Seismic sequence at Eyjafjarðaráll in October 2012.

Earthquake sequence offshore North Iceland


An earthquake sequence at the southern end of the Eyjafjarðaráll graben has been ongoing since Saturday 20 October. The source region of the events is approximately 20 km north-northeast of Siglufjörður and slightly southwest of the seismic sequence observed last September.

The strongest earthquakes occurred on early Sunday morning, 21 October, at 00:10 (M4.8) and 01:25 (M5.6). The stronger event came first up as M5.2 but has been revised to M5.6 by including seismic data from mainland Europe, Greenland and Northern America. It was widely felt in North Iceland, from Ísafjörður to Seyðisfjörður, as well as in higher houses in the capital region.

Hundreds of aftershocks have been detected, some of them M>4. Although the sequence is presently calming down, events of M>3 still occur occasionally. It is further impossible to predict how long the sequence will continue. Earthquakes of around M4 or even stronger may have to be expected.

Eyjafjarðaráll is a graben system between the Húsavík Flatey Fault and the southern end of Kolbeinsey ridge. Seismicity in this area is quite common, however the activity observed during the weekend is above the average. The M5.6 event was the strongest earthquake offshore North Iceland since the 1976 earthquake close to Kópasker. The present activity is purely tectonic.

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