Scientists reassure public, but caution about aftershocks

Four days after the biggest earthquake in Taiwan's history, scientists said that people should be not be overly anxious about another major earthquake in the Chianan Plain (嘉南平原) in southern Taiwan because the probability is currently very low.

However, scientists cautioned people should be prepared for aftershocks, especially those who live east of the epicenter, 12.5km west of Sun Moon Lake (日月潭) in Nantou County.

"Is that [Tuesday's tremor] the `big one' scientists expected?" people have been asking since Sept. 21. Based on information gathered in a three-day field investigation, the National Science Council (NSC, 國家科學委員會) provided the answer yesterday.

"Science experts conclude that only a low possibility of another big quake following in southern Taiwan exists," said NSC chairman Huang Chen-tai (黃鎮台).

"Some aftershocks, possibly over six on the Richter scale, are expected. We need to warn people, especially those who live in areas east of the epicenter, to be careful about aftershocks," said Tsai Yi-ben (蔡義本), professor and dean of the College of Earth Sciences at National Central University (中央大學地球科學院).

Scientists are still working out the precise sequence of events that led to the earthquake.

The epicenter lay between the Chelungpu fault (車籠埔斷層) and the Tamaopu-Shuangtung fault (大茅埔-雙冬斷層), but Tsai said that it was difficult to tell which fault failed first. The faults are approximately 20km apart. He added that both faults slipped and the interaction between the two contributed to the size of Tuesday's quake.

To evaluate earthquake disasters, officials from the NSC's National Center for Research on Earthquake Engineering (NCREE, 國家地震工程研究中心) said yesterday that data modelling by the HAZ-Taiwan computerized earthquake simulation system could be helpful.

"By simulating the earthquake, we can know immediately which parts of the island could have been most seriously affected. We have provided the disaster rescue center a list of areas that will most need emergency services," said Loh Chin-hsiung (羅俊雄), the NCREE's director.

Meanwhile, the Central Weather Bureau says there is a rumor spreading across the island that there will be aftershocks of even greater magnitude than Tuesday's jolt. The bureau dismisses this idea, and has posted vital information on its World Wide Web site (http://www.cwb.gov.tw) to explain why the rumor is groundless.

Bureau officials said yesterday that they had recorded more than 5,000 aftershocks since the seismic activity started.

"People don't have to be worried by this rumor, the aftershocks are releasing stored-up energy in a gradual manner," said Hsin Tsai-chin (辛在勤), the bureau's deputy director-general.

More worrying, according to officials at the bureau, is an approaching storm. The bureau cautioned those in disaster areas to prepare for possible heavy rain and low temperatures brought on by Tropical Storm Cam (凱姆颱風), which was southwest of Taiwan yesterday evening. Officials said the temperature during the night in mountain areas in central Taiwan might drop to 10°C or lower.