Testing Transient Triggering of Earthquakes with Aftershock Spatial Distributions

本建议的目的是阐明应力扰动的瞬态和永久分量在触发地震余震中的相对重要性。PI建议利用现有数据对全球范围进行研究。这项工作背后的简单概念遵循了先前关于兰德斯地震引发余震的研究。对于以单边破裂传播为特征的地震，永久（静态）应力变化在空间上是对称的，而峰值瞬态（动态）应力是不对称的。这种差异提供了一种方法来研究这些应力扰动的每个组成部分的相对作用。建议的工作将试图确定余震分布的空间对称性与主震的传播特性（破裂指向性）之间是否存在系统关系。该研究将：1)调查数据库和文献，以确定哪些地震既具有可靠的指向性效应估计（或不存在指向性效应），又具有统计可靠的余震（和主震前）目录；2)设计并应用比较应力场空间分布与余震发生模式的指标，重点关注空间对称或不对称。其他的研究步骤也将包括，如至少一些地震的波形建模，以约束地震发震深度的动应力模型和数值弹性建模，以估计静态应力场的变化。

The objective of this proposal is to illuminate the relative importance of the transient and permanent components of stress perturbations in triggering earthquake aftershocks. The PI proposes to undertake a study of the global scale that uses existing data. The simple notion that underlies the proposed work follows previous research on triggering of aftershocks by the Landers earthquake. For earthquakes that feature unilateral rupture propagation, permanent (static) stress changes are spatially symmetric while peak transient (dynamic) stresses are asymmetric. This difference provides a means to study the relative roles of each of these components of stress perturbations. The proposed work will seek to determine whether a systematic relationship exists between the spatial symmetries of aftershock distributions and the propagation characteristics (rupture directivity) of the mainshock. The research will: 1) survey databases and the literature to determine which earthquakes have both reliable estimates of directivity effects (or their absence), and statistically reliable aftershock (and before mainshock) catalogs, and 2) devise and apply metrics that compare the spatial distribution of stress fields with aftershock occurrence patterns, focussing on spatial symmetry or asymmetry. Additional research steps will also be included, such as waveform modeling of at least some earthquakes to constrain models of dynamic stresses at seismogenic depths and numerical elastic modeling to estimate the static stress field changes.