ACTIVE TECTONIC SETTING OF THE GREAT 1976 TANGSHAN EARTHQUAKE (M = 7.8), NORTH CHINA

The M = 7.8 Tangshan earthquake occurred on July 28 1976 with an epicenter located ~120 km east of Beijing. The earthquake killed more than 240,000 people, making it the deadliest earthquake of the 20th century. Due to extensive Quaternary cover the earthquake fault is poorly exposed, leading to debates on its geometry, kinematics, and Quaternary slip rate. To resolve these problems we began a mapping project to document the geologic setting for the earthquake using satellite images (LANDSAT, ASTER, and CORONA) and topographic data (SRTM and detailed Chinese topographic maps). Identification of active faults and determination of their kinematics are based on topographic expression, offset geomorphic features, and disruption of drainage systems. Our analysis reveals three sets of kinematically linked active faults in the Beijing-Tangshan region. The dominant set is expressed by NNE-striking right-slip faults. The Tangshan earthquake occurred on one of these faults, which has a prominent topographic expression with two prominent restraining bends. One of the bends located in the city of Tangshan was the site of eearthquake nucleation. The second set consists of east-striking normal faults with lengths varying from 30 to 60 km. They are concentrated along the east-trending topographic front of the Yanshan Range and are linked with the longer NNE-striking right-slip faults extensively developed in the northern North China Plain. The third set is composed of NW-striking left-slip faults; they are commonly shorter than 30 km in length and merge with the NNE-striking right-slip faults forming conjugate fault sets. The geometry and kinematics of the active fault patterns in the Beijing-Tangshan region are consistent with a constrictional strain field with N-S extension and E-W contraction.