A deterministic approach toward isostatic gravity residuals—A case study from South America

Geophysics ◽  
1996 ◽  
Vol 61 (4) ◽  
pp. 1022-1033 ◽  
Author(s):  
David A. Chapin
Keyword(s):  
South America ◽  
Gravity Data ◽  
Crustal Thickness ◽  
Crustal Thickening ◽  
Density Contrast ◽  
Data Sets ◽  
Topographic Effects ◽  
Continental Scale ◽  
Free Air ◽  
Free Air Gravity

A new deterministic method for correcting isostatic effects in gravity data sets overcomes the deficiencies of empirically based methods. This technique produces a superior gravity image for South America and has application to other continental‐scale gravity data sets. The basis for the correction is the Airy‐Heiskanen isostatic model, which assumes that surface topography is supported by crustal thickening. The three key parameters, (1) the crustal thickness at sea‐level, (2) the surface reduction density, and (3) the density contrast between the crust and the mantle, are determined directly from the elevation, free‐air gravity, and Bouguer gravity data sets. The surface density parameter of 2.60 g/cc is determined using a new fractal technique. This technique assumes that the topography is fractal. The best value for density is that which minimizes the fractal component caused by topographic effects. The new value is substantially different than the 2.67 g/cc density assumed by many previous workers for most continental‐scale data sets. The crust/mantle density contrast parameter of 0.45 g/cc is determined by comparison between the densities determined from crossplots of the Bouguer values versus elevation. The crustal thickness parameter of 30 km is determined using a spectral method applied to the free‐air gravity. The results of this work are not only an isostatic residual map, but a methodology that cross checks the data for quality control. The final isostatic residual map can be used with confidence for basin evaluation throughout the continent of South America. Basins at high elevations, like the eastern foreland basins of the Andes and the Altiplano Basin, are imaged better by using this method.

Crustal modeling from spectrally correlated free‐air and terrain gravity data—A case study of Ohio

Geophysics ◽  
2000 ◽  
Vol 65 (4) ◽  
pp. 1057-1069 ◽  
Author(s):  
Jeong Woo Kim ◽  
Ralph R. B. von Frese ◽  
Hyung Rae Kim
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Crustal Thickness ◽  
Earthquake Hazards ◽  
Spectral Correlation ◽  
Free Air ◽  
Correlation Spectrum ◽  
Gravity Effects ◽  
Thickness Variations ◽  
Free Air Gravity

We investigate the use of spectral correlation theory to analyze terrain gravity effects and free‐air gravity anomalies of Ohio for possible constraints on the thickness variations and neotectonics of the crust. Terrain gravity effects are computed from the topography by Gauss‐Legendre quadrature integration and are compared against independent free‐air gravity anomaly observations for their wavenumber correlation spectrum. Spectral correlation filters are designed accordingly to extract terrain‐correlated free‐air gravity anomalies that are subtracted from the terrain gravity effects for estimates of the compensated terrain gravity effects. These effects are used to model the Moho by inversion, assuming they predominantly reflect crustal thickness variations. Our results characterize the middle third of Ohio as a broad zone of thickened Precambrian crust, which also may include rifted regions where the thickness of the prerift crust has been reduced greatly. Furthermore, we find that about 83% of the instrumentally determined earthquake epicenters are located within the inferred thinner regions of Ohio’s crust or at their margins where compressional stresses may dominate. In general, these crustal thickness variations provide new constraints on modeling the tectonic evolution and geotechnical parameters of the crust—constraints that are important for evaluating earthquake hazards, the distribution and extraction of crustal resources, and the storage of hazardous waste and other crustal engineering applications.

scholarly journals Inversion of IceBridge gravity data for continental shelf bathymetry beneath the Larsen Ice Shelf, Antarctica

2012 ◽  
Vol 58 (209) ◽  
pp. 540-552 ◽  
Author(s):  
James R. Cochran ◽  
Robin E. Bell
Keyword(s):  
Continental Shelf ◽  
Ocean Circulation ◽  
Gravity Data ◽  
Radar Data ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Free Air ◽  
Free Air Gravity ◽  
Larsen Ice Shelf ◽  
Possible Cause

