Earthquakes are considered one of the most deadly natural catastrophes that can affect human life.

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EarthquakesEarthquakes are considered one of the most deadly natural catastrophes that can affect human life. Most often, a quake occurs in earthquake-prone zones where two tectonic plates meet, split, or slip by one another; the type of plate contact determines whether the earthquake will be shallow or deep. During the movement of these plates, intense forces overcome the friction between the plates. If the plates become "locked together," forces build up and eventually must give away - with the plates lurching into new positions and creating an earthquake. Other earthquakes form in association with volcanic regions, where the buildup of heat and pressure often triggers smaller tremors and localized quakes.The focus is the point under the Earth's surface where the earthquake energy is released. The point on the surface just above the focus is called the epicenter. Most earthquake foci occur no more than 62 miles (100 kilometers) below the surface.Earthquake waves, or seismic waves, travel out from the focus of an earthquake in all directions. Primary waves (P-waves) move in a back-and-forth direction; they are the fastest seismic waves, reaching the far side of the globe in 20 minutes. The waves travel though the Earth's molten core. Secondary waves (S-waves) move in a side-to-side direction; they are slower than P-waves and can move only through solids, stopping at the Earth's central molten core. Love and Raleigh waves (both called L-waves) travel along the Earth's surface, moving up, down, and sideways and creating much of the structural damage associated with earthquakes.The
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Threat of TsunamisA tsunami (or seismic sea wave), from the Japanese words tsu ("harbour") and nami ("wave"), is a very large wave caused by underwater earthquakes or volcanic eruptions. Often incorrectly called "tidal waves," tsunamis are not caused or influenced by the tides, though at high tide, the size of a tsunami may be significantly increased.About 80 percent of these great waves occur in the Pacific Ocean, about 10 percent in the Atlantic Ocean, and 10 percent in other oceans. Tsunami wavelengths, or crest-to-crest measurements, often reach up to 600 miles (965 kilometres), but their amplitudes, or heights, range only ...

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