HR: 08:30h
AN: S31D-03    [Abstracts]
TI: Structures Formed in Experimentally Sheared Artificial Fault Gouge: Precise Statistical Measurements
AU: * Dilov, T
EM: trilo@dges.tohoku.ac.jp
AF: Department of Geoenvironemental Sciences, Graduate School of Science, Tohoku University, Aza-Aramaki, Aoba-ku, Sendai, 980 8578 Japan
AU: Yoshida, S
EM: shingo@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1 Yayoi 1-chome, Bunkyo-ku, Tokyo, 113 0032 Japan
AU: Kato, A
EM: akato@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1 Yayoi 1-chome, Bunkyo-ku, Tokyo, 113 0032 Japan
AU: Nakatani, M
EM: nakatani@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1 Yayoi 1-chome, Bunkyo-ku, Tokyo, 113 0032 Japan
AU: Mochizuki, H
EM: h-mochi@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1 Yayoi 1-chome, Bunkyo-ku, Tokyo, 113 0032 Japan
AU: Otsuki, K
EM: otsuki@dges.tohoku.ac.jp
AF: Department of Geoenvironemental Sciences, Graduate School of Science, Tohoku University, Aza-Aramaki, Aoba-ku, Sendai, 980 8578 Japan
AB: The physical parameters governing earthquakes change with the ongoing formation and evolution of structures, formed in the course of a single or multiple earthquakes, within a particular fault zone or in a broad volume containing interacting tectonic faults. Our precise knowledge of these complex phenomena is still elusive. Especially, works considering geometrical evolution of shear structures under controlled conditions are rare. In order to gain some insights we accomplished a set of 12 laboratory experiments using a servo-controlled direct-shear apparatus, under room temperature and without controlling the air humidity. Two fault gouge layers (industrially produced quartz powder, average particle size of 5 $\mu$m, and pre-shear thickness of 1.5, 2.0 and 3.0 mm,) were sandwiched between three granite blocks. The middle block was slid in order to create frictional structures within the simulated gouge. The total imposed shear strain varies between 0.14 and 11.80. The post-shear gouge layer thickness ranges from 0.99-2.11 mm. Each experiment was run under a constant normal stress (varying from 10-44 MPa through the experiments) and at a constant shear velocity (0.07, 0.7 and 7 $\mu$m/s, through the experiments). Later, in cross-sections of solidified by epoxy glue gouge (parallel to the shear direction, normal to the gouge walls,) we quantified the numerous R-shears, according to their density distribution, fracture thickness (measured perpendicularly to the fracture walls), fracture angle and morphology, and fracture length. In gouge views parallel to the sliding blocks, we measured fracture length and along-strike R-shear morphology. Although the latter data are with lower quality, both observational sets provide precise statistical fracture data as well snapshots of evolving 3D structures. We observe shear localization with decreasing gouge layer thickness and with increasing normal stress. The average density of major fractures increases from 2.83 to 3.67 [fracture/cm] for decrease of the post-shear gouge layer thickness. This is at the expense of a considerable decrease of visible more diffusive minor fractures. On the other hand, the fractures formed at lower normal stress are more irregular and show average fracture density of 4.48 [fracture/cm]. The latter decreases down to 3.64 at higher normal stress, as the fracture morphology becomes more regular. The fracture density increases abruptly from zero, after a small total shear strain (0.15-0.50), and later the change is slower or none with the increase of the total shear strain; the fractures are already localized and they accommodate most of the brittle deformation. Also we observe weak polarity in fracture development in accordance to the sliding sense, especially in the subset of fractures starting from the gouge wall and dying out within the gouge layer. More such fractures are developed along the leading part of the sliding blocks. Our results throw new light over the formation and development of fault-related structures and their dependency on the earthquake-governing physical parameters.
DE: 8010 Fractures and faults
DE: 8030 Microstructures
DE: 8123 Dynamics, seismotectonics
DE: 7209 Earthquake dynamics and mechanics
DE: 3902 Creep and deformation
SC: Seismology [S]
MN: 2004 AGU Fall Meeting