PH less at risk from sea-based quakes - Phivolcs

Posted at 09/02/2012 4:44 PM | Updated as of 09/03/2012 8:24 AM

MANILA, Philippines -- The Philippines was fortunate that the 7.7-magnitude earthquake that struck off the east coast came from the sea and not on land or else the reported number of damages and fatalities would have been a lot higher.

In an interview with radio dzMM, Philippine Institute of Volcanology and Seismology (Phivolcs) director Renato Solidum said less would be at risk from a tsunami compared to ground-shaking.

Based on his study, Solidum said a population of 10 million would be at risk from a tsunami, specifically those living in coastal areas. But even when a tsunami alert is issued, local governments would have time to warn and evacuate families living in coastal areas.

However, if the epicenter had been on land, "there would have been more destruction,” he said, citing the 6.9-magnitude earthquake that hit the Negros and Cebu provinces in February 2012 that killed more than 50 people.

The quake last Friday triggered a landslide, killing one woman.

A tsunami warning was later issued, covering Indonesia, Japan, Taiwan and Papua New Guinea. Big waves hit parts of the country, but these were deemed not damaging and Phivolcs subsequently lifted the alert.

Solidum said the quake happened more than 100 kilometers away from land, which is why “the magnitude of its energy was already not enough when it hit land.”

“In general, the trenches from the sea can generate a magnitude of 7 to 8…The good thing is that it is far from land. The intensity of the ground-shaking is not that strong,” he explained.

As of 8 a.m. on Sunday, Phivolcs had already recorded 270 aftershocks with the strongest recorded only at magnitude 5. “This is why most of the aftershocks have not really been felt,” he said.

He also noted that aftershocks most often become weak after a massive earthquake. “It would be extraordinary if there will be a stronger earthquake that would follow a big one,” he said.

But Solidum said Philvolcs is not closing the possibility it could still happen as he warned the public to always be vigilant.