Geoscience Reference
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3.5 The Event of 1117
This earthquake is by far the largest one occurred in the investigated area. It has been
the object of various studies which, during the years, modified the interpretation.
The earthquake was studied as early as 1980s by Magri and Molin (1986),
Guidoboni (1984), Guidoboni and Boschi (1989), ENEL (1986a). The reader may
refer to the papers by Galadini et al. (2001a), Galli (2005), Guidoboni and Comastri
(2005), Guidoboni et al. (2005), in order to have a complete picture of the litera-
ture on this complex event. All these papers interpret the event as a complex, not
easily explained seismic sequence; one of the main unresolved points is that the
area from which damage is reported is much larger than allowed, even by a less
probable 7.5 Mw event. It must also be said that many earthquake records come
from single, monumental buildings, and that the typologies of the non-monumental
building stock is poorly known.
The main problem hampering the solution of the case is that most accounts do not
clearly differ in time; therefore, the solutions are generally based on how to split the
available intensity distribution in some more or less reasonable intensity distribu-
tion, to be consistent with one or more events. The most recent work by Guidoboni
et al. (2005) splits the event into three earthquakes, to have occurred respectively
in Southern Germany, Northern Italy and North-Western Tuscany, with damage at
Pisa. This interpretation is mainly based on the fact the sources report two shocks,
with a difference in time of about 12 h for 8 localities: Disibodenberg, Freising,
Augsburg, Zwiefalten, Melk, Salzburg, Saint Blaisien, Peterhausen, located in to-
day Switzerland, Austria and Germany (Fig. 14). The remaining localities are then
grouped according to the two timings and the intensity datapoints split into three
groups: one in Germany, one in the traditional area around Verona and one near
Pisa. Moreover, in the quoted paper and the companion volume by Guidoboni and
Comastri (2005) - both items refer to one another - some 40 intensity datapoints are
missing with respect to the recent interpretation by Boschi et al. (2000). As a matter
of fact, the attribution of the records to the two origin times ends up in intensity
distributions which show strange pattern, and give rise to parameters of the two
events which have to considered with caution.
Although the interpretation of the primary sources remains controversial, disre-
garding here the presumed events near Pisa and in Southern Germany, all interpre-
tations admit that this earthquake was responsible for significant damage in a large
sector of Northern Italy, reaching a very high level of damage in the area of Verona.
In addition:
i) the sources report significant geological effects (large landslides) due to the
shaking in the Adige valley between Verona and Trento (Galadini et al., 2001;
Guidoboni et al., 2005);
ii) archaeoseismological information permitted to infer high damage also at Trento
(Galadini et al., 2001) and Cremona (Galli, 2005), to which the intensity 8 MCS
has been attributed on historical basis by Guidoboni et al. (2005);
iii) high damage is reported also for Padova (I 8 MCS by Guidoboni et al. 2005).
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