Iceland, Tjornes Fracture Zone

More Trembles in the Tjörnes Fracture Zone

Good Evening!

A large earthquake swarm started in Iceland in the Tjörnes Fracture Zone (TFZ) on 19 June 2020, still ongoing at the time of writing.  The Civil Protection Authority, Iceland, has declared a state of uncertainty; the TFZ is capable of producing large destructive earthquakes. 

The Icelandic Meteorological Office (IMO) has reported that over 9,000 earthquakes have been detected by their SIL earthquake monitoring system.  The swarm includes three earthquakes over 5.0: on 20/06/2020 a 5.6 and a 5.4, both 20 km north east of Siglufjörður; and, on 21/06/2020, a 5.8 30 km north, north east of Siglufjörður.  The day before the swarm started there was a small earthquake with a depth of 92.3 km, which is unusually deep for the area.

 IMO is in the process of manually confirming the earthquakes – a mammoth task!  We have updated our earthquake data set up to 28 June 2020 based on the earthquakes confirmed so far in order to take a look at the swarm.  In the area, 65.25°N, 21.5°W to 67.25°N, 15.0°W, 2,010 earthquakes from 1 June 2020 to 28 June 2020 were available to download.

Statistics so far

Fig 1: Summary of earthquakes for 1 June 2020 to 28 June 2020 by the author; © All rights reserved 2020.  A later download may give a more comprehensive picture.

Updated earthquake plots

Our plot for month 54 (1 June 2020 to 28 June 2020) shows that the swarm is occurring on the western end of the TFZ, near the junction of the Eyjafjarðaráll Rift and the Húsavík-Flatey Fault.

Fig 2.1:   Earthquakes 1 June 2020 to date in the Tjörnes Fracture Zone by the author. Green dots denote earthquakes less than 2.0M; yellow circles, quakes between 2.0M and 3.0M; red stars, quakes over 3M; orange triangles, volcanoes or volcanic features. Image on the right is a zoom in on the current earthquake swarm. © All rights reserved, 2020.
Fig 2.2:  Earthquakes 1 January 2016 to 28 June 2020 in the Tjörnes Fracture Zone by the author. Green dots denote earthquakes less than 2.0M; yellow circles, quakes between 2.0M and 3.0M; red stars, quakes over 3M; orange triangles, volcanoes or volcanic features. Red ellipse indicates the location of the current swarm. © All rights reserved, 2020.

So what is going on?

Prior to this swarm, most activity in our data set from 1 January 2016 had been on the Grímsey Oblique Rift and Húsavík-Flatey Fault, with a large swarm occurring to the north west of Grímsey in February 2018 (see our earlier post).  The current swarm appears to be the western end of the system catching up. 

This swarm is, however, relatively deep for oceanic crust.  Whether or not there is any associated volcanic or geothermal activity remains to be seen. 

The swarm on the Reykjanes Peninsular that started in late 2019 is still ongoing, albeit at a reduced rate. Are the two swarms linked? The obvious answer is yes – they are both on transform fault systems which accommodate the spreading from the Mid Atlantic Ridge as it crosses Iceland. But is there more to it? Possibly, the crust could be fracturing to accommodate other activity in Iceland – e.g. uplift from the mantle plume. If yes, we may see some more activity e.g. in the vicinity of the Vatnajökull Icecap in the next few months. But we’ll have to wait until the real experts opine.

For updates, please consult IMO.

The Armchair Volcanologist

29 June 2020.

Source for earthquake data: Icelandic Meteorological Office (IMO): https://en.vedur.is

Plots are the author’s own work.

© Copyright remains with the author; all rights reserved, 2020