K. SameeraK.K.R.Gowtham Concept School

Kakinada

Earthquakes

Any sudden movement of the earth’s surface is called Earthquake.

Focus & Epicentre

• The point from which an earthquake originates is called the ‘focus’ and the point on the earths surface, directly above this is called the ‘Epicentre’.

Types of sysmic waves

Types of Seismic waves.(Earth waves)

1.P-Waves (Primary Wave)

2.S-Waves (Secondary Wave)

3.L-Waves (Long/Love Wave)

4.R-Waves (Rayleigh Wave)

P - WAVE

• Primary(P) waves cause the particles of rock to vibrate backwards and forwards in the wave direction.

S - WAVE

• Secondary(S) waves cause the particles to oscillate at right angles to the wave direction.

L - WAVE

• When P and S waves reach the surface they are converted into long(L) waves.• They cause the particles to travel in transverse horizontal motion, perpendicular to the

direction of propagation and generally parallel to the Earth’s surface.• It is the L waves that produce the most violent shocks and the resultant destruction.

• Motion is both in the direction of propagation and perpendicular (in a vertical plane), and “phased” so that the motion is generally elliptical – either prograde or retrograde.

RAYLEIGH WAVE

SEISMOGRAPH

• The instrument used to detect and record the seismic waves is called “Seismograph” and the record, which appears like a graph is called “Seismogram.”

Richter Scale

• Richter scale is used to measure the magnitude of the earthquakes. A magnitude of 2 is rarely felt, while a magnitude of 7 indicates the lower limit of an earthquake that has devastating effect over a large area.

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