Iceland's Tjörnes Fracture Zone Having Massive Quake Swarm

ICELAND

The Tjörnes Fracture Zone has recently reactivated with two separate quake swarms. The first, starting sometime in the last couple of weeks, had been occurring offshore near Grimsey Island. Yesterday, another swarm began taking place near the town of Kopasker, Öxarfjordur, NE Iceland, which has now generated a very long lasting swarm of quakes. Largest quake in this swarm so far had a magnitude of 4.2.

Statement from Iceland Meteorological Office

At the time of this writing, nearly 2000 events have now been recorded, with the swarm ongoing. There has been no determination whether these are purely tectonic quakes in nature, although there has also been no mention of volcanic tremor. This is of course, Iceland though, so anything can happen, as it is part of the Atlantic rifting zone. If there was ever anywhere most likely for a new volcano to pop up, it's Iceland. 

Screen grab from Iceland Meteorological Office detailing the ongoing quake sequence

Tectonic swarms like this are not uncommon around the world. In highly volcanic areas though, they are always worth watching. This particular area does not have any Holocene (past 10,000 years) eruptive centers, although some long lava flows from distant centers are present. There is a Pliocene-Pleistocene ridge to the NW of Kopasker, which appears to have formed subglacially.

New volcanoes can form in Iceland where there were previously no obvious volcanoes. The island of Surtsey was formed to the SW of Vestmannaeyjar in 1967 in a similar fracture zone. Vestmannaeyjar itself had a new volcano, Helgafell, form in 1973 with little warning, forcing the evacuation of residents, and prompting an ambitious (and ultimately successful) effort to slow and cool advancing lava with cold ocean water, to protect the harbor.

Until new data analysis emerges however, speculation is just speculation. It is likely that the swarm will eventually end, with no volcanic activity. But you never, never, discount that possibility in a place like Iceland until the facts are in. There is a concern that if the quake continues for a long period of time, it could generate up to a 6.0 magnitude quake.


****UPDATE 3/29/2019****

Statement from Iceland Meteorological Office:

Earthquake swarm in Öxarfjordur, NE-Iceland.

 The earthquake swarm in Öxarfjordur is ongoing, about 6 km SW of the town of Kópasker. The swarm began on last Saturday 23 of March.

Eight earthquakes of magnitude 3 or higher have been measured, the largest of which measured M4.2 on March 27th. Around 2200 earthquakes have been detected since the earthquake swarm started.

Today ( March 29th ) around 350 earthquakes have been detected, the largest one M2.7 at 07:18. During the last 24 hours the intensity has decreased a lot. The swarm is still ongoing. Monitoring of the earthquakes will be followed closely during the week-end.