There are various different factors that affect the impact that an earthquake has, not only on humans but the environment. Earthquakes are fundamentally caused by friction between lithospheric plates moving in different directions either constructively or destructively. Therefore, the major earthquakes occur at the boundaries of the lithospheric plates. Examples of these are Kobe quake in Japan on 17th January 1995 and Loma Prieta quake in San Francisco on October 17th 1989. (Seismologists have discovered both as being on plate boundaries.)
It is therefore obvious that an enormous factor that affects the impact of an earthquake is its proximity to a plate boundary. The larger earthquakes occur at plate boundaries and can have dramatic effect but are some what expected. Japan is noted to have 4 earthquakes a day! However, minor earthquakes can occur on smaller fault lines on the major plates. An example of such an earthquake was Richter 3.9 in the Manchester area, England on Monday 21st October 2002 that was followed by 13 after shocks. Although earthquakes at plate boundaries can be catastrophic is size and damage caused, the local populations are educated that earthquakes can occur. This was unlike England where some people were quite anxious and disturbed at a small quake and chimney’s that had collapsed were not covered on insurance.
Whether or not an area is prepared for an earthquake can have a direct impact on the consequences that the earthquake has. Mexico dramatically improved its emergency response systems after over 10,000 deaths in the Michoacan Gap Earthquake of 1995. Mexico had developed an emergency response system called the – National System for Civil Protection in 1985, the quake of October 9th 1995 which allowed only 50 deaths despite a 7.9 magnitude quake.
Because Mexico was much more prepared for an earthquake, the death toll was dramatically reduced. In 1975, an earthquake was successfully predicted in China and so the death toll much reduced. At 2 pm, 4th Feb 1975 3 million people were ordered to spend the night outside in southern Liaoing province. The 7.8 earthquake occurred at 7.36pm and flattened the town of Haichang. Only 500 people were killed as the population was warned of a possible tremor and were told immediately before on what to do. The impact of the earthquake was therefore dramatically reduced due to the preparedness of local people. The Loma Prieta Earthquake was the first major rupture along the San Andreas Fault since 1906. Because of this, many people had not experienced such a disaster in their life time and it is a small miracle that not more than 62 lives were taken as the people were less knowledgeable of the consequences of such an earthquake.
Fast response to an earthquake will ensure a lower death toll as medical attention early on can save lives. During the Kobe quake, people’s reaction times were slow and people were seen running outside buildings and were hit by falling debris or walking aimlessly about the streets ignoring small fires. There was a five-hour delay before calling in the Self-Defence Force (army) and even then only 200 troops were mobilised. Only by 21st January, 4 days later, were 30,000 troops helping with the rescue.
Political issues also increase the impact of an earthquake. In Kobe there were delays in accepting international help from the U.S military based in Japan or allowing medical teams and sniffer dogs into aid rescue operations. There was a similar incident in Bam, Iran where the government were reluctant to allow U.N assistance due to the political climate of the Middle East. The Mexican government turned down offers of international aid in the first few days after the quake in 1985 believing that it could cope alone.
Richer countries that are susceptible to earthquakes and tremors invest in ‘earthquake friendly’ housing and commercial buildings. MEDC’s have the technology to develop items such as rolling weights that counter act shock waves. Underneath skyscrapers, rubber shock absorbers can be placed in the foundations to reduce the impact of the earthquake on the building. In addition, panels of marble and glass constructed with the steel frame add flexibility to the superstructure.
Also, reinforced latticework foundations are placed deep into the bedrock. Steel cables attached to bridge girders and to columns to restrain movement of roads as can concrete walls added between existing columns to make structure more rigid. This must be noted that LEDC’s cannot afford neither to research such methods nor implement them. However, it could be argued that in LLEDC’s there isn’t the need for such measures, as the area is not developed enough. The infrastructure of developed nations is by far superior to LEDC’s. Access to remote areas is better as is phone networks, TV and radio availability and more people have cars or alternative modes of transport allowing those uninjured to aid rescue teams and clear up where it is needed. In addition, richer countries have a better health service more equip to cope with major national hazards. This is mainly due to the fact that the developed world has more doctors per head than in less economically developed states. There are also more hospitals per 10km2 to accommodate injured.
Primarily, an earthquake with a higher magnitude will be physically greater in scale than a slight earth tremor. Earthquake magnitude is measured using the Richter scale. Because the Richter scale is logarithmic, an earthquake of magnitude 7 earthquake causes a ten times larger amplitude and about 30 times more energy is released than a magnitude 6 earthquake. An example of is the Chilean quake in 1960 was magnitude 9 which had the equivalent effect of 32 billion tonnes of dynamite of seismic energy yield whereas the San Francisco quake in 1906 was Richter 8 and was equivalent to 1 billion tonnes of TNT. Therefore, the strength of the quake would have dramatic consequences over the impact on the population and the surrounding area.
In addition to the direct effects of the earthquake are secondary disasters. Large fires following strong earthquakes have long been considered to be capable of producing losses comparable to those resulting from the shaking, this happened in Kobe. The risks are particularly high in Japan because of high population densities; very narrow streets and alleys, which cannot act as fire breaks; numerous old wood-frame smaller commercial and residential buildings mixed in the commercial zones of towns; unanchored or unprotected gas storage tanks or heaters; and a mix of collapse-prone old buildings in all built-up areas.
These risks were most recently exhibited in the large fire that destroyed much of the town of Aonae on the Island of Okushiri during the Mw7.8, July 12, 1993, Hokkaido Nansei-oki Earthquake. Also liquifaction is a major secondary hazard. This is a phenomenon in which sand saturated with groundwater temporarily behaves like quicksand when strongly shaken. This occurred in San Francisco’s Loma Prieta earthquake where damage related to liquifaction and soil consolidation in the area caused damage to water mains and disturbed numerous older masonry buildings. The earthquake caused landslides along the steep slopes from hills in the epicentral area to at least as far north as the Pacific coast just south of San Francisco. Several residential developments in the Santa Cruz Mountains were badly damaged by these slides.
In conclusion to my essay, I have discovered that there are many different factors that can effect the impact of an earthquake which are not necessarily associated with the magnitude. A true disaster would have to be in conjunction with many preparation and financial shortcomings and a true hazard success story would attempt to avoid many of the factors mentioned above. However this is not always possible, as environmental, political, economic and social difficulties cannot always be elevated.