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January 3, 2011

Quake Predictor

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  Understanding Earthquakes

Up-to-the-minute Southern California Earthquake Map

Earthquake Simulator

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What if you could check the earthquake forecast the way you check the weather? As this ScienCentral News video explains, scientists drilling into the San Andreas Fault this summer hope to learn whether earthquakes are predictable.

Understanding Earthly Rumbles

The strategy was straightforward. Blow up one city block ahead of fires trotting up 5th, Van Ness Avenue and nearly ever major thoroughfare in San Francisco to create a firewall. But, as with all simple plans aimed at outwitting a very complicated Mother Nature, it wasn't enough.

"All day and night the detonations resounded in one's ears and yet the fire continued to make headway…as far as the eye could see, clouds of smoke and flames were bursting forth," wrote Arnold Genthe, a San Franciscan who survived the 1906 catastrophe. As the city burned, deep below, plates that had shifted to cause the massive, 7.8 magnitude earthquake that precipitated the inferno were settling in for a long sleep.

Scientists who study quakes, like geophysicist Mark Zoback of Stanford University, say technology is handing researchers cards that could trump huge earthquakes' surprise factor and maybe even the devastating effects that follow, like the fires mentioned above. One plan starts with a drill burrowing into the San Andreas Fault, where sensitive instruments will spy on magnitude-two earthquakes we can't feel, but which routinely register every couple of years. Researchers plan to decode earthly grumbles and geophysical changes likely to precipitate quakes to see if it's possible to predict them in advance. One day, you might check the earthquake forecast the way you tune in to monitor weather.

image: USGS
"The observations we're making have never, ever been made before and will help calibrate and constrain a lot of models and hypotheses," says Zoback, one of many scientists overseeing a project called the "San Andreas Fault Observatory at Depth," or SAFOD. It's been 12 years in the making and is part of a larger scientific effort called Earthscope that will monitor geophysical changes on the North American continent.

At SAFOD's heart is an oil industry drill that's boring 1.1 miles into the Earth, turning east for 1.8 miles and stopping at a stress point along the San Andreas Fault where small quakes begin. There, instruments like seismometers, accelerometers, strainmeters, temperature sensors and fluid-pressure transducers will measure things like tilt, which Zoback says "is how the earth deforms slowly" during a quake, and pore pressure, or the pressure of fluids in the fault's cracks and pores.

Shooting through fiber optic cables, instrument readings will stream real-time into databases where scientists can evaluate "precursory signals before the earthquake occurs and then exactly what's happening as the earthquakes are occurring," Zoback explains, adding that such information will be a first. "We've never, ever had data like this before. For example, there are hypotheses that the fault moves slowly before it accelerates into the fast slip that occurs in an earthquake. Well, we'll be able to determine this with the instrumentation we've installed."

imag: NSF
So far, what scientists know about earthquakes is this: Rocks along fault lines suddenly break after pressure keeping two plates together builds. Resulting energy dispersion creates seismic waves that jostle the ground. Where the rock breaks is an earthquake's focus, while what's directly above is a quake's epicenter. As the Earth rattles and slides, plates move until they get stuck again, essentially slumbering until the next rupture. The San Andreas Fault is divvied into segments so those movements can occur anywhere along its 800-mile stretch at depths of up to ten miles.

"What makes the San Andreas Fault unique, I think, are two things," says Zoback. "Studying earthquakes and earthquake effects along the San Andreas has a tremendous societal impact [because of population density]…And second, as a result of decades of research, we know quite a bit about the San Andreas Fault so anything we do that is new can be done in the context of a lot of research that has happened before and that maximizes the return on experiments such as ours."

But how will learning about small quakes translate into understanding the bigger, badder kind? Simple, says Zoback, "Large earthquakes start as small earthquakes." This summer, the SAFOD drill will reach its end destination and by 2007 information will start filling a database that scientists all over the world can access.

For Californians, the stakes of a successful SAFOD experiment are higher than ever. Huge population jumps along the San Andreas mean many more could die in a quake than in 1906, when the death toll reached over 3,000. But Zoback says a very broad range of research efforts could dampen earthquake damage: "Some of those efforts are to simulate the occurrence of past earthquakes as accurately as possible so we know how to prepare for future earthquakes."

If SAFOD works the way scientists hope, deciphering what happens during breaks below could save lives up here.

This research was funded by the National Science Foundation and was published in Geophysical Research Letters, June 30, 2004.

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