Cover Image
close this book Disasters and development: A peace corps pre-service training module
close this folder Participant references
close this folder Earthquakes
View the document References: Earthquakes


Earthquakes are one of the most dangerous and destructive forms of natural hazards. They strike with sudden impact and little warning. They may occur at any time of day or on any day of the year. An earthquake can devastate an entire city or a region of hundreds of square kilometers. They can reduce buildings to a pile of rubble in seconds, killing and injuring their inhabitants.


The regions of the world where earthquakes occur are characterized by certain geological aspects. The earth's crust is broken into a series of blocks or "plates" that are separated by deep fractures called faults. Faults form lines of weakness in the masses of rock at the earth's surface. Pressures build up below the surface which eventually force a sudden shift between two of these blocks. This sudden shift is the earthquake.

Why these pressures build up and cause the movements is explained by the theory of continental drift or "plate tectonics". Briefly, this theory holds that all the earth's land area once was a single mass. This mass broke apart, and the pieces began drifting. Wherever plates meet there is a high degree of earthquake activity or "seismicity".

The fault movement, at these meetings of plates, is the result of elastic rebound, the slow build-up and sudden release of strain within masses of rock. The place at which the stresses are released is known as the focus of an earthquake. From this point, mechanical energy is initiated in the form of waves that radiate in all directions through the earth. When this energy arrives at the earth's surface, it forms secondary surface waves. The frequency and amplitude of the vibrations produced at the surface, and thus the severity of the earthquake, depend on the amount of mechanical energy released at the focus, the distance and depth of the focus, and the structural properties of the rock or soil on or near the surface.


A. Primary Effects

The onset of a large earthquake is initially signaled by a deep rumbling, followed shortly by a series of violent motions in the ground. Often the ground fissures or cracks, and there can be large permanent displacements horizontally - sometimes as much as 10-15 meters.

Description of an earthquake


Motion of the earth's plates causes increased pressure at faults where the plates meet Eventually the rock structure collapses and movement occurs along the faull. Energy is propagated to the surface above and radiates outward. These waves of motion in the earth's crust shake landforms and buildings causing damage

As the vibrations and waves continue to move through the earth, structures on the earth's surface are set in motion. Each type of structure responds differently, depending on the type of materials of which it is made. When the waves strike, the earth begins to move backward and forward along the same line. The lower part of a building on the earth's surface immediately moves with the earth. The upper portion, however, initially remains at rest; thus the building is stretched out of shape. Gradually the upper portion tries to catch up with the bottom; but as it does so, the earth moves in the other direction causing a "whiplash" effect, speeding up the top of the building, and creating a vibration known as resonance. The resonance can cause structural failure in itself, or adjacent buildings having different response characteristics (caused by different building materials) can vibrate out of phase and pound each other. The walls of buildings without adequate lateral bracing frequently fall outward, allowing the upper floors or roof to collapse into the inside of the structure.

Another primary effect is known as liquefaction. Loose sandy soils with a high moisture content separate when shaken by an earthquake. The water then moves upward, turning the surface into a consistency much like that of quicksand. Heavy structures resting on these soils will slowly sink into the ground.

B. Secondary Effects

Often as destructive as the earthquake itself are the resulting secondary effects such as landslides, fires, tsunamis, and floods. Landslides are especially damaging and often account for the majority of lives lost.

Of less concern, except for countries in the Pacific Basin, are tsunamis. A tsunami is a large seawave caused by an earthquake abruptly lifting the ocean floor. The waves move outward at a high velocity and can cross thousands of kilometers before they run up on shore. At sea, their low wave height gives little evidence of their existence; however, as they approach land, their velocity decreases and their height increases. In this way a 5meter crest moving at 600 kph in the open ocean becomes a devastating 30-meter-high wave moving at 50 kph when it reaches shore.

The risk of fire immediately following an earthquake is often high due to the breakage of electrical lines and gas mains. In recent years, devices have been installed in most of the world's major cities that shut these services down automatically if an earthquake strikes. Yet the threat still exists in many smaller cities and the squatter settlements of larger cities where open fires are used for cooking, heating and lighting.

How an earthquake damages a house


C. Impact of Earthquakes

The principal concern about an earthquake is the impact it has on the built environment and its inhabitants. Approximately 90 percent of the loss of life in all earthquakes is the result of structural collapse. There are five primary elements that influence damage to man-made structures:

1. Strength of the earthquake waves reaching the surface. The stronger the fault movement, the stronger the earthquake waves.

2. Length of earthquake motion. The fluctuating series of tremors can last from 10 seconds to a minute or more. It is the cumulative effect of this motion that works on structural walls and is the usual cause of collapse.

3. Proximity to the fault. Generally there is greater danger closer to the fault than further away. However, there are other important considerations such as structural inadequacies and types of ground condition.

4. Geologic foundation. Structures built on solid rock fare better than those built on softer ground or, worse yet, those built partly on solid ground and partly on soft ground or fill - a condition commonly found on hillsides.

