Tsunamis

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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.

CGS Tsunami Banner Image

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 go to www.tsunamizone.org.

Historic Tsunamis in California

The table below shows data from some of the tsunamis recorded in central and southern California from 1812 to 2012 (Source: http://www.ngdc.noaa.gov/nndc/servlet/ShowDatasets).

DateSource LocationTsunami Location
Travel Time
(hrs:mins)
Height
(m)
Source Magnitude
(Ms / Mw)
12/21/1812Purisima, CaliforniaEl Refugio (Gaviota)?3.47.7 / -
12/21/1812Purisima, CaliforniaSanta Barbara?27.7 / -
12/21/1812Purisima, CaliforniaVentura?27.7 / -
9/24/1856Tokaido, JapanSan Diego?3.6?
9/24/1859Northern CaliforniaHalf Moon Bay?4.6?
5/27/1862Southern CaliforniaSan Diego?1.25.8 / -
10/21/1868San Francisco area, CaliforniaSan Francisco Bay?4.56.8 / -
8/13/1868Northern ChileSan Pedro?1.88.5 / -
8/13/1868Northern ChileWilmington?1.88.5 / -
4/16/1877CaliforniaAnaheim Landing?1.8?
4/16/1877CaliforniaCayucos?3.6?
5/10/1877Northern Chile
Gaviota?1.88.3 / -
5/10/1877Northern ChileSan Pedro?18.3 / -
5/10/1877Northern ChileWilmington?1.78.3 / -
11/22/1878Southern CaliforniaWilmington?1?
12/17/1896Southern CaliforniaSanta Barbara?2.5?
6/15/1896Sanriku, JapanSanta Cruz?1.57.6 / -
11/4/1927CaliforniaSurf?1.87.3 / -
4/1/1946E. Aleutian Islands, AlaskaArena Cove?2.47.3 / -
4/1/1946E. Aleutian Islands, AlaskaAvila Beach5:361.37.3 / -
4/1/1946E. Aleutian Islands, AlaskaDrakes Bay?2.67.3 / -
4/1/1946E. Aleutian Islands, AlaskaHalf Moon Bay?2.67.3 / -
4/1/1946E. Aleutian Islands, AlaskaMorro Bay?1.57.3 / -
4/1/1946E. Aleutian Islands, AlaskaSan Luis Obispo5:361.37.3 / -
4/1/1946E. Aleutian Islands, AlaskaSanta Catalina Island?1.87.3 / -
4/1/1946E. Aleutian Islands, AlaskaSanta Cruz?1.57.3 / -
11/4/1952Kamchatka, RussiaAvila Beach8:361.48.2 / 9.0
5/22/1960Central ChileMonterey?1.1- / 9.5
5/22/1960Central ChilePacifica?1.2- / 9.5
5/22/1960Central ChilePismo Beach?1.4- / 9.5
5/22/1960Central ChilePort Hueneme14:041.3- / 9.5
5/22/1960Central ChileSanta Monica14:121.4- / 9.5
5/22/1960Central ChileStinson Beach?1.5- / 9.5
5/22/1960Central ChileWilson Cove13:431.2- / 9.5
3/28/1964Gulf of AlaskaArena Cove?1.8- / 9.2
3/28/1964Gulf of AlaskaAvila Beach5:101.6- / 9.2
3/28/1964Gulf of AlaskaCapitola?2.1- / 9.2
3/28/1964Gulf of AlaskaMartins Beach?3- / 9.2
3/28/1964Gulf of AlaskaMonterey?1.4- / 9.2
3/28/1964Gulf of AlaskaMoss Landing?1.4- / 9.2
3/28/1964Gulf of AlaskaPacifica?1.4- / 9.2
3/28/1964Gulf of AlaskaSan Francisco5:061.1- / 9.2
3/28/1964Gulf of AlaskaSan Rafael?1.5- / 9.2
3/28/1964Gulf of AlaskaSanta Cruz?1.5- / 9.2
3/28/1964Gulf of AlaskaSanta Monica5:391- / 9.2
3/28/1964Gulf of AlaskaSausalito?1.2- / 9.2
3/28/1964Gulf of AlaskaSea View?3.8- / 9.2
3/28/1964Gulf of AlaskaTomales Bay?1- / 9.2
11/29/1975?Santa Catalina Island?1.47.2 / -
10/18/1989Loma Prieta, CaliforniaMoss Landing?17.1 / -
11/4/2000Pt. Arguello, CaliforniaPoint Arguello???
11/15/2006So.Kuril Islands, RussiaArena Cove8:160.617.8 / 8.3
11/15/2006So.Kuril Islands, RussiaCrescent City8:310.887.8 / 8.3
11/15/2006So.Kuril Islands, RussiaLa Jolla9:410.17.8 / 8.3
11/15/2006So.Kuril Islands, RussiaLos Angeles?0.117.8 / 8.3
11/15/2006So.Kuril Islands, RussiaNorth Spit Humboldt Bayunknown0.177.8 / 8.3
11/15/2006So.Kuril Islands, RussiaPoint Reyes8:360.337.8 / 8.3
11/15/2006So.Kuril Islands, RussiaPort San Luis?0.567.8 / 8.3
