UTILIZING GEOLOGIC SAMPLES POST PLATE BOUNDARY OBSERVATORY BOREHOLE STRAINMETER NETWORK CONSTRUCTION

The Plate Boundary Observatory’s borehole strainmeter network is made up of 80 stations at various locations across the Western United States. During the construction of the network, 6” boreholes were drilled to depths of 450 to 800 feet. Samples were collected, in most cases drill cuttings, but some boreholes were cored. Geophysical logs were run at all boreholes, using acoustic televiewer, caliper, full-waveform sonic, and e-tool. The cuttings and core samples have been photographed and are available to view online or by request. The logs are also available online.

The Plate Boundary Observatory borehole strainmeter network was primarily installed between 2005 and 2008. Site locations were focused around tectonic areas of interest, such as the San Andreas Fault, the San Jacinto Fault, the Cascade Subduction Zone, Mt St Helens Volcano, and Yellowstone Caldera. In most cases, a UNAVCO representative with a geology background would observe the drilling, collect samples, and document fractures and water. Cuttings were collected every 10 feet, with the exception of Yellowstone, where they were collected every 5 feet. Core exists for 15 sites, but because of time and budget constraints the majority of boreholes were rotary drilled. The core we have is from the Cascadia subduction zone on the Olympic Peninsula and the Parkfield and San Juan Bautista segments of the San Andreas Fault.

While our primary mandate is operations and maintenance of the network, the data collected during drilling has value and we want to ensure researchers are aware it exists. This data could be helpful for igneous petrologists, structural geologists, stratigraphers, and sedimentary petrologists. For example, our nine boreholes in Yellowstone were the first drilling in the park since the 1970s, so these data are unique. We will outline the resources and how to access them.