TITLE

Crustal velocity structure of the southern Nechako basin, British Columbia, from wide-angle seismic traveltime inversion

AUTHOR(S)
Stephenson, A.L.; Spence, G.D.; Wang, K.; Hole, J.A.; Miller, K.C.; Clowes, R.M.; Harder, S.H.; Kaip, G.M.; Mareschal, Jean-Claude
PUB. DATE
June 2011
SOURCE
Canadian Journal of Earth Sciences;Jun2011, Vol. 48 Issue 6, p1050
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
In the BATHOLITHS onland seismic project, a refraction - wide-angle reflection survey was shot in 2009 across the Coast Mountains and Interior Plateau of central British Columbia. Part of the seismic profile crossed the Nechako Basin, a Jurassic-Cretaceous basin with potential for hydrocarbons within sedimentary strata that underlies widespread volcanic rocks. Along this 205 km-long line segment, eight large explosive shots were fired into 980 seismometers. Forward and inverse modelling of the traveltime data were conducted with two independent methods: ray-tracing based modelling of first and secondary arrivals, and a higher resolution wavefront-based first-arrival seismic tomography. Material with velocities less than 5.0 km/s is interpreted as sedimentary rocks of the Nechako Basin, while velocities from 5.0-6.0 km/s may correspond to interlayered sedimentary and volcanic rocks. The greatest thickness of sedimentary rocks in the basin is found in the central 110 km of the profile. Two sub-basins were identified in this region, with widths of 20-50 km and maximum sedimentary depths of 2.5 and 3.3 km. Such features are well-defined in the velocity model, since resolution tests indicate that features with widths greater than ∼13 km are reliable. Beneath the sedimentary rocks, seismic velocities increase more slowly with depth - from 6.0 km/s just below the basin to 6.3 km/s at ∼17 km in depth, and then to 6.8-7.0 km/s at the base of the crust. The Moho is found at a depth of 33.5-35 km beneath the profile, and mantle velocities are high at 8.05-8.10 km/s.
ACCESSION #
65537125

 

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