Taiwan's anti-earthquake efforts after the 921 disaster

The earthquake that claimed the lives of more than 2,400 people in 1999 prompted Taiwan to change its construction regulations and focus on strengthening against vibrations.

The 7.4 magnitude earthquake occurred at 7:58 a.m. (6:58 a.m. Hanoi time) with the epicenter located in the east of Taiwan island, off the coast of Hualien district, at a depth of 15.5 km. This is the strongest earthquake on the island in the past 25 years , after a 7.6 magnitude earthquake called Earthquake 921 that killed 2,400 people in 1999.

The image is easy to see, although this earthquake was 7.4 magnitude, many high-rise buildings only tilted instead of completely collapsing. According to Standard & Poor's, Taiwan is one of the 10 most earthquake-prone countries in the world . Most earthquakes after 1999 were smaller in scale and caused fewer casualties. However, they have learned many lessons from the disaster and are prepared to prevent damage if a similar large earthquake occurs.

A building in Sinjhuang District collapsed in the 921 earthquake. (Photo: New Taipei City Public Works Department).

Establish regulations on earthquake resistance of high-rise buildings

After the number of serious casualties in the 921 earthquake, many people called for changes in building regulations and construction methods . The government reclassified earthquake zones with updated data, adding more homes in strong earthquake zones. Authorities also introduced new regulations on high-rise building construction, including quality control, earthquake resistance assessment and building reinforcement measures.

For example, the 1999 Seismic Design Standards and Regulations on High-Rise Buildings classifies the Chelungpu fault that caused the 921 earthquake as a type 2 active fault. This classification does not require buildings to be built on the fault line. The fracture must have good earthquake resistance.

Hwang Shyh-Jiann, general director of the Center for Earthquake Research and Engineering (NCREE) and professor of civil engineering at Taiwan University, said "investigation results reveal the collapse of buildings in The 921 earthquake was mainly caused by improperly installed concrete reinforcement structures . Poor reinforcement techniques include a support base that is not strong enough to hold the reinforcing steel bars, steel bars placed too far apart, or using poor quality materials that result in low-strength concrete, among other problems.

Reinforce buildings vulnerable to earthquakes

After the 921 earthquake, in addition to buildings that collapsed completely or partially, a large number of houses were identified as vulnerable structures. Since it is impossible to demolish and rebuild the entire building, the government initiated a structural reinforcement plan for the fragile building to increase its earthquake resistance. According to Hwang, reinforced concrete buildings, including public and private buildings, built before the 921 earthquake account for 59% of the floor area in all current high-rise buildings in Taiwan. These buildings are in the most urgent category, requiring assessment to determine whether reinforcement is necessary.

Public buildings include schools, police departments, fire stations and offices and the fortification plan focuses on schools. Since 2009, Taiwan's Ministry of Education began promoting earthquake resistance assessments and reinforcement plans for schools. The importance of earthquake reinforcement became clear during the 2010 Kaohsiung earthquake. After the earthquake, the pillars of an unreinforced school were visibly damaged with exposed steel bars, while The structure of another school is only 1.2 km away and has been reinforced with no signs of damage.

Technological development

Although earthquake prediction technology still needs to be perfected, Taiwan has developed the means to provide warnings. Through integrating monitoring equipment with other technology, when seismic waves are detected, the system can quickly estimate the scope of the area affected by the earthquake and its destructive power, then issue a warning. , giving people a few more seconds to act before the shaking arrives.

The 2016 major earthquake concentrated in My Nung district of Kaohsiung city prompted scholars and the Central Weather Bureau (CWB) to co-develop an automatic system to determine the location of earthquakes, which can localize the center of earthquakes. shock within seconds of starting.

Next, the system estimates the seismic scale and intensity across Taiwan, then transmits this information to the earthquake rapid warning system for notification. In a strong earthquake event of 5 degrees or more, the system can provide mobile phone warnings to communities in districts and cities within 10 seconds.

According to Chen Kuo-chang, director of the Seismology Center of CWB, with the automatic positioning system's accuracy of more than 60%, they hope to be able to reduce notification delivery time to 5 seconds in the future, helping Taiwan has the fastest earthquake warning in the world, surpassing even Japan.

In 2022, Professor Yen Horng-yuan and his colleagues at the Department of Earth Sciences of the National Central University achieved a breakthrough in earthquake prediction by comparing geoelectrical, geomagnetic and ionospheric data. in earthquakes of magnitude 6 or higher between 2013 and 2018. The analysis results reveal corresponding anomalies, which can become earthquake prediction factors.

More than 70% of Taiwan's earthquakes occur off the coast of Yilan and Hualien counties. Chen explained that this area is a subduction zone at the edge of the Eurasian tectonic plate, geologically very complex with many faults. The Manila Trench running from near Phuong Son, Binh Dong to the Philippines has the potential to produce earthquakes and tsunamis. Therefore, Taiwan installed observation stations on the seabed connected via submarine cables from Taucheng in Yilan district to Fangshan, and southward from Fangshan along the eastern edge of the Manila Trench. This system reduces the time needed to calculate offshore earthquake parameters from 35 seconds to 20 seconds, allowing CWB to warn of tsunamis. So far, only Taiwan, Japan and the US have established such undersea surveillance networks.

Located at the intersection of the Eurasian and Philippine plates, Taiwan is seismically active with 33 faults and many other underground faults throughout the island. About 8.6 million people live within 10 km of the active fault.

Taiwan experiences an average of 100 earthquakes a day, but most are small tremors that most people don't feel. An earthquake needs to be at least 3.5 - 4.5 magnitude to be felt by people near its epicenter.