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The Weiguan Jinlong residential building in Tainan after collapse. The surrounding buildings do not appear to have severe damage.

Taiwan earthquake update

Taiwan lies on the boundary between the Eurasian Plate and the Philippine Sea Plate, which are converging at 80 mm per year. The island is the result of uplift caused by the collision of the northern end of the Luzon Arc and the continental margin of China.

On the 6 Feb 2016 a Mw 6.4 earthquake occurred at a depth of about 20 km, about 40 km east of the southern Taiwanese city of Tainan, which has a population of 1.9 million. The seismic waves travelling northwest to Tainan from the earthquake source were amplified by the the soft sediments of the Chianan Plain, which may have contributed to the damage in Tainan.

The earthquake occurred about 20 km west of the 4 March 2010 Mw 6.4 Jiashian earthquake and appears to be a delayed continuation of the stress release of that event. The worst affected city was Tainan, where numerous buildings collapsed including a 17‐story residential building with about a hundred people still trapped inside. Eight buildings in Tainan collapsed or were semi‐collapsed, and five others were left leaning at alarming angles, evidently due to column failures on lower floors. According to the National Fire Agency, the quake left about 400,000 households without water nationwide. Power outages affected about 121,000 residences in Tainan and hundreds in Kaohsiung.

Ground motion intensity map of the Tainan earthquake (Central Weather Bureau).

Ground motion intensity map of the Tainan earthquake (Central Weather Bureau).

A Central Emergency Operation Center was set up shortly after the earthquake had occurred. From the operations center, President Ma Ying-jeou coordinated the rescue efforts and travelled to Tainan to view rescue efforts. The Tainan emergency services also set up emergency response centre minutes after the quake. Premier Chang San-cheng cancelled his itinerary to see for himself the devastation in Tainan. The Ministry of Health and Welfare launched six regional emergency operation centers. The National Defense Ministry confirmed that army units were dispatched for the rescue efforts consisting of 810 personnel, 11 medical teams, 24 search and rescue teams and 38 vehicles. The Army Command Headquarters based in Guiren District sent two helicopters to survey the damaged areas. Kaohsiung Armed Forces General Hospital dispatched 30 medical personnel to Tainan. Armed Forces Chief of the General Staff Yen Teh-fa was stationed at the joint military operations command center to oversee the rescue efforts. A total of 1,200 beds in four locations were prepared by the military for people who lost their homes due to the earthquake. The Tainan Air Force Base was turned into a temporary shelter that could accommodate up to 1,400 people left homeless by the quake.

Rescue teams from Japan and People’s Republic of China provided advice on the search and rescue efforts.

The damage caused by the quake in the worst affected city of Tainan was enormous with numerous buildings reportedly collapsed, including at least one 17-story residential building in Yongkang District, with hundreds of people trapped in the collapsed buildings. About 115 people died inside the Weiguan Jinlong building in Tainan City, including a six-month-old infant who died a few hours later in hospital. Officials reported that 397 people were rescued, with 104 of them taken to hospital. More than 500 people in total were injured from a disaster that struck during the most important family holiday in the Chinese calendar — the Lunar New Year holiday.

Accelerogram of the 2016 earthquake recorded in central Tainan, with the horizontal axis showing time in seconds.

Accelerogram of the 2016 earthquake recorded in central Tainan, with the horizontal axis showing time in seconds.

Location map, with the epicentre of the 2016 and 2010 earthquakes shown by the orange and black stars respectively; orange lines show mapped active faults.

Location map, with the epicentre of the 2016 and 2010 earthquakes shown by the orange and black stars respectively; orange lines show mapped active faults.

A total of 34 historical buildings around Taiwan were damaged, of which 23 are located in Tainan. Public Work Bureau of Kaohsiung City Government discovered 314 broken bridges in the city with 5 of them deemed unusable.

Taiwan Power Company initially reported that 121,000 households experienced power outage after the quake, and quickly restored power to most of those homes. The National Fire Agency reported that about 400,000 households were left without water supply.

Taiwan High Speed Rail (THSR) cancelled all train services between Taichung Station and Zuoying Station due to damage to the train power systems and extensive damage to its tracks north of Tainan.

Taiwan Semiconductor Manufacturing Company reported that the silicon wafers at its Tainan factory were damaged, although it did not affect much of its current shipment. United Microelectronics Corporation said that the earthquake triggered its plant safety measures to shut down the machines and that they would need recalibrating.

On 13 February 2016, Tainan Mayor William Lai declared the search and rescue mission for the earthquake victims were over. During the 7 days of search and rescue, military, fire and police rescue teams worked tirelessly with overseas assistance from China and Japan under extremely difficult conditions. Many people owe their life to these teams.

This earthquake is relevant to Australia because events of this magnitude occur somewhere in Australia about once per decade. The magnitude of the earthquake was not very large and the ground motions recorded in the surrounding region were not particularly strong. However, at about 0.25g, the peak accelerations in central Tainan were about four times stronger than typical building code values for Australia’s capital cities. The building code peak acceleration of about 0.6g in Tainan is about ten times higher than in Australia.

For more information, go to www.riskfrontiers.com

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Professor Paul Somerville is Chief Geoscientist at Risk Frontiers. His main interests are in earthquake and tsunami hazards, and he has quantified these hazards and applied them in engineering practice to the seismic design and analysis of major buildings, bridges, dams and power generation facilities in Australia, New Zealand, Japan, the United States, and many other countries around the Pacific Rim. He has been involved in the development of building codes in the United States, and led developments in the engineering characterization of near-fault ground motions.