A series of earthquakes over the past few days were likely aftershocks of the April 3 earthquake in Hualien County, with further aftershocks to be expected for up to a year, the Central Weather Administration (CWA) said yesterday.
Based on the nation’s experience after the quake on Sept. 21, 1999, more aftershocks are possible over the next six months to a year, the agency said.
A total of 103 earthquakes of magnitude 4 on the local magnitude scale or higher hit Hualien County from 5:08pm on Monday to 10:27am yesterday, with 27 of them exceeding magnitude 5. They included two, of magnitude 6 and 6.3, which struck at 2:26am and 2:32am yesterday.
Photo: CNA
The aftershocks have primarily been in northern Hualien County, but have progressively moved southward to include Shoufeng (壽豐) and Fenglin (鳳林) townships, Seismological Center Director Wu Chien-fu (吳健富) said.
Aftershocks of a significant earthquake tend to dissipate over time, but there would be sudden spikes due to stress adjustments, Wu said, adding that the agency is not ruling out another large earthquake, although it would be unlikely to be magnitude 7 or higher.
The aftershocks were felt more strongly over the past two days than in the previous two weeks, because they were shallow and their epicenters further inland, he said.
Photo courtesy of the Fengbin Township Office via CNA
Commenting on the extremely shallow earthquakes, some as shallow as 1.5km, Wu said this could be due to statistical error or the region’s unique geology.
The agency also advised the public to avoid visiting mountainous regions due to expected aftershocks and rainfall from a series of weather fronts.
National Central University Graduate Institute of Applied Geology professor Lee Chyi-tyi (李錫堤) said the frequent aftershocks were due to stress adjustments after the April 3 quake, adding that the public should not be too worried.
Lee said that similar earthquakes could occur and that if they did, it could see Taipei shake for longer than three minutes.
Taipei shook for one-and-a-half minutes in the 1999 earthquake.
Design response reports for buildings that are at least 50m tall or 15 floors were compiled after 1999, Lee said, adding that the results showed that these buildings in the Taipei basin could withstand such major earthquakes.
After yesterday morning’s quakes, a defunct two-story factory and a residential building in Hualien County that had been marked as structurally unsafe each partially collapsed, but no one was injured.
The factory on Ziqiang Road in Jian Township (吉安) was vacant, Hualien County Economic Affairs Department Director Teng Zeu-yu (鄧子榆) said.
It had been assessed as structurally unsafe following the April 3 quake, and when its first floor collapsed yesterday, it damaged two adjacent buildings housing a steak restaurant and warehouse, he said.
The factory would soon be torn down and its water and power supplies cut, and officials would assess whether to demolish the two other affected buildings, Teng said.
Two floors of the residential building in Shoufeng Township collapsed during yesterday’s quakes.
The quakes have so far left four buildings, including the Full Hotel on Zhongshan Road and the Tong Shuai building, partially collapsed or tilted, the Hualien County Government said.
Full Hotel had been undergoing a renovation while the unoccupied Tong Shuai building was already marked for demolition following the April 3 quake.
The county plans to demolish both buildings to prevent the risk of further collapse, Teng said, adding that it would take two weeks to demolish the two buildings.
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