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Robert Tenzer - One of the best experts on this subject based on the ideXlab platform.
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Combined Gravimetric-Seismic Moho Model of Tibet
Geosciences, 2018Co-Authors: A. A. Baranov, M. Bagherbandi, Robert TenzerAbstract: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.
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Moho Modeling Using FFT Technique
Pure and Applied Geophysics, 2017Co-Authors: Wenjin Chen, Robert TenzerAbstract:To improve the numerical efficiency, the Fast Fourier Transform (FFT) technique was facilitated in Parker–Oldenburg’s method for a regional gravimetric Moho recovery, which assumes the Earth’s planar approximation. In this study, we extend this definition for global applications while assuming a spherical approximation of the Earth. In particular, we utilize the FFT technique for a global Moho recovery, which is practically realized in two numerical steps. The gravimetric forward modeling is first applied, based on methods for a spherical harmonic analysis and synthesis of the global gravity and lithospheric structure models, to compute the refined gravity field, which comprises mainly the gravitational signature of the Moho geometry. The gravimetric inverse problem is then solved iteratively in order to determine the Moho depth. The application of FFT technique to both numerical steps reduces the computation time to a fraction of that required without applying this fast algorithm. The developed numerical producers are used to estimate the Moho depth globally, and the gravimetric result is validated using the global (CRUST1.0) and regional (ESC) seismic Moho models. The comparison reveals a relatively good agreement between the gravimetric and seismic models, with the RMS of differences (of 4–5 km) at the level of expected uncertainties of used input datasets, while without the presence of significant systematic bias.
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Moho modeling in spatial domain: A case study under Tibet
Advances in Space Research, 2017Co-Authors: Wenjin Chen, Robert TenzerAbstract:Abstract 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.
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Isostatic GOCE Moho model for Iran
Journal of Asian Earth Sciences, 2017Co-Authors: Mehdi Eshagh, Sahar Ebadi, Robert TenzerAbstract:Abstract 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 Sjoberg 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 Sjoberg and Jeffrey’s solutions, reaching up to about 3 km, are caused by a smoothing effect of Sjoberg’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.
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Moho density contrast in central Eurasia from GOCE gravity gradients
Remote Sensing, 2016Co-Authors: Mehdi Eshagh, Robert Tenzer, Matloob Hussain, Mohsen RomeshkaniAbstract:Seismic data are primarily used in studies of the Earth’s inner structure. Since large parts of the world are not yet sufficiently covered by seismic surveys, products from the Earth’s satellite observation systems have more often been used for this purpose in recent years. In this study we use the gravity-gradient data derived from the Gravity field and steady-state Ocean Circulation Explorer (GOCE), the elevation data from the Shuttle Radar Topography Mission (SRTM) and other global datasets to determine the Moho density contrast at the study area which comprises most of the Eurasian plate (including parts of surrounding continental and oceanic tectonic plates). A regional Moho recovery is realized by solving the Vening Meinesz-Moritz’s (VMM) inverse problem of isostasy and a seismic crustal model is applied to constrain the gravimetric solution. Our results reveal that the Moho density contrast reaches minima along the mid-oceanic rift zones and maxima under the continental crust. This spatial pattern closely agrees with that seen in the CRUST1.0 seismic crustal model as well as in the KTH1.0 gravimetric-seismic Moho model. However, these results differ considerably from some previously published gravimetric studies. In particular, we demonstrate that there is no significant spatial correlation between the Moho density contrast and Moho deepening under major orogens of Himalaya and Tibet. In fact, the Moho density contrast under most of the continental crustal structure is typically much more uniform.
Mei Feng - One of the best experts on this subject based on the ideXlab platform.
