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Off‐fault heterogeneities promote supershear transition of dynamic mode II cracks
Author(s) -
Albertini Gabriele,
Kammer David S.
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2017jb014301
Subject(s) - shear (geology) , homogeneous , mechanics , shear matrix , geology , shear stress , rayleigh scattering , slip (aerodynamics) , rayleigh wave , reflection (computer programming) , amplitude , shear waves , antiplane shear , fault (geology) , wave speed , fracture mechanics , wave propagation , materials science , seismology , physics , optics , composite material , petrology , statistical physics , stress intensity factor , alloy , thermodynamics , programming language , amorphous metal , computer science
The transition from sub‐Rayleigh to supershear propagation of mode II cracks is a fundamental problem of fracture mechanics. It has extensively been studied in homogeneous uniform setups. When the applied shear load exceeds a critical value, transition occurs through the Burridge‐Andrews mechanism at a well‐defined crack length. However, velocity structures in geophysical conditions can be complex and affect the transition. Damage induced by previous earthquakes causes low‐velocity zones surrounding mature faults and inclusions with contrasting material properties can be present at seismogenic depth. We relax the assumption of homogeneous media and investigate dynamic shear fracture in heterogeneous media using two‐dimensional finite element simulations and a linear slip‐weakening law. We analyze the role of heterogeneities in the elastic media, while keeping the frictional interface properties uniform. We show that supershear transition is possible due to the sole presence of favorable off‐fault heterogeneities. Subcritical shear loads, for which propagation would remain permanently sub‐Rayleigh in an equivalent homogeneous setup, will transition to supershear as a result of reflected waves. P wave reflected as S waves, followed by further reflections, affect the amplitude of the shear stress peak in front of the propagating crack, leading to supershear transition. A wave reflection model allows to uniquely describe the effect of off‐fault inclusions on the shear stress peak. A competing mechanism of modified released potential energy affects transition and becomes predominant with decreasing distance between fault and inclusions. For inclusions at far distances, the wave reflection is the predominant mechanism.