Active and Passive Seismic at the Unstable Rock Slide of Åknes (Norway)

The unstable rock slope of Åknes, Western Norway, has been recently identified as a potential threat for people and infrastructure in the inner Storfjord system. The unstable part has an estimated total volume of 30 to 40 million m3 based on recent geological and geophysical mapping. It is moving with a mean rate of about 4 cm/year, but with a rate as high as 15 cm/year in some parts. Such rock slide, when hitting the water in the fjord, could generate a flood wave (tsunami) with severe consequences, as experienced in the past by the local population. During the 2005 field campaign, three seismic measurements/installations were made: 1) a refraction seismic experiment in the center of the slope to map a potential sliding plane, 2) a temporary installation of 10 seismic mini-arrays of 9 channels each for passive monitoring of seismic events and noise measurements, and 3) a permanent installation of a smaller-scale seismic network for long-time monitoring of the site with real-time data access.