Earthquakes

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Earthquakes

Introduction

The earth is believed to be supported by tectonic plates that that are integral to the formation of the various landmasses in the world. Tectonic plates are highly mobile infusing an element of unsteadiness in their functioning that result into land movements like the earthquakes amongst others (Kusky 13). The movement of the plates does not constitute to the earthquake, but rather the friction that occurs between the landmasses resulting into vibrations that release themselves on the earth surface. Scientists believe that several thousand earthquakes take place daily across various places in the world but since the magnitude is very weak, they often pass unobserved. On an annual term, at least five hundred thousand earthquakes are noted with most of them being very low. Scientific date has revealed that destructive earthquakes are noted once in a period of every five years.

Origins of Earthquakes

Faults

The earth’s surface is characterized by various cracks that are referred to as faults that are located along continental tectonic plate borders. These faults constitute to the lithosphere and their sizes are enhanced by the tectonic movements. Deep faults appear as valleys on the earth surface and their length may be thousands of kilometers. Some notable faults include the San Andreas within the Californian region with a length of more than one thousand kilometers. The fault actually passes in close proximity to the Los Angeles and San Francisco (Lassieur 14). The Great Rift Valley in the continent of Africa is another prominent fault that covers a distance of over four thousand kilometers. When land shifts occur along these faults, it results into earthquakes. The 1995 earthquake that took place in the region of Kobe in Japan resulted from fault movements that were barely twenty centimeters resulting into a huge earthquake that had a magnitude of 6.9 (Rohr 7).

Various types of faults have been identified with the initial being referred to as the normal fault, resulting from a drift of tectonic plates in a manner that creates a valley with one of the two sides being higher than the other is. The reverse fault is an inverse of the normal fault as it occurs through friction of tectonic plates in a manner that one of the areas overlaps the other regions creating a high and lower land. The strike-slip fault occurs when two tectonic plates under motion are moving in opposite directions such that they glide in opposition to each other in a horizontal pattern (National Geographic, 2011). The San Andreas falls within the strike-slip category. Researchers in the Rice University attempted a study on the San Andreas which sought to measure the pressures occurring within the fault in a bid to determines whether a definite pattern could be noted as an indicator that would aid determine the location and time before the actual quake is noted within the surface.

The study focused on pressure changes as they are the most difficult in tracking and it was discovered that before an actual surface eruption, the velocities of the waves evidenced in the seismographs was slower and sluggish and indication of the opposing waves within the earth layers (Branan, 2008). The last type referred to as the dip-slip occurs when a strike-slip occurs in conjunction with a normal or reverse fault such that one amongst the two tectonic plates shifts sideways while the other shifts in a downward manner.

Diagram indicating the various types of faults

 

Intra-plate Quakes

Apart from the boundaries, earthquakes may also be experienced in areas that are located far away from the faults. These are referred to as intra-plate quakes and scientists believe that they result from pressure within the earth’s compositions notably the rocks. During tectonic shifts, rocks may be split or rubbed together during the process resulting into pressure builds within the affected areas. Mild movements only offer a small enhancement of the pressure within the rocks in accordance to the amassed energy and as the spasm passes through, it affects other rocks within the surrounding environment. These small pressures when experienced over time gradually weaken the rock composition until the optimal sustaining level is broken and then the rocks crumble. For an earthquake to the recorded, the rocks must disintegrate unexpectedly over a large area with the pressure being high to create an energy pool that would cause notable high tremors to the earth’s surface (Lassieur 13).

The most notable intra-plate quake occurred within the nineteenth century as three tectonic plates collided causing a massive quake in New Madrid with the effects being transmitted to areas like Canada and Cincinnati a distance of at least six hundred kilometers from the area that the quake occurred in (National Geographic, 2011). Areas that are prone to this type of earthquake are those located within the tectonic plate that supports the Pacific Ocean and all tectonic plates supporting the landmasses that are in close proximity to the Pacific Ocean. Examples of geographic locations situated within this arrangement are Hawaii, California and Alaska. The second most affected region is the tectonic plate holding the Mediterranean Sea covering the region that the water body begins from and transversing towards the east side into the Asian continent.

Development Stages of an Earthquake

An earthquake’s lifecycle begins with the hypocenter which is the initial area in which the shift it noted. Scientists through the application of the seismograph are well able to locate the hypocenter and this may be noted as deep within the earth or in close proximity to the surface depending on the strength of the quake. A hypocenter being the central spring of the quake disseminates various shocks that determine the magnitude of a quake. The shocks that are produced initially from the hypocenter are referred to as the primary waves. The velocity of the primary spasms is very high and strong covering a length of eight kilometers in one second (Rohr 8). Contrary to the notion created, primary waves tend to accord slight harm as they only affect the deeply seated rocks within the earth’s interiors. Additionally, the waves create an aggressive atmosphere within the air trapped within the earth such that the pitch is heightened to roaring levels that can be clearly heard prior to the projection of an actual earthquake within the surface.

The subsequent waves from the primary ones are the secondary waves, which are recorded within the subterranean layer of the earth. These tend to be less speedy than the primary waves and only move at a velocity of four and a half kilometers every second. The force exerted by the secondary waves does not break rocks but rather causes a ripple effect over a wide area with the rock bed being swayed sideways in a wave-like pattern. The last type is referred to as the surface waves and these are known to be the actual expression of the earthquake on the surface and are ranked as the most destructive of the three waves. Surface waves hit the surface with a velocity of one and a half kilometer per second (Rohr 8). The point in which an earthquake is noted within the surface is termed as the epicenter and it is located on a straight line emanating from the hypocenter. With the surface waves spreading within the mentioned speed in general directions, the effects tend to spread with the areas in close proximity to the epicenter having the highest damages noted. However, far locations due to the reduction of the velocity tend to be less affected.

Conclusion

The causes and areas most prone to earthquakes have been noted within the scientific community and refinements are being made within the subject to address the warning systems for greater preventive measures. This would be very beneficial in terms of life saving abilities due to the destructive ability attached to earthquakes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Works Cited

Branan, Nicole. “Creeping faults warn of impending earthquakes?” American Geological Institute. Earth Magazine, 29 Aug. 2008. Web. 13 April 2011.

Kusky, Timothy. Earthquakes: Plate Tectonics and Earthquake Hazards. New York: Infobase Publishing, 2008. Print.

Lassieur, Allison. Earthquakes. Bloomington: Capstone Press, 2000. Print.

National Geographic. Forces of Nature: Earthquakes. 2011. Web. 13 April 2011. <http://environment.nationalgeographic.com/environment/natural-disasters/forces-of-nature.html?section=t>.

Rohr, Ian. Earthquake. Glebe: Blake Education, 2006. Print.