MULTIPLE RUPTURE CHARACTERISTICS OF THE 1920 HAIYUAN M8(1/2) EARTHQUAKES

Field survey by the authors reveals that, the overall length of the earthquake fault for the great 1920 Haiyuan, China, M8(1/2) Earthquake is 225 km, and that the fault consists of 6 sub-faults which show different geometries and stretch regularly in en-echelon configuration. Each subfault can be divided into three segments with different deformation features: the middle segment is essentially strike-slip type, while the two end-segments show predominant vertical displacement, being essentially normal or thrust type respectively. Measurements give the result that maximum horizontal displacement appears at the middle part of each subfault, and dies away gradually near the two ends, while the vertical displacement distributes in just thte opposite way, being small at the middle and large at the ends. The whole fault exhibits several peak displacements.This implies that the 6 subfaults of the great Haiyuan Earthquake are all independent displacement dis-continuities (dislocations), and each of them represents a rupture event. In this regard the authors suggest that the great M8(1/2) Haiyuan Earthquake might be the result of 6 successive subevents which occurred independently of each other.