Tsunamis in California: The Risk to the Coastline and How to Prepare Yourself

what is a tsunami

After the recent tsunami advisories in California, some are wondering whether a tsunami could really strike the California coastline. The answer is yes, and in fact, a number of tsunamis have been recorded in California over the past 100 years. Knowing that the risk for a tsunami is real, those living along the beautiful California coastline should be prepared in case one does hit. 

The disastrous 8.3 earthquake and subsequent tsunami that destroyed parts of Samoa and American Samoa resulted in a number of tsunami warnings for the Eastern Pacific. Many people did not realize that the risk of a tsunami in California is real. The California Earthquake Safety Foundation (CALESF) reports, "Locally generated tsunamis are possible along the whole Pacific Coast of North America. Some of the offshore faults are thrust faults and any earthquake shaking can cause underwater landslides, which create tsunamis."

What is a Tsunami?

Tsunami is often used loosely to describe large sized waves.  A true tsunami is a series of sea waves, most commonly caused by an earthquake beneath the sea floor.  In the open ocean, waves can travel up to 600 miles per hour and as they enter shallow water, they can rapidly rise.  As history has shown, the waves can cause significant destruction, injury, and even death to those in it's path.  The first wave may not always be the largest, and in fact, later waves that continue to bash the coastline for several hours could be larger than the initial one. 

Types of Tsunamis

When talking about tsunamis, terms like 'locally generated' and 'distant source' are used to describe how a tsunami developed.  Locally generated tsunamis form when a large earthquake strikes near the coast, sending large waves within minutes.  In those situations, agencies usually have no time to get a warning issued.

Distant source tsunamis are generated after large earthquakes elsewhere in the Pacific Ocean.  In the case of the earthquake that caused the tsunami in Samoa, it would've been termed a distant source tsunami had it affected California.  These types of waves can reach the coastline hours later, giving agencies time to issue warnings, and in some cases, evacuate areas if necessary.  Some remote areas may not receive warnings so it is best to be prepared if you live somewhere that you know will not receive a tsunami warning. 

Historic California Tsunamis

Although the risk of a large tsunami actually hitting the California may be fairly rare, there have been several documented accounts over the years where large waves have made contact with the California coastline.

In 1812, a locally generated tsunami struck Santa Barbara County after an earthquake. While historical accounts differ on the size of the waves, the earthquake and subsequent large waves are not in dispute. The tsunami came with very little warning after a 7.2-magnitude earthquake struck just off the coast. Reports of the tsunami were as far north as San Francisco and the waves in Ventura were reported to wash inland three city blocks.

Crescent City, California is no stranger to tsunamis. Crescent City is located at the very northern tip of California and has suffered the wrath of a number of typhoons over the years.  According to Humboldt University, Crescent City was hit by tsunami size waves 17 times between 1943 and 1994.  One of the worst came in 1964 when a deadly 21-foot tsunami wave killed 11 people and destroyed much of the town center. This devastating tsunami was a result of a large earthquake that rocked Alaska.  In 2006, some Crescent City residents had a flashback to the 1964 tsuami when advisories were issued after an 8.3 earthquake in the West Pacific.  Although the warning was later rescinded, the city was still hit by a storm surge, damaging several docks and boats. 

Tsunami Advisory Warnings

If there is a risk of a tsunami to California, The National Oceanic and Atmospheric Administration (NOAA) has a warning system in place.  The NOAA operates a Pacific Ocean Tsunami Warning System to detect and provide warnings.  According to the CALSEF, the system relies on seismic data from the California Integrated Seismic Network, supported by the California Office of Emergency Services (OES) and the Advanced National Seismic System (ANSS) of the US Geological Survey.  The system is triggered by quakes of 7.0 or greater magnitude.  When a 7.0 or greater earthquake is detected, the system uses tide gauges and deep water buoys to detect the water waves. 

How to Prepare Yourself in case of a Tsunami

The San Diego Supercomputer Center (SDSC) provides some valuable information on how to prepare for a tsunami.  The SDSC is located on the University of California, San Diego campus.  They are recognized as an international leader in data management, biosciences, geosciences, grid computing, and visualization.

The first is to learn how to predict when you when you should evacuate.  The SDSC notes that tsunami-producing earthquake will typically shake the ground strongly for at least 20 seconds.  They recommend you get into the habit of counting how long the shaking lasts  If you notice the shaking lasts longer than 20 seconds, it would be prudent to evacuate, as soon as it's safe to do so.

Prior to a tsunami,  the SDSC has five invaluable tips to take note of:

  1. Make disaster plans now. Talk to the people you live with about what may happen during a strong earthquake. If you live or work in a low-lying coastal area, know where to go to survive a tsunami. Hold earthquake/tsunami drills at home or at work.
  2. Assemble a portable disaster supply kit. Have a kit available in your car, at home and at work. Your kit should include a portable radio with fresh batteries, water, first aid supplies, flashlight, and extra clothes or a blanket. Put your kit in a backpack and leave it in a convenient place.
  3. Contact local emergency officials. Find out what areas are most vulnerable to tsunami hazards, which areas are safe, and which routes are best for evacuation.
  4. Take a first aid class. Learn survival skills, talk with your family, friends and neighbors. Knowledge is your greatest defense against any potential disaster.
  5. Join a neighborhood emergency response team. Contact your local Office of Emergency Services to learn whether there is such a program in your city or county. Or start one in your own neighborhood.

The most important element to remember is to try and remain calm, keeping the preparedness tips in mind, since you will really need to put them to good use now. 

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