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