The Great Earthquake 1755 Content from the guide to life, the universe and everything

The Great Earthquake 1755

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Earthquakes have occurred throughout the centuries in Western Europe as the African plate moves north and America moves away on the other side of the mid-Atlantic ridge.

The Tremors

On All Saints' Day, 1 November, at approximately 9.30am, the whole of Western Europe was shaken by a tremendous earthquake. The epicentre is calculated to have been about 200km west-south-west of Cape St Vincent, the most south-westerly tip of Europe, at around 36°N 10°57'W. The strength appears to have been around 8.2, or possibly more, on the Richter Scale1.

Being nearest to the source of the tremor, Portugal suffered the most. The initial triple shock waves lasted for nearly ten minutes.

In the Algarve there was great destruction and nearly all buildings were damaged. Churches came down on top of congregations who had been attending the Holy Day Mass. Two-storey buildings were flattened. In the town of Vila do Bispo, just 20km inland from Cape St Vincent, only one house was left with any walls standing. Spain and Morocco were also badly hit. Some 300km to the north, the quayside in Lisbon sank into the river Tagus and the recording of the human tragedy began with the report that 600 people had disappeared with the destruction of the quays. Fires broke out in the city.

Even people on the Orkney Isles felt the tremor. But worse was to follow.

The Tsunami2

The undersea quake generated a tsunami. The sea retreated, revealing the sea bed, and many survivors rushed to see the unusually exposed ocean floor, but then they were overwhelmed by the thundering wall of water returning. The wave reportedly crashed over the cliffs at Sagres, at a height approaching 30m or more. All along the south coast, the boats were swept clear away from the little fishing villages, some ending up at least a kilometre or two inland. Buildings that lay on the east side of the bays, already ruined by the tremors, were totally demolished. The tsunami reached Cadiz 78 minutes after the quake.

To the north, Lisbon was struck by the wave at around 11am, when the force and height was greatly enhanced by the funnelling effect of the Tagus estuary. Possibly then 5m high, the wave engulfed the thousands who had flocked to the open squares next to the river, mistakenly believing these areas to be safer.

Further north, the wave, now only 2m high, reached Cornwall a little after 2pm and then swept up to the Orkneys and even into the Baltic, where it was noticed in Finland along with the occurrence of seiches3.

After sweeping Madeira, to the west, at around the same time as it hit Lisbon, the tsunami thundered on across the Atlantic to be recorded in the Bahamas, Martinique and Newfoundland, with a height of between 1 and 2m.

Eyewitness Accounts

From the Algarve

Report from the Parish Priest, Lagos (translated):

There was a ghastly noise, like a never-ending roll of thunder. The ground shook and didn't seem to stop. The buildings started to fall down. The only noise then was tumbling masonry and the screams of my parishioners trapped in the church. I, with my own eyes, saw a crack nearly an ell4 wide open up in the churchyard. Looking east I could see the sea disappearing as if sucked down a hole. Then the ocean returned, all at once, taking with it the church of São Roque and the bridge.

Many reports from the villages:- There is just a pile of rubble. Even our Church has gone.

From Lisbon

Written by an English eyewitness several days after the event:

On the 1st November, 1755, the barometer standing at 27 inches 8 lines, and Reaumur's thermometer at 14 above freezing, the weather being fine and serene, at 9.45am. The earth trembled, but so slightly that it was attributed by most to a passing wagon. This agitation lasted 2 minutes. After the lapse of another 2 minutes, the earth shook with so much violence that the houses began to split and to crack. This second shock lasted about 10 minutes, and the dust was so great to obscure the sun. There was then an interval of 3 minutes, and the dust subsided, so that people could recognise one another. Then the third and most tremendous shock succeeded. The greater part of the city was in a moment laid in ruins. The sun was perfectly obscured and it seemed as if the earth was about to be reduced to chaos. The screams of the living, the groans of the dying, and the profound darkness, increased the horror. In 20 minutes all had become calm. Everyone endeavoured to escape into the country; but our misfortunes had not yet reached their height. As soon as we began to breath more freely, fires broke out in various parts of the city. The wind blew strongly; no one attempted to stop the progress of the flames; each endeavoured to save his own life. Some attempt might perhaps have been made to subdue the conflagration, if the sea had not at the same time threatened to overwhelm Lisbon... I write this in the fields; I cannot find a single house in which to shelter myself. Lisbon has disappeared.

From Newfoundland, Bonavista

The sea retired and left the bed of the harbour dry for the space of ten minutes, when it again flowed in and rose to an unusual height, overflowing several meadows for about the same space of time as it had retired...the waters on both sides of the cape were greatly agitated
– Rev Philip Tocque in Wandering Thoughts.

From Literature

Scarcely had they ceased to lament the loss of their benefactor and set foot in the city, when they perceived that the earth trembled under their feet, and the sea, swelling and foaming in the harbour, was dashing in pieces the vessels that were riding at anchor. Large sheets of flames and cinders covered the streets and public places; the houses tottered, and were tumbled topsy-turvy even to their foundations, which were themselves destroyed, and thirty thousand inhabitants of both sexes, young and old, were buried beneath the ruins.
– In Voltaire's Candide5, Chapter 5.


