- Earthquakes - Extent of damage caused by earthquakes - Risks associated with earthquakes

1. Phenomena at
Different Plate Boundaries
Earthquakes:
 Formation
 Different parts
 Types (deep/shallow focus)
 Aftershocks
 Measurement (seismograph)
 Magnitude (Richter scale)

2. What do you think happened here?

3. What do you think happened here?
How many earthquakes do
you think happened today?
Let’s check it out!
http://quakes.globalincidentmap.com/

4. Definition of earthquakes
• A vibration or tremor in the earth’s crust caused by the
sudden release of stored energy in the rocks found along
fault lines.

5. Formation of earthquakes
• Plate movements cause the slow build-up of stress on the
rocks found on either side of the fault.
• When the rocks can no longer
withstand the increasing stress,
they can sudden slip many
metres, causing an earthquake.

6. Formation of earthquakes
• EQs release energy in the form of seismic waves, which
radiate out from a point of sudden energy release, called
the focus.
• The point on the earth’s surface directly above the focus is
the epicentre.

7. Parts of an earthquake
Seismic waves

8. Deep-focus vs Shallow-focus EQs
Which do you think
has a greater
impact on land?

9. Shallow-focus:
• Upper 70km of earth’s crust
• Stronger vibrations
• Greater impact on land
Deep-focus:
• Between 70 and 700km
below earth’s surface
• Weaker vibrations
• Smaller impact on land
Deep-focus vs Shallow-focus EQs

10. Aftershocks
• After an earthquake event, the stress from the ground
within the earth’s crust may cause many smaller EQs called
aftershocks along the fault line.
• Aftershocks are dangerous as they are usually
unpredictable and can be of large magnitude.
• Can cause building collapse
• A series of aftershocks may occur for several months after
the initial EQ

11. Earthquakes vs Aftershocks
Earthquakes: Aftershocks:
• Earthquakes are
vibrations in the
earth’s crust caused by
the sudden release of
stored energy in the
rocks found along fault
lines.
• Aftershocks are smaller earthquakes
caused by the stress from the ground
within the earth’s crust after an
earthquake event.
• Can occur several months after initial
EQ.
• Can be as powerful as original EQ.

12. Measuring earthquakes
• A seismograph records the seismic waves released by an EQ

13. (D) Earthquakes
Measuring EQs:
• A seismograph records the seismic waves released by an EQ

14. Extent of earthquakes
• EQs release different amounts of energy.
• Magnitude of an EQ = the amount of energy released.
• Richter scale is used to measure the magnitude of an EQ.
• For each increasing magnitude on the Richter Scale,
the impact of the EQ becomes 10 times greater.
• http://www.learningliftoff.com/2nd-grade-science-activity-
richter-scale-activity/#.WGI191V97IV

15. • According to the Richter scale,
higher magnitude = more extensive damage.
Is this always the case?
Extent of earthquakes

16. Watch this 
• Video 1 - Haiti, 2010
https://www.youtube.com/
watch?v=4770QrLTgHE
• Video 2 – Chile, 2010
https://www.youtube.com/
watch?v=cNkgyIRBBLQ
Japan
Chile
What magnitude do you think they are?
Extent of earthquakes

17. Video 1 - Haiti, 2010 https://www.youtube.com/watch?v=4770QrLTgHE

18. Video 2 – Chile, 2010 https://www.youtube.com/watch?v=cNkgyIRBBLQ

19. Let’s do a comparative study:
• Haiti, Jan 2010
• Chile, Feb 2010
Chile
7.0
Extent of earthquakes

20. Phenomena at
Different Plate Boundaries
Earthquakes:
 Extent of damage
 Distribution/Locations
i. Population density
ii. Level of preparedness
iii. Distance from epicentre
iv. Time of occurrence
v. Type of soil

21. Depends on (i) Population Density
Great Hanshin EQ in Kobe, Japan
(1995)
Great Alaskan EQ in Alaska
(1964)
Magnitude 7.2 Magnitude 9.2
• 6,300 people died
• 300,000 homeless
• 180,000 buildings destroyed
• > 350 fires broke out
• 131 people died
• Major structural damage
• Kobe was a more densely built-up
city
• Port city of 1.5 million people
• Death toll was extremely small for
a quake of this magnitude due to
low population density
Extent of damage caused by EQs

22. Depends on (i) Population Density
Extent of damage caused by EQs
Haiti, Jan 2010 Chile, Feb 2010
Magnitude 7.0 Magnitude 8.8
• 300, 000 deaths
• 1.3 million homeless
• US$7.8~$8.5billion in damage
• 60% of govt buildings &
80% of schools destroyed
• 600 people died
• 2 million homeless
• US$15~30billion in damage
• Infrastructure largely intact
• Densely populated • Sparsely populated

23. • E.g. having evacuation plans, trained rescue workers &
a range of action plans (e.g. relief actions – food supply,
shelter etc)
Depends on (ii) Level of Preparedness
Extent of damage caused by EQs

