Brace for more aftershocks after consecutive quakes – PHIVOLCS

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A PHIVOLCS scientist says aftershocks can occur weeks and even months after the main shock. (FILE PHOTO)

Metro Manila (CNN Philippines, April 25) — More tremors may still occur after a series of earthquakes rocked the country’s main islands this week, a scientist projected.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) said there have been 680 aftershocks recorded in Zambales while 80 aftershocks were felt in Samar as of 4 am Thursday. However, there may still be more of these tremors, but they will be much weaker than the strength of the previous quakes.

“The rule of thumb is that the aftershock would be one magnitude lower than the main shock,” said Teresito Bacolcol, a PHIVOLCS scientist.

The aftershocks may occur weeks or even months after the main shock, Bacolcol added.

On Monday, residents of Luzon were stunned by a 6.1 earthquake that originated from Castillejos, Zambales. At least 16 people died from the temblor while 85 were injured and 14 are still missing . The Clark International Airport suffered damages, resulting to cancelled flights while a supermarket in Porac, Pampanga collapsed from the intensity, killing five people and trapping dozens more.

The day after, a 6.5 earthquake brought alarm over residents in Visayas. The second quake came from San Julian town in Eastern Samar but no residents were harmed and buildings were left unscathed.

Bacolcol said the maximum strength of an aftershock from the Visayas quake would be around 5.5.

Mindanao also had its share of scares after a 4.7 temblor jolted waters near Baganga, Davao Oriental on Wednesday and a 4.4 quake shook the sea near Davao Occidental on Thursday.

Bacolcol explained that the Zambales quake was triggered by an “unnamed” local fault, while the Philippine Trench, which runs from Bicol to Mindanao, was responsible for the subsequent shocks in Visayas and Mindanao.

As for the West Valley Fault, the 100-kilometer line that stretches from Bulacan to Cavite, Bacolcol said it is "ripe for movement" meaning it can move at anytime. The fault line can produce earthquakes as strong as magnitude 7.2 based on its length but it only moves every 400 hundred years.

“The last time it moved was in 1658,” Bacolcol said.