HR: 09:00h
AN: S31D-05    [Abstracts]
TI: Direct Observation of Depth Variation in Fault Zone Structure Through and Below the Seismogenic Crust: Preliminary Results From the SEMP Fault System in Austria
AU: * Frost, E K
EM: efrost@usc.edu
AF: University of Soutern California, 3651 Trousdale Blvd, Los Angeles, CA 90089 United States
AU: Dolan, J
EM: dolan@usc.edu
AF: University of Soutern California, 3651 Trousdale Blvd, Los Angeles, CA 90089 United States
AU: Sammis, C
EM: sammis@usc.edu
AF: University of Soutern California, 3651 Trousdale Blvd, Los Angeles, CA 90089 United States
AU: Hacker, B
EM: hacker@geol.ucsb.edu
AF: University of California at Santa Barbara, UC Santa Barbara - BUilding 526, Santa Barbara, CA 93106 United States
AU: Ratschbacher, L
EM: lothar@geo.tu-freiberg.de
AF: Institut f�r Geologie, Technische Universit�t Bergakademie Freiberg, Gustav-Zuener-Strasse 12, Freiberg, D-09599 Germany
AB: One of the most exciting and important frontiers in earthquake science is the linkage between the internal structure and the mechanical behavior of fault zones. In particular, little is known about how fault-zone structure varies as a function of depth, from near-surface conditions down through the seismogenic crust and into the ductile lower crust. Such understanding is vital if we are to understand the mechanical instabilities that control the nucleation and propagation of seismic ruptures. This imperative has led us to the Oligo-Miocene Salzach-Ennstal-Mariazell-Puchberg [SEMP] fault zone in Austria. The SEMP system is an extremely rare example of a major strike-slip fault that has been exhumed differentially such that it exposes a continuum of structural levels along strike. This exhumed fault system thus provides a unique opportunity to systematically examine depth-dependent changes in fault-zone geometry and structure along a single fault. Our ongoing field studies focus on structural transects across the SEMP fault zone at exhumation levels ranging from the near-surface at the eastern end of the fault (Vienna pull-apart basin), within the seismogenic crust (central Austria), and down into the ductile lower crust exposed in the Tauern window of western Austria. In addition to detailed field mapping of structural fabrics, fluid-rock interactions, relative timing relationships, and variations in fault geometry, we are also conducting detailed analyses of fault-zone rocks designed to explore deformation at a wide range of scales using petrographic microscopy, cathodoluminescence microscopy, fluid-inclusion studies, scanning-electron microscopy, and transmission/analytical-electron microscopy. Preliminary results from one of our first detailed study sites, at Ges�use in central Austria, reveal strikingly asymmetric damage across the fault. The limestones exposed south of the fault are fractured, but relatively coherent to within a few meters of the main fault trace. In contrast, the dolomites exposed north of the fault are pervasively sheared and fractured to the cm scale for a distance of at least 200 m from the main fault trace. This extreme asymmetry in damage is consistent with recent models of dynamic rupture in which the rupture propagation direction is controlled by material contrasts across the fault. Detailed studies such as these will allow us to create a synoptic view of the SEMP fault zone from top to bottom - a view that describes how the fault zone varies in its characteristics at different depths.
DE: 8010 Fractures and faults
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting