From time to time, Earth’s crust is suddenly put in motion and changes its surface: this phenomenon is an earthquake, one of the most frightening natural phenomena. In large cities, are truly destructive earthquakes.
Huge natural forces
The earthquake is one of the most destructive natural phenomena on Earth. May cause damage to ten thousand times greater than the atomic bomb dropped over Hiroshima in 1945.
Many earthquakes occur a movement of the soil, like a boat rocking. Depending on the intensity of the earthquake, the soil is fine or jerky move in waves down. Sometimes undulations are visible and the surface soil: eyewitnesses claim that the San Francisco earthquake of 1906 ground was one meter high waves. By stopping the earthquake, triggering its place, St. Andrew refractive line went 6 feet.
Most earthquakes last only a few seconds, but there are some that take up to a minute or more. San Franciscoearthquake of 1906 lasted only eg 40 seconds, and one in Alaska, from January 24, 1964 over 7 minutes.
The main earthquake intensity is followed by others increasingly smaller. They are caused by dislodged rocks that are starting to readjust in a stable position, which again can cause enormous damage. In 1985, the center of Mexico, a 11-degree earthquake on the Mercalli scale caused widespread devastation. Reply the following day, the Mercalli intensity scale 10 and destroyed what remained. The two earthquakes together have killed about ten thousand people and ruined buildings in the city.
Mercalli Scale, named after the Italian Giuseppe Mercalli consider the effect of an earthquake or another point on Earth, setting 12 degrees. For example:
Grade 2: very weak. small vibrations. Objects swings suspended fine
Grade 5: pretty strong. Effects can be better observed. Liquids are poured, the windows broken.
Grade 7: very strong, fall off the roof tiles.
Grade 8: destroying the weak, statues and walls may crumble
Grade 10: disaster, many buildings are destroyed, soil cracks. Are possible landslides
Grade 12: catastrophic. Soil deforms, it amended. Waves spread from the epicenter of the earth. Objects are thrown into the air.
Tension is released during the rupture. Fracture lines can be spread over distances of several kilometers, the Earth’s surface and depth. Earthquake occurs when rocks on the refraction lines are folded under the pressure plate collision.
The edges of tectonic plates
Although earthquakes can occur all over the world, are more common in regions close to the edges of tectonic plates. One of the most famous is the line of refraction of St. Andrew, it stretches along the west coast of the United States, being the starting point of earthquakes in California.
Earthquakes are triggered deep beneath the earth’s crust. Earth’s shell is composed of highly tectonic plates moving. The strongest earthquakes occur within the earth, the edges of these plates. Plate movement is not uniform, a voltage builds up along the edges, until the rocks break and enter in the balance sheets. Stored energy is released in the form of smaller or larger earthquakes.
The effect depends on the intensity of the earthquake, the depth at which occurs and the nature of the surface rocks. Earth poses open or collapse.
In the mountains can cause avalanches, landslides, and even less steep slopes, clay soils can also leak molten lava. Loose sand and clay mixture is subjected to a force so great that it liquefies and turns into quicksand. This happened at the 1964 Alaska earthquake.
Marine earthquakes cause huge waves. They may advance on the ocean with a speed of 790 km / h, but there are barely visible. Approaching the shore, the waves slow down, but at the same time it and stood up.
When waves approach the shore, the initial sea retires, then flood the shore with a series of waves.
Waves entering the narrow bays, can be lifted to a height of 20 feet, sweeping everything in their path.
In 1775 after an earthquake hit Lisbon on top of a wave 17 meters high, and the replica earthquake caused landslides and fires. There have been three-quarters of the buildings destroyed and 60,000 people lost their lives.
Earth is in constant motion, but fortunately, catastrophic earthquakes are rare. Specialists in earthquakes, seismologists, every year about 500 000 earthquakes, ie earthquakes per minute. Most of these vibrations remain unnoticed, just as seismologists detected using a sensitive device, called a seismograph.
In the past, seismologists measured the intensity of earthquakes – the amount of energy released – on the Richter scale. It was named after American researcher CF Richter, being introduced by him in 1935.
Today Mercalli scale is used more, it was designed by seismologist Giuseppe Mercalli, 1902.
