Shear Band Formation in Numerical Simulations Applying a Continuum Damage Rheology Model

Abstract

Abstract-In seismically active regions, faults nucleate, propagate, and form networks that evolve over time. To simulate crustal faulting processes, including the evolution of fault-zone properties, a rheological model must incorporate concepts such as damage rheology that describe the various stages of the seismic cycle (strain localization, subcritical crack growth and macroscopic failure) while accounting for material degradation and healing and off-fault deformation. Here we study the fundamental patterns of strain-localisation within the framework of a continuum damage rheology by performing a shear band analysis (linear instability analysis) and comparing predictions of shear band orientations with numerical results of the nonlinear problem. We find (analytically and numerically) that the angle between the shear band and the less compressive (transverse) direction is between 47°in compression tests with a strain ratio of 0.25 (highly confined compression test), and 60°for a strain ratio higher than 1.4 (axial compression and transverse extension). In addition we find that shear bands exhibit local dilation (I 1 [ 0) in a wide range of strain ratios excluding only simulations with highly confined compression (which yield compacting shear bands or non-localized deformation). Finally, we discuss the applicability of the damage model for simulating deformation in the seismogenic, brittle crust.

Predicting rupture arrests, rupture jumps and cascading earthquakes

“…In fact, our simulations show that in dilational step‐overs where pore fluids and inter‐seismic deformation are observed and significant energy dissipation is expected, ruptures may arrest at steps as narrow as 1.8 km (Figure 6, lower blue curves α ≤ 0.5). As dilational step‐overs may be associated with porosity increase [ Hamiel et al , 2005; Finzi et al , 2012], the above results were obtained from simulations with damage‐related porosity and dynamic pore pressure changes. The effect of porosity evolution is implemented by adjusting the velocity in simulations as a function of density (assuming local porosity increase <4% and fluid filled pores).…”

Melt and shear interactions in the lithosphere: Theory and numerical analysis of pure shear extension

“…While such studies clearly highlight the importance of melt, they describe neither the coupled evolution of melt and strain structures nor the enhancement of shear‐melt interactions through dilation of shear structures, modification of bulk viscosity, and the compressibility of partially molten rocks. A better understanding of melt‐strain interactions and deformation patterns in compressible material is particularly important in studies of lithospheric extension, where shear zones are expected to dilate [ Menéndez et al ., ; Wu et al ., ; Finzi et al ., ] and where magma intrusion is expected to modify the continental lithosphere [ Ebinger , ; Corti , ].…”

Damage in step‐overs may enable large cascading earthquakes

“…The insights gained from our analysis are instructive in assessment of fault‐system stability incorporating additional information on material properties. For example, damage‐zone dilation [ Finzi et al , 2012] or porosity increase [ Hamiel et al , 2005] will reduce material‐density within the step‐over and velocity‐contrast across step‐bounding faults (resulting in a subtle stabilizing effect). In such conditions, pore‐pressure changes would further stabilize a fault‐system with releasing step‐overs [ Harris and Day , 1993; Cocco and Rice , 2002].…”