Preparatory Slip in Laboratory Faults: Effects of Roughness and Load Point Velocity

Abstract

Aseismic slip may occur during a long preparatory phase preceding earthquakes, and what controls it remains poorly understood. In this study, we explored the role of load point velocity and surface roughness on slow slip during the preparatory stage prior to stick‐slip events. To that end, we conducted displacement‐rate controlled friction experiments by imposing varying load point velocities on sawcut granite samples with different surface roughness at a confining pressure of 35 MPa. We measured the average slip along the fault with the recorded far‐field displacements and strain changes, while acoustic emission sensors and local strain gages were used to capture local slip variations. We found that the average amount of aseismic slip during the preparatory stage increases with roughness, whereas precursory slip duration decreases with increased load point velocity. These results reveal a complex slip pattern on rough faults which leads to dynamic ruptures at high load point velocities.

Experimental Insights Into Fault Reactivation and Stability of Carrara Marble Across the Brittle–Ductile Transition

“…In the triaxial shear configuration used here (Figure 1a), the stiffness of loading system k s may be calculated from the combined contribution of the apparatus and the rock matrix (Guérin‐Marthe et al., 2023; He et al., 1998), as given by $$${k}_{\mathrm{s}}=\frac{{\cos }^{2}\hspace*{.5em}\beta \hspace*{.5em}\sin \hspace*{.5em}\beta }{1/{k}_{\mathrm{m}}+1/{k}_{\text{app}}}$$$ where k app is the apparatus axial stiffness and k m represents the axial stiffness of the rock matrix. The apparatus stiffness is ∼83 kN/mm, equivalent to k app ≈ 1,060 MPa/mm for a sample diameter of 10 mm.…”

“…In the triaxial shear configuration used here (Figure 1a), the stiffness of loading system k s may be calculated from the combined contribution of the apparatus and the rock matrix (Guérin-Marthe et al, 2023;He et al, 1998), as given by 2). Clearly, the observed unstable sliding in our experiments (at least for T = 200-400°C) is reasonably consistent with the theoretical prediction as k s < k c .…”

Preparatory Process in Advance of Runaway Fault Rupture through Fluid Injection Observed in Laboratory Experiments Using a Large Specimen of Sub-meter scale

“…As in situ observations of unstable slips at deep depths are di cult, a number of attempts have been made to reproduce these slips in the laboratory (Lockner et al, 1982;Ohnaka, 1986 In the case of injection-induced earthquakes, fault slip is initiated by uid pressure applied locally, and it sometimes expands unstably over a wide area such that it results in elastic waves having magnitudes that can induce felt earthquakes. Thus, reproducing the unstable expansion of initial slips in laboratory is important; however, it is hard to reproduce the process by general setup of laboratory experiment such as triaxial loading tests on cylindrical specimens with inclined faults, which have been used for the laboratory studies of natural earthquakes (Bartlow et al, 2012;Guérin-Marthe et al, 2023). The specimens used for those studies are generally less than 100 mm in diameter, and if such specimens are used to reproduce injectioninduced earthquakes, an inlet hole for uid injection into fault is to be located in the near distance of 50 mm or less from the fault edge.…”

Fault roughness controls injection-induced seismicity

“…Likewise, ground motion, radiation pattern and source parameters of seismic events ( 17 – 19 ), and the distribution of off-fault damage zones ( 8 , 17 , 20 ) are linked to fault structures. Laboratory friction experiments highlight the important role of fault roughness in controlling rupture nucleation and slip instability ( 21 – 27 ). When compared to smooth faults, rough faults display longer nucleation time and larger nucleation length but lower macroscopic slip velocities and a wider range of rupture speeds ( 21 , 25 , 26 , 28 ).…”