Quake triggered by 'blind thrust fault'

MANILA, Philippines - The magnitude 6.9 earthquake that hit parts of Visayas and Mindanao yesterday was triggered by a “blind thrust fault,” the Philippine Institute of Volcanology and Seismology (Phivolcs) said.

A blind thrust fault is a fault that does not rupture all the way up to the surface so there is no evidence of it on the ground, according to the website of the United States Geological Survey (USGS).

It is “buried” under the uppermost layers of rock in the crust, the USGS said.

Phivolcs deputy director Bartolome Bautista said the active fault in Negros Oriental was not visible in the active fault map of Phivolcs.

He said Phivolcs would send a team to Negros Oriental, the epicenter of the quake, to conduct a seismic study.

As of yesterday evening, a total of 42 aftershocks were recorded following the magnitude 6.9 earthquake.

Phivolcs director Renato Solidum said an earthquake of such strength is not common in the area.

Solidum said offshore quakes like the one that hit Negros Oriental are hard to trace.

The tremor left at least nine people dead.