THE FOCAL CHARACTERISTICS OF THE TONGHAI EARTHQUAKE, YUNNAN PROVINCE,ON JANUARY 5,1970
ZHANG ZHI-LI LIU SHIN-MEI (Institute of Geophysics, State Seismological Bureau)
The fracture processes and focal parameters of the Tonghai earthquake (Ms=7.7) which occurred on January 5, 1970 are estimated from the data of the P waves. This earthquake occurred on the Qujiang (#) fault striking NWW and propagated nearly, along it with an asymmetric bilateral fracture which propagated 26 km northwestward and 40 km southeastward with an average velocity of 2.3 km/sec. Estimation of the seismic moment of this earthquake by spectral analysis gives a value of 4.34#1026 dyne-cm. This value is considerably lower than that given by geodetic data. This difference indicates that some aseismic slips had taken place on the fault before and after Tonghai earthquake.As in Tangshan (#) earthquake, most of the aftershocks of this earthquake occurred along the fracture branches at both ends of the main fault. On the other hand, the fracture branch on the southeast end is noticeable for Tonghai earthquake. This fracture branch is located in the dilatational quarters and makes an angle of about 80 with the main fault.