A sequence of tremor events in Camarines Norte that has been going on since Oct. 14 can be considered as an "earthquake swarm," the Philippine Institute of Volcanology and Seismology (Phivolcs) said on Monday, Oct. 18.
"This sequence of events, showing no identifiable large event, can be considered as an earthquake swarm that may occur in a tectonically active region, as suggested by sparse seismicity in this area of the Bicol region," Phivolcs explained in a statement.
The initial event, which occurred at 10:08 p.m. on Oct. 14, was a small shallow-seated earthquake with a magnitude of 4.3 and a depth of 4 kilometers.
Phivolcs traced the quake's epicenter at 3 kilometers (km) northwest of Canaman, Camarines Sur.
"After the initial event, a sequence of small earthquakes followed and were recorded and subsequently located in this general location," Phivolcs said.
A total of 27 earthquakes were recorded by the nearest Phivolcs earthquake monitoring station located in San Jose, Camarines Sur.
These earthquakes have magnitudes that ranged from 1.7 to 4.3 with crustal shallow depths between 1 km and 40 km.
The last recorded event associated with this earthquake sequence was at 1:22 a.m. on Monday, Oct. 18.
Of the 27 recorded earthquakes, 10 were felt at various intensities in Camarines Norte, Camarines Sur, and Albay.
Phivolcs also noted that a similar short-duration burst of earthquake activity occurred back in Dec. 13, 1993, which did not culminate in a major event.
"Back then, areas do not have wider built-up areas and are sparsely populated to cause observable effects to warrant public attention," it pointed out.
Phivolcs said it will continue to closely monitor this earthquake activity.