Chapter 4

3. Earthquake is a feeble shaking
to violent trembling of the
ground produced by the
sudden displacement of rocks
or rock materials below the
earth’s surface.

4. Potentials for damage to
man and his environment
that may result from the
occurrence of natural events
such as volcanic eruptions,
earthquakes, floods and
storm surges.

6. Natural events like volcanic
eruptions or landslides can
also shake the ground
tremendously.

7. Ground shaking or vibration is
what we feel when energy built up
by the application of stress to the
lithosphere is released by faulting
during an earthquake.

8. Ground Shaking is the destructive up-
down and sideways motion felt during an
earthquake. Strong ground shaking can
cause object to fall, break windows among
others. Strong ground shaking can also
result to minor damages to buildings and
worse, cause collapse of a structure.

9. collapse of Hyatt Hotel, Baguio City after
the 16 July 1990 Luzon Earthquake

11. Most natural earthquakes are
caused by sudden slippage
along a fault zone.
Slippage along a fault is
hindered because there are
irregularities on the fault
plane.

12. Elastic strain energy builds
up in the deforming rocks
on either side of the fault
until it overcomes the
resistance posed by any
irregularity on the fault
plane.

13. This theory was discovered by
making measurements at a number
of points across a fault.

14. When the slippage occur, energy is
released . The elastic energy released is
transported by seismic waves and we
feel these as vibrations.

17. • “body waves”
• can travel through fluids and
solids and are longitudinal
• transfer energy parallel to
the direction of the wave
• fastest of the three seismic
waves
• “body waves”
• cannot travel through air or
water, only through solids,
but they have a larger
amplitude
• they are transverse waves

18. • Final type of seismic wave occurs along the boundary
between two different substances
• Can be either longitudinal (Rayleigh) or transverse
(Love and Rayleigh)
• Slower than both S and P waves, but have a higher
amplitude and so can be the most destructive of all
the seismic waves

20. The strength of ground shaking is
measured in terms of velocity,
accelerations, frequency content of
the shaking, and how the shaking
continues (duration).
These terms are also used by scientist
and engineers to describe the
swaying motion of buildings and
other structures as a reaction to the
shaking of the ground during an
earthquake.

21. Vocabulary or Definitions
Frequency
How often a vibration occurs. The unit of measurement is
hertz (Hz) or cycles per second. The product of wavelength
and frequency is velocity.
Natural Frequency
The frequency at which a system naturally vibrates once it
has been set into motion. The natural frequency depends
on the stiffness and mass of the system.

22. Vocabulary or Definitions
Period
The time (in seconds) it takes for one full cycle
to occur. The period is equal to the reciprocal
for frequency (1/frequency)
Acceleration
Is the rate of change of velocity expressed as a
ratio of the acceleration of gravity.

23. How intense the ground shaking that a site
may experience will depend on earthquake
magnitude, depth of focus, distance from the
epicenter, and the duration of shaking
The ground acceleration can be calculated
from many models relating only the
magnitude to time interval between p- and s-
wave arrival and distance from the earthquake
source.

24. Peak ground acceleration may be
expressed as a ratio or as a percentage
of g (acceleration of gravity; 1g=9.81
m/s^2 = 981 gals)
• A g value of 0.001 is perceptible by people
• A g value of 0.1 is sufficient to produce some
damage to weak construction
• G values of 0.1 and 0.2 would be difficult for
most people to keep their balance.
• A figure of 1.0 can cause total destruction of
buildings.

26. Ground shaking cannot harm you if you are in
an open field.
It is the failure of a building due to interior
design, poor construction, or weak foundation
that cause people harm or death.
The importance of the stability of a building’s
contents is often overlooked in preventing
injuries and fatalities.

28. Date
January 12,
2010
Location
Haiti
Deaths
316,000
Magnitude
7.0

29. Date
October 8, 2005
Location
Pakistan
Deaths
86,000
Magnitude
7.6
Comments
More than
69,000 injured

30. Date
December 26,
2004
Location
Sumatra,
Indonesia
Deaths
227,898
Magnitude
9.1

31. Date
May 12, 2008
Location
Sichuan China
Deaths
87,587
Magnitude
7.9
Comments
374,177 injured
18,392 missing
and presumed
dead

32. Most fatal earthquake to have hit the country. More than 5,000
people died in the province of Cotabato and surrounding
provinces.

