Horizontal Gravity Gradient Research Articles

Impact of salt diapir geometry and caprock composition on gravity survey results

With respect to difficulties seismic and magnetotellurics may have in accurate definition of exact salt diapir geometry, we performed various gravity simulations and calculations to investigate such exploration targets. Our motivation included the fact that not much has been done on caprock impact on the gravity signal. A very significant favorable condition is the high contrast of rock density between salt and basin sedimentary formations, especially carbonates. However, this can be more complicate if caprock formation is present. Therefore we defined approximate bulk density of typical caprock formation based on its usual composition, resulting in density values 2.45–2.70 g/cm3.We modelled by forward and inverse procedures the gravity signal Gz of salt diapirs with caprock of variable thickness to demonstrate to which extent the salt diapir negative gravity anomaly may be reduced by the impact of caprock formation. In the tested cases the gravity anomaly was reduced by more than 30% depending on respective caprock composition and thickness. Significant contribution to the delineation of salt diapirs themselves, as well as diapirs hidden under caprock, came from the application of horizontal gravity gradients Gzx. We showed the difference of Gzx spikes indicating the edges of density contacts according to the type of gravity survey – land or airborne. It was also proved by calculating the gravity effect of laboratory analogue models of salt deformation and extrusion.We demonstrated that gravity is still a valuable and relatively cheap tool for in-detail investigations of the salt structures within exploration projects.

Crustal architecture of the Dharwar craton and Southern Granulite Terrane, Southern India, from the analysis of gravity-magnetic data

The potential field (gravity & magnetic) data, along with results of available seismic and magnetotelluric studies over the Southern India Shield comprising the Dharwar craton (DC), Southern Granulite Terrane (SGT) and southern part of the Eastern Granulite Mobile Belt (EGMB), were synthesized. The study attempts to elucidate the geometry and continuity of greenstone belts/shear zones, isostatic condition and deeper crustal architecture. We observed a characteristic elevation-gravity relationship for each of the tectonic domains. The greenstone belts of the DC are characterized by N-S to NW-SE trending positive residual gravity anomalies and continue beneath the Cuddapah sediments. The basement of the Cuddapah basin is characterized by NW-SE trending greenstone belts with low-density intrusive rocks. The gravity anomaly suggests occurrence of a high-density rock unit occurs at mid-crustal depth beneath the ‘Closepet granite’ and ‘Chitradurga schist belt’. The potential field signatures of the DC and SGT are distinctly different. The Cauvery Shear Zone is characterized by positive residual gravity and magnetic anomalies with ∼E-W to ENE-WSW trend that continues further east under sediment covers of the east coast. The residual gravity signatures and horizontal gravity gradient signatures suggest that the orogenic systems encompassing the Cauvery Shear Zone and the eastern part of the EGMB may be a part of a common structural belt or tectonic regime associated with the assembly of the Gondwana supercontinent. The potential field modelling reveals the presence of a thick, high-density material resting over the base of the crust in the entire stretch of the east-coast of India.

Gravity Interpretations to Investigate the Deep Geological and Structural Status of Middle Atlas Chain Region, Morocco

The Moroccan Middle Atlas is an intracontinental chain characterized by a combination of tectonic, sedimentary, and magmatic events. These events influenced the Middle Atlas basement structure and its morphology. In order to improve our understanding of the subsurface and deep geological structures, a gravimetric investigation was carried out. A residual gravity map and its horizontal derivative were computed and interpreted. We present in this work the main findings: The residual gravity anomaly map shows fourteen positive anomalies which are well correlated with the undulated Paleozoic basement in the Middle Atlas or with the High Moulouya and the Merhraoua Anticlinorium in the Northeastern part of the Middle Atlas chain.It also exhibits sub-circular negative anomalies related to the thick subsurface Meso-Cenozoic cover of the Middle Atlas chain depocenters located in the center and southeastern parts of this chain. These anomalies are correlated with the Bou Anguer, Bekrit, Tazouta, Enjil, and Almis Mermoucha basins; the Bounacer mount; and the extension of Boumia granite in the High Moulouya. The horizontal gravity gradient map discloses that the study area is mainly affected by the NE-SW trends as major faults, while the N-S, NW-SE, and E-W are minor faults. They’re superposed with the Southern Middle Atlas Accident, the North Middle Atlas Accident the Tizi N’tretten Accident, and their branches. They are due to the alpine neotectonic reactivation phases of the Paleozoic and Jurassic heritaged faults. A synthetic structural map displaying the lateral extension of most Middle Atlas faults was postulated. Consideration is also being given to explore the buried faults or unmapped ones. Our final map represents an efficient and effective tool to help decision-makers during mining exploration.

