HR: 1400h
AN: G43A-02    [Abstracts]
TI: The Plate Boundary Observatory (PBO) Network in the PNW region of the United States
AU: * Hafner, K
EM: hafner@unavco.org
AF: UNAVCO, Inc., 801 S. Ruby Street, Ellensburg, WA 98926, United States
AU: Austin, K
EM: austin@unavco.org
AU: Feaux, K
EM: feaux@unavco.org
AU: Jackson, M
EM: jackson@unavco.org
class='hr'> AU: Fengler, K
EM: fengler@unavco.org
AU: Doelger, S
EM: doelger@unavco.org
AB: The Pacific Northwest Region (PNW) of the United States contains a variety of geologic regions and tectonic problems. These include the Cascadia Subduction Zone, Mt. St. Helens and the transition to the Basin and Range province. Since September of 2003, the Plate Boundary Observatory (PBO), which is part of the larger NSF-funded EarthScope project, has been installing a network of continuously operating GPS, strainmeter and tiltmeter instruments. There are currently 78 GPS, 13 strainmeter/borehole seismometers, and 4 tiltmeters operating in the PNW region. The data from this network has already been used to study Episodic Tremor Events (ETS) during September 2005 and January 2007, and renewed activity on Mt. St. Helens that began on September 23, 2004. The goal is have 134 continuously operating GPS stations by the end of September 2008. The locations of the GPS stations were determined by scientific committees. Whenever possible, multiple instruments are deployed at the same location, and share power and communications resources. Examples of this are GPS antennas mounted on top of strainmeter boreholes in the forearc region of western Washington and tiltmeters collecting data through GPS receivers on Mt. St. Helens. In addition, a number of stations provide real time kinematic data to professional surveyors within the region. During the fall of 2006, a 16 GPS and 4 tiltmeter station network was completed on Mt. St. Helens. Results from analysis of both PBO and USGS GPS stations on the mountain, show a radially inward and downward motion, with the maximum vertical offsets high on the mountain and the maximum horizontal offsets located at distances of 5-10km from the crater. Displacements are small over the 2004-present eruption with a maximum of 3cm of inward movement. GPS stations installed high on the mountain experience severe weather and heavy rime accumulations for approximately 6 months of the year. Ice build-up causes distortion of the GPS antenna phase center, and sun blockages on solar panels at several sites. Due to the large battery storage capacity, there have been very few power failures, however the build up of ice on the GPS antennas causes cm-level pseudo- displacements that mask the ground movements associated with the eruption.
UR: http:pboweb.unavco.org
DE: 1209 Tectonic deformation (6924)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 1294 Instruments and techniques
DE: 1295 Integrations of techniques
SC: Geodesy [G]
MN: 2007 Joint Assembly