THE TETON FAULT, WYOMING - TOPOGRAPHIC SIGNATURE, NEOTECTONICS, AND MECHANISMS OF DEFORMATION

We integrated geophysical and geological methods to evaluate the structural evolution of the active Teton normal fault, Wyoming, and its role in the development of the dramatic topography of Teton Range and Jackson Hole. The Teton fault bounds the precipitous eastern front of the Teton Range and is marked by large, well-preserved postglacial fault scarps that extend for 55 km along the range front. Comparison of variations in surface offsets with the topographic expression of the Teton range crest and drainage divide, and the overall structure of the range, suggests that the effects of postglacial faulting cannot be discriminated from the influence of pre-extensional structures and differential erosion on the footwall topography. In contrast, the effects of multiple scarp-forming normal faulting earthquakes are expressed by the anomalous drainage pattern and westward tilt of the hanging wall, Jackson Hole, toward the Teton fault. Kinematic boundary element fault models suggest that the westward tilt of the valley floor is the product of 110-125 m of displacement on a 45 degrees-75 degrees E dipping Teton fault in the past 25,000-75,000 years. Comparisons with historic normal faulting earthquake displacements imply that this range of displacement corresponds to 10-50, M > 7 scarp-forming earthquakes. A total throw of 2.5 to 3.5 km across the Teton fault is suggested by inverse ray-tracing and forward gravity models. These models also suggest that Laramide age structures have been offset across the Teton fault and obscure its geophysical signature but also continue to influence the structural and topographic expression of the footwall and hanging wall blocks. Paleomagnetic analyses of the similar to 2.0 Ma Huckleberry Ridge Tuff suggest that the overall westward tilt of the Teton Range is a result of about 10 degrees of west side down tilt across the Teton fault since tuff emplacement. This suggests that much if not all of the throw across the Teton fault has accumulated in the past 2 m.y. Complex demagnetization and rock magnetic behavior and local emplacement of the Huckleberry Ridge Tuff on preexisting topography preclude determination of the amount or variations in throw along strike of the Teton fault from the paleomagnetic data.