11/15/2006So.Kuril Islands, RussiaRichmond?0.097.8 / 8.3
11/15/2006So.Kuril Islands, RussiaSan Diego?0.097.8 / 8.3
11/15/2006So.Kuril Islands, RussiaSan Francisco9:060.167.8 / 8.3
11/15/2006So.Kuril Islands, RussiaSanta Barbara?0.47.8 / 8.3
11/15/2006So.Kuril Islands, RussiaSanta Monica10:080.157.8 / 8.3
8/16/2007PeruCrescent City12:110.167.9 / 8.0
9/30/2009Samoa IslandsArena Cove10:270.448.1 / 8.0
9/30/2009Samoa IslandsCrescent City10:560.338.1 / 8.0
9/30/2009Samoa IslandsLos Angeles?0.138.1 / 8.0
9/30/2009Samoa IslandsMonterey11:380.158.1 / 8.0
9/30/2009Samoa IslandsPoint Reyes11:020.398.1 / 8.0
9/30/2009Samoa IslandsPort San Luis11:430.288.1 / 8.0
9/30/2009Samoa IslandsSan Francisco11:000.18.1 / 8.0
9/30/2009Samoa IslandsSanta Barbara?0.258.1 / 8.0
9/30/2009Samoa IslandsSanta Cruz?0.78.1 / 8.0
9/30/2009Samoa IslandsSanta Monica10:510.158.1 / 8.0
2/27/2010Central ChileArena Cove14:140.368.5 / 8.8
2/27/2010Central ChileCrescent City15:060.648.5 / 8.8
2/27/2010Central ChileDana Point Harbor?0.78.5 / 8.8
2/27/2010Central ChileHalf Moon Bay?0.68.5 / 8.8
2/27/2010Central ChileLa Jolla13:280.68.5 / 8.8
2/27/2010Central ChileLos Angeles13:410.428.5 / 8.8
2/27/2010Central ChileMonterey13:570.368.5 / 8.8
2/27/2010Central ChileMorro Bay Harbor?0.58.5 / 8.8
2/27/2010Central ChileMoss Landing?0.38.5 / 8.8
2/27/2010Central ChileMarina Del Rey?0.18.5 / 8.8
2/27/2010Central ChileMission Bay San Diego?0.68.5 / 8.8
2/27/2010Central ChileNorth Spit Humboldt Bay15:020.238.5 / 8.8
2/27/2010Central ChileNewport Beach?0.58.5 / 8.8
2/27/2010Central ChileOxnard?18.5 / 8.8
2/27/2010Central ChileOceanside Harbor?0.68.5 / 8.8
2/27/2010Central ChilePismo Beach?1.28.5 / 8.8
2/27/2010Central ChilePoint Reyes14:250.468.5 / 8.8
2/27/2010Central ChilePort Hueneme?0.78.5 / 8.8
2/27/2010Central ChilePort San Luis?0.88.5 / 8.8
2/27/2010Central ChileSan Diego13:300.48.5 / 8.8
2/27/2010Central ChileSan Francisco14:460.328.5 / 8.8
2/27/2010Central ChileSanta Barbara13:560.918.5 / 8.8
2/27/2010Central ChileSanta Cruz?0.98.5 / 8.8
2/27/2010Central ChileSanta Monica13:510.648.5 / 8.8
2/27/2010Central ChileSunset?0.58.5 / 8.8
2/27/2010Central ChileVentura?0.98.5 / 8.8
3/11/2011Honshu, JapanAlameda10:490.518.3 / 9.0
3/11/2011Honshu, JapanArena Cove9:441.748.3 / 9.0
3/11/2011Honshu, JapanAlbion?0.88.3 / 9.0
3/11/2011Honshu, JapanBallona Creek?0.68.3 / 9.0
3/11/2011Honshu, JapanBerkeley Marina?0.518.3 / 9.0
3/11/2011Honshu, JapanBodega Bay/Spud Point Marina?0.78.3 / 9.0
3/11/2011Honshu, JapanBolinas Stinson Beach?0.98.3 / 9.0
3/11/2011Honshu, JapanCrescent City9:472.478.3 / 9.0
3/11/2011Honshu, JapanCarlsbad?0.68.3 / 9.0
3/11/2011Honshu, JapanChannel Islands Harbor?1.28.3 / 9.0
3/11/2011Honshu, JapanChula Vista Marina?0.28.3 / 9.0
3/11/2011Honshu, JapanClipper Yacht Harbor, Sausalito?0.88.3 / 9.0
3/11/2011Honshu, JapanCoronado Island Lifeguard HQ?0.68.3 / 9.0
3/11/2011Honshu, JapanDana Point Harbor?0.68.3 / 9.0
3/11/2011Honshu, JapanDel Mar?0.98.3 / 9.0
3/11/2011Honshu, JapanDolphin Isle Marina, Noyo River?0.88.3 / 9.0
3/11/2011Honshu, JapanEmery Cove Yacht Harbor?0.68.3 / 9.0
3/11/2011Honshu, JapanEncinitas Batiquitos, San Elijo?18.3 / 9.0
3/11/2011Honshu, JapanHalf Moon Bay?0.78.3 / 9.0
3/11/2011Honshu, JapanHarbor Island West Marina?0.38.3 / 9.0
3/11/2011Honshu, JapanHuntington Harbor?0.728.3 / 9.0
3/11/2011Honshu, JapanImperial Beach?0.58.3 / 9.0
3/11/2011Honshu, JapanJenner Russian River?18.3 / 9.0
