Inelastic response of compliant fault zones to nearby earthquakes in three dimensions

Using dynamic modeling of earthquake rupture on a strike-slip fault and seismic wave propagation in a three dimensional inhomogeneous elastoplastic medium, we investigate the inelastic response of compliant fault zones to nearby earthquakes. We primarily examine the plastic strain distribution within the fault zone and the displacement field that characterizes the effects of the presence of the fault zone. We find that when the fault zone rocks are close to failure in the prestress field, plastic strain occurs along the entire fault zone near the Earth's surface and some portions of the fault zone in the extensional quadrant at depth, while the remaining portion deforms elastically. Plastic strain enhances the surface displacement of the fault zone, and the enhancement in the extensional quadrant is stronger than that in the compressive quadrant. Inelastic response may be distinguished from elastic response by sympathetic motion (or reduced retrograde motion) exhibited in the fault-parallel horizontal surface displacement in conjunction with enhanced vertical surface displacement in a strike-slip faulting environment. These findings suggest that taking into account both elastic and inelastic deformation of fault zones to nearby earthquakes may improve our estimations of fault zone structure and properties from small-scale surface deformation signals. Furthermore, identifying the inelastic response of nearby fault zones to large earthquakes may allow us to place some constraints on the absolute stress level in the crust.

利用走滑断层上的地震破裂动态建模以及三维非均匀弹塑性介质中的地震波传播，我们研究了软弱断层带对附近地震的非弹性响应。我们主要考察了断层带内的塑性应变分布以及表征断层带存在影响的位移场。我们发现，当断层带岩石在预应力场中接近破坏时，在地表附近的整个断层带以及深部伸展象限的部分断层带会出现塑性应变，而其余部分则发生弹性变形。塑性应变增强了断层带的地表位移，且伸展象限的增强程度强于压缩象限。在走滑断层环境中，非弹性响应可通过断层平行的水平地表位移中表现出的同向运动（或减弱的逆向运动）以及增强的垂直地表位移与弹性响应区分开来。这些研究结果表明，考虑断层带对附近地震的弹性和非弹性变形，可能会改进我们从小规模地表变形信号对断层带结构和性质的估计。此外，识别附近断层带对大地震的非弹性响应，可能使我们能够对地壳中的绝对应力水平施加一些限制。