An earthquake swarm started on June 30, 2015 at 21:00 UTC in the Reykjanes volcanic system at the southwest tip of the Reykjanes Peninsula, Iceland. Around 400 earthquakes have been detected by 14:00 UTC on July 1.
By July 3, the frequency of earthquakes has significantly decreased:
Earthquake swarm on the Reykjanes ridge by 13:50 UTC on Wednesday, July 1, 2015.
Earthquake swarm on the Reykjanes ridge by 08:10 UTC on Friday, July 3, 2015.
The strongest earthquake so far was a magnitude M5.0 at 02:25 UTC on July 1 and it was well felt on the peninsula and in the capital area, as well as on a ship around 10 km away from the epicenter. A few more events of magnitudes between M4 and M5 have been detected since the onset of the swarm, and are still under manual revision, the Icelandic Met Office reports.
Earthquake swarms in this area are common, and they don't usually lead to an eruption.
Image credit: IMO.
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 volcanic system (also known as the Reykjanes/Svartsengi volcanic system) is covered by Holocene lavas.
Photo by Oddur Sigurdsson, 1998 (Icelandic National Energy Authority).
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 at Reykjaneshryggur 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. (GVP)
Featured image credit: USGS.