Real-time Phase Correction of Acausal Seismic Data Using Allpass Filter

Abstract

Earthquake Observation Center (EOC), ERI is using Δ-Σ type AD converters with FIR digital filters at several stations of its seismic observation network. These filters produce acausal signals before the arrival of real seismic waves and this had been a problem in phase picking work. We constructed an allpass filter to minimize this acausal signal and introduced it to the automatic data processing system of EOC. The acausal signals are reduced significantly, although a few percent of them still remain in the worst case.＜論説