The Influence of Loading Path on Fault Reactivation: A Laboratory Perspective

Abstract

The loading path the fault experiences is often neglected when evaluating its potential for reactivation and the related seismic risk. However, stress history affects fault zone compaction and dilation, and thus its mechanics. Therefore, in incohesive fault cores that could dilate or compact, the role of the loading path could not be ruled out. Here we reproduce in the laboratory different tectonic loading paths for reverse (load-strengthening in the absence of significant fluid pressure increase) and normal gouge-bearing faults (load-weakening) to investigate the loading path influence on fault reactivation and seismic potential. We find that, before reactivation, experimental reverse faults undergo compaction, whereas experimental normal faults experience dilation. Additionally, when reactivated at comparable normal stress, normal faults are more prone to slip seismically than reverse faults. We infer that the higher mean stress normal faults experience compacts more efficiently the fault rock, increasing its stiffness and favoring seismic slip.Plain Language Summary Slip along pre-existing faults in the Earth's crust occurs whenever the shear stress resolved on the fault plane overcomes its frictional strength, potentially generating catastrophic earthquakes. The increase in the shear stress can follow different tectonic loading paths, and in particular, load-weakening versus. load-strengthening paths when it is coupled respectively to a decrease versus. an increase in the normal stress clamping the fault. The role of the loading path cannot be ruled out, especially in the presence of a thick, incohesive fault zone that can change its volume under different stress conditions. However, in most friction experiments, the fault is loaded under constant or increasing the normal stress, that is, load-strengthening. Here, we bridge the gap in laboratory loading paths simulating reactivation at the same normal stress clamping the fault but with different tectonic stress histories. Interestingly, our results suggest contrasting hydro-mechanical behavior for loadstrengthening versus. load-weakening path: (1) before reactivation, fault zone compaction versus. dilation and (2) when reactivated at comparable normal stress, stable creep versus seismic slip, respectively. Our study has only scratched the surface of the loading-path influence on thick fault stability and potential implications for fluid circulation in fault zones, stressing the importance of further investigating the loading path influence.

The Effect of Shear Displacement and Wear on Fault Stability: Laboratory Constraints

“…In addition to the stability transition with increasing shear displacement, faults have been shown to have a stability transition with sliding velocity (e.g., Guérin‐Marthe et al., 2019; Kato et al., 1992; Leeman et al., 2018; Marone, 1998a; Mclaskey & Yamashita, 2017; Xu et al., 2018), normal stress (e.g., Bedford & Faulkner, 2021; Chambon & Rudnicki, 2001; Dieterich & Linker, 1992; Giorgetti & Violay, 2021; He et al., 1998; Leeman et al., 2018), temperature (e.g., Blanpied et al., 1998), fluid pressure changes (e.g., Noël, Passelègue, et al., 2019; Scuderi et al., 2017), fault heterogeneity (e.g., Bedford et al., 2022), roughness (e.g., Fryer et al., 2022; Harbord et al., 2017), fabric evolution (e.g., Pozzi et al., 2022), etc. This study, as well as several others, demonstrates that the stability parameters ( a ‐ b ) and D c , derived from the rate‐and‐state friction laws are not material (or interface) properties.…”

On the Unloading‐Induced Fault Reactivation: The Effect of Stress Path on Failure Criterion and Rupture Dynamics

“…It is striking that the fault is reactivated well before the stress path intersects the failure envelope. Thus, the previously confirmed mechanism for unloading‐induced fault reactivations (Giorgetti & Violay, 2021; Ji et al., 2019) does not apply to Case II with stress reversal. The fitted failure envelope for the fault reactivation in Case II implies that the critical friction is about 0.2, notably smaller than that for loading‐induced events and fault reactivations in Case I (∼0.44).…”

“…Another hypothesis is that both the reduction of normal stress and the increase of shear stress in unloading could reactivate fault (Kaiser & Cai, 2012). This mechanism has been confirmed in triaxial tests featuring lateral relaxation (French et al, 2016;Giorgetti & Violay, 2021). Lateral relaxation can lead to an increase in shear stress and a reduction in normal stress simultaneously, driving the fault to failure.…”

“…Another important aspect revealed by experiments is that unloading-induced fault reactivations adhere to the Coulomb failure criterion derived from the loading-induced fault failure (French et al, 2016;Giorgetti & Violay, 2021;Ji et al, 2019). This indicates that the failure envelope is independent on the stress path, whether it is load-strengthening (i.e., an increase in shear stress coupled with an increase in normal stress) or load-weakening (i.e., an increase in shear stress coupled with a decrease in normal stress).…”

Development of a method for clusterization of the dissipative structures

“…The history of irreversible ground movement depends on the loading path [9]. Therefore, one should monitor the irreversible ground movements as accurately as possible to detect essential features of the irreversible process.…”