Repeated drainage from megathrusts during episodic slow slip
Repeated drainage from megathrusts during episodic slow slip
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DOI：
10.1038/s41561-018-0090-z
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发表时间：
2018-05
影响因子：
18.3
通讯作者：
J. Nakajima;N. Uchida
中科院分区：
文献类型：
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作者：
J. Nakajima;N. Uchida
孔隙-流体压力水平被认为是调节地球上最大地震发生的巨型逆冲的摩擦强度和滑动行为的因素。一些分析表明，在巨型逆冲地震期间，渗透性密封的破裂会导致随后从巨型逆冲中排水。然而，对于排水是否伴随着间歇性慢滑事件的频繁发生，目前还知之甚少。本文分析了日本关东地区2004-2015年间的地震波形资料，发现菲律宾海板块巨型断裂上方的地震活动速率和地震衰减响应于加速慢滑而呈周期性变化。这些观察结果被解释为在每隔大约一年重复发生的慢滑事件期间密集的排水，以及随后流体向可渗透的上覆板块的迁移。我们的观察表明，如果慢滑事件发生在不透水的上覆板块下，由于慢滑事件而排出的流体可能会被迫流经巨型逆冲带，潜在地增加了上倾、锁定的孕震巨型逆冲带的孔隙-流体压力。这一过程可能会增加在慢滑移地区附近触发大地震的可能性。虽然应力传递被认为是触发巨型逆冲断裂的重要因素，但伴随着幕式慢滑事件的流体传递将在巨型逆冲断裂的弱化中起到额外和关键的作用。
Pore-fluid pressure levels are considered to regulate the frictional strength and slip behaviour at megathrusts, where the largest earthquakes on Earth occur. Some analyses have suggested that the breaking of permeability seals during megathrust earthquakes causes subsequent drainage from the megathrust. However, it is poorly understood whether drainage follows frequent occurrences of episodic slow slip events. Here we analyse seismic waveform data beneath Kanto, Japan, for the period from 2004 to 2015 and show that seismicity rates and seismic attenuation above the megathrust of the Philippine Sea slab change cyclically in response to accelerated slow slip. These observations are interpreted to represent intensive drainage during slow slip events that repeat at intervals of approximately one year and subsequent migration of fluids into the permeable overlying plate. Our observations suggest that if slow slip events occur under an impermeable overlying plate, fluids draining due to slow slip events could be forced to channel within the megathrust, potentially enhancing pore-fluid pressure at an up-dip, locked seismogenic megathrust. This process might increase the potential to trigger large earthquakes near slow slip areas. Although stress transfer is recognized as an important factor for triggering megathrust failure, fluid transfer accompanied by episodic slow slip events will thus play an additional and crucial part in megathrust weakening.