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Moho map of South America from receiver functions and surface waves
Journal of Geophysical Research, 2010Co-Authors: Simon Lloyd, Suzan Van Der Lee, George Sand França, Marcelo Assumpção, Mei FengAbstract:We estimate crustal structure and thickness of South America north of roughly 40 degrees S. To this end, we analyzed receiver functions from 20 relatively new temporary broadband seismic stations deployed across eastern Brazil. In the analysis we include teleseismic and some regional events, particularly for stations that recorded few suitable earthquakes. We first estimate crustal thickness and average Poisson`s ratio using two different stacking methods. We then combine the new crustal constraints with results from previous receiver function studies. To interpolate the crustal thickness between the station locations, we jointly invert these Moho point constraints, Rayleigh wave group velocities, and regional S and Rayleigh waveforms for a continuous map of Moho depth. The new tomographic Moho map suggests that Moho depth and Moho relief vary slightly with age within the Precambrian crust. Whether or not a positive correlation between crustal thickness and geologic age is derived from the pre-interpolation point constraints depends strongly on the selected subset of receiver functions. This implies that using only pre-interpolation point constraints (receiver functions) inadequately samples the spatial variation in geologic age. The new Moho map also reveals an anomalously deep Moho beneath the oldest core of the Amazonian Craton.National Science Foundation (NSF)[EAR 0538267
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Moho map of South America from receiver functions and surface waves
Journal of Geophysical Research, 2010Co-Authors: Simon Lloyd, Suzan Van Der Lee, George Sand França, Marcelo Assumpção, Mei FengAbstract:[1] We estimate crustal structure and thickness of South America north of roughly 40°S. To this end, we analyzed receiver functions from 20 relatively new temporary broadband seismic stations deployed across eastern Brazil. In the analysis we include teleseismic and some regional events, particularly for stations that recorded few suitable earthquakes. We first estimate crustal thickness and average Poisson's ratio using two different stacking methods. We then combine the new crustal constraints with results from previous receiver function studies. To interpolate the crustal thickness between the station locations, we jointly invert these Moho point constraints, Rayleigh wave group velocities, and regional S and Rayleigh waveforms for a continuous map of Moho depth. The new tomographic Moho map suggests that Moho depth and Moho relief vary slightly with age within the Precambrian crust. Whether or not a positive correlation between crustal thickness and geologic age is derived from the pre-interpolation point constraints depends strongly on the selected subset of receiver functions. This implies that using only pre-interpolation point constraints (receiver functions) inadequately samples the spatial variation in geologic age. The new Moho map also reveals an anomalously deep Moho beneath the oldest core of the Amazonian Craton.
M. Bagherbandi - One of the best experts on this subject based on the ideXlab platform.
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Combined Gravimetric-Seismic Moho Model of Tibet
Geosciences, 2018Co-Authors: A. A. Baranov, M. Bagherbandi, Robert TenzerAbstract: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.
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Towards the Moho depth and Moho density contrast along with their uncertainties from seismic and satellite gravity observations
Journal of Applied Geodesy, 2017Co-Authors: Majid Abrehdary, Lars E Sjoberg, M. Bagherbandi, D. SampietroAbstract:We present a combined method for estimating a new global Moho model named KTH15C, containing Moho depth and Moho density contrast (or shortly Moho parameters), from a combination of global models o ...
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Modelling Moho depth in ocean areas based on satellite altimetry using Vening Meinesz–Moritz’ method
Acta Geodaetica et Geophysica, 2016Co-Authors: M. Abrehdary, L. E. Sjöberg, M. BagherbandiAbstract:An experiment for estimating Moho depth is carried out based on satellite altimetry and topographic information using the Vening Meinesz–Moritz gravimetric isostatic hypothesis. In order to investigate the possibility and quality of satellite altimetry in Moho determination, the DNSC08GRA global marine gravity field model and the DTM2006 global topography model are used to obtain a global Moho depth model over the oceans with a resolution of 1° × 1°. The numerical results show that the estimated Bouguer gravity disturbance varies from 86 to 767 mGal, with a global average of 747 mGal, and the estimated Moho depth varies from 3 to 39 km with a global average of 19 km. Comparing the Bouguer gravity disturbance estimated from satellite altimetry and that derived by the gravimetric satellite-only model GOGRA04S shows that the two models agree to 13 mGal in root mean square (RMS). Similarly, the estimated Moho depths from satellite altimetry and GOGRA04S agree to 0.69 km in RMS. It is also concluded that possible mean dynamic topography in the marine gravity model does not significantly affect the Moho determination.
