Tagbilaran City (CNN Philippines) — A 4.2-magnitude earthquake woke residents in at least seven towns and Tagbilaran City in Bohol at around 4:19 a.m Tuesday (August 11).
The tremor had a depth of six kilometers with its epicenter located two kilometers northeast of Cortes.
Nolan Evangelista, Philippine Institute of Volcanology and Seismology (Phivolcs) in-charge for Bohol, said it is still an aftershock of the magnitude 7.2 earthquake on October 15, 2013.
Evangelista explained the position of the ground shaking is within the rupture zone of the 2013 earthquake.
He said that the ground shaking was traced to offshore of Cortes and Maribojoc towns.
Since its depth is just six kilometers, its intensity felt on the surface is stronger, according to Evangelista.
The effect could have been destructive had it lasted two seconds, he said.
However, Antequera Municipal Councilor Asterio Coquilla said they felt the ground shaking for 5-6 seconds, and things placed on their aparadors had fallen, making them believe that it was stronger than magnitude 4.2.
Evangelista explained that the actual ground shaking was only two seconds, but its intensity could be felt longer in areas with loose ground.
The quake was felt in in towns surrounding the epicenter such as Antequera, Balilihan, Sikatuna, Corella, Tagbilaran, Maribojoc, Loon, and Tubigon.
Since the force is northwest — that is towards Cebu, there has been no ground shaking felt in Panglao and Dauis.
Evangelista also explained that the frequency of ground shaking is one earthquake per month. Since there are several active faults in the Philippines, an average of 13 earthquakes are recorded per day.
However, this month, Phivolcs already recorded two earthquakes in Bohol.
Prior to the aftershock this morning, Phivolcs also recorded a magnitude-3 quake last August 3, at around 1:55 a.m. with a depth of 16 kilometers and its epicenter traced to six kilometers south from the east of Carmen.
