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92 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 93