Seismic structure of the crust and upper mantle in the Peace River Arch region

Colin Andrew Zelt
The Peace River Arch (PRA) is a regional ~E-W trending geological structure within the Western Canada Sedimentary Basin whose Phanerozoic history of vertical movements is anomalous with respect to the basin as a whole. Four intersecting ~300-km-long reversed refraction lines within the PRA region in northwestern Alberta and northeastern British Columbia have been interpreted for crustal and upper mantle P-wave velocity structure. The data have been analyzed using a new two-dimensional ray-trace
more » ... forward modelling algorithm to match travel times and amplitudes of first and coherent later arrivals. An inversion of first arrival travel times along a fan shot profile has been performed to constrain crustal thickness northwest of the arch in a region not sampled by the in-line profiles. 5-waves and the observed spectra of the refraction data have been analyzed to infer a regional Poisson's ratio and Q structure, respectively. The consistency of the seismic models with the observed Bouguer gravity data was studied. The new algorithm for tracing rays and calculating amplitudes in two-dimensional media is based on a simple, layered, large-block velocity model parameterization in which velocity is an analytic function of position. This allows for computationally efficient ray tracing. The user's ability to specify kinematically-similar ray families permits practical and rapid forward modelling of refraction data. In addition, the routine allows for 5-wave propagation, converted phases, multiple and surface reflections, approximate attenuation, head waves, a simulation of smooth layer boundaries, and a reverse ray-direction amplitude calculation. Amplitude calculations are based on zero- and first-order asymptotic ray theory. The main attributes of the routine are illustrated with several examples. The major features of the interpreted structural model of the PRA region are (1) weak to moderate lateral variations in crustal structure with no evidence of significant layering or thick low-velocity zones within the crust, [...]
doi:10.14288/1.0052504 fatcat:2xbcoloa75dtldosn42vpp32zy