Seismic swarm near Grímsey: update 15:00, 19 February
At 05:38 UTC this morning an earthquake of magnitude M5.2 occurred 14 km ENE of Grímsey. It was felt widely in the Northern part of the country. Five more earthquakes with magnitude between 4-4.9 were detected over the past night. The earthquakes originate from the so-called Grímsey oblique rift zone in the northern Skálfandadjúp basin within the Tjörnes fracture zone. The earthquakes from this swarm originate at an average of around 10 km depth and the focal mechanism of the largest earthquake indicates normal faulting on a northerly striking fault.
The swarm began at the end of January, and almost continuous activity has been recorded since February 14th. As of the time of writing, the swarm is continuing. This seismic swarm is the largest in this area since April 2013 when the largest event had a magnitude M5.5.
Earthquakes are common in this area. Swarms of similar magnitude occurred for example in May and September 1969, during the Christmas period in 1980, in September 1988 and April 2013.
The Grímsey oblique rift zone hosts submarine volcanoes, so it is natural to wonder if this swarm is reflecting any volcanic activity. This seismic swarm is occurring within the submarine volcanic system called Nafir. The closest continuous GPS station located on Grímsey does not show any visible deformation that might indicate magmatic intrusion. This, together with the depth of the earthquakes, suggests that the current seismic activity is most likely related to tectonic processes at a divergent plate boundary, and not related to the movement or accumulation of magma.
Scientists at the Icelandic Meteorological Office and the Institute of Earth Sciences .
Figure: Red points show the locations of manually checked earthquakes since midnight, 19th February; the green ones show the locations of earthquakes since January 2018. Earthquakes with magnitude larger than 4 are shown as black stars and the white star indicates the location of the M5.2 earthquake. The beachball (black/white ball) shows its focal mechanism, normal faulting. Grey dots show seismicity over the period 1994-2017. The brown lines show the Húsavík fault on-land and the black arrows the direction of plate motion along the Húsavík-Flatey fault (HFF). Black triangles denote IMO's seismic stations.
