Mid-crustal controls on episodic stress-field rotation around major reverse, normal and strike-slip faults
Published:January 01, 2011
Jens-Alexander Nüchter, Susan Ellis, 2011. "Mid-crustal controls on episodic stress-field rotation around major reverse, normal and strike-slip faults", Geology of the Earthquake Source: A Volume in Honour of Rick Sibson, Å. Fagereng, V. G. Toy, J. V. Rowland
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Numerical models are used to investigate the geometry of coseismic stress-field perturbation in the crust surrounding a reverse fault, a normal fault and a strike-slip fault. The results predict a coseismic stress drop in the upper crust and loading to high stress below the brittle–ductile transition (BDT) due to the taper-off in fault slip. Coseismic stress deflections occur for each fault type as a result of the coseismic stress redistribution and is at a maximum in the middle crust where fault slip tapers-off. The zone of high-stress deflection extends downwards to the base of the crust. During the post-seismic interval, the stress-field geometry recovers towards the pre-earthquake stress state, but simple stress-field geometries cannot be re-established. The numerical results indicate that: (1) stress deflection due to slip taper-off below the BDT is important for the stress perturbation throughout the crust; (2) predictions for coseismic stress deflection exclusively based on the fault-parallel shear-stress drop ratio systematically underestimate stress deflection in the entire crust; (3) stress rotation is persistent throughout the crust in seismically active regions; and (4) the geometry of secondary faults is expected to be affected by the perturbed stress field.
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Geology of the Earthquake Source: A Volume in Honour of Rick Sibson
Professor Richard (Rick) Sibson revolutionized structural geology by illustrating that fault rocks contain an integrated record of earthquakes. Fault-rock textures develop in response to geological and physical variables such as composition, environmental conditions (e.g. temperature and pressure), fluid presence and strain rate. These parameters also determine the rate- and state-variable frictional stability of a fault, the dominant mineral deformation mechanism and shear strength, and ultimately control the partitioning between seismic and aseismic deformation. This volume contains a collection of papers that address the geological record of earthquake faulting from field-based or theoretical perspectives. The papers cover observations in active fault zones, the relationships between fault rocks and fault-slip styles, interpretation of fault-rock textures from the base of the seismogenic zone, consideration of the effects of fluids on faulting, discussion of fault reactivation v. initiation, and a review of future directions in geological earthquake research by Professor Sibson.