Identifying salt flanks using low-frequency ambient OBN surface-wave seismology

Abstract

Long-time seismic recordings are becoming more common with the increased use of ocean bottom nodes (OBN). These records allow for the use of ambient seismic wavefields at frequencies lower than the typical minimum values in activesource compressed air-gun surveys (i.e., sub-3 Hz). Crosscoherence-plus-stack processing on three-component geophone data allows for the extraction of low-frequency interferometric responses in virtual source gathers (VSGs). Using 40 days of continuous OBN recordings in a large-N array from a field experiment in the Gulf of Mexico, we show that sub-1.8 Hz surface-wave energy is both strongly coherent and exhibits identifiable spatially varying characteristics in the computed VSGs. In particular, after rotating the data components we find that radial-radial VSGs show the direct influence of salt bodies on surface-wave propagation. This suggests that low-frequency ambient surface-wave seismology could be important for estimating long-wavelength elastic material proprieties and identifying the lateral boundaries of salt bodies without any prior knowledge of the geology, both of which are important for accurate seismic imaging and inversion.