Kano Masayuki, Kato Aitaro, Ando Ryosuke, Obara Kazushige
Earthquake Research Institute, The University of Tokyo, Tokyo, Japan.
Department of Geophysics, Graduate School of Science, Tohoku University, Sendai, Japan.
Sci Rep. 2018 Feb 26;8(1):3655. doi: 10.1038/s41598-018-22048-8.
Deep low frequency tremors are indicators of slow slip transients in the brittle-ductile transition zone along subducting plates. Investigation of comprehensive tremor activities is therefore an important issue for understanding the seismic/aseismic characteristics in transition zones. Here, we focus on the radiated energy from tremors to reveal the along-strike heterogeneity in the strength of tremor patches. Based on a tremor catalog that more accurately evaluates radiated energy, we examine the spatio-temporal activity of tremors accompanied by slow slip events (SSEs) in western Shikoku, southwestern Japan. The new finding of this study is that the energy radiated from tremors is positively correlated with the speed of tremor migration front and the slip rate along the plate interface during a SSE. This can be qualitatively explained by a stress diffusion model, which consists of along-strike heterogeneities in the effective strength of tremor patches embedded in a ductile shear zone. This effective strength heterogeneity is supported by a lateral variation in the stress drop of a SSE; it is consistent with the fluid pressure distribution along the plate boundary fault and the tidal sensitivity of tremors. Accurate evaluation of tremor activities, especially the radiated energy, can be used to infer the spatial distribution of the strength of tremor patches in transition zones worldwide.
深部低频震颤是俯冲板块沿脆性-韧性过渡带发生慢滑瞬变的指标。因此，开展全面的震颤活动研究对于理解过渡带的地震/非地震特征而言是一个重要课题。在此，我们聚焦于震颤的辐射能量，以揭示震颤斑块强度沿走向的非均匀性。基于一个能更准确评估辐射能量的震颤目录，我们考察了日本西南部四国西部伴随慢滑事件（SSEs）的震颤的时空活动。本研究的新发现是，震颤辐射的能量与震颤迁移前沿的速度以及SSE期间沿板块界面的滑动速率呈正相关。这可以用一个应力扩散模型进行定性解释，该模型由嵌入韧性剪切带的震颤斑块有效强度的沿走向非均匀性组成。这种有效强度的非均匀性得到了SSE应力降横向变化的支持；它与沿板块边界断层的流体压力分布以及震颤的潮汐敏感性相一致。准确评估震颤活动，尤其是辐射能量，可用于推断全球过渡带震颤斑块强度的空间分布。
