More tremors possible after morning quake: bureau

‘WITHIN EXPECTATION’::If it were a foreshock, another earthquake of magnitude 6 or greater can be expected, but if it were the main quake, aftershocks are not likely

By Shelley Shan  /  Staff reporter

Fri, Aug 09, 2019 - Page 1

A magnitude 6 earthquake struck just off the coast of Yilan County at 5:28am yesterday, the Central Weather Bureau said, adding that it does not exclude the possibility that a bigger earthquake could happen near the epicenter within a week.

Data from the Seismological Center showed that the epicenter was 36.5km southeast of Yilan County at a depth of 22.5km.

The earthquake was detected nationwide, except on Hengchun Peninsula, center Director Chen Kuo-chang (陳國昌) said.

The highest intensity felt was level 6 in Yilan County’s Wuta (武塔), bureau data showed.

A level 5 intensity was recorded in Yilan City, while a level 4 intensity was detected in Hualien County, New Taipei City, Taipei, Hsinchu County, Taoyuan and Taichung, the data showed.

The bureau has recorded three earthquakes at or exceeding magnitude 6 this year, including yesterday’s, Chen said.

There was a magnitude 6.3 earthquake on April 18 and a magnitude 6.1 quake on July 27, although the latter was not within the bureau’s monitoring zone, so did not count toward the official tally, he said.

On average, the nation records two or three earthquakes at magnitude 6 or greater per year, Chen said, adding that the bureau had previously said that another magnitude 6 quake was likely to happen in the second half of this year.

“It is a good sign that the seismological energy was released at a location within our expectation,” he said.

Regarding the cause, Chen said that the epicenter was at a fracture zone south of Yilan.

Most of the nation’s earthquakes exceeding magnitude 6 come from the zone, he said, adding that a magnitude 8 earthquake occurred there in 1920.

Ma Kuo-fong (馬國鳳), a professor in National Central University’s department of earth science, has listed the area as one of the top earthquake-prone regions in the nation, Chen said, adding that small and medium-size earthquakes have happened more frequently there this year compared with the past few years.

In terms of depth, most of the earthquakes in the zone happen 15km to 20km below the ground, he said.

“If yesterday’s earthquake was a foreshock, we do not exclude the possibility that it could be followed by another earthquake exceeding magnitude 6. If the earthquake is a main earthquake, there should not be too many aftershocks,” Chen said, adding that the bureau would closely monitor seismic activity for a week.

A magnitude 4.6 earthquake at 7:02am yesterday was not related to the magnitude 6 quake, Chen said.