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January 3, 2011

Tsunami Sounds

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  Quake Predictor
(04.29.05) - What if you could check the earthquake forecast the way you check the weather? Scientists drilling into the San Andreas Fault this summer hope to learn whether earthquakes are predictable.

Quake Swarms
(03.08.05) - Clues to future earthquakes in the tsunami-ravaged areas around the Indian Ocean might just come from studies done off the west coast of the United States. Studies are finding that there's a pattern to that area's largest earthquakes.

Tsunami Warning
(02.20.03) - Researchers studying the movement of water are now creating better ways to predict where and how tsunamis can affect us.

  National Geographic – Tsunami: Facts About Killer Waves


USGS – The Latest Quake Info

The Pacific Tsunami Museum

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As countries on the Indian Ocean continue to recover from the damage of last year's tsunami, scientists are studying a sound recording of the earthquake that caused it. As this ScienCentral News video reports, that information could lead to better warnings for future tsunamis.

The Sound of Waves

The Christmas Tsunami of 2004, triggered by one of the largest recorded earthquakes, devastated countries along the Indian Ocean, killing more than 280,000 people and leaving millions more destitute.

Hours before the raging ocean hit coastlines of Indonesia, Sri Lanka, the Maldives, India, Thailand, the Seychelles, and Myanmar, a massive earthquake — measuring 9.0 on the Richter scale — tore open the ocean floor. But scientists were only able to find out details of what happened thousands of feet below the wave during the months that followed .

Using hydrophones — underwater microphones originally used by the U.S. Navy to listen for enemy submarines — they were able to hear and record the earthquake that set off the deadly tsunami.

"We were able to hear the earthquake rupture," says marine seismologist Maya Tolstoy, from Columbia University's Lamont Doherty Earth Observatory. "It's a very eerie sound, obviously. It definitely sends shivers down your spine... It's the sound of the earth ripping apart for that long."

T wave
Tolstoy studies chains of volcanoes and earthquakes on the seafloor, listening to the happenings at the bottom of the ocean. "I study the little earthquakes that are produced there, and I do other work with monitoring the ocean, listening for those earthquakes, and whale calls and iceberg noises — all the things you can hear in the ocean," she explains.

Studying the recordings from the tsunami, Tolstoy and her colleagues discovered that the quake was even more destructive than originally thought. She says, "One thing that we are learning is that big earthquakes are sort of a different beast unto themselves."

They analyzed a portion of the recording called a tertiary wave, or T wave, which is only present in underwater earthquakes. "The earthquake, as it ruptures… creates energy and also creates what's called a T wave in the water, and that's the waterborne phase of the earthquake," Tolstoy explains. "It comes in much slower, so by the time it arrives, [the primary and secondary waves before it] have all gone through already, so you get a very clean look at the rupture."

The T wave yields precise details about a quake's speed and size. It revealed that in 2004, an area of seafloor the length of California — three times bigger than first estimated — suddenly ripped apart in a matter of minutes, producing two big pulses of energy — essentially two earthquakes back to back.

"It's the longest earthquake we've ever observed on modern seismic networks. It's the longest in terms of length, and of duration. It is unusual, it's off the charts," Tolstoy says, adding that, "The amount of energy released in this eight minute earthquake was equivalent to the amount of energy that the U.S. uses in six months… it's so humbling in terms of the power of the planet, and how tiny we are compared to these geological forces."

Studying T waves they can determine the geographic range of the earthquake.
image: Columbia University
Since sound waves travel much faster than ocean waves, and even tsunamis, Tolstoy says T wave-quake information could help save lives by giving more accurate warnings, and telling disaster relief workers the breadth of the affected area.And she hopes that faster analysis of T waves will let scientists give earlier warning for the next killer wave.

"With these data, if we had them in real time, we could have told in about an hour the scale of [the 2004] event," she says. "That would be useful for sending emergency services to the area that ruptured, but also in terms of providing tsunami warning for more distant areas."

Obtaining measurements that quickly is still difficult, but Tolstoy says better underwater monitoring equipment could be in place around the globe by the end of the decade.

Oceanographers hope to build a network of fiber-optic cables off the coast of Oregon, Washington and Canada to better observe the happenings on Pacific seafloor as it happens. Researchers are also testing GPS devices in tsunami warning systems, to compliment the undersea sound recordings.

Tolstoy's research was published in the July/August 2005 issue of Seismological Research Letters, and was funded by Lamont-Doherty Earth Observatory of Columbia University.

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