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We develop an algorithm for a Moho depth recovery from gravity and gravity gradiometry data and apply this method to estimate the Moho depth beneath the Tibetan Plateau. The basic idea of this algorithm is to describe mathematically the Moho depth undulations in terms of a condensation layer with respect to a mean Moho depth, instead of applying more commonly used isostatic compensation schemes. Expressions that functionally relate gravity field quantities with a (Moho) condensation layer are derived in spectral and spatial domains. The main advantage of this algorithm is that a functional relation between gravity field quantities and surface density anomalies, and consequently Moho depth undulations, has a linear form. The proposed algorithm is tested using satellite gravity and gravity gradiometry data. The Moho depth (taken with respect to the geoid surface) estimates obtained based on applying this algorithm are validated against global and regional seismic Moho results at the study area of Tibet. We also compare the result with the corresponding Moho depth estimates obtained by applying the Parker–Oldenburg and Vening Meinesz–Moritz (VMM) methods. The validation shows that results from all three gravimetric methods are similar, and they also closely agree with a regional seismic Moho model. Nevertheless, the VMM method and our algorithm in this comparison overperform the Parker–Oldenburg's method. The analysis of results also reveals that the newly developed algorithm provides better result (in terms of the RMS fit with a regional seismic Moho model) when applied for a Moho determination from gravity gradiometry instead of gravity data. Key Points: We developed a condensation method for Moho recovery and tested using satellite gravity and gravity gradiometry dataThe advantage of the proposed algorithm is that the relationship between gravity field quantities and surface density anomalies is linearEarth's satellite observation data are now used to recovery the Moho depth [ABSTRACT FROM AUTHOR]

Considering that Venus has a size very similar to Earth, thermal evolution of both planets should be comparable. Nonetheless, there is no clear evidence of plate tectonics or plate motions on Venus. Instead, various surface deformations attributed to volcanism, resurfacing, localized subduction and other geologic processes were recognized on the planet. In this study we attempt to classify the origin of lithospheric forces on Venus based on using topographic and gravity information. For this purpose, we also estimate the Venusian crustal thickness. In agreement with findings from previous studies, the signature of past or recent global tectonism in the body-force vector pattern on Venus is absent, while exhibiting only regional anomalies. The maximum intensity inferred in the Atla and Beta Regios is likely attributed to mantle upwelling. This is also confirmed by the gravity-topography spectral correlation and admittance analysis that shows the isostatic relaxation of these volcanic regions. The regional body-force pattern in the Bell Regio suggests that a much less pronounced force intensity there is possibly related to crustal load of lava flows. Elsewhere, the body-force intensity is relatively weak, with slightly more pronounced intensity around the Ishtar Terra and the Arthemis Chasmata. The body-force pattern in the Arthemis Chasmata supports the hypothesis that coronae structures are the result of mantle upwelling and the subsequent (localized) plume-induced subduction with only limited horizontal crustal motions. The prevailing divergent pattern of body-force vectors in the Ishtar Terra region suggests the presence of tensional forces due to the downwelling mantle flow that is responsible for a crustal thickening along the Freyja and Maxwell Montes. Except for the Atla and Beta Regios where the isostasy is relaxed by the (active) mantle plumes, the crustal thickness is spatially highly correlated with the topography, with a thin crust under the plains and a thick crust under the plateaus. The maximum Moho depth under the Maxwell Montes in the Ishtar Terra exceeds 90 km. [ABSTRACT FROM AUTHOR]

The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz's inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48-50 km) and the Kottas Mountains (48-50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34-38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24-28 km), while in West Antarctica the Moho depth minima are along the West Antarctic Rift System under the Bentley depression (20-22 km) and Ross Sea Ice Shelf (16-24 km). The gravimetric result confirmed a maximum extension of the Antarctic continental margins under the Ross Sea Embayment and the Weddell Sea Embayment with an extremely thin continental crust (10-20 km). [ABSTRACT FROM AUTHOR]