24. • One of the most famous successful EQ predictions:
Occurred in the town of Haicheng, China, 1975.
Chinese scientists noticed:
- The slow tilting of the land surface
- Changes in ground water levels
- Numerous foreshocks (low-magnitude tremors)
- Unusual animal behavior (screaming of normally quiet pandas).
The authorities took heed and evacuated 90,000 people before a magnitude
7.3 earthquake occurred and destroyed 90% of the city’s buildings.
Depends on (ii) Level of Preparedness
Extent of damage caused by EQs

25. • Nearer the epicenter:
receives strongest
shock waves  most
devastating damage
Focus
Epicentre
Depends on (iii) Distance from the Epicentre
Extent of damage caused by EQs

26. • Time of day when EQ occurs + where/what people are doing
 affects their chances of survival
• E.g. Sun Moon Lake Region in Taiwan (1999)
• More than 2,400 people died when an EQ occurred a
couple of hours after midnight
•  people were sleeping!
•  trapped in the houses & did not escape in time
Depends on (iv) Time of Occurrence
Extent of damage caused by EQs

27. • Eg. In the 1985
earthquake that hit
Mexico, Mexico City was
severely damaged
compared to Acapulco
although it was further
away from the
epicentre.
Severely
damaged
Depends on (v) Type of Soil
Extent of damage caused by EQs

28. (D) Earthquakes
Extent of EQs depends on:
v. Type of soil
A comparison of the extent of shaking of buildings on loose sediment, reclaimed land and solid bedrock

29. How liquefaction occurs in saturated soil during an earthquake (https://www.youtube.com/watch?v=-eH5fh0YEuQ)

30. Phenomena at
Different Plate Boundaries
Earthquakes:
 Distribution

31. Distribution of Earthquakes
(Euro-centric map):

32. Distribution of Earthquakes
(American-centric map):

33. • At convergent, divergent and transform plate boundaries
• Most frequently at convergent plate boundaries
• More stress builds up when a plate subducts beneath another
• 75% of EQ which occur each year are found along the Pacific Ring of Fire.
• Occasionally, some EQ can occur some distance away from plate
boundaries
Distribution of Earthquakes

34. Phenomena at
Different Plate Boundaries
Earthquakes:
 Risks i. Tsunamis
ii. Disruption of services
iii. Landslides
iv. Destruction of properties
v. Destruction of infrastructure
vi. Loss of lives

35. (i) Tsunamis
• Tsunami refers to an usually large sea wave.
• Caused by:
• Movement of sea floor during a large EQ at subduction zones;
• An explosive underwater volcanic eruption; or
• Landslide above sea level which causes materials to plunge into the water.
• An earthquake near or in the sea generates seismic sea waves called
tsunamis.
• Huge tsunamis cause extensive damage to coastal areas.
• E.g. The 2004 Indian Ocean Tsunami was the result of an earthquake which
took place beneath the ocean.
Risks associated with EQs
TB pg. 34-35
Tsunamis:
- Causes
- Formation
- Damage caused

36. How tsunamis are formed (https://www.youtube.com/watch?v=aHljDIDf6js)

37. (i) Tsunamis
Risks associated with EQs

38. • An earthquake can disrupt services
such as the supply of electricity, gas
and water, which can affect a large
area.
• Communication services such as television broadcast and
telephone connections can also be affected.
• Eg. The earthquake in Kobe, Japan, in 1995 disrupted
electricity, gas and water supplies to about a million of Kobe
city’s 1.4 million residents.
(ii) Disruption of Services
Risks associated with EQs

39. • The shaking of the ground during EQs can
weaken the slopes of hills and mountains.
• Results in landslides: rapid downslope
movements of soil, rock and vegetation.
• Landslide can travel fast and flatten towns,
killing people.
• Mudflows may also occur when there is
heavy rainfall, causing mixed soil debris to
flow down the slope.
(iii) Landslides
Risks associated with EQs

40. • Earthquakes can cause widespread destruction to many homes.
• People may be without homes after the disaster, thus they may
have to reside at temporary
shelters while their homes are
being rebuilt.
(iv) Destruction of Properties
Risks associated with EQs

41. • Earthquakes may cause cracks to form in infrastructure such as
roads and bridges.
• Transportation can be disrupted as
it is unsafe
to use the
damaged
roads.
(v) Destruction of Infrastructure
Risks associated with EQs

42. • Earthquakes and their
associated hazards often
threaten the lives of those
living in earthquake zones.
• People could be buried in
the buildings that topple.
(vi) Loss of Lives
Risks associated with EQs

43. Phenomena at
Different Plate Boundaries
Earthquakes:
 Risks i. Tsunamis
ii. Disruption of services
iii. Landslides
iv. Destruction of properties
v. Destruction of infrastructure
vi. Loss of lives