Hwa Chong Institution
Geography
Worksheet 8: Earthquake &Tsunami – ANSWER 15
Name: ____________________________ ( ) Date: _________ Class: ______
Answer the following questions on foolscap paper.
1 On 26 December 2004, an underwater earthquake with a magnitude of 9.0 (the most severe category of earthquake) occurred off the western coast of northern
Sumatra, Indonesia.
Fig. 1 shows the Indian Ocean Earthquake and Tsunami region. Fig. 2 shows earthquake magnitude and deaths in some regions around the world, including the
Indian Ocean earthquake and tsunami.
Fig. 1
Source: GeoActive Online 340 and Geography Insights 3
Date
26 Dec 2004
Region
Indian Ocean
26 Dec 2003 South-eastern Iran
22 Jan 2003
17 Aug 1999
17 Jan 1995
28 Jul 1976
Colima, Mexico
Turkey
Kobe, Japan
Tangshan, China
Magnitude
9.0
6.6
7.6
7.6
7.2
7.6
Deaths
275 000
31 000
29
15 000
5 000
230 000
Fig. 2
Source: GeoActive Online 336
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(a) What is meant by the term “magnitude” of an earthquake, and how is this different from the “intensity” of an earthquake? [3] magnitude is the amount of seismic energy released which is measured by seismometer, on Richter scale (open-ended scale)
•
• intensity is the extent of damage done to human structures. ie the effects of the earthquake, which is not totally affected by magnitude it is measured on the Mercalli scale (1-12)
(b) Draw a well-labeled cross-section through the destructive plate boundary off
Sumatra. [3]
Diagram should include/label: o names of plates o arrows showing plate movement o subduction zone o stress build up o magma melting and rising o volcano o crust compressing to form fold mountains (Barisan Mountain)
Also include: o box for diagram o a title eg Destructive Boundary off Sumatra
(c) Describe the processes and features associated with this section of the destructive plate boundary, and explain how the earthquake that caused the tsunami was generated. [5]
 here the Indian (or Indo Australian) plate converges with the Sunda (Eurasian) plate
 the less dense Indian plate subducts under the Sunda plate
 this forms a deep depression , called the Sunda Trench forms here
 the continental crust is folded, crumpled and uplifted to form fold mountains, the
Barisan Mountains
 some of the subducted plate melts and forms magma
 this rises through cracks in the crust to form volcanoes eg Toba

Subduction is not a smoothproces s

A lot of stress is built up over time.
 when the rocks cannot withstand the stress, stress is suddenly released and rocks jerk , and slip many meters
 this earthquake took place under the sea
 and caused the water column to be displaced up, forming a huge wave, called a a tsunami
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(d) With reference to Fig. 2, explain why it is difficult to decide which earthquakes are more serious than others? [4]
NOTE: this question tests your knowledge on factors affecting earthquake damage, as well as data interpretation.
Content: Factors affecting earthquake damage:
 magnitude
 distance from epicenter
 population size, density

level of preparedness
 type of buildings , etc….
These factors must be weaved into the essay to support the data and not merely listed!!
 generally the higher the magnitude, the greater the damage as the amount of energy released is many times more
 eg the Dec 2004 had the highest magnitude of 9 and the most deaths too.

However , the lowest earthquake of magnitude 6.6 had more deaths than the
7.6 quake in Mexico

this could be due to difference in distance from epicenter

places nearer the epicenter suffer much more damage than places further away

Iran could have been closer to the epicenter than Mexico

Also the Colima,Mexico , Turkey and Tangshan quakes have the same magnitude of 7.6,

but the number of deaths are very different
– from 29 to 230000

this could be due to type of buildings

the buildings in Tangshan could have been less strong, hence causing more damage and deaths
Hence difficult to decide which earthquakes are more serious than others by looking at the magnitude alone.
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