LEGAZPI CITY, March 22 -- The Philippine Institute of Volcanology and Seismology (Phivolcs) on Sunday raised Alert Level 1 (low-level unrest) over Bulusan Volcano in Sorsogon due to weeks of seismic activity.

In an advisory, Phivolcs said the Bulusan Volcano Network recorded a total of 475 volcanic earthquakes since March 15.

Most earthquakes were weak volcano-tectonic events associated with rock fracturing at shallow depths beneath the volcanic edifice, it added.

Phivolcs noted that their general characteristics are similar to the seismicity observed before the June 2022 and April 2025 eruptions.

Ground deformation data from continuous global positioning system and electronic tilt monitoring indicate inflation or swelling of the west...