MANILA, Philippines – Not one but two separate earthquakes jolted the province of Quezon, Wednesday, September 4, state volcanologist Phivolcs said.
The first earthquake occurred at 7:16 A.M. at magnitude 5.3 while the other happened at 7:55 a.m. with a magnitude of 4.9. Both earthquakes struck at a depth of 001 kilometer.
No, the second isn’t an aftershock of the first one, these two events are called a “doublet.”
“Doublet earthquakes happen when two earthquakes of nearly the same size happen together in the same area. While they may be similar they’re actually two separate events,” said Phivolvs Director Teresito Bacolcol in a telephone interview with Orionpost.
“Faults are complex, causing stress to trigger multiple events in quick succession. Isa lang ‘yung stressor nila but faults are complex kaya nagkakaroon ng earthquakes almost of the same size in the same region,” he said.
Stresses are what pushes rocks against each other and when their elastic strain reaches limit, earthquakes happen, said Bacolcol.
Past instances of doublet earthquakes include the 7.4 magnitude event at the Philippine Trench last December 2 shortly followed by a 6.8 magnitude quake in the same area, 1992 also in the Philippine Trench with magnitudes 7.5 and 7.1 separated by only 26 minutes and only 20 kilometers from each other.
In events of doublet earthquakes, attributing the ground shake that produced a particular aftershock is difficult because of their nearness to each other, said Bacolcol.
No damage has been recorded but aftershocks are expected.
