Negros Trench could trigger 3-story tsunami in Iloilo City

By Rjay Zuriaga Castor

A powerful earthquake from the Negros Trench could trigger a localized tsunami that may reach parts of Iloilo City within 15 minutes and could rise as high as a three-story building, the City Disaster Risk Reduction and Management Office (CDRRMO) said.

The Negros Trench is an oceanic trench located west of Negros Island and lies approximately 46 to 69 kilometers from Iloilo City, and according to the CDRRMO a magnitude 8.2 earthquake in the trench could trigger a localized tsunami that may affect coastal areas of Antique and Iloilo City.

Darwin Joemil Papa, head of CDRRMO’s Quick Response Division, said the worst-case scenario indicates a tsunami with a wave height of up to 11.54 meters, equivalent to three floors.

Papa warned that Iloilo City would have very little time to react, with an estimated 15-minute lead time for waves to reach coastal areas of the city.

“Right from the start of the shaking, by the time it’s possible it will hit us, there’s no chance for us to prepare,” he said.

“Worst comes to worst, actually greater of two evils or lesser of two evils — surviving the magnitude 8.2 quake or the tsunami that comes after,” he added.

Papa also emphasized that Iloilo City is geographically flat, making evacuation to high ground difficult.

He added that residents would have no time and nowhere to run, leaving vertical evacuation—climbing to higher floors of strong buildings—as the only survival option.

“There is nowhere to go because Iloilo City is relatively flat. Our option is to go up to standing and high-rise buildings,” he said.

The nearest elevated area outside the city is Cabatuan, Iloilo, but Papa noted that it would be almost impossible to reach within 15 minutes after a massive earthquake.

He said residents must identify strong vertical evacuation sites in advance, including buildings designed to withstand major quakes.

One example, he said, is the Iloilo City Hall, which is rated to withstand a magnitude 8 earthquake for two minutes and can serve as a vertical evacuation building.

Papa advised residents to check the PHIVOLCS tsunami hazard maps and identify nearby high-rise buildings that can serve as evacuation shelters.

The Philippines sits along the Pacific Ring of Fire, and the Negros Trench is part of a subduction zone capable of generating strong earthquakes and tsunamis.