Geoscience Reference
In-Depth Information
In other localities, new churches were built, but without any relationship to the earth-
quake, even if damage and repairs related to this event were observed. This was the case in
Dongelberg, Glabeek, and Lens-Saint-Remy.
Pathologies and repairs in churches not confirmed by historical sources
The interpre-
tation of all the damage observations discussed in the previous section provided a set of
damage characteristics that earthquakes similar to the 1828 one might produce in churches.
This damage dataset has been used to identify in the existing pathologies or visible repairs
the consequences of the 1828 earthquake in other churches located in the earthquake
epicentral area, and for which no report has been found describing the consequences of this
seismic event. This damage has been classified in seven categories from CD1 to CD7. We
list in
Table 8.1
the churches where these different types of pathologies, damage or repairs
have been observed.
The most frequently observed damage (CD1) is cracks above and under windows and
especially at the level of the first window of the nave beyond the tower. One can observe such
cracks in half of the inspected churches. Some of them even have all windows systematically
cracked. These pathologies could arise from the earthquake but also from the problem of
differential settling caused by the difference in height and weight of the tower in comparison
with the nave, or from the problem of poor foundations or loose substrates. However, it
is also possible that the settling of the ground may have been induced by the earthquake,
which appears to be the case in the village of Jauche (
Figure 8.6
D).
Cracks on the tower or cracks at the intersection of two faces of the tower are also
observed (CD2) in almost all churches. These types of damage are mentioned in historical
reports for some of the church towers in the epicentral area of the 1828 earthquake. Their
repair can be confirmed by the presence of cramp irons in the faces of some of these towers.
They are used to hold a wall or two opposite faces together, preventing the splitting of walls
and the detachment of the front from adjacent walls from bottom to top, which result from
seismic action.
Face detachment (CD3) can also happen with the two perpendicular walls of the nave.
Cracks can also be observed in reflex angles (CD4) of the churches of Grand-Hallet,
Perwez, Petit-Hallet, Hakendover, Incourt, and Jauche.
About 25% of the visited churches presented displacement of window keystones (CD5).
In Jauche, one can see a similar principle of repair and consolidation with two small cramp
irons, rounded spirals, at the two corners of the keystones (
Figure 8.6
d
), which suggests
repairs after the earthquake, as in Marilles and Racour.
Other pathologies and associated repair characteristics associated with earthquake shak-
ing are cracked window sills (CD6) or cracks on the vaults (CD7).
From this investigation of churches in the central part of Belgium, we found evidence of
pathologies and repair traces that could result from the 1828 earthquake because they are
similar to those observed in the churches for which historical sources prove the damage.
To confirm this hypothesis, we will first describe a survey of churches outside the 1828
