Ambient noise to estimate depth to basement: case studies from East Africa basins

Abstract

Passive recording of background noise have been successfully used to retrieve information about the large-scale structure of a sedimentary basin. Ambient noise can be used to retrieve velocity profiles in order to investigate the velocity structure and the depth of a sedimentary basin, in an unexplored area and/or when additional constraints on the basement depth may be needed for interpretation of active seismic or non-seismic data. We exploit techniques usually used in geotechnical or earthquake hazard/engineering studies. Surface wave dispersion analysis can be used to obtain 1D velocity-depth profiles below an array of seismic stations which record passive ambient noise. Analogously, the horizontal-to-vertical spectral ratio of both the surface and body waves can provide 1D velocity-depth profiles below standalone seismic stations which record passively ambient noise. We successfully applied this technique in Uganda, Ethiopia and Kenya, where field surveys were carried out to recover the depth to basement. With this work we present and discuss the results we obtained in those areas, the accuracy of which was validated by comparing with depth values obtained by other seismic and non-seismic datasets (independently acquired and processed).