EC project "Review of Historical Seismicity in Europe" (RHISE) 1989-1993

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• Introduction
• Archive research
• Data analysis and results
• Discussion
• Conclusions
• References

Introduction
During the period 1427-1428 a series of earthquakes produced important damage in an area of the Eastern Pyrenees in Catalonia. It is known (Olivera et al., 1992) that the main events of the series were that of 15 March 1427, with main damage in the village of Amer, that of 15 May 1427, which destroyed the town of Olot and that of 2 February 1428 with epicenter located more to the NW between Puigcerdà and Camprodon (see Fig.1).

The severity (in intensity and extension of damage) of these events had caused many catalan historians to be interested in their study. Thus, around 1550, the historian Jeroni Pujades transcribed and summarized a set of documents on the effects of the earthquakes in the bishopric of Girona. This manuscript, known as "Flosculi", is now at the Biblioteque National in Paris and was published by Giralt (1889) and Montsalvatge (1906).
As said, the 1427 earthquakes destroyed the village of Amer and an important part of the town of Olot. Because of this, some local historians such as Bolós (1841), Paluzie (1860) and Danes i Torras (1937) carried out various studies on their effects. The above mentioned sources are essentially the origin of the data on these events contained in the main earthquake catalogues, in particular that of Fontserè and Iglésies (1971), which is a valuable data collection on earthquakes occurred in Catalonia, Valencia and Balearic Islands. This compilation should be considered as the starting point for any research on historical seismicity of these regions, since it includes a large amount of data together with complete references. More recently, new information sources coming from Spanish archives have been brought by Rubió (1961) and Prades (1989), while Riu (1980) and Del Valle (1990) have contributed with new data from foreign archives. Based on data contained in the compilation by Fontserè and Iglésies (1971), Cadiot (1979) and Banda and Correig (1984) published isoseismal maps for the February 2, 1428 earthquake. This earthquake took place in a region already damaged by the former events of the series and there is evidence that some of their reported effects could possibly be mixed (Olivera et al., 1991).
The purpose of this paper is to present the results of the research carried out on the 1427 events, within the frame of the CEC project Review of Historical Seismicity in Europe (RHISE). Here the seismic period 1420-1427 is reviewed as a contribution to the programme for hazard evaluation in Catalonia.

Archive research
The starting point of our research has been the Fontseré and Iglésies (1971) compilation. The research work has been organized in two parts.

Critical review of Fontserè and Iglésies catalogue
A critical review of the information contained in the Fontserè and Iglésies catalogue has been carried out by a systematical classification and quality evaluation of sources. The majority of sources considered in this catalogue are published accounts, not contemporary to the events. Research on these secondary sources has been carried out in the following archives and libraries in Barcelona: Biblioteca de Catalunya, Biblioteca de la Secció d'Estudis Medievals de la Institució Milà i Fontanals (CSIC), Biblioteca de la Universitat de Barcelona, Biblioteca de la Facultat d'Història de la Universitat de Barcelona; and the Biblioteque National in Paris.
Great effort has been devoted to the investigation on how information was transmitted through different secondary sources and trying to recover the references to original sources contemporary to the earthquakes. Many multiplicities in pieces of information that actually come from the same single source have been confirmed.

Retrieval of sources contemporary to the events used by former compilers and search for new original documents
Abundant contemporary reports were expected to exist given the particular organization of Catalonia during the Middle Age, and in particular concerning the central archives of the Crown (Arxiu de la Corona d'Aragó) that has a section (Cancilleria Reial) in which a copy of all documents sent by the king are still preserved.
The sources that were investigated are of different types: 1) historiographic records (royal, noble and municipal chronicles, monastic and urban annals, diaries); 2) Royal Chancellor Registers (in Catalonia they begun in 1250 and provide balanced, reliable information on all the regions in the kingdom); 3) municipal records (Council agreement books, public announcements, Clavaria -accounting books-, letter registers); 4) ecclesiastical records (pastoral visits, Comunium -in which the register of letters from the bishop is kept-, books on cathedral works, capitular acts); 5) lawsuit record; 6) calendars; 7) notaries' documents (wills, loans, purchase of land for rebuilding).
Intensive search for contemporary sources was undertaken in archives in the following towns: Barcelona (Arxiu de la Corona d'Aragó, Institut Municipal d'Història, Arxiu Diocessà, Arxiu Capitular and Arxiu Històric de Protocols), Girona (Municipal, Diocessà and Capitular), Olot (Municipal), Camprodon (Municipal), Sant Joan de les Abadesses (Municipal), Seu d'Urgell (Municipal, Diocessà and Capitular), Vic (Municipal, Diocessà and Capitular), Cervera (Municipal), Lleida (Municipal and Capitular), Balaguer (Municipal), Tàrrega (Municipal), Terrassa (Municipal), Manresa (Municipal), Igualada (Municipal), Tortosa (Municipal) and Madrid (Archivo Histórico Nacional.).
A highly rich source that has been investigated are the Visites Pastorals of the Girona diocese (Riera-Melis et al., 1993); these are detailed written accounts of the visits to ecclesiastic properties (monasteries, convents, churches, hermitages, chapels). As this visit took place four years after the earthquakes (in 1432) it is not possible to distinguish between the effects of the different events of the series. Nevertheless, it provides a detailed description of damages caused to churches over a wide area. It gives a picture of the extension and severity of the global damage produced by the complete seismic crisis and in some case could be of great help to avoid over and underestimation of intensity.
Critical revision and classification of the sources contained in Fontserè and Iglésies (1971) catalogue concerning 1427 events, together with the analysis of the new pieces of information that have been found, allow us to see how the information in some primary sources was transmitted to the catalogue and how some original sources were never consulted.

