Tsunami risks close to home

With its offshore faults and low-lying beach areas, Southern California has been hit by tsunamis in the past and will always be at some risk. In a worst-case scenario, experts say, up to 75,000 people could die. Here are the three types of geological events that researchers say could one day send a flood of ocean water our way:

1. Local underwater hazards

The Catalina fault is a prime local tsunami hazard. A big quake there could push up the seafloor, displacing water that would swamp the shoreline. Such a quake might also have a domino effect, triggering tsunamis as a result of undersea landslides closer to shore in one of the following hazard zones:

Point Dume: Offshore wall shows signs of having failed in the past. Low-lying areas from Malibu to Santa Monica could flood.

Redondo Canyon: Collapse of the canyon walls could flood low-lying areas. Inundation zones might include Marina del Rey and the shores of Santa Monica and the South Bay beach cities.

Palos Verdes Canyon: Inundation from an offshore collapse could stretch from the Los Angeles-Long Beach port area to Sunset Beach in Orange County. Santa Catalina Island might also be affected.

Historical tsunamis in California:

*--* Run-up* Source of Date Location in feet tsunami Aug. 31, 1930 Redondo Beach- 20 Uncertain Santa Monica Aug. 21, 1934 Newport Beach 39.4 Uncertain March 28, 1964 Crescent City 20 9.2 quake, Gulf of Alaska Oct. 18, 1989 Moss Landing 3.3 7.1 quake, Loma Prieta Nov. 4, 2000 Santa Barbara 16.4 Uncertain County *--*

*Water height above sea level. Some measurements may be estimates.

2. Subduction under the Pacific Northwest

The Cascadia subduction zone in the Pacific Northwest is similar in its potential for major earthquakes to the one off Sumatra that caused the devastating tsunami in December. A big quake along the Cascadia fault could affect areas throughout the Pacific, including California. Here is a comparison of the two continental shelves: (see graphic)

3. A faraway quake

Historically, the tsunami threat in the Pacific Ocean is greatest as a result of a major quake in Chile, Alaska or Japan. A large enough quake could pose a danger to the West Coast of the United States.

The Dec. 26 quake off Sumatra created a tsunami in the Indian Ocean that flooded shorelines thousands of miles away.

Sources: USC Tsunami Research Center, Governor’s Office of Emergency Services, California Geological Survey, Earthquake Engineering Research Institute, NOAA, USGS, Caltech, Southern California Earthquake Data Center, Associated Press. Graphics reporting by Cheryl Brownstein-Santiago

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