US researchers said on Thursday they have found evidence that tropical cyclones in Haiti and Taiwan were followed by earthquakes, suggesting that heavy rains and landslides may unleash temblors.
“Very wet rain events are the trigger,” said University of Miami scientist Shimon Wdowinski, an associate research professor of marine geology and geophysics.
“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,” he added.
Wdowinski and a colleague from Florida International University analyzed data from major earthquakes — magnitude 6.0 and higher — in Taiwan and Haiti over the past 50 years and found that large quakes tended to follow within four years of a very wet tropical cyclone season.
In some recent cases, quakes happened sooner, such as in 2009 when Typhoon Morakot in Taiwan was followed the same year by a magnitude 6.2 quake and another 6.4 quake last year.
Morakot killed 614 people and left 75 missing, burying entire villages and dumping a record 3m of rain in what is considered one of Taiwan’s worst natural disasters.
Typhoon Herb hit in 1996, killing hundreds in China and Taiwan, and was followed two years later by a 6.2 earthquake, and then a 7.6 earthquake in 1999.
Typhoon Flossie in 1969 was followed three years later by a magnitude 6.2 quake in 1972, the researchers said.
The team also looked at the magnitude 7 earthquake in Haiti last year and found it came a year-and-a-half after two hurricanes and two tropical storms drenched the island nation within 25 days.
The quake hit in January last year and leveled the capital Port-au-Prince, killing more than 225,000 people and leaving one in seven homeless. An ensuing cholera epidemic left more than 5,000 people dead.
The researchers said their theory is that the heavy rains and landslides shift enough weight away from the surface load above the fault that a quake is triggered.
“The reduced load unclamp the faults, which can promote an earthquake,” Wdowinski said.
The hypothesis only fits areas where there are fault lines on an incline, such as mountainous regions where the waters would push the land significantly far away from cracks deep in the Earth’s bedrock.