Structural control on a Ypresian karstic aquifer revealed by an integrated geophysical and geological approach: the Mateur imbricated thrust zone (northern Tunisia)

We present a characterization of a poorly studied karstic aquifer, documenting the geometry, resistivity properties and the control of structural discontinuities that affect the Ypresian limestone cropping out in the Mateur imbricated thrust zone in northern Tunisia. The karst system was produced by meteoric diagenesis. Geophysical methods and field investigations were useful in extracting geological features. First, our findings suggest that N110–N140 directions are the preferred dissolution paths orientated parallel to strike-slip and extensional faults. Second, the gravity data analysis (regional–residual separation, horizontal gravity gradient and Euler deconvolution) show a particular tectonic node as a junction of the NE–SW and NW–SE directions. Third, 2D electrical resistivity models display various karstification typologies with high (>1000 Ω m), medium (between 200 and 1000 Ω m) and low (<100 Ω m) electrical resistivity zones. These electrical resistivity models have contributed to the establishment of a conceptual structural model of the global karst features. Finally, 2D electrical resistivity tomography (ERT) and 1D time-domain electromagnetic analysis highlighted the presence of potential water zones integrated into the aquifer. Thematic collection: This article is part of the Karst: Characterization, Hazards & Hydrogeology collection available at: https://www.lyellcollection.org/topic/collections/karst

Determination of radii of curvature for high resolution geoid models using the harmonic synthesis algorithm

Different types of radii of curvature were assessed for the geoid based on the GECO geopotential model, up to degree and order 2190. The route values of gravity and the three horizontal gravity gradients were computed based on such geopotential model and the angular velocity of the Earth. The investigation was performed on coarse global grids and finer grids covering the Egyptian territory. Respective latitudinal and longitudinal profiles for the geoidal radii were extracted. Comparisons were held with the radii of curvature on the WGS-84 ellipsoid, and with the geoidal radii derived from other models of lower resolutions. Unlike the ellipsoid, the values of the geoidal radii exhibited a rather irregular behaviour that is far from any geographical symmetry. The principal radii of the geoid do not generally occur along the meridian and prime-vertical directions. Such irregularities were found to be more exaggerated with higher degrees. At all investigated resolution levels, the signs of the principal radii assured the convexity of the geoid surface. This enabled to define, compute and compare the Gaussian mean radii for the geoid. The local residual geoidal radii showed a decaying spectral tendency. Also, the results implied that the utilized algorithm proved to be convergent.

Interpretation of Airborne Gravity Data over Kushaka Schist Belt, Northwestern Nigeria