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Effect of the lithospheric thermal state on the Moho geometry
2016Co-Authors: M. Bagherbandi, Lars E Sjoberg, Robert Tenzer, Majid Abrehdary, Yongliang Bai, Silvia Miranda, Juan Manuel Alcacer SanchezAbstract:Isostasy is a key concept in geoscience to interpret the state of mass balance between the Earth’s crust and mantle. There are four well-known isostatic models: the classical models of Airy/Heiskanen (A/H), Pratt/Hayford (P/H), and Vening Meinesz (VM) and the modern model of Vening Meinesz-Moritz (VMM). The first three models assume a local and regional isostatic compensation, whereas the latter one supposes a global isostatic compensation scheme.A more satisfactory test of isostasy is to determine the Moho interface. The Moho discontinuity (or Moho) is the surface, which marks the boundary between the Earth’s crust and upper mantle. Generally, the Moho interface can be mapped accurately by seismic observations, but limited coverage of seismic data and economic considerations make gravimetric or combined gravimetric-seismic methods a more realistic technique for imaging the Moho interface either regional or global scales.It is the main purpose of this dissertation to investigate an isostatic model with respect to its feasibility to use in recovering the Moho parameters (i.e. Moho depth and Moho density contrast). The study is mostly limited to the VMM model and to the combined approach on regional and global scales. The thesis briefly includes various investigations with the following specific subjects:1) to investigate the applicability and quality of satellite altimetry data (i.e. marine gravity data) in Moho determination over the oceans using the VMM model, 2) to investigate the need for methodologies using gravimetric data jointly with seismic data (i.e. combined approach) to estimate both the Moho depth and Moho density contrast over regional and global scales, 3) to investigate the spherical terrain correction and its effect on the VMM Moho determination, 4) to investigate the residual isostatic topography (RIT, i.e. difference between actual topography and isostatic topography) and its effect in the VMM Moho estimation, 5) to investigate the application of the lithospheric thermal-pressure correction and its effect on the Moho geometry using the VMM model, 6) Finally, the thesis ends with the application of the classical isostatic models for predicting the geoid height.The main input data used in the VMM model for a Moho recovery is the gravity anomaly/disturbance corrected for the gravitational contributions of mass density variation due in different layers of the Earth’s crust (i.e. stripping gravity corrections) and for the gravity contribution from deeper masses below the crust (i.e. non-isostatic effects). The corrections are computed using the recent seismic crustal model CRUST1.0.Our numerical investigations presented in this thesis demonstrate that 1) the VMM approach is applicable for estimating Moho geometry using a global marine gravity field derived by satellite altimetry and that the possible mean dynamic topography in the marine gravity model does not significantly affect the Moho determination, 2) the combined approach could help in filling-in the gaps in the seismic models and it also provides good fit to other global and regional models more than 90 per cent of the locations, 3) despite the fact that the lateral variation of the crustal depth is rather smooth, the terrain affects the Moho result most significantly in many areas, 4) the application of the RIT correction improves the agreement of our Moho result with some published global Moho models, 5) the application of the lithospheric thermal-pressure correction improves the agreement of VMM Moho model with some other global Moho models, 6) the geoid height cannot be successfully represented by the classical models due to many other gravitational signals from various mass variations within the Earth that affects the geoid.
