OPERATING THE PBO BOREHOLE STRAIN AND SEISMIC NETWORK

In addition to the 1100 station GPS network, UNAVCO built an 80-station borehole strain and seismic network between 2005 and 2008 as part of the Plate Boundary Observatory (PBO). The stations were installed in arrays, with each intended to focus on a specific tectonic or volcanic feature. The largest of these arrays focuses on the Cascadia subduction zone, with 35 stations ranging from Vancouver Island down to the Mendocino Triple Junction. Many of these stations regularly observe the annual episodic tremor and slip (ETS) signal in both strain and seismic data. The typical borehole PBO station includes a Gladwin Tensor strainmeter and Malin 3-component geophone installed in a 6” borehole at depths of 500-800 ft, as well as surface temperature, rainfall, and barometric pressure sensors. Depending on the location, stations may also include continuous high-rate GPS, pore pressure or MET packs. Volcanic sites collect tilt data. There is also a wealth of geologic data collected during the drilling of the boreholes, including cutting samples, some limited amounts of core, and a suite of geophysical logs.

UNAVCO has been operating this network continuously since 2008. 2.4 TB of strain and 5.6 TB of seismic data have been collected to date, all of which is archived at UNAVCO and IRIS. As part of Earthscope, all data are freely available at unavco.org; the seismic data is available in real-time while the strainmeter data is available with a 1 to 2 hour latency.

This poster will describe in detail the equipment deployed across the network, available data streams, sample ETS observations, dataflow and archiving paths, and what is involved in operating this sort of spatially diverse geophysical network.