s Western Yunnan is located at the boundary of collision or underthrusting zone of Eurasian plate and is influenced by many times tectonic movements. With very complex geological environment and tectonic background, i...s Western Yunnan is located at the boundary of collision or underthrusting zone of Eurasian plate and is influenced by many times tectonic movements. With very complex geological environment and tectonic background, it is one of the seismically active areas. In the paper, the teleseismic records were selected from 16 national, local and mo-bile stations, including 4 very-wide-band mobile stations of PASSCAL. And nearly 2 000 receiver functions were extracted. Two measuring lines are 650 km and 450 km, respectively and across some major tectonic units in Western Yunnan. It is indicated that Nujiang might be a seam characterized by underthrusting. The western and eastern boundaries of Sichuan-Yunnan rhombus block, i.e., Honghe and Xiaojiang faults, might be an erection seam or collision belt. Panxi tectonic zone still has the characteristics of continental rift valley, that is, the surface is hollow and the upper mantle is upwarping. The tectonic situation in Western Yunnan is of certain regulation with the interlacing distribution of orogenic zone and seam. The crustal thickness decreases gradually from the north to the south and the S wave velocity is globally lower here.展开更多
As the stress concentrated area of the Euro\|Asia and Indian plates collision, Tibet plateau has its special geological structure background.And its evolution has been drawing attentions of more and more geologists.Th...As the stress concentrated area of the Euro\|Asia and Indian plates collision, Tibet plateau has its special geological structure background.And its evolution has been drawing attentions of more and more geologists.The Sino\|French lithoscope group deployed 28 three\|component seismometers in 1998 from Gonghe to Yushu in Qinghai Province. These stations was distributed on most tectonic unit in Eastern Tibet, which are Eastern Qaidam Basin\|Gonghe Basin, Eastern Kunlun Fault\|Maqin Suture,Bayan Har\|Ganzi Terrane,Jinsha Suture and Qiangtang Block from north to south.According to 19 well\|recorded P wave events, after the data processing such as broading the frequence band,integration to get ground motions,then filtering and deconvolution, most stations’ data can achieve good receiver function with clear Ps conversions which show a step\|shaped Moho with southward dipping. The biggest Ps conversions occur 5～9 seconds after P arrival from north to south. Broad peak and its perturbations mean thicker sediments in Gonghe Basin and south of Jinsha Suture. And correspondent inversion shows there are two discontinuous positions where Kunlun Fault and Jinsha Suture are located. The crust thickness is about 55km in Gonghe Basin and nearby, deeper to 70km in Bayan Har Terrane, and 75～80km in the Qiangtang Block. A 20～40km deep low\|velocity zone can be traced along the profile although it is displaced by the faults. In Bayan Har Terrane some stations show a little eastward inclination of Moho due to comparing the receiver function from different back\|azimuth. A model is deduced that support both Qilian Plate and Qiangtang Block’s subduction beneath Bayan Terrane, and do uble\|crust and escape\|structure is therefore possible because of the stress st ate.展开更多
基金State Key Basic Research Development and Programming Project of China (G1998040700).
文摘s Western Yunnan is located at the boundary of collision or underthrusting zone of Eurasian plate and is influenced by many times tectonic movements. With very complex geological environment and tectonic background, it is one of the seismically active areas. In the paper, the teleseismic records were selected from 16 national, local and mo-bile stations, including 4 very-wide-band mobile stations of PASSCAL. And nearly 2 000 receiver functions were extracted. Two measuring lines are 650 km and 450 km, respectively and across some major tectonic units in Western Yunnan. It is indicated that Nujiang might be a seam characterized by underthrusting. The western and eastern boundaries of Sichuan-Yunnan rhombus block, i.e., Honghe and Xiaojiang faults, might be an erection seam or collision belt. Panxi tectonic zone still has the characteristics of continental rift valley, that is, the surface is hollow and the upper mantle is upwarping. The tectonic situation in Western Yunnan is of certain regulation with the interlacing distribution of orogenic zone and seam. The crustal thickness decreases gradually from the north to the south and the S wave velocity is globally lower here.
文摘As the stress concentrated area of the Euro\|Asia and Indian plates collision, Tibet plateau has its special geological structure background.And its evolution has been drawing attentions of more and more geologists.The Sino\|French lithoscope group deployed 28 three\|component seismometers in 1998 from Gonghe to Yushu in Qinghai Province. These stations was distributed on most tectonic unit in Eastern Tibet, which are Eastern Qaidam Basin\|Gonghe Basin, Eastern Kunlun Fault\|Maqin Suture,Bayan Har\|Ganzi Terrane,Jinsha Suture and Qiangtang Block from north to south.According to 19 well\|recorded P wave events, after the data processing such as broading the frequence band,integration to get ground motions,then filtering and deconvolution, most stations’ data can achieve good receiver function with clear Ps conversions which show a step\|shaped Moho with southward dipping. The biggest Ps conversions occur 5～9 seconds after P arrival from north to south. Broad peak and its perturbations mean thicker sediments in Gonghe Basin and south of Jinsha Suture. And correspondent inversion shows there are two discontinuous positions where Kunlun Fault and Jinsha Suture are located. The crust thickness is about 55km in Gonghe Basin and nearby, deeper to 70km in Bayan Har Terrane, and 75～80km in the Qiangtang Block. A 20～40km deep low\|velocity zone can be traced along the profile although it is displaced by the faults. In Bayan Har Terrane some stations show a little eastward inclination of Moho due to comparing the receiver function from different back\|azimuth. A model is deduced that support both Qilian Plate and Qiangtang Block’s subduction beneath Bayan Terrane, and do uble\|crust and escape\|structure is therefore possible because of the stress st ate.
