Earthquake Impacts - Article Example

Earthquake Impacts An earthquake is literally defined as "a sudden and sometimes catastrophic movement of a part of the Earth's surface Wikipedia", 2006). Caused as a result from the dynamic release of elastic strain energy that radiates seismic waves, earthquakes typically result from the movement of faults, planar zones of deformation within the Earth's upper crust. Earthquakes most often occur in places where the stress level which results from the differential motions of these plates is stronger than the strength of the crust in that same area. The areas in which the tectonic plates are found are also the areas with the greatest stress level, which explains why these areas experience a greater number of earthquakes than anywhere else. Although more times than not earthquakes are tectonic, they can also occur in volcanic regions. Although many people seem to think that the only earthquakes that take place are those which can be felt, that belief is completely false. Instead, large numbers of earthquakes take place daily across the world, but the majority of these can only be felt by seismometers and cannot be felt by the person and cause no structural damage of any sort. The strength and damage caused by an earthquake can vary dramatically, depending on the strength of the earthquake. Smaller earthquakes may go completely unnoticed, while larger earthquakes can cause serious destruction and massive loss of life. In fact, most of the larger earthquakes are then followed by smaller ones - these are otherwise known as foreshocks or aftershocks; foreshocks being smaller earthquakes which precede the larger earthquake, and aftershocks being those which procede it. The first method of recording earthquakes was through of certain scales called intensity scales. The United States, Japan, and Europe each have their own form of scales. However the problem with all of these scales is that they are often a poor measure for the relative size of different events in different places. Seismologists now favor a measure called the seismic movement, which relates to the concept of moment in physics, to measure the size of a seismic source. The 1995 Great Hanshin Earthquake - which is commonly referred to as the Kobe earthquake due to the fact that it took place near Kobe, one of Japan's largest and most populated cities - was one of the most devastating earthquakes to ever hit Japan. Although over ten years have passed now since this earthquake hit, it is still considered to be one of the most disastrous ever to hit Japan since the Great Kanto earthquake of 1923, and will not soon be forgotten. In due to this earthquake, more than 5,500 people were killed, with more than 26,000 left injured. The total economic loss was estimated as being approximately $200 billion USD. During this earthquake, it was recorded that the ground moved 7 inches in horizontal shaking, and 4 inches in the vertical direction, and the earthquake itself is actually still active, with 716 aftershocks recorded by 10 AM as of January 18, 1996, 74 of these could be felt by the human body, and 14 of these occurred on the 18th. The epicenter of the earthquake was 20km underneath the island of Awaji, across a strait from Kobe. With a magnitude of 6.9 (Mw) and a duration of roughly 20 seconds, in regards to the structural damage caused by the earthquake, there were: 144,032 buildings destroyed by ground shaking, 7,456 buildings destroyed by fire, 82,091 collapsed buildings, and 86,043 severely damaged buildings. All Kobe ports were shut down to international shipping, there was substantial damage to containing loader piers, and all access to Kobe via highway and railway were blocked. The Kobe earthquake struck early in the morning without any warning, taking the city completely by surprise. It was due to the city of Kobe's high population density and linear layout, that there was such substantial damage and trauma caused; infrastructure networks were made much less redundant because of this, and this was a key factor in the significant structural damage caused. Buildings in every part of the city were destroyed or left hanging or leaning on their foundations, and many houses simply collapsed entirely. "As few as 20% of the buildings in downtown Kobe were usable following the earthquake." ("Wikipedia", 2006). In regards to the structural damage caused, the worst of all took place in Nagata Ward, and among the buildings damaged were the Takarazuka Revue, a theater housing; and Koshien Stadium. Most railways in the region were damaged, and artificial islands in the Port of Kobe suffered some subsidence as their soil collapsed into Osaka Bay. Somewhat strangely, the Akashi Kaikyo Bridge, which was under construction at the time, and was even surprisingly close to the earthquake's epicenter, was not damaged but instead actually