AbstractA possible cause for accelerated thinning and break-up of floating marine ice shelves is warming of the water in the cavity below the ice shelf. Accurate bathymetry beneath large ice shelves is crucial for developing models of the ocean circulation in the sub-ice cavities. A grid of free-air gravity data over the floating Larsen C ice shelf collected during the IceBridge 2009 Antarctic campaign was utilized to develop the first bathymetry model of the underlying continental shelf. Independent control on the continental shelf geologic structures from marine surveys was used to constrain the inversion. Depths on the continental shelf beneath the ice shelf estimated from the inversion generally range from about 350 to 650 m, but vary from <300 to >1000 m. Localized overdeepenings, 20-30 km long and 900-1000 m deep, are located in inlets just seaward of the grounding line. Submarine valleys extending seaward from the overdeepenings coalesce into two broad troughs that extend to the seaward limit of the ice shelf and appear to extend to the edge of the continental shelf. The troughs are generally at a depth of 550-700 m although the southernmost mapped trough deepens to over 1000 m near the edge of the ice shelf just south of 68° S. The combination of the newly determined bathymetry with published ice-draft determinations based on laser altimetry and radar data defines the geometry of the water-filled cavity. These newly imaged troughs provide a conduit for water to traverse the continental shelf and interact with the overlying Larsen C ice shelf and the grounding lines of the outlet glaciers.

Sea floor topography modeling by cumulating different types of gravity information

2020 ◽  
Author(s):  
Lucia Seoane ◽  
Benjamin Beirens ◽  
Guillaume Ramillien
Keyword(s):  
New England ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Extended Kalman Filtering ◽  
Sea Floor ◽  
Single Beam ◽  
Free Air ◽  
Free Air Gravity ◽  
Great Meteor Seamount

&lt;p&gt;We propose to cumulate complementary gravity data, i.e. geoid height and (radial) free-air gravity anomalies, to evaluate the 3-D shape of the sea floor more precisely. For this purpose, an Extended Kalman Filtering (EKF) scheme has been developed to construct the topographic solution by injecting gravity information progressively. The main advantage of this sequential cumulation of data is the reduction of the dimensions of the inverse problem. Non linear Newtonian operators have been re-evaluated from their original forms and elastic compensation of the topography is also taken into account. The efficiency of the method is proved by inversion of simulated gravity observations to converge to a stable topographic solution with an accuracy of only a few meters. Real geoid and gravity data are also inverted to estimate bathymetry around the New England and Great Meteor seamount chains. Error analysis consists of comparing our topographic solutions to accurate single beam ship tracks for validation.&lt;/p&gt;

The unification of gravity data for Ireland-Northern Ireland

2020 ◽  
Vol 39 (2) ◽  
pp. 135-143
Author(s):  
Sajjad Sajjadi ◽  
Zdeněk Martinec ◽  
Patrick Prendergast ◽  
Jan Hagedoorn ◽  
Libor Šachl ◽  
...  
Keyword(s):  
Northern Ireland ◽  
Tide Gauge ◽  
Gravity Data ◽  
Base Station ◽  
Base Stations ◽  
Data Format ◽  
Free Air ◽  
Vertical Datum ◽  
Systematic Biases ◽  
Free Air Gravity

The systematic biases and errors associated with gravity data in Ireland and Northern Ireland and the conversion of gravity to a consistent and unified system are analyzed. The gravity data in Ireland and Northern Ireland are given in different coordinate systems (Irish Grid and Irish Transverse Mercator), different gravity base stations (Dunsink and Cambridge), and different vertical datums (Malin Head and Belfast tide gauge). The conversion of the gravity data to a consistent system, which refers to unified coordinates, base station, and vertical datum, is essential in geophysics and geodesy, especially in geoid determination. A new standardized and unified data format is computed and proposed for the supply of gravity data for Ireland and Northern Ireland to minimize the potential of misinterpreting the data. As part of this study, simple Bouguer and free-air gravity anomaly maps are produced for Ireland and Northern Ireland to give an example of how to integrate the data.