5. Building design. To resist damage in an earthquake, a building must be adequately braced, have structural continuity with secure anchoring and bonding of all elements, be well balanced and tied together.

Until recently, the great loss of life and property was unavoidable. However, now that more is known about the nature of earthquakes and their effects, we have engineering techniques to make new structures reasonably earthquake-resistant at a small additional cost and are rapidly developing techniques to make older buildings safer. A high loss of life from the collapse of weak buildings is now avoidable, and even structures made of materials such as adobe and brick in the poorest settlements of the Third World can be made relatively safe, thus substantially reducing the loss of life.


Widespread destructive earthquakes can have a significant impact on economic development. Because they damage man-made structures, reconstruction costs can be substantial. When thousands of buildings must be replaced, the costs can exceed the national budget. This means that reconstruction will compete with development projects for money and other resources. To reduce costs, emphasis must be placed on the private sector and especially on self-help activities. This emphasis provides many opportunities to expand development. Technical assistance in self-help construction, credit and public works can all contribute to improving people's capabilities to deal with their own needs.

In their rush to help survivors, relief agencies often offer a wide range of services and relief materials. Unless caution is exercised, expectations can be raised that can actually become a disincentive to self-help and local initiative. This is especially true in the housing sector. (This is one of the reasons why more enlightened relief agencies provide building materials instead of tents as emergency shelter. Materials imply that the emphasis will be on self-help.).

Earthquakes also heighten awareness of social stratification. It is usually obvious that it is the poor, living in low-quality buildings, who suffer the greatest number of deaths, injury and loss of property. This awareness has been called "instant consciousness-raising" and can be a powerful force for change if properly directed. If ignored, adverse political consequences can result. It is not uncommon to see an increase of land invasions, major shifts of population from rural to urban areas, sad a decline in the number of skilled workers in rural areas in the aftermath of an earthquake. How governments and development agencies respond to these changes can have a major impact on future development.


The study of geology, specifically the nature and causes of earthquakes, has been relatively recent. It is, therefore, understandable that people throughout history have created their own explanations for the occurrence of earthquakes.

Frequently, traditional cultures believe that earthquakes are caused by a god. They believe their god uses an earthquake to express displeasure for some fault or sin of the community. Other people claim there is a correlation between earthquakes and weather patterns. More current speculation has suggested that the explosion of nuclear bombs provokes earthquakes.

These misconceptions, in turn, affect what people think they can do about earthquakes. For example, they may simply resign themselves to suffer the "act of God" if that is God's intention.

Examining past earthquakes has, of course, demonstrated many lessons:

A. Because people often assume there is nothing they can do to avoid the impact or destruction of an earthquake, there is a tendency for survivors to reconstruct buildings in the same manner (and with the same degree of danger) as the pre-disaster buildings.

B. Designs that affect reconstruction planning are usually made in the first month following the earthquake. This means that technical assistance and improvements must be provided soon after the quake in order to have an effect.

C. Most survivors will build an emergency shelter from the rubble of their house. They prefer these shelters to tents because the makeshift houses provide more protection and serve as a means of protecting recoverable building materials.

D. Earthquakes and the threat of continuing tremors rarely are sufficient reason to evacuate an affected area.

E. Health threats in the aftermath are grossly exaggerated. Communicable diseases almost never "break out" unless people are forced to evacuate an area and move into camps.

F. Reconstruction always takes longer than estimated. Full recovery may take 10 years or more.

Analysis shows that many of the losses from earthquakes can be avoided. Various techniques for their avoidance will be discussed below.




A. Earthquake Mitigation

Fortunately, a great deal can be done to prevent earthquakes from becoming disasters. First, the general public as well as engineers, planners, politicians and others, need to understand the nature of earthquakes. Based on that understanding, a decision and various levels of commitment are needed to implement measures to mitigate earthquake damage.

The first level of commitment requires that government and policy-makers create strategic development and investment programs. A comprehensive approach would establish geographic zones and a target population.

A second level is design of an extensive public awareness program. This program informs the public about the earthquake hazard and illustrates what can be done to prevent a disaster.

The third level is a technical assistance program. This could include architectural and engineering assistance in improved building design, construction, and siting; training local residents in these techniques; and conducting projects that demonstrate the nature of these techniques.

The implementation of these mitigation measures must be preceded by collection of background information. One primary task is to identify where earthquakes are likely to occur and the relative probability that they will occur; this is referred to as risk mapping .

The second task is to identify communities that occupy high risk sites. In these, the various types of structures should be studied to determine which are likely to fail in an earthquake. This is called vulnerability mapping and identifies specific populations in danger.

The next task is to conduct a survey of construction methods, techniques and materials to determine ways to improve the buildings. This should be done with an understanding of the overall economic and cultural process by which houses or public buildings are built.

