Supplementary Education Service - SCIENCE 8-2-1.pptx

Supplementary
Education Service –
Science
Level 8
Unit 2: Earth and Space
Chapter 4: Earthquakes and Faults

Objectives:
At the end of the session, the students should be able
to:
1. demonstrate understanding of the relationship between
faults and earthquakes;
2. differentiate the focus of an earthquake from its
epicenter;
3. differentiate the magnitude of an earthquake from its
intensity;

Objectives:
4. demonstrate understanding of how earthquakes cause
tsunamis;
5. explain how earthquake waves provide information
about Earth’s interior;
6. show emergency preparedness before, during, and
after an earthquake;
7. identify faults in the community; and
8. create a model earthquake emergency plan.

Introduction:
 Earth's Dynamism: Earth is a dynamic planet due to the
high temperatures and pressures in its mantle and core.
 Surface Changes: These extreme conditions cause rocks
to contract and expand, leading to temporary or
permanent deformation of Earth's surface.
 Natural Calamities: The deformation of Earth's surface
can result in natural disasters such as earthquakes.

Introduction:
 Earthquake Preparedness: Since there is no
effective warning system for earthquakes,
taking preliminary precautions is critical.
 Active Faults Awareness: Knowing the active
faults in a community is essential for
earthquake preparedness.

Faults
 Earth’s Crust: The crust is the solid, outermost layer of Earth,
composed of various types of rocks.
 Stress and Deformation: The crust is constantly deformed due to
different types of stress, which is the force applied per unit area.
 Tectonic Plates: Most stress is caused by the movement of massive,
irregularly shaped slabs of rock called tectonic plates, which move
and interact along plate boundaries.
 Plate Boundaries: These are regions where tectonic plates move
and interact. The movement is slow and continuous.

Faults
 Formation of Faults: If the stress from plate movements
overcomes the strength of the rocks, the crust may fracture,
forming a fault.
 Faults: A fault is a planar fracture between two massive blocks of
rock. Faults can range from micrometers to thousands of
kilometers long and approximately 10 km deep.
 Surface Interaction: Not all faults intersect the Earth’s surface,
but when they do, the ground and objects on it may fracture,
rise, or depress.

Parts of a Fault
Fault Plane: The flat surface of a fault where a slip occurs.
It can be vertical or inclined.
Hanging Wall: The block of rock above an inclined fault
plane.
Footwall: The block of rock below an inclined fault plane.
Fault Line: The surface along which rocks have been
displaced.

Parts of a Fault
Fault Scarp: A step-like feature on Earth’s surface caused
by a slip on the fault.
Fault Zone: An area of complex deformation associated
with the fault plane. Fault zones are usually narrow but
can be up to 2000 km wide.

Types of Faults
 Classification of Faults: Faults are classified based on their
motion and the relative position of their fault plane.
 Types of Faults:
o Strike-Slip Faults: Form due to horizontal compressional
stress, causing rocks to move laterally past each other.
These faults usually occur along convergent plate
boundaries and have near-vertical fault planes, so they lack
hanging walls and footwalls.

Types of Faults
 Types of Faults:
o Normal Faults: Occur due to tensional stress, which forces rocks
apart. This process typically happens along divergent plate
boundaries, where two plates move away from each other. In
normal faults, the hanging wall moves downward relative to the
footwall.
o Reverse (Thrust) Faults: Form as a result of horizontal
compressional stress and are associated with convergent plate
boundaries. In reverse faults, the hanging wall moves upward
and over the footwall. Both normal and reverse faults have
inclined fault planes.

Active and Inactive Faults
 Active Faults:
o A fault is considered active if it has moved repeatedly in
the past and is likely to move again.
o Movements of rocks along active faults are caused by the
continuous movements of tectonic plates.
o Active faults can offset or cut through entire sedimentary
rock layers, indicating continuous activity.

 Example of an Active Fault:
o Valley Fault System (VFS) in the Philippines, also known as the
Marikina Valley Fault System, traverses the whole length of
Metro Manila.
o The VFS is 146.71 km long and consists of two major active
fault lines: the East Valley Fault (17.24 km) and the West Valley
Fault (129.47 km).
o The West Valley Fault could generate a 7.2 magnitude
earthquake, potentially leaving roughly 3.15 million people

 Inactive Faults:
o A fault is considered inactive if it has shown no signs of
movement or generating earthquakes for hundreds of
millions of years.
o Inactive faults are confined within older sedimentary rock
layers and do not cut through or deform younger layers.
o Some inactive faults can become active again.

