In 2011, a megathrust earthquake off the coast of Japan produced a huge tsunami that killed over 15,000 people. The 9.0 magnitude quake was so big it shifted the Earth’s axis and moved the coast of Honshu, Japan’s main island, by 8 feet.
Scientists now say a similar earthquake could take place off the coast of Alaska, resulting in a dangerous tsunami that could devastate parts of the state and reach southerly parts of North America, Hawaii and beyond.
In a study published in the journal Nature Geoscience, researchers at Columbia University’s Lamont-Doherty Earth Observatory created new, detailed maps of an area of the seafloor off Alaska called the Shumagin Gap. This is a creeping subduction zone at the end of the Alaska Peninsula, 600 miles from Anchorage.
Previously, scientists thought this area was fairly benign, steadily releasing tension as the plates moved slowly past one another. But this is not the case. Instead, the researchers found a geological structure similar to that seen at the site of the 2011 Tohoku earthquake, suggesting this site could also slip suddenly and produce a huge tsunami.
The Tohoku earthquake took place at a creeping segment of the seafloor. It was thought that the frequent, small earthquakes at the site meant it could never build up enough tension to produce one large quake.
What scientists failed to realize was that part of the edge of the continental plate had become detached—and that this posed a major risk. A smaller earthquake dislodged the detached section, creating the huge earthquake and tsunami that followed. While scientists knew this fault existed, they did not understand the devastation it could cause.
In their study, researchers found a region of the Shumagin Gap that is detached in the same way. The fault they identified stretches about 90 miles roughly parallel to the land and extends over 20 miles down. The maps suggest the seafloor has dropped to one side and risen on the other. Researchers also found a cluster of seismic activity near where the new fault meets the plate boundary, indicating it is active.
While the newly identified fault could be the remains of a previous earthquake rather than one to come, the findings show this part of Alaska is “particularly prone to tsunami generation,” lead author Anne Bécel said in a statement.