基于川滇地区3D格林函数的震源机制研究

地震震源机制解对于研究发震构造有着重要意义，目前多数震源机制解的求解，仍然使用横向均匀的一维速度模型计算格林函数。结构的近似会导致震源机制的不准确，前人研究显示震源的非双力偶分量可能部分是模型不准确带来的假象。川滇地区是典型的地壳结构横向不均匀十分显著的地区，又是地震多发区域，如2019年6月17日的四川长宁M6.0级地震即有着显著的非双力偶分量。近年来有多个川滇速度模型的成果发表，但仍缺乏研究，以量化评估模型对增进震源机制解求解精度的作用。基于多个最新的川滇速度结构模型，正演机制较确定的事件的理论波形(如2013年芦山Mw6.6级地震等)，通过与实际记录的比较，以误差函数评价，并选定最优的模型，使用谱元法计算建立川滇区域3D格林函数库。利用3D格林函数，研究区域内2010年以来M>4.5级的震源机制解，特别是2019年长宁M6.0级地震，增进对近年来多次5-6级强震发震机理的认识。

The focal mechanism is significant for investigating the causative tectonic structures. At present, most of the focal mechanism solutions are still constrained by the Green’s functions calculated in the transverse homogenous one-dimensional velocity model. The inaccurate velocity model will lead to the inaccurate focal mechanism. The previous researches show that the non-double couple component will dramatically decrease when a 3D velocity model is used. Chuandian region is a typical area with obvious lateral non-homogenous crustal structure and high seismicity. For example, the M6.0 earthquake in Changning, Sichuan Province, which occurred on June 17, 2019, has significant non-double couple component. A series of results of velocity model in Chuandian region have been published. However, we doesn’t carefully evaluate how state-of-the-art velocity models improve the study of the focal mechanism. Based on state-of-the-art Chuandian velocity models, synthetic waveforms of ground-truth events (for example, the 2013 Lushan Mw6.6 earthquake) are simulated. After comparing the synthetic waveforms with the observed records, the preferred model is selected to build the 3D Green’s functions by spectral element method. Using 3D Green’s functions, the focal mechanisms of earthquakes with M > 4.5 since 2010, are investigated, especially the M6.0 Changning earthquake in 2019. The results will improve the understanding of the causative tectonic structures of a series of strong earthquakes with magnitude from 5 to 6 during the past two years.