"West Coast at Risk: New Research Suggests Imminent Megathrust Quake"

Recent research reveals that the West Coast is at heightened risk of a significant megathrust earthquake, suggesting that such a seismic event could be imminent. This study underscores the urgency for increased preparedness and assessment of potential impacts on the region. The findings highlight the need for proactive measures to mitigate the risks associated with a major earthquake.

Large-scale earthquakes and tsunamis have historically impacted the western regions of the U.S. and Canada, and they are expected to continue doing so in the future.

A 600-mile stretch off the southern coasts of British Columbia, Washington, Oregon, and northern California features the Pacific Ocean floor gradually subducting beneath North America. This area, known as the Cascadia Subduction Zone, contains a megathrust fault where tectonic plates move against each other, leading to significant seismic activity. The Cascadia Subduction Zone can periodically accumulate stress as the tectonic plates lock together over large areas, eventually releasing this stress in powerful earthquakes. These events can cause massive shaking of both seabed and land, and generate tsunamis that reach heights of 100 feet or more. Similar faults have caused major disasters, such as the 2011 Fukushima nuclear incident in Japan. The Cascadia fault is believed to produce major earthquakes approximately every 500 years, with the last significant event occurring in 1700.

Researchers have been studying the Cascadia Subduction Zone to understand its structure and behavior better, aiming to predict the likelihood of earthquakes and their potential warning signs. Although precise earthquake predictions are not possible, scientists attempt to forecast probabilities to aid in creating effective building codes and warning systems. A recent study has made significant progress in understanding this seismic zone. Using advanced geophysical instruments, researchers conducted a comprehensive survey of the area, revealing detailed information about the complex structures beneath the seafloor. This includes the geometry of the subducting ocean plate and the overlying North American plate. The findings were published in the journal Science Advances.

Suzanne Carbotte, a marine geophysicist at Columbia University’s Lamont-Doherty Earth Observatory, led the study and noted that previous models were based on outdated data. The new research offers a more accurate framework for assessing earthquake and tsunami hazards. The study, funded by the U.S. National Science Foundation, was conducted during a 41-day cruise in 2021 aboard the Marcus G. Langseth. Researchers used powerful sound pulses to create images of the seafloor, similar to medical imaging techniques. One significant discovery is that the megathrust fault zone is divided into at least four segments, each potentially insulated from the others. This segmentation could affect how seismic activity propagates. Scientists have debated whether past quakes ruptured the entire fault zone or just parts of it, which impacts the size of the resulting earthquakes.

The data indicate that these segments are separated by buried features like major faults, which may prevent movement in one segment from affecting others. This suggests the possibility of segmented ruptures, though more research is needed to confirm this. The study also identified that the segmentation results from the varying rock types in the North American plate. The differences in rock density and pressure cause the oceanic plate to bend and twist, affecting the fault’s behaviour. The researchers found that one segment, running from southern Vancouver Island to the Oregon border, is smoother and might rupture along its entire length, making it potentially more dangerous.

Additionally, the shallow subduction angle in this segment may extend directly under Washington’s Olympic Peninsula, potentially increasing shaking intensity in areas like Tacoma and Seattle. This requires further study to assess its impact on land. With funding from the U.S. Geological Survey, state and federal agencies, and academic institutions, researchers are analyzing the data to understand its implications better. Tsunami hazard assessments are still ongoing, with efforts focusing on modelling seafloor features that might generate tsunamis.

Practical assessments, which could influence building codes and preparedness measures, are expected to be published as early as next year. The research highlights the complexity of the fault zone and underscores the need for updated hazard assessments. Reference: “Subducting plate structure and megathrust morphology from deep seismic imaging linked to earthquake rupture segmentation at Cascadia” by Suzanne M. Carbotte et al., 7 June 2024, Science Advances.

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Source: scitechdaily‍