Seismic evidence for high pore pressures in the oceanic crust: Implications for fluid‐related embrittlement
Seismic evidence for high pore pressures in the oceanic crust: Implications for fluid‐related embrittlement
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洋壳高孔隙压力的地震证据：对与流体相关的脆化的影响
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
T. Matsuzawa
中科院分区：
文献类型：
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作者：
T. Shiina;J. Nakajima;T. Matsuzawa
我们使用P-to-S转换波的到达时间数据估算了日本东北部俯冲太平洋板块地壳的P波速度结构。结果表明，俯冲地壳的P波速度沿弧沿着变化，在100 km深度处突然增大，弧前为6.5-7.0 km/s，弧后为7.5-8.5 km/s。弧前的P波速度比变质洋中脊玄武岩材料的理论预期值低约10%。俯冲地壳中的地震活动在70-80 km深处最为活跃，那里的P波速度最低。P波速度的显著降低表明含水流体与含水矿物共存。丰富的流体提高了孔隙流体压力，降低了有效正应力，促进了低速地壳中的强烈地震活动。我们的观测提供了地震证据，证明俯冲地壳中的地震是由流体相关的脆化促进的。
We estimated the P wave velocity structure of the crust of the subducting Pacific plate beneath northeast Japan using arrival time data of P‐to‐S‐converted waves. The results show that the P wave velocity of the subducting crust varies along the arc and increases abruptly at a depth of ~100 km, from 6.5–7.0 km/s in the fore arc to 7.5–8.5 km/s in the back arc. The P wave velocity in the fore arc is ~10% lower than theoretically expected values for the metamorphosed mid‐ocean ridge basalt material. Seismicity in the subducting crust is most active at depths of 70–80 km where P wave velocities are lowest. The marked reduction of P wave velocity suggests the coexistence of aqueous fluids with hydrous minerals. Abundant fluids elevate pore fluid pressures and reduce effective normal stress, promoting intensive seismic activity in the low‐velocity crust. Our observations provide seismic evidence that earthquakes in the subducting crust are facilitated by fluid‐related embrittlement.