The Plate Boundary Observatory Borehole Network: Geologic Resources from Drilling and Logging

The Plate Boundary Observatory Strainmeter Borehole Network has a total of 79 operational boreholes, with depths drilled from 420 to 800 feet. All drill cuttings, core samples and logs are stored and catalogued. The cuttings for each successful borehole were recently photo documented and will be placed on the UNAVCO website to be readily available to the public, as well as to request samples. The drill cuttings were collected in 10 foot intervals, and in Yellowstone they were collected in five foot intervals. The extent of the borehole network includes sites near the San Jacinto fault, San Andreas Fault, throughout the Cascadia region, Mt St Helens and Yellowstone. These locations provide a wide array of tectonic and volcanic environments. In the case of Yellowstone, the park has not been drilled in for four decades. Due to the circulation of hot fluids, holes are at a shallower depth ( > 420 feet). These cuttings provide a resource of understanding the history and dynamics of fluid interaction in Yellowstone. Along the San Jacinto fault and San Andreas fault, these cuttings can help to build better models of the fault dynamics through evaluating the stratigraphy, fractures, rock strength, structural geology and fluid interaction near and along the fault zones. The stranmeter sites in the Pacific NW were chosen for the subduction zone, and are therefore not near a major plate boundary. They could instead be used to understand local regional fault dynamics, stratigraphy, structural geology and volcanic history of the NW. Presented will be examples of interest from each region, from cuttings, core, logs, to correlated network observations. For example, a site on the San Jacinto fault, near Anza has recorded creep events. This site is the closest to the fault and during drilling fault gouge was observed. While in Parkfield, cuttings and core reveal different fault blocks for sites that are 1000 feet apart in distance. As UNAVCO cannot provide any analysis on these samples, the documentation and variability of these resources will be presented. The availability of these resources and an interest of understanding the hydrology and structural geology could provide new incite for understanding strike slip faulting as well as additional resources for understanding volcanic history.