Firemen in Taipei carry out a rescue drill yesterday to prepare themselves for natural disasters. Taiwan will mark the 10th anniversary of the most deadly earthquake in the island's history, which claimed 2,400 lives on September 21, 1999. CNA

TAIPEI: The 20 earthquakes that hit Yilan county's Nanao area during a 14-hour period earlier this week do not necessarily presage a major earthquake, a Central Weather Bureau official said yesterday.

Hsiao Nai-chi, a division chief at the Central Weather Bureau's Seismology Center, was commenting on the 23 earthquakes that rocked the northeastern county and the two eastern counties of Hualien and Taitung between 4:45 pm Tuesday and 6:42 am Wednesday, with 20 centered around Nanao township.

"Only one of those quakes was a magnitude 5 on the open-ended Richter scale, and the remaining quakes were magnitude 4 or even less intense," Hsiao said, adding that most of the tremors affected only limited areas.

Yilan and Hualien have traditionally been the areas most prone to seismic activity in Taiwan because of the movement and collisions of crustal plates, Hsiao said.

Speculation that a major quake may strike soon has arisen recently because of the higher-than-normal frequency of earthquakes around Taiwan in recent days.

On Sunday alone, two medium-intensity tremors jolted Taiwan. One, magnitude 5.4, was centered in Mingchien township in central Taiwan's Nantou county.

The other, a magnitude 5.5 quake, struck 15 kilometers northwest of the Yuli seismic station in Hualien county at a depth of 2.5 kilometers.

As this year marks the 10th anniversary of the deadly September 21, 1999 earthquake, Sunday's earthquake in Nantou area added fuel to anxieties among some local residents that Taiwan may have entered yet another seismic peak cycle.

The mountainous Nantou county took the brunt of the 921 earthquake, the worst natural disaster to hit Taiwan in the last century. The quake killed around 2,500 people.

Hsiao said, however, that speculation that a strong earthquake is imminent is groundless.

"As a matter of fact, the recent spate of earthquakes has allowed the normal release of gravitational energy, a trend that could theoretically help stem a devastating temblor," Hsiao explained.

Practical observations also show that the number of tremors does not correlate with the occurrence of major earthquakes, he added.

According to Seismology Center statistics, Taiwan was hit by an average of 21,295 earthquakes annually between 1994 and 2008.

In the first half of this year, 8,918 quakes were recorded, Hsiao said. He added that the number did not exceed the norm.

Hsiao also dismissed speculation that a strong earthquake would hit once every 10 years, saying no basic rule can be derived from the frequency of earthquakes with casualties of more than 100 that hit Taiwan during the 20th century.

For example, a magnitude 7.1 earthquake hit the Meishan area in 1906, just two years after the Douliou earthquake was recorded with similar magnitude.

In 1935, a magnitude 7.1 earthquake struck the Hsinchu-Taichung area, followed by a major quake in Chungpu, Chiayi county in 1941, a Hsinhua earthquake in 1946 and a Chiayi-Tainan earthquake in 1964.

Taiwan was rocked by temblors of magnitude 7 or above twice in the closing decade of the 20th century, in 1996 and 1999. Another hit Taiwan in 2004, but only the 1999 quake took a heavy toll in human lives and property. The other two struck at sea, well off Taiwan's coast.

China Daily/CNA

(HK Edition 07/30/2009 page2)