Dynamic variation characteristics of tectonic stress field in the middle-southern segment of Tan-Lu fault zone before and after the 2011 Tohoku-Oki Mw9. 0 earthquake

Taking the middle-southern segment of Tan-Lu fault zone and its periphery as the study area, the paper calculated and obtained the focal mechanism of 1148 earthquakes in the study area during 1970-2016, and inverted the tectonic stress field with the damping stress tensor method, it discussed the influence of the M(w)9. 0 earthquake in Japan on the middle-southern segment of Tan-Lu fault zone and its periphery, based on the analysis of temporal and spatial dynamic change process of stress field and the characteristic of seismicity. The result shows that M(w)9. 0 earthquake in Japan has a significant impact on the middle-southern segment of Tan-Lu fault zone and its surrounding areas, showing disturbance change of stress field and significant increase of seismic activity. The background stress field, which is dominated by extrusion, presents a certain tension effect, and the stress structure and stress direction has changed. The maximum principal stress sigma(1)-axis plunge increased, The medium principal stress sigma(2)-axis plunge decreased, and the maximum principal stress a sigma(1)-axis deflected slightly counterclockwise. There are a series of significant medium-strong seismic cluster activities in Eastern China, including the study area. There is a good correlation between disturbance variation of stress field and seismic fluctuation activity, and it shows 3 different stages. The periodic change of tectonic stress action caused by disturbance is the dynamic mechanism of increased seismicity. The results also show that the disturbance of stress field and increase of seismic activity started 1 similar to 2 years before the M(w)9. 0 earthquake in Japan. It reveals that the influence of the Japan earthquake is not limited to coseismic and post-earthquake. It has already had an impact on eastern China continent in the late period of earthquake preparation. The results can provide a reference for the study of the influence of the Japanese subduction zone earthquake on the tectonic activity of the Chinese mainland.