The Plate Boundary Observatory (PBO) is the geodetic component of the EarthScope project, designed to study the 3D strain field across the active boundary zone between the Pacific and North American tectonic plates in the western United States. Data from PBO's integrated network of GPS stations, strainmeters and seismometers, coupled with aerial and satellite imagery, are providing important temporal constraints on plate boundary deformation and are improving our knowledge of the fundamental physics that govern deformation, faulting, and fluid transport in earth’s lithosphere.
PBO Instrumentation Network
1100 permanent Global Positioning System (GPS) stations, 78 Borehole Seismometers, 74 Borehole Strainmeters (BSM), 26 Tiltmeters and 6 Laser Strainmeters (LSM) are currently deployed in the integrated PBO network and are collecting data on a real-time to near-real-time basis. Taken together, these instruments span the broad temporal and spatial spectrum of plate boundary deformation anticipated in the EarthScope project area.
The geodetic focus of the Plate Boundary Observatory will address the following scientific questions:
- What are the forces that drive plate-boundary deformation?
- What determines the spatial distribution of plate-boundary deformation?
- How has plate-boundary deformation evolved?
- What controls the space-time pattern of earthquake occurrence?
- How do earthquakes nucleate?
- What are the dynamics of magma rise, intrusion, and eruption?
- How can we reduce the hazards of earthquakes and volcanic eruptions?
While GPS measures millimeter-scale ground movement on time scales of days to decades and over large spatial scales, borehole strainmeters measure strain change by sensing changes in the shape of an instrument cemented into rock. They play a central role in observing the deformation that accompanies and precedes earthquakes and volcanic eruptions.
Long-baseline laser strainmeters measure the change in distance between two points several hundred meters apart on the Earth's surface. Laser strainmeters have the high resolution of the borehole strainmeters combined with the long-term stability of GPS measurements.