Plate Tectonics and Its Role in the Occurrence and Prediction of Earthquakes - Essay Example

Plate tectonics and its role in the occurrence and prediction of earthquakes Name Course & Code Instructor’s Name Date Executive summary The lithosphere is actually a fluid mosaic of many irregular plates or segments called plate tectonics. These plates are in continuous motion. As the plates move, they may drift away from one another or collide with each other. This results in formation of different boundaries which can be divergent, convergence or transform fault boundaries. The movement of these plates are said to be behind the occurrence of earthquakes. Various studies by scientists on the movement of these plates and the fault system of these plates provide some information that is used by scientists to predict the possible occurrence of earthquakes in certain region. However, scientists cannot precisely use this information to give a specific date when the earthquake could occur. Table of Contents Introduction 4 Plate tectonics 4 Plate tectonics theory 5 Plate boundaries 6 Divergent boundaries 6 Convergent boundaries 7 Oceanic continental convergence boundaries 7 Oceanic-oceanic convergence boundaries 7 Continental-continental convergence boundaries 8 Transform fault boundaries 8 Fault line and earthquake prediction 8 Conclusion 10 References 11 Introduction For many years, the lithosphere was thought to be a continuous unbroken crust. Contrary to this, the lithosphere is actually a fluid mosaic of many irregular plates or segments (Bhattaharyya & Chakrabarti 67). This paper examines plate tectonics and its role in the occurrence and prediction of earthquakes. The boundaries formed as a result of the movement of the plates is also discussed. The paper aims to shed light on the role of movement of the tectonic movement on the occurrence and prediction of the earthquakes. Plate tectonics The outer shell of the earth is referred to as lithosphere. For many years, the lithosphere was thought to be a continuous unbroken crust. Contrary to this, the lithosphere is actually a fluid mosaic of many irregular plates or segments. The lithosphere is made up of cool solid rock that ranges from 4 to 40 miles in thickness (Meissner 103). These plates of the crust of the earth vary enormously in terms of size and shape. The plates have definite borders which cut through both oceans and continents (Johnson 60). The continental crust is thicker and less dense than the oceanic crust. In total there are nine large plates and several numbers of smaller plates (Stille 64). Apart from the giant Pacific plate which is almost entirely oceanic and the tiny Turkish Aegean plate that is entirely made of continental crust, most plates are made up of both continental and oceanic crust. Six of the nine large plates are named for the continents embedded in them (Bhattaharyya & Chakrabarti 93). These are the South American, the North American, the African, the Antarctic, the Eurasian and the Indo Australian plates. The remaining three plates are oceanic plates which include the Pacific, the Cocos and the Nazca plates (Schubert, Turcotte & Olson 34). The tiny plates neither diminish their impact on the surface activity of the planet nor their significance. For instance, the movement of the tiny Juan de Fuca Plate located between the North American and the pacific plate is said to be responsible for the frequent occurrence of tremors and periodic volcanic eruptions near the state of Washington. Plate tectonics theory According to this theory, the two types of tectonic plates, continental and oceanic, are in constant motion along their boundaries which vary in speed (Meissner 52). The movement is powered by forces which originate in the earth’s radioactive, solid inner core. The plates usually move in different directions atop the athenosphere which is made of much hotter, softer and more malleable rock. The high temperatures and immense pressures found in the athenosphere results in the uppermost part of this part of the earth to become deformed and to flow almost plastically just beneath the lithosphere (Bhattaharyya & Chakrabarti 121). This feature of the athenosphere to flow makes the plates to inch along their continuous movements around the earth surface. The ability of the athenosphere to flow is explained in terms of convectional currents. As the mantle rocks come near the radioactive core, they are heated and as a result they become less dense than the cold uppers mantle rocks. This results in the sinking of the colder mantle rocks and the rising of the warm rocks. This creates slow vertical currents within the mantle. The movement of the warmer and cooler rocks results in the creation of pockets of circulation called convection cells. The circulation of these convection cells is believed to be the driving force behind tectonic plates movement over the athenosphere. Collision of the moving plates results in the creation of landforms such as coastal