NEXT L.A.: A look at issues, people and ideas helping to shape the emerging metropolis. : Getting a Step Ahead of Seismic Surprises : A network of sensors will someday detect shock waves crucial seconds before they hit heavily populated areas, scientists say.

When Mexico City radio stations sounded a warning 50 seconds before a magnitude 7.2 earthquake struck on Sept. 14, queries poured in to the Pasadena field office of the U.S. Geological Survey.

“People wanted to know why we don’t have a warning system here,” said Jim Mori, the Geological Survey’s scientist-in-charge in Pasadena. “Even a member of the [Los Angeles County] Board of Supervisors was curious.”

And the answer?

“We had to tell them that here, it’s more difficult.”

But not impossible. The federal Geological Survey, Caltech and two dozen local companies and utilities are collaborating to develop an automated system they hope will soon flash a warning when a damaging earthquake begins in Southern California.

Such a system would rely on the physics of quakes to give a warning. The most damaging energy waves unleashed by a quake surge through the ground at about 2 1/2 miles a second. The epicenter of the quake two weeks ago was 190 miles from Mexico City, so the ground didn’t begin to shake in the capital for about 76 seconds.

The warning system uses sensors to detect the initial ground shaking, then feeds that information back to a computer ahead of the approaching seismic waves. Radio stations in Mexico City received an automated alert that triggered a broadcast urging listeners to take cover.

While quakes felt in Mexico City often begin near the distant Pacific coast, Los Angeles faces a different situation. Shock waves from the nearest point on the mighty San Andreas Fault are only about 16 seconds from Downtown Los Angeles (and waves travel from Northridge to Downtown in eight seconds)--hardly enough time for a signal to be picked up, processed and broadcast so that people can react.

Better if a major quake should occur on the San Andreas Fault near Indio. The shaking would take about 45 seconds to reach Los Angeles, allowing more warning time.

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According to Caltech seismologist Egill Hauksson, it will be at least five years before an early warning system comes on line in Southern California for utilities and law enforcement.

It will be even longer before the public hears sirens or broadcasts that relay the warnings.

But eventually, according to Hauksson and other scientists on the project, the Southern California system will be more elaborate and reliable than the one in Mexico.

Although plans in Mexico call for relaying alarms directly to schools and hospitals and airing warnings on television as well as radio, false alarms have been an occasional problem. Relatively few sensors are used to detect the start of an earthquake.

To avoid false alarms, the California scientists have decided that at least three seismographic sensors will have to record shaking before any warning is disseminated. And because earthquakes here can come from almost any direction at any time, “we’re going to need 200 to 250 sensors [compared to 16 now],” Mori said.

In a briefing last week, Hauksson said that when the $18-million Southern California system is fully operational, it should be able to display a computerized map of the shaking intensities of a magnitude 6 earthquake centered 175 miles from Los Angeles even before any shaking begins in the city.

A first warning that a powerful quake is occurring, and where it is, will arrive before the shaking for any magnitude 6 quake more than 35 miles away, he said. Ground motion estimates will arrive before the shaking for such a quake more than 50 miles away.

(Already, Caltech has a computer that flashes news that a big quake is occurring to the school’s Seismological Laboratory before the shaking arrives, but it doesn’t say where the quake is located).

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For larger quakes, the first warnings will come as quickly. But in magnitude 7 and 8 temblors, because of the greater duration of the shaking and larger size of the rupture zone, the ground motion readings and maps of the shaking will take longer.

Hauksson said that shaking maps are a higher priority than early warnings because having quick information about the magnitude, location and distribution of a quake’s power will help police and fire departments, electric and gas utilities and railroads respond to emergencies.

Hiroo Kanamori, director of the Caltech Seismological Laboratory, expressed some doubt about the value of an early warning system for the general public. “It’s not too useful for ordinary people--at least ones who are not well educated on what to do,” he said.

Hauksson recalled that the late Charles Richter, a famed Caltech seismologist, always said that the safest thing to do in an earthquake was to remain inside for at least 15 seconds. Then, if the shaking was intensifying, one should run outside--with a wary eye peeled for falling objects--because the building might collapse.

Both Hauksson and Kanamori said that any system to warn the public would be wasted without a mass campaign to educate the public on safety procedures. For now, it is the quick generation of maps after an earthquake that has the scientists and their supporters interested.

The project has drawn strong interest from agencies and firms interested in the earliest possible quake detection. Twenty-five private firms and public agencies are supporting the work, some putting up $25,000 a year. There is also a $450,000 National Science Foundation grant for installing sensors, some USGS and state funds and a Caltech contribution, and an application is being made to the Federal Emergency Management Agency for other funds.

“As we reduce the time it takes to get out the information, we approach an early warning system anyway,” Hauksson said. “Pretty soon, the information will be out on some quakes before the shaking arrives.”

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On Oct. 1, in another step toward providing rapid information, the CUBE system (an acronym for Caltech-U.S. Geological Survey Broadcast of Earthquakes), will be capable of displaying the peak ground acceleration in various locations.

Ground acceleration maps can be used to dispatch emergency crews to areas with the most severe damage in a major earthquake.

“We are gradually moving from a system run by academics for the instruction of students to a system with many public safety functions,” Hauksson said.

“Today, we can provide a quake’s location within a minute of its occurrence, and its magnitude within a couple of minutes. Tomorrow, we’ll have the parameters of the shaking, and after that early warning.”

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Quake Warning System

Fifty seconds before a magnitude 7.2 earthquake rocked Mexico City on Sept. 14, radio stations broadcast a warning to citizens. Similar technology may soon be able to alert Southern California that a major quake has begun on the San Andreas Fault.

Even a few seconds of warning could let trains, elevators and sensitive industrial processes shut down before the main shock wave hits the Los Angeles area and also give emergency crews crucial time to respond.

Eventually, warnings could be sent directly to schools and hospitals or broadcast over the airwaves.

Background And Expectations

* Practical early warnings are about five years away, scientist say. But the system already lets Caltech, the USGS and paying clients know the location and magnitude of a quake within minutes.

* After Oct. 1, scientists will also know immediately after a quake the severity of ground shaking in different areas. That information will help emergency teams know where to start looking for casualties and heavy damage.

* About two dozen public utilities, railroads, insurance companies and other institutions are paying up to $25,000 each year to fund the system.

How It Works

Ground sensors: Southern California Seismographic Network

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A system now in development by Caltech and the U.S. Geological Survey would use ground sensors to detect the initial signs of an earthquake and transmit the data over dedicated lines to computers. Destructive energy from a quake travels through the ground at about 2 1/2 miles a second. If the epicenter of a temblor is far enough away, there would be time for the computers to sound alarms and trigger precautionary actions in the Los Angeles area.

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Approximate times for secondary, or destructive, energy waves to reach Downtown Los Angeles from an earthquake under:

1. Northridge: 8 seconds.

2. Nearest point on San Andreas near Palmdale: 16 seconds.

3. Indio on southern segment of San Andreas: 45 seconds.

4. Imperial Valley: 70 seconds.