GPS stations key to state's quake warning system

Earthquake scientists have found powerful new tools to alert Californians when distant earthquakes are about to cause dangerous ground-shaking where they are. Global Positioning Systems, high-tech versions of the devices that guide ships at sea and drivers through unfamiliar city streets, can instantly measure even tiny disruptions of the Earth's crust caused by major quakes, said Richard Allen, director of the UC Seismological Laboratory at Berkeley.
"We can now do a better job of swiftly estimating the magnitude of large earthquakes as they rupture the ground, and we have shown that we can successfully process the data in real time," he said, reporting the advance Thursday at a meeting of the American Geophysical Union in San Francisco.

Allen is a member of the California Integrated Seismic Network, a consortium of the state's major universities, research institutions and the U.S. Geological Survey, whose scientists have been developing and testing a prototype Early Warning System statewide for nearly a dozen years.
The need for adding GPS was stimulated by Japan's great undersea Tohoku earthquake and tsunami in April 2011 which killed more than 15,000 people and destroyed three major nuclear power plants, Allen said in an interview.
When the earthquake struck, its magnitude was first estimated by Japan's automatic early warning system at 7.5. The magnitude was quickly recalculated to a 9, but the difference led the system to briefly underestimate the intensity of ground-shaking on parts of Japan's main island, he said. That underestimation left some people without adequate warning of what was to come.

Bay Area stations

Some 40 large GPS stations are operating in the Bay Area, and their measurements of the Earth's distortion along a major fault as it ruptures can add significantly to the accuracy of early automatic estimates of a quake's magnitude. That means it will improve the accuracy of the warning system's forecasts of intense ground-shaking, its developers say.
Ronni Grapethin, a postdoctoral fellow from the University of Alaska who currently is working in the Berkeley seismology laboratory, joined Allen in the report.
"This will be an essential part of the early warning system," said geophysicist Peggy Hellweg of the Berkeley lab. "It is an extremely important add-on, especially when very large earthquakes can produce extremely strong ground-shaking," she said.
The completed warning system, known as ShakeAlert, could give Bay Area residents up to a full minute of warning when a major quake starts rupturing the ground hundreds of miles away, and even a few crucial seconds of warning if the quake hits closer to home, scientists say.