Geoscience Reference
In-Depth Information
a shallower earthquake with a similar magnitude because the seismic energy reaching the
surface is more attenuated, but of course the affected area is of larger dimension. Hence,
the moderate and extensive damage caused to houses and churches during the 1828 earth-
quake appear as more important than for the 1938 seismic event, but they are located in
a more restricted region. This is particularly evident when looking at
Figure 8.4
,
bythe
comparison of damage to churches.
8.6.5 Risks from large earthquakes
Three earthquakes of magnitude around 6.0 have occurred in the studied area since 1350.
These earthquakes have a destructive potential that is important to evaluate. This is why we
focused part of our work on evaluating the destruction caused by the M
, 1692 Verviers
buildings suffered damage of grade 4 and 5 in villages of the epicentral area. Based on a
precise inventory of the houses and of their pathologies and repair traces in the centre of the
village of Soiron, one of most affected localities, we were able to formulate a hypothesis on
the damage and destruction caused by this earthquake. This analysis is limited by a lack of
knowledge on the vulnerability of the buildings. If the buildings are considered as a mixture
of vulnerability classes A and B of the EMS-98macroseismic scale, it is coherent to consider
that the less vulnerable (of class B) were on average less damaged, probably corresponding
to extensive damage states (one-third of the total number of houses). Together with the
complete damage of the other part of the building stock, this is compatible with intensity
equal to VIII.
Considering the high seismic vulnerability of part of the present-day building stock of
the study area and its high population density, the consequences of an earthquake of this
magnitude would certainly be catastrophic in terms of victims and destruction.
=
6
ΒΌ
8.6.6 The importance of investigations of the architectural heritage
A few years ago, we found it hard to imagine that it was possible in Western Europe to
retrieve traces of past earthquakes in heritage buildings. Our study on the village of Soiron
in the epicentral area of the 18 September 1692 earthquake and the churches affected by the
23 February 1828 earthquake drastically changed our point of view on this problem. Our
results suggest that most of the buildings of Belgium and its surrounding regions should
present pathologies or repairs associated with earthquake activity if they were constructed
before the end of the seventeenth century. Up to now, we have developed a naturalist method-
ology based on field observations and measurements. Future methodological advancements
will require the evaluation of the seismic vulnerability of these buildings and numerical
modelling of earthquake effects to compare them with the observations.
The results presented in this chapter are a strong motivation to investigate other destruc-
tive past earthquakes, and also to study in more detail the different aspects that influence
