With an earthquake of 5.5-5.7 R we will have landslides and with 6 R a small tsunami - The faults that gave the great earthquake of 1956 cannot be activated - The government has prepared for the worst case scenario

Scientists recommend to wait at least two more weeks to be able to predict with greater certainty the evolution of the phenomenon in Santorini. From the first moment of the earthquake activity three scenarios were formed for what could happen, with the worst one, that is, a 6 magnitude earthquake and the tremors recorded being the pre-earthquake sequence, now weakening and gathering the lowest probability.

The scientists, with Athanasios Ganas, director of Research at the Geodynamic Institute of Athens among the first, estimated that the most likely version is that it is a series of earthquakes. As he told protothema.gr, the seismic activity has now shifted to Anydro and does not seem to be progressing any further. As he points out, the seismic energy released up to Friday by the 1,291 earthquakes of the Santorini series is equivalent to a 6 Richter earthquake!

According to Mr Gunnas, it is good that there were fewer tremors recorded in the 4-5 Richter range: on Friday by afternoon there had been 6 tremors between 4.1- 4.8 Richter, while on Thursday there were 28 earthquakes between 4.0- 4.6 Richter. “we need to wait for a few weeks before we can talk about a de-escalation,” he says, noting that the measures taken are about the precautions to be taken for the worst case scenario.

The earthquakes, however, continue in the Cyclades. After a relative calm, a barrage of seismic tremors occurred early Sunday night with the Geodynamic Institute recording a 5.0 Richter at 21:05 with the epicentre in the sea area 21 km SW of Arkesini Amorgos at a distance of 226 km SE of Athens. The vibration was also felt in Athens. Earlier, at 20:53, there was a 4.7 Richter vibration centered in the sea area 21km SW of Arkesini Amorgos, at a distance of 230 km SE of Athens.

The three scenarios

OASP chairman and geology professor Ethymios Lekkas, describing the three scenarios for what could happen, noted that in the first the phenomenon would continue until it comes full circle, with seismic activity of the same magnitude. Small magnitude tremors that is. The second is to have a relief “with a 5.5- 5.7 magnitude earthquake that will not cause damage”. And the third, to which he gives the lowest probability, “to have a maximum earthquake of 6 Richter, whereas at the first meeting (of the Seismic and Volcanic Risk Committee) we were talking about a maximum earthquake of 6.2 Richter.”

Activity in the Santorini area did not begin last Friday. As Mr Ganas says, we are talking about a new earthquake volcanic crisis that started last August, but was not noticed by residents since it was manifested by micro-earthquakes.

Both he and the academic, Professor of Natural Disasters, Kostas Synolakis, refer to the earthquake-volcanic crisis that had started inside the Caldera of Santorini on February 12, 2011 and had ended on 3 May of 2012. “The seismic series then had a long duration and was inside the Caldera,” Mr. Synolakis said, adding that “now the seismic activity is more intense outside the Caldera as well.

The most likely scenario is that we will have the serpentine effect, but it is too early to talk about a release – we will assess it with more certainty when the tremors are below 4 Richter. It should be noted that in Anydro where the seismic activity is located we have a cluster of faults, and it is very important that the State has prepared for the worst case scenario, but citizens should be calm, life must go on.”

“We are increasingly optimistic,” said Aristotle University of Thessaloniki geology professor Kostas Papazachos, who sees the scenario of a stronger tremor becoming increasingly unlikely. As he explained, “we are increasingly optimistic because we see the part of the fault, which now has clearer characteristics after the densification of the recording network, starting to “fill in”, that is, the chances are getting further and further away, the scenario of a stronger tremor is becoming more and more unlikely.”

What is the bad scenario

However, the bad scenario that wants a strong or, more correctly, stronger tremor than those recorded so far and not exceeding 5 Richter has not been taken off the “map”. Scientists say that if the phenomenon erupts with an earthquake of about 5.5 to 5.7 on the Richter scale, it is very difficult to cause damage to buildings in Santorini and Amorgos – which are closer to the epicenter – and endanger lives.

OASP president Ethymios Lekkas appeared confident that a tremor of this magnitude would cause no damage, while Kostas Papazachos also noted that even a stronger tremor would have a relatively more limited impact on the island. “The scenarios that we have ‘run’ do not indicate anything significant,” he said.

The very bad scenario is the one everyone is dismissing. Although the vast majority of scientists agree that this scenario is becoming increasingly remote, Kostas Papazachos’ statement that “nothing can rule out nature and surprises” is typical.

