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FAQ About Tsunamis

Introduction

What is a tsunami?

What are the sources for and examples of tsunamis
that might affect California?

How can I determine whether tsunamis are possible where I live,
and what kind of warning could I get?

Are there any warning signs of an impending tsunami?

What should I do before, during, and after a tsunami in my area?

Historic Tsunamis in California

Introduction

The California Geological Survey (CGS) provides geologic and seismic expertise to the public, other State government offices, such as the California Governor’s Office of Emergency Services (CalOES), and local government agencies (cities and counties).  For tsunami hazards, CGS works closely with CalOES and the Tsunami Research Center at the University of Southern California to produce statewide tsunami inundation maps and preparedness information for California. CGS is also the Scientific Representative for California on the National Tsunami Hazard Mitigation Program Coordinating Committee, a state and federal cooperative responsible for developing policies and standards for tsunami mitigation efforts in the United States and its territories.

What is a tsunami?

A tsunami is a wave, or series of waves, generated by an earthquake, landslide, volcanic eruption, or even large meteor hitting the ocean (The Japanese word tsu means “harbor”; nami means “wave”). What typically happens is a large, submarine earthquake (magnitude 8 or higher) creates a significant upward movement of the sea floor resulting in a rise or mounding of water at the ocean surface. This mound of water moves away from this center in all directions as a tsunami. A tsunami can travel across the open ocean at about 500-miles per hour, the speed of a jet airliner. As the wave approaches land and as the ocean shallows, the wave slows down to about 30 miles-per-hour and grows significantly in height (amplitude).

Although most people think a tsunami looks like a tall breaking wave, it actually resembles a flood or surge.

What are the sources for and examples of tsunamis that might affect California?

More than eighty tsunamis have been observed or recorded in California in historic times. Fortunately, almost all of these were small and did little or no damage. Though damaging tsunamis have occurred infrequently in California, they are a possibility that must be considered in coastal communities. There are two sources for California tsunamis, based on distance and warning time:

Local sources - Local tsunami sources, like large offshore faults and massive submarine landslides, can put adjacent coastal communities at the greatest risk of a tsunami because the public must respond quickly with little or no official guidance. The Cascadia Subduction Zone is an example of a local tsunami source that could threaten northern California. Stretching from Cape Mendocino, California, to Vancouver Island, British Columbia, this 700-mile long submarine fault system forms the crustal plate boundary where the offshore Gorda and Juan de Fuca plates dive, or subduct, beneath the North American plate. Examples of local tsunamis that have impacted California include:

January 26, 1700 - An earthquake estimated at a magnitude 9 ruptured the entire length of the Cascadia Subduction Zone, likely causing a 50-foot tsunami in parts of northern California. Though there were no local written accounts, scientists have reconstructed the event based on geologic evidence and oral histories from the Native American people in the area, and determined the exact date and time from Japanese documents that describe the effects of a large tsunami that hit the coast of Japan later that same day.

December 21, 1812 – A tsunami struck the Santa Barbara and Ventura coastline shortly after a large earthquake was felt in the area. Though reports of the size of this tsunami have been debated, the event was large enough to inundate lowland areas and cause damage to nearby ships. One theory is that the tsunami was caused by a nearby submarine landslide triggered by the earthquake.

Distant sources - A tsunami caused by a very large earthquake elsewhere on the Pacific Rim could reach the California coast many (4 to 15) hours after the earthquake. The Alaska-Aleutians Subduction Zone is an example of a distant source that has caused destructive tsunamis in California. Notable distant tsunamis that have impacted California include:

April 1, 1946 – A magnitude 8.8 earthquake in the Aleutian Islands generated a tsunami that caused damage along the coast of California, including flooding over 1000-feet inland in Half Moon Bay.

March 28, 1964 – Twelve people were killed in California when a tsunami was generated by a magnitude 9.2 earthquake off the coast of Alaska. A surge approximately 20-feet high flooded 29 city blocks of Crescent City.

March 11, 2011 – A magnitude 9.0 earthquake in the Tohoku region of Japan produced a moderate amplitude tsunami in California. Although it did not generate significant flooding in California, strong tsunami currents caused one death and over $100-million in damages to 27 harbors statewide, with the most significant damage occurring in Crescent City and Santa Cruz.

The table appended to the bottom of this page contains information on some additional tsunamis in California from 1812 to 2012, compiled from the following website: http://www.ngdc.noaa.gov/nndc/servlet/ShowDatasets.

How can I determine whether tsunamis are possible where I live, and what kind of warning could I get?

Tsunamis generally affect coastal communities and low-lying (low-elevation) river valleys in the vicinity of the coast.  Buildings closest to the ocean and near sea level are most at jeopardy. Type in an address or city using the CGS Information Warehouse to access Statewide Inundation Maps to see if areas where you live, work, or visit are in tsunami inundation areas.

In order to determine whether a tsunami has been generated following a large earthquake, scientists from the West Coast and Alaska Tsunami Warning Center monitor an array of buoys and tide gauges that measure vertical changes to the ocean surface (more info on ocean tides and currents).  If a potentially damaging tsunami is headed towards California, a warning will be broadcast through the Emergency Alert System and the National Oceanic and Atmospheric Administration (NOAA), National Weather Service (NWS) Weather Radio (http://www.nws.noaa.gov/nwr/ ). Check with your local city or county to see what ways they will notify you of a tsunami.

In situations where tsunami travel times are short (due to nearby earthquakes or landslides), it is difficult for government agencies to identify and warn the public. Individuals should know what the natural warning signs of a tsunami are and have a plan to evacuate if necessary.

Are there any warning signs of an impending tsunami?

One noticeable, but not universal, sign is the rapid receding of ocean water from the beach before the first tsunami wave hits.  In many accounts (including the current Indian Ocean tsunami), this effect has caused greater loss of life because it became a curiosity that attracted people to the oceanfront.  

Very strong ground shaking along the coast is an indication of an earthquake that could cause seafloor displacements and/or a submarine landslide large enough to generate a tsunami.  Though many large earthquakes have occurred along the coast without causing a tsunami, you should still be aware of the potential and plan accordingly.  In the event you are at the coast and feel strong shaking, it may be prudent to move to higher ground.

What should I do before, during, and after a tsunami in my area?

Education and preparation are the best ways to avoid injury and increase your chances for survival.  Know whether you are in a potential tsunami zone by observing street signs or looking online to see if you are in a zone. Know the evacuation routes for your area. Contact your local city and/or county government to see what the evacuation plan is for your area and where you will be expected to evacuate to. Have a “to go bag” ready, in the event you have to evacuate. Do not return to the evacuated zone until officials tell you it is safe to do so. The first tsunami is not always the largest, and tsunami waves, flooding and strong currents can last for several hours.

For more information about tsunami preparedness to go www.tsunamizone.org.

Historic Tsunamis in California

The chart below shows data from some of the tsunamis recorded in central and southern California from 1812 to 2012 (from

http://www.ngdc.noaa.gov/nndc/servlet/ShowDatasets ):

 

 

Date

Travel (hours)

Time (minutes)

Tsunami Location

Height (meters)

Source Location

Source Event

Source Magnitude (Ms)

Source Magnitude (Mw)

