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首页> 外文期刊>Bulletin of the Seismological Society of America >Variations of P-wave travel-time residuals before and after the 1999 Chi-Chi, Taiwan, earthquake
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Variations of P-wave travel-time residuals before and after the 1999 Chi-Chi, Taiwan, earthquake

机译：台湾1999年集集地震前后P波传播时间残差的变化

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摘要

P-wave velocity variations may provide precursory information before large earthquakes. We present results from a simple study on variations of P-wave travel-time residuals before and after the 1999 Chi-Chi, Taiwan, earthquake. The short-period seismic network deployed in Taiwan by the Central Weather Bureau (CWB) is routinely used for earthquake location. The accuracy of earthquake location is often judged by the travel-time residual of seismic waves. Because the velocity model used by the CWB was one-dimensional, the travel-time residuals will show lateral inhomogeneity of the velocity structures and unmodeled vertical structures. Also, the travel-time residuals may change with time if the velocity structure changes temporally. We used the data of the Central Weather Bureau Seismic Network (CWBSN) from 1991 to 2002 to obtain the difference between observed and calculated P-wave travel times, which is defined as the P-wave travel-time residual. The purpose of this study is to find the mean value of the P-wave travel-time residuals at each station and its possible temporal changes at stations near the Chelungpu fault. Our results show that the mean P-wave travel-time residuals at stations 40 km east of the Chelungpu fault changed very little before and after the Chi-Chi earthquake. But the mean P-wave travel-tinie residuals at the stations immediately west of the Chelungpu fault clearly changed before and after the Chi-Chi earthquake. The anomalous zone is bounded by stations NSY, TWQ1, TCU, WNT, WGK, CHN5, YUS, WDT, and WHF. These temporal changes of P-wave travel-time residuals can be attributed to changes in the velocity structure, which in turn might be caused by crustal deformation east of the Chelungpu fault beginning about 6 years before the Chi-Chi earthquake. In other words, before the Chi-Chi earthquake, there was a long-term 6-year precursor of P-wave velocity decrease possibly due to dilatancy or development of cracks. The variations of P-wave travel-time residuals with time at the anomalous stations are also confirmed by statistical tests that show clear significance. This method can be used to monitor and identify variations of P-wave travel-time residuals which may be precursors to a large earthquake.
机译：纵波速度变化可能会在大地震之前提供先兆信息。我们提供的简单研究结果是对1999年台湾集集地震前后P波传播时间残差的变化进行的。中央气象局（CWB）在台湾部署的短期地震网络通常用于地震定位。地震定位的准确性通常由地震波的传播时间残差来判断。由于CWB使用的速度模型是一维的，因此行进时间残差将显示速度结构和未建模的垂直结构的横向不均匀性。同样，如果速度结构随时间变化，则行进时间残差可能随时间变化。我们使用了1991年至2002年中央气象局地震台网（CWBSN）的数据来获得观测到的和计算出的P波传播时间之间的差，这被定义为P波传播时间残差。这项研究的目的是找出在切龙普断裂附近的每个站的P波传播时间残差的平均值及其可能的时间变化。我们的研究结果表明，在Chi-Chi地震前后，切伦堡断层以东40公里处的平均P波传播时间残差变化很小。但是，在志吉浦地震前后，切伦堡断层以西的台站的平均P波行进趋势残差明显改变了。异常区的边界为NSY，TWQ1，TCU，WNT，WGK，CHN5，YUS，WDT和WHF。 P波传播时间残差的这些时间变化可以归因于速度结构的变化，而速度结构的变化又可能是由自Chi-Chi地震发生约6年以来切龙普断裂以东的地壳变形引起的。换句话说，在Chi-Chi地震之前，有一个长期的6年纵波速度下降的前兆，可能是由于扩张或裂缝的发展。统计波测试也证实了异常站P波传播时间残差随时间的变化，这显示出明显的意义。此方法可用于监视和识别可能是大地震发生的P波传播时间残差的变化。

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