The offshore earthquakes off Ilocos Sur, which were traced to the Manila Trench that could trigger a magnitude 8.4 earthquake, have already declined, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said.

“Mula noong December 17 nang ma-monitor ng DOST-PHIVOLCS ang sunud-sunod na lindol sa Manila Trench offshore ng Santa Catalina, Ilocos Sur, makikita sa graph ang pinakamaraming naitalang recorded (naitala ng isang seismic station) at plotted (naitala at na-locate ng tatlo o higit pang seismic stations) earthquakes noong December 19 to 20,” PHIVOLCS said in an update on Wednesday evening, according to a report on GMA News Online.

(Since December 17, when the DOST-PHIVOLCS was able to monitor the series of earthquakes in the Manila Trench offshore of Santa Catalina, Ilocos Sur, the graph showed that the most recorded earthquakes took place December 19 to 20.)

“Sa nakalipas na limang araw, bumaba na ang bilang ng mga ito,” PHIVOLCS added.

(In the past five days, the number of earthquakes has decreased.)

From December 17 to 20, PHIVOLCS said 49 earthquakes have been recorded in the area. 

The sequence of earthquakes haS raised the possibility of a worst-case scenario: a magnitude 8.4 earthquake originating from the movement of this segment of the Manila Trench.

In a tsunami simulation, PHIVOLCS said such an earthquake could generate a tsunami with waves ranging from three to 15 meters in height.

The tsunami could arrive in as little as two minutes in Palauig, Zambales, according to PHIVOLCS. The highest waves, reaching up to 14.7 meters, could hit Vigan, Ilocos Sur.

—VAL, GMA Integrated News