The definition of Earthquakes:
Earthquakes are a sudden vibration affects the earth's crust when rocks explode, which was subjected to the process of expansion, and may be vibration is great, but almost hardly notice may be devastating, severely.
How made earthquakes?
During the process of vibration affecting the earth's crust generated six types of waves, shocks, two of which relate to the body of the earth where affect on the inner part of the land, while the four waves of the other are surface waves, and can distinguish between these waves also through the types of movements that affect the particles Rock, Where to send the initial waves or ضغط pressure waves particles oscillate back and forth inin the same direction as the course of these waves ,while the secondary movement of waves or transverse vibrations perpendicular to the direction of travel . Usually transmitted primary waves more quickly than secondary waves, and then, when an earthquake occurs, the first waves of up and recorded in the geophysical research stations all over the world are the primary waves.
Types of earthquakes:
Known Aljiuljeon three general types of earthquakes are:
• tectonic earthquakes
• volcanic earthquakes
• earthquakes produced industrially.
Tectonic earthquakes:
التكتونية earthquakes are more destructive species and represent a particular difficulty for scientists who are trying to develop ways to predict them. The main reason for these earthquakes is tectonic pressure resulting from the movement of big and small classes that constitute the earth's crust and a total of twelve layer. And most of these earthquakes occur on the borders of these layers in areas where some layers slide on each other or slip underneath. These earthquakes occur, such as this slip is the cause in about half of the devastating seismic events that occur in the world and about 75 per cent of the seismic energy of The focus of these earthquakes in the region called the "Ring of Fire"which is a narrow belt with a length of around (38.600) joined with the limits for how the Pacific Ocean. There are points where the explosions that occur in the earth's crust, such as the earthquakes in distant parts below the surface of the ground at depths of up to (645) km. Examples of this kind of earthquake, the devastating earthquake in Alaska called "a Fraiday"which was signed in 1383 / 1964. The tectonic earthquakes are also located outside the "circle of fire"in several different geological environments, where mountain ranges are located in the middle of the ocean from the site of many such events of seismic intensity and moderate earthquakes occur at these relatively shallow depths. And rarely feel that earthquakes of any person which is why in about 5 per cent of the seismic energy of the land but recorded daily in the documents of the international network of seismic stations. There are other environment prone to earthquakes, tectonic stretching across the Mediterranean Sea and the Caspian Sea to the Himalayas and ends at the Bay of Bengal. Represent in this region about 15% of the Earth's energy seismic land masses, where they accumulate continuously from each of the classes the European, Asian, African and Australian ends the existence of a small mountain ranges and high. Has resulted in earthquakes generated by these movements to the destruction of parts of Portugal, Algeria, Morocco, Italy, Greece, Yugoslavia, Macedonia, Turkey and Iran in numerous incidents. Among other types of tectonic earthquakes that destroyed the huge earthquakes that do not fall frequently, and these occur in areas far from those where there is tectonic activity.
Volcanic earthquakes:
The types of non-tectonic earthquakes, and earthquakes volcanic origins rarely be huge and devastating. This type of earthquakes is important because it often warning signs of imminent volcanic eruptions. These arise when earthquakes take the magma on its way to the top where the filled cavities located beneath the volcano. When the swell aspects of the summit of the volcano slope and begin to decline, a series of small earthquakes may be a harbinger of explosion of volcanic rocks. Seismometer has recorded about a hundred small earthquake before the explosion.
Earthquakes produced industrially
The third type of earthquakes is that which a person may cause it through several activities such as filling the tanks or new warehouses or underground nuclear explosions or pumping fluids to the ground through wells.
The effects of earthquakes
And the effects of devastating earthquakes, their effects vary in their potency has caused earthquakes in extensive loss of life as destroy buildingsوالجسور and dams, may also lead to devastating landslides. Among the other devastating effects of earthquakes they cause in the so-called tidal waves. And where such waves are not related to islands, it is called a seismic sea waves. The nature and causes of past earthquakes
And I have occupied the minds of the nature of earthquakes, the people who live in areas prone to earthquakes since ancient times. Where attributed some of the ancient Greek philosophers to earthquakes hidden under the wind, while others returned to the fire in the depths of the earth. And about the year 130 AD, the Chinese scientist Zhang Heng believed that the waves that come from the ground coming from the source of the earthquake, and then He created the bronze bowl tightly to record the passage of such waves. Has been installed eight balls in the mouths of eight dragons have developed around the perimeter of the container, as any seismic wave will lead to the fall of the ball and one or more.