Data analysis and results
In the data analysis and interpretation which follows only documentary sources generated prior to February 1428 have been considered in order not to confuse and mix the effects of the 1427 events with those of 1428, in particular with the large one of 2nd February 1428. Critical revision and analysis of the sources yield a re-evaluation of the earthquakes which occurred during the period 1420-1427.
In this analysis different methodological criteria have been followed. An important point is that any event which had been previously catalogued on the basis only of secondary sources, from which it is not possible to identify the original primary source, will be considered as a fake earthquake. Also, given the historical context of Catalonia in the 15th century, when there was a quite evolved administrative system, it is reasonable to consider that a large earthquake has to be reported in more than one document. Thus, if a single source described important damage in a given area and no complementary documents supported this description then we looked for possible duplications of events due to confusion of data in successive transcriptions.
In the analysis of the information sources it should be taken into account that Barcelona was the most important city in the country; it was the residence of the king and held the headquarters of the administration besides being a big commercial and economic centre. For all these reasons a much larger amount of written accounts were generated in this town compared with the other areas of the country.
Therefore, a quite large amount of pieces of information on earthquakes felt in Barcelona have to be considered to be effects of distant, moderate events occurred in the Pyrenees, even though there are no documents reporting them from the epicentral area. This was not considered properly in some former compilations which included epicenters in Barcelona on the basis of these pieces of information. Local information referring to Barcelona are to be used cautiously, considering that even today events of epicentral intensity V, in Pyrenees regions further than Amer and Olot, are often felt in Barcelona.
The new EMS-92 scale (Grünthal, 1993) has been used to assess intensity to the sites where damage is reported. One of the main problems in intensity assessment from historical records is that damage often refers to a single monumental building, involving two main problems: one, the assessment of vulnerability class and, second, the difficulty to define quantities (percentage) of grades damage, which cannot be defined on a statistical basis.

Seismic activity during the period 1420-1427
With the above considerations the documents referring to the period 1420-1427 have been analyzed. The results of this analysis are summarized in Tab. 1 together with the corresponding conclusions from previous studies as contained in the Fontserè and Iglésies (1971) and Instituto Geográfico Nacional (IGN) (1991) catalogues.
From the 20 events analyzed, 7 have been considered to be fake earthquakes, one of them (1426.03.03) having been previously catalogued as intensity VII.
Most of these fake earthquakes were product of data confusions and then duplications of other events of the series. In some other cases they had been catalogued on the basis of dated descriptions of processions or other religious celebrations which actually were social reactions to former earthquakes.
Only two events of the series were destructive earthquakes: that of 15 March 1427 with epicenter in the village of Amer (Io= VIII-IX) and that of 15 May 1427 (Io = IX) with epicentre in the town of Olot. These two earthquakes have been studied in some detail and the results are presented further on. As seen in Tab. 1 the epicenter and maximum intensity that has been obtained in this study on the basis of only primary sources do not differ very much from the catalogued data in Fontserè and Iglésies (1971) and in the catalogue from the Instituto Geográfico Nacional (1991). Critical review and analysis of primary sources confirm the location and the severity of these earthquakes.
Many of the minor events listed in Tab. 1 are mentioned in one source in Barcelona (Manual de Novells Ardits, which compiles official registers from the municipality of Barcelona). Some of them were probably more strongly felt in the town of Girona and its bishopric as they are reported as foreshocks without references to damage, in a letter from the members of the Council of Girona to the king in which they informed about the damages produced by the main shock of 15 March 1427 that destroyed the village of Amer. Some later events are only mentioned in the above referenced source from Barcelona and there is not information related to Girona territories. It is nevertheless reasonable to also consider these events as foreshocks located near Amer, at the same epicentral area as the main shock, rather than near Olot as considered in the IGN catalogue.

