During the deadly 6.9-magnitude Loma Prieta quake in 1989, houses shook and smoke belched from fires in the area. The Marina district, built on landfill, was created for the 1915 Panama Pacific International Exposition. After San Francisco's fabled 1906 earthquake, a lagoon was drained and rubble from the fires that burned for four days was dumped into it along with sand. That turned into the site of the exposition, and eventually the Marina district. Much of the destruction from the 1989 quake resulted from liquefaction, including the collapse of Oakland's Cypress Freeway.
Liquefaction occurs when sandy soil becomes saturated by groundwater and then is shaken.
The maps released in 120 cities, including Oakland, Berkeley and areas around Los Angeles, are not meant to deter people from living in the hazard areas. Instead, they're a tool homeowners are urged to use to ensure their houses are reinforced before the next big quake rocks the Bay area, an event seismologists predict will occur within the next three decades. We remove the fear with the strength of knowledge. They can make their building stronger. Building officials advise homeowners living in liquefaction or landslide zones to hire an engineer to analyze the soil beneath the house.