Recent tectonic stress field and major earthquakes of the Bohai Sea basin

The Bohai Sea basin is located in the east to the Cenozoic rift basin of North China. It is a inner-land sea basin formed during Late Quaternary time. In this basin there are numerous active faults and many major earthquakes have occurred. Its major active tectonic zones are the northern section of the NE trending Yingkou-Weifang fault zone, Miaoxibei-Huanghekou-Linyi fault zone, and NW striking Beijing-Penglai fault zone, which intersect at the center of the Bohai Sea basin. These tectonic zones subdivide the sea area into four secondary neotectonic areas, which are subject to the recent tectonic stress field. Using the data of 38 focal plane solutions and 75 drill stress measurements, and the result of numerical modeling, we analyze the recent tectonic stress field of this region. Our result shows that this stress field is characterized by dominant horizontal or nearly horizontal stress. Its compres-sive stress is in the direction NE60～90, and the tensional stress is in NS-NW30. There are some differences of principal stress between secondary tectonic areas. A remarkable feature of the Bohai Sea basin is a conjugate shear rupture zone, which develops in the crust and is the major seismogenic structure.