Located at the northeastern margin of the Tibetan plateau,the Ordos block is a stable tectonic unit in North China.With its active boundary fault zones,the Ordos block played an important role in the eastward extrusio...Located at the northeastern margin of the Tibetan plateau,the Ordos block is a stable tectonic unit in North China.With its active boundary fault zones,the Ordos block played an important role in the eastward extrusion mechanism of the Tibetan plateau.Peking University deployed a linear array of 15 portable broadband seismometers across the western Weihe graben during September 2005 to August 2006 and later a 2-D seismic array（Southwest Ordos Array） of 14 portable broadband seismometers during 2007-2008 at its southwestern boundary.Analyses of shear wave splitting of SKS and SKKS phases at these stations show that the fast directions trend ～110° with an average delay time of 0.9 s in the southwestern margin of the Ordos block.The agreement between the lithosphere deformation indicated by GPS data and Quaternary fault slip-rate observations and the mantle flow represented by shear wave splitting implies that accordant deformation patterns from lithosphere to asthenosphere in relation to the eastward extrusion of the Tibetan plateau could extend at least to 200 km depth.Spatial distribution of splitting polarization directions indicates that the mantle flow driven by the Tibetan plateau is blocked by the Ordos block and locally restricted in a narrow channel along the Qinling-Dabie fault zones between the Ordos block and Sichuan basin.展开更多
A portable broadband seismic array was deployed from the northeast Tibetan Plateau to the southwest Ordos block,China.The seismic structure of the crust and uppermost mantle of the Liupanshan area is obtained using re...A portable broadband seismic array was deployed from the northeast Tibetan Plateau to the southwest Ordos block,China.The seismic structure of the crust and uppermost mantle of the Liupanshan area is obtained using receiver function analysis of teleseismic body waves.The crustal thickness and Poisson's ratios are estimated by stacking the weighted amplitudes of receiver functions.Our results reveal complex seismic phases in the Liupanshan area,implying intense deformation at the boundary between the Tibetan Plateau and the Ordos block.The average crustal thickness is 51.5 km in the northeast Tibetan Plateau,53.5 km in the Liupan Mountain and 50 km in the southwest Ordos block,resulting in a concave Moho beneath the Liupan Mountain.The Poisson's ratio of the Liupanshan area varies between 0.27-0.29,higher than the value of 0.25-0.26 to the east and west of the Liupan Mountain,suggesting partial melting in the lower crust.The variance in Poisson's ratio across the Liupan Mountain indicates notable changes in the crustal composition and mechanical properties,which may be formed by the northeastward flow of the Tibetan lower crust during the India-Eurasia collision.展开更多
文摘Located at the northeastern margin of the Tibetan plateau,the Ordos block is a stable tectonic unit in North China.With its active boundary fault zones,the Ordos block played an important role in the eastward extrusion mechanism of the Tibetan plateau.Peking University deployed a linear array of 15 portable broadband seismometers across the western Weihe graben during September 2005 to August 2006 and later a 2-D seismic array（Southwest Ordos Array） of 14 portable broadband seismometers during 2007-2008 at its southwestern boundary.Analyses of shear wave splitting of SKS and SKKS phases at these stations show that the fast directions trend ～110° with an average delay time of 0.9 s in the southwestern margin of the Ordos block.The agreement between the lithosphere deformation indicated by GPS data and Quaternary fault slip-rate observations and the mantle flow represented by shear wave splitting implies that accordant deformation patterns from lithosphere to asthenosphere in relation to the eastward extrusion of the Tibetan plateau could extend at least to 200 km depth.Spatial distribution of splitting polarization directions indicates that the mantle flow driven by the Tibetan plateau is blocked by the Ordos block and locally restricted in a narrow channel along the Qinling-Dabie fault zones between the Ordos block and Sichuan basin.
基金supported by the National Natural Science Foundation of China(91855207,42074067,and 42030308)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB18000000)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2017093)。
基金Supperted by the National Basic Research Program of China(Grant No.2003CB214607)the National Natural Science Foundation of China(Grant No.40574015)SRFDP(Grant No.20050284040)
文摘A portable broadband seismic array was deployed from the northeast Tibetan Plateau to the southwest Ordos block,China.The seismic structure of the crust and uppermost mantle of the Liupanshan area is obtained using receiver function analysis of teleseismic body waves.The crustal thickness and Poisson's ratios are estimated by stacking the weighted amplitudes of receiver functions.Our results reveal complex seismic phases in the Liupanshan area,implying intense deformation at the boundary between the Tibetan Plateau and the Ordos block.The average crustal thickness is 51.5 km in the northeast Tibetan Plateau,53.5 km in the Liupan Mountain and 50 km in the southwest Ordos block,resulting in a concave Moho beneath the Liupan Mountain.The Poisson's ratio of the Liupanshan area varies between 0.27-0.29,higher than the value of 0.25-0.26 to the east and west of the Liupan Mountain,suggesting partial melting in the lower crust.The variance in Poisson's ratio across the Liupan Mountain indicates notable changes in the crustal composition and mechanical properties,which may be formed by the northeastward flow of the Tibetan lower crust during the India-Eurasia collision.