When the earthquake is triggered from the epicenter, ie di point above the fireplace earthquake shock waves will start. The first wave will start, or where the primary wave is called P. They are longitudinal waves that propagate like sound waves: in effect, produce movements before – back in the direction of propagation. Primary waves are followed by secondary waves or S waves under the effect of that is to say their rocks will shake the perpendicular direction of travel. The third type of surface waves, causing soil undulations and accentuates the damaging effect of secondary waves.
Scientists have begun to map the places where earthquakes are frequent earthquakes before to understand why. Earthquakes can meet at any place where rocks move along the tracks, but most large earthquakes occur in some areas, well-defined. They are very common in volcanic regions, such as the circle of fire around the Pacific Ocean.
As the methods for determining the location of earthquakes have become more precise, and maps have been improved, they outline a much clearer picture about the seismic activity.
Seismology actually “mature” when they began studying how it can comply with the Convention on the prohibition of nuclear experiments. Researchers were commissioned to study whether they can detect small underground nuclear explosions, they have installed some seismic detection stations, collected and analyzed all the vibration apparatus. Map of seismic activity formed in this way has shown that earthquakes occur most frequently in the oceanic crust and oceanic trenches, those along the lines of refraction, young mountain chains and volcanic areas.
Tectonic plate movement
This product is extremely slow and not uniform. Long would appear that nothing happens but because rock friction plates maintain their place. When the voltage exceeds the force resistance of the rocks, the plates move, causing a crack suddenly – an earthquake.
Nobody can predict exactly when the earthquake onset. By mapping and thorough observation of seismic activity, scientists were able to identify seismic zones and were able to establish the frequency of major events. Several large earthquakes have “announced” the arrival of a series of small earthquakes and Russian researchers have found that major earthquakes before P-wave velocity changes of smaller earthquakes. Fine changes of surface forms, and local undulations of the earth’s magnetic field are studied as a possible warning of earthquakes
Animal behavior may signal change near an earthquake. In 1975, residents of a Chinese city have seen more evidence of the earthquake, including the strange behavior of animals, leaving their homes a few hours before the earthquake.
Researchers study water wells and seismic zones. Once underground rock breaks into pieces, their crystalline structure is open, then open again, releasing radon in ground water, radon and reach wells. Increasing the concentration of radon in well water may be a warning to the earthquake.
Just before the earthquake may release gas and electricity load. They are weak incandescent, are called “earthquake lights.” Researchers have observed that before the earthquake, the concentration of hydrogen is ten times higher near the line of refraction. Unfortunately, not all earthquakes are accompanied by such phenomena. For this reason, scientists have developed various techniques for accurate forecasting.
They used separate special measure to detect the voltage increases above the lines of refraction. These cracks can be immense stretches a few kilometers from the earth’s surface or in depth.
Apparatus for measuring the inclination – they like the carpenters and masons level used – produced the movements aimed at the earth’s surface and measuring devices slipping – along cables stretched refraction lines – indicate lateral movements.
This action and sensitive equipment measures the tiny vibrations on the ground that turns them into electrical signals and record them on a graph. From reading the chart, seismologists can immediately see the lowest voltage produced in the rocks.
Another method of observing the movements of the earth is sending different signals from satellites to ground receiving stations.
The network signals via satellite, scientists can figure out if it changed its position to one another satellite receiver.
Seismograph is a device specifically designed for measuring seismic waves. It consists of two components: a weight suspended on the bow and a cylinder driven by a clock. Skeleton device is immersed in a bed of rock. Seismic waves caused by a possible earthquake, causing a horizontal motion, moving back and forth. Pen attached to the pendulum will move in the same direction and this change will mark the paper: it is formed seismogram.
Reduce the damaging effect
Although none of the methods listed is not infallible, they have greatly contributed to enrich our knowledge about earthquakes. Researchers are studying the possibilities of reducing the destructive effect of earthquakes. After some small explosions can cause low-intensity earthquakes, thus weakening the rock tension causing strong earthquakes.
In some places water injected refraction lines, causing small earthquakes. Hence they concluded that the small earthquakes can release the tensions along the lines of refraction.
Manufacturers of America and Japan to study earthquake resistant construction methods. The walls that collapse during earthquakes is one of the greatest dangers. This can be avoided by designing buildings without heavy ornaments and baskets. Residential houses and administrative buildings to be constructed on a particular background, which reduces the third declination during the earthquake.