HR: 0800h
AN: T11A-0343    [Abstracts]
TI: Analysis of Fragmentation Mechanisms in Fault-Core and Damage Zone: Application of Fractal Fragmentation Theory
AU: * Antoniucci, A
EM: angelaantoniucci@hotmail.it
AF: Dipartimento di Scienze della Terra Universita' di Perugia, Piazza dell'Universita' 1, Perugia, 06100, Italy
AU: Perugini, D
EM: diegop@unipg.it
AF: Dipartimento di Scienze della Terra Universita' di Perugia, Piazza dell'Universita' 1, Perugia, 06100, Italy
AU: Collettini, C
EM: colle@unipg.it
AF: Dipartimento di Scienze della Terra Universita' di Perugia, Piazza dell'Universita' 1, Perugia, 06100, Italy
AB: The study of physical mechanisms triggering fragmentation processes in fault zones is of paramount importance for understanding the mechanics of faulting. In the last twenty years a plethora of works indicated that a suitable characterization of fragmentation processes can be attained by studying the size distribution of rock fragments around fault zones. In particular, fractal geometry techniques have been proven to unravel information that would be otherwise inaccessible by conventional particle size analysis. Although these studies allowed to understand some of the basic mechanisms acting on a rock formation and producing the observed fractal fragment size distributions, a few works focussed on the continuous characterization of the size distribution from the fault core to the damage zone. The aim of this contribution is to study the evolution of fragmentation processes within cataclastic fault rocks from the fault core into the damage zone by using fractal analysis. From a small displacement (slip <10m), dolomite-bearing fault, a large rock sample (40x20x20 cm) containing the fault core and a portion of the damage zone has been collected. The sample has been cut along both fault orthogonal and fault parallel cross sections. For each section the size distribution of fragments has been obtained by image analysis. Results indicate that all distributions are fractal as they can be approximated by a power-law relationship whose exponent (D) is the fractal dimension of fragmentation. An unusual result from our analysis is the switch of D values by passing from the damage zone (D=2.84±0.03) to the fault core (D=2.61±0.03); this variation is consistently observed for both parallel and orthogonal cross sections. Results from our analysis are interpreted in the light of two fractal fragmentation models: the so-called "pillar-of- strength" and "comminution" model. The first model is typically invoked to account for the catastrophic fragmentation occurring during the initiation of faulting, i.e. when the fault plane develops, and generates fragment size distributions with D=2.84. The second model, is commonly claimed to account for the grinding of fragments occurring along the fault core as the result of localised deformation, and produces fragment size distributions with D=2.58. The difference in the D values from the fault core to the damage zone suggests that the latter experienced catastrophic events, D=2.84±0.03, whilst the fault core was affected by a progressive grinding of fragments generating a fragment size distributions with D=2.61±0.03.
DE: 4425 Critical phenomena
DE: 4440 Fractals and multifractals
DE: 8010 Fractures and faults
DE: 8020 Mechanics, theory, and modeling
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting