The Finite Element Numerical Simulation of Tectonic Stress Field In and Around the Okhotsk Micro-plate

The subduction zone in the northwest Pacific region is a very active and typical subduction zone where the Eurasian plate, Philippine Sea plate, Pacific plate and North American plate interact with each other. The subduction process mainly affects the tectonic stress field and dynamic process within the plate. The Okhotsk micro-plate is separated from the North American plate. Its eastern boundary, the Kuril-Kamchatka area, is under the strong subduction of the Pacific plate and in a state of frequent earthquakes. The study on the distribution characteristics of tectonic stress field in this region can help us to well understand the earthquake preparation law related to the plate subduction and the formation mechanism of stress field in the plate.

We divided the Okhotsk micro-plate into seven different parts along the north-south direction for statistics and discussion. We collected 4741 effective seismic data from International Seismological Center about the region. These earthquakes were all above five magnitude. They occurred within 150 kilometers of the subduction zone boundary. We obtained the characteristic information of stress field related to each earthquake through conversion. We used three-dimensional viscoelastic finite element method to simulate and analyze characteristics and control factors of the plate stress field. Because the geometrical shape of the east side of the Okhotsk micro-plate changes greatly along south to north direction, we constructed a variety of three-dimensional subduction structural models with different geometric forms. We obtained some relatively clear distribution images of tectonic stress field both horizontally and vertically through numerical simulation. These images are consistent with the distribution of stress state obtained from seismic data. The analysis results show that the stress structure of the subduction zone in the Kuril-Kamchatka island arc area is relatively consistent, and the main stress orientation is on the whole uniformly distributed. There is no significant difference between normal subduction and oblique subduction about stress mechanism distribution and principal stress trend distribution.