We apply the adaptive moving window method of Sun et al. to the most recent catalog data and the data recorded by portable stations to construct the velocity structure of the crust and upper mantle, and to determine t...We apply the adaptive moving window method of Sun et al. to the most recent catalog data and the data recorded by portable stations to construct the velocity structure of the crust and upper mantle, and to determine the depth of the Moho interface beneath the Tibetan plateau and other areas of China. We first select 2 600 locations in the study region with 1° intervals, then at each location invert for a five-layer 1-D P-wave velocity model from the surface down to the uppermost mantle by performing a Monte Carlo random search. The Moho depth at each location is then determined, and the Moho interface beneath the study region is obtained through proper interpolation with certain smoothing. Compared to depths obtained by previous studies, our results show more accurate Moho depths in the Tibetan plateau, Tianshan region and other areas of the study region.展开更多
The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of ...The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of the ultra- slow spreading Southwestern Indian Ridge （SWIR）. This paper firstly deduces the characteristics and do- mains of seismic phases based on a theoretical oceanic crust model. Then, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age. The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.展开更多
BP( Back Propagation) neural network and PSO( Particle Swarm Optimization) are two main heuristic optimization methods,and are usually used as nonlinear inversion methods in geophysics. The authors applied BP neural n...BP( Back Propagation) neural network and PSO( Particle Swarm Optimization) are two main heuristic optimization methods,and are usually used as nonlinear inversion methods in geophysics. The authors applied BP neural network and BP neural network optimized with PSO into the inversion of 3D density interface respectively,and a comparison was drawn to demonstrate the inversion results. To start with,a synthetic density interface model was created and we used the proceeding inversion methods to test their effectiveness. And then two methods were applied into the inversion of the depth of Moho interface. According to the results,it is clear to find that the application effect of PSO-BP is better than that of BP network. The BP network structures used in both synthetic and field data are consistent in order to obtain preferable inversion results. The applications in synthetic and field tests demonstrate that PSO-BP is a fast and effective method in the inversion of 3D density interface and the optimization effect is evident compared with BP neural network merely,and thus,this method has practical value.展开更多
Surface-wave inversion is a powerful tool for revealing the Earth's internal structure.However,aside from shear-wave velocity(v_(S)),other parameters can influence the inversion outcomes,yet these have not been sy...Surface-wave inversion is a powerful tool for revealing the Earth's internal structure.However,aside from shear-wave velocity(v_(S)),other parameters can influence the inversion outcomes,yet these have not been systematically discussed.This study investigates the influence of various parameter assumptions on the results of surface-wave inversion,including the compressional and shear velocity ratio(v_(P)/v_(S)),shear-wave attenuation(Q_(S)),density(ρ),Moho interface,and sedimentary layer.We constructed synthetic models to generate dispersion data and compared the obtained results with different parameter assumptions with those of the true model.The results indicate that the v_(P)/v_(S) ratio,Q_(S),and density(ρ) have minimal effects on absolute velocity values and perturbation patterns in the inversion.Conversely,assumptions about the Moho interface and sedimentary layer significantly influenced absolute velocity values and perturbation patterns.Introducing an erroneous Mohointerface depth in the initial model of the inversion significantly affected the v_(S) model near that depth,while using a smooth initial model results in relatively minor deviations.The assumption on the sedimentary layer not only affects shallow structure results but also impacts the result at greater depths.Non-linear inversion methods outperform linear inversion methods,particularly for the assumptions of the Moho interface and sedimentary layer.Joint inversion with other data types,such as receiver functions or Rayleigh wave ellipticity,and using data from a broader period range or higher-mode surface waves,can mitigate these deviations.Furthermore,incorporating more accurate prior information can improve inversion results.展开更多
The explosive seismic sounding profile across the transition zone from the west Kunlun Mts. to the Tarim Basin revealed the complex deep structure formed by continent-continent collision on the northern margin of the ...The explosive seismic sounding profile across the transition zone from the west Kunlun Mts. to the Tarim Basin revealed the complex deep structure formed by continent-continent collision on the northern margin of the Tibetan Plateau. The profile shows that the attitude of the Moho is in agreement with that of the crystalline basement in the Tarim Basin and the whole crust dips as a thick slate southwards with an angle from 5° to 7°. Meanwhile, the Moho depth increases from 40 km to 57 km within a distance of 150 km in the southern Tarim region, depicting the subduction of the crust of this region towards the west Kunlun Mts. The crust of the northern slope of the west Kunlun Mts. shows an evident compressed and shortened feature, that is, the basement is uplifted, the interface dips northwards and the Moho rises abruptly to become flat, so that the lower crust is as thick as 20 km.展开更多
The results of global and regional studies often show significant disagreement between the Moho depths determined using seismic and isostatic models. In this study, we estimate the differences between these two models...The results of global and regional studies often show significant disagreement between the Moho depths determined using seismic and isostatic models. In this study, we estimate the differences between these two models in central Eurasia. The Vening Meinesz-Moritz （VMM） inverse problem of isostasy is utilized to determine the isostatic Moho depths. The estimated VMM Moho depths are then corrected for the sediment density contrast. The application of this correction improves the agreement between the isostatic and seismic Moho models. The existing discrepancies between the isostatic and seismic models are finally modeled by applying the non-isostatic correction, which accounts for the unmodelled mantle density heterogeneities and other geodynamic processes, which are not taken into account in classical isostatic models. Our results reveal that the non-isostatic correction still cannot fully describe mechanisms affecting the Moho geometry along the convergent continent-tocontinent tectonic plate boundaries occurring beneath Himalayas despite an overall good performance of the applied method.展开更多
基金supported by the Defense Threat Reduction Agency under Contract Number DTRA01-00-C-0024supported by Chinese Academy of Sciences fund KJCX2-EW-121
文摘We apply the adaptive moving window method of Sun et al. to the most recent catalog data and the data recorded by portable stations to construct the velocity structure of the crust and upper mantle, and to determine the depth of the Moho interface beneath the Tibetan plateau and other areas of China. We first select 2 600 locations in the study region with 1° intervals, then at each location invert for a five-layer 1-D P-wave velocity model from the surface down to the uppermost mantle by performing a Monte Carlo random search. The Moho depth at each location is then determined, and the Moho interface beneath the study region is obtained through proper interpolation with certain smoothing. Compared to depths obtained by previous studies, our results show more accurate Moho depths in the Tibetan plateau, Tianshan region and other areas of the study region.
