Review Article Removing Regional Trends in Microgravity in Complex Environments: Testing on 3D Model and Field Investigations in the Eastern Dead Sea Coast (Jordan (original) (raw)
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International Journal of Geophysics, 2013
Microgravity investigations are now recognized as a powerful tool for subsurface imaging and especially for the localization of underground karsts. However numerous natural (geological), technical, and environmental factors interfere with microgravity survey processing and interpretation. One of natural factors that causes the most disturbance in complex geological environments is the influence of regional trends. In the Dead Sea coastal areas the influence of regional trends can exceed residual gravity effects by some tenfold. Many widely applied methods are unable to remove regional trends with sufficient accuracy. We tested number of transformation methods (including computing gravity field derivatives, self-adjusting and adaptive filtering, Fourier series, wavelet, and other procedures) on a 3D model (complicated by randomly distributed noise), and field investigations were carried out in Ghor Al-Haditha (the eastern side of the Dead Sea in Jordan). We show that the most effective methods for regional trend removal (at least for the theoretical and field cases here) are the bilinear saddle and local polynomial regressions. Application of these methods made it possible to detect the anomalous gravity effect from buried targets in the theoretical model and to extract the local gravity anomaly at the Ghor Al-Haditha site. The local anomaly was utilized for 3D gravity modeling to construct a physical-geological model (PGM).
International Journal of Geophysics
Microgravity investigations are now recognized as a powerful tool for subsurface imaging, and especially for the localization of underground karsts. However numerous natural (geological), technical and environmental factors interfere with microgravity survey processing and interpretation. One of natural factors that causes the most disturbance in complex geological environments is the influence of regional trends. In the Dead Sea coastal areas the influence of regional trends can exceed residual gravity effects by some tenfold. Many widely applied methods are unable to remove regional trends with sufficient accuracy. We tested number of transformation methods (including computing gravity field derivatives, self-adjusting and adaptive filtering, Fourier series, wavelet and other procedures) on a 3D model (complicated by randomly distributed noise), and field investigations carried out in Ghor Al-Haditha (the eastern side of the Dead Sea in Jordan). We show that the most effective met...
Geochemistry Geophysics Geosystems, 2006
[1] A detailed three-dimensional (3-D) gravity model of upper crustal structures was created for the Dead Sea Transform in the Araba/Arava Valley, located some 80 km south of the Dead Sea Basin. The density model covers an area of 30A^30kmandincorporatesresultsfromseveralrecentgeophysicalexperimentsperformedinthisregion.Themodelpresentedisalocaldensitymodelthatfocusesontheuppermostcrustallayerstoadepthof30 Â 30 km and incorporates results from several recent geophysical experiments performed in this region. The model presented is a local density model that focuses on the uppermost crustal layers to a depth of 30A^30kmandincorporatesresultsfromseveralrecentgeophysicalexperimentsperformedinthisregion.Themodelpresentedisalocaldensitymodelthatfocusesontheuppermostcrustallayerstoadepthof5 km. Therefore, in order to separate the effect of regional structures (such as the crust-mantle boundary) from that of local structures within the crust, a residual anomaly was computed from a newly compiled Bouguer gravity anomaly database. In contrast to the Bouguer anomaly, which is negative across the entire study area, the residual gravity field contains both positive and negative values. The 3-D structural image of the upper crust reveals that the basement east and west of the Dead Sea Transform is vertically offset by 1.5 to 2.8 km. Considering the 105 km of sinistral displacement of the Dead Sea Transform, this result confirms the findings of other geophysical measurements that show an abrupt change in the physical parameters and geometry of the two lithological blocks that are juxtaposed along the Dead Sea Transform. Additionally, analysis of the calculated gravity gradients suggests that the Dead Sea Transform and the neighboring Zofar fault could be offset at depth with respect to the present-day traces at the surface.
Geophysical Journal International, 2018
This study provides interpretation and modelling of gravity survey data to map the subsurface basement relief and controlling structures of a coastal area in the southwestern part of Saudi Arabia as an aid to groundwater potential assessment. The gravity survey data were filtered and analysed using different edge detection and depth estimation techniques and concluded by 2-D modelling conducted along representative profiles to obtain the topography and depth variations of the basement surface in the area. The basement rocks are exposed in the eastern part of the area but dip westward beneath a sedimentary cover to depths of up to 2200 m in the west, while showing repeated topographic expressions related to a tilted fault-block structure that is dominant in the Red Sea rift zone. Two fault systems were recognized in the area. The first is a normal fault system trending in the NNW-SSE direction that is related to the Red Sea rift, and the second is a cross-cutting oblique fault system trending in the NE-SW direction. The interaction between these two fault systems resulted in the formation of a set of closed basins elongated in the NNW-SSE direction and terminated by the NE-SW fault system. The geomorphology and sedimentary sequences of these basins qualify them as potential regions of groundwater accumulation.
Al-Azhar Bulletin of Science
The purpose of the gravity approach is to detect subsurface structures using disturbances in the earth's gravitational field produced at the surface. Gravity was used to outline the subsurface structures; due to the study area includes many huge national projects such as Assiut Cement, New Nasser City and Assiut International Airport, It is important to assess the subsurface geological structures in the area. Bouguer gravity data of Egyptian General Petroleum Company (EGPC 1984) was used to performed Bouguer gravity anomaly map at the study area to start the gravity interpretation by separation of the residual anomaly from regional anomaly and then the data was filtered by mathematical methods called Tilt derivative (TDR), low pass, high pass and downward continuation to apply the gravity filtering using commercial software Oasis Montaj 2015. The Bouguer, residual and regional maps depict multiple structural features (mainly normal faults) with varied tendencies, such as E-W, NE-SW, and NW-SE. The source body derived from these data had depths varying from less than 2000 m to more than 4000 m. The basement depth in the research area below sea level varies between 2160 m and more than 2900 m.
