Due to this article being so graphics heavy, I had to break it up into two parts, with the second part coming tomorrow evening.
It is somewhat ironic that my brain is operating mainly in a graphical mode, and that I think in visualisations and graphic models, whereas at the same time I am about as artistic as a four-year old doodling stickmen using a dead carp as a pen.
This has led me to rely on some truly talented people producing the visuals through the years. Among them are the talented Andreij Fliis of Severe Weather Europe-fame. Grindavik brought him out from his weathering, and he delivered some truly stupendous plots for me to expound upon.
Albert was also the sounding board for this, and he did the heavy mathematical lifting in producing the volumes and flow rates mentioned tomorrow.
What came out in these extremely exact plots is that from a geologic, seismologic, volcanological and tectonic standpoint a true Cherenkov coloured swan is happening.
For those not familiar with Cherenkov radiation, it is blue incandescent light caused by neutrons radiated from a reactor core through water and these fast neutrons are travelling faster than light through the water. There are also other instances where Cherenkov radiation can occur. And if you believe that nothing can go faster than the light in water, well then you can go ahead and argue with Einstein.
What I am trying to say with this analogy is that what we are seeing is exceedingly rare, a once in a lifetime opportunity to see a geologic process. After all, you rarely see swans that glow blue in the dark.
The MAR & The Dyke
The regular readers in here know that I always harp on about how important it is to only use earthquakes above a certain size that are appropriate for the area. The reason is that it is easier to manually correct a larger and more distinct earthquake compared to a smaller one, this makes the larger ones more exactly placed on the map.
In Reykjanes 2Mw is enough to get specific EW/NS-locationing, but you need 2.5Mw to get a good depth-location.
I also always harp on the necessity of only using manually corrected earthquakes when making assessments.
If one does not follow these two rules you will be led astray, or be overwhelmed by what you see. I guess that most readers have seen the hopelessly messy standard plot put out be the IMO that is containing uncorrected earthquakes of all sizes, and that is including “ghost earthquakes” that the automatic system is picking up from reflections.
During a large seismic crisis this otherwise nice map is rendered useless. Now, put that messy map in your head and compare them to the laser-sharp plots by Andreij below.
They are in turn, all corrected earthquakes, 2Mw and above, 3Mw and above, and finally Mw4 and above. In all of them the data timeframe is June to October 15. Note how the details emerge.
What we are seeing is what I believe to be the clearest locationing of the Reykjanes part of the Mid-Atlantic Ridge (MAR) to date. It was always a fairly amorphous and badly located entity. It was not until this event that we got the data needed to pinpoint this part more accurately.
One of the reasons for it being sort of shy is that it is predominantly strike-slip faulting, with a minute part of spreading. Whereas Iceland is rifting apart at a rate of 2.8cm per year, this part is moving along each other instead.
Rifting is comparatively silent compared to having two tectonic plates rub against each other in a noisy manner.
At many points a strike-slip fault will lock against outcrops building up a lot of strain. The total pent-up strain in Reykjanes is above Mw7, and in this section it is above Mw6.
This is why the bulk of the Mw4 earthquakes are along the MAR section in these plots, and not along the dyke/Graben formation.
It is also likely that this area is pre-disposed to Graben-formation and as such already weakened.
After all, normally a Graben/dyke event of this size would have come with an Mw6 earthquake along the fault.
It obviously also rifted apart and those are as mentioned a bit “quieter” compared to other modes of faulting.
We also see the Sill that was produced during the intrusion of magma, and we clearly see the dyke as it went up North of the MAR and down south into the Atlantic.
Now it is time to go deep.
Into the Abyss
“Deeper and deeper, harder and harder”
General Kyrylo Budanov
This famous expression lends itself to geology as well. The deeper an earthquake is, the harder it is to correctly locate the depth.
Here we have two depth plots by Andreij showing the shape of what is happening at depth, both are filtered with a cutoff at Mw2.
The first image is showing the depth of the Sill and the dyke as it passes by Grindavik. From this we get a good visualisation of the depth and size of the sill. We also get a feeling of how the dyke dips downwards as it enters under the sea in a slightly unusual fashion.
The latter indicate that there’s a difference in the geology of the plate as it enters into the ocean, it is far harder and less easy to fracture nearer to the surface. One probable reason is that no previous eruptive period has fissured this far out.
On the second image we can also see that the dyke dips down at the northern end. This is logical since there are comparatively fewer eruptions North of the MAR, and there should be less faulting in this direction and a far harder overburden to crack open.
In the middle you see a few deep earthquakes that belong to the deep feeder from the MOHO. Above that you see a region of more shallow earthquakes making the dyke to all points and purposes look like a funnel. This shallow area is where an eruption is most likely to happen.
There is also a curious aseismic area in the middle of the left plot on the second image at a depth of between 5 and 3.5km. At a central volcano I would have assumed that this is the location of the magma reservoir, but supposedly there is none here.
It could though be where the magma ended up in the 2019-2020 intrusive period. Let us just say that unexpected aseismicity normally indicate a very hot and ductile area and I will leave it up to you to draw your own conclusions about the reservoir, and if you are a young strapping Ph.D.-student, please feel free to include us in your references if you write a paper about it.
I will here leave things hanging until tomorrow, then I will deal with temporal evolvement, and draw my conclusions.
CARL REHNBERG, ANDREIJ FLIIS & ALBERT