基金The National Natural Science Foundation of China under contract Nos 41176053,41076029,91028002 and 41176046Dayang 115 under contract No.DYXM-115-02-3-01
文摘The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of the ultra- slow spreading Southwestern Indian Ridge （SWIR）. This paper firstly deduces the characteristics and do- mains of seismic phases based on a theoretical oceanic crust model. Then, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age. The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.
基金Supported by National High-tech Research&Development Program of China(863 Project)(No.2014AA06A613)
文摘BP( Back Propagation) neural network and PSO( Particle Swarm Optimization) are two main heuristic optimization methods,and are usually used as nonlinear inversion methods in geophysics. The authors applied BP neural network and BP neural network optimized with PSO into the inversion of 3D density interface respectively,and a comparison was drawn to demonstrate the inversion results. To start with,a synthetic density interface model was created and we used the proceeding inversion methods to test their effectiveness. And then two methods were applied into the inversion of the depth of Moho interface. According to the results,it is clear to find that the application effect of PSO-BP is better than that of BP network. The BP network structures used in both synthetic and field data are consistent in order to obtain preferable inversion results. The applications in synthetic and field tests demonstrate that PSO-BP is a fast and effective method in the inversion of 3D density interface and the optimization effect is evident compared with BP neural network merely,and thus,this method has practical value.
基金supported by the Special Fund of the Institute of Geophysics, China Earthquake Administration (No. DQJB21B32)the National Key R&D Program of China (No. 2022YFF0800601)。
文摘Surface-wave inversion is a powerful tool for revealing the Earth's internal structure.However,aside from shear-wave velocity(v_(S)),other parameters can influence the inversion outcomes,yet these have not been systematically discussed.This study investigates the influence of various parameter assumptions on the results of surface-wave inversion,including the compressional and shear velocity ratio(v_(P)/v_(S)),shear-wave attenuation(Q_(S)),density(ρ),Moho interface,and sedimentary layer.We constructed synthetic models to generate dispersion data and compared the obtained results with different parameter assumptions with those of the true model.The results indicate that the v_(P)/v_(S) ratio,Q_(S),and density(ρ) have minimal effects on absolute velocity values and perturbation patterns in the inversion.Conversely,assumptions about the Moho interface and sedimentary layer significantly influenced absolute velocity values and perturbation patterns.Introducing an erroneous Mohointerface depth in the initial model of the inversion significantly affected the v_(S) model near that depth,while using a smooth initial model results in relatively minor deviations.The assumption on the sedimentary layer not only affects shallow structure results but also impacts the result at greater depths.Non-linear inversion methods outperform linear inversion methods,particularly for the assumptions of the Moho interface and sedimentary layer.Joint inversion with other data types,such as receiver functions or Rayleigh wave ellipticity,and using data from a broader period range or higher-mode surface waves,can mitigate these deviations.Furthermore,incorporating more accurate prior information can improve inversion results.
基金the Ministry of Land and Resources of China (Grant No. 9501204), the National Natural Science Foundation of China (Grant No. F49734230), National 305 Project of Xinjiang Uygur Autonomous Region of China (Grant No. 96-915-07-03), and Chinese National Key
文摘The explosive seismic sounding profile across the transition zone from the west Kunlun Mts. to the Tarim Basin revealed the complex deep structure formed by continent-continent collision on the northern margin of the Tibetan Plateau. The profile shows that the attitude of the Moho is in agreement with that of the crystalline basement in the Tarim Basin and the whole crust dips as a thick slate southwards with an angle from 5° to 7°. Meanwhile, the Moho depth increases from 40 km to 57 km within a distance of 150 km in the southern Tarim region, depicting the subduction of the crust of this region towards the west Kunlun Mts. The crust of the northern slope of the west Kunlun Mts. shows an evident compressed and shortened feature, that is, the basement is uplifted, the interface dips northwards and the Moho rises abruptly to become flat, so that the lower crust is as thick as 20 km.
基金financial support (No.214273812)supported by the Swedish National Space Board (SNSB) (No.76/10:1)
文摘The results of global and regional studies often show significant disagreement between the Moho depths determined using seismic and isostatic models. In this study, we estimate the differences between these two models in central Eurasia. The Vening Meinesz-Moritz （VMM） inverse problem of isostasy is utilized to determine the isostatic Moho depths. The estimated VMM Moho depths are then corrected for the sediment density contrast. The application of this correction improves the agreement between the isostatic and seismic Moho models. The existing discrepancies between the isostatic and seismic models are finally modeled by applying the non-isostatic correction, which accounts for the unmodelled mantle density heterogeneities and other geodynamic processes, which are not taken into account in classical isostatic models. Our results reveal that the non-isostatic correction still cannot fully describe mechanisms affecting the Moho geometry along the convergent continent-tocontinent tectonic plate boundaries occurring beneath Himalayas despite an overall good performance of the applied method.
