Earthquakes
EarthquakesAn earthquake is shaking or trembling of the earth that is volcanic or tectonic in origin.
"A broadly satisfying explanation of the majority of earthquakes can be given in terms of what is called plate tectonics. The basic idea is that the Earth's outermost part also called the lithosphere consists of several large and fairly stable slabs of solid and relatively rigid rock called plates" (Branely 154).
These plates continuously move pushing and rubbing against each other.
Since the earliest of time people have been looking for an explanation for earthquakes. The people of Maori in New Zealand believed the god of earthquakes, Ruaumoko is said to have pressed into the earthquake as his mother turned face downward while feeding him. According to the legend, he has been growling and spitting fire ever since. Aristotle believed that "mild earthquakes were caused by wind escaping from caves within the bowels of the earth and severe shocks were by gales that found their way into great subterranean caverns" (Matthys 87). However, with modern technology we found that what actually causes earthquakes is tectonic plates which on average move only two inches per year they are driven by convection currents which is the upward movement of heated particles rising from the earth's molten core. As the plates are driven against each other one will try to and eventually will slip underneath the other. When plates move quickly an earthquake is the result.
Before the availability of instruments capable of a quantitative measure of their magnitude, earthquakes were classified according to their intensity. In 1931 a
seismologist came up with twelve degrees of intensity ranging from I (felt only by a few) to XII (total damage) this was called a Modified Mercalli scale. However according to Dr. Pignataro "Even with such scales, the subjectivity of the observer renders their use less then perfect, since today even experienced seismologists sometimes assign different intensities to the same earthquake." If the magnitude of an earthquake is to be compared worldwide, a measure is needed that does not depend (as does intensity) on the density of the population and type of construction. A strictly quantitative scale that can be applied to earthquakes in both inhabited and unhabited regions was originated in 1931 by Charles Richter in California.
"Because the size of earthquakes varies enormously, the amplitudes of the ground motions differ by factors of thousands from earthquake to earthquake. It is therefore most convenient to compress the range of wave amplitudes measured on seismographs using some mathematical device" (Bolt 118).
The first earthquake recorder described in any detail was an artistic device invented by the Chinese scholar Chang Heng about 132A.D. The instrument was a seismoscope: unlike a seismograph, it did not give the complete time history of earthquake shaking but simply the direction of the principal impulse due to the earthquake.
Along seacoasts, another disaster may follow large...
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