The word tsunami comes from the Japanese. Tsu meaning harbor, and nami means wave. Tsunamis occur frequently in Japan. Japanese history has recorded at least 197 tsunami occurred in Japan.
On several occasions, likened to a tsunami tidal wave. In recent years, this perception has been declared not fit anymore, especially in the research community, because the tide has nothing to do with the tsunami. This perception formerly popular because of the appearance of the tsunami that resembles a high tide.
See also: causes of earthquakes
Tsunamis and tidal waves are both produce waves of water that move inland, but in the event of a tsunami, a wave motion is much larger and longer, so it gives the impression of a very high tide. Although definitions equate with “tidal” include “similarity” or “have a common character” with the tide, this understanding is no longer appropriate. A tsunami is not limited to the port. Because of the geological and oceanographic strongly recommend to use this term.
Why of Tsunami
Tsunamis can occur if an interruption occurs that causes the displacement of large amounts of water, such as volcanic eruptions, earthquakes, landslides or meteorite that fell to earth. However, 90% of tsunamis is the result of underwater earthquakes. In the recording of the history of some of the tsunami caused by volcanic eruptions, for example, when the eruption of Mount Krakatoa.
Vertical movement in the Earth’s crust, can lead to the seafloor rise or drop suddenly, resulting in disruption of water balance that was on it. This resulted in the energy flow of sea water, which when it reached the coast into big waves resulting tsunami.
The speed of a tsunami depends on the depth of the ocean where the waves occurred, where speed can reach hundreds of kilometers per hour. When the tsunami reaches the shore, its speed will be approximately 50 km / h and energy is very damaging coastal path. In the middle of the ocean tsunami wave height is only a few centimeters to a few meters, but when it reaches shore wave height could reach tens of meters due to an accumulation of past water. When the tsunami reaches the coast will creep in mainland away from the shoreline with a range of several hundred meters to several kilometers even.
This vertical movement can occur on earth fault or faults. The earthquake also occurred in subduction zones, where oceanic plates menelusup under the continental plate.
Landslides on the seabed and volcanic debris can also cause interference with seawater to generate a tsunami. The quake that caused the movement perpendicular to the layer of earth. As a result, the sea floor heaving suddenly so that the balance of seawater on it undisturbed. Similarly, cosmic or meteor that fell from above. If the size of the meteor or landslide is big enough, it can happen megatsunami which reaches hundreds of meters.
The earthquake that caused the tsunami
- The earthquake centered in the middle of the sea and shallow (0-30 km)
- An earthquake with a strength of at least 6.5 on the Richter Scale
- An earthquake with a pattern reverse fault or the fault down