Question

If an old masonry building in your area started to sink into the ground, would you suspect subsidence or liquefaction as the cause?

Answer

You would need a little more information to decide which is the more likely cause. If the building is known to be on fill material or highly compressive organic material, or if subsoil removal of oil, gas, or water is know to have occurred, then it is probably a case of subsidence. In that case, the building and surrounding soils might have both sunk.

If the drop is sudden and following an earthquake, it is most likely a case of liquefaction, where the existing granular soils (such as sand) were transformed from a stable state to a state having liquid characteristics due to the earth vibrations caused by the earthquake.