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COMPILATION OF DAMAGING EARTHQUAKES OF THE PHILIPPINES
Bohol Earthquake - 27 May 1996

Preliminary reports indicated that there were damages in Clarin, Inabanga, Trinidad, Tubigon and Loay Municipalities all in Bohol, as well as in the cities of Cebu and Mandaue in Cebu Island. Due to these reports, a Quick Response Team was immediately dispatched to investigate the reported affected areas. The team consists of a personnel from the main office and two field station observers from Tagbilaran and Lapu-lapu Seismic Stations. Investigation commenced on the 29th of May at Cebu Island. Buildings and other structures at the reclamation areas of Mandaue City (Landmark Cinema, SM Shopping Mall) and in Cebu City (Skyways, City Hall and buildings along M.J. Cuenco Avenue) were inspected. After that the team proceeded to Bohol Island to verify reports of damages in the towns of Clarin, Inabanga, Tubigon, Loay and Trinidad.

 

Date of Event May 27, 1996
Origin Time 1:45 p.m. (0545 GMT)
Epicenter 09.98 N Latitude 124.10 E Longitude or In between Clarin and Inabanga, Bohol
Magnitude 5.6Ms
Depth approximately 4 km from the surface.

 

Intensity Report:

Intensity VI             Clarin-Bohol, Inabanga-Bohol
Intensity V              Cebu City, Lapu-lapu City, Trinidad-Bohol, Tubigon-Bohol
Intensity IV             Tagbilaran City , Loay-Bohol
Intensity III              Cadiz City, Negros Occidental
Intensity II                Iloilo City, Bacolod City
Intensity I                 Palo-Leyte, Camiguin Island
Note: Intensity scale used in these observation was the Rossi-Forel Earthquake Intensity Scale.

 

Findings of the QRT Team:

Cebu

The SM Mall located at the reclamation area in Mandaue City reportedly sustained cracks on the wall plaster and floor tiles due to the earthquake but Mall Manager Ranier Matubayas disproved the alleged report about the damages. He said that a press conference was being held at the Mall when the earthquake occurred. The media people attending the conference witnessed the panicking public that caused them to attribute the pre-existing hairline cracks on the wall plaster and floor tiles to the earthquake. Likewise, the owner of Landmark Cinema disproved that the pre-existing cracks on the pebble washout plastering were related to the said earthquake. There were no damages found in buildings and houses along M.J. Cuenco Avenue as reported earlier. However, minor cracks were found at some non-structural parts of Cebu City Hall, which was rebuilt in 1946. These cracks developed on old masonry wall near the windows, below the beams, above the doors and other masonry parts of the building. Moreover, City Hall employees confirmed that some of these cracks can be attributed to already existed after the 08 February 1990 earthquake and was only aggravated by the ground sharing during the 27 May 1996 earthquake. Continuous cracks across the Skyway Bridge were seen under the two identical skyways situated at Fuente-Osmeña Boulevard and Avellano High School - Osmeña Boulevard. The cracks formed on plasters that were used to cover the space along shear gaps between two adjacent bridges. Cebu City is 38 kilometers away from the epicentral area.

 

Loay, Bohol

Loay is about 40 kilometers south-southwest from the epicenter. Inspite of its closeness to the epicenter, only few residents felt the earthquake. Injured were Mr. Escolastico Borong and his wife who sustained minor injuries caused by the collapse of their old wooden shanty at Barangay Bonbon. The posts of the shanty was not firmly fixed to the ground. Its collapse made the other residents aware of the occurrence of the earthquake. No other damages to buildings and infrastructues were observed elsewhere in Loay.

 

Tubigon, Bohol

Tubigon is about 10 kilometers west-southwest from the epicenter. In general, ground shaking only produced minor cracks on the walls and plaster of the column, about 2 millimeters opening and 3 meters long, of the Tubigon Municipal Hall. However, it was observed that the reinforced concrete linings of the same walls were damaged by peeling-off from the piled limestone blocks normally used in the olden times as construction materials in Bohol. Slight cracks were also observed on one of the walls of the Priest's room of San Isidro Labrador Church.