We develop and apply the algorithm for a regional gravimetric Moho recovery in spatial domain. The functional relation between the (known) refined gravity field and the (unknown and sought) Moho depth is defined by means of solving the Fredholm integral equation of the first kind. Linearization is applied to define the Moho depth corrections with respect to the mean Moho depth. The system of linearized observation equations is solved to find the Moho depth corrections, and Tikhonov’s regularization is applied to stabilize this ill-posed inverse problem. Developed algorithm is applied to model the Moho depth regionally under the Tibetan Plateau and Himalayas, while adopting the uniform and variable Moho density contrast models, and gravimetric results are validated using the CRUST1.0 seismic model. Our results show a relatively good agreement between gravimetric and seismic models, without presence of a significant systematic bias. Our result, however, indicates that for a regional study the variable Moho density contrast might not improve the results especially when density structure of the lower crust and uppermost mantle is not know accurately. In that case, the use of the uniform Moho density contrast for a regional Moho recovery is more appropriate. [ABSTRACT FROM AUTHOR]

We investigate the sub-crustal stress in the Taiwan region. A tectonic configuration in this region is dominated by a collision between the Philippine oceanic plate and the Eurasian continental margin. The horizontal components of the sub-crustal stress are computed based on the modified Runcorn's formulae in terms of the stress function with a subsequent numerical differentiation. This modification increases the (degree-dependent) convergence domain of the asymptotically-convergent series and consequently allows evaluating the stress components to a spectral resolution, which is compatible with currently available global crustal models. Moreover, the solution to the Vening Meinesz-Moritz's (VMM) inverse isostasy problem is explicitly incorporated in the stress function definition. The sub-crustal stress is then computed for a variable Moho geometry, instead of assuming only a constant Moho depth. The regional results reveal that the Philippine plate subduction underneath the Eurasian continental margin generates the shear sub-crustal stress along the Ryukyu Trench. Some stress anomalies associated with this subduction are also detected along both sides of the Okinawa Trough. A tensional stress along this divergent tectonic plate boundary is attributed to a back-arc rifting. The sub-crustal stress, which is generated by a (reverse) subduction of the Eurasian plate under the Philippine plate, propagates along both sides of the Luzon (volcanic) Arc. This stress field has a prevailing compressional pattern. [ABSTRACT FROM AUTHOR]

In classical isostatic models, a uniform crustal density is typically assumed, while disregarding the crustal density heterogeneities. This assumption, however, yields large errors in the Moho geometry determined from gravity data, because the actual topography is not fully isostatically compensated. Moreover, the sub-crustal density structures and additional geodynamic processes contribute to the overall isostatic balance. In this study we investigate the effects of unmodelled density structures and geodynamic processes on the gravity anomaly and the Moho geometry. For this purpose, we define the residual isostatic topography as the difference between actual topography and isostatic topography, which is computed based on utilizing the Vening Meinesz–Moritz isostatic theory. We show that the isostatic gravity bias due to disagreement between the actual and isostatically compensated topography varies between −382 and 596 mGal. This gravity bias corresponds to the Moho correction term of −16 to 25 km. Numerical results reveal that the application of this Moho correction to the gravimetrically determined Moho depths significantly improves the RMS fit of our result with some published global seismic and gravimetric Moho models. We also demonstrate that the isostatic equilibrium at long-to-medium wavelengths (up to degree of about 40) is mainly controlled by a variable Moho depth, while the topographic mass balance at a higher-frequency spectrum is mainly attained by a variable crustal density. [ABSTRACT FROM AUTHOR]

