🌎 A Mega-Earthquake Coming to the United States, Where It Was Least Expected

A new study reveals that the northern coast of Oregon in the United States could experience a future mega-earthquake. The cause: the Juan de Fuca plate lying closer to the surface than previously assumed, along with an unknown sedimentary basin beneath the town of Tillamook.

To reach these conclusions, researchers deployed nearly 200 temporary seismometers between 2021 and 2022 to probe the depths of this subduction zone. The data show that the plate interface lies at a depth of about 12 miles (20 kilometers) near the coast, roughly 3 miles (5 kilometers) shallower than earlier estimates. Such a difference may seem modest, but it has direct consequences on the expected intensity of ground shaking.


According to Erin Wirth, a seismologist at the U.S. Geological Survey, this reduced depth could increase peak ground acceleration along the northern Oregon coast by 9 to 17 percent. Shallow earthquakes indeed generate stronger vibrations at the surface, as seismic energy has less distance to travel before attenuating. This finding is based on analysis of seismic waves recorded by the seismometer network.

Researchers also identified a deep sedimentary basin beneath Tillamook, with its shape and depth measured directly for the first time. These structures, comparable to a bowl of gelatin, amplify seismic waves and prolong the duration of shaking, posing an increased hazard to tall buildings. The basin effect is well known in other regions, such as the Seattle basin.

This study fills a significant gap in the understanding of the Cascadia subduction zone. The northern Oregon region is seismically quiet, leaving few earthquakes to analyze for understanding underground structure. Data from nodal seismometers, combined with an offshore survey conducted in 2021 from Vancouver Island to northern California, have provided a more precise image of the subsurface.

Work continues to analyze other basins, such as the Tualatin basin near Portland. These results should help refine seismic hazard maps and better prepare populations for an inevitable major event in this region. The collaboration between onshore and offshore studies proves promising for revealing the characteristics of the subduction zone.