Where buildings do collapse, the occupants are more likely to survive when the walls and roof are made of lightweight materials rather than heavy ones.
Rubble-masonry buildings or brick buildings with low-quality mortar do not withstand earthquakes well; wooden or steel-framed buildings are generally much better, providing they are correctly braced.
Building design is also important. Buildings shake when the frequency of the seismic waves is close to the natural frequency of vibration of the building, an effect known as resonance. The resonant frequency depends on the height of the building: low-frequency shaking might cause tall buildings to shake violently while having little effect on low-rise buildings nearby, although higher frequencies of vibration might have the opposite effect.
In the Mexico City earthquake in , the majority of buildings with severe damage were those with 6—15 storeys; the resonant frequency of these buildings was the frequency most amplified by the subsoils in the city.
Damage is often concentrated on the upper storeys of taller buildings because the motion is greater there. The upper floors of several tall buildings like this hotel collapsed. Continental Hotel, Mexico City, Damage to tall buildings is often concentrated on the upper storeys, where the motion is greater.
However, tall structures can survive low-frequency vibrations if they are designed to do so. This typically involves making sure that lower floors are stronger and heavier than upper floors, and avoiding large, unsupported spaces; it may also include extra reinforcement with steel cables, or even placing the building on a foundation which reduces the amount of shaking transmitted to the building structure. Buildings with large and unsupported spaces, like viaducts or car parks, can be particularly vulnerable.
This map is best viewed in full screen mode. To enter full screen mode use button below the zoom controls. Click on the map circles for more information. The yellow circles show the biggest earthquakes ever recorded and the red circles show the deadliest. The orange circles show earthquakes that were particularly deadly and big. Discovering Geology introduces a range of geoscience topics to school-age students and learners of all ages.
A variety of structures have been damaged by surface faulting, including houses, apartments, commercial buildings, nursing homes, railroads, highways, tunnels, bridges, canals, storm drains, water wells, and water, gas, and sewer lines. Damage to these types of structures has ranged from minor to very severe. An example of severe damage occurred in when three railroad tunnels were so badly damaged by faulting that traffic on a major rail linking northern and southern California was stopped for 25 days despite an around-the-clock repair schedule.
The displacements, lengths, and widths of surface fault ruptures show a wide range. Fault displacements in the United States have ranged from a fraction of an inch to more than 20 feet of differential movement. As expected, the severity of potential damage increases as the size of the displacement increases. The lengths of the surface fault ruptures on land have ranged from less than 1 mile to more than miles. Most fault displacement is confined to a narrow zone ranging from 6 to 1, feet in width, but separate subsidiary fault ruptures may occur 2 to 3 miles from the main fault.
The area subject to disruption by surface faulting varies with the length and width of the rupture zone. Liquefaction is not a type of ground failure; it is a physical process that takes place during some earthquakes that may lead to ground failure. As a consequence of liquefaction, clay-free soil deposits, primarily sands and silts, temporarily lose strength and behave as viscous fluids rather than as solids.
Liquefaction takes place when seismic shear waves pass through a saturated granular soil layer, distort its granular structure, and cause some of the void spaces to collapse.
Disruptions to the soil generated by these collapses cause transfer of the ground-shaking load from grain-to-grain contacts in the soil layer to the pore water. This transfer of load increases pressure in the pore water, either causing drainage to occur or, if drainage is restricted, a sudden buildup of pore-water pressure. When the pore-water pressure rises to about the pressure caused by the weight of the column of soil, the granular soil layer behaves like a fluid rather than like a solid for a short period.
In this condition, deformations can occur easily. Liquefaction is restricted to certain geologic and hydrologic environments, mainly areas where sands and silts were deposited in the last 10, years and where ground water is within 30 feet of the surface. Generally, the younger and looser the sediment and the higher the water table, the more susceptible a soil is to liquefaction. Liquefaction causes three types of ground failure: lateral spreads , flow failures, and loss of bearing strength.
In addition, liquefaction enhances ground settlement and sometimes generates sand boils fountains of water and sediment emanating from the pressurized liquefied zone. Sand boils can cause local flooding and the deposition or accumulation of silt.
Lateral Spreads - Lateral spreads involve the lateral movement of large blocks of soil as a result of liquefaction in a subsurface layer. Movement takes place in response to the ground shaking generated by an earthquake. Lateral spreads generally develop on gentle slopes, most commonly on those between 0.