The Origin of Lunar Mascon Basins

Science ◽  
2013 ◽  
Vol 340 (6140) ◽  
pp. 1552-1555 ◽  
Author(s):  
H. J. Melosh ◽  
Andrew M. Freed ◽  
Brandon C. Johnson ◽  
David M. Blair ◽  
Jeffrey C. Andrews-Hanna ◽  
...  
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Element Model ◽  
Isostatic Adjustment ◽  
Melt Pool ◽  
Free Air ◽  
Free Air Gravity ◽  
Bull's Eye ◽  
Gravity Recovery ◽  
The Impact

High-resolution gravity data from the Gravity Recovery and Interior Laboratory spacecraft have clarified the origin of lunar mass concentrations (mascons). Free-air gravity anomalies over lunar impact basins display bull’s-eye patterns consisting of a central positive (mascon) anomaly, a surrounding negative collar, and a positive outer annulus. We show that this pattern results from impact basin excavation and collapse followed by isostatic adjustment and cooling and contraction of a voluminous melt pool. We used a hydrocode to simulate the impact and a self-consistent finite-element model to simulate the subsequent viscoelastic relaxation and cooling. The primary parameters controlling the modeled gravity signatures of mascon basins are the impactor energy, the lunar thermal gradient at the time of impact, the crustal thickness, and the extent of volcanic fill.

Recent progress in landslide dating

2014 ◽  
Vol 39 (2) ◽  
pp. 168-198 ◽  
Author(s):  
Tomáš Pánek
Keyword(s):  
South America ◽  
Recent Progress ◽  
Age Determination ◽  
Cosmic Ray ◽  
Data Sets ◽  
Mountain Areas ◽  
Scottish Highlands ◽  
Exposure Dating ◽  
Continental Scale ◽  
Dating Methods

Recent progress of dating techniques has greatly improved the age determination of various types of landslides. Since the turn of the 21st century, the number of dated landslides throughout the world has increased several fold and the introduction of modern dating methods (e.g. cosmic ray exposure dating) has enabled the dating of new landslide features and elements. Based on the analysis of >950 dated landslides (of which 734 have been dated since the year 2000), it is clear that the predominant traditional strategies have continued to rely on the radiocarbon method; however, there is a remarkable trend of using cosmic ray exposure techniques for dating both the accumulation (e.g. landslide boulders) and the depletion (e.g. landslide scarps) parts of landslides. Furthermore, an increasing number of slope failures is determined by a multi-dating approach, which enables the verification of particular dating methods. Although coherent regional landslide chronologies are still relatively scarce in comparison with extensive databases of fluvial, glacial and/or eolian landforms, they offer important insights into temporal landslide distribution, long-term landslide behavior and their relationships with paleoenvironmental changes. The most extensive data sets exist for the mountain areas of North America (Pacific Coast Ranges), South America (Andes), Europe (Alps, Scottish Highlands, Norway, Carpathians and Apennines), the Himalaya-Tibet orogeny and the Southern Alps of New Zealand. Dated landslides in the plate interiors are lacking, especially in South America, Africa and Australia. Despite the fact that some dating results are well correlated with major regional and continental-scale changes in the seismic activity, moisture abundance, glacier regimes and vegetation patterns, some of these results contradict previously established straightforward hypotheses. This indicates the rather complex chronological behavior of landslides, reflecting both intrinsic (e.g. gradual stress relaxation within a rock mass) and external factors, including high-magnitude earthquakes or heavy rainfalls.

scholarly journals Usporedba različitih pristupa Bouguer-ove redukcije na temelju satelitskih gravimetrijskih podataka

Geofizika ◽  
2020 ◽  
Vol 37 (2) ◽  
pp. 237-261
Author(s):  
Fan Luo ◽  
Xin Tao ◽  
Guangming Fu ◽  
Chong Zhang ◽  
Kun Zhang ◽  
...  
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Gravitational Effect ◽  
Seismic Profile ◽  
Bouguer Gravity ◽  
Seismic Profiles ◽  
Satellite Gravity ◽  
Free Air ◽  
Free Air Gravity

