Physical GEOG: Chapter 5 - Earthquakes


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Physical GEOG: Chapter 5 - Earthquakes

  1. 1. An earthquake is a vibration or tremor of the Earth’s surface caused by the sudden release of energystored in the crust. The focus is the point of release of energy within the Earth’s crust. The epicentre is thepoint on the Earth’s surface that lies directly above the focus.Formation of earthquake When (plate name) converge/diverge/slide past (plate name), the plate movements are not smooth. A lot of pressure is built up because of the tremendous amount of friction. As the rocks are forced to bend, large amounts of energy are stored in the rocks. When the stress become too immense to be held by the rocks, they jerk free into new positions along a fault line. The stored energy is released in the form of seismic waves which causes the ground to vibrate. Factors affecting STRENGTH of earthquake Description Shockwaves are felt more strongly near the Distance from epicentre epicentre as the waves are not weakened much. Shallow focus leads to a stronger earthquake as Depth of focus vibrations are not weakened as they travel upward. Type of hazard Earthquake hazard Description - Urban features (eg. flyovers, bridges, buildings) may not be able to withstand vibrations of earthquake. Collapse of infrastructure - Foundations may be weakened and aftershocks may collapse entire structure. - People are trapped under rubble Direct and they may die. - Earthquake causes ground to shake, loosening soil causing it to slide down a slope, barying people and buildings along the Landslides way. - Worsened by deforestation, without roots, nothing to bind soil together. - Damaged wires, overturned stoves, broken gas pipes will cause sparks to light a fuel source Indirect Fires which will cause fires. - People may be burnt, buildings may collapse when burnt badly leading to high loss of lives.
  2. 2. - Earthquakes causes displace- ment of seabed which displaces water and causes a tall wave to crash onto shore. - Floods may wash away people and they drown. Buildings are severely damaged by Indirect Tsunamis floodwaters. - Formation of tusnami: SAME AS FORMATION OF SWASH. - 2004 Indian Ocean Tsunami was triggered by an undersea earthquake where >250k lives lost. Impacts of earthquake Elaboration - Earthquakes can cause loss of live through abovementioned hazards. Loss of lives - Further worsened if emergency efforts is slow to arrive. Aftershocks may also cause as much loss of lives as the main earthquake. - Destruction of infrastructure inconveniences businesses located in affected area because consumers or products cannot get to shop. - Tourism is affected as rubble in unappealing andNegative economic consequences no tourists would want to visit the earthquake-hit country, fearing another one will occur. - Cost of reconstruction and repairing is high especially in well-developed urban areas (eg. cost of reparations of 1995 Kobe EQ: S$100 bil) - Survivors would live in overcrowded makeshift shelters that lack in proper sanitation facilities and clean drinking water. Spread of diseases - Spread of water-borne diseases occurs, unremoved dead bodies and sewage water pollute water and reduces amount of clean drinking water.
  3. 3. - Coupled with image of disasters, loss of lives, Trauma monetary and housing worries leave victims paranoid and scared of the future. - People with coastal jobs (eg. owners of beach Disruption of jobs resorts, fishermen) would temporarily have no jobs, creating worries about their livelihood.Factor influencing extent of damage Description Example - The stronger the earthquake, the - In the 2010 San Francisco EQ more powerful the seismic waves with magnitude of 4.2, there was and the more destruction occurs hardly any casualties. In the 2010 Magnitude of earthquake at the earthquake zone. Haiti EQ with magnitude of 7.0, there were 200 000 deaths reported. - Shockwaves are felt more - In the 1993 Maharashtra EQ, strongly near the epicentre as the Killari which was 12km from Distance from epicentre waves are not weakened much. epicentre had far more deaths than Gulbarga which was 84 km from the epicentre. - A place with a sparse - In the 1964 Anchorage EQ, a population and few buildings will 9.2 magnitude earthquake killed Population density have few deaths as there is not only 115 people because Anchor- many collapses. age had a sparse population then. - Places with soft soil experience - In the 1985 Mexico City EQ, stronger shock waves than places more damage was seen in Mexico with hard soil because soft soil City (built on soft soil) than Geology amplifies the shock waves. Acapulco (built on hard soil) even though Acapulco was nearer the epicentre. - In places where people are - In Japan, frequent drills are held more prepared and buildings are to educate the public hence it Level of preparedness more resistant, there would be does not have much injuries or less deaths and less building casualties during its frequent collapse. earthquakes.
  4. 4. Adaptation Description + - Example - If possible, infra- - Increases - Illegal slums - In USA, earth- structure should be distance from built by the poor quake risk maps as far away from epicentre hence can inhibit efforts have been drawn Planning the earthquake prone weaker seismic to relocate, poor to draw up location of zone. Estimation waves reach the cannot move into building guidelines infrastructure of level of risk of place, may be so proper houses. to ensure minim- ground failure little to cause no um damage during advised. damage. earthquakes. - New infrastru- - More resistant - Very expensive - In California, cture can be built to earthquake to build and USA, the to withstand tremors preventing maintain. Transamerica strong tremors collapse and loss Pyramid at S$75 - Historical caused by earth- of lives. mil to build.Designing new buildings are not quakes. Make useinfrastructure conserved as these of latest tech- - In Tokyo alone, buildings are nology (eg. steel there are more required to be bars, shock absor- than 1.8 mil old demolished. bers) to dissipate buildings. energy - Steel frames, - Historical - Not as resistant - In the 1994 rods wrapped buildings are as compared to Northridge EQ, around pillars of conserved as these new buildings buildings and buildings and buildings hold flyovers strengthe- Strengthening bridges. Fireproof significance to the ned with steel existing materials and auto country. frames were dama- infrastructure shut-off valves can ged despite the be installed to - Cheaper than new earthquake- reduce chance of demolishing and resistant buildings fire. rebuilding. remain-ing unchanged. - Regular drills to - People are well - Complacency is - Research shows familiarise with prepared and they an issue as people that people in warning signals, know what to do in do not take this Tokyo are more Education posters to educate an earthquake. drills seriously. complacent as a public major earthquake has not happened recently. - Sophisticated - Gives time for - Authorities and - In the 1975 instruments (eg. evacuation if businesses ignore Haicheng EQ, 90 Earthquake seismometers, detected early, warnings to 000 people weremonitoring and underwater tsun- reduces loss of prevent loss of evacuated aswarning systems ami sensors) warn lives. business and scientist could people to evacuate interruption to detect ground early when detect- services. changes early. ed.