地表起伏对极浅源地震深度反演的影响研究

Most intraplate earthquakes occur in the depth range of 5 to 25 km. However, there are some extremely shallow earthquakes in the north-east part of Longmenshan Fault Zone (LFZ), of which the focal depths may be shallower than 3 km. Accurately inverting the depths of these earthquakes can provide key information for improving our understanding of the mechanism of shallow earthquakes. However, in some areas, the surface topography varies dramatically, which may affect the accuracy of determining the depths of extremely shallow earthquakes with regular methods. In this study, we plan to choose the shallow earthquakes in the northeastern region of the LFZ to analyze the topographic effects. Based on the 3D seismic wave simulation and source parameters inversion method, we will study the effects of different terrain conditions on the source inversion of the shallow earthquakes. Then, using the 3D Green's functions, the focal depths of shallow earthquakes in the region will be inverted. Finally, combing with previous studies including the tectonic backgrounds and tomography results, we will analyze the mechanism of the extremely shallow earthquakes in the northeastern region of the LFZ and provide references to similar cases in other places.

一般来说，大陆板块内部天然构造地震大多发生在5-25km深度范围，然而龙门山东北缘等地区存在一些极浅源中强地震，其震源深度可能浅于3km。准确地反演这些地震的深度可为研究极浅震成因提供基础信息，然而在一些地区，较为剧烈的地表起伏可能会严重影响极浅地震深度的测定精度。本项目计划以龙门山东北缘极浅震为研究对象，基于三维地震波模拟以及震源参数反演方法，对比讨论不同地形条件对浅源地震震源反演造成的影响，然后基于考虑地形的三维格林函数反演该地区极浅震深度。利用反演得到的深度信息，结合地质构造背景以及前人的成像结果，分析龙门山东北缘极浅震发震机理，并为其它地区极浅源地震研究提供参考。

大陆板块内部天然构造地震大多发生在5-25km深度范围，然而龙门山东北缘等地区存在一些极浅源中强地震，其震源深度可能浅于3km。准确地反演这些地震的深度可为研究极浅震成因提供基础信息，然而在一些地区，较为剧烈的地表起伏可能会严重影响极浅地震深度的测定精度。本项目以龙门山东北缘极浅震为研究对象，基于三维地震波模拟以及震源参数反演方法，对比讨论不同地形条件对浅源地震震源反演造成的影响，然后基于考虑地形的三维格林函数反演该地区极浅震深度。我们测试了不同测试地形对该地区震源深度反演的影响。结果显示；在体波和面波分别为0.05~0.3 Hz和0.05~0.2 Hz的滤波频率条件下，天然地震震源深度反演中，地形对反演影响较小，基于层状介质假设的波形反演可以得到较为准确的震源深度。同时研究基于平层假设反演的震源深度是基于自由地表的埋藏深度，而非海平以下的深度。