89 Advancing Earthquake Geology and Surficial Deformation from Geologic Provinces to Political Entities through Multidisciplinary High-Resolution Data

Understanding earthquakes and surface deformation requires integrating geologic, geophysical, and remote sensing data. This session welcomes research using diverse methods—paleoseismology, LiDAR, structure-from-motion photogrammetry, geochronology, and analog modeling to refine fault behavior, rupture dynamics, segmentation, and recurrence from various tectonic settings.

Monday, 20 October 2025
8:00 AM - 12:00 PM
HBGCC, 217D

2025 QG&G Kirk Bryan Award: Refined Earthquake History at the Cascadia Subduction Zone

Paper number: 89-10
Program: Technical Sessions
Time: 10:30 AM – 10:55 AM

Authors

Abstract

In our 2021 Kirk Bryan Award paper, we proposed a maximum earthquake rupture model for Cascadia that compared overlaps among age probability distributions based largely on early (1986-2015) 14C ages with large errors to correlate coastal earthquake evidence at sites from Humboldt Bay, CA to Willapa Bay, WA. Now, a new generation of onshore and offshore researchers is applying improved dating methods and increased numbers of ages to develop increasingly complex reconstructions of Cascadia’s great (magnitude >8) earthquake history. Over the past three decades the accuracy of 14C-based times of earthquakes have dramatically increased through (1) the routine use of AMS 14C samples that weigh 1-0.1 mg, (2) thorough pretreatment of single-genera samples, (3) a >5-fold increase in routine analytical precision, and (4) sedimentation-rate-based Bayesian statistical age models of earthquake sequences, rather than the single-age-bracketing, stratigraphic-position-based, models that we used in 2021. Continually improving methods of luminescence dating of quartz and feldspar sand grains (particularly on deposits of great-earthquake tsunamis), date sequences where 14C samples are lacking and(or) help us evaluate conflicting 14C ages, as do comparisons of climate proxy data from earthquake sequences with regional climate histories. New methods of dendrochronology applied to stumps of earthquake-killed trees may yield ages spanning only a few years for the most recent earthquakes. Although comparisons of different types of ages on the same earthquake contacts help evaluate ages, of greatest importance is the new focus on comparing age sequence models developed for estuarine sites with those being developed for lacustrine (turbidite) coastal sites and new offshore cores (marine turbidites). Lacustrine and offshore sites commonly host longer earthquake records with more consistent sedimentation rates and greater numbers of ages, which yield more precise reconstructions that better test earthquake histories through identifying age differences among sites.  The longer, more precise reconstructions being developed, along with a sustained interest of onshore and offshore researchers in collaboration, are helping us reach our goal of the past four decades of mapping and dating partial as well as full-margin ruptures of the past 14,000 years along the subduction zone. 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412538

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