We employed a double-difference algorithm （hypoDD） to relocate earthquakes within the region bounded by 66°E-78°E and 32°N-42°N in the period of 1964-2003 reported by the International Seismologi...We employed a double-difference algorithm （hypoDD） to relocate earthquakes within the region bounded by 66°E-78°E and 32°N-42°N in the period of 1964-2003 reported by the International Seismological Center （ISC）. The improved hypocentral locations delineate a double-layered Wadati-Benioff zone in the eastern Hindu Kush intermediate seismic belt. Based on this feature and other evidences, we propose that the intermediate-depth earthquakes beneath the Pamir-Hindu Kush region may occur in two collided subduction zones with opposite dip directions.展开更多
The current stress state of the Earth's crust in Central Asia depends entirely on the interaction of the Eurasian plate with the Indian and Arabian plates.Moreover,an essential role in this action is played by the...The current stress state of the Earth's crust in Central Asia depends entirely on the interaction of the Eurasian plate with the Indian and Arabian plates.Moreover,an essential role in this action is played by the subduction process in the Pamir-Hind Kush zone.In this region,deep earthquakes and anomalies in seismic velocities indicate subduction of the Indian Plate.To determine the effect of earthquakes on the stress state of the Earth's crust in Central Asia,we analyzed the hypocenters according to the available data over a hundred years.Taking the envelope of the hypocenters as the surface of the subducted indenter,we analyzed its penetration into the mantle.Instead of the pushing force of the indenter,the velocity of the Indian plate is taken into consideration.A model of the stresses is constructed on the equations of creeping motion of a viscous incompressible fluid.The stress variation in the Earth's crust and mantle was calculated as the stress difference before and after the earthquake.The mechanism of earthquakes is modelled by an introduction of equivalent volume forces in the equilibrium equations corresponding to a couple dipoles without a moment.The equations of creeping motion are numerically solved using boundary element methods.Numerical experiments with different physical model pa-rameters for the Earth's crust and mantle were conducted.To introduce the negative buoyancy of the subducting plate,partial eclogitization of the rocks in the collision zone was assumed.As a result,a certain combination of stiffness and density was determined for the lithosphere and mantle,which explained the peculiarities of this region.The influence of crustal and mantle earthquakes in the Pamir-Hindu Kush region on the change in background stresses in Central Asia was analyzed which are not higher than 2-3%.展开更多
The Pamir-Hindu Kush region at the western end of the Himalayan-Tibet orogen is one of the most active regions on the globe with strong seismicity and deformation and provides a window to evaluate continental collisio...The Pamir-Hindu Kush region at the western end of the Himalayan-Tibet orogen is one of the most active regions on the globe with strong seismicity and deformation and provides a window to evaluate continental collision linked to two intra-continental subduction zones with different polarities.The seismicity and seismic tomography data show a steep northward subducting slab beneath the Hindu Kush and southward subducting slab under the Pamir.Here,we collect seismic catalogue with 3988 earthquake events to compute seismicity images and waveform data from 926 earthquake events to invert focal mechanism solutions and stress field with a view to characterize the subducting slabs under the Pamir-Hindu Kush region.Our results define two distinct seismic zones:a steep one beneath the Hindu Kush and a broad one beneath the Pamir.Deep and intermediate-depth earthquakes are mainly distributed in the Hindu Kush region which is controlled by thrust faulting,whereas the Pamir is dominated by strike-slip stress regime with shallow and intermediate-depth earthquakes.The area where the maximum principal stress axis is vertical in the southern Pamir corresponds to the location of a highconductivity low-velocity region that contributes to the seismogenic processes in this region.We interpret the two distinct seismic zones to represent a double-sided subduction system where the Hindu Kush zone represents the northward subduction of the Indian plate,and the Pamir zone shows southward subduction of the Eurasian plate.A transition fault is inferred in the region between the Hindu Kush and the Pamir which regulates the opposing directions of motion of the Indian and Eurasian plates.展开更多
基金partly sup-ported by the National Fundamental Science Program of China under(No.2004cb418406)the National Natural Science Foundation of China(No.90814002)Key Projects in the National Science & Technology PillarProgram during the Eleventh Five-year Plan Period(No.2008BAC38B02-4)
文摘We employed a double-difference algorithm （hypoDD） to relocate earthquakes within the region bounded by 66°E-78°E and 32°N-42°N in the period of 1964-2003 reported by the International Seismological Center （ISC）. The improved hypocentral locations delineate a double-layered Wadati-Benioff zone in the eastern Hindu Kush intermediate seismic belt. Based on this feature and other evidences, we propose that the intermediate-depth earthquakes beneath the Pamir-Hindu Kush region may occur in two collided subduction zones with opposite dip directions.