12/21/1812 EL REFUGIO (GAVIOTA), CA 3.4 CA Purisima 7.7
12/21/1812 SANTA BARBARA, CA 2 CA Purisima 7.7
12/21/1812 VENTURA, CA 2 CA Purisima 7.7
9/24/1856 SAN DIEGO, CA 3.6 Japan Tokaido
9/24/1859 HALF MOON BAY, CA 4.6 N. CA
5/27/1862 SAN DIEGO, CA 1.2 S. CA 5.8
10/21/1868 SAN FRANCISCO BAY, CA 4.5 SF area 6.8
8/13/1868 SAN PEDRO, CA 1.8 N. Chile 8.5
8/13/1868 WILMINGTON, CA 1.8 N. Chile 8.5
4/16/1877 ANAHEIM LANDING, CA 1.8 CA
4/16/1877 CAYUCOS, CA 3.6 CA
5/10/1877 GAVIOTA, CA 1.8 N. Chile 8.3
5/10/1877 SAN PEDRO, CA 1 N. Chile 8.3
5/10/1877 WILMINGTON, CA 1.7 N. Chile 8.3
11/22/1878 WILMINGTON, CA 1 S. CA
12/17/1896 SANTA BARBARA, CA 2.5 S. CA
6/15/1896 SANTA CRUZ, CA 1.5 Japan Sanriku 7.6
11/4/1927 SURF, CA 1.8 CA 7.3
4/1/1946 ARENA COVE, CA 2.4 Alaska E. Aleutian Islands 7.3
4/1/1946 5 36 AVILA BEACH, CA 1.3 Alaska E. Aleutian Islands 7.3
4/1/1946 DRAKES BAY, CA 2.6 Alaska E. Aleutian Islands 7.3
4/1/1946 HALF MOON BAY, CA 2.6 Alaska E. Aleutian Islands 7.3
4/1/1946 MORRO BAY, CA 1.5 Alaska E. Aleutian Islands 7.3
4/1/1946 5 36 SAN LUIS OBISPO, CA 1.3 Alaska E. Aleutian Islands 7.3
4/1/1946 SANTA CATALINA ISLAND, CA 1.8 Alaska E. Aleutian Islands 7.3
4/1/1946 SANTA CRUZ, CA 1.5 Alaska E. Aleutian Islands 7.3
11/4/1952 8 36 AVILA BEACH, CA 1.4 Russia Kamchatka 8.2 9
5/22/1960 MONTEREY, CA 1.1 Chile Central Chile 9.5
5/22/1960 PACIFICA, CA 1.2 Chile Central Chile 9.5
5/22/1960 PISMO BEACH, CA 1.4 Chile Central Chile 9.5
5/22/1960 14 4 PORT HUENEME, CA 1.3 Chile Central Chile 9.5
5/22/1960 14 12 SANTA MONICA, CA 1.4 Chile Central Chile 9.5
5/22/1960 STINSON BEACH, CA 1.5 Chile Central Chile 9.5
5/22/1960 13 43 WILSON COVE, CA 1.2 Chile Central Chile 9.5
3/28/1964 ARENA COVE, CA 1.8 Alaska Gulf of Alaska 9.2
3/28/1964 5 10 AVILA BEACH, CA 1.6 Alaska Gulf of Alaska 9.2
3/28/1964 CAPITOLA, CA 2.1 Alaska Gulf of Alaska 9.2
3/28/1964 MARTINS BEACH, CA 3 Alaska Gulf of Alaska 9.2
3/28/1964 MONTEREY, CA 1.4 Alaska Gulf of Alaska 9.2
3/28/1964 MOSS LANDING, CA 1.4 Alaska Gulf of Alaska 9.2
3/28/1964 PACIFICA, CA 1.4 Alaska Gulf of Alaska 9.2
3/28/1964 5 6 SAN FRANCISCO, CA 1.1 Alaska Gulf of Alaska 9.2
3/28/1964 SAN RAFAEL, CA 1.5 Alaska Gulf of Alaska 9.2
3/28/1964 SANTA CRUZ, CA 1.5 Alaska Gulf of Alaska 9.2
3/28/1964 5 39 SANTA MONICA, CA 1 Alaska Gulf of Alaska 9.2
3/28/1964 SAUSALITO, CA 1.2 Alaska Gulf of Alaska 9.2
3/28/1964 SEA VIEW, CA 3.8 Alaska Gulf of Alaska 9.2
3/28/1964 TOMALES BAY, CA 1 Alaska Gulf of Alaska 9.2
11/29/1975 SANTA CATALINA ISLAND, CA 1.4 7.2
10/18/1989 MOSS LANDING, CA 1 CA Loma Prieta 7.1
11/4/2000 POINT ARGUELLO, CA unknown CA Pt. Arguello