The Kushaka Schist Belt has a peculiar importance due to its minerological potential. The area is located on the Latitudes 10°30’-110 and Longitude 6°30’-7° in the northwestern part of Nigeria. Kushaka airborne dataset (Sheet 222) obtained from Nigerian Geological Survey Aagency was interpreted to delineate litho- structural architectures that could favour the exploitation of potential economic minerals over the area. The analyzed results of the bouguer map of Kushaka show the distribution of the gravity anomalies and magnitudes of the concealed shear and weak zones being characterized by low to very high gravity anomalies. The upward continued bouger anomaly map at distance of 3000m reveal the regional trends so as to generate a subsequent residual field where several filtering operations were carried out. Several enhancement techniques were carried out on the airborne gravity data to reveal the locations, edges/boundaries, trends, and depths of gravity anomalies. The analytic signal gravity and its superimposed maps reveal areas with low to high amplitude signals. Low amplitude regions are suggested to be dominated by highly fractured schistose, quartzitic rocks and fractures. On the other hand, high amplitude regions are likely occupied by denser biotite granitic and gneissic rocks. Also, the First Vertical Derivative gravity anomaly map shows low gravity region which indicate the presence of fracture. The horizontal gravity gradient map shows high, positive gravity regions which may be attributed to the presence of a regional structure trend in the area. Low gradient anomalies can also denote presence of graben-like structures or other geological depressions. The depth analysis over Kushaka schist Belt suggests depth to top for shallow bodies ranging from 385m to 560 m with an average depth of 440.55 m while the deep sources have depths ranging from 1910m to 2480m with an average depth of 2111.1m. The obtained Euler anomalies depths ranged from <2607m to >5858m suggesting that mineralization around the study area is structurally controlled, an evidence of hydrothermal alteration zones. The structural solution (S.I=0) result displays two NW-SE trending short linear features, an indication of tectonic metamorphic phases of Pan-African orogeny that harbor mineralization. The results therefore, suggested intensed deformation of the basement rocks with tectonic framework suitable for mineralization.

Geothermal Reservoir Identification in Way Ratai Area Based on Gravity Data Analysis

Gravity research in the Way Ratai geothermal prospect area was conducted to determine geothermal reservoirs, heat sources, and the structure of the geothermal reservoir. The research carried out includes 3D inversion modeling of gravity data. The Bouguer anomaly in the study area has 50 mGal to 120 mGal with low anomalies located in the southeast (Ketang and Kelagian), Northeast (Gedong Air, Sungai Langka, Gunung Betung) areas, and in the Pesawaran mountain area. The high anomaly is in Merawan – Hanuberak – Padang Cermin, Sumbersari and Kaliawi. The horizontal gravity gradient map analysis shows a pattern of fault structure trending northwest-southeast and southwest-northeast, according to the main fault structure in the area. 3D inversion modeling obtains a density distribution between 1.8 g/cc to 3g/cc with a low-density distribution in the south, Mount Pesawaran/Ratai, Gunung Betung, and Sidoharum. The location of the manifestation is 9 km southeast of the Mount Ratai/Pesawaran summit. The existence of geothermal reservoirs is estimated to be in the Lubuk Badak and Miwung Hills areas which are located between the peaks of Mount Ratai/Pesawaran and geothermal manifestations. This is supported by the low-density distribution in the area and the resistivity map from audio-magnetotelluric data.

Curvature interpretation of gravity data for delineating structural features across the transition zone of Narmada–Son lineament in central India

Potential-field anomalies can be converted to a common function which describes the ridge, peaks over an isolated source. In this study, attempt has been made to interpret curvature attributes of equipotential surface using gravity gradients for delineating thrust–fault locations in one of the seismically active transition zones of Narmada–Son Lineament (NSL) in central India. The NSL is oriented in the ENE–WSW direction, divides the area into two geological provinces. The northern part of this NSL comprises Vindhyan formations and southern part covers Gondwana formations. It has been observed that, the northern part (around Jukehi) of the area has higher elevation with lower gravity anomaly and the southern part (around Khamaria and Kataria) has lower elevation with higher gravity anomaly. The tectonic activities like intrusions, volcanisms and earthquake occurrences were the sources of crustal resettlement during the past in this area. Various researchers commented about the structural configuration; however, the present study helps to understand the structural features using various curvature analysis like maximum, minimum, most-positive, most-negative, mean, dip (profile), strike (tangential), contour (plan), curvedness, shape index and Gaussian curvatures. Out of these curvatures most positive, maximum, mean, dip and curvedness show more effective results compared to other curvatures. However, shape index states domes, ridge, flat, valley, bowl shape type structures. The results are also correlated with the conventional horizontal gravity gradient, analytic signal and tilt derivative analysis. The colour contrast variation of these differential curvatures make in-depth understanding with extensive multiplicities of integrity for delineating subsurface structures.

