Philippines: Philvocs cites importance of public awareness on tsunami

By Ma. Cristina Arayata

Will there be a tsunami after an earthquake? How can one recognize the signs that a tsunami might occur? Where should the people go?

The Philippine Institute of Volcanology and Seismology (Phivolcs) on Monday emphasized the importance of public awareness about tsunamis so people could be informed, prepared and save themselves.

The agency has organized a two-day forum in Parañaque City from Nov. 5 to 6, in time for the observance of World Tsunami Awareness Day on November 5.

According to Department of Science and Technology (DOST) Undersecretary Renato Solidum, the factors which might trigger tsunami are movement of fault or trench underwater, and eventually cause the water to rise; landslides beside an island; underwater landslide; submarine eruption; and fall of meteorites or meteorite's impact.

Solidum said the most common cause is the movement of fault or trenches, and this is associated with an earthquake. 

"Every place or seashore facing the trenches might experience tsunami," he said. The second common cause is submarine landslide also caused by an earthquake. 

Mylene Villegas, Phivolcs chief science research specialist, noted that not all earthquakes would cause a tsunami. 

"Only earthquakes that occur underwater would cause a tsunami. If the earthquake is on land, this would not trigger a tsunami," she said. 

Villegas added that tsunamis are a series of big waves due to underwater earthquakes, and said that shallow earthquakes don't trigger this.

According to her, even if the earthquake, for instance, is magnitude 6, but is shallow or has a less than 50-km depth, this will not be a cause of tsunami. 

Signs of an approaching tsunami

There are three signs, which Solidum calls "shake, drop or rise, roar".

The first sign is there's a big earthquake. Second is the sudden rise or fall of water due to the movements of the trenches. Third is the unusual sound or noise, which he compared to the sound of a jet plane.

"These signs have to be sequential. There must be an earthquake first. That's why the key words are 'shake, drop or rise, roar," Solidum remarked. 

There are two types of tsunamis -- local if the earthquake happens locally and distant if the earthquake happens outside the country.

Both Villegas and Solidum explained that strong earthquakes abroad might still affect the Philippines since it's in the Pacific Ocean. 

"This is why it is very important that the public is aware of tsunami. If the earthquake occurs nearby, it will be difficult for Phivolcs to mobilize people. So, if the people know the natural signs, they will be aware that they need to move to a higher land or be far away from their area," Villegas added.

Villegas noted that local tsunami might occur 10-15 minutes after an earthquake, while distant tsunami might happen an hour to 24 hours after the earthquake.

"See the difference. There's plenty of time for warning for distant tsunami. For local tsunami, there's almost none, and people need to move fast," she added. 

Villegas said that the 7.1 magnitude earthquake that happened in Mindoro in 1994 has caused a tsunami in less than five minutes after the quake.

She said it is also important to have a community post in barangays to keep the communities informed and warned. 

Evacuation centres

Meanwhile, Lucille Rose Sanico, also a Phivolcs research specialist, shared some pointers that local government units must consider when putting up evacuation centres:

• Create the safest, shortest and fastest way to get to the area or evacuation centre.
• Check or estimate how many minutes it will take to get there.
• As much as possible, the evacuation centre must be in a place where there are no bridges -- simply because earthquakes might cause damages in infrastructures.
• The evacuation must be perpendicular with the sea. The waves' direction must be against the people.
• Put up signage going to the centre.
• Create an evacuation map that will be easily understood by anyone. The map should clearly describe where the evacuation centre is located.

Sanico added that it would also help if the LGU will conduct a small workshop and tsunami drill to better prepare the community.