Why are earthfill dams made with hydraulic fill especially vulnerable to earthquakes?

Earthfill dams constructed using hydraulic fill technology are particularly vulnerable to earthquakes because they retain a large quantity of water within their soil structure. When subjected to seismic shock, this saturated soil is prone to liquefaction, a process that causes the soil to lose its strength and behave like a fluid. This loss of stability can lead to the soil "slipping," which may result in the partial or total collapse of the dam structure.12

In contrast to modern embankment dams that utilize compacted layers of earth to ensure stability, hydraulic fill dams are created by washing earthy materials into place using water. Because this method leaves the soil saturated and less dense than mechanically compacted fill, these dams lack the necessary resistance to withstand the intense ground motions and pore pressure increases triggered by seismic activity.3451