Santorini Earthquake Update 21.3.25 – Is It Changing?
The Santorini earthquake swarm looked to have reached a lower plateau (which was still well above normal activity) but things might be changing. In this Santorini earthquake update we’ll look at the trends since the last update to see what might be a cause for concern.
Data Sources here
Santorini Earthquake Update – Cumulative Data
Using the data from the excellent website VolcanoDiscovery.com there has been a change in earthquake intensity if not the earthquake frequency.
Looking at the previous 90 days first.
I said we appeared to have reached a base level of activity which is still well above the norm. The area of the South Aegean is still receiving around 3-4 times as many earthquakes as would normally be expected. Energy released is still over double the normal level also.
Zooming in to the last 30 days.
The number of earthquakes as a whole has been decreasing but the percentage of the quakes that are M2 and above has been increasing. To put it another way, the number of M1 quakes, has been decreasing while the number of quakes M2 and above, has decreased less and now make up a much greater percentage of all the quakes. For example, around the 9th of March M1 quakes made up around 80% of all earthquakes but for the past 3 days they make up less than 20% of the quakes.
Tides
It could be argued that we have been seeing an uptick in activity at the start of the neap-tide/spring-tide cycles. Perhaps we will see more increased activity as we enter the next spring tide building phase which starts around the 25th of March.
GNSS Data – Ground Movement
I have been saying since the start of these updates that it would be nice to have one more station at the centre of the swarm. Unfortunately things have gone the other way and we have lost two stations around the centre of the swarm. We no longer have data from Amorgos island and Ios.
Santorini Ground Movement
Fortunately, we still have data coming from Santorini so let’s take a look at that.
East-West and North-South movement is still stable. But vertical movement has changed.
We went through a period of rapid rise at the start of the earthquakes and then a period of rapid fall in height. Now things seem to have changed again and we are seeing rapid rise again, perhaps even faster than we did at the start of the swarm.
Looking at the graph above, it looks like we have seen a land rise of around 15mm in 10 days. At the SNT1 station.
Seismograph – Anydros Island
The go-to seismograph and it’s showing that today we have seen three notable earthquakes in rapid succession and of increasing magnitude.
The spikes spike vertically indicating Anydros was right over or very close to the epicentres.
Epicentre Locations
Epicentres over the past 3 days are following the general trend ie to the west of the Anydros ridge. Nothing new to see here really.
Summary
It’s disappointing to see the loss of two ground movement stations, they gave very interesting data. But if things continue to quieten its not so much of an issue.
Activity still massively down from the peak activity period in mid February.
But earthquake activity is remaining stubbornly high vs the norm and the percentage of all quakes above M2 is a potential worry. It would be preferable to see frequency and intensity reduce together, unfortunately only frequency of small quakes is reducing.
Speculation
Some wild speculation
Is it possible that the drop in seismic activity in March was down to magma finding a pressure release along SW-NE running faults to the east of Anydros?
And is this the reason we saw land dropping in Santorini? Was this magma pressure under Santorini being released?
And are we now seeing these faults becoming full with magma and causing magma pressure to build again under Santorini? Is this the reason we are seeing fast land rise in Santorini currently?
Next Few Days
It will be interesting to see what happens around the 24th/25th of March. Will we see another uptick in activity as the spring tides start building?
The increasing ground level at SNT1 station on Santorini is also something that is worth keeping an eye on, especially if we see an uptick in earthquake activity.