33. Most destructive earthquake to have hit the country.

35. Intensity of an earthquake ground shaking
would depend to a large degree on the
nature of the earthquake source.
Intensity of vibration increases with
earthquake magnitude but decreases with
distance away from the earthquake source as
energy dissipates.
Decline in intensity as distance increases,
depends upon direction.

36. ISOSEISMAL LINES
rarely circular and
either show an
elliptical elongation in
the direction of some
major structural

37. Size of the fault rupture may greatly affect the distance-
intensity relation of ground shaking.
Fault breakage extends to the surface, heavy shaking is
concentrated in a narrow region along the length of the
fault and isoseismal lines are highly elongated parallel
to the fault trace.
Much of the energy release. Earthquake ground
motions will be more severe in the direction of rupture
propagation
Strong patches along the source fault may radiate more
seismic energy

38. Vibration Hazard Zoning

39. The intensity of shaking also depends on the
characteristics of the materials the ground is made
of.
Various types of foundation respond differently to
seismic waves.
Shear wave velocity of different rocks is a good
measure of ground shaking potential
Identified relations between shear wave velocity and
several other physical properties that can be mapped
more readily on a more regional scale as an
alternative

40. Strong material at
high frequency
(high velocity)
Weaker material at
low frequency (low
velocity)

41. • Soft and hard rock properties are used as proxies for velocity to
estimate ground shaking
• Grain size if often used for grouping sediment units to units of
different shaking. Shear wave is directly proportional to grain
size
• Greater velocity, lower amplitude
• The older the sediment, the less will be its shaking response

42. SHEAR WAVE VELOCITY OF ROCKS AND
SEDIMENTS
Go – the ratio between the shearing stress and the resulting
deformation
Shearing stress – force applied parallel to one face while and
equal force is applied to the opposite force
More rigid the higher the shear stimulus, more force is required
to attain deformation
Shear strain – transverse displacement of a body deformed by
shearing

43. • For bedrock materials, the effect of the presence of the crack to
the velocity of seismic shear waves is nearly the same as that of
pores
• Crack in rocks life fractures and contacts between layers, affect
seismic velocity by lowering it
• Hardness, also affects the shear wave velocity. It is a measure of
the strength and toughness of different rock types

45. Place heavier objects on lower shelves to prevent
breakage and personal injury.
Locate master switches and shutoff valves for all utilities
and know how to turn them off. Your local utility
company can show you.
Keep on hand a flashlight; a portable radio with fresh
batteries; a firs-aid kit; a fire extinguisher; a three-day
supply of fresh water; non-perishable, ready-to-eat
foods; and an adjustable wrench for turning off gas and
water.

46. stay calm and stay put
IF INDOORS, TAKE NOTE OF THE FOLLOWING:
DROP to the ground
Take COVER by getting under a sturdy table or other
piece of furniture
And HOLD ON until the shaking stops. If there isn’t a
table or desk near you, cover your face and head with
your arms and crouch in an inside corner of the building,
under a desk or table. Stay away from windows,
bookcases, cabinets and mirrors.

47. IF OUTDOORS, TAKE NOTE OF THE FOLLOWING:
Stay away from buildings, trees and power lines.
IF DRIVING:
Move away from overpasses
Stop slowly in a safe area
Stay in your vehicle
Stay off the bridges

48. IF IN A HIGH-RISE BUILDING:
Stay in the building, on the same floor
Get under a desk and stay away from
outside walls and windows
Do not use the elevator.

49. Expect aftershocks. These secondary shockwaves
are usually less violent than the main quake but
can be strong enough to do additional damage.
Check for injuries and apply necessary first aid
Check gas, water, electrical lines, and appliances
for damage.

50. Check to see that sewage lines are intact before you
use the toilet. Plug bathtub and sink drains to
prevent sewage backup.
Clean up spilled medicines, bleaches, gasoline, and
other flammable liquids.
Check for building damage and potential safety
hazards like cracks around chimneys or foundations.

