A Portuguese newspaper published in the 7th April 1761 (Gazeta de Lisboa, 1761) gives the following report: “Last Tuesday, last day of March, after noon an earthquake was felt in this city, lasting for more than 3 minutes, it was preceded by a large subterranean noise that was heard but not generally. The inhabitants of this city, used to natural repetitions of similar phenomena, most of them did not leave their homes, and having the shock return after noon near 3 o'clock everything was in perfect tranquillity. The shock did not generate considerable damage”. Sousa (1919) quotes a coeval document (manuscript 1229) where a more detailed description of the damage in Lisbon is made: “several walls collapsed and a few properties ruined among which some in Rua Augusta (Lisbon downtown)”.
A letter dated the 2nd April 1761, published by the Philosophical Transactions gives the following description: “The earthquake happened by the 31st last month, precisely at twelve o’clock, and lasted full five minutes, with a smart and equal vibration. It exceeded all the others, except that of the first November 1755. Thank God, it was attended with no other consequences, but that of alarming the inhabitants, throwing down some home ruins, and rending some houses” (Unknown a, 1761). Another letter published in the 1761 volume of the Philosophical Transactions confirms the time of occurrence and the duration of the event and describes its effects in the following way: “Many buildings have tumbled down, but few people were killed, some have died through fear” (Molloy, 1761).
In a letter sent from Coruña to The London Chronicle (Unknown b, 1761) the 2nd April and published in April 21st, we can read: “On the 31st ult. we had a terrible shock of an earthquake, which lasted between three and four minutes, but thank God has done very little damage, which, next to the Divine Mercy, is ascribed to the evenness or its motion. As false reports may be spread amongst you on this occasion, this packet is dispatched to prevent them gaining credit”. In the same journal, we can also read: “The King George packet-boat, Captain Bowne, is arrived at Falmouth from Lisbon, in 16 days. She brings an account, that they had there a violent shock of an earthquake on the 31st ult. but that no lives were lost; that only a few old houses were shattered, and some new ones cracked; it lasted five minutes, and was thought as severe as that in 1755” (Unknown c, 1761).
The Annual Register (1761) includes the following letter in pages 93-94: “Lisbon, April 15. We had an earthquake here the 31st ultimo, which lasted longer, and to the apprehension of the inhabitants was much brisker than that which overturned the city; but passing in a direct line, did no other mischief than splitting most of the walls, more or less: Villa Franca, however, is reduced to a heap of rubbish, and St. Ubes (now, Setúbal) and some other country places had suffered severely. There are several rents or charms in the earth, through which considerable quantities of sand or shells have been thrown […]. The sea and the rivers gave visible marks of an uncommon agitation for ten days. […]. They apprehend this city not to have been the centre of it; and that it has been more fatal to the northward”.
According to The London Chronicle (Unknown d, 1761) “By letters from Oporto of the 13th ult. we have an account, that the earthquake which happened on the 31st of March, was felt there very strong, but did no damage; but at a village about twenty miles distance, three or four houses were thrown down, by which several people were killed”.
One year after, Borlase (1762) makes a first synopsis of all information available on the 1761 earthquake. He quotes The London Chronicle (p. 426) and describes the effects in Oporto as: “Shock felt very strong (without damage); but at a village 20 miles distance, some houses were thrown down, and several people killed”. He also quotes eye witnesses on board of an English vessel at the London Chronicle (p. 426) “[…] I saw the ruins of the last earthquake falling heap upon heap, and, turning round, beheld the rocks on the opposite side falling from the mountains, followed by a continual cry of the people; the buildings erected in 1755 damaged, to the amount of 20,000 moidores at least”.
Eigthy five years later, Perrey (1847) makes a new synopsis: “1761, 31 March, 0 hours 5 minutes afternoon, in Lisbon, a strong vertical shock lasting 5 minutes and generating some damage [One hour and a half after, water showed an elevation of 8 feet]. At midnight, a second shock was felt and other three during the night. […] Apparently other shocks were felt before the one felt at noon and also others were felt after that day. The noon shock was very strong at Oporto where, according to some, lots of buildings were thrown down and, according to others, little damage was observed. The direction was from north to south. St-Ubes [Setubal] suffered a lot”.
Sousa (1919), who was the most systematic researcher of the 1755 earthquake, describes significant destruction in Beja, Coimbra, Setúbal and Oporto, that he attributes to the 1761 event. Beja observations were based on a coeval document (Notícias várias de Évora) that describes: "In the 31st of March 1761 at half past eleven an earthquake lasted for half quarter of an hour, (...) the land and walls had less damage than in the thanksgiving day earthquake (…) in Beja a wall collapsed killing three persons, S Francisco monastery was severely damaged". Moreira et al. (1993) summarizes most of the above descriptions in the following way: “Mainland Portugal: Felt all over the country at about 12 o'clock. Damage in several places especially in old buildings. At Oporto opened cracks in almost every house. At a village about 20 miles from Oporto 3 or 4 houses were destroyed and some people killed. The earthquake was strong in Coimbra. In Lisbon was largely felt, but was not so violent as the earthquake of 1 Nov. 1755. A few old houses were thrown down and some ones cracked. New buildings at Rua Augusta (Lisbon) underwent damage. In Setúbal several buildings were overthrown. In Évora it opened some cracks.”
Heberden (1761) describes the 21st May 1761, the damage in Funchal, the following way: “[…] it began at thirty-five minutes after eleven o’clock in the morning, and lasted (by my watch) full three minutes […]. It has separated some rocks in the eastern part of the island, which have fallen from the cliffs to the sea. It has likewise damaged the walls of several buildings: among the rest my house has suffered, the stone-walls thereof, which are two feet thick, being split in several places, which has happened in particular to the walls, which stand in a direction north and south”.
A letter published in The London Chronicle, dated August 29th 1761, written by the British Consul in the Island of Terceira, Azores (Fearns, 1761) gives the following description: “Since the last of November we have felt several earthquakes […]”.
Borlase (1762) in the synopsis cited above, resumes the observations compiled for Madeira Island: “Shock very violent, did no damage in the town: some rocks split, and fell into the sea; in the island, one church destroyed, four people killed, two of which were fishing near the shore when the rocks fell. Some of the roads suffered.” He also evaluates the time of occurrence as 10 a.m. (Borlase, 1762). For the Azores, Borlase resumes, based upon the London Chronicle from July 1761, the occurrence of an earthquake: "[…] we are alarmed with frequent shocks of earthquakes. The most violent shock we have had of late was on the 31st March last". Perrey (1847) and Mallet (1852) concluded that the event was felt very violently in the Azores and Canaries.
Several records from Spanish observations related with the 1761 earthquake can be found in The London Chronicle. For example, a letter sent from Coruña (Unknown b, 1761) reads: “We had this day at noon a most violent shock of an earthquake, which lasted some minutes: no houses fell down at this place, but many removed some feet from where they stood before. The Consul’s house, which may be numbered amongst the strongest houses in all Europe, has been moved at least four feet forward to the sea, and its front towards the water side, have altered their aspect (in sea phrase) better than two points of the compass”. The London Chronicle April 18th includes also a letter from Amsterdam (Unknown e, 1761) where we can read: “We have an account from Paris, that a little before the departure of the post for this country, an express arrived there, in seven days, from Madrid, with advice, that a violent shock of an earthquake had been felt there, and along the coast of Spain, on the 31st of March”.
For the Spanish mainland there is a coeval systematic compilation made by the president of the Real y Supremo Consejo de Castilla (Royal and Supreme Council of Castilla) also bishop of Cartagena, Diego de Rojas y Contreras who sent a letter to all local authorities to ask for information of the 31 March 1761 earthquake, including reports of the earthquake occurrence, number of victims and damage (De La Torre, 1997). These answers, which correspond to the largest dataset for this event, were reviewed recently by De la Torre (1997).
