Great Lisbon Earthquake 1755
Monday, 14. April 2008, 08:02:09
I am back home from a week in Lisbon, where I was several times reminded of the Great Lisbon Earthquake.
On 1 November 1755 Lisbon was shaken by a violent earthquake. It occurred at 9:40 in the morning during High Mass - a mass to celebrate All Saints' Day, also known as All Hallows or Hallowmas, an important religious holiday in this strong Roman catholic country.
Geologists today estimate the Lisbon earthquake approached magnitude 9 on the Richter scale, with an epicentre in the Atlantic Ocean about 200 km west-south-west of Cape St. Vincent (See map). Estimates place the death toll between 60,000 to 100,000 people, making it one of the most destructive earthquakes in history.
More than 20 churches collapsed, and due to the candles lit for the celebration fire quickly broke out, and flames raged for five days. Gigantic fissures up to five metres wide appeared in the city centre. Survivors rushed to the open space of the docks for safety and watched as the water receded revealing the sea floor. Approximately forty minutes after the earthquake, an enormous tsunami engulfed the harbour and downtown, rushing up the Tagus river. It was followed by two more waves.
Many people at the time saw the disaster a God’s punishment - because the town was too rich, because of the inquisition (the Spanish Inquisition was established in 1478), because of idolatry or other sins? Apart from theological, philosophical (including work by Voltaire), and literary discussions, however, scientists got involved. It was the first earthquake studied scientifically for its effects over a large area, and it led to the birth of modern seismology.
I stayed at a hotel a few hundred metres from the Santa Justa Lift (also known as the Carmo Lift). The Santa Justa Lift was designed by an apprentice of Gustave Eiffel (the one with the Eiffel Tower). The iron lift is 45 metres tall and it brought me from the downtown streets to the uphill Carmo Square. From the roof of the lift construction (with a bar, where I had an espresso) there is a nice view over downtown Lisbon and the Carmo Convent. This mediaeval convent was ruined in the Earthquake, and the ruins of its Gothic church are the main trace of the great earthquake still visible in the city. The ruins were preserved to remind Lisboners of the destruction.
I went down to the docks and took the train to see one of the most impressive monuments in Lisbon, the Jeronimos Monastery. The vaulting in the church withstood the earthquake of 1755, which probably says something about the architecture. In the same district - called Belém, which is in fact Portuguese for Bethlehem, and pronounced more or less as “blem” - there is an old tower, the Torre de Belém. The tower was built in the same style as the Monastery between 1515 and 1519 in the middle of the river Tagus to defend Lisbon and the monastery. Today, however it stands on the water’s edge practically moored to the north bank, the river having altered course during (and after) the earthquake and tsunami of 1755.
From there the train moves on to the romantic fishing port - and holiday resort with yacht harbour - of Cascaias, about half an hour’s ride from Lisbon (30 kilometres west of Lisbon). A large portion of the village was destroyed during the earthquake in 1755. But today it is bustling, and I had a nice evening meal at the beach with cockles and local wine.
PS of 17 April 2008
The position of the epicentre is disputed (See comments). The source mechanism seems to require generation at a subduction zone, but where would that be?
On 1 November 1755 Lisbon was shaken by a violent earthquake. It occurred at 9:40 in the morning during High Mass - a mass to celebrate All Saints' Day, also known as All Hallows or Hallowmas, an important religious holiday in this strong Roman catholic country.
Geologists today estimate the Lisbon earthquake approached magnitude 9 on the Richter scale, with an epicentre in the Atlantic Ocean about 200 km west-south-west of Cape St. Vincent (See map). Estimates place the death toll between 60,000 to 100,000 people, making it one of the most destructive earthquakes in history.More than 20 churches collapsed, and due to the candles lit for the celebration fire quickly broke out, and flames raged for five days. Gigantic fissures up to five metres wide appeared in the city centre. Survivors rushed to the open space of the docks for safety and watched as the water receded revealing the sea floor. Approximately forty minutes after the earthquake, an enormous tsunami engulfed the harbour and downtown, rushing up the Tagus river. It was followed by two more waves.
Many people at the time saw the disaster a God’s punishment - because the town was too rich, because of the inquisition (the Spanish Inquisition was established in 1478), because of idolatry or other sins? Apart from theological, philosophical (including work by Voltaire), and literary discussions, however, scientists got involved. It was the first earthquake studied scientifically for its effects over a large area, and it led to the birth of modern seismology.
