• Introduction
• Historical Research Methodology
• Conclusions
• Acknowledgements
• References

Introduction
The subproject "Review of the historical seismicity in the Gulf of Cadiz area before the 1 Nov. 1755 earthquake" is included in a more vast project - "Review of historical seismicity in Europe" - the aim of which is to establish a common methodology among European seismologists and historians on research of historical seismicity and to get a significant set of data on earthquake potential and effects. In this report, which corresponds to the whole period of the execution of the project (1989-91), are referred the main results obtained. The execution of this project is under the responsibility of the National Institute for Meteorology and Geophysics of Portugal and the National Geographic Institute of Spain. It is believed that the long-term precedent research carried out in Portugal immediately before the beginning of this project (Moreira, 1984; 1991; Runa e Morais Freire, 1985; Themudo Barata et al., 1988; 1989) and by Pereira de Sousa (1919-32) in the second and third decades of the present century led to the acquisition of a large part of the existing data about the earthquakes that occurred after the 16th century. Anyway, research in libraries and archives continued both in Portugal and Spain during the period covered by this project and several reports were produced showing the results. Meetings to examine the state-of-the-art of the project and define the methodology, in which participated Dr. Stucchi, coordinator of the project "Review of historical seismicity in Europe", Dr. Paola Albini, historian who assists Dr. Stucchi, the Portuguese and Spanish groups were held in Lisbon in 1989 and 1990. In 1989 and 1990 was paid special attention to the research in archives and libraries in Algarve and Alentejo - the southernmost provinces of Portugal - the most affected regions by earthquakes which occurred in the period covered by the project. In Spain a research was carried out in 1990 in several archives and libraries of the southwestern part of the country (Moreira, 1990). In the last part of 1990 and 1991 was made an intense research in the National Archive of Torre do Tombo in Lisbon, looking for documentation of the main convents and for documentation left by diarists, journalists, members of the diplomatic body and other erudite people, following the recommendations of Dr. Stucchi in his note of June 1990 "Remarks and recommendations after the first year".

Historical Research. Methodology
The first work which was carried out for the execution of this project was the collection of all available data which had already been obtained from the precedent long-term research carried out by historians and seismologists (Moreira, 1984; 1991; Themudo Barata et al., 1988; 1989). With these data was possible to do a basic catalogue for the Gulf of Cadiz area covering the period of the project (Moreira, 1992). The following step was to try to get more information looking for contemporary press reports and manuscripts that could exist in the main libraries and archives in southern Portugal. One historian carried out research of this type in libraries and archives during about one year in Algarve and Alentejo (Ferrão, 1989a; 1989b; 1990a; 1990b).
Some information was found about small earthquakes which occurred during the period of the project. This research was carried out mainly in 1989 and 1990. During this period was also prepared a study on the religious settlement, showing the distribution of the military orders, monasteries, centres of clerical administration, convents and other institutions all over the country, that could have worked as macroseismic observatories and therefore could furnish information on the main earthquakes felt during the period of the project (Fig. 1). Based on the report presented by the historian who carried out that work (Moreira, 1990), an intensive research was carried out in the National Archive of Torre do Tombo in Lisbon with the aim of obtaining information from documents written by people who lived in the institutions above referred and that surely felt the earthquakes that occurred in that time, especially the earthquake of 27 Dec. 1722. To do this work different types of sources were searched, as follows: contemporary letters, eye-witnesses reports, invoices of sums paid to repair damaged buildings, contemporary texts with religious or religious and economical tendency, non-contemporary texts containing transcriptions of contemporary manuscripts.
This research could also select the places to get data if we could infer the way that some documentation followed. Among others, documentation of the following convents and monasteries was consulted:
- Avis: S. Bento convent
- Beja: N. Sra. da Conceição convent, Santa Clara convent
- Estremoz: S. Francisco convent
- Évora: N. Sra. do Espinheiro convent, Sta. Clara convent, S. João Evangelista convent, N. Sra. do Paraiso monastery
- Faro: Sto. António convent, Ordem Terceira da Penitência convent

- Lagoa: Carmo convent
- Lisboa: S. Francisco convent, S. Bento convent
- Marvão: N. Sra. da Estrela convent
- Sertã: Sto. António convent
- Setubal: Sta. Teresa de Jesus convent
- Tavira: S. Francisco convent
- Tibães: S. Martinho convent

