Rey Anthony Chiu
TAGBILARAN CITY, December 13, 2013 (PIA) – Enough of the viral text messages saying Bohol is a goner after the 6,000th aftershock.
Local seismologist and in charge of the Philippine Volcanology and Seismology (PhiVolcs) said aftershocks do not sink Bohol, but an innermost energy strong, maybe stronger than the 7.2 magnitude earthquake that could allow the alter of Bohol landscape.
Engr. Nolan Evangelista, seismology graduate at International Institute of Seismology and Earthquake Engineering (IISEE) in Tsukuba Japan averred that aftershocks, which do not surpass the main shock which occurred on the morning of October 15, are way too inconsequential for people to get alarmed.
As of December 11, the main shock last October 15 has had produced 4,215 aftershocks, about 118 of them felt in areas in Bohol.
By December 12, at least two perceptible aftershocks sent the already traumatized people for open grounds: the 9:51 am intensity 3 in Tagbilaran and the 1:59 Intensity 2 in Panglao.
The data is also based on strategically located seismic monitoring stations in the Visayas and in Bohol, Evangelista said.
Speaking at the Kapihan sa PIA Thursday and aired live over DyTR, Engr. Evangelista said the 7.2 magnitude earthquake has caused a reverse fault in Bohol, its most visible sign is an increase in elevation of about three meters in Anonang, Inabanga.
A reverse fault simply is a thrusting upward of one break in a plane, like a land form moving up relative to its other part of the plane. This results in elevation differences where subsidence or uplift-ment happens.
Another fault, called lateral is simply the lateral movement of both planes, as forced by the forces acting on them, like compression for example.
In Bohol, PhiVolcs noticed indications of uplift-ment in Bohol areas in Tubigon where a general increase in elevation of a few centimeters on the average, following the trajectory of northeast in Inabanga to southwest of Bohol, in Maribojoc.
While it may be imperceptible to many except to those who has available satellite images showing pre and post earthquake Bohol, the tremor has caused a general uplift of ¾ of Bohol island, Evangelista shared.
In fact, through a slide presentation citing satellite imagery gathered by the Department of Science and Technology through Renato Solidum showed that the massive tremor has pushed the southwestern part of Bohol towards Cebu by 55 centimeters.
On this, the local seismologist noted that the northern part of Bohol stayed put, but the southwestern part pivoted some 55 centimeters towards Cebu.
This may be the reason why Bohol appears to be round, because of the twisting movement, according to Evangelista.