1) An earthquake is caused by a sudden release of energy in the Earth's crust that creates seismic waves. 2) Earthquakes occur along fault lines in the Earth's lithosphere where tectonic plates meet. As the plates slowly move and push against each other, stress builds up until the fault slips, releasing energy in the form of seismic waves. 3) Earthquakes are measured on the Richter scale based on the logarithm of the wave amplitude as recorded by a seismograph. The magnitude indicates the amount of energy released by an earthquake.

1. MODULE 2
EARTHQUAKE
LANDSLIDE

2. What is Earthquake?
An earthquake 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
The seismic activity of an area refers to the frequency,
type and size of earthquakes experienced over a period of
time

3. • For example: If you throw
stone in a pond of still water,
series of waves are produced
on the surface of water, these
waves spread out in all
directions from the point
where the stone strikes the
water.
• similarly, any sudden
disturbances in the earth’s
crust may produce vibration
in the crust which travel in
all direction from point of
disturbances.

4.  The earth has four major layers: the inner core, outer core,
mantle and crust
 The crust and the top of the mantle make up
LITHOSPHERE

5. • LITHOSPHERE is made up of many pieces like a
puzzle covering the surface of the earth, TECTONIC
PLATES
• And, these puzzle pieces keep slowly moving around,
sliding past one another and bumping into each other
• The edges of the plates are called the plate boundaries

6. • The plate boundaries are made up of many faults, and
most of the earthquakes around the world occur on
these faults.
“A Fault is a break or fracture b/w two blocks of rocks
in response to stress.”
• Since the edges of the plates are rough, they get
stuck while the rest of the plate keeps moving.
• Finally, when the plate has moved far enough, the
edges unstick on one of the faults and there is an
earthquake.

7. Why does the earth shake when there
is an earthquake?
• when the edges of faults are stuck together, and the
rest of the block is moving, the energy that would
normally cause the blocks to slide past one another is
being stored up.
• When the force of the moving blocks finally
overcomes the friction of the jagged edges of the fault
and it unsticks, all that stored up energy is released.

8. • The energy radiates outward from the fault in
all directions in the form of seismic waves.
• The seismic waves shake the earth as they
move through it, and when the waves reach the
earth’s surface, they shake the ground and
anything on it.

9. TERMS
• Focus (Hypocenter): Focus
is the point on the fault
where rupture occurs and the
location from which seismic
waves are released.
• Epicenter: Epicenter is the
point on the earth’s surface
that is directly above the
focus ,the point where an
earthquake or underground
explosion originates

10. • Fault Line: A Fault line is
the surface trace of a fault,
the line of intersection
between the earth’s surface.
• Fault plane: The plane in
which the fault occurred.
• Fault Scrap: A Fault scrap
is the topographic
expression of faulting
attributed to the
displacement of the land
surface by movement along
faults.

11. Classification Of Faults
• Normal fault:
Happen in areas where the rocks are pulling apart
(tensile forces) so that the rocky crust of an area is
able to take up more space.
The rock on one side of the fault is moved down
relative to the rock on the other side of the fault.
Normal faults will not make an overhanging rock
edge.
In a normal fault it is likely that you could walk on an
exposed area of the fault.

12. • Reverse fault:
Reverse faults happen in areas where the rocks are
pushed together (compression forces) so that the
rocky crust of an area must take up less space.
The rock on one side of the fault is pushed up
relative to rock on the other side.
In a reverse fault the exposed area of the fault is often
an Overhang. Thus you could not walk on it.

13. • Strike-slip fault:
 Left-lateral strike-slip fault : It is one on which the
displacement of the far block is to the left when
viewed from either side.
 Right-lateral strike-slip fault: It is one on which
the displacement of the far block is to the right when
viewed from either side.

