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首页> 外文期刊>Pure and Applied Geophysics >Auto Correlation Analysis of Coda Waves from Local Earthquakes for Detecting Temporal Changes in Shallow Subsurface Structures: the 2011 Tohoku-Oki, Japan Earthquake
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Auto Correlation Analysis of Coda Waves from Local Earthquakes for Detecting Temporal Changes in Shallow Subsurface Structures: the 2011 Tohoku-Oki, Japan Earthquake

机译：用于检测浅层地下结构时间变化的局部地震的尾波自动相关分析：2011年日本东北冲地震

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For monitoring temporal changes in subsurface structures I propose to use auto correlation functions of coda waves from local earthquakes recorded at surface receivers, which probably contain more body waves than surface waves. Use of coda waves requires earthquakes resulting in decreased time resolution for monitoring. Nonetheless, it may be possible to monitor subsurface structures in sufficient time resolutions in regions with high seismicity. In studying the 2011 Tohoku-Oki, Japan earthquake (Mw 9.0), for which velocity changes have been previously reported, I try to validate the method. KiK-net stations in northern Honshu are used in this analysis. For each moderate earthquake normalized auto correlation functions of surface records are stacked with respect to time windows in the S-wave coda. Aligning the stacked, normalized auto correlation functions with time, I search for changes in phases arrival times. The phases at lag times of < 1 s are studied because changes at shallow depths are focused. Temporal variations in the arrival times are measured at the stations based on the stretching method. Clear phase delays are found to be associated with the mainshock and to gradually recover with time. The amounts of the phase delays are 10 % on average with the maximum of about 50 % at some stations. The deconvolution analysis using surface and subsurface records at the same stations is conducted for validation. The results show the phase delays from the deconvolution analysis are slightly smaller than those from the auto correlation analysis, which implies that the phases on the auto correlations are caused by larger velocity changes at shallower depths. The auto correlation analysis seems to have an accuracy of about several percent, which is much larger than methods using earthquake doublets and borehole array data. So this analysis might be applicable in detecting larger changes. In spite of these disadvantages, this analysis is still attractive because it can be applied to many records on the surface in regions where no boreholes are available.
机译：为了监视地下结构的时间变化，我建议使用在地表接收器处记录的本地地震产生的尾波的自动相关函数，该声波可能包含比面波更多的体波。使用尾波需要地震，导致监测的时间分辨率降低。但是，在地震活动度较高的区域中，有可能以足够的时间分辨率监视地下结构。在研究2011年日本东北冲绳地震（Mw 9.0）时，以前曾报道过这种地震的速度变化，我尝试验证该方法。该分析使用了本州北部的KiK-net站。对于每个中度地震，相对于S波尾迹中的时间窗，将地面记录的归一化自相关函数进行堆叠。将堆叠的归一化自动相关函数与时间对齐，我搜索相位到达时间的变化。对滞后时间<1 s的相位进行了研究，因为重点是浅深度的变化。到达时间的时间变化是基于拉伸方法在站点测量的。发现明显的相位延迟与主震有关，并随时间逐渐恢复。相位延迟量平均为10％，在某些站点最大约为​​50％。使用同一站点的地面和地下记录进行反卷积分析以进行验证。结果表明，去卷积分析的相位延迟比自相关分析的相位延迟要小一些，这表明自相关的相位是由浅深度处较大的速度变化引起的。自动相关分析似乎具有约百分之几的精度，这比使用地震双峰和井眼阵列数据的方法要大得多。因此，该分析可能适用于检测较大的更改。尽管存在这些缺点，但是这种分析仍然很有吸引力，因为它可以应用于没有钻孔的区域中的许多地面记录。

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