The Dynamics of Unlikely Slip: 3D Modeling of Low‐Angle Normal Fault Rupture at the Mai'iu Fault, Papua New Guinea

Abstract

Normal-sense slip on shallowly dipping (<30°) detachment faults has helped accommodate tens of kilometers of geologically recorded localized extension in a variety of rift settings (e.g., Collettini, 2011). The mechanics of these low-angle normal faults (LANFs) have been extensively debated because such shallowly dipping normal faults appear to defy classic fault mechanical theory. Anderson-Byerlee frictional fault reactivation theory predicts that extension of crustal rocks with Byerlee friction (0.6 ≤ static friction coefficient, μ s ≤ 0.85) in an Andersonian stress field (characterized by one vertical principal stress direction) should form normal faults

Modeling of Continental Normal Fault Earthquakes

“…In this way, their estimated event magnitude strictly depends on the amount of extension of the model during the loading phase. 3D rupture modeling of CNFE in Biemiller et al (2022) also produces large hanging wall subsidence while footwall uplift is significantly smaller, as modeled here. The key difference between the current study and the one by Biemiller et al (2022) is that here we model a realistic stress field through an extension of the model while in the latter stress field is predefined.…”

“…However, we cannot exclude the existence of low-angle faults in low heat flow environment as they can be reactivated faults or suture zones. In addition, the observational and numerical studies by Biemiller et al (2020Biemiller et al ( , 2022 on the Mai'iu fault support the possibility of strong earthquakes on low-angle faults. Also, the mechanical properties of the fault zone evolve with progressive extension and fault maturity.…”

“…In this work, we use RSF parameters (Figure 2) from high-velocity friction experiments for granite (Blanpied et al, 1995). These parameters in terms of amplitude and temperature range are close to those used in Biemiller et al (2022) 2022) use the velocity-weakening behavior of the fault rocks as the only mechanism to decrease fault strength during an earthquake, which alone can result in earthquake nucleation. However, the role of the changing pore pressure during the seismic cycle, as suggested by Doglioni et al (2014) and Albano et al (2021b), cannot be excluded.…”

A Diffuse Interface Method for Earthquake Rupture Dynamics Based on a Phase‐Field Model

“…Alternative nucleation strategies that are smooth in space and/or time can reduce numerical artifacts in spontaneous dynamic rupture problems, such as stress localization in the surroundings of a sharply defined nucleation patch. Such smooth approaches also minimize the influence of a potentially ill‐constrained nucleation procedure on the subsequent stages of realistic earthquake scenario simulations (e.g., Biemiller et al., 2022; Harris et al., 2021). We observe comparable numerical artifacts, apparent especially in the stress fields, at quadrature points of element cells located only partially within the diffuse fault zone, for example, in the mesh‐independent fault configurations using low polynomial order (see Figures 4, 7, and C3).…”

Regional‐Scale Low‐Angle Normal Fault Friction and Cohesion Constrained From Mohr‐Coulomb Models of Active and Abandoned Range‐Front Faults in Papua New Guinea

“…This assumption has little impact on the modeling results because the D t is shallower than 1.9 km BSL for all model scenarios. The Mohr-Coulomb based analytical approach can elucidate the overall behavior and slip style of convex-upward normal faults, and can constrain input parameters for geodynamic models and dynamic rupture simulations of detachment faults (e.g., Biemiller et al, 2022). The analytical modeling of fault strength, fault geometry, and rider block geometry developed by Choi and Buck (2012) is inspired by key geodynamic processes (for instance the syn-exhumational fault weakening caused by a reduction of friction and/or cohesion with progressive slip).…”