Past and Future of Historical Seismicity Studies in France - Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes - page 133

be assessed with higher precision if one concentrates on the macroseismic study of
aftershocks rather than that of the main shock. The inhabitants that live very close
to the hypocenter often feel aftershocks of very low magnitudes, smaller than 1
(Thouvenot and Bouchon 2008). Researching such local testimonies for historical
earthquakes may lead to greater accuracy on the position of the main shock. Small
earthquakes are also very useful to define seismic zones, or even to identify active
faults. Many catalogues do not assign an epicentre to small events felt in only one
or two places. However, in most cases, the description is sufficiently accurate to as-
certain that it corresponds to a local earthquake; it is then usually possible to assign
the epicentre to the place where it was felt without incurring the error of assigning
an epicentre in the middle of the poorly defined isoseismals of a larger event.
It is thus necessary to try and be as exhaustive as possible when investigating
historical earthquakes. For each event, it is necessary to make exhaustive use of all
existing catalogues in order to identify the least trace of earthquake, aftershock, and
background seismicity. Once an event date and location is known approximately,
it is usually straightforward to search for original descriptions in newspapers, pe-
riodicals, etc., for the last three centuries at least. For events in earlier periods, the
collaboration of historians is advisable (Alexandre 1990), and finding new sources
may be very infrequent.
The feasibility of exhaustive analysis of a given earthquake has been much im-
proved since the digital revolution and the Internet. Old topics and periodicals are
scanned and made available online by libraries worldwide in continuously growing
number. Archive depositories prepare digital catalogues of their collections. Gallica,
the French Bibliotheque Nationale digital library (http://gallica.bnf.fr), provides us
with a wealth of scanned topics and periodicals, annually increased by 100,000 new
documents. To cite just a few, the Journal des Savants ,the Histoire de l'Academie
Royale des Sciences ,orthe Philosophical Transactions of the Royal Society of
London are available. It gives online access to the catalogues of Arago (in Annales
de Chimie et de Physique ), von Hoff (in Annalen der Physik und Chemie ), and
Perrey (in Annales de la Societe d'Emulation du Departement des Vosges ). Regional
learned society periodicals, and newspapers (mainly from the XIX century), are be-
ing scanned. The European Library (http://www.theeuropeanlibrary.org), presently
under development, will give access to digital (text) documents from a large number
of European libraries.
Scientific disciplines rely on specialized documents that are not often available
through general digital libraries. This implies the necessity of specialized digitiza-
tion programmes, such as Numdam (http://www.numdam.org) for mathematics, or
ADS (http://cdsads.u-strasbg.fr) for astronomy. Geosciences unfortunately do not
yet benefit from such a digital library. Scanned or digital documents related to
historical seismicity do exist, but they are dispersed among many institutions. In
the course of our research on seismological history we were led to scan a num-
ber of useful documents, including catalogues, creating access for some of them
on an Internet page, GeoArchive (http://eost.u-strasbg.fr/jv/geoarchive). A number
of Perrey's regional catalogues are available on GeoArchive, as are all his annual
catalogues. It has already been observed that annual catalogues include supplements