Department of Science and Technology (DOST)- Philippine Institute of Volcanology and Seismology (Phivolcs) Undersecretary Renato Solidum said only long fault lines are capable of generating strong earthquakes but not the shorter ones.

“Only the Makilala to Malungon Fault with a range of 65 kilometers, and the Tangbulan Fault measured at 69 kilometers are capable of generating 7.2 magnitude earthquakes. One of which is the cause of the 6.9 magnitude quake on December 15,” Solidum said during a briefing inside the office of Digos City Mayor Josef Cagas.

The Phivolcs chief said that when a particular fault capable of producing 7.2 magnitude earthquakes had already released a 6.9 earthquake, “there is no chance it could trigger its maximum capability since it already let go more than 50 percent of its stress level.”

“Of course we are expecting a series of aftershocks with lesser magnitude after the strong earthquake that may take weeks or months,” Solidum said, noting that around 800 aftershocks have been registered since the 6.9 magnitude quake hit this province.

He said the maximum capability of the Digos Fault is only magnitude 6.3 if it moves since it is only 12.3 kilometers in length.

Solidum said residents should not be afraid to go back to their homes “at this point,” noting that the extent of damage after the 6.9 temblor on December 15 has not been extensive.

For multi-level buildings, however, he said authorities must ensure that the facilities are built within the standards of the National Building Code of the Philippines before they are occupied again.

He said that Phivolcs team of engineers is in the area to conduct ocular inspections using high-tech instruments to determine the vulnerability structures in the province

“Knowing all the facts, there must be changes in our way of building houses and commercial establishments in the city to protect lives and destruction of properties,” he added.

Phivolcs said Digos City sustained intensity 7 during the latest tremor.

On the other hand, Solidum allayed speculations that the series of earthquakes that struck Southern Mindanao were man-made, saying there are no known human activities that could generate such forces from three kilometers underneath the earth.

Solidum said that a 6.9 magnitude quake is equivalent to the intensity of 30 nuclear bombs dropped in Hiroshima, Japan during World War 2. (PNA)