An Interview with Charles F. Richter Earthquake Expert
Charles F. Richter, renowned seismologist, is a professor emeritus of seismology at the California Institute of Technology. He received his Ph.D. from Caltech in 1928. He is best known to the public for the Richter magnitude scale and he is equally recognized in the scientific community for his books Elementary Seismology and Seismicity of the Earth (coauthored with B. Gutenberg, 1954). Dr. Richter is probably the only man in the world who has a seismograph in his living room. Now 71, he retired from Caltech in July 1970.
Q:
Dr. Richter, the general public
most often associates your name with earthquake magnitude.
What factors were involved in the initial development
of the magnitude scale?
A:
The magnitude scale developed
unexpectedly out of a wish to accompany
a listing of earthquakes
instrumentally located in southern
California with some indication as to
which were large and small, based
on something more objective than
personal judgement, preferably on the
instrumental recordings themselves.
It soon appeared that the new scale
would be a useful means to clear out
errors and confusion from
earthquake statistics.
Q:
Much confusion exists in the public
mind regarding the different
magnitude scales, the difference
between magnitude and intensity, and the
erroneous impression that the
"Richter magnitude is based on a scale
of 10." Would you clarify some
of these points?
A:
The original magnitude scale,
which I published in 1935, was set
up for southern California only,
depending on the particular types of
seismographs in use there. Extension
to earthquakes the world over, and
to recordings by other instruments,
was accomplished beginning in 1936
in collaboration with the late
Dr. Beno Gutenberg. This extension was
based on reported amplitudes of surface waves.
Dr. Gutenberg later,
without any significant contribution
by me, developed a version of the
scale using the measured amplitudes
and periods of recorded body waves
(P, S, and PP); this was applied systematically
in our joint work on seismicity
of the earth. Later, Gutenberg
was in favor of using the body wave
scale in preference to the surface
wave scale. I had doubts at the time,
and now feel that the body wave
scale is still not satisfactory for
general use, since it will give results
comparable with Gutenberg's only
if his procedure is closely followed.
Magnitudes should not be based on
body waves alone when surface wave
data are available; nor should they
be based on P amplitudes alone. Still
worse is the practice of assigning
magnitudes on the first few waves of
the P group. Gutenberg invariably
used the largest P waves, not the
usually smaller beginning, so that
application of his tables and charts
to the initial waves is erroneous. In
many instances it has been shown
that the initial waves are those of
a small foreshock, to which alone
the magnitude supposedly determined
for the following shock will then
apply.
The relation between magnitude and intensity is one that is familiar in the physics of radiation; it applies in seismology because seismographs record the waves of elastic disturbance radiated from the earthquake source. Magnitude may be compared to the power output in kilowatts of a broadcasting station; local intensity, on the Mercalli or similar scale, is then comparable to the signal strength noted on a receiver at a given locality, Intensity, like signal strength, will generally fall off with distance from the source; it will also depend on local conditions at the point of observation, and to some extent on the conditions along the path from source to that point.
Magnitude is a sense involves steps of 10, since every increase of one magnitude represents a 10-fold multiplication of the ground motion; but there is no "scale of 10" in the sense of an upper limit. (The intensity scales do have such a limit - formerly 10, later 12.) Magnitude numbers simply represent measurement - logarithmically to be sure, but with no imposed ceiling. The highest magnitudes thus far assigned to actual earthquakes do not quite reach 9, but that is a limitation in the earth, not in the scale.
There is common misapprehension that the magnitude scale is itself some kind of instrument or apparatus. Visitors will ask to "see the scale," and are disconcerted by being referred to tables and charts used for applying the scale to readings taken from the seismograms.
Q:
What are the most interesting
aspects of California earthquakes?
A:
The most intersting aspect of
California earthquakes is the
unnecessary death and destruction they cause.
Q:
What State has done most toward
protecting its inhabitants by:
A:
There are now measures for
earthquake safety in many States,
some of them being adopted from
the Uniform Building Code.
Comparisons are undesirable, but in any
case they should be made by competent
engineers.
Q:
There are numerous high-rise
structures in the San Francisco - Los
Angeles areas. How do you think
they would fare in a magnitude 8
earthquake?
A:
Quite variously. Some of those
erected in the 1940's in the range
between 13 and 20 stories are
considered unsafe by many engineers.
Q:
How do you define earthquake
prediction?
A:
I don't define it. I think that
harping on prediction is something
between a will-o'-the-wisp and a red
herring. Attention is thereby diverted
away from positive measures to
eliminate earthquake risk.
Q:
What are your thoughts on the
possibility of predicting earthquakes
in the next two decades.
A:
None.
Q:
How cant he study of United States
earthquakes be improved?
A:
By continuous earnest efforts to
find out what is going on, without
running after prediction.
Q:
What has been your most memorable
experience in an earthquake?
A:
Difficult choice. Perhaps the Long
Beach earthquake of 1933, when
I was at the laboratory in Pasadena
at the moment of occurrence.
Q:
If the building you are in now
started to shake and you knew an
earthquake was occurring, what
would you do?
A:
I would walk - not run - to the nearest seismograph.
Abridged from the Earthquake Information Bulletin. Vol. 3, No. 4, July - August, 1971.
