Earthquakes result from disturbance in the outer layer of the Earth. This causes the vibration of the Earth’s surface. Another reason for the occurrence of earthquakes is the sudden release of energy that had been dormant in the core of the Earth. This energy creates strain in the rocks, subsequently; it is transferred in the form of waves to the Earth’s surface (Bolt, 2005 ). The force or magnitude and the period of time that had elapsed determine the destructive effect of an earthquake. The seismic waves and their intensity determine the destructive power of an earthquake.
Structural damages caused by an earthquake depend on the design of the structure and the materials used in its construction. Earthquakes differ in magnitude. They may be small or unnoticeable or they may be so large that their intensity can be detected from distant places. The aftermath of an earthquake may cause the distortion of the ground or damage to buildings. Some earthquakes occur under the sea and cause tsunamis. Whatever the form of the earthquake, many of them endanger the lives of humans through their destructive force (Bolt, 2005 ).
The surface of the Earth consists of lithospheric plates. These plates are always in motion and this causes compressional stresses at their edges. The sudden release of such stress can be attributed to earthquakes. Most earthquakes are caused due to the moving of these lithospheric plates. During the course of their movement, these plates collide with each other and enormous tensional stress is released through the faults present in the earth’s crust. The vibrations of the earthquake spread throughout the earth in the form of waves.
Shallow earthquakes occur due to volcanic eruptions, the falling of huge rocks, landslides and bomb explosions. Such earthquakes are limited to the area surrounding the place of such occurrences (Earthquake, 2004). The impact of an earthquake spreads through a large area surrounding the epicenter of the earthquake. The surface of earth cracks due to the transmission of faults to the surface from within the earth. This results in horizontal and vertical deformation of the surface for over several meters. There is no such transfer of faults to earth’s surface during major earthquakes.
Shallow earthquakes can be felt through the cyclical movements of the earth’s surface, which is termed as fault creep. The characteristics of the ground determine the magnitude of an earthquake’s vibrations and its destructive power. For instance, river beds, or nonintegrated ground surface could carry the effect of an earthquake to large area. Whereas, areas made up of bedrock transmit an earthquake that is significantly weaker. Loss of human lives would be more in places where buildings are not constructed to withstand immense shocks and vibrations.
In those areas L waves of an earthquake could cause the pipe lines that supply gas to burst thereby causing destructive fires (Earthquake, 2004). Injuries and deaths could result from the collapse of buildings and sharp objects transported by the wind. Structural characteristics could also result in damages. For instance, flexible structures constructed on bedrock suffer less damage where as rigid structures built on loose soil suffer greater damage. In hilly regions, earthquakes cause landslides and mudslides, which could submerge the inhabitants.
Earthquakes that occur under the seas could cause tsunamis, which give rise to destructive waves of water from the epicenter of the earthquake and flood the cities on the coast (Earthquake, 2004) The sudden movement of rocks along a fault causes vibrations and the transmission of energy through the Earth. Such waves are termed as body waves and their propagation is subterranean. These waves are classified as P waves or primary waves and S waves or secondary waves. The latter tend to displace the ground forwards and backwards and are consequently known as shearing waves (Bolt, 2006).
The world experienced a number of earthquakes in the year 1990. The Iranian earthquake in the month of June of that year claimed nearly fifty thousand human lives and its intensity was measured at 7. 7 on the Richter scale. Earthquakes are caused by plate tectonics and most of the earthquakes occur in regions that are in close proximity to the margins of the Earth’s plates. Fault activity is the main reason for earthquakes in these regions. Iran is located on the boundary between the Arabian and the Asian plates.
Areas where there was no fault activity also suffered from earthquakes such as Missouri in the US where an earthquake occurred on the 26th of September 1990, Welsh borders and Sheffield in the UK sustained an earthquake on the 2nd of April and the 8th of February 1990 (Seismology: Earthquake Prediction, 2005). Stanford University developed measures to predict the occurrence of earthquakes by detecting the fluctuations in very low frequency radio waves that were transmitted through rocks a few hours before the occurrence of an earthquake.
This phenomenon is a result of electrical currents produced by pressure in the rocks and is also attributed to the opening of microscopic cracks in the rocks. Japanese scientists discovered that electromagnetic radiation was emitted before an earthquake. (Seismology: Earthquake Prediction, 2005). A number of earthquakes occur in the seas, which do not cause damage, but major earthquakes occurring in densely populated areas could result in immense destruction to property and life.
