Seismic sequence at Eyjafjarðaráll.

Earthquake activity offshore North Iceland continues



The earthquake sequence which started last Saturday offshore North Iceland continues.

Yesterday morning (22. October) between 01:00 and 08.00, several earthquakes were detected slightly south-east of the main cluster where the M5.6 event occurred on Sunday morning. Yesterday's cluster is located slightly closer to the Húsavík Flatey Fault and strongest events were around M3.9 at 05:25 and 05:32.

Another M3.5 earthquake at 21:16 on 22. October and an earthquake M4.0 at 05:27 on 23. October were again located in the area of the M5.6 main shock further northwest. These earthquakes are purely tectonic and no signs of volcanic activity have been observed.

The analysis of the M5.6 main shock revealed a normal-faulting source mechanism (downwards movement), which indicates it to be linked to the extension of the Eyjafjarðaráll graben system and not directly to the Húsavík Flatey Fault, which shows horizontal strike-slip movements. It is neither possible to estimate how long this activity will be ongoing, nor can further earthquakes of M>4 be excluded.

This seismic sequence is located close to the western end of the Húsavík Flatey Fault and it can not be ruled out that it will effect the stress field of this fault. A rifting episode during the Krafla fires 1975-1984 caused a stress decrease on the Húsavík Flatey Fault and stress is accumulating on the fault system again since then. Deformation measurements (GPS) reveal that the Húsavík Flatey Fault has accumulated enough stress for an earthquake around M6.8 (Metzger o.fl., 2011).

The strongest earthquakes known on the fault were around M7, e.g. 1755 and 1872 in the Skjálfandi bay.

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