An earthquake (also known as a quake, tremor or temblor) is is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to the people around and destroy whole cities.
2. An earthquake (also known as
a quake, tremor or temblor) is is the shaking of the
surface of the Earth, resulting from the sudden
release of energy in the Earth's lithosphere that
creates seismic waves. Earthquakes can range in size
from those that are so weak that they cannot be felt to
those violent enough to the people around and
destroy whole cities.
3. The seismicity or seismic activity of an area refers to
the frequency, type and size of earthquakes
experienced over a period of time.
At the Earth's surface, earthquakes manifest
themselves by shaking and sometimes displacement
of the ground. When the epicenter of a large
earthquake is located offshore, the seabed may be
displaced sufficiently to cause a tsunami.
4. Earthquakes are usually caused when rock
underground suddenly breaks along a fault. This
sudden release of energy causes the seismic waves
that make the ground shake. When two blocks of rock
or two plates are rubbing against each other, they
stick a little. They don't just slide smoothly; the rocks
catch on each other. The rocks are still pushing
against each other, but not moving.
5. After a while, the rocks break because of all the
pressure that's built up. When the rocks break, the
earthquake occurs. During the earthquake and
afterward, the plates or blocks of rock start moving,
and they continue to move until they get stuck again.
The spot underground where the rock breaks is called
the focus of the earthquake. The place right above the
focus (on top of the ground) is called the epicenter of
the earthquake.
7. Earthquake-like seismic waves can also be caused by
explosions underground. These explosions may be set
off to break rock while making tunnels for roads,
railroads, subways, or mines. These explosions,
however, don't cause very strong seismic waves.
Sometimes seismic waves occur when the roof or walls
of a mine collapse. The largest underground explosions,
from tests of nuclear warheads (bombs), can create
seismic waves very much like large earthquakes. This
fact has been exploited as a means to enforce the global
nuclear test ban, because no nuclear warhead can be
detonated on earth without producing such seismic
waves.
8. Most earthquakes occur along the edge of
the oceanic and continental plates. The earth's crust
is made up of several pieces, called plates. The plates
under the oceans are called oceanic plates and the rest
are continental plates. The plates are moved around
by the motion of a deeper part of the earth
(the mantle) that lies underneath the crust.
These plates are always bumping into each other,
pulling away from each other, or past each other.
Earthquakes usually occur where two plates are
running into each other or sliding past each other.
9. The impact of an earthquake will be measured
by using a seismometer. A seismometer detects
the vibrations caused by an earthquake. It
plots these vibrations on a seismograph. The
strength, or magnitude, of an earthquake is
measured using the Richter scale. The Richter
scale is numbered 0-10.
12. Earthquakes measuring just one or two on the scale
are very common and can happen everyday in places
like San Francisco. These earthquakes are so small
that people cannot feel them, they can only be picked
up by a seismometer.
Earthquakes measuring around 7 or 8 on the Richter
scale can be devastating. The earthquake in China's
south-western Sichuan province in May 2008
measured 7.8 on the Richter scale.
13. Earthquake prediction is a branch of the
science of seismology concerned with the
specification of the time, location,
and magnitude of future earthquakes within
stated limits, and particularly "the
determination of parameters for the next strong
earthquake to occur in a region.
14. Earthquake prediction is sometimes distinguished
from earthquake forecasting, which can be defined as
the probabilistic assessment of general earthquake
hazard, including the frequency and magnitude of
damaging earthquakes in a given area over years or
decades. Prediction can be further distinguished
from earthquake warning systems, which upon
detection of an earthquake, provide a real-time
warning of seconds to neighbouring regions that
might be affected.
15. There are four different types of earthquakes:
Tectonic
Volcanic
Collapse and
Explosion.
16. (Cont..)
A tectonic earthquake is one that occurs when the
earth's crust breaks due to geological forces on
rocks and adjoining plates that cause physical and
chemical changes.
A volcanic earthquake is any earthquake that
results from tectonic forces which occur in
conjunction with volcanic activity.
17. (Cont..)
A collapse earthquake are small earthquakes in
underground caverns and mines that are caused by
seismic waves produced from the explosion of rock
on the surface.
An explosion earthquake is an earthquake that is the
result of the detonation of a nuclear and/or chemical
device.
18. Earthquakes may be categorized into the following
three types based on the depth of the focus/hypocenter
of the earthquake.