There are many ways to reduce earthquake damage. Possible actions include:

1. developing construction techniques that are seismic resistant;

2. conducting a program to introduce improved construction techniques to the building industry and the general public;

3. determining which sites are safe for construction through analysis of the soil type and geological structure;

4. instituting incentives to remove unsafe buildings and buildings on unsafe sites or, more probable, to upgrade their level of safety;

5. instituting incentives to encourage future development on safer sites and safer methods of construction through: a. land use controls (zoning); b. building codes and standards and means of enforcing them; c. favorable taxation, loans or subsidies to qualifying building methods and sites; d. land development incentives.

6. reducing possible damage from secondary effects by: a. identifying potential landslide sites and restricting construction in those areas; b. installing devices that will keep breakages in electrical lines and gas mains from producing fires; c. verifying the capability of dams to resist earthquake forces, and upgrading as necessary.

B. Earthquake Preparedness

Vulnerable communities should institute preparedness programs. Preparedness includes educating the public about what they should do in case of an earthquake and preparing public officials and services to react to the emergency. Activities include:

1. training teams for search and rescue operations;

2. training teams for disaster assessment;

3. identifying safe sites where people living in areas threatened by landslides in secondary tremors could be relocated;

4. training adequate personnel in trauma care;

5. maintaining stocks of trauma-related medical supplies;

6. reviewing the structural soundness of facilities that are essential for the operation of disaster response such as hospitals, fire stations, government buildings, communications installations; upgrading them as necessary;

7. preparing plans and necessary equipment for alternative water supply if the current system is vulnerable;

8. preparing plans for clearing streets on a priority basis (to provide emergency access);

9. preparing emergency communication systems as well as messages to the public regarding matters of their health, safety and security;

10. training teams to determine if buildings are safe for reoccupancy.




A. Earthquake Response

The immediate impact of an earthquake affects virtually all sectors of the community. Initial response by local authorities should include implementing the activities identified in the preparedness stage. Initial emphasis will be on search and rescue of the victims, attempting as far as feasible to account for all members of the affected population. Second, provide emergency medical assistance. There will be a high incidence of surgical needs during the first 72 hours; additional medical needs will fall off sharply after that time. Contrary to myth, there are no actual immediate epidemiological threats or patterns of disease resulting directly from an earthquake.

Third, conduct a damage and needs assessment. The local government as well as international donors need to know as quickly as possible the scale of the disaster and what sort of assistance (and how much) is needed.

Fourth, provide relief to the survivors. Response can take several forms. Of the greatest value is cash, allowing survivors and local agencies discretion to focus resources where the most urgent needs are. International donors can assist in reopening roads, reestablishing communications, making contact with remote areas, conducting disaster assessment, and providing building materials for reconstruction. The popularly known forms of foreign relief such as food, blankets and clothes are totally inappropriate.

In all emergency activities it is of prime importance that information for the public about what they should do and where they can go for services be immediately available and accurate, and that decision-makers act according to priorities.

B. Earthquake Rehabilitation, Reconstruction and Recovery

At the end of the emergency period, a transition to long-term recovery occurs. Local authorities should concentrate their assistance in the following areas:

1. repair and reconstruction of "lifelines", i.e. water, sewer, electrical services and roads;

2. technical, material and financial assistance for the repair and reconstruction of housing and public buildings;

3. economic programs that create jobs to help rejuvenate the economy;

4. financial assistance to survivors, including lines of credit and assistance to businesses, to enable them to participate in recovery efforts.

International donors will be able to provide assistance in all of these same activities. The most cost-effective support they can provide is technical and financial assistance.

The following are some lessons for planning and administration of reconstruction programs:

- Aid should not be provided in such a way that it inhibits the recovery process and creates dependency relationships between victims and donors.

- The hierarchical structure of donor organizations should facilitate, not inhibit, the flow of information on the real needs of victims to the decision-makers.

- Reconstruction must be carried out by properly-trained program administrators and technicians, not well-intended lay-persons.

- Donor organizations need to be cautious about providing emergency shelter; rarely is it an appropriate form of aid. Even less likely is the appropriateness of a high technology, imported emergency shelter design.



There are many ways for Peace Corps Volunteers to participate in earthquake mitigation, preparedness, response or recovery. All Volunteers can participate in public awareness activities in earthquake-prone communities. There are also many specific activities that are appropriate for full or part-time Volunteer assignments. These include:

A. Housing Improvement. Peace Corps engineers and architects, or PCVs with construction skills, can help plan and execute programs to improve local housing to an earthquakeresistant standard in both mitigation as well as reconstruction programs.

B. Site Selection. City planners, geologists and geographers can help urban governments conduct risk and vulnerability analyses and can advise urban dwellers about safe siting of their houses.

C. Structural Surveys. Peace Corps engineers and architects can assist in assessing building safety before and after earthquakes.

D. Economic Mitigation. Economic development specialists can encourage the establishment of lending institutions to provide money for housing improvement and encourage the poor to establish cash reserves for possible emergencies. Co-ops are a major source of reconstruction loans to the poor who often cannot qualify for other financial assistance.

E. Emergency Response. All PCVs can help in an emergency. Roles might include:

- search-and-rescue

- distribution of relief

- distribution of shelter materials

- disaster assessment

- needs assessment

- translation services for foreign disaster officials