State seismologists on Thursday raised Alert Level 1 in Mt. Pinatubo due to the persistence of seismic activity in the volcano.
PHIVOLCS said Alert Level 1 means "there is low-level unrest that may be related to tectonic processes beneath the volcano."
However, "no imminent eruption is foreseen," PHIVOLCS said in its Thursday morning bulletin.
Those who wish to enter the Pinatubo Crater area must do so "with extreme caution and should be avoided if possible," PHIVOLCS said.
It added that communities and local government units surrounding Pinatubo should be always prepared for both earthquake and volcanic hazards.
They are also urged to review, prepare and strengthen their contingency, emergency and other disaster preparedness plans.
According to PHIVOLCS bulletin on Thursday, 1,722 "imperceptible earthquakes" have been recorded beneath the Pinatubo edifice since January 20, 2021.
It said the first cluster of earthquakes on January 20-26 occurred along the Sacobia Lineament at depths of 15-28 kilometers and ranged between ML1.0 and ML2.5 in magnitudes.
"This has been succeeded by a more persistent cluster of earthquakes occurring along a north-northwest-south-southeast-trending structure 10 to 35 kilometers beneath the center of the edifice itself, with a few shallower earthquakes occurring on both ends of the cluster," it added. The earthquakes ranged between ML0.5 and ML2.8 in magnitude.
"All earthquakes recorded are associated with rock-fracturing processes," PHIVOLCS said. --KBK, GMA News