The earthquake swarm at Herðubreiðartögl has now continued unabated for four days without a letup, during the first two days there were 4 earthquakes above M3 with the largest earthquake at M3.9 and by now the count of earthquakes has passed 1 000.
As such this is not the largest earthquake swarm to hit this volcano, but it is definitely a noteworthy earthquake swarm. Most of the earthquakes have been ranging between 8 and 5 kilometers depth with a few above and some below that depth.
After the larger earthquakes, especially the M3.9 the frequency of the earthquakes went down for a while before returning to earthquakes with a higher frequency. The baseline (bottom of the tremor graph) has continuously been slightly elevated with clear and visible tremor peaks during and after the two largest earthquakes.
The GPS-network does not give a lot of clues, probably due to the lack of a comprehensive GPS-system in the area. The nearest accessible GPS-stations gave a slight deflation dip before and during the onset of the earthquake swarm, probably related more to temporary crustal thinning as the tectonic plates started to suddenly move apart. As the swarm progress normal values returned.
Currently nothing is pointing towards an eruption starting, but the longer the earthquake swarm continues, the higher the risk becomes that a magmatic conduit forms, the trail of the earthquakes seems to indicate a stack building through the crust.
In this 3D-plot by DFM you will notice a slightly tilted wedge that has formed, the tilt of the wedge is probably due to the tectonic boundary being tilted in the same direction. Here is DFMs explanation of the plot:
“On this video, the quakes are shown according to magnitude. A scale is given on the plot. The left scale of the color bar shows the date, the right shows terrain elevation. The first part is a 360 ° rotation. The following parts show the quakes according to other orientations. The main activity seems to move to the west in a parallel plane. Look at 0’22. Data from IMO and NOAA, made on Gnu Octave 3.2.4 (Linux).“
The same trend is also quite visible on this plot by KarenZ showing longitude versus depth. The tilted wedge is here showing clearly.
CARL, DFM & KarenZ