日本海沟俯冲带热结构与深源地震

本文利用有限差分方法,计算了全地幔对流模式和双层地幔对流模式下日本海沟俯冲带热结构、浮力及P波速度异常分布,基于亚稳态橄榄石相变模型推测亚稳态橄榄石的存在范围,同时分析了热传导系数、热膨胀系数和热源对俯冲带热结构的影响,以及俯冲带所受浮力与俯冲带形态的关系.结果表明,双层地幔对流模式下模拟的P波速度异常分布与层析成像结果更为相符,也与深源地震的分布有较好的相关性.板块内部亚稳态橄榄石的存在范围随热传导系数和热膨胀系数的减小而增大,同时忽略相变潜热和剪切生热的影响也会造成模型所预测的亚稳态橄榄石范围偏大.俯冲带所受负浮力在400 km深度附近达到最大值,亚稳态橄榄石的存在使负浮力逐渐减小,甚至在板块内部产生正浮力,不利于俯冲带穿透660 km相变界面.

Thermal structure of Japan Trench subduction zone and deep-focus earthquakes

The present study calculated the thermal structure, the distribution of buoyancy, and P-wave velocity anomalies in Japan Trench subduction zone using finite difference method, and predicted the range of metastable olivine according to whole and layered mantle convection models. We analyzed the influences of multiple coefficients, such as thermal conductivity, thermal expansion, and heat sources on the thermal structure. The relation between the buoyancy of subduction zone and its shape were also discussed. Interesting results for layered mantle convection model demonstrated that the modeled P-wave velocity anomalies not only matched seismic tomography results much better, but also highly correlated to the distribution of deep-focus earthquakes in Japan Trench subduction zone. The areas of metastable olivine inside slabs became larger with decreasing values of thermal conductivity and thermal expansion coefficients and ignoring phase change heating and shear heating would also induce larger areas of modeled metastable olivine. The maximum value of negative buoyancy reached the depth of about 400 km. The metastable olivine resulted in the decrease of negative buoyancy, or even positive buoyancy within the subduction zone against the penetration of the subduction zone into the 660 km discontinuity.