volcanoes, mountain chains and island arcs (Johnson 62). Tectonic plates moving apart results in production of new ocean floor as the magma originating from the mantle rises up through volcanoes and deposits new rocks along the boundaries of the plate. In cases where plates slide over one another no destruction or creation of new landforms take place. According to this theory, the movement of the plates results in vibrations which causes earthquakes. Plate boundaries Three tectonic plate boundaries exist. These are the convergent boundaries, the divergent boundaries and the transform boundaries. In the course of giant plate movements, some plates are pushed together while others are pulled apart along their boundaries. During these movements, enormous amounts of energies are released and this results in tremors that transform the surface of the earth (Kusky 51). Even though the plates move at relatively different speeds and independent to one another, the plates are interconnected. Thus the movement of one plate has an effect on other plate’s mobility and the activity of one plate can have an impact on the other plate located thousands of miles away. For instance, the movement of the African plate away from the south American plate is resulting in the widening of the Atlantic ocean while the pacific sea floor is being consumed in deep subduction trenches over thousands of miles away. Divergent boundaries Divergent boundaries are characterized with creation of new crust as two or more plate move away from one another. This results in creation of oceans and their widening. When diverging plates occur on land a land rift occurs or a separation will rise that may be broken into distinct land masses over time and the surrounding water will fill the space created between the two separated land masses (Bhattaharyya & Chakrabarti 37). For instance a divergent boundary is being created between the north American and Eurasian plates as a result of the splitting of Iceland along the Mid Atlantic Ridge (Silverstein & Silverstein 33). As the Eurasia plate is moving eastward and the north America plate moves westward, new crust is being created on both sides of the boundary. It is expected that Iceland will eventually break apart into two separate land masses over time. The widening and deepening space between the two masses is expected to be filled by the Atlantic waters. Convergent boundaries Convergent boundaries are characterized with destruction of the crust and recycling back into the interior of the earth as one plate dives under another (Johnson 73). These zones are referred to as subduction zones. Volcanoes and mountains are often found in such areas where plates converge. Convergent boundaries are grouped into oceanic continental convergence, oceanic-oceanic convergence and continental convergence. Oceanic continental convergence boundaries Oceanic continental convergence boundaries occur when an oceanic plate pushes into and subducts under a continental plate. This leads to creation of a mountain range as a result of the overriding continental plate being lifted up (Kusky 74). In addition, the deepest part of the subducting oceanic plate breaks into smaller pieces. The smaller pieces remain locked in place for prolonged period of time before moving suddenly. This results in occurrence of earthquakes. Such earthquakes are accompanied by uplifting of land masses by a few meters. Oceanic-oceanic convergence boundaries Oceanic-oceanic convergence boundaries occur when two oceanic plates converge. One of these plates is usually subducted under the other. This results in formation of a deep oceanic trench (Oreskes 63). For instance, the Marianas Trench was created as a result of the Philippine plate subducting under the pacific plate. Such convergence can also result in the formation of undersea volcanoes. Over time, the erupted lava and volcanic debris accumulate on the floor of the ocean until a submarine volcano rises above the sea level to form an island volcano. These kind of volcanoes are usually strung out in chains referred to as island arcs. Continental-continental convergence boundaries This occurs where two continental plates meet head on. None of the two plates is subducted since the continental rocks are relatively light (Johnson 38). As a result, the crust tends to be buckled and be pushed sideways or upward. For instance, the collision of India into Asia resulted in the crumpling of Eurasian plate upward overriding the Indian plate. The continuous convergence of these two plates resulted in the Himalayas and the Tibetan plateau to be pushed up to their present heights. Transform fault boundaries This occurs when two plates slide horizontally past one another. Such boundaries are also referred to as transform boundaries or faults (Kusky 89). Such boundaries are common on the ocean floor. They often offset active spreading ridges resulting in the production of zigzag plate margins. They are usually characterized by shallow