Satellite gravity data are widely used in the field of geophysics to study deep structures at the regional and global scales. These data comprise free-air gravity anomaly data, which usually need to be corrected to a Bouguer gravity anomaly for practical application. Bouguer reduction approaches can be divided into two methods based on the coordinate system: the spherical coordinates method (SBG) and the Cartesian coordinates method; the latter is further divided into the CEBG and CBG methods, which do and do not include the Earth’s curvature correction. In this paper, free-air gravity anomaly data from the eastern Tibetan Plateau and its adjacent areas were used as the basic data to compare the CBG, CEBG, and SBG Bouguer gravity correction methods. The comparison of these three Bouguer gravity correction methods shows that the effect of the Earth’s curvature on the gravitational effect increases with increasing elevation in the study area. We want to understand the inversion accuracy for the data obtained by different Bouguer gravity reduction approaches. The depth distributions of the Moho were obtained by the interface inversion of the Bouguer gravity anomalies obtained by the CBG, CEBG, and SBG, and active seismic profiles were used as references for comparison and evaluation. The results show that the depths of the Moho obtained by the SBG inversion are more consistent with the measured seismic profile depths. Therefore, the SBG method is recommended as the most realistic approach in the process of global or regional research employing gravity data.

scholarly journals Seafloor Density Contrast Derived From Gravity and Shipborne Depth Observations: A Case Study in a Local Area of Atlantic Ocean

2021 ◽  
Vol 9 ◽  
Author(s):  
Xiaoyun Wan ◽  
Weipeng Han ◽  
Jiangjun Ran ◽  
Wenjie Ma ◽  
Richard Fiifi Annan ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Local Area ◽  
Density Variation ◽  
Mean Difference ◽  
Density Contrast ◽  
Data Sets ◽  
Marine Gravity ◽  
Band Pass

Marine gravity data from altimetry satellites are often used to derive bathymetry; however, the seafloor density contrast must be known. Therefore, if the ocean water depths are known, the density contrast can be derived. This study experimented the total least squares algorithm to derive seafloor density contrast using satellite derived gravity and shipborne depth observations. Numerical tests are conducted in a local area of the Atlantic Ocean, i.e., 34°∼32°W, 3.5°∼4.5°N, and the derived results are compared with CRUST1.0 values. The results show that large differences exist if the gravity and shipborne depth data are used directly, with mean difference exceeding 0.4 g/cm3. However, with a band-pass filtering applied to the gravity and shipborne depths to ensure a high correlation between the two data sets, the differences between the derived results and those of CRUST1.0 are reduced largely and the mean difference is smaller than 0.12 g/cm3. Since the spatial resolution of CRUST1.0 is not high and in many ocean areas the shipborne depths and gravity anomalies are much denser, the method of this study can be an alternative method for providing seafloor density variation information.

A discussion on the structure and evolution of the Red Sea and the nature of the Red Sea, Gulf of Aden and Ethiopia rift junction - Seismic and gravity data from afar in relation to surrounding areas

1970 ◽  
Vol 267 (1181) ◽  
pp. 339-358 ◽  
Keyword(s):  
Red Sea ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Seismic Energy ◽  
Free Air ◽  
Seismic Surface Waves ◽  
Free Air Gravity ◽  
Surrounding Areas ◽  
Tectonic Features ◽  
Afar Triangle

The Afar triangle is bordered, to the west, by a seismic belt running along and on top of the escarpment. Seventy-five percent of the seismic energy of the area is released along this belt. The epicentre distribution along the western escarpment coincides either with major north-south marginal tectonic features or with cross-rift faulting. A second epicentre lineation runs at N 15° E through central Afar. To the south-east, in the region of the Gulf of Tadjura, epicentre locations offer no distinct lineation. The sum of the free-air gravity anomalies over Afar is almost zero; Bouguer values are generally negative and strictly proportional to elevation. Absolute Bouguer positive values are found only over volcanic centres and along the northeastern coast; their maximum does not compare with the positive values found over the nearby Red Sea trough. Evidence based on attenuation and dispersion of seismic surface waves and on gravity profiles suggests a continental crustal structure of relatively ‘standard’ thickness under the Afar triangle.

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