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No description available.

Seismic imaging of shallow sediment hosted massive sulphides has not been studied in detail. In this research two shallow sediment hosted massive sulphide deposits (one deeper and larger than the other) were modeled and synthetic seismic data generated using a 2D elastic wavefield finite difference code. F-k filtering can be used to attenuating surface waves (conventional processing). This requires small trace spacing so that spatially aliasing of energy is avoided. An alternative to this involves avoiding the surface wave using an optimum offset window technique. Both of these approaches, attenuation and avoidance, produce a high amplitude image of the deeper larger orebody. For the smaller, shallower orebody, conventional processing produced only a weak image of the orebody. However, there is a significant amount of shear wave energy from this target, and therefore multicomponent geophones should be used to capture this energy.

Oil and gas exploration in Northern Canada uses explosive-based seismic techniques to locate hydrocarbon reserves beneath waterbodies not frozen to the bottom. The use of explosives in, or near, waterbodies has the potential to harm fishes, primarily through instantaneous pressure changes (IPCs) generated from the detonations. These IPCs can damage soft tissues through the rapid compression and expansion of the swimbladder as the pressure wave passes. In Canada, a document entitled Guidelines for the Use of Explosives In or Near Canadian Fisheries Waters recommends that peak pressures not exceed 100 kPa for the protection of fish, however damage has been reported below this level. To simulate seismic exploration and examine potential pathological changes surrounding the current Guideline, fish across different developmental stages and with varying degrees of swimbladder presence were exposed to a variety of explosive based IPC levels in field experiments. Early life stages of rainbow trout (Oncorhynchus mykiss) including eyed eggs, sac fry, and juveniles were caged and exposed to discrete detonations from 0 to 280 kPa in the Mackenzie Delta, NWT. These fish were subsequently examined for both gross pathological and histological changes to cranial structures as well as swimbladder, kidney, liver and gill tissue. Results showed changes in both the area and circumference of the cranial region of eyed eggs, as well as swimbladder, ocular and kidney damage in juveniles. Additionally, caged adult swimbladder bearing lake trout (Salvelinus namaycush) and non-swimbladder bearing slimy sculpin (Cottus cognatus) were exposed to explosive based IPCs ranging in peak pressure from 0 to 127 kPa at the Experimental Lakes Area, Ontario. Fish were later examined grossly and blood, liver, kidney, intestine, and spleen were examined to determine the presence of any traumatic based pathological changes. Results indicated the occurrence of swimbladder hemorrhage in lake trout exposed to IPCs near the current Guideline level. Finally, a risk assessment for lake trout of the Mackenzie Delta exposed to IPCs was undertaken; to examine the potential for adverse risk to individuals and populations, and the likelihood of populations being unable to recover. Based on the findings of the aforementioned studies, the recommended Guideline level is not protective of early life stages of rainbow trout and furthermore represents the threshold at which damage to the swimbladder in adult lake trout does not occur, as such, a re-examination of the recommended Guideline level is warranted.

Seismic imaging of shallow sediment hosted massive sulphides has not been studied in detail. In this research two shallow sediment hosted massive sulphide deposits (one deeper and larger than the other) were modeled and synthetic seismic data generated using a 2D elastic wavefield finite difference code. F-k filtering can be used to attenuating surface waves (conventional processing). This requires small trace spacing so that spatially aliasing of energy is avoided. An alternative to this involves avoiding the surface wave using an optimum offset window technique. Both of these approaches, attenuation and avoidance, produce a high amplitude image of the deeper larger orebody. For the smaller, shallower orebody, conventional processing produced only a weak image of the orebody. However, there is a significant amount of shear wave energy from this target, and therefore multicomponent geophones should be used to capture this energy.

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No description available.

No description available.

Three possible mechanisms for the onset of excess pore water pressure generation due to seismic excitation of saturated soil are investigated using downhole array data from sixteen real earthquakes. The downhole data are used to synthesize both stress and strain at various depths within the ground. Stresses, strains and dissipated energy are then investigated as potential liquefaction trigger mechanisms. The hypothesis that the shear strain threshold is a liquefaction trigger mechanism is strongly supported by the results presented here. In all but one case the shear strain threshold accurately predicts the time of pore pressure rise for real earthquakes in the field. Additionally, the onset of energy dissipation is found to signal the initial rise in measured excess pore pressure remarkably accurately. The results suggest a fundamental link between Nemat-Nasser and Shokooh's pore pressure - dissipated energy.density relationship (1979) and Mindlin and Deresiewicz's (1953) theoretical strain threshold. Mindlin and Deresiewicz's work (1953) defined a theoretical strain threshold as the mechanism for the onset of gross sliding, and 'its associated energy dissipation'. Therefore the onset of energy dissipation constitutes a second, independent verification of the strain threshold hypothesis. The relationship between stress invariants and pore pressure increase is less clear. To date there does not appear to be an acceptable theory that describes a trigger mechanism in terms of stress alone.