EARTHQUAKES
& FAULTS
PREPARED BY: CHERYL L. RECIPROCO
Using models or illustrations,
explain how movements along faults
generate earthquakes S8ES -IIa - 14
Differentiate the epicenter of an
earthquake from its focus; 2
intensity of an earthquake from its
magnitude; 3 active and inactive
faults S8ES -IIa - 15
How do earthquakes occur
and how are they
detected?
How can people be prepared
for earthquakes?
ACTIVE and INACTIVE FAULTS
EARTH
CRUST
The
surface/outermost
layer of the Earth
Earth’s Crust Two Sections
Continental Crust
Makes up Earth’s landmasses
Oceanic Crust
Found in the ocean floor and
usually thinner than continental
crust
Why are some parts of the crust
thicker than other?
How does the crust change its
shape over time?
Some force is at work pushing and
pulling on the crust causing
changes on the surface and often
well beneath the surface
• This push-pull is called stress
• As rocks undergo stress, they slowly
change shape and volume.
What can stress do to rocks?
A
rock to become more compressed or
squeezed
• Becomes smaller in volume
• A rock to stretch out over a large area.
• The volume increases
• The rock to twist or tear apart.
• Causes the formation of fault
What can stress do to rocks?
A
rock to become more
compressed or squeezed
• Becomes smaller in volume
• A rock to stretch out over a large area.
• The volume increases
• The rock to twist or tear apart.
• Causes the formation of fault
What is a fault?
Fracture in rocks along which
movement occured.
Some faults may cause the ground to
crack, rise or lower.
Two blocks of a faulted rock
Hanging Wall
• The block of rock above the fault
Foot Wall
• The block of rock below the fault
Kinds of fault
Normal Fault/Normal Dipslip Fault
• If a stress pulls the rocks apart
due to tension, the hanging wall
will move down relative to the foot
wall.
Kinds of fault
Reverse
Dip-slip Fault/
Thrust Fault
• If stress squeezed the rocks due
to compression, the hanging wall
will move up relative to the foot
wall.
Kinds of Fault
Strike – slip Fault/Wrench Fault
The blocks move by sliding and
slipping along each other
horizontally but in opposite
directions.
Active faults
are structure where there is displacement
Usually produce a shallow earthquake
One that has moved in the past and
expected to move again.
Inactive Faults
are
structures that can be identified but
which do not cause earthquakes.
• If a fault has been inactive for million
years, it is safe to call it inactive.
PHIVOLCS
Philippine
Institute of Volcanology
and Seismology
• Philippines has several fault lines
• Faults and trenches are found in the
entire country
• Trenches are the deepest part of
the oceans and are usually VShaped.
Faults & Trenches
Are found close to the continents
Near strings of islands.
Near these TRENCHES:
– The crust is active causing stress and
creating faults.
About trenches…
Scientist
believe that the ocean floor is
being pushed down deep into Earth along
the trenches
When
these rocks are pushed deep
enough, they are melted by the heat of
Earth.
Some
of the molten rocks will rise up
through the crust and produce volcanoes
but most of it will become part of the
Earth’s Mantle.
EARTHQUAKE Focus and Epicenter
Earthquake…
• Shaking and trembling of earth
that results from the sudden
movement of Earth’s crust
Faulting…
• The most common cause of
earthquake
During Faulting…
• Energy is released as the rocks
break and move.
• As they move, they cause the
nearby rocks to move also.
• The rocks continue to move this
way until the energy is used up.
Tsunami…
Giant ocean wave cause by Earthquake
that occur on the ocean floor.
• These waves can travel at speed of 700 – 800km/h.
• Can be as high as 10 – 20 meters (as they approach the
coast).
• The effects are devastating
• One of the world’s worst natural disaster
Focus
• The point/region where an earthquake
ruptures and the rocks break
• hypocenter
• Underground point of origin of an
Earthquake.
Epicenter
• The point on Earth’s surface directly
above the focus
• This where the most violent shaking
of the ground occurs.
Focal Depth
• The distance between the
focus and the epicenter
Earthquake Waves…
• Seismic Waves
• Are the waves of energy caused by
the sudden breaking of rock within
the Earth or an explosion.
• They are the energy that travels
through Earth and is recorded on
seismographs.
Three main types of Seismic
Waves
Primary Waves (P Waves)
• The fastest of the seismic wave
• The first to arrive at a seismic
station before any other type of
seismic wave
• Can move through the solid rocks
and fluids (like water and liquid
layers of Earth)
Three main types of Seismic
Waves
• Can move through the solid rocks
and fluids (like water and liquid
layers of Earth)
Three main types of
Seismic Waves
Secondary Wave (S Wave)
• The second wave you feel in an
earthquake
• S wave is slower than a P wave and
can only move through solid not
through liquid or gases
What
happens to S
WAVES when they
reach the liquid part
of the earth?
• S waves move rock particles up
and down, or side – to – side perpendicular to the direction the
wave is traveling in.
Three main types of
Seismic Waves
Surface Wave (L Wave)
Travel
from focus directly upward
to the epicentre.
Earth’s
surface moves up and
down with each L wave that
passes
Cause
most of the damage during
the earthquake because they
bend and twist Earth’s surface.
Seismograph…
An instrument that detects and measures
waves.
Seismograms…
• Seismograph’s record of the waves.
Richter Scale…
Measures
how much energy an
earthquake releases by assigning
the earthquake number from 1
to 10.
• The more energy the earthquake
releases, the stronger the
earthquake is.
Earthquake Magnitude and
its Effects
Richter Magnitude
Effects Near Epicenter
2.0 and below
Generally not felt, but recorded
2.0 – 2.9
Potentially perceptible
3.0 – 3.9
Felt by some
4.0 – 4.9
Felt by most
5.0 – 5.9
Damaging Shocks
6.0 – 6.9
Destructive in populous regions
7.0 – 7.9
Major earthquake; inflict serious damage
8.0 and above
Great earthquake; Destroys communities
near epicenterr
0
