Major Issues on Earthquakes - Essay Example

Introduction Earthquakes occur within the Earth’s crust along fault lines that suddenly release large amounts of energy that have built up over long periods of time. This buildup of extraordinary stresses in the rocks that compose the Earth’s crust brings about movement under the surface that causes a sudden shaking of the ground. The Earth’s crust is composed of large pieces called tectonic plates that move slowly around the globe where they meet, grind against each other leading to accumulation of stress in all the surrounding rocks. Eventually, the stress becomes too much for the rocks to withstand and they suddenly shift along a fault and due to the friction created by high confining pressure, the fault blocks do not move. According to Stein and Wysession (217), earthquakes can also occur due to the elastic rebound theory, which says that in various situations energy is accumulated in rock that is being acted upon by tectonic forces to a degree that the energy rises above the bonding forces holding the rocks causing to break, suddenly returning to its original shape, and the crust moves violently as a result of the quickly released force. However, not all earthquakes are linked to with preexisting faults rather some are linked to intensely buried fold structures, volcanic environments among others in which the molten rock is forcefully pushing out of the crust. The cracking of a rock known as faulting leads to the discharge of energy when stored stress is rapidly transformed to movement and produces vibrations called seismic waves. These seismic waves then move outwards in all directions at a speed of nearly 14 kilometers per second, distorting the rocks they pass through, but the rock returns to its original shape afterwards. The speed of seismic waves is dependent on the plasticity of the media they travel through such as rocks which portray elastic properties. In the event of external forces acting on the rock, they are forced to alter their shapes and since rocks just like other elastic materials, they have an elastic limit after which application of any additional force deforms the shape of the rock. Seismic Waves During earthquakes, the discharge of stress as energy leads to the creation of three different types of waves. The first one, primary waves or P-Waves is the fastest moving waves with the ability to pass through both liquid and solid rock, expanding and compressing the rocks as they move and are the first to be detected by seismographs (Qazi 78). The second type of waves created is the secondary waves or S-waves which unlike P-waves cannot pass through liquids. As these waves move, they are able to cut across the rocks they pass through at positions that are perpendicular to the direction they are moving towards. Due to their large size in comparison to primary waves, S-waves are considered the most dangerous type of waves and they produce both vertical and horizontal motion as they travel. The seismic activity are terms used to describe the rate of occurrence, cause and magnitude of earthquakes an area experiences over a certain length of time, the instrument used to measure earthquakes is known as a seismometer while a device that not only measures but also records the magnitude is called a seismograph. Seismologists have come up with two scales of measurement to measure the quantitative magnitude of earthquakes one is the Richter scale, named after the American seismologist Charles Francis Richter. This scale is used to measure the movement of the land surface one hundred kilometers from the epicenter, the point on the Earth’s surface directly above the source of the earthquake, also known as the focus and can be as deep as seven hundred kilometers. However, quakes are not known to occur past this level since rocks are no not very firm at these higher pressures and temperatures. Smaller tremors are frequently experienced but these tremors usually cause little or no damage. The Richter scale is a logarithmic scale with a magnitude seven earthquake moving the land ten times farther than a magnitude six earthquake, hundred times farther than a magnitude 5 quake, thousand times farther than a magnitude four quake, and so on. The other scale that was first formulated by the Italian seismologist Giuseppe Mercalli, is used to measure the magnitude of tremors and is graded ranging from I to XII. Due to the fact that the surface effects of seismic waves reduce as one move farther away from the focus of the quake, the Mercalli rating assigned to the earthquake depends on the location where it was measured. Intensity I on this scale is defined as an occurrence of an earthquake felt by a small number of people while intensity XII is given to a disastrous event that leads to total destruction while events of intensities II to III are approximately equivalent to quakes of magnitude 3 to 4 on the Richter scale, and XI to XII on the Mercalli scale can be correlated with magnitudes 8 to 9 on the Richter scale (Prasad 66). There is no part of the Earth's surface that is immune from the occurrence of earthquakes; however, the frequency differs from one region to the other. The plate boundaries are the most prone to occurrence of earthquakes are the plate boundaries where different tectonic plates convene or collide causing a huge build up of stress. It is estimated by geological scientists that almost eighty percent of all earthquakes take place at the circum-Pacific seismic belt. On the other hand, an intraplate earthquake, that is an earthquake occurring within a single tectonic plate, are usually less common