Causes and Effects of Earthquakes

What is an Earthquake ?

• Earthquakes are the shaking, rolling or sudden shock of the earth’s surface.

• They are the Earth's natural means of releasing stress.

What causes an Earthquake ?

• There are about 20 plates along the surface of the earth that move continuously and slowly past each other. When the plates squeeze or stretch, huge rocks form at their edges and the rocks shift with great force, causing an earthquake.

• As the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy, which moves through the Earth in the form of waves, which we feel and call an earthquake.

What is Epicenter ?

• The Epicenter is the point on the Earth’s surface i.e. directly above the hypocenter or focus, the point where an earthquake or underground explosion originates.

• In the case of earthquakes, the epicenter is directly above the point where the fault begins to rupture, and in most cases, it is the area of greatest damage.

What is a fault ?

• A fault is an area of stress in the earth where broken rocks slide past each other, causing a crack in the Earth's surface.

Causes of EarthquakesNatural cause:

Earthquakes are the result of slow-moving processes that operate within Earth.

Earth was hot when it formed, and has been cooling ever since (near the surface, for each km into Earth, the temperature rises by about 30deg. Celsius).

Earth's cooling causes the portions of Earth to move, and that movement is what we call an earthquake.

Some of the human decisionsthat have induced earthquakes:

• Dams and reservoirs:It's just water, but, water is heavy. Large reservoirs of water created by dams have a long history of inducing earthquakes. The 2008 earthquake in Sichuan, China, that killed nearly 70,000 people was one of the most devastating in recent memory, and some scientists think it was triggered by the construction of the Zipingpu Dam nearby.

• Groundwater extraction:Taking water out of ground, which causes the water table to drop, can also destabilize an existing fault.

• Geothermal power plants:As the geothermal field operations have ramped up, seismic activity has increasedthere.

• Fracking and injection wells:When waste fracking fluid is injected back underground into deep wells. The fluid can seep out and lubricate faults, causing them to slip more easily.

• Skyscrapers:It is about putting too much pressure on the soft sedimentary rock below. This stress is due to all the extra steel and concrete used to make the skyscraper solid enough to withstand earthquakes.

Effects of Earthquakes

The destructive effects of an earthquake can be classified into primary and secondary effects.

Primary effects:They are the immediate damage caused by the quake, such as collapsing buildings, roads and bridges, which may kill many people. Those lucky enough to survive can suffer badly from shock and panic.

Secondary effects: They are the after-effects of the earthquake.

Secondary effects of earthquakes

Tsunamis Soil liquefaction Fire Disease and

famine Landslides

• Fire: earthquakes destroy gas pipes and electric cables, causing fires to spread. Broken water mains prevent the Fires being extinguished. Fires spread very quickly in cities, especially in poor-quality housing areas where wooden buildings are common.

• Tsunamis: an earthquake on the sea floor or close to the coast may cause huge waves.

• Landslides: earthquakes often cause landslides, especially in steep river valleys and areas of weak rocks.

• Disease and famine: fresh water supplies are often cut off causing typhoid and cholera. Lack of shelter and food causes much suffering.

• Soil liquefaction: when soils with a high water content are violently shaken they lose their mechanical strength and behave like a fluid and sobuildings can literally sink.

Mitigation

• The instigation of siting, structural, and land use regulations to decrease existing risk, and prevent future risk.

• Retrofitting existing buildings• Transferring the responsibility of the risk by

getting insurance.• Also educating the public and raising

awareness of earthquake risks

Precautionary MethodsPersonal LevelBefore

• Ensuring that the building in which you live meets construction requirements to withstand earthquakes.

• Secure cupboard doors with latches

• Bolt and secure heavy objects to the floor and walls

• Repair and cracks as earthquakes can turn cracks into ruptures

• Ensuring that the building in

which you live meets construction requirements to withstand earthquakes.

• Secure cupboard doors with latches

• Bolt and secure heavy objects to the floor and walls

• Repair and cracks as earthquakes can turn cracks into ruptures

During

• When indoors stand in doorways and crouch under desks and tables

• When outside stand in large open areas away from light poles, trees, and anything that may fall

• In an automobile drive away from bridges and stop in the safest place possible

After

• Evacuate the building as soon as shaking stops

• Check for injured persons

• Check for safety hazards, broken gas mains, etc.

• Turn off utilities and do

no use any open flames• Keep battery operated

radio and listen for updates

• Wear shoes and protective clothing

• Be prepared for aftershocks

Government level

• Provide a building standard for contractors to allow for sound housing.

• Educating the population on earthquakes as a hazard.

• Putting in place safety regulations such as a standard for the number of emergency exits.

• Providing service teams for search and rescue operations after the earthquake.

Prediction Methods and Techniques

Methods• Examining historical evidence• Monitoring crustal movement and volcanic

activity• Studying the electrical and magnetic changes

in rocks• Watching for unusual behaviour in animals

Developed vs. Developing countriesDeveloping countries tend to suffer more damage than Developed countries because

The buildings in LDC’s are of a poorer quality and are more subject to collapsing during earthquakes, as building codes are not enforcedLack of resources for proper evacuation leading to a greater loss of lifeMore developed countries however will have a greater cost of overall damageThey will also have a smaller amount of casualtiesThere is a general lack of scientific knowledge about disaster preparedness

Earthquake Zoning for Pakistan