INTRODUCTION TO EARTHQUAKES & FAULTS.pdf.pdf

about earthquakes

1. What is an Earthquake?
What causes Earthquakes?

2. What is an Earthquake?
An earthquake is a sudden release of energy in the
Earth's crust that creates seismic waves.
What causes Earthquakes?

3. What is an Earthquake?
An earthquake is a sudden release of energy in the
Earth's crust that creates seismic waves.
What causes Earthquakes?
Most earthquakes occur due to the movement of
tectonic plates, which are large pieces of the Earth's
crust that fit together like a jigsaw puzzle.

4. Types of Faults
Faults are fractures or cracks in the Earth's crust where movement occurs.
Normal faults
Occur when rocks move apart
due to tensional forces.
Reverse faults
Occur when rocks are pushed
together due to compressional
forces.
Strike-slip faults
Occur when rocks slide
horizontally past each other
due to shear forces.

6. NORMAL
FAULT
a type of fault (crack in the Earth's crust) that
occurs due to extensional forces—when the
Earth's crust is being pulled apart
How It Works:
The Earth's crust stretches due to forces pulling in
opposite directions.
A crack (fault) forms, and one block of rock (hanging
wall) moves downward compared to the other block
(footwall).
Over time, tension builds up because the rocks resist
movement.
When the stress becomes too much, the rocks break
suddenly, releasing energy as seismic waves—which
we feel as earthquakes!

8. REVERSE
FAULT
The Earth's crust is getting squeezed
(compression), usually happens where tectonic
plates push against each other, like at
convergent boundaries (where plates collide)
How It Works:
The Earth's crust is getting pushed together due to
strong forces.
A crack (fault) forms, and one block of rock (hanging
wall) moves up over the other block (footwall).
Over time, pressure builds up because the rocks resist
movement.
When the pressure becomes too much, the rocks
break suddenly, releasing energy as seismic waves—
causing an earthquake!

10. STRIKE-SLIP
FAULT
A strike-slip fault is a crack in the Earth where
two big pieces of land move sideways past each
other
How It Works:
As they push against each other, they get stuck
because of friction, like when you rub your hands
together.
This makes pressure build up where they’re stuck.
When the pressure gets too strong, the plates
suddenly slip past each other.
This quick movement releases energy in waves called
seismic waves.
These waves shake the ground, and that’s what we
feel as an earthquake!

11. In the Philippines...
the most common types of faults are
typically strike-slip faults and thrust
(reverse) faults. The country is
located along the boundary of the
Philippine Sea Plate and the Eurasian
Plate, where the movement is
predominantly lateral (strike-slip)
and compressional (thrust). These
types of faults are responsible for the
significant seismic activity and
earthquakes experienced in the
region.

12. are you in safe
location?
Which locations does the
West Valley Fault passed
through?
How about the East
Valley Fault?
Considering your location,
do you think you are
safe?

13. PHILIPPINE FAULT
ZONE (PFZ)
a transform boundary
formed by the
movement of the
Philippine Sea Plate
and the Eurasian Plate

14. ACTIVE vs INACTIVE
FAULT
Active faults are structures
where we expect displacement to
occur. Because a shallow
earthquake is a mechanism that
causes displacement across a
fault, they must all occur on
active faults. Inactive faults are
features that we can recognize
but do not produce earthquakes