In this documentation was found some information about the 1 Nov. 1755 earthquake. It was also found information about an obscure earthquake occurred in June 1769 (ANTT, 1776-1808). Till now it was only known that that earthquake had been felt in Lisbon without any damage. The new information shows that was also felt in Setúbal where it caused destructions. Its epicentre is probably localized in the same area of the 11 Nov. 1858 earthquake. It was supposed that diplomatic correspondence could give useful information. The following diplomatic correspondence was consulted:
"Correspondence sent to the Portuguese Legation in London" (1723-1725, 1737-1741);
"Legation of Portugal in Hague": correspondence sent to several consuls (1819-1826) and correspondence received from several consuls (1802-1824);
"Legation of Portugal in London": letters sent to several people;
"Consulate of Portugal in Cadiz": several documentation, private correspondence (1834-1837).

In this documentation was not found any reference to earthquakes or any reference which could lead to the localization of any document, interesting this project, in another archive. Documentation from centres of clerical administration and religious orders was also consulted.
It was supposed that the archives of the only Portuguese newspaper that was published in the first half of the 18th century - Gazeta de Lisboa - could give some information. Unhappily that archive was not yet found till now. The same happens with the documentation left by diarists.
Anyway, as a result of this research some information was found to join to the basic catalogue that was referred in the beginning of this paragraph, but most of the information that was found is concerned with the 1755 earthquake. Information about the 1 Nov. 1755 earthquake itself was not considered for this project but all the available data on precursory phenomena of this earthquake were collected (Fig. 2). Details are given in Tabb. 1 and 2.

A catalogue of aftershocks of the 1 Nov. 1755 earthquake with the corresponding descriptions and references was prepared (Moreira, 1992).
On the other hand, documentation about the 31 March 1761 earthquake which was found during this research was considered and included in this project. This earthquake which is considered by many authors as a late aftershock of the 1 Nov. 1755 earthquake (Montandon, 1953; Mezcua y Martinez Solares, 1983) reveals, in the light of the new data, that really appears not to be.

The most striking point is that no data from Algarve were found till now.
This fact, conjugated with the circumstance that the 1761 earthquake was stronger at Oporto than the 1755 earthquake, was felt in southern Ireland and southwest England, was strongly felt by ships that navigated off the Finisterre cape (Philos. Trans. Roy. Soc. London, 1761; p. 421), reinforces the hypothesis that this earthquake was not an aftershock of the 1755 earthquake, having epicentre in another area, probably in the Galiza Bank region. Detail about this earthquake are given in Tabb. 3 and 4. More data are given by Moreira (1989).
Contacts with the "Institut Scientifique de Rabat" were established. No data about the 27 Dec. 1722 were found in Morocco. It is nearly sure that this earthquake was not felt in that country (Dr. Cherkaoui, personal communication).

However, in the research carried out in Portugal and Spain was found some more information about the 27 Dec. 1722 earthquake to join to that already available in the basic catalogue above referred. This information is concerned with the effects of the earthquake in Lisbon, where it is now known that, at least, bells rung in a church situated in the eastern part of the city (Belém, 1750; p. 200) and in Seville (AMSev, XVIII).

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 houses. At a village about 20 miles from Oporto 3 or 4 houses were destroyed and some people killed. 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 (Lisboa) underwent damage. In Setubal several buildings were overthrown. In Évora it opened some cracks.
Spain	Felt in Madrid, where it shook the houses throwing down the furnitures. Felt in Aranjuez, Alcalá la Real and Jaen.
Ireland	In Cork an earthquake was felt at a quarter after noon. Was considered to be more violent than that of 1 Nov. 1755.
United Kingdom	The Lock Ness rose about 2 feet in the afternoon and continued alternately rising and falling for the space of three quarters of an hour. Similar to the 1 Nov. 1755.
France	Felt at Bayonne and Bordeaux (Perrey, 1847).
Netherlands	At Amsterdam the lamps of the synagogue and of the Maesland Church were observed to vibrate between one and two o'clock.

Tab. 3 - Earthquake of 31 March 1761. Macroseismic data taken from Philos. Trans. Roy. Soc. London, 1761 (Courtesy of Dr. Robert Muir Wood, Cambridge, England).

PLACE	TIME	EFFECTS
Some leagues of the shore from Lisbon, lat. 43o	10 min. a.m.	Violent shock. It shook the needle off the spindle of the compass.
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.
Several leagues to the west of Cape Finisterre		It appeared that the ship had struck on sunken rocks.
It was felt more violently on the ocean, between the coasts of Spain and the British Channel.

