This document discusses earthquakes and seismic waves. It defines an earthquake as any sudden movement of the earth's surface. The focus is where the earthquake originates underground, and the epicenter is directly above on the surface. There are four main types of seismic waves: P-waves, S-waves, L-waves, and R-waves, which each cause different particle motions. The Richter scale is used to measure earthquake magnitudes from 2 to 7, with higher magnitudes capable of greater devastation.

1. K. Sameera
K.K.R.Gowtham Concept School
Kakinada

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

4. 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’.

5. Types of sysmic waves

6. 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)

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

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

9. 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.

10. RAYLEIGH WAVE
• 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.

11. 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.”

13. 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.

14. THE END