Identifying and locating tectonic tremor beneath the San Andreas Fault near Parkfield, CA, with the PASO array

Dana E. Peterson, Clifford H. Thurber, Emily K. Montgomery-Brown, Justin R. Brown, & David R. Shelly

Published December 2011, SCEC Contribution #2057

Tectonic tremor is a weak but persistent shaking of the Earth that was first discovered in subduction zones and later found beneath the San Andreas Fault (SAF). Tremor events represent spasmodic slip on the deep extension of the SAF, occurring at a depth of about 20-25 kilometers. Tremor occurs deeper than the nearby regular earthquakes, which can be found at maximum depths of 12-15 kilometers. Tremor is characterized by bursts of low frequency and/or very low frequency earthquakes (LFE/VLF) with dominant energy in the 1-10 Hz range. Tremor tells us about fault slip at depth in both space and time by illuminating the fault down to about the base of the crust. In the pursuit of deriving information about deep fault behavior and crustal structure, we are analyzing continuous data from the previously untapped Parkfield Area Seismic Observatory (PASO) temporary array, operated in 2000-2002 and 2004-2006. We started the identification process by correlating templates of known events from a nearby station array based on an existing catalog of tremor events. Using the dense PASO array and various correlation methods, including autocorrelation (Brown et. al. 2008), a scanning algorithm (Rowe, 2005), and cross correlation of template events (Shelly et al., 2007), we will refine the locations of these known events and seek to identify undiscovered clusters of LFEs and tremor. After generating an updated catalog initially for the month of September 2002, we will use S-wave arrivals from the 59 stations comprising the PASO array to provide strong constraints on the locations of identified events.

Citation
Peterson, D. E., Thurber, C. H., Montgomery-Brown, E. K., Brown, J. R., & Shelly, D. R. (2011, 12). Identifying and locating tectonic tremor beneath the San Andreas Fault near Parkfield, CA, with the PASO array. Presentation at 2011 AGU Fall Meeting.