Integrated Studies of Internal and Permeability Structures, and Rheological Properties of Fault Zones

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Despite enormous amount of descriptions on faults in geological literature, the nature of faults and fault zones are not yet fully elucidate-d owing to the lack of unified viewpoint for comprehensive and interdisciplinary studies of faults. The purpose of this study is to pose a prototype of integrated fault study based on the analyses of natural fault zones and on laboratory deformation and fluid-flow experiments trying to reproduce intrafault processes in nature and determine physical properties of faults. The present research fund was to used to purchase a precise surface grinder and a lathe, and this nearly completed the specimen preparation laboratory after the principal investigator (T. Shimamoto) moved to Kyoto University two years ago. A new method of drilling through a fault zone was attempted for Nojima fault using pressurized air and bubble as coolant and lubricator, without using mud water as in ordinary drilling which is likely to damage fragile fault rocks and change thei … More r permeability. The drilling was proven to be effective in collecting nearly intact fault gouge and breccia. The major outcomes of the present research are as follows :Internal and permeability structures of fault-zonesFault-zone permeability structure is not known well irrespective of its crucial significance in fluid circulation in fault zones and in thermal pressurization of pore fluid at and prior to seismic fault motion. Thus a new servo-controlled gas apparatus was used to study permeability structures of Nojima fault, Neodani fault, Median Tectonic line and Yanagase fault. The results have revealed that the fault zones consist of very impermeable fault gouge and fault breccia zones with quite variable permeability. Internal and permeability structures of fault zones are very variable, and thermal pressurization may or may not occur depending on fault zones. The present work will be extended to the examination of other faults and to permeability measurements at high temperatures.High-velocity friction of faults and earthquake-generating processesExperiments on the slip-weakening processes during frictional melting using a high-velocity rotary shear apparatus have revealed that the weakening is caused by the growth of molten layer, not by the reduction of melt viscosity. This suggests that the rate of melting, rather than the surface topography of faults, is the most critical factor in determining the slip weakening distance (a critical parameter for fault instability). This work will be extended to high-velocity friction experiments under pore-water pressure. Less