When there is a shaking and vibration at the surface of the earth caused by underground movement along a fault plane or by volcanic activity, then it is the time of earthquake. The scale of earthquake is commonly measured by Richter scale which compares the maximum heights of the seismic waves at a distance of 100 kilometers from the point on the earth's surface directly above where the earthquake originated within the earth, the epicenter. The Richter scale then divided into categories called Magnitudes which are the estimation of the energy released by an earthquake.
Earthquake happens because the Earth’s tectonic plates are always moving and floating on molten rock. An earthquake can last few seconds to a few minutes, which can be followed after-shocks. Most earthquakes occur on the edge of plates, especially where one plate is forced under another such as happens off Sumatra or past another as occurs in California.
The earth's outer shell is divided into seven major and some smaller plates which are constantly in a dynamic state, pushing against, pulling away from, or grinding past one another. Forces build up as the plates attempt to move in relation to each other. When the adhesions along the fault give way, stored energy is released in the form of earth tremors, volcanic activity etc. Types of plate movements and principal effects of earthquake:
- Oceanic plates pulling away from each other leads to hot volcanic material being expelled from cracks to form mid-ocean ridges.
- Oceanic plates colliding with and forced under continental plates leads to mountain ranges being pushed up, accompanied by earthquakes and volcanic eruptions.
- Collisions of continental plates force up mountain ranges; release compression energy in quakes.
See also a paper about earthquake characteristics published by Montana government.
There are several primary impacts of earthquake:
- Total or partial destruction of structures.
- Blockage or breakage of transport activities.
- Interruption of Water Supply.
- Breakage of Sewage Disposal Systems.
- Loss of Public Utilities, eg. electricity & gas
Earthquakes will give various effects of damages while it depends on the scale. An example of massive damages of earthquake was on 2004 when an earthquake was occurred in Sumatra-Indonesia. It was not only affected Indonesia, but also several countries such as Thailand, Sri Lanka, etc. See also the damages of earthquake in Aceh-Indonesia 2006 and environmental impacts in Haiti earthquake 2010.
When in a situation of emergency, we should consider where we are, a good basic knowledge of emergency will be helpful in emergency situation.
If you are indoor, take cover under a heavy desk or table. If you get under a table and it moves, try to move with it. It would be better if you stay away from falling objects, glasses, hanging objects, huge furniture that can be fallen. If you are in a public building, do not rush for the doorways and do not use elevators.
If outdoors, move away from buildings and utility wires. The greatest danger from falling debris is just outside doorways and close to outer walls. Once in the open, stay there until the shaking stops.
If you are in automobile stop as quickly and safely possible but not under a potential materials that could fall but into an open space. When you drive on, watch for hazards created by the earthquake, such as breaks in the pavement, downed utility poles and wires, a fallen overpasses and bridges.
There are many ways to reduce earthquake damages. Possible actions include:
· Developing construction techniques that are seismic resistant.
· Conducting a program to introduce improved construction techniques to the building industry and the general public.
· Determining which sites are safe for construction through analysis of the soil type and geological structure.
· Instituting incentives to remove unsafe buildings and buildings on unsafe sites or, more probably, to upgrade their level of safety.
· Instituting incentives to encourage future development on safer sites and safer methods of construction through:
Land use controls (zoning).
Building Codes and standards and means of enforcing them.
Favourable taxation, loans, or subsidies to qualify buildings, methods and sites.
Land development incentives.
· Reducing possible damage from secondary effects by:
Identifying potential landslide sites and restricting construction in those areas.
Installing devices that will keep breakages in electrical lines and gas mains from producing fires.
Verifying the capability of dams to resist earthquake forces, and upgrading as necessary.
Learn also a guidance manual on nonstructural earthquake mitigation by FEMA and a mitigation plan which is developed by Nevada government.
Several actions related to earthquake management planning.
1. A journal on contingency planning for earthquake in Asia. (click here)
2. GIS for Earthquake, developed by ESRI. (click here)
3. A case study on earthquake risk management in Italian region. (click here)