Strength of slab inferred from the seismic tomography and geologic history around the Japanese Islands



I analyze the seismic tomography around the Japanese Islands to elucidate the present slab morphology. A simple conversion from the high speed to the temperature anomaly is done based on the recent study of the conversion coefficient from the velocity to the thermal anomaly and on the study of the relation between the seismicity and the temperature in the slab. I find recognizable amount of cold temperature anomalies under the subducting slab. This suggests a rather continuous slab throughout the mantle consistent with the results of many recent numerical models. However, there still is a gap in the slab or diluted slab under the transition zone. To understand this, I construct a simple half-kinematic model of subduction zone in which a Byerlee's type yield stress and the depth independent yield stress are assumed. Taking into account the geologic history around the Japanese Islands, I find that the slab morphology similar to the tomographic image is obtained when the yield stress is O(100 MPa). The present study shows that the detailed studies of seismic tomography and the tectonic history of the surveyed area can provide the constraints on the slab dynamics.