Earthquakes triggered by tropical cyclones

Posted by Kate Taylor

Tropical cyclones could be triggering earthquakes, say scientists studying last year's temblors in Haiti and Taiwan.

University of Miami (UM) scientist Shimon Wdowinski says he's found a strong relationship between the two events, with large earthquakes occurring within four years of a very wet tropical cyclone season.

"Very wet rain events are the trigger," he says. "The heavy rain induces thousands of landslides and severe erosion, which removes ground material from the Earth's surface, releasing the stress load and encouraging movement along faults."

Over the last 50 years, three very wet tropical cyclone events - Typhoons Morakot, Herb and Flossie - have been followed within four years by major earthquakes in Taiwan's mountainous regions. The 2009 Morakot typhoon was followed by a magnitude 6.2 quake in 2009 and a magnitude 6.4 in 2010.

The 1996 Typhoon Herb was followed by a magnitude 6.2 quake in 1998 and a magnitude 7.6 in 1999. The 1969 Typhoon Flossie was followed by a magnitude 6.2 quake in 1972.

The 2010 magnitude 7 earthquake in Haiti occurred in the mountainous region one-and-a-half years after two hurricanes and two tropical storms drenched the country over a 25-day period.

The reason, suggest the researchers, is that rain-induced landslides and excess rain carries eroded material downstream. As a result the surface load above the fault is lessened.

"The reduced load unclamps the faults, which can promote an earthquake," says Wdowinski.

This earthquake-triggering mechanism appears to be viable only on inclined faults, where the rupture has a significant vertical movement.

Wdowinski's team now plans to analyze patterns in other seismically active mountainous regions - such as the Philippines and Japan - that regularly experience tropical cyclones.