Philvocs cites importance of public awareness on tsunami

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) emphasized the importance of public awareness about tsunami so citizens could be informed, prepare and save themselves. Undersecretary Renato Solidum, of the Department of Science and Technology, said 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, adding, the second common cause is submarine landslide also caused by an earthquake.

He said 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 said.

He said there are two types of tsunamis - local if the earthquake happens locally and distant if the earthquake happens outside the country. 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 said 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. Both Villegas and Solidum explained that strong earthquakes abroad might still affect the Philippines because it is situated 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 said, noting 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 said. Villegas said that the 7.1 magnitude earthquake that happened in Mindoro in 1994 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. (Maria Cristina Arayata)