More than 13 000 earthquakes at Tjörnes Fracture Zone since June 19, Iceland

More than 13 000 earthquakes at Tjörnes Fracture Zone since June 19, Iceland

Earthquake swarm at the Tjörnes Fracture Zone continues, with more than 13 000 quakes detected since the swarm started on June 19, 2020. This is the largest earthquake swarm in the region recorded in the past 40 years.

According to the Icelandic Met Office (IMO) report on July 15, more than 13 000 earthquakes were detected since the swarm started, with three over M5. The largest was M5.8 on June 21, 34 km (21 miles) NNE of Siglufjörður. The two others were M5.4 and M5.6 on June 20, both located around 20 km (12.4 miles) NE of Siglufjörður.

"Seismic activity is still ongoing and there are chances of more earthquakes of this magnitude occurring in the area," IMO said.

Two weeks ago, Kristín Jónsdóttir, IMO's Earthquakes Hazards Officer, said this is the largest earthquake swarm in the Tjörnes Fracture Zone recorded in the past 40 years. At the time, the number of registered quakes was about 9 000.

"It is very difficult to say when the swarm will end," she said at the time. "The behavior is episodic, we record hundreds of earthquakes in a few hours and then it becomes quiet and all of a sudden it starts again. The last swarm in 2012 was ongoing for a few weeks. Let's hope we only have a few weeks to go."

IMO is still investigating the cause of earthquakes.

They are shallow so it could be that they are related to geothermal production in the region, as they are located near a geothermal power plant, Jónsdóttir said.

Geological summary

The offshore Tjörnes Fracture Zone is an oblique transform zone that separates the northern volcanic zone of Iceland from the Kolbeinsey Ridge, part of the Mid-Atlantic Ridge north of Iceland.

A submarine eruption was reported during 1867-1868 at the SE part of the fissure system off the northern coast of Iceland along the Manareyjar Ridge immediately north of Manareyjar Island. (GVP)

Featured image: Google, EMSC, TW

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