Options
Dipartimento di Fisica e Astronomia, Universita`di Catania, Catania, Italy
2 results
Now showing 1 - 2 of 2
- PublicationOpen AccessPhysical and transport properties of isotropic and anisotropic cracked rocks under hydrostatic pressure(2006)
; ; ; ; ; ; ;Benson, P.; Mineral, Ice and Rock Physics Laboratory, University College London, London, UK. ;Schubnel, A.; Lassonde Institute, University of Toronto, Toronto, Ontario, Canada. ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Trovato, C.; Dipartimento di Fisica e Astronomia, Universita`di Catania, Catania, Italy ;Meredith, P. G.; Mineral, Ice and Rock Physics Laboratory, University College London, London, UK. ;Young, P. R.; Lassonde Institute, University of Toronto, Toronto, Ontario, Canada.; ; ; ; ; A key consequence of the presence of microcracks within rock is their significant influence upon elastic anisotropy and transport properties. Here two rock types (a basalt and a granite) with contrasting microstructures, dominated by microcracks, have been investigated using an advanced experimental arrangement capable of measuring porosity, P wave velocity, S wave velocity, and permeability contemporaneously at effective pressures up to 100 MPa. Using the Kachanov (1994) noninteractive effective medium theory, the measured elastic wave velocities are inverted using a least squares fit, permitting the recovery of the evolution of crack density and aspect ratio with increasing isostatic pressure. Overall, the agreement between measured and predicted velocities is good, with average error less than 0.05 km/s. At larger scales and above the percolation threshold, macroscopic fluid flow also depends on the crack density and aspect ratio. Using the permeability model of Gue´guen and Dienes (1989) and the crack density and aspect ratio recovered from the elastic wave velocity inversion, we successfully predict the evolution of permeability with pressure for direct comparison with the laboratory measurements. We also calculate the evolution of the crack porosity with increasing isostatic pressure, on the basis of the calculated crack density, and compare this directly with the experimentally measured porosity. These combined experimental and modeling results illustrate the importance of understanding the details of how rock microstructures change in response to an external stimulus when predicting the simultaneous evolution of rock physical properties.226 529 - PublicationRestrictedUnderstanding the seismic velocity structure of Campi Flegrei caldera (Italy): from the laboratory to the field scale(2006)
; ; ; ; ; ; ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Trovato, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Meredith, P.; Department of Earth Sciences, University College London, ;Benson, P. M.; Department of Earth Sciences, University College London, ;Troise, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;De Natale, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; ; ; ; We report laboratory measurements of P- and S-wave velocities on samples of tuff from Campi Flegrei (Italy), and a new tomographic velocity map of the Campi Flegrei caldera. Laboratory measurements were made in a hydrostatic pressure vessel during both increasing and decreasing effective pressure cycles. Selected samples were also thermally stressed at temperatures up to 600 C to induce thermal crack damage. Acoustic emission output was recorded throughout each thermal stressing experiment, and velocities were measured after thermal stressing. Laboratory P- and S-wave velocities are initially low for the tuff, which has an initial porosity of 45%, but both increase by between 25 and 50% over the effective pressure range of 5 to 80MPa, corresponding to a decrease of porosity of 70%. Marked velocity hysteresis, due to inelastic damage processes, is also observed in samples subjected to a pressurization-depressurization cycle. Tomographic seismic velocity distributions obtained from field recordings are in general agreement with the laboratory measurements. Integration of the laboratory ultrasonic and seismic tomography data indicates that the tuffs of the Campi Flegrei caldera can be water or gas saturated, and shows that inelastic pore collapse and cracking produced by mechanical and thermal stress can significantly change the velocity properties of Campi Flegrei tuffs at depth. These changes need to be taken into account in accurately interpreting the crustal structure from tomographic data.159 31