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

地震重新定位技术的最新发展导致在不同的构造环境中发现了许多重复的星系团。这些地震很可能是由周围断层面上的无地震蠕变加载的凹凸体的破坏造成的。由于它们反复破裂相同的断裂带，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裂带属性的细微时间变化提供了宝贵的来源。本项目旨在基于重复地震的波形分析，量化在中大地震中最近破裂的主要断裂带的破坏和修复过程。针对特定类型的波传播，进行了以下两种类型的计算：1)根据S和重复地震产生的早期S尾波的互相关，测量震源-接收器路径和附近接收器累积的走时的细微变化；以及2)量化大地震震源区附近重复地震的震源性质(如地震矩、拐角频率、应力降和破裂速度)的变化。这两种测量方法对于提高我们对大地震周期中断裂带性质演化的了解至关重要。更好地了解活动断裂带内的损伤和修复过程有望在地震和断层的物理学中产生重大影响。弄清断裂带的空间分布，特别是损伤和修复过程的深度程度，有助于更好地了解断层上和断层外损伤的来源，并由此了解大地震期间的能量收支。断裂带性质随时间的变化提供了关于原地条件下断裂作用的流变学和力学的关键信息。对震源和断裂带性质的时空演变的更好理解可能为破译下一次大地震可能发生的时间和地点提供至关重要的新信息。

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.