earthquakes. Some of such boundaries also occur on land although their numbers are a few. An example of land transform boundary is the San Andreas fault zone in California. Fault line and earthquake prediction Earthquake is the trembling or the shaking of the crust of the earth which results from abrupt release of energy (Johnson 60). Earthquakes results from collision or drifting tectonic plates away from one another. The prediction of the possible occurrence of earthquake is usually very difficult. However, scientists are able to make prediction of possible occurrence of earthquakes by studying fault line of different tectonic plates. Through the study of fault system by seismologists and geologists have been able to understand earthquakes better (McKnight 87). Through the study of the geologic history of such fault lines and determining the normal rate of slippage between tectonic plates, scientists are able to establish the behavior pattern of the plates across hundred of years (Oreskes 64). This information is used by scientists to determine when the quake is likely to occur in a given area by lack of recent slippage of the tectonic plates. In addition, scientists are capable of identifying seismic gaps which are areas of the fault line that sustain the greatest strain by studying this fault system. Scientists pay a close attention to precursors of earthquakes such as seismic silence which is an indication of absence of slippage (Kusky 129). By examining any recent lack of occurrence of a major quake within a past span where major earthquakes had previously followed a regular pattern scientists are also able to use such information for predicting the occurrence of an earthquake in such region (Johnson 24). These key precursors of occurrence of an earthquake enable scientists to predict with reasonable accuracy the likelihood of the occurrence of an earthquake in a specified region. In spite this; scientists are not able to make predictions which shows a specific date when the earthquake will likely take place (Bhattaharyya & Chakrabarti 18). Instead, the scientists can only make a prediction of the likelihood of the quake taking place within a broad time frame of a decade. Scientists also estimate the likelihood of occurrence of an earthquake by studying how fast pressure accumulates. When the strain in the rocks caused by plate movements builds to a critical level, rocks will suddenly break up and slip to a new position. Scientists use measurements such as the accumulation of strain along fault segment on yearly basis to make prediction on the possible occurrence of an earthquake (Bhattaharyya & Chakrabarti 56). This is compared to how much time has elapsed since the last earthquake along the segment and how much pressure was released in the last quake. Scientists use this data to calculate the required time for the strain to build to the levels that result in occurrence of earthquake. In spite many researches in this field the known and unknown precursors of earthquakes has not yielded consistent results. Conclusion The lithosphere is made up of nine large plates and several smaller plates. These plates are in constant continuous motion which differ from one plate to another. The movement can either be away from one another or toward one another. Plates drifting away from one another results in formation of divergence boundaries while those moving toward one another may result in convergence boundaries. If those plates moving toward one another results in the sliding of one plate over the other, transform fault boundary is formed. The movement of plates is believed to be responsible for the occurrence of earthquakes. Various studies by scientists on the movement of these plates and the fault system of these plates provide some information that is used by scientists to predict the possible occurrence of earthquakes in certain region. However, scientists cannot precisely use this information to give a specific date when the earthquake could occur. References Bhattaharyya Pratip & Chakrabarti Bikas. Modelling critical and catastrophic phenomena in geoscience: a statistical physics approach. New York: Springer, 2006. Johnson Rebecca. Plate tectonics. New York: Twenty-First Century Books, 2006. Kusky Timothy. Earthquakes: plate tectonics and earthquake hazards. London: Infobase Publishing, 2008. McKnight, Tom. Geographica: The complete illustrated Atlas of the world. New York: Barnes and Noble Books, 2004. Meissner, Rolf. The Little Book of Planet Earth. New York: Copernicus Books, 2002. Oreskes, Naomi. Plate Tectonics: An Insider's History of the Modern Theory of the Earth. Westview, 2003. Schubert Gerald, Turcotte Donald, & Olson Peter. Mantle Convection in the Earth and Planets. Cambridge: Cambridge University Press, 2001. Silverstein Alvin & Silverstein Virginia. Plate Tectonics. New York: Twenty-First Century Books, 2009. Stille Darlene. Plate tectonics: earth's moving crust. Chicago: Compass Point Books, 2006. Read More