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

Abstract

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 about400 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.