Yes, a tsunami can hit Los Angeles, and the risk is a persistent reality due to the city’s location along the seismically active Pacific Rim. A tsunami is a series of powerful, long-wavelength ocean waves caused by the sudden, massive displacement of water. This displacement is most often triggered by large underwater earthquakes, but can also result from volcanic activity, submarine landslides, or meteorite impacts. The vulnerability of the California coast is confirmed by both geological evidence and documented historical events.
The Science of Tsunami Generation
Tsunamis are seismic sea waves generated by the vertical movement of the seafloor, unlike typical wind-driven surface waves. This powerful upward or downward shift, usually from a large subduction zone earthquake, displaces the entire water column above the rupture. The resulting waves can travel across the deep ocean at speeds exceeding 500 miles per hour, similar to a jet airplane, though wave heights are often less than three feet in the open ocean.
These events are categorized as either distant or local tsunamis, based on the distance from the source to the coast. A distant, or tele-tsunami, originates thousands of miles away, allowing for hours of warning time before the wave arrives in Los Angeles. Conversely, a local tsunami is generated close to the coast, often by a near-shore earthquake or landslide, and can strike in less than 30 minutes, providing minimal time for official warnings.
Historical Context of California Tsunami Events
Past events confirm the tsunami threat to the California coast, including Southern California. The 1964 Great Alaska Earthquake, a magnitude 9.2 event, generated a tele-tsunami that caused widespread destruction in Northern California, particularly in Crescent City. Though further south, the Los Angeles and Long Beach Harbors also experienced significant damage from the resulting strong currents and surges.
More recently, the magnitude 9.0 Japan Tohoku earthquake in 2011 sent a tsunami across the Pacific, impacting the California coastline nine to eleven hours later. While the damage was most severe in northern harbors, Southern California felt the effects. Harbor pilots in the Port of Los Angeles/Long Beach reported significant tidal flow and currents exceeding six knots, leading to operational challenges and minor damage to docks in some small boat harbors.
Primary Threat Sources for Southern California
The primary tsunami threats to the Los Angeles area stem from both distant and local seismic activity across the Pacific basin. Distant sources are the most common cause of tsunamis that reach LA. These include the Cascadia Subduction Zone off the Pacific Northwest, the Alaska-Aleutian Trench, and subduction zones off South America, such as Chile.
A worst-case scenario from a magnitude 9.3 earthquake in the eastern Aleutian Islands could give Los Angeles approximately six hours of warning time. A major event off the coast of Chile would provide a longer lead time, potentially up to 13 hours.
Local sources, while less common, represent the most dangerous scenario due to the minimal warning time they provide. Tsunamis generated by near-shore submarine landslides or movement along local offshore faults could reach the coast in 10 to 15 minutes. This rapid-onset wave could be triggered by an underwater landslide off the Palos Verdes Peninsula or near the Channel Islands, generating a rapid-onset wave.
Coastal Vulnerability and Inundation Zones
The geography of the Los Angeles coastline makes certain areas highly vulnerable to tsunami inundation and destructive currents. Long, gently sloping shorelines and the funneling effect of harbors and estuaries tend to amplify the incoming waves.
Specific high-risk areas in Los Angeles County are formally mapped as tsunami hazard zones. These include the Ports of Los Angeles and Long Beach, which are low-lying areas with immense economic significance. Marina del Rey, the coastal city of Venice, and parts of the South Bay are also included.
Models for a worst-case distant tsunami predict inundation heights up to 15 feet above mean sea level in areas like Marina del Rey and Naples. A local-source tsunami could potentially produce wave heights up to 24 feet at Palos Verdes Hills and 30 feet at Catalina Island.
Detection and Public Alert Systems
The infrastructure for detecting tsunamis and alerting the public is managed by the U.S. National Tsunami Warning Center (NTWC) in Alaska. This center relies on a network of sensors to monitor for seismic activity and confirm the generation of a tsunami.
The backbone of the warning system is the globally distributed network of Deep-ocean Assessment and Reporting of Tsunami (DART) buoys. These buoys use seafloor bottom pressure recorders to detect the pressure changes of a tsunami wave passing overhead in the deep ocean.
Once a threat is confirmed, the NTWC issues official alerts categorized as an advisory, watch, or warning. These alerts are disseminated to local authorities and broadcast in Los Angeles through multiple channels, including the Wireless Emergency Alert system, NOAA Weather Radio, and local media.