Regional landslide occurrences and possible post-glacial earthquake avtivity in northwest Western Norway: Phase A2; Penetration echo- sounding in 5 lakes in Sunnfjord and Nordfjord

Abstract

Fives lakes in Ørsta, Volda and Nordfjordeid communes are mapped using aKnudsen 320 M\/P 12 Khz echo-sounder. From the echo-sounding profiles thereare made maps for the lakes.The acoustic profiles are interpreted at NGU with regard to disturbances ofthe lake-sediments - like slides or tectonic shaking. Slides are registered inall lakes. In four of the lakes these slides may have been generated from steepslopes surrounding the lakes, while in the fifth - Storesetervatnet in Nord-fjordeid - the disturbances seen, have happened entirely within the lakesediments themselves. Based on the interpretation, we suggest a coring programcovering all five lakes to verify the genesis of these disturbances and to datethem. Adjustment to the program must be expected during coring when seismicdata and cores can be related.