Liang C., Ampuero Jean-Paul, Munoz D. P. (2021). Deep ductile shear zone facilitates near-orthogonal strike-slip faulting in a thin brittle lithosphere. Geophysical Research Letters, 48 (2), e2020GL090744 [9 p.]. ISSN 0094-8276.
Titre du document
Deep ductile shear zone facilitates near-orthogonal strike-slip faulting in a thin brittle lithosphere
Année de publication
Liang C., Ampuero Jean-Paul, Munoz D. P.
Geophysical Research Letters, 2021,
48 (2), e2020GL090744 [9 p.] ISSN 0094-8276
Some active fault systems comprise near-orthogonal conjugate strike-slip faults, as highlighted by the 2019 Ridgecrest and the 2012 Indian Ocean earthquake sequences. In conventional Mohr-Coulomb failure theory, orthogonal faulting requires a zero frictional coefficient (pressure-insensitive), which is unlikely in the brittle lithosphere. The simulations developed here show that near-orthogonal faults can form in the brittle layer by inheriting the geometry of orthogonal shear zones nucleated in the deep ductile (pressure-insensitive) layer. In particular, if the brittle layer is sufficiently thinner than the ductile fault root, near-orthogonal faulting is preserved at the surface. The preservation is further facilitated by a depth-dependent strength in the brittle layer. Conversely, faults nucleated within the brittle layer are unlikely to form at orthogonal angles. Our model thus offers a possible explanation for orthogonal strike-slip faulting and reveals the significant interactions between the structure of faults in the brittle upper lithosphere and their deep ductile roots. Plain Language Summary Some notable earthquakes have occurred on sets of horizontally sliding vertical faults that cross each other at almost right angles (90 degrees). This is puzzling because the conventional theory of how Earth's brittle outer shell, the crust, breaks predicts a narrower angle between faults, close to 60 degrees. Our work offers an explanation to this puzzle. Theory also predicts that faults can form at right angles in rocks whose strength does not depend on the pressure acting on them. This is precisely the case in the deep viscous rocks that lie below the crust. Our computer simulations show that a pair of faults formed at right angle in deep viscous rocks can then grow upwards, gradually evolving to the narrower angle expected in the crust. If the crust is too thin, the faults reach the surface with almost right angles. Our proposed mechanism is effective on brittle crusts that are thinner than their viscous roots, which is the case in some regions where faulting at right angle is observed. Thus, our results show that the ductile root has important effects on the geometry of faults in the crust. Key Points . Simulations reveal shear bands in deep ductile layer induces orthogonal strike-slip faulting in thin brittle lithosphere Faults nucleated in brittle lithosphere are unlikely to form at orthogonal angles Low confining pressure at shallow depth facilitates near-orthogonal strike-slip faulting
Plan de classement
Sciences fondamentales / Techniques d'analyse et de recherche 
Géophysique interne 
Fonds IRD [F B010080961]