Oceanic Sounds of Last Year's Earthquake

DoctorBit writes "Columbia University's Lamont-Doherty Earth Observatory is reporting that some of their researchers have analyzed recordings of the underwater sound produced by last year's magnitude 9.3 Sumatra earthquake. By studying the ocean's sound waves rather than the Earth's seismic waves, the researchers measured the earthquake's speed and duration with unprecedented accuracy."

Comments

Re:Detecting Submarines

[Anonymous Coward]

Probably not.

I haven't RTFA, but at a guess they're taking what they use to listen to nuclear submarines and using that to listen to the Sumatran earthquake.

Yes, THAT earthquake

[Anonymous Coward]

For those "in the know" asking the same question as I did: Yes, it is about that earthquake that was predicted by Sollog.

Not really surprising

[Derling Whirvish]

It's not really surprising at all. A lightning bolt makes a distinct short crack if you are close to it, which becomes the sustained rumble of thunder if you are much distance away. In fact, the length of the rumble increases as the distance between you and the lightning bolt increases. It's due to the reflection of the sound off other objects spreading the sound out. The same phenomenon should happen with the sound of an earthquake as it travels through the earth's crust should it not? Because the sound was recorded some distance away, it should not equal the same length of time the "earth's crust was ripping" anymore than the sound of thunder some distance away from a thunderstorm is a record of the duration of the earth's atmosphere ripping from a lightning strike.

Don't hear anything...

[antdude]

Maybe it is these cheap headphones, but does this MP3 require a subwoofer (I'm at work so...) to hear as well? I hear nothing even though Winamp shows audio movements in its visualizer.

Sonar and Detecting Submarines

[AtomicSnarl]

This array would likely be able to do it's share in submarine tracking, but only as piece of a larger system.

Part of the adventure of sonar detection is that low frequencies, especially the 30-100Hz range, travel thousands of miles with very little loss. This trick to long range submarine detection is listening for sounds from pumps, fans, etc, in those low ranges. Next, you need a wide baseline to triangulate a position. The SOSUS arrays covering the Greenland-Iceland-Britan gap covered hundreds of miles.

Now comes the problem of sound ducting. The temperature and salinity gradients of seawater can steer sound in much the same way as a mirage is from bent light due to temperature gradients in the air.

The Fata Morgana mirage, also called Looming, is a prime example of a sonar problem. By eye, you see a mirror image of a distant, even over-the-horizon object reflected as if by a mirror -- the temperature inversion layer. By ear, you care only for the direction of the sound, but now the problem is "which mirror?" As the sound curves up to the sea surface, it reflects back down, then curves up once again, and reflects again, at about 33 mile intervals. This is called a Convergence Zone.

These complexities go on and on, and require a wide range of sensors by depth and distance to detect and resolve the location of a sound source. The computers come in handy to do the filtering ID work, so you don't mistake a squid or a beluga for a Typhoon or Krasnodar...

Subwoofer!

[antdude]

Listen to speakers with a subwoofer. I had the same problem. I couldn't hear anything with headphones at work. I am at home now, and I listened to it again with my old Klipsch ProMedia v2-400. Wow. Nice bass!! It's all about bass with this audio clip.