利用接收函数方法研究四川地区地壳结构

采用接收函数反演和共转换点(CCP)偏移叠加成像方法, 利用四川数字地震台网宽频带的52个区域固定地震台站和布设的两条52个宽频带流动地震观测台站的远震地震波形数据资料, 对四川地区地壳结构进行研究。 结果表明, 四川地区的Moho面深度在青藏高原和四川盆地差异明显, 在川西高原地区地壳厚度为52~68 km, 在川滇地块地壳厚度为50~60 km, 在中地壳内存在不连续的低速层分布; 而在四川盆地地壳厚度为38~45 km, 地壳内没有低速层存在。 Moho面深度从川西高原的60多公里至四川盆地的约40 km, 在二者的交界处龙门山断裂带下面, 存在厚度约30 km左右宽的下降过渡带, 说明其下的Moho面可能受断层影响, 结构比较复杂; 在高原地区的上地壳界面和下地壳上界面比四川盆地的相应界面深; 高原地区在中地壳的上部有不连续的低速层分布, 在松潘—甘孜地块的上地壳下部存在向南东运动的脆性推覆体, 在羌塘—理塘地块的上地壳下部存在向南东和南运动的脆性物质流动。

Crustal Structure of Sichuan from Receiver Functions

Using digital waveform data of 52 regional fixed broad band stations in the Sichuan Digital Seismic Network and two profiles of 52 temporary broad band seismic stations, we applied the receiver function inversion and the common conversion point (CCP) stacking method to study crustal structure in Sichuan area. The result shows that there is obvious difference in the depth of Moho between Tibetan Plateau in west Sichuan and the Sichuan basin, the crust in the western plateau of Sichuan is about 52~68 km thick, and the crust in Sichuan—Yunnan block is about 50~60 km thick, the discontinuous low velocity layer is found at the middle crust. The crust thickness of the Sichuan basin is about 38~45 km, and there is no low velocity layer in the crust. The Moho depth is from more 60 km in the west Sichuan to about 40 km in the Sichuan basin. In the boundary zone located in the Longmenshan fault, there is a decline belt of the depth about 30 km, which shows that the Moho discontinuity is complex due to be affected by the Longmenshan fault, and the interface of the upper crust in the plateau is deeper than that in the basin. The upper middle crust has a discontinuous lowvelocity layer in the plateau. There is a brittle nappe moving south east in the bottom of Songpan—Ganzi upper crust, and brittle materials flow to the south and south east in the bottom of Qiangtang—Litang upper crust.