 

Trinidad, Bohol

The town of Trinidad is about 15 kilometers northeast from the epicentral area. The rail-guard and pathways of four wooden bridges were damaged. These bridges are very old that their use must be limited to light vehicles even before the earthquake. Pre-existing cracks on the floor and entrance steps of the Municipal Health Center grew and became more pronounced after the earthquake. Health workers confirmed that some of the cracks already existed before the earthquake but new minor cracks appeared on the walls of the center after the 27 May 1996 earthquake. Local officials were able to report the cited damages because of their available communication lines e.g. handheld radio.

 

Inabanga, Bohol

During the visit to Inabanga Municipal Hall, Vice Mayor Victoriano M. Basilan reported that the arch at Barangay Kagawasan Chapel and one side of the walls of the buildings of Nabuad High School collapsed. Likewise, cracks on the walls of an abandoned Gabaldon-type building of Inabanga Elementary School were aggravated. This prompted the Municipal Office to act for demolition of said building. The Municipal Hall itself also suffered minor cracks of about 3 millimeters opening and at least a meter high length on the wall and other non-structural parts of the building. Employees narrated that some of the books from their shelved, as well as the tropies placed on top of the cabinets fell down the floor. Also, residents and storeowners reported falling objects from open shelved and racks such as bottled and canned goods, medicine etc. The earthquake caused general panic among the residents because of sudden jolt with both vertical and horizontal motions and accompanied by rumbling sound. Inabanga town is about 5 kilometers from the epicenter.

 

Clarin, Bohol

One of the residents said that sleeping persons were awakened by the strong jolt accompanied by rumbling sound apparently originating from below the ground. Books from shelves fell down. One parked motorcycle and a refrigerator toppled during the earthquake. Concrete hollow blocks to be used for construction of a residential house was crushed. Masonry oven (pogon) owned by Mr. Ponciano Rama was damaged, an example of unreinforced masonry vulnerable to ground shaking. Bottled and canned goods, paints, groceries etc. fell down.

The rear masonry wall of Barangay Cumang Ricemill collapsed inward the building. That was due to the poor connection between the said wall and the wooden parts. The wall also served as load-bearing wall of earth materials and rice shells dumped at the read side of the building. Walls of Clarin Elemntary School suffered minor cracks. Pronounced damages were sustained in Sam Miguel Church particularly on the bell tower, which suffered cracks on the walls, across the columns, along the beams, the peeled-off decorative masonry works. The front door, which is under the bell tower, was closed to the public after the earthquake, avoiding eminent danger from such damages. The church was built in 1924 with reinforced concrete and its oldness is one of the factors of suffering such damages during earthquake.

Three residents were injured. One was hit by falling object, another fell down from the stairs due to panic and the last, a fisherman, met an accident while on his pump boat. The latter was 15 meters away from the shore when he allegedly encountered two sea waves, about a meter high that damaged his boat and caused injuries to his right ankle and leg. The victim however was uncertain whether the incident was simultaneous with the earthquake occurrence or not.

 

Summary:

The 27 May 1996 earthquake did not cause major damages to properties. Damages were confined to poorly built structures and/or old wooden, masonry, limestone walls of houses and buildings, generally due to ground shaking. There were no reports and observations that can be attributed to other phenomena such as liquefaction, ground subsidence, landslide and any other geologic ground disturbances.

 

Recommendation:

1. A public information forum for municipal and barangay officials should be organized by NDCC and RDCC with PHIVOLCS assisting to explain to the people the phenomena related to earthquake. This is to avoid misconception, exaggeration of the facts about earthquake and to allay the fear and panic. Earthquake disaster mitigation plan should be considered on these affected places.

2. Since the place is rarely visited by major earthquakes, information campaign should be conducted from time to time to keep the level of awareness of the people to various earthquake hazards.

3. There should be an immediate inspection and repair/replacement/retrofitting/demolition of the old and poorly-built structures and affected infrastructures such as roads and bridges.

 

Intensity VI          Clarin-Bohol, Inabanga-Bohol
Intensity V           Cebu City, Lapu-lapu City, Trinidad-Bohol, Tubigon-Bohol
Intensity IV          Tagbilaran City , Loay-Bohol
Intensity III           Cadiz City, Negros Occidental
Intensity II            Iloilo City, Bacolod City
Intensity I             Palo-Leyte, Camiguin Island

Pictures

Loay

 

Loay, Bohol. Collapsed shanty of Mr. Escolastico Borong at barangay Bonbon.
The house is made of wooden materials not firmly attached to the ground.

Tubigon
Trinidad
Clarin
Cebu