Fracture characteristics of the 1997 Jiashi, Xinjiang, China, earthquake swarm inferred from source spectra

Broadband P and S waves source spectra of 12 M _S≥5.0 earthquakes of the 1997 Jiashi, Xinjiang, China, earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propagation of the earthquake faulting has also been inferred from the azimuthal variation of the corner frequency. The main results are as follows: 1 The rupture size of M _S≥6.0 strong earthquakes is in the range of 10–20 km, while that of M _S=5.0–5.5 earthquakes is 6–10 km. 2 The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. 3 Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earthquakes. 4 For each M _S≥6.0 earthquake there exists an apparent azimuthal variation of the corner frequencies. Azimuthally variation pattern of corner frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists. This study is supported by the Chinese Joint Seismological Science Foundation (96913070401).