Liquefaction

During a strong earthquake, loose, water-saturated soil can briefly behave like a liquid. Solid-looking ground loses its strength, and buildings can sink, tilt, or float. That is liquefaction, and it is the difference between a cracked wall and a house leaning on its side.

This is the one layer we label as an estimate, on purpose. PHIVOLCS has an authoritative liquefaction map, but it is not openly licensed, so we cannot ship it. Until it opens, we screen each property using the terrain signals we do have and we always show our work.

In the 1990 Luzon earthquake, liquefaction in Dagupan City made multi-storey buildings sink and tip over while the structures themselves stayed largely intact. The ground, not the building, failed.

Much of low-lying Metro Manila and many coastal towns sit on exactly the soft, wet, sandy soil that liquefies. Knowing this before you build changes the foundation design, which is far cheaper to get right on paper than to fix later.

We combine two ingredients: how soft and wet the soil likely is (from elevation, slope, and distance to the nearest waterway, plus a coastal bump) and how hard the ground is likely to shake (from distance to the nearest active fault).

Those combine into a 0-12 score that maps to Low, Moderate, High, or Very high. Because it is an estimate, it is always tagged as such and it never sets the headline rating of your report; it only informs the conversation.

This layer is modelled from the SRTM elevation grid, the waterway network, and the active-fault distance. It is a screening proxy, not a geotechnical survey.

When PHIVOLCS opens its liquefaction map under a usable license, we will swap the real data in and retire the estimate. Until then, treat a high score as a reason to ask a professional, not as a verdict.