To what extent is the impact of an earthquake related to its strength
An earthquake is a sudden release of tension between two plate margins, which had a built-up seismic pressure. When two crusts are deformed/displaced due to plate crustal movement in a result of convection currents, tremor can be caused. Earthquakes occur at all plate margins as well as intra-plate locations such as old relic fault lines. The most destructive earthquakes are related to destructive or strike-slip fault. The magnitude/strength can be measured by the Richter scale, which is a numerical scale which is calculated using a seismograph, this scale is logarithmic.
The impact caused by an earthquake can be related to physical or human factors. The location of the epicentre is a physical variable which could be considered. If the location of the epicentre is closer to the Earth’s surface the tremor will be more concentrated; therefore, a greater amount of vibration may cause more destruction. A comparison which supports this variable is between Haiti and Chile. Chile’s earthquake was 8. 8 in magnitude however the epicentre was 35 km deep. In contrast, Haiti’s magnitude was seven, but the epicentre was 13 km deep.
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There were only 400 people killed in Chile which can be considered very little compared to Haiti’s death toll of 230,000. Obviously, there are a lot of different variables that must be taken into consideration when regarding the death toll, but with Chilies earthquake being three hundred times stronger we must consider that the strength of the earthquake is not directly related to the impact. Geology is another physical variable which could be considered having an effect on the impact. If the earthquakes foci are surrounded by soft sediment, there may be a greater amount of destruction.
Soft sediment will amplify seismic waves this is because seismic waves travel faster through hard rock and soft soil as the amplitude of the wave needs to increase to be able to carry the same amount of energy, therefore, creating stronger shaking. Comparing Chile to Haiti; the main focus of Haiti is located on a river delta compared to Chile where there is harder rock because of the Andes mountain range. So, it can be said that the geology is also another variable factor which will affect the impact created by an earthquake. The duration of shaking is also variable which may cause the impact to be greater. This also includes after-shocks.
If it is a longer amount of vibration bonds within infrastructure will become weaker this is because fair is a greater amount of bond movement loosening each particle. Haiti experience 52 after-shocks, all greater than a magnitude of four. Chile only experienced one seismic tremor. Haiti experience 250,000 residences and 30,000 commercial buildings severely damaged and ready for demolishing. In contrast, 500,000 houses were made uninhabitable in Chile, considering Chilies earthquake was 300 times larger and strengthen Haiti’s this still can be considered a factor which increases the impact of an earthquake.
However, this does show that an increase in strength has played a significant role in the destruction of infrastructure. There are also specific scenarios which are dependent on strength such as tsunamis. An extreme magnitude can become the most significant factor when the epicentre is beneath the water. In March 2011, an earthquake the magnitude of nine was located off the coast of Japan caused the sea level to surge to form a wave of 39 meters. Roughly 16,000 people died because of this event. And due to the specific circumstances of this event, there was nothing Japan, and MEDC, could do to prevent this tsunami of such extreme magnitude.
This shows that in extreme circumstances strength can become the most important influence on the impact of society, the environment and the economy. Human factors can also affect the destruction caused by earthquakes. The level of development can be considered a large variable on how the country can cope with the ability to react, recover and prepare for an earthquake. If the country is and MEDC/NIC the country will have a greater amount of GDP or windfall profit which can be used on these three factors.
An example of a NIC is Chile the GDP per capita is $15,000. Chile is also well known for the world’s largest copper producer. As their more developed country and Chile is a quake-prone area preparedness was high, this is because they have the income to spend on close monitoring and aseismic buildings. As Chile has a well-structured government they have strict planning policies, building codes require shake resistant construction and rapid emergency response systems, therefore, reducing the risk of destruction, due to intense vibrations.
After the earthquake and the twit on 27th February, the country was able to use the $16 billion windfall profits of the copper industry, which is nationalised, to recover and provide immediate response to the locations in distress. This also means the money was used to rebuild roads, bridges, ports and the 1. 5 million homes affected; this meant economic loss was minimised. So, this shows that MEDCs have the ability to minimalize impact which could be related to physical factors including strength. In contrast, LEDC’s don’t have the ability to prepare, recover and react to the situation.
This is due to the low income and low political stability, which also includes corruption in some situations. This means they simply cannot afford recovery and rely on other countries and charities providing aid to support the effects of the impacts. An example is Haiti, where the GDP is $1100 per capita. Little was done to react in the short term apart from appeals for humanitarian aid. Haiti also relied on the United States however due to the little amount of immediate clear up traffic congestion is, and blocked roads hampered relief effort.
Due to Haiti being in LEDC they don’t provide strict planning regulations; therefore, masonry buildings were easily destroyed, and the government did not prevent construction on Haiti’s river delta as Haiti’s main city Port-au-Prince was located there. This shows how a low developed country can amplify the impact due to lack of preparedness and lack of money to respond, therefore the strength and other physical factors can be influenced by the development of the country. The extent of impact can be affected by the location of infrastructure.
If the focus of an earthquake is located in a rural area, there will be less building density thus a small amount of destruction and infrastructure, therefore reducing the extent of the impact. The earthquake in Chile was located near a small coastal town called ‘Constitucion’. As it is a coastal town it identifies that there is a smaller building density, therefore, a lesser risk of destruction which will cause a loss of life. This shows that a rural area can have a significant role in the depending factors that suggest the impact of an earthquake, not only just relating to strength.
Lastly, in comparison, an urban area which has a significantly greater population and building density could be affected to a greater extent changing the impact of an earthquake. The reasoning behind this is because buildings at a greater density more likely to fall onto a person, with a higher population there is a greater risk. Haiti can be used in this example, Port-au-Prince Haiti’s capital city was highly populated, with little planning regulations, therefore, people built masonry buildings close together.
With the epicentre only being 25 km west of Port-au-Prince the greater amount of infrastructure meant there is a greater impact. With there being a greater impact but an earthquake 300 times less than Chillies it is clear evidence that there are other variables that can affect the impact of an earthquake. To conclude, the impact is primarily related to physical factors such as the location of the epicentre, the geology, the duration of the earthquake and the strength. All these factors play a balanced role on the effects of an earthquake. However, an earthquake with a magnitude less than 5. could be considered non-detrimental therefore discarding other factors. And in contrast that, an earthquake with an extreme magnitude could be considered detrimental and be the most significant factor to the impact. Secondly, the impact is also related human factors and how well we can manage the environment to prepare for such events. As shown above, the Park model can show the level of the economy and how the time and economy can recover. The dashed line shows and MEDC’s/NIC such as Chile and the filled line show an LEDC such as Haiti.
We can see that it takes a longer time for the economy to recover in LEDC due to the factors I’ve identified in the previous paragraphs. If the country is not in the situation to prepare itself, physical factors can be amplified therefore creating a greater impact. The location of the epicentre concerning urban and rural areas is also factors that can supplement physical factors increasing the impact of an earthquake, if in an urban area. However, strength is still the primary factor that at a certain magnitude other human and physical factors come into play.