Scientists have made the surprising finding that typhoons trigger slow earthquakes, at least in eastern Taiwan. Slow earthquakes are non-violent fault slippage events that take hours or days instead of a few brutal seconds to minutes to release their potent energy.

"From 2002 to 2007, we monitored deformation in eastern Taiwan using three highly sensitive borehole strainmeters installed 650 to 870 feet deep. These devices detect otherwise imperceptible movements and distortions of rock," explains coauthor Selwyn Sacks of The Carnegie Institution for Science’s Department of Terrestrial Magnetism. "We also measured atmospheric pressure changes, because they usually produce proportional changes in strain, which we can then remove."

Taiwan has frequent typhoons in the second half of each year, but is typhoon-free during the first 4 months. During the 5-year study period, the researchers identified 20 slow earthquakes that each lasted from hours to more than a day. The scientists did not detect any slow events during the typhoon-free season. Eleven of the 20 slow earthquakes coincided with typhoons. Those 11 also were stronger and characterized by more complex waveforms than the other slow events.

"These data are unequivocal in identifying typhoons as triggers of these slow quakes. The probability that they coincide by chance is vanishingly small," remarks coauthor Alan Linde, also of Carnegie.