Terrawatch: lasting legacy of Taiwan's 2009 typhoon season

Eleven years ago, Typhoon Morakot slammed into Taiwan, deluging the country with 3,000 litres of rain per square metre in three days. Catastrophic flooding and landslides followed and more than 600 people died.

It is considered one of the worst tropical cyclones in Taiwan’s recorded history. But that wasn’t the end of it. New research reveals that the typhoon also left Taiwan with a legacy of extra earthquakes for the next few years.

By studying the number and pattern of quakes in the years before and after Typhoon Morakot, Philippe Steer, an assistant professor of geosciences at Rennes University in France, and colleagues were able to show there were significantly more low-magnitude shallow earthquakes in the two and a half years after the typhoon.

The additional quakes were clustered in the regions that had experienced the greatest amount of landslide activity. The scientists believe the huge amount of material that was washed away during the typhoon-triggered landslides lifted the load on underlying rocks, changing the stress pattern in the upper part of the Earth’s crust.

The spate of shallow quakes over the following months and years occurred in response to this, as the upper crust re-equilibrated its stress field. Their findings are published in Scientific Reports.