Some Problems of Seismic Data Processing. Part 2. Data Processing Techniques for the Detection and Analysis of P and S Waves of Local Earthquakes

Abstract

The automated-analysis system for P and S waves of the local earthquakes obtained by the short-period system set up at the Amagase Crustal Movement Observatory are described. Firstly, as the basic knowledges necessary for automated analysis, the nature of noise, the frequency characteristics of P and S waves and the nature of particle motions are described. The system is composed of the determination of P onset, the determination of the directions of arrival and incidence of P waves, the determination of onsets of SH and SV waves and the computations of spectra of P, SH and SV waves. Onsets of P and S waves are determined by utilizing changes of both amplitude level and frequency between noise and signal. In the present method, it may be possible to determine the onset time of P wave with accuracy of ±0.05 sec for 90%, of local earthquakes with magnitude above 1.0. As for S wave, the onset time can be determined with accuracy of ±0.2 sec for about 90% of events of which the P onset time is defined.