Earthquakes
 Definition of Earthquake: An earthquake is a sudden shaking
of Earth’s surface caused by volcanic activities or the
movement of tectonic plates.
 Origin of Earthquakes: Earthquakes originate within Earth’s
crust and can occur in both the continental crust (forming
continents and shallow seabeds) and the oceanic crust
(forming the uppermost layer of the seafloor).

Earthquakes
 Destructive Effects: Earthquakes can cause massive
destruction, including:
o Infrastructural damages  Landslides
o Avalanches  Fires
o Flashfloods  Tsunamis
o Soil liquefaction (conversion of soil into a fluid-like mass
during a seismic event)

How Movements Along Faults Generate
Earthquakes
 Cause of Earthquakes: Earthquakes are caused by a sudden
slip of rocks on a fault.
 Deforming Stress: Plate movements push rocks on opposite
sides of a fault together, causing deforming stress.
 Frictional Force: The frictional force on the fault surface
holds the rocks together, preventing them from slipping
instantly.

Earthquakes
 Elastic Energy Buildup: Over time, stress causes a buildup of
elastic energy in the rocks.
 Sudden Slip: When the stress overcomes the rocks’ elasticity,
the rocks slip suddenly to relieve the stress.
 Seismic Waves: The accumulated energy is released as
seismic waves, which radiate outward from the source and
cause earthquakes when they reach Earth’s surface

Earthquakes

Focus and Epicenter
 Focus (Hypocenter): The point of origin of an earthquake
within Earth’s crust.
 Classification by Depth:
o Shallow-Focus Earthquakes: Originate at depths less than
70 km and cause the most damage. About 80% of
recorded earthquakes are shallow-focus.

Focus and Epicenter
 Classification by Depth:
o Intermediate-Focus Earthquakes: Originate between 70 km
and 300 km below the surface. About 12% of recorded
earthquakes fall into this category.
o Deep-Focus Earthquakes: Originate between 300 km and
700 km below the surface. About 3% of recorded
earthquakes are deep-focus.

Focus and Epicenter
 Epicenter: The point on Earth’s surface directly above the
focus. It can be located using the triangulation method,
which involves data from at least three seismograph
stations.
 Seismograph: An instrument used to detect and record
seismic waves. It consists of a base, frame, spring, weight,
pen, and rotating drum. The pen records the motion of
seismic waves on the rotating drum, creating a
seismogram.

Focus and Epicenter
 Seismogram: The paper recording of an earthquake. Long
wiggly lines indicate large earthquakes, while short wiggly
lines indicate small earthquakes.

Intensity and Magnitude
 Earthquake Intensity: Measures the extent of damage caused
to Earth’s surface, infrastructure, and life. Intensity varies
by location, with areas near the epicenter experiencing
higher intensities.

 Intensity Scales:
o Mercalli Intensity Scale: Devised by Giuseppe Mercalli in
1902, uses Roman numerals to describe increasing levels
of intensity and their effects on Earth’s surface and
people. It has been revised over the years and is now
known as the modified Mercalli intensity scale.
o PHIVOLCS Earthquake Intensity Scale (PEIS): Used in the
Philippines to measure earthquake intensity.

 Earthquake Magnitude: Measures the amount of energy
released during an earthquake.
o Richter Magnitude Scale: Devised by Charles F. Richter,
based on the amplitude of seismic waves. Larger
earthquakes cause stronger seismic vibrations.

How Earthquakes Generate Tsunamis
 Definition of Tsunami: A series of large ocean waves with
extremely long wavelengths.
 Causes: Often caused by shallow-focus earthquakes near or
under the ocean floor, usually along convergent plate
boundaries. These earthquakes result from the sudden
displacement of a large section of the ocean floor, which
vertically displaces a huge amount of water.

 Wave Formation: Tsunami waves form as the displaced water
tries to recover its equilibrium.
 Wave Travel: Tsunami waves travel outward in all directions
from the source. They can travel at speeds up to 900 km/h in
the deep ocean but slow down and increase in height near
the coast, increasing their destructive capability.