The first scientific description of the nature of earthquakes
The first scientific description of the causes of earthquakes was at the hands of Muslim scholars in the fourth century AH / tenth century. Ibn Sina mentions in his book describes the eyes of wisdom and why earthquakes occur and what types of words: "movement was a part of parts of the earth because of what is beneath it will inevitably cause to him to move and then moves higher, and the body that can move under the ground, either the body of steam smokeless strong rush of the wind, Or body of water Sial, and either body antenna, and either the body of a bullet, or the body of land. And body ground does not display his movement also but for some reason such as why the presentation of this body ground shall be the primary cause the actor to the earthquake that, either the body wind, firearm or non-firearm, it must be is emitted under the ground, positive to the rippling ground in more it. "
He adds Ibn Sina-capable browser and phenomena associated with mentions in his book Survival: "And may retain vapors inside the earth tend to hand out Vnbard Vtsthil water Vestmd terms" Mtdafaqa "not nine Vtnhq Earth zooms eyes And probably did not let it heat water and condense and becomes abounded that degrade and too dense for that carried out in the sewers Msthvsp was intensified for the most Asthsafa Mgarr I met the other can not arise outside the earth shook and the first smoke that Aizelzlha wind, And perhaps intensified Style Fajsvet the earth, and may have occurred in the sound of movement would also be a ripple of air in the smoke. The earthquake may have occurred from the high things in the ground by the air rife with Vemuj Vezlzl Earth and perhaps sprang eyes followed the earthquake. "
The Ibn Sina reported a visualization of the locations of earthquakes, recalled: "And what's more be the earthquake in the country Mtkhalkhalp Gore Earth Mtkatvp her face, or face immersed in water. " Which is consistent with the findings of the scientists now that the areas of occurrence of earthquakes are in the areas of weakness in the earth's crust where it is the movement of rocks on the surface, and allow the exit gases. Ibn Sina describes the types of earthquakes, he says: "which have to adhere to the above, some of which have with a tendency to hand, were not points of the earthquake in line, but it was earthquakes Rgevip, so imagine them that the earth is thrown up, some of which are convulsive cross Raship, some of which are inclined to The two countries and called sleet, and had gone with him in the show goes on the rise also called peacefully. "
The Suyuti, who reported the information identifying the locations of most earthquakes accurately, occur in the book reveal Asalsalp to describe the earthquake of intensity through the description of their destructive effects such as weight falling rock, and measurements of cracks caused by earthquakes, the number of cities, villages, dwellings destroyed, and the number of silos and minarets destroyed, and the number of dead . He also described the Suyuti degrees earthquakes expressions like a modern standards such as a very nice, and great and tremendous. Has identified the duration of the earthquake using the unique way he recalled: "As long as the earthquake as far as human reads the Cave. "
Measuring earthquakes
It was noted waves of earthquakes is in this way in several other ways for centuries, and in the eighties of the في nineteenth century, he was able geologist Englishman John Milne 1266 AH -1850 AD / 1331 AH -1913 m from the invention of the machine recording earthquakes is considered a pioneer of its kind, namely, the seismometer, It is a simple pendulum and needle suspended over a glass slab. This was the meter is the first machine of its kind, allows to distinguish between seismic waves, primary and secondary. The seismometer was invented by a contemporary in the twentieth century Russian seismologist Prince Boris Julizin 1278 AH -1862 AD / 1334 AH -1916 AD. Has been used in this machine magnetic pendulum suspended between the poles of an electromagnet, and this was a breakthrough invention in the research of earthquakes in modern times.
Richter scale
Then enables seismologists later invention of the two measures to help them in the measurement of how earthquakes. One is the Richter scale, the proportion of the world of Charles Francis Richter in 1317 AH -1900 AD / 1405 AH -1985 AD, which has manufactured. A device to measure the energy emitted from the focus or epicenter. This device is a logarithmic scale of 1 to 9, where the earthquake measuring 7 degrees stronger ten times of earthquake with a magnitude of 6 degrees, and most powerful 100 times of an earthquake measuring 5 degrees, and most powerful 1000 earthquake measuring 4 degrees and so on. Estimated number of earthquakes with a measure of its strength from 5 to 6 degrees, which occur annually in the world about 800 earthquake while located about 50.000 earthquake with a magnitude of 3 to 4 degrees per year, and an earthquake and one annually measuring 8 to 9 degrees. In theory, not the end of the Richter scale, the degree of specific, but in 1979 an earthquake measuring 8.5 degrees and there was the belief that a stronger earthquake could happen. Since then, enabled the developments that have occurred in the techniques of measuring earthquakes, seismologists from the introduction of amendments to the measure where it is believed now that the degree of 9.5 is a practical limit of the Based on the new meter rate, has been modified force San Francisco earthquake, which occurred in 1906 from 8.3 to 7.9 degrees, while Alaska, the stronger the earthquake that took place in 1383 / 1964 from 8.4 to 9.2 degrees.
Degree Mercali
Another measure is the invention of the Italian Giuseppe Mercali 1266 AH -1850 / 1332 -1914, and e measures the strength of vibration of varying I even XII. Since the effects of the earthquake less away from the epicenter, depends degrees Mercali allocated to measure earthquakes on the site, which is the measurement. For example, are Class 1 earthquake felt by very few people while the class XII devastating earthquake leads to a mass destruction. The degree of force II to III had to rely earthquake with a magnitude of 3 to 4 degrees on the Richter scale, while the equivalent of grades XI to XII Mercali scale earthquake with a magnitude of 8 to 9 on the Richter scale.
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