June 7, 2013
Underwater Earthquake Sounds May Help Predict Tsunamis
Brett Smith for redOrbit.com - Your Universe Online
While seismologists have the ability to detect undersea earthquakes, they don´t know which ones will turn into tsunamis. Some ocean-based sensors are able to detect an approaching tsunami, but they can only provide a few minutes of advanced warning.According to a new report in The“¯Bulletin of the Seismological Society of America, two Stanford University researchers have identified key acoustic characteristics of the 2011 Japan earthquake that“¯could be used to significantly improve tsunami warning systems.
The researchers stumbled onto the acoustic signature somewhat accidentally while working with advanced computer models designed to simulate the catastrophic quake. While investigating the quake, the seismologists were puzzled over the reason behind why the earthquake rupture propagated from the fault deep below the ocean all the way up to the seafloor, creating a massive upward thrust and a resulting tsunami.
The two geophysicists“¯Eric Dunham and Jeremy Kozdon began using the powerful supercomputers at Stanford's“¯Center for Computational Earth and Environmental Science (CEES) to model the tremors as they moved through the Earth´s crust and through the ocean.
Although direct observations of the earthquake were scare, the researchers created a high-resolution model that used known geologic features of the Japan Trench and CEES simulations to identify previous earthquake events that matched the available data.
The Stanford models were able to accurately recreate the seafloor uplift in the 2011 earthquake, which caused the gigantic tsunami wave heights. The model also revealed sound waves that propagated within the ocean during the event.
The researchers found that surface-breaking ruptures, like the 2011 earthquake, create higher amplitude ocean acoustic waves than those that do not. These sound waves would have traveled through the water and reached shore 15 to 20 minutes before the tsunami, according to the report.
"We've found that there's a strong correlation between the amplitude of the sound waves and the tsunami wave heights," Dunham said. "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."
According to the researchers, their model could be used on fault zones around the world that have the potential to generate a massive tsunami, including faults near Japan, the Pacific Northwest and Chile.
"The ideal situation would be to analyze lots of measurements from major events and eventually be able to say, 'this is the signal'," Kozdon said. "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."
The researchers said underwater microphones would still need to be deployed on the seafloor or using buoys to establish an early warning system. Any acoustic signals would then need to be analyzed to confirm a threat. They expect policymakers would coordinate with scientists to determine a course of action in the event that a tsunami is detected.