Earthquake as Catastrophic Phenomenon - Coursework Example

Earthquake INTRODUCTION: It is the time to be on bed and you are about to fall in a deep sleep. All of a sudden you hear an echoing sound. You wakeup and realize that there is something wrong. You realize that the earth is shaking, your wall is flustering, your lights swing hard, all the books kept on the shelf are falling down and they crash onto the floor. It is an Earth Quake. “An earthquake is a sudden and sometimes catastrophic movement of a part of the Earths crust.” (http://en.wikipedia.org/wiki/Earthquake) The losses which occur because of the earthquake vary with what part was hit by it. If the region on which earthquake has taken place is not hugely occupied, then the humans and things will be the only outcome of damage, but on the other side, if the breaking takes place in a hugely populated place, then a large amount of destruction will be caused in addition to the lives which will be lost in it. Mainly the cities which are targeted, they are mainly the cities which are heavily populated. As the population of the world is increasing, more and more people are losing their lives because of the earthquake. Once an earthquake comes, it leaves back its impact in the appearance of aftershocks. Earthquake has the ability to blow off the deepest rooted tree, and squeeze the biggest building in powder. Not just that, it can also give rise to other natural disasters like floods, tsunamis, and landslides. There is one amazing fact that when an earthquake comes, the building which is located exactly at the epicenter will be least damaged as compared to other buildings hit by the same earthquake. Buildings which are made up of bricks are the “most helpless.” Regions which are made up of soil are the ones that can get the worst affect since they face the shock waves most directly. The buildings which are made up on rock layer face the lowest destruction because there grounds are harder. There are no serious casualties caused by just trembling, but fire and floods can take place as a result of it. An earthquake of 60 seconds or less than that can cause destruction that “continues for years after the first tremor.” In the year 1972, a series of extreme earthquakes hit Managua, Nicaragua. Fifteen years after this earthquake, the city still seems to look in the style as it was a week after the earthquake hit as the country did not have money to build the city again. (http://library.thinkquest.org/C003603/english/earthquakes/earthquakedamage.shtml) BACKGROUND: Earthquake means the shivering and vibrating faction on the “earth’s surface” occurred due to the instant progress of the “Earth’s rocky outer layer.” (Encarta Encyclopedia, 2005) Most of the earthquakes are just insignificant vibrations or tremors. In fact, the bigger earthquakes mostly start off with minor vibration but then right away take the shape of one or more severe shocks, and end up “in vibrations of gradually diminishing force called aftershocks (Columbia Encyclopedia, 2004). Earthquakes take place when energy stored within the Earth, typically in the shape of damage in rocks, suddenly releases. This energy is broadcasted to the surface of the Earth by earthquake waves. (Encarta Encyclopedia, 2005) The bottomless point of beginning of an earthquake is known as its focus; the point right on the top of the focus is the epicenter. “The magnitude and intensity of an earthquake is determined by the use of scales, e.g., the Richter scale and the Mercalli scale” (Columbia Encyclopedia, 2004). The study of earthquakes and their waves which they create is known as seismology (from the Greek seismos, “to shake”). Scientists who study earthquakes are called seismologists (Encarta Encyclopedia, 2005). Plate tectonics is considered a unique logic of geology. It was made up in the 1960’s, and is considered as “one of the most recent revolutions in all of science.” The hypothesis explains the lithosphere (the outer rocky layer of the earth) as a compilation of unbending plates that move sideways above a less unbending layer called the asthenosphere. The asthenosphere is created by rock that is under incredible force, which lessens it and allows it to shift and travel slowly. Plate tectonics is helpful in the pasture of geology because it can be used to clarify a variety of geologic processes, including volcanic activity, earthquakes, and mountain building (Encarta Encyclopedia, 2005). The results of an earthquake are “strongest” in a wide zone surrounding the epicenter. “Surface ground cracking associated with faults that reach the surface often occurs, with horizontal and vertical displacements of several yards common.” Such association does not have to happen through a foremost earthquake; small cyclic movements called fault creep can be attended by microearthquakes too small to be felt. The degree of earthquake shaking and consequent harm to an area is partially reliant on features of the ground. For example, earthquake vibrations last longer and are of greater wave amplitudes in “unconsolidated surface material”, such as badly dense fill or river deposits; bedrock areas obtain less effect. The most horrible harm occurs in thickly populated urban areas where structures are not constructed to endure powerful shaking. There, L waves can make harsh vibrations in buildings and smash water and gas lines, starting unmanageable fires. Harm and thrashing of life continued during an earthquake outcome from falling structures and flying glass and objects. A submarine earthquake can cause a tsunami, “a series of damaging waves that ripple outward from the earthquake epicenter and inundate coastal cities.” (http://en.wikipedia.org/wiki/Earthquake). Most huge earthquakes are accompanied by other earthquakes, which are smaller ones, caused by either before or after the main shock, termed as foreshocks and aftershocks respectively. Most of the earthquakes have aftershocks while foreshocks only take place in about 10% of the earthquakes. Usually the strength of an earthquake can lie within a specific area, but at times when the earthquakes are very large, they can extend over the whole planet. Ground motions caused by very distant earthquakes are called teleseisms. Using such ground motion records from around the world, seismologists can identify a point from which the earthquakes seismic waves apparently originated. That point is called its focus or hypocenter and usually coincides with the point where the fault slip