To better understand the effects of Laramide deformation, deep seismic reflection data in the Wind River (WR) Range area of Wyoming have been migrated using a 45° ^ohgr-Finite-difference depth migration. The algorithm allows velocity to vary laterally and with depth, contains the thin lens (or shifting) term, and correctly migrates energy in laterally varying media within the limits of a 20 algorithm and 2D dataset. Each migrated section shown is the best from a series of migrations.

Major structural features displayed in the migrated data are the Pacific Creek (PC) anticline and the WR thrust. The PC anticline is underlain by a thrust fault similar in geometry to the WR thrust. The base of the Green River basin sediments has a seismically observed vertical offset of 0.6 km. The intra-basement PC thrust reflections are as conspicuous as the WR thrust reflections, yet the movement along the PC thrust was 0.02 of that of the WR fault. The reflectivity of the PC fault is attributed to the change in seismic impedance of the fault-zone constituents. The thinning of sediments over the anticline in Late Cretaceous time (possibly Lewis, certainly earliest Lance time) indicates that the anticline is part of the Laramide deformation. The anticline continued to grow by fault ng and buckling the lower 2 km

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and folding the upper sediments during the WR thrust deformation through latest Cretaceous and Paleocene time.

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