and take place in the relatively stable interior of continents, away from plate boundaries, originating at more shallow levels. Causes and Types of Earthquakes The leading causes of earthquakes are as a result of plate tectonic movement leading to occurrence of tectonic earthquakes which are the most common, volcanic disruptions of the Earth’s crust causing volcanic earthquakes and explosions. The type of earthquake a region experiences is largely dependent on the geological composition of the area. The most common type of earthquake is the tectonic earthquakes which takes place as a result of breakage of rocks in the Earth’s crust due to forces resulting from the movement of the tectonic plates. The second most common type of earthquakes is the volcanic earthquakes which happen as a result of movement of the Earth’s crust in conjunction with volcanic activity. Besides these two common types of earthquakes including collapse earthquakes which are smaller in magnitude are mainly occur in underground taverns and mines and explosion earthquakes resulting from the explosion of nuclear and chemical devices. This paper discusses the two most common types of earthquakes that are caused by tectonic movement of the palates and a disruption caused by volcanic activity. Tectonic Earthquakes When the plates forming the subdivided surface of the earth force a large amount of pressure on each other, the activity leads to earthquakes and eruption of volcanoes. The area at which two different tectonic plates converge is called the plate boundary. The three main plate boundaries are, first, the divergent boundary which mostly occurs at mid-oceanic ridges when two plates move away from each other to form a rift in the Earth’s crust. The magma found deep inside the Earth’s crust, the mantle, rushes upward to fill the gap left by the drifting to form a new crust. The second type of plate boundary is the convergent boundary which occurs when two tectonic plates move toward each other to meet, forcing the plate with the denser oceanic crust to sub-duct or slide beneath the other. However, in case they are composed of similar crust with similar density, very little subduction occurs and the plates push toward each other causing them to cave in and lead to formation of valleys, ridges and high mountains. The third type of plate boundary is known as the transform boundary occurring when plates slide roughly on the sides in opposite directions. As they go past each other, the plates generally stick together leading to a buildup of stress which eventually forms an earthquake when released. The theory of plate tectonics is a relatively new term dating to the 1990s when Alfred Wegener came up with the theory of continental drift and later on Arthur Holmes proposed a mechanism to explain how the continents could have moved across Earth’s surface due to circular convection currents of molten matter deep within Earth (Kemp 35). By the late 1960, evidence of seafloor spreading cemented the theory of plate tectonics which explains not only the destruction of the ancient crust but also the creation of the new ocean floor. The regions surrounding the plate boundaries are the most geologically active and earthquakes usually happen along all types of boundaries while volcanoes are mostly linked to divergent and convergent ones. There is a well known boundary christened the Ring of Fire which encircles the Pacific Ocean and experiences a very high frequency of volcanic activity and occurrence of earthquakes. At the plate boundaries, there are usually various disruptions experienced as the plates act on each other when they move. When the plates move away from each other, the interaction leads to seafloor spreading while collision of different mountains toward each other leads to formation of mountain ranges. On the other hand, some plates interact by slipping past each other leading to subduction zones as earlier explained. All these movements of the plates lead to intense buildup of stress or tension along the plate boundaries which ultimately leads to formation of earthquakes when the energy is released. Volcanic Earthquakes Earthquakes that are triggered by volcanic activity have the potential to lead to cracks, the ground deforming, and destruction of manmade properties. These types of earthquakes are usually smaller in magnitude than those that are caused by non-volcanic earthquakes. Volcanically triggered earthquakes are caused as a result of slip on a fault near a volcano in areas where there is a weak crust and the mass of the volcano itself contributes to the regional strain. These types of earthquakes, also known as volcanic-tectonic earthquakes do not have any association with magmatic system of the volcano but rather they occur as a response to regional stress or tension on an area that has weaker faults. Volcanic-tectonic earthquakes may also occur due to changes of pressure under the volcano which are caused by addition or subtraction of magma from the volcanic system leading to a gap which has to be filled to form a new crust. This leads to the collapse of the rocks that surround the area of removal to fill the gap hence leading to earthquakes Volcanic-tectonic movements can also lead to deformation of land and collapse of the ground but these effects are usually not easily noticeable and do not leave any traces on the surface. Even though these earthquakes can cause damage, the effect is usually not of a massive level because of their small magnitude and reach. Earthquakes that are caused as a result of volcanic activity can produce hazards such as ridges on the ground, loss of