Earthquakes are caused by the sudden release of energy in the Earth's crust from tectonic plate movement. They generate seismic waves that propagate outward from the earthquake's hypocenter or focus. The epicenter is the point on the Earth's surface directly above this focus. Earthquake magnitude is measured by the Richter scale, with each increasing whole number representing a tenfold increase in measured amplitude. Major earthquakes of magnitude 8 or above can cause widespread damage depending on their depth and location.

1. 1
An earthquake (also known as a quake,
or tremor) is a violent movement of the
rocks in the Earth's crust and is the
result of a sudden release of energy in
the Earth's crust that creates seismic
waves.
Technically, earthquake may be defined
as “vibrations induced in the earth’s
crust due to internal or external causes
that virtually shake up a part of the
crust and all the structures and living
and non-living things existing on it”.

2. Causes Of EARTHQUAKE
Earthquakes are caused by tectonic
movements in the Earth's crust.
The main cause is that when
tectonic plates collide, one rides
over the other, causing mountain
building, earthquakes and
volcanoes.

3. Earthquakes is the sudden release of
stress along a fault, or fracture in
the earth's crust, resulting in
movement of the opposing blocks of
rock past one another.
Volcanic eruptions, rock falls,
landslides, and explosions can also
cause a quake, but most of these are
of only local extent. Shock waves
from a powerful earthquake can
trigger smaller earthquakes in a
distant location hundreds of miles
away if the geologic conditions are
favorable.

4. There are three main types of
fault that may cause an
earthquake: normal, reverse
(thrust) and strike-slip.
Normal faults occur mainly in
areas where the crust is being
extended. Earthquakes associated
with normal faults are generally
less than magnitude 7.
FAULTS
Aerial photo of the San Andreas Fault

5. Reverse faults occur in areas
where the crust is being
shortened. They are associated
with the most powerful
earthquakes, including almost all
of those of magnitude 8 or more.
Strike-slip faults are steep
structures where the two sides
of the fault slip horizontally past
each other. They can produce
major earthquakes up to about
magnitude 8.

6. FOCUS AND EPICENTER
An earthquake's focus
also known as hypocenter
is the position where the
strain energy stored in
the rock is first released,
marking the point where
the fault begins to
rupture. This occurs
directly beneath the
epicenter, at a distance
known as the focal.

7. In the case of earthquakes,
the epicenter is directly above
the point where the fault
begins to rupture, and in most
cases, it is the area of
greatest damage. However, in
larger events, the length of
the fault rupture is much
longer, and damage can be
spread across the rupture
zone.
For example, in the magnitude 7.9, 2002 Denali
earthquake in Alaska, the epicenter was at the western
end of the rupture, but the greatest damage occurred
about 330 km away at the eastern end of the rupture
zone.

8. seismic waves
Seismic waves are waves of energy
that travel through the Earth's layers,
and are a result of an earthquake,
explosion, or a volcano.
PRIMARY WAVES
P-waves are longitudinal in
nature. P waves are pressure
waves that travel faster than
other waves through the
earth to arrive at
seismograph stations first
hence the name "Primary".
These waves can travel
through any type of material,
including fluids, and can travel
at nearly twice the speed of S
waves, they travel at the
speed of sound.

9. SECONDARY WAVES
S-waves are shear waves and
are transverse in nature.
These waves arrive at
seismograph stations after the
P waves during an earthquake
and displace the ground
perpendicular to the direction
of propagation S waves can
travel only through solids, as
fluids (liquids and gases) do not
support shear stresses.
S waves are about 60% slower
than P waves.

10. Effects of earthquakes
Shaking and ground rupture are
the main effects created by
earthquakes, principally
resulting in more or less severe
damage to buildings and other
rigid structures
Landslides and avalanches
Earthquake can produce
slope instability leading to
landslides, a major
geological hazard.

11. Tsunamis are long-wavelength,
long-period sea waves produced by
the sudden or abrupt movement of
large volumes of water.
Tsunamis travel 600-800
kilometers per hour, depending on
water depth. Large waves
produced by an earthquake or a
submarine landslide can overrun
nearby coastal areas in a matter of
minutes. Tsunamis can also travel
thousands of kilometers across
open ocean and wreak destruction
on far shores hours after the
earthquake that generated them.

12. RICHTER SCALE
The Richter magnitude
scale is a scale of
numbers used to tell
the size of
earthquakes. The scale
is logarithmic, with a
base of 10.
Developed in 1935 by
Charles Francis
Richter in partnership
with Beno Gutenberg,
Kinemetrics seismograph

13. Descriptor
Richter
Magnitude
number
Damage caused by the earthquake Frequency of occurrence
Micro Less than 2.0 Micro earthquakes, people cannot feel these. About 8,000 each day
Very minor 2.0-2.9
People do not feel these, but seismographs
are able to detect them.
About 1,000 per day
Minor 3.0-3.9
People often feel these, but they rarely cause
damage.
About 49,000 each year
Light 4.0-4.9
Objects inside houses are disturbed, causing
noise. Nothing is damaged.
About 6,200 each year
Moderate 5.0-5.9
Buildings that are not built well may be
damaged. Light objects inside a house may
be moved.
About 800 per year
Strong 6.0-6.9
Moderately powerful. May cause a lot of
damage in a larger area.
About 120 per year
Major 7.0-7.9
Can damage things seriously over larger
areas.
About 18 per year
Great 8.0-9.9
Massive damage is caused. Heavy objects
are thrown into the air and cracks appear
on the ground, as well as visible
shockwaves. Overhead highways may be
destroyed, and buildings are toppled.
About 1 per 20 years

14. EARTHQUAKE PROOFING
To be earthquake proof, buildings, structures and their
foundations need to be built to be resistant to sideways
loads. The lighter the building is, the less the loads.
Buildings are basically designed to support a vertical
load in order to support the walls, roof and all the stuff
inside to keep them standing
As the buildings get bigger and taller other techniques
are employed such as “base isolation.” During the past
30 years, engineers have constructed skyscrapers that
float on systems of ball bearings, springs and padded
cylinders. Acting like shock absorbers in a car, these
systems allow the building to be decoupled from the
shaking of the ground. These buildings don’t sit directly
on the ground, so they’re protected from some
earthquake shocks. In the event of a major earthquake,
they can sway up to a few feet.
730 ton motion damper
inside the Taipei 101
skyscraper