scholarly journals Supplemental Material: Minimal stratigraphic evidence for coseismic coastal subsidence during 2000 yr of megathrust earthquakes at the central Cascadia subduction zone

2020 ◽  
Author(s):  
A.R. Nelson ◽  
et al.
Keyword(s):  
Transfer Function ◽  
Subduction Zone ◽  
Tidal Marsh ◽  
Cascadia Subduction Zone ◽  
Radiocarbon Age ◽  
Megathrust Earthquakes ◽  
Sampling Locations ◽  
Data Summaries

Includes tables and imagery showing core and sampling locations; figures showing stratigraphy at additional sites and results of transfer function reconstructions of elevation using diatom floras from core S; tables of foraminiferal and diatom data; summaries of previous investigations; the tidal marsh setting of our study site; methods of measuring sampling elevations; explanation of variance added to radiocarbon age errors; and listing of code for OxCal radiocarbon age models.

scholarly journals Supplemental Material: Minimal stratigraphic evidence for coseismic coastal subsidence during 2000 yr of megathrust earthquakes at the central Cascadia subduction zone

2020 ◽  
Author(s):  
A.R. Nelson ◽  
et al.
Keyword(s):  
Transfer Function ◽  
Subduction Zone ◽  
Tidal Marsh ◽  
Cascadia Subduction Zone ◽  
Radiocarbon Age ◽  
Megathrust Earthquakes ◽  
Sampling Locations ◽  
Data Summaries

Includes tables and imagery showing core and sampling locations; figures showing stratigraphy at additional sites and results of transfer function reconstructions of elevation using diatom floras from core S; tables of foraminiferal and diatom data; summaries of previous investigations; the tidal marsh setting of our study site; methods of measuring sampling elevations; explanation of variance added to radiocarbon age errors; and listing of code for OxCal radiocarbon age models.

scholarly journals A maximum rupture model for the central and southern Cascadia subduction zone—reassessing ages for coastal evidence of megathrust earthquakes and tsunamis

2021 ◽  
Vol 261 ◽  
pp. 106922
Author(s):  
Alan R. Nelson ◽  
Christopher B. DuRoss ◽  
Robert C. Witter ◽  
Harvey M. Kelsey ◽  
Simon E. Engelhart ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Cascadia Subduction Zone ◽  
Megathrust Earthquakes ◽  
Rupture Model

scholarly journals Minimal stratigraphic evidence for coseismic coastal subsidence during 2000 yr of megathrust earthquakes at the central Cascadia subduction zone

Geosphere ◽  
2020 ◽  
Author(s):  
Alan R. Nelson ◽  
Andrea D. Hawkes ◽  
Yuki Sawai ◽  
Ben P. Horton ◽  
Rob C. Witter ◽  
...  
Keyword(s):  
Transfer Function ◽  
Sea Level ◽  
Function Analysis ◽  
Detection Threshold ◽  
Cascadia Subduction Zone ◽  
Tsunami Deposit ◽  
Diatom Assemblages ◽  
14C Dating ◽  
Megathrust Earthquakes ◽  
Transfer Function Analysis

Lithology and microfossil biostratigraphy beneath the marshes of a central Oregon estuary limit geophysical models of Cascadia megathrust rupture during successive earthquakes by ruling out >0.5 m of coseismic coastal subsidence for the past 2000 yr. Although the stratigraphy in cores and outcrops includes as many as 12 peat-mud contacts, like those commonly inferred to record sub­sidence during megathrust earthquakes, mapping, qualitative diatom analysis, foraminiferal transfer function analysis, and 14C dating of the contacts failed to confirm that any contacts formed through subsidence during great earthquakes. Based on the youngest peat-mud contact’s distinctness, >400 m distribution, ∼0.6 m depth, and overlying probable tsunami deposit, we attribute it to the great 1700 CE Cascadia earthquake and(or) its accompanying tsunami. Minimal changes in diatom assemblages from below the contact to above its probable tsunami deposit suggest that the lower of several foraminiferal transfer function reconstructions of coseismic subsidence across the contact (0.1–0.5 m) is most accurate. The more limited stratigraphic extent and minimal changes in lithology, foraminifera, and(or) diatom assemblages across the other 11 peat-mud contacts are insufficient to distinguish them from contacts formed through small, gradual, or localized changes in tide levels during river floods, storm surges, and gradual sea-level rise. Although no data preclude any contacts from being synchronous with a megathrust earthquake, the evidence is equally consistent with all contacts recording relative sea-level changes below the ∼0.5 m detection threshold for distinguishing coseismic from nonseismic changes.

