Basin Delineation with a 40-Hour Passive Seismic Record

Several geophysical methods exist to delineate the lower interface of a sedimentary basin. Most popularly employed are gravity and magnetic surveys and surface-wave inversion. While all three methods are successful overall in estimating an average basin depth, they fail to find a more detailed depth variation. As an alternative, we consider three passive seismic techniques, using especially body waves. We analyze 40 hours of data, recorded with 110 stations installed over the Abu Gharadig basin in Egypt. In an earlier study we found the frequency band of 0.09-1.0 Hz to be dominated by body waves. As a first method we apply body-wave seismic interferometry (SI). Using body-wave noise, we extract PP and SS reflections from the basin floor. We estimate the depth of the basin to be around 4.8 km. As a second technique we estimate the resonance spectra of the basin, using the horizontal-to-vertical (H/V) spectral ratio. Using surface-wave noise, we find an extremum that is probably related to the complete sedimentary package. Using this peak, we find a basin depth of 5.4 km. Using S-phase arrivals, we find two extrema in the H/V, which are probably related to the S-wave resonances of two distinct layers in the basin. As a third method we compute receiver functions (RFs). Based on the RFs, we can confirm the presence of a large interface in the upper crust, but we cannot well constrain its depth.