The information available for the last event (1427.12.25) contradicts the intensity VIII in Olot assigned in the IGN catalogue. The only reliable source (Llibre de Solemnitats de Barcelona) reports that the event was felt in Barcelona. As explained before, it is then reasonable to think that the epicenter was in the Olot region, but the intensity must have been much lower.

The earthquake of 15 March 1427
Only primary sources dated prior to 15th May are considered in order to reliably determine the epicentral location and intensity of the earthquake without any confusion with the next large event. Some of these sources, in particular the above mentioned letter from the members of the Council of Girona to the king, accurately dates the event and gives a detailed description of the destruction of the village and monastery of Amer.
With the available information on sites where damage took place, intensity values have been assessed and they are represented in Fig. 2. Reported damage is concentrated close to Amer, town in which maximum destruction occurred.
It would not be reliable to draw isoseismals with these data points and, in fact, they are not necessary to define epicenter, which is assumed to be in Amer, with an epicentral intensity VIII-IX.
An apparently discordant data point appears in St. Feliu de Guíxols, on the coast, at about 40 km from Amer. Two newly found documents (two letters from the king Alfons el Magnànim, one to the General Governor and the other one to the members of the councils of the village), which are reliable under the historical point of view, indicate that there was some damage produced by the earthquake to the city walls. Being cautious about this information, and given the distance of this locality to the epicentre, an intensity VI-VII can be assigned.

The earthquake of 15 May 1427
For the study of this earthquake historical accounts have been analyzed with the same criteria as above, considering only primary sources with a date prior to 2nd February 1428.
Fig. 2 also shows the sites for which data are available from primary sources describing damage. Intensity IX is assigned to the town of Olot, which, according to the documents, was destroyed so that the king gave permission to rebuild it in another place (Riera-Melis et al., 1992). A number of points of intensity VIII are located around Olot, extending mainly to the South as far as 15 to 20 km. There is no damage record outside this area.
No isoseismals can be drawn with these data but given that the descriptions of the most severe damage corresponds to the town of Olot, epicentre can be assigned with a reasonably good accuracy to this locality with Io = IX.

Discussion
Quantified the intensities for the 15 March and 15 May events from unambiguous primary data we take up again the information issued from the analysis of the Pastoral Visit of 1432 to the diocese of Girona (Riera-Melis et al., 1993). In that analysis data from 387 churches and other ecclesiastical buildings inspected by the visitor were identified, located and classified according to degree of earthquake damage (completely devastated, destroyed in a very large proportion, partially destroyed, with some form of slight damage and with no noticeable effects). As the Visit was carried out in 1432, the reports of damage have to be considered to correspond to the accumulated effects of the 1427-1428 series. This Visit should be taken only as a complementary data set to be interpreted together with pieces of information confidently ascribable to the individual events.
Using EMS-92 scale, a first attempt to assess intensity has been made from the data reported in the Pastoral Visit. Given that a single building is referred to on each site and that vulnerability class is difficult to assess then large uncertainties in intensity evaluation appear. In Fig. 3 intensity points from the Visit are plotted together with the contour lines surrounding the areas of intensity equal or larger than VII for the earthquake of 15 March and equal or larger than VIII for the earthquakes of 15 May. The two stars represent the assigned epicenters. Within these contouring areas of damage there is a quite good agreement between intensities assigned with sources mentioned in the study of the individual events and those estimated from the descriptions of the Pastoral Visit.
It is interesting to point out that there is a site reported in the Visit quite far from the epicentral areas, towards the Southeast, near the coast, with intensity VI-VII. This site is located at 10 km distance from the "discordant" point (Sant Feliu de Guíxols) which was described in the 15 March study (see Fig. 2). Therefore there is an agreement between both data points.

Fig. 3 - Intensity points obtained from the Pastoral Visit to the Diocese of Girona of 1432 together with contours of intensity VII for the 15 March 1427 earthquake and contours of intensity VIII for the 15 May 1427 earthquake. Stars represent the epicenters of the two events. Small dark points indicate sites with explicit unnoticeable effects. Possible associated tectonic accidents are sketched with solid lines.

A number of points from the Visit located to the North of Girona remain unexplained and they will have to be analyzed together with the data from the 1428 earthquake.
In Fig. 4 the Amer-Brugent fault system (NW-SE oriented) interrupted by the Vallfogona thrust (W-E oriented line) are sketched (Goula et al., 1992). The 1427 earthquakes can be associated to this NW-SE system; the rupture evolved from South (15 March) to North (15 May).

