During the heyday of classical Greece, the city of Helike was the renowned cult centre for worship of Poseidon, the god of the sea and of earthquakes.

Ironically, on a winter night in 373 BC, a violent earthquake and seismic sea-wave (tsunami) destroyed and submerged the city.

At the time of its destruction, Helike was capital of a con federation of city states on the southern shores of the Gulf of Corinth, and was probably located southeast of the modern city of Aigion, roughly 150 kilometres west of Athens. Its precise location has long been the subject of debate among historians and archaeologists.

Ancient writers were insistent that the city lay off limits beneath the waters of the Corinthian gulf, but modern marine surveys had repeatedly failed to locate it there. Last week came the news that ruins of ancient Helike had been uncovered onshore, three to four metres beneath the mud and gravel of the Aigion coastal plain.

There was perhaps forewarning that an earthquake was about to strike Helike, but not of its scale. Writing in the 2nd-3rd century AD, Aelian described how five days before the earthquake, all the animals had left the city en masse, much to the puzzled amusement of the local people.

Ancient writers record that the earthquake which struck in the night destroyed every single building in the city and that with the receding waters of the tsunami, which came with the dawn, Helike was dragged down along with every living person, the foundations of the city lost forever.

Until, that is, excavations this summer. The possible discovery of Helike was announced formally last week by Dr Dora Katsonopoulou, a Greek archaeologist, and Dr Steven Soter, an astrophysicist from the American Museum of Natural History. Their discovery was no accident. The locations of the excavations had been carefully targeted following 12 years of subsurface probing by boreholes and geophysical imaging (radar and magnetometry) by Soter and Katsonopoulou.

Nevertheless, the nature of the finds still took both by surprise. In the most important excavation, ruined walls and building foundations were found buried below thick deposits of black peat and lagoonal and marine muds. The discovery of these ruins entombed in a mixed blanket of terrestrial, brackish and marine sediments is certainly consistent with a classical city engulfed by a tsunami.

However, the excitement is tempered by the realisation that only a few square metres of the wide coastal plain has so far been excavated.

For archaeologists, the prize is that, given the nature of Helike's demise, the resurrected city may provide an unplundered, unmodified "time capsule" from the classical era. Its shallow onshore location may allow the greater part of the city to be excavated, giving Greece its very own Pompeii.

For earthquake geologists, Helike offers a different prize. For us, the city is fossilised result of a scale of seismic event that we know can strike the earthquake-prone shores of the Aegean region but for which we have no modern analogue.

Killer earthquakes struck the Aigion shores in 1861 and 1995, but while they caused widespread coastal submergence and some loss of life, neither of them were of the enormity of the 373 BC event.

So how often do such catastrophic sea-quakes occur in this region?

In the early 1990s, I first went to the Helike area with that question in mind. As part of a Royal-Society-funded honeymoon I studied the earthquake fault that ruptured in 1861, and from raised shorelines along the Helike coast I suggested that the same fault probably moved violently around the time of the 373 BC event.

In 1995, I turned my attention 100 kilometres northwards to another earthquake-prone coast - the Gulf of Atalanti. Here, with two research students (Vik Buck and Thomas Dewez), and in collaboration with Stella Kortekaas (Coventry University) and Andy Cundy (now at the University of Sussex), we investigated the effects of coastal flooding triggered by a damaging earthquake and tsunami in 1894.

We were able to detect signs of this seismic disturbance in the modern marsh sediments, so Soter and Katsonopoulou were interested in whether we could detect the older but much larger Helike inundation event.

This summer, funded by Brunel University and an EU project investigating long-term seismic hazard in the Gulf of Corinth, I returned to Helike. I was joined by Thomas, Andy and a new Brunel colleague Suzanne Leroy, professor in palaeoenvironmental reconstruction. Working alongside Soter and Katsonopoulou, our task was to drill shallow boreholes in a suspected former lake bed. For the archaeologists, the lake was potentially the sacred grove of Poseidon for which ancient Helike was famed.

For us, the site lay a few tens of metres from the Helike fault, which we suspected had ruptured during the 373 BC earthquake, and therefore the lake may preserve an archive of that past earthquake activity. However, the freshly recovered sediment cores have yet to reveal their story.

U ndoubtedly the most popular aspect of the Helike discovery will be its association with the Atlantis legend. The story of Atlantis is first recorded by the Athenian philosopher Plato, writing in the mid-fourth century BC.

Plato would have been in his early 50s when the 373 BC earthquake obliterated the thriving city of Helike, and the tragedy would have been reminiscent of a similar catastrophic event that struck mainland Greece around the time of his birth.

In 426 BC, a major earthquake caused widespread seismic destruction and tsunami inundation around the Gulf of Evvia, including, in the Gulf of Atalanti, the reported separation of Atalanti Island from the mainland.

In his "dialogue" Timaeus, Plato recounts how "there occurred violent earthquakes and floods" and then, in one awful day and night "the island of Atlantis _disappeared in the depths of the sea." The parallels between Plato's Atlantis and the 373 BC and 426 BC earthquakes are enticing, particularly given that even after two and a half millenia of notable historical seismicity in Greece, these two earthquakes stand out as particularly catastrophic events. Perhaps the Atlantis legend is the real legacy of Helike.

• Iain Stewart is a senior lecturer in geography and earth sciences at Brunel University. His research is in earthquake geology, and he has recently co-edited books on The Archaeology Of Geological Catastrophes and Coastal Tectonics.