Southern California residents have long prepared against the threat of earthquakes, but a new study suggests that a different natural disaster could pose a bigger danger: tsunamis. If a magnitude-9.1 earthquake were to hit in coastal waters off the Alaskan Peninsula, waves could flood Southern California’s low-lying coastal areas, forcing up to 750,000 residents to evacuate, a federal study reported. Damage to marinas, businesses and homes could cost the state between $3.5 billion and $6 billion.