Physical properties of Hradište border fault (Turiec Basin, Western Carpathians, Slovakia) inferred by multidisciplinary geophysical approach

The Hradiste border fault zone has played an important role in the development of the tectonic contact of the Cenozoic sediments of the Turiec Basin with the Mala Fatra Mountains crystalline basement. Seismic, geoelectric, radiometric, gravimetric, magnetometric and ground penetrating radar measurements were used to study the physical properties and determine the exact position and inclination of this fault zone down to a depth of up to 40 m. The Hradiste border fault zone represents an almost vertical physical boundary characterized by decreasing seismic velocity (from 3.0 km.s−1 to 2.2 km.s−1) and decreasing electrical resistivity (500 to 150 Ω.m) when passing from the basement west of the fault to sediments to its east. It corresponds also to a compact segment of the lowest volume activity of radon 222Rn values in soil air (8 kBq.m−3 on average) and maximum horizontal gravity gradient (−0.0076 mGal.m−1). The discovery of this anomalous zone also helps us to distinguish two different anomalous blocks. The block west of the fault represents the orthogneisses of the Tatric crystalline complex belonging to the Mala Fatra Mountains. The eastern block is built-up by the Bystricka Member Pliocene sediments of the Turiec Basin. Our study serves as a case study for geophysical research on faults in different tectonic units of the Western Carpathians and other similar orogens.

Interpretation of gravity anomaly to delineate thrust faults locations at the northeastern part of India and its adjacent areas using source edge detection technique, tilt derivative and Cos(θ) analysis

The Northeast India and its adjacent areas converge among the three different plates, viz. Eurasia, India and Sunda plates. The tectonic interaction of Northeast India and underlying dynamics of the Himalayas as well as the Indo-Burma Ranges might cause the Assam Syntaxis. The area of study is located between latitude 23°–28°N and longitude 88°–96°E and situated in one of the most seismically active tectonic provinces in the world with seismic zone-V. This area had demonstrated several thrust faults activities and tectonic evident accomplishments during the recent past. The complicated geotectonic setups inspirits various smaller magnitude earthquakes, and the current seismicity shows seismic activities are still enduring in the Shillong Plateau, Arakan-Yoma fold belt, Bengal Basin, Naga Hills, Mikir Hills, Upper–Lower Brahmaputra Valley and Mismi Hills of Himalayan foothills. It is imperative to obtain wide-ranging learning tectonic configuration, thrust faults delineation for improved geoscientific study. Parts of the areas are extremely unreachable, and very limited thrust faults were marked by studying GIS map received from the various agencies and field geological study. During the past studies, most of the prominent lineaments/thrusts are marked; however, many active and hidden thrust faults are still unidentified. Seismic data can provide better information about the thrust faults locations, but due to small number of seismic data, the information is not adequate. In this paper, attempt has been made to study and reinterpret the available ground gravity data of northeastern parts of India for understanding thrust fault locations using various applications of gravity derivatives like analytical signal, horizontal gravity gradient, tilt derivative, horizontal tilt angle derivative and Cos(θ) analysis. Source edge detection technique has also been premeditated to categorize thrust fault locations. It is understandable that the low gravity is observed at Assam Valley which contributed sediment accumulations and higher gravity anomaly observed at Shillong Plateau and Bengal Basin containing denser formations. Bouguer gravity data is used after isostatic correction assuming Airy’s isostasy root depth model and first-order trend removal using least square technique. The derived thrust fault locations from the present study are superimposed with the existing thrust-fault locations for correlation. Some additional thrust faults are narrated which are not previously mapped. It is also suggested that Brahmaputra Thrust, Dauki Fault, Naga Thrust, Disang Thrust and Kopili Fault have key responsibility for high seismicity and tectonic movement causing upliftment and depression that encouraged some anticlockwise rotation in the area.

