IMO reported that a M 5.6 earthquake was recorded at 1343 on 20 October beneath Nupshlidarhals, a hill about 5 km W of the geothermal area in Seltun. This was the largest earthquake since 2003 recorded in the Reykjanes peninsula. There were about 1,700 aftershocks recorded in the following 24-hour period. IMO received reports of rockfalls in steep areas and increased gas odors in the vicinity of Graenavatn at Nupshlidarhals. Four landslides were noted near the epicenter; some existing ground cracks were displaced and new cracks had formed in Krysuvikurbjarg. On 26 October IMO stated that seismic activity had significantly decreased in recent days; about 180 earthquakes below M 2.2 had been detected during the previous two days.

Geological Summary. The Reykjanes volcanic system at the SW tip of the Reykjanes Peninsula, where the Mid-Atlantic Ridge rises above sea level, comprises a broad area of postglacial basaltic crater rows and small shield volcanoes. The submarine Reykjaneshryggur volcanic system is contiguous with and is considered part of the Reykjanes volcanic system, which is the westernmost of a series of four closely-spaced en-echelon fissure systems that extend diagonally across the Reykjanes Peninsula. Most of the subaerial part of the system (also known as the Reykjanes/Svartsengi volcanic system) is covered by Holocene lavas. Subaerial eruptions have occurred in historical time during the 13th century at several locations on the NE-SW-trending fissure system, and numerous submarine eruptions dating back to the 12th century have been observed during historical time, some of which have formed ephemeral islands. Basaltic rocks of probable Holocene age have been recovered during dredging operations, and tephra deposits from earlier Holocene eruptions are preserved on the nearby Reykjanes Peninsula.

Source: Icelandic Meteorological Office (IMO)