Winona basin, West Coast Canada: Crustal structure from marine seismic studies
Winona basin is a deep water sedimentary basin forming part of Explorer plate and located off the northern end of Vancouver Island, British Columbia. During 1975 a deep seismic sounding survey, using explosive charges and multiple hydrophones as receivers, was carried out over the basin. Three reversed refraction profiles were shot, one along and two across the basin. A preliminary look at data along the basin indicated reasonable lateral homogeneity so interpretation was based on both travel time and amplitude characteristics through the use of synthetic seismograms. However, the two profiles across the basin indicated significant lateral variations in crustal structure, so a ray tracing approach was used. The sediments of Winona basin have a maximum thickness of approximately 5 km, consisting of approx.2 km of low-velocity (average approx.2.5 km/s) layers and approx.3 km of higher-velocity (approx.4.3 km/s) material. Beneath the sediments there is a rapid increase in velocity to approx.5.4 km/s, the top of the oceanic crust. Below this and along the basin, the interpretation indicates three zones with thicknesses of 1 to 3 km and having low-velocity gradients; these being separated by transition zones with depth intervals less than 1 km and having high-velocity gradients. The three zones with low-velocity gradients are represented approximately by 1 km at 5.4 km/s, 2.7 km at 6.2 km/s, and 2.5 km at 6.7 km/s. With the inclusion of the zones of high-velocity gradient, an average subsedimentary crustal velocity of approx.6.3 km/s and thickness of approx.8 km are obtained. The upper mantle velocity is approx.7.8 km/s. Across the basin, the crustal model shows layers dipping eastward from the westward side, forming a bowllike structure. Two-dimensional gravity calculations based on the seismic model are compatible with a gravity profile derived from a free air anomaly map.
- Research Organization:
- Department of Geophysics and Astronomy, University of British Columbia, Vancouver, Canada V6T 1W5
- OSTI ID:
- 6767907
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 86:B1, Issue B1
- Country of Publication:
- United States
- Language:
- English
Similar Records
Upper crustal structure of the Yellowstone Caldera from seismic delay time analyses and gravity correlations
1978 Yellowstone-eastern Snake River Plain seismic profiling experiment: Data and upper crustal structure of the Yellowstone region