BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:Quantifying Fault Damage Zone Permeability in Crystalline Rocks - Dan Faulkner (University of Liverpool) DTSTART:20081202T163000Z DTEND:20081202T173000Z UID:TALK14285@talks.cam.ac.uk CONTACT:Francis Rowland DESCRIPTION:Determining fault zone permeability is essential for understan ding a number of geological and geophysical processes. These include earth quake rupture\, crustal strength\, sub-surface fluid flow in hydrocarbon r eservoirs and around waste repositories\, and fault-hosted base metal ore deposition. In nature\, permeability is enhanced in the damage zone of fau lts\, where fracturing occurs on a wide range of scales. Here we analyze t he contribution of microfracture damage on the permeability of faults that cut through low porosity\, crystalline rocks by combining field and labor atory measurements. Microfracture densities surrounding strike-slip faults with well-constrained displacements ranging over 3 orders of magnitude (~ 0.12 m - 5000 m) have been analyzed.\n\nThe faults studied are excellently exposed within the Atacama Fault Zone\, where exhumation from 6-10 km has occurred. Microfractures in the form of fluid inclusion planes (FIPs) sho w a log-linear decrease in fracture density with perpendicular distance fr om the fault core. Damage zone widths defined by the density of FIPs scale with fault displacement\, and an empirical relationship for microfracture density distribution throughout the damage zone with displacement is deri ved. Damage zone rocks will have experienced differential stresses that we re less than\, but some proportion of\, the failure stress.\n\nAs such\, p ermeability data from progressively loaded\, initially intact laboratory s amples\, in the pre-failure region provide useful insights into fluid flow properties of various parts of the damage zone. The permeability evolutio n of initially intact crystalline rocks under increasing differential load leading to macroscopic failure was determined at water pore pressures of 50 MPa and effective pressure of 10 MPa. \n\nPermeability is seen to incre ase by up to\, and over\, two orders of magnitude prior to macroscopic fai lure. Further experiments were stopped at various points in the loading hi story in order to correlate microfracture density within the samples with permeability. By combining empirical relationships determined from both qu antitative fieldwork and experiments we present a model that allows microf racture permeability distribution throughout the damage zone to be determi ned as function of increasing fault displacement.\n\n*Some relevant refere nces*:\n\nMitchell\, T.M. and Faulkner\, D.R. Experimental measurements of permeability evolution during triaxial compression of initially intact cr ystalline rocks and implications for fluid flow in fault zones. In press: Journal of Geophysical Research\, July 2008\n\nFaulkner\, D.R.\, Mitchell\ , T.M. and Rutter\, E.H and Cembrano\, J. 2008. On the structure and mecha nical properties of large strike-slip fault zones. In: Wibberley C. A. J.\ , Kurtz W.\, Imber J.\, Holdsworth R. E. & Collettini C. (eds) The Interna l Structure of Fault Zones: Implications for Mechanical and Fluid-Flow Pro perties. Geological Society of London Special Publication 299\, 139-150\, doi: 10.1144/SP299.9.\n\nFaulkner\, D.R.\, Mitchell\, T.M.\, Healy\, D. an d Heap\, M.J. 2006. Slip on 'weak' faults by the rotation of regional stre ss in the fracture damage zone. Nature\, 444\, 922-925. doi:10.1038/nature 05353. LOCATION:Tilley Lecture Theatre\, Department of Earth Sciences END:VEVENT END:VCALENDAR