Submarine landslide and associated polygonal faults development: a case study from offshore Norway

Abstract

Submarine slide and polygonal faults have been investigated using high-resolution 3D seismic data, over an area of 2,300 km2. The study area is located on the continental slope, offshore Norway. Submarine sliding covers more than half of the study area, and is part of the Storage slide. The slide developed a series of extensional faults at the upper extensional zone which is gradually changed to chaos seismic facies, interpreted as mass transport deposits. There is no clear evidence of compression/contractional zone downslope. Polygonal faults are highly developed in the KS1 and KS2 interval, corresponding to the Lower Miocene age. The fault has small offset of c. 10÷30 ms TWT, spacing ranges between c. 500 m and 1 km. Within this faulted interval, faults tend to develop intensively below the submarine sliding and much less out of that area. Bright amplitude anomalies are observed within the north south – elongated anticline structure. It has been mapped over an area of c. 135 km2 coinciding with the top anticline. Among those, there are two obvious negatives, bright amplitude reflectors which are relatively flat at 2670 ms TWT (flat spot 1) and 2800 ms TWT (flat spot 2). These flat spots are interpreted as hydrocarbon-brine contacts. Flat spot 2 is bounded by the structure contour but there is no evidence for the unconformable with the lithologic reflections from the trap boundary, thus this still needs to be confirmed by well data. Bright amplitude anomalies suggest the existence of hydrocarbon in the trap, in addition, the occurrence of polygonal faults is linked to seal potential covering the underneath petroleum reservoir, proving the great hydrocarbon potential in this area.