Evidence of large ancient earthquakes of the Cascadia fault

evidence-of-large-ancient-earthquakes-of-the-cascadia-fault

The coastal salt marshes of the Cascadia subduction zone (CSZ) preserve evidence from several large earthquakes, between 8 and 9 in magnitude, according to paleoseismologists. So far, the scientists have been using only the stratigraphic data records to gain insight into the mechanism of ancient earthquakes, however, the microfossils from the area have been discovered to contain more records on these intense events, the Geological Society of America (GSA) announced on November 1, 2015.

Now, for the first time the scientists have used both stratigraphic data and records from the microfossils to observe three CSZ earthquake zones at Jacoby Creek, Arcata Bay, California.

Stratigraphic evidence collected over the last 30 years provided evidence of the subsidence that occurred during earthquakes beneath the salt marshes of Humbolt Bay, California, at the southern end of the CSZ. The researchers from the University of Rhode Island now use the foraminera fossil to estimate this subsidence north of Humboldt Bay, at Arcata Bay.

"Previous investigations were able to provide estimates of subsidence with large errors, which are only so helpful to the modelers," J. Scott Padgett, University of Rhode Island, noted.

The new, improved, analysis on the microfossil data in Oregon allowed the scientists to estimate the subsidence with significantly smaller errors. This provided the seismologists with much more accurate data to enable producing earthquake models more consistent with observed subsidence measurements seen in today's instrumented earthquakes.

A research similar to this one is also taking place at a small coastal drainage, Jacoby Creek, flowing into northern Arcata Bay. Three sharp contacts between salt marsh peat and intertidal mud, dating over 2 000 years back in the past have been uncovered in the area. Plant macrofossils at the top of buried peats have been estimated to be 195, 1 280 and 1 710 years old, according to radiocarbon analysis. These, newly estimated, ages have provided tighter constraints on the timing of past earthquakes and subsidence at the southern end of the CSZ.

Strong evidence has been provided to support the results of the research conducted at Jacoby Creek: "These include the sharp mud-over-peat contacts that are laterally continuous over 5 kilometers, changes in fossil foraminifera assemblages across the buried peat contacts, long-lasting submergence also derived from fossil foraminifera records, and radiocarbon ages of plant macrofossils taken from buried peat deposits that are consistent with other southern Cascadia earthquake chronologies derived from buried peat and tsunami deposits."

Plate tectonics along the Pacific Northwest region of North America. Image credit: Google / Stephen Hicks

The stratigraphic records in combination with the microfossils from the CSZ area are expected to allow the researchers to learn more about potential major hazards in store for the area, as well as provide more information about the large ancient earthquakes in general.

Reference:

  • "Stratigraphic and microfossil evidence for three Cascadia subduction zone earthquakes at Jacoby Creek, Arcata Bay, California, USA", J. Scott Padgett, Simon E. Engelhart, Eileen Hemphill-Haley, Harvey M. Kelsey, Robert C. Witter – 2015 GSA Annual Meeting in Baltimore, Maryland US

Featured image: Cascadia Subduction Zone. Imagery ©2015 Google.

If you value what we do here, create your ad-free account and support our journalism.

Share:


Your support makes a difference

Dear valued reader,

We hope that our website has been a valuable resource for you.

The reality is that it takes a lot of time, effort, and resources to maintain and grow this website. We rely on the support of readers like you to keep providing high-quality content.

If you have found our website to be helpful, please consider making a contribution to help us continue to bring you the information you need. Your support means the world to us and helps us to keep doing what we love.

Support us by choosing your support level – Silver, Gold or Platinum. Other support options include Patreon pledges and sending us a one-off payment using PayPal.

Thank you for your consideration. Your support is greatly appreciated.

Sincerely,
Teo Blašković

$5 /month

  • Ad-free account
  • Clean user interface and fast browsing
  • Direct communication with us via chat and email
  • Suggest new features, content and applications
  • Early access to new apps and features

$50 /year

$10 /month

  • Ad-free account
  • Clean user interface and fast browsing
  • Direct communication with us via chat and email
  • Suggest new features, content and applications
  • Early access to new apps and features

$100 /year

$25 /month

  • Ad-free account
  • Clean user interface and fast browsing
  • Direct communication with us via chat and email
  • Suggest new features, content and applications
  • Early access to new apps and features

$200 /year

You can also support us on Patreon

support us on patreon

or by sending us a one-off payment using PayPal:


Commenting rules and guidelines

We value the thoughts and opinions of our readers and welcome healthy discussions on our website. In order to maintain a respectful and positive community, we ask that all commenters follow these rules:

  • Treat others with kindness and respect.
  • Stay on topic and contribute to the conversation in a meaningful way.
  • Do not use abusive or hateful language.
  • Do not spam or promote unrelated products or services.
  • Do not post any personal information or content that is illegal, obscene, or otherwise inappropriate.

We reserve the right to remove any comments that violate these rules. By commenting on our website, you agree to abide by these guidelines. Thank you for helping to create a positive and welcoming environment for all.

Leave a reply

Your email address will not be published. Required fields are marked *