Anglická četba: Zemětřesení
An earthquake is characterised by vibrations generated in the crust of the Earth during the sudden rupture of rocks that accumulated elastic strain and then rebounds. The vibrations produced can vary from hardly perceptible to appallingly damaging. Earthquakes have the potential of releasing energy more than a thousand times greater than the world's first atomic bomb.
There are three general types of earthquakes being recognised: volcanic, tectonic, and artificially produced. Among the three, the tectonic type is by far the most destructive, and this same type of earthquake establish specific intricacies for scientists attempting to build on methods of predicting them.
Earthquakes bring about several aspects of concern to the people residing in these so-called seismically active areas. This natural calamity can produce immense loss of life by annihilating structures like bridges, buildings, dams, and other infrastructures and it can even start devastating landslides.
Another fatal result of earthquakes is the creation, oftentimes by undersea vibrations, of so-called tidal waves. Since such waves are not related to the tides, they are more appropriately called as seismic sea waves or tsunamis. These high rising walls of water have smacked inhabited coastal areas with such fierce rage that whole towns have been damaged.
Seismologists, the scientists who study earthquakes, have created two measurement scales that would enable them to categorise earthquakes quantitatively. First is the Richter scale, which was coined in honor of the American seismologist Charles Francis Richter. It gauges the energy given off at the focus of a quake. Its scale ranges from 1 to 9. One being the weakest and 9 as the most destructive.
The other scale is the Mercalli scale that was introduced during the start of the 20th century by the Italian seismologist Giuseppe Mercalli. It measures the intensity of shaking with gradations from I to XII. The Mercalli rating depends on the site where the measurement was taken since the seismic surface effects decrease with distance from the focus of the quake. Intensity I on the Mercalli scale is described as an earthquake perceived by very few people, while intensity XII is designated to a disastrous occurrence that brings about full-blown devastation.
Efforts on forecasting the time and place earthquakes will take place have had some positive accomplishments in recent times. At the moment, countries like Russia, Japan, China, and the United States are the nations putting in significant efforts to support earthquake research. Several predicted occurrences of earthquakes date back in 1975 when the Chinese forecasted a 7.3 Richter scale magnitude quake at Haicheng, that made them evacuate less than a hundred thousand inhabitants only a couple of days before the quake actually happened which damaged or destroyed 90 per cent of the city's buildings. Low-magnitude vibrations or tremors or foreshocks are some indicators of an incoming earthquake. Some other possible hints being inspected are bulging or titling of land surfaces and modifications in the magnetic field of the earth, in the depth of wells, and even in behaviour of animals.
by Mark Saunders
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