Analogue models of obliquely convergent continental plate boundaries

Abstract

Abstract. Analogue models are used to examine crustal-scale faulting at obliquely convergent continental plate boundaries. A uniform Coulomb material is deformed with basal kinematic boundary conditions to model two obliquely convergent lithospheric plates. The mantle part of one plate is assumed to detach from its overriding crust and then be subducted beneath the other plate. The obliquity of the collision is assumed to remain constant throughout the deformation. Experiments are run with obliquities ranging from pure convergence (low obliquity) to pure strike slip (high obliquity). Reverse faults are observed for all obliquities with a nonzero convergent component. By contrast, only collisions with a large amount of strike slip motion exhibit wrench faulting. In experiments dominated by their convergent component, the strike slip motion is totally accommodated by oblique slip along the reverse faults. Strain partitioning between reverse faults and wrench faults is only observed for experiments run above a certain critical partitioning obliquity. From the observed initial faults, we can deduce the change in orientation in the principal stress triad as the obliquity is changed. We propose that the initial direction of maximum compressive stress (•rl) rotates horizontally as the obliquity is changed, which in turn affects the geometry of the initial faults formed in the material. In the case of reverse faults, the rotation increases their dip measured along the direction of pure convergence. The relative magnitude of the minimum horizontal stress and the vertical stress determine whether reverse faults or strike slip faults are the first to form. Although long term deformation is more difficult to analyze, a simple relationship for the angle at which strain partitioning occurs is derived.

An Abrupt Transition in the Mechanical Response of the Upper Crust to Transpression along the Queen Charlotte Fault

“…Analog models in which the deformation of brittle (dry sand) and/or ductile (silicone putty) layers is documented in response to forcing by motion of a rigid base (Burbridge and Braun, 1998;Casas et al, 2001) show behavior that is generally consistent with these theoretical results. In the Burbridge and Braun (1998) model, a Mylar sheet forming the base of one plate was pulled at a series of oblique angles through a slit in the middle of the base of the model box.…”

“…In the Burbridge and Braun (1998) model, a Mylar sheet forming the base of one plate was pulled at a series of oblique angles through a slit in the middle of the base of the model box. In contrast, in the Casas et al (2001) model, a thin plastic plate that extended halfway across the model box was pushed from the side.…”

Short-lived tectonic switch mechanism for long-term pulses of volcanic activity after mega-thrust earthquakes

“…In oblique subduction zones the shear component is accommodated in the overriding plate by trenchparallel, regional-scale, strike-slip faults that are localised within the volcanic belt because of the higher geothermal gradients. Several authors investigated the dynamics of strain partitioning using mathematical (Platt, 1993;Braun and Beaumont, 1995), experimental (Pinet and Cobbold, 1992;Burbidge and Braun, 1998), and field (Rosenau et al, 2006) studies. Fitch (1972) suggests that the strike-slip component relates linearly to the incidence angle of the subduction, with some relation between normal and shear stresses.…”

A Probabilistic Tsunami Hazard Assessment for Western Australia

“…These are thought to be a combination of events on the Mentawai and the Great Sumatran faults. Motion on these faults appears to reflect strain partition of the oblique subduction (BURBIDGE and BRAUN, 1998) in the Sumatra section of the Sunda Arc. The Great Sumatran fault will not produce any tsunami since it is entirely onshore, so it is not included in the tsunami hazard analysis.…”

“…The strike-slip faults take all the lateral motion, while the thrust fault takes up the convergent component of the motion. Using an argument based on work minimization (BURBIDGE and BRAUN, 1998), one can show that the only megathrust fault considered in this study that will be strain partitioned is Sumatra. This is consistent with the fact that only Sumatra has large strike-slip faults between the trench and the coast.…”