Gravity survey of the central Alpine Fault near the DFDP-2 drill site, Whataroa, South Island, New Zealand

ABSTRACTWe present a high-precision gravity survey of the Whataroa River valley near the DFDP-2 drill site. We measured 466 new sites and achieved a standard error on repeat measurements of 0.015 mGal. We combined existing data from 134 sites. A negative residual gravity anomaly of up to 6 mGal is interpreted as a buried glacial channel 350–450 m beneath the valley floor. It is apparently dextrally offset and upthrown to the southeast by the Alpine Fault. We are able to better constrain the surface trace location of the Alpine Fault by combining gravity models with surface mapping. A high horizontal gravity gradient near the DFDP-2 drill site requires a steeply-dipping or overhanging bedrock surface, and indicates that an active reverse fault might bound the base of the hillslope. A 4 mGal residual gravity minimum near the axis of the valley near the DFDP-2 drill site is interpreted as the deepest point upstream of the fault of what was a lake that formed at the end of the Last Glacial Maximum (∼18 ka).

A torsion balance device for measuring the gravity gradient

Based on the principle of torsion balance measuring gravity gradient, designed a torsion balance gravity gradiometer, consisting of a torsion balance system, an angle measurement system, an amplitude attenuation system, a turntable system, a vacuum container system. considering the stable time of torsion balance suspension system was too long, which had great impacted the efficiency of the gravity gradient measurement, designed an amplitude attenuation system in combination with PID control technology. Simulation results show that, the curvature and horizontal gravity gradient could be measured, the accuracy was as high as 0.5 E(1E = 1 × 10−9m/s2), and the limit efficiency of measuring a group of gravity gradients was better than an hour.

Hydro-geophysical and geochemical studies of the aquifer systems in El Kef region (Northwestern Tunisia)

In El Kef region, Northwestern Tunisia, the evolution of the agricultural and industrial sectors has exacerbated the need for water which caused a significant increase in groundwater extraction. In this context, several geologic and geophysical studies conducted on the groundwater resources of the concerning area were meant to give us insight into the geometry of the reservoirs and structural architecture of the basin and to identify the various reservoirs such as the Mio-Plio-Quaternary, the Lower Eocene and the Campanian–Maastrichtian aquifers. In this study, we used the geochemical study and analysis of gravity data (Horizontal and vertical derivative, horizontal gravity gradient maxima…) to improve the knowledge of the dip and direction fault and the geological structures in El Kef region (NW Tunisia) that control the groundwater hydrodynamic. Furthermore, the techniques of horizontal gradient and upward extension were applied to determine the gravity lineaments that represent the location of density contrasts and to locate the various faults that contribute to the structuring of the study area. Additionally, this study aims to assess the spatio-temporal evolution of the hydrodynamic parameters of the aquifers and to characterize the groundwater mineralization (salinity, chemical facies relationship, etc.). Our study showed the presence of four types of water facies: Ca–Mg–SO4; Na–Cl–NO3; Ca–Mg–HCO3 and Na–K–HCO3. The isotopic study is used to provide some information about the groundwater recharge and to define the different sources of water mixing. That way we could have better understanding to the hydrologic cycle and to the paleoclimate of the study area. Generally, the geochemically evolved groundwaters of the aquifer systems of El Kef region are relatively isotopically depleted when compared to the present day meteoric waters reflecting recharge under cold climate and high altitude. Conversely, the continuous increase of the annual mean temperature and the decrease of precipitations have been observed for the second half of the 20th century in North Africa. It is likely related to the warmer and drier conditions associated with the climate change phenomenon.

