The earthquake was caused by the sudden shifting of two tectonic plates in the Visayas area. The shift was from a “blind fault” some 20kms below the earth between Negros and Cebu.
Dr. Ishmael Narag, chief of Phivolcs’ Seismological Observation and Earthquake Prediction Division, said that the February 6 earthquake was not traced to any known existing faults in the area, suggesting the presence of a previously unmapped fault.
According to Phivolcs deputy director Bart Bautista, the fault that caused the February 6 earthquake was uncommon in that its movement was vertical, whereas most faults in the Philippines move horizontally.
The Philippines, due to its location in the Pacific Ring of Fire naturally has at least dozens of fault lines and is prone to earthquakes. But “many fault lines are yet to be mapped,” Bautista said, blaming the lack of trained geologists in the country.
He also lamented the lack in the first place of high-resolution base maps of the country’s fault lines.
Narag cautioned that residents near the epicenter of the quake might experience several aftershocks for several weeks, although these are not expected to be as strong as Monday’s quake.