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Modelling Moho parameters and their uncertainties from the combination of the seismic and satellite gravity data
2016Co-Authors: Majid Abrehdary, Lars E Sjoberg, M. Bagherbandi, D. SampietroAbstract:Isostasy is a key concept in geoscience to interpret the state of mass balance between the Earth’s crust and mantle. There are four well-known isostatic models: the classical models of Airy/Heiskanen (A/H), Pratt/Hayford (P/H), and Vening Meinesz (VM) and the modern model of Vening Meinesz-Moritz (VMM). The first three models assume a local and regional isostatic compensation, whereas the latter one supposes a global isostatic compensation scheme.A more satisfactory test of isostasy is to determine the Moho interface. The Moho discontinuity (or Moho) is the surface, which marks the boundary between the Earth’s crust and upper mantle. Generally, the Moho interface can be mapped accurately by seismic observations, but limited coverage of seismic data and economic considerations make gravimetric or combined gravimetric-seismic methods a more realistic technique for imaging the Moho interface either regional or global scales.It is the main purpose of this dissertation to investigate an isostatic model with respect to its feasibility to use in recovering the Moho parameters (i.e. Moho depth and Moho density contrast). The study is mostly limited to the VMM model and to the combined approach on regional and global scales. The thesis briefly includes various investigations with the following specific subjects:1) to investigate the applicability and quality of satellite altimetry data (i.e. marine gravity data) in Moho determination over the oceans using the VMM model, 2) to investigate the need for methodologies using gravimetric data jointly with seismic data (i.e. combined approach) to estimate both the Moho depth and Moho density contrast over regional and global scales, 3) to investigate the spherical terrain correction and its effect on the VMM Moho determination, 4) to investigate the residual isostatic topography (RIT, i.e. difference between actual topography and isostatic topography) and its effect in the VMM Moho estimation, 5) to investigate the application of the lithospheric thermal-pressure correction and its effect on the Moho geometry using the VMM model, 6) Finally, the thesis ends with the application of the classical isostatic models for predicting the geoid height.The main input data used in the VMM model for a Moho recovery is the gravity anomaly/disturbance corrected for the gravitational contributions of mass density variation due in different layers of the Earth’s crust (i.e. stripping gravity corrections) and for the gravity contribution from deeper masses below the crust (i.e. non-isostatic effects). The corrections are computed using the recent seismic crustal model CRUST1.0.Our numerical investigations presented in this thesis demonstrate that 1) the VMM approach is applicable for estimating Moho geometry using a global marine gravity field derived by satellite altimetry and that the possible mean dynamic topography in the marine gravity model does not significantly affect the Moho determination, 2) the combined approach could help in filling-in the gaps in the seismic models and it also provides good fit to other global and regional models more than 90 per cent of the locations, 3) despite the fact that the lateral variation of the crustal depth is rather smooth, the terrain affects the Moho result most significantly in many areas, 4) the application of the RIT correction improves the agreement of our Moho result with some published global Moho models, 5) the application of the lithospheric thermal-pressure correction improves the agreement of VMM Moho model with some other global Moho models, 6) the geoid height cannot be successfully represented by the classical models due to many other gravitational signals from various mass variations within the Earth that affects the geoid.
Carla Braitenberg - One of the best experts on this subject based on the ideXlab platform.
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Moho topography ranges and folds of tibet by analysis of global gravity models and goce data
Scientific Reports, 2015Co-Authors: Young Hong Shin, C K Shum, Carla Braitenberg, Sangmook Lee, Kwang Sun Choi, Houtse Hsu, Youngsue Park, Mutaek LimAbstract:The determination of the crustal structure is essential in geophysics, as it gives insight into the geohistory, tectonic environment, geohazard mitigation, etc. Here we present the latest advance on three-dimensional modeling representing the Tibetan Mohorovicic discontinuity (topography and ranges) and its deformation (fold), revealed by analyzing gravity data from GOCE mission. Our study shows noticeable advances in estimated Tibetan Moho model which is superior to the results using the earlier gravity models prior to GOCE. The higher quality gravity field of GOCE is reflected in the Moho solution: we find that the Moho is deeper than 65 km, which is twice the normal continental crust beneath most of the Qinghai-Tibetan plateau, while the deepest Moho, up to 82 km, is located in western Tibet. The amplitude of the Moho fold is estimated to be ranging from −9 km to 9 km with a standard deviation of ~2 km. The improved GOCE gravity derived Moho signals reveal a clear directionality of the Moho ranges and Moho fold structure, orthogonal to deformation rates observed by GPS. This geophysical feature, clearly more evident than the ones estimated using earlier gravity models, reveals that it is the result of the large compressional tectonic process.
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three dimensional fold structure of the tibetan Moho from grace gravity data
Geophysical Research Letters, 2009Co-Authors: Young Hong Shin, C K Shum, Carla Braitenberg, Sangmook Lee, Kwang Sun Choi, Jeong Ho Baek, Jong-uk ParkAbstract:[1] Although the prevailing wavelength of the Moho fold has been estimated from the spectral analysis of gravity and topography, there has not been a suggested method developed to reveal its structure. Here we present a threedimensional (3D) Moho fold structure beneath Tibet which clearly reflects the continental collision. For the structure estimation a new method has been introduced based on the gravity inversion and flexural model. The estimated direction and wavelength of the Moho fold are consistent with the velocities calculated from Global Positioning System (GPS) and with an elastic plate model under horizontal compression. The prevailing wavelength of the Moho fold is estimated to be 300 to 420 km, which corresponds to an elastic plate with effective elastic thickness (EET) of about 35 km, and much smaller than the prior estimates of 500 to 700 km. Citation: Shin, Y. H., C.-K. Shum, C. Braitenberg, S. M. Lee, H. Xu, K. S. Choi, J. H. Baek, and J. U. Park (2009), Three-dimensional fold structure of the Tibetan Moho from GRACE gravity data, Geophys. Res. Lett., 36, L01302, doi:10.1029/2008GL036068.
