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Looking for the Great Thrust Fault in Cascadia

Looking for the Great Thrust Fault in Cascadia

Susanna Cabot
|June 29, 2021

We are going on a nearly six-week expedition along the coast of Oregon to British Columbia to investigate the Cascadia subduction zone. This subduction zone used to be the site of the “super thrust” earthquake, the largest earthquake on the planet, but it is currently very quiet, with almost no seismic activity detected from Oregon to Washington. Scientists believe that this lack of seismic activity reflects the current “lock-in” state of the giant thrust fault. As the Juan de Fuca plate system continues to dive (subduct) below North America, strain quietly accumulates. All or part of the accumulated strain will eventually be released in the next major earthquake.

Little is known about the nature or even the location of the fault zone that produced the devastating earthquake. During our voyage, we used sound to probe the bottom of the seafloor, looking for a giant thrust fault that covers the depths of several kilometers of sediments in the downward Juan de Fuca plate. Our investigation will be the first seismic imaging study ever spanning almost the entire Cascadia subduction zone. We will use modern advanced seismic imaging technology to detect and characterize the fine structures in the subduction zone to help solve a series of scientific problems related to earthquakes and earthquakes. Tsunami Hazards in the Pacific Northwest.

For our investigation, we are using Colombian R/V Marcus G. Lances, One of the large global-class research ships in the American academic research fleet.This Lances It is a unique ship in the research fleet. It is equipped with advanced seismic imaging equipment and has high-quality sound sources. It can tow a series of monitoring equipment called hydrophones up to 15 kilometers behind the ship to listen to the seabed The echo back and the depths below.

Above: Cascadia fault map, with the Juan de Fuca plate sliding under the North American plate. The red arrow points to the potential area that may cause the largest earthquake in the fault. Bottom: A chart showing the ship’s sound transmitter and sound waves bouncing from different layers below the sea floor. The hydrophone streamers towed behind the ship listened for these echoes.

We have an amazing team of scientists and students from Columbia University, University of Texas Institute of Geophysics, Woods Hole Oceanographic Institution, University of Washington, and Oregon State University/NOAA.We also have professional scientific and technical personnel operating advanced seismic equipment and teaching us along the way. Marine mammal observers tell us when marine mammals are nearby so that we don’t disturb them with our audio equipment, and LancesThe most capable officials and crew, they ensure our investigations and the safe operation of our ships. For most of us, this is the first time we have been outside of our “bubble” with a group of people since the beginning of the pandemic, and we are very happy to be on this expedition together.

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