2001年昆仑山口西MS8.1地震对周围断层的应力影响数值分析

大地震的发生往往会引起周围区域形变场和应力场变化，且对临近断层上的应力状态也有影响.2001年11月4日，昆仑山口西发生了半个世纪以来中国最大的M_S8.1级地震.本文基于已有的滑动模型，建立了三维含地形高程的横向不均匀性椭球型地球有限元模型，采用等效体力方法，分析了此次M_S8.1地震产生的全球同震位移和应力场变化.与解析方法相比，该模型考虑了地形、Moho面起伏和地球介质横向不均匀性；与一般的有限元数值模拟相比，该模型考虑了地球曲率和椭率，合理地规避了有限块体模型假定边界位移为零所引入的误差.计算得出同震位移与GPS观测数据可以很好地吻合.据库仑破裂应力准则和震源参数，计算得出昆仑山口西M_S8.1地震的发生造成了汶川、芦山、改则和当雄地震的发震断层上库仑应力增加，对这些地震的发生起促进作用；而造成玉树和德令哈地震发震断层上的库仑应力变化为负值，在一定程度上抑制了这些断层的地震活动性.此外，计算结果显示地球地形高程、介质非均匀性和椭率对昆仑山口西M_S8.1地震同震变化计算有一定的影响，其中地形和椭率造成的同震位移场相对误差约10%.

Numerical study on the co-seismic stress changes of surrounding faults due to the MS8.1 earthquake, 2001, Kokoxili earthquake

The occurrence of large earthquake often induces obvious deformation and stress changes in the surrounding area, especially on the adjacent faults. On Nov.4, 2001, the huge Kokoxili M_S8.1 earthquake, one of the largest earthquakes in China since half a century ago, occurred in the Kunlunshan area. Based on the existing slip model, a global transversely heterogeneous ellipsoid model with the Earth's ellipticity and topography is established. The coseismic displacements and stress changes due to this earthquake are calculated using the equivalent-bodyforce numerical method. The results of coseismic displacements in the near-field are consistent with the GPS observation data, which indicate the reliability of our results. Further, the Coulomb failure stress on the seismogenic faults of Wenchuan, Lushan, Garzê and Dangxiong earthquakes increased due to the M_S8.1 earthquake, which means that the Kokoxili earthquake may promote the nucleation of these earthquakes. On the other hand, the Coulomb failure stress changes at the hypocenters of Yushu and Delingha earthquakes are negative, which indicates that the Kokoxili earthquake reduced the seismic risks at those sites of seismic activity. In addition, the effects of heterogeneous heterogeneity, terrain and ellipticity of the Earth's on the coseismic calculation are further analyzed. For the Kokoxili earthquake, the average relative error caused by the ellipsoid ellipticity and topography is about 10%.