Residents in Cebu and Bohol were jolted anew by a 4.3 magnitude earthquake that was felt at 4:21 p.m. yesterday, Dec. 29.
The Philippine Institute of Volcanology and Seismology (Phivolcs) in Lapu-Lapu City said the tremor was traced to be in Buenavista town area or 59 kilometers northeast of Tagbilaran City.
The earthquake was felt at Intensity 4 in Mandaue City and felt at intensity 2 in the cities of Cebu and Lapu-Lapu, seismic observer Robinson Jorgio said.
Phivolcs said that yesterday’s earthquake was an aftershock of the powerful temblor that jolted Bohol and Cebu provinces two months ago.
The agency said that the aftershock was the 4,465th it recorded from the October 15 magnitude 7.2 earthquake, which relesed energy equivalent to 32 Hiroshima bombs.
Phivolcs research specialist Henry Penarubia said that of the 4,465 aftershocks, 122 were felt, adding that it was normal for a major powerful earthquake to generate aftershocks long after it happened.
Penarubia said that yesterday’s earthquake had a depth of seven kilometers.
Jorgio, for his part, said he was waiting for the feedbacks from Bohol and other areas to determine the intensities of the tremor in their areas.
There was no report of injury or damage, though people who were staying in high buildings felt the tremor.
Jorgio said the quake was still part of the series of aftershocks after the magnitude 7.2 quake hit Bohol and Cebu last October.
In fact, yesterday, two slightly-felt tremors were also recorded in the Bohol area.
Jorgio said a magnitude 2.3 quake was felt at intensity one in the Bohol towns of Maribojoc and Antequera at 5:15 a.m. yesterday, followed by another magnitude 2.8 quake that was felt at intensity 1 again in the same towns.
Intensity, Magnitude
Based on the Phivolcs Earthquake Intensity Scale (PEIS), an intensity IV is moderately strong and may be felt by some people indoors and outdoors. The vibration felt is similar to that of a passing heavy truck and hanging objects swing considerably. Dinner, plates, glasses, windows and doors rattle while floors and walls of wood framed buildings creak. Standing motor cars may rock slightly while liquids in containers are slightly disturbed. A rumbling sound may sometimes be heard.
A magnitude is the measurement of the energy released at the source of the earthquake while intensity quantifies the strength of shaking produced by the tremor.