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Abstract Fault regions inferred to be slowly slipping are interpreted to accommodate much of tectonic plate motion aseismically and potentially serve as barriers to earthquake rupture. Here, we build on prior work using simulations of earthquake sequences with enhanced dynamic fault weakening to show how fault regions that exhibit decades of steady creep or transient slow‐slip events can be driven to dynamically fail by incoming earthquake ruptures. Following substantial earthquake slip, such regions can be under‐stressed and locked for centuries prior to slowly slipping again. Our simulations illustrate that slow fault slip indicates that a region is sufficiently loaded to be failing about its quasi‐static strength. Hence, if a fault region is susceptible to failing dynamically, then observations of slow slip could serve as an indication that the region is critically stressed and ready to fail in a future earthquake, posing a qualitatively different interpretation of slow slip for seismic hazard.
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Episodic creep events on the San Andreas Fault caused by pore pressure variations
Recent seismic and geodetic observations indicate that interseismic creep rate varies in both time and space. The spatial extent of creep pinpoints locked asperities, while its temporary accelerations, known as slow-slip events, may trigger earthquakes. Although the conditions promoting fault creep are well-studied, the mechanisms for initiating episodic slow-slip events are enigmatic. Here we investigate surface deformation measured by radar interferometry along the central San Andreas Fault between 2003 and 2010 to constrain the temporal evolution of creep. We show that slow-slip events are ensembles of localized creep bursts that aseismically rupture isolated fault compartments. Using a rate-and-state friction model, we show that effective normal stress is temporally variable on the fault, and support this using seismic observations. We propose that compaction-driven elevated pore fluid pressure in the hydraulically isolated fault zone and subsequent frictional dilation cause the observed slow-slip episodes. We further suggest that the 2004 Mw 6 Parkfield earthquake might have been triggered by a slow-slip event, which increased the Coulomb failure stress by up to 0.45 bar per year. This implies that while creeping segments are suggested to act as seismic rupture barriers, slow-slip events on these zones might promote seismicity on adjacent locked segments.
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- Award ID(s):
- 1735630
- PAR ID:
- 10065220
- Date Published:
- Journal Name:
- Nature Geoscience
- ISSN:
- 1752-0894
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41561-018-0160-2
