Historical tsunami in Okushiri, Japan on July 12, 1993


[sound of waves crashing] In the Sea of Japan there is a small island
whose name is Okushiri. On the southern tip of this island there is a small village by
the name of Aonae. All of these homes were present before July 12, 1993. And one can look at the monument that stands
up in the center of your screen as a marker. 10 o’clock at night on July 12 a magnitude
7.6 earthquake occurred that produced 1 hour of tsunami attacks followed by intense fires. These pictures were taken moments after the
tsunami had destroyed most of the village and the fires that are raging are the effects
of such a tsunami disaster. Oftentimes people do not consider that tsunamis,
which basically flood the coastline, can also start fires. But in fact, for this particular
event, the fire did the most damage to the community of Aonae. [sounds of fire] Now we are looking at the breakwater that
was supposed to protect this village. It has been breached by the weight of the tsunami
during the 1 hour of attacks that occurred the evening before. Examine all of the debris in the water and those
are the remnants of the homes that we saw prior to this tsunami in July of 1993. We are now looking at the waterfront area
which the weight of the water crushed many of the homes and many of the buildings that
were along the waterfront. But in addition to the weight of the water
by the tsunami, floating debris, such as large fishing vessels, also crashed into these buildings,
and as a result of this weight of the water plus the debris in the water, it had the effect
of demolishing everything in its path. In this over flight of the southern tip of
Okushiri Island shows the devastating effect of these waves. Notice all the brown debris
in the water are the remnants of the 500 homes that were on this tip. And now it’s only
a sheet of sand with a scattering of fishing boats that tell us what happened here. There
is the monument that we saw earlier. How could such a disaster occur, what are
the processes of Earth that could create such a disaster? The Earth could be considered a large hot
ball of molten lava and the top of this large hot ball are plates that are cool. These plates, as they rub against one another
and as they dive beneath each other, build up stress during this motion and this stress
is eventually relieved through the form of an earthquake. If we look at the plates as they exists today
on the surface of the planet we see that in the Sea of Japan there is an intersection
of three of these plates and it just so happens that one plate, the Asian plate, is diving
under the North Pacific Plate, precisely where Okushiri Island exists. So we can visualize then this process of a
plate diving underneath another plate, building up stress, and as it relieves that stress
through a rebounding process it would lift up the water overlying and produce a tsunami
as this animation depicts. That’s the genesis of a tsunami, born of
fire. The map you are looking at shows the areas
where the largest earthquake occurred, as indicated by the red circle and a series of
aftershock earthquakes that are indicated by the small white circles. The combination
of this area, which is highlighted by light blue, is an indication of the area that was
actually uplifted during this particular tsunami-causing earthquake. So that we have an idea of the spatial dimensions
of the formation of this tsunami. As you can see from this animation, once the
tsunami is formed in the Sea of Japan it propagates very quickly to the island of Okushiri. This
wave will continue to wrap around the north and south parts of the island at the same
time it is hitting the other island of Hokkaido and notice as the two waves wrap around the
back side of the island they combine to reinforce each other to cause wave heights to be unusually
large at an unexpected location, at the back side of the island. This is not uncommon, because tsunami waves
wrap around objects and intersect the island coastline in a wide variety of ways, but the
most important aspect of this is the damage it causes once it gets near the coastline. This animation of run-up depicts the overtopping
of the southern tip of Aonae and then, notice how the waves in this animation depict the
flooding that takes place along the coast. So now if we look at the entire process from
earthquake generation, shaking this Island for about 30 seconds, followed by an attack
of 3-4 tsunamis lasting for about an hour that gave rise to fires which burned all night,
then we see that the origins of the earthquake is basically within the bowels of the earth
and causes massive destruction and kills people. Now that you understand how tsunamis are formed
and the potential destruction that they can bring, I would like to share with you a few
safety tips of how you can protect yourself in the event of this natural disaster. Safety tip #1 is the earthquake itself. If
you feel a shaking of the earth while you are on the coastline, this is nature’s warning
that a tsunami could have been generated. So you are advised to seek higher ground as
quickly as possible. Safety tip #2 is unusual water level changes.
Oftentimes tsunamis will, as they are approaching the coastline, the first indication of a
tsunami’s arrival will be the withdrawal of water, that is the draining away of the ocean
away from the coastline. If you see large areas of the coastline exposed by this draining
of the water, that is a natural warning that a tsunami is arriving. So, as quickly as it drained away, it will
comeback with an enormous force and a very fast speed which you cannot outrun. So you are
advised if you observe this change in sea level to seek higher ground as quickly as
possible. Safety tip #3 is the sound of the tsunami.
Accounts of massive tsunamis which have created death and destruction here in the last few
decades are always accompanied by a load roar. [roar of tsunami waves] So if the tsunami occurs in the evening, it’s
dark, you cannot see the ocean, you cannot see the draining of the ocean, and if you
hear a load roar from the ocean that too is nature’s indication that a tsunami is approaching. So the three tips are: you feel an earthquake,
if you see unusual wave, sea level changes on the coastline or hear a load roar from
the ocean that’s a natural signal a tsunami is approaching. If you heed these signs you can save your
life by quickly running to higher ground. [sound of waves crashing]

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