AN EARTHQUAKE LOCATION PROGRAM WITH MULTIPLE VELOCITY MODEL AND ITS APPLICATION IN THE BEIJING SEISMIC NETWORK

With a new earthquake location program HYPO81, developed by W.H. K. Lee, G. Nelson, P. Ward, and the author, the earthquakes recorded by the Beijing Seismic Network from Jan. 1, 1979 through June 30, 1980 are relocated and the results are compared with the earlier reported ones. The features of the new location program can be summarized as: (1) different multi-layered velocity models can be used for different group of stations and low velocity layers are allowed to be included in the models; (2) several kinds of weightings are used; (3) single value decomposition technique is used in the least-squares iterations; (4) the quality of the results is evaluated in several ways; and (5) different kinds of phase data can be used.In order to reflect the lateral variation of the velocity structure in Beijing area, three different multilayered velocity models are used for the northwestern mountain area, the southeastern plain, and the area between them, respectivety. In locating the earthquakes, direct P, refrected P, and direct S arrival data are used. According to the quality criteria in HYP081, over three quarters of the events relocated fall into the catagories of quality C and D, indicating the necessity of increasing stations in the network and improving the accuracy of the phase data.