51. Be prepared for aftershocks, which can further
damage weakened structures.
Listen to the radio for public safety instructions.

54. Earthquakes occur by the sudden motion along
lithospheric breaks called faults. During strong
earthquakes, faulting may reach the earth’s
surface as ground ruptures.

55. Ground ruptures are earthquake faults that have
reached the surface. No opening or fissuring happens
during movement of the fault, so it should remain
closed.

56. Ground Rupture is the displacement on the ground
due to the movement of fault. The movement may
have vertical and horizontal component and may be
as small as less than 0.5 meters (Masbate 2003
Earthquake)

57. Another example of Ground Rupture to as big
as 6 meters (16 July 1990 Earthquake)

59. It is formed when the lithosphere breaks due to the amount of stress
applied
An earthquake is generated when a fault moves, as its frictional
resistance could not match the large amount of accumulated stress
related to plate motion
When earthquake is strong enough, faulting initiated at depths, may
breach the earth’s surface to form a ground rupture
Faulting tends to occur along zones of weakness. Stresses need to
overcome frictional resistance acting on broken rock

61. Formation of faults has been subjected to stresses related to the
motion of the plates.
As plate positions and stress direction change, younger faults form
but many of the older faults reactivated when the applied stress is
enough to overcome resistance among fault planes
Faults are active if they moved under the current stress field and
caused an earthquake in the recent geologic past
Recency of activity is an indication of a fault’s tendency to give way
to pressure under the current stress regime

64. These determine how long ground ruptures are How and by
how much the earth’s surface breaks along ground ruptures
Type of Fault Movements (reverse, normal , strike slip) and the
inclination of the fault plane
Depth and Nature of sedimentary materials overlying the
bedrock fault may determine the pattern of surface fault traces.
Well established active faults develop more ground ruptures
while more recently developed for less distinct deformation
zones

65. Faulting causes movement of the ground in many ways. It may
cause lateral shifting, uplift, subsidence, extension or
compression
The width of deformation along the length of the ground
rupture also largely depends on the type of faulting
Deformation-consists of horizontal and vertical displacement
along the fault trace and folding or bending along the adjacent
area

67. Motion along the main trace involves horizontal or
vertical displacement or combination of both
Floors, walls may not only break horizontally or
vertically but undergo twisting and tilting
Rupturing can cause a lot of damage in areas such as
roads, tunnels, dams, pipelines etc.

69. Sound engineering and construction practice may be
adopted to prevent total destruction
The best way is to avoid active fault traces and
deformation zones while planning a construction

71. Major risk for large engineering
structures such as dams, bridges and
nuclear power stations and requires
careful mapping of existing faults to
identify any likely to break the
ground surface within the life of the
structure

73. Earthquakes may cause water and sediments to be
squeezed out toward the surface like "quicksand".
When this happen, the soil loses strength to hold
rocks together
In this phenomenon, buildings or other structures
topple, tilt, but not collapse.

74. This may happen in beach zones, sand spits, sand
bars, and wide coastal plains and in areas underlain
by sands lahar deposits

75. Liquefaction Is a process that
transforms the behavior of a body of
sediments from that of a solid to that
of a liquid when subjected to
extremely intense shaking. As a
result, any heavy load on top of the
sediment body will either sink or tilts
as the sediment could no longer hold
load

77. When the ground shakes, some areas especially those made
of wet fine sand are subjected to liquefaction
Because of the passing of seismic waves (shaking), causes
loss of equilibrium or disturbance of the granular structure
When pressure exceeds the weight of overlying material,
water will be released and sediment grains will be separated
From solid state to increase in pore-water pressure

79. FLOW
FAILURES
Considered the most dangerous type of ground failure due
to liquefaction, this occurs on liquefiable slope material with
steepness greater than 3 degrees. Blocks of overlying
material slide down so fast (as much as kms/hr) that these
reach distances tens of kilometers

80. LATERAL
SPREADING
Blocks or the broken pieces of the flat or very gentle
ground (less than 3 degrees) slows a liquefied zone move
laterally

