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

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Pierre Gouin *
* Observatoire de Géophysique, Collège Jean-de-Brébeuf, 3200 Chemin de la
Côte-Sainte-Catherine, Montréal H3T 1C1, Québec.

Interpreting original reports on
"historic earthquakes" in Québec

Each region of the world has a specific seismic history usually subdivided into three periods: the first - the "paleo- or fossil- seismicity" period - for which the records of the largest events lie buried with the old faults of the land waiting for geologists to determine their age and the landscape alterations they could have produced. Follows the so-called "historic period" in which the effects of some seismic events are qualitatively described by non-scientific authors; if well interpreted, these descriptions could often allow the determination of a time, a location, one or more intensities and often an "equivalent magnitude".
By their nature, these "historic" records are incomplete in scientific content and number. The third and last period, called the period of "instrumental seismology", began in most regions very modestly towards the end of the last century with the installation of uncalibrated equipment but achieved in less than fifty years a remarkable degree of accuracy.

As a result, the bank of accurate quantitative seismic data covers only a few decades; that of qualitative "historic documents", a few centuries and that of undetermined paleo-seismic records, millions of years. Hence the present interest for improving the quality of interpretation of the documents from the "historic" period in order to extend towards the past the coverage of the data bank of later years by increasing the reliability of the location and "equivalent magnitude" assigned to the most important seismic events.

In order to attain that goal, it must first be realised that, because of different environments, this "historic" period differs in length and quality from one region to the other and requires a different approach in the interpretation of its elements and original documents. Québec, a former part of la Nouvelle-France and now a region of the eastern part of North America is taken as an example.

Problems specific to Québec
The methodology for properly interpreting historical earthquake records, as laid out by Vogt (1979), must be supplemented by the specific exigencies of each region. In Québec:

Length of the "historic seismicity period"
The "historic" part of the seismicity in Québec only goes as far in time as the Indian oral traditions take us, that is to the second half of the 16th century, and ends practically on 28 February 1925 when parameters of a local earthquake could be determined from recorded seismograms (Kent, 1992; Gouin, 1994). This is a very short period of time when compared to the historic seismicity of either Europe, the Near or the Far East.

Types of documents available
To begin with, the Indians who lived in eastern North America did not use writing as means of communication; they had oral traditions apparently skipping the information they thought needed not be remembered - for instance, not referring the event they reported to a more noted event which could be dated - and intentionally camouflaging the message in a way that only they could understand, not the enemy (Trigger, 1976). Then came the Europeans who, at the time in Europe, could not boast of having a high rate of literacy; the result is that in most colonies only a few could read and write.
Fifty five years after the foundation of its capital, in 1663 when the largest earthquake Québec had probably ever felt occurred, the total number of Europeans in la Nouvelle-France was barely 3000 (Trudel, 1973; Campeau, 1974) mostly confined to the forts of Québec, Trois-Rivières and Montréal. It is only around 1680 that the south shore of the Saint Lawrence started to be inhabited and in 1720 that its population reached the 3000 level (Laberge, 1993).

At the beginning therefore the documents were scarce. The written ones are mainly restricted to official correspondence between members of the local government and their headquarters in Europe or between religious superiors and their head-office or benefactors abroad. Perforce, the origin of these documents was limited to the cities where government offices were located and to the regions near Québec, Trois-Rivières and Montréal; a few came from south of the border, as far south as Rhode Island and Connecticut. Others came from missionaries who followed their flocks in the forests; they covered a large, but scattered area.

In 1764, the press appeared in Québec and Montréal. The country had been conquered; the French institutions were banned and the "élite" sent home. The personal correspondence almost completely disappeared and most of the information took the general form, style and reliability of the media. The inhabited land, first restricted to the Saint Lawrence valley because the river was then the only means of transportation, progressively expanded, but "les pays d'en haut", the far North, the whole Northeast and many other regions of Québec remained and still are, by European standards, under-inhabited. Under these conditions, the suggested rejection of seismic reports by a unique observer but not confirmed by other sources, is often not applicable.

