A Method for Reading and Checking Phase Time in Auto-Processing System of Seismic Wave Data

Abstract

In automatic processing of seismic waves, it is important not only to make efforts to read the arrival times of P and S phases with better accuracy for each observation station but to check the validity of results of reading in order to reject the misread items automatically. With this point of view, a practical method for reading and checking the seismic data in automatic processing system was designed, making a comparison with data from the manual processing system of the Regional Center for Earthquake Prediction, Kyoto University. An outline of the method is summarized as follows; (1) Basic principle for reading the phase times Reading the arrival times is equivalent to dividing a section into two parts in time series. For the criterion of dividing, AIC (Akaike Information Criterion; defined as AIC=-2{maximum log, likelihood-number of free parameters of model}) was adopted. (2) Reading P times a) Use of low cut filter for elimination of microseisms. b) Use of normal distribution model and also autoregressive model for further improvements. (3) Checking P times a) Quantification of the degree of certainty of reading values. b) Check by means of apparent velocity between observation stations. c) Check by means of hypocenter calculation. (4) Reading S times a) Finding out a time window for S times when a hypocenter cannot be determined. b) Applying a bivariate normal distribution model to horizontal components if available. (5) Checking S times a) Use of P time-(S-P) time graph (the Wadachi diagram). (6) Hypocenter calculation a) Use of robust estimation. This method was tested for the seismic wave data observed by the network at the Regional Center, from 5th to 8th and from 17th to 19th December, 1984. As regards the differences between the respective P times read out manually and automatically, the relative •º ˜a60"N4OEŽ6"ú "-•\