Impact of faults on the remote stress state

Abstract

Abstract. The impact of faults on the contemporary stress field in the upper crust has been discussed in various studies. Data and models clearly show that there is an effect, but so far, a systematic study quantifying the impact as a function of distance from the fault is lacking. In the absence of data, here we use a series of generic 3-D models to investigate which component of the stress tensor is affected at which distance from the fault. Our study concentrates on the far field, located hundreds of metres from the fault zone. The models assess various techniques to represent faults, different material properties, different boundary conditions, variable orientation, and the fault's size. The study findings indicate that most of the factors tested do not have an influence on either the stress tensor orientation or principal stress magnitudes in the far field beyond 1000 m from the fault. Only in the case of oblique faults with a low static friction coefficient of μ=0.1 can noteworthy stress perturbations be seen up to 2000 m from the fault. However, the changes that we detected are generally small and of the order of lateral stress variability due to rock property variability. Furthermore, only in the first hundreds of metres to the fault are variations large enough to be theoretically detected by borehole-based stress data when considering their inherent uncertainties. This finding agrees with robust stress magnitude measurements and stress orientation data. Thus, in areas where high-quality and high-resolution data show gradual and continuous stress tensor rotations of >20∘ observed over lateral spatial scales of 10 km or more, we infer that these rotations cannot be attributed to faults. We hypothesize that most stress orientation changes attributed to faults may originate from different sources such as density and strength contrasts.

The effect of stiffness contrasts at faults on stress orientation

“…The importance and impact of individual processes depends on the purpose of a model. Thus, models tend to implement faults in different ways with a different focus (Henk, 2020;Reiter et al, 2024). Instead of aiming at a realistic representation of a fault, different aspects of a fault properties are commonly investigated individually.…”

“…However, various different approaches to include faults exist that have different implications for the stress state . (Henk, 2020;Reiter et al, 2024;Treffeisen and Henk, 2020).…”

“…However, Reiter et al (2024) showed with a comprehensive study using a generic geomechancial model that fault induced stress changes beyond a distance of a few hundred meters from the fault core are too small to be resolved by stress data.…”

“…Furthermore, the contrast in material properties is the basis for any stress rotation and in particular the stiffness (Young's modulus) is demonstrated to have a significant influence (Hergert et al, 2015;Reiter, 2021;Ziegler, 2022). Eventually, the angle between the fault strike and the orientation of S Hmax is investigated as an influential parameter (Reiter et al, 2024;Siler, 2023).…”

“…We use a generic geomechanical-numerical model that allows a systematic and comprehensive investigation of the model parameter space in terms of stiffness contrast, stress ratio, and angle of the fault with respect to the far field stress state. We focus on the near field of the fault at scales of 10s of meters and limit the investigation to the linear elastic response of the stress state to rock stiffness contrasts which has not been investigated in previous studies that focused on processes (Ziegler et al, 2017), did not investigate the full range of parameters (Reiter, 2021) and methods of fault representation due to a different objective (Reiter et al, 2024). Herein, we conduct an exhaustive study and investigate the entire parameter space.…”