Collaborative Research: Waveform Analysis of Repeating Earthquakes - Implications for Fault Damage and Healing Processes

近年来，随着地震定位技术的发展，在不同的构造环境中识别出了许多重复的震群。这些地震很可能是由周围断层面上的地震蠕变所加载的凹凸体的破坏所产生的。由于它们重复破裂同一断层片，并产生几乎相同的波形，它们为检测与大地震发生相关的断层带性质的微妙时间变化提供了宝贵的资源。本项目旨在基于重复地震的波形分析，量化最近在中到大地震中破裂的主要断层带的破坏和愈合过程。执行以下两种类型的计算以针对特定种类的波传播：1）从由重复地震产生的S和早期S尾波波形的互相关测量在源-接收器路径期间和接收器附近累积的行进时间的细微变化;以及2）量化重复地震的源属性的变化（例如，地震矩、拐角频率、应力降和破裂速度）。这两种测量方法对于提高我们对大地震周期中断层带性质如何演化的认识至关重要。更好地了解活动断层带内部的损伤和愈合过程有望对地震和断层物理学产生重大影响。阐明空间分布，特别是断裂带的破坏和愈合过程的深度范围，有助于更好地了解断层上和断层外破坏的起源，以及大地震期间的能量收支。断裂带性质随时间的变化为研究原地条件下的流变学和断裂力学提供了重要信息。对震源和断裂带性质的时空演化的更好理解可能为破译下一次大地震何时何地可能发生提供重要的新信息。

Recent development in earthquake relocation techniques has led to many sets of repeating clusters identified in different tectonic environments. These earthquakes are most likely produced by the failure of asperities that are loaded by aseismic creep on the surrounding fault plane. Since they rupture the same fault patch repeatedly and generate nearly identical waveforms, they provide invaluable sources for detecting subtle temporal changes in fault zone properties associated with the occurrence of major earthquakes.This project aims to quantify damage and healing processes in major fault zones that are recently ruptured in moderate to large earthquakes based on the waveform analysis of repeating earthquakes. The following two types of calculations are performed to target for specific kinds of wave propagation: 1) measuring subtle changes in travel times accumulated during source-receiver paths and near receivers from cross-correlation of S and early S-coda waveforms generated by repeating earthquakes; and 2) quantifying variations in the source properties of repeating earthquakes (e.g., seismic moment, corner frequency, stress drop, and rupture velocities) near the hypocentral regions of large earthquakes. Both measurements are critical for improving our knowledge of how fault zone properties evolve during a large earthquake cycle.A better understanding of damage and healing processes inside active fault zones is expected to have significant implications in the physics of earthquakes and faults. Clarifying the spatial distribution and especially the depth extent of the damage and healing processes in fault zones help to better understand the origins of on and off-fault damage, and from that the energy budget during large earthquakes. The time-dependent changes of fault zone properties provide critical information on the rheology and mechanics of faulting under in situ conditions. An improved understanding of the spatio-temporal evolution of earthquake source and fault zone properties may provide crucial new information for deciphering when and where the next major earthquake might strike.