Geoscience Reference
In-Depth Information
any absurdities, bearing in mind that some anomalies will always be found.
Occasionally there will be things that indicate very high intensity when it is
obvious that the intensity is low, and more rarely there will be effects which
indicate low intensity when it is obvious that the intensity must have been
high.”
187
the purpose of an intensity scale was to rate earthquakes relative to
each other in terms of destructive effects and human impacts. “Anomalies”
were unavoidable because the thresholds for different forms of damage var-
ied. even after eliminating any “absurdities,” the seismologist would still be
left with the problem that no intensity scale could, in every case, express his
own overall intuition of the violence of the shock. Still, a consistent rating
scheme was necessary for seismology's
public
dimension.
this need became pressing in the aftermath of the devastation of Long
Beach in 1933. Wood and his colleagues quickly got the sense that this
earthquake had been far more destructive than it had any right to be: 120
deaths and over $40 million of damage for a shock that (as future com-
mentators would note) rated only 6.2 on Richter's new scale.
188
It was clear
to Wood that foolish building practices were to blame. the question in
1933 was how to express that perception to the public. Unusually, Wood
chose to use the modified term “'apparent' intensity.” Of course, he knew
that intensity was always a measure of appearances. It was, however, es-
sential at this moment to convey to the public that the damage due to this
shock was out of all proportion to its intrinsic force—however that force
might be measured. He struggled to convey this counterfactual claim to the
press: “While the total amount of damage was large, there is good evidence
from numerous well-distributed structures which survived the shock with
little or no obvious injury, and from the sparseness of minor geological
evidence of hard shaking, that the intensity or violence of the shaking was
no greater than is usual in strong local shocks. . . . the nature and amount
of the structural damage was out of proportion to the energy and violence
of the shock. . . . 'Apparent' intensity of this value [grade 9, 1931 scale]
was manifested in a number of places on exceptionally bad ground, where
the intrinsic intensity as shown on good ground near by was substantially
less.”
189
Here we can see Wood grasping for words to convey his conviction
that the earthquake had caused more damage than it should have. What was
the telling variable: “energy,” “violence,” “intrinsic intensity”? At the time,
rumors were circulating that Long Beach was one of the strongest earth-
quakes of all time. Wood was furious about these “wholly irresponsible and
mischievous” reports. Different versions cited different forms of quantita-
tive “evidence” to back their claim. In a bitter letter to the
Los Angeles Times,
Wood offered the following example:
