Deep Sea Mud Unlocks Secrets of Giant Pacific Coast Earthquakes

Marine turbidites are layers of mud and sand deposited on the deep ocean floor by massive underwater landslides and are often used as a historical record for reconstructing earthquake histories. However, they can be unreliable because it is difficult to show they were not triggered by a storm or flood rather than a quake. In a new study published in the journal Science Advances, researchers detail a new way to link these mud layers to the specific landslides that caused them. This could mean much more accurate earthquake timelines. Mapping the deep Turbidite layers are difficult to study and connect to their sources because of the ocean's extreme depth and the blurry maps scientists have previously used. So U.S. Geological Survey research geologist Jenna Hill and her colleagues used autonomous underwater drones and tethered robots to create high-definition maps of the seafloor off Crescent City, California. They also drilled long tube samples of mud from the turbidites and the steep hills they fell from. The researchers then radiocarbon dated the two sets of samples to compare their ages. They found that the mud on the hills was the same age as the mud on the floor. In most places, sediment settles from the top down, so you would expect a landslide to leave much older mud underneath. However, because the ages matched, it suggests the hills are being "refilled" from below. This happens because the study area sits on a subduction zone where one tectonic plate slides under the other. As the plates grind together, the movement squeezes fresh mud up from beneath the seafloor to the tops of steep hills. Because these hills are located in the deep ocean, surface storms have no effect. Therefore, the researchers can now have much greater confidence that when this mud slides, the cause is an earthquake, not the weather. New research tools As they state in their study, this new approach may change the way we study ocean history: "Our results present a paradigm for marine turbidite paleoseismology and have important implications for site selection and seismoturbidite interpretations along subduction zones globally." Using this method, the team was able to create a precise timeline of massive earthquakes that occurred across the entire 600-mile stretch of coastline from Northern California up to Canada. Their findings confirmed that these giant quakes occur on average every 500 years. Since the last big one happened in the year 1700, they now have a much clearer window for when the next one might hit the Pacific Northwest. © 2026 Science X Network