Substantial progress has been achieved over the last four decades to better understand a deep structure in the Himalayas and Tibet. Nevertheless, the remoteness of this part of the world still considerably limits the use of seismic data. A possible way to overcome this practical restriction partially is to use products from the Earth's satellite observation systems. Global topographic data are provided by the Shuttle Radar Topography Mission (SRTM). Global gravitational models have been derived from observables delivered by the gravity-dedicated satellite missions, such as the Gravity Recovery and Climate Experiment (GRACE) and the Gravity field and steady-state Ocean Circulation Explorer (GOCE). Optimally, the topographic and gravity data should be combined with available results from tomographic surveys to interpret the lithospheric structure, including also a Moho relief. In this study, we use seismic, gravity, and topographic data to estimate the Moho depth under orogenic structures of the Himalayas and Tibet. The combined Moho model is computed based on solving the Vening Meinesz–Moritz (VMM) inverse problem of isostasy, while incorporating seismic data to constrain the gravimetric solution. The result of the combined gravimetric-seismic data analysis exhibits an anticipated more detailed structure of the Moho geometry when compared to the solution obtained merely from seismic data. This is especially evident over regions with sparse seismic data coverage. The newly-determined combined Moho model of Tibet shows a typical contrast between a thick crustal structure of orogenic formations compared to a thinner crust of continental basins. The Moho depth under most of the Himalayas and the Tibetan Plateau is typically within 60–70 km. The maximum Moho deepening of ~76 km occurs to the south of the Bangong-Nujiang suture under the Lhasa terrane. Local maxima of the Moho depth to ~74 km are also found beneath Taksha at the Karakoram fault. This Moho pattern generally agrees with the findings from existing gravimetric and seismic studies, but some inconsistencies are also identified and discussed in this study. [ABSTRACT FROM AUTHOR]

One of the major issues associated with a regional Moho recovery from the gravity or gravity-gradient data is the optimal choice of the mean compensation depth (i.e., the mean Moho depth) for a certain area of study, typically for orogens characterised by large Moho depth variations. In case of selecting a small value of the mean compensation depth, the pattern of deep Moho structure might not be reproduced realistically. Moreover, the definition of the mean compensation depth in existing isostatic models affects only low-degrees of the Moho spectrum. To overcome this problem, in this study we reformulate the Sjöberg and Jeffrey’s methods of solving the Vening-Meinesz isostatic problem so that the mean compensation depth contributes to the whole Moho spectrum. Both solutions are then defined for the vertical gravity gradient, allowing estimating the Moho depth from the GOCE satellite gravity-gradiometry data. Moreover, gravimetric solutions provide realistic results only when a priori information on the crust and upper mantle structure is known (usually from seismic surveys) with a relatively good accuracy. To investigate this aspect, we formulate our gravimetric solutions for a variable Moho density contrast to account for variable density of the uppermost mantle below the Moho interface, while taking into consideration also density variations within the sediments and consolidated crust down to the Moho interface. The developed theoretical models are applied to estimate the Moho depth from GOCE data at the regional study area of the Iranian tectonic block, including also parts of surrounding tectonic features. Our results indicate that the regional Moho depth differences between Sjöberg and Jeffrey’s solutions, reaching up to about 3 km, are caused by a smoothing effect of Sjöberg’s method. The validation of our results further shows a relatively good agreement with regional seismic studies over most of the continental crust, but large discrepancies are detected under the Oman Sea and the Makran subduction zone. We explain these discrepancies by a low quality of seismic data offshore. [ABSTRACT FROM AUTHOR]

In this paper a new gravimetric–isostatic crustal thickness model (VMM14_FEN) is estimated for Fennoscandia. The main motivation is to investigate the relations between geological and geophysical properties, the Moho depth and crust–mantle density contrast at the crust–mantle discontinuity. For this purpose the Bouguer gravity disturbance data is corrected in two main ways namely for the gravitational contributions of mass density variation due to the different layers of the Earth's crust such as ice and sediments, as well as for the gravitational contribution from deeper masses below the crust. This second correction (for non-isostatic effects) is necessary because in general the crust is not in complete isostatic equilibrium and the observed gravity data are not only generated by the topographic/isostatic masses but also from those in the deep Earth interior. The correction for non-isostatic effects is mainly attributed to unmodeled mantle and core boundary density heterogeneities. These corrections are determined using the recent seismic crustal thickness model CRUST1.0. We compare our modeling results with previous studies in the area and test the fitness. The comparison with the external Moho model EuCRUST-07 shows a 3.3 km RMS agreement for the Moho depth in Fennoscandia. We also illustrate how the above corrections improve the Moho depth estimation. Finally, the signatures of geological structures and isostatic equilibrium are studied using VMM14_FEN, showing how main geological unit structures attribute in isostatic balance by affecting the Moho geometry. The main geological features are also discussed in the context of the complete and incomplete isostatic equilibrium. [ABSTRACT FROM AUTHOR]

