On July 16, 1990, 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 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.
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 they carried to Baguio was key to their limited communication.
He cannot overemphasize the importance of periodic evacuation drills. 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.
