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# Topic 3 Factors affecting damage of earthquake, Chapter 3.2 (Variations in disaster risks caused by earthquakes and volcanic eruptions across places) ## 1. Duration of Shaking (Nature of hazard) * Extent of disaster risk is influenced by the length of time of ground shaking. * Longer duration of...

# Topic 3 Factors affecting damage of earthquake, Chapter 3.2 (Variations in disaster risks caused by earthquakes and volcanic eruptions across places) ## 1. Duration of Shaking (Nature of hazard) * Extent of disaster risk is influenced by the length of time of ground shaking. * Longer duration of ground shaking → More damage * Structures (buildings and bridges) subjected to long periods of stress → More likely to collapse * Example: 2011 Tohoku, Japan earthquake (Mw 9.0) lasted for 6 minutes, causing massive damage to buildings. ## 2. Time of day (Nature of hazard) * Time of day influences the activities carried out & how people respond to earthquakes. * If people are asleep at night vs if people are at work/school during the day * *Less alert + unable to evacuate quickly* VS *More alert & able to evacuate quickly* * Less likely to be trapped → Less injuries + death * Example: 1995 Kobe, Japan earthquake (Mw 6.9), occurred at 6 a.m. → Many people were asleep, trapped at home → More than 6000 deaths ## 3. Population density (Exposure) * Refers to the amount of people per unit area (usually quoted as per square kilometer (km²)). * Higher population density → greater amount of people and buildings exposed * Example: 1995 densely populated industrial city of Kobe earthquake (Mw 6.9) → Death = Over 6000 people, Injuries ≈ 40000 people → Population density ≈ 3000 people per km² ## 4. Soil and rock properties (Vulnerable conditions) * Extent of disaster risk is also influenced by the soil and rock properties of the area. * Potentially open up the area to other earthquake hazards (liquefaction) - shaking of soil that is saturated and loose → Buildings may sink into the liquidified soil and tip over * Softer soil → Higher disaster risk * Seismic waves get amplified as they travel from hard rocks to soft soil * Waves slow down but become bigger when passing from rock to soil * Softer, loose soil shakes more intensely than hard rock → Increased likelihood of buildings and bridges collapsing → More likely to be trapped → More injuries + death * Example: 2010 Mw 4.0 earthquake in Port-au-Prince, Haiti (large areas of soil layers are soft soil) → many buildings collapse + more than 220,000 deaths. ## 5. Quality of building design and construction (Vulnerable conditions) * Plays a huge part in determining the extent of disaster risk. * Generally, earthquakes kill buildings and their contents, too. * Poorer the quality of building design and construction → more likely buildings to collapse; more trapped, injuries, and deaths * Factors of collapsing: Low-quality materials (e.g. zinc sheets) that are rigid and unable to withstand the shaking * Lack of earthquake-resistant features (reinforced steel walls) * Example: 2010 Mw 7.0 earthquake in Port-au-Prince, Haiti: many buildings and infrastructures collapsed as they were made of poor-quality materials, concrete pillars were poorly reinforced → More than 90% of buildings near the epicenter were destroyed ≈ 220,000 deaths ## Minimum * Building codes set by the authorities **Distance from epicenter (Exposure)** * Closer the city to the epicenter, greater the amount of people & buildings exposed → Greater disaster risk * Less energy is absorbed by the rock before reaching the city → Seismic waves reaching the city will be stronger & cause more violent shaking → Buildings & bridges are more likely to collapse. * Example: 2010 Mw 7.0 earthquake in Port-au-Prince, Haiti: epicenter was only about 25 km west of the city. More than 220,000 deaths