Plate Boundary Observatory
The Plate Boundary Observatory or (PBO) is one of three components of the Earthscope project, along with USArray and SAFOD (the San Andreas Fault Observatory at Depth).[1] The PBO precisely measures Earth deformation resulting from the constant motion of the Pacific and North American tectonic plates in the western United States. These Earth movements can be very small and incremental and not felt by people, or very large and sudden such as those that occur during earthquakes and volcanic eruptions. PBO measures Earth deformation through its arrays of Global Positioning System (GPS) receivers, strainmeters, seismometers, and other geodetic instruments.
The GAGE Facility, operated by UNAVCO, Inc., is responsible for instrument installation, ongoing maintenance, communications, data archiving, data processing, and data availability for the geodetic instruments that comprise the Plate Boundary Observatory. UNAVCO a membership-governed consortium funded by the National Science Foundation (NSF) and NASA. The network includes 1100 permanent, continuously operating Global Positioning System (GPS) stations many of which provide data at high-rate and in real-time, 78 borehole seismometers, 74 borehole strainmeters, 26 shallow borehole tiltmeters, and six long baseline laser strainmeters. These instruments are complemented by InSAR (interferometric synthetic aperture radar) and LiDAR (light detection and ranging) imagery and geochronology acquired as part of the GeoEarthScope initiative. PBO also includes comprehensive data products, data management and education and outreach efforts.
The GPS stations are categorized into five clusters. The transform cluster is in the vicinity of the San Andreas transform fault, which cuts through California; the subduction cluster is in the Cascadia subduction zone, which includes northern California, Oregon, Washington, and southern British Columbia, and is a result of the Juan de Fuca plate subducting under the North American plate; the extension cluster is in the Basin and Range region; the volcanic cluster is in volcanic regions such as the Yellowstone caldera, the Long Valley caldera, and the Cascade volcanoes; the backbone cluster is at 100–200 km across the United States to provide complete spatial coverage.
The GPS instrumentation is high-precision and continuously operating. High-precision means the units can detect sub-centimeter motion, and continuously operating means a 15 second sampling rate and one data file for every 24 hours. A completed PBO GPS station occupies an approximately three by three meter plot of land.
Some scientific questions that are being addressed by the EarthScope project and the PBO include:
- How does accumulated strain lead to earthquakes?
- Are there recognizable precursors to earthquakes?
- How does the evolution of the continent influence the motions that are happening today?
- What happens to geologic structures at depth?
- What influences the location of features such as faults and mountain ranges?
- Is it inherited from earlier tectonic events or related to deeper processes in the mantle?
- How is magma generated? How does it travel from the mantle to reach the surface?
- What are the precursors to a volcanic eruption?[2]
References
- ^ EarthScope: An Earth Science Program
- ^ National Research Council, Review of EarthScope Integrated Science (Washington D.C., National Academy Press, 2001).
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