山西断陷带地壳结构的接收函数研究

Receiver function analysis at Shanxi Rift

利用2006年8月到2008年3月北京大学在山西断陷带南部架设的两条东西向流动观测地震台阵记录的远震资料,提取各台站接收函数,然后进行倾斜叠加(Slant stack)和台阵偏移成像,获得了沿台阵横穿山西断陷带的地壳和上地幔的精细结构变化.研究结果显示,山西断陷带下面莫霍面存在明显不连续,莫霍面上隆约4～6 km,纵横波速比从两侧的1.75上升为山西断陷带内部2.0左右,且中、下地壳可能存在一个低速层.山西断陷带的构造模式沿相距140 km的两条剖面表现出明显差异:南端的临汾盆地为拉张作用下的纯剪切模式,向北转化为太原盆地的简单剪切模式.

Shanxi Rift, which separates the stable Ordos Block and extensional North China Basin, is thought to have resulted from the differential extrusion of Tibean Plateau between the North and South China blocks. During August 2006 to March 2008, Peking University deployed two linear arrays （140 km apart） of 45 portable broadband seismometers across the southern part of Shanxi Rift. Slant-stacking and migration images of receiver functions reveal an uplift about 4-6 km of the Moho and an increase of the Vp/Vs ratio from about 1.75 beneath Ordos Block and Taihang uplift to 2.0 under the rift. A low velocity layer may exist in the crust beneath the rift. We conclude that Sbanxi Rift has accommodated much of the difference in stress field and tectonic activity between Ordos and North China Basin. We also observe a transition in the basin formation mechanism from a pure-shear model at Linfen Basin in the south to a simple-shear model at Taiyuan Basin.