The sound waves from an undersea earthquake could offer an early warning that a large tsunami is on the way.
Because the sound from a seismic event will reach land well before the water itself, researchers at Stanford University suggest that identifying the specific acoustic signature of tsunami-generating earthquakes could lead to a faster-acting warning system.
The finding was something of a surprise.
Analysis of the 2011 magnitude 9.0 earthquake off the shore of Japan traced the epicenter of the quake to the underwater Japan Trench, a subduction zone about 40 miles east of Tohoku, the northeastern region of Japan’s larger island.
Based on existing knowledge of earthquakes in this area, seismologists puzzled over why the earthquake rupture propagated from the underground fault all the way up to the seafloor, creating a massive upward thrust that resulted in the tsunami that killed more than 15,000 people.
Direct observations of the fault were scarce, so Eric Dunham, an assistant professor of geophysics in the School of Earth Sciences, and Jeremy Kozdon, a postdoctoral researcher working with Dunham, began using supercomputers to simulate how the tremors moved through the crust and ocean.
The researchers built a high-resolution model that incorporated the known geologic features of the Japan Trench and used simulations to identify possible earthquake rupture histories compatible with the available data.
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 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.
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