In order to limit the dangers of an earthquake, it is necessary to develop a system of earthquake prediction. At present the seismic gap theory has met with some success in locating earthquake prone regions. Most earthquakes occur in the region of the San Andreas Fault in California since the North American plate and Pacific plate move past each other. The North Pole is being shifted towards Japan at a slow pace of six centimeters in every hundred years by earthquakes. This drift of pole is as result of major earthquakes that occur along shore the Pacific Rim (Earthquake, 2005).
Despite the fact that earthquakes cannot be prevented the severity of the destruction caused by them can be mitigated appreciably by adopting suitable communication strategies, appropriate structural design of buildings, implementing a well planned course of action during an earthquake, appropriately educating the public and ensuring that safer building standards are in place. Several countries have instituted earthquake safety and regulatory agencies in response to the severe damage caused to life and property by earthquakes.
In respect of Tsunamis, a proper early warning system can significantly reduce the damage caused, due to the fact that tsunami waves are propagated at low speeds. These waves are slower than seismic P and S waves and travel at a tenth of the speed of seismic waves in the rocks below. Thus, seismologists have ample time at their disposal to warn the areas that could be affected by the killer waves (Bolt, 2006). The occurrence of intraplate earthquakes is much less in comparison to plate boundary earthquakes. They occur due to the internal fracturing of rock masses.
Examples of such earthquakes were 1811 New Madrid earthquake and the 1812 Missouri earthquake, which were very severe. From the reports of the damage recorded, scientists have opined that their intensity should have been of the order of 8. 0 on the Richter scale (Bolt, 2006). Around eighty percent of the energy released by earthquakes can be attributed to the earthquakes that take place in the area surrounding the Pacific Ocean. More than a thousand tremors of intensity in excess of 3. 5 in magnitude occur in Japan annually.
Another region that is notorious for earthquakes is the western coast of North and South America (Pendick). One of the techniques employed by seismologists in order to measure earthquakes is the Richter magnitude scale, which was developed by Charles Richter. The Richter magnitude is determined on the basis of the maximum vibration strength and the distance from earthquake’s epicenter. This scale is logarithmic and accordingly, a 6 magnitude earthquake is ten times stronger than a 5 magnitude earthquake. However, the Richter magnitude is inaccurate if the earthquake being measured is more than 310 miles from the seismograph.
Accordingly, seismologists developed other earthquake magnitude scales; however these scales cannot be applied to all type of earthquakes due to the resulting inaccuracies (Pendick). As the distance increases the seismic waves exhibit a loss of strength. In general, the greatest effect of an earthquake will be at its epicenter. Some earthquakes are so powerful that the ground shaking can be greater than the acceleration due to gravity and this could result in rocks and boulders being propelled into the air with great force. This actually transpired in 1897 when a major earthquake occurred in Assam, India (Pendick).
In the USA, earthquakes are a major cause of loss to property and endanger about seventy – five million US citizens. The loss caused by earthquakes can be significantly mitigated by efficient disaster planning, adoption of preventive measures like implementing better safeguards while constructing buildings and providing information about earthquakes that could occur immediately to the populace. The U. S. Geological Survey (USGS) is the team leader of the effort to warn people in a timely manner regarding earthquakes about to take place in the US (USGS Science Helps Build Safer Communities Earthquake Hazards—A National Threat ).
Earthquakes claimed millions of human lives in the past five hundred years. In the year 1976, the infamous T’ang – Shan earthquake that hit China claimed nearly two hundred and forty thousand lives. Earthquakes also cause immense damage to property and structures. Precautionary measures to counter the effects of an earthquake such as education, planning in emergency, and flexible, structural designs could contain the severity of the damage caused by an earthquake . (Bolt, 2005 ). References 1. Bolt, B. (2005 ). “Earthquake. “. Microsoft® Encarta® 2006 [DVD] . Redmond, WA: Microsoft Corporation.
2. Earthquake. (2004). Retrieved June 21, 2007, from 2004: http://www. xreferplus. com/entry. jsp? xrefid=4270901&secid=. 1. – 3. Earthquake. (2004). Retrieved June 21, 2007, from http://www. xreferplus. com/entry. jsp? xrefid=4270901&secid=. 3 4. Earthquake. (2005). Retrieved June 21, 2007, from In The Hutchinson Unabridged Encyclopedia including Atlas: http://www. xreferplus. com/entry/6422915 5. Seismology: Earthquake Prediction. (2005). Retrieved June 21, 2007, from In The Hutchinson Unabridged Encyclopedia including Atlas: http://www. xreferplus. com/entry. jsp? xrefid=6481861&secid=. 1
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