People should look out for aftershocks of magnitude 4 or bigger until Sunday and aftershocks measuring magnitude 3 or bigger in the coming week after a magnitude 6.2 temblor rocked Taiwan on Thursday, the Central Weather Bureau (CWB) said.

According to data on the CWB’s website, the earthquake’s epicenter was located at sea about 29.1 km southeast of the Hualien County Government. It had a depth of only 5.7 km and reached 5-weak on Taiwan’s 7-tier intensity scale.

The epicenter was located in an area that historically has had more deep earthquakes than shallow ones, and reaching magnitude 6 also made Thursday’s earthquake an even rarer occurrence, said Chen Kuo-chang (???), head of the CWB’s Seismological Center.

Since the CWB began tracking earthquakes in Taiwan in 1973, only two in the aforementioned area reached magnitude 6 — a magnitude 6.0 quake in 1982 and a magnitude 6.7 one in 1990, he said.

The long intervals between those three earthquakes indicate that it is an area not often hit by strong earthquakes, which could be due to that area having “broken tectonic structures,” he said.

This structure could also give rise to a higher likelihood of concentrated but smaller aftershocks in the coming week, he said.

As to why the CWB only sent cell phone earthquake alerts to residents in Yilan and Hualien counties when other cities and counties also reached the threshold for receiving the messages, Chen said that it was due to a technical fault in estimating the intensity of the temblor.

However, it only took the system 12 seconds to issue the alerts, whereas it used to take 20 seconds to do so in the event of an at-sea earthquake, which was proof that improvements had been made to the system, he said.

Asked by reporters whether 2022 can be considered a year of extreme tectonic activity, given that this year marked the most magnitude 6 or bigger earthquakes since the magnitude 7.3 earthquake on Sept. 21, 1999, Chen said that most of the stronger quakes this year were concentrated to the north and the south of the east coast where the Eurasian Plate and the Philippine Sea Plate converge, which could suggest increased tectonic activity.

However, the tectonic activity in an area is usually measured by decades, and it would take another one to two years of observation before a conclusion could be drawn, he said.

Source: Focus Taiwan News Channel