Factors affecting extent of earthquake

Question 1

Nature of hazard

Answer 1

Duration of shaking
○ The greater the magnitude, the more violent the shaking, and the longer the vibrations will last.
○ The longer the duration of shaking, the greater the damage
○ more stress from the vibrations, and thus infrastructures more likely to collapse on people and kill/ injure them
● Eg. Tohoku earthquake lasted for 6 minutes, many buildings collapsed and many people died

Time of shaking
time of shaking: time of the day that the earthquake happens
○ It affects what people are doing and how able they are to respond to the hazard
○ If the earthquake happens at midnight → people will likely be asleep → less likely and able to respond → trapped under buildings when it collapses
○ Earthquake happens in the day → people are out and about → more able to respond and evacuate → lower deaths and injuries
● Eg. Kobe earthquake 1995. Occurred at 6am, 6000 dead

Question 2

Vulnerability conditions

Answer 2

-quality design and construction
○ Better quality designs mean less vulnerability to earthquake damage, as buildings are less likely to collapse
○ Low quality buildings (zinc, lack reinforcements to support buildings during earthquakes, does not following building safety codes) are more likely to collapse and fall apart, thus killing/ injuring people
● Eg. 2010 Port-au-Prince, Haiti 90% of buildings near epicentre destroyed contributing to more than 220,000 lives lost

-Soil and rock properties
● nature of the soil and rock on which towns and buildings are built on
● Reclaimed land or soil that has high water content (ie. high levels of groundwater or near water bodies) will lead to soil liquefaction → buildings become unstable and collapse, or people buried/ drowned in the liquified soil
● Soft soils also amplify seismic waves more than hard soils Soft/loose soil → more violent vibrations thus causing more violent vibrations, more damage, and more loss of lives as buildings collapse
● Eg. Port-au-Prince, lie on layers of relatively soft soil when 2010 Haiti earthquake struck, collapse 250,000 houses and 220,000 deaths

Question 3

Exposure to earthquake

Answer 3

Population density
● Population density: number of people per unit area of land (per km2).
● The higher the population density, the greater the number of people and
buildings (homes/ shops) exposed to the earthquakes.
● This will lead to more damage to the local area as well as more deaths and injuries, compared to somewhere else with lower population density (eg. Antarctica, desert)
● Kobe, 1995 densely populated industry city, severely affected many ppl die and injured

Distance from epicentre
● Epicentre: the part on the Earth’s surface directly above the focus from which the waves are released.
● Being closer to the epicentre, less seismic waves are absorbed by the rocks before it reaches human settlements
● Seismic waves that reach the city are stronger and will cause more violent shaking, making buildings and infrastructure more likely to collapse, trapping and killing people. (ie. closer to epicentre → more shockwaves → more damage)
● Eg. Port-au-Prince, 2010—>many death as Haiti earthquake about 23km west of epicentre