HR: 0800h
AN: T21B-0463    [Abstracts]
TI: The balance of frictional heat production, thermal pressurization, and slip resistance on exhumed mid-crustal faults (Adamello batholith, Southern Italian Alps)
AU: * Griffith, W A
EM: wagrif@pangea.stanford.edu
AF: Department of Geological and Environmental Science, Stanford University, Braun Hall, Building 320, Stanford, CA 94305 United States
AU: Di Toro, G
EM: giulio.ditoro@unipd.it
AF: Dipartimento di Geologia, Paleontologia e Geofisica, Universit… di Padova, Padova, 35137 Italy
AU: Pollard, D D
EM: dpollard@pangea.stanford.edu
AF: Department of Geological and Environmental Science, Stanford University, Braun Hall, Building 320, Stanford, CA 94305 United States
AB: Exhumed faults cutting the Adamello batholith (Italian Alps) were active ca. 30 Ma at seismogenic depths of 9-11 km. The faults "exploited preexisting joints and can be classified into three groups containing: (A) only cataclasite (a fault rock with no evidence of melting), (B) cataclasite and pseudotachylyte (solidified friction-induced melts produced during earthquakes), and (C) only pseudotachylyte. The majority of pseudotachylyte-bearing faults in this outcrop overprint pre-existing cataclasites (Type B), suggesting a transition between slip styles; however, some faults exhibiting pseudotachylyte and no cataclasite (Type C) display evidence of only one episode of slip. Faults of Type A never transitioned to frictional melting. We attempt to compare faults of type A, B, and C in terms of a simple one-dimensional thermo-mechanical model introduced by Lachenbruch (1980) describing the interaction between frictional heating, pore fluid pressure, and shear resistance during slip. The interaction of these three parameters influences how much elastic strain is relieved during an earthquake. For a conceptualized fault zone of finite thickness, the interplay between the shear resistance, heat production, and pore fluid pressure can be expressed as a non-linear partial differential equation relating these processes to the strain rate acting within a fault zone during a slip event. The behavior of fault zones in terms of these coupled processes during an earthquake depends on a number of parameters, such as thickness of the principal slipping zone, net coseismic slip, fault rock permeability and thermal diffusivity. Ideally, the governing equations should be testable on real fault zones if the requisite parameters can be measured or reasonably estimated. The model can be further simplified if the peak temperature reached during slip and the coseismic slip rate can be constrained. The contrasting nature of slip on the three Adamello fault types highlights (1) important differences between slip processes on cataclastic and melt-producing faults at depth and (2) some limitations of applicability of such models to real faults.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8010 Fractures and faults
DE: 8036 Paleoseismology (7221)
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: Fall Meeting 2005