Tab. 4 - Earthquake of 31 March 1761. Observations in ships. Data taken from Philos. Trans. Roy. Soc. London, 1761 (Courtesy of Dr. Robert Muir Wood, Cambridge, England).

Fig. 3 - Isoseismal map of the 27 Dec. 1722 earthquake.

With the data now available was possible to draw the isosseismal map shown in Fig. 3.
On the other hand no contemporary data were found in Morocco about the so-called 1731 Agadir earthquake and corresponding tsunami (Dr. Cherkaoui, personal communication), what places this earthquake in the category of the doubtful ones. The only source known is Verneur (1822); he reports that an earthquake destroyed the city of Santa Cruz (Agadir).
Although this document was published about one century after the event,that information has been copied by several authors, as Perrey (1847), Galbis Rodríguez (1932) and others (Cherkaoui, personal communication). Taher (1979), who consulted a considerable number of arab documentation, to prepare his catalogue, does not mention this earthquake.

Conclusions
As a result of the research carried out in several archives in southern Portugal in 1989 and 1990 and in the National Archive of Torre do Tombo in Lisbon in 1990 and 1991 some new data were found. This data refer essentially to:

a) some information about several small earthquakes,
b) new data about the Setubal earthquake of June 1769, till now considered to be an obscure earthquake only felt slightly in Lisbon,
c) development of the information about the 31 March 1761 earthquake leading to the establishment of a new position of the epicentre giving up the classical hypothesis that considered this earthquake as a late aftershock of the 1 Nov. 1755 earthquake,
d) new data about the 27 Dec. 1722 earthquake. It is now known that this earthquake was slightly felt in Seville (Gonzalez Jiménez, 1990; Lopez Arroyo, 1990) and in Lisbon and probably was not felt in Morocco,
e) new data were collected about precursory phenomena of the 1 Nov. 1755 earthquake. This achievement is one the most important obtained in the frame of this project because this new data reveal to have high interest in the important problem of earthquake prediction.

The data obtained till now as a result of this research reveal to have high interest for the improvement of the knowledge of the seismicity of the Gulf of Cadiz area and constitute an important contribution for the preparation of the Portuguese National Seismic Catalogue.

Acknowledgements
Many thanks are due to Mrs. Maria Jerónima Taquelim and Mrs. Maria de Lourdes Aleixo for the contribution in the research carried out in archives and libraries which revealed very useful for the execution of the project. Thanks are extended to Mr. Colaço who drew the figures.

References
Amezua, F. Lopez de, 1755. Carta philosophica. Madrid.
AMSev (Archivo Municipal de Sevilla), XVIII. Papeles del Conde del Aguila, 3, 11.
ANTT (Arquivo Nacional da Torre do Tombo, Lisboa), 1776-1808. Convento de Sta. Clara, Évora, Livro de foros e rendas, 35.
Belém, Fr. J. de, 1750. Chronica Serafica da Santa Provincia dos Algarves, da Regular Observancia do Nosso Senhor Padre S. Francisco, Em que se trata de sua Origem, Progressos e Fundações de seus Conventos, Parte Primeira. Lisboa.
Ferrão, N., 1989a. Relatório da pesquisa efectuada no arquivo histórico de Loulé (INMG internal report).
Ferrão, N., 1989b. Relatório da pesquisa efectuada na biblioteca pública, arquivo distrital de Évora (INMG final report, Annex 1).
Ferrão, N., 1990a. Relatório da pesquisa efectuada entre Dezembro e Janeiro - 89/90 (INMG final report, Annex 2).
Ferrão, N., 1990b. Pesquisa de fontes históricas. Projecto e progressão (INMG annual report 1990, Annex 1).
Galbis Rodríguez, J., 1932. Catálogo Sísmico. Inst. Geog. Catastral y de Estadística, Madrid.
Gonzalez Jiménez, M., 1990. Terremotos en Sevilla (siglo XVIII). Informe (INMG report 1990, Annex 3).
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Kant, I.M., 1910b. Geschichte und Naturbeschreibung der merkwürdigsten Vorfälle des Erdbebens, welches am Ende des 1755sten Jahres einen grossen Teil der Erde erschüttert hat. In: "Kants Werke", Vorkritische Schriften, vol 1. Königlich Preussiche Akademie der Wissenschaften, Berlin.
Lopez Arroyo, A. (Editor), 1990. La sismicidad historica del Golfo de Cadiz (primera mitad del siglo XVIII) (INMG final report, Annex 3).
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