11/15/2006 8 16 Arena Cove, 0.61 Russia So.Kuril Islands 7.8 8.3
11/15/2006 8 31 Crescent City 0.88 Russia So.Kuril Islands 7.8 8.3
11/15/2006 9 41 La Jolla 0.1 Russia So.Kuril Islands 7.8 8.3
11/15/2006 Los Angeles 0.11 Russia So.Kuril Islands 7.8 8.3
11/15/2006 9 418 North Spit Humboldt Bay 0.17 Russia So.Kuril Islands 7.8 8.3
11/15/2006 8 36 Point Reyes, 0.33 Russia So.Kuril Islands 7.8 8.3
11/15/2006 Port San Luis 0.56 Russia So.Kuril Islands 7.8 8.3
11/15/2006 Richmond 0.09 Russia So.Kuril Islands 7.8 8.3
11/15/2006 San Diego 0.09 Russia So.Kuril Islands 7.8 8.3
11/15/2006 9 6 San Francisco, CA 0.16 Russia So.Kuril Islands 7.8 8.3
11/15/2006 Santa Barbara 0.4 Russia So.Kuril Islands 7.8 8.3
11/15/2006 10 8 Santa Monica 0.15 Russia So.Kuril Islands 7.8 8.3
8/16/2007 12 11 Crescent City 0.16 Peru Peru 7.9 8
9/30/2009 10 27 Arena Cove 0.44 Samoa Samoa Islands 8.1 8
9/30/2009 10 56 Crescent City 0.33 Samoa Samoa Islands 8.1 8
9/30/2009 Los Angeles 0.13 Samoa Samoa Islands 8.1 8
9/30/2009 11 38 Monterey 0.15 Samoa Samoa Islands 8.1 8
9/30/2009 11 2 Point Reyes 0.39 Samoa Samoa Islands 8.1 8
9/30/2009 11 43 Port San Luis 0.28 Samoa Samoa Islands 8.1 8
9/30/2009 11 0 San Francisco 0.1 Samoa Samoa Islands 8.1 8
9/30/2009 Santa Barbara 0.25 Samoa Samoa Islands 8.1 8
9/30/2009 Santa Cruz 0.7 Samoa Samoa Islands 8.1 8
9/30/2009 10 51 Santa Monica 0.15 Samoa Samoa Islands 8.1 8
2/27/2010 14 14 Arena Cove 0.36 Chile Central Chile 8.5 8.8
2/27/2010 15 6 Crescent City 0.64 Chile Central Chile 8.5 8.8
2/27/2010 Dana Point Harbor 0.7 Chile Central Chile 8.5 8.8
2/27/2010 Half Moon Bay 0.6 Chile Central Chile 8.5 8.8
2/27/2010 13 28 La Jolla 0.6 Chile Central Chile 8.5 8.8
2/27/2010 13 41 Los Angeles 0.42 Chile Central Chile 8.5 8.8
2/27/2010 13 57 Monterey 0.36 Chile Central Chile 8.5 8.8
2/27/2010 Morro Bay Harbor 0.5 Chile Central Chile 8.5 8.8
2/27/2010 Moss Landing 0.3 Chile Central Chile 8.5 8.8
2/27/2010 Marina Del Rey 0.1 Chile Central Chile 8.5 8.8
2/27/2010 Mission Bay San Diego 0.6 Chile Central Chile 8.5 8.8
2/27/2010 15 2 North Spit Humboldt Bay 0.23 Chile Central Chile 8.5 8.8
2/27/2010 Newport Beach 0.5 Chile Central Chile 8.5 8.8
2/27/2010 Oxnard 1 Chile Central Chile 8.5 8.8
2/27/2010 Oceanside Harbor 0.6 Chile Central Chile 8.5 8.8
2/27/2010 Pismo Beach 1.2 Chile Central Chile 8.5 8.8
2/27/2010 14 25 Point Reyes 0.46 Chile Central Chile 8.5 8.8
2/27/2010 Port Hueneme 0.7 Chile Central Chile 8.5 8.8
2/27/2010 Port San Luis 0.8 Chile Central Chile 8.5 8.8
2/27/2010 13 30 San Diego 0.4 Chile Central Chile 8.5 8.8
2/27/2010 14 46 San Francisco 0.32 Chile Central Chile 8.5 8.8
2/27/2010 13 56 Santa Barbara 0.91 Chile Central Chile 8.5 8.8
