In Newport Beach, the "Big One" might be an earthquake, or the tsunami that follows one.
Tsunami and emergency response experts at a Newport workshop last week offered tips on how to avoid the devastation of the quake-triggered waves.
The keys, they said, are preparedness and recognition.
A large swath of Newport Beach sits below 32-foot elevation, the most at-risk "run-up area." A city map shows the Balboa Peninsula, the harbor islands, the Corona del Mar beaches and much of the area along Upper Newport Bay as being in the hazard zone.
Tsunamis can come from movement along relatively nearby offshore faults or from major distant seismic events, such as the magnitude 8.8 quake that struck Chile in 2010 or the 9.0 Japanese quake of 2011.
For distant quakes, authorities have hours to assess the possible ocean surge and send out tsunami warnings. Those can come via radio, television, phone, text message or Newport's tsunami sirens, which the city tests once a month.
But for nearby events, the waves can arrive within 10 to 30 minutes, said Cynthia Pridmore, a geologist and tsunami and quake expert from the California Geological Survey. That's too soon for official warnings.
Therefore, she said, coastal residents and visitors need to be observant.
"They're not common events, but they can be catastrophic, so they're worth our time and effort to be prepared for them and understand what to do," Pridmore said.
Yvette LaDuke from the California Office of Emergency Services said there are three clues that a tsunami is imminent: strong shaking of the earth, receding water exposing the sea floor, and a loud ocean roar.
But, she said, people shouldn't wait for all three before deciding to evacuate low-lying areas.
If it comes time to flee to higher ground, follow marked tsunami evacuation routes, LaDuke said. Newport's routes follow Superior, Avocado, Goldenrod and Marguerite avenues; Balboa, Newport and MacArthur boulevards; Jamboree and Newport Coast roads and Dover Drive to Irvine Avenue.
If that's impossible, try to get to the fourth floor or higher of a sturdy concrete or steel building, she said. And stay away from the coast until authorities say it's safe to return.
The size of the surge and how far inland it goes depends on many factors — the magnitude of the quake, the tides, the marine terrain, debris it picks up on the way. The state generally recommends getting to 100 feet above sea level or two miles inland, or "as high as possible."
The tsunami after the Japanese quake caused millions of dollars in damage at the harbors in Santa Cruz and Crescent City, Calif. Pridmore said the Chile- and Japan-connected tsunamis created surges of about 1 to 2 feet in Newport Beach, which she said is plenty to damage ports and harbors.