Geologic structure found off Alaska could signify future major tsunami

A team of scientists mapping the seafloor off Alaska have identified a geologic structure that could portend a major tsunami similar in origin and effect to the one that killed tens of thousands of people in Japan in 2011.

Such a tsunami could potentially affect Hawaii as well as southerly North American coasts and parts of the Pacific, according to project head Anne Becel of Columbia University’s Lamont-Doherty Earth Observatory.

The team’s findings are reported in the Tuesday print edition of the journal Nature Geoscience.

In a statement released upon the publication of the study, Becel said the discovery “suggests this part of Alaska is particularly prone to tsunami generation” and that similar structures could exist unnoticed in other areas around the world.

“The possibility that such features are widespread is of global significance,” she said.

At issue is an approximately 90-mile fault within the Shumagin Gap, a so-called “creeping subduction zone” near the end of the Alaska Peninsula about 600 miles from Anchorage.

As the scientists explain, the structure is similar to one that produced the Tohoku tsunami that killed approximately 20,000 people, caused widespread damage and prompted the meltdown of three nuclear reactors in Japan.

In that case, the leading edge of a continental plate abutting another giant plate detached from the main mass and was then dislodged by a relatively modest earthquake. The wedge “jumped,” producing a 130-foot wave.

What went unrecognized before the disaster was that a large fault existed in the zone where the two plates initially met. Becel’s team found that the fault discovered in the Shumagin Gap bore similar features.

Using state-of-the-art technology to generate CAT-scan-like maps of the surface of the seafloor and the mass beneath it, the team was able to identify the massive fault running parallel to land, extending down about 20 miles to where two plates are moving against each other.

“With that fault there, that outer part of the plate could move independently and make a tsunami a lot more effective,” said Lamont- Doherty seismologist and study co-author Donna Shillington. “You get a lot more vertical motion if the part that moves is close to the seafloor surface.”

Similar fault structures are known to exist off of Russia’s Kuril Islands. However, Shillington said data is generally lacking and that more comprehensive study would likely find evidence of many more such structures around the world.