81. GROUND
OSCILLATION
Due to the or nearly flat slope, the ground is unable to
spread and instead oscillates like a wave (back and forth
and up and down). Water and wet sand are ejected through
the fissures that form conical-shaped mounds of sand at the
surface (sand blows)

82. LOSS OF BEARING
STRENGTH
Loss of strength of sediments resulting in tilting of houses
and floating of buoyant structures (e.g fuel tank) that are
anchored on the liquefied zone

83. SETTLEMENT
vertical readjustment or settlement within the liquefied zone
as a result of dissipation of pore-water pressure or the
ejection of materials during the formation of sand boils
(fountains of water and sediment coming from the
pressurized liquefied zone)

85. Liquefaction causes some of the most
striking ground failures and damages to
structures
Damage during liquefaction results from the
settlement of structures into the soil, flow
spreading landslides, and the ejection of water and
sediment at the surface in the form of sand blows
or sand boils, fountains or even seepage of water
that leads to flooding

87. Maps showing the potential of areas seismically-induced
liquefaction
Occurs in areas underlain by layers of loose, well sorted water
saturated sand and silty sand within 30 meters of sediment
Maps may factor in the intensity of seismic shaking or the
pressure the sediments subjected to
The ease with which a fine sandy sediment is liquified depends
on how loose the material is, amount of clay between particles,
amount of drainage restriction

88. DENSIFICATION
results in increased pore water pressure and
decreased strength

89. Liquefaction decreases with depth because of the heavy
load of overlying sediments. Water saturation lightens this
load.
With a higher water table, liquefaction susceptibility of
sediment becomes higher
A lesser number of occurrences have taken place in
areas where the groundwater tables is lower than 20
meters from the surface

90. The younger sediment deposit, the greater its susceptibility
to liquefaction
Liquefaction hazard zones should also include areas known
to have experienced liquefaction during historic quakes

92. Hazard zone maps are prepared to identify areas
potentially subject to liquefaction
Used by property owners to identify vulnerable
structures

93. EARTHQUAKE-INDUCED
GROUND SUBSIDENCE
LIQUEFACTION
related settlement - The eruption of boils leads to
localized differential settlement. Flow failure,
lateral spreading, and loss of bearing strength can
also cause large vertical readjustments when
earthquake shaking has subsided

94. TECTONIC SUBSIDENCE
Significant subsidence often accompany the
ground rupture process. The amount of
subsidence will depend on how large the vertical
displacement component is. Lake and ponds may
form on the downthrown side nearby fault where
the vertical displacement is usually greatest. The
amount of subsidence diminishes with distance
away from the fault

96. Landslides occur when an object is released from
one’s grip, it yields to the pull of gravity and must
come down.
Slope failures occurs when part of it changes from
stable to an unstable condition

97. Regardless of how a landslide is triggered, gravity is
always the primary force that enables any landslide
to occur, Many know devastating landslides had
been triggered by earthquakes

98. Earthquake-induced landslide Loose
thin soil covering on the slopes of
steep mountains are prone to mass
movement, especially when shaken
during an earthquake

100. Removal of support
Groundwater (pore water) pressure
Volcanic eruptions
Intense rainfall

101. Snowmelt
Human interventions
Earthquakes

103. TOPPLES
occur suddenly when a massive part
of very steep slopes break loose and
rotate forward

104. ROCK FALLS
collapse of material from a cliff or
steep slope

105. SLIDES
involve large blocks of bedrock that
break free and slide down along a
planar or curved surface

106. LATERAL
SPREADS
triggered by earthquakes and affect
gentle slopes with less than 10
degrees inclination

107. FLOWS
involve downslope motion of fine
grained clay, silt, and fine sand
made mobile by water saturation

109. The downslope component of the force acting
on a rock mass must overcome the shearing
strength of the material
When a slide occurs, either the force acting on
the material increased or the shearing
resistance of the material was lowered

110. Depending on the type of slope material, the
steepness of the slope and strength-related
properties of the materials involved, various
types of landslide may occur during an
earthquake

