image: The GPS component of an advanced seismometer sits atop Radar Ridge outside Astoria, Ore. The installation is part of the Pacific Northwest Seismic Network. view more
Credit: Pacific Northwest Seismic Network
When a magnitude 9 earthquake devastated Japan in March some residents got a warning, ranging from a few seconds to a minute or more, that severe shaking was on the way.
Now, with a $2 million grant from the Gordon and Betty Moore Foundation to the University of Washington, a similar warning system could be operational in the Pacific Northwest in as little as three years.
One-quarter of the grant money will go to placing 24 sensors that combine strong-motion detection and GPS readings along the coast to record the first signals from a major earthquake on the Cascadia subduction zone, which is just off the Pacific Coast from northern California to southern British Columbia.
"The main point is to spot a big earthquake at the time it starts. The main motivation for these stations is Puget Sound," said John Vidale, a UW professor of Earth and space sciences and director of the Pacific Northwest Seismograph Network based at UW.
The cities of Portland, Ore., and Vancouver, B.C., also would benefit from the system, but they are not believed to be as vulnerable as Seattle and the surrounding area, which is closer to the subduction zone. In addition, much of Seattle is built on a softer basin more susceptible to shaking in a huge quake.
The system is designed to provide warning for very large coastal earthquakes. Smaller earthquakes might be more dangerous locally, if they happen for example in the immediate Puget Sound region, but it is more difficult and costlier to provide warning for them.
A warning that strong shaking is coming from a coastal quake could, for example, allow a doctor to halt a surgery. Trains could be stopped before they reach vulnerable bridges and sensitive equipment could be shut down before suffering significant damage.
Inexpensive and very simplified systems that send alarms when shaking is detected – such as those that close gates on the Alaskan Way Viaduct in Seattle – are currently in operation, but Vidale noted that they provide much less lead time and much less accurate warning.
The San Francisco-based Moore Foundation also is making $2 million grants to the University of California, Berkeley, and the California Institute of Technology to build on a prototype earthquake early warning system already in development in California. The three universities will collaborate with the U.S. Geological Survey on the project.
It is estimated that a comprehensive earthquake early warning system along the West Coast would cost $150 million over five years, about $70 million of that in the Northwest.
The work in the Northwest will build on work already being done in California, Vidale said, though the seismic characteristics of the two regions are different. California already makes warnings available to some emergency managers, a capability still several years away in the Northwest.
The new monitors will send data on strong shaking associated with an earthquake, which will help seismologists determine the size of the quake. But they also will provide GPS data, monitored at Central Washington University, to show how far the ground is moving. That can be a key piece of information in determining quickly whether an earthquake is occurring in the subduction zone, where it could grow to a magnitude 9 and trigger a Pacificwide tsunami. In such a quake, ground can move from several inches to several feet.
Some of the monitors could be placed along the Washington coast, though more likely they will be deployed along the northern California-Oregon coast, Vidale said. There already are some monitors along the Washington coast and there is much less data available farther south.
In the easiest scenario, Vidale said, the system could detect a magnitude 7 or 7.5 earthquake within the first 30 seconds. A quake of that intensity could grow to a magnitude 9 as the rupture spreads along the fault line.
Vidale said geologic evidence indicates that, historically, perhaps half of the Cascadia subduction zone earthquakes that achieved a magnitude of 7 or 7.5 grew to the range of magnitude 9. Scientists have shown that the last major quake on the subduction zone, in January 1700, was likely a magnitude 9 that set off a tsunami across the Pacific and caused land along the Washington coast to drop substantially.
Detecting a magnitude 7 or 7.5 quake at the southern end of the fault, off northern California or southern Oregon, could provide as much as five minutes warning to the Seattle area, he said. A rupture of that magnitude off the Washington coast might provide only 30 seconds of warning to the Seattle area, but Portland and Vancouver would still receive warning.
In the early stages of the system's operation, Vidale said, data will be shared only with a few companies on a test basis because there will not be enough confidence in the information.
"We have to learn what we're doing before we tell the public about it," he said. "I think at the end of three years we could have enough confidence to share the information with the public. But we have to have confidence and we have to have a delivery system."
Implementing delivery will be up to emergency managers in three states and one Canadian province, he noted, and so will require a great deal of coordination and cooperation. The Moore Foundation grant is for three years, so additional funding would be needed after that.
For more information, contact Vidale at 310-210-2131 or vidale@uw.edu, or Bill Steele, Pacific Northwest Seismic Network coordinator, at 206-685-2255 or wsteele@uw.edu.
A YouTube video (see http://bit.ly/tdrCPW) shows what one Japan resident experienced from the country's early earthquake warning system during the March disaster.
This news release provides details specific to the Northwest and adds to information contained in a primary news release found at http://usgs.gov/newsroom/article.asp?ID=3041.