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Moho undulations beneath Tibet from GRACE-integrated gravity data
Geophysical Journal International, 2007Co-Authors: Young Hong Shin, Carla Braitenberg, Jian Fang, Yong WangAbstract:SUMMARY Knowledge of the variation of crustal thickness is essential in many applications, such as forward dynamic modelling, numerical heat flow calculations, seismologic applications and geohistory reconstructions. We present a 3-D model of the Moho undulations over the entire Tibetan plateau derived from gravity inversion. The gravity field has been obtained by using the Gravity Recovery and Climate Experiment (GRACE) potential field development which has been integrated with terrestrial data, and is presently the best available in the studied area. For the effective use of the global geopotential model that has no height information of observation stations, upward continuation is applied. The Moho model is characterized by a sequence of troughs and ridges with a semi-regular pattern, which could reflect the continent‐continent collision between the Indian and Eurasian plates. The three deep Moho belts (troughs) and shallow Moho belts (ridges) between them are clearly found to have an E‐W directional trend parallel to the border of the plateau and tectonic lines, while variation of the directionality is observed in central to southeast Tibet. To describe the distinctive shape of the Moho troughs beneath Tibet, we introduce the term, ‘Moho ranges’. The most interesting aspects of the Moho ranges are (1) that they run in parallel with the border and tectonic sutures of the plateau, (2) that the distances between ranges are found at regular distances of about 330 km except in northeast Tibet and (3) that the splitting of the ranges into two branches is found as the distance between them is increasing. From our study, we conclude that the distinctive undulations of the Tibetan Moho have been formed by buckling in a compressional environment, superimposed on the regional increase in crustal thickness. According to our analysis, the GRACE satelliteonly data turns out to have good enough resolution for being used to determine the very deep Moho beneath Tibet. Our Moho model is the first one that covers the entire plateau.
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The gravity and isostatic Moho undulations in Qinghai–Tibet plateau
Journal of Geodynamics, 2000Co-Authors: Carla Braitenberg, Jian Fang, M. Zadro, Yuejun Wang, H.t. HsuAbstract:Abstract It is our interest to study the Moho depths in the Qinghai–Tibet. An iterative hybrid spectral–classical methodology is applied to invert the gravity data and obtain the 3D variation in Moho depth. The gravity inversion is constrained by results from deep seismic sounding and seismological investigations. The Moho is found between 70 and 75 km depth over most of Tibet. Maximum depths of up to 80 km are found along the margins of the plateau, and shallower depths of 65 km correlate with an important suture running along central Tibet (Bangong Nujiang). At Moho level most of Tibet is isostatically compensated at 90–110%, according to the Airy isostatic model. The Qaidam basin in North-Eastern Tibet and the Tarim basin to the North-West are found to be over-compensated.
Rui Gao - One of the best experts on this subject based on the ideXlab platform.
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investigation of the Moho discontinuity beneath the chinese mainland using deep seismic sounding profiles
Tectonophysics, 2013Co-Authors: Jiwen Teng, Baojun Yang, Zhongjie Zhang, Xiankang Zhang, Chunyong Wang, Rui Gao, Yonghu Qiao, Yangfan DengAbstract:Abstract We herein describe the depth distribution of the Moho beneath the Chinese mainland, determined via compilation and resampling of the interpreted results of crustal P-wave velocity structures obtained from deep seismic soundings (DSSs) performed since the pioneering DSS work carried out in the Qaidam basin in 1958. For the present study, 114 wide-angle seismic profiles acquired over the last 50 years were collated; we included results for crustal structures from several profiles in Japan and South Korea, to improve the reliability of the interpolation of the Moho depth distribution. Our final Moho map shows that the depth of the Moho ranges from 10 to 85 km. The deepest Moho discontinuity—at approximately 70–85 km beneath the Tibetan Plateau—was formed by ongoing continent–continent collision. The Moho beneath the eastern North China craton, at a relatively constant 30–35 km, has endured mantle lithosphere destruction. The Moho depths determined from active seismology are consistent (within 3–5 km) with results obtained from gravity inversion and surface wave tomography. The spatial variation of the Moho depth, crustal formation, and composition of different tectonic blocks contribute to controls on the spatial distribution of the seismicity and rheology in the crust beneath mainland China.
