HR: 0800h
AN: S41B-0963 INVITED     [Abstracts]
TI: Induced Seismicity at the Canadian Underground Research Laboratory 1987-2004
AU: * Young, R P
EM: paul.young@utoronto.ca
AF: University of Toronto, Lassonde Institute, 170 College Street,, Toronto, M5S3ES Canada
AU: Collins, D
EM: dave@seismology.org
AF: University of Toronto, Lassonde Institute, 170 College Street,, Toronto, M5S3ES Canada
AB: The Underground Research Laboratory (URL) is a facility established by Atomic Energy of Canada Ltd. (AECL) in Manitoba to investigate the rock mechanical and geotechnical aspects of the safe geological disposal of radioactive waste. It represents a unique facility to study the fundamental behaviour of initially unfractured granite in situ. The facility consists of a network of tunnels that have been excavated at a depth of 420 meters below the surface. As part of the extensive suite of instrumentation installed to monitor the rock mass behaviour both a microseismic (detecting events in the -4 $<$ M $<$ -1 range) and an ultrasonic (detecting events in the -7 $<$ M $<$ -5 range) system were installed. These systems will detect the formation of, and movement on, cracks ranging in size from cms down to the grain boundary scale. During the excavation of the tunnel network at the 420m level of the URL an extensive data-set of induced seismicity data was recorded from which an understanding of the rock mass response was obtained. This seismicity was concentrated in zones of `excavation disturbance' around the tunnels, and the activity level was observed to fall away to almost nothing a few days after the excavation was complete in each tunnel section. However these disturbed zones are observed to be only meta-stable, as further perturbations of the system result in a re-activation of the damage zone. This has been observed, for example, when; (1) Loose material has been removed from the tunnel floor resulting in observed seismicity in the rock beneath the floor; (2) Activity associated with heating of the rock during a series of "heated-failure tests"; (3) Activity in the roof and floor of nearby tunnels during the excavation of new galleries. The system can therefore be considered to be at best meta-stable, with very small changes in the stress resulting in induced seismic activity. This fact, together with the extensive instrumentation suite available with which to detect small changes in the rock response, makes this site ideal for studying remotely triggered seismicity. Results from studies since 1987 and the insights gained for earthquake seismology and future proposed underground earth science research facilities will be described.
UR: http://www.lassondeinstitute.utoronto.ca/young/research/url/url.html
DE: 8123 Dynamics, seismotectonics
DE: 5102 Acoustic properties
DE: 5104 Fracture and flow
DE: 7209 Earthquake dynamics and mechanics
DE: 1734 Seismology
SC: Seismology [S]
MN: 2004 AGU Fall Meeting