Shallow or Normal: The focus point of the earthquake
is less than 60kms.
Intermediate: The focus/hypocenter point of the
earthquake is between 60kms and 300kms.
Deep: The focus point of this type of earthquake is
between 300kms to 700kms.
19. Earthquake refers to a sudden violent shaking and
vibration of the earth surface resulting from
underground movement along a fault plane or from
volcanic activity. Earthquakes can cause serious
destruction to property, injury to people and even kills.
It happens when there is sudden movement or breaking
of the tectonic plates.
20. Tectonic plates are huge rock pieces within the earth’s
crust. The plates are usually marked by fractures or
fault lines formed when the plates tear apart or slide or
collide past each other. This results in a change of the
earth’s interior masses which send out powerful shock
waves with enough force to alter the surface of the
earth. The shock waves can thrust up cliffs and open
huge cracks on the ground leading to an earthquake
event.
21. Things that cause earthquakes
Groundwater extraction – decrease in pore pressure
Groundwater – increase in pore pressure
Heavy rain
Building dams
Stress transfer
Surface quarrying
Volcanoes
Explosions
Deep penetrating bombs
Deforestation
Climate change
Geothermal energy
22. Loss of Property: Severe earthquakes reduce to rubble
human structures ranging from huts to palaces and
single storey to multi storey buildings. Even pipelines
lay under the ground and railway lines are damaged or
displaced. The best example of this type of damage is
Koyana earthquake in 1970.
Loss of Life: An Earthquake tremor of a few seconds
takes the lives of thousands of people. Many people
have been rendered homeless or suffered injuries in
various ways.
23. Changes in the course of rivers: On account of the
impact of earthquakes, sometimes rivers also change
their course. Consequently, when floods come they
play havoc with people's lives.
Cracks in Earth Crust: Earthquake cause cracks in
earth's crust anywhere in fields, roads, parks and even
hills. They are thus rendered useless. The San
Andreas fault in California, U.S.A. was created in a
similar manner.
24. Tsunamis: The earthquakes in the sea generate
massive waves called Tsunami in Japanese language.
It sometimes rises to the height of 20-25 metres. It
causes great damage to life and property of people
living in coastal areas as well as to tourists. Tsunami
caused by an earthquake in the sea near Sumatra on
26th Dec, 2004 hit south east Asian countries
including India and Sri Lanka. There was heavy
damage in these countries. More than 3 lakh people
died.
25. About 90% of the world's earthquakes and 81% of
the world's largest earthquakes occur along the Ring
of Fire.
26. Geographical Distribution of Earthquakes
It is true that the earthquakes can happen in any part of
the world. But in the areas of faulting and folding or of
crustal weakness, the frequency of earthquakes is more
than anywhere else. The earthquakes are concentrated
in two main belts.
Circum-Pacific Earthquake Belt
Mediterranean-Asia Earthquake Belt
27. This belt includes all the coastal areas around the vast
Pacific Ocean. This belt extends as an isostatically
sensitive zone through the coasts of Alaska, Aleutian
Islands, Japan, Philippines, New Zealand, North and
South America. This zone accounts for 68% of all
earthquakes on the surface of the earth. The most
talked about earthquake areas in this zone include
Japan, Chile, California and Mexico.
28. This belt begins from Alps mountain range and
passes through Turkey, Caucasus Range, Iran,
Iraq, Himalayan mountains and Tibet to China.
One of its branches passes through Mongolia
and Lake Baikal and another branch extends to
Myanmar. About 31% of world's earthquakes
are located in this region.
29. These include Northern Africa and Rift
Valley areas of the Red Sea and the
Dead Sea. In addition to these, the
ocean ridges are also active
earthquake zones.
30. Ministry of Earth Sciences is nodal agency of Government of
India dealing with various activities in the field of seismology
and allied disciplines. The major activities currently being
pursued by the National Center for Seismology include:
Earthquake monitoring on 24X7 basis, including real time
seismic monitoring for early warning of tsunamis,
Operation and maintenance of national seismological network
and local networks
Seismological data centre and information services,
Seismic hazard and risk related studies
Field studies for aftershock monitoring, site response studies
Earthquake processes and modelling, etc
31. The vulnerability to earthquake disaster has increased in
India due to unplanned urbanization as well as substandard
construction.
