Mechanism and distribution of earthquake
Published on 31 Jan 2025
Earthquake is the sudden release of energy upon the movement of continental plates which generates seismic waves that travel in all directions.
Types
Earthquake types can be- Fault Zones, Tectonic Earthquakes, Volcanic Earthquake, and Human Induced Earthquakes.
Distribution
Circum pacific belt: Known as ring of fire. Experiences frequent and powerful earthquakes due to complex tectonic plate interactions encircling the Pacific Ocean. - Accounts for 80% of earthquakes.
Example: Alaska Earthquake of 1991
Trans Eurasian Belt: Spanning Europe and Asia, is characterized by ongoing seismic activity resulting from the complex interactions of tectonic plates in the region. Accounts for 15% of earthquake.
Example: 2023 Turkey earthquake
Mid oceanic ridges: Region of shallow earthquake.
Example: Earthquake in mid Atlantic ridge
Intra-plate earthquakes: Because of the reactivation of ancient faults.
Example: Gujarat earthquake 2001
Role of seismic waves in understanding the earth’s interior
Earthquake wave or seismic wave are basically of two types- Body waves and Surface waves .Body waves is again of two kinds – S wave and P wave. While P waves passes through both solids and liquids, S waves passes only through solids. This character of S wave helped to understand the interior of earth.
Absence of waves: Absence of S waves beyond 1050 degree and P waves between 1050 – 1450 highlighted the distinction between solid mantle and liquid outer core.
Differential speed: Seismic waves travel at different speeds through different materials. By observing changes in velocity of the wave, density of the earth as a whole can be estimated.
Change in direction: By observing changes in direction of propagation of waves, nature of different layers can be identified.
Observations made from the nature of seismic waves
Liquid nature of outer core: As S wave do not pass through outer core, it is liquid in nature.
Change of medium: Deflection of P at the boundary between inner core and outer core showed the change in medium.
Velocity and time: By measuring time taken for waves to reach throughout earth, velocity structure of earth can be identified.
Presence of various layers: Shift in velocity as moving deeper into the earth indicate the presence of interface between earth’s various layers, each made up of distinct materials.