A major earthquake probably will strike Southern California within the next 20 years, experts warned. Members of the state Assembly Committee on Governmental Organization heard testimony in Los Angeles from a variety of earthquake safety experts who discussed buildings that could collapse in a major earthquake. A spokesman for the state's Seismic Safety Commission said unreinforced buildings should be strengthened to meet safety standards or be demolished. "We've heard some frightening revelations here," said Assemblywoman Sally Tanner (D-Los Angeles.) "We all realize earthquakes can be devastating and we need to respond." Paul Fratessa, a structural engineer, said California would not suffer damage as severe as that in Mexico City, where recent quakes killed at least 5,000 people, injured more than 30,000 and toppled almost 500 buildings. "The building code requirements are less stringent in Mexico than in California," he said.