Geodetic Measurements of Slow Slip and Tremor in Parkfield, CA

Brent G. Delbridge, Roland Bürgmann, & Robert M. Nadeau

Published August 15, 2016, SCEC Contribution #7033, 2016 SCEC Annual Meeting Poster #065

It has been proposed that large bursts of deep tremor ( >20km depth) near Parkfield, CA are associated with quasi-periodic shear dislocations on the deep extent of the San Andreas Fault. Geodetic studies have shown that slow slip accompanies tremor in several subduction zones. However, prior to this study deformation associated with tremor in a transform fault environment had not been observed despite the ubiquitous presence of tremor and LFEs and targeted attempts to observe this deformation. In this study we report geodetic measurements of surface strains associated with large tremor swarms that are inferred to be concurrent with slow-slip events with moment magnitudes exceeding 5. The strain rates associated with these events are below the detection level of GPS networks, thus in order to observe this deformation we have utilized two long-baseline laser strainmeters (LSM) located in Cholame, CA. In order to overcome a small signal-to noise-ratio in the strainmeter data, we have stacked the strain records associated with more than 50 large tremor-burst events, each approximately 10 days in duration. The average surface strains associated with these events are on the order of several nanometers and correspond to fault slip on the order of 5 millimeters per event (assuming a fault patch extending ~25 km along-strike and ~15km in depth). The measured moment associated with these events is a factor of two smaller than previously proposed based on theoretical estimates.

Key Words
Geodesy, Tremor, Slow Slip

Citation
Delbridge, B. G., Bürgmann, R., & Nadeau, R. M. (2016, 08). Geodetic Measurements of Slow Slip and Tremor in Parkfield, CA. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)