Based on this scenario, which is the most “useful” in the marketing of those who bet on terror, the activity could be triggered by a very large earthquake, of magnitude above 6.5 or even above 7, or even by the eruption of the volcano, events that would cause tsunamis in addition to catastrophes.

These frightening scenarios are so worrying people that in neighbouring Turkey, seismologist Ramadan Demirtas, fed up with the thousands of questions from citizens whom he was unable to reassure, was forced to put up a post on X, stressing that if there was evidence of an imminent volcanic eruption in Santorini, the scientific community would have been informed, “since if this happens, we will all go to heaven“.

However, the bad history of the area, which in modern history, in 1956, has given as many as 7.8 chills, makes scientists consider all possibilities. OASP chairman Efthimios Lekkas says it is a low probability that we could have a maximum 6-magnitude earthquake.

He even greatly downgrades the estimate of the maximum magnitude that the fault system exhibiting the current activity, which was previously estimated at 6.2 Richter. Kostas Synolakis, however, points out that the seismic activity is far from the faults that gave the 1956 earthquake, and further notes that it is too short an interval between then and now for the same fault to give a large earthquake.

Commenting on the predictions and rumors of a volcano eruption, Evi Nomikos, Professor of Geological Oceanography Evi Nomikos, asks “to focus on seismic activity. We are talking about intense seismic activity on the seabed of Santorini next to the underwater volcano of Kolumbo”. She, who has been studying the volcanic zone of Santorini for years, also asked members of the scientific community to be careful in their statements, especially about reports that an eruption of Kolumbo is expected. “Let them come and show us the data that supports that,” he said.

When will it end?

If there is anything that torments the people of Santorini more than the fear of an earthquake, it is the endless wait for the phenomenon to end. The question, then, is almost self-evident: until when do we have to wait for this swarm of earthquakes to stop and life to return to normal or, in any case, to do what has to be done?

And here again scientists are very careful in what they say by observing the evolution of the phenomenon. A glimmer of optimism, however, seems to be beginning to emerge. For example, Kostas Papazachos says that “every day, I think, we are going slightly for the better, but our disengagement will not be so fast. We’re going to have to give the residents here a little bit of patience, maybe next week. I hope things are getting better.”

The director of the Geodynamic Institute, Vassilis Karastathis, seems to agree with the conclusion of the EKPA report that sees the phenomenon as having stabilized. This, according to the seismologist, is a good thing, as it may lead to the “ending of the alert”. “We are in a phase of stability,” Karastathis says, adding that “from one moment to the next we may go into a decay”. However, when asked about this, the OASP chairman replies that “it is undetermined when the de-escalation will come“.

The Rifts

These days, the scientists’ offices are abuzz. They are recording the data provided by the constant tremors that they “place” on the mapped faults and volcanoes under which the magma flows. In the earthquake-volcanic crisis of 2011-12, 12.6 million cubic meters of magma had entered the magma chamber. According to preliminary data for the crisis that began last August, 5 million cubic meters of magma have been injected.

The answer as to the behavior of the earth in the Aegean at this time, however, is provided by the fault system from which this swarm of earthquakes originated.

As explained by Professor of Geological Oceanography Evi Nomiko, who participated in the official briefing under Kyriakos Mitsotakis at noon on Wednesday, “the whole area next to the Anydros fault, which we call the tectonic horn around Anydros, has been active.”

This very horn is an area of small faults that give off small earthquakes of small sizes and, according to scientists’ data, lack the potential to activate larger ones and thus cause a domino effect with a larger earthquake.

Ms. Legal said that “this is an area that is fragmented by many smaller zones and that is why we have many small earthquakes: because each time a different area is activated.”

This area is located near the submarine volcano of Colombo. It is the small uninhabited island of the southeastern Cyclades called Anydros or Amorgopoula. It is located approximately in the center of the sea area enclosed by the islands of Santorini, Amorgos, Ios, Anafi and Astypalaia. It is 10 nautical miles from Amorgos and about 15 from Santorini. Administratively it belongs to the community of Arkesini of the Municipality of Amorgos, while before 2011 it belonged to the local department of Thira of the Municipality of Thira. Amorgopoula has been a privately owned island since 1860. Its area is about 1,200 acres.

David Pyle: “We have no evidence that the two volcanoes have been affected by the earthquakes”

“A rare phenomenon.” That’s how the swarm of earthquakes that has been shaking Santorini, Amorgos and the surrounding islands in recent days is described by University of Oxford volcanologist David Pyle, considered one of the world’s leading volcanologists, who has worked extensively on the study of both Santorini and Colombo.