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Moho Depth of Qinghai-Tibet Plateau Revealed by Seismic Probing
Journal of Earth Science, 2009Co-Authors: Xiaosong Xiong, Rui GaoAbstract:The Qinghai (青海)-Tibet plateau is the newest and biggest orogenic belt in the world and a natural laboratory for researching continental geodynamics, such as continent-continent collision, convergence, subduction, and plateau uplift. From the 1950s to the present, there have been many active-source (deep seismic sounding and deep seismic reflection profiling) and passive-source seismic probing (broadband seismic observations) implemented to reveal the crust-mantle structure. In this article, the authors mainly summarize the three seismic probings to discuss the Moho depth of the Qinghai-Tibet plateau based on the previous summaries. The result shows that the Moho of the Qinghai-Tibet plateau is very complex and its depth is very different; the whole outline of it is that the Moho depth is deeper beneath the south than the north and deeper in the west than in the east. In the Qiangtang (羌塘) terrane, the hinterland of the Qinghai-Tibet plateau, the Moho is shallower than both the southern and the northern sides. The deepest Moho is 40 km deeper than the shallowest Moho. This trend records the crustal thickening and thinning caused by the mutual response between the India plate and the Eurasia plate, and the eastward mass flow in the Qinghai-Tibet plateau.
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Moho-mapping in the Dabie ultrahigh-pressure collisional orogen, central China
American Journal of Science, 2008Co-Authors: Shu-wen Dong, Rui Gao, Fu-tian Liu, Xiaochun Liu, Huai-min Xue, Ye GuanAbstract:Eight wide angle reflection/refraction seismic profiles (with a total length of ∼1700 km) and near-vertical reflection seismic profiles (with a total length of ∼340 km) across the Dabie Orogen, eastern China have been completed in recent years, and allow the Moho depth and uppermost-mantle velocity to be mapped across ∼40,000 km 2 . These data reveal the detailed structure of the crust and upper mantle of this orogen that resulted from collision of the North China craton (NCC) with the Yangtze Craton (YC). The Dabie Orogen is an asymmetric orogen, with a thin crustal root (∼6 km) preserved in its northern part, highlighted by a north-dipping Moho. Compared to the nearly seismically-transparent lower crust, the Moho crust-mantle transition zone under the Dabie Orogen is a prominent north-dipping, strongly layered reflection, which is inferred to reflect the remnants of subduction of YC under the edge of the NCC or post-collisional exhumation of ultrahigh-pressure (UHP) rocks, and indicates the northward polarity of subduction of the YC. The Moho of the YC and NCC meet beneath the northern part of the Dabie Mountains, and the NCC Moho (north) is uplifted by ∼4 to 5 km (Offset 1) over the YC Moho (south), marking the NCC-YC collision zone. Along the southern margin of the Dabie Mountains, the Moho below the Yangtze foreland is underthrust beneath the Moho of the Dabie Mountains, forming another Moho overlap (Offset 2) with a depth difference of 5 to 6 km. The two Moho overlaps (offsets) at both flanks of the Dabie Mountains formed two crustal-scale boundaries at depth between the NCC and the Dabie Orogen, and the Dabie Orogen and the YC respectively. Offset 1 is considered to be the Triassic suture between the YC and NCC as supported by the metamorphic ages of UHP rocks. This displays a wedge-shaped offset zone opening towards the east that acted as a channel for exhumation of UHP rocks. Offset 2 under the southern margin of the Dabie Orogen is connected to the Xiangfan-Guangji fault that gave rise to a large-scale thrust detachment that propagated towards the foreland of the Dabie Orogen during the Jurassic. Thus our Moho mapping confirms that there are structural remnants of the Triassic deep continental subduction preserved, despite the superimposed Jurassic deformation.
