Deep low‐frequency tremor that correlates with passing surface waves
Deep low‐frequency tremor that correlates with passing surface waves
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DOI：
10.1029/2006jb004890
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发表时间：
2008
影响因子：
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通讯作者：
M. Miyazawa;E. Brodsky
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作者：
M. Miyazawa;E. Brodsky
地球物理研究杂志，第113卷，B 01307，doi：10.1029/2006 JB 004890，2008与通过的面波相关的深低频震颤Masatoshi Miyazawa 1和艾米丽E. 2006年12月5日接收; 2007年7月23日修订; 2007年9月28日接受; 2008年1月24日出版。[ 1 ] 2004年苏门答腊-安达曼地震的巨大面波动态地扰动了日本的上地幔结构，并在四国东部和西部、东海西部和中部以及纪伊半岛引发了周期性的深低频地震震颤。我们利用触发地震的振幅与地震波应力之间的关系来研究深源低频地震的机制。来自15-30 s瑞利波的体积应变变化在强触发中起重要作用，可能通过库仑破坏应力变化。建立在以前的结果，震颤信号变得越来越强，增加扩张，我们观察到一个明显的增加，在触发震颤的扩张，由于瑞利波在30公里深的震源区。我们还观察到一个相关的库仑破坏应力变化解决在一个适当的平面上。触发地震的信号幅度与震源区的扩容和库仑剪应力之间存在指数关系。这与震颤包的形状相结合意味着震颤幅度是基于入射波的幅度可预测的。振幅的变化可以解释的震颤源区域中的源的分布。引文：Miyazawa，M.，和E. E. Brodsky（2008），与通过的表面波相关的深低频震颤，J. Geophys。结果：113，B01307，doi：10.1029/2006JB 004890。1.简介[ 2 ]俯冲板片上的深低频震颤是最近发现的一种新的地震信号[Obara，2002]。这些波的振幅周期非常长，信号通常是连续的，在几十分钟到几天的时间内几乎没有标点符号。这些地震特征经常出现在火山地区，通常被解释为该环境中充满流体的共振管道的迹象。因此，早期对深部板状地震的研究通过类比提出了流体源。地球化学和岩石学的限制支持了这一推断，表明流体是在地震深度的一系列脱水反应中从俯冲板片中释放出来的[例如，Toriumi和Inui，2001年; Omori等人，2004年]。同时，地震与慢滑动的同时发生也表明，地震与30 ~ 40 km深度的大规模板片过程有一定的物理联系。[ 3 ]最近的研究表明，在俯冲和火山背景下，低频地震和震颤可以由简单的剪切破坏产生。低破裂速度或低应力降可导致低频波，并且重叠地震可产生明显连续的信号[哈灵顿和Brodsky，日本京都京都大学灾害预防研究所。美国加州圣克鲁斯市加州大学地球科学系。版权所有2008年由美国地球物理联盟。0148-0227/08/2006 JB 004890$09.00 2007; Shelly等人，2006年]。尽管如此，在脱水深度发生的震颤和缓慢滑动表明，液体可能是一个重要的组成部分。[ 4 ]在这里，我们通过使用由来自远震的地震波触发的板状震颤的特殊情况所构成的约束来研究板状震颤的起源。2004年苏门答腊-安达曼地震（M w 9.2）非常严重，在日本测量到的表面波振幅与2002年德纳里地震（M w 7.9）相当或大几倍，该地震导致了北美周围经过充分研究的地震触发[例如，Prejean等人，2004年]。Miyazawa和Mori [2006]表明，日本西部深层低频事件的周期性触发是由于苏门答腊地震的瑞利波，并表明触发与震源区的大拉伸扩张有很好的相关性（图1和2）。类似的触发震颤发生在小型地方地震和大型地震之后[Obara，2003]，以及2003年十胜冲地震（Mw 8.1）的面波期间[Miyazawa and Mori，2005]。这些最初的观测结果被认为是将震颤与阿拉斯加由剪切破坏引发的普通地震区分开来[West等人，2005年]。最近，Rubinstein等人[2007]发现卡斯卡迪亚俯冲带类似的非火山性震颤的爆发被2002年德纳里地震的Love波所触发。[ 5 ]更仔细地分析地震波的输入应变和由此产生的震颤之间的关系可能有助于我们解开日本西部深板震颤的机制。B01307 1/17
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, B01307, doi:10.1029/2006JB004890, 2008 Deep low-frequency tremor that correlates with passing surface waves Masatoshi Miyazawa 1 and Emily E. Brodsky 2 Received 5 December 2006; revised 23 July 2007; accepted 28 September 2007; published 24 January 2008. [ 1 ] The large surface waves from the 2004 Sumatra-Andaman earthquake dynamically perturbed the upper mantle structure in Japan and triggered periodic deep low-frequency seismic tremor in eastern and western Shikoku, western and central Tokai, and the Kii peninsula. We use the relationship between the amplitude of the triggered tremor and the stresses of the seismic waves to investigate the mechanism of deep low-frequency seismic tremor. Volumetric strain changes from the 15–30 s Rayleigh waves play an important role in the strong triggering, likely via Coulomb failure stress changes. Building on previous results that the tremor signals become increasingly strong with increasing dilatation, we observe a clear increase in the triggered tremor with an increase in the dilatation due to the Rayleigh waves at the 30 km depth source regions. We also observe a correlation with the Coulomb failure stress change resolved on an appropriate plane. There is an exponential relationship between the signal amplitude from triggered tremor and both the dilatation and the Coulomb shear stress at the source region. This combined with the shape of the tremor packets implies that the tremor amplitude is predictable based on the amplitude of the incoming waves. The amplitude variations can be explained by a distribution of sources in the tremor source region. Citation: Miyazawa, M., and E. E. Brodsky (2008), Deep low-frequency tremor that correlates with passing surface waves, J. Geophys. Res., 113, B01307, doi:10.1029/2006JB004890. 