Inspections on the popular island of Santorini have discovered dozens of illegal buildings that could be at risk in the event of future earthquakes.

The Greek Ministry of the Environment and Energy released details of its findings this week, following inspections conducted in October and November last year.

Authorities discovered that many of the hotels and tourist accommodations on the island had falsely registered as pre-1955 structures to bypass stringent regulations.

The crescent-shaped ‘caldera,’ the edge of an ancient volcano, has been particularly closely regulated to preserve its iconic white cliffside buildings. Even here, where rules are tightest, illegal construction has been found.

Among the buildings identified in the report was a tourist accommodation located in the caldera’s protected zone that exceeded its approved size. For this, authorities issued a fine of €191,000.

Other buildings were found to have installed hot tubs and swimming pools that violated protection laws. Altogether, fines totalling more than €900,000 were issued in relation to illegal developments in areas near the caldera.

New rules mean illegal structures can be removed if they violate Santorini’s protection laws, with owners given 30 days from the date of the decision to take them down.

To further bolster protection of the islands, the ministry is investing €130 million in satellite imagery and AI to better identify constructions of concern. It hopes to have the system operational by summer 2026.

Greek seismologist Akis Tselentis took to social media to highlight the ‘urban building crimes’ on Santorini with the topography of the island making it easy for developers to ‘hide’ their building activity.

“Illegal structures are being built under the nose of the Authorities that maintain the island,” Tselentis says. “When man’s greed for profit blinds him and he does not see that he lives or invests in an environment within which there are two active volcanoes and a seismic fault beyond.”

Why are these buildings illegal?

Santorini first sought to limit development on the island following a devastating earthquake in 1956. With much of the island’s infrastructure destroyed, the rebuilding effort was guided by strict regulations that aimed to preserve its unique architectural heritage.

But when tourism boomed in the 1980s, development picked up the pace in an attempt to accommodate the influx of visitors. Local authorities tightened up building regulations to control the scale and style of new constructions and to limit where they were built.

Fast forward a few more decades, and Santorini is bursting at the seams. In 2023, 3.4 million tourists arrived on the island, which is home to only 25,000 people. On some days, as many as 17,000 cruise ship passengers would descend on the locals, prompting the government to implement caps and fees for this year’s arrivals.

Along with this surge in visitors has been a surge in development. In 2023, authorities issued 470 building permits and a further 300 permits for renovations on the island, causing concern among locals and conservationists alike.

“We live in a place of barely 25,000 souls and we don’t need any more hotels or any more rented rooms,” mayor of Santorini Nikos Zorzos told the Guardian. “If you destroy the landscape, one as rich as ours, you destroy the very reason people come here in the first place.”

In an attempt to curb development, the Environment Ministry announced a suspension of all building licenses in the caldera zone of Santorini and the nearby island of Therasia in August 2024. The suspension covers new buildings, extensions and the addition of swimming pools and hot tubs.

As part of the crackdown, local planning authorities were tasked with reviewing all building permits issued in the previous five years and inspecting the islands for unauthorised developments.

Why illegal building is a concern for earthquake-prone Santorini

Santorini is part of the Hellenic Volcanic Arc, a highly active tectonic region. The island itself is the remnant of a massive volcanic eruption that occurred around 1600 BCE, one of the largest in recorded history.

While development doesn’t directly cause earthquakes, unchecked and illegal buildings could have catastrophic consequences in the event of tectonic activity.

Many of the buildings in the caldera cling to the side of the cliff. Troglodyte homes, built in caves dug into the cliffside, undermine the buildings above them, and the weight of pools and hot tubs risks destabilising the ground.

Seismologists warn that overdevelopment could increase the risk of devastating landslides and structural collapse during an earthquake. New, unregulated buildings may not be adequately designed to withstand seismic events.

“They wanted to develop the island and didn’t pay attention to environmental and safety issues,” says Dimitris Papanikolaou, professor of geology at the University of Athens.

“Nothing should have been built in this zone,” he added, referring to the soft, volcanic soils that make up the cliffs of the caldera.

Even before the recent earthquakes, concerns for Santorini’s structures were emerging. In 2021, a report by the Hellenic Society for Environment and Cultural Heritage said the safety of the buildings on the caldera urgently needed to be assessed. It added that many buildings had no permits, and that a quarter of those were tourism businesses.

Some individuals have flagged concerns even with permitted developments, which they say are being built in unsuitable areas.

“Building permits were granted and were built in Fira, in Oia and Alachua, heavy constructions (including hotels with swimming pools) on the slopes to the sea, under the traditional settlement, with false foundations,” Tselentis says. “With a relatively small earthquake, these won’t collapse, but they’ll slide right into the sea.”

“I would ask politicians to prioritise science and do seismological assessments,” Tselentis continues. “If they want to contribute, let them trample urban illegalities by turning deaf ears to hotel interests and letting scientists do their jobs.”

According to the National and Kapodistrian University of Athens, seismic activity in the region between Santorini and Amorgos has been declining since 15 February. Tremors are now less frequent and less intense, although some are still noted to be taking place.

Since the onset of the Santorini earthquakes, more than 23,500 events have been recorded by the university’s Seismological Laboratory, with some exceeding a magnitude of 5.0. Since 20 February, no tremors over a magnitude of 4.0 have been identified.

Is it safe to visit Santorini?

Santorini remains in a state of emergency until March 1, keeping its emergency services on high alert for a rapid response to any incidents. Anafi and Amorgos will stay in a state of emergency until mid-March. Across all the islands, the schools remain closed.

Despite this, there has been no official instruction not to travel to the Cyclades from either the Greek government or other European governments. The EU advises exercising caution if a visit is planned and urges travellers to keep up to date with the latest news from Greece.

Specifically, visitors are advised to stay away from old and abandoned buildings and avoid large indoor gatherings. In the event of a strong tremor, stay away from the ports of Amoudi, Armeni, Korfos, and the Old Port of Fira, as they could be at risk of a tsunami.

The population of Santorini is returning to the island after thousands evacuated when the earthquakes started. Early reports suggest the tourists have begun arriving too, and the island is hopeful of getting back to normal in time for the peak season.

Nevertheless, when visiting any area of seismic activity, it pays to be alert.

“Nature can take revenge if we do not respect it,” concludes Tselentis. “The growth of tourism is nice, but the earthquake comes to remind us that it’s not only humans who are in charge on the planet.”