A system for preventing seismic liquefaction of the ground in an urban area built on reclaimed land consisting of a loose fine grained layer vulnerable to liquefaction underlain with a soft cohesive layer liable to uneven settlement. The system includes a plurality of vertically-extending wells with submerged pumps which pump pore water out of the loose layer, creating pore voids therein. An air-tight tank pressurizes the pumped pore water and, using an air compressor, pushes the water into a deep layer below the cohesive layer. A regulating receptacle injects a tap water mixture to fill the pore voids in the loose layer, with the mixture reducing the degree of pore water saturation therein, preventing seismic liquefaction due to earthquake.