15. Over hanging rock ledge

16. Major causes of earthquakes
Tectonic causes
Volcanic causes
Explosion

17. Tectonic cause
• Structural disturbances resulting in the parts of the
lithosphere is the main cause of this type of earthquake.
• Most of the disastrous earthquakes belong to this
category and occur in areas of great faults and fractures.
• Sudden yielding to strain produced on the rocks of
accumulating stress causes displacements especially
along old fault zones known as great transform faults

18. Volcanic cause:
Volcanic eruptions produce earthquakes. Earthquakes may
precede, accompany and frequently follow volcanic eruptions.
They are caused by sudden displacements of lava within or
beneath the earth crust.

19.  The volcanoes which are most likely to explode violently are
those which produce acidic lava.
 Acidic lava cools and sets very quickly upon contact with the
air.
 This tends to chock the volcanic vent and block the further
escape of pressure.
 That is, the lava solidified before it could flow down the sides.
 Instead it forms a spine of solid rock within the volcano vent.
 The only way in which such a blockage can be removed is by
the build up of pressure to the point at which the blockage is
literally exploded out of the way
 When extraordinary levels of pressure develop, the resultant
explosion can be devastating, producing an earthquake of
considerable magnitude.

20. Explosion
 earthquake which results of nuclear and chemical devices.
 This occurs when enormous energy, nuclear energy is
released during underground nuclear explosions, which
when bottled within, increases a thousand times more than
the atmospheric pressure, in intensity.

21. Types of Earthquakes
• 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.
• A collapse earthquake is 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

22. Based on location
INTERPLATE INTRAPLATE
occurs at a plate boundary occurs in the interior of a tectonic plate
Recurrence time is less Recurrence time is longer
Interplate Earthquakes are recognized at surface Intraplate earthquakes are rarely recognized at
the surface. This is because the faults are buried
under several kilometers of surface materials &
the longer recurrence intervals allow any surface
expression of faulting to be eroded.
Interplate earthquakes release less stress & are
dissipated quickly because of weaker rocks near
plate boundaries
Intraplate earthquakes release more stress. The
ground motion caused by intraplate earthquake
seismic waves dissipates more slowly. The
strong, coherent rocks that make up the interiors
of plates transmit seismic energy more
efficiently over longer distances than the less
coherent, weaker rocks near plate boundaries

23. Based on focal depth
SHALLOW DEEP
Shallow-focus earthquakes occur at depths less
than 70 km
Deep-focus earthquakes occur at greater focal
depths of 300 – 700 km.
Shallow focus earthquakes are found within the
earth’s outer crustal layer
Deep focus earthquakes occur within the deeper
subduction zones of the earth
Shallow focus earthquakes are of smaller
magnitudes, of a range 1 to 5
Deep focus earthquakes are of higher magnitudes,
6 to 8 or more.
Less energy is released during a shallow focus
earthquakes
Tremendous energy accumulates during a deep
focus earthquake
Shallow focus earthquakes happen frequently and
at random within the earth’s crust, often going
unrecorded
Deep focus earthquakes occur every 20 to 30
years along a given fault line.
Shallow focus earthquakes are barely perceived
and are rarely destructive
Deep focus earthquakes leave a deeper impact on
civilisation with widespread destruction and
permanent changes within the earth’s geology,
giving rise to tsunamis.
Shallow-focus earthquakes begin where the
crustal plates of the earth are moving against one
another
Whereas deep-focus earthquakes begin where one
tectonic plate moves under another or sub-ducts,
at the boundary of oceanic and continental plates.
During shallow focus earthquakes, rocks and
plates buckle, deform and fault.
In the deep focus earthquakes, the rocks being at
greater depths and extremely hot under high
pressure, deform by flowing, rather than breaking
and faulting.

