Coseismic and post-seismic velocity changes detected by Passive Image Interferometry: comparison of one great and five strong earthquakes in Japan
Coseismic and post-seismic velocity changes detected by Passive Image Interferometry: comparison of one great and five strong earthquakes in Japan
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DOI：
10.1093/gji/ggw066
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发表时间：
2016-05-01
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
我们提出了一个系统的研究地震速度变化与一个大逆冲断层和五个强烈的地壳地震在日本。我们分别对站对和站进行互相关和单站互相关分析。环境地震噪声的相关性使我们能够重建波传播的绿色函数。通过将每日绿色函数的尾波部分与长期参考绿色函数相关联，确定剪切波速度变化。我们分析了日本发生大地震的四个地区的数据：岩手宫城（2008年岩手-宫城内陆6.9兆瓦地震），新泻（2004年中越M-W 6.6、2007年中越冲M-W 6.6和2011年长野/新泻MW 6.2地震），诺托半岛（2007年M-W 6.7诺托坂东地震）和福冈（2005年M-W 6.6福冈地震）。在所有地区，我们分析了从各自地震前开始，一直持续到2011年M-W 9.0 Tohoku-oki地震后的时间序列。在0.125和4.0 Hz之间的五个不同频率范围内的分析产生不同站对或站的速度变化的时间序列。在各自的地震时，我们观察到同震速度下降，其次是部分震后恢复过程中的所有领域。对于东北冲地震，在所有地区都可以观察到同震速度下降。在所有四个地区，同震速度降随频率的增加而增加。最大的同震落差出现在断层带附近。在观测的时间范围内，震后恢复只是部分的，大约一半的同震速度下降没有恢复。恢复部分的特征恢复时间在所有地区和频率范围内相似，平均值为0.55年。我们模拟不同地震的体积应变变化，发现这些模型不能解释所观察到的同震速度下降的模式。不同台站的同震速度降与峰值地面速度和相关的动应变的相关性比与峰值地面加速度的相关性好，但相关性仍然很差。这表明，在地震过程中，强烈的地面运动所造成的非线性效应可以解释至少部分的同震速度下降。
We present a systematic study of seismic velocity changes associated with a megathrust and five strong crustal earthquakes in Japan. We perform both cross-correlation and single-station cross-correlation analysis for station pairs and stations, respectively. The correlation of ambient seismic noise allows us to reconstruct the Green's functions of the wave propagation. 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. We analyse data from four areas in Japan where large earthquakes occurred: Iwate-Miyagi (2008 MW 6.9 Iwate-Miyagi Nairiku earthquake), Niigata (2004 M-W 6.6 Chuetsu, 2007 M-W 6.6 Chuetsu-oki and 2011 MW 6.2 Nagano/Niigata earthquakes), Noto Peninsula (2007 M-W 6.7 Noto Hanto earthquake) and Fukuoka (2005 M-W 6.6 Fukuoka earthquake). In all areas, we analyse time-series which start before the respective earthquakes and last until after the 2011 M-W 9.0 Tohoku-oki earthquake. The analysis in five different frequency ranges between 0.125 and 4.0 Hz yields time-series of the velocity changes for the different station pairs or stations. At the time of the respective earthquakes, we observe coseismic velocity drops in all areas which are followed by a partial post-seismic recovery process. For the Tohoku-oki earthquake, coseismic velocity drops can also be observed in all regions. There is a general trend of increasing coseismic velocity drops with frequency in all four areas. The largest coseismic drops are observed close to the fault zones. Over the observed time range, the post-seismic recovery is only partial and around half of the coseismic velocity drops do not recover. The characteristic recovery times for the recovering part are similar in all areas and frequency ranges, with an average value of 0.55 yr. We model the volumetric strain changes for the different earthquakes and find that the observed pattern of the coseismic velocity drops cannot be explained by these models. The coseismic velocity drops at the different stations are better related with the peak ground velocities and the associated dynamic strain than with the peak ground accelerations, but the correlation is still poor. This suggests that non-linear effects caused by the strong ground motion during the earthquake can explain at least part of the coseismic velocity drops.