California Department of Transportation

Readying Californians for a Tsunami:
The Great ‘Harbor Wave’

Three north coast counties lead the way in preparing California’s coastline
for future tsunamis.

The Pacific “Ring of Fire” etches a huge parabolic arc up from New Zealand and Asia through the Aleutian Islands of Alaska, and ultimately south along the coast of California and the Americas. It is home to more than 75 of the world's active and dormant volcanoes. Therefore, it is the land both of earthquakes and tsunamis, their seaborne offspring.

Tsunami, which means “harbor wave” in Japanese, can be caused by earthquakes, landslides, huge meteorites slamming into the ocean, or great tectonic plates that snap and lurch under the seabed. The resulting series of watery undulations, called a “wave train,” races along the ocean surface, until it batters some island, archipelago or continent unfortunate enough to stand in the way.

sign installationCalifornia knows about these malicious waves based on grim experience. A reminder of their dangers arrived the morning of March 11 when a tsunami triggered by a 9.0-magnitude earthquake
in Japan slammed into the California coastline. Governor Jerry Brown declared states of emergency in six northern and central California counties -- Del Norte, Humboldt, San Mateo and San Cruz counties on March 11, and in Mendocino and San Luis Obispo counties five days later.

Santa Cruz and its small craft harbor was among the most-affected communities in California. It suffered significant damage to piers and watercraft. Unfortunately, California has seen such waves before, and the next one could be much worse.

More than 80 tsunamis have pummeled the California coast in the last 150 years. For example, the 8.8-magnitude earthquake in Chile on February 27, 2010, resulted in the National Weather Service (NWS) issuing a tsunami advisory along the entire California coastline — a reminder that we need to plan for more than just home-grown earthquakes. Only a few feet high, this tsunami turned out to be minor when it reached California.

The 1964 Alaska tsunami was generated by a 9.2-magnitude earthquake near Prince William Sound. The damage was greatest along the Alaska coastline, resulting in $300 million to $400 million in damage and 119 deaths. In California, the great wall of water killed 12 people and caused an estimated $17 million in damage (about $118 million in today’s dollars) as it bullied its way southward along the coast. Most of the damage was at Crescent City, which was inundated with a 21-foot wave, causing 10 deaths, flooding a large portion of the city, and causing $15 million in damage. Two other deaths occurred in Bolinas, barely 10 miles north of San Francisco, and in Los Angeles.

All of these tsunamis originated at great distances from California, allowing for warning times measured in hours. But a local tsunami, generated by an offshore earthquake or submarine landslide, could allow residents just minutes of notice before slamming into the shoreline. In either case, a good warning system is critical in reducing deaths when the next large tsunami occurs. Information is vital for people in the tsunami hazard zone; anywhere less than 30 feet above sea level.

The nationwide Emergency Alert System (formerly the Emergency Broadcast System) is
in place to notify the public in times of emergency. For example, tornado warning tests occur annually throughout much of the United States. The next big tsunami could hit at any time, yet until recently most coastal communities had never tested their tsunami warning communications systems.

The Japan tsunami activated the Emergency Alert System for real (ironically cancelling the next test, which had been scheduled for March 23). The participating federal, state, and local agencies will use information gathered from this recent event to improve next year’s test, or the next tsunami warning.

Since 2008 Caltrans District 1, located in California’s northwest corner, has participated in annual tsunami warning communications tests, in coordination with federal, state, and local partners, including the NWS, California Emergency Management Agency (Cal EMA, formerly the Governor’s Office of Emergency Services), and the counties of Del Norte, Humboldt, and Mendocino. These tests, first conducted in Humboldt County and then expanded to include Del Norte County in 2009 and Mendocino County in 2010, are providing valuable information that will improve the local tsunami warning system.


The most recent exercise, on March 24, 2010, simulated a distant tsunami that would have provided local officials some time for preparation. It included a broadcast on the National Oceanic and Atmospheric Administration weather radio and a message on local radio and television stations. It also included activating four remote sirens, testing reverse 911 telephone calls, powering up Caltrans' changeable message signs and highway advisory radios, and flying an airplane along the coast from Crescent City to northern Humboldt County broadcasting audibly to those along the shore. The results of the test included one siren that failed to activate, a radio station that did not receive the message, and plane problems that limited the range of its message. However, a practice drill is the best time to discover and deal with such problems.

The lessons learned will also be applied statewide as the tests are expanded southward. Each year one or more counties will be added to the test until all of California’s 15 coastal counties are participating. This area encompasses three major urban areas, 73 cities, and four major ports. In addition, the California coastline attracts up to two million visitors during the summer months.

Still, warning the public is not enough if residents are unaware they are within a tsunami hazard zone. A person could be far from the ocean and still be in danger, so Caltrans and local agencies are installing signs to alert the public when they are entering, within, or leaving a tsunami hazard zone. In some areas, evacuation signs have also been installed to direct people to safe ground.

Public education is being conducted through brochures and the news media, in addition to the tsunami hazard signs. Brochures are available from Cal EMA and NWS. News organizations are provided with information prior to each test to prepare the public, and then post-test information reinforces the success and rationale for the exercise. Finally, the tsunami hazard signs are a constant reminder to those who live, work, and travel through areas that could be inundated during a tsunami.

Tsunamis may always be capricious, but with a bit of warning, California hopes to protect human lives and property when these great walls of water wash upon our shores.

For more tsunami information, visit:
National Weather Service’s Tsunami Center:
Emergency Management Agency:


Tsunami warning levels:

  • Warning: A potential tsunami with significant widespread inundation is imminent or expected. Widespread, dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after the arrival of the initial wave.
  • Advisory: A potential tsunami which may produce strong currents or waves exists. Significant widespread inundation is not expected.
  • Watch: A potentially dangerous distant seismic event has occurred which may later impact the watch area with a tsunami. Be ready to take action if a warning is issued.
  • Information Statements: An earthquake has occurred or a tsunami warning, watch, or advisory has been issued for another section of the ocean. In most cases, information statements are issued to indicate there is no threat of a destructive tsunami in your area.

Tsunami safety rules:

  • Keep calm and listen to emergency officials.
  • If you can see the tsunami it is too late; tsunamis move faster than you can run.
  • A tsunami is a series of waves that continue for many hours; not one single wave.
  • Move to high ground: 100 feet above sea level or 1 mile inland, away from river valleys.
  • If you cannot move to high ground, a concrete building’s upper floor may be safe. Use the stairs.

Strong coastal earthquakes can trigger tsunamis. Know nature’s warning signs:

  • A strong earthquake lasts 30 seconds or longer and causes difficulty in standing.
  • Noticeable rapid rise or fall of coastal water.
  • A large ocean roar may precede a tsunami.
  • Not every earthquake will cause a tsunami.
  • Local tsunamis often happen more quickly than warnings can be issued.
  • When in doubt, evacuate.
  • A small tsunami at one beach can be giant a few miles away. All tsunamis are potentially dangerous even though they may not damage every coastline they strike.
  • Stay tuned to your radio, marine radio, NOAA Weather Radio, or television.
  • Keep emergency supplies at the ready. Prepare for power failures and water shortages.
  • Wait for emergency officials’ “All clear.”