The Plate Boundary Observatory Borehole Strainmeter Program: Overview of Data Analysis and Products

The PBO borehole strainmeter network is now the largest in the US with 19 strainmeters installed along the Western US Plate Boundary: 14 in the Pacific North West and 5 in Anza, Southern California. With five drilling crews operating though October 2006 the network should grow to 28 strainmeters by December 2006. The areas include Parkfield and Mt St. Helens, PBO's first strainmeter installation in a volcanic region. PBO strainmeter sites are multi-instrumented. Seismic, pore pressure, atmospheric pressure, rainfall and temperature data are measured at almost all sites. Tiltmeters will also be installed at some sites. The strainmeters record at 20-sps, 1-sps and 10-minute interval and are downloaded hourly. The 1-sps data are sent to the NCEDC and IRIS DMC within a few minutes of being retrieved from the strainmeter. The data are archived in SEED format and can be viewed and analyzed with any SEED handling software. PBO's Borehole Strainmeter Analysis Center (BSMAC) in Socorro, NM, produces processed strain data every 10 to 14 days. The data are stored in XML format giving the user the option to use PBO edits or to work with unedited data. The XML file contains time series corrections for the atmospheric pressure, the Earth tides and borehole effects. Every 3 months the data are reviewed and the borehole trends and tidal signal are re- estimated to form the best possible processed data set. PBO reviewed the quality of the data collected by the first 8 strainmeters in a workshop in January 2006. The group discussed coring, examined the borehole trends, tidal signal, and a PSD analysis of data from each strainmeter. A second workshop, focusing on data analysis and in-situ calibration, will take place in October 2006. The UNAVCO strainmeter web page (http://pboweb.unavco.org) provides links to the raw and processed data and is a source for information on data formats, links to software and instrument documentation. An XML log file for each strainmeter provides a history of firmware upgrades and details anything that might affect data quality. A homepage has been developed for each strainmeter where plots of strain and state-of-health data can be viewed. UNAVCO has provided training in processing strainmeter data both at the BSMAC and through short courses. In June 2006 UNAVCO hosted the joint GPS and Strainmeter Short course where the topics of data analysis, calibration, hydrological signals and noise models where taught using PBO data. The next UNAVCO strainmeter course is planned for summer 2007.