This lecture helps you to understand the basic terminologies of earthquakes. In this lecture you will also learn how to calculate the Earth Quakes.

1. Ahmad Hassan
2016-Civ-321
REFERENCE Chapter 1 Page 3 to 7 The Earth; Surface Structure andAge (AGeology
for Engineers 7th Edition by F.G.H. Blyth and M.H. de Freitas), lecture slides & class
notes
Earthquake

2. Outline
What is an Earthquake?
Cause of Earthquake
Measuring Earthquake
Earthquake’s Epicenter Located?
Size and Strength of an Earthquake Measured?
Destruction from Earthquake
Earthquake Prediction
Remedial Measures
Case Studies

3. What IsSeismology?
 Seismology is the study of earthquakes andseismic
wavesthat move through and around the earth. A
seismologist is ascientist who studies earthquakes
and seismic waves.
 Seismic waves are the wavesof energy causedby
the sudden breaking of rock within the earth or an
explosion. Theyare the energy that travelsthrough
the earth and is recorded onseismographs.

4. Typesof SeismicWaves
 There are several different kinds of seismic waves,
and they all move in different ways. The two main
types of wavesare body waves and surfacewaves.
 Body waves can travel through the earth's inner
layers, but surface waves can only move along the
surface of the planet like ripples on water.
Earthquakes radiate seismic energy as both body
and surface waves.

5. Measuring Earthquakes
What are Seismic Waves?
Response of material to the arrival of energy fronts
released by rupture
Body Waves: P and S waves
Surface Waves: R and L waves

6. Seismic wave behavior
– P waves arrive first, then S waves, then L and R
– Average speeds for all these waves is known
– After an earthquake, the difference in arrival times at a
seismograph station can be used to calculate the distance
from the seismograph to the epicenter.
How is an Earthquake’s EpicenterLocated?

7. Body waves
 Traveling through the interior of the earth, body
waves arrive before the surface waves emitted by
an earthquake. These waves are of a higher
frequency than surface waves.

8. P- waves
Thefirst kind of body wave is the P wave or primary wave.
Thisis the fastest kind of seismic wave, and, consequently, the
first to 'arrive' at aseismic station. ThePwave can move
through solid rock and fluids, like water or the liquid layers of
the earth. It pushes and pulls the rock it moves through just like
sound waves push and pull the air.
Haveyou ever heard abig clap of thunder and heard the
windows rattle at the sametime? Thewindows rattle because
the sound waves were pushing and pulling on the windowglass
much like Pwaves push and pull onrock.

9. P- waves
Sometimes animals canhear the Pwavesof an earthquake. Dogs,
for instance, commonly begin barking hysterically just before an
earthquake 'hits' (or more specifically, before the surface waves
arrive). Usually people canonly feel the bump and rattle of these
waves.
Pwavesare also known ascompressional waves, becauseof the
pushing and pulling they do. Subjected to aPwave, particles move in
the samedirection that the the wave is moving in, which is the
direction that the energy is traveling in, and is sometimes called the
'direction of wavepropagation.

10. Pwaves

11. S-Waves
The second type of body wave is the S wave or
secondary wave, which is the second wave you
feel in an earthquake. An Swave is slower than a
Pwave and can only move through solid rock, not
through any liquid medium.
It is this property of S waves that led
seismologists to conclude that the Earth's outer
core is a liquid. S waves move rock particles up
and down, or side-to-side-perpendicular to the
direction that the wave is traveling in (the
direction of wavepropagation).

12. S-Waves

13. S& Pwaves

14. Surfacewaves
Travelling only through the crust, surfacewaves
are of alower frequency than body waves,and
are easily distinguished on aseismogram asa
result.
Though they arrive after body waves,it is surface
wavesthat are almost entirely responsible forthe
damageand destruction associated with
earthquakes. Thisdamageand the strength of the
surface wavesare reduced in deeper
earthquakes.

15. LoveWaves
• Thefirst kind of surface wave is called aLove
wave, named after A.E.H.Love,aBritish
mathematician who worked out the
mathematical model for this kind of wave in
1911.
• It's the fastest surface wave and movesthe
ground from side-to-side. Confined to the
surface of the crust, Lovewavesproduce
entirely horizontal

16. LoveWaves

17. RayleighWaves
• Theother kind of surface wave is the Rayleigh
wave, named for JohnWilliam Strutt, Lord
Rayleigh, who mathematically predicted the
existence of this kind of wave in1885.ARayleigh
wave rolls along the ground just like awave rolls
acrossalake or an ocean.
• Becauseit rolls, it moves the ground up and
down, and side-to-side in the samedirectionthat
the wave is moving. Most of the shaking felt from
an earthquake is due to the Rayleigh wave,which
canbe much larger than the otherwaves

18. RayleighWaves

19. LoveWaves

20. RayleighWaves

21. What Is anEarthquake?
Earthquakes
 An earthquake is the vibration of Earth
produced by the rapid release of energy
 Focus and Epicenter
• Focus or hypocenter is the point within Earth where the
earthquake starts.
• Epicenter is the location on the surface directly above
the focus.
 Faults
• Faults are fractures in Earth where movement has
occurred or breaking of rocks.

