The impact of the earthquake activity in Western Europe from the historical and architectural heritage records - Intraplate Earthquakes - page 224

unreinforced brick-masonry constructions, which are sometimes very old. This has been
dramatically demonstrated for the 1983 Liege earthquake. Of course, the more modern
buildings constructed in steel or reinforced concrete were far less affected by the Liege and
Roermond earthquakes and the application of the paraseismic Eurocode-8 building code
should improve the resistance of new buildings in the future. Nevertheless, the risks will
be present for a long time because poorly constructed masonry buildings will remain a
significant part of the building stock in the old cities of Western Europe.

8.6.2 Damage and intensity

Using the Royal Observatory of Belgium macroseismic inquiry for earthquakes felt in
Belgium since 1932, which includes a report on the percentage of damaged chimneys in
each affected locality, we were also able to evaluate the quantity of damaged buildings
presenting greater than or equal to moderate damage states caused in Belgium by the
11 June 1938 and 28 March 1967 earthquakes. We also added information provided by
Musson et al .( 1990 ) on the epicentral area of the British Colchester 1884 seismic event in
our dataset. The complete dataset, presented in Figure 8.3 , is more precise than the intensity
for the destructiveness of the earthquakes and can be more directly related to the associated
losses ( Figure 8.2 ) . This dataset is also, in essence, a basis on which to evaluate intensity
in localities where damage was observed. It is very useful because, in the case of the most
affected localities in the Netherlands and Germany during the 1992 Roermond earthquake,
this allows us to evaluate the intensity as equal to VI on the EMS-98 macroseismic scale
based on the damage statistics, which is less than the value of VII proposed by the official
inquiry published after the earthquake (Haak et al ., 1994 ) .

8.6.3 The complementarity of studying damage in classical houses and churches

The fundamental mode of vibration of traditional masonry houses ranges from a few to
10 Hz, which means that these structures are sensitive to the high-frequency range of
seismic energy. On the other hand, the major buildings of the architectural heritage such as
churches and castles are of larger dimensions and often of very complex structure. Their
fundamental mode is thus at lower frequency (

1 Hz). As an example, the fundamental
mode of the Boussu church tower, located near the city of Mons, has been evaluated at
a frequency of 1.41 Hz (Defaut and Deneyer, 1999 ) . Therefore, analyzing the damage
caused to these large structures and comparing it to that of traditional buildings can shed a
different light on the factors influencing the damage produced by an earthquake ( Figures 8.3
and 8.4 ) .
We observe that the spatial extent and the magnitude of the damage caused to churches
increase significantly with earthquake magnitude. Two of the studied earthquakes caused
moderate to heavy damage at large distances from their epicentre the 1992 Roermond and
1692 Verviers earthquakes ( Figure 8.4 ) . This is a clear indication of the lower frequency
content of the seismic energy generated by these earthquakes, which is representative of