PBO STRAINMETER MEASUREMENTS OF TRANSIENT DEFORMATION ALONG THE PACIFIC AND NORTH-AMERICA PLATE BOUNDARY

The growth of regional scale integrated seismic and geodetic networks globally over the past two decades is revealing that plate boundary deformation spans the temporal range from seismic to slow-slip processes where fault slip occurs so slowly that the seismic energy released may be negligible. Very low frequency earthquakes with source durations of tens of seconds have been detected in subduction zones in Japan and Costa Rica. Slow earthquakes, occurring over hours, have been recorded using strainmeters along the creeping section of the San Andreas while episodic tremor and slip (ETS) events where weeks of low frequency tremor are accompanied by slip on the subduction zone plate interface are now known to occur i­n Japan, New Zealand, Mexico and Cascadia. A fundamental goal of the NSF funded Plate Boundary Observatory (PBO) is to enable investigation of the role slow-slip phenomena such as these play in the release of accumulated stress along plate boundaries. To achieve this PBO, operated by UNAVCO, includes 80 stations with strainmeters and seismometers installed in arrays along the western US plate boundary within a framework of 1100 continuously operating GPS sites. Designed to perform well at periods of minutes to weeks, the strainmeters are providing remarkable temporal resolution of Cascadia ETS events and creep signals along the central section of the San Andreas. In addition to operating the network, UNAVCO generates Earthscope Level 2 data products for the strainmeters. These products include models for the earth tides, barometric response, long-term borehole trends plus areal and shear strain time-series. The processed data are updated automatically every 24 hours and a follow-up data set that has been reviewed by a data engineer is released every 7 to 10 days. Site information, data quality assessment, strain plots and time-series data for all PBO strain instruments can be obtained from the UNAVCO strain and seismic web page (http://www.unavco.org/data/strain-seismic/strain-seismic.html). In this presentation we will highlight some of the strain transients these instruments have meausred, outline the processing steps required to extract these signals from the some times noisy data and describe the strainmeter data products available UNAVCO.