Influence of frozen ground on seismic data
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The interest for subsurface exploration in the arctic is increasing. Thus knowledge about the effects of glaciers and permafrost on seismic data is needed. This thesis focuses on five questions that are relevant in this respect: How do the seismic velocities of the glacier influence seismic data? How does the glacier thickness affect the seismic data? How does the permafrost affect the seismic data? How do thickness variations of the permafrost layer affect the seismic data? How do saturation and freezing conditions in the near-surface sediments influence the seismic data? Various scenarios of glacier thickness, near-surface sediment saturation/freezing conditions and thickness variations of the near surface sediments were tested on seismic data acquired on two glaciers on Nathorst Land on Svalbard. Velocity models generated in NORSAR 2D/3D (NORSARa 2011; NORSARb 2011) and comprehensive processing using Geocluster (CGGVeritas 2008) resulted in seismic sections providing answers for the previous mentioned questions. The glacier thickness and velocities, in addition to the saturation of the near-surface sediments underneath the glacier may have a tremendous effect on the seismic data. Amplitude differences, travel-time shift and decreased continuity of the reflectors may occur if the velocity model is not in correspondence with the actual geology. When the sediments are 100% water saturated it appears as a low-velocity layer. This layer show the largest effect on the seismic data, compared to 100% ice filled sediments, if not included in the velocity model. This thesis concludes that the near-surface sediments are ≈ 100% frozen.