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Monday, 29 October 2007 00:32

Earthquake Devastates Philippines

Written by  Cathy Clark and Jim Taylor
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On July 16, 1990 at 4:26 p.m. local time, a severe earthquake registering 7.7 on the Richter scale struck the northern Philippines. The earthquake caused damage over a region of about 7700 square miles, extending northwest from Manila through the densely populated Central Plains of Luzon and into the mountains of the Cordillera Central.

Over 5,000 people were reported dead or injured, and in excess of 2300 infrastructures were either destroyed or seriously damaged. While the quake was devastating, it was not an unusual occurrence in the Philippines; since 1950 alone there have been six major earthquakes at various locations in the archipelago, having magnitudes ranging from 7.3 to 8.3.


Buildings were decimated by ground shaking, soil failure and liquefication (causing them to settle into the ground), and landslides.

Nearly all multistory buildings in the Philippines are constructed of reinforced concrete frames, supporting slab floors. Short-column failure was evident in many buildings observed to have the classic diagonal cracking where the column was acting as a short shear wall and could not carry the loads. Many unreinforced masonry infilled walls separated from the concrete frames and collapsed.

In the heavily shaken regions, two general types of disastrous failure to multistory, larger reinforced concrete buildings were observed--failed first stories and total building collapse.

First-story (or Soft-story) Failures

The ground floor of a building is frequently the weakest part of the structure. It is seldom enclosed on all four sides by walls capable of resisting shear forces, and it is also generally taller than upper floors. Ground floor shops, stores, lobbies, or garages normally allot most of their front wall area to doors or plate glass, leaving one side of the building with no shear resistance. Bending and shear forces induced by strong ground shaking are therefore concentrated in the ground-floor columns. As a result, the building may fail by collapse of only its first story, with the stronger upper section of the building remaining intact.

Multistory Failures

Many multistory building failures or “pancake” collapses (typically with structures of six to ten stories) were observed in the city of Baguio. One such collapse included a nine-story hotel which killed over a dozen occupants on the ground floor. This type of damage has been observed repeatedly in numerous earthquakes throughout the world where design and construction deficiencies exist.


The earthquake inflicted serious damage on Dagupan City, essentially destroying its central business district. Soft soil regions such as Gerona and the river delta town of Agoo were also hard hit. The most extensive shaking damage and multistory building destruction, however, occurred in the resort city of Baguio.

With a population of 200,000, Baguio attracts between 90,000 and 120,000 tourists a day. Most of the city’s better hotels were devastated. Ground settlement over large populated areas caused extensive damage to transportation systems, power systems, utilities and particularly to underground piping. Many buildings also sustained considerable devastation and fire damage from aftershocks.

Several employees of Texas Instruments (TI) based in Baguio experienced the havoc and destruction firsthand. “The limited news reports that most of you viewed can in no way convey the extent of destruction in this community and the resulting trauma and shock that our TIers experienced,” said one TI witness.


All 700 employees of Texas Instruments were evacuated when the earthquake struck. The initial shock and immediate aftershocks cut all communications with the plant, landslides closed highways, and the airport was damaged. Although the TI plant was damaged, it withstood the quake relatively unscathed, and all employees escaped with only minor injuries reported. The plant had been built to withstand a Class 3 earthquake, but the July 16 earthquake was actually a Class 4. Some other buildings in the industrial park located in the export processing zone were leveled.


TI organizations worldwide worked together to meet the needs for replacement parts, equipment, and personnel, said Charles Wofford, SC Group vice president and project coordinator for the recovery effort.

“We’ve gotten superb teamwork from TI organizations worldwide,” he said. “If you consider the damage, it’s unbelievable that they have been able to get equipment back in place and some of it checked out and operating in a matter of days,” he said.

Wofford has been in communications twice a day with local management in the Philippines to expedite restoration efforts. Semiconductor customers are kept informed on a regular basis regarding progress at the plant. More than 50 percent of the 1687 TIers were back at work in August, and three-shift operations resumed July 30.

Water, power, air-conditioning, communications and computer operations have been partially restored at the TI plant. However, communications and transportation links between Baguio and Manila are still limited. Only one of three highways is open, and surface roads are frequently closed as a result of the landslides. Electrical power and water have not yet been restored in many areas of the community. Some 90,000 people have been left homeless.


Herby Locke, a TI employee who experienced the quake, expressed some of the more crucial considerations to keep in mind in lieu of a future similar disaster.

Facility Evacuation

“I cannot overemphasize the importance of periodic evacuation drills,” he said. Because all the employees were cognizant of the nearest exits, the spontaneous evacuation was successful; while all employees escaped serious injury, many others trapped in buildings in Baguio were crushed.

Facility Power

Electricity, power, water, etc. should be well planned and duty personnel should be well trained on emergency shut-down procedures, Locke says. “If we have a case where perimeter mains of a significant size are totally collapsed, I can well assure you that reservoirs can be drained in a relatively short period of time unless the pumps are manually turned off,” he said.


In an event such as a large-scale earthquake, communications are almost certain to be either hindered or temporarily destroyed. Thus, backup communications are vital. “The Motorola cellular phone that I carried to Baguio was key to our limited communication,” said Locke. Ham radio and VHF radios could also be used.

Site Plans and Drawings

It is important to know the precise layout and location of routing for water mains, sewer mains, gas lines, and underground power lines, to name a few, Locke stresses. “When initiating repairs, it could be of vital importance from an expediency viewpoint to have detailed drawings of the total factory structure available at each site.”

Insurance Claims

Only a limited number of employees were involved in incidents that involve a substantial claim. However, Locke observed that it would be prudent to consider a detailed check-off list and maybe a video tape that could be made available to each factory site for quick reference and training as required. On this issue, he said that pre-training is probably not important.


“Do not underestimate the awesome and destructive force of Mother Nature,” Locke warns. “It is an incredible experience to stand on a TI parking lot that is moving in several different directions at the same time and witness an entire mountain range and thousands of trees shaking like a dog shaking a toy doll,” he said, recalling the moments that the quake rumbled through the Philippines.

Despite the enormity of lost life and property resulting from the Philippine earthquake, the TI branch in Baguio emerged from under the rubble relatively unshaken. It is no coincidence that they fared so well while surrounding buildings collapsed, incurring both death and destruction. Thorough planning and preparedness are what enabled TI to perform and survive so successfully.

Contributor to this article include Jim Taylor, Cathy Clark, Dot Adler, Texas Instruments and EQE Engineering, Inc.

This article adapted from Vol. 3 No. 4, p. 6.

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