Please enable JavaScript to use all features of this website. The CAscadia Seismic Imaging Experiment 2021 (CASIE21): All Aboard the R/V Marcus G. Langseth!
Pacific Northwest Seismic Network

The CAscadia Seismic Imaging Experiment 2021 (CASIE21): All Aboard the R/V Marcus G. Langseth!

Four people on a boat deck in hard hats and lifejackets are working with power tools. There is also someone's hand holding a clipboard with information visible in the corner.

This past June, I hopped aboard Columbia University’s R/V Marcus G. Langseth to participate in the CAscadia Seismic Imaging Experiment 2021 (CASIE21), a 41-day research cruise funded by the National Science Foundation. Our mission: to image the Cascadia Subduction Zone, where the Juan de Fuca plate collides with and dives beneath the North American plate offshore the Pacific Northwest coast of North America.

Dark eerie graphic where the Cascadia Subduction Zone is highlighted off the coast of Oregon and Washington State. The Queen Charlotte Fault, off the coast of Vancouver Island, and the Blanco fault, off the coast of Oregon and Washington, are also highlighted. Below the water the tectonic plates are drawn to shoe the direction of motion and how the faults are formed. Right under where the faults are drawn the Pacific Plate and the Juan De Fuca Plate are drawn having arrows moving away from each other. Right under where the Cascadia Subduction Zone the Juan De Fuca Plate is drawn going under the North American Plate.

This collision of tectonic plates results in megathrust earthquakes, the largest earthquakes in the world, capable of producing damaging tsunamis like those of the 2004 Mw 9.1 Sumatra and 2011 Mw 9.1 Japan megathrust earthquakes. The seismic images of the Cascadia subduction zone collected by the CASIE21 cruise will allow us to "see" deep beneath the floor of the Pacific Ocean to observe the structures and physical properties of the megathrust fault zone, accretionary wedge, and downgoing Juan de Fuca plate.

My PhD research will be focused on splay faults, which are steeply-dipping thrust faults that branch off the megathrust fault and cut through the accretionary wedge up to the seafloor. It is important to understand splay faulting in Cascadia because if these faults are activated in future megathrust earthquakes, they can significantly increase tsunami size and, therefore, should be considered in tsunami hazard assessments.

Overall, scientific studies using the new seismic images collected by the CASIE21 cruise will allow us to develop a better understanding of earthquake and tsunami hazards at the Cascadia subduction zone.

Ten people looking and smiling at the camera while standing on a research boat close to land.

During my time on board the Langseth, I had the opportunity to work with an incredible team of scientists from research institutions across the country, led by chief scientist Suzanne Carbotte of Columbia University’s Lamont-Doherty Earth Observatory (LDEO) and co-chief scientists Brian Boston of LDEO and Shuoshuo Han of the University of Texas, Austin Institute for Geophysics.

Hypsometric map of the coast of Washington state and the South Coast of British Columbia that includes the Salish Sea. The map has red circles labeled off the coast and red lines drawn between them. The lines create an imagine of rectangles that stem out into the ocean around 50 miles. There is a key at the bottom that reads the red lines as "Seismic Line" and the red dots as "Startr on Line"

As a part of the CASIE21 science team, I assisted in the collection of seismic and seafloor bathymetry data along 18 dip lines and 7 strike lines over the Cascadia subduction zone from southern Oregon to Vancouver Island. This involved deploying our 15-km-long steamer cable of 1,200 hydrophones which recorded the seismic waves created using our array of 36 air guns after they bounced off layers of sediment and rock in the subsurface.

Simple illustration of a research boat ontop of the water with the water column and sea floor layers pictured below. The seafloor is split into three layers. The boat is labeled "R/V Langseth" and has two more illustration labeled "air guns" and "streamer" webbing off of it and shown floating right below the water surface. Off of the illustration labeled "air guns" is an arrow drawn all the way through the three layers of seafloor labeled "source wave." The graphic labeled "streamer" features a yellow line, that is shown to measure 15 kilometers, with three red squares evenly spaced across and labeled "hydrophones." From the red squares labeled "hydrophones" there are three dotted lines drawn from each connecting almost perpendicularity to the "source wave" arrow and they are labeled "reflected waves." Also, connected to the "streamer" is an simple drawing of a gray square floating on the water surface labeled "tall buoy"

Once our instruments were deployed, I spent my much of my time on-duty in the Langseth’s science lab monitoring and processing the incoming seismic data and building the CASIE21 website and blog. In my off-duty time, I often went up the Langseth’s observation tower to hang out with the Protected Species Observers (PSOs) who were tasked with monitoring for protected species such as whales, dolphins, sea turtles, and birds. If the PSOs detected a nearby protected marine animal, we shut down our air guns and waited for the animals to move a safe distance away. You can learn more about this important work on our blog post.

A women wearing a mask working at a desk with around 10 monitors that all have different data being displayed.

With millions of people living along the Pacific Northwest coast, it is vital to understand future megathrust earthquakes and tsunamis at the Cascadia subduction zone. As the first modern, region-scale marine seismic imaging survey of the Cascadia subduction zone, the CASIE21 research cruise provides a foundational dataset for future studies of earthquakes and tsunamis in the region. I am grateful for my experience onboard the Langseth and look forward to working on this new dataset and sharing the results with the community!

Photo list and credits:

  1. streamer deployment photo – PC: Liam Moser

  2. cascadia subduction diagram – Pablo Canales (WHOI) https://pnwgeohazards.whoi.edu/

  3. science team photo – PC: Shaun Shaver

  4. link tracks figure – Suzanne Carbotte (LDEO)

  5. survey design figure – Madeleine Lucas

  6. science lab photo – PC: Michelle Lee