Reprosessing of refraction seismic data from Åknes, Stranda municipality, Møre og Romsdal

Abstract

In continuation to the various ground geophysics data collected at the unstable rock slope area at Åknes during the past 15 years, NVE commissioned GeoExpert AG from Switzerland to perform additional seismic investigations. These investigations were aimed at helping to determine the thickness of the overburden material and of the fractured bedrock. It was also of interest to image tectonic faulting within the bedrock. The seismic acquisition was distributed in three profiles with a total length of 2.7 km. During the processing stage, GeoExpert AG implemented WET (Wave Eikonal Traveltime) inversion on these three profiles using Rayfract software. Inversion utilized a starting model acquired by DeltatV method and a 50-iterations single run. Results were presented in a report delivered to NVE, together with the first break pickings of the raw data.NGU has done extensive research and testing on the use of Rayfract program and has obtained specific knowledge via modeling of synthetic data and real data processing as to the optimized parameters a user should pick when vertical structures such as fracture zones in bedrock are investigated. NVE has provided NGU with the refraction seismic data to undergo reprocessing in Rayfract using a different approach than GeoExpert AG. Eventually, results would be delivered to NVE in a format compatible with the Åknes 3D model built in PETREL software by Schlumberger.