Tsunami

11. Origin of term "Tsunami"

The term "tsunami" comes from the Japanese. Tsu means "harbor" and nami means "wave", so tsunami is "harbor wave". The term first appeared in the Japanese fishermen. Because at the time was in the middle of the ocean, the tsunami wave length is so low that the fishermen do not feel any waves. However, upon arrival at the port, they found the area around the port were badly damaged. That's why they concluded that tsunami waves occur only in the region around the port, not in the deep sea. The tsunami was always regarded as a tidal wave, tsunami and tidal waves because both produce waves of water that move inland. But the actual tsunami wave is not at all related to the events tides. To avoid misunderstanding, oceanographic experts use the term "seismic sea waves (Seismic Sea Wave)" to refer to a tsunami, which is scientifically more accurate. Understanding Tsunami is a huge wave of water caused by a variety of disturbances in the ocean. Tsunami waves move very quickly with low altitude in the middle of the ocean so it is not visible when they are far away, but as he reached the edge (shallow areas), these waves move slower but also higher.

2.    Tsunami in Indonesia Based on the earthquake catalog (1629-2002) in Indonesia Tsunami never happened as much as 109 times, the first time in a landslide (landslide), 9 times due to the volcano (volcanic) and 98 times by the earthquake tectonic

·         megatsunami

Megatsunami is a tsunami with a height of over 100 meters. According to geologists, megatsunami landslides caused by the huge collapse of an island, volcanic eruptions such as Krakatoa eruption or a large meteorite collision, but it is not caused by an earthquake unless you produce landslides. Megatsunami can go up to hundreds of meters, with a speed of 890 kilometers per hour, and may strike as far as 20 miles inland. In the middle of the ocean, megatsunami hardly be felt. Sea level rise vertically only about one meter, with a vast area to hundreds of kilometers. When a tsunami reaches shallow water, the waves only seen about 30 cm. However, when it reaches land, a tsunami rises drastically.

Megatsunami in history-In 1792, the eruption of Mount Aso in Japan makes the mountain falling into the sea, causing a tsunami as high as 100 meters. - In 1958, a large landslide caused a tsunami as high as 524 meters in Lituya bay. - In 1963, above the dam Vajont Landslide causes tsunamis as high as 250 meters and killed about 2000 people. - In 1980, eruption of Mount St. Helens in the United States caused landslides and tsunami as high as 260 meters making.

Megatsunami prehistoric-65 million years ago, currently forming meteorite impact crater Chicxulub, caused a tsunami as high as 3 kilometers. - 35 million years ago, a meteorite collision at bay megatsunami Chesepeake cause repetitive. - There has also been around the British Columbia, Mount Etna in Sicily, in the Norwegian sea, the islands Réunion, east of Madagascar, and the islands of Hawaii.

• Potential threats megatsunami-sinking an island affected by the tsunami-enormous toll-large property losses-Extinction of life

3. Tsunami speed of tsunami waves moving at hundreds of kilometers per hour in the deep ocean and can hit the ground with wave heights reaching 30 m more. Magnitude Tsunamis in Indonesia ranges from 1.5 to 4.5 Imamura scale, with a maximum wave height reaches shore ranged from 4-24 meters and wave to reach the mainland ranges from 50 to 200 meters from the shoreline.

4. Tsunami Speed ​​For 24 Hours

5. Signs of occurrence of Tsunami

• sea water receded abruptly

• The smell was overpowering salty

• From a distance looks white waves and a very loud roar

• limit horizon between sea and sky pins (as seen cloudy)

• Feel the earthquake

• Will usually gas bubbles appear on the surface of the water and made the beach look like boiling

6. Tsunami occurs when:

• The earthquake epicenter was in the ocean floor earthquake magnitude> 7.0 SR

• The depth of the earthquake is less than 60-70 km

• There is a vertical deformation of the sea floor

• magnitude earthquakes greater than 6.0 on the Richter Scale.

• Type patahannya down (normal fault) or fault ride (thrush fault)

7. Relations between the Physics Tsunami

Tsunami events can be explained using wave propagation Fisikayaitu transversely or perpendicular denganarah knock. Tsunami wave height is strongly influenced by panjanggelombang. A tsunami has a wavelength ratusankm, behave as shallow-water waves is a gelombangketika panjanggelombangnya comparison with the water depth, less than 0.05.

Formula shallow-water wave speed is:

v = √ (g.d)

• g (acceleration of gravity)

• d (depth of water)

• v (shallow-water wave velocity)

8. However, the energy contained in the wave is not reduced much. This corresponds to the rate of energy loss relations (energy loss rate) that "wave is inversely proportional to its wavelength," in other words "the greater the wavelength the less energy is lost", so that the energy contained in the tsunami can be considered constant. Since the energy is constant, the reduced rate will make the wave height (amplitude) increases. Scientists noted dengankecepatan 1,000 km / h towards the coast, the waves can rise up to 30 meters. Another theory also explains that the shallow sea, the wave slows down and rising. This is because the front of the wave slows down and pushed by the back of the wave that rose.