Masbate, 1990 Luzon earthquakes triggered by same fault—Phivolcs

MANILA, Philippines—The 5.2-magnitude earthquake that rocked Masbate province Tuesday morning was triggered by the same fault zone responsible for the cataclysmic 1990 Luzon earthquake, the Philippine Institute for Volcanology and Seismology said.

Joan Salcedo, a seismologist at the agency, said Tuesday’s earthquake generated a “very strong” impact on the ground because it was shallow and was triggered by the very active Philippine fault zone.

“It happened close to the surface. The Philippine fault zone has many segments and one of its segments moved,” Salcedo said in a phone interview Tuesday.

The 1,200-kilometer fault zone, which transects the entire Philippines from Luzon to Mindanao, sparked a 7.9-magnitude tremor that devastated Baguio City in July 1990. In 2003, the fault zone also produced a 6.2-magnitude earthquake in Masbate province.

The Masbate earthquake, which occurred at 7:06 a.m. Tuesday, was moderately strong at 5.2-magnitude.

Phivolcs said the shift in the plates happened 23 kilometers below the surface. As such, the ground caught much of the energy that was released by the movement of the plates.

The quake was tectonic in nature and struck at 3 km north of Masbate City. Salcedo said no tsunami warning was raised in the area.

Intensity VI, which is described by Phivolcs as “very strong,” was felt in the capital of the province. An Intensity VI tremor could cause cracks in buildings and trigger landslides in mountainous areas.

Intensity IV was felt in Sorsogon and Capiz provinces. Intensity I was reported in Aklan.

Because the tremor produced strong shaking on the ground, Phivolcs said it expected the quake to damage weak structures. Salcedo said they were verifying reports that a building collapsed in Masbate.

Phivolcs said it was expecting aftershocks in Masbate. As of Tuesday afternoon, three more earthquakes, all in the magnitude 3 level, have been recorded in Masbate.