In table I we present a synopsis of his conclusions, and we assign geographic coordinates and macroseismic intensity to each one. We can see a significant range of macroseismic intensities, between I and VI (MSK). Largest effects were observed in Alcantara, Ayamonte, Baeza, Coria (damage on the Cathedral Tower), Granada and Puerto de Santa Maria.
The 1761 edition of the Annual Register includes an extract from a letter “from a gentleman of Santa Cruz, South Barbary [Agadir] dated April 17th 1761: “I am sorry to tell you we have had two shocks of an earthquake, first was the 31st of March, at twelve at noon, which was very slight, and did no damage; the second was the 9th inst. at half past seven in the evening, and a most dreadful one it was; it did not last above a quarter of a minute; had it lasted half a minute longer, the town had been infallibly laid in ruins; it has split the walls of most of the houses; and ours, though one of the strongest, has suffered greatly. We were writing when the dust and small stones began to rattle about us; we immediately ran up on the top of the house, and the dreadful terror we pall that night in, fearing a return can only be known by those that felt it. We are very far from being recovered from the consternation it put us in. The noise alarms us; and we frequently think the ground shakes when there is no such thing. God preserve us, and send us safe out of this dreadful country.” (Annual Register, 1761, page 95).
The 1761 event was observed in several places along UK and Ireland coasts. A letter reproduced in the London Chronicle, 9th April 1761, and included in the page 92 of Annual Register (1761) reads: “Cork, March 31. A quarter after twelve this day a shock of an earthquake was felt here in the Exchange, in the Merchants Coffee-house, and from the beginning of the Red-house Walk, to the East-Marsh, between the gates only, just as it was in November 1755: but allowed to be more violent by all that felt it. It did not continue above one minute, undulating from east to west and vice versa”. The same letter is reproduced by Borlase (1762) and quoted from The London Chronicle, page 350.
In a letter from Kinsale, published by The London Chronicle also reproduced with the date April 7th, by the Annual Register (1761), this conclusion does not seem so evident. “As to what is mentioned in Cork News-paper, about the shock of an earthquake on Tuesday last, there might be one felt there; but here I cannot find any person felt any such thing”. Eighty five years later, Perrey (1847), however, summarizes this way: “a violent shake was felt in Cork (Ireland) between noon and one o’clock and oscillations stand for one minute. This is reported as being more violent than 1755 event.”
A letter published by the London Chronicle, reproduced also in the Annual Register (1761) reports the effects of the earthquake effects in France: ”This new is confirmed by letters from Bayonne, which add, that a pretty smart shock, which lasted three minutes, was felt there the same day. And from Bordeaux they write that a shock of an earthquake was felt there on the 1st April, about one in the afternoon”. Perrey (1847) considered this report from Bordeaux related with the same earthquake.
The influence of the above information on the readers of London Chronicle and Philosophical Transactions was significant and new “possible” observations of the 1761 earthquake were described. This is the case of the Maesland-Slys synagogue: “These accounts have made us recollect the vibrations which we thought we observed here (at Amsterdam) on the 31st of March, between half an hour after one and two in the afternoon, particularly in the Synagogue, where the branches seemed to move; and in the great church of Maesland-Slys, the branches moved about a foot from the perpendicular; and the vessels in the harbour were agitated” (Unknown e, 1761). The same letter is reproduced in the Philosophical Transactions and in the Annual Register (1761). Most of the ulterior studies incorporated this observation (e.g. Borlase, 1762, Perrey, 1847, Mallet, 1852).
A letter dated the 2nd April 1761, published by the Philosophical Transactions gives the following description: “About an hour and a quarter afterwards [after the earthquake] the sea began to flow and ebb, about eight fleet [feet?] perpendicular, every six minutes, and continued till night” (Unknown a, 1761). Another letter dated from the 3rd April 1761 describes the tsunami at Lisbon in the following way: “The agitation at sea was very great, during the time of the tremor; and, for some hours after it, the waters ebbed and flowed many feet perpendicularly, several times in the space of every six minutes. Ships at anchor in the river, though riding in some fathoms of water, were left dry at some intervals” (Molloy, 1761).
