银川盆地岩石圈结构——长观测距宽角反射与折射剖面结果

Lithosphere structure of Yinchuan basin from a long-range seismic wide angle reflection and refraction profile

利用2014年完成的穿过银川盆地人工源宽角反射与折射剖面的3炮长观测距资料,采用基于地震波走时反演方法的Rayinvr算法得到了研究区地壳和上地幔的速度结构.结果表明:研究区地壳厚度为42—48km,莫霍面沿剖面展布形态呈现出东西两侧浅、中部较深的特征,莫霍面最深的区段位于贺兰山下方.P波速度沿剖面随着深度的增加呈正梯度增大,然而在深度约为90—103km的岩石圈地幔中,识别出两组较明显的反射界面,两组界面之间并未发现P波速度随深度而显著增加,表明研究区下方存在与地球平均模型中速度随深度增加而增大不相符的速度结构,推测银川盆地下方岩石圈与软流圈之间可能存在速度过渡带.

By using P-wave travel time data from three shots of the deep seismic sounding profiles passing through Yinchuan basin in 2014,based on travel time inversion method Rayinvr,we get the crustal and upper-mantle structure in the studied area.The results show that crustal thickness in the studied area varies from 42 km to 48 km,Moho depth is shallower in the east and west sides of the profile,and much deeper in the middle segment,the deepest Moho interface is beneath Helan mountain.P wave velocity increases with the increasing of depth in a positive gradient,but two distinct interfaces can be identified in the lithosphere mantle within the depths of 90--103 km.This layer does not exhibit the characteristic that the velocity increases obviously with the depth,suggesting the structure in the studied area present a characteristic that did not conform to the global average model,whose velocity increases according to the depth,therefore it is deduced that a velocity transition zone exists between lithosphere and asthenosphere beneath Yinchuan basin.