A three-dimensional local-scale P-velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event-to-receiver seismic rays from 5856 aftershocks recorded by a newly deployed...A three-dimensional local-scale P-velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event-to-receiver seismic rays from 5856 aftershocks recorded by a newly deployed temporary seismic network. Checkerboard tests show that our tomographic model has lateral and vertical resolution of -2 km. The high-resolution P-velocity model revealed interesting structures in the seismogenic layer： （1） The Guanxian-Anxian fault, Yingxiu-Beichuan fault and Wenchuan-Maoxian fault of the Longmen Shan fault zone are well delineated by sharp upper crustal velocity changes; （2） The Pengguan massif has generally higher velocity than its surrounding areas, and may extend down to at least -10 km from the surface; （3） A sharp lateral velocity variation beneath the Wenchuan-Maoxian fault may indicate that the Pengguan massif＇s western boundary and/or the Wenchuan-Maoxian fault is vertical, and the hypocenter of the Wenchuan earthquake possibly located at the conjunction point of the NW dipping Yingxiu-Beichuan and Guanxian-Anxian faults, and vertical Wenchuan-Maoxian fault; （4） Vicinity along the Yingxiu- Beichuan fault is characterized by very low velocity and low seismicity at shallow depths, possibly due to high content of porosity and fractures; （5） Two blocks of low-velocity anomaly are respectively imaged in the hanging wall and foot wall of the Guanxian-Anxian fault with a -7 km offset with -5 km vertical component.展开更多
In the southern South-North Seismic Zone,China,seismic activity in the Yingjiang area of western Yunnan increased from December 2010,and eventually a destructive earthquake of Ms5.9 occurred near Yingjiang town on 10 ...In the southern South-North Seismic Zone,China,seismic activity in the Yingjiang area of western Yunnan increased from December 2010,and eventually a destructive earthquake of Ms5.9 occurred near Yingjiang town on 10 March 2011.The focal mechanism and hypocenter location of the mainshock suggest that the Dayingjiang Fault was the site of the mainshock rupture.However,most of foreshocks and all aftershocks recorded by a portable seismic array located close to the mainshock occurred along the N-S-striking Sudian Fault,indicating that this fault had an important influence on these shocks.Coulomb stress calculations show that three strong （magnitude ≥5.0） earthquakes that occurred in the study region in 2008 increased the coulomb stress along the plane parallel to the Dayingjiang Fault.This supports the Dayingjiang Fault,and not the Sudian Fault,as the seismogenic fault of the 2011 Ms5.9 Yingjiang earthquake.The strong earthquakes in 2008 also increased the Coulomb stress at depths of ≤5 km along the entire Sudian Fault,and by doing so increased the shallow seismic activity along the fault.This explains why the foreshocks and aftershocks of the 2011 Yingjiang earthquake were located mostly on the Sudian Fault where it cuts the shallow crust.The earthquakes at the intersection of the Sudian and Dayingjiang faults are distributed mainly along a belt that dips to the southeast at ～40°,suggesting that the Dayingjiang Fault in the mainshock area also dips to the southeast at ～40°.展开更多
The Gamburtsev Antarctic Mountains Seismic Experiment （GAMSEIS, 2007-2010） was jointly conducted by the United States, China, and Japan during and after the International Polar Year 2007-2008. Broadband seismic stat...The Gamburtsev Antarctic Mountains Seismic Experiment （GAMSEIS, 2007-2010） was jointly conducted by the United States, China, and Japan during and after the International Polar Year 2007-2008. Broadband seismic stations were deployed across the ice-covered Gamburtsev Subglacial Mountains （GSM） and other previously unexplored areas in the interior of East Antarctica. Using GAMSEIS data, published results not only have revealed the deep structure of Antarctica, but also improved our understanding of the tectonic evolution of Antarctica and the supercontinent Gondwana, and of the relationship between geothermal heat flux and glaciers. This contribution draws together the major findings from recent studies, and also offers further investigation into the relationship between tectonic history and the East Antarctic Ice Sheet. The elevation of the GSM is largely supported by thickened crust, with Moho depths of ~60 km near the crest of the range. The GSM are underlain by thick （〉200 km） and cold continental lithosphere that likely formed after collision of two ancient crustal blocks during the pan-African orogeny. Heat flux results obtained from seismic inversion support a model of ice sheet basal melting that depends more strongly on bedrock topography than on geothermal heat flux, while ice surface and ice thickness are inversely correlated with heat flux.展开更多
