Waveform Station Anomaly. Definition and Example for J-Array Stations.

Abstract

We introduce the waveform station anomaly (WSA) of teleseismic P-waves to investigate the crustal and uppermost mantle structure beneath stations, which is a natural extension of relative travel-time and amplitude anomalies. WSA is defined as the observed waveform deconvolved by the average waveform of stations in an array. Since source time function and mantle response are almost identical across the array and cancelled out by the deconvolution, WSA approximately represents the effect of the receiver structure and the instruments peculiar to each station. The procedure was applied to short-period teleseismic waveforms recorded by the J-Array, a large-aperture and short-period seismic array covering the entire Japanese Islands. WSA was consistently determined for a cluster of deep events in the Tonga-Fiji region, with almost identical back azimuth and incidence angle. Especially, near-station reverberations inherent to each station were effectively extracted by the deconvolution. However, relative travel-time residuals showed a slight scatter due to the unequal number of stations used for analysis of each event. Despite the small number of events used in this study, WSA clearly changes with the arrival direction, which indicates that we have to consider a laterally heterogeneous structure beneath the Japanese Islands to explain the observed WSA.