1. Introduction [ 2 ] Deep low-frequency tremor on subducting slabs is a recently discovered and novel seismic signal [Obara, 2002]. The waves are unusually long-period for their amplitude and the signal is often continuous with little punctuation over times ranging from tens of minutes to a few days. These seismic features are often seen in volcanic regions and usually interpreted as signs of fluid-filled resonant conduits in that setting. Therefore early work on deep, slab tremor suggested a fluid source by analogy. Geochemical and petrological constraints supported the inference by suggesting that fluids are released from the subducting slab in a series of dehydration reactions at the depth of the tremor [e.g., Toriumi and Inui, 2001; Omori et al., 2004]. The coincidence of the tremor with slow slip also suggests that there is some physical connection with the large-scale slab processes at the depth of 30 –40 km. [ 3 ] More recent work has suggested that low-frequency earthquakes and tremor can be generated by simple shear failure in both the subduction and the volcanic settings. A low rupture velocity or low-stress drop can result in the low- frequency waves and overlapping earthquakes can generate the apparently continuous signal [Harrington and Brodsky, Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan. Department of Earth Sciences, University of California, Santa Cruz, California, USA. Copyright 2008 by the American Geophysical Union. 0148-0227/08/2006JB004890$09.00 2007; Shelly et al., 2006]. Still, the occurrence of the tremor and slow slip at the depth of dehydration suggests that fluids may be an important component. [ 4 ] Here we study the origin of slab tremor by using a constraint posed by special cases of slab tremor that are triggered by the seismic waves from distant earthquakes. The 2004 Sumatra-Andaman earthquake (M w 9.2) was enor- mous and the surface wave amplitudes measured in Japan were comparable to or a few times as large as those from the Denali earthquake (M w 7.9) in 2002 that contributed to the well-studied earthquake triggering around North America [e.g., Prejean et al., 2004]. Miyazawa and Mori [2006] showed that periodic triggering of deep low-frequency events in western Japan was due to the Rayleigh waves from the Sumatra earthquake, and suggested that the triggering is well correlated with the large tensile dilatation at the source regions (Figures 1 and 2). Similar triggered tremor occurred after small local earthquakes and large teleseisms [Obara, 2003], and during the surface waves of the 2003 Tokachi-oki earthquake (M w 8.1) [Miyazawa and Mori, 2005]. These initial observations were thought to distinguish the tremor from the ordinary earthquakes triggered in Alaska that were promoted by shear failure [West et al., 2005]. Recently, Rubinstein et al. [2007] found that the bursts of similar nonvolcanic tremor in Cascadia subduction zone were trig- gered by Love waves from the 2002 Denali earthquake. [ 5 ] More careful analysis of the relationship between the input strains of the seismic waves and the resultant tremor may help us untangle the mechanisms of deep-slab tremor in western Japan. B01307 1 of 17