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No Moment Too Small

On October 17, 1936, Japanese geophysicist Hiroo Kanamori was born. Recipient of many prizes and awards, he has spent his life investigating the magnitude and energy releases of great earthquakes.

Like Charles Richter, Kanamori has taught at the California Institute of Technology. The original Richter Scale was published in 1935 and designed for measuring the size of earthquakes in southern California. The scale rates an earthquake calculated from data from magnitude of the seismic surface wave and the ground motion measured at a specific distance from the quake’s centre. It is valid only within certain frequency and distance ranges.

Born in a land of very large earthquakes, Kanamori recognized that a scale was required to measure larger earthquakes whose wave energy saturated or overwhelmed the seismic recording equipment of the mid-20thcentury. Of special concern were earthquakes that occurred the length of very long fault lines. The worst earthquakes have slow waves that last longer… that can produce tsunamis that ripple across oceans.

With Caltech colleague Thomas C Hanks, Kanamori spent well over a decade of work examining the acute moment of earthquake rupture. They extended the Richter concept to measure both the smaller earthquake magnitudes and the largest tectonic ruptures that occur within thousand year time frames. They produced a scale that measures the amount of energy released and the averaged amount of slip and area size of the earthquake. Although consistent with Richter’s medium-sized earthquake ratings, Hanks-Kanamori provides a more uniformly applicable rating, known as the Moment-Magnitude Scale.

The U.S. Geological Survey adopted the Moment-Magnitude Scale as its standard in 2000. The MMS is now used in almost every area on Earth … although still often miscalled “Richter”.

Caltech professor emeritus and Kyoto Prize honoree, Kanamori continues to pursue measurement research on earthquake foreshocks, working for the day when long-period waves lead to an earthquake early warning system. His work has contributed to a global positioning system network that detects fault slip events so small they do not produce destructive waves, a real-time tsunami warning system, and proposals for reducing seismic hazards.

Kanamori envisions “smart” technologies connected to an earthquake early warning system such as buildings that shut off gas and electricity and deliver elevators to the next floor, releasing people so they are able to reach safety. The smallest fault slip increases our knowledge of our ever-changing planet.

B Bondar / Real World Content Advantage