Heavy Rainfall Can Cause Huge Earthquakes

People cross a makeshift bridge over floodwater from Typhoon Morakot in Taiwan.

Stranded villagers cross a bridge over Typhoon Morakot’s floodwaters in southern Taiwan in 2009.

Photograph by Peter Parks, AFP/Getty Images

Heavy rainfall can trigger earthquakes in what one scientist calls “disaster triggering disaster.”

Shimon Wdowinski, of the University of Miami in Florida, first noticed a connection between storms and earthquakes last year.

The devastating magnitude 7.0 earthquake that hit Haiti in early 2010 came only 18 months after Haiti had been deluged by several hurricanes and tropical storms.

And  another large earthquake, a magnitude 6.4 temblor that rocked Taiwan in  2009, occurred only seven months after the area had been hit by Typhoon  Morakot, which dropped 9.5 feet (2.9 meters) of rain in five  days. Hurricanes are called typhoons in parts of Asia.

To put that in perspective, “that’s about five times the average [annual] rainfall of San Francisco … in five days,” Wdowinski said last week at a meeting of the American Geophysical Union in San Francisco.

Quakes Triggered by Rain-Induced Erosion

To  test the rainfall-earthquake link, Wdowinski dug through the past  50 years of earthquake and weather records for Taiwan, an island that  experiences a lot of severe rainstorms and earthquakes.

He  found that a magnitude 7.6 earthquake had struck in 1999, only three years  after Typhoon Herb soaked Taiwan with 6.6 feet (2 meters) of rain.

Overall,  his analysis revealed that Taiwan’s large earthquakes—deemed as  magnitude 6 and higher—were five times more likely to occur within four  years after such storms than if the storms had had no effect.

The weight of the water itself does not trigger the earthquake—rather, it’s the ensuing erosion from landslides, which subsequent storms steadily wash into the sea.

“There’s  less stress [on the underlying rocks], and it’s easier for the fault to  move,” he said. “These are small changes, but are apparently enough to  trigger the earthquake.”

However, this doesn’t mean typhoons spark earthquakes in regions where quakes wouldn’t otherwise occur, Wdowinski noted.

“The typhoon just determines the timing” of the quake, he said. The main driver that causes earthquakes is the slow process of plate tectonics.

Himalaya Monsoons Linked to Quakes

Other  scientists are finding similar effects in the Himalaya, where summer  monsoons dump heavy rainfall onto the Indian side of the mountain range.

The Himalaya were created by the movement of the Indian Plate, which is  ramming northward into Eurasia, producing a giant fault zone marked by  the mountains.

When the monsoons hit, a lot of water flows into the Indian lowlands, said Thomas Ader, a Ph.D. student at the California Institute of Technology in Pasadena.

The  water’s enormous weight causes the Indian plate to bend slightly under  the pressure. That, in turn, causes the edge of the plate to move  slightly.

“Imagine having a big book and bending it in the middle,” Ader said. “The pages want to slide against each other at the edges.”

(During  Asia’s wet season, the bending offsets the  building tectonic strain on the fault, reducing the short-term risk of  earthquakes.

But in winter, the effect reverses as the lowlands dry out, letting the plate unbend, and the earthquake rate rises.

To date, there’s no way to use the research for earthquake predictions.

Still, Wdowinski noted in a follow-up email, “It might be useful to issue a general forecast for a higher earthquake risk in central Taiwan after the next very wet typhoon.”

Richard A. Lovett

National Geographic News

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About pagan66

I am Pagan, a Witch, a Healer, Mystic & Dreamer. I live in Service to the One. I will Protect & Respect Her bounties to my last breath. I am a Seeker of Truth, a Reformer, A Historian - an Advocate for Religious Freedom, Tolerance & Human Rights. I am a Protector of Animals & Children & those less fortunate than myself. I am a Reader & a Writer - an Artist. I am a Drummer, Gardener & Cook. I listen to the Wisdom of the Ancients. If you take a copy of the Christian Bible and put it out in the wind and the rain, soon the paper on which the words are printed will disintegrate and the words will be gone. Our bible IS the wind and the rain." Herbalist Carol McGrath as told to her by a Native-American woman. "When one defines oneself as Pagan, it means she or he follows an earth or nature religion, one that sees the divine manifest in all creation. The cycles of nature are our holy days, the earth is our temple, its plants and creatures our partners and teachers. We worship a deity that is both male and female, a mother Goddess and father God, who together created all that is, was, or will be. We respect life, cherish the free will of sentient beings, and accept the sacredness of all creation." Edain McCoy View all posts by pagan66

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