HR: 1330h
AN: S22A-0425    [PDF]
TI: Creep: Long-term Time-Dependent Rock Deformation in a Deep-sea Laboratory in the Ionian sea: a Pilot Study
AU: * Meredith, P G
EM: p.meredith@ucl.ac.uk
AF: Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT Italy
AU: Boon, S
EM: s.boon@ucl.ac.uk
AF: Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT Italy
AU: Vinciguerra, S
EM: sergio.vinciguerra@ct.infn.it; vinciguerra@ov.ingv.it
AF: Osservatorio Vesuviano - Istituto Nazionale di Geofisica e Vulcanologia, Via Diocleziano 328, Naples, 80124 Italy
AU: Vinciguerra, S
EM: sergio.vinciguerra@ct.infn.it; vinciguerra@ov.ingv.it
AF: Dipartimento di Fisica e Astronomia, Universita di Catania, Via S. Sofia 64, Catania, 95123 Italy
AU: Bowles, J
EM: j.bowles@ucl.ac.uk
AF: Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT Italy
AU: NEMO Group, .
EM: riccobene@lns.infn.it
AF: Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Via S. Sofia 44, Catania, 95123 Italy
AB: Time-dependent brittle rock deformation is of first-order importance for understanding the long-term behavior of water saturated rocks in the Earth's upper crust. Interpretation of results from traditional laboratory brittle creep experiments have generally been in terms of three individual creep phases; primary (decelerating), secondary (constant strain rate or quasi-steady-state) and tertiary (accelerating or unstable). The deformation may be distributed during the first two, but localizes onto a fault plane during phase three. More recently, models have been proposed that explain the trimodal shape of creep curves in terms of the competition between a weakening mechanism and a strengthening mechanism, with the weakening mechanism eventually dominating and leading to localized failure. However, a major problem is that it is difficult to distinguish between these competing mechanisms and models given the lower limit of strain rates achievable in laboratory experiments over practicable time scales.\\ This study aims to address that problem directly by extending significantly the range of achievable strain rates through much longer-term experiments conducted in a deep-sea laboratory in the Ionian sea. The project takes advantage of a collaboration with the NEMO Group-INFN, a consortium that is developing a large volume (1 km3) deep-sea detector for high-energy ($>$1019 eV) cosmic neutrinos. A suitable test site has been identified, some 20km north-east of Catania in Sicily, at a depth of 2100m.\\ Within the CREEP deformation apparatus, confining pressure is provided by the ambient water pressure ($>$22MPa), and the constant axial stress is provided by an actuator that amplifies this pressure. Measurement transducers and a data acquisition system are sealed internally, with power provided for up to 6 months by an internal battery pack. The great advantage of operating in the deep sea in this way is that the system is essentially passive, has few moving parts, and requires no maintenance. The apparatus is held in place by a disposable cast-iron anchor and supported above the seabed by a deep-sea buoyage system. On completion of each experiment, an acoustic release detaches from the anchor and allows the apparatus to float to the surface to be recovered by the oceanographic research vessel.
DE: 3902 Creep and deformation
DE: 5104 Fracture and flow
SC: Seismology [S]
MN: 2003 Fall Meeting