A team of scientists found something hidden off the coast of Alaska that suggests a significant risk for future tsunamis in the area.
(From Forbes / by Trevor Nace) — The team made the discovery as they were conducting seismic surveys off the Alaskan coast to better understand the regional plate tectonics and subduction.
The research, published in Nature Geoscience, provides evidence for an increased tsunami risk in an area previously thought to be low risk for tsunamis. The feature was found by a research team at the Lamont-Doherty Earth Observatory of Columbia University. It is similar to the feature that produced the devastating Tohoku tsunami in 2011 off Japan, which killed approximately 20,000 people and caused three nuclear reactors to melt down.
Upon finding this feature, the known risk of a deadly earthquake triggered tsunami significantly increases. The research can also be translated globally to help scientists better understand tsunami risk globally.
Tsunamis occur when an earthquake jolts the sea floor vertically, forcing the overlying water to be diverted toward shore. This is akin to sitting in a pool and thrusting both hands up suddenly, you will notice a wave spreading out in all directions. Once that wave moves toward the coast, water is forced vertically producing the circular wave feature we see at the beach.
In order for an earthquake to form a tsunami, there must be a significant vertical offset of the crust, which causes displacement of the water. In this region of Alaska, the research team found that there is a normal fault which splits the overriding continental plate into a larger continental piece and a chip close to the coast. The small wedge is located in between the subducting plate and the overriding continental plate.
The splitting of the continental crust along the coast causes significantly higher risk for a tsunami. This is because during an earthquake the smaller wedge will be thrust upward easier than the larger continental crust. In effect, you have a light “chip” of continental crust that can easily be jolted upward, triggering a tsunami. Here’s a great example of how this specific tsunami may be triggered.
In this part of the world, the denser and thinner Pacific plate is being subducted underneath the less dense and thicker North American plate. This subduction causes earthquakes and volcanism as the two plates rub against one another.
After studying the 2011 Japan tsunami, geologists found that a relict fault parallel to the coastline represented a normal fault, which produced a detached wedge. Now that a similar fault has been found along the Alaskan coast, scientists are warning of the potential for a large and destructive tsunami.