The sequences of earthquakes in the waters of Ilocos Sur have started to decrease, the Philippine Institute of Volcanology and Seismology (Phivolcs) reported.
Since the earthquakes were recorded on 17 December, a gradual decrease has been observed, starting last Sunday, 22 December.
Based on the histogram uploaded by Phivolcs, most of the earthquakes occurred from 19 to 20 December, wherein 70 earthquakes were recorded.
During this period, seven earthquakes with a magnitude of 4.0 or higher were recorded, with the strongest one occurring at 9:09 a.m., measuring a magnitude of 5.0.
After 10 earthquakes were recorded between 21 December and 23 December, the number of recorded earthquakes dropped to 2 between 23 December and Christmas Day, 25 December.
Despite the observed decrease in earthquakes, Phivolcs advised the residents to remain observant and vigilant “at all times.”
The series of earthquakes in the area of Manila Trench in the West Philippine Sea sparked alarm among the residents, especially in the western portion of Luzon due to the possibility of movement of the 900-kilometer long trench.
Earlier this week, Phivolcs uploaded a tsunami simulation in case the Manila trench moves.
“Based on the model, the worst-case scenario is that Segment 2 of Manila Trench could generate a Magnitude 8.4 earthquake,” the Phivolcs warned.
The agency’s advisory also noted that once the quake generates a tsunami, its waves could reach the town of Palauig in Zambales within two minutes and Pagudpud in Ilocos Norte within three minutes.
In case of a tsunami event, Phivolcs emphasized evacuating to higher grounds and moving away from the sea.