The role of elasticity in simulating long-term tectonic extension

Abstract

S U M M A R YWhile elasticity is a defining characteristic of the Earth's lithosphere, it is often ignored in numerical models of long-term tectonic processes in favour of a simpler viscoplastic description. Here we assess the consequences of this assumption on a well-studied geodynamic problem: the growth of normal faults at an extensional plate boundary. We conduct 2-D numerical simulations of extension in elastoplastic and viscoplastic layers using a finite difference, particle-in-cell numerical approach. Our models simulate a range of faulted layer thicknesses and extension rates, allowing us to quantify the role of elasticity on three key observables: fault-induced topography, fault rotation, and fault life span. In agreement with earlier studies, simulations carried out in elastoplastic layers produce rate-independent lithospheric flexure accompanied by rapid fault rotation and an inverse relationship between fault life span and faulted layer thickness. By contrast, models carried out with a viscoplastic lithosphere produce results that may qualitatively resemble the elastoplastic case, but depend strongly on the product of extension rate and layer viscosity U × η L . When this product is high, fault growth initially generates little deformation of the footwall and hanging wall blocks, resulting in unrealistic, rigid block-offset in topography across the fault. This configuration progressively transitions into a regime where topographic decay associated with flexure is fully accommodated within the numerical domain. In addition, high U × η L favours the sequential growth of multiple short-offset faults as opposed to a large-offset detachment. We interpret these results by comparing them to an analytical model for the fault-induced flexure of a thin viscous plate. The key to understanding the viscoplastic model results lies in the rate-dependence of the flexural wavelength of a viscous plate, and the strain rate dependence of the force increase associated with footwall and hanging wall bending. This behaviour produces unrealistic deformation patterns that can hinder the geological relevance of long-term rifting models that assume a viscoplastic rheology.

Morphotectonic Evolution of Passive Margins Undergoing Active Surface Processes: Large‐Scale Experiments Using Numerical Models

“…However, it is worth mentioning that the importance of elasticity remains a matter of debate in the community. Olive et al () showed that contrary to visco‐elasto‐plastic model visco‐plastic models such as the one used in this study are strongly dependent on the product of extension rate and viscosity. This has consequence on faulting development and may affect the resulting topography.…”

Marine Ice Cliff Instability Mitigated by Slow Removal of Ice Shelves

“…This motivates our numerical analysis (described in detail within section S2.2 of the supporting information), in which we explore the effects of non-Newtonian viscoelastic rheologies on ice cliff deformation in the 2-D geometry shown in Figure 1. We use the model SiStER (Simple Stokes solver for Exotic Rheologies; Olive et al (2016)) to run simulations over a range of subaerial cliff heights (h) and transition times (Δt) and evaluate the stress and strain-rate fields to determine if and where the cliff reaches our failure criteria. In all cases, we find strain rates are highest near sea level at the end of the transition (Figure 3, top row).…”

Band Formation and Ocean‐Surface Interaction on Europa and Ganymede

“…Model calculations were carried out using the finite difference code SiStER (Simple Stokes solver with Exotic Rheologies), which has previously been applied to solve terrestrial tectonics problems (e.g., Olive et al, 2016). We extend SiStER to simulate the full rheology of ice I, including ductile flow, elastic bending, plastic yielding, and spontaneous brittle localization.…”

“…Model calculations were carried out using the finite difference code SiStER (Simple Stokes solver with Exotic Rheologies), which has previously been applied to solve terrestrial tectonics problems (e.g., Olive et al, 2016).…”