TAIPEI (Taiwan News) — The Central Weather Administration said dozens of aftershocks were detected within a few hours after a magnitude 6.4 earthquake struck Chiayi County on Tuesday, the strongest in the area in five decades.
CWA Seismological Center Director Wu Chien-fu (吳健富) said shaking from the earthquake, which started at 12:17 a.m., lasted 43 seconds, per UDN. Wu said this was followed by 53 aftershocks within five hours, per ETtoday.
Most aftershocks were centered in Tainan's Nanxi and Nanhua districts. The strongest aftershock, a magnitude 5, occurred at 12:26 a.m. in Nanxi, Tainan, at a depth of 11 km.
Wu explained that the 6.4 magnitude quake in Chiayi County's Dapu Township recorded an intensity of 6. Taiwan uses an intensity scale of 1 to 7 to gauge the degree to which a quake is felt at a specific location.
Wu said the epicenter in Dapu Township is in a mountainous area known for its fractured geological structure, which frequently experiences minor earthquakes and occasionally sees quakes measuring magnitude 5 and over. Wu explained that numerous faults and fracture zones near the Dapu Township epicenter contributed to the high frequency of aftershocks.
He said most earthquakes in western Taiwan are caused by the compression of the Eurasian plate, with stress transmitted to the west. Wu said the shallower depths of western earthquakes make them particularly noticeable, even more so when ambient noise is minimal late at night.
The seismologist noted that historical data within 30 km of the epicenter revealed 22 earthquakes of a magnitude 5 or higher since 1976. The most notable was a magnitude 5.59 earthquake on Feb. 16, 2000.
Wu said Tuesday's magnitude 6.4 quake was the first to exceed magnitude 6 in the area in 50 years and set a new record as the strongest in the vicinity.