Source azimuth determination of ambient seismic noise in the Eastern Cape Karoo, South Africa

Abstract

Ambient seismic noise correlation is increasingly used as a tool to image the subsurface at local and global scale. Cross-correlating ambient noise records relies heavily on the temporal and spatial destribution of the ambient noise. Specifically, the ambient seismic noise of the earth, is almost never homogenous at any moment in time and azimuth, therefore it is important to characterize the source direction, since this could lead to bias in seismic velocities in tomography application. In this study, the cross-correlations between pairs of stations deployed in the Eastern Cape Karoo of South Africa are used to determine the approximate source azimuth of the ambient seismic noise. This is done by measuring normalized amplitudes of the Rayleigh wave arrivals and station-station azimuths for positive and negative correlation times. Analysis of the multiple cross-correlation pairs and resulting azimuthal distribution show that most of the Eastern Cape Karoo ambient noise is generated near the coast of South Africa.