The 1755 Lisbon earthquake, also known as the Great Lisbon earthquake, occurred on Saturday, 1 November, All Saints' Day, at around 09:40.
In combination with the subsequent fires and a tsunami, the event destroyed Lisbon almost totally and caused death and destruction up the west coast and across the Algarve.
The tsunami destroyed some coastal fortresses in the Algarve and, in the lower levels, it razed several houses.
Almost all the coastal towns and villages of the Algarve were heavily damaged, except Faro, which was protected by the sandbanks of the Ria Formosa lagoon.
In Lagos, the waves reached the top of the city walls.
Other towns of different Portuguese regions, such as Peniche, Cascais, and even Covilhã near the Serra da Estrela mountain range in central inland Portugal, were affected.
The shock waves of the earthquake destroyed part of Covilhã's castle walls and its large towers.
On the island of Madeira, Funchal and many smaller settlements suffered significant damage. Almost all of the ports in the Azores archipelago suffered most of their destruction from the tsunami, with the sea penetrating about 150 metres inland.
A three-metre tsunami hit Cornwall on the southern English coast. Galway, on the west coast of Ireland, was also hit, resulting in partial destruction of the Spanish Arch section of the city wall. At Kinsale, several vessels were whirled round in the harbour and water poured into the marketplace.
Seismologists today estimate the Lisbon earthquake had a magnitude in the range 8.5–9.0 on the Richter scale with its epicentre in the Atlantic Ocean about 200 km west-southwest of Cape St. Vincent.
Estimates place the death toll in Lisbon alone between 10,000 and 100,000 people, making it one of the deadliest earthquakes in history, more powerful than the 2011 disaster in Japan which was recorded at 8.9 on the Richter scale.
The 1755 earthquake occurred exactly 261 years ago today and the construction and seismic protection specialist, Cristina Oliveira, warns of the possibility of history repeating itself.
The Professor at Tecnologia do Barreiro, Instituto Politécnico de Setúbal, says that Portugal is not prepared and not concerned with seismic activity, unlike in Italy where people are sensitised and the authorities are prepared for such events. If the August earthquake that hit Amatrice in Italy had happened in Lisbon, the capital again would have been largely destroyed, says the professor.
Portugal has had anti-seismic regulations for buildings since 1958 but those built before this date are at a higher risk.
"Houses should be inspected from time to time, but nothing is done. Last year, legislation was passed that largely has been ignored because it states that in the renovation of buildings you cannot reduce the existing seismic resistance. But you are not obliged to reinforce what is there and if you don’t have reinforcement, then you don’t have to put any in.”
Portugal is under the influence of a subduction* zone where plates converge off the Algarve coastline making large earthquakes more likely than in, for example, Italy which has many small ones.
"There is always pressure building up, we just do not know when it will be released,” said Oliveira adding that the lessons of 1755 have not been learned and the Portuguese are not prepared or aware or even concerned.
“In 1755 no one was prepared for an earthquake and it still happened,” said the Prof. - and she is quite right.
(* Subduction: the sideways and downward movement of the edge of a plate of the earth's crust into the mantle beneath another plate.)
