A new map of the ocean floor off the coast of Alaska shows geological features that resemble the area that generated the 2011 Tohoku tsunami in Japan. This recent discovery implies that previous models might have underestimated the tsunami risk in the region.
The finding, published in Nature Geoscience, shows how the region, called the Shumagin Gap, is a “creeping subduction zone” that stretches for 145 kilometers (90 miles) parallel to the Alaskan coast. The research team recorded a series of small earthquakes in the region that suggest the fault is active.
“[The discovery] suggests this part of Alaska is particularly prone to tsunami generation,” lead author Dr Anne Bécel, from Columbia University’s Lamont-Doherty Earth Observatory, said in a statement. “The possibility that such features are widespread is of global significance.”
Before the 2011 Japan tsunami, it was thought that regular subduction zones were the most dangerous ones. In those areas, one plate is sinking under another one, building up tension until it’s released as a powerful earthquake. Creeping subduction zones, on the other hand, tend to release tensions in frequent small quakes, so this should prevent the formation of larger tidal waves.
But researchers now think that creeping subduction zones might be partially detached from the main plate. Even a modest quake could make the ocean floor jump up and down, creating a powerful tsunami on the surface.
“With that big fault there, that outer part of the plate could move independently and make a tsunami a lot more effective,” said co-author Professor Donna Shillington. “You get a lot more vertical motion if the part that moves is close to the seafloor surface.”
The creeping subduction zone is much smaller and lighter than the rest of the plate, so once movement happens below it, it raises higher and faster than the rest.
While the danger is higher than previously thought, it is difficult to quantify exactly how risky it is to live near such areas. We still don't fully understand these regions and researchers think this configuration might not be an exclusive of the Pacific.
“We don’t have images from many places," Shillington added. "If we were to look around the world, we would probably see a lot more."
Every scrap of information provides a more complete picture, and hopefully we’ll soon know enough to improve the safety of the inhabitants before another devastating tsunami happens.