Fictionalized image of a tsunami bearing down on Downtown Los Angeles. Photo images derived from Pixabay.com.
Yes, Los Angeles County can experience a tsunami. The two types of tsunamis are a local-source tsunami and a distant-source tsunami.
A distant-source tsunami comes from a far-away earthquake. It may arrive in five to 13 hours, depending on its point-of-origin. For Southern California, distant-source tsunamis would likely arrive from Japan, Chile or Alaska. Southern California’s worst-case scenario would be a tsunami originating from the eastern Aleutian Islands in Alaska. Such a tsunami would arrive to our shores in five to six hours.
A local-source tsunami is caused by a nearby offshore earthquake or by underwater landslides. This tsunami could arrive within minutes.
Southern California is more likely to face a small tsunami than a large one. A small tsunami might cause crazy currents at beaches, harbors and bays and threaten, perhaps, a crowded beach. However, a high-magnitude quake, occurring south of California or in Alaska, or even a smaller quake just offshore, would be much more devastating. One source estimates that Southern California faces more than a 40% chance of a large tsunami. Vulnerable low-lying coastal communities, according to the California Geological Survey, would be Santa Monica, Malibu, Venice, Marina del Rey, Redondo Beach, and Long Beach. An Alaskan quake would give Southern Californians five to six hours to evacuate to higher ground. A tsunami from a large offshore underwater quake near Southern California’s islands, however, would reach our shoreline within minutes.
Tsunami Hazard Zone warning sign. Photo from National Oceanic & Atmospheric Administration.
If Southern Californians were to feel an earthquake lasting 20 seconds or longer or see the ocean rapidly receding, those near the shoreline should immediately evacuate to any higher ground, even if not hearing a tsunami warning. A local-source tsunami would offer little time to issue a tsunami warning. It should be also noted that, for those might see a tsunami as an opportunity for amazing surfing, tsunami waves are very unsafe, typically filled with debris and other hazardous materials.
California’s most destructive tsunami hit Crescent City on March 28, 1964. Four hours after a magnitude 9.2 earthquake occurred in Alaska, a 20-foot high wave surged into the coastal community, flooding almost 30 blocks of the business district. More than 100 people along the entire West Coast were killed.
The belief that the Channel Islands (including Santa Catalina Island) might offer natural barriers to tsunamis may be wishful thinking. Although small islands might force massive surges to break around them, they have a high likelihood of reforming after passing around islands and may even pick up energy.
Sources:
Los Angeles County Tsunami Hazard Areas - California Geological Survey
Can a tsunami happen in Southern California? What should you do about it? - L.A. Times
The Science of Tsunamis and SoCal - LAist
Could It Happen Here? - U.S. Geological Survey
Also see:
-- Will Los Angeles Eventually Fall Into the Ocean?
-- Can a Volcanic Eruption Occur in Los Angeles?
-- Do Tornadoes Occur in Los Angeles County?
