Geoscience Reference
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macroseismic intensity magnitude M
m
, determined by Swiss and Italian agencies,
range between 6.2 and 6.4. The seismic analysis was set using 310 macroseismic
intensity site-points (Fritsche et al. 2006).
The main shock of July 25th, 1855, at 11 h 50 min was followed by a series of
aftershocks, the strongest one on July 26 at 9 h 15 min (I
0
=
7
0
), another one at 13 h
6
0
). Other large aftershocks were detected on July 28 at
20 min the same day (I
0
=
7
0
), August 24, October 28 at 1 h 30 min, and November 6, at 3 h 30 min,
all of them reaching an intensity of I
0
=
10 h (I
0
=
6 at least. The majority of this information
comes from Volger's extensive study of the event, where he collected hundreds of
observations in the epicenter area but also farther away.
The most affected region was the center of the Valais, at the border of the Rhone-
Valley plane, with heavy damage of buildings and the environment. Visp, a village
of about 130 buildings, was destroyed. People had to leave their buildings and live
in tents for several days (Fig. 2). Houses built of stones were heavily damaged,
many of them completely destroyed, and even wooden buildings suffered much
harm (Fig. 3). Secondary effects impacted the environment of Visp. Several kinds
of cracks, as well as clefts in the rocks, emerged from the seismic shocks (Fig. 4). In
the area of Stalden, St. Niklaus and Grachen, effects of rock falls, landslides, cracks
and rifts in the ground and newly emerged sources were easily identified. Thanks
to particular contemporary sketches of the scene we know of a storehouse that was
destroyed by a rock fall and a similarly destroyed stone house in St. Niklaus, the
village that is supposed to have suffered most. Significant damage was also re-
ported for Stalden, where the destruction was less than in Visp because of the large
Fig. 2
Local inhabitants at a mass served under the open sky near Visp (“in den Baumgarten”).
Xylographic newspaper illustration, reproduced from an unidentified German journal of the time.
Depicted by R. Kummer. Private collection, Prague
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