lengthened a full meter due to plate tectonics. Other infrastructure damage included that of power, telephone, water, and natural gas lines, with the water and gas mains operating at less than half their regular capacity even a month after the earthquake. As an end result, the Kobe earthquake caused over $100 USD in damage, and most of the losses were uninsured, as "only 3$ of property in the Kobe area was covered by earthquake insurance, compared to 16% in Tokyo." ("Wikipedia", 2006). However there were certain benefits or positive outcomes from this disaster, such as the fact that it was a huge wake-up call for Japanese disaster prevention authorities. After they had seen the damage and life loss caused by the Kobe earthquake, it was an obvious knowing that no one wanted another disaster like that again. Due to this, the national government changed its disaster response policies and its response to earthquakes of more recently have been found as significantly and substantially quicker. The Niigata earthquake of 1964 also occurred in Japan, and had a magnitude of 7.5 and also caused incredibly severe damage to many structures. The most outstanding result of the Niigata earthquake was the extensive damage caused to engineering structures that occurred as a result of liquefaction of the sandy soil on which the structures were supported. With a magnitude of 7.5, the Niigata earthquake caused considerable damage to Niigata City and the surrounding area, especially because of this liquefaction phenomenon. Approximately 300 of the 1500 reinforced concrete buildings in Niigata City were damaged, but of those, roughly 200 settled back into place without any significant structural damage. Many buildings - as was in the Kobe earthquake - were left tilting or leaning on their foundations, while others crumbled and collapsed. Even though about 2000 homes were totally destroyed, only 28 lives were lost. The epicenter of this earthquake was located 35 miles north of the city of Niigata, in the Japan Sea. A tsunami hit the shoreline of the Japan Sea 15 minutes after the main shock from the earthquake hit, with the tsunami recorded as being from 3m to 5m high at its highest point near the source region. This earthquake even caused Awashima Island to rise by 1m as a whole. The Niigata earthquake is "notorious both for being the first widespread documentation of soil liquefaction, and for the infamous 80 degree tilt of one of the apartment buildings at Kawagishicho" (Hausler & Sitar, n.d.). The Niigata earthquake has been extensively studied by Japanese seismologists, "and in particular, by Keiiti Aki, who introduced the concept of seismic moment, estimated its value for the Niigata earthquake based on spectral analysis of its seismic waves, and discussed the significance of seismic moment as a source parameter." ("Iris", 2006). There are many significant resemblances, as well as differences involved when comparing the Niigata earthquake of 1964 and the Kobe earthquake of 1995. Both earthquakes took place in Japan, and both caused a significant amount of damage. Although the death toll was remarkably higher in regards to the Kobe earthquake than the Niigata, the structural damage from both was exhausting. Factors such as the buildings left leaning on their foundations, and the structural damage caused to railways and engineering structure are evident in both the Kobe and the Niigata earthquake, while factors such as the death toll are strikingly different. Only 28 people died in the Niigata earthquake, while a staggering 5,500 people died in the Kobe earthquake, with over 20,000 left injured. The fact that both of these earthquakes took place in Japan, and the clear observation of the difference in the death toll makes one understand how far disaster prevention authorities in Japan really have come. After the Niigata earthquake hit, disaster prevention authorities took notice but it wasn't truly until the Kobe earthquake disaster that something was really done about it. Both earthquakes - mainly due to the enormous amount of damage caused - are constantly scrutinized and studied by experts, in hopes of determining the cause and perhaps preventing such a severe incidence in the future. Works Cited Hausler, E. & Sitar, N. "Performance of Soil Improvement Techniques in Earthquakes." 25 Mar. 2006 http://72.14.203.104/searchq=cache:cARF0Cncap4J:www.ce.berkeley.edu/hausler/quakes/NIGquake.pdf+Niigata+earthquake&hl=en&gl=ca&ct=clnk&cd=6 "Iris". "1964 Niigata (Japan) Earthquake Archive: In Honor of Professor Keiiti Aki." Iris. 22 Mar. 2006 http://www.iris.edu/seismo/quakes/1964niigata/ "University of Washington". "1995 Kobe earthquake, Japan." University of Washington. 22 Mar. 2006 < http://www.ce.washington.edu/liquefaction/html/main.html> "Wikipedia". "Earthquake". Wikipedia. 23 Mar. 2006 http://en.wikipedia.org/wiki/Earthquake Read More