Subduction zone heterogeneity observed across the magnitude spectrum for megathrust earthquakes

2021 ◽  
Author(s):  
Susan Bilek ◽  
Emily Morton
Keyword(s):  
Spatial Heterogeneity ◽  
Subduction Zone ◽  
Stress Drop ◽  
Subduction Zones ◽  
Cascadia Subduction Zone ◽  
Ocean Bottom ◽  
Small Earthquake ◽  
Megathrust Earthquakes ◽  
Seismic Slip ◽  
Subduction Zone Earthquakes

<p>Observations from recent great subduction zone earthquakes highlight the influence of spatial geologic heterogeneity on overall rupture characteristics, such as areas of high co-seismic slip, and resulting tsunami generation.  Defining the relevant spatial heterogeneity is thus important to understanding potential hazards associated with the megathrust. The more frequent, smaller magnitude earthquakes that commonly occur in subduction zones are often used to help delineate the spatial heterogeneity.  Here we provide an overview of several subduction zones, including Costa Rica, Mexico, and Cascadia, highlighting connections between the small earthquake source characteristics and rupture behavior of larger earthquakes.  Estimates of small earthquake locations and stress drop are presented in each location, utilizing data from coastal and/or ocean bottom seismic stations.  These seismicity characteristics are then compared with other geologic and geophysical parameters, such as upper and lower plate characteristics, geodetic locking, and asperity locations from past large earthquakes.  For example, in the Cascadia subduction zone, we find clusters of small earthquakes located in regions of previous seamount subduction, with variations in earthquake stress drop reflecting potentially disrupted upper plate material deformed as a seamount passed.  Other variations in earthquake location and stress drop can be correlated with observed geodetic locking variations. </p>

scholarly journals Toward an Integrative Geological and Geophysical View of Cascadia Subduction Zone Earthquakes

2021 ◽  
Vol 49 (1) ◽  
Author(s):  
Maureen A.L. Walton ◽  
Lydia M. Staisch ◽  
Tina Dura ◽  
Jessie K. Pearl ◽  
Brian Sherrod ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Pacific Northwest ◽  
Current Knowledge ◽  
Cascadia Subduction Zone ◽  
Annual Review ◽  
Publication Date ◽  
Data Sets ◽  
Megathrust Earthquake ◽  
Megathrust Earthquakes ◽  
National Boundaries

The Cascadia subduction zone (CSZ) is an exceptional geologic environment for recording evidence of land-level changes, tsunamis, and ground motion that reveals at least 19 great megathrust earthquakes over the past 10 kyr. Such earthquakes are among the most impactful natural hazards on Earth, transcend national boundaries, and can have global impact. Reducing the societal impacts of future events in the US Pacific Northwest and coastal British Columbia, Canada, requires improved scientific understanding of megathrust earthquake rupture, recurrence, and corresponding hazards. Despite substantial knowledge gained from decades of research, large uncertainties remain about the characteristics and frequencies of past CSZ earthquakes. In this review, we summarize geological, geophysical, and instrumental evidence relevant to understanding megathrust earthquakes along the CSZ and associated uncertainties. We discuss how the evidence constrains various models of great megathrust earthquake recurrence in Cascadia and identify potential paths forward for the earthquake science community. ▪ Despite outstanding geologic records of past megathrust events, large uncertainty of the magnitude and frequency of CSZ earthquakes remains. ▪ This review outlines current knowledge and promising future directions to address outstanding questions on CSZ rupture characteristics and recurrence. ▪ Integration of diverse data sets with attention to the geologic processes that create different records has potential to lead to major progress. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 49 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Discordant 14C Ages from Buried Tidal-Marsh Soils in the Cascadia Subduction Zone, Southern Oregon Coast

1992 ◽  
Vol 38 (1) ◽  
pp. 74-90 ◽  
Author(s):  
Alan R. Nelson
Keyword(s):  
Subduction Zone ◽  
Tidal Marsh ◽  
Late Holocene ◽  
Cascadia Subduction Zone ◽  
Buried Soils ◽  
Oregon Coast ◽  
Coos Bay ◽  
Accelerator Mass Spectrometer ◽  
The Times ◽  
Stratigraphic Sequences

AbstractPeaty, tidal-marsh soils interbedded with estuarine mud in late Holocene stratigraphic sequences near Coos Bay, Oregon, may have been submerged and buried during great (M > 8) subduction earthquakes, smaller localized earthquakes, or by nontectonic processes. Radiocarbon dating might help distinguish among these alternatives by showing that soils at different sites were submerged at different times along this part of the Cascadia subduction zone. But comparison of conventional 14C ages for different materials from the same buried soils shows that they contain materials that differ in age by many hundreds of years. Errors in calibrated soil ages represent about the same length of time as recurrence times for submergence events (150–500 yr)—this similarity precludes using conventional 14C ages to distinguish buried soils along the southern Oregon coast. Accelerator mass spectrometer 14C ages of carefully selected macrofossils from the tops of peaty soils should provide more precise estimates of the times of submergence events.

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