We apply three methods to relocate 599 earthquake events that occurred from August 2004 to August 2005 in the northeastern Tianshan Mountains area ( 85°30' ～ 88°30'E,43°00' ～ 44°40...We apply three methods to relocate 599 earthquake events that occurred from August 2004 to August 2005 in the northeastern Tianshan Mountains area ( 85°30' ～ 88°30'E,43°00' ～ 44°40' N ) by using travel times recorded by regional seismic network and 10 portable seismic stations deployed around the Urumqi city. By comparing the reliability of different results,we determined a suitable location method,and an improved 1-D crustal velocity model of the study area. The uncertainty of earthquake location is significantly reduced with combined data of seismic network and portable stations. The relocated events are clearly associated with regional tectonics of the northeastern Tianshan Mountains area, and are also in agreement with the existence of active faults imaged by deep seismic reflection profile. The relocated seismicity discovers some potential traces of buried active faults,which need to be validated further.展开更多
A phase-matched filtering technique is applied to extract fundamental mode signals from Rayleigh waves recorded at 62 digital seismic stations in the Yunnan and Sichuan regions.We use the fundamental mode of vibration...A phase-matched filtering technique is applied to extract fundamental mode signals from Rayleigh waves recorded at 62 digital seismic stations in the Yunnan and Sichuan regions.We use the fundamental mode of vibrations at two stations that are located on the same great circle as the focus to calculate an inter-station attenuation coefficient of the Rayleigh wave with periods between 0.40 and 80.64 s,and invert for the inter-station S-wave Q-factor (Qβ) at depths of 0-200 km.The results indicate that Qβ in Yunnan is 20-140,presenting a low Qβ background with apparent lateral variation.Taking the Honghe Fault as the boundary,Qβ of the crust is only 20 on the west side,extending to a depth of 120 km.The distribution of Qβ is consistent with large-scale Cenozoic volcanic and intrusive rocks in western Yunnan,implying that the crust and mantle are in the thermally active state.In the eastern Yunnan Block,east of the Xiaojiang Fault,Qβ in the upper 120 km is 140 in the south but only 20 in the north.Additionally,around the Dukou-Chuxiong in the mid-Yunnan Block,Qβ in the lithosphere is relatively high at 60-100,corresponding to a stiff crust.This is because the suture between the Indian and Eurasian plates reversed the tension in the rifting stage into the compression of orogenesis,leading to the closure of a gap in the crust.After some time,interstitial fluids gradually disappeared,resulting in a high velocity layer in the crust and low heat flow on the surface.The Yunnan region consists of an obvious block of elevated Qβ,distributed within the low background,consistent with the distribution of heat-flow values on the surface.The Honghe and Xiaojiang faults are tectonic boundaries in addition to being boundaries between regions of high and low crustal Qβ.The low Qβ is probably the result of crustal rupture and disturbance caused by strong earthquakes and the upwelling of hot substances along the deep fault zones.展开更多
基金supported by the Basic Research Project of Institute of Earthquake Science,CEA (2012IES010103)the National Natural Science Foundation of China (41204037)
文摘We apply three methods to relocate 599 earthquake events that occurred from August 2004 to August 2005 in the northeastern Tianshan Mountains area ( 85°30' ～ 88°30'E,43°00' ～ 44°40' N ) by using travel times recorded by regional seismic network and 10 portable seismic stations deployed around the Urumqi city. By comparing the reliability of different results,we determined a suitable location method,and an improved 1-D crustal velocity model of the study area. The uncertainty of earthquake location is significantly reduced with combined data of seismic network and portable stations. The relocated events are clearly associated with regional tectonics of the northeastern Tianshan Mountains area, and are also in agreement with the existence of active faults imaged by deep seismic reflection profile. The relocated seismicity discovers some potential traces of buried active faults,which need to be validated further.
基金supported by National Natural Science Fundation of China (Grant No. U0933602)Professional Projects of the Chinese Seismological Bureau (Grant No. 200808061)
文摘A phase-matched filtering technique is applied to extract fundamental mode signals from Rayleigh waves recorded at 62 digital seismic stations in the Yunnan and Sichuan regions.We use the fundamental mode of vibrations at two stations that are located on the same great circle as the focus to calculate an inter-station attenuation coefficient of the Rayleigh wave with periods between 0.40 and 80.64 s,and invert for the inter-station S-wave Q-factor (Qβ) at depths of 0-200 km.The results indicate that Qβ in Yunnan is 20-140,presenting a low Qβ background with apparent lateral variation.Taking the Honghe Fault as the boundary,Qβ of the crust is only 20 on the west side,extending to a depth of 120 km.The distribution of Qβ is consistent with large-scale Cenozoic volcanic and intrusive rocks in western Yunnan,implying that the crust and mantle are in the thermally active state.In the eastern Yunnan Block,east of the Xiaojiang Fault,Qβ in the upper 120 km is 140 in the south but only 20 in the north.Additionally,around the Dukou-Chuxiong in the mid-Yunnan Block,Qβ in the lithosphere is relatively high at 60-100,corresponding to a stiff crust.This is because the suture between the Indian and Eurasian plates reversed the tension in the rifting stage into the compression of orogenesis,leading to the closure of a gap in the crust.After some time,interstitial fluids gradually disappeared,resulting in a high velocity layer in the crust and low heat flow on the surface.The Yunnan region consists of an obvious block of elevated Qβ,distributed within the low background,consistent with the distribution of heat-flow values on the surface.The Honghe and Xiaojiang faults are tectonic boundaries in addition to being boundaries between regions of high and low crustal Qβ.The low Qβ is probably the result of crustal rupture and disturbance caused by strong earthquakes and the upwelling of hot substances along the deep fault zones.
