6.7-magnitude quake was a `normal energy release'

Following yesterday's noontime earthquake, which rattled the east and north of the country, seismologists moved quickly to reassure a panicky public.

The scientists said the temblor was a normal phenomenon and part of the planet's energy-release mechanism. There were no reports of earthquake-related damage or casualties yesterday.

Ground motion lasted for more than 10 seconds.

According to the Central Wea-ther Bureau (CWB), the quake, which struck at 12:02pm yesterday, registered 6.7 on the Richter scale, making it the strongest this year. It was the strongest quake since a quake measuring 7.0 on the Richter scale struck on July 16 last year.

The epicenter of yesterday's earthquake was 32.2km below the surface and 139.5km southeast of the bureau's Hsioulin seismic monitoring station (秀林地震站) in Hualien County.

In Ilan County the intensity of the quake was measured as a 4 on Taiwan's unique scale of tremor-intensity measurement -- which classifies tremor-intensity into seven categories. In Taipei and Hualien the intensity measurement was 3. The intensity in other counties was recorded at between 1 and 2.

The quake was followed by dozens of aftershocks. To avoid possible disaster, all lines of the mass rapid transit system in Taipei were shut down immediately. They were reopened 16 minutes later.

"The earthquake was a result of the Philippine tectonic plate sliding into the Ryukyu oceanic trench (琉球海溝) where it collides with the Eurasian tectonic plate," said Kuo Kai-wen (郭鎧紋), director of the bureau's seismology center, adding that the phenomenon occurs once every three to five years.

Seismologists also explained the reason why the ground motion lasted so long.

"Because the epicenter was remote and deep, the period of the seismic wave was relatively long. That's why the tremor's duration was relatively long,"

Since the devastating tremor of Sept. 21, 1999 -- which claimed more than 2,400 lives in Taiwan -- seismologists have tried to remind people that minor earthquakes in Taiwan are a relatively common occurrence.

Seismologists said that Taiwan experiences frequent earthquakes because of the constant, slow collision of the Philippine and Eurasian tectonic plates, which causes pressure to build up and then be released.