Chichi, Taiwan Earthquake of September 21, 1999
This post-event report provides insight from the Chichi, Taiwan earthquake that occurred on September 21, 1999. The report discusses the effects on the people, structures, and the country of Taiwan. Beginning the day of the earthquake, EQE International had a team of engineers on the ground in the affected area, investigating and researching the damage, providing support to our clients, and documenting lessons learned to prevent such catastrophic losses in future earthquakes.
Overview of the Chichi Earthquake
An earthquake of magnitude 7.6 occurred in Taiwan at 1:47 a.m. on September 21, 1999. The epicenter was approximately 7 km NW of Chichi, a small town bordering a mountainous resort area, located 155 km from Taipei, the capital. The duration of severe ground shaking was about 40 seconds. The earthquake was felt over the entire island. In the 5 days following the earthquake, there were many aftershocks, several from M6.0 to M6.8.
This earthquake is of particular importance because of its impact on the high-tech facilities that are a crucial part of the supply chain to the worldwide computer manufacturing industry. Business interruption in these facilities has repercussions for major computer companies in Silicon Valley and elsewhere.
This was the largest earthquake to hit Taiwan in recent history. High ground accelerations on the order of 0.5g to 1.0g were recorded in the epicentral region. Significant ground failures of various types were observed. One of the most spectacular aspects of this event was the extreme amount of vertical ground offset observed along the fault rupture. Offsets measured 3m to 6m in many regions. At the dam in Shihkang, nearly 15m of vertical offset was noted, disrupting water supply to Taichung.
Impact on High-Tech Facilities
Hsinchu is located about 110 km from the epicenter and is the site of the Science Based Industrial Park, a major development where about 30 companies provide a significant percentage of the world’s semiconductor manufacturing and silicon processing. Even though the facilities were a long distance away from the epicenter, there was still a major business interruption consequence from this earthquake for this key industry.
The overwhelming problem caused by the earthquake was loss of electrical power. Almost all of the Science Park was down for several days, resulting in business interruption costs of about $50 million to $100 million per day. Earthquake damage to distant 345 kV transmission towers and a switching station made it impossible for the park to receive power from the usual steady supply from the South of Taiwan. Power was slowly restored to major users in the area by rationing residential and small commercial customers in other parts of the country, including Taipei. Some facilities were able to maintain emergency power through the use of generators with varying success. One wafer fabrication company sustained a large loss when the generators burnt up after running continuously for 40 hours after the earthquake. With loss of the standby power, this facility went completely black, and lost power to fans that maintain the clean room environment.
The large business interruption costs due to this power failure clearly demonstrate the need to consider the risk not just to the facility, but also to the surrounding infrastructure.
The ground shaking intensity in the Science Park area was low, with ground accelerations of less than 0.15g. As such, damage to buildings in the Science Park was limited to minor breakage of windows and small cracks in concrete walls. Some facilities sustained partial failure of raised floors and dropped ceilings. Had the earthquake ground motion been more intense, the business interruption as a result of structural failure would have been worse. The buildings in the Science Park can be categorized according to age: mid-80s, late 80s to early 90s, and mid-to-late 90s. There are significant differences between the building codes for these three periods. Heavy concrete was used in most of the buildings, some with and some without special shear walls. Some buildings, mainly those that are newer and taller, were built with structural steel. With more intense shaking, there could have been widespread business interruption caused by structural damage to the mid-to-late 80s and early 90s buildings.
Well over 10,000 buildings collapsed or were severely damaged. The collapsed buildings were predominately of reinforced concrete framing, with infill masonry walls or reinforced concrete walls, and ranged from older, smaller buildings to modern high-rises.
Within about 5 km of the fault line, ground accelerations approached 1.0g in the E-W direction. The “softer” first story of many older buildings collapsed as a result of severe ground shaking, especially those oriented such that E-W was their weaker direction. Most of the buildings in Chichi were destroyed by the earthquake. Other towns that were hit exceptionally hard were Chungliao, Wufeng, Tali, Takeng, Shihkang, and Tungshih.
Directly on the fault line, vertical ground offsets caused complete destruction of all buildings that straddled the fault. This was observed in Mingchien, Takeng, and Shihkang.
More than about 5 km from the fault line, it was repeatedly observed that the older buildings performed well, but many of the modern structures over six stories tall performed poorly. This can be attributed to faulty design and construction, and improper enforcement of seismic design provisions in the building code - even though the building code used in Taiwan is comparable to those used in Japan and in California.
