Glacial Deposits.indd - Department of Geography - Geology - Illinois ...

EARTHSCOPE: UNLOCKING THE SECRETS OF
THE NORTH AMERICAN CONTINENT
By Robert S. Nelson
I
llinois State University is one of almost 100 schools participating in EarthScope. EarthScope
is the largest continental geology project ever funded by the National Science Foundation
(NSF), in partnership with the United States Geological Survey, and with the collaboration of
UNVACO Inc., Incorporated Research Institutions for Seismology (lRIS), Stanford University,
and NASA. Its goal is to explore the geologic structure and evolution of the North American
continent and understand the processes controlling earthquakes and volcanoes. EarthScope
will look into Earth and reveal the inner workings of the planet much like the Hubble Telescope
is revealing the early history of the universe.
EarthScope began in 2003 with a five-year (2003-2008) budget of about $200,000,000 from the
NSF Major Research Equipment and Facility Construction Account to construct four facilities
(the infrastructure for major research thrusts). (1) The San Andreas Fault Observatory at Depth
(SAFOD) is an instrumented borehole through the San Andreas Fault, just north of Parkfield,
California. The tight seismometer and strain meter grids at Parkfield and SAFOD, make this part
of the San Andreas Fault the most instrumented fault segment on the planet. (2) The Advanced
National Seismic System consists of broad band seismometers located on a 350 kilometer grid.
I was contracted by the United States Geological Survey to locate an appropriate location for
one of these stations in 2005. Station HDIL was constructed in 2006 at Mackinaw River State
Fish and Wildlife Area about 20 miles west of the Illinois State campus. Seismic data from this
station go by satellite telemetry every 15 seconds to the United States Geological Survey
Albuquerque Seismological Laboratory. I remain the local contact for the station. (3) The Plate
Boundary Observatory consists of 875 ultrahigh resolution global positioning system stations.
Each station’s position is continuously determined and reported by satellite telemetry to
UNAVCO in Boulder, Colorado. Station HDIL is also part of the Plate Boundary Observatory.
Data since the station went on line in 2006 indicate that the station is moving south 60 o west at a
velocity of roughly 1.5 mm/y and is going down about 5.07 mm/y. The horizontal motion is
consistent with the general counterclockwise rotation of the North American Tectonic Plate.
There are two major hypotheses for the vertical motion: post-glacial isostatic adjustment or
collapse of the aquifer beneath the station as water is withdrawn in seeps and springs in the
valleys on either side of the station. (4) The USArray consists of 400 high quality broad band
seismometers deployed on a 75 kilometer grid. These were first deployed in California, Oregon,
and Washington along the coast in 2006 (the 100 th anniversary of the San Francisco
Earthquake). Each seismometer remains in place for about two years and then is moved to a
new location, just east in the grid. In this fashion the USArray is rolling across the United States.
The actual location for the USArray stations in Illinois will be determined this summer and
installed next year for the 200 th anniversary of the New Madrid Earthquakes. In 2014 the
USArray moves to Alaska for the 50 th anniversary of the 1964 Alaska Earthquake (the second
largest recorded earthquake).
In addition to the science, EarthScope has an education and outreach component. We obtained
a major Math and Science Partnership Grant from the U.S. Department of Education through
the Illinois State Board of Education to conduct Illinois EarthScope, a workshop for teachers. A
pilot two-week workshop was conducted for 18 teachers in late July and early August 2009 with
follow-up weekend sessions in November and January. In addition to hearing presentations by
Drs. Dunn, Malone, and Nelson and Mr. Shields and participating in field trips led by Drs.
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