A team of Academia Sinica researchers has found a correlation between the amount of rainfall and the frequency of earthquakes in Taiwan.
“The relationship between seismicity and hydrological loading cycles could provide valuable insights for improved regional hazard assessment,” the team wrote in its study, the lead author of which is Academia Sinica Institute of Earth Sciences research fellow Hsu Ya-ju (許雅儒).
A magnitude 6.4 earthquake in Kaohsiung’s Jiasian District (甲仙) on March 4, 2010, a magnitude 6.4 earthquake in Pingtung County’s Wutai Township (霧台) on Feb. 26, 2012, and a magnitude 6.6 earthquake in Kaohsiung’s Meinung District (美濃) on Feb. 6, 2016, all happened in the same season, Hsu said.
Photo: Billy H.C. Kwok, Bloomberg
Medium-level earthquakes in Taiwan occur more frequently in February and March, and less so in summer, she said.
The frequency of magnitude 2.5 to magnitude 6 earthquakes is higher in winter and early spring, and lower in the July-to-September period, Hsu said.
After identifying the seasonality of earthquakes, she analyzed the changes in water conservation and groundwater levels, Hsu added.
Changes in hydrological loading are a key factor driving the seasonal changes in seismicity, she said.
In Taiwan, there is usually more rainfall in summer due to typhoons and heat convection, increasing the hydrological loading on a thrust fault line, making it less likely to slide, she said.
When the loading decreases in winter, the fault is more likely to slide, which increases seismicity, she added.
“Taiwan is on a convergent plate boundary with abundant thrust fault earthquakes that can be used to test the influence of loading and unloading on earthquake modulation,” the study said.
While seismicity in eastern Taiwan shows the same seasonal pattern, the team’s findings are less pertinent to shallow earthquakes, at a depth of up to 18km, Hsu said.
The nation faces a prolonged dry spell this year, and the Central Weather Bureau has said seismicity so far this year is higher than previous years, corresponding with the team’s findings, she added.
The study, titled “Synchronized and asynchronous modulation of seismicity by hydrological loading: A case study in Taiwan,” was published in the journal Science Advances on Wednesday last week, and includes contributions from Canadian, Japanese and US researchers.
In related news, the bureau yesterday said rain is possible nationwide starting from today due to an approaching cloud band and a weather front, but it is unlikely to relieve the water shortage.
The cloud band is expected to move in from eastern China today and would bring rain, with brief showers possible in northern and eastern Taiwan, while precipitation is also likely in the mountainous areas in the west, particularly in the afternoon, the bureau said.
On Wednesday, a weather front is expected to approach Taiwan, with brief rain possible in northern and eastern Taiwan, it said.
The weather system is expected to strengthen and move quickly on Thursday, bringing more showers and thundershowers to the areas north of central Taiwan, it added.
However, the rain would not persist and would not be sufficient to relieve the water shortage, which has caused water to be rationed in parts of the nation, it said.
Heavier rainfall that could help to ease the dry conditions is unlikely until the upcoming plum rain season, which is expected to begin next month.
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