Turbidite Event History—Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone

摘要: Turbidite systems along the continental margin of Cascadia Basin from Vancouver Island, Canada, to Cape Mendocino, California, United States, have been investigated with swath bathymetry; newly collected and archive piston, gravity, kasten, box cores; accelerator mass spectrometry radiocarbon dates. The purpose this study is test applicability Holocene turbidite record as a paleoseismic for subduction zone. an ideal place develop paleoseismologic method paleoearthquakes because (1) single subduction-zone fault underlies submarine-canyon systems; (2) multiple tributary canyons variety sedimentary sources exist use in tests synchronous triggering; (3) trench completely sediment filled, allowing channel trend seaward across abyssal plain, rather than merging trench; (4) shelf wide, favoring disconnection river their largely Pleistocene canyons; (5) excellent stratigraphic datums, including Mazama ash distinguishable sedimentological faunal changes near PleistoceneHolocene boundary, are present correlating events anchoring temporal framework. Multiple tributaries Channel 50to 150km spacing, wide other different contain 13 post-Mazama-ash 19 turbidites. Likely correlative sequences found Channel, Juan de Fuca off Washington, Hydrate Ridge slope basin Astoria Fan northern central Oregon. A probable sequence turbidites also cores on Rogue Apron southern include 12–22 interspersed thinner beds respectively. We 14C dates, relative-dating at confluences, correlation determine whether deposited separate correlative—triggered by common event. In most cases, these can earthquake-triggered turbidity currents possible sources. 10,000-year passes several triggering correlates well shorter onshore record. synchroneity turbidite-event 500 km half zone best explained great earthquakes. Similarly, we find likely Cascadia, correlated additional margin. examine regional triggers, such storm waves, surges, hyperpycnal flows, teletsunami, specifically average age oldest emplacement event 10–0-ka series 9,800±~210 cal yr B.P. youngest 270±~120 B.P., indistinguishable A.D. 1700 (250 B.P.) earthquake. define earthquake recurrence ~500–530 years. times averages supported thickness hemipelagic between beds. Oregon California margins represent least three segments that all ruptures, ~22 restricted latitude range sites. At two sites, Trinidad Eel Canyon/pools, turbidites, which may be mix sedimentologically or storm-triggered events, particularly during early when close connection existed associated systems. combined correlations, analysis, framework suggest has rupture modes: 19–20 full-length nearly 1 State University, Corvallis, OR 2 Instituto Andaluz Ciencias del la Tierra, Universidad Granada, Spain 3 Institute Geochemistry, Siberian Branch Russian Academy Sciences, Irkutsk, Russia; Chevron Energy Technology Company, Houston, TX 4 Centre Mediterrani d’Investigacions Marines i Amvientals Unitat Tecnologia Marina, Barcelona, 5 Department Earth Environmental East Bay, Hayward, CA 6 Geological Survey Canada—Pacific, Sydney, B.C., Canada 7 Canada; Royal Roads Victoria, 8 U.S. Survey, Menlo Park, Event History—Methods Implications Paleoseismicity Subduction Zone full length ruptures; four ruptures comprising 50–70 percent margin; 18–20 smaller southernmargin past 10 k.y., possibility southern-margin presently uncorrelated. extents correspond spatial interpreted limited record, supporting segmentation Cascadia. 41 defines period ~240 years k.y. Time-independent probabilities segmented 7–12 50 ~21 rupture. Time-dependent similar ~7–12 37–42 Failure analysis suggests year 2060, will exceeded ~27 intervals 85 long established allows models rarely elsewhere. per reveals consistent many infer larger Mass magnitude estimates correlate modestly following time each event, suggesting weakly support time-predictable model recurrence. pattern clustered earthquakes includes five cycles separated unusually intervals. longer function high supply incoming plate, smoothing asperities, potential barriers. sections potentially greater interaction lowerplate upper-plate heterogeneities. 42° 40° 44° 46° 48° 130° 128° 126° 124°