Automated phase picker and source location algorithm for local distances using a single three-component seismic station

Abstract

Procedures for automatic location of local events by using single-site, three-component seismogram records are described. Epicentral distance is determined from the time difference between P- and S-onsets. For onset times estimates a special phase picker algorithm is introduced. Onset detection is accomplished by comparing short-term average with long-term average after multiplication of north, east and vertical components of recording. For epicentral distances up to 100 km, errors seldom exceed 5 km. The slowness vector, essentially the azimuth, is estimated independently by using the Christoffersson et al. “polarization” technique, although a- priori knowledge of the P-onset time gives the best results. Differences between “true” and observed azimuths are generally less than 12°. Practical examples are given by demonstrating the viability of the procedures for automated three-component seismogram analysis. The results obtained compare favourably with those achieved by a miniarray of three stations.