I stayed at a hotel a few hundred metres from the Santa Justa Lift (also known as the Carmo Lift). The Santa Justa Lift was designed by an apprentice of Gustave Eiffel (the one with the Eiffel Tower). The iron lift is 45 metres tall and it brought me from the downtown streets to the uphill Carmo Square. From the roof of the lift construction (with a bar, where I had an espresso) there is a nice view over downtown Lisbon and the Carmo Convent. This mediaeval convent was ruined in the Earthquake, and the ruins of its Gothic church are the main trace of the great earthquake still visible in the city. The ruins were preserved to remind Lisboners of the destruction.
I went down to the docks and took the train to see one of the most impressive monuments in Lisbon, the Jeronimos Monastery. The vaulting in the church withstood the earthquake of 1755, which probably says something about the architecture. In the same district - called Belém, which is in fact Portuguese for Bethlehem, and pronounced more or less as “blem” - there is an old tower, the Torre de Belém. The tower was built in the same style as the Monastery between 1515 and 1519 in the middle of the river Tagus to defend Lisbon and the monastery. Today, however it stands on the water’s edge practically moored to the north bank, the river having altered course during (and after) the earthquake and tsunami of 1755.
From there the train moves on to the romantic fishing port - and holiday resort with yacht harbour - of Cascaias, about half an hour’s ride from Lisbon (30 kilometres west of Lisbon). A large portion of the village was destroyed during the earthquake in 1755. But today it is bustling, and I had a nice evening meal at the beach with cockles and local wine.
PS of 17 April 2008
The position of the epicentre is disputed (See comments). The source mechanism seems to require generation at a subduction zone, but where would that be?
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By hypocentre, # 14. April 2008, 09:55:58
Ole, have you an idea about it?
The fact is that there is a seismic beld, elongated E-W, in the ocean south of Portugal, where the 1755 eq must be placed.
But Hypocentre right observes that only subduction quakes can arrive to so high M values.
I ask you if the epicenter has been determined simply by the time gap beetwen the eq and the tsunami arriving or if the location is based upon the occurence of the sismic belt and/or the geologic setting of the area?
Now I'm searching something about Messina 1908 hq in which there is another strange thing: a strong tsunami with a relatively moderate (M=7) earthquake. Perhaps that's because the depht of the event was low? Strange, since that the 1908 fault is still unknown.
So, both the quakes show some mysteries. It's somehow a link..
By piombaldo, # 14. April 2008, 23:10:11
The Cadiz-Gibraltar subduction is indeed a candidate for the 1755 quake - Geophysical Research Abstracts, Vol. 8, 04287, 2006: Thiebot and. Gutscher The seismogenic zone of Cadiz - Gibraltar subduction and the source of the 1755 Lisbon earthquake and tsunami - and the distance would probably be right, but as far as I know there has been controversies whether this is an active subduction zone or not?
Best regards
Ole
By nielsol, # 15. April 2008, 15:18:03
I think that the Cadiz - Gibraltar subduction zone can be the source of the event.
There is another question that I have forgotten yesterday: how deep was the quake?
By piombaldo, # 15. April 2008, 21:08:26
The 1755 Lisbon earthquake and tsunami had one of the highest magnitudes in the history of Europe. The source mechanism requires generation at a subduction zone. Intensity distribution and tsunami modelling excludes the Gorringe Bank as a source area and suggests generation by the incipient convergence of the Atlantic with the Southwest Iberia and Morocco margin rather than at the less active Gulf of Cadiz Accretionary Prism. The comparison with the 2004 Sumatra earthquake and tsunami supports this interpretation. A tsunami warning alert system is urgent for the Atlantic.
By piombaldo, # 15. April 2008, 21:19:04
For the epicenter, most authors agree with the traditional position in the atlantic ocean, with the plate boundary in wich there is at our times the incomng of a subduction of the atlantic crust under iberia and northern africa. Soe other ones prefere a more eastern solution, in the Cadiz gulf, always depicting an incoming of the same subduction but not related to the Azores - gibraltar System
By piombaldo, # 17. April 2008, 22:45:03
Best regards
Ole
By nielsol, # 18. April 2008, 07:41:51
I am searching news about older tsunamies in the area. I have found something new. But the informations are very poor!
By piombaldo, # 23. April 2008, 23:10:54