Taipei: The Central Weather Administration (CWA) announced that a magnitude 4.9 earthquake that struck off the eastern coast of Taiwan on Sunday is considered an independent event and part of a stress-adjustment process. The earthquake occurred at 4:47 p.m., with the epicenter located at sea approximately 45.4 kilometers south of Yilan County Hall at a depth of 5.9 kilometers.

According to Focus Taiwan, the quake's intensity was highest in several townships in Yilan and neighboring Hualien County, where it measured 4 on Taiwan's seven-tier intensity scale. Lin Po-yu, a division chief at the CWA's Seismological Center, stated that the earthquake took place in the Heping Basin, an offshore area between Yilan and Hualien, and was caused by the Philippine Sea Plate subducting beneath the Eurasian Plate, with fracturing occurring during the process.

Wu Chien-fu, the director of the Seismological Center, clarified that the quake was not an aftershock of the magnitude 7.0 earthquake from December 27 last year. Its more southerly location and shallow depth led the agency to preliminarily classify it as an independent event. Lin also noted that a magnitude 4.6 earthquake struck the same area on Friday, followed by another magnitude 4.7 tremor around 1 a.m. on Sunday.

From 1973 to the present, there have been 20 earthquakes of magnitude 5.5 or higher within a 20-kilometer radius of Sunday's magnitude 4.9 quake epicenter, including a magnitude 6 event on May 10, 2024. Wu explained that earthquakes occurring in basins are typically shallow, citing the recent quakes with depths of around 10 kilometers or less.

The recent sequence of earthquakes is likely part of a stress-adjustment process, Wu said, as energy release in one area can lead to stress buildup in surrounding regions, increasing strain on rock layers and making additional quakes more likely as the system seeks a dynamic balance. Wu also mentioned that most earthquakes of around magnitude 4.5 occur along fractured zones and release relatively limited energy, after which the area enters a new phase of energy accumulation.

With approximately 70 percent of Taiwan's earthquakes occurring in the island's eastern half and its offshore waters, Wu indicated that magnitude 4 to 5 quakes are common in the region, and there is little need to classify magnitude 3 tremors as aftershocks.