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Young, P. R.
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Young, P. R.
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- 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 - PublicationRestrictedImaging slow failure in triaxially deformed Etna basalt using 3D acoustic-emission location and X-ray computed tomography(2007-02-06)
; ; ; ; ; ;Benson, P. M.; UCL, London, UK ;Thompson, B. D.; Univ. of Toronto, Canada ;Meredith, P. G.; UCL, London, UK ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Young, R. P.; Univ. of Toronto, Canada; ; ; ; We have deformed basalt from Mount Etna (Italy) in triaxial compression tests under an effective confining pressure representative of conditions under a volcanic edifice (40 MPa), and at a constant strain rate of 5 10 6 s 1. Despite containing a high level of pre-existing microcrack damage, Etna basalt retains a high strength of 475 MPa. We have monitored the complete deformation cycle through contemporaneous measurements of axial strain, pore volume change, compressional wave velocity change and acoustic emission (AE) output. We have been able to follow the complete evolution of the throughgoing shear fault without recourse to any artificial means of slowing the deformation. Locations of AE events over time yields an estimate of the fault propagation velocity of between 2 and 4 mm/s-1. We also find excellent agreement between AE locations and post-test images from X-ray microtomography scanning that delineates deformation zone architecture. Citation: Benson, P. M., B. D. Thompson, P. G. Meredith, S. Vinciguerra, and R. P. Young (2007), Imaging slow failure in triaxially deformed Etna basalt using 3D acoustic-emission location and X-ray computed tomography174 24 - PublicationOpen AccessLinking elastic, mechanical and transport properties in anisotropically cracked rocks(2007-09-25)
; ; ; ; ; ; ;Schubnel, A.; ENS, France ;Benson, P.; UCL, UK ;Nasseri, M. H. B.; Univ. of Toronto, Canada ;Guéguen, Y.; ENS, France ;Meredith, P.; UCL, UK ;Young, P.; Univ. of Toronto, Canada; ; ; ; ; ; ; ; ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bernabé, Y.; MIT, USA; see Abstract Volume108 458 - PublicationOpen AccessLaboratory AE simulation of the transition between VT and LP events in active volcanoes(2007-09-25)
; ; ; ; ;Benson, P.; UCL, UK ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Meredith, P.; UCL, UK ;Young, P.; Univ. Toronto, Canada; ; ; ; ; ; ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bernabé, Y.see Abstract volume124 289 - PublicationRestrictedLaboratory Simulation of Volcano Seismicity(2008-10-10)
; ; ; ; ;Benson, P.; Univ. Toronto, Canada ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Meredith, P.; UCL, UK ;Young, P.; Univ. Toronto, Canada; ; ; Physical processes generating seismicity within volcanic edifices are highly complex and remain not fully understood. We report results from a laboratory experiment in which basalt from Mount Etna volcano (Italy) was deformed and fractured. The experiment was monitored using an array of transducers around the sample to permit full-waveform capture, location and analysis of microseismic events. Rapid, post-failure decompression of the water-filled pore volume and damage zone triggered many low frequency events, analogous to volcanic long period seismicity. The low-frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample; these events exhibited a weak component of shear (double-couple) slip, consistent with fluid-driven events occurring beneath active volcanoes.153 30 - PublicationRestrictedSpatio-temporal evolution of volcano seismicity: A laboratory study(2010)
; ; ; ; ;Benson, P.; UCL, UK ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Meredith, P.; UCL, UK ;Young, P.; Univ. of Toronto, Canada; ; ; We report a laboratory and microstructural study of a suite of deformation experiments in which basalt from Mount Etna volcano is deformed and fractured at an effective confining pressure representative of conditions under a volcanic edifice (40 MPa). Particular attention was paid to the formation of a fracture and damage zone with which to stimulate coupled hydro-mechanical interactions that create the various types of seismicity recorded on volcanic edifices, and which usually precede eruption. Location of AE events through time shows the formation of a fault plane during which waveforms exhibit the typical high frequency characteristics of volcano-tectonic (VT) earthquakes. We found that these VT earthquakes were particularly pronounced when generated using dry samples, compared to samples saturated with a pore fluid (water). VT events generated during deformation of water saturated sample are characterised by a distinctive high frequency onset and a longer, low frequency coda exhibiting properties often seen in the field as hybrid events. We present evidence that hybrid events are, in fact, the common type of volcanic seismic event with either VT or low frequency (LF) events representing end members, and whose proportion depend on pore fluid being present in the rock type being deformed, as well as how close the rock is to failure. We find a notable trend of reducing instances of hybrid events leading up to the failure stage in our experiments, suggesting that during this stage, the pore fluid present in the rock moves sufficiently quickly to provide a resonance, seen as a LF coda. Our data supports recent modeling and field studies that postulate that hybrid events generated in volcanic areas are likely to be generated through the interaction of hydrothermal fluids moving through a combination of pre-existing microcrack networks and larger faults, such as those we observe in forensic (post-test) examination.111 21