Efforts by scientists to predict earthquakes have proven disappointing. But hopes that big cities can get at least some warning after a quake has occurred but before its shock waves hit got a big boost from the Sept. 14 experience of Mexico City. Twelve accelerometers placed along the coast of Guerrero state gave residents in the capital, 190 miles from the epicenter, a 40-to-50-second warning that a destructive temblor was coming--enough time to take cover or flee unreinforced buildings.
Unfortunately, geology and urban realities conspire against such a warning in California. Los Angeles and San Francisco sit astride major geologic faults, while those that threaten Mexico City are about 200 miles away. Because quake waves travel at about 2.5 miles a second, a Mexico City warning of up to 80 seconds is possible, at least in theory. A quake under the populous L.A. Basin would produce virtually no warning; only 16 seconds' alert would result from a shift of the dreaded San Andreas fault at its nearest point to Los Angeles.
Still, even such a brief warning could be useful. Caltech and the U.S. Geological Survey are designing a warning system for Southern California, with financial support from utilities, a railroad and the National Science Foundation. Even if there is no time to alert the public, computers could allow railroads to stop trains, buildings to halt elevators and telephone companies to assign priority to police, fire and other emergency forces. After the pre-shock warning, the system of sensors could produce "shaking maps" that would tell emergency personnel where the damage might be worst.
Some argue that with such short warnings, it would be pointless to issue public alerts lest they cause panic. Still the warning system, which envisions placing 200 to 250 sensors in this region, is worth pursuing. Its completion depends on an $18-million grant that Caltech hopes to get from the Federal Emergency Management Agency as part of FEMA's $600-million national quake-mitigation program. After the initial investment, the program would require only $1 million to $2 million a year.
In these days of valid questioning of public spending, this is the kind of universal threat--to rich and poor of all communities--that demands a firm response from government.