3.1.1. Earthquakes

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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.









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.

2. The second factor involves the time of day when the earthquake occurs. The fact that earthquakes in Guatemala (1976), Bolivia (1998), and Iran (2003) occurred at night proved very deadly, as most damage damage occurred in adobe houses. In urban areas where houses are well constructed but schools and offices not so well built, daytime earthquakes produce greater mortality. Such was the case of the earthquake that shook two Venezuelan cities in 1997. In Cumaná an office building collapsed, while two schools were destroyed in Cariaco. Those buildings were the sites of the greatest number of deaths and injuries. In the El Salvador earthquake of 13 January 2003, the number of injuries and deaths was moderate in comparison with the massive material damage. One of the reasons was the fact it was a Saturday, rather than a working day. The time (11:33 a.m.) was also a positive factor, since a great number of people were outside their houses. 

3. The third factor is population density. More densely populated areas tend to have the highest death toll and number of injuries. However, some age groups are more affected than others: adults in good health are safer than young children and older persons, who are less able to protect themselves. Nevertheless, 72% of the deaths due to collapsing buildings in the Mexican earthquake of 1985 were in the 15-to 64-year-old age bracket. Earthquakes can be followed by secondary disasters that increase the number of victims requiring medical care. Although fire has historically been the greatest threat, fires have been rare after earthquakes in the last few decades that have caused massive loss of life. On the other hand, the consequences of the earthquake that ravaged Kobe, Japan in 1995 included over 150 fires, to which some 500 deaths were attributed, as well as damage to approximately 6,900 structures. 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. 


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. 

Limited information is available on the types of injuries caused by earthquakes. Despite the number of fatalities, it is common to see a large number of people with minor contusions, a smaller number with simple fractures, and a minority with serious multiple fractures or internal injuries that require surgical care or other intensive treatment. In one Haitian hospital after the earthquake, 16.6% of the patients had head or spinal injuries, while fractures represented 26.9%, burns 4.7%, penetrating trauma 3.1%, crush injuries 5.6%, contusions 2.1%, infections 18.4%, cuts 15.5%, and amputations 4.4%. 

Most of the demand for health services occurs in the first 24 hours following an event and the injured tend to arrive at medical facilities in massive numbers only during first three to five days, after which the pattern returns to pre-disaster levels. . A good example of the chronology for timely emergency care may be seen in the number of admissions to a field hospital after the 1976 earthquake in Guatemala. Admissions fell markedly from the sixth day on, despite an intensive continued search for victims in remote rural areas.

In Haiti, however, according to a study prepared by PAHO, the injured seeking medical care close to the epicenter accounted for 9.2% of total number of patients, while in departments further from the capital of Port-au-Prince, the number of earthquake-related injuries reached 15.2 % of the total number of patients seen. What this reflects is that the loss of medical facilities close to the epicenter forced people to displace and seek medical attention elsewhere where health facilities were still intact (more patients were treated in hospitals close to the border with the Dominican Republic than in Port-au-Prince.) The medical teams that arrived in the hardest-hit areas two weeks later found infected wounds, fractures, and more demand for treatment of routine pathologies than for earthquake-related conditions.