Abstract
Geophysical surveys were conducted in June, 2014 in the area offshore of Seal Rock Oregon for the purpose of characterizing potential renewable energy installation sites and cable routes from the shore seaward to the South Energy Test Site (SETS). The geophysical surveys included 1) a high‐resolution chirp multibeam sonar survey producing detailed bathymetry and backscatter coverage of the SETS area and potential cable routes; 2) A chirp sub bottom survey; 3) a boomer seismic survey; 4) a magnetic survey. The survey area can be characterized as a fold‐thrust belt associated with the Cascadia Subduction Zone, and locally dominated by the N‐S trending Seal Rock Anticline, which bring Miocene age rock to the surface in the inshore parts of the study area. The older rocks are intruded and modified by the Columbia River Basalt group flows that crop out onshore at Seal Rock. West of the Anticline, the western flank dips westward into a N‐S trending basin bounded to the west by the Stonewall Anticline. The SETS area is located in the synclinal sedimentary basin that lies between these two major structures. The major rock outcropping in the area is the probable Miocene Astoria Formation/Nye Formation rocks of the Seal Rock Anticline. A pass through the anticline axis is formed by a paleo‐channel likely linked to Beaver Creek. Initial desktop investigations suggested that the Beaver Creek paleo‐channel might offer a burial option for a cable through the extensive rock outcrops of the exposed and eroded anticline. Initial sub bottom surveys suggested that this pass was very thinly covered with sand, likely insufficient for cable burial. Other routes were investigated south of the southward plunging anticline. These additional routes avoided the major hard‐rock outcrops, but encountered outcrops of gravel and probable Pleistocene paleo landforms including paleo‐channels, paleo topography both exposed and shallowly buried, and paleo subaerial aeolian dunes. Analysis of potential cable routes using the surface and subsurface geophysical data includes mapping of subsurface paleo‐topographic and physiographic features to find the simplest routes to the SETS area.