According to De La Torre (1997) there are observations of sea water changes in Ayamonte, Puerto de Santa Maria, Cadiz and Barcelona. Several ships on sea, near to Lisbon, noticed the shake (Philosophical Transactions. Vol. LII, pages 141, 155, 422, 425, 428). This information is also reproduced by Von Hoff (1841) (in De La Torre, 1997) and Perrey (1847).
Heberden (1761) describes the observations in Funchal, on a letter dated May, 21st 1761: “[…] The sea was agitated very sensibly, fluctuating several times between high-water and low-water mark. The fluctuation of the sea continuated longer in the eastern parts of the island, than in this part”. Perrey (1847) reproduces this observation: “the waters were highly agitated in the eastern shore”.
In a letter published in The London Chronicle, August 29th, 1761 written by the British Consul in the Island of Terceira, Azores (Fearns, 1761) we get the following description: “[…] on the 31st of March the sea rose to a great height, and fell again so low, that the Quays were left dry; all the lighters and fishing-boats that were hauled un in Porto Rico were carried down into the bay and broke to pieces upon the rocks”. Borlase (1762) partially quotes this description.
The French newspaper “Mercure de France”, July 1761, describes: “[from London, 31st May]: "A ship coming from Canary Islands reported an earthquake on past 31st March, felt there with lots of violence". In its October 1761 volume, we get the following description "[Madrid, 25th August]. According to news from Terceira Island, the sea around the island raise up on the 31st March last, to a great height and, some minutes after, recovered the usual level. For a 3 hours interval, it raise up and down several times in succession" (in De La Torre, 1997).
Mason (1761) in a letter to the Royal Society describes what he has observed in Barbados: “Barbadoes, May 30, 1761. I cannot omit giving you an account of a very extraordinary motion of the sea, I think it was the last day of March past, unlike that, remarked here, on the dreadful day of calamity, which happened at Lisbon, with this difference, the last was not so sudden as the former, in the flux and reflux, which suddenly shews, that the shock must have been greater, that occasioned it, as it is most likely they proceeded from the same cause, (viz.) that of an earthquake, whereby some place, under the surface of the sea has been sunk. According to the best observations that could be made, the tide ebbed and flowed, in about eight minutes, between eighteen inches and two feet, and continued so three hours, regularly decreasing till night, when it was no more observable”.
In the Annual Register (1761) we can also read: “Barbadoes, April. On the 31st of March, at four o’clock in the afternoon, fluxes and refluxes of the sea here, which about eight seemed to abate, but at ten considerably increased, and continued till six o’clock next morning. It is observed that the same agitation of the water was perceived here, at the time the earthquake happened at Lisbon in 1755”. This description is quoted by Von Hoff (1841) (in De La Torre, 1997) and Perrey (1847) which conclude that significant water agitation of the sea was observed in Barbados at 4:30 pm, corresponding to 8:30 pm Lisbon time (De La Torre, 1997).
The identification of the 1761 tsunami in Barbados has been considered in most of the tsunami catalogues for the Caribbean (Zahibo and Pelinovski, 2001) but according to Shepherd (2001) it is not supported by any local source.
While earthquake observation in southern Ireland seem not well established, a letter from Kinsale, published by The London Chronicle on its 11th April 1761 issue and also reproduced in the Annual Register (1761): “[…] it was about six o’clock in the evening; near dead low-water the tide rose suddenly in our Strand, about two feet higher that it was, and went out again in the space of four minutes with great force, which repeated several times, but the first was the greatest.”
