PBO Borehole Strainmeters

UNAVCO is a non-profit, community-based organization funded by the National Science Foundation to install and operate the geodetic component of EarthScope called the Plate Boundary Observatory (PBO). UNAVCO will install 103 borehole tensor strainmeters/seismometers and 28 borehole tiltmeters These instruments will be used to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States in hopes of increasing our understanding of the causes and mechanisms associated with earthquakes and volcanic activity. This represents almost a tripling of all installed borehole strainmeters in North America. Since the initial deployment of strainmeters in the early 1980's, borehole strainmeters have contributed valuable data at periods ranging from minutes to weeks with sensitivities two to three orders of magnitude better than continuous GPS at periods of days to weeks. Borehole strainmeters have been used to image earthquakes, slow earthquakes, creep events and volcanic eruptions in the US, Iceland and Japan. Initial PBO strainmeter deployments show promising results but there are still major hurdles to overcome in production, installation processes, data quality control, data processing and near real time delivery of calibrated strain data. PBO has made significant steps forward with the installation of 19 borehole strainmeters as of September 1st, 2006 with 28 total instruments planned by early December. In addition to strainmeters, each borehole contains a three-component geophone and a pore pressure transducer. A subset of the boreholes are also used for heat flow measurements. When completed the PBO borehole strainmeter network will be the largest network of strainmeters installed to date and one of the world's largest borehole seismic networks. These instruments will bridge the gap between seismology and space-geodetic techniques and represents the first dense, geographically distributed observations in this temporal regime in the US.