Rethinking turbidite paleoseismology along the Cascadia subduction zone

Geology
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Abstract

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.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Rethinking turbidite paleoseismology along the Cascadia subduction zone
Series title Geology
DOI 10.1130/G35902.1
Volume 42
Issue 9
Year Published 2014
Language English
Publisher Geological Society of America
Contributing office(s) Earthquake Science Center
Description Article: 4 p.; Supplemental figure
First page 827
Last page 830
Country Canada, United States
Other Geospatial Cascadia subduction zone