Exploiting Ambient Seismic Noise - Spectral Broadening via Transfer Functions and Surface Wave Tomography

The exploitation of ambient seismic noise can be enhanced by a slight change in the standard processing scheme. The transfer function between the noise at two stations is calculated rather than the cross-correlation. The phase response is the same as for the cross-correlation, but the frequency response is broadened by eliminating the concentration on the microseismic peak. The transfer function approach has been tested on the vertical components of a deployment of 20 portable broad-band seismic stations within the TASMAL experiment located in central Australia. This deployment straddles the surface boundary between the Precambrian rocks of central and western Australia and the Phanerozoic belts in the east. The transfer function results clearly display packets of Rayleigh wave energy to 2000 km separation as in the cross-correlation method, but with enhanced low-frequency propagation from south to north from Southern Ocean noise sources. Ambient noise surface wave tomography is carried for the region using estimated Rayleigh group velocities for the period range from 5 sec to 15 sec. The results clearly indicate the transition between the Phanerozoic and Precambrian regions of Australia.