The Berill Fault of northern West Norway, documented here for the first time, is a N-S striking and moderately west dipping reverse fault with a throw of 2 to 4 metres. It is responsible for an escarpment, up to 6 metres in height, which can be followed across a prominent mountain ridge. The mapped escarpment, well displayed both in Quarternary sediments and bedrock, is approximately 2.5 km long. The bedrock of the hanging wall displays a number of clefts and fractures, as do overlying till and colluvium. In one part of the hanging wall, a 400 to 700 m large collapse field (slide block), has loosened and slid several tens of metres down slope. Since the fault affects Quaternary deposits of Younger Dryas age, movement must post -date the latter. Little modification of the faulted colluvial fans suggests that movement took place in the second half of the Holocene. In a regional perspective, the fault may be associated with a series of strike parallel lineaments in the bedrock. If these lineaments constitute segments of a neotectonic fault zone, the throw versus surface- rupture-length ratio becomes approximately 2 x 10-4, a realistic number compared to the high value of c. 1,2 x I 0-3 for the Berill Fault escarpment; the former number is more feasible when weighted against observations in other neotectonic regions. There is a higher frequency of rock avalanches near the Berill Fault and in the surrounding region, suggesting a link between rockslope failures and a major palaeoseismic event.
The Berill Fault - first evidence of neotectonic faulting in southern Norway