HR: 1340h
AN: T33C-1391    [Abstracts]
TI: Quaternary Tectonism in a Collision Zone, Northwest Washington
AU: * McCrory, P A
EM: pmccrory@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Wolf, S C
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Intelmann, S S
EM: pmccrory@usgs.gov
AF: Olympic Coast National Marine Sanctuary, 115 E Railroad Avenue, Port Angeles, WA 98362 United States
AU: Danforth, W W
AF: US Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Weldon, R J
AF: University of Oregon, Department of Geological Sciences, Eugene, OR 97403 United States
AU: Blair, J L
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: Kinematic, geodetic, and geologic observations define a region with 6-8 mm/y of north-south contraction between the Columbia River and Vancouver Island. We attribute this contraction to differential forearc-block motion within the Cascadia subduction system where the Oregon Coast Range block is moving northward relative to Vancouver Island. The contraction is accommodated by a combination of distributed uplift in the Olympic Mountains, and faulting along the margins of the Coast Range and Vancouver Island blocks. The tide gauge at Neah Bay, which records one of the highest rates of uplift anywhere along the Cascadia subduction margin, suggests that a significant portion of this north-south contraction occurs between the northern Olympic Peninsula and Vancouver Island. The northwest-trending Calawah fault, extending from Makah Bay eastward to near Lake Crescent, appears to mark the modern boundary between the Olympic Mountains block and the Vancouver Island block in northwestern Washington. Onshore, the 80+ km-long Calawah fault displaces late Quaternary glacial sediments and geodetic uplift rates increase abruptly across the fault zone. Offshore in Makah Bay, new multibeam, sidescan-sonar, and high-resolution seismic reflection data image a complex, multi-strand fault zone that offsets the seafloor and moves Cape Flattery rocks seaward. Two parallel, northwest-trending fault strands bound a down-dropped block that in turn terminates along a northward-trending anticlinal fold and thrust fault. These data suggest that the Calawah fault zone currently accommodates contraction both by uplift and by seaward translation of rocks north of the forearc-block boundary. Our geologic mapping in the Cape Flattery area indicates that differential block motion is accommodated by a combination of crustal uplift, folding, and left-lateral, strike-slip faulting.
DE: 8015 Local crustal structure
DE: 8158 Plate motions--present and recent (3040)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
DE: 1208 Crustal movements--intraplate (8110)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting