HR: 1340h
AN: T33C-1492    [Abstracts]
TI: Clay-clast Aggregates: A New Textural Evidence For Seismic Fault Sliding ?
AU: * BOUTAREAUD, S
EM: boutareaud@voila.fr
AF: LABORATOIRE DE GEOPHYSIQUE INTERNE ET TECTONOPHYSIQUE, MAISON DES GEOSCIENCES - BP 53 - CEDEX 09, GRENOBLE, F-38041, France
AU: FABBRI, O
EM: olivier.fabbri@univ-fcomte.fr
AF: UNIVERSITY OF FRANCHE-COMTE, DEPARTMENT OF GEOSCIENCES, 16, ROUTE DE GRAY, BESANCON, 25030, France
AU: CALUGARU, D
EM: calugaru@math.univ-fcomte.fr
AF: UNIVERSITY OF FRANCHE-COMTE, DEPARTMENT OF MATHEMATICS, 16, ROUTE DE GRAY, BESANCON, 25030, France
AU: HAN, R
EM: rhhan@korea.ac.kr
AF: KOREA UNIVERSITY, DEPARTMENT OF EARTH AND ENVIRONMENTAL SCIENCES, ANAM-DONG, SEONGBUK-GU, SEOUL, 136-701, Korea, Republic of
AU: SHIMAMOTO, T
EM: shima007@hiroshima-u.ac.jp
AF: HIROSHIMA UNIVERSITY, DEPARTMENT OF EARTH AND PLANETARY SYSTEMS SCIENCE, HIGASHI-HIROSHIMA, HIROSHIMA, 739-8526, Japan
AB: To identify the particle dynamic processes responsible of slip-weakening in clay-rich seismic slip zones, several rotary-shear experiments were conducted at coseismic slip-rates (equivalent to 0.09, 0.9 and 1.3 m/s) at a fixed normal stress of 0.6 MPa, on a natural clay-rich gouge for saturated and for non-saturated initial conditions. The representative mechanical behavior of the simulated faults show a reproducible slip-weakening behavior, whatever initial moisture conditions. Total achieved displacements are comprised between 4 and 64 m. Detailed examination of gouge obtained at the residual friction stage in saturated and non-saturated initial conditions allows to define two types of microstructure implying two deformation regimes: a rolling regime with formation of clay-clast aggregates, and a sliding regime with formation of a foliated layer localized along the gouge-wall-rock interfaces. The observed slip-weakening behavior of simulated faults appears to be related to a decrease of the proportion of grain rolling to grain sliding with increasing slip displacement. Elevation of pore fluid pressure in the first meters of slip displacement, which represents the major contribution to the total energy budget experimentally produced, is thought to create the excess space necessary for grain rolling and subsequent formation of clay- clast aggregates. Spherical aggregates have already been reported from natural environments involving rapid slip along a seismogenic fault, landslide sole discontinuity, or sole of pyroclastic flows for which such aggregates are known to be formed by accretion of a cortex around a central spherical or ellipsoidal clast in an expanded fluidized granular flow. Therefore, the occurrence of clay-clast aggregates in natural clayey fault gouges could constitute a new potential textural evidence for thermal pressurization and consequently for past-seismic fault sliding.
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8030 Microstructures
DE: 8045 Role of fluids
DE: 8123 Dynamics: seismotectonics
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: 2007 Fall Meeting