2/27/2010 Santa Cruz 0.9 Chile Central Chile 8.5 8.8
2/27/2010 13 51 Santa Monica 0.64 Chile Central Chile 8.5 8.8
2/27/2010 Sunset 0.5 Chile Central Chile 8.5 8.8
2/27/2010 Ventura 0.9 Chile Central Chile 8.5 8.8
3/11/2011 10 49 ALAMEDA, CA 0.51 Japan Honshu 8.3 9
3/11/2011 9 44 ARENA COVE, CA 1.74 Japan Honshu 8.3 9
3/11/2011 Albion, CA 0.8 Japan Honshu 8.3 9
3/11/2011 Ballona Creek, CA 0.6 Japan Honshu 8.3 9
3/11/2011 Berkeley Marina, CA 0.51 Japan Honshu 8.3 9
3/11/2011 Bodega Bay/Spud Point Marina, CA 0.7 Japan Honshu 8.3 9
3/11/2011 Bolinas Stinson Beach, CA 0.9 Japan Honshu 8.3 9
3/11/2011 9 47 CRESCENT CITY, CA 2.47 Japan Honshu 8.3 9
3/11/2011 Carlsbad, CA 0.6 Japan Honshu 8.3 9
3/11/2011 Channel Islands Harbor, CA 1.2 Japan Honshu 8.3 9
3/11/2011 Chula Vista Marina, CA 0.2 Japan Honshu 8.3 9
3/11/2011 Clipper Yacht Harbor, Sausalito, CA 0.8 Japan Honshu 8.3 9
3/11/2011 Coronado Island Lifeguard HQ, CA 0.6 Japan Honshu 8.3 9
3/11/2011 Dana Point Harbor, CA 0.6 Japan Honshu 8.3 9
3/11/2011 Del Mar, CA 0.9 Japan Honshu 8.3 9
3/11/2011 Dolphin Isle Marina, Noyo River, CA 0.8 Japan Honshu 8.3 9
3/11/2011 Emery Cove Yacht Harbor, CA 0.6 Japan Honshu 8.3 9
3/11/2011 Encinitas Batiquitos, San Elijo, C 1 Japan Honshu 8.3 9
3/11/2011 HALF MOON BAY, CA 0.7 Japan Honshu 8.3 9
3/11/2011 Harbor Island West Marina, CA 0.3 Japan Honshu 8.3 9
3/11/2011 Huntington Harbor, CA 0.72 Japan Honshu 8.3 9
3/11/2011 Imperial Beach 0.5 Japan Honshu 8.3 9
3/11/2011 Jenner Russian River 1 Japan Honshu 8.3 9
3/11/2011 KLAMATH RIVER 2.5 Japan Honshu 8.3 9
3/11/2011 King Harbor , Redondo Beach 0.7 Japan Honshu 8.3 9
3/11/2011 11 La Jolla 0.39 Japan Honshu 8.3 9
3/11/2011 La Jolla 0.9 Japan Honshu 8.3 9
3/11/2011 Long Beach Marina 0.7 Japan Honshu 8.3 9
3/11/2011 Los Angeles 0.49 Japan Honshu 8.3 9
3/11/2011 Mare Island 0.07 Japan Honshu 8.3 9
3/11/2011 Martinez 0.06 Japan Honshu 8.3 9
3/11/2011 10 1 Monterey 0.7 Japan Honshu 8.3 9
3/11/2011 Morro Bay Harbor 1.6 Japan Honshu 8.3 9
3/11/2011 Marina Del Rey 1 Japan Honshu 8.3 9
3/11/2011 Mission Bay 0.9 Japan Honshu 8.3 9
3/11/2011 Moss Landing 2 Japan Honshu 8.3 9
3/11/2011 North Spit Humboldt Bay 0.97 Japan Honshu 8.3 9
3/11/2011 Coronado Naval Air Base 0.3 Japan Honshu 8.3 9
3/11/2011 New Port Beach Harbor 0.3 Japan Honshu 8.3 9
3/11/2011 Noyo River Harbor 1 Japan Honshu 8.3 9
3/11/2011 OXNARD 1.2 Japan Honshu 8.3 9
3/11/2011 Ocean Beach 1 Japan Honshu 8.3 9
3/11/2011 Oceano Dunes SRA 1 Japan Honshu 8.3 9
3/11/2011 Oceanside Harbor 0.5 Japan Honshu 8.3 9
3/11/2011 PISMO BEACH 1 Japan Honshu 8.3 9
3/11/2011 PLATFORM HARVEST 0.15 Japan Honshu 8.3 9
