Episodic creep events on the San Andreas Fault caused by pore pressure variations

Abstract

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 hydraulically isolated fault zone and subsequent frictional dilation cause the observed slow slip episodes. We further suggest that the 2004 M6 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.

Seismic Velocity Change Patterns Along the San Jacinto Fault Zone Following the 2010 M7.2 El Mayor‐Cucapah and M5.4 Collins Valley Earthquakes

“…Our data suggest an evolving medium response because the properties of the creep events inferred by Inbal et al (2017) are more similar to each other than the amplitude and duration of the associated dv / v patterns imply. The results extend observations related to interaction mechanisms between different slip and deformation modes along faults that are typically obtained from satellite, geodetic, and seismicity data (Donnellan et al, ; Inbal et al, ; Jolivet et al, ; Khoshmanesh et al, ; Khoshmanesh & Shirzaei, ; Linde et al, ; Meng & Peng, ; Rousset et al, ). Seismic noise‐based estimates of the associated velocity changes complement the array of observation techniques that can be used to study the coupling behavior along strike and down dip of the seismogenic zone and relaxation processes in the surrounding crust.…”

Modulation of Seismic Attenuation at Parkfield, Before and After the 2004 M6 Earthquake

“…Keeping in mind that more negative amplitudes mean higher attenuation, the time series plotted in Figures a and b show that at higher frequencies there is an immediate increase in attenuation on the Pacific side, and a decrease of smaller amount on the North American side (see close‐up in Figures a and b). Such an opposite effect on the two sides of the SAF is not easily explained with just the static stress changes, and there are conflicting results with regards to possible accelerations in the creep rate at seismogenic depths during this time period (i.e., InSAR‐derived slip transient; Khoshmanesh & Shirzaei, ) versus stable rates of repeater occurrence (Turner et al, ) and microseismicity (Aron & Hardebeck, ). All these findings are consistent with our idea that during T1 the Pacific side of the SAF was undergoing decreasing compression, and consequently increasing crack porosity.…”

“…However, in studying crustal rocks we need to take into consideration seasonal and tidal stress variations, pore fluid pressure, and thermal stress changes (Johnson et al, ; Wang et al, ). Variations of a rock's crack density are also related to other phenomena: for example, periodic 1.5–4‐year fluctuations of creep rates occur along the San Andreas Fault (SAF) at Parkfield (Khoshmanesh & Shirzaei, ; Nadeau & McEvilly, ; Turner et al, ).…”

Probing the Variation in Aseismic Slip Behavior Around an Active Suture Zone: Observations of Repeating Earthquakes in Eastern Taiwan

“…As addressed in Nadeau and McEvilly (2004), the variation of the deep creep rate correlates well with the geodetic measurements, and Turner et al (2015) documented an approximately 2‐year dominant periodic for both repeating earthquakes and InSAR data. Increase of the surface creep rate corresponds to elevation of the pore pressure and the reduction of effective normal stress, which may facilitate episodic aseismic creep at depth (Khoshmanesh & Shirzaei, 2018).…”