Hanks ’66 and a colleague developed the moment-magnitude
scale, a successor to the Richter scale. (courtesy Thomas
January 25, 2006:
PROFILE Quake watcher Thomas Hanks ’66 strives to predict the earth’s violent
When the earth shakes, the media report how high the temblor registered
on the Richter scale. But despite its frequent use, the famous rating
system created by Charles Richter in 1935 is no longer how seismologists
gauge the size of earthquakes. They actually use a scale invented
in 1979 by Thomas Hanks ’66 and a colleague, Hiroo Kanamori,
known as the moment-magnitude scale.
Like its better-known counterpart, the scale developed by Hanks
and Kanamori rates earthquakes by their size, or magnitude, but
the moment-magnitude-scale calculations are far more reliable for
large seismic events. The U.S. Geological Survey adopted the moment-magnitude
scale as its standard in 2000.
Because the new system sounds just like the old scale, most reporters
don’t know they are citing the wrong scale. “Every magnitude
you see these days is a moment-magnitude,” says Hanks.
For Hanks, a geophysicist with the U.S. Geological Survey in Menlo
Park, Calif., the moment-magnitude scale is just one of a series
of quiet contributions made over a 33-year career that have helped
scientists understand why earthquakes occur.
A geological engineering major at Princeton, Hanks developed his
fascination with quakes after witnessing firsthand, as a graduate
student at the California Institute of Technology, the devastating
1971 San Fernando earthquake in Los Angeles — which leveled
buildings and claimed 65 lives.
Since then, Hanks has studied the causes and effects of earthquakes
in New Zealand, Mongolia, Mexico City, China, and miles deep in
South African gold mines.
In 1981, Hanks and another colleague also developed a more accurate
way to describe how a quake’s energy will materialize as strong
ground motion, helping engineers design buildings that can withstand
the most vigorous shaking they can expect during the buildings’
The most important location Hanks has analyzed for seismic safety
is the designated federal site for nuclear-waste disposal at Yucca
Mountain in Nevada. For two years, he chaired a committee whose
job it was to predict how much the ground around the repository
would move when very rare earthquake ground motion occurs —
that is, ground motion that might happen once in 100 million years.
“A hundred million years is a long, long time,” Hanks
says, “and we are only beginning to understand the things
that the earth can do over such time intervals.”
When the next earthquake takes place, and the media scramble to
report the latest readings on the “Richter scale,” Hanks
won’t mind letting his credit go elsewhere. “Charles
Richter is one of the great saints in the field of seismology, and
I don’t want to get in his way at all,” Hanks says.
Besides, the “Hanks-Kanamori scale” just doesn’t
have the same ring.
By Justin Nyberg ’01
Justin Nyberg ’01 is a writer for Outside magazine
in Santa Fe, N.M.