earthquake its causes and measurement

1. Disaster management
&mitigation
Earthquakes

2. What is earthquake?
An earthquake is the shaking of the tectonic plates ,
resulting from the sudden release of energy in the
Earth's lithosphere that creates seismic waves.

3. What is a tectonic plate?
A tectonic plate (also called lithospheric
plate) is a massive, irregularly shaped slab
of solid rock, generally composed of both
continental and oceanic lithosphere. Plate
size can vary greatly, from a few hundred
to thousands of kilometers across, the
Pacific and Antarctic Plates are among the
largest.

4. • Focus : it is the point where the earthquake starts.it is also called as
hypocenter
• Epicentre : it is the point perpendicular to the focus

5. Causes of Earthquake
• Tectonic Plate movement
• Volcanic activities
• Underground explosions

6. Tectonic plate
movement
Tectonic Plate movements cause the
majority of the earthquakes. The
movements occur because the plates float
on the hotter and denser rock of the mantle

7. Volcanic
activities
Apart from tectonic plate movements,
volcanic activity can significantly
cause massive earthquakes.
Earthquakes normally accompany
escaping magma as it rises to the crust
during a volcanic eruption. This is
mainly due to the sudden
displacement and shaking of
underground rocks.

8. Underground explosions
Seismic waves (wave shocks) similar to the ones causing earthquakes
can be generated by underground explosions. These explosions can be as
a result of underground mining or during the construction of railroads,
subways, or underground tunnels. However, some of the seismic waves
produced by these activities are not as strong as those produced by real
earthquakes.

9. Measurement of
an earthquake
Seismic waves are the vibrations
from earthquakes that travel
through the Earth, they are
recorded on instruments called
seismographs.

10. Richter magnitude scale
The Richter magnitude scale assigns
a magnitude number to quantify the
size of an earthquake
The potential hazard corresponding
to magnitude is as shown in figure