Insights From Micromechanical Modeling of Intact Rock Failure: Event Characteristics, Stress Drops, and Force Networks

Abstract

We use a bonded‐particle method to investigate event characteristics, b values, internal force distributions, and stress drops in triaxial deformation tests. We simulate brittle through ductile deformation regimes. We find the following: (1) Event rates are proportional to anelastic axial strain: (i) significant and accelerating events rates only occur near peak stress (brittle deformation); (ii) event rates gradually increase until the anelastic strain plateaus (ductile deformation). (2) b value patterns show a systematic decrease when approaching peak stress, after which (i) they increase again (brittle case) or (ii) reach a constant minimum (ductile case). A decrease in b values is indicative of progressive internal damage, with an increasing event rate. (3) Weak‐ and strong‐force networks exist within the sample. Macrofailure of the sample occurs due to collapse of the strong‐force network. Acoustic emissions predominantly occur (i) within the weak‐force network allowing for tensile crack opening and closing despite the large compressive external stresses, and (ii) in areas with the largest spatial force gradients, close to the strong‐force networks. All internal compressive and extensional normal forces display exponential distributions despite uniform boundary stresses. (4) Stress drops of the largest events are inversely proportional to peak stress; the largest stress drops occur for brittle failure, progressively approaching a zero magnitude for ductile deformation. The systemic correlations between b values, the number of acoustic emissions, and stress drops with the maximum principal stress may offer opportunities to invert for changes in the stress state from these remote observables during earthquake cycles.

Fracture and Damage Characteristics of Granite under Uniaxial Disturbance Loads

“…The crack-closure stress, crack-initiation stress, and crack-damage stress are separately 0.2, 0.4, and 0.7 times the peak stress. Combining with previous research [38,39], different types of rocks feature significantly different characteristic stresses. The difference is mainly related to factors including mineral compositions, internal structure, and petrogenic environment of rocks.…”

The Rise, Peak and Decline of the Seismic Hazard Related to Hydraulic Fracturing Activities in the Duvernay Play, Fox Creek Area, Alberta

“…This is one of the key observations in the present study, where there is a large difference in seismic hazard between the Eastern and Western sections of the seismic cluster in Fox Creek due to the large difference in their $$b$$‐values (Figure 4). On the other hand, various laboratory and numerical studies (Amitrano, 2003; Goebel et al., 2013; Meredith et al., 1990; Scholz, 2015; Van der Baan & Chorney, 2019) have found that the $$b$$‐values are anticorrelated to the differential stresses σ 1 ‐σ 3 , that is, the differential between the maximum (σ 1 ) and minimum principal stress (σ 3 ). It is possible that the observed difference in $$b$$‐values between the Eastern and Western sections is a consequence of distinct differential stresses, σ 1 ‐σ 3 , among these regions.…”

Are Aftershock Sequences Pertinent to Long‐Term Seismic Hazard Assessments? Insights From the Temporal ETAS Model

“…For instance, various laboratory and numerical studies have found that b values are anticorrelated to the differential stresses, that is, the differential between the largest and smallest principal stress (Amitrano, 2003;Goebel et al, 2013;Meredith et al, 1990;Scholz, 2015;Van der Baan & Chorney, 2019). If mainshocks lead to significant local shear stress release, this may affect the differential stresses after its occurrence, thereby causing differences in b values of mainshocks and aftershocks.…”