A Brief History of Earthquake Warnings

The idea of using seismic waves to provide advanced warning of impending doom is not new. In 1868, a doctor named J.D. Cooper laid out his vision of such a system in an editorial for the San Francisco Daily Evening Bulletin :

”A very simple mechanical contrivance can be arranged at various points from 10 to 100 miles from San Francisco, by which a wave of the earth high enough to do damage will start an electric current over the wires now radiating from this city and almost instantaneously ring an alarm bell, which should be hung in a high tower near the center of the city.”

More than a century later, in a 1985 paper in Science , Caltech geophysicist Thomas Heaton sketched out a modern-day version, which he dubbed SCAN, for Seismic Computerized Alert Network. A SCAN, he argued, could be used to protect computer systems, isolate power grids, close off natural-gas valves, and protect rail lines, among other precautionary actions.

”That may have been the first Western paper to describe such a system,” Heaton told IEEE Spectrum . ”But at the time, I wasn’t even aware of what the Japanese were doing.”

In the 1960s, engineers at Japanese National Railways (now Japan Railways, or JR) were preparing to introduce their high-speed shinkansen , known as bullet trains. Well aware of the earthquake risks, they decided to install seismometers along the routes. At first, the seismometers simply issued an alert when ground acceleration exceeded some threshold; the alert was then relayed to train operators, who manually slowed their trains.

An enhancement in the 1970s automated the alerts, so that train braking could occur without human intervention when seismometers detected seismic intensity greater than 4 on the Japanese scale of 1 to 7. Later, the seismometers were moved farther from the rail lines, to increase the time available to take action. Fifteen years ago, the railroad company introduced a further expansion of its seismic network, called the Urgent Earthquake Detection and Alarm System, or UrEDAS, which exploits the difference between the nondestructive P (primary) waves and the damaging S(secondary) waves.

UrEDAS quickly became the model for other seismic networks. It drew the attention of the Japan Meteorological Agency, which collaborated with JR’s Railway Technical Research Institute to deploy its nationwide system of seismic stations.

In the early 1990s, Mexico became the first country outside Japan to copy the UrEDAS approach, creating an early-warning system for Mexico City.

The JR system wasn’t able to prevent the October 2004 derailment of a bullet train following an earthquake in Niigata prefecture, north of Tokyo. The system apparently operated just fine, but the epicenter was so close that there wasn’t sufficient time to slow the train, which had been traveling at 210 kilometers per hour. It was the first derailment in the high-speed rail’s 40-year history. Remarkably, none of the 155 passengers were injured.

Since August, other private railroads in Japan that haven’t had the benefit of the JR seismic network can now make use of JMA’s early-warning alerts. At Tokyo-based Odakyu Electric Railway Co., which operates commuter trains in the Tokyo and Kanagawa prefectures, the company’s data center receives a JMA alert and immediately forecasts how much damage is probable along its route, based on past earthquakes. It then broadcasts an alarm to those trains likely to be affected. The whole process takes 2 seconds.

Japan Railways has also recently been discussing using JMA’s early-warning data, according to Yukio Fujinawa, managing director of the Real-Time Earthquake Information Consortium. The reason? Operating and maintaining UrEDAS is extremely costly.

To see all of Spectrum 's special report on The Megacity, including online extras and audio and video exclusives, go to http://spectrum.ieee.org/moremegacity.

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