1. TSUNAMI ....
Arch 613 Neha Sivaprasad Spring 2005
2. Tsunami………….
Japanese word for “harbor wave”
How is a tsunami generated?
Causes by a sudden rise or fall of part of the earth's
crust under or near the ocean. Less powerful tsunami
waves can also be triggered by volcanic activity. They
are most common in the Pacific Ocean. In addition,
landslides, explosions, and even the impact of cosmic
bodies, such as meteorites, can generate tsunamis.
A tsunami is not a single wave, but a series of waves
that can travel across the ocean at speeds of more
than 800kmh. In the deep ocean, hundreds of
kilometers can separate wave crests.
How do earthquakes generate tsunamis?
Tsunamis can be generated when the sea floor
abruptly shifts and vertically displaces the overlying
water from its equilibrium position. Waves are formed
as the displaced water mass attempts to regain its
equilibrium. The main factor which determines the
initial size of a tsunami is the amount of vertical sea
floor deformation.
3.
4. How do tsunamis differ from other water waves?
Tsunami waves are shallow-water waves with long
periods and wave lengths. (A wave is classified a shallow-
water wave when the ratio between the water depth and
its wavelength gets very small.
Shallow water waves are different from wind-generated
waves Wind-generated waves usually have period (time
between two successive waves) of five to twenty seconds
and a wavelength of about 50 to 600 feet (15 to 200
meters)
A tsunami can have a period in the range of 10
minutes to 1 hour and a wavelength in excess of 700
km (430 miles) .
What happens to a tsunami as it approaches the
shore?
"As the tsunami wave reaches the shallower water above
a continental shelf, friction with the shelf slows the front of
the wave. When the tsunami enters the shoaling water of
coastlines in its path, the velocity of its waves diminishes
and the wave height increases. It is in these shallow
waters that a large tsunami can crest to heights exceeding
100 feet (30 m) and strike with devastating force.
5. Tsunami Warning…
In instances where the leading edge of the tsunami wave
is its trough, the sea will recede from the coast half of
the wave's period before the wave's arrival. If the slope is
shallow, this recession can exceed many hundreds of
meters. People unaware of the danger may remain at the
shore due to curiosity, or for collecting fish from the
exposed sea bed.
Japan has implemented an extensive program of building
tsunami walls of up to 4.5m (13.5 ft) high in front of
populated coastal areas. Other localities have built
floodgates and channels to redirect the water from
incoming tsunamis
A tsunami warning system is a system to detect
tsunamis and issue warnings to prevent loss of life. It
consists of two equally important components: a network
of sensors to detect tsunamis and a communications
infrastructure to issue timely alarms to permit evacuation
of coastal areas.
6. Deep ocean tsunami detection
The Tsunami Warning stations along the
pacific coast give detailed information
about tsunamis while they are still far off
shore. Each station consists of a sea-bed
bottom pressure recorder (at a depth of
about 6000 m) which detects the passage
of a tsunami and transmits the data to a
surface buoy via sonar. The surface buoy
then radios the information to the PTWC
via the GOES satellite system.
7. Radar detection from space
Radar Satellites can record the
height of the tsunami waves after
an earth quake. During the 2004
Indian Ocean tsunami, data from
four radar satellites recorded the
heights of tsunami waves: at two
hours after the earthquake. It
should be noted that the satellite
observations of the Indian Ocean
tsunami would not have been of
any use in delivering warnings, as
the data took at least five hours to
process and it was pure chance
that the satellites were overhead at
that time.
8. Tsunami on the Indian Ocean…
The total energy released by the earthquake in the Indian
Ocean has been estimated as 2.0×1018 joules. This is
enough to boil 150 litres (40 US gallons) of water for every
person on Earth. It is estimated to have resulted in an
oscillation of the Earth's surface of about 20 to 30 cm,
equivalent to the effect of the tidal forces caused by the Sun
and Moon.The shock waves of the earthquake were felt
across the planet - as far away as Oklahoma, vertical
movements of 0.12 i
Because the 1,200 km of faultline affected by the quake was
in a nearly north-south orientation, the greatest strength of
the tsunami waves was in an east-west direction.
Due to the distances involved, the tsunami took anywhere
from fifteen minutes to seven hours (for Somalia) to reach
the various coastline. The northern regions of the Indonesian
island of Sumatra were hit very quickly, while Sri Lanka and
the east coast of India were hit roughly 90 minutes to two
hours later. Thailand was also struck about two hours later,
despite being closer to the epicentre, because the tsunami
travelled more slowly in the shallow Andaman Sea off its
western coast
