Coseismic velocity change in and around the focal region of the 2008 Iwate-Miyagi Nairiku earthquake
Coseismic velocity change in and around the focal region of the 2008 Iwate-Miyagi Nairiku earthquake
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DOI：
10.1029/2012jb009252
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发表时间：
2012-06
影响因子：
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通讯作者：
R. Takagi;T. Okada;H. Nakahara;N. Umino;A. Hasegawa
中科院分区：
文献类型：
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作者：
R. Takagi;T. Okada;H. Nakahara;N. Umino;A. Hasegawa
[1]2008年岩手-宫城内陆7.2级地震发生在日本东北部，那里有密集的地震台网。利用这些台网的资料，我们用两种不同的方法：环境噪声干涉法和尾波垂直阵列干涉法测定了与这次地震有关的同震地震速度变化。本文的目的是将这两种方法结合起来，揭示流速变化的空间分布和原因。环境噪声干涉测量表明，同震瑞利波速度下降0.1-0.5%，在0.25-0.5 Hz。我们还估计了层析反演的速度变化的空间分布。血流速度的降低主要分布在病灶区及其周围。在第二种方法中，我们将互相关分析应用于KiK网垂直阵列观测到的尾波。我们检测到的剪切速度下降约5%，在浅层高达几百米的深度。定量比较表明，浅层剪切速度降低5%可以解释瑞利波速度降低0.1-0.5%。速度衰减的分布与强地面运动和静应力变化的分布相似。然而，在压缩区域中没有观察到显著的速度增加，在压缩区域中预期速度增加。根据观测结果，我们认为影响速度变化的主要因素是由于强震动引起的浅层损伤。静应力变化的影响可能被更大的强震影响所掩盖。
[1] The 2008 M7.2 Iwate-Miyagi Nairiku earthquake occurred in NE Japan where dense seismic networks exist. Using the data from these networks, we determined the coseismic seismic velocity change associated with this earthquake by two different methods: ambient noise interferometry and vertical array interferometry of coda wave. The purpose of this article is to reveal the spatial distribution and the cause of the velocity change by integrating these two approaches. Ambient noise interferometry revealed a coseismic velocity decrease of Rayleigh wave by 0.1–0.5% at 0.25–0.5 Hz. We also estimated the spatial distribution of the velocity change by a tomographic inversion. The velocity decrease was distributed in and around the focal area. In the second method, we applied cross-correlation analysis to coda waves observed by the KiK-net vertical array. We detected a shear velocity decrease of approximately 5% in shallow layers up to a few hundred meters depth. Quantitative comparison of the two results reveals that the 5% shear velocity decrease in shallow layers can explain the 0.1–0.5% decrease of Rayleigh wave velocity. The distribution of the velocity decrease is similar to that of the strong ground motion and the static stress change. However, a significant velocity increase is not observed in the compression area, where a velocity increase is expected. Based on the observations, we consider that the primary factor affecting the velocity change is damage in shallow layers due to strong motion. The effect of the static stress change might be masked by the larger effect of the strong motion.