Santorini Quake Update – 24.2.25 – Volcano Possibility?
As of 12:06 GMT, tide activity is at it’s minimum, earthquake intensity and frequency have found a baseline (still above the norm) and epicentre area is widening. In this Santorini earthquake update we’ll look at the data from the last 24 hours and then dig into signs of volcanic activity. What are the chances of seeing lava seepage?
The Data
Intensity & Frequency Data – VolcanoDiscovery.com
The 7 day frequency data might be showing an uptick in earthquake frequency over the past 12 hours. Looking at the 24 hour chart that seems to be confirmed, frequency of quakes has increased from around 10 hours ago.
Epicentre Location & Movement
Looking at the NOA data for the past few days, the location of the epicentres are becoming more spread out. Usually it’s quite easy to say where the focus of the epicentres are but for the last 24 hours the epicentres are spread over a large area. But as usual, Anydros is in the middle of the general area. Perhaps we are seeing an evening out of activity in a north east line passing through Anydros.
Ground Movement (data source is around 3 days delayed)
Santorini’s speed of movement is staying constant. Downward movement could still be accelerating.
Ios, north and west movement maintaining same speed. Uplift may be turning into downward movement.
Amorgos, Southerly movement tuning into northerly movement. Westerly movement may have stopped. Uplift may be turning into downward movement.
If we look back at the image I used in the update for the 18th and see how these new movements fit in.
The big stress riser was Amorgos and Santorini moving towards each other. If we are seeing a long term trend where Amorgos starts moving north and stops moving west this could be relieving stress in the area between Amorgos and Sanotorini. This could potentially explain the reduction in seismic activity until now and also explain Amorgos being able to move down with Ios. Time will tell if this is what is actually happening.
Summary
From a volcanic point of view, I think the general trend towards downward movement my be a good thing indicating less pressure from below. But this is assuming we are not seeing uplift at Anydros which is absorbing magma from surrounding areas. Again, a shame we don’t have vertical movement data for Anydros.
Seismograph Comparison – Anydros
Lines on the 24th look to be smoother in general vs the 22nd, perhaps the frequency of spikes is around the same but their general amplitude is less. Wind is also low on Anydros today, wind may effect seismograph readings.
Volcano Activity – How Likely?
There has been some speculation of a volcanic eruption being possible be it Santorini itself, Kolumbo or perhaps a new vent somewhere else.
What are the general signs of an imminent volcanic eruption and how do they compare to what we are seeing around Santorini?
Geonet New Zealand has an article here which describes many of the potential signs.
While the Santorini earthquake swarm is giving us some evidence which may suggest volcanic activity ie the earthquakes and ground movement, I think those things on their own may not be enough. So far the highest uplift number I have seen hinted at, is an 80mm rise in Anydros island. I think something of a meter plus would be more conclusive of magma rising. But we do not have firm figures for Anydros.
And with regards to gasses being emitted, I can’t find any data sources so I don’t know if the chemical composition of the gases being emitted around the earthquake zone has been changing.
Earth Observation
The Euro-Med Seismological Centre is linking to this video. It’s in French but has subtitles. The video gives some great background information on the South Aegean.
The key things I took from the video.
Their assessment is the earthquake swarm is very unusual, perhaps unprecedented. They did give the example of a storm in another part of the world but that one only lasted one week. The key thing that they found unusual with this crisis is that there was no big shock to start.
Another aspect they highlighted as unusual is the moving of the centre of the earthquakes. We have been seeing the swarm move around in a group up and down the line between Santorini and Amorgos. They would expect slower movements and not jumping from one place to another.
And the last thing that caught my attention was a diagram they had of Anydros (below). It showed magma rising below the island with the island being on top of a constructive plate margin. Magma rising under Anydros and then flowing north west and south east.
Image from this study “Moment tensor inversion of microearthquakes along the Santorini-Amorgos zone: Tensile faulting and emerging volcanism in an extensional setting” https://www.sciencedirect.com/science/article/abs/pii/S0377027321002237
In the abstract to this study it says
In Anydros, most of the microearthquakes have positive non-DC components associated with the opening of cracks. It is possible that the extensional deformation and high pore fluid pressure in the area opens subvertical cracks that become pathways for upward migrating fluids. The upward migration of magmatic fluids in an extensional regime such as the Santorini-Amorgos zone can also be viewed as an indication of emerging volcanic activity in this area.
The earthquakes we are seeing around Anydros now, are they caused by cracks opening and fluid rising? The depth of earthquakes had been getting shallow until a few days ago. But on the other hand, activity has declined a lot.
Volanco Summary
I would say the amount of data available is not great. We have three GNSS stations around the swarm but not one on the island in the middle. And we do not have tilt meter data and we do not have monitoring of the Kolumbo volcano, at least that the public has access to. We can only go with what we know ie seismographs, GNSS data and feeds showing us earthquake magnitude and location. And from these data sources alone and their current trends, I don’t think it’s pointing towards volcanic eruption. Having said there is key data eg gas emissions, vertical movement Kolumbo/Anydros which we don’t have access to.
Santorini Quake Update 24.2.25 – Summary
A lot of data is pointing toward a calming of seismicity in the area. A possible exception is the earthquake frequency over the 24 hours. Tomorrow’s Santorini update will help us judge if this is just a blip.
If the tide is having any effect, now would be the quiet time. The next step up in the tide size will be tomorrow the 25th from around 1:00am onwards. High-tide is at 3:40am and this will go to quiet a low low-tide around 10:40am. If the tides are having an effect, there may be some increases in activity around these times
Further Reading
Geonet, Reading Seismographs
We regularly look at seismographs in these updates. Geonet has a great article looking at the patterns we get on seismographs and what they can be indicating.
There are some gems of information, for example, the sharper the spike ie the speed at which the graph ramps up and then decays, is an indicator with regards to how far away the earthquake occurred. The faster the the change in amplitude the closer the earthquake epicentre was to the the stations. Like wise a slow increase and slower decrease indicates a quake further away.