Conclusions
The seismic period 1420-1427 in the Pyrenees has been revised through an exhaustive and critical archivistic research. From the 20 events contained in the most used Spanish compilations, 7 have been found to be fake earthquakes, one of them (3 March 1426) previously catalogued as Io= VII. The intensity of one earthquake previously catalogued as VIII (25 December 1427) has been lowered to less than VI. Mislocations of some low intensity events have also been corrected. Only two events of the series have been found to be destructive: that of 15 March 1427 and that of 15 May 1427.
Original primary sources contemporary to the events have been analyzed to assess point intensities, according to the EMS-92 scale, for the 15 March 1427 and 15 May 1427 earthquakes and epicentral areas for both events have been delimited.
The epicentre of the 15 March earthquake is located in Amer, with intensity VIII-IX while the 15 May epicenter is located in Olot, with intensity IX.
The results from this study confirm the severity of damage in Catalonia of these two events and are of great interest for the evaluation of the earthquake hazard in Catalonia and the South of France.

References
Banda, E. and Correig, A., 1984. The Catalan earthquake of February 2, 1428. Eng. Geol., 20: 89-97.
Bolós, F., 1841. Noticia de los extinguidos volcanes de Olot y de sus inmediaciones hasta Amer, y de los nuevamente descubiertos, todos en la provincia de Gerona. Barcelona.
Cadiot, B., 1979. Les effets en France du séisme Catalan de 1428. In: J. Vogt (Editor), Les tremblements de terre en France, BRGM Mémoire 96, Orléans, pp. 166-172.
Danes i Torras, J., 1937. Pretèrits Olotins. Olot.
Del Valle, C., 1990. Una fuente hebrea sobre los terremotos de Gerona de 1427. Revista de Girona.
Fontserè, E. and Iglésies, J., 1971. Recopilació de dades sísmiques de les terres catalanes entre 1100 i 1906. Fundació Salvador Vives Casajuana, Barcelona, 547 pp.
Giralt, E., 1889. Flósculi. Revista de Girona, pp. 55-82.
Goula, X., Olivera, C., Escuer, J., Fleta, J. and Bousquet, J.C., 1992. Neotectonics and seismicity of the area of the seismic crisis of 1427-1428 in Catalonia. In: A. Roca and D. Mayer-Rosa (Editors), Proceedings of the XXII ESC General Assembly and Activity Reports 1988-1990, Barcelona, t. 1, pp. 333-357.
Grünthal, G. (Editor), 1993. European Macroseismic Scale 1992 (up-dated MSK-scale). Cahiers du Centre Européen de Géodynamique et de Séismologie, Luxembourg, 7, 79 pp.
Instituto Geográfico Nacional, 1991. Earthquake Database for the Iberian Peninsula.
Montsalvatge, F., 1906. Colección Diplomática del Condado de Besalú, III. Imp. Juan Bonet, Olot.
Olivera, C., Banda, E. and Roca, A., 1991. An outline of historical seismicity studies in Catalonia. Tectonophysics, 193: 231-235.
Olivera, C., Riera, A. and Roca, A., 1992. Study of the 1427 earthquakes in Catalonia. In: A. Roca and D. Mayer-Rosa (Editors), Proceedings of the XXII ESC General Assembly and Activity Reports 1988-1990, Barcelona, t. 1, pp. 327-331.
Paluzie, E., 1860. Olot y su comarca, sus extinguidos volcanes, su historia. Barcelona.
Prades, I., 1989. Els terratrèmols de la sèrie olotina i el cas de la vila d'Amer. Quadern de la Selva-2 Sta. Coloma de Farners, s.d., pp. 103-112.
Riera-Melis, A., Escuer, J., Fleta, J., Goula, X. and Olivera, C., 1992. The 1427-28 earthquakes in Catalonia: Historical traces and geological context. Excursion guide text. In: A. Roca and D. Mayer-Rosa (Editors), Proceedings of the XXII ESC General Assembly and Activity Reports 1988-1990, Barcelona, t. 1, pp. 387-399.
Riera-Melis, A., Roca, A. and Olivera, C., 1993. Analysis of the Pastoral Visit of 1432 to the Diocese of Girona for the study of the seismic series 1427-1428 in Catalonia. In: M. Stucchi (Editor), Materials of the CEC project "Review of Historical Seismicity in Europe", 1, Milano, pp. 161-172.
Riu, M., 1980. Una font polonesa per a l'estudi del terratrèmol de 1427. Annals de l'Institut d'Estudis Gironins, Girona, XXV, 1: 357-362.
Rubió, J., 1961. Documents sobre els terratrèmols de 1427-28 a terres de Girona, Miscel.lània Fontserè, Ed. Gustavo Gili, Barcelona, pp. 357-375.

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