What are Earthquakes? Elaborate on the various causes and consequences of earthquakes.

An earth quake can be defined as a sudden violent shaking of the ground as a result of movements

in the earth’s crust or volcanic action. These movements result in the release of energy along a fault

and cause the earth to shake. An earthquake, like volcanoes is a type of endogenic processes.

Causes of Earthquakes:

• Most earthquakes are causally related to compressional or tensional stresses built up at the

margins of the huge moving lithospheric plates.

• The immediate cause of most shallow earthquakes is the sudden release of stress along a fault,

or fracture in the earth’s crust.

• Sudden slipping of rock formations along faults and fractures in the earth’s crust happen due to

constant change in volume and density of rocks due to intense temperature and pressure in the

earth’s interior.

• Volcanic activity also can cause an earthquake but the earthquakes of volcanic origin are

generally less severe and more limited in extent than those caused by fracturing of the earth’s

crust.

• Earthquakes occur most often along geologic faults, narrow zones where rock masses move in

relation to one another. The major fault lines of the world are located at the fringes of the huge

tectonic plates that make up Earth’s crust.

• Plate tectonics: Slipping of land along the fault line along, convergent, divergent and transform

boundaries cause earthquakes. Example: San Andreas Fault is a transform fault where Pacific

plate and North American plate move horizontally relative to each other causing earthquakes

along the fault lines.

Human Induced Earthquakes

• Some earthquakes are human induced.

• Earthquakes in the reservoir region, mining sites etc. are human induced.

Some Earthquake- inducing anthropogenic activities

• Deep mining

• Underground nuclear tests

• Reservoir induced seismicity (RIS)

• Extraction of fossil fuels

• Groundwater extraction

• Artificial induction

• In fluid injection, the slip is thought to be induced by premature release of elastic strain, as in

the case of tectonic earthquakes, after fault surfaces are lubricated by the liquid.

EFFECTS OF EARTHQUAKE

Earthquake is a natural hazard. The following are the immediate hazardous effects of earthquake:

1. (i) Ground Shaking

2. (ii) Differential ground settlement

3. (iii) Land and mud slides

4. (iv) Soil liquefaction

5. (v) Ground lurching

6. (vi) Avalanches

7. (vii) Ground displacement

8. (viii) Floods from dam and levee failures

9. (ix) Fires

10. (x) Structural collapse

11. (xi) Falling objects

12. (xii) Tsunami