"Southern California is at great risk for extreme catastrophic losses owing to numerous natural hazards, such as earthquakes, wildfires, floods, tsunamis, landslides and coastal changes, that occur in this area (fig. 1). Expected losses from these hazards are estimated to exceed $3 billion per year in the eight counties of southern California. In southern California: A) Natural hazards have devastating consequences, including loss of life and injury, replacement costs of buildings and infrastructure, loss of function of critical facilities, service and infrastructure outages, business interruption, loss of jobs, and a decrease in the quality of life. B) Multiple natural hazards are commonplace and often overlap to create secondary hazards. For example, earthquakes can produce landslides and severe fires and heavy storms can produce debris flows."
U.S. Geological Survey: http://www.usgs.gov/