 Magnitude and Severity: Tsunamis can vary in magnitude and
severity. Small tsunamis occur daily and are often seen as strong,
fast-moving tides along shorelines. Large tsunamis can cause
widespread destruction, including massive property damage and
loss of lives.
 Example: The 2011 tsunami in Japan, caused by a magnitude 9
earthquake, had waves as high as 38 meters, flooded over 500
km² of coastal land, resulted in approximately 20,000 fatalities,
and displaced around 500,000 people. The effects were felt
globally, with debris washing up on North American beaches

How Earthquake Waves Provide Information
About Earth's Interior
 Earth’s Depth: The average distance from Earth’s surface to
its center is approximately 6371 km. Current technology can
only penetrate about 12 km below the surface, so direct
exploration of Earth’s internal layers is not feasible.
 Indirect Evidence: Scientists rely on indirect evidence, such
as studying earthquakes, to understand Earth’s interior.

 Seismic Waves: Earthquake waves, or seismic waves, are
energy waves released during an earthquake. Their
behavior changes when they travel through different
materials, refracting (bending) and changing speed based
on the material’s density.

 Types of Seismic Waves:
o Body Waves: Travel through Earth’s interior and are used
to study its internal structure. They include:
• P-Waves (Primary Waves): Travel faster, arrive first at
seismograph stations, and can move through both solid
and liquid materials.
• S-Waves (Secondary Waves): Travel slower, arrive second,
and can only move through solid materials.
o Surface Waves: Travel across Earth’s surface.

 Studying Earth’s Interior: By examining the arrival times and
behavior of P-waves and S-waves, scientists can infer the
structure and behavior of Earth’s internal layers:
o Mantle: Inferred to be solid because both P-waves and S-waves
travel through it.
o Outer Core: Believed to be liquid because S-waves are not
detected in this layer.
o Inner Core: Inferred to be solid because P-waves are refracted
around the boundary between the inner and outer core,
indicating different materials and densities.

Earthquake Preparedness
 Importance of Earthquake Preparedness: Knowledge of safety
measures during an earthquake is critical for survival.
Earthquake drills help people react appropriately during an
earthquake.
 Basic Safety Measures:
o Do not panic at the first sign of tremors.
o Evacuate to a safer place with essential supplies.
o If unable to evacuate, seek shelter under a sturdy table.

 Basic Safety Measures:
o Move to an open space away from tall structures.
o Avoid electric wires.
o Stay away from the foot of mountains or hills to avoid
landslides or mudslides.

 Unusual Animal Behavior: Some people associate unusual
animal behavior with impending earthquakes.
 Scientific Prediction: Scientists predict earthquake-prone
areas by monitoring tectonic plate movements and fault
zones.

 Technologies for Predicting Natural Disasters:
o Pagers and Seismographic Network: Collect and analyze seismic
data to determine the earthquake’s epicenter and magnitude,
helping authorities respond quickly.
o Radio Technology: Used by emergency agencies to protect rescue
workers from aftershocks.
o Seismic Gap: Identifies areas where stress builds up along faults,
helping predict future earthquakes.
o Tsunami Warning System: Monitors seismic and tidal stations to
detect and warn about potential tsunamis.

Summary:
1. Earthquakes are caused by the movements of tectonic
plates or by volcanic activities. A fault is a planar fracture
or discontinuity in a rock mass. Most earthquakes occur on
active faults.
2. In a strike-slip fault, the blocks of rocks on both sides of the
fault move laterally (either to the left or to the right) and
pass each other along the fault plane. In a normal fault, the
hanging wall moves down relative to the footwall. In a
reverse fault, the hanging wall moves upward and over the
footwall.

Summary:
3. The hypocenter or focus is the point of origin of an earthquake.
The epicenter is the point on Earth's surface that is directly
above the focus.
4. Magnitude is the measure of the energy released in rocks during
an earthquake, whereas intensity is the measure of the effect of
an earthquake on Earth's surface.
5. A tsunami is generated when the epicenter of a large, shallow-
focus earthquake is near or under the ocean floor. This type of
earthquake displaces an enormous amount of water, resulting in
powerful tsunami waves that travel outward in all directions.

Summary:
6. Seismic waves are energy waves that travel through Earth's
interior and surface. The two types of body waves are P-
waves and S-waves. The behavior and nature of P-waves
and S-waves are useful in understanding the composition
and structure of Earth's internal layers.
7. An emergency plan and an emergency kit are necessary for
earthquake preparedness.

Supplementary Education Service - SCIENCE 8-2-1.pptx

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Supplementary Education Service - SCIENCE 8-2-1.pptx