A. Not really, says Clifford Thurber, a professor of geophysics at UW-Madison, although this decade is shaping up to be extremely active. Three of the 10 largest earthquakes since 1900 occurred in the 1950s, three more in the 1960s, and three more since 2000.

Because the death rate is also influenced by the number of people living in earthquake zones, the deadliest decades for earthquakes began in 1920, 1970, and 2000. Earthquakes that trigger the giant ocean waves called tsunamis are particularly deadly, as occurred in 2004 when a quake in the Indian Ocean caused a tsunami that killed about 230,000.

Earthquakes result from sudden slips along the boundaries between the giant tectonic plates that make up Earth 's strong outer shell. The gradual movement of one plate relative to another creates stress that eventually breaks the fault, or joint, between them, causing an earthquake.

These faults occur in many parts of the world, and earthquakes may seem random, but they also show patterns. One earthquake can trigger another in an adjacent section of fault, so there is "potentially a domino effect that causes subsequent failures, " Thurber said. This phenomenon is occurring near Sumatra, he said.

Furthermore, earthquakes result from the steady movement of plates, which can be interpreted in terms of geologic history.

"If you look at any segment of a plate-boundary fault, we know how fast the plates are moving, and we know how much it moved in the last earthquake, " Thurber said. "So it becomes a matter of simple math to estimate when the strain will be big enough to cause another earthquake -- but that 's only an estimate. "

-- Produced in cooperation with University Communications

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