An earthquake occurs when accumulated energy stored in rocks is suddenly released, causing seismic waves that radiate outward from the focus of the earthquake. The Earth's interior is composed of layers including the crust, mantle, and core. Plate tectonics theory explains that the Earth's outer layer is made up of plates that move relative to each other, causing earthquakes at their boundaries. When faulting occurs, seismic waves propagate outward from the hypocenter, and the point on the surface directly above is called the epicenter.

2.  An earthquake is the vibration of Earth
produced by the rapid release of
accumulated energy in elastically strained
rocks
 Energy released radiates in all
directions from its source, the focus .
 Energy propagates in the form of
seismic waves .
 Sensitive instruments around the world
record the event .

3.  Crust:
 Continental crust (25-40
km)
 Oceanic crust (~6 km)
 Mantle
 Upper mantle (650 km)
 Lower mantle (2235 km)
 Core
 Outer core: liquid (2270
km)
 Inner core
 Values in brackets
represent the
approximate thickness of
each layer

4.  The theory of Plate tectonics was proposed in
1960s based on the theory of continental drift.
 This is the Unifying theory that explains the
formation and deformation of the Earth’s surface.
 According to this theory, continents are carried
along on huge slabs (plates) on the Earth’s outermost
layer (Lithosphere).
 Earth’s outermost layer is divided into 12 major
Tectonic Plates (~80 km deep). These plates move
relative to each other a few centimeters per year.

6.  Divergent plate
boundaries:
where plates move
apart
 Convergent Plate
boundaries:
where plates come
together
 Transform plate
boundaries:
where plates slide
past each other

7. Movement of Tectonic Plates
Earth is divided into sections called Tectonic
plates that float on the fluid-like interior of the
Earth. Earthquakes are usually caused by
sudden movement of earth plates
Rupture of rocks along a fault
Faults are localized areas of weakness in the
surface of the Earth, sometimes the plate
boundary itself

8.  The point within
Earth where faulting
begins is the
focus, or
hypocenter
 The point directly
above the focus on
the surface is the
epicenter

9. Explains how energy is stored in rocks:
 Rocks bend until the strength of the rock is
exceeded.
 Rupture occurs and the rocks quickly rebound
to an undeformed shape.
 Energy is released in waves that radiate
outward from the fault.

10. When a earthquake
occurs, two types of seismic
waves are generated:-
 Body waves, that travel
through the interior of the
earth. They are of two types-
 P-wave- primary waves or
push-pull waves or
compression waves.
 S-waves- shear
waves, secondary waves or
traverse waves.
 Surface waves, that travel
along the surface layers of the
earth. They are of two types-
 Love waves
Rayleigh waves

11. • INTENSITY • MAGNITUDE
 Qualitative measure of an  Quantitative measure of the
earthquake which describes the earthquake which is related to
effect of an earthquake at a the amount of energy released
particular location. to cause the earthquake.
 Isoseismal lines identify areas of  It is measured by Richter scale
equal intensity. and Seismograph.
 It is measured by modified-  Magnitude is same for a
mercalli intensity scale. particular earthquake.
 Intensity changes with distance
from epicenter of earthquake.

12.  PEAK GROUND
MOTION
 DURATION OF
GROUND MOTION
 FREQUENCY
CONTENT

13.  They are the instruments
used to record strong ground
motion i.e. motion large
enough to be potentially
damaging.
These instrument record
acceleration of the ground as
a function of time.
Triaxial acceleographs are
able to measure ground
motion in two perpendicular
horizontal directions and in
the vertical directions.

15.  EARTHQUAKE MAGNITUDE
 EPICENTRAL DISTANCE
 LOCAL SOIL CONDITION
 CHARACTERISTIC OF LOCAL GEOLOGY ALONG
THE PROPAGATION PATH
 SOURCE MECHANISM OF THE EARTHQUAKE

16.  INTERNAL FORCES DUE TO LARGE PEAK GROUND ACCELERATIONS CAUSES
STRUCTURAL FAILURE, LANDSLIDES, RETAINING WALL FAILURE.
 LIQUEFACTION OF SATURATED SOIL CAUSES STRUCTURAL FAILURES, LARGE
LATERAL DISPLACEMENT OF SLOPES, INCREASED LATERAL PRESSURE ON RETAINING
WALL
EARTHQUAKE INDUCED FIRE CAUSES LOSS OF PROPERTY
EARTHQUAKE INDUCED WATER WAVES KNOWN AS TSUNAMIS CAUSE
SUBMERGENCE OF SHORE AREAS CAUSING DEATH AND LOSS OF PROPERTY
RARELY THERE MIGHT BE A PERMANENT CHANGE IN GROUND ELEVATION

18.  Strange Animal Behavior
stress in the rocks causes tiny hairline fractures to
form, the cracking of the rocks evidently emits high
pitched sounds and minute vibrations imperceptible
to humans but noticeable by many animals.
 Foreshocks
unusual increase in the frequency of small
earthquakes before the main shock
 Changes in water level
porosity increases or decreases with changes in strain
 Seismic Gaps
based of the chronological distribution of major
earthquakes

19. Prepare a Seismic Risk Map for the globe which identifies rock
types, liquefaction potential, landslide potential.
Extensive geologic surveying has to be done to identify all active
faults, including hidden faults.
Earthquake Resistant Design of Structures
Enact building codes to design and build earthquake-resistant
structures in high seismic risk areas. wood, steel and reinforced
concrete are preferred as they tend to move with the shaking ground
(unreinforced concrete and heavy masonry tend to move independently
and in opposition to the shaking, battering one another until the
structure collapses)
Critical facilities such as nuclear power plants and dams should
be built on stable ground and as far as possible from active faults.