A Comprehensive Study of Shear-Wave Splitting and Related Signals Using the Chi-Chi Earthquake Sequence

这是1999年台湾赤赤7.6级大地震震源体中剪切波分裂的地震学研究。该研究还利用世界上最好的数据集之一，在高自然地震活动性地区研究了引导断裂带波和非线性波在受损断裂带岩石中的传播效应。对应力诱发的地壳各向异性进行了全面测量，并通过其他可能的断裂带物质特征进行了补充，该项目还评估了观测结果与大地震发生的关系（因此具有预测潜力）。本文采用了台湾中央气象局地震台网（CWBSN）从1990年到2000年收集的大量数据。在m7.6地震前后，对剪切波分裂和其他信号与区域地应力变化和时间推移的相关性进行了严格的测试。该数据集可追溯到1970年，提供了一个30年的地震数据库，用于监测集集地震序列之前、期间和之后的大块地壳性质。CWBSN运营着一个由650多个台站（站间距5公里）组成的三分量、大动态范围和宽带加速度计网络和一个由75个台站组成的三分量高增益短周期地震仪网络。来自中下地壳的数千次m3事件被完美地记录下来，信噪比优异。对于大多数3级地震的数据集，发现震源正上方有多个记录台站，震中距离小于20公里。本项目的软件进行粒子极化分析，同时通过自动最大化两个匹配的水平分量信号的互相关联函数提取剪切波溢出延迟时间。这使得精确的测量可以用来测试剪切波分裂作为未来大地震的潜在指标的想法。这个研究项目的潜力更加全面和明确的剪切波爆裂比任何工作,迄今为止到目前为止完成的。

This is a seismological study of shear-wave splitting in the source volume of the large Mw 7.6 Chi-Chi, Taiwan, earthquake of 1999. The study also investigates the guided fault zone waves, and non-linear wave propagation effects in damaged fault zone rock, using one of the best data sets in the world in a region of high natural seismicity. A comprehensive measurement is carried out on the stress-induced crustal anisotropy, augmented by other possible signatures of damaged fault zone material, and the project also evaluates the relationship of observations with (therefore predictive potential of) the occurrence of great earthquakes. The extensive data set is used that has been collected by the Taiwan Central Weather Bureau Seismic Network (CWBSN) from 1990 to 2000. Rigorous tests are conducted on the correlation of shear-wave splitting and on other signals with regional crustal stress variations and lapse time before and after the Mw 7.6 event. This data set extends back to 1970, providing a 30-year seismic database for monitoring the bulk crustal properties before, during, and after the Chi-Chi earthquake sequence. The CWBSN operates a network of more than 650-station (at 5-km station spacing) of 3-component, large dynamic range, and broadband accelerographs and a network of 75-station 3-component high-gain short-period seismometers. Thousands of M 3 events from the middle-lower crust have been beautifully recorded with excellent S/N ratios. For most M 3 earthquake in the data set, found that there are a number of recording stations directly above the source with epicentral distance less than 20 km. The software for this project performs particle polarization analysis and at the same time extracts the shear-wave spiltting delay times through an automated maximization of the cross-correlation function of the two matched horizontal component signals. This allows accurate measurements to be made for testing the idea of shear-wave splitting as a potential indicator for a large earthquake in the future. This research project has the potential of being more comprehensive and definitive than any shear-wave splitting work that has so far been done to date.