断层两侧各向异性介质对地震破裂过程影响的有限单元法模拟研究

断层两侧介质物理性质的差异（bimaterial contrast）会对震源破裂过程产生重要影响，而地球介质的各向异性十分常见，但对于断层两侧材料的各向异性对断层破裂动力学过程有何影响，目前不甚了解，而国内外也未见相关研究报道.为此，研究中利用有限单元法，对断层两侧材料存在各向异性时的破裂行为进行模拟研究.计算结果表明，断层两侧材料的各向异性性质对断层破裂动力学过程有重要作用，并且材料性质与破裂之间的关系非常复杂.对于正交各向异性材料，当断层两侧各向异性材料主方向上的杨氏模量不同时，特别是当平行于断层走向的材料其一侧杨氏模量显著大于另一侧时，断层出现不对称的双侧破裂，成核中心一侧的位错显著大于另外一侧，破裂长度也是一侧显著大于另一侧（亦称单侧破裂）.沿着断层走向的材料主轴方向上的杨氏模量对于破裂过程的影响大于垂直于断层走向的杨氏模量，但随着各向异性材料主轴方位的变化，这种影响也发生相应地改变.模拟结果表明材料主轴方向的变化对破裂过程的影响也很显著.此外，通过模拟还发现，若断层两侧材料为相同的各向异性介质时（即断层两侧为同样的各向异性材料），则不会影响断层破裂的空间对称性分布；而当其中一侧的各向异性材质主轴方位发生变化时，断层破裂的空间对称性会受到一定程度的影响，但其影响很小；然而，随着正交各向异性材料剪切模量的增加，断层破裂会被终止，无法产生特大地震.可见，本研究对于深入认识震源动力学过程及地震灾害评估等有重要的科学意义及实用价值.

FEM simulations of spontaneous rupture propagations along the fault with dissimilar anisotropic materials

Bimaterial contrast across the fault has an important influence on seismic rupture propagation. As we know, the anisotropy of the Earth's medium is very common, so what is the impact of the anisotropy of the materials across the fault on the dynamic processes of fault spontaneous rupture? This question remains unclear. However, we haven't seen any research reports concerned all over the world. To this end, in the study we simulated rupture processes along fault with dissimilar anisotropic media across the fault by means of finite element method. The simulated results show that the anisotropic properties of the materials across the fault have a major impact on the dynamic process of fault rupture, and the relationship between the material property and rupture behavior is very much complex. For orthotropic materials, when the Young's modulus in the main direction of anisotropic media on both sides of the fault is different, especially when the principal axis of orthotropic material is parallel to the fault's strike and its Young's modulus on one side is significantly larger than the other one, the fault rupture propagation appears asymmetrically distributed in space. Meanwhile, the dislocation on one side of the nucleation center is significantly larger than on the other side, and the corresponded length of the rupture is also greatly larger, which is also known as a unilateral rupture. The Young's modulus in the principal direction of the orthotropic material along the fault strike has a greater influence on rupture behaviors than that of the Young's modulus perpendicular to the fault strike, but the influence changes with the orientation of the material's principal axis, even if in some cases the effect of the changes of material orientation on the rupture process is not particularly significant. In addition, it has been found through simulation that when the anisotropic media across the fault are the same anisotropic material (i.e., the same anisotropic material is assigned on both sides of the fault), the rupture is symmetrically distributed in space, similar to the case where the media on both sides of the fault are homogeneous. Meanwhile, with the changes of principal axis orientation of the anisotropic material on one side of the fault, the spatial symmetry of the fault rupture will be affected to some extent, but the orientation change has small effects on the rupture dynamic process. However, with the increase of shear modulus of orthotropic material, the rupture may propagate shortly along the fault from the nucleation zone, and it will stop quickly, in which no large earthquake could occur. Thus, it can be expected that the results of this study have important scientific significance and some implications for the better understanding of the focal processes and seismic hazard assessments.