EARTHQUAKE AND ITS CAUSES,MITIGATION ETC

2. Contents
 INTRODUCTION
WHAT IS AN EARTHQUAKE?
SEISMIC WAVES
CAUSES
CLASSIFICATION
EFFECTS OF EARTHQUAKE
SPECIAL REFERENCE TO NORTHEAST INDIA
MITIGATION MEASURES
CASE STUDY:NEPAL EARTHQUAKE, 2015
CONCLUSION

3. Introduction
Earthquake is a natural phenomenon. However, it may become
a disaster if somebody is exposed to it.
Earthquake
Hazard
Disaster

4. WHAT IS AN EARTHQUAKE?
Sudden and temporary vibration setup on the earth surface due to
release of some energy(seismic waves).
Usually associated with faulting or breaking of rocks.
They are the earths natural means of releasing stress.

6. Seismic Waves
Response of material to the arrival of energy fronts released by
rupture.
TYPES:-
 P wave or Primary wave.
 S wave or secondary wave.
 L wave or surface wave.

7. P wave or Primary Wave
Longitudinal waves with shorter wavelength and high
frequency.
Travels through both solid and liquid.

8. S wave or secondary wave:-
 Transverse wave with shorter wavelength and high
frequency.
 Can move through only solid medium.

9. L wave or surface wave:-
 Transverse wave with longest wavelength and low
frequency.
 Developed in immediate neighbourhood of the
epicenter.

10. Causes of earthquake
Earthquake originates due to various reasons
which fall into two major categories. They are:
Tectonic
Non-tectonic

11. Tectonic Causes
 Caused by faulting or folding in the crust.
 Elastic rebound theory propounded by H.F.Reid (1906) is widely
acclaimed as a satisfactory explanation.

12. Non Tectonic
This includes those associated with the geological agents operating
upon the surface of the earth, volcanic eruptions as well as with the
collapse of sub- terranean cavities.
a) Surface causes: perceptible variations may set up by-
• the dashing waves and crashing breakers along the sea shore
• rock falls and avalanches in mountains, large landslides etc.
b) Volcanic causes: Volcanic earthquakes occur around active
volcanoes mainly due to explosive eruption and also due to the
hydraulic shocks of magma that forcibly fills underground chambers
and channels.

13. Classification of earthquake
Earthquakes are classified on the following basis:
Cause
Depth of focus
Intensity and magnitude

14. CAUSE OF
ORIGIN
tectonic
Non
tectonic
Surface
cause
Volcanic
cause
Collapse of
cavity roof

15. Depth of focus
Surface (<10km)
Shallow
focus(10-50 km)
Intermediate
focus(50-300
km)
Deep focus(300-
500 km)

16. CLASS MAGNITUDE
A >7.8
B 7 – 7.7
C 6 - 7.7
D 5.3 - 6
E < 5.3
On the basis of magnitude

17. Effects of earthquake
Primary Effects:-
1)Creation of slopes 2)Warping of strata

18. 3)Subsidence or emergence of coastlines 4)Changes in the coarse of stream

19. Secondary effect:-
1) Buildings are damaged 2) Roads are fissured, railway lines are
twisted and bridges are destroyed

20. 3)Landslides occur in hilly regions 4) Tsunamis may be as high as 20m

21. MITIGATION MEASURES
BEFORE AN EARTHQUAKE:
• Repair defective electrical wiring
• Store bottle, foods, glass, china clay and other breakable in low
shelves or in cabinets
• Spread awareness on earthquake
• Locate safe spot on each room
• Install flexible pipes fitting to avoid gas or waste leak

22. During AN EARTHQUAKE :
1) If indoor:
• Take cover under a place of heavy furniture or against inside a wall, stay away
from glass, windows
2) If outdoor:
• Find a clear spot and move into open area away from buildings, trees,
electrical
3)If in a moving vehicle:
• Stop as quickly as safety permits and avoid stopping under or near buildings,
trees etc.

23. After AN EARTHQUAKE :
• Be prepared for after shocks
• Help injured or trapped persons and give first aid where appropriate
• Stay out of damaged buildings and return home only when authorities say it is
safe

24. Earthquake: Special Reference to NE India
• Earthquake occurs frequently due to the
presence of-
• A major earthquake occurred in Meghalaya as a
result of Dauki fault on 12th June 1987.
• In upper Assam a heavy earthquake occurred
due to present of Po-Chu Fault on 15th August
1950.

25. PLACE YEAR MAGNITUDE REMARK
CACHAR MARCH 21, 1869 7.8 NUMEROUS EARTH FISSURES
AND CRATERS
SHILLONG PLATEAU June 12,1891 8.7 About 1542 people died
Dhubri July 2,1930 7.1 Railway lines, culverts and
bridges cracked
Arunachal July7,1947 7.5 Destruction of Property
Upper Assam August 15,1950 8.7 About 1520 people died, one
of the biggest known quake in
the history.
Manipur Burma Border March 21, 1954 7.4 Property Damaged
Sikkim September 18,2011 6.9 Destruction of Property, loss
of lives, 67 dead.

26. CASE STUDY
NEPAL
EARTHQUAKE
TH

27. INTRODUCTION
 Experienced a 7.8 magnitude earthquake on 25th April, 2015.
• Its epicenter was east of Gorkha District at Barpak, Gorkha.
• About 22k people were injured and killed over 8k in addition causing
infrastructural damage
• Triggered an avalanche on Mount Everest, killing 21, making April 25,
2015 the deadliest day on the mountain in history.
• Intermittent electricity, cell tower and landline outages meant a lot of
people were stranded without a means of contracting help.

28. CAUSES:
• Caused by a certain thrust or release of built up stress along the
major fault line, where the Indian plate diving underneath the
Eurasian plate

29. DAMAGES:
• Killed over 8k people and injured more than 22k
• Caused significant infrastructural damages
• Triggered huge avalanche in the Langtang valley, more than 250
people were missing.
• Thousands of people were made homeless with the entire village
flattened.
• Centuries-old buildings were destroyed at UNESCO world heritage
sites in Kathmandu Valley including the Changu Narayan Temple, the
Bhaktapur Durbar Square and the Swayambhunath Stupa.

31. ECONOMIC DAMAGES
Overall damage is estimated to be at about $10 billion (according to
the Nepal govt.
Estimated cost for rebuilding homes, roads and bridges alone could
run up to $5 billion dollar.
Damages 14 hydropower projects out of the atleast 23 operational
ones. This means a loss of 150 Mw of power
Owes $1.5 billion to the World Bank, $1.44 billion to the Asian
Development Bank and $54 million to IMF.

33. CONCLUSION
• Despite claims