Natural Hazards: Causes and Effects - Disaster Management Center ...

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 human-produced
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, lasting from 10 seconds
to 3-5 minutes, produces a cumulative effect of this motion that works on structural walls. It
is the usual cause of collapse.
3. Proximity to the fault. Generally there is greater danger closer to the fault than farther
away. However, there are other important considerations such as structural inadequacies
and type of ground conditions.
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. It must have structural continuity with secure anchoring and bonding of all
elements, and it must 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, engineering techniques have been
developed to make new stuctures reasonably earthquake-resistant at a small additional cost.
Techniques to make older buildings safer are also being rapidly developed. A high loss of life
from the collapse of weak buildings is now avoidable. Even in the poorest settlements of the
Third World, structures made of materials such as adobe and brick can be made relatively safe,
thus substantially reducing the loss of life. 12
Impact on Development
Widespread destructive earthquakes can have a significant impact on economic development.
Because they damage human-produced 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. In many economies it becomes necessary to place an emphasis 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 some 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 the poor, living in lowquality
buildings, will suffer the greatest number of deaths, injury and loss of property. This
awareness has been called “instant consciousness-raising.” It can be a powerful force for
change if properly directed. If ignored, adverse political consequences can result. It is not
uncommon in the aftermath of an earthquake to see an increase of land invasions, major shifts