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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This study was funded by National Science Foundation grants EAR-1357079 and EAR-1735630, and NASA Earth and Space Fellowship No. 80NSSC17K0371. The InSAR time series was obtained from refs 20,]25. The seismic catalogue was obtained from ref. 50. The creepmeter data at Slacks Canyon were obtained from the United States Geological Survey. We greatly thank H. Perfettini and D. Shelly for comments and suggestions.
The authors declare no competing interests.
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Khoshmanesh, M., Shirzaei, M. Episodic creep events on the San Andreas Fault caused by pore pressure variations. Nature Geosci 11, 610–614 (2018). https://doi.org/10.1038/s41561-018-0160-2
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