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首页> 外文期刊>Earth, planets and space: EPS >Deep crustal structure around the Atotsugawa fault system, central Japan: A weak zone below the seismogenic zone and its role in earthquake generation
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Deep crustal structure around the Atotsugawa fault system, central Japan: A weak zone below the seismogenic zone and its role in earthquake generation

机译：日本中部Atotsugawa断层系统周围的深地壳结构：地震发带下方的薄弱带及其在地震发生中的作用

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摘要

We carried out travel-time tomography around the Atotsugawa fault in central Japan, using arrival-time data obtained from a dense temporary seismograph network in joint observations by the Japanese University group. The observed velocities beneath the fault are 10-13% lower than those of the assumed host rocks (pyroxene amphibolite and hornblende-pyroxene gabbro) in the lower crust. Because the seismogenic layer is thickest in the central part of the fault, reaching a depth of ～15 km, we infer that the low-velocity anomaly is caused by aqueous fluids. Fluid fractions in the lower crust are estimated to be 2-3% and ～10%, assuming pyroxene amphibolite and hornblende-pyroxene gabbro, respectively. A distinct low-velocity anomaly is imaged in the central part of the Atotsugawa fault at a depth of 10 km, where seismic activity is very low at the upper 7 km and creeplike movement is observed at the surface. This anomaly is horizontally isolated but vertically connected to the low-velocity anomaly in the lower crust. We interpreted that abundant aqueous fluids supplied from the lower crust are responsible for this anomaly. High pore fluid pressure may enhance the stability of frictional slip, resulting in aseismic or episodic slip along the fault.
机译：我们使用日本大学集团联合观测中从密集的临时地震仪网络获得的到达时间数据，对日本中部原子津川断裂附近的行进时间层析成像。断层下方的观测速度比下地壳中假定的宿主岩（辉石闪石和角闪石-辉石辉长岩）的速度低10-13％。由于断层中部的致震层最厚，达到〜15 km的深度，因此我们推断出低速异常是由含水流体引起的。假设辉石两闪石和角闪石-辉石辉长岩分别位于下地壳中，流体分数估计为2-3％和〜10％。在Atotsugawa断层的中部，在10 km的深度处成像到一个明显的低速异常，那里的地震活动在上方7 km处非常低，并且在地表观察到蠕动。该异常是水平隔离的，但垂直连接到下地壳的低速异常。我们解释说，由下地壳供应的大量含水流体是造成这种异常的原因。高孔隙流体压力可能会增强摩擦滑动的稳定性，导致沿断层发生地震或偶发滑动。

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