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
• 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
• 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