Bayesian approach for detecting dynamically triggered very low-frequency earthquakes in the Nankai subduction zone and application to the 2016 Mw 5.9 off-Kii Peninsula earthquake, Japan
Bayesian approach for detecting dynamically triggered very low-frequency earthquakes in the Nankai subduction zone and application to the 2016 Mw 5.9 off-Kii Peninsula earthquake, Japan
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用于检测南海俯冲带动态触发甚低频地震的贝叶斯方法及其在 2016 年日本纪伊半岛外 Mw 5.9 地震中的应用
DOI：
10.1093/gji/ggz073
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发表时间：
2019
影响因子：
2.8
通讯作者：
Miyazawa Masatoshi
中科院分区：
文献类型：
--
作者：
Nakagawa Takashi;Iwamori Hikaru;Yanagi Ryunosuke;Nakao Atsushi;Nakagawa Takashi;Miyazawa Masatoshi
利用贝叶斯方法研究了南海俯冲带中大型远距离地震的面波对甚低频地震的远距离触发。先前使用简单的信号处理技术发现了另一种类型的构造慢地震/震颤和慢滑动的触发，这些技术利用了触发和触发事件波形的不同特征周期。与此同时，当高振幅地震波具有相似的特征周期时，检测嵌入在高振幅地震波中的低振幅VLF地震是具有挑战性的，因为在这种情况下，已建立的检测算法是不适用的。在这里，我们使用粒子滤波器/平滑的时间序列分析结合马尔可夫链蒙特卡罗方法，检测地震信号和估计的最大似然源参数的甚低频事件，可能已经远程触发的表面波从一个中等到大，遥远的地震，在数据中的表面波和目标信号都有占主导地位的周期在10和100秒之间。这种方法被应用于2016年Mw5.9离Kii半岛地震（日本）的地震图，记录在日本四国西部的KiK网钻孔阵列，在那里VLF事件以前报告。使用钻孔阵列是因为比较地面和钻孔记录可以基于深度相关的相位差来识别垂直入射体波，这不会出现在水平传播的表面波的记录中。在粒子滤波/平滑方面，通过三维结构模型中的全波场模拟和估计地面和井中传感器之间旅行时间的地震干涉测量法，预测每个地震台站可能发生的甚低频事件的波形。一个最大似然方法是用来估计源参数，最好的解释地面观测预测的钻孔观测和可能的甚低频信号。我们发现6个震级为3.4 ≤Mw≤ 4.3的VLF事件可能发生在周围低频地震/震颤（LFEs）的孕震区，并且可能由高振幅面波的到来触发。触发应力的变化估计为0.4至1.5千帕，类似的触发LFE以前报告的值。由于在2016年Mw5.9地震后，四国西部没有触发LFE，这些VLF地震对大地震面波引起的应力变化更敏感。这是首次报道的VLF地震动态触发的例子。
Remote triggering of very low-frequency (VLF) earthquakes in the Nankai subduction zone by surface waves from a moderate to large, distant earthquake was examined using a Bayesian approach. The triggering of another type of tectonic slow earthquake/tremor and slow slip was previously discovered using simple signal processing techniques that exploit the different characteristic periods of the triggered and triggering event waveforms. Meanwhile, detecting low-amplitude VLF earthquakes embedded in high-amplitude seismic waves is challenging when they have similar characteristic periods, as established detection algorithms are inapplicable in such cases. Here we use a particle filter/smoother for time-series analysis combined with Markov chain Monte Carlo methods, to detect seismic signals and estimate the maximum likelihood source parameters of VLF events that might have been remotely triggered by surface waves from a moderate to large, distant earthquake, in data where the surface waves and target signals both have predominant periods between 10 and 100 s. This approach was applied to seismograms of the 2016Mw5.9 off-Kii Peninsula earthquake (Japan), recorded by the KiK-net borehole array in western Shikoku, Japan, where VLF events were previously reported. The borehole array is used because comparing surface and borehole records can identify vertically incident body waves based on depth-dependent phase differences, which do not appear in records of horizontally propagating surface waves. In particle filtering/smoothing, waveforms of a probable VLF event at each seismic station are predicted by a full-wavefield simulation in a 3-D structure model, and seismic interferometry that estimates traveltimes between surface and borehole sensors. A maximum-likelihood approach is used to estimate source parameters that best explain the surface observations predicted by the borehole observations and probable VLF signals. We found that six VLF events with magnitudes 3.4 ≤Mw≤ 4.3 likely occurred in the seismogenic regions of ambient low-frequency earthquakes/tremors (LFEs), and were likely triggered by the arrivals of high-amplitude surface waves. The triggering stress changes are estimated from 0.4 to 1.5 kPa, similar to the values for triggered LFEs reported previously. Since there were no triggered LFEs in western Shikoku following the 2016Mw5.9 earthquake, these VLF earthquakes are more sensitive to stress changes caused by surface waves from large earthquakes. This is the first reported example of dynamic triggering of VLF earthquakes.