Geoscience Reference
In-Depth Information
Several names can be connected to this effort. Schiantarelli in Italy was the first
to make simple quantifications of damage in 1783 after the Calabrian earthquake
of that year. It was the German geologist Christian Leopold von Buch (1774-1853)
who considerably improved the endeavor in macroseismic analysis by studying the
1799 Silesian earthquake: he collected macroseismic observations from the resi-
dents of the affected region and plotted the obtained data into local geographical
maps. This enabled him to determine the size and shape of the zone in which the
earthquake was experienced, and hence to locate the 'epicenter zone' of the respec-
tive earthquake (Buch 1801). Gunther (1897) names the German mathematician and
naturalist P.N.C. Egen as the author of the first macroseismic map. Egen (1828) ana-
lyzed the February 28, 1828, North Rhine earthquake by using a large set of macro-
seismic data collected from local inhabitants. He was able to delineate the zones of
the strongest effect. By doing so, he located the epicenter zone of the earthquake.
He defined and applied the first empirical scale of macroseismic intensity, and in
his earthquake map he recorded the directions of seismic movements, an endeavor
that has already been undertaken in Hungary by Kitaibel and Tomtsanyi (1814),
who analyzed the 1810 Mor earthquake in central Hungary. For the ellipse of the
largest seismic effects, Egen marked its two main axes; the longer axis coinciding
with the longitudinal direction of the affected part of the Rhine Valley. However,
the proposed scale has failed to receive widespread acceptance, as has the one by
Robert Mallet, and as a result was of limited use in comparing earthquakes from
different regions (Valone 1998). In Germany, Johann Jakob Noggerath (1788-1877),
professor of mineralogy and mining at the University of Bonn, presented a 'modern'
map of the July 29, 1846 Rhine-region earthquake (Noggerath 1847). Therein he
depicted isoseismic lines, using several reports from the public (Davison 1978).
It was the German mineralogist and geologist Georg Heinrich Otto Volger
(1822-1897) and the geographer and cartographer August Petermann (1822-1878)
who presented an important study on the earthquake series after the July 25, 1855
Visp event. Their modern approach to the subject significantly enhanced this emerg-
ing discipline. In what follows, we will discuss their endeavor in detail, starting with
a short outline of the 1855 Valais event.
3 The July 25, 1855 Valais Event: Synopsis and Overview
On July 25, 1855, a strong earthquake struck the southwestern region of Switzer-
land, the Valais, causing heavy damage in a wide range around Visp. It is known
as one of the strongest earthquakes within Switzerland. The event was widely
commented on and discussed in these regions as well as in border areas such as
Northern Italy and Eastern France. According to modern classification the main
shock occurred at 11 h 50 min UTC on July 25, 1855, with epicenter coordinates
46.23
◦
N, 07.85
◦
E,
20 km, near the village of T orbel. It was a deep event (h = ca.
12 km); its epicenter intensity I
0
reached VIII (
±
5) according to the EMS-98 scale
(Grunthal 1998). Moment magnitude M
w
is parameterized as 6.4 (
±
0
.
±
0
.
5); additional
Search WWH ::
Custom Search