3.1.1. Earthquakes
An earthquake is a term used to describe both a sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip, or by volcanic or magmatic activity, or other sudden stress changes in the earth. (U.S. Geological Survey)
Worldwide, more than one million earthquakes occur each year, or an average of two a minute. A major earthquake in an urban area is one of the worst natural disasters that can occur.
During the last four decades (1970-2010), earthquakes have been responsible for over a million deaths around the world – in Armenia, China, Guatemala, Haiti, Iran, India, Indonesia, Japan, Mexico, Pakistan, Peru, and Turkey.
Excessive urbanization in various seismically active parts of the world has led to megacities with population densities of 20,000 to 60,000 inhabitants per square kilometer. Such cities are highly vulnerable to earthquake hazards, which include high case-fatality rates for trauma, asphyxiation, hypothermia, and acute respiratory insufficiency, in addition to fractures and other injuries caused by the destruction of infrastructure.
The number of victims, injuries, and negative effects of an earthquake depend on its magnitude, depth, proximity to urban centers, and on the community’s preparedness and the extent to which it has adopted mitigation measures. Recent examples of mega-earthquakes—in China, Haiti and Indonesia, each with more than 220,000 reported fatalities—illustrate the importance of mitigation.
Structural collapse is the risk factor that can cause the most deaths, and thus earthquake safety should be a priority in zoning and in building design and construction. For the health sector in particular, it is important to take account of the implications of earthquakes, which create high demand for surgical services in the first weeks and treatment for burns and trauma, etc.
In earthquake-prone areas, training and education in first aid and rescue should be integral to every community program on emergency and disaster response. However, often there are relatively long periods of time between major earthquakes, resulting in a loss of collective memory of the events. This poses yet another challenge for public officials, who must effectively explain to the public the dangers and the need to reduce risk by improving safety measures.
In spite of major scientific advances in anti-seismic engineering and seismology in recent years, ensuring the adoption of stringent earthquake safety standards is a goal still not reached in many parts of the world.
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As a result of the destruction of dwellings, earthquakes can cause numerous deaths and injuries. The outcome basically depends on three factors:
1. The first is type of housing. Unreinforced masonary houses or those built with adobe or dry stone without masonry reinforcement, even if they are single story, are very unstable, and when they collapse they claim many victims. Light buildings, especially wooden structures, have been proven to be much less dangerous. For example, after the 1976 earthquake in Guatemala, a survey conducted in a town of 1,577 inhabitants revealed that the 78 deaths and severe injuries caused by the earthquake involved people who lived in adobe dwellings, while those who lived wood-built structures had a much higher survival rate. In the earthquake that ravaged the Bolivian towns of Aiquile and Totora in 1988, 90% of deaths were the result of collapsed adobe houses.
Streets that were blocked by fallen buildings and rubble, as well as severe damage to the water supply system, hindered efforts to put out the fire. |
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