August 19, 2008
Network of Sensors Can Track Land’s Movement
SAN JOSE, Calif. - How do you measure a restless landscape?
It takes an earthquake for humans to feel the shift of geological plates beneath our feet. But a new network of hypersensitive tools installed around the Bay Area detects even the most subtle shrugs, providing important insights about the slow stretching, splitting and drifting of the region.
Mounted on four legs for stability, these so-called "monuments" are tiny laboratories that talk to GPS satellites to transmit a steady stream of data, documenting millimeters of motion relative to the stable central region of the United States.
When mapped over time, each monument is watched as it migrates. Geologists hope that these maps will yield a clearer understanding of the forces that are building the terrain - forces that will someday trigger a catastrophic earthquake.
"GPS is great at observing motions that a person cannot feel," said geophysicist Jessica Murray-Moraleda of the U.S. Geological Survey in Menlo Park.
A network of 1,000 GPS instruments was installed in a gridlike pattern along the West Coast and will eventually occupy about 2,000 locations across the continental United States over the next decade.
Some of the stations include "strainmeters," clustered along active faults and in volcanic areas. When a rock squeezes or relaxes, the strainmeters sense changes in their diameter to a part in a billion.
In other parts of the U.S., the monuments reveal different problems. A collapsing station might mean too much groundwater is being pumped out. On a melting glacier, they measure the speed of retreat.
Originally published by San Jose Mercury News.
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