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jueves, 11 de junio de 2009

Typhoons Can Trigger Earthquakes, Study Suggests

Typhoons can trigger slow earthquakes—and that could be a good thing, according to new research.

Slow earthquakes are seismic events during which pressure is released along fault lines over the course of minutes or even days. (Get plate tectonics facts.)

The slow quakes are so subtle that regular seismometers can't detect them, and people on land can't feel them. But the events interest scientists, because the slow quakes could be breaking up larger regions of seismic stress that would otherwise create more powerful temblors.

Alan Linde of the Carnegie Institution for Science in Washington, D.C., and colleagues placed highly sensitive equipment along the eastern coast of Taiwan to record the otherwise imperceptible slow quakes. (See a Taiwan map.)

To their surprise, the scientists noticed a strong link between slow quakes and typhoons, the name used for hurricanes in the western Pacific.

Over a five-year study period, slow earthquakes happened only during the annual typhoon season, and 11 of the recorded quakes happened at the same time as typhoons.

"We had no idea that we'd see [these] events triggered by typhoons. That never crossed our minds," Linde said.

Last Straw

Despite the surprise, the connection makes sense, the researchers say.

Typhoons are low-pressure systems. When the storms stir up the ocean, local sea levels change to maintain a balance in pressure on the ocean floor.

"On the land side, however, there's nothing to move [to create such a balance], so the pressure on the land is slightly decreased during the typhoon," Linde said.

This means the storm becomes the proverbial last straw, pushing faults that were on the verge of movement into action.

"The typhoons act as a trigger, but they can only do this if the fault is almost ready to fail," Linde said.

The new findings help shed light on how and why different kinds of earthquakes happen, which could eventually lead to better earthquake predictions.

Slow earthquakes, for example, are already suspected of relieving seismic pressure in certain parts of the world. The relatively quiet events could explain why Taiwan has so much seismic motion but so few major quakes.

"The Earth is so wretchedly complicated," Linde said. "Every time you get some new information that tells you something about the way a fault fails, it helps."

Findings presented in this week's issue of the journal Nature.

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