基于接收函数约束的川滇地区莫霍面深度反演研究

本文利用川滇地区宽频地震接收函数结果和WGM2012全球布格重力场模型数据,采用正则化参数和接收函数结果交叉验证得到最优莫霍面参考深度和上下界面密度差,使用基于球坐标系下的快速非线性重力反演方法建立川滇地区莫霍面深度模型.研究结果显示,川滇地区整体莫霍面深度介于30～69km,青藏高原内部地区莫霍面深度大于50km;四川盆地莫霍面深度在36～38km;攀枝花地区莫霍面出现明显的隆起和下凹,变化范围在42～48km;川滇菱形地块莫霍面深度在40～50km;滇西和滇南地块莫霍面深度由南向北逐渐变深,变化范围在38～44km.本文反演莫霍面深度与接收函数结果平均误差为0.18km,与该区域天然地震层析成像、人工地震探测以及重力数据反演结果基本一致,但细节更加丰富,进一步确认了莫霍面在攀西裂谷地区存在隆起,小江断裂带下方存在下凹的特征.该结果可作为精细化川滇地区地壳密度界面模型,为研究该地区岩石圈结构和地质构造演化提供参考.

Inversion of Moho surface depth in Sichuan-Yunnan area based on the constraint of receiving function

In this paper, we combined the results of broadband seismic reception function and global bouguer gravity field model of WGM2012 to establish the Moho depth model for Sichuan-Yunnan region based on the method of fast nonlinear gravity inversion in spherical coordinates. The optimal Moho reference depth and density difference between the upper and lower interfaces were obtained by the Cross-validation of regularization parameters and the results of receiving function. The results show that the overall Moho surface depth is ranging from 30 and 69 km in Sichuan-Yunnan region and more than 50 km in the inner region of Tibetan plateau.The Moho surface depth of Sichuan basin and Sichuan-Yunnan lozenge block is 36~38 km and 40~50 km, respectively. The Moho surface in Panzhihua area fluctuates with a range of 42~48 km. The blocks in Western Yunnan and Southern Yunnan gradually become shallows from the north to the south of the Moho surface, with a range of 38~44 km. The average error of the inversion of Moho surface depth in this paper and the result of receiving function is 0.18 km, which is mainly consistent with the inversion results of seismic tomography, artificial seismic sounding and gravity data in this region. However, our results, with more details, further confirm that there is uplift of Moho surface in Panxi rift area and depression of Xiaojiang fault zone. The results can be used as a suitable model for crustal density interface in the Sichuan-Yunnan region and provide a reference for the study of lithospheric structure and geological structure evolution.