New insights on structures and active faults in northeastern Tunisia (Utica-Mateur region) from a gravity analysis: Geodynamic implications

Gravity data were analyzed in conjunction with earthquake, seismic reflection, and geological data to investigate the upper crustal structure of the Utica-Mateur region of northeastern Tunisia and relate this structure to the current tectonic environment of northern Tunisia. To accomplish this goal, gravity anomaly maps were constructed using isostatic gravity residual methods, match-filtering to create residual anomalies, and horizontal gravity gradients. Additionally, the depths to the major density contrasts were determined using a 2D power spectrum analysis and Euler deconvolution and 2D forward modeling. The residual gravity anomalies interpreted in conjunction with gradient determined lineaments indicate that there are several gravity maxima related to uplifted regions bounded by lineaments that trend mainly to northeast- and northwest. Based on the Euler deconvolution analysis, the majority of these lineaments are located at shallow depths (<6 km) and can be related to the seismic activity of the region. Correlating these newly imaged lineaments, uplifts and subsiding areas with seismicity and focal mechanism studies, a new structural map is proposed for the Utica-Mateur region. The majority of the region can be interpreted by uplifts and subsiding (pull apart basins) areas bounded by strike-slip faults that contain compressional and extensional stress components. This stress regime is thought to be caused by the reactivation of older structures by the current compressional stress regime due to the convergent of Africa and Eurasia and active rifting of the Sicily basin. However, the proposed recent segmentation of a northeast-retreating subducting slab under Africa that caused a major lithospheric discontinuity to the south of the Utica-Mateur region added second and third order tectonic variations. These variations modified the stress regime which caused the formation of strike-slip faults and the gravity analysis indicates that the entire Utica-Mateur region is still affected by this stress field change.

Preliminary structural configuration of the Goubellat Upper Cretaceous carbonate aquifers using gravity method (Northwestern Tunisia)

Gravity method can help locate hidden structural blocks bounded by faults related to the Upper Cretaceous carbonate aquifers of Goubellat region (Northwestern Tunisia). The Quaternary deposits are present over the majority of the Goubellat plain basin and cover the Upper Cretaceous carbonate. The produced residual gravity map supported by vertical and tilt angle derivatives was used to reveal the subsurface structural framework of the study area shaped by uplifted (high gravity anomalies) and downlifted areas (low gravity anomalies). The horizontal gravity gradient and Euler deconvolution maps were elaborated in order to locate major faults. These faults are primordial for the subsurface water recharge pathways. Finally, the presented lineament/structural map is very useful for large-scale structures and lineaments mapping giving the principal keys of the preliminary structural configuration of the Goubellat Upper Cretaceous carbonate aquifers.

The role of E–W basement faults in the Mesozoic geodynamic evolution of the Gafsa and Chotts basins, south-central Tunisia

The Gafsa and Chotts intracratonic basins in south-central Tunisia are transitional zones between the Atlasic domain to the north and the Saharan platform to the south. The principal aim of this paper is to unravel the geodynamic evolution of these basins following an integrated approach including seismic, well log and gravity data. These data are used to highlight the tectonic control on the deposition of Jurassic and Lower Cretaceous series and to discuss the role of the main faults that controlled the basin architecture and Cretaceous–Tertiary inversion. The horizontal gravity gradient map of the study area highlights the pattern of discontinuities within the two basins and reveals the presence of deep E–W basement faults. Primary attention is given to the role played by the E–W faults system and that of the NW–SE Gafsa fault which was previously considered active since the Jurassic. Facies and thickness analyses based on new seismic interpretation and well data suggest that the E–W-oriented faults controlled the subsidence distribution especially during the Jurassic. The NW–SE faults seem to be key structures that controlled the basins paleogeography during Late Cretaceous–Cenozoic time. The upper Triassic evaporite bodies, which locally outline the main NW–SE Gafsa fault, are regarded as intrusive salt bodies rather than early diapiric extrusions as previously interpreted since they are rare and occurred only along main strike-slip faults. In addition, seismic lines show that Triassic rocks are deep and do not exhibit true diapiric features.

