Determination of Phase Velocity and Direction of Wave Approach from Station Arrays

Abstract

The multipartite station array method is described in comparison with the conventional tripartite technique, to obtain the apparent wave velocity and direction of approach averaged over a limited area, in the studies of crustal structures, velocity distribution with depth, epicenter determination and so forth. These averaged values and their probable errors can be determined from arrival times of coherent waves at more than four stations by means of linear least squares. The two methods were applied to teleseisms recorded at the Berkeley network, California and to near earthquakes observed at the Wakayama network, western Japan. The results have shown that the multipartite least squares gave the averages which in most cases agree within the probable errors with their expected values, while selected sets of tripartite net yielded a mean variation of 20% in the velocity and 9 degrees in the direction. Some significant deviation in the former case might be associated with variations in crustal structure. To detect local anomalies within the area investigated, the tripartite method may be useful when compared with the multipartite results.