3/11/2011Honshu, JapanKlamath River?2.58.3 / 9.0
3/11/2011Honshu, JapanKing Harbor, Redondo Beach?0.78.3 / 9.0
3/11/2011Honshu, JapanLa Jolla11:000.398.3 / 9.0
3/11/2011Honshu, JapanLa Jolla?0.98.3 / 9.0
3/11/2011Honshu, JapanLong Beach Marina?0.78.3 / 9.0
3/11/2011Honshu, JapanLos Angeles?0.498.3 / 9.0
3/11/2011Honshu, JapanMare Island?0.078.3 / 9.0
3/11/2011Honshu, JapanMartinez?0.068.3 / 9.0
3/11/2011Honshu, JapanMonterey10:010.78.3 / 9.0
3/11/2011Honshu, JapanMorro Bay Harbor?1.68.3 / 9.0
3/11/2011Honshu, JapanMarina Del Rey?18.3 / 9.0
3/11/2011Honshu, JapanMission Bay?0.98.3 / 9.0
3/11/2011Honshu, JapanMoss Landing?28.3 / 9.0
3/11/2011Honshu, JapanNorth Spit Humboldt Bay?0.978.3 / 9.0
3/11/2011Honshu, JapanCoronado Naval Air Base?0.38.3 / 9.0
3/11/2011Honshu, JapanNew Port Beach Harbor?0.38.3 / 9.0
3/11/2011Honshu, JapanNoyo River Harbor?18.3 / 9.0
3/11/2011Honshu, JapanOxnard?1.28.3 / 9.0
3/11/2011Honshu, JapanOcean Beach?18.3 / 9.0
3/11/2011Honshu, JapanOceano Dunes SRA?18.3 / 9.0
3/11/2011Honshu, JapanOceanside Harbor?0.58.3 / 9.0
3/11/2011Honshu, JapanPismo Beach?18.3 / 9.0
3/11/2011Honshu, JapanPlatform Harvest?0.158.3 / 9.0
3/11/2011Honshu, JapanPoint Arena?1.748.3 / 9.0
3/11/2011Honshu, JapanPoint Reyes10:061.358.3 / 9.0
3/11/2011Honshu, JapanPort Chicago?0.048.3 / 9.0
3/11/2011Honshu, JapanPort Hueneme?1.48.3 / 9.0
3/11/2011Honshu, JapanPort San Luis10:232.028.3 / 9.0
3/11/2011Honshu, JapanPacifica?18.3 / 9.0
3/11/2011Honshu, JapanPier 39, San Francisco?0.68.3 / 9.0
3/11/2011Honshu, JapanPillar Point Harbor?0.78.3 / 9.0
3/11/2011Honshu, JapanPt Loma Sub Base/Ballast Pt?0.58.3 / 9.0
3/11/2011Honshu, JapanRedwood City11:540.128.3 / 9.0
3/11/2011Honshu, JapanRichmond?0.358.3 / 9.0
3/11/2011Honshu, JapanSan Diego11:200.638.3 / 9.0
3/11/2011Honshu, JapanSan Francisco?0.628.3 / 9.0
3/11/2011Honshu, JapanSanta Barbara10:401.028.3 / 9.0
3/11/2011Honshu, JapanSanta Monica10:560.858.3 / 9.0
3/11/2011Honshu, JapanShelter Cove Marina, San Diego?0.38.3 / 9.0
3/11/2011Honshu, JapanShelter Island Dock, San Diego?0.88.3 / 9.0
3/11/2011Honshu, JapanSmith River?28.3 / 9.0
3/11/2011Honshu, JapanSanta Cruz Harbor?1.98.3 / 9.0
3/11/2011Honshu, JapanScripps?0.258.3 / 9.0
3/11/2011Honshu, JapanSilver Strand State Beach?0.68.3 / 9.0
3/11/2011Honshu, JapanTijuana River Wetlands?0.28.3 / 9.0
3/11/2011Honshu, JapanVentura Harbor?1.38.3 / 9.0
3/11/2011Honshu, JapanWaldo Point Marina, Sausalito?1.58.3 / 9.0
10/28/2012Queen Charlotte Islands, CanadaAlameda4:080.117.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaArena Cove2:570.357.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaCrescent City2:400.447.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaLa Jolla4:370.057.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaLos Angeles4:240.087.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaMonterey3:300.147.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaNorth Spit, Humboldt Bay2:420.127.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaPoint Reyes3:150.247.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaPort San Luis3:540.277.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaRichmond4:040.097.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaSan Diego6:000.057.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaSan Francisco3:480.147.5 / 7.7
10/28/2012Queen Charlotte Islands, CanadaSanta Monica4:190.087.5 / 7.7

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