By: Ellalyn V. Ruiz
The destructive earthquake that jolted Leyte and nearby provinces last Thursday was not the first, as moderate magnitude tremors have affected the area in the past, the Philippine Institute of Volcanology and Seismology said.
Phivolcs said four moderate earthquakes occurred on the island in 1947, 1890, 1994, and 1863.
On June 7, 1947, a magnitude-6.9 earthquake with the epicenter in Carigara, Leyte affected the entire province.
A 6.4-magnitude quake that occurred on February 7, 1890 in Barugo, Leyte was strongly felt at Intensity 8 there, while other towns in Leyte were shaken by intensities ranging between five to seven.
On July 5, 1994, a magnitude-6.2 earthquake was generated by the movement of the Philippine Fault. Strong ground shaking was felt in Hinundayan, Hinunangan, San Juan, Anahawan, and St. Bernard in Southern Leyte.
A magnitude-6.1 earthquake, which occurred on September 27, 1863 with epicenter in Kananga, Leyte, which coincidentally was near the epicenter of last Thursday’s tremor, was felt at Intensity 6 in Ormoc, Jaro, and Leyte.
Phivolcs said these earthquakes caused significant damage to buildings and roads. Liquefaction and landslide were also documented in some areas.
From time to time, Phivolcs noted that a series of moderately-sized earthquakes, referred to as seismic swarms, are generated by active faults in the area.
Some of the seismic swarm episodes occurred in 2012, 2007, 1998, 1994, and 1991 in Southern Leyte, with magnitudes ranging from 4.3 to 5.5. These events also caused damages to buildings and some infrastructures.
Phivolcs explained that earthquakes occur in Eastern Visayas, including Leyte, as it is one of the seismically-active areas in the country because of the Philippine Fault and the Philippine Trench, which are the main earthquake generators that can affect the area.
In addition, there are other local faults which can be sources of small- to large-magnitude earthquakes, it added.
Phivolcs warned that the 6.5-magnitude earthquake that occurred last Thursday may continue to generate aftershocks for several days to weeks, some of which may be felt.
Meanwhile, the probability of an earthquake higher than magnitude 6.5 from occurring is low, it pointed out.
Phivolcs reminded people to be cautious of structures visibly weakened or with signs of damage due to last Thursday’s earthquake.
In case of houses and other buildings with visible damage, it is best to contact the municipal or city engineering office for advice, Phivolcs said.
Likewise, it said, slopes should be checked for tension cracks that may have resulted from the strong ground shaking.
Tension cracks may make slopes more susceptible to landslides, Phivolcs said. These areas should be avoided.
In case of another felt earthquake, it is recommended that people protect themselves by doing the “duck, cover and hold,” Philvocs said.