Biggest quake yet could be still to come on Greek tourist island, seismologist warns

Such behavior typically amounts to “foreshock” activity – seismic activity that occurs before the main shock of the sequence – meaning that the largest earthquake could be yet to come, seismologist warns.

(CNN) — The seismic activity rattling Santorini and other Greek islands is not over and the biggest quake yet could be still to come, a seismologist has warned.

Rémy Bossu, Secretary-General of the European-Mediterranean Siesmological Centre, said “days, or perhaps, weeks” would be needed to evaluate the unusual tremors but said that the series of quakes typically occur in the build-up to a larger tremor.

A state of emergency has been declared in the idyllic Greek island of Santorini amid a series of near-constant tremors in recent days, which have almost emptied the famous Greek tourist haven of visitors and residents.

The largest tremor so far was recorded on Wednesday evening, when a quake with a magnitude of 5.2 coursed through the island. It was the first to exceed 5.0 since the tremors began last week.

Sitting near the boundary of the massive African and Eurasian tectonic plates, Santorini often experiences seismic activity, but rarely so intensely for so long. As well as Santorini, the nearby islands of Amorgos and Ios have also been shaken.

Bossu described the current seismic activity rocking Santorini – which is known as an “earthquake swarm” – as “very unusual.”

Normally, he says, “what you observe is a large earthquake followed by aftershocks which decrease with time in magnitude and frequency.

“Here, we observe a very different (phenomenon). We see that the magnitude has been increasing with time and the rate has been increasing, so this is not typical behavior,” he told CNN.

Hundreds of the tremors, which have hit Santorini every few minutes for days, have had a magnitude of around 3.0 and are considered “slight” quakes. At over 5.0, Wednesday’s quake is considered “moderate.” It was followed by at least five quakes with a magnitude of 4.0 and above, which are considered “light.”

According to Bossu, such behavior typically amounts to “foreshock” activity – seismic activity that occurs before the main shock of the sequence – meaning that the largest earthquake could be yet to come.

“This is why the Greek authorities are taking precautionary measures,” he said, pointing to the organized evacuations and the readying of rescue forces.

As the earthquakes continued, Greek Prime Minister Kyriakos Mitsotakis made a brief visit to the island on Friday morning to inspect emergency preparations.

“I want to assure the residents of Santorini and the neighbouring islands, which are being tested these days, that the state mechanism is on their side,” he said.

“We hope this phenomenon ends quickly and the island fully returns to its normal pace.”

Greece’s Earthquake Planning and Protection Organization has estimated that the intense seismic activity may continue for many more days, if not weeks.

While not currently in peak season, the island of Santorini is a popular tourist hotspot, attracting more than 3.4 million tourists a year. It is also home to some 20,000 permanent residents.

Around 11,000 people are thought to have fled the island so far due to the tremors. “We are going to leave because I am afraid, there are constantly earthquakes, we have to leave for the kids, so the kids can calm down,” Beni Ouklala, 38, who has temporary work on Santorini, told Reuters.

Tourist boat captian Eftichis Diamantopouulos, 63, was less concerned. “Why should we leave?” she questioned. “If something happens, it happens.”

Greek authorities have arranged additional flights to help people flee to the safety of the mainland, but evacuation efforts were complicated on Wednesday, with ferries not allowed to leave the ports due to high winds. Normal service had resumed by Thursday.

The earthquake sequences are not located beneath the island of Santorini, but rather between Santorini and another island called Amorgos.

They are occurring about 25 kilometers northeast of Santorini, and 20-25 kilometers southwest of Amorgos, according to Bossu.

At that distance they are felt in Santorini. “Of course, when you have such a large number of earthquakes felt by the population, it raises anxiety,” Bossu said. “The people in the area are very concerned… And it is logical because nobody can tell how it evolves.”

He added, “We have to wait at least days, or perhaps, weeks, to evaluate how it may evolve.”

The region last suffered a major earthquake in 1956, when a tremor with a magnitude of 7.7 struck to the south of the island of Amorgos, followed minutes later by a magnitude 7.2 earthquake near Santorini. This caused significant damage to both islands and also triggered a 25-meter-high (around 80 feet) tsunami. In total, 53 people were killed during these events, and a further 100 were injured.

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