On-going post-glacial reverse faulting in Scandinavia, field evidence from Finnmark, northern Norway
Abstract
Deglaciation in Scandinavia was followed by a dramatic seismic burst as evidenced by the numerous post-glacial fault scarps documented in Lapland. The post-glacial faults usually show reverse slip and trend NE-SW. This climax of earthquake activity is believed to have been triggered by the sudden removal of the glacial load and Scandinavia is considered tectonically quiet present-day. Roberts (1991, 2000) observed in Finnmark, northern Norway, various boreholes offset by reverse faults with few cm of displacement. It was unclear if these reverse faults represented active faulting or stress-relief features. Following Roberts, a field work campaign was conducted in July 2002. The purpose was to examine boreholes along road-sections and in quarries of Finnmark. About 20 drill-hole reverse offsets ranging from a few mm up to 14 cm were measured in western and central Finnmark. The azimuth of the associated slip vectors was found to be consistent towards the E-SE. In the Ifjord area, central Finnmark, some of the fault planes offsetting boreholes show continuous mud-smears of ~10 cm long. In the same area, additional observations include two reverse faults with 2 cm of offset each. The first one disrupts a wall road worked out in 1986. The second reverse fault disrupts a natural scarp presumably of glacial origin. In direct connection with these observations numerous rock blocks are seen to disrupt the ground surface. The most impressive ones are more than 1 m high. The blocks are bounded by pre-existing fractures and cleavage and appear to be displaced to the SE as well. These "standing-stones" are interpreted as small-scale tectonic push-ups. Field observations argue for active reverse faulting in Finnmark. The documented fault motions agree with a regional NW-SE compression induced by the North Atlantic ridge-push.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....3980P