Taal remains on Alert Level 1, Phivolcs says recent tremors part of volcano’s ‘day-to-day seismic activity’

Published April 23, 2020, 12:00 AM

by manilabulletin_admin

 

By Alexandria San Juan

Alert Level 1 remains in place over Taal Volcano on April 23, Thursday, despite a series of minor earthquakes felt in the province of Batangas, the Philippine Institute of Volcanology and Seismology (Phivolcs) said.

The main crater of the Taal Volcano is seen during an aerial survey done by government officials, more than a week after the eruption of Taal Volcano in Batangas. (Mark Balmores / MANILA BULLETIN)
The main crater of the Taal Volcano is seen during an aerial survey done by government officials, more than a week after the eruption of Taal Volcano in Batangas. (Mark Balmores / MANILA BULLETIN)

According to Phivolcs, 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 on April 22 by the Philippine Seismic Network (PSN).

The largest of these events, Phivolcs said, occurred at 11:19 a.m. and was felt at Intensity III in Mabini; Intensity II in Taal and Lemery; and Intensity I in Agoncillo, Batangas province.

In a statement, Phivolcs pointed out that these tremors were categorized 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,” the agency added.

Other earthquakes can be classified as “tectonic,” which is produced by sudden movement along faults and plate boundaries, or “volcanic,” which is caused by the movement of magma or magmatic fluids or rock-fracturing beneath volcanoes.

Meanwhile, Phivolcs explained 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.

With this, the bureau reiterates its strong recommendation that entry into the volcano, which is a permanent danger zone, especially within the vicinities of the Main Crater and the Daang Kastila fissure, must remain “strictly prohibited.”

Local government units are also advised to continuously assess previously evacuated barangays around Taal Lake for damages and road accessibilities, and to strengthen preparedness, contingency, and communication measures in case of renewed unrest.

The public is also urged to observe precautions due to ground displacement across fissures, possible ashfall, and minor earthquakes.

 
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