Seismicity of Iceland

Abstract

Earthquakes in Iceland located teleseismically are mainly confined to a zone off the northern coast (the Tjörnes Fracture Zone), a narrow E-W zone in S-Iceland (including the Reykjanes Peninsula), and the eastern volcanic zone. Destructive historic earthquakes of magnitude up to 7 or 8 are known to have occurred in these zones, except in the eastern volcanic zone and the western part of the Reykjanes Peninsula. Local instrumental observations show that significant seismic activity occurs in other parts of the country. Smaller earthquakes and earthquake swarms occur frequently on the Reykjanes Peninsula and in the western and the eastern volcanic zones.

Detailed investigations of the seismicity of the Reykjanes Peninsula have been carried out since 1971. The mid-Atlantic plate boundary can be traced as a narrow zone of epicenters extending from the southwestern tip of the peninsula 40 km eastwards along the volcanic zone. Most of the earthquakes occur at 2 to 5 km depth and to date no earthquake has been located in seismic layer 4 (V_p =7.2 km/sec) lying at a depth of 8–9 km under the region. Focal mechanism solutions on the Reykjanes Peninsula consistently have a horizontal tensional axis with a NW trend. The compressionsl axis varies between the vertical and horizontal direction giving rise to both normal and strike-slip faulting.

Seismic activity in other parts of Iceland is not as well known in detail but strike-slip earthquakes seem to prevail in the zones of large earthquakes in S-Iceland and off the northern coast.

Volcanic eruptions are generally accompanied by earthquakes. During the Heimaey eruption in 1973 earthquakes were found at a depth of 20–30 km or well within the anomalous upper mantle.

Lamont-Doherty Geological Observatory contribution 2152.