Lithological relevance of near-surface seismic velocity model

The objective of this work is twofold. One of the objectives is to assess the viability of the seismic refraction tomography method to delineate shallow subsurface information using first arrival traveltimes from standard reflection data. In a standard seismic reflection method it is difficult or impossible to obtain information in the very near surface depth range where surface waves or refracted waves overlap seismic reflections. To fill this lack of information arrival times of refracted waves – unwanted signals in the reflection survey – are analysed by the first arrival refraction tomography method with the aim to complement the stacked seismic section by a detailed velocity model for the near-surface area. 

The second objective is using high resolution seismic reflection P- and S-wave data: to adapt the P-wave survey parameters for high resolution information, to use shear waves instead of compressional waves for near-surface study, and to demonstrate the significance of the Vp to Vs ratio to characterize the near-surface lithology. Even though high-resolution P- and S-wave seismic reflection methods have been used for mapping the near-surface of the earth, there still remains need for further enrichment of these methods for accurate lithological discrimination. This work tries to arrive at an increased understanding of these methods with the aid of newly developed acquisition devices, consisting of a P- and S-wave landstreamer unit and P- and S-wave vibrators (Polom et al., 2007).