Converted-wave analysis


During seismic exploration, P-waves penetrate down into the earth. When a P-wave hits an interface, it can reflect upwards as an S-wave. Other P-wave to S-wave conversions can occur, but the down-up conversion is the primary focus. Unlike P-waves, converted shear waves are largely unaffected by fluids. By analyzing the original and converted waves, seismologists obtain additional subsurface information, especially due to differential velocity, asymmetry in the waves' angles of incidence and reflection and amplitude variations.
As opposed to analysis of P-wave to P-wave reflection, c-wave analysis is more complex. C-wave analysis requires at least three times as many measurement channels per station. Variations in reflection depths can cause significant analytic problems. Gathering, mapping, and binning c-wave data is also more difficult than P-P data. However, c-wave analysis can provide additional information needed to create a three-dimensional depth image of rock type, structure, and saturant. For example, changes in VS with respect to VP suggest changing lithology and pore geometry.