Shaky future

This month, a new study challenged conventional wisdom about forecasting earthquakes. By examining the pressure waves associated with 71 earthquakes, two scientists posited that large earthquakes have a different signature “P-wave” than smaller earthquakes, making it possible to distinguish between the Big One and an ordinary one in the seconds before a quake hits. P-waves are the newest member of the great parade of earthquake prediction theories below.

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Birthrates rise more than threefold.

Advance warning: One day

Reliability: Not born out by statistics.

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Cellphones, TVs, radios and regular telephones experience disturbances.

Advance warning: 100-150 minutes

Reliability: The evidence is not consistent enough to draw conclusions.

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Earthquake weather -- especially in the form of long, stringy black clouds whose tail ends mark the epicenter.

Advance warning: One day

Reliability: “It’s not that we can rule out some of these things,” said Susan Hough, a seismologist with the U.S. Geological Survey. “But there’s nothing that has held up when you look at it carefully.”

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“Earthquake-sensitive” animals and certain people behave strangely.

Advance warning: 10-20 hours until immediately beforehand

Reliability: “Everyone is always looking for the silver bullet, if they can see a signal or go out and observe that all horses get jumpy,” said Tom Jordan, a member of the California Earthquake Prediction Council, which tests theories such as this. “To my knowledge, none of those methods provides significant predictability.”

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Sudden changes in underground water levels.

Advance warning: One to three days.

Reliability: Hough noted that there are instances of such changes -- notably before quakes in Loma Prieta in 1989 and Kobe, Japan, in 1995. “It’s possible that fluids are moving around,” Hough said. “But if you look at it scientifically, it doesn’t happen before every earthquake.”

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Studies of geologic faults, ruptures and plate movements show areas susceptible to quakes.

Advance warning: Several years, decades or even centuries

Reliability: This method is the only reliable way to foresee earthquakes, Jordan said. But it is a broad indicator, not the kind of precise forecast touted by other theories because, to date, “we don’t know how to predict earthquakes,” he said.

- SWATI PANDEY