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Sensitivity Testing of Cascadia Marine Turbidite Ages and Comparison With Onshore Megathrust Evidence

Session: Earthquake Science, Hazards and Policy in Cascadia I

Type: Oral

Date: 4/20/2021

Presentation Time: 03:00 PM Pacific

Description: 

Marine turbidite studies infer ~19 full margin ~M9 earthquakes in the past 10 kyr along the Cascadia subduction zone. This conclusion relies on several assumptions for turbidite age analysis: (1) sedimentation rate is accurately calculated from correlation between offshore turbidites and onshore subsidence events (2) basal erosion is accurately estimated from core stratigraphy and (3) local ¹⁴C marine reservoir corrections from shallow coastal sites apply to offshore foraminifera dated for marine core chronology. Furthermore, the published radiocarbon calibration used software that employs an outdated ¹⁴C marine reservoir age correction.

In this work, I isolate each variable and systematically test how prior assumptions and new calibration curves affect estimated turbidite ages. I use Calib software version 8.1.0 with the most recent Marine20 calibration curve. This new calibration curve differs from past iterations by permitting more complex and realistic changes in the carbon cycle over time. I calculate turbidite age and uncertainty using a Monte Carlo approach, where I sample each variable’s probability distribution 10,000 times. By simply updating the software used, the calculated turbidite age is ~60 years younger on average and up to several hundred years different for specific data points, compared to the published estimates. The combined effect of updating software version, slightly modifying local reservoir correction, and by uniformly sampling a wide range of sedimentation rate, rather than prescribing a single value, the calculated turbidite age is ~125 years younger on average compare to published estimates. These results highlight how recent advancements on the global marine radiocarbon calibration have a major impact on coseismic marine turbidite chronology in Cascadia. Future work on improving constraints on the spatial and temporal variation in local reservoir correction and sedimentation rate in the Pacific Northwest is critical for accurate turbidite age estimates and comparison with onshore megathrust records.

Presenting Author: Lydia M. Staisch

Student Presenter: No

Authors