started. The location on the surface directly above the hypocenter is known as the epicenter. The total length of the section of a fault that slips, the rupture zone, can be as long as 1,000 km for the biggest earthquakes (http://en.wikipedia.org/wiki/Earthquake) How can we find the epicenter? “The main flaw of the Modified Mercalli scale is its subjectivity, or its reliance on the opinions of human observers. No instruments are used to measure ground motion. Instead, seismologists who use the Modified Mercalli scale gather information after an earthquake by means of letter questionnaires sent to earthquake victims or reports from the local population. After assigning Mercalli numbers to points in the affected areas, a seismologist draws contours, called isoseismal lines, on a map to separate places of equal intensity. The pattern of isoseismal lines indicates the regions of greatest shaking and provides evidence that can be used to locate the epicenter. If geological conditions such as soil composition and rock structure are similar near the epicenter, the isoseismal lines create a uniform, circular pattern. However, isoseismal lines are usually irregular in shape because the geology and soil conditions of the affected areas vary” (Encarta Encyclopedia, 2005). Richter Scale is a way of “ranking the strength or size of an earthquake.” It is also known as the “local magnitude scale, was devised in 1935 by the American seismologist Charles F. Richter to rank earthquakes occurring in California. Richter and his associates later modified it to apply to earthquakes anywhere in the world.” The Richter scale gets position of earthquake depending on how much the ground shakes within the 100 km from the epicenter of earthquake. This movement of the ground is computed by an instrument known as seismograph. This instrument can notice movements from 0.00001 mm to about 1 m. For dealing with numbers comprised in a wide range, the Richter scale is a logarithmic scale. Each increment of 1 shows the “tenfold” increment in the movement. That means that a scale of 7 is 10 times stronger than 6. Earthquakes having a Richter scale of 5 are counted as reasonable, 6 are counted as “large”, 7 is counted as “major” and 8 or larger are counted as “great.” The Richter scale is only one of several scales used to calculate earthquakes. Recently, the scale most commonly used by seismologists to rank the effects of earthquakes is the Modified Mercalli Intensity Scale, or MM scale. The MM scale measures the effects of an earthquake at different sites and thus the same earthquake has different MM scale values at different sites. American seismologists Harry O. Wood and Frank Neumann generated the Modified Mercalli scale in 1931 to calculate the strength of earthquakes that occur in California. The Modified Mercalli scale, or a scale similar to it, is now used worldwide. The scale comprises of 12 levels of intensity. Each rank is classified by a cluster of apparent earthquake effects, such as vibration of the ground and harms to structures such as buildings, roads, and bridges. The levels are designated by the Roman numerals I (for barely detectable) to XII (for almost complete destruction). Levels I through VI is used to explain what people notice and experience during a small to reasonable earthquake. Levels VII through XII are used to expose harm to structures during a reasonable to disastrous earthquake. “On average, about one earthquake of level X to XII occurs worldwide every year; 10 to 20 earthquakes of level VII through IX occur each year; and over 500 earthquakes of level I to VI occur every year. Each year over 100,000 earthquakes occur that are not noticed by the human population and therefore are not rated on the Modified Mercalli scale (Encarta Encyclopedia 2005). A 60-second or fewer earthquakes can cause devastation that continues for years after the first tremor. In 1972, a series of severe earthquakes struck Managua, Nicaragua. Fifteen years later, the city still looked the way it had a week after the earthquake hit, because the country did not have the money necessary to rebuild (Encarta Encyclopedia, 2005). WHAT ARE THE CAUSES OF THE EARTHQUAKE? The movement of Earth in the slow movement to which we call plate tectonics. The entire sphere is covered by those plates. As they are in motion, at some places they tend to rub against each other, and at other places it moves apart. In such kind of places the movement is not smooth. As the movement continues, there is a point where there is a twist at the certain place at which there cannot be any further bending where there cannot be any further bending. If there is a pitch, the rock breaks and the two sides would move. The earthquake comes out of the breaking rock. Earthquake is the huge amount of energy released when accumulated strain causes a fault to rupture. Earthquakes occur all the time all over the world. They occur with plate edges as well as along faults. Most of the time the earthquakes that occur, they occur along the corner of the oceanic plates and continental plates. The oceanic plates are the plates that occur under the oceans and the rest of it is called the continental plates. Both the plates move around by the movement of the deeper part of the earth that lies under the crust. Occurance of earthquake happens when both the plates are sliding over each other. Another leading cause of the earthquake is due to the faults, which is the split in the earth due to which the plates starts moving in different directions. Faults are due to the bumping that the plates caused. There are mainly three types of the faults.normal faults. Strike-slip faults, and reverse faults. In normal fault one block is descending and away from the other piece of rock. Strike-slip faults are the crack between two plate that are descending each other. In reverse cracks, one plate pushes another plate (http://www.soest.hawaii.edu/GG/ASK/earthquakes.html) REFERENCES: Wikipedia, 9 May 2006, Earthquake: http://en.wikipedia.org/wiki/Earthquake Columbia University Press, 2004, Sixth edition, The Earthquake, New York. Microsoft Encarta Encyclopedia Standard, 2005, Earthquake. Columbia University Press, 2004, Sixth edition, Richter Scale, New York. Dr. Gerard Fryer, What Causes Earthquakes: http://www.soest.hawaii.edu/GG/ASK/earthquakes.html E a r t h q u a k e s   :   Ea r t h q u a k e   D a m a g e: http://library.thinkquest.org/C003603/english/earthquakes/earthquakedamage.shtml Word Count: 2,032 Read More