Observing the Roiling Earth
Oct. 28, 2004
PASADENA, CA — In the 1960s the theory of plate tectonics rocked geology's world by determining that the first 60 miles or so of our planet—the lithosphere—is divided into about a dozen rigid plates that crawl along by centimeters each year. Most manifestations of the earth's dynamics, like earthquakes and volcanoes, occur along the boundaries of these plates.
As a model, the theory of plate tectonics continues to serve us well, says Jean-Philippe Avouac, a professor of geology at the California Institute of Technology. Plate tectonics is a powerful description of the large scale deformation of the earth's lithosphere over millions of years, but it doesn't explain the physical forces that drive the movements of the plates. Now, thanks to a $13,254,000 grant from the Gordon and Betty Moore Foundation, Caltech has established the Tectonics Observatory, under the direction of Avouac, with the ultimate goal, he says, of "providing a new view of how and why the earth's crust is deforming over time scales going from a few tenths of seconds, the typical duration of an earthquake, to several tens of millions of years.
"Most of the outstanding questions in earth science concern processes that take place at the boundaries of the earth's tectonic plates," says Avouac, so their scientific efforts will be centered around major field studies at a few key plate boundaries in such areas of the world as western North America, Sumatra, Central America, and Taiwan. Among the questions they hope to answer are:
- Tectonic plates move gradually when viewed on large time scales, but sometimes undergo sharp "jerks" in speed and direction. What's the cause?
- Earthquakes can be damaging events to humans. What physical parameters control their timing, location, and size?
- Subduction zones, where oceanic plates sink into the Earth's mantle, are needed to accommodate and perhaps drive plate motion. How do these subduction zones originate and grow?
While the observatory will occupy existing but refurbished space on campus, the bulk of the grant will be spent on new technologies and acquiring data that will be used to observe and model these boundary zones. "We plan to take advantage of a number of new technologies that will allow us to measure the deformation of the crust, and image the earth's interior with unprecedented accuracy," says Avouac. "More powerful computers and advanced computational techniques will also allow us to develop models at the scale of the global earth. The breakthroughs will probably result primarily from the interactions among the various disciplines that will contribute to the project."
In addition to seismometers and GPS receivers (and the hands-on work of installing them at plate boundaries around the world), other equipment and data that's needed will include space-based GPS, that will allow geologists to measure the relative velocity of two points on the earth's surface to within a fraction of a millimeter per year; satellite images to map displacements of broad areas of the ground's surface over time; geochemical fingerprinting methods, to analyze and date rocks that have been brought to the surface by volcanic eruptions or erosion, thus helping to characterize the composition of the earth far below; and of course, massive computation to analyze all the data.
"We've already begun this work," says Avouac. "For example, in Mexico we are imaging and monitoring seismic activity and crustal deformation along a major subduction zone. Right now, geologists are in the field installing what will be a total of 50 seismometers."
Few institutions are capable of mounting this kind of sustained, diverse effort on a single plate boundary, or of mining data from multiple disciplines to create dynamic models, he says. "That's what Caltech is capable of doing," says Avouac. "We hope to train a new generation of earth scientist, offering students an exceptional environment with access to all of the modern techniques and analytical tools in our field, while interacting with a group of faculty that have diversified expertise."
The Gordon and Betty Moore Foundation was established in September 2000 to create positive outcomes for future generations. The Foundation funds outcome-based grants and initiatives to achieve significant and measurable results. Grantmaking supports the Foundation's principal areas of interest: global environmental conservation, science, and the San Francisco Bay Area.
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