Single-station cross-correlation analysis of ambient seismic noise: application to stations in the surroundings of the 2008 Iwate-Miyagi Nairiku earthquake
Single-station cross-correlation analysis of ambient seismic noise: application to stations in the surroundings of the 2008 Iwate-Miyagi Nairiku earthquake
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DOI：
10.1093/gji/ggu115
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发表时间：
2014-07-01
影响因子：
2.8
通讯作者：
Nakahara, Hisashi
中科院分区：
文献类型：
--
作者：
Hobiger, Manuel;Wegler, Ulrich;Nakahara, Hisashi
我们介绍了处理环境地震噪声的单台互相关(SC)技术，并将其结果与已建立的互相关(CC)和自相关(AC)技术进行了比较。CC是两个地震台信号之间的相关性，AC是信号与自身的相关性，SC是单个三分量地震传感器的两个不同分量的相关性。三种不同相关技术的比较表明，CCS在0.5赫兹以下的频率下给出了最好的结果，而SCS在更高的频率下给出了最好的结果。在所有三种处理技术中，环境地震噪声都是相关的，以便重建描述第一和第二传感器之间的波传播的格林函数。通过将逐日格林函数的尾波部分与长期参考格林函数联系起来，确定了剪切波速度的变化。本文对日本本州岛北部协调世界时2008年6月13日(日本标准时间2008年6月14日)发生的岩门-宫城奈陆6.9级地震断裂带周围20个地震台的资料进行了分析。数据范围为2008年1月至2011年6月，因此包括2011年3月11日发生在本州北部海岸的东北地震(M-W=9.0)。这些数据在0.125至4.0HZ之间的五个不同频率范围内进行了分析。数据显示了两次地震的同震速度变化，随后是震后速度恢复。一般来说，同震速变化随频率增大而增大。对于岩门-宫城奈陆地震，最强烈的速度变化发生在断裂带附近。快速恢复的同震速度变化可以与在研究期间没有恢复的变化分开。对于东北地震，整个地区都受到同震速度变化的影响。同震速度变化深度的模拟表明，岩门-宫城奈陆地震既可以用浅层速度大变化来解释，也可以用小而深的变化来解释。对于一个观测站，观测结果只能通过假设更深层次的变化来解释。对于东北地震，模型显示研究区域的不同部分受到不同程度的影响，有的表现为浅层变化，有的表现为更深层次的变化。此外，速度还存在季节变化，这种变化与0.5赫兹以上不同台站的速度变化是一致的，秋季的速度最大。
We introduce the single-station cross-correlation (SC) technique of processing ambient seismic noise and compare its results with the established cross-correlation (CC) and autocorrelation (AC) techniques. While CC is the correlation of the signals of two seismic stations with each other and AC is the correlation of a signal with itself, SC is the correlation of two different components of a single three-component seismic sensor. The comparison of the three different correlation techniques shows that CCs give the best results at frequencies below 0.5 Hz and that SCs give the best results at higher frequencies. In all three processing techniques, ambient seismic noise is correlated in order to reconstruct the Green's function describing the wave propagation between the first and the second sensor. By relating the coda parts of the daily Green's functions with the long-term reference Green's functions, shear wave velocity changes are determined. Here, we apply this technique to the data of 20 seismic stations in the surroundings of the fault zone of the Iwate-Miyagi Nairiku earthquake (M-W = 6.9), which occurred on 2008 June 13, UTC (2008 June 14, Japan Standard Time) in the northern part of the Japanese island Honshu. The data range from 2008 January to 2011 June and therefore include the Tohoku earthquake (M-W = 9.0), which occurred on 2011 March 11, off the coast of northern Honshu. The data are analysed in five different frequency ranges between 0.125 and 4.0 Hz. The data show coseismic velocity changes for both earthquakes followed by a post-seismic velocity recovery. In general, the coseismic velocity changes increase with frequency. For the Iwate-Miyagi Nairiku earthquake, the strongest velocity changes occur close to the fault zone. Quickly recovering coseismic velocity changes can be separated from changes not recovering during the study period. For the Tohoku earthquake, the complete area is affected by coseismic velocity changes. A modelling of the depth of the coseismic velocity changes indicates that the Iwate-Miyagi Nairiku earthquake can be explained either by large shallow velocity changes or by small, but deep changes. For one station, the observations can only be explained by assuming deeper changes. For the Tohoku earthquake, the modelling shows that different parts of the study area are affected in different ways, some showing shallow changes, others deeper changes. Furthermore, seasonal velocity variations occur, which are compatible for the different stations above 0.5Hz, with velocity maxima in autumn.