Varying degrees of damage to industrial facilities were observed. Aggregate and concrete batch plants were damaged heavily throughout Taiwan. Silos and hoppers with heavy fill loads collapsed, causing severe damage to adjacent structures and equipment as they fell. Within about 40 km of the fault line, damage was observed at essentially every aggregate and concrete batch plant. The seismic design practice that is used for the design and construction of such facilities clearly requires a major revision.
In the city of Puli, a 30-year-old winery sustained heavy damage. Many of the buildings were constructed of reinforced concrete frames with masonry infill walls, and many collapsed. A brewery in the city of Nantou experienced losses from a fire resulting from spilled spirits ignited by sparks. Business interruption costs are projected to be very high.
At Taichung Port, about 70 km from the epicenter, many large flat-bottom steel storage tanks containing molasses were affected by the earthquake. Sloshing of the contents caused heavy damage to the roof and walls of the tanks, resulting in content spillage. A nearby food processing plant had several grain silos, which were filled with product by plant operators because of an impending typhoon predicted before the earthquake. When the earthquake hit, all of the full silos collapsed.
Infrastructure affected by the Chichi earthquake include lifelines, ports, water supply, and roads.
Electrical power supply throughout the country was partially restored within a few days. Long outages occurred due to a combination of extensive switchyard and substation damage, high-voltage transmission tower damage, and a trip off-line of two nuclear power plant units. Water and gas supplies in Taipei were also impacted by the power outage. Telephone service was continuously interrupted.
The amount of liquefaction in the port of Taichung was severe despite its distance from the fault. Up to 20m wide sink holes developed, apparently due to liquefaction of deep silty sand layers below the reclaimed land. Quay walls tilted slightly; with the land behind them settling up to 2m. The effort to rebuild the Taichung port facilities is estimated to take up to 2 years. Other major ports in Taiwan performed well.
The drinking water reservoir in Shihkang was lost due to failure of the dam. The left side of the dam dropped about 15m due to ground faulting. The tremendous force of the earthquake distorted the entire massive structure (all gates are inoperable) and caused one section to fail. The dam will likely not be repaired. Reportedly, a new dam will be constructed upstream.
The significant ground heaving in Shihkang diverted the flow in a drinking water channel completely away from its original path. Temporary channels were hurriedly dug to restore the water flow. Open culverts and buried water piping were broken at fault crossings. Within 4 days of the earthquake, much new piping had already been laid in newly dug trenches.
Numerous road sections were heavily damaged by vertical ground offsets from the fault rupture and landslides. Repair work, removal of collapsed buildings, and emergency supply vehicles desperately trying to get to damaged areas resulted in extreme traffic jams.
On the outskirts of the city of Nantou, sections of the new (Nantao) elevated expressway were shored-up due to earthquake damage distress to the superstructure. There was severe cracking at the tops of the massive support piers, and the outboard traffic lane was sagging.
The Chichi, Taiwan earthquake provides lessons that unfortunately have been taught repeatedly by past devastating earthquakes:
- The significant business interruption to the crucial high-tech industry could have been minimized through adequate seismic strengthening of equipment and the proper implementation of emergency plans that would have more specifically addressed the loss of off-site power in detail.
- Loss of life and building collapse were avoidable. Today, it is horrifying that new buildings are being designed and constructed in an unsafe manner without regard to earthquakes and other natural disasters. This is especially true given the generally good design criteria provided in the Taiwan building code. The presence of a good building code does not guarantee good performance of buildings and their contents. It is critical to also have adequate design, construction quality, and especially independent review of design and inspection of construction.
- Owners do not understand the intent of the building code. Buildings properly designed to code requirements will sustain damage during major earthquakes. The intent of the code is to ensure that buildings remain safe and occupants can exit. If building owners want better buildings, then this will have to be specifically requested, and can be accomplished by more sophisticated, “performance-based designs.”
- Severe industrial losses also were avoidable. None of the industrial losses that occurred in this earthquake were surprises. All of the losses could have been readily predicted. The lack of redundancy in the power grid was a problem identified well before the earthquake. Construction of a back-up line had begun years ago, but progress was reportedly on hold due to land acquisition problems. In this earthquake, there are no significant lessons with respect to structural behavior. Experienced structural engineers could have pinpointed and remedied most building and equipment configurations that led to earthquake damage.
- Limited earthquake insurance availability. There are reports that less than 1% of the residences in Taiwan are insured for earthquakes. Improvements in hazard mapping and use of sophisticated catastrophe management software will hopefully enable Taiwan to improve insurance availability through risk-based catastrophe policy pricing. Risk-based underwriting and pricing could also provide support for changes in land use planning, mitigation and building retrofit programs, and improvements in building construction practices.
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