The impact of the earthquake activity in Western Europe from the historical and architectural heritage records - Intraplate Earthquakes - page 201

two recent damaging earthquakes also occurred in the city of Liege on 21 December 1965
(M

4.6).
Another zone of concentrated seismic activity is the region of the Hainaut province of
Belgium, between the cities of Mons and Charleroi. Despite the fact that none of these
earthquakes exceeded magnitude 4.5, some of them caused some damage locally due to
their shallow depths (

= 4.3) (Van Gils, 1966 ) and 8 November 1983 (M =

3-5 km). Reported damage during these earthquakes concerns
mainly the collapse or partial collapse of chimneys, broken windows, cracked ceilings
and walls. The tectonic origin of these earthquakes is debated, as it is possible that part of
the reported activity in this area could be related to the extensive mining works that took
place in this area from the end of the nineteenth century to the beginning of the 1970s
(Descamps, 2009 ) .
Another particularity of the study area is that part of the seismic activity appears to be
spatially diffuse and sporadic, as is common in many plate interior regions worldwide. For
instance, in the Strait of Dover and southern North Sea, seismic activity has been weak
since the beginning of the seventeenth century; however, three historical earthquakes that
occurred in this area on 21 May 1382, 23 April 1449 and 6 April 1580 produced significant
damage in southern England, northern France, and Belgium (Melville et al ., 1996 ) . In the
same way, the Brabant Massif region has not shown any significant earthquake activity
since the installation of the modern seismic network in Belgium in 1985, but this region
was violently shaken on 23 February 1828 and on 11 June 1938 by two M

5.0 earthquakes

that caused widespread damage.

8.3 The background and methodologies of historical seismicity in Western Europe

The retrieval and analysis of information on earthquake effects, whatever the epoch
of the earthquake, are part of the research field called “historical seismicity”. Most of
the information on historical earthquakes in northwestern Europe, spanning a period from
the earliest available sources ( c . AD 700) to the present, can be found in the database that we
have developed at the Royal Observatory of Belgium, which is partly accessible on the
Internet (Camelbeeck et al ., 2009 ) .
In this chapter, we will focus specifically on the information concerning reported damage
with the purpose of evaluating the local and global impacts of destructive earthquakes.
This objective requires more detailed information on the damage characteristics and their
spatial distribution than that of classical investigations evaluating earthquake location and
magnitude from intensity datasets. According to the differences in the type of documentation
that can be collected on damaging earthquakes, in this study we differentiate between the
information that was collected before and since the development of regional and national
seismic observatories, which corresponds roughly to the year 1900.

8.3.1 The period from 1900 to the present

In the study area of Western Europe, many permanent seismological observatories were
established at the end of the nineteenth century or at the beginning of the twentieth century.
For example, in France, the first seismological measurements were conducted in 1892 in