Multicomponent seismic survey over ground-fast and floating ice, MacKenzie Delta, N.W.T.

Kevin W. Hall, Carlos E. Nieto, Eric V. Gallant, Robert R. Stewart

In the spring of 2001, the CREWES project in conjunction with Devon Canada Ltd. (formerly Anderson Exploration Ltd.) and acquired a six kilometre test line (MKD-8), centred over the transition zone from floating to ground-fast ice in the Mackenzie Delta. Several different types of receivers, including 3-C geophones were laid out, and the entire line was shot with two tracked Vibroseis vehicles, and again with dynamite. A series of sweep tests and noise strips were also recorded. A hammer seismic survey of thirty meters length was also carried out, recorded by the 3-C geophones only. The hammer seismic survey included vertical hits on the ice, forty-five degree hits in opposite directions into forty-five degree V-shaped notches chopped into the ice, and tests hitting steel plates, wood blocks or the ice directly. Ice velocities from the hammer seismic profiles give P-wave values of 3137 m/s and S-wave velocities of 1900 m/s.

A preliminary analysis of dynamite and vibrator gathers has been made. The transition from ground-fast to floating ice has a profound (and deleterious) effect on seismic data quality. The vertical component of data recorded by the 3-C geophones for the vibrator source has been processed to a brute stack, and shows good reflectivity under the ground-fast ice. Reflections are also present under the floating ice, but have a poorer signal-noise ratio and less coherence. Frequencies up to at least 90 Hz are observed in the data. There is a distinct change in reflection character across the transition zone.