The Effect of Normal Stress Oscillations on Fault Slip Behavior Near the Stability Transition From Stable to Unstable Motion

Federico Pignalberi (1) , Carolina Giorgetti (1) , Corentin Noël (2, 3) , Chris Marone (1, 4) , Cristiano Collettini (1, 5) , Marco Maria Scuderi (1)

1 Dipartimento di Scienze della Terra, Università di Roma La Sapienza, Rome, Italy
2 Sapienza Università di Roma - Dipartimento di Scienze della Terra
3 GEOAZUR 7329 - Géoazur
4 Department of Geosciences, Pennsylvania State University
5 Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy

Abstract Tectonic fault zones are subject to normal stress variations with a wide range of spatio‐temporal scales. Stress perturbations cover a wide range of frequencies and amplitudes from high frequency seismic waves generated by earthquakes to low frequency transients associated with solid Earth tides. These perturbations can reactivate critically stressed faults and trigger earthquakes. Here, we describe lab experiments to illuminate the physics of such changes in friction and the mechanics of earthquake triggering and fault reactivation. Friction tests were done in a double direct shear configuration for conditions near the stability transition from stable to unstable motion. We studied simulated fault gouge composed of quartz powder and conducted experiments at reference normal stress from 10 to 13.5 MPa. After shearing to steady state sliding, we applied sinusoidal normal stress oscillations of amplitude 0.5–2 MPa, and period of 0.5–50 s. We performed numerical simulations using measured values of rate and state friction (RSF) parameters to assess our data. Our results show that low frequency stress oscillations cause a Coulomb‐like response of shear strength that transitions from stable slip to slow lab earthquakes as frequency increases. At the critical frequency predicted by RSF we observe periodic stick‐slip behavior. Perturbations of high amplitude and short period weaken the fault, while lower amplitudes strengthen the fault. We find that a modified RSF formulation is able to accurately match our laboratory data. Our findings highlight the complex effects of stress perturbations on fault strength and the mode of fault slip.

Domaines: Géophysique [physics.geo-ph]

Federico Pignalberi, Carolina Giorgetti, Corentin Noël, Chris Marone, Cristiano Collettini, et al.. The Effect of Normal Stress Oscillations on Fault Slip Behavior Near the Stability Transition From Stable to Unstable Motion. Journal of Geophysical Research : Solid Earth, 2024, 129 (2), ⟨10.1029/2023JB027470⟩. ⟨hal-04456699⟩