ground shape, and small damage to human property. The other type of volcanic earthquakes is long period earthquakes whose occurrence is as a result of additional magma being introduced into the nearby rock where the volcanic activity has taken place. This category of earthquakes is due to the fluctuations in the pressure when the magma is unsteadily moving into the mantle. When the addition of magma is continued for a period of time, successive earthquakes are produced. This type of activity indicates that a volcano is about to erupt and scientists use seismographs to record the signal from these earthquakes, a signal known as volcanic tremor. Those earthquakes that exhibit a volcanic tremor usually indicate a warning of an eruption that is about to occur and leds to evacuation of people from the area to avoid loss of life. This volcanic tremor signaling has been fruitfully applied in the prediction of the nineteen eighty eruptions in Mount Saint Helens and the nineteen ninety one eruption of Pinatubo (Nagle 16). Such volcanic-tectonic eruptions can lead to damage of manmade properties and to avoid such an occurrence, structures should be put up in accordance with earthquake standards and foundations should be laid on firm ground and not unconsolidated matter that could amplify the intensity of the earthquake. The earth’s inner crust is made of hot liquid which is continuously cooling on its surface. When the surface has adequately cooled, it contacts drawing the earth on it downwards and leads to cracking in the process. This gives rise to release of a mass of steam which expands due to the intense tension and dashes to come out violently shaking the earth and leads to tremors or in extreme cases earthquakes. Effects of Earthquakes The movement of surfaces due to seismic waves usually leads to destruction of buildings and depending on the severity or intensity of the earthquake, gas pipes may break leading to break out of numerous fires. The foreshocks that usually occur just before a larger earthquake hits the earth can be used to predict calamity and accordingly evacuate people. Following the earthquake, there could be numerous aftershocks which could be equally destructive therefore until an area is deemed quake-free; it is advisable to stay away till the effects of aftershocks have all diminished. Movement of the ground could also lead to landslides and other rapid mass wasting activities that lead to loss of human life and destruction of manmade property. A mass?wasting variation is a landslide by liquefaction, whereby water?soaked dregs moves downward the slope like slurry and buildings constructed on solid sediment may sink if liquefaction occurs. An earthquake can also lead to permanent displacement of rocks and fault blocks may move vertically, forming a new scarp along the fault plane. Horizontal movement caused as a result of the earthquake may lead to cracks on the roads, pipelines, and any other buildings that are constructed across the fault zone however this displacement hardly reaches up to 7 meters. The sudden displacement of water as a result of the sea floor shifting upward or downward leads to seismic sea waves, or tsunamis but unlike even the greatest storm waves, tsunamis can be up to 90 meters (300 feet) high and move at speeds of up to four hundred miles per hour. These seismic sea waves have wavelengths that can be as long as 160 kilometers (John, Hazlett and Bierman 313.) and the water do not easily leave the coast after the tsunami ends rather it goes on to rising for almost ten minutes until the long wavelength has passed through, leading to extensive coastal damage. Conclusion Depending on the intensity and strength with which they strike, earthquakes have been known to be some of the worst disasters, claiming thousands of lives and leading to loss property worth billions of dollars. Earthquakes occur due to the sudden motion of material along a fault zone beneath the surface, usually centered in areas that are active with tectonic plate movement. Those earthquakes that occur beneath the ocean causes enormous sea waves called seismic sea waves that extensively damage the coastlines. Scientists who carry out studies on earthquakes hope to ultimately devise ways that can lead to successful prediction of earthquakes before they hit an area, additionally engineers are nowadays challenged to come up with new designs that will ensure that buildings can withstand the forces of earthquakes. It has been accidentally found that pumping water with high pressure into the earth’s inner surface can lead to earthquakes since the water probably lubricates the fault zones, causing movement, or helps dissipate the strain that was being stored in the rocks. Similarly, such a technique could be applied to help in discharging the enormous accumulation of rock stress in areas that are more susceptible to occurrence of an earthquake through a series of nondestructive, low?magnitude, timed quakes. Works Cited John, Trent, Hazlett, Richard. and Bierman, Paul. Geology and the Environment. Stamford: Cengage Learning, 2010 Print. Kemp, David D. Exploring Environmental Issues: An Integrated Approach. London: Routledge,2004. Print. Nagle, Garrett. Advanced Geography. Oxford: Oxford University Press, 2001. Print. Prasad, Bharat B. Advanced Soil Dynamics and Earthquake Engineering. New Delhi: PHI Learning Private Limited, 2011. Print. Qazi, S A. Principles of Physical Geography. New Delhi: APH Pub. Corp, 2004. Print. Stein, Seth, and Michael Wysession. An Introduction to Seismology, Earthquakes, and EarthStructure. Malden, MA: Blackwell Pub, 2003. Print. Read More