112. Developing and enforcing ordinances
Creating emergency management programs
Partnership with the private sector
Establishing hazard maps
Teaching people what to do before, during, and
after a landslide

114. Many parameters when maps are drawn showing
landslide susceptibility of areas including the strength of
the materials, topographic characteristics, and triggering
mechanism
The (MGB) Mines and Geosciences Bureau – rain-
induced landslide
The PHIVOLCS – earthquake-induced hazard maps
Longer and steeper slopes

115. ASPECT OF THE SLOPE
Plays a role in where landslides occur. The surface
curvature has an influence to seismic slope
stability. Large landslides are usually vertical
convex slopes

116. GEOLOGICAL FACTORS
Determine which part of the landscape are prone
to landslides are those that contribute to low
strength rock or soil materials

120. Tsunamis are giant sea waves generated mostly by
submarine earthquakes
It can only occur when the earthquake is shallow-
seated, and strong enough about (M6) to displace
parts of the seabed and disturb the mass of water
over it

121. Other causes of tsunamis include submarine or
coastal landslides, pyroclastic flows and large volume
debris avalanches from submarine and partly
submerge volcanoes, and caldera collapse

122. Tsunami Is a series of sea waves
generated by various geological
processes and commonly generated
by under-the-sea earthquakes and
whose heights could be greater than
5 meters.

126. An event like an underwater earthquake
happens. The movement forces a lot of water to
move very quickly
The whole water column (the water from surface
all the way to the seafloor) moves at speeds of
up to 1000km per hour away from the
earthquake location.
Because of the way tsunami are caused, they
produce multiple waves (like the ripples you get
when you drop a stone into water).

127. As the front edge of the wave gets to shallower
water it slows. However, the back of the wave in the
deeper water is still moving fast so the water ‘piles
up’, and the tsunami wave height grows as it
reaches the coast.
Sometimes it looks like the water sucks down and
away from the coast, then rushes back in with
enormous speed and force. Sometimes there is no
‘sucking out’. This depends on if the high part
(crest) or the low part (trough) of the wave reaches
the coast first.

128. When the wave reaches shore it travels inland
on gentle slopes or flat land or pushes uphill on
steep slopes, travelling at speeds similar to a fast
car.
As the waves move they carry debris (like trees,
rocks, boats, vehicles or bits of building) that
cause damage.

130. The displaced water forms a tsunami wave that can travel
thousands of kilometers before it reaches land
During the deep ocean propagation stage, the wave
height is small compared to the wavelength and the ocean
depth
The wavelength is typically 200 kilometers
V = (gb)² where b is the depth of the ocean, and g = (9.8
m/s²) is the force of gravity

132. Tsunami waves causes inundation of coastal waves
Tsunami wave heights could reach tens of meters above the
normal sea level
As tsunami waves gets closer to the shore, It slows down
because of decreasing depth. The decrease in depth to sea
bottom causes an increase in wave height
A ∝ 1/√b where A = wave amplitude
B = water depth
Destructive power of tsunamis is caused by shoaling effect.
The deeper the water, the longer the wave, the faster the
tsunami propagate

134. Tsunamis are generated during an
earthquake along a body of water.
Earthquake triggered landslides
occurring under the ocean or coastal
areas

135. Any submarine or coastal activity that
can trigger tsunami by displacing
large amount of water
Meteorite falling in the ocean

137. LOCAL TSUNAMI
Are confined to coasts within a hundred kilometres
from the source. It is usually generated by
earthquakes and landslides or pyroclastic flow. It
can reach the shoreline within 2 to 5 minutes.
FAR FIELD OR DISTANT
TSUNAMI
Can travel from 1 to 24 hours before reaching the
coast of the nearby countries. These tsunamis
mainly coming from the countries bordering Pacific
Ocean like Chile, Alaska in USA and Japan.

138. Produced up to 9 meter high
tsunamis which devastated the
coast of Mindanao and left more
than 4,000 people dead, with at
least 2,000 people missing.

