Alaska at Risk of a Massive Earthquake and Tsunami Similar to Devastating 2011 Japan Event

Shumagin Gap
The area studied off the coast of Alaska is known as the Shumagin Gap. Anne Becel

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.

Kodiak Island Alaska's Kodiak Island is near where the geological structure was found. Matthias Delescluse

With the potential for a huge tsunami to be unleashed, the team says, it is imperative to gain a better understanding of this structure. “The importance of recognizing the hazard posed by the weakly coupled Shumagin Gap was emphasized by a recent tsunami scenario for the Alaska subduction zone showing that a large tsunami in this segment could have devastation consequences to coastal communities locally in Alaska and around the Pacific Ocean,” the researchers wrote.

The findings also have wider implications: The team says there could be far more similar fault structures around the world. “The possibility that such features are widespread is of global significance,” Bécel said.

Study co-author Donna Shillington added: “We don’t have images from many places. If we were to look around the world, we would probably see a lot more.”

In conclusion, the team wrote, “Creeping regions might have greater tsunami potential than previously recognized. Identifying and characterizing active crustal-scale normal faults…is thus essential to a complete and comprehensive understanding of hazards in the global subduction system.”