HR: 1340h
AN: S53A-1091    [Abstracts]
TI: 3D Strain Modelling of Tear Fault Analogues
AU: * Hindle, D
EM: hindle@msu.edu
AF: Michigan State University, Dept. Geol. Sci. 206 Nat. Sci. Building, East Lansing, MI 48824-1115 United States
AU: Vietor, T
EM: tim.vietor@nagra.ch
AF: GeoForschungsZentrum, Telegrafenberg C2, Potsdam, 14473 Germany
AB: Tear faults can be described as vertical discontinuities, with near fault parallel displacements terminating on some sort of shallow detachment. As such, they are difficult to study in "cross section" i.e. 2 dimensions as is often the case for fold-thrust systems. Hence, little attempt has been made to model the evolution of strain around tear faults and the processes of strain localisation in such structures due to the necessity of describing these systems in 3 dimensions and the problems this poses for both numerical and analogue modelling. Field studies suggest that strain in such regions can be distributed across broad zones on minor tear systems, which are often not easily mappable. Such strain is probably assumed to be due to distributed strain and to displacement gradients which are themselves necessary for the initiation of the tear itself. We present a numerical study of the effects of a sharp, basal discontinutiy parallel to the transport direction in a shortening wedge of material. The discontinuity is represented by two adjacent basal surfaces with strongly contrasting (0.5 and 0.05) friction coefficient. The material is modelled using PFC3D distinct element software for simulating granular material, whose properties are chosen to simulate upper crustal, sedimentary rock. The model geometry is a rectangular bounding box, 2km x 1km, and 0.35-0.5km deep, with a single, driving wall of constant velocity. We show the evolution of strain in the model in horizontal and vertical sections, and interpret strain localization as showing the spontaneous development of tear fault like features. The strain field in the model is asymmetrical, rotated towards the strong side of the model. Strain increments seem to oscillate in time, suggesting achievement of a steady state. We also note that our model cannot be treated as a critical wedge, since the 3rd dimension and the lateral variations of strength rule out this type of 2D approximation.
DE: 8010 Fractures and faults
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8111 Continental tectonics: strike-slip and transform
SC: Seismology [S]
MN: Fall Meeting 2005