Listening Post

Corvallis seismic monitoring station feeds data to an international network

Like some peace and quiet? You can find it where scientists listen for earthquakes.

John Nabelek, OSU geophysicist, manages the Corvallis seismic station (Photo: Nick Houtman)

John Nabelek, OSU geophysicist, manages the Corvallis seismic station (Photo: Nick Houtman)

On a remote hilltop west of Corvallis, John Nabelek unlocks a door into an underground bunker covered with bushes and blackberry vines. Inside, cold air bathes a rack of electronic gear fed by power cables that lie like snakes along the concrete walls. Ignoring a “Do Not Enter” sign, he opens another door, crosses a narrow airspace and enters an inner chamber through a third door.

Quiet. Not a sound.

If your ears could listen with the sensitivity of the instruments in this room, you would hear the planet tremble as tectonic plates grind against each other, continents rise and fall imperceptibly in tidal cycles and ocean waves crash on distant beaches. All the resulting vibrations — short- and long-wave from all parts of the compass, the Himalayas, the Caribbean, the Middle East, Alaska, the Cascadia Subduction Zone off the Oregon Coast — are picked up here as they pass through Western Oregon.

“Most of the noise we see in the data comes from ocean waves at the coast,” says Nabelek, a geophysicist in OSU’s College of Oceanic and Atmospheric Sciences. “We have to filter that out to detect seismic waves with the same or lower amplitude.” Other seismic monitoring stations have the same problem. West Coast surf is detectable in the middle of the country.

Moreover, the station itself is on the move. “Relative to North America, we are moving north at about two centimeters per year,” he adds. Data from the GPS receivers established here in 1996 conclusively showed that the Oregon Coast pivots around a point in northeastern Oregon.

Node on Global Network

The station near Corvallis is the Pacific Northwest’s primary international listening post for the tremors beneath our feet. Nabelek manages the facility, which was built in 1950 by the University of California. It is known as “COR” on the global seismographic network that is supported by the National Science Foundation, and in 1989, became one of a select group of stations managed by IRIS (Incorporated Research Institutions for Seismology), a non-profit scientific organization in Washington D.C.

The Corvallis seismic station is one of more than 150 stations in the Global Seismic Network managed by the U.S. Geological Survey and the Incorporated Research Institutions for Seismology.

The Corvallis seismic station is one of more than 150 stations in the Global Seismic Network managed by the U.S. Geological Survey and the Incorporated Research Institutions for Seismology.

Seismometers are exquisitely sensitive to local vibrations, even changes in atmospheric pressure, says Nabelek. So COR’s instruments are shielded in vacuum chambers that sit on concrete pillars extending deep into the soil beneath the bunker. To isolate the instruments from local traffic, a flexible membrane separates each pillar from the bunker’s concrete floor. The vacuum chambers sit loosely on each pillar, unattached. If the North American plate on which the station sits lurches, as it has done so many times in the past, “these instruments would go flying,” says Nabelek. A backup seismometer would continue to operate; it is bolted to its foundation.

Gone Broadband

COR is a study in contrasts. It contains the latest seismometer technology (purchased in 2010 with federal Stimulus Bill funds), but still sitting in the instrument room is one of the original devices that, says Nebelek, is too heavy to move. In 1950, seismic data were recorded on photographic paper, and the instrument chamber was essentially a darkroom. A technician had to renew the paper role daily. Black paint still covers the walls, but a bright fluorescent light has replaced the red bulb that originally hung from the ceiling.

Seismometers operate in sealed containers to eliminate interference from changes in atmospheric pressure.

Seismometers operate in sealed containers to eliminate interference from changes in atmospheric pressure.

At the heart of most seismometers in the past was a heavy stationary object. The instrument’s frame vibrated around the object, giving scientists a measure of seismic waves.

Like everything else, seismology has gone digital. Today’s instruments record vibrations by the electronic resistance they generate with an object that is light by contrast. Known as “broadband” technology, they are sensitive to the full range of seismic wave frequencies. “Broadband seismometers changed everything,” says Nabelek. Technicians visit the station only when problems arise. Data are sent in real-time to the U.S. Geological Survey in Golden, Colorado, and automatically posted to the station’s website.

Despite its quiet surroundings, the station witnesses some of the most violent events on the planet. In the past few years, it has documented the planetary echoes of cataclysmic shaking in China, Indonesia, Haiti, Iran, Chile and New Zealand. Tremors show up just as clearly when faults closer to home slip, but one day soon, it will ring when the coiled spring of our own Cascadia Subduction Zone lets loose.

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Resources

OSU is a member of the Pacific Northwest Seismic Network at the University of Washington.

Read a story about what the Christchurch, New Zealand, earthquake means to the U.S. West Coast.

Robert Yeats has devoted his career to raising awareness about earthquake risks in the Pacific Northwest.

In Uncharted Waters, read about how OSU engineers work with coastal communities to prepare for earthquake-generated tsunamis and connect with Pat Corcoran’s tsunami page at Oregon Sea Grant.

Learn about the Earthscope program, funded by the National Science Foundation and headquartered at Oregon State University.

Oregon State University scientists and engineers responded to the 2010 earthquake in Chile and a resulting tsunami.

Bob Butler and Tammy Bravo at the University of Portland produce up-to-date Teachable Moment earthquake information through IRIS Education and Outreach.

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