139. NATURAL SIGNS OF AN
APPROACHING LOCAL TSUNAMI

141. The degree of tsunami hazard
that a coastal area faces
depends on the exposure to
offshore earthquake generators
The Philippines is surrounded
by trenches that had been the
source of tsunamigenic
earthquakes

145. Prepare to vacate
Always keep a radio or other source of information
Bring a survival kit
Stay in the designated evacuation center

146. Take escape routes that are safe from tsunami waves and
floods
If it is too late to escape, cling on to floating objects to
prevent drowning
Stay alert

148. PACIFIC TSUNAMI WARNING CENTRE
monitors the ocean surface using satellites, radar, and
buoys in the water that measure speed and waves
Once tsunamis is generated, PTWC alerts local authorities
of areas
PTWC relays information and warning
PHIVOLCS has been setting-up tsunami warning systems

150. Providing warning systems and evacuation plans
LGUs and gov’t agencies concerned need to
constantly remind the people through information
and education campaigns about the dangers involved
Homeowners should adopt measures before a
tsunami strikes

151. SOME NOTABLE
TSUNAMIS OF
THE WORLD

152. 2011
TSUNAMI
JAPAN

153. 2004
TSUNAMI
INDONESIAN

154. 1998
TSUNAMI
PAPUA NEW GUINEA

156. EARTHQUAKE
DRILL
The conduct of earthquake drill in school requires through
planning and designing of evacuation procedure, as well
as orienting the teachers, students and other school staff
on how to go about with this.

157. SMDC (School Disaster Management Committee)
OVERALL COORDINATOR
In charge of the coordination of activities of the SMDC. As part
of preparedness, takes the lead in the programming of
activities such as conduct of drills
EVACUATION TEAM
Responsible for designing the evacuation plan, dissemination
and ensuring implementation of the plan during earthquake
emergencies

158. SMDC (School Disaster Management Committee)
FIRST AID TEAM
Responsible for training a group of people on how to
handle first aid
FIRE SAFETY
In charge of ensuring that the school is fire-proof and safe

159. SMDC (School Disaster Management Committee)
During non-disaster, in charge of disseminating
earthquake preparedness information to increase
awareness, during actual earthquake emergency, is
responsible for giving announcement of relevant
information
COMMUNICATION TEAM

160. SMDC (School Disaster Management Committee)
BUILDING SAFETY INSPECTION TEAM
Knowledgeable in building safety and they should,
together with an expert in structural engineering to inspect
regularly the school facilities
SITE SECURITY TEAM
Ensures the safety of people and protects schools
properties during an emergency

161. This can be started by having a class activity wherein
teachers and students go around the school premises to get
acquainted with safe spots in the school campus and
identify unsafe practices, potential hazards, danger zones at
school, in case of a strong earthquake
SCHOOL WATCHING EXERCISE

163. An earthquake affects the whole building and nearby areas
People perform duck, cover and hold (DCH) during an earthquake
and evacuate the building after if necessary
Immediate outside help is not a guarantee especially after a
strong earthquake
The area for evacuation after an earthquake is limited only to
open spaces that re safe from falling debris
There is aftershock in an earthquake event

164. PHASES OF AN EARTHQUAKE DRILL
Alarm Response Evacuation

165. PHASES OF AN EARTHQUAKE DRILL
Assembly Head Count Evaluation

167. A fire is concentrated in one area of the building
People need to immediately evacuate and put out the
fire
Outside help will arrive definitely at the soonest time
Affected building occupants can be evacuated
anywhere outside the building farthest from the fire

169. What will be felt? Weak or strong shaking
What may be heard? Low or loud rumbling noise followed
by shaking sounds of cracking and creaking wood
What may be seen? Hanging objects swing violently or
may even fall; some objects may rattle and may even break

171. 1-minute strong shaking signified by 1 minute siren or bell
Person cannot stand
Buildings may have been damaged but no collapse
Possible falling objects including glass windows
Self-help and sustenance is required
Possible injuries, fear, panic, among students and teachers

173. A school earthquake evacuation plan should have provision to
utilize all available open spaces nearest the building that are
safe from falling debris
Is there sufficient area for all?
Identify temporary refuge per class
Exit points and routes
Finalize the map
Disseminate information