A 6.8 magnitude earthquake struck Taiwan on Sunday, triggering at least three buildings to collapse, damaging roads, bridges and derailing train carriages in the sparsely populated southeastern region. According to the island’s weather bureau, the epicentre was in Taitung county and followed a 6.4 magnitude quake in the same region on Saturday evening. No casualties have been reported from both incidents.
Tremors were also felt in capital Taipei and the southwestern city of Kaohsiung.
China’s Central Weather Bureau (CWB) designated the 6.8 earthquake that struck Taitung as a “main shock" and the magnitude 6.4 quake on Saturday and 70 quakes previously recorded as aftershocks, now reclassified as foreshocks, reported Taiwan’s Central News Agency (CNA).
Taiwan President Tsai Ing-wen has urged people to be vigilant for further aftershocks in the coming hours. “Water and electricity supplies in some areas are also affected by the earthquake," she wrote on Facebook. “The related disaster relief work is in full swing."
The United States Geological Survey (USGS) said the quake hit Taiwan at 2:44 pm on Sunday about 50 kilometres (30 miles) north of Taitung at a depth of 10 kilometres. According to reports, the jolt was reported as magnitude 7.2 initially but was later downgraded to 6.9.
In Hualien’s Yuli township, the quake caused a three-story 7-Eleven convenience store building to collapse. Four people who were trapped in the building were rescued, the Hualien fire department was quoted as saying by AFP. Two other buildings in the town collapsed but no one was inside them. Two nearby bridges collapsed while two others were damaged, the report said.
Meanwhile, the Taiwan Railways Administration (TRA) said a train derailed at Dongli station in Hualien.
While Japan’s Meteorological Agency and the Pacific Tsunami Warning Center issued tsunami advisories shortly after the quake, both later updated their alerts stating there was no threat of high waves.
What is a Tsunami?
Tsunamis are giant waves caused by large earthquakes that occur near or under the ocean, volcanic eruptions under the sea, submarine landslides or onshore landslides in which large volumes of debris fall into the water.
Earthquake Causing Tsunami
According to the USGS, earthquakes of magnitudes between 6.5 and 7.5 do not usually cause destructive tsunamis but small sea leave changes are likely observed in the vicinity of the epicentre. “Tsunamis capable of producing damage or casualties are rare in this magnitude range but have occurred due to secondary effects such as landslides or submarine slumps," it states.
Earthquakes of magnitudes between 7.6 and 7.8 might produce destructive tsunamis, especially near the epicentre. But it is considered rare for a tsunami in this magnitude range to cause damage at great distances.
However magnitude of 7.9 and greater causes significant destruction, especially if the epicentre is near the seashore. For earthquakes measuring magnitude 9.0 or greater, there are high chances of an aftershock of magnitude 7.5 or greater causing further loss of life and property.
China’s Central Weather Bureau (CWB) has said that the magnitude 6.4 quake in Taiwan on Saturday has now been reclassified as foreshocks. “There have previously been instances when a major earthquake was later re-designated as a foreshock following another bigger temblor," Chen Kuo-chang was quoted as saying. He also said the spate of quakes over the weekend may have been triggered by the Central Mountain Range fault system.
What is a fault?
A fault is a fracture or zone of fractures between two blocks of rock of the earth’s crust. When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other.
Taiwan lies at the boundary between the Eurasian plate and the Philippine Sea which is in a seismically active zone also known as the Pacific Ring of Fire. The horseshoe-shaped belt region encircles the Pacific Ocean where plate tectonics are intensively active. Geologists have identified several active faults on the island, but most of the earthquakes detected in Taiwan are due to the convergence of the Philippine Sea plate and the Eurasian Plate to the east of the island.
China’s Central Geological Survey (CGS) updated the number of active faults in Taiwan to 36 in June after the discovery of three more active faults in Kaohsiung City, Tainan City and Nantou County.
Between 1901 and 2000, there were 91 major earthquakes in Taiwan of which 48 of them resulted in loss of life, according to China’s Central Weather Bureau. In 2013, two earthquakes measuring magnitudes 6.2 and 6.5, named the Nantou earthquake series, struck central Taiwan. This earthquake series caused the collapse of three buildings, the deaths of four people and several injuries. Taiwan’s deadliest ever was a 7.6 magnitude quake in September 1999 that killed over 2,400 people.