Gravimetric methods applied for Moho recovery in areas with sparse and irregular distribution of seismic data often assume only a constant crustal density. Results of latest studies, however, indicate that corrections for crustal density heterogeneities could improve the gravimetric result, especially in regions with a complex geologic/tectonic structure. Moreover, the isostatic mass balance reflects also the density structure within the lithosphere. The gravimetric methods should therefore incorporate an additional correction for the lithospheric mantle as well as deeper mantle density heterogeneities. Following this principle, we solve the Vening Meinesz-Moritz (VMM) inverse problem of isostasy constrained by seismic data to determine the Moho depth of the South American tectonic plate including surrounding oceans, while taking into consideration the crustal and mantle density heterogeneities. Our numerical result confirms that contribution of sediments significantly modifies the estimation of the Moho geometry especially along the continental margins with large sediment deposits. To account for the mantle density heterogeneities we develop and apply a method in order to correct the Moho geometry for the contribution of the lithospheric thermal state (i.e., the lithospheric thermal-pressure correction). In addition, the misfit between the isostatic and seismic Moho models, attributed mainly to deep mantle density heterogeneities and other geophysical phenomena, is corrected for by applying the non-isostatic correction. The results reveal that the application of the lithospheric thermal-pressure correction improves the RMS fit of the VMM gravimetric Moho solution to the CRUST1.0 (improves ∼ 1.9 km) and GEMMA (∼1.1 km) models and the point-wise seismic data (∼0.7 km) in South America. [ABSTRACT FROM AUTHOR]

We use gravity information obtained from the XGM2016 global gravitational model together with topographic, bathymetric and seismic data to interpret the crustal structure beneath Cameroon and adjoined geological regions. For this purpose, we apply the regularized non-linear gravity inversion for a gravimetric determination of the Moho depth utilizing existing results of seismic data analysis as constraints. The estimated Moho model reflects regional tectonic configuration and geological structure of this region, mainly consisting of two major geological units, i.e. the Cameroon Volcanic Line and the Congo Craton. A validation of gravimetric result at sites of the Cameroon Broadband Seismic Experiment (CBSE) reveals overall similarities between gravimetric and seismic estimates. A comparison of our result is also conducted with previously published results. The cross-comparison of these results reveals a good agreement between them, particularly beneath the Cameroon Volcanic Line, the Adamawa Plateau and the Garoua Rift. Nevertheless, some relatively large inconsistencies roughly reaching ±10 km in estimated values of the Moho depth are identified in geological regions of the Congo Craton and the Yaoundé domain. The spatial correlation analysis between the Moho geometry and the topography indicates an isostatic state of particular geological units, suggesting their compensation stage. Our result closely agrees with the assumption that most of isostatically over compensated geological structures were formed during a compressional tectonic regime, except for the Garoua Rift that was likely formed during an extensional regime. We also computed the Bouguer gravity data at different constant elevations above sea level in order to supress a gravitational signature of shallower sources, while enhancing a gravitational signature from deeper crustal and lithospheric structures, focusing primarily on cores of major cratonic formations. The Bouguer gravity maps indicate that the Yaoundé domain likely represents the crustal manifestation of the suture zone between the Congo Craton and the Adamawa-Yadé domain, acting as a micro-continent. • Highlights (85 characters maximum by bullet, space included): • We produced a new high-resolution gravity derived Moho model for Cameroon. • We found thicker Moho depth beneath the Ntem complex and the Adamawa Plateau. • The Moho under the Mount Cameroon deepens to only about 30 km. • Our crustal thickness model revealed E-W trending along with the Oubanguides Belt. [ABSTRACT FROM AUTHOR]