Researchers at Stanford University have found a new possible way to alert that a major tsunami is following an earthquake, based on a study of the circumstances surrounding the March 2011 events in Japan.
That 9.0-magnitude undersea earthquake off the coast of Japan created a tsunami that hit eastern Japan about 30 minutes later, killing more than 15,800 people.
Stanford researchers now suggest that sound waves in the ocean from an earthquake like that one could reach land tens of minutes before the tsunami itself, according to an article published on the university’s website.
“Because the sound from a seismic event will reach land well before the water itself, the researchers suggest that identifying the specific acoustic signature of tsunami-generating earthquakes could lead to a faster-acting warning system for massive tsunamis,” the article noted.
The research team, led by assistant geophysics professor Eric Dunham and a postdoctoral researcher, Jeremy Kozdon, used supercomputers at Stanford’s Center for Computational Earth and Environmental Science (CEES) to simulate how tremors from the 2011 earthquake moved through the crust and ocean.
“Retroactively, the models accurately predicted the seafloor uplift seen in the earthquake, which is directly related to tsunami wave heights, and also simulated sound waves that propagated within the ocean,” the Stanford article explained. “...tsunamigenic surface-breaking ruptures, like the 2011 earthquake, produce higher amplitude ocean acoustic waves than those that do not.”
The researchers found that the sound waves generated by the March 2011 quake reached Japan’s shore 15 to 20 minutes before the tsunami.
“We've found that there's a strong correlation between the amplitude of the sound waves and the tsunami wave heights,” Dunham said in the article.
“Sound waves propagate through water 10 times faster than the tsunami waves, so we can have knowledge of what's happening a hundred miles offshore within minutes of an earthquake occurring. We could know whether a tsunami is coming, how large it will be and when it will arrive.”
While the model could have implications worldwide, the crust composition and faults around the world are all very different, the researchers noted.
“The ideal situation would be to analyze lots of measurements from major events and eventually be able to say, 'this is the signal',” Kozdon noted in the Stanford article.
“Fortunately, these catastrophic earthquakes don't happen frequently, but we can input these site specific characteristics into computer models – such as those made possible with the CEES cluster – in the hopes of identifying acoustic signatures that indicates whether or not an earthquake has generated a large tsunami.”
To complete the warning system, “underwater microphones called hydrophones would need to be deployed on the seafloor or on buoys to detect the signal, which would then need to be analyzed to confirm a threat, both of which could be costly,” the Stanford article noted.
“Policymakers would also need to work with scientists to settle on the degree of certainty needed before pulling the alarm.”