Multifold optimization of surface-wave methods for imaging of sharp lateral variations

Surface waves propagating parallel to the ground surface can be used to effectively delineate sharp lateral variations is the subsurface. Several surface-wave based methods are reported in literature for the identification of these anomalies. The computation of energy and energy decay exponent along the acquired seismic line can be adopted for location purposes. Beside locating the discontinuity, the evaluation of the attenuation coefficient and the autospectrum plot also provide an estimation of the related embedment depth. Finally, when the location of the anomaly is known, the transmitted-over-incident (T/I) spectral ratio technique can be used to further confirm the depth estimation. We compare these five methods to test their consistency and sensitivity to different anomaly shapes, embedment depths and lateral velocity contrasts. Using multifold data, implementations of energy, attenuation coefficient and autospectrum methods are proposed to image the investigated subsurface and to strengthen the effects of the discontinuity presence. Results are presented on a simple 2-D finite-element-method model, to enable direct comparison of the different methods and evaluate the related reliability and uncertainties in data interpretation.