摘要
A more detailed and deep-going analysis of tectonic conditions for the 1989 Bohai Sea M 7.4 earthquake area has been made based on the data of oil geological exploration and results of seismological researches. The obtained result fills the gap in seismotectonic research of Large Bohai Sea earthquake area of North China. The earthquake area is located in the eastern part of Cenozoic rifted basin of the Bohai Gulf, along the intersection zone between the NNE-trending Yingkou-Weifang fault zone and the NW-trending Beijing-Penglai fault zone. In the early-Tertiary fault-depression stage, three sets of faults, the NNE-, NW-, and W-E-trending faults, were developed in the upper crust in the area. They are listric and planar in the form, of normal fault character and mostly the major faults in faulted depressions. In the fault-depression stage since late Tertiary, the preexisting faults have undergone movement to different extent. Meanwhile, a new NE-trending Huanghekou (Yellow River Mouth)-Miaoxibei fault zone was developed. The focal faulting of the M 7.4 earthquake, striking to N45°E and dipping to SE, is nearly vertical, with dextral strike-slip nature, and buried down to depth of 15～34 km. The seismogenic fault for the large earthquake is not the Yingwei fault, but the newly generated Huanghekou-Miaoxibei fault.
A more detailed and deep-going analysis of tectonic conditions for the 1989 Bohai Sea M 7.4 earthquake area has been made based on the data of oil geological exploration and results of seismological researches. The obtained result fills the gap in seismotectonic research of Large Bohai Sea earthquake area of North China. The earthquake area is located in the eastern part of Cenozoic rifted basin of the Bohai Gulf, along the intersection zone between the NNE-trending Yingkou-Weifang fault zone and the NW-trending Beijing-Penglai fault zone. In the early-Tertiary fault-depression stage, three sets of faults, the NNE-, NW-, and W-E-trending faults, were developed in the upper crust in the area. They are listric and planar in the form, of normal fault character and mostly the major faults in faulted depressions. In the fault-depression stage since late Tertiary, the preexisting faults have undergone movement to different extent. Meanwhile, a new NE-trending Huanghekou (Yellow River Mouth)-Miaoxibei fault zone was developed. The focal faulting of the M 7.4 earthquake, striking to N45°E and dipping to SE, is nearly vertical, with dextral strike-slip nature, and buried down to depth of 15～34 km. The seismogenic fault for the large earthquake is not the Yingwei fault, but the newly generated Huanghekou-Miaoxibei fault.
基金
theFoundationforNationalKeyBasicResearchDevelopmentProjectsgrantNo .95 130 30 5 ,China
