FISH Seminar: Brent Delbridge (Harvard)
Geodetic and Seismological Constraints on Quasi-episodic Slow Slip on the San Andreas Fault
It is thought that large bursts of deep tremor (> 20 km depth) near Parkfield, CA are associated with quasi-periodic shear dislocations on the deep extent of the San Andreas Fault. Slow slip has been discovered in subduction zones worldwide and manifests aseismically as geodetic transients in GPS and seismically as a long duration, low amplitude seismic signal known as tectonic tremor. However, deformation associated with tremor in a transform fault environment has not previously been observed despite the ubiquitous presence of tremors and low frequency earthquakes (LFEs) and targeted attempts to observe this deformation. 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 strainmeter located in Cholame, CA and the PBO borehole strainmeter network to place a lower upper bound on their moment release. In order to overcome a small signal-to noise-ratio in the strainmeter data, we have stacked the strain records associated with more than 80 large tremor-burst events, each approximately 10 days in duration. We also explore the deformation associated with a large increase in tremor activity following the August 24, 2014 M6.0 Napa earthquake, the largest observed burst in the Parkfield-Cholame area since the large tremor rate increase associated with the 2004 Parkfield M6 earthquake. We suggest that the tectonic tremor and LFEs likely reflect distinct faulting behaviors.
About the Speaker
Brent Delbridge is a Postdoctoral Fellow working in the Harvard Seismology Group, Department of Earth and Planetary Sciences, Harvard University. His research focuses on developing new tools and constraints to evaluate mathematical models of physical processes and Earth structures. He is currently working to develop new theoretical and observational frameworks to utilize the information about earthquake source processes and Earth structure contained within long-period recordings of seismic energy.
About the Series
The Friday Informal Seminar Hour [FISH, Earth Resources Laboratory] is a postdoc-run weekly seminar series within the ERL. Topics include research relating to geophysics, and in particular seismology, with applications in Earth resources exploration such as e.g. seismics exploration, microseismicity, earthquake physics, and Earth imaging techniques. The seminars usually take place on Fridays at 12 noon in 54-209 (term-time only).