22. Focus,Epicenter,and Fault

23. Cause of Earthquakes
 Elastic Rebound Theory
Most earthquakes are produced by the rapid release of
elastic energy stored in rock that has been subjected to
great forces.
When the strength of the rock is exceeded, it suddenly
breaks, causing the vibrations of an earthquake.
Rupture occurs and the rocks quickly rebound to an un
deformed shape
Energy is released in waves that radiate outward from the
fault

24. Elastic ReboundTheory

25. Cause of Earthquakes
 Aftershocks and Foreshocks
• An aftershock is a small earthquake that
follows the main earthquake. Continuing
adjustment of position results in aftershocks.
• A foreshock is a small earthquake that often
precedes a major earthquake.

26. Measuring Earthquakes
Earthquake Waves
 Seismographs
are instruments
that record
earthquake
waves.
 Seismograms are
traces of amplified,
electronically
recorded ground
motion made by
seismographs.

27. Seismograph

28. How is an Earthquake'sEpicenter
Located?
• In order to locate the epicenter of an earthquake you will
need to examine its seismograms as recorded by three
different seismic stations. On each of these seismograms
you will have to measure the S - P time interval (in
seconds). The S - P time interval will then be used to
determine the distance the waves have traveled from the
origin to thatstation.
• The actual location of the earthquake's epicenter will be on
the perimeter of a circle drawn around the recording
station. The radius of this circle is the epicentral distance.
One S - P measurement will produce one epicentral
distance: the direction from which the waves came is
unknown. Three stations are needed in order to
"triangulate" the location.

29. Example
• Step 1:
• Locate the required
Area.
• Wehave selected “San
Francisco area”.

30. Example
hundredsof
• Step 2:
• There are
seismic datarecording
stations throughout the
United States and the rest
of the world. In order to
locate the epicenter of this
earthquake, you need to
estimate the time interval
between the arrival of the P
and Swaves(the S-P
interval)on the
threeseismograms from
different stations.

31. Example
• Step2:
• You have to measure the
interval to the closest
second and then use a
graph to convert the S-P
interval to the epicentral
distance. On the sample
seismogram at the right
the vertical lines are
spaced at 2 second
intervals and the S-Ptime
is about 36interval
seconds.

32. Eureka,CA Seismic
Station S-PInterval
Find S-Ptime interval
from the given
Seismograph.
Scale:1 big box is
equal to 10seconds.

33. Elko,NV Seismic
Station S-PInterval
Find S-Ptime interval
from the given
Seismograph.
Scale:1 big box is
equal to 10seconds.

34. Las Vegas, NV Seismic
Station S-PInterval
Find S-Ptime interval
from the given
Seismograph.
Scale:1 big box is
equal to 10seconds.

35. Example
• Usethe S-Pgraph to the
right and the estimates
you made for the S-Ptime
intervals for the three
seismograms (shown
again for your
convenience) to complete
the table below. The
horizontal grid is in one
second intervals. Then
click the Find Epicenter
button.

36. Example

38. How is an Earthquake’sEpicenter
Located?
zones.
 Earthquake Distance
• The epicenter is located using the
differencein the arrival times between P
and S wave recordings, which are related
to distance.
 Earthquake Direction
• Travel-time graphs from three or more
seismographs can be used to find the
exact
location of an earthquake epicenter.
•A circle where the radius equals the
distance to the epicenter is drawn.
• The intersection of the circles locates
the epicenter
 Earthquake Zones
• About 95 percent of the major
earthquakes occur in a few narrow

39. Locating an Earthquake
The farther away a seismograph is from the focus of an earthquake,
the longer the interval between the arrivals of the P- and S- waves

40. Size and Strength of an Earthquake
Measured?
 Historically, scientists have used two different
types of measurements
 intensity
 magnitude

41. How are the Size and Strength of an Earthquake Measured?
• Modified Mercalli Intensity Map
– 1994 Northridge, CA earthquake,
magnitude 6.7
• Intensity
– subjective
measure of the
kind of damage
done and
people’s
reactions to it
– isoseismal lines
identify areas of
equal intensity

42. Modified Mercalli Scale
I. Instrumental
II. Feeble
III. Slight
IV. Moderate
V. Rather Strong
VI. Strong
VII. Very Strong
VIII. Destructive
IX. Ruinous
X. Disastrous
XI. Very Disastrous
XII. Catastrophic
Not felt except by a very few under especially favorableconditions.
Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects
may swing.
Felt quite noticeably by persons indoors, especially on the upper floors of buildings. Many do not
recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a
truck. Duration estimated.
Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors
disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars
rocked noticeably. Dishes and windows rattle.
Felt by nearly everyone; many awakened. Some dishes and windows broken. Unstable objects
overturned. Clocks may stop.
Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books
off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damageslight.
Difficult to stand; furniture broken; damage negligible in building of good design and construction; slight to
moderate in well-built ordinary structures; considerable damage in poorly built or badly designed
structures; some chimneys broken. Noticed by persons driving motorcars.
Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial
collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments,
walls. Heavy furniture moved.
General panic; damage considerable in specially designed structures, well designed frame structures
thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off
foundations.
Some well built wooden structures destroyed; most masonry and frame structures destroyedwith
foundation. Rails bent.
Few, if any masonry structures remain standing. Bridges destroyed. Rails bentgreatly.
Total damage - Almost everything is destroyed. Lines of sight and level distorted. Objects thrown into the
air. The ground moves in waves or ripples. Large amounts of rock may move.

43. How are the Size and Strength of an Earthquake Measured?
• Magnitude
– Richter scale
measures total
amount of energy
released by an
earthquake;
independent of
intensity
– based onAmplitude
of the largest wave
produced by an
event is corrected
for distance and
assigned a value on
an open-ended
logarithmic scale
Each unit of Richter magnitude equatesto
roughly a 32-fold energy increase

44. Size and Strength of an Earthquake
Measured?
 Momentum Magnitude
• Derived from the amount of displacement
that occurs along the fault zone
• Moment magnitude is the most widely used
measurement for earthquakes because it is the
only magnitude scale that estimates the energy
released by earthquakes.
• Measures very large earthquakes
(surface area of fault) x(avg. displacementalong
fault) x(rigidity ofrock)

45. Earthquake Magnitudes

46. Some NotableEarthquakes

47. The Economics and Societal Impacts of EQs
Damage in Oakland, CA, 1989• Building collapse
• Ground failure /
Liquefaction
• Tsunami
• Fire

48. Destruction from Earthquakes
Seismic Vibrations
The damage to buildings and other structures
from earthquake waves depends on
several factors.
 the intensity
 duration of the vibrations
 the nature of the material on which the
structure is built
 the design of the structure.

50. Destruction from Earthquakes
Seismic Vibrations
 Liquefaction
• Saturated material turns fluid
• Underground objects
may float to surface

51. Destruction from Earthquakes
Tsunamis: the Japanese word for “seismic sea wave”
 Cause of Tsunamis
ab•A tsunami triggered by an earthquake occurs where asl
of the ocean floor is displaced vertically along a fault.
•A tsunami also can occur when the vibration of aquake
sets an underwater landslide into motion.
Although tsunamis travel quickly, there is sufficient time to
evacuate all but the area closest to the epicenter.

52. Destruction from Earthquakes
Other Dangers
 Landslides
• With many earthquakes,
the greatest damage
to structures is from
landslides and ground
subsidence, or the sinking of
the ground triggered by
vibrations.
 Fire
• In the San Francisco earthquake of 1906, most
of the destruction was caused by fires that started when gas and
electrical lines were cut.

53. Predicting Earthquakes
 Short-Range Predictions
• So far, methods for short-range predictions of earthquakes have
not been successful.
 Long-Range Forecasts
• Scientists don’t yet understand enough about how and where
earthquakes will occur to make accurate long-term predictions.

54. Remedial Measures
Increase public awareness about hazardrisk
management.
Build capacity of professionals andgovernment
officials.
 Safebuilding practices and earthquake
resistant design.
Develop and enforce simple building codes for
rural and peri-urbanareas.

55. CASE STUDIES
Kashmir Earth Quake
Chile Earth Quake

56. Kashmir Earthquake
8th October 2005
7.6-magnitude
earthquake took place on
Saturday 8th October at
0925 local time.
The epicentre was
Muzzaffarabad the capital
of the Pakistan
administered region of
Kashmir, 80km north-east
of Islamabad.
It was followed by 20
powerful aftershocks

58. Thanks