Enhancement of a thumper source far offset refracted phases using super virtual interferometry (SVI)

Abstract

Super-virtual interferometry (SVI) is a technique in which cross-correlation between consecutive receiver responses is carried out to obtain the virtual head-wave arrivals, which are then convolved with the initially recorded traces to get the super-virtual trace. SVI can be used to enhance the refracted phases by stacking all the arrivals acquired using multiple shots at one position, leading to an improved SNR by a factor of √n, where ‘n’ is the number of sources and receivers to generate the head-waves. In this study, we have generated few synthetic common shot gathers (CSGs) using forward modelling over a three-layer velocity–depth model with an embedded spherical anomaly, a complex five-layer velocity–depth model and the Marmousi model. Certain amount of noise is added on these gathers and then SVI technique is applied on the gathers which has resulted in an improved SNR of refracted phases at the far offset. We have further tested this technique on a field dataset acquired from the Kumaon Himalayan region using a 450 kg thumper as an energy source and 111 active channel remote acquisition unites (RAUs) with 5 Hz geophones as sensors. The resulting SVI gathers show the refracted arrivals more clearly. Continuity in the phases is increased after stacking and iterative SVI.