# Why do some earthquakes cause tsunamis and others do not?

Why do some earthquakes cause tsunamis and others do not? It is interesting

Magnitude 9 earthquake off the coast of Sumatra on 26 December 2004 caused a powerful tsunami, which took place around the Indian Ocean. March 11, 2011 in the east of the Japanese island of Honshu, an earthquake measuring 8.9, provoked a tsunami 10 meters high. U.S. National Weather Service warned of the danger of over 50 countries and territories within the Pacific Ocean. In particular, the tsunami waves have left their mark in the Hawaiian Islands. So why do some earthquakes cause tsunamis and others do not?

To understand this, you must consider several factors: the strength of the earthquake, aftershocks orientation and topography of the seabed.

First, the intensity of the earthquake, which is a measure of the breadth of seismic waves exceed a certain threshold. The earthquake in Japan caused a tsunami force 8.9, as well as an earthquake of magnitude 7.7 in Indonesia in 2010. Magnitude is measured on a logarithmic scale, so the seismic waves of the earthquake force 5 will be 10 times more powerful than the waves of the earthquake intensity 4. Usually less than 7.5-magnitude earthquake and 7 provoked a tsunami, but it happens that the 6-magnitude earthquake followed by a tsunami, though less destructive. For example, in Haiti in January 2010, an earthquake of magnitude 5.3 caused a series of small tsunamis.

Second, earthquakes generate tsunamis when the seismic activity causes the land along the lines of active destruction. When the seafloor moves vertically, rising or falling, this leads to a shift of huge reservoirs of water. Thus, a wave of energy that speeds up the movement of water. If the earthquake is characterized by a horizontal direction, then, most likely, the destructive waves will not be: there is no decrease or increase the level of water that can cause a tsunami. Consequently, if the tsunami wave energy feeds, the weather conditions did not have any significant impact on the tsunami.

Since the height of the tsunami caused by the waves depends on the vertical movement of the sea floor, the changes in its topography can either enhance or suppress the wave during its movement. The ocean wave usually has a top speed of 800 to 1,000 kilometers per hour, roughly speaking, the speed of a jet plane. But it starts to fall, when the wave approaches the coast. The sudden departure is a sign of the approaching wave tsunami. Sometimes tsunamis occur in pairs, as occurred during the earthquake of magnitude 7.7 in Indonesia.

To make predictions about the expected tsunami and its destructive power, scientists use data-level measurements and wave energy obtained using tide gauges and ocean pressure sensors.

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