Group A, Poster #125, Fault and Rupture Mechanics (FARM)

Afterslip and triggered creep in the rate-dependent framework: Inversion of borehole strain and GNSS displacements for the Mw 7.1 Ridgecrest earthquake

Catherine Hanagan, Richard A. Bennett, Amanda N. Hughes, & Andrew J. Barbour
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Poster Presentation

2023 SCEC Annual Meeting, Poster #125, SCEC Contribution #12994 VIEW PDF
The elusive transition toward afterslip following an earthquake is challenging to capture with typical limits on data resolution in the presence of overlapping deformation processes operating on similar timescales. Considerable evidence supports afterslip in the stress-driven, rate-dependent frictional framework; however, there remains a lack of clear consensus for its detailed evolution spanning seconds to months. On July 6th, 2019, a dense geodetic network captured the Mw 7.1 Ridgecrest earthquake, including 16 Global Navigation Satellite System (GNSS) stations and 3 borehole strainmeters (BSM); the BSMs provide sub-nanostrain precision and temporal resolution that bridges conventional sei...smologic and geodetic methods, located at near-to-intermediate distances from the rupture. In particular, BSM station B921, < 2 km from the mainshock plane, recorded rotational, non-monotonically decaying postseismic deformation, apparently at odds with common cumulative afterslip models. We jointly invert GNSS displacements and BSM strains for coseismic slip and postseismic slip in 7 independent periods spanning hours to months after the mainshock. The best-fitting slip models explain nonmonotonic transient deformation at B921 and are validated by a forward-model comparison with near-field campaign GNSS displacements (Brooks et al., 2020; SRL). The spatiotemporal evolution of mainshock afterslip adheres to several patterns expected from the rate-dependent framework, with most notable variability in the early postseismic timeframe (<1-2 weeks). The extended pattern of slip, including afterslip on the foreshock fault segments and prolonged creep on the neighboring Garlock fault, highlights variability within the complex fault network that potentially stems from different stress-histories and/or fault properties, critical to our understanding of postseismic crustal stress redistribution and evolving hazard.