Detecting the top and base subsea permafrost from 2D seismic reflection data in shallow marine settings is a non‐trivial task due to the occurrence of strong free surface multiples. The potential to accurately detect permafrost layers on conventional 2D seismic reflection data is assessed through viscoelastic modelling. Reflection imaging of permafrost layers is examined through the evaluation of specific characteristics of the subsurface, acquisition parameters and their impact. Results show that limitations are related to the principles of the method, the intrinsic nature of the permafrost layers, and the acquisition geometry. The biggest challenge is the occurrence of free surface multiples that overprint the base permafrost reflection, with the worst‐case scenario the case of a thin layer of ice‐bonded sand. Wedge models suggest that if the base permafrost is dipping, it would intersect internal and free surface multiples of the seafloor and the top permafrost and be detected. Also, the amplitude ratio of the base permafrost reflection and the multiples decreases with the increasing thickness of permafrost. Therefore, the crosscutting relationship between the reflection at base permafrost reflection and the multiples might not be enough to detect the base permafrost for thicker permafrost layers. Finally, the experiment results show that, for partially ice‐bonded layers, the attenuation combined with the low reflectivity of the basal interface limits the likelihood to resolve the base permafrost, especially for thick permafrost layers.
Monitoring the change in permafrost conditions and distribution is crucial for forecasting global warming. As seismic velocities increase with ice content, marine seismic surveys can map the top of ice-bearing subsea permafrost on a large scale. However, conventional seismic methods cannot fully map internal velocity variations linked to changes in ice content because the removal of guided waves and multiples is challenging for reflection processing. Nevertheless, these arrivals carry information about velocity variations with depth. We investigate if a joint analysis of various wave arrivals could provide information about velocity variations within permafrost and accurately estimate the permafrost thickness. Through a sensitivity analysis, we estimate the feasibility of using different wave arrivals, such as reflections, refractions, multiples, and guided waves, to better characterize permafrost conditions. We show that guided waves are sensitive to velocity variations within permafrost and can detect the depth of the permafrosts base under certain geological conditions. Then, we combine the analysis of all seismic arrivals to derive a subsurface permafrost model for a seismic line collected in the Beaufort Sea. The joint analysis reveals the transitions in depth between ice-bonded and partially ice-bonded permafrost and offers a crude estimate of permafrost thickness.
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