Late Quaternary Crustal Deformation Along the Cascadia Subduction Zone in Southern and Central Coastal Oregon

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Research objectives are the following: (1) to map marine terraces in four field areas where at least four flights of marine terraces are present; (2) to establish numerical ages of terraces through collection of datable material form terrace deposits; (3) to study soil development on marine terraces for identifying soil chronosequences and soil chronofunctions, correlating terraces based on soil development, and investigating capabilities of a computer-simulation model for assigning numerical ages to marine terraces; (4) to correlate terraces among study sites; and (5) to analyze late Quaternary deformation. The last objective entails compilation of absolute magnitudes of deformation at the different sites, compilation of uplift, tilt and fault-slip rates, and determination of the extent to which deformation is segmented into structural domains along the coast. We anticipate that we will be successful in assigning numerical ages to at least the lower one or two terraces at each study site. If the soil development simulation model is feasible, then numerical ages of all terraces are a possibility. Mapping to date (described below) demonstrates that deformation along the southern coast of Oregon is not uniform in space or in time, but rather the coast is segmented into broad warps. Faults are associated with these broad warps, and some of these faults appear to be boundaries of structural segments. Therefore, we also anticipate that we will be able to identify tectonic segments that have different coastline lengths, areas, and deformation rates (or ranges of rates). Both the lengths of segments and the relative ages of deformation within these segments should serve as a basis for identifying segments of the coast with different characteristic tectonic responses to subduction.