基于流固耦合作用研究2013年芦山地震静态库仑应力时空演化对余震的触发

The 2013 Lushan earthquake occurred on the southwest segment of the Longmenshan fault zone. A large number of aftershocks were recorded within half a year after the mainshock. Using traditional static Coulomb stress triggering model to test the relationship between the mainshock and the aftershocks, we found that the aftershocks cannot be explained by the static Coulomb stress change (ΔCFS) generated by the mainshock. What are the factors contributing to the particularity of the relationship between the Lushan earthquake and its aftershocks? For the traditional Coulomb triggering model, only solid medium was employed in the calculation. However, the underground fluid flow would affect the stress field during the co-seismic and post-seismic process, and afterslip would further adjust the post-seismic Coulomb stress changes. Therefore, this study will use the finite element method to calculate the temporal-spatial evolution of co-seismic and post-seismic distribution of stress field based on the hydro-mechanical coupling visco-elastic material. The dynamic reasons of why the aftershocks of Lushan earthquake cannot explain by the ΔCFS will be discovered through the numerical simulation. The effects of the seismic dislocation, hydro-mechanical coupling effect and afterslip will be discussed to study the stress triggering model systematically. This study will provide scientific reference for the understanding the physical mechanism of the stress evolution, seismic stress triggering problem and strong aftershock prediction.

2013年芦山Ms7.0地震发生在龙门山断裂带南段，震后半年内记录到大量余震。利用传统静态库仑应力触发模型对芦山地震主震和余震进行分析，发现芦山地震的余震无法由主震的静态库仑应力变化（ΔCFS）来解释。是什么因素造成了芦山地震主-余震之间关系的这种特殊性呢？传统的静态库仑应力触发模型仅使用固体介质计算同震过程的影响，然而地下流体会在同震及震后不断改变应力场，震后余滑也会进一步调整库仑应力变化。因此，本研究利用有限元模拟的方法，采取流固耦合的黏弹性材料，计算芦山地震同震及震后应力场的空间分布及其随时间的演化。通过数值模拟，给出芦山地震余震无法使用主震产生的静态库仑应力变化解释的动力学原因；进一步分析同震位错、流固耦合作用及震后余滑等作用对库仑应力变化的影响，从而系统地研究芦山地震的应力触发问题。本项目研究对于认识强震后应力场演化的物理机制、深入理解地震应力触发问题和强余震预测等提供科学参考。

2013年芦山Ms7.0地震发生在龙门山断裂带南段，震后一个月内记录到大量余震。利用传统静态库仑应力触发模型对芦山地震主震和余震进行分析，发现芦山地震的余震无法由主震的静态库仑应力变化（ΔCFS）来解释。是什么因素造成了芦山地震主-余震之间关系的这种特殊性呢？传统的静态库仑应力触发模型仅使用固体介质计算同震过程的影响，当考虑孔隙介质时，孔隙压会在同震及震后不断改变应力场。因此，本研究利用基于孔隙弹性介质的有限单元法，计算芦山地震同震及震后应力场的空间分布及其随时间的演化。通过数值模拟，可以得知当考虑孔隙弹性介质时，约82%的余震处于孔隙压力正值区，约76%的余震处于主震产生的正库仑应力变化区域，为主震所触发。另外，孔隙压的震后调整虽然未能使部分余震受到的应力加载达到触发阈值，但其仍有一定的影响。相比于以往研究最优情况下37%的大余震为主震所触发，本项目使用的方法可以更好的 (77~94%) 解释余震的发生。

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