The Crustal Structure From Teleseismic P-Wave Coda-I. Method

Abstract

The crustal structure beneath a broad-band station has a strong influence on the recorded body wave coda. Conversely, it is evident that crustal receiver effects can be employed to obtain information about the crustal structure at the receiver site. In this paper we present a method to estimate the crustal receiver response, and we invert the response to obtain a model of the most distinct features of the crustal structure beneath the station. The crustal receiver response of a station is determined from the P-wave coda of deep teleseisnic events by deconvolution with an empirically determined source wavelet. This source wavelet is assumed to incorporate source, attenutation and instrument effects. Responses obtained from clusters of events are stacked to enhance the signal-to-noise ratio of the data, and to obtain an estimate of the variance of the data. The crustal P- and S-velocity structure at the station is determined by non-linear waveform inversion of its crustal responses. An inversion strategy was developed to search efficiently for the global minimum in the misfit between data and synthetics. The inversion appears to be most sensitive to large velocity constrasts in the velocity structure which give rise to high-amplitude reflected and converted phases. The method is illustrated by the inversion of the crustal responses of NARS station NE05. It is shown that a thin layer (1.2 km) of unconsolidated sediments and a strong mid-crustal discontinuity at 11 km depth constitute the most prominent features of the crustal structure at this station. They cause an apparent delay of the first arrival on the radial component of the seismograms and produce high amplitude SV-multiples in the P-wave coda.