Earthquakes: What affects the extent of damage during/after earthquake

Question 1

Factors that affect the extent of damage during/after earthquake

Answer 1

• magnitude
• depth of focus
• distance from epicentre
• geology of epicentre (type of soil at epicentre)
• population density
• time of occurence
• level of preparedness of ppl

Question 2

Magnitude

Answer 2

• higher magnitude, greater damage
• larger amt of energy released by earthquake
• Richter Scale used to measure magnitude
• for each increasing magnitude on Richter Scale, impact of earthquake becomes 10x greater than previous one

Question 3

Depth of focus

Answer 3

• shallower depth of focus, greater extent of damage of an earthquake
• becose most seismic waves reach land surface quickly than deep focus earthquake
• deep-focus vs shallow focus earthquake

Question 4

Deep-focus earthquake

Answer 4

location: occurs between 70 to 700km below earth’s surface
Impact on land: smaller impact, seismic waves take longer time to reach surface, would have lost most of their energy by then

Question 5

Shallow-focus earthquake

Answer 5

location: occurs in upper 70km of earth’s crust

impact on land: greater impact as seismic waves reach land surface more quickly

Question 6

Distance from epicentre

Answer 6

• closer the place is to epicentre, greater extent of damage of an earthquake
• places near epicentre receive strongest shock waves
• e.g. 2011 Christchurch : epicentre few km away from city

Question 7

Geology of epicentre (type of soil)

Answer 7

• softer/looser/more unconsolidated the soil, greater extent
• seismic waves are amplified when soil is soft, structures more likely to collapse
• structures built on saturated and unconsolidated sediments can be affected by liquefaction
• liquefaction is when ground becomes unstable and saturated soil flows like liquid
• e.g. 6.3 earthquake Christchurch, many houses and buildings had to be abandoned due to liquefaction after earthquake in 2011

Question 8

Stable soil to liquefied soil (Liquefaction)

Answer 8

stable soil: loosely packed grains of soil held tgt by friction
-pore spaces filled with water
-building stands erect on stable soil
liquefied soil: shaking destabilizes soil by increasing space between grains
-with structure lost, soil flows like liquid

Question 9

Population density

Answer 9

• refers to no. of ppl per unit area
• higher the population density, higher chances of ppl being killed or injured during earthquake
• more people, more deaths

Question 10

Time of occurrence

Answer 10

• time of day in which earthquake occurs determines where ppl are and what they are doing
• affect ppl chance of survival
• e.g. if earthquake occurs at night when ppl are sleeping, higher chance of being trapped in houses, more deaths (not as alert)
• e.g. more than 24000 ppl died when earthquake occured @1:47am in Sun Moon Lake Region in Taiwan, 1999

Question 11

Level of preparedness of ppl

Answer 11

• amt of preparation taken by authorities and citizens makes a significant difference to impact of earthquake
• e.g. evacuation plans, trained rescue workers, earthquake-resistant buildings
• e.g. Japan (prone to earthquakes due to geographical location) hold drills for earthquakes in both workplaces and schools regularly
• damage caused by earthquakes more manageable if ppl are btr prepared