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In the BATHOLITHSonland 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.

APPENDICES (2) 1994 recording of airgun signals on a 4.2-km-long seismic streamer towed by the R.V. Ewing along the offshore parts of Lines 1, 2, and 3 (Brocher and others, 1995) (3) 1994 recording of airgun signals on ocean-bottom seismographs along the offshore parts of Lines 1 and 2 (ten Brink and others, 1996) (4) 1994 onshore recording of the airgun signals along Lines 1, 2, and 3 (Okaya and others, 1996a) (5) 1994 onshore recording of earthquakes along Lines 1, 2, and 3 (8-day period) (Okaya and others, 1996b). (6) 1994 recording of borehole explosions along Line 1 (Murphy and others, 1996) (7) 1997 recording of local and distant earthquakes along Line 1 in the Los Angeles basin (9-month period) (Kohler and others, 2000) (8) 1998-1999 recording of local and distant earthquakes along Line 2 (6.5-month period) (Kohler and Kerr, in preparation) A variety of seismic instrumentation was used in these imaging surveys and was obtained from collaborators from around the world, including the Geological Survey of Canada (

Lemon Creek Glacier, a temperate valley glacier in the Juneau Icefield of Southeast Alaska, is the site of long running (>60 years) glaciological studies. However, the most recent published estimates of its thickness and subglacial topography come from two ~50 years old sources that are not in agreement and do not account for the effects of years of negative mass balance. We collected a 1-km long active-source seismic line on the upper section of the glacier parallel and near to the centerline of the glacier, roughly straddling the equilibrium-line altitude. We used these data to perform joint reflection-refraction velocity modeling and reflection imaging of the glacier bed. We find that this upper section of Lemon Creek Glacier is as much as 150 m (~65%) thicker than previously suggested with a large overdeepening in an area previously believed to have a uniform thickness. Our results lead us to reinterpret the impact of basal motion on ice flow and have a significant impact on expectations of subglacial hydrology. We suggest that further efforts to develop a whole-glacier model of subglacial topography are necessary to support studies that require accurate models of ice thickness and subglacial topography.

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