Thousands of sinkholes have appeared in the Dead Sea (DS) coastal area in Israel and Jordan during two last decades. The sinkhole development is recently associated with the buried evaporation karst at the depth of 25-50 m from earth's surface caused by the drop of the DS level at the rate of 0.8-1.0 m/yr. Drop in the Dead Sea level has changed hydrogeological conditions in the subsurface and caused surface to collapse. The pre-existing cavern was detected using microgravity mapping in the Nahal Hever South site where seven sinkholes of 1-2 m diameter had been opened. About 5000 gravity stations were observed in the area of 200×200 m 2 by the use of Scintrex CG-3M AutoGrav gravimeter. Besides the conventional set of corrections applied in microgravity investigations, a correction for a strong gravity horizontal gradient (DS Transform Zone negative gravity anomaly influence) was inserted. As a result, residual gravity anomaly of -(0.08÷0.14) mGal was revealed. The gravity field analysis was supported by resistivity measurements. We applied the Emigma 7.8 gravity software to create the 3-D physical-geological models of the sinkholes development area. The modeling was confirmed by application of the GSFC program developed especially for 3-D combined gravity-magnetic modeling in complicated environments. Computed numerous gravity models verified an effective applicability of the microgravity technology for detection of karst cavities and estimation of their physical-geological parameters. A volume of the karst was Correspondence to: L. V. Eppelbaum (levap@post.tau.ac.il) approximately estimated as 35 000 m 3 . The visual analysis of large sinkhole clusters have been forming at the microgravity anomaly site, confirmed the results of microgravity mapping and 3-D modeling.
Three-dimensional Gravity Model of the southern Jordan Dead Sea Transform
An-Najah University Journal for Research - Natural Sciences, 2005
A three-dimensional interpretation of the newly compiled Bouguer anomaly map of the Dead Sea Transform (DST) is presented. A high-resolution 3-D model constrained with the seismic results reveals a possible crustal thickness and density distribution beneath the Rift. The negative Bouguer anomalies (-130 mGal) along the axial portion of the Rift floor, as deduced from the modelling results, are mainly caused by deep seated basins of light sediments (≥10 km). The inferred zone of intrusion coincides with the maximum gravity anomaly over the eastern flank of the Rift. 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 ~ 107 km at the boundary between the African and Arabian plates, and constrained with recen...
2017
A combination of relative microgravity measurements at ground surface, and depth to water and water table measurements from adjacent wells were used to estimate geospatial variation of groundwater. A highly accurate portable Grav-Map gravimeter was used for gravimetric measurements at locations nearby a 42 well water table monitoring program. To efficiently correlate the two data sets, wells were clustered into five groups by geological unit and water saturation. Microgravity data was processed, interpreted, and correlated with both the depths to groundwater and the water table levels. Regression analyses revealed a strong negative correlation for micro-gravity and depth to groundwater in all five clusters; correlation coefficients varied between 0.70 and 0.97, and measured 0.78 over the entire study area. Microgravity values increased as groundwater depth decreased, likely because rising groundwater fills voids and fractures within soil and rocks, increasing rock density and therefore relative gravity. To validate the correlation, we superimposed a map of depths to water on the first derivative of microgravity measurements. The shallowest groundwater depths were positively related to the zero first derivatives, having intersection areas within a 75 % significance interval. Negative first derivatives covered the rest of the study area, with relative gravity decreasing with increasing groundwater depth. This technique can precisely and efficiently determine changes in subsurface geology and geospatial changes in depths to the groundwater table. Distances between microgravity stations should be small, to better detect small changes in gravity values, reflecting density contrasts underground.
Research Sequare, 2023
The Southern Desert of Iraq covers a vast region in southwest Iraq. The stratigraphic column comprises relatively thick sedimentary strata, which overlay a Neoproterozoic basement and dip gently towards the northeast. The ground surface is depicted by intensive karst forms of variable dimensions, especially within carbonate rocks of the Dammam Formation (Middle-Upper Eocene). In the present study, we use the Bidimensional Empirical Mode Decomposition technique for analyzing the gravity eld into multiresidual elds and one regional. Analyzing and interpreting the resultant elds utilizing the geological data are the aims of this study. A free download MATLAB code is applied to the gravity data of the Southern Desert which is designed to separate the two-dimensional gridded gravity map into three residual maps and a regional one. These maps may re ect depths at different levels; shallow, intermediate, deep, and near the Moho discontinuity, respectively. According to the available information about the geology of the area, the residual maps can be interpreted in terms of shallow-depth geological structures, which have an economic interest in hydrocarbon exploration, intra-basement structures, and variation in the density of the basement terranes. The regional map, however, is interpreted to be related to a deep-seated gravity source most likely near the Moho. Further, the results illustrate an obvious relation between some of the gravity positives, in the rst residual map, and the drilled exploration wells. This suggests a delineation of newly prospected structural highs. In addition, the second residual map shows gravity negatives that probably delineate basement basins/sub-basins.