The earthquake measuring 7.2 on the Richter scale in Hualien County on Wednesday was a very rare case involving continuous movement and the deformation of compressed plates.
Taipei and New Taipei City, with a combined area of 2,457 km2 and a population of nearly 7 million, are largely located in a weak lake sedimentary basin. As a result, the magnitude and duration of shaking during the earthquake were greater there than in other areas, and were even close to what occurred in areas near the epicenter of the earthquake.
Fortunately, the seismic resistance capacity structures in Taiwan are markedly better than those in many other countries.
From the instantaneous ground motion seismogram, one can see that the highest intensity, level 6, was detected in Hualien County’s Heping (和平) Station, which is only about 38km away from the epicenter — with the highest north-south, east-west and vertical acceleration of gravity being 363, 352 and 224 gal respectively, while the duration of shaking was about 60 seconds.
Hualien City was only about 25km from the epicenter of the earthquake — with its highest north-south, east-west and vertical acceleration of gravity being 458, 256 and 209 gal respectively, while the duration of shaking was about 60 seconds.
The observation stations in Taipei are about 145km from the epicenter of the earthquake — but the highest north-south, east-west and vertical acceleration of gravity recorded was 86, 57 and 36 gal respectively, while the duration of shaking was about 100 seconds.
As the duration was no less than that of the 921 Earthquake, the amplitude and lengthened duration of oscillation could damage high-rise buildings. This is the nature of buildings in a basin, so all one can do is try to avoid living in dangerous areas or invest heavily in improving the safety coefficient.
Taiwan is located in the island arc of the Circum-Pacific seismic zone, where about 90 percent of the world’s earthquakes occur.
The five major north-south mountain ranges in Taiwan have taken shape because the active Philippine Sea plate moves by 8cm about 35 degrees toward the northwest every year, pushing against the Eurasian continental plate.
Consequently, there are countless faults and steep mountains all over Taiwan, with 268 mountains that are more than 3,000m high, which is far more than the roughly 10 in Japan and about 20 in New Zealand. The number of high mountains shows the complexity of Taiwan’s geological structure and the natural disasters it can cause, which are very risky and should not be underestimated.
Taiwan’s key national policies should therefore include: planning of a second capital for emergency preparedness; restriction of the use of mountainous areas for national land development; management of coastal areas, rivers and outlying islands; connections between public facilities and urban communities; resilience against disasters; and post-disaster recovery.
The administrations of the outgoing and incoming presidents would surely take into consideration the chances of such natural disasters. They should implement more carbon reduction projects, “green” buildings and standard modular construction made of pre-cast units.
Promoting such sustainable self-supporting buildings would lead Taiwan on the road to prosperity.
Lai Ming-huang is an engineer with a doctorate from National Cheng Kung University and a former regional engineering department head of the Directorate-General of Highways.
Translated by Eddy Chang
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