Automatic seismogram analysis: Statistical phase picking and locating methods using one-station three-component data

Abstract

Seismic events at local and regional distances are located using data from the Vaasa (VAF 63.0 °N, 22.7 °E) three-component station in western Finland. The analysis is performed off-line after pseudo on-line detections. The continuous data are first recorded on long disk loops. These loops can cover 10 days of data. The events are picked using Murdock-Hutt detector and after that they are recorded as separate files for further analysis. The direction of approach, which estimates the polarization state of the signal, is determined by the well-established maximum likelihood method. The difference between the arrival times of P and S phases is used to estimate the distance. Phases observed up to 185 km distance from the source are assumed to be Pg and Sg and beyond that Pn and Sn. The onset times of the phases are estimated by a statistical data-adaptive method. The onsets calculated in this way are very accurate when compared with earlier methods like STA/LTA. Epicenter locations are similar to those of FINSA network reported in Helsinki bulletins. The median of the location differences is about 50 km.