CRUSTAL STRUCTURE BENEATH THE XINGTAI EARTHQUAKE AREA IN NORTH CHINA AND ITS TECTONIC IMPLICATIONS

The Xingtai earthquakes of 1966 occurred in the central North China ba sin. To obtain detailed crustal structures and then to understand the seismotectonics of the Xingtai earthquakes, three deep seismic reflect ion profiles were conducted in the Xingtai earthquake area in recent y ears. The common depth point (CDP) stacked sections show basin and ran ge structure in the shallow crust, and a large-scale detachment in the middle crust. In addition, a high-angle fault in the mid-lower crust is referred to according to the discontinuity and inclination of the r eflection events on these sections. The moderate-low-angle normal faul t in shallow crust, the high-angle fault in mid-lower crust, and the d etachment in middle crust are located in the Xingtai earthquake area. There is stress concentration and energy accumulation at the junction of the three faults. The high-angle fault in the mid-lower crust is a possible seismogenic fault of the Xingtai earthquakes. The regional co mpressive tectonic stress in a nearly EW direction and additional stre ss produced by the upwelling of magma jointly may act on the fault to cause the Xingtai earthquakes.