Geoscience Reference
In-Depth Information
scientific definition is attempted the term comes to include much more
than is ordinarily meant. Any mechanical disturbance whatever, either on
or within the surface of the earth, sets up a state of elastic vibration which is
propagated to all adjacent parts of the crust by elastic waves which may or
may not be evident to human senses. This motion constitutes an earthquake.
Scientifically, therefore, an earthquake is the result of any elastic vibrations
in the earth's crust, whether they are produced by volcanic eruptions, by the
sliding of great strata . . . or even by the tread of a foot. in popular language,
however, we are in the habit of restricting the use of the word earthquake to
comparatively violent motions of short vibration-period which extend over a
considerable area, and especially to such motions as are produced by some-
what obscure causes. it is necessary to our popular use of the term earthquake
that the cause, while natural, should be somewhat obscure.
81
Holden's contrast between “scientific” and “popular” language remained
elusive. Apparently, the term “earthquake” was “popular” because it re-
ferred to “obscure” causes. in what sense, though, were these causes ob-
scure? Holden did not explain. Likely, he would not have been able to. He
was searching the seismology of his day for a clear line between a “scien-
tific” and a “popular” perspective; but that division simply did not exist.
From Holden's “mechanical” perspective, eyewitness reports of earth-
quakes were at best a supplement to the spotty coverage of seismographs—
at worst, a source of exaggerations and distortions. Holden, a humanist and
language lover, did not fail to appreciate earthquake narratives as a literary
genre. But he drew a firm divide between earthquake “narratives in which
the human element enters,” proper to the domain of poetry, and earthquake
“statistics,” containing information of use to science.
82
Holden would rely
on human observations only if they could be reduced to their instrumental
equivalents. “in the investigation of the effects of any particular earthquake
it is of prime importance to escape as soon as possible from the exaggerated
accounts of special correspondents or of the inhabitants who wish to mag-
nify the importance of their neighborhood or of themselves, and to obtain
a numerical and quantitative basis for such comparison.”
83
Like generations
of astronomers before him, Holden hoped to replace unreliable observers
with self-registering instruments. To do so, he intended to deduce mechani-
cal equivalents for each Rossi-Forel degree of intensity. He began by defin-
ing intensity as the maximum acceleration of the seismic wave.
84
(This was
a correction to his earlier statement that intensity could be measured by the
length of the line traced by the duplex seismometer, i.e., the maximum dis-
