Controls on strain localization in a two‐dimensional elastoplastic layer: Insights into size‐frequency scaling of extensional fault populations

Abstract

[1] We use a two-dimensional (2-D) finite element code to investigate how mechanical properties and boundary conditions influence progressive strain localization during extension of a 2-D elastoplastic layer. The deforming medium is modeled using a strain softening Von Mises rheology, with a Gaussian heterogeneity in yield strength distributed randomly in space. Specifically, we examine the effects of changing (1) the thickness of the deforming layer, (2) the basal boundary condition, (3) the range of strengths in the deforming layer, (4) the strength loss on failure, and (5) the total accommodated strain. Discrete zones of plastic shear strain are observed to nucleate and grow progressively during each experiment. In order to quantify and thus discriminate between the deformation patterns produced under differing conditions, we calculate the size-frequency distributions of the shear band populations. Size is defined as the total plastic strain represented by each discrete structure. A wide range of size-frequency distributions is observed, including both power law and exponential as well as distributions that show breaks in scaling with a transition from power law (at small sizes) to exponential (at large sizes). We show that these variations in population statistics are directly reflecting a change in strain localization in space and time caused by changing model parameters. Furthermore, by making an analogy between the model shear bands and tectonic faults, we provide insights into key features of fault size-frequency distributions that have been measured in continental and oceanic extensional settings and also observed in analogue experiments.INDEX TERMS: 8015 Structural Geology: Local crustal structure; 8020 Structural Geology: Mechanics; 8010 Structural Geology: Fractures and faults; 8109 Tectonophysics: Continental tectonics-extensional (0905); 8159 Tectonophysics: Rheology-crust and lithosphere; KEYWORDS: faulting, localization, scaling, extension, modeling Citation: Hardacre, K. M., and P. A. Cowie, Controls on strain localization in a two-dimensional elastoplastic layer: Insights into size-frequency scaling of extensional fault populations,

Statistical mechanics and scaling of fault populations with increasing strain in the Corinth Rift

“…The Rift presents high earthquake activity, with several earthquakes of magnitude greater than 6 reported in both historic and instrumental records (Papazachos and Papazachou, 1997). Most of the computed focal mechanisms for both strong events and microearthquakes are in agreement with geodetic data and fault geometry, indicating normal faulting associated with N-S extension Hatzfeld et al, 2000).…”

“…Quaternary geology, geodetic strain rates and the earthquake activity indicate that the currently active Rift zone is confined in the narrow offshore zone of the Gulf of Corinth, extending to the east to the Alkyonides Gulf and the Perachora Peninsula (e.g., Hatzfeld et al, 2000;Briole et al, 2000;Roberts et al, 2009;Leeder et al, 2012) (area covered with faults in red in Fig. 1).…”

Structural Styles and Tectonic Evolution of Onshore and Offshore Abu Dhabi, UAE

“…These studies indicate that the large volume of relatively undeformed rock located between faults and fault zones contains a rich history of small-scale deformation (Narteau, 2000;Hardacre and Cowie, 2003). This deformation includes small structures that formed early and were later abandoned in favor of other structures that eventually grew to seismic scale features.…”

Generalized statistical mechanics approaches to earthquakes and tectonics

“…exponential). In addition, simulations on numerical models [60,69,70] and on analogue laboratory experiments [65,71] showed that the frequency-size distribution depends on the total strain that the fault system has been imposed on and the competition between the different stages of fault growth, i.e. fault nucleation, growth and coalescence.…”