Horizontal movements on lateral spreads commonly are as much as 10 to 15 feet, but, where slopes are particularly favorable and the duration of ground shaking is long, lateral movement may be as much as to feet.
Lateral spreads usually break up internally, forming numerous fissures and scarps. Damage caused by lateral spreads is seldom catastrophic, but it is usually disruptive. For example, during the Prince William Sound, Alaska, earthquake, more than bridges were damaged or destroyed by lateral spreading of flood-plain deposits toward river channels.
These spreading deposits compressed bridges over the channels, buckled decks, thrust sedimentary beds over abutments, and shifted and tilted abutments and piers. Lateral spreads are destructive particularly to pipelines. In , a number of major pipeline breaks occurred in the city of San Francisco during the earthquake because of lateral spreading.
Breaks of water mains hampered efforts to fight the fire that ignited during the earthquake. Thus, rather inconspicuous ground-failure displacements of less than 7 feet were largely responsible for the devastation to San Francisco in Flow failures, consisting of liquefied soil or blocks of intact material riding on a layer of liquefied soil, are the most catastrophic type of ground failure caused by liquefaction.
These failures commonly move several tens of feet and, if geometric conditions permit, several tens of miles. Flows travel at velocities as great as many tens of miles per hour. Flow failures usually form in loose saturated sands or silts on slopes greater than 3 degrees. Flow failures can originate either underwater or on land.
Furthermore, earthquakes, together with severe storms, coastal wave attacks, wildfires, and volcanic activity can create slope instability which leads to landslides. This occurs mainly in areas with steep slopes. Landslides flatten and destroy houses resulting in added loss of life. In Japan, the Great Kanto earthquake erupted a fire that killed more than 92, people.
In , the tsunamis unleashed by the Indian Ocean earthquake killed a total of , people in Indonesia, Thailand, India, and Sri Lanka. The Tohoku earthquake in created great tsunami waves that destroyed the communities and killed about 18, people.
This devastating disaster kills thousands and thousands of people yearly. Since , over 2. The chart below shows the earthquakes with the highest death toll since then. Source: Statistics. Furthermore, earthquakes can also cause fires by destroying the gas lines or electrical power.
When this occurs, it is difficult to stop the spread of the fire and this, in turn, leads to extensive damage and loss of life. For instance, the fire caused by an earthquake caused thousands of deaths in the San Francisco earthquake in The social impact on humans is one of the main effects of earthquakes.
A strong earthquake destroys factories, buildings, shops, bridges, schools, and roads, these render thousands of people homeless and a lot of children became orphans. Even after 6 years, there were still about 60, people homeless. These conflicts can also bring about deeply rooted issues connected to negative opinions about people of society who are vulnerable, poor, or marginalized. Moreover, those who survived the attack start to live in crowded shelter places with minimal or no sanitary facilities.
These cause a break out of communicable water-borne diseases like dysentery, cholera, protozoa infections, e. In addition to the loss of life, earthquakes cause a lot of traumatic injuries to humans. These results from flying glass, falling objects, and collapsing walls caused by the earthquake. Some of these earthquake-related injuries are always complex and of different patterns. And If not managed correctly, they lead to long-term disability and functional impairment due to irreparable damage to the eyes, limbs ears, e.
Examples of such injuries include fractures that develop complications such as alignment problems or infection, spinal cord injuries, and crush injuries of extremities needing amputation. Also, damage to buildings, elevators, structural elements, fire protection systems, and stairs, caused by the shaking from a strong earthquake can play a vital part in the spread of fire and hinder the ability of residents to evacuate.
This is a serious problem that can result in injuries such as burns. Earthquakes can also affect humans mentally or psychologically. What must it be like to see your family or friends trapped inside a collapsed building or missing, assumed dead, or your home getting destroyed? I have met people who have not been able to restore balance in their everyday lives; because anytime the earth twitches, they panic.
Any little noise, they run for cover. Some are so traumatized that a well-meaning, but an unexpected touch from a friend can cause them to scream out in fright. Their body is always on high alert for another threat to their safety and this makes them feel jumpy.
Also, some of them who are directly involved in the incident will show lots of psychological symptoms that look like Post-Traumatic Stress Disorder PTSD such as intense fear, nightmares, and flashbacks, or they continuously experience the event in their head.
In addition, Search and Rescue teams who look out for survivors in the collapsed buildings can also be affected. Yes, this is their job, but it must be terrible to find different dead bodies when searching for survivors.
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