By Ellalyn De Vera-Ruiz
Another earthquake fault which is different from the Cotabato Fault System that caused the earthquake swarm in Mindanao last October, has triggered the powerful tremor in Davao del Sur on Sunday.
The Philippine Institute of Volcanology and Seismology (Phivolcs) is currently looking into the Tangbulan Fault as the possible source of the 6.9-magnitude earthquake in Davao del Sur on December 15, according to science research specialist Erlinton Olavere.
“Tangbulan Fault is the closest earthquake fault to the epicenter in the municipality of Matanao and Padada, Davao del Sur,” he said.
“The Cotabato Fault System, which caused the earthquakes in October, is on the other side of the Tangbulan Fault. Most likely we are looking at another earthquake fault that caused the strong tremor in Mindanao last Sunday,” he pointed out.
Phivolcs has already sent additional teams of experts to focus the investigation on the Tangbulan Fault.
Olavere said Phivolcs will still investigate the possible relation of the 6.9-magnitude earthquake to the strong tremors in October, as roughly the same area of Mindanao between October and December, felt the earthquakes.
The 6.9-magnitude shallow quake was the fifth one above magnitude 6 that rocked Mindanao in the past two months. Strong earthquakes occurred in Cotabato and nearby provinces on October 16 (6.3-magnitude), October 29 (6.6 and 6.1-magnitude), and October 31 (6.5-magnitude).
“We can say that this is an unusual event because in almost two months, the people in Mindanao have experienced big earthquake events. We are continuously studying any possible trend of seismic activity to make sure that we are experiencing an unusual occurrence of strong earthquakes in a specific area within a short period of time,” Olavere explained.
“Aftershocks from time to time could continue for days to weeks,” he said.
Although chances remain low, Phivolcs is not discounting the possible occurrence of a 7.2-magnitude tremor, which is the maximum earthquake magnitude the Tangbulan Fault could generate.