravity Field from GRACE

NASA Technical Reports Server (NTRS)

2003-01-01

[figure removed for brevity, see original site] [figure removed for brevity, see original site] Map 1Map 2

Gravity and the Earth's Shape Gravity is the force that is responsible for the weight of an object and is determined by how the material that makes up the Earth is distributed throughout the Earth. Because gravity changes over the surface of the Earth, the weight of an object changes along with it. One can define standard gravity as the value of gravity for an perfectly smooth 'idealized' Earth, and the gravity 'anomaly' is a measure of how actual gravity deviates from this standard. Gravity reflects the Earth's surface topography to a high degree and is associated with features that most people are familiar with such as large mountains and deep ocean trenches.

Progress in Measuring the Earth's Gravity Field Through GRACE Prior to GRACE, the Earth's gravity field was determined using measurements of varying quality from different satellites and of incomplete coverage. Consequently the accuracy and resolution of the gravity field were limited. As is shown in Figure 1, the long wavelength components of the gravity field determined from satellite tracking were limited to a resolution of approximately 700 km. At shorter wavelengths, the errors were too large to be useful. Only broad geophysical features of the Earth's structure could be detected (see map 1).

In contrast, GRACE, by itself, has provided accurate gravity information with a resolution of 200 km. Now, much more detail is clearly evident in the Earth's geophysical features (see map 2). High resolution features detected by GRACE that are representative of geophysical phenomena include the Tonga/Kermadec region (a zone where one tectonic plate slides under another), the Himalayan/Tibetan Plateau region (an area of uplift due to colliding plates), and the mid-Atlantic ridge (an active spreading center in the middle of the Atlantic ocean where new crust is being created). Future GRACE gravity models are expected to increase the resolution further. The second figure confirms that the Grace data is global, homogeneous and highly accurate. These are all properties that have been sought for gravity model development.

[figure removed for brevity, see original site] Ocean Circulation Measurements from Grace The arrows in the three data sets in Figure 3 depict ocean currents off the East Coast of the United States, 1,000 meters (approximately 3,280 feet) beneath the surface. The top panel is obtained from the GRACE geoid, satellite altimetry and ship measurements of temperature and salt. The bottom panel is computed in the same manner as the top one, except that the best geoid prior to GRACE is used instead of the GRACE geoid. The middle panel shows direct measurement of those currents by floats deployed from ships. Notice that the current arrows in the Gulf Stream extension, East and slightly South of Washington DC, point eastward, toward Europe, in the two upper panels, but in the opposite direction in the lower panel. Colors indicate the strength of the ocean current, with red being strongest and blue-green weakest. Areas in white have no available data.

The Gulf Stream region of the North Atlantic is among the best studied in the world's oceans, with a significant quantity of high-quality data available on it as a result of shipborne instrument measurements. In less well studied regions, the new information provided by GRACE, together with satellite altimetry, will increase our knowledge of ocean circulation.

Mapping experiment with space station

NASA Technical Reports Server (NTRS)

Wu, S. S. C.

1986-01-01

Mapping of the Earth from space stations can be approached in two areas. One is to collect gravity data for defining topographic datum using Earth's gravity field in terms of spherical harmonics. The other is to search and explore techniques of mapping topography using either optical or radar images with or without reference to ground central points. Without ground control points, an integrated camera system can be designed. With ground control points, the position of the space station (camera station) can be precisely determined at any instant. Therefore, terrestrial topography can be precisely mapped either by conventional photogrammetric methods or by current digital technology of image correlation. For the mapping experiment, it is proposed to establish four ground points either in North America or Africa (including the Sahara desert). If this experiment should be successfully accomplished, it may also be applied to the defense charting systems.