The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

We describe the computation of the first Australian quasigeoid model to include error estimates as a function of location that have been propagated from uncertainties in the EGM2008 global model, land and altimeter-derived gravity anomalies and terrain corrections. The model has been extended to include Australia’s offshore territories and maritime boundaries using newer datasets comprising an additional {sim }280,000 land gravity observations, a newer altimeter-derived marine gravity anomaly grid, and terrain corrections at 1^{prime prime }times 1^{prime prime } resolution. The error propagation uses a remove–restore approach, where the EGM2008 quasigeoid and gravity anomaly error grids are augmented by errors propagated through a modified Stokes integral from the errors in the altimeter gravity anomalies, land gravity observations and terrain corrections. The gravimetric quasigeoid errors (one sigma) are 50–60 mm across most of the Australian landmass, increasing to {sim }100 mm in regions of steep horizontal gravity gradients or the mountains, and are commensurate with external estimates.

Changes in gravitational parameters inferred from time variable GRACE data—A case study for October 2005 Kashmir earthquake

The earth's gravity changes are attributed to the redistribution of masses within and/or on the surface of the earth, which are due to the frictional sliding, tensile cracking and/or cataclastic flow of rocks along the faults and detectable by earthquake events. Inversely, the gravity changes are useful to describe the earthquake seismicity over the active orogenic belts. The time variable gravimetric data are hardly available to the public domain. However, Gravity Recovery and Climatic Experiment (GRACE) is the only satellite mission dedicated to model the variation of the gravity field and an available source to the science community. Here, we have tried to envisage gravity changes in terms of gravity anomaly (Δg), geoid (N) and the gravity gradients over the Indo-Pak plate with emphasis upon Kashmir earthquake of October 2005. For this purpose, we engaged the spherical harmonic coefficients of monthly gravity solutions from the GRACE satellite mission, which have good coverage over the entire globe with unprecedented accuracy. We have analysed numerically the solutions after removing the hydrological signals, during August to November 2005, in terms of corresponding monthly differentials of gravity anomaly, geoid and the gradients. The regional structures like Main Mantle Thrust (MMT), Main Karakoram Thrust (MKT), Herat and Chaman faults are in closed association with topography and with gravity parameters from the GRACE gravimetry and EGM2008 model. The monthly differentials of these quantities indicate the stress accumulation in the northeast direction in the study area. Our numerical results show that the horizontal gravity gradients seem to be in good agreement with tectonic boundaries and differentials of the gravitational elements are subtle to the redistribution of rock masses and topography caused by 2005 Kashmir earthquake. Moreover, the gradients are rather more helpful for extracting the coseismic gravity signatures caused by seismicity over the area. Higher positive values of gravity components having higher terrain elevations are more vulnerable to the seismicity and lower risk of diastrophism otherwise.

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

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

A 3D model of the Wathlingen salt dome in the Northwest German Basin from joint modeling of gravity, gravity gradient, and curvature

In the past few decades, numerous attempts have been made on modeling of salt tectonics and deciphering the geometry of salt domes, which is a key challenge in petroleum exploration. We have derived a 3D density model of the Wathlingen salt dome, situated in the southern part of the Northwest German Basin from joint modeling of reprocessed torsion balance measurements. Gravity, gravity gradients [Formula: see text], curvature derived from horizontal gravity gradients [Formula: see text], and horizontal directive tendency are jointly modeled to decipher the geometric structure of the salt dome. The model was constrained by geologic and borehole information. We found that the Wathlingen salt dome is a mushroom-structured salt body, which is 14-km long, 4–8-km wide extending up to [Formula: see text] depth. The top mushroom structure of the salt is horizontally spread up to [Formula: see text]. It would not have been possible to derive the complex 3D structure from modeling of gravity data alone.