Rethinking turbidite paleoseismology along the Cascadia subduction zone

A stratigraphic synthesis of dozens of deep-sea cores, most of them overlooked in recent decades, provides new insights into deep-sea turbidites as guides to earthquake and tsunami hazards along the Cascadia subduction zone, which extends 1100 km along the Pacific coast of North America. The synthes...

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Bibliographic Details
Published in:Geology (Boulder) 2014-09, Vol.42 (9), p.827-830
Main Authors: Atwater, Brian F, Carson, Bobb, Griggs, Gary B, Johnson, H. Paul, Salmi, Marie S
Format: Article
Language:English
Subjects:
Cascadia subduction zone
Cenozoic
channels
cores
currents
depositional environment
Earthquakes
East Pacific
geologic hazards
Holocene
lithostratigraphy
marine sediments
natural hazards
North Pacific
Northeast Pacific
ocean floors
Pacific Ocean
paleoseismicity
Quaternary
Quaternary geology
sediment transport
Sediments
Seismic engineering
seismic risk
Stratigraphy
submarine canyons
transport
Tsunamis
turbidite
turbidity currents
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Summary:A stratigraphic synthesis of dozens of deep-sea cores, most of them overlooked in recent decades, provides new insights into deep-sea turbidites as guides to earthquake and tsunami hazards along the Cascadia subduction zone, which extends 1100 km along the Pacific coast of North America. The synthesis shows greater variability in Holocene stratigraphy and facies off the Washington coast than was recognized a quarter century ago in a confluence test for seismic triggering of sediment gravity flows. That test compared counts of Holocene turbidites upstream and downstream of a deep-sea channel junction. Similarity in the turbidite counts among seven core sites provided evidence that turbidity currents from different submarine canyons usually reached the junction around the same time, as expected of widespread seismic triggering. The fuller synthesis, however, shows distinct differences between tributaries, and these differences suggest sediment routing for which the confluence test was not designed. The synthesis also bears on recent estimates of Cascadia earthquake magnitudes and recurrence intervals. The magnitude estimates hinge on stratigraphic correlations that discount variability in turbidite facies. The recurrence estimates require turbidites to represent megathrust earthquakes more dependably than they do along a flow path where turbidite frequency appears limited less by seismic shaking than by sediment supply. These concerns underscore the complexity of extracting earthquake history from deep-sea turbidites at Cascadia.
ISSN:0091-7613
1943-2682
DOI:10.1130/G35902.1