Earthquakes’ sound waves could warn of approaching tsunami

New research from Stanford scientists could lead to tsunami early warning system

Researchers from Stanford University in California may have discovered a new technique to warn of impending tsunamis.

Computer simulations by Stanford scientists reveal that sound waves in the ocean produced by the 2011 earthquake that occurred off the coast of Japan probably reached land tens of minutes before the devastating tsunami hit.

The scientists state that, if correctly interpreted, these sound waves could have offered a warning that a large tsunami was on the way.

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According to the Stanford release, there are various systems that can detect undersea earthquakes, but they can’t reliably tell which will form a tsunami, or predict the size of the wave. There are also ocean-based devices that can sense an oncoming tsunami, but they typically provide only a few minutes of advance warning.

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 researchers discovered that tsunamigenic surface-breaking ruptures, like the 2011 earthquake, produce higher amplitude ocean acoustic waves than those that do not.

Read: Is Japan set for another earthquake?

Their model showed how those sound waves would have traveled through the water and indicated that they reached 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,” said Eric Dunham, an assistant professor of geophysics in the School of Earth Sciences, in a press release. “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.”

The team’s model could apply to tsunami-forming fault zones around the world, though the characteristics of telltale acoustic signature might vary depending on the geology of the local environment. The crustal composition and orientation of faults off the coasts of Japan, Alaska, the Pacific Northwest and Chile differ greatly.

“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,” said Jeremy Kozdon a researcher who is now an assistant professor of applied mathematics at the Naval Postgraduate School.

Dunham and Kozdon pointed out that identifying a tsunami signature doesn’t 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. Policymakers would also need to work with scientists to settle on the degree of certainty needed before pulling the alarm.

If these points can be worked out, though, the technique could help provide precious minutes for an evacuation.

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Transcontinental Media G.P.