PHIVOLCS: Manila Trench source of magnitude 5.6 quake in Ilocos Norte

The magnitude 5.6 earthquake that jolted Bangui, Ilocos Norte last December 30 could have possibly originated from the Manila Trench, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said on Wednesday.

State seismologists said the earthquake of tectonic origin that hit the town on Monday had an upward vertical movement.

“Based on the hypocentral location and focal mechanism, the event is likely associated with subduction along the Manila Trench,” said PHIVOLCS in a briefer. “This shallow earthquake likely occurred along the low-angle subduction interface of the Manila Trench.”

PHIVOLCS added the magnitude 5.7 earthquake that also hit Bangui on December 4 also “exhibited a reverse faulting mechanism likely along the subduction interface.”

But seismologists pointed out that the recent earthquakes in Bangui, Ilocos Norte and the series of offshore quakes in Santa Catalina, Ilocos Sur last December 17, while they happened in different segments of the Manila Trench, are not fully related.

“Further studies are needed to understand the tectonic processes driving these events. Nonetheless, these earthquakes underscore the ongoing tectonic and seismic activities along the Manila Trench, highlighting the region’s risk to geologic hazards,” said PHIVOLCS.

During a strong earthquake the state seismology bureau reminded the public to practice “duck, cover, and hold”: 

• Get down on the ground to avoid being knocked over.
• Take shelter under a sturdy table, or protect your head and neck with your arms. Stay away from windows, glass, and heavy objects.
• Hold on to your position until the shaking stops.

“If any of these signs occur, immediately move to high ground or away from the shore,” PHIVOLCS advised. —Vince Angelo Ferreras/RF, GMA Integrated News