HR: 09:45h
AN: S21D-07    [Abstracts]
TI: Quantitative, Calculable, Fluid-Rock Deformation
AU: Zatsepin, S
EM: szats@glg.ed.ac.uk
AF: School of GeoSciences, Edinburgh Univ., Grant Inst., West Mains Road, Edinburgh, EH9 3JW United Kingdom
AU: * Crampin, S
EM: scrampin@ed.ac.uk
AF: School of GeoSciences, Edinburgh Univ., Grant Inst., West Mains Road, Edinburgh, EH9 3JW United Kingdom
AB: As a result of stress-aligned fluid-saturated microcracks, seismic shear-wave splitting is seen with similar parameters in almost all rocks from 1% porosity granites to 20% porosity sandstones. These microcracks are the most compliant elements of in situ rock and the response/deformation of microcracked rock can be modeled by Anisotropic Poro-Elasticity (APE). The mechanism is based on the unique correspondence between the distribution of fluid-filled microcracks and the evolving differential stress field in all fluid-saturated rocks. Numerical modeling with APE matches a huge range of phenomena. These include: accurate 3C reflection surveys, where the response to both high- and low-pressure CO2-injections was matched exactly; and monitoring stress-accumulation before earthquakes, where on one occasion the time and magnitude of a M 5 earthquake was successfully stress-forecast in SW Iceland. There are many other important implications. The rock mass is highly compliant and varies spatially and temporally. This means that high-resolution seismic measurements may degrade (by one or two ms) from the moment they are recorded. (The key to achieving such accuracy is using the highly repeatable shear-wave source, the Downhole Orbital Vibrator.) In contrast, if appropriate data are available the response of the rock mass to known changes can be calculated or predicted. Consequently, if changes in conditions are known, the response of in situ rock can be controlled by feedback. Note that the key observable is shear-wave splitting. P-waves are sensitive to many phenomena, but only stress-controlled shear-wave splitting that can monitor the evolution of fluid-saturated microcracked rock. As a result the understanding of shear-wave splitting has advanced substantially in the last few years. Recent papers and preprints can be found at http://www.glg.ed.ac.uk/$\sim$scrampin/opinion/.
DE: 7260 Theory and modeling
DE: 8168 Stresses--general
DE: 7203 Body wave propagation
DE: 3902 Creep and deformation
SC: Seismology [S]
MN: 2004 AGU Fall Meeting