Characteristics of Tsunamis and Evacuation Reminders

Preparing for Tsunami
We never know when and where tsunamis may strike. Therefore, acquiring correct information
about tsunamis is important for everyone, not just those who live near the coast.

What Causes Tsunamis
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Even when the estimated arrival timeof the wave has passed and even after
the initial wave has subsided, keep
evacuating until the Tsunami
Warning/Advisory is lifted and safety
is assured.

Tsunamis drastically become higher when they
are closer to the coast and when water depth isshallower. They may
also get higher incertain places due togeographical features
such as a V-shaped bay
or at the tip of a cape.

Tsunamis may be caused by anearthquake or other factors in faraway
locations. It's important to pay attention
to Tsunami Warnings/Advisories thatwill not be caused by earthquakes inoceans near Japan as well.

run-upheightSea level before
the earthquake
An earthquake causes thesea ﬂoor to be raised ordropped. This results in adisplacement of a large
volume of water.

The force is transmitted
in all directions aswaves, but they will not
be very high.

The waves become
higher as the water
depth becomesshallower.

The waves become
even higher due tothe topography of thesea ﬂoor.

Tsunamis come not only once but
multiple times, and later waves may behigher.

Waves crash and breakover the land.

●The "tsunami height" announced by the Japan Meteorological Agency refers to the height of the sea level near the coast.
●When a tsunami runs inland from the coast, it is called a "run-up." This can sometimes reach several tens of meters.

Elevation Signs●Tsunami heights can reach several times higher than the expected height depending on the topography of the coast

They are displayed on utility
poles, etc., less than 16
meters above sea level. They
indicate the elevation of thatlocation and also act as a signfor tsunami evacuation sites.

and bay. Therefore, even if the expected tsunami height is low, it is important to stay alert.

Tsunami Warning / Advisory and Actions to Be Taken
When a tsunami disaster is expected to occur, the Japan Meteorological Agency will issue a Major Tsunami Warning,Tsunami Warning, or Tsunami Advisory approximately three minutes after an earthquake. After the warning/advisory isissued, information such as the "Estimated Tsunami Height" and "Estimated Arrival Time of Tsunami" will be announced.
If a Tsunami Warning/Advisory is issued for the Seto Inland Sea coast of Oita Prefecture, please take immediate action to protect yourself.
Category

Criteria for announcementby the Japan
Meteorological Agency

Estimated maximum
tsunami heights
Quantitative expression(estimated tsunamiheight classiﬁcation)

Qualitativeexpression

Over 10 m（10m< estimated height）

Major
When the maximum
Tsunami t s u n a m i h e i g h t i s10ｍ
Huge
Warning（5m<estimated height≦10m）
expected to exceed
3 m.

5ｍ

（3m<estimated height≦5m）

TsunamiWarning

TsunamiAdvisory

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When the maximum
tsunami height is
3ｍ
expected to exceed 1 m （1m< estimated height ≦3m）
but not exceed 3 m.
When the maximum
tsunami height is
expected to exceed
1ｍ
0 . 2 m a n d c a u s e （0.2m≦ estimated height ≦1m）
potential damage butnot exceed 1 m.

Expected damage andactions to be taken

Tsunami Evacuation Building Signs

Elevation Signs

This height of a run-up is called the "run-up height."（ ビ ル 名 ）They are posted on buildings that canbe used as temporary or emergency
evacuation buildings when a tsunami
is approaching. Please evacuate to
the 4th ﬂoor of the building or higher.
*See P.68 for the list of Tsunami
Evacuation Buildings.

Preparing for Storm Surge

Tsunamis travel so fastthat it is too late toevacuate after
seeing themphysically.

Preparing for Tsunami

Waterfront is dangerous
even in the case of aTsunami Advisory.
Immediately move awayfrom the coastand riverside.

Preparing for Storm Surge
In coastal areas, be aware of storm surges during typhoons.
If a storm surge is predicted, evacuate early.

How storm surges form
Wooden structures are expected to be completely
destroyed and/or washed away; anybody exposed
will be caught in tsunami currents.
People in the coastal or riverside area should
evacuate immediately to a safe location such as
an elevated ground or a tsunami evacuationbuilding.

HighTsunami waves will hit, causing damage to low-lying
areas. Buildings will be ﬂooded, and anybody
exposed will be caught in tsunami currents.
People in the coastal or riverside area should
evacuate immediately to a safe location such as anelevated ground or a tsunami evacuation building.

(N/A)

Anybody exposed will be caught in strong
tsunami currents in the sea. Fish farming
facilities will be washed away, and small vessels
may capsize.
People in the ocean should immediately get outof the water and stay away from the coast.
Source: Japan Meteorological Agency Website

A storm surge is a phenomenon that occurs when the sea level becomes unusually high during the approach of a typhoon or adeveloped low pressure. When a storm surge occurs and strong winds and waves agitate high tide, seawater levels may exceed
the levee and flood the inland area behind them. If there are rivers flowing into the sea where a storm surge is occurring, the hightide level and wind waves block the river flow. Rivers are flooded as a result, and they overflow into riverside areas, causing damage
even in inland locations away from the coast.
Strong winds by typhoon

Typhoon or low pressure

SuckedupwardSuction effect

Rising sea level due to decreased air pressure

When the center of a typhoon or a developed low pressure approaches,
the air pressure near the center gets low, and the sea surface is sucked
upward and raised. As the atmospheric pressure lowers by 1 hPa, the sea
level rises by 1 cm. For example, when a typhoon of 950 hPa approaches,
the sea level goes up by 50 cm from the time of 1000 hPa.

Normal tide heightWind-drift effect
When strong winds caused by a typhoon continue to blow against thecoast for a long time, the seawater is blown and drift toward the coast,
raising the sea level near the coast unusually high. The wind-drift
effect varies greatly depending on the wind speed and coastal
features. It becomes higher in the interior of a V-shaped bay.
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