About a third of the population of Lisbon, estimated at around 275,000, had perished and 85% of the buildings were destroyed by the earthquake and the aftermaths of fire and tsunami. The fires raged for five days.

In 1755, Lisbon was one of the largest cities in Europe and famed for its diverse architecture with examples of buildings ranging from the Moorish occupation, through the Renaissance to the current day. The Opera House had only been opened that June. The Cathedral and all the major churches were ruined; neither public building nor Royal Palace remained habitable; the hospital had been consumed by the flames, with great loss of life.

The loss of property was reckoned to be around £20 million6.

The Royal family escaped any injury due to the fact that the King, José I, had succumbed to the whim of one of his daughters and, after a very early morning Mass, had taken everyone out to the countryside for the holiday. Ever after the King had a fear of living within walls, and the court, when it returned to Lisbon, lived in a complex of tents and pavilions among the hills of Ajuda, west of the ruins.

The Prime Minister at the time was Sebastião José de Carvalho e Mello7. When the King mournfully inquired as to what was to be done, the Prime Minister replied 'Bury the dead, and feed the living'. It is probably due to his prompt action that Lisbon was spared the epidemics of disease that customarily follow such devastation. He was in Lisbon when the earthquake struck, and was to spend the next fortnight driving and riding round the city, night and day; sending out fire-fighters; arranging the collection and burial of corpses; setting up posts for soldiers to guard against looting and pillage and safeguarding what little remained.

An Earthquake relief fund was started in England, resulting in the donation of some £50,0008. Both Spain and England sent food relief.


Reconstruction was started quickly. The whole of the debris in Lisbon was cleared within a year, and it started to rise again, based on a grand design by the Prime Minister, which included wide avenues on a grid plan. Vila Real de Santo Antonio, on the borders of the Algarve and Spain, was another town to benefit from his plans, though here his efforts were not appreciated.

To attempt to insure against the collapse of buildings in an earthquake the first testing of models took place. Scale houses were constructed, then the army and cavalry were sent to parade back and forward past them to see if the vibrations set up by the weight of men and horse had any effect.

The Enquiry

Sebastião de Carvalho soon sent a questionnaire out to all the parish priests and other literates in the country, containing such questions as:

  • How long did the earthquake last?
  • How many aftershocks were felt?
  • What kind of damage was caused?
  • Did animals behave strangely?
  • What happened in the wells?
Their answers are archived in the Tower of Tombo, Campo Grande, Lisbon.

Sebastião de Carvalho could be considered as the Father of Seismology. The testing of structures constructed to withstand vibrations, the questions asked – especially on the behaviour of animals and phenomena observed in wells before the event – and the correlation of the answers to provide a clearer picture of the disaster were all firsts.

Modern seismologists have scientifically studied these reports and can now suggest the location of the epicentre and the probable cause. Studies have also been made on the tsunami. The earlier theory was that there was a displacement in the Gorringe Ridge at 36°N 10°57'E. The current theory (2003) is that there was a simultaneous event involving two separate faults along the African Plate boundary, both faults displacing by around 20m. The first, the Marquêz de Pombal Thrust, lies NW/SE approximately through the assumed epicentre, but the second, along the Guadalquivir Bank, is some 100km closer to Cape St Vincent. A total sea floor area of around 20,000 square km was likely to have been involved with great mud flows and turbidity9 currents complicating the situation and increasing the amplitude of the tsunami.

More Recent Events

These findings have been compared with the strongest recent earthquake in Portugal - that on 28 February, 1969 - which was about 7.9 on the Richter scale, with an epicentre at 36°N 10°2'W, but very deep. This only generated a small tsunami of about 2m. Two people were killed in Portugal and ten in Morocco. Bridges were destroyed in the Algarve and some buildings damaged, but mainly the effects were light due to modern construction methods. Cars were damaged in Lisbon by falling chimneys and balconies. The greater loss of life in Morocco was due to the abundance of adobe10 structures, and the recent wet spell that had left the soil saturated. This earthquake was felt over a 1,300km distance, being reported in Bordeaux, France and the Canary Islands.

San Francisco, USA, 1906, measured 7.9 on the Richter scale and involved a slip of the San Andreas Fault.

Kobe, Japan, 1995, measured 6.9 on the Richter scale.

Bam, Iran, 2003, was only 6.7 on the Richter scale, but the predominence of old adobe buildings led to great loss of life.

References and Acknowledgements

Current Earthquake Occurrences

1The Richter Scale is an exponential measure of seismic wave energy or magnitude. 8.5 is reckoned to be the equivalent of 5 billion tons of TNT.2A Japanese term meaning 'harbour wave'; (Pacific), now generally scientifically used as the term for a tidal wave (Atlantic) or any great wave generated by earthquake, volcano or massive landslip.3A seiche is an earthquake-generated agitation of water in inland lakes and bodies of water.4An ell is a measurement of 45 inches (around 1.15m).5As quoted at Online Literature Library.6At 1875 value.7This Portuguese Statesman is better known internationally as the Marquis of Pombal, the title granted him in 1779.8At 1875 value.9Turbidity is the cloudiness caused by solids suspended in water.10Sun-dried mud brick.

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