Dr. Ruey-Chyuan Shih of the National Chung Cheng University (CCU) Graduate Institute of Seismology deduces the possible westward extension of the Meishan fault based on soil liquefaction data
2019 marks the 20th anniversary of the Jiji earthquake. Recent minor quakes around the country have raised concerns over the possibility of a stronger quake occurring. In the past, the Meishan fault was consistently regarded as a hot spot for strong earthquakes. More recently, scholars have conducted seismic studies in the area, so as to investigate the possibility of the fault’s regional extension. Associate Professor Ruey-Chyuan Shih from the National Chung Cheng University (CCU) Graduate Institute of Seismology analyzed subsurface soil liquefaction structures and indirectly verified that the Meishan fault has extended to the vicinity of Singang Township, which is further west than its previous known range, which extended only to Minsyong Station.
Dr. Shih has studied Taiwan’s faults for more than 20 years and has visited 33 active faults in the country. On the day of the Jiji earthquake, Dr. Shih could very well have been the geologist who was closest to the fault that caused the quake when it happened. As Dr Shih recalled, “The day before the quake occurred, I was at the Chelongpu fault. I never thought that such a strong quake would happen the day after.” While flipping through his photos, Dr. Shih says that, after the quake, he spent half a year recording data relating to landslides and collapsed bridges and houses in the disaster zones around Taichung. He also provided first-hand fault data to the government as references for subsequent studies.
Prior to the Jiji Earthquake, the worst quake in Taiwan’s history was the 7.1-magnitude earthquake in 1906 caused by the Meishan fault. Due to its close proximity to the Meishan fault, CCU emphasized the seismic resistance coefficients (SRCs) of its buildings during its founding years. Dr. Shih points out that CCU buildings comply with the law, which states that buildings must be at least 100 m away from faults, and that the SRCs of CCU’s phase-one buildings are as high as 0.7g, meaning that these buildings can withstand earthquakes with magnitudes above 7. Buildings constructed in later phases had SRCs of 0.4g, similar to those of nuclear power plants. As a result, the damage suffered by CCU during the Jiji earthquake was relatively minimal. Recalling his participation in the university’s relief efforts, Dr. Shih said that the collapsed bookshelves in the library were the most seriously damaged items, while vulnerable items such as window ventilators and books sustained minor damages.
The Meishan fault is a 13-km active fault that stretches southwest from Meishan Township towards the northwest region of Nanhua University and CCU, and also extends westwards to Minsyong Station. Based on graphical documentation of the fault that was produced during the Japanese colonial era, Dr. Shih speculates that the fault’s extended region could go beyond Minsyong Station. According to Dr. Shih, many have questioned the actual length of the Meishan fault over the years, with some claiming that the Japanese-era documents only recorded soil liquefaction areas. This issue had polarized scholars over time.
In light of the wide soil liquefaction areas in Minsyong and Singang townships caused by the Meishan earthquake that occurred more than a century ago, Dr. Shih’s recent studies have focused on the relationship between faults and soil liquefaction. Using petroleum mining techniques to measure the occurrence of soil liquefaction around Minsyong and Singang, he found that it is evident that areas of soil liquefaction have converged and formed linear structures in certain regions. According to Dr. Shih, “The results indicate that since these areas are relatively close to the fault, the stress is strong enough to compress the water inside the soil, which causes serious soil liquefaction.” Based on measurement data, Dr. Shih also deduced that the Meishan fault could be longer than its previous known range (which extended only to Minsyong Station), and may extend westwards to Singang Township.
In recent years, scholars have predicted that the Meishan fault is at a risk of a major earthquake. Since Minsyong and Singang townships suffer from serious soil liquefaction, there are concerns over the residents’ safety and livelihood if a major earthquake occurs. However, according to Dr. Shih, most of the soil liquefaction areas are farmland, while the seismic resistance levels of buildings in the Chiayi region have been reinforced in the wake of previous quakes, and old buildings are gradually being demolished. Therefore, the risk of buildings collapsing due to earthquake-induced soil liquefaction is rather low. However, he notes that there is nonetheless a high possibility of secondary damage after a quake. Therefore, attention should be given towards problems such as old pipes and narrow escape lanes, so as to reduce the risk posed by a quake.