The Rupture Mode of Earthquakes and Fault Zone Properties >

本研究强调地震的破裂方式与断层非均质性的性质和分布之间的关系。主要目的是确定非均质性是结构特征还是由随时间变化的应力和滑动变化引起的特征。我们将通过分析最大地震及其余震的波形来研究地震的破裂模式与断层非均质性的关系。通过分析局部地震活动产生的折射波，沿断层的长度和深度绘制了非均质性。这一信息反映了在断裂带并置的不同物质之间的速度对比。我们的分析表明，速度对比不是随机分布的，而是发生在一个值范围占主导地位的斑块上。我们建议扩展我们的重新定位地震数据集，并改进用于速度对比映射补丁的折射角分析。波形的有限差分建模将更好地定义折射分析所映射的非均质性的性质。初步结果表明，自1936年以来，研究区域（加利福尼亚州中部的圣安德烈亚斯断层）发生的最大地震集中在速度对比差异很大的小块附近，并破裂成速度对比更均匀的大块。结合主震的波形分析，我们可能能够比以前更大程度地表征断裂带的非均质性和主震破裂过程。

This study emphasizes the relationship between the rupture mode of earthquakes and the nature and distribution of heterogeneities along a fault plane. A primary objective is to determine whether heterogeneities are structural features or are features induced by stress and slip variations that change with time. We will investigate the rupture mode of earthquakes relative to the fault heterogeneities through analysis of waveforms of the largest events and their aftershocks. Heterogeneities are mapped along the length and depth of a fault plane by analyzing refracted waves generated by local seismicity. This information reflects the velocity contrast between differing materials that are juxtaposed in the fault zone. Our analyses reveal that the velocity contrasts are not randomly distributed, but rather occur in patches where one range of values predominates. We propose to extend our dataset of relocated earthquakes and to refine the refraction angle analyses for mapping patches of velocity contrast. Finite-difference modeling of the waveforms will better define the nature of the heterogeneities that are mapped by refraction analysis. Preliminary results indicate that the largest earthquakes in the study region (San Andreas fault, central California) since 1936 nucleate in the vicinity of small patches with high variance of velocity contrast and rupture into larger patches of more homogeneous velocity contrast. Combined with waveform analysis of the mainshocks, we may be able to characterize fault zone heterogeneities and the mainshock rupture process to a greater degree than has previously been done.