Geoscience Reference
In-Depth Information
tious and “lay,” Volger was challenging a class-based claim to adjudicate
“science.”
18
At the same time, Volger's trust in the testimony of local residents suited
his explanation of seismic activity. If water seepage could induce tremors
by causing the collapse of subterranean caves, then rainfall and humidity
were a proximate cause of earthquakes. Volger therefore needed reports on
meteorological conditions not merely at the time of the quake, but also
in the preceding weeks. He needed to trust the local residents, and he did.
He spiritedly defended the experiential knowledge of locals against the ex-
aggerations of well-to-do travelers. for instance, he rejected a “traveler's”
account of a sulfurous smell (associated with “Plutonistic” explanations)
on the ground that the witness lacked the experience to recognize the “half-
musty, half-smoky scent of freshly overturned earth.”
19
remarkably, what might appear to be the work of a pugnacious upstart
turned out to be a pioneering contribution to seismology. Volger's research
was original both in its conclusions and methods. His critique of Plutonism
was apt, in so far as it cast earthquakes not as the product of eruptive forces
but as a result of preexisting ground conditions, exacerbated by fleeting ex-
ternal factors.
20
Volger himself drew an analogy to the breakup of a layer
of ice on a lake. His point of view stimulated further studies of the local
geology of earthquake zones. It also inspired the compilation of historical
earthquake catalogs on the model of Volger's own
Chronik der Erdbeben in
der Schweiz,
the first volume of his publication on the Visp quake. Last but
not least, Volger succeeded in developing one of the first quantitative scales
for measuring an earthquake's intensity, as well as one of the first maps
of the geographic distribution of intensity. His map introduced a stan-
dard convention of macroseismology today: isoseismals, or lines of equal
seismic intensity. The final version used seven colors to plot the variation
of intensity for the main shock; it also showed the limits of perception for
three aftershocks. The map summarized Volger's research in a manner well
suited to a popular audience. It displayed information about the distribu-
tion of seismic hazard at a glance and without technicalities. Indeed, the
conventions of seismic intensity maps constitute a visual scientific vernacu-
lar, much like the weather maps that were becoming popular in the nine-
teenth century.
21
There is little sign, however, that these innovations were appreciated by
Volger's contemporaries. The immediate significance of Volger's study was
instead its demonstration that a thorough survey of eyewitnesses and of
historical sources could produce valuable evidence for the scientific analysis
