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ambience: underwater earthquake
When a powerful earthquake occurred in the Indian Ocean it generated a devastating tsunami that took the lives of over a hundred thousand people. Although seismologists tracked the earthquake, there was not an adequate warning issued of the tsunami. What went wrong? I’m Jim Metzner, and this is the Pulse of the Planet.
Gerard Fryer is an associate geophysicist and tsunami Researcher at the University of Hawaii.
“When an earthquake happens, seismic energy radiates all around the globe, and if you want to measure how big the earthquake is, and you want to get a good, reliable measurement, you have to wait for the largest seismic waves, the surface waves, to reach seismometers that are appropriately placed. That takes about an hour. An hour is an awful long time to wait if you’re in a potential warning situation. So what the tsunami warning people do is to look at the first arriving energy they see from an earthquake on seismometers that are close to the source. And they can approximate how big the earthquake is just by looking at the first two minutes of motion. But the problem with the Sumatran earthquake was that the rupture lasted for so long. The earth was moving for six minutes, but they were trying to measure the earthquake just looking at two minutes of data. So they came up with a number that was just profoundly wrong. They thought it was magnitude eight, and it was actually magnitude nine. If they had known in the beginning that it was magnitude nine, they would’ve got warning to everybody if they possibly could. That’s the biggest lesson from this event, that if it’s a really big earthquake, some of these techniques we use for quick and dirty measurement of how big the earthquake is just don’t work, and now we know. But it took a magnitude nine earthquake to wake us up.”