A seismic structural section across the southern Queen Charlotte transform fault zone, which separates the oceanic Pacific plate from the continental America plate off western Canada, has been determined from an offshore-onshore refraction experiment. Two explosion profiles, one parallel and one perpendicular to the fault strike, were recorded on three ocean bottom seismographs (OBS) and seven land-based seismographs (LBS). Assuming lateral homogeneity along the parallel profile recorded over oceanic crust at one OBS, one-dimensional amplitude modeling produced a velocity model with the characteristics of standard ocean crust. The partially reversed perpendicular profile recorded at two OBS's and one good quality LBS extended across the fault zone, which in bathymetric cross section shows two linear fault escarpments separated by a flat terrace. An initial velocity structure, provided by time term analysis of the complete data set, was modified by ray tracing until the travel time data for the three stations were satisfied by one seismic structural section. This model shows three distinctive crustal blocks (the oceanic, terrace, and continental blocks) separated by two major, crustally pervasive faults, the outer and inner Queen Charlotte faults. The rock units composing the terrace block have lower velocities at equivalent depths than those of the blocks on either side. This may have resulted from deformation associated with oblique convergence and/or the effects of a jump in the position of the active Queen Charlotte fault from its outer to inner positions from 1-0.5 Ma ago. Depth to the base of the crustal section increases from 12 to 18 km below sea level across the terrace zone, representing an eastward dip of about 20¿. The seismic model, after conversion to a density model, agrees well with the gravity anomaly along the profile. The interpreted structural section is consistent with recent tectonic models that require a component of convergence along the transform fault zone.