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Scientists warn of aftershocks

Rescuers pull out an injured person trapped in a damaged building on Taipei's Chengteh Road after yesterday's earthquake. PHOTO: CHIANG YING-YING, TAIPEI TIMES

Residents living in the north and northeast should be well-prepared for powerful aftershocks, that could exceed five on the Richter scale, Central Weather Bureau seismologists said yesterday.

"In the following two weeks, some strong aftershocks of the earthquake will strike Taiwan," said Kuo Kai-wen (郭鎧紋), director of the bureau's seismology center.

"People should secure shop signs [and other large objects] and stay calm," Kuo said.

Yesterday's tremor, measuring 6.8 on the Richter scale, struck the island at 2:52pm, making it the strongest earthquake in the past 20 months. It was the strongest since a quake measuring 7.0 on the Richter scale struck on July 16 in 2000.

Since the devastating 921 earthquake, which registered 7.3 on the Richter scale and claimed more than 2,400 lives, seismologists have reminded the public that minor earthquakes in Taiwan are a relatively common occurrence.

Yesterday, seismologists said that the earthquake resulted from a collision between the Philippine and Eurasian tectonic plates, which are in continuous motion relative to each other.

The greatest intensity of the quake was measured at Nanau (南澳) of Ilan, as six on Taiwan's unique scale of tremor-intensity measurement -- which classifies tremor-intensity into seven categories.

In Taipei, roughly 100km away from the epicenter, the intensity was measured as five, which is the same as that in Hualien. The epicenter was 44.3km east of the bureau's Hsioulin seismic monitoring station in Hualien County.

Seismologists said that a basin effect could explain why an earthquake occurring in Hualien could create such an impact in Taipei.

"The intensity of seismic waves was magnified when entering Taipei Basin, which is composed of soft sediment," said Chen Kuo-chang (陳國昌), a seismologist at the bureau.

Chen said that a similar earthquake occurred near Hualien in November of 1986, leading to 13 deaths and 45 casualties in Taipei.

Another earthquake, registering 4.9 on the Richter scale, occurred at 4:02pm in Ilan yesterday. The epicenter was 16.7km east of the bureau's Nanau seismic monitoring station in Ilan County.
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