BY BJORN CAREY
Stanford scientists have identified key acoustic characteristics of the 2011 Japan earthquake that indicated it would cause a large tsunami. The technique could be applied worldwide to create an early warning system for massive tsunamis.
Eric Dunham, assistant professor of geophysics in the School of Earth Sciences, talks about the research.
On March 11, 2011, a magnitude 9.0 undersea earthquake occurred 43 miles off the shore of Japan. The earthquake generated an unexpectedly massive tsunami that washed over eastern Japan roughly 30 minutes later, killing more than 15,800 people and injuring more than 6,100. More than 2,600 people are still unaccounted for.
Now, computer simulations by Stanford scientists reveal that sound waves in the ocean produced by the earthquake probably reached land tens of minutes before the tsunami. If correctly interpreted, they could have offered a warning that a large tsunami was on the way.
Although various systems can detect undersea earthquakes, they can't reliably tell which will form a tsunami, or predict the size of the wave. There are 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.
Discovering the signal
The finding was something of a surprise. The earthquake's epicenter had been traced 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.
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 the cluster of supercomputers at Stanford's Center for Computational Earth and Environmental Science (CEES) 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 CEES 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.
In addition to valuable insight into the seismic events as they likely occurred during the 2011 earthquake, the researchers identified the specific fault conditions necessary for ruptures to reach the seafloor and create large tsunamis.
The model also generated acoustic data; an interesting revelation of the simulation was that tsunamigenic surface-breaking ruptures, like the 2011 earthquake, produce higher amplitude ocean acoustic waves than those that do not.
The 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," 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."
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.
"The ideal situation would be to analyze lots of measurements from major events and eventually be able to say, 'this is the signal'," said Kozdon, who is now an assistant professor of applied mathematics at the Naval Postgraduate School. "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."
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.
The study is detailed in the current issue of the journal The Bulletin of the Seismological Society of America.
Western Indian Ocean Earthquake and Tsun
Massive Amounts of Charcoal Enter the Wo
Marine Research Can Solve Some of Europe
Breathing Underwater: Scientists Find E
Deep-sea Study Reveals Cause of 2011 Tsu
NOAA: Coastal Ocean Aquaculture can be E
Success for Datafish Acoustics Survey at
New £8 Million Training Center for the O
What Has Happened to the Tsunami Debris
Florida State University: Researchers Fi
UCSB Researchers Create First Regional O
Triton Imaging and Applied Acoustics Ann
Airborne Radar Surveys and Data-Based Mo
Coral Reefs Provide Protection from Stor
Applied Acoustics Introduces New Low Cos
Researchers at GEOMAR and Kiel Universit
Can Coral Save Our Oceans?
From Despair to Repair: Dramatic Decline
The Future Is Now: Navy’s Autonomous Swa
EvoLogics Modems Provide Acoustic Link f
Researchers Find Hurricanes Help The Spr
Divers Find 2,000 Priceless Gold Coins
Researchers Turn to the Ocean to Help Un
HRI Researchers Tag ‘Monster Mako’ for S
The Oceans Can’t Take Any More: Research
Applied Acoustics Introduces New ‘Blowfi
Department of Defense Awards Funds to Ei
New Study from Florida Tech Finds Pacifi
Computer Models Show Significant Tsunami
Can a Lobster be an Archaeologist? SUT t
UM Researchers Awarded Grants From Feder
Japanese Guidelines Could Assist Other T
CCC Selects Sonardyne Ranger 2 Acoustics
IUCN and UNESCO Explore how World Herita
Researchers Creates New Design for Low-C
WOC and Maersk Line Partner with Univers
New Seafloor Map Helps Scientists Find N
Greenhouse Gas Can Escape the Deep Ocean
Digitizing the Coral Reef: You Can Only
Ocean Networks Canada to Coordinate Eart
Boeing Unmanned Undersea Vehicle Can Ope
The Ocean`s Twilight Zone can Feed the W
Exeter Researchers Launch New Robotic Ma
Police and Dive Companies Find Many Uses
Acoustic Devices Help Researchers and Ma
Expedition Yacht in Ecuador to Support E
Leftover Warm Water in Pacific Ocean Fue
Can Underwater Drones Gather Data Cheape
Stanford Scientists Discover Coral Reef
Magseis Selects Sonardyne Acoustics for
Researchers Build a Crawling Robot from
Researchers Pinpoint Abrupt Onset of Mod
Ocean Network Canada Deploys the First S
Expedition to Understand Causes of 2004
Underwater Video Aids Aquaculture and Ma
Fugro Selects Sonardyne Acoustics for Fl
Sonardyne Acoustics Selected for Six Mor
University Students and Researchers Test
Wave Energy Researchers Dive Deep to Adv
Researchers Study Sea Spray to Improve H
Researchers Capture First Glimpse of Rub
Scripps Researchers Collaborate on New T
Gas Hydrate Breakdown Unlikely to Cause
Marine Researchers Consider the Possibil
Saab Seaeye Launches Recruitment Drive t
Study Finds Massive Rogue Waves Aren’t a
New Study Shows Red Tides Can Be Predict
Could Ocean Robots Help Decide if Oil-Ri
WSU Researchers Find Wealth of Fish at D
Applied Acoustics Supplying Nexus 2 Syst
BP & Kosmos Energy Announces Major Gas
Researchers Return to Gulf of Mexico to
Massive Craters Formed by Methane Blow-O
Stanford Researchers Discover Biological
What Does It Take to Get Permits for a 1
New Images from Under Alaska Seafloor Su
Manual for Real-Time Quality Control of
ONC’s WERA Radar Detected Tsunami Event
U.S. and Canadian Scientists Explore Maj
Indian Tsunami Detection Network Undergo
Photomosaic Technology to Find Order in
Scientists Find Cryptic Methane-Fueled E
Marine Organisms Can Shred Plastic Bags
Teledyne Oil & Gas Releases CAN Bus Acti
Teledyne Marine’s Technology for Global
Ocean Researchers Showcase Advances in O
Researchers Pioneer Observations of Hurr
Researchers Capture Underwater Volcano E
Applied Acoustics Launches New Products
New Control Methods Can Help Protect Cor
The Edge of Darkness: WHOI Researchers t
Transparent Eel-Like Soft Robot Can Swim
Researchers Hunting Microplastic with Je
Cutting Edge Technology in Underwater Ac
Oceanscan Invests in Sonardyne Acoustics
Researchers to Present New Results on Hu
Researchers Test New Sampling Device Usi
Can Artificial Intelligence Keep the Oil
Applied Acoustics Adding New Engineers t
Kongsberg Hugin Helps Find Deep Sea Mine