3/11/2011 POINT ARENA 1.74 Japan Honshu 8.3 9
3/11/2011 10 6 POINT REYES 1.35 Japan Honshu 8.3 9
3/11/2011 PORT CHICAGO 0.04 Japan Honshu 8.3 9
3/11/2011 PORT HUENEME 1.4 Japan Honshu 8.3 9
3/11/2011 PORT OF LONG BEACH Japan Honshu 8.3 9
3/11/2011 10 23 PORT SAN LUIS 2.02 Japan Honshu 8.3 9
3/11/2011 Pacifica 1 Japan Honshu 8.3 9
3/11/2011 Pier 39, San Francisco 0.6 Japan Honshu 8.3 9
3/11/2011 Pillar Point Harbor 0.7 Japan Honshu 8.3 9
3/11/2011 Pt Loma Sub Base/Ballast Pt 0.5 Japan Honshu 8.3 9
3/11/2011 11 54 REDWOOD CITY 0.12 Japan Honshu 8.3 9
3/11/2011 RICHMOND 0.35 Japan Honshu 8.3 9
3/11/2011 Rio Del Mar/Aptos Japan Honshu 8.3 9
3/11/2011 11 20 SAN DIEGO 0.63 Japan Honshu 8.3 9
3/11/2011 SAN FRANCISCO 0.62 Japan Honshu 8.3 9
3/11/2011 10 40 Santa Barbara 1.02 Japan Honshu 8.3 9
3/11/2011 10 56 SANTA MONICA 0.85 Japan Honshu 8.3 9
3/11/2011 SHELTER COVE MARINA, SAN DIEGO 0.3 Japan Honshu 8.3 9
3/11/2011 SHELTER I. DOCK, SAN DIEGO 0.8 Japan Honshu 8.3 9
3/11/2011 Smith River 2 Japan Honshu 8.3 9
3/11/2011 Santa Ana River Japan Honshu 8.3 9
3/11/2011 Santa Cruz Harbor 1.9 Japan Honshu 8.3 9
3/11/2011 Scripps 0.25 Japan Honshu 8.3 9
3/11/2011 Silver Strand State Beach 0.6 Japan Honshu 8.3 9
3/11/2011 Tijuana River Wetlands 0.2 Japan Honshu 8.3 9
3/11/2011 Two Harbors Catalina Japan Honshu 8.3 9
3/11/2011 Ventura Harbor 1.3 Japan Honshu 8.3 9
3/11/2011 Waldo Point Marina, Sausalito 1.5 Japan Honshu 8.3 9
10/28/2012 4 8 ALAMEDA 0.11 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 2 57 ARENA COVE 0.35 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 2 40 CRESCENT CITY 0.44 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 4 37 LA JOLLA 0.05 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 4 24 LOS ANGELES 0.08 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 3 30 MONTEREY 0.14 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 2 42 NORTH SPIT, HUMBOLDT BAY 0.12 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 3 15 POINT REYES 0.24 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 3 54 PORT SAN LUIS 0.27 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 4 4 RICHMOND 0.09 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 6 SAN DIEGO 0.05 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 3 48 SAN FRANCISCO 0.14 Canada Queen Charlotte Islands 7.5 7.7
10/28/2012 4 19 SANTA MONICA 0.08 Canada Queen Charlotte Islands 7.5 7.7

 

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Web page created by M. Reichle, D. Hoirup, R. Wilson, and E. Mattison, California Geological Survey, 2005.
Updated 4/20/2015 by Cindy Pridmore, California Geological Survey