Megaquake cycle at the Tohoku subduction zone with thermal fluid pressurization near the surface
Megaquake cycle at the Tohoku subduction zone with thermal fluid pressurization near the surface
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DOI：
10.1016/j.epsl.2012.01.026
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发表时间：
2012-04
影响因子：
5.3
通讯作者：
Y. Mitsui;N. Kato;Y. Fukahata;K. Hirahara
中科院分区：
文献类型：
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作者：
Y. Mitsui;N. Kato;Y. Fukahata;K. Hirahara
对于2011年东北地震，我们提出了一个力学模型来解释俯冲带逆冲断层上罕见的巨型（M9级）和频繁的大地震（M7级）。观测结果表明，在东北9级地震中，浅层发生了几十米左右的极大滑动，释放了滑动赤字，而包括7级地震震源区在内的深层发生了大约10米左右的大滑动。在这里，我们提出了一个模型，在该模型中，极大的滑移是由热液弱化（动态热加压的孔隙流体）的断层面上，而不是由摩擦性能的对比率和状态相关的摩擦。该模型解释说，东北地震在两天内发生了一次M7级地震，但M7级地震并不总是伴随着大地震。在巨震中，大的同震滑动可以发生在准静态滑动，即7级地震后滑或自发慢滑动事件发生的地区。浅部应力状态的微小差异会导致同震滑动的显著差异。进一步进行了不同水力参数和有效弱化区长度的数值试验。实验表明，监测有效热液弱化区的观测需要10公里或更细的空间分辨率。
For the 2011 Tohoku earthquake, we propose a mechanical model to explain rare giant (M9-class) and frequent large (M7-class) earthquakes on a thrust fault in the subduction zone. Observations implied, in the M9 Tohoku earthquake, that extremely large slip on the order of tens of meters occurs in a shallower part to release a slip deficit, as well as substantial slip about ten meters or so in a deeper part including the source area of the M7-class earthquakes. Here, we present a model in which the extremely large slip is caused by hydrothermal weakening (dynamic thermal pressurization of pore fluid) on the fault plane, not by contrast of frictional properties in terms of rate- and state-dependent friction. The model explains that the Tohoku earthquake followed a M7-class earthquake in two days, but M7-class earthquakes are not always followed by a giant earthquake. In a giant event, large coseismic slip can occur over an area where quasistatic slip, namely, afterslip of M7-class earthquakes or spontaneous slow slip events, takes place. Slight differences of stress state in the shallow part can result in drastically different coseismic slips. We further perform numerical experiments varying hydraulic parameters and the length of effective hydrothermal weakening area. The experiments imply that observations for monitoring the effective hydrothermal weakening area need spatial resolution on the order of 10km or finer.