Earthquakes are caused by the movement of tectonic plates underground. There are three types of waves produced by earthquakes: P-waves, which move through solid material; S-waves, which move perpendicular to the direction of the wave; and surface waves, which travel along the Earth's surface. Earthquakes are measured using seismographs, which record the direction and timing of the different waves, and scales like the Richter scale and Mercalli scale, which measure the intensity and effects of the earthquake. Major historical earthquakes include ones in Shansi, China in 1556 that killed 83,000 people and in Kolkata in 1737 that killed 300,000 people.

3. ANATOMY OF AN EARTHQUAKE
POWERFUL VIBRATIONS ARE RELEASED DUE TO
THE MOVEMENT OF THE EARTHS PLATES.
THESE VIBRATIONS TRAVEL IN THREE TYPES OF
WAVES:
P-WAVES OR PRIMARY WAVES
S-WAVES OR SECONDARY WAVES OR SHEAR
WAVES
L-WAVES OR LONG WAVES OR SURFACE WAVES

4. PRIMARY WAVES
 PARTICLES VIBRATE IN
THE DIRECTION OF
WAVES
 CAN PASS THROUGH
SOLID LIGUID AND
GASES
 FIRST TO BE
RECORDED ON
SEISMOGRAPH

5. SECONDARY OR SHEAR WAVES
 PARTICLES VIBRATE AT
RIGHT ANGLES TO
THE DIRECTION OF
MOVEMENT OF THE
WAVE
 CANNOT PASS
THROUGH LIQUIDS
 RECORDED AFTER P
WAVES ON
SEISMOGRAPH

6. LONG OR SURFACE WAVES
 TRAVEL ALONG THE
SURFACE OF THE
EARTH
 RECORDED AFTER
PRIMARY AND
SECONDARY WAVES
 TWO TYPES OF L
WAVES ARE:LOVE
WAVES AND RAYLEIGH
WAVES

8. MEASUREMENTS
SEISMOGRAPH
RICHTER SCALE
MERICALLI SCALE

9. SEISMOGRAPH
 TO MEASURE DIRECTION
OF MOVEMENT OF WAVES
 IT HAS A PEN ATTACHED
TO IT THAT RECORDS THE
MOVEMENTS OF THE
WAVES ON A STRIP OF
PAPER.
 ALSO CALCULATES THE
DIFFERENCE BETWEEN
THE RECORDING STATION
AND EPICENTRE BY
CALCULATING THE
DIFFERENCE IN ARRIVAL
OF P AND S WAVES.

10. RICHTER SCALE
 TO MEASURE
INTENSITY (THE
AMOUNT OF ENERGY
RELEASED DURING AN
EARTHQUAKE)
 MEASURES THE
POWER OF AN
EARTHQUAKE ON A
SCALE OF ONE TO
NINE

11. MERICALLI SCALE
 TO MEASURE
INTENSITY (THE
AMOUNT OF ENERGY
RELEASED DURING AN
EARTHQUAKE)
 GRADES THE
EARTHQUAKES ON
THE BASIS OF
OBSERVED EFFECTS
ON A -12 POINT SCALE

12. SHANSHI (CHINA -1556),830000
KILLED

13. KOLKATA -1737,300000 KILLED

14. CONSTRUCTIVE EFFECTS OF
EARTHQUAKES
ENERGY RELEASE:
i. EARTH RELEASES ITS
STORED UP ENERGY
ii. ENERGY RELEASE
HELPS IN KEEPING
THE EARTH IN A
PROPER SHAPE

15. LANDFORMS
IN THE OCEAN BELTS
THE EARTHS CRUST
MAY BE EITHER
RAISED OR LOWERED
DUE TO VERTICAL OR
LATERAL
DISPLACEMENT.