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Malcolm White, PhD student at U. of Southern California, presents “Illuminating the San Jacinto fault zone region of Southern California with a new earthquake catalog” at the MIT Earth Resources Laboratory.
Livestream video of this talk will be available on our Youtube channel.
“The San Jacinto is the most seismically-active fault-zone region in Southern California and is known to produce magnitude 7 and greater ruptures with a ~250-year recurrence interval; it threatens large urban areas like Los Angeles and San Diego, and can provide detailed information on seismogenic processes in a complex active plate-boundary region. Between large events, microseismicity dominates fault-zone activity, illuminating damage structures and potentially harboring precursory signals to large events. To explore microseismicity in the San Jacinto fault zone region, we develop an automated processing procedure and apply it to raw waveform data to derive a new catalog of earthquake locations, magnitudes, and potencies between 2008 and 2016. Our procedure accounts for detailed 3D velocity structure using a probabilistic global-search location inversion, and obtains high-precision relative event locations using differential travel times measured by cross-correlating waveforms. The obtained catalog reveals spatiotemporal seismicity patterns in the fault zone with observations for 108,800 earthquakes in the magnitude range -1.8 to 5.4. Inside a focus region consisting of an 80-km by 50-km rectangle oriented parallel to the main fault trace, we estimate a 99% detection rate of earthquakes with magnitude 0.6 and greater, and detect and locate about 16 events for every 10 present in the Southern California Seismic Network catalog. The results provide the most complete catalog available for the focused study region during the analyzed period. The seismicity exhibits a variety of complex patterns that contain important information on deformation processes in the region. Only about 3% of event pairs have waveforms with cross-correlation coefficients ≥0.95, indicating diverse processes operating in the fault zone. At the seminar I will discuss the automated procedure developed, fault-zone features illuminated by the new catalog, and future directions for this work.”