OBSERVATIONS OF THE PBO BOREHOLE STRAINMETER NETWORK IN THREE REGIONS: THE SAN ANDREAS FAULT, CASCADIA SUBDUCTION ZONE AND YELLOWSTONE VOLCANO

The PBO construction phase ended in late September 2008, resulting in 74 Borehole Strainmeters ranging in location along the San Andreas Fault to the Mendocino Triple Junction, the Cascadia Subduction Zone from Victoria, Canada to Northern California, Mt St Helens and Yellowstone. Each site contains a Gladwin tensor strainmeter, seismometer, and at volcano sites a tiltmeter. Sites in the Yellowstone National Park array also contain pipe for access to measure borehole temperature. Four regional field engineers currently maintain these sites, each focusing on a different tectonic or volcanic environment. This is to ensure the understanding of the region, individual site issues, and communicating with researchers inquiring about regional issues affecting data quality. After a year of maintaining the PBO sites, working with the data analysis center and other scientists using the freely available PBO network data, the Gladwin tensor strainmeter has yielded results in observing geophysical signals in both tectonically and volcanically active regions. The instruments display sensitivity varying from observing earth tides to geophysical processes. Along the San Andreas, within the Parkfield region, creep events are observed, while in Cascadia slow episodic tremor events show the Juan de Fuca Plate subduction, and in Yellowstone earthquake swarms. With a growing increase in interest from outside researchers as well as with the help of the outside science community these geophysical observations can be documented and interpreted. Strong communication between the scientific community and UNAVCO will ensure the continuing success of the PBO strainmeter project in achieving a better understanding of these active processes.