NEW INTERPRETATION OF MECHANISM OF 1976 TANGSHAN EARTHQUAKE, NORTH CHINA

Depends on the field geological survey, shallow seismic and geophysical detections, trenches and borehole researches, as well as the chronological data analysis, and relocations of after shocks of Tangshan earthquake, Tangshan earthquake faults can be divided into three segments. The southwest segment, with dextral strike-slips and normal fault features, form a extensional depression area (about 10km long, and 5km width) in the west part, and compressive uplift area (several km long and width) in the east part of Tangshan earthquake fault. The middle segment, with dextral strike-slips and thrust fault features, form a compressive uplift area in urban area of Tangshan of the west part of fault belt. The northeast segment, with dextral strike-slips and normal fault features, form a compressive uplift area (several km long and width) in the west part, and extensional depression area (about 10km long, and 5km width) in the east part of Tangshan earthquake fault. It is determined that the width of earthquake fault in middle segment is about 20m in the trench, and shows a flower structures. Depends on the scale of surface rupture in trench of Tangshan asylum, the magnitude of paleo-earthquake could be Ms 8.5 and more large then the Tangshan Earthquake in 1976. There are more than 3 times of strong active and earthquake periods since 80 ka. A new model of earthquake mechanism will be suggested.