HR: 17:15h
AN: T34A-04    [Abstracts]
TI: Mechanical Evolution of Relay Zones in Normal Faulted Terranes: Insights From Three Dimensional Elastoplastic Finite Element Models
AU: * Goteti, R
EM: gsrajesh@earth.rochester.edu
AF: Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, United States
AU: Mitra, G
EM: mitr@troi.cc.rochester.edu
AF: Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, United States
AU: Sussman, A
EM: spring@lanl.gov
AF: EES: Geophysics, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AU: Lewis, C
EM: clewis@lanl.gov
AF: EES: Seismic Hazards, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AB: We present a 3D nonlinear finite element model to gain insights into the evolution of relay zones in normal faulted terranes. The model comprises two listric frictional sliding surfaces that act as faults and are arranged en echelon in an elastoplastic medium. We have investigated various Synthetic and Antithetic (both convergent and divergent) relay zone configurations to study the influence of (1) fault overlap/spacing ratio (-2 to 2), (2) material strength (3) coefficient of sliding friction on the faults (0.1 - 0.6) and (4) orthogonal vs. oblique extension, on the incremental evolution of stresses and strain paths in relay zones. The results suggest that a relay zone evolves in a three dimensional strain field under a combination of rotational and distortional strains. In isotropic rocks, the maximum extensional strains in the relay zone initiate oblique to regional extension and progressively rotate toward regional extension with increasing displacement on the faults. The relay zone evolves along a non-coaxial strain path and the total strain ellipsoid shape (oblate vs. prolate) is dependent on the relative orientation of the primary faults and amount of extension on them, and structural position in the relay zone. With all other parameters being identical, magnitudes of von Mises stresses at the ground surface are highest in convergent relay zones and lowest in divergent relay zones. Thus subsidiary oblique structures are more likely to develop in convergent relay zones than in synthetic or divergent relay zones. Assuming uniform fault propagation, it is possible to gain insights into relay zone evolution during fault tip propagation by comparing models with different fault overlap/spacing ratios. Model plastic strains suggest that hard linkage can develop between adjacent faults with a gap or minimal overlap; however, the occurrence of oblique, strain transferring structures increases with increasing fault overlap. The orientations of the maximum extensional strains throughout the deformation suggest that primary faults can propagate towards each other and link-up in synthetic and convergent relay zones and propagate away from each other in divergent relay zones. For layered rock volumes, mechanical stratigraphy plays a major role by influencing both the orientations and magnitudes of strains in adjoining layers. Our results give critical insights into the variations of dominant fracture/fault trends with geometry and structural position in relay zones, and show how these trends evolve in mechanically contrasting adjoining layers.
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8020 Mechanics, theory, and modeling
SC: Tectonophysics [T]
MN: 2009 Joint Assembly