MANILA — A recent series of offshore earthquakes in Ilocos Sur has raised significant concerns about the potential for a high-magnitude earthquake originating from the Manila Trench. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) has been closely monitoring the situation since the tremors began on December 17, with officials now warning that a worst-case scenario could involve an 8.4 magnitude earthquake, potentially triggering a destructive tsunami.

The earthquakes, which have occurred near the coastal town of Santa Catalina, Ilocos Sur, have been attributed to movements along Segment 2 of the Manila Trench, an oceanic trench located to the west of the Philippines. Since the initial tremors, PHIVOLCS has recorded a total of 178 earthquakes, with magnitudes ranging from 1.8 to 5.0. The agency stated that 62 of these earthquakes have been precisely located by at least three seismic stations, although only two have been felt by residents. The tremor activity has significantly decreased following a peak on December 19 to 20.

Despite the decrease in frequency, PHIVOLCS continues to monitor the situation closely, with experts noting the potential for a much larger quake if the entire Segment 2 of the Manila Trench were to shift. According to PHIVOLCS’ simulation, such an earthquake could generate a tsunami with waves ranging from three to 15 meters in height.

In their computational model, PHIVOLCS divided the Manila Trench into four segments to assess the risks more accurately. If Segment 2 were to move in a worst-case scenario, the simulation predicts that the first tsunami wave could hit the coastal provinces of Zambales, Pangasinan, La Union, Ilocos Sur, Ilocos Norte, and Cagayan within two to 15 minutes. The highest waves, which could reach up to 14.7 meters, would impact Vigan City, Ilocos Sur, with the initial waves arriving in as little as four minutes.

“Kapag nakalikha ito ng tsunami, ang unang alon ay makakarating sa baybayin ng mga probinsya ng Zambales, Pangasinan, La Union, Ilocos Sur, Ilocos Norte, at Cagayan sa loob ng dalawa (2) hanggang 15 minuto. Samantala, ang taas ng alon ay maaaring umabot ng tatlo hanggang 15 metro,” PHIVOLCS warned in a statement.

While the potential for a large earthquake and tsunami remains a concern, PHIVOLCS stressed that it is impossible to predict the exact timing of such events. The agency has emphasized the importance of vigilance, urging the public to watch for key signs of a tsunami, including strong earthquakes, sudden changes in sea level, and unusual sounds coming from the sea, such as a loud roar or rumble.

In the event that any of these signs occur, PHIVOLCS recommends that residents evacuate immediately to higher ground or away from coastal areas. The agency is also coordinating with local authorities and disaster response teams to ensure preparedness in case of an emergency.

The Manila Trench is known to be one of the most active seismic zones in the Philippines, with a history of producing strong earthquakes and tsunamis. The trench reaches depths of up to 5,400 meters and runs along the western side of the Philippine archipelago. The region has experienced several significant earthquakes in the past, making it a focal point of ongoing seismic monitoring efforts.

As of Sunday, December 22, the frequency of tremors has decreased significantly. However, PHIVOLCS continues to track seismic activity in the area, and residents in affected provinces are advised to stay alert and be prepared for any further developments.

The government, along with local risk reduction and management councils, is coordinating efforts to educate the public about the risks and safety measures related to tsunamis. Evacuation drills and preparedness campaigns are being implemented in coastal communities to ensure that residents are aware of the necessary actions to take in the event of a tsunami.

For now, PHIVOLCS is urging the public to remain cautious, monitor official advisories, and prepare for the possibility of sudden changes in seismic activity. The agency continues to emphasize the importance of early warning systems, disaster preparedness, and community awareness to mitigate the potential impact of a tsunami or earthquake.

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