【摘要】 选用密集的高精度地震台网Hi-net 2002~2004年记录的836个地震事件的23,895条P波和21,969条S波的到时资料,计算得到了日本西南地区水平分辨率约33 km,垂直分辨率4~15 km的三维地壳P波和S波速度结构,并进一步获得泊松比分布.研究表明,在大山火山下存在显著的低速异常,表明该火山可能是一个潜在的活火山.速度异常图像清楚地显示了菲律宾板块俯冲至西南日本地区下,其上方存在的低速高泊松异常表明可能有流体的存在,分析得出可能来自板块俯冲过程中的脱水作用.并进一步探讨了流体在地震孕育及触发的过程中可能起的重要作用.更多还原

【Abstract】 We used 23,895 P and 21,969 S wave high-quality arrival times from 836 local earthquakes during 2002 to 2004 recorded by the dense High-sensitivity Seismic Network(Hi-net) on the Japan islands.Detailed three-dimensional seismic velocity(Vp and Vs) structures of the crust under Southwest Japan are determined with a horizontal resolution of about 33 km and a depth resolution of 4~15km.We also estimated the Poisson’s ratio(σ) structure by using the inverted Vp and Vs data.Our results revealed a significant low-velocity anomaly beneath the Daisen volcano,which suggests that Daisen is potentially an active volcano.The subducting Philippine Sea plate is clearly imaged beneath Southwest Japan.Low-velocity and high-Poisson’s ratio anomalies are visible above the Philippine Sea slab,which may indicate the existence of fluids released by the slab dehydration.In addition,we discuss the important role of fluids played in the generating and triggering processes of large crustal earthquakes.更多还原