Effects of earthquakes
There are two scales used to measure the size of earthquakes. The Modified Mercalli scale indicates the
intensity (or damage) of an earthquake, whereas the Richter scale refers to its magnitude.
The intensity of an earthquake at a particular locality is a measure of the violence of earth motion produced
there by the earthquake. It is determined from reported effects of the tremor on human beings, furniture and
buildings. The Modified Mercalli scale is based on what we can see and feel, whereas the Richter scale is based
on a precise scientific measurement.
Modified Mercalli scale
Richter scale
I
Felt by almost no one.
2.5 Generally not felt, but recorded on seismometers.
II
Felt by very few people.
III Tremor noticed by many, but they often do not realize it is
an earthquake.
3.5 Felt by many people.
IV Felt indoors by many. Feels like a truck has hit the building.
V
Felt by nearly everyone; many people awakened.
Swaying trees and poles may be observed.
VI Felt by all; many people run outdoors. Furniture moved,
slight damage occurs.
4.5 Some local damage may occur.
VII Everyone runs outdoors. Poorly built structures
considerably damaged; slight damage elsewhere.
VIII Specially designed structures damaged slightly, others
collapse.
6.0 A destructive earthquake.
IX All buildings considerably damaged, many shift off
foundations. Noticeable cracks in ground.
X
Many structures destroyed. Ground is badly cracked.
XI Almost all structures fall. Very wide cracks in ground.
7.0 A major earthquake.
8.0 and up: Great earthquakes.
XII Total destruction. Waves seen on ground surfaces,
objects are tumbled and tossed.
Note: The comparison is generalised and approximate.
(Source: North Carolina Geological Survey website)
1 Plot the earthquakes from this table onto the scatter graph below.
Place
Tangshan, China 1976
Sumatra 2004
Haiti 2010
Ashgabat, Turkmenistan
1948
Sichuan, China 2008
Kashmir, Pakistan 2005
Chimbote, Peru 1970
Iran 1990
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Magnitude
7.8
9.1
7
Death toll
245,000
230,000
220,000
7.3
110,000
7.9
7.6
7.9
7.4
88,000
86,000
70,000
50,000
2 Why would knowing the intensity of an earthquake (i.e. the Mercalli scale) in a particular area be of more
use to rescuers than knowing the magnitude (Richter scale)?
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