Seismic imaging of upper crustal basement faults in the Skagerrak Sea

Abstract

The continental upper crystalline crust appears almost non-reflective on many deep seismic reflection profiling sections. Typically, only the major faults and lithological boundaries are imaged, whereas smaller-scale faults are usually not identified. A deep seismic survey (0–16 s TWT) covering the Skagerrak Sea was undertaken in 1987. Although the northeastern part of the Skagerrak has only thin or no sediment cover, the data in the depth range 0–6 s TWT were reprocessed to commercial exploration standards. Close inspection of these high quality sections provides evidence of abundant, moderately steep dipping (20–50°) faults that can be traced to depths of 10–13 km. Fault geometry, which can be inferred at profile intersections, is in accordance with the general tectonic fabric observed on land and beneath the Skagerrak Sea. These areas were deformed during the Proterozoic Sveconorwegian orogeny and during the formation of the Permian Oslo Rift. Due to post-Permian erosion of the Skagerrak Sea proper, the relative age and movements of the basement faults could not be determined. This study shows that under favorable conditions, faults in the upper crystalline crust are mappable by seismic means. Such measurements have the potential for resolving variations in block geometry with depth and also recent seismotectonic movements.