Northern Taiwan was rocked by a magnitude 4 earthquake at 12:31am yesterday, renewing concerns about the potential for volcanoes in the Tatun Volcano Group (大屯火山群) in Yangmingshan National Park to erupt.
At press time, no casualties had been reported from the quake and only minor damage — to the Pingdeng Elementary School on Yangmingshan — was reported.
Many residents in the area were startled by the quake, which caused a loud rumbling sound.
Central Weather Bureau data showed that the epicenter of the quake was in Taipei’s Shilin District (士林), 11.8km north of Taipei City Hall at a depth of 6.3km.
The strongest intensity of the quake, Level 4, was detected on Yangmingshan, followed by Level 3 in Wugu (五股) in New Taipei City (新北市) and Taoyuan City, and Level 2 in Taipei and Keelung.
The bureau’s records show that 19 earthquakes with a magnitude exceeding 3 have occurred within a 5km radius of the epicenter of yesterday’s quake since 1980. The largest one was in 1988, with a magnitude of 5.3.
Yesterday’s quake was the strongest within the perimeter of the Tatun group in 26 years, the bureau said.
Seismology Center Director Kuo Kai-wen (郭鎧紋) said the earthquake was a stress adjustment that occurs after lava cools down.
“When the lava in a volcano cools down, it shrinks in size. This will subsequently lead to gaps in the rock layers. Pulled by gravity, the rock layer on top falls. This kind of stress adjustment is quite normal,” he said.
Yesterday’s quake was not caused by the active fault at the foot of Yangminshan, as its epicenter and the fault are about 6km apart, Kuo said.
Nevertheless, the earthquake generated concern that one or more of the Tatun volcanoes might erupt soon.
Kuo said that was an unlikely scenario.
“The volcanoes in Tatun are generally considered dormant. Currently, only three to five small earthquakes happen in the area per day. On average, the volcanoes could erupt if there are more than 100 to 200 earthquakes per day, and they have to escalate from deep earthquakes to shallow earthquakes,” he said.
However, National Taiwan University professor Chen Hongey (陳宏宇) said the government needs to carefully examine the correlations between yesterday’s magnitude 4 earthquake and the active fault, adding that it was quite unusual for an earthquake to occur at the volcanic zone.