Geoscience Reference
In-Depth Information
6: “the earthquake is felt by everyone with terror, so that very many flee their
dwellings; many feel like they will fall over.”
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in these ways, Sieberg's scale exploited much of what nineteenth-century
seismology had learned about human responses to earthquakes.
By 1939 there were thirty-nine versions of the Rossi-Forel scale in use.
Some revisions expanded descriptive language, while others pruned it. in
Wood and Neumann's 1931 revision to the Sieberg scale, for instance, the
line “Plants, the branches and weaker boughs and trees sway visibly, as they
do with a moderate wind” became “trees, bushes, shaken slightly.” A recent
critic judges that the earlier version was “more vivid and clearer.”
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indeed,
devising intensity scales posed a rare challenge to scientists' communicative
skills. Composing a scale was no less than a poet's quest for the evocative
image, the telling detail.
Moreover, the descriptive criteria used to classify shocks were highly
dependent on local cultures. it mattered how easily the masonry cracked,
whether the houses had chimneys, how much of the population worked
indoors, how given they were to panic. in Santiago, Montessus de Ballore
found counterintuitively that “the observation 'felt by persons walking' cor-
responds to a greater intensity than the record 'felt by everyone.' this seems
to be due to the more or less coherent nature of the subsoil at Santiago.”
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in the United States, Charles Rockwood noted that the report of “heavy”
damage by an earthquake in the eastern United States was equivalent to
“light” in reports from Peru.
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When edward holden adapted the Rossi-
Forel scale for use in California, he appended each degree with a word or
phrase typically used by local witnesses, such as “slight” or “violent.” Yet
his assignments of intensity were unreliable because he was, inexplicably,
“partial to intensity V.”
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how then could earthquakes be compared internationally? Montessus
again drew a comparison to meteorology, specifically to the humboldtian
methods of global physical geography: “When meteorologists draw their
isobars or isothermic curves, they begin by reducing the temperatures or
the atmospheric pressures to sea level by means of appropriate formulae. in
other words, they calculate these elements according to what they should
have measured in places equally distant from the earth's center. But as re-
gards the earthquake observations of intensity, we cannot conceive of any
method or formula which would enable us to reduce all estimates to uni-
form exterior circumstances, that is to say, to uniformity of subsoil, rigid-
ity of buildings, temperament of the observers, etc. the mere enumeration
of these requirements shows clearly the illusiveness of such an attempt.”
