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This presentation covers the basics of Tsunamis here in California. We will learn more about
what a tsunami is, and how it is generated, as well as how earthquakes are related to
tsunamis and what types of hazards these can bring to California.
What does a tsunami look like? Each tsunami is unique. A tsunami moves with incredible
speed potentially moving more than 500 miles per hour over the deep ocean. In the ocean
the wave can be only a few feet high but as it gets closer to land, the water begins to
rise. It looks more like a river in flood stage than a wave that can be surfed.
Tsunamis look different from the normal waves that we see at the beach. The tsunami moves
very fast across the open ocean and then slows down as it gets close to shore. A tsunami
is better described as a surge of water instead of a wave that breaks. The water may flow
onto land in a surge for 10 minutes or more, then the water will rush back out. When the
water rushes out the current can be just as strong as when it rushed in.
Let’s learn first about earthquakes and the types of earthquakes that can occur in
California. There are two different kinds of faults. The first is called a “strike
slip” fault where the two different plates will move side by side in opposite directions.
The famous San Andreas Fault is this type of fault. The second type of fault is called
a “Subduction Fault” this is where one plate will slide underneath of another plate.
There is a fault called the “Cascadia Subduction Zone” which runs under the Pacific Ocean
from Northern California to British Columbia. Both kinds can produce large and destructive
earthquakes. The Subduction fault is more likely to produce stronger earthquakes and
larger tsunamis. Some tsunamis are created by earthquakes that
are far away. These tsunamis are known as “distant source tsunamis”. The area many
many far away earthquakes occur is the Pacific “Ring of Fire”. These orange areas show
the faults in the earth’s crust where earthquakes are typically generated. The orange area near
the Pacific Northwest is the “Cascadia Subduction Zone”. This is a subduction fault where
the plate beneath the ocean slides under the plate beneath the continent, this action discplaces
a large amount of water and is more likely to produce a destructive tsunami.
Here in California we can also have earthquakes generated locally, in addition to the far
away earthquakes. In the Monterey Bay region, there are numerous faults that are present.
The San Andreas Fault is the most commonly known. It has produced several large and destructive
earthquakes throughout history. This includes the 1906 San Francisco Earthquake and the
1989 Loma Prieta Earthquake. Fortunately for the area, these faults are not “subduction
faults” which means they are not likely to produce large and destructive tsunamis.
One particular hazard for this area would be from a local earthquake that produces an
underwater landslide. There is an underwater feature in Monterey Bay, known as the Monterey
Canyon. A large earthquake in this area could produce a landslide into this canyon. This
could produce a large tsunami in Monterey Bay. The numbers here show possibly how high
a tsunami could be in the Monterey Bay area from one of these underwater landslides. This
type of tsunami is dangerous because it would take only 10 to 15 minutes to reach the coast.
If the type of landslide shown here occurred, some of the highest tsunami inundation would
be observed in Monterey and could do damage to the water front areas of the city. Scientists
have found evidence that this type of landslide has happened in the past and it is possible
that it could happen again in the future. If you are in this area and you feel an earthquake,
you should move away from the water’s edge to safer areas.
Here is a summary of what we’ve covered today. Tsunamis are a strong surge of water.
They are not and do not look like a wave that can be surfed. The tsunami is often filled
with dangerous debris. A Tsunami is often generated by an earthquake. It can be generated
from an earthquake that is far away, but can also be created from a local earthquake here
in California. Not every earthquake will generate a tsunami. Strong earthquakes are more likely
to generate a tsunami. The type of fault that is most likely to generate a tsunami is called
a “subduction fault”. This type of fault will produce a large displacement of water
generating a tsunami. Here are some sources on the web for Tsunami
Information. The National Weather Service is a good place to learn more about the weather
and types of weather hazards that can impact you on a daily basis. The West Coast – Alaska
Tsunami Warning Center is responsible for monitoring all earthquakes in the area and
they will send out information on tsunami alerts, watches, or warnings, if a tsunami
is expected to occur. And finally, the marine debris program can provide you more information
on debris in the ocean, including debris that may be present in the Pacific from the large
tsunami occurring in Japan in 2011. We want to give special thanks to the California
Emergency Management Agency and the California Geological Survey for their assistance in
creating this presentation. These agencies help our local communities and citizens to
better understand and prepare for tsunami threats here along the coast of California.
Visit the National Weather Service Websites for the latest and most up to date forecasts
and watches and warnings. The National Weather Service covers all of the United States, and
our office in Monterey provides information for both the San Francisco and Monterey Bay
areas. Information is available through various social media outlets as well.