Borlase (1762) describes: “On the Tuesday, the 31st of March 1761, about five o’clock in the afternoon, there was a very uncommon motion of the tide in Mount’s-bay, Cornwall. […] After the tide has ebbed about four hours and half, (for the time is not determined with precision) instead of continuing to retreat gradually, as usual, till it had completed the six hours ebb, on a sudden it advanced as it is usually at the time of the Moon, at an hour and half high-water. It then retreated nigh to the point of low-water, then it advanced again, and retreated, making five advances, and as many recesses, in the space of one hour; viz. from about five to six o’clock; which was the whole time, that these uncommon stretches of the tide continued. But the first motion was most considerable, the sea advancing the first time to a quarter ebb; but the second advance was but as far as the sea reaches at half ebb. A small sloop of 30 tons burthen, at that time laden and dry in Penzance pier, by the first surge, was fleeted; by which it appears, that the waters rose at this place six feet perpendicular, that sloop requiring six feet of water to fleet it. At the pier of St Michael’s mount, three miles to the east of Penzance the tide was observed, at the same time, to rise and fall about four feet. At Newlyn, (a mile west of Penzance) the tide rose to the same height nearly, as at Penzance. At Moushole pier, (three miles SW of Penzance) it was only observed, that the sea was in great agitation, and the fishing boats in danger. At the islands of Scilly, the sea was judged to raise about four feet; but the agitation to have continued longer than in Mount’s-bay, viz. more than two hours”. In a table included in his compilation, Borlase (1762) completes this description with a table where we can read: "Scilly Islands, time of beginning: About five PM [...], degrees of violence, and variety of circumstances: Sea rose two feet".
Borlase (1762) includes also a description of a similar phenomenon in the Lochness: “On the coast of Scotland, from Fort Augustus on Lochness, we had accounts, that, on the same 31st of March, about two in the afternoon, Lochness rose, on a sudden, about two feet perpendicularly, and continued, alternately, rising and falling, for the space of three quarters of an hour” (Borlase, 1762). This last information deserves a comment because it is reproduced elsewhere (e.g. Annual Register, 1761, Perrey, 1847). A letter published in The London Chronicle, April 9th, and dated 30 March 1761 describes “A very uncommon phenomenon happened here [Fort Augustus] yesterday. About two in the afternoon Loch Ness rose on a sudden about two feet in perpendicular height, and continued, alternately, rising and falling, for the space of three quarters of an hour” (Unknown f, 1761). The Portuguese newspaper Gazeta de Lisboa, from May 19th 1761 gives a similar report: “ We know that on the 29th of the some month the waters of Loch Ness, in Scotland, raise and grow in the center of the lake, 2 feet above the ordinary level”. In this case it is clear that there is no mistake on the date (29 March 1761) and it is considered a foreshock of the earthquake: “we can rightly hypothesize that it was a precursor of the earthquake that was felt the 31st March in Cork, having the same cause”. Being so, we can discard any connection between the 1761 earthquake and Loch Ness observations.
In The London Chronicle 2nd May 1761 we can read the following description: “They write from Cork, that on the 16th past, the Amey of Bristol, Capt. Condon, arrived there from Lisbon, who in his passage from thence on the 31st ult., in the latitude of 43º, not many leagues off shore, felt a most violent shock, which from the agitation of the matters he soon discovered to be the effects of an earthquake. The concussion was so great as to shake the needle off the spindle of the compass, and immediately after, there arose such a storm of wind and raia [rain?] as he never before met with – By the captain reckoning, he felt this shock ten minutes AM (PM?) being half an hour before it was felt at Cork, and five hours before the waters rose in Kinsale on the some day” (Unknown g, 1761).
According to Van Hoff (1841, in De La Torre, 1997) “some ships, at sea, at a certain distance from Lisbon suffered two shocks at 11h 45m and 11h 50m in the morning. A needle felt off the spindle of the compass; a submarine noise was heard”.
