Santorini earthquakes: What is causing 'unusual' seismic activity and what is the advice for tourists visiting Greece?

Multiple earthquakes rattling the Greek island of Santorini have prompted thousands of people to flee, disrupted travel for tourists and damaged infrastructure.

Quakes up to a magnitude of five have been recorded in the region since Friday, with the island's mayor warning that seismic activity could continue for weeks.

It has been described by Greek Prime Minister Kyriakos Mitsotakis as an "extremely complex and intricate geological phenomenon," according to state broadcaster EPT.

Here is everything you need to know about the earthquakes hitting one of Greece's most popular tourist destinations.

What's happening?

Hundreds of quakes with magnitudes between 3 and 4.9 have been registered since Saturday between Santorini and the nearby island of Amorgos - which are both part of the Cyclades Islands.

There have been a further 440 earthquakes below a magnitude of three and 73 above a magnitude of four since 1 February, EPT reported, citing the Geodynamic Institute.

Seismologists have described the event as a series of tremors of similar magnitude occurring in clusters.

They add that although Greece is no stranger to earthquakes, seismic activity of such frequency and intensity without having been preceded by a major quake is unusual.

The epicentres of the quakes are beneath the seabed, which experts have said is good news as they will not be as destructive.

Authorities said on Wednesday they have bolstered their emergency plans in case the tremors are a sign a larger quake will follow.

There is also a possibility that an earthquake could trigger a volcanic eruption or tsunami.

"We are obliged to draw up scenarios for better and for worse regarding the prolonged seismic activity," civil protection minister Vassilis Kikilias said during a meeting with security officials, scientists and the prime minister.

So far, there has been no significant damage and no injuries, although some minor rock slides have occurred and cracks in some older buildings have been reported.

Public events have all been banned and local authorities were restricting access to clifftop areas that are among the biggest tourist draws to the island.

Huge swathes of people have also left the islands due to the tectonic activity.

Families have been pictured carrying young children, tourists dragging their suitcases, and car parks have filled with vehicles belonging to those who have left via ferry.

A number of schools have also closed across several Greek islands.

Why is it happening?

Earthquakes occur when tectonic plates move suddenly along a fault line, releasing energy in the form of seismic waves.

The shaking that results from these waves is what we feel during an earthquake.

The fault line producing the current earthquakes in the Greek islands runs for about 120km (75 miles) but only the part between Santorini and Amorgos has been activated so far.

Experts are still trying to determine whether the multiple quakes are foreshocks - smaller earthquakes before a major tremor - or whether they are part of an earthquake swarm of smaller quakes that could continue for weeks or months.

"There is no serious technology or approach to be able to predict what will happen from here on," Costas Papazachos, professor of applied geophysics and seismology at the University of Thessaloniki, said.

How likely is volcanic activity?

Santorini lies along the South Aegean Volcanic Arc, a chain of volcanoes which stretches from the Peloponnese in southern Greece through the Cyclades Islands.

The island also has a caldera - a large, circular hollow that remains when the central part of a volcano falls in after an eruption.

Last week, Greece's Climate Crisis and Civil Protection Ministry announced that sensors had picked up "mild seismic-volcanic activity" inside the caldera.

There are two volcanoes in the area: Nea Kameni, which is within Santorini's caldera and Kolumbo, a volcano under the sea which is about 8km (5 miles) northeast of the island.

There is also the volcanic island of Palia Kameni.

Scientists have since said the current quakes are unrelated to the volcanic activity.

Efthymios Lekkas, seismologist and head of the scientific monitoring committee for the Aegean Volcanic Arc, added that it has been 3,000 years since the last explosion.

"We have a very long time ahead of us before we face a big explosion," he said.

Advice for tourists

In an update to visitors on Tuesday, the government of Santorini warned hotels and all kinds of tourist accommodations to "inform their visitors to avoid the dangerous points of the island".

The UK Foreign Office also shared a warning from the Greek ministry of civil protection that people are advised "not to attend large indoor gatherings and to avoid old or abandoned buildings".

People have been advised to avoid the ports of Amoudi, Armeni, Korfos and Old Port in the area of Fira and to choose safe routes when travelling, particularly in areas where the landslide risk is high.

"In case of a strong tremor, people should immediately depart coastal areas," the ministry said.

Push alerts have also been sent to mobile phones, and hotels have been urged to drain swimming pools because the water movement in a major quake could destabilise buildings.

One resident who has already evacuated is tour guide Kostas Sakavaras who told Sky News' The World With Yalda Hakim that his family had fled to Athens "as a precaution".

"It's nerve-wracking to have every few minutes some tremor happening, even though it's not a very devastating one," he said.

He added he had a "feeling increasingly more people are leaving the island".

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How long will the tremors last?

In a meeting on Wednesday, Prime Minister Kyriakos Mitsotakis said he was "more optimistic" than he was on Tuesday about the earthquakes not causing a bigger tremor, but could not make any firm predictions, EPT reported.

Kostas Papazachos, professor of geophysics and seismology, added: "Residents will continue to feel vibrations for the next period of time, and they should remain calm about it.

"The situation seems to be moving towards a better scenario in relation to seismic activity."

The Earthquake Planning and Protection Organisation said last week the epicentre of the earthquakes in the Aegean Sea was moving northwards away from Santorini.

It emphasised there was no connection to the area's dormant volcanoes.

Some residents of the island have decided to remain in their homes while the seismic activity continues.

Retired police officer and ship worker Panagiotis Hatzigeorgiou, who has lived on Santorini for more than three decades, said: "Older residents are used to the earthquakes.

"But it's different this time. It's not the same to have earthquakes every two to three minutes. The main thing is not to worry," he said, adding: "Now we can listen to music alone and have coffee by ourselves."

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