Speaking to protothema.gr, he says that at present the volcanoes do not appear to be getting ready to wake up. However, he stresses that measures should continue to be taken, along with the continuation of studies at the site, as there is always the risk of escalation.

Dr Pyle has traveled to most of the planet’s active and non-active volcanoes, from Vesuvius to Egyafiatlagyokutl in Iceland, from the Caribbean to Ghana and of course to Santorini, where in 2011 he was one of the experts called in to study it closely to conclude whether it was about to erupt.

In the first instance, he believes that there is no link to a possible activation of the volcano, although, as he points out, the “earthquake storm” phenomenon recorded in Santorini at this time is very rare both in intensity and in number (as the 2011 earthquake swarm was much smaller in magnitude).

For this reason, David Pyle explains, and because the proven dynamics of the area make the potential for escalation with a larger earthquake strong, it is right to take action and be vigilant.

– In recent weeks, intense seismic activity has been recorded in the wider Santorini area. You have worked in the area in the past investigating seismic faults and volcanoes. What conclusion did you come to in terms of fault dynamics and volcanic activity?

The seabed between Santorini and Amorgos is geologically complex. We know that this region is volcanically active, with the volcanoes of Santorini and Colombo, and seismically active, with many earthquakes associated with the faults that cross the region. On a geological scale we expect that there are connections between some of the faults and volcanoes, but we are still trying to work out these connections.

– As you can see, people are concerned. Many people are leaving the area and there is a lot of concern about the upcoming tourist season. Everyone is wondering how this very extensive seismic activity will play out. There are estimates that the area that is giving these earthquakes today cannot give a tremor greater than 6 Richter, there are others that say that earthquakes of magnitude 5.2 are pre-seismic activity.

It is rare to have such an intense and recurring cluster of earthquakes, so we don’t have a very clear picture of how these seismic clusters can develop or how long they can last. What we do know is that there are several large faults on the seabed between Colombo, Anydro and Amorgos – and that there have been some very significant earthquakes in this area over the last 70 years. This means that there is a risk of escalation into a larger earthquake – and for this reason, even if this scenario is considered unlikely, we should be wary of what might happen next.

– There are also many who wonder if the Santorini or Colombo volcano is about to erupt…

Most of the earthquakes detected in late January and early February have foci located 20 to 40 kilometers away from Santorini. For this reason, the earthquakes are not considered to be directly related to either Santorini or Colombo. At present there are no clear signs of changes in either Santorini or Colombo and both volcanoes will need to be closely monitored as the sequence of earthquakes continues.

– Do you think this swarm of earthquakes is related to the volcano and if so, which one? For example, is it possible that these earthquakes are in some way setting us up to see an eruption of Colombo?

At this time the earthquake swarm is not associated with either volcano and we have no evidence that either volcano has been affected by the earthquakes.

– We have two relatively recent past examples of intense volcanic and seismic activity in the Santorini area. That of 2011 and that of 1956, both of which had different discharge/recovery, with the more recent one not giving a major event and the one in ’56 giving a catastrophic earthquake. What conclusions can we draw by comparing these to the current activity in the area?

The earthquake was a 7.8 magnitude earthquake followed by a second 7.2 magnitude quake and a devastating tsunami. There were no precursors to this event, but several months of aftershocks followed. This large earthquake was very different from the current cluster of events – most of which were smaller than magnitude 5. Since 2011-2012 there has been a smaller and less intense cluster of earthquakes just below Santorini. Most of these events were smaller than magnitude 3 (Richter) and their epicenter was located below the Caldera of Santorini. There were some minor accompanying changes in the volcano at that time that were detected by satellites and GPS instruments, and the conclusion was that the 2011 cluster was associated with the movement of a small amount of magma beneath the island. There was no eruption. The current earthquake swarm is larger and more energetic, but not directly related to the volcano.

– Regardless of how the phenomenon unfolds today, what should we expect in the future in terms of seismic and volcanic activity in Santorini? Is there a pattern by which we can predict that every few years we will have a strong earthquake or volcanic eruption?

It is very likely that in the future we will see clusters of earthquakes in the area both below Santorini, as in 2011, and further away. It is only in the last few decades that we have developed the instruments to detect these small swarms, so so far we don’t know if they follow a periodic pattern or just occur intermittently every few decades. Only time will tell.

– Can a large earthquake or volcanic eruption trigger other faults and especially other volcanoes in the Aegean volcanic arc and cause a kind of volcanic dominoes?

This remains an open question, which has not been resolved anywhere in the world: it is certainly possible that very large earthquakes can stimulate smaller-scale activity on other faults and volcanoes, but the effect is considered quite small, and a very significant earthquake is required in the first instance.