The Seismology Center of the Central Weather Bureau (CWB) yesterday corrected the magnitude of an overnight earthquake to 6.7 from 5.7 on the Richter scale.
Seismologists said a smaller quake coming a few seconds before the strong quake had disrupted the reading and caused the rare mistake.
The 6.7-magnitude earthquake occurred at 11:54pm on Monday night, with the epicenter located 96.6km east of Hualien and 10km under the seabed, according to the center.
The tremor was felt in most parts of Taiwan. No casualties or damage was reported.
It was first mistakenly reported by the center as measuring 5.7 on the Richter scale and occurring at 11:55pm from an epicenter 1km northwest of Nanao, Ilan County, and 19km underground.
CWB Deputy Director-General Hsin Tsai-chin (辛在勤) said because the smaller quake came just four seconds before the 6.7-magnitude quake, the computer-aided automatic locating system confused the shockwaves of the two quakes.
The bureau discovered the mistake and immediately released a correction about one hour later after a manual analysis of the recorded data, Hsin said.
In Taipei, buildings swayed for more than one minute during the quake. Some residents in Ilan City fled their homes after being awoken by the strong tremor, local cable news network said, adding that the quake also triggered rock falls onto a highway.
Yesterday, another moderate earthquake hit Hualien at 11:16am, but no injuries or serious damage were immediately reported, the CWB said.
The 3.9-magnitude quake's epicenter was 11km west of Hsilin, close to Hualien, the bureau said.
A total of 122.5 of every 1,000 insurance policies issued last year included coverage against earthquake damage, compared with only 1.7 out of every 1,000 in the previous year, the Directorate General of Budget, Accounting and Statistics (DGBAS) reported yesterday.
While 934,000 household insurance policies contained an earthquake insurance clause last year, 99,000 fire insurance policies had supplementary earthquake coverage, according to the DGBAS.
Since April 2002, housing fire insurance policies in Taiwan have automatically included one-year coverage against earthquakes, known as basic housing earthquake insurance.