2. OBJECTIVES
At the end of the lesson, the students will be
able to:
Define what is an earthquake
Identify various potential earthquake
hazards
Apply precautionary and safety measures
before, during, and after an earthquake
4. Is a vibration of the ground produced by a sudden
released of energy due to the disturbance of the
stability of the rock masses beneath the Earth’s
surface.
The sudden shaking or trembling of earth’s surface
is called “Earthquake”.
Is one of the of the most dangerous natural
disasters everyone could experience.
No one can detect the occurrence of an earthquake.
7. PLATE TECTONIC THEORY
The theory of plate tectonics is generally
accepted as explanation why earthquake
occurs. According to this theory, the Earth’s
outer layer called LITHOSPHERE, is broken
into large and small plates that are floating
on a hot asthenosphere. This plate fits
together closely although in many places
their boundaries are not clearly visible at the
ground level.
18. CONTINENTAL CRUST
Layer of rock which forms the continents
Floats on top of the mantle
(asthenosphere)
Older than oceanic crust
Thicker and less dense than oceanic crust
19. OCEANIC CRUST
A thin layer of crust that
underlies the ocean basins
Younger than continental crust
More dense than the continental
crust
20. WHAT HAPPENS AT PLATE
BOUNDARIES
PLATES DO ONE OF 3 THINGS:
1.CONVERGE – colliding of coming together
2.DIVERGE – dividing or moving apart
3.TRANSFORM / STRIKE – SLIP – sliding
past each other
TAKE NOTE: Velocities of the relative motion between adjacent plates range
from less than 1cm to about 13 cm per year.
28. STRIKE - SLIP FAULT
Strike - slip fault is a
fault – zone where two
blocks of land move
horizontally rather than
vertically along a fault
plane.
29. SEISMIC WAVES
Waves of energy that travel through
Earth’s layers, and are a result of
earthquake, volcanic eruptions, magma
movement, large landslides and large
man – made explosions.
31. SEISMOLOGIST
is an expert in seismology, or the study of
earthquakes. Both words are rooted in the Greek
seismos, or "a shaking," and seismologists study
the factors that lead to the extreme shaking
caused by quakes.
32. 2 TYPES OF SEISMIC WAVES
1. BODY WAVE - can travel through
the Earth's inner layers
2. SURFACE WAVE - can only move
along the surface of the planet like
ripples on water. And it is the most
destructive wave
34. P - WAVE
Primary or pressure wave
First signal to arrive at seismograph
Fastest seismic wave
Maybe transmitted through solid, liquid or gas.
35. S - WAVE
Secondary wave, Shear wave, Shaking wave.
Next to be detected after P – Wave
Moves in a transverse motion.
Transmitted in solid only.
36. 2 TYPES OF SURFACE WAVES
1. RAYLEIGH WAVE
2. LOVE WAVE
40. ELASTIC REBOUND THEORY
The triggering mechanism of an earthquake – a slippage
of rock along a fault – was explained by Harry Fielding
Reid an American seismologist on the basis of his studies
of San Francisco Earthquake. Reid observed that the
rocks are elastic and can, up to the point, accumulate
strain where adjacent areas are subjected to forces that
either pushing or pulling them. Eventually the strain
exceeds the friction, as in the case of a rubber band
stretched beyond elasticity, the fault ruptures at its
weakest point.
46. RICHTER SCALE
Richter Scale measures the
magnitude of an earthquake (how
powerful it is)
Developed by Charles F. Richter of
the California Institute of
Technology.
47. HOW IS SEISMOGRAPH
SIMILAR TO RICHTER SCALE?
The seismograph, also known as a
seismometer, is a device that monitors
ground vibrations, including seismic waves
generated by earthquakes, volcanic
eruptions, and other seismic events. The
Richter scale assigns a number based on
the amount of energy generated during the
quake.
48. INTENSITY
Is a number describing the severity
of an earthquake in terms of its
effects on the earth’s surface and on
humans and their structures.
51. In the Philippines, PHIVOLCS earthquake
Intensity Scale is use for measuring and
reporting to the public the intensities
observed after perceptible earthquake
events.
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52. A very severe earthquake is usually
associated with many shocks that can take
place before or after the earthquake event.
These associated shocks are called
FORESHOCKS ( those occurring before
the main shock), and AFTERSHOCK
(those occurring after the main shock).
54. EFFECT OF GROUND SHAKING
Buildings can be damaged by the
shaking itself or by the ground
beneath them settling to a different
level than it was before the
earthquake.
55. LIQUEFACTION
Buildings can even sink into the ground if soil
liquefaction occurs. Liquefaction is the destabilization
of sand or soil when groundwater (water underground)
is forced out from between grains during the shaking of
a moderate or strong earthquake. If liquefaction occurs
under a building, it may start to lean, tip over, or sink
several feet. The ground firms up again after the
shaking has stopped. Liquefaction is a hazard in areas
that have groundwater near the surface and sandy
soil.
56. GROUND DISPLACEMENT
The second main earthquake hazard is
ground displacement (ground
movement) along a fault. If a structure
(a building, road, etc.) is built across a
fault, the ground displacement during
an earthquake could seriously damage
or rip apart that structure.
57. FLOODING
The third main hazard is flooding. An
earthquake can rupture (break) dams
or levees along a river. The water from
the river or the reservoir would then
flood the area, damaging buildings and
maybe sweeping away or drowning
people.
58. TSUNAMI
Tsunamis and seiches can also cause a great deal of
damage. A tsunami is what most people call a tidal
wave, but it has nothing to do with the tides on the
ocean. It is a huge wave caused by an earthquake
under the ocean. Tsunamis can be tens of feet high
when they hit the shore and can do enormous damage
to the coastline. Seiches are like small tsunamis. They
occur on lakes that are shaken by the earthquake and
are usually only a few feet high, but they can still flood
or knock down houses, and tip over trees.
59. FIRE
The fourth main earthquake hazard is
fire. These fires can be started by
broken gas lines and power lines, or
tipped over wood or coal stoves. They
can be a serious problem, especially if
the water lines that feed the fire
hydrants are broken, too.
60. Most of the hazards to people come from
man-made structures themselves and the
shaking they receive from the earthquake.
The real dangers to people are being
crushed in a collapsing building, drowning in
a flood caused by a broken dam or levee,
getting buried under a landslide, or being
burned in a fire.