24. BASED ON THE CAUSE: ??
BASED ON EPICENTRE DISTANCE
– Local Earthquakes: Affected area is very less,
within 1 degree of the epicenter of the
earthquake
– Regional Earthquakes: 1 degree to 10 degree
– Tele seismic Earthquakes: greater than 10 degrees

25. STRENGTH of earthquake
 Scientists measure the strength of earthquakes using
machines known as seismographs
 The data obtained from seismograms can be used to
determine time, epicenter, focal depth, type of faulting of an
earthquake.
 Also estimate quantum of energy released.
 The recording they make is known as seismogram

26. MEASUREMENT
 The seismograph has a base that sets firmly in the ground,
and a heavy weight that hangs free.
 Earthquake causes the ground to shake, the base of the
seismograph shakes too, but the hanging weight does not.
 Instead the spring or string that it is hanging from absorbs
all the movement.
 The difference in position between the shaking part of the
seismograph and the motionless part is what is recorded.
 Seismology is the scientific study of earthquakes and the
propagation of elastic waves through the Earth

28. The magnitude and strength of an earthquake
is measured on Richter scale, the scale
invented by Charles Richter California ,USA
in 1935 which categories earthquake on the
basis of energy released.
Definition: “the logarithm to base ten of the
maximum seismic-wave amplitude recorded
on a standard seismograph at a distance of 100
kilometers from the earthquake epicenter.”

29. • Scale uses log raging from 1 to 10
• Magnitude two is the smallest and magnitude
greater than 5.5 are progressively damaging to
property and human life.

31. • A – the measure of the amplitude of the earthquake
wave
• A0 – the amplitude of the smallest detectable wave
(or standard wave)
From this you can find R, the Richter scale measure of
the magnitude of the earthquake using the formula:

33. • A difference of 1 point on the Richter scale equates to a
10-fold difference in the amplitude of the earthquake
• This means that an earthquake that measures 3.6 on the
Richter scale has 10 times the amplitude of one that
measures 2.6.
• Let’s look back at the example just shown. In that
example, the wave amplitude of the earthquake was
392 times normal. What if it were 10 times that, or
3,920 times normal? To find the measurement of that
size earthquake on the Richter scale, you find log 3920.
A calculator gives a value of 3.5932…or 3.6, when
rounded to the nearest tenth. One extra point on the
Richter scale can mean a lot more shaking

34. • Modified mercalli intensity (MMI)- Measure
of how it felt on surface
• Determined by physical observation of the
impact of earthquake
• Intensity is measured
• Measured on a scale of 1-12 where one is very
minor and 12 is extreme.

35. TYPES OF ZONE
The earthquake zoning map of India divides India into 4
seismic zones Based on the observations of the affected area
due to Earthquake, India divided into four types of zones:
 Zone - II: This is said to be the least active seismic zone.
 Zone - III: It is included in the moderate seismic zone.
 Zone - IV: This is considered to be the high seismic zone.
 Zone - V: It is the highest seismic zone.

37. Seismic waves
• Body waves
– Body waves travels in all directions in the body of earth
(earth’s inner layer)
– Body wave arrives before surface waves.
– higher frequency than surface waves.
– Velocity of these waves depends on the density of materials.
– Two types of body waves- P and S
P waves
 First recorded in graph is P waves
 P stands for primary or pressure waves
 The P wave can move through solid rock and fluids, like water
or the liquid layers of the earth.
 It pushes and pulls the rock it moves
 animals can hear the P waves of an earthquake

38. S waves
S stands for secondary or shear waves
S wave is slower than a P wave and can only move through
solid rock, not through any liquid medium
surface gets Compressed and expanded
shear waves moves slowly like a swaying or rolling
motion perpendicular to the direction of the wave.
Last recorded is surface waves
Surface waves moves along the surface like ripples
lower frequency than body waves
Cause most of the destruction

39. • 2 types:
– Rayleigh waves: move horizontally as well as
vertically
– Love waves: only horizontal motion

42. Impact ??

43. • Ground shaking
• Faulting and Ground Rupture
• Ground subsidence
• Damage to man-made structures
• Fires
• Spill of hazardous chemicals
• Initiation of slope failures
• Liquefaction
• Tsunami