基金the Basic Research Foundation of the Institute of Geomechanics,CAGS(grant DZLXJK200707)Natural Science Foundation of China grant 40674058)
文摘A three-dimensional local-scale P-velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event-to-receiver seismic rays from 5856 aftershocks recorded by a newly deployed temporary seismic network. Checkerboard tests show that our tomographic model has lateral and vertical resolution of -2 km. The high-resolution P-velocity model revealed interesting structures in the seismogenic layer： （1） The Guanxian-Anxian fault, Yingxiu-Beichuan fault and Wenchuan-Maoxian fault of the Longmen Shan fault zone are well delineated by sharp upper crustal velocity changes; （2） The Pengguan massif has generally higher velocity than its surrounding areas, and may extend down to at least -10 km from the surface; （3） A sharp lateral velocity variation beneath the Wenchuan-Maoxian fault may indicate that the Pengguan massif＇s western boundary and/or the Wenchuan-Maoxian fault is vertical, and the hypocenter of the Wenchuan earthquake possibly located at the conjunction point of the NW dipping Yingxiu-Beichuan and Guanxian-Anxian faults, and vertical Wenchuan-Maoxian fault; （4） Vicinity along the Yingxiu- Beichuan fault is characterized by very low velocity and low seismicity at shallow depths, possibly due to high content of porosity and fractures; （5） Two blocks of low-velocity anomaly are respectively imaged in the hanging wall and foot wall of the Guanxian-Anxian fault with a -7 km offset with -5 km vertical component.
基金supported by the National Natural Science Foundation of China (NSFC-41174039)the China Geological Survey
文摘In the southern South-North Seismic Zone,China,seismic activity in the Yingjiang area of western Yunnan increased from December 2010,and eventually a destructive earthquake of Ms5.9 occurred near Yingjiang town on 10 March 2011.The focal mechanism and hypocenter location of the mainshock suggest that the Dayingjiang Fault was the site of the mainshock rupture.However,most of foreshocks and all aftershocks recorded by a portable seismic array located close to the mainshock occurred along the N-S-striking Sudian Fault,indicating that this fault had an important influence on these shocks.Coulomb stress calculations show that three strong （magnitude ≥5.0） earthquakes that occurred in the study region in 2008 increased the coulomb stress along the plane parallel to the Dayingjiang Fault.This supports the Dayingjiang Fault,and not the Sudian Fault,as the seismogenic fault of the 2011 Ms5.9 Yingjiang earthquake.The strong earthquakes in 2008 also increased the Coulomb stress at depths of ≤5 km along the entire Sudian Fault,and by doing so increased the shallow seismic activity along the fault.This explains why the foreshocks and aftershocks of the 2011 Yingjiang earthquake were located mostly on the Sudian Fault where it cuts the shallow crust.The earthquakes at the intersection of the Sudian and Dayingjiang faults are distributed mainly along a belt that dips to the southeast at ～40°,suggesting that the Dayingjiang Fault in the mainshock area also dips to the southeast at ～40°.
文摘The Gamburtsev Antarctic Mountains Seismic Experiment （GAMSEIS, 2007-2010） was jointly conducted by the United States, China, and Japan during and after the International Polar Year 2007-2008. Broadband seismic stations were deployed across the ice-covered Gamburtsev Subglacial Mountains （GSM） and other previously unexplored areas in the interior of East Antarctica. Using GAMSEIS data, published results not only have revealed the deep structure of Antarctica, but also improved our understanding of the tectonic evolution of Antarctica and the supercontinent Gondwana, and of the relationship between geothermal heat flux and glaciers. This contribution draws together the major findings from recent studies, and also offers further investigation into the relationship between tectonic history and the East Antarctic Ice Sheet. The elevation of the GSM is largely supported by thickened crust, with Moho depths of ~60 km near the crest of the range. The GSM are underlain by thick （〉200 km） and cold continental lithosphere that likely formed after collision of two ancient crustal blocks during the pan-African orogeny. Heat flux results obtained from seismic inversion support a model of ice sheet basal melting that depends more strongly on bedrock topography than on geothermal heat flux, while ice surface and ice thickness are inversely correlated with heat flux.
