An Automatic S-Phase Arrival Time Picker

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

Accurate automated onset time determination of S phases is important for the automatic real-time location of local, regional and teleseismic events. A new method is developed for automatic detection of S phases in single-component acceleration or broadband velocity records. The algorithm “S_PHASEP_ICKER” transforms the signal into a response domain of a single-degree-of-freedom (SDF) oscillator with viscous damping, and then tracks the rate of change of dissipated damping energy in order to pick S-wave phases. The SDF oscillator has a high damping ratio (60% of critical). At this damping level, the frequency response approaches the Butterworth “maximally flat” magnitude filter, and phase angles are preserved. The relative input energy imparted to the oscillator by the input signal is converted to elastic-strain energy and then dissipated by the damping element as damping energy. The damping energy yields a smooth envelope over time; it is zero in the beginning of the signal, zero or near zero before the P-phase arrival, and builds up rapidly with the S-wave. Since the damping energy function changes considerably at the onset of the emergent or impulsive S-wave arrival, it is used as a metric to track and pick the arrival time. The S_PHASEP_ICKER detects S-phase onset using the histogram method. The proposed algorithm is applied to a data set recorded by a dense regional seismic network in northern California. The picking algorithm is tested by comparing analysts’ S-phase readings, serving as reference picks, with the corresponding automatically derived S-wave arrival times.

Presenting Author: Erol Kalkan

Authors