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FRIDAY MAY 19, 2023 @ 1P PDT
Measuring healing and failure in experiments on clay-bearing fault gouges
Caroline Seyler, University of Southern California

Frictional healing and earthquake failure are two fundamental components of the seismic cycle. Deformation experiments can provide quantitative estimates of the frictional properties behind these processes that then can be compared with estimates from seismology and feed into models that simulate earthquakes, the seismic cycle, and fault dynamics more broadly. Because faults are typically hosted in clay-rich gouges, I will present results from experiments conducted on clay-bearing gouges to measure (1) frictional healing rates with increasing clay content in synthetic gouges, and (2) fracture energy of clay-rich sediments from the Cascadia subduction zone. In slide-hold-slide tests on quartz-smectite mixtures from 10–100% smectite, the healing rates decreased from 0.008 to 0.002 /decade. This decrease is likely caused by the tendency for clay grains, which are flaky in shape, to align and limit the ability for the fault gouge to increase its contact area, thus limiting healing. In high-velocity rotary shear tests, there was little difference in the fracture energy between lithologies (35–45% clay). But when compared with a compilation of previous high-velocity tests conducted on wet gouges, dry gouges, and intact rocks, the fracture energy of sediments at Cascadia is an order of magnitude higher than sediments from other subduction margins. This relatively high fracture energy may inhibit large amounts of shallow earthquake slip and dynamic overshoot. Overall, clay content plays an important role in dictating the behavior of fault gouges throughout the seismic cycle.