Three‐dimensional models of deformation near strike‐slip faults

Abstract

We use three‐dimensional elastic models to help guide the kinematic interpretation of crustal deformation associated with strike‐slip faults. Deformation of the brittle upper crust in the vicinity of strike‐slip fault systems is modeled with the assumption that upper crustal deformation is driven by the relative plate motion in the upper mantle. The driving motion is represented by displacement that is specified on the bottom of a 15‐km‐thick elastic upper crust everywhere except in a zone of finite width in the vicinity of the faults, which we term the “shear zone.” Stress‐free basal boundary conditions are specified within the shear zone. The basal driving displacement is either pure strike slip or strike slip with a small oblique component, and the geometry of the fault system includes a single fault, several parallel faults, and overlapping en echelon faults. We examine the variations in deformation due to changes in the width of the shear zone and due to changes in the shear strength of the faults. In models with weak faults the width of the shear zone has a considerable effect on the surficial extent and amplitude of the vertical and horizontal deformation and on the amount of rotation around horizontal and vertical axes. Strong fault models have more localized deformation at the tip of the faults, and the deformation is partly distributed outside the fault zone. The dimensions of large basins along strike‐slip faults, such as the Rukwa and Dead Sea basins, and the absence of uplift around pull‐apart basins fit models with weak faults better than models with strong faults. Our models also suggest that the length‐to‐width ratio of pull‐apart basins depends on the width of the shear zone and the shear strength of the faults and is not constant as previously suggested. We show that pure strike‐slip motion can produce tectonic features, such as elongate half grabens along a single fault, rotated blocks at the ends of parallel faults, or extension perpendicular to overlapping en echelon faults, which can be misinterpreted to indicate a regional component of extension. Zones of subsidence or uplift can become wider than expected for transform plate boundaries when a minor component of oblique motion is added to a system of parallel strike‐slip faults.

Combining satellite and seismic images to analyse the shallow structure of the Dead Sea Transform near the DESERT transect

“…These models show that fault-perpendicular subsidence and extension, as well as compression, can occur due to interaction of en echelon strike-slip faults. Additionally, the fault tip of a single strike-slip fault is associated with coupled uplift and subsidence (ten Brink et al 1996). ten Brink et al (1996) further suggest that the amount of uplift or subsidence depends on the shear stresses acting on the fault.…”

“…Additionally, the fault tip of a single strike-slip fault is associated with coupled uplift and subsidence (ten Brink et al 1996). ten Brink et al (1996) further suggest that the amount of uplift or subsidence depends on the shear stresses acting on the fault. In their models, the vertical movements are significant, if the faults are 'weak'.…”

“…Numerical and analogue (sandbox) modelling showed, however, that most of these features can be explained by pure strike-slip motion (e.g. ten Brink et al 1996;Dooley and McClay 1997). These models show that fault-perpendicular subsidence and extension, as well as compression, can occur due to interaction of en echelon strike-slip faults.…”

A structural model of the Fábrica Nova region, Santa Rita syncline, Quadrilátero Ferrífero: flanking folds as a folding mechanism

“…Cover deformation mechanisms induced by a basement-involved structures can behave actively (e.g Wilcox et al 1973, Naylor et al 1986, Brink et al 1996, Erslev 1991, Narr & Suppe 1994, Erslev & Mayborn 1997, Tindall 2000 or passively (e.g Passchier 2001, Grasemann & Stüwe 2001, Exner et al 2004). …”

Three-dimensional numerical models of the evolution of pull-apart basins

“…So far, this kind of modeling has been limited to either 2-D thin-plate approximations, which do not resolve the depth distribution of stress and strain (e.g., Segall and Pollard, 1980) or to 3-D models in the small-strain elastic approximation (Katzman et al, 1995;ten Brink et al, 1996), M a n u s c r i p t 4 which strongly oversimplify real rheology (which is visco-elastic-plastic), and therefore can only investigate geodynamic tendencies rather than long-term evolution.…”