2019年6月17日四川长宁6.0级地震震后应力演化与余震关系

2019年6月17日四川长宁县发生6.0级地震，该次地震余震活动频度高、强度大，其中超过5.0级的强余震就有4次，具有不同于以往6.0级地震的独特特征.余震活动与震后区域应力变化密切相关，为研究它们之间的关系，考虑区域主要活动构造、地表起伏和深部反演结果，建立长宁地区岩石圈三维黏弹性有限元模型.采用数值方法重建基本符合研究区GPS观测和最大水平主压应力方向测量结果的现今构造背景应力场.进而依次模拟了长宁6.0级地震和5.0级以上强余震序列.通过计算库仑破裂应力变化研究了震后应力演化与余震分布，以及主震和5.0级强余震序列之间的关系.研究表明，长宁6.0级地震的发生可能与区域内非构造加载因素有关，余震活动明显受震后区域应力变化的控制.长宁地震后，于滩-长宁背斜在10 km深度应力得到充分释放，库仑破裂应力明显减小；而在3 km深度库仑破裂应力明显增加，应力水平仍然较高. 

Relationship between Stress Evolution and Aftershocks after Changning M 6.0 Earthquake in Sichuan on 17 June, 2019

On 17 June, 2019, an M 6.0 earthquake occurred in Changning County, Sichuan Province, with high aftershock activity frequency and intensity. And among the aftershocks, there are 4 strong ones with M≥5.0, which is different from the previous M 6.0 earthquakes. The aftershock activity is closely related to the regional stress change after the mainshock. In order to study the relationship between them, a 3D viscoelastic finite element model of the lithosphere in the Changning area is established. In the model, the main active structures, topographic relief and deep inversion results were considered. By using numerical method, the present tectonic background stress field in the study area is reconstructed to conform to the GPS observed value and the measured one of maximum horizontal principal compressive stress direction. Then the Changning M 6.0 earthquake and its strong aftershock sequence with M≥5.0 were simulated sequentially. The relationship between the stress evolution and aftershocks, as well as the mainshock and the strong aftershock sequence with M≥5.0 were studied by calculating the Coulomb failure stress. The results show that the occurrence of the Changning M 6.0 earthquake may be independent with the regional tectonic loading factors, and the aftershock activity is obviously controlled by the regional stress change after the mainshock. After the Changning earthquake, the stress at the depth of 10 km in the Yutan-Changning anticline was fully released, and the Coulomb failure stress decreased significantly. However, at the depth of 3 km, the Coulomb failure stress increases obviously and the stress level is still high.