. >> reporter: but even more surprising is this area at van nuys and vallejo. stan lives along this lot. >> we're on rock, solid rock. >> reporter: not according to the map. this area is actually color coded red or landfill. the same type of soil that's in the marina. some other unexpected findings, seismologists say that a two story building will have the same kind of damage whether it's on sand or landfill. >> that means that for those homeowners who live on sand which is most of the city, i would say get rid of the false security. >> reporter: city planners say the new detailed plan could ultimately change building codes throughout san francisco. >> it's a useful tool for the engineers so they know what they're about to face when they start the building. >> still to come on a second look. the connection between one of san francisco's greatest events and one of its greatest disasters. >>> and later, what brought down this part of the city? >>> in 1989 the loma prieta devastated parts of the san francisco district. why was that area hit so hard. the answer lie