India has experienced several destructive earthquakes of
high intensity in the recent past years. Some of the major
earthquakes include:
• Uttarkashi - 1991
• Latur - 1993
• Jabalpur - 1997
• Chamolli - 1999
• Kutch - 2001
34. The Indian subcontinent has a history of
devastating earthquakes. The major reason for
the high frequency and intensity of the
earthquakes is that the Indian plate is driving
into Asia at a rate of approximately
47 mm/year. Geographical statistics of India
show that almost 54% of the land is vulnerable
to earthquakes.
35. The latest version of seismic zoning map of
India given in the earthquake resistant design
code of India [IS 1893 (Part 1) 2002] assigns
four levels of seismicity for India in terms of
zone factors. In other words, the earthquake
zoning map of India divides India into 4
seismic zones (Zone 2, 3, 4 and 5) unlike its
previous version, which consisted of five
zones for the country.
36. The Himalayan mountain areas and its
foothills are vulnerable to earthquakes. The
Gangetic plains and north eastern part of India
are prone to earthquake to some extent. The
earthquake prone zones of India are
represented in the Indian map. The intensity of
earthquakes is less in zone I relatively high in
zone V
38. The IS code assigns zone factor of 0.36 for Zone 5.
Structural designers use this factor for earthquake
resistant design of structures in Zone 5. The zone factor
of 0.36 is indicative of effective (zero period) level
earthquake in this zone. It is referred to as the Very
High Damage Risk Zone. The region of Kashmir, the
Western and Central Himalayas, North and Middle
Bihar, the North-East Indian region, the Rann of Kutch
and the Andaman and Nicobar group of islands fall in
this zone. Generally, the areas having trap rock or
basaltic rock are prone to earthquakes.
39. The IS code assigns zone factor of 0.24 for Zone 4
Jammu and Kashmir, Himachal Pradesh, Uttarakhand,
Sikkim, the parts of Indo-Gangetic plains (North
Punjab, Chandigarh, Western Uttar Pradesh, North
Bengal, Sundarbans) and the capital of the country
Delhi fall in Zone 4. In Maharashtra, the Patan area is
also in zone no-4. In Bihar the northern part of the
states, Near the border of India and Nepal, is also in
zone no-4.
40. The IS code assigns zone factor of 0.16 for
Zone 3. The region includes the Andaman and
Nicobar Islands, some parts of Kashmir and
western Himalayas, Kerala, Goa,
Lakshadweep Islands some parts of Punjab,
Rajasthan, Madhya Pradesh, Bihar, Jharkhand,
Chhattisgarh, Maharashtra, Orissa, Andhra
Pradesh.
41. ZONE -2
The zone is referred as low intensity zone/low damage
risk zone. It includes some parts of central Andhra
Pradesh, Karnataka, coastal regions of Orissa and
Tamilnadu.
ZONE - 1
This zone may be called as the lowest risk zone. It
includes the central region of Karnataka, Andhra
Pradesh, Orissa, coastal regions of Maharashtra, Kerala
and major parts of Gujarat (except Rann of Kutch
region).
43. Avoid construction of house in areas which are highly prone
to earthquakes. The ground should be stable, consisting of
solid rocks, rather than sandy or muddy soil, so as to
prevent sinking or collapsing of taller buildings.
Building constructed on areas prone to earthquakes should
be equipped with seismic retrofitting so as to prevent their
collapse.
• Steel used should be flexible.
• The base of the building should contain shock absorbing
rubber blocks
• Fire proof materials should be used while constructing
buildings.
44. Gas pipes and electricity supplies should be
automatically shut when an earthquake strikes.
This prevents outbreaks.
The public should be alerted in advance about
the striking of earthquake striking of
earthquakes as and when detected in
seismograph recording.
The dumping of fluid waste by injecting it in
deep wells should be avoided.
45. Carrying off nuclear blasts for testing leads to
development of tremors in the earth. This could
lead to earthquakes.
Digging of excessive bore wells can also lead to
earthquake as the ground water table levels
decreases.
People inhabited in earthquake prone areas should
be made aware to take preventive measures in
order to save themselves when an earthquakes
strikes.
46. Structural defects in buildings such as cracks in
ceiling or foundations should be repaired promptly.
Large items like T.V, computers, etc., must be secured
properly.
The book cases, tall furniture and showcases should
be bolted to the walls.
Heavy items such as pictures and mirrors should be
fixed away from the beds and seating arrangements.