MANILA – The country’s chief seismologist on Wednesday reiterated the need to take earthquake preparedness seriously, after two strong tremors hit parts of Luzon and Visayas.

"We have to prepare ourselves, know what to do before, during and after the earthquake. Make sure that our families also know what to do," Phivolcs Executive Director Renato Solidum said.

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Solidum said now is the best time for families to map out their preparedness plan: where to go for evacuation, prepare emergency bags enough for family members, participate in drills, and listen to credible authorities.

He added, the public should not rely solely on what is posted on social media.

"What is important is understand the scenario. Earthquake will happen. Follow the building code, prepare yourself and your family and you will be okay," he said.

Solidum said Phivolcs monitor an average of about 20 earthquakes in normal days, many of which are small events and not felt by people.

"The Philippines is an archipelago with many active faults crisscrossing many islands. One of which passes through Metro Manila and some in Luzon, Visayas and Mindanao," Solidum said.

He said strong to large earthquakes also happen from time to time since faults are moving.

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Solidum said Phivolcs has more stations now at 101, compared to only 64 when he became director of the agency in 2003.

"If we have more stations, we can detect even more smaller magnitude earthquake events. It would not mean that earthquakes are getting more. It would mean the detection capability system is getting better that is why we are detecting smaller and smaller earthquake events," he explained.

A magnitude 6.1 earthquake jolted Central Luzon, killing at least 16 people and shutting Clark Airport for 48 hours. The quake also caused a 4-storey supermarket in the town of Porac to collapse, trapping workers and shoppers underneath rubble.

While rescuers were racing against time to look for survivors under the collapsed supermarket on Tuesday, another strong quake occurred, this time in San Julian in Eastern Samar. The quake was felt in different areas in Visayas, Caraga and Bicol regions.

"In essence, earthquakes are waves and the larger the energy of the wave the farther the wave will reach. In essence, a 6.1 earthquake would have caused an earthquake from 100 to 150 kilometers away from the epicenter," he said.

Solidum stressed that the two earthquakes were different and did not trigger the movement of the other.

• Luzon, Visayas quakes 'not related' - Phivolcs

"The magnitude it generated was not large enough to put stress on neighboring faults," he said.

A magnitude 7 earthquake could be felt from 200 to 300 kilometers away, he added.