THEORIES OF TECHTONIC EARTHQUAKE

THEORIES OF TECHTONIC EARTHQUAKE:-

Various causes of tectonic earthquake occurring on earth surface
have been explained by the scientists and geologists on the basis of
following theories:
1. ELASTIC REBOUND THEORY
2. THEORY OF PLATE TECTONICS
ELASTIC REBOUND THEORY
• According to this theory, earthquakes are caused by gradual
accumulation and release of stress and strain in layers of rocks
forming the earth’s crust.
• In this we consider an individual rock unit in which
continuously increasing shear strain is acting.
• Firstly the condition is of no strain.
• When the stress exceeds the elastic limit, a crack or fracture is
developed.
• Due to friction between rock masses there is no movement,
but the blocks are distorted and blocks are said to be strained.
• In order to reduce the strain to a minimum, the two distorted
and fractured blocks tends to slip off from one another to a
position of no strain. This is known as ELASTIC REBOUND.

THEORY OF TECTONIC PLATES
➢ According to this theory, the outer most layer of earth’s surface
consist of major tectonic plates.
➢ These plates comprising outer crust and some portion of
mantle are floating on hot molten outer core.
➢ The sliding of earth blocks or layers take place in pieces called
tectonic plate.
➢ Earthquake occur due to interplate action or movement of
plates in different direction.
➢ There are three type of interplate actions:
a) When two plates move away from one another and rifts are
created, is termed as DIVERGENT BOUNDARY.
b) When two plates move towards each other and one plate sinks
under the another, is termed as CONVERGENT BOUNDARY.
c) When two plates move side by side or horizontally slide past one
another, is termed as TRANSFORM BOUNDARY.

FAULTS
➢ A Fault is defined as a fracture or a crack, in the rocks, along
which definite movement has taken place.
➢ Earthquake are caused due to sudden slip at the faults which
result in shaking of the earth.
TERMINOLOGY RELATED TO FAULTS
1) FAULT PLANE
• The plane splitting the rock into two blocks along which
movement occurs is known as fault plane.
2) DIP AND STRIKE OF THE FAULT
• The inclination of the fault plane with the horizontal is
called as DIP OF THE FAULT
• The direction perpendicular to dip is called STRIKE OF THE
FAULT.
3) HADE
• It is the angle which a fault make with the vertical.
4) THROW AND HEAVE
• The total vertical displacement in a fault is known as
throw of fault.
• The total horizontal displacement is known as heave of
the fault.

5) SLIP OF THE FAULT
• The relative displacement of two points which were
initially against each other is known as slip of fault.
• Maximum displacement is NET SLIP.
• Displacement along the strike is STRIKE SLIP.
• Displacement along dip of the fault plane is called as DIP
SLIP.
6) HANGING WALL AND FOOT WALL
In case of an inclined fault plane, the block which rests over the
other is known as HANGING WALL, the underlying block is
called as FOOT WALL.