Alert Level 1 remains over Taal Volcano despite the series of minor earthquakes that rocked Batangas, the Philippine Institute of Volcanology and Seismology said yesterday.
Phivolcs said at least 23 earthquakes with a magnitude range of 1.2 to 3.7 were recorded in Mabini, Batangas and adjacent areas of Balayan Bay last Wednesday by the Philippine Seismic Network.
The largest of these events, Phivolcs said, occurred at 11:19 a.m. and was felt at Intensity 3 in Mabini; Intensity 2 in Taal and Lemery, Batangas, and Intensity 1 in Agoncillo, Batangas.
Phivolcs said that these tremors were classified under a new classification of earthquakes called “volcano-tectonic” which the agency said “should not be interpreted by default as being related to the renewal of magmatic unrest; rather, day-to-day seismic activity in Taal Volcano.”
Phivolcs described volcano-tectonic earthquakes as quakes associated with failure or breakage of rock material along faults and fractures beneath active volcanoes.
“The mechanism that produces tectonic earthquakes is similar, although the root causes are different. Volcano-tectonic earthquakes are normally triggered by excess heat and pressure from, or adjustment of the crust around, a magmatic body beneath the volcano, whereas purely tectonic earthquakes are driven by regional tectonic plate motion.”
Earthquakes are classified as tectonic, which is produced by sudden movement along faults and plate boundaries, and volcanic which is caused by the movement of magma or magmatic fluids or rock-fracturing beneath volcanoes.
Phivolcs reminded that at Alert Level 1, sudden steam-driven or phreatic explosions, volcanic earthquakes, minor ashfall, and lethal accumulations or expulsions of volcanic gas can occur and threaten areas within the Taal Volcano Island.
It reiterated its strong recommendation that entry into the volcano, which is a permanent danger zone, especially the vicinities of the main crater and the Daang Kastila fissure, must remain “strictly prohibited.” (Alexandria San Juan)
