The magnitude 8.9 earthquake that ruptured the seafloor off Japan was the first major test of the nation's $1 billion investment in earthquake early-warning technology.
Similar systems could be installed in California, scientists said, but it would be expensive.
There's another consideration -- what to do with the information.
"It has to be a very clear message, and people have to know what to do with the information," said John Vidale, director of the Pacific Northwest Seismic Network at the University of Washington.
The rising death toll in Japan underscores the limitations of a warning system. Alerts are most valuable to those in communities distant from the epicenter. For those near Ground Zero, like the Japanese coastal cities flattened by tsunami waves, there's not enough time to sound the alarm.
Even 15 or 20 seconds can be enough time for people to dive under a table, for train operators to hit the brakes and for factories to shut down production lines, said Tom Jordan, director of the Southern California Earthquake Center.
"In my book, every second counts," he said.
Along with the U.S. Geological Survey, Jordan and a consortium of colleagues have been fine-tuning and testing a prototype warning system in California for years. Rolling it out statewide would cost $100 million, he said.
In Japan, where earthquake preparedness is woven into the fabric of life, the government spares little expense to protect its citizenry.
"For every 10 seismic stations we buy (in the United States), they buy a thousand," Cal Tech geophysicist Egill Hauksson said.
Japan's warning system is the most advanced in the world. A dense network of seismic instruments detect initial tremors generated by an earthquake. These so-called p-waves race through the earth but cause little damage. The warning is sounded in the interval before more destructive, but slower-moving, tremors called s-waves arrive.
As the frantic search for survivors continues in Japan, it's too early to quantify benefits from the alert system. But the technology itself performed well, and the messages undoubtedly saved many lives, Jordan said.
Warnings that featured a countdown clock were broadcast via television, radio and cellphone eight seconds after the quake was first detected, Hauksson said. In Tokyo, more than 200 miles from the epicenter, preliminary reports estimate warning times ranged between 30 and 60 seconds.
Many industries, medical facilities and transportation networks, such as the country's bullet trains, are hard-wired to respond. Schools automatically route alerts through public-address systems. Students drill several times a year in duck-and-cover protocols.
To educate the wider public about the system, videos from Japan's Meteorological Agency dramatize scenarios. A family that reacts with fear and confusion loses their chance to take cover. The mother who calmly switches off the stove and herds her children under the kitchen table avoids a falling cabinet. Drivers are advised to switch on their emergency blinkers and slow down, instead of braking suddenly.
"The ticklish issue is to make sure people don't respond badly," Vidale said. "It only takes a few mistakes to lose credibility."
To avoid the possibility of widespread panic, a system could be designed to notify only critical facilities, such as airports, hospitals, power grids and mass transit. But Jordan is convinced the information should be disseminated widely.
"We can't do anything about earthquakes, but we should learn how to use every second of warning we can get,'' he said.
An early-warning system for earthquakes also might help improve tsunami warnings, Jordan added. Sensitive GPS instruments can be wired into the system to detect the ground motion that accompanies a quake and that can trigger deadly surges of water.
In experimental mode, the California prototype has been able to detect a few small earthquakes and send out warning signals seconds ahead of the ground-shaking, Hauksson said. Engineers on San Francisco's BART system last year tested their ability to bring the trains to a stop upon receiving a mock earthquake warning.
Vidale said he believes there's a "99 percent chance'' the Northwest eventually will have a warning system. But it will come only after a large-scale network is vetted in California.
"The question is how long it will take," he said.