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BY
ERIC VAN
DYKE
July 2005:
A few weeks ago, a strange, five-foot-tall, dome-capped,
spider-like apparatus appeared on the Reserve. This highly
accurate Global Positioning System (GPS) is part of a growing
network of permanent reference stations that will eventually
number more than 800. Its purpose? To increase our understanding
of how continents develop and evolve by precisely measuring
long-term crustal motion here along the boundary between
the Pacific and North American plates.
The theory of plate tectonics, which has developed over
the past few decades, tells us that our central coast region
is situated on a line of collision between heavier, younger
rocks that are emerging from the ocean basins and older,
lighter rocks that form the continents. Frequent earthquakes
along the San Andreas Fault are indications of this ongoing
collision, as are occasional volcanic eruptions in the Pacific
Northwest.
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The
GPS unit.
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The
EarthScope Observatory, a long-term collaboration between
the National Science Foundation, the U.S. Geological Survey,
NASA, and various universities, will be one of the largest
(and most expensive) scientific research projects ever constructed.
The Observatory includes several components, each of which
involves a staggering collection of high-tech computers
and instrumentation. The United States Seismic Array component
of EarthScope will share several hundred advanced seismometers
between 2000 sites scattered throughout the United States,
monitoring earthquake motion and eventually producing a
high-resolution seismic map of the entire country. Drilling
for the San Andreas Fault Observatory at Depth component
has been underway at Parkfield in southeastern Monterey
County for much of the past year. When completed, this two-mile-deep
hole will allow the placement of instruments into the heart
of one of the fault’s most earthquake-prone sections
to monitor strain within the rocks and to measure the pressure,
temperature, and chemistry of groundwater. Finally, the
Plate Boundary Observatory (PBO) component will install
a network of strain meters and GPS receivers along the boundary
between the Pacific and North American plates, from the
Mexican border to Alaska. The strain meters will measure
tiny crustal movements within short periods (days), while
the GPS receivers measure larger patterns of crustal motion
over long periods (years). ESNERR will be a Plate Boundary
Observatory GPS site.
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