Study On The Relocation Of Intermediate And Deep Earthquakes In The Subducted Pacific Slab With High-precision And Its Implications

Due to the subduction of the western Pacific plate, there are numbers of intermediate and deep earthquakes below the island arc area of the northern Japan. The subduction is also related with the deep seismic zone below the northeastern China. In order to explore the structure of the plate and the mechanism of seismic zone, we use the traveling time data from networks of Japan and the northeastern China to relocate the intermediate and deep earthquakes. Then we use the focal mechanism which we have gotten from the relocation to explore the structure of the plate.We chose the improved double-different location as our relocated approach: 3-D ray tracing method is used to trace the seismic ray; Using spherical coordinate system in calculating the partial derivative can improve the precision of the relocation; The improved J-B model is more similar to the underground structure. Before the relocation, we made a theory test to make sure that the improved double-different location approach is effective and high-precision. During the test, we get the suitable parameter. We also implement the visualization of the source program to make the operation easier.After the relocation of intermediate earthquakes in Japan, we find that there are two parallel seismic zone under this area. And the two zones is converging in the deep. We calculate the focal mechanism of part of earthquakes, and find out the stress state of the plate: the upper plate is in pressing strain; the lower plate is in tensile strain. We conclude that when the subducting plate arrives at the mantle transition zone, its subducting velocity is getting smaller. And the plate stuck in the mantle transition zone. The gravity make the plate to bend down.After the relocation of deep earthquakes in the northeastern China, we find that when the subducting plate arrives the mantle transition zone, its subducting velocity is getting smaller. The plate does not reach the lower mantle through the mantle transition zone. But it stays in the mantle transition zone. In our points of view, there is metastable peridotite in the subducting plate. Under the common function of buoyancy and gravity, the metastable peridotite is in pressing train. We think that this is why the deep seismic zone below the northeastern China took shape.