Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

subsidence of the floor of about 50 cm with lateral
dragging can be observed and furthermore a concrete
reconstruction of the subsided floor during Carolingian
times. Up to now this is the only part of the Cathedral
where two ground floors of Carolingian age can be found
(Fig. 5). During the still lasting excavation further cracks
have been found in the wall of the octagon. Cracks are
systematically (Fig. 6) with a maximum oriented NW‐SW
according to the present‐day principal stresses in Central
Europe (Reicherter et al., 2008).
Large cracks have also been found in the roof of the
chapel (Fig. 7). These cracks are lead‐filled and sealed
with Carolingian mortar. This evidence also suggests an
intra‐Carolingian phase of repair.
Archaeological investigations imply that obviously the
chapel was architectonically not finished, when the
damage occurred. Most probably the damage happened
before the official inauguration.
Equal Area
Fig. 5: Ground floor damage and repair
N = 13 Circle = 31 %
Fig. 6: Orientation of the wall cracks
Geological evidence
In the WNW section, the loessy and loamy sediments
show angular cracks and fragments (Fig. 8 and 9), which
are not related to permafrost features but are interpreted
as liquefaction. Furthermore, some of the cracks are filled
with black sterile clay from below as they open
downwards. These structures may be interpreted as
“injection structures” or features of weathered Devonian
claystones into the overlying Pleistocene.
However, some of the upper portions of the cracks yield
Roman ceramic fragments and charcoal, quite similar to
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology)
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Fig. 7: Damage in the roof of the chapel
those sediments found in adjacent Roman waste dumps,
pointing to a mixture of underlying and covering
materials. Liquefaction and injections structures occur
usually during earthquake with a magnitude higher than
5.5, which is corroborated by large cracks in the massive
outer walls.
Fig. 8: Clay‐filled cracks in the sterile soil of the chapel
(Pleistocene Loess)
HISTORICAL EARTHQUAKES AND DATING
The earthquake catalogues (e.g., von Hoff, 1840) and the
Annales regni Francorum (Kurze, 1895) provide two
important passages for historical earthquakes in the
region of Aachen. Both fall into a relatively short time
interval. One in winter 803 AD: “Hoc hieme circa ipsum
palatium et finitimas regiones terrae motus factus et
mortalitas subsecuta est.“ The later 829 AD (between Ash
Wednesday and Easter) description „Aquisgrani terrae
motus noctu factus ventusque tam vehemens coortus ut
non solum humiliores domos, verum etiam ipsam sanctae
Dei genitricis basilicam, quam capellam vocant, tegulis
plumbeis tectam non modica denudaret parte“. Both
notes tell of earthquake shaking and significant structural
damage (e.g. lead bricks fallen off the roof) and fatalities.
Due to rich findings and dating of charcoal in several
levels, the original and the restored floor, successful
radiometric dating was carried out to get time constraints