The dating of documents
Since 10 October 1582, all documents in French, Latin and Italian are dated according to the New Style, i.e. the Gregorian calendar. South of the border, it is different. Prior to 2 September 1752, the British Plantations used some of the Old Style forms of the Julian calendar. On 2 September of that year, the difference between the two calendars being exactly 11 days, the order came from England to adopt the Gregorian calendar (Mather et al., 1927).

Effects of bilingualism
From 1534 to 1763, Québec was part of la Nouvelle-France and under French rule; in 1763, Britain took over; a totally different administration was installed. English became the official language.
Linguistic changes particularly affected local geographical names which, in fact, also used in others parts of Canada, still cause confusion and often occasion a misplacement of localities: e.g. Saint-Jean (sur Richelieu) was St. John's, often mistaken for the capital of Newfoundland or St. John in New Brunswick; Saint-André (Avelin) was St. Andrews, often interpreted as St. Andrews in New Brunswick or St. Andrew's in Newfoundland, etc...

Résumé of the information compiled from the "historical" reports on earthquakes in Québec
From the analysis of the presently available primary reports on some 500 events quoted in the literature as being of seismic origin, it may be said that:
- the highest "equivalent magnitude" reported felt in Québec prior to 1925 was ² 6.5 and therefore the macroseismicity of the region was "moderate";

- the two largest "historic earthquakes" reported happened on 5 February 1663 and 20 October 1870;
- there were some 5 "historic earthquakes" of equivalent magnitude ³ 5.5 which could have caused damage (1663, 1732, 1860, 1870 and 1925);
- the damage in Montréal in 1732 was due in part to two previous conflagrations (1695 and 1721) which devastated the town and weakened the masonry re-used as walls of new buildings such as those of Hotel-Dieu;
- there are voids in the seismic records: among others, from 1673 to 1732, 1791 to 1831 and 1871 to 1877. These voids do not indicate an absolute zero in the seismicity of the region; there were earthquakes during these periods but insignificant, not worth reporting (Hamel, 1745; Dawson, 1879; Laflamme, 1907).
- And there is the special case of casualties - special because of its humanitarian impact directly connected to earthquakes. In so far as Québec is concerned, we can say that in the "historic period" no one, during an earthquake, was trapped under the ruins of a house and died from it; on 28 February 1925, three ladies - two with hearth conditions and one pregnant - died immediately or shortly afterwards (Hodgson, 1950) and on 20 October 1870, four were slightly wounded at Bay St-Paul by stones falling from chimney tops of the girls' school (Jr. de Québec, 22 oct. 1879, p. 2, col. 4-5).

Campeau, L., 1974. Les Cent-Associés et le peuplement de la Nouvelle-France (1633-1663). Editions Bellarmin, Montréal. 175 pp.
Gouin, P., 1994. About the first earthquake reported in Canadian History. BSSA, 54, 2: 478-483.
Hamel, H.Ls du ... , 1745. Observations Botanico-Météorologiques faites à Québec pendant les mois d'Octobre, Novembre & Décembre de l'année 1743, & Janvier, Février, Mars, Avril, Mai, Juin, Juillet, Aout & Septembre de l'année 1744. Mém. Acad. Roy., Paris, pp. 194-229.
Hodgson, E.A. (1950). The St. Lawrence Earthquake, March 1, 1925. Pub. Dom. Obs, VII, 10, Ottawa, pp. 365-436.
Laberge, A. (Editor), 1993. Histoire de la Cote-du-Sud. Québec, 647 pp.
Laflamme, J.-C.K. (1907). Les tremblements de terre de la région de Québec. Mém. Soc. Roy. Canada, Ottawa, Section IV, pp. 157-183.
Mather, K.F., Godfrey, H. and Hampson K., 1927. The Earthquake Record in New England. [Type written manuscript].
Trigger, B.G., 1976. The Children of Aataentsic: A History of the Huron People to 1660. McGill-Queen's University Press. Kingston and Montreal. 913 pp.
Trudel, M., 1973. La population du Canada en 1663. Fides. Montréal. 368 pp.
Vogt, J. (Editor), 1979. Les tremblements de terre en France. BRGM Mémoire 96. Orléans, France. 224 pp.

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