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.
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.
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.
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.
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.
There are numerous high-rise
structures in the San Francisco - Los
Angeles areas. How do you think
they would fare in a magnitude 8
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.
How do you define earthquake
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.
What are your thoughts on the
possibility of predicting earthquakes
in the next two decades.
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.
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.
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.