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Geology

Scientists unsure what's going around Grímsey: Massive earthquake swarm might have peaked

By Staff

  • A quiet fishing village Lífe in Grímsey revolves around the sea. Photo/Pjetur

The intense earthquake swarm at Grímsey island appears to have slowed down somewhat today. The swarm, which began on Wednesday, has continued unintirrepted, but the power of the quakes has dropped since early morning. Only two magnitude 3+ quakes have been detected since 8:35 today, Monday morning.

Earth has been shaking since February 14

grimsey_map.jpg

Grimsey A tiny island off the north coast of Iceland. Photo/Google Maps

The current swarm, which began on Wednesday February 14, is only the latest in an episode of intense seismic activity which began on January 28. The quakes peaked yesterday evening and early morning, with a total of 64 powerful 3+ earthquakes, including 8 quakes which were 4 and above on the Richter scale. The largest quake to day, a massive 5.2 magnitude earthquake, hit at 5:38 this morning.

Read more: Intense earthquakes in Grímsey highly unusual. Volcanic eruption unlikely

The Icelandic Meteorological Office lists several recent seismic episodes which bear some resemblance to the current episode. In April 2013 a powerful earthquake swarm followed a large 5.5 magnitude quake. Similar swarms have been detected in May and September 1969, late December 1980 and in September 1988.

Did the swarm already peak?
Scientists at the Icelandic Meteorological Office say it is difficult to predict what will happen next. Gunnar Guðmundsson, a geophysicist at the IMO told the National Broadcasting Service RÚV that the 5.2 magnitude quake could have been the "main quake" of the seismic episode, signaling the peaking of the activity. If that is the case we can expect the activity to slow down and things return to normal for the 90 inhabitants of Grímsey.

Read more: Grímsey residents refuse to be rattled by constant quakes: Kids' birthday party turned into geology lesson

Gunnar told RÚV that while the current episode is somewhat unique it has parallels in previous episodes of seismic activity in the area.

"We know of earthquake swarms which have hit the area. These have included quakes which are around 5 on the Richter scale. For example in September 1988, when we saw an intense swarm which lasted 10 days. This swarm included several quakes which were 5 or above."

A more powerful quake or an eruption looming?
However, Gunnar admits that while he things the most likely next step will be that the swarm begins to slow down, there are also other examples from history which might be relevant. This includes a 1910 earthquake event south of Grímsey when a 7+ magnitude quake hit the area. "We can't rule out more powerful quakes, and it's very difficult to predict those quakes".

Read more: Why the constant earthquakes? Iceland is slowly being torn apart

A volcanic eruption is also a distinct possibility. All the quakes have been in the Tjörnes fracture zone, which is known for high levels of geothermal and seismic activity. A volcanic system called Nafir is located beneath the fracture zone. The system is known to have been active since Iceland was settled, but it has not produced any known major eruptions in the past 1,000 years. 

Gunnar told RÚV that there are no signs of magma movements associated with the earthquakes. "We haven't seen anything which suggests magma movements. The quakes seem to be caused by tectonic movements, but it is also likely that there are some fluids involved, perhaps also gases, that these are being pushed to the surface. 

Grímsey earthquakes 19.feb.18

Grímsey earthquakes Black triangles show the location of seismic montiroring stations. Grímsey island is at the center of the map. The image shows the location of all earthquakes measured in 1994-2017 (gray dots). The gray dots outline the layout of the fracture zones off the north coast of Iceland. The black arrows, marked HFF show the directions of the movement of the crust at the Húsavíkur-Flateyjarmisgengið, which is the southernmost part of the Tjörnes fracture zone. The red dots show the location of quakes in the current seismic episode, black stars are quakes larger than 4 and the white star shows the epicenter of the 5.2 magnitude quake. The current seismic episode is centered in Skjálfandadjúp, a submarine rift valley, along Grímseyjarbrotabelti, which is part of the Tjörnes fracture zone. Photo/IMO

 

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