Earthquakes in Taiwan are linked to seasonal changes in water levels

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New Scientist Default Image — A building damaged by an earthquake in eastern Taiwan in 2018

Ritchie B Tongo/EPA-EFE/Shutterstock

Earthquakes in Taiwan may be linked to seasonal variations in the water cycle, driven by the Asian monsoon.

Taiwan has both a high frequency of damaging earthquakes and a wide variation in the amount of precipitation and water stored in the ground, as a result of the heavy rains and typhoons that buffet the island between May and September.

Ya-Ju Hsu at Academia Sinica in Taiwan and her colleagues analysed earthquake data in western and eastern Taiwan, and found a correlation between seismic activity and fluctuations in the water cycle.

Hsu had initially noticed that many earthquakes of magnitude 6 or greater seemed to occur during Taiwan’s dry season between about February and April.

She and her colleagues analysed seismic data between 2002 to 2018, as well as groundwater measurements from 40 monitoring stations and data on how the Earth’s crust changes in response to seasonal water loading.

They found that in western Taiwan, seismic activity was highest in the dry season and lowest between July and September, at the end of the monsoon season.

“In the dry season we see more earthquakes because the water load has been removed,” says Hsu. The researchers found that this decreased groundwater resulted in a peak in the Earth’s crust rebounding even when under low amounts of stress.

Eastern Taiwan had a more complex pattern of seismic activity. There, deeper earthquakes tended to occur more frequently between December to February.

Shallow earthquakes were also linked to the variations in groundwater level and crust changes, but there was greater variability in their timing.

The researchers also looked at records between 1604 and 2018 of 63 earthquakes of magnitude 6 or greater, and found similar trends in the seasonal variation in seismic activity.

The high amount of seismic activity during the dry season may increase the chances of rupturing a larger fault system, says Hsu, resulting in more large earthquakes in the dry season.

Journal reference: Science Advances, DOI: 10.1126/sciadv.abf7282