Wiring the Earth to Eavesdrop on Quakes

To understand how earthquakes are born, a group of scientists wants to wire the entire Western United States into a $100-million network of sensors in perhaps the most ambitious--and costly--seismic research project ever proposed.

The project builds on seismic research networks already taking shape in Southern California, the San Francisco Bay Area and the Pacific Northwest, and it might take 20 years to complete. The finished system would encompass thousands of sensors installed across eight states.

This unusual terrestrial observatory would, for the first time, allow scientists to measure the inexorable forces building up across millions of square miles of countryside. Those forces are generated by the Pacific and North American tectonic plates grinding against each other in a broad band reaching from the beaches of Malibu to the high mountain passes of Colorado.

The jostling of these titanic shards of the planet’s crust powers thousands of earthquakes every year, from tiny temblors barely strong enough to rattle teacups to the rare quake powerful enough to lay waste to densely populated metropolitan areas such as Los Angeles.

The proposal is one measure of how radically new sensors, space-based surveying systems and high-speed computers transformed the study of the Earth.

“We now have the capability of collecting and dealing with a lot more data than we ever could before about what is going on beneath our feet,” said UC San Diego seismology expert Duncan Agnew.

But the new systems and sensors also are an acknowledgment that geologists and geophysicists are still stymied in their effort to understand the fundamental forces that cause earthquakes, much less where or when they might strike, experts said.

Not so long ago, most experts were convinced that earthquake faults were isolated from one other.

Now scientists are certain that earthquake faults are as interconnected as strands of a spider’s web, with the tectonic energy that builds up in the Earth constantly shifting as tension mounts along one fault or relaxes along another.

A tiny fraction of that energy may be released harmlessly in infinitesimal movements that geologists call seismic creep, or in so-called slow earthquakes that may take hours or even days to occur.

Most of it, however, is released in the explosive burst of an earthquake.

As the energy level changes, faults can affect each other in ways no one yet understands, even across great distances or gulfs of time.

Indeed, some experts speculate that the cause of the 1994 Northridge earthquake might have been the 1964 Alaska earthquake, thousands of miles to the north. That magnitude 9.2 quake 30 years before, some speculate, may have set in motion powerful slow-motion ripples in the Earth that eventually affected the balance of Southern California’s fault systems.

Certainly, if scientists are ever going to come to terms with these destructive forces, they must understand the subterranean tensions at work across the entire range of a tectonic plate boundary, said Paul G. Silver, a geophysicist at the Carnegie Institution of Washington, a leader of the observatory project. The group includes Thomas Henyey, director of the Southern California Earthquake Center, and UC San Diego’s Agnew.

“Our present inability to predict earthquakes, rather than reflecting the basic unpredictability of the thing itself, points to a fundamental gap in our knowledge about earthquakes, especially how they are triggered,” Silver said.

“We know that the ultimate cause of nearly all earthquakes is the motion of tectonic plates, yet the details of how steady plate motion ultimately produces an individual earthquake are not known,” he said.

To supplement the traditional land-based seismographs and strain meters now in use, Silver and his colleagues want to install 1,000 sensors linked to the orbiting Global Positioning System. That would allow researchers to track movements of the Earth’s crust with unprecedented precision.

Together, the network’s sensors could monitor subtle, momentary fluctuations in the crust from Mexico to Canada, as well as slower plate movements that can take decades to unfold.

“It would open a new window into the Earth,” said U.S. Geological Survey geophysicist Alan Lindh, who studies the earthquake faults of the Bay Area. “The really exciting thing about a new window into the Earth is finding something you never dreamed of.”

Nevertheless, many researchers are worried about the cost of such projects, which might drain resources from equally pressing projects aimed at mitigating the hazards earthquakes pose to inhabited areas.

Some geophysicists are laying the groundwork for a 10-year effort to create a detailed seismic map of the entire North American continent. The National Science Foundation is seeking $81.9 million to link 30 research centers across the country into one computerized virtual laboratory “that will change the shape of earthquake engineering,” according to foundation Deputy Director Joseph Bordogna.

In the months to come, the observatory proposal will be a subject of considerable debate, several experts said.

If the science foundation approves the project, it will seek the required funding from Congress.

“This [observatory] would provide very useful information regarding the long-term process leading up to earthquakes,” said Hiroo Kanimori, director of the Caltech Seismological Laboratory. “The question is whether we can spend that much money on this. A $100-million project is pretty high for geophysics.”

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Building an Earth Observatory

To analyze the forces that power earthquakes, scientists want to wire the western United States into a $100-million network of sensors that could measure the tectonic forces building up across millions of square miles.

The proposed system, called the Plate Boundary Observatory, would build on seismic research networks already taking shape in Southern California, the San Francisco Bay Area and the Pacific Northwest.

The observatory would monitor the broad boundary between the Pacific Plate and the North American Plate.

Source: Carnegie Institution of Washington, Incorporated Research Institutions for Seismology (IRIS).