The Annual Register (1761) reproduces a letter from on board his majesty’s ship Gosport, in the Downs, dated April 16, where we can read: “On the 31st ult. in our passage here from Lisbon, being then in the latitude of 44.8 N long 5.10. off the rock of Lisbon, Cape Finisterre bearing ESE about 80 leagues, at three quarters past eleven in the forenoon, the weather was quite calm, we were alarmed with two violent shocks of an earthquake, which was felt by all merchantmen under our convoy, some of whom the violence of the shocks caused to make water: The first continued near a minute and a half; the second not so long: The shaking of the ship was not unlike that occasioned by letting go an anchor, and the cable running fast round the bits, or by a ship’s striking on a sunken rock, which many abroad thought to be the case, till they recollected the shocks felt by ships at sea during the great earthquake at Lisbon the 1st November 1755, and which the shocks they now felt perfectly resembled”.
Robert Muirwood (in Moreira et al., 1993) quotes another probable seaquake description “off Lisbon; 44º 29' N; 11º 19' W. The ship shook so dreadfully that the crew threw out the boat in order to leave her”. He also considers that it was felt more violently on the ocean, between the coasts of Spain and the British Channel. However we were unable to find the original source of this description.
Annual Register, 1761. Volume 4, pages 92-95.
Borlase, W. 1762. Some Account of the extraordinary Agitation of the Waters in Mount’s-bay, and other Places, on the 31st of March 1761: In a Letter for the Reverend Dr. C Lyttelton, Philosophical Transactions of the Royal Society, vol. 52, Page 418-431.
De la Torre, F. R, 1997. Revisión del Catálogo Sísmico Ibérico (años 1760 a 1800) Estudio realizado para el Instituto Geográfico Nacional, mediante convenio de investigación número 7.070, de 1997. Madrid.
Fearns, J., 1761. Letter to The London Chronicle N. 731, page. 214.
Gazeta de Lisboa published the 7th April 1761.
Heberden, T., 1761. An Account of the Earthquake felt in the Island of Madeira, March 31, 1761. Communicated by W Heberden, Philosophical Transactions of the Royal Society, vol. 52, pag 155.
Mallet, R., 1852. Report on the Facts of Earthquake Phenomena.
Mason, Abraham, Letter to the Reverend Thomas Birch, D. D. Secretary to the Royal Society, relating to an extraordinary agitation of the Sea there, 31st of March 1761, Philosophical Transactions of the Royal Society, vol. 52, page 477-478.
Molloy, 1761. Philosophical Transactions of the Royal Society, Vol. 52, Page 142-143.
Moreira, V, Sousa, J. S. Marques, J. F. Cruz, J. C. Nunes, EC project "Review of Historical Seismicity in Europe" (RHISE) 1989-1993.
Perrey, A., 1847. Sur les tremblements de terre de la Peninsule Ibérique. Annales des sciences physiques et naturelles, d'agriculture et d'industrie, X. Societé Royale d'agriculture, d'histoire naturelle et des arts utiles, Lyon.
Shepherd, J. B., 2001. Tsunami Hazard in the Eastern Caribbean, Workshop On Volcanic And Seismic Hazards In The Eastern Caribbean.
Sousa, F. L. P. 1919. O terremoto do 1º de Novembro de 1755 em Portugal e um estudo demográfico, Servicos Geológicos, 4 vols.
Unknown a, 1761. An Account of the Earthquake at Lisbon, 31st March 1761: In a Letter from thence, dated 2nd April 1761, to Joseph Salvador, Esq. F.R.S. Philos. Trans. Letter XXVI. pp. 141-142.
Unknown b, 1761. Letter from Corunna to The London Chronicle, April 21-23, p 390.
Unknown c, 1761. The London Chronicle, “The King George packet-boat, Captain Bowne”.
Unknown d, 1761. The London Chronicle, “By letters from Oporto”.
Unknown e, 1761. The London Chronicle, Maesland-Slys, of April 18th.
Unknown f, 1761, The London Chronicle, Letter from Fort Augustus.
Unknown g, 1761. The London Chronicle, May 2-5, p 226.
Zahibo N and E. N. Pelinovsky, 2001. Evaluation of tsunami risk in the Lesser Antilles, Natural Hazards and Earth System Sciences (2001) 1: 221–231.
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