基金This work was supported by grants from the Ministry of Inno-vation of Uzbekistan(No.8-007 and No.20170918111).
文摘The current stress state of the Earth's crust in Central Asia depends entirely on the interaction of the Eurasian plate with the Indian and Arabian plates.Moreover,an essential role in this action is played by the subduction process in the Pamir-Hind Kush zone.In this region,deep earthquakes and anomalies in seismic velocities indicate subduction of the Indian Plate.To determine the effect of earthquakes on the stress state of the Earth's crust in Central Asia,we analyzed the hypocenters according to the available data over a hundred years.Taking the envelope of the hypocenters as the surface of the subducted indenter,we analyzed its penetration into the mantle.Instead of the pushing force of the indenter,the velocity of the Indian plate is taken into consideration.A model of the stresses is constructed on the equations of creeping motion of a viscous incompressible fluid.The stress variation in the Earth's crust and mantle was calculated as the stress difference before and after the earthquake.The mechanism of earthquakes is modelled by an introduction of equivalent volume forces in the equilibrium equations corresponding to a couple dipoles without a moment.The equations of creeping motion are numerically solved using boundary element methods.Numerical experiments with different physical model pa-rameters for the Earth's crust and mantle were conducted.To introduce the negative buoyancy of the subducting plate,partial eclogitization of the rocks in the collision zone was assumed.As a result,a certain combination of stiffness and density was determined for the lithosphere and mantle,which explained the peculiarities of this region.The influence of crustal and mantle earthquakes in the Pamir-Hindu Kush region on the change in background stresses in Central Asia was analyzed which are not higher than 2-3%.
基金jointly supported by National 985 Platform construction project,China Geological Survey(Grant No.12120114002211)National Nature Science Foundation of China(Grant No.41230206)a fund of the Graduate School of the China University of Geosciences for visiting and conducting research abroad。
文摘The Pamir-Hindu Kush region at the western end of the Himalayan-Tibet orogen is one of the most active regions on the globe with strong seismicity and deformation and provides a window to evaluate continental collision linked to two intra-continental subduction zones with different polarities.The seismicity and seismic tomography data show a steep northward subducting slab beneath the Hindu Kush and southward subducting slab under the Pamir.Here,we collect seismic catalogue with 3988 earthquake events to compute seismicity images and waveform data from 926 earthquake events to invert focal mechanism solutions and stress field with a view to characterize the subducting slabs under the Pamir-Hindu Kush region.Our results define two distinct seismic zones:a steep one beneath the Hindu Kush and a broad one beneath the Pamir.Deep and intermediate-depth earthquakes are mainly distributed in the Hindu Kush region which is controlled by thrust faulting,whereas the Pamir is dominated by strike-slip stress regime with shallow and intermediate-depth earthquakes.The area where the maximum principal stress axis is vertical in the southern Pamir corresponds to the location of a highconductivity low-velocity region that contributes to the seismogenic processes in this region.We interpret the two distinct seismic zones to represent a double-sided subduction system where the Hindu Kush zone represents the northward subduction of the Indian plate,and the Pamir zone shows southward subduction of the Eurasian plate.A transition fault is inferred in the region between the Hindu Kush and the Pamir which regulates the opposing directions of motion of the Indian and Eurasian plates.
