HR: 1340h
AN: T23A-0553    [Abstracts]
TI: Dramatic frictional-viscous slip fluctuations within an exhumed multi-strand fault; evidence of fluid- with velocity-sensitivity?
AU: * EDWARDS, M A
EM: michael.edwards@univie.ac.at
AF: Structural Processes Group, Dept. of Geological Sciences, University of Vienna Althanstrasse 14, Vienna, A-1090 Austria
AU: RATSCHBACHER, L
EM: lothar@geo.tu-freiberg.de
AF: Institut f�r Geologie, TU - Bergakademie Freiberg, Freiberg, D-09596 Germany
AU: GRASEMANN, B
EM: bernhard.grasemann@univie.ac.at
AF: Structural Processes Group, Dept. of Geological Sciences, University of Vienna Althanstrasse 14, Vienna, A-1090 Austria
AB: Detailed field surveying of exhumed fault strand domains on the pull-apart basin flanks of a still active transtensional fault zone reveal intriguing fault rocks that are highly informative of the relationships between aseismic creep and co-seismic accelerated slip. We examine part of the 100's km Damxung-Jiali Shear Zone (DJSZ) in eastern Tibet, a crustal-escape-tectonics lithospheric failure zone whose locally exceptional width (5-15 km) incorporates a range of protoliths. This wide, multi-lithology fault architecture is associated with extensive pseudotachylite and cataclasite development, co-located with a range fault rocks that failed with plastic bulk-rheology. Highly unusual S-C fabrics in cataclasites are identified as well as spectacular subsequent re-brecciation indicating dramatic temporal fluctuations in viscous and frictional failure processes. Their co-location across a broad (original) depth interval together with numerous pseudotachylite generations (from co-existence with quartz flowing at 300-350 deg.C to low-cohesion cataclasites) indicates repeated excursions into velocity weakening exploited instabilities as displacement has continued. Extensive fluid-involvement in both frictional and viscous processes in all the fault strand lithologies is taken as evidence of "fluid sensitivity" as well as velocity sensitivity. Pseudotachylite-coated brittle localisation surfaces that short-cut stronger domains between creeping (i.e. metavolcanics versus carbonates) indicate the interplay of stable creep versus co-seismic slip acceleration with velocity weakening amongst the strand domains. We propose that the multiple strand and multi lithology nature of the fault zone allowed unstable stress/slip values to be preferentially enhanced in key fault strands (i.e. restricted cross-fault permeability "compartments") while other compartment were reciprocally undergoing stable creep. This provides a view of the potentially very complex nature of co-seismic slip frictional-viscous interplay and evolution in a heterogeneous, large fault zone.
DE: 7230 Seismicity and seismotectonics
DE: 8020 Mechanics
DE: 8045 Role of fluids
DE: 8107 Continental neotectonics
DE: 7209 Earthquake dynamics and mechanics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting