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III living with the earth‘s endogenous forces
Earthquakes – moving facts
Earthquakes – moving facts
Dangers
[…] The first danger from such an earthquake arises from the effects of the ground
movements.
Along with the direct damage to buildings
from the tremors themselves, the ground
on which the buildings stand may also be
damaged. […].
As a consequence of the ground tremors,
landslides and mudslides can also be triggered.[…]
The second danger comes from the permanent displacement of ground after very
strong quakes, from which buildings located
in the immediate vicinity of faults may sustain severe damage.
The third danger consists of flooding. Earthquakes can destroy dams or damage dykes
[…].
The fourth source of danger is fire. Earthquakes can destroy supply and disposal
lines. […]
Fires become an even more serious problem
when no water is available for fire-fighting
on account of burst water pipes. […]. The real
dangers for people come from being struck
by parts of buildings, drowning in floods from
broken dams, being buried under landslides
or trapped by the ensuing fires.
Susceptibility to earthquakes –
Chile and Haiti
“Earthquakes by themselves do not kill anybody. And they also do not
cause any damage when there is nothing there to be destroyed,” concluded
an American geophysicist after the major earthquake in Chile in 2010. But
what factors are responsible for turning a natural event into a disaster?
This question can be answered by comparing two countries, Haiti and Chile,
which both suffered massive earthquakes within a short period in 2010.
1.
Locate Chile and give reasons for its earthquake risk (M1).
2. Compare the earthquake events, their effects, and the respective political, economic and social situations in the two
countries (M2/ M4).
3. A
Chile and Haiti are susceptible or vulnerable to natural
disasters in different ways. Explain.
B Summarise: What turned the earthquake in Haiti into such a great disaster?
4.
Explain the structure of the Earth and characterise its individual shells with reference to their important features
(M6).
5. After the melting of large ice masses, as for example in
Scandinavia at the end of the Ice Age, compensatory movements take place. Explain why historic seaports there are
now situated many metres above sea level.
M3 Temporary tent camp for victims of the earthquake disaster in
Haiti
Nazca Plate with Cocos Plate
Under-
South America
Ocean
Deep-sea trench
Subduction zone
North America
Pacific
Himalayas
Alps
Upper crust
(granite, gneiss)
0
-10
Lower crust (basalt),
lithospheric upper mantle
-20
-30
Oceanic
crust
-40
Upper mantle
(asthenosphere)
-50
Conrad Discontinuity
-60
Mohorovičić Discontinuity
Boundary area between the
upper continental granitic crust,
with a density of 2.6 – 2.7 g/cm³,
and the underlying heavier basalt
crust (density 2.9 – 3.0 g/cm³).
This discontinuity is not
detectable beneath oceans.
(short form: Moho - D.)
Boundary area between the
oceanic crust and the mantle;
density rises abruptly to ~3.2 g/cm³,
thus accompanied by an abrupt
increase in the propagation speed
of seismic (volcanic) waves.
11061E_2
The speed of the waves depends on the ruling density of the rock or the physical state
of the material.
Higher-density rock transmits seismic waves
faster than rock with a lower density. Fluids
transmit the waves slower than solid bodies
or not at all.
When the speed and direction of the seismic
waves abruptly change, it can be concluded
by scientists that boundary layers, so-called
discontinuities in the Earth’s structure, are
present.
Source: www.seismo.uni-koeln.de
Based on: V. Kaminske, 2005
M5 Dangers from earthquakes
M7 Seismic waves
M8 Profile along the 45th parallel of the
Northern Hemisphere. The Earth’s
crust and the uppermost part of the
mantle together form the lithosphere,
the solid rock shell of the Earth. This
floats like a thin skin on the viscous asthenosphere and is pushed, distorted,
broken and shifted by forces from the
Earth’s interior. Portions of the lithosphere (plates) are immersed into the
asthenosphere like icebergs floating
in the water. The continental crust immerses more deeply into the denser
mantle.
American Plate
Andes
(fold mountains)
Pazific
Pacific
km
+10
Volcanic acticity
Atlantic
Ocean
water
volcanoes
Ocean surface
Magma chamber
Earthquake
hypocentres
Ascending
magma
Continental crust
(continental slope)
Oceanic crust
Convection
currents
1339E_22
M1 Geological situation of Chile
Strength of earthquake on the moment magnitude
scale
Number of deaths
Chile
Haiti
8.8
7.0
700
220,000
Estimated material damage
30 bill. $
8 bill. $
Population
17 mill.
10 mill.
Gross National Product (adjusted for purchasing
power)
243 bill. $
11.5
bill. $
GNP per capita (adjusted for purchasing power)
14,311 $
1,151 $
863 $
58 $
21
146
Public health spending (per capita)
Corruption Index: Position in country ranking
(Position 1 = least corrupt)
Source: Bündnis Entwicklung Hilft, 2012
M2 Comparison of earthquake regions
The earthquake in Chile was significantly stronger than that in Haiti,
yet it was in the small Caribbean country that considerably more
people lost their lives. How come?
The answer is very simple: Chile is far better prepared for such disasters. Latin America’s most prosperous country has strict building
regulations, which are also generally adhered to. And there was also a
disaster plan in existence, which was put into operation immediately
after the severe earthquake. In Haiti, no such plan exists. It is not
the strength of an earthquake that causes buildings to collapse, but
above all their building structure. In the past years, and particularly
in the public housing sector, many houses have been built in accordance with strict earthquake safety provisions. Thus the poorer
districts in particular were spared from massive destruction – in
stark contrast to Haiti.
In Chile, not only the architects and building owners but also the
public authorities including the rescue services are prepared for
earthquakes. In May 1960, the Andean country suffered what was
then the strongest earthquake ever recorded anywhere in the world,
and the February 2010 quake was its third with a magnitude above
8.8. In Haiti, on the other hand, the last comparably severe quake
was 250 years ago. And finally, Chile is rich enough to enable the
population affected by the earthquake to provide for themselves.
Haiti, by contrast, will be dependent on international aid supplies
for months, if not years. Its notoriously poor infrastructure and
governance are responsible for this.
Crust – Divided into continental and oceanic crust.
The boundary between the crust segments does not follow
the edges of the continents. They are composed of different
material. Connected with this is a difference in density:
The granitic, continental rock is considerably lighter than
the basaltic rock of the oceanic crust.
°C
Mantle – The dynamics that predominate here also
determine tectonic events on the Earth’s surface.
The upper part of the mantle is solid. Below this is
the asthenosphere, which is characterised by a
viscous texture.
Core – The interruption of seismic waves indicates
that the outer core is liquid while the inner core is
solid, although temperatures of 6000 °C prevail there.
The inner core consists of a vast ball of iron.
M6 The Earth‘s shell structure
Rift
Subduc
1000
Co
ntin
ent
al
pla
te
tion zon
0
1500
Based on: F. Bajak, Associated Press, 28.2.2010
M4 Two earthquakes with differing consequences
Oceanic
plate
e
Si
,O
Convection
cell
400
kbar
Mo
2
Ri
ft
Si
,O
Cru
st (
soli
d)
De
2
Dis
g/c nsity
con
m3
tinu
Li
ity
2000
sph tho3.3 ere
Ast
sp hen
Wich
er
(pa here 3o3700 2900 1500
Discot-Gute
th rt of .5
ntin nb
3000
ma e uppe
uit erg
ntle
y
Fe
Lo
) r
ma wer
n
(sol tle 5
id)
.6
CM
4000
B
(co
re m
ant
le b
oun
Out
dar
e
r
liq
y)
5000
withuid co
re
3400
con
4600 5150
vec
Ni
tion
12.
Fe
km
1
Sol
id
in
cor ner
e1
6000
2.5
6371
3600 kbar
ho
22140E_1
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