seismic hazards

Question 1

how do earthquakes occur

Answer 1

• caused by tension that builds up at all plate margins
• as the plates jerk past each other they send out shockwaves (the earthquake)
• shockwaves spread out from the focus which can be multiple points and is typically at the fault line
• the epicentre is the point on the earths surface directly above the focus where the earthquake is first felt
• earthquakes cause ruptures along the fault

Question 2

how is the magnitude of earthquakes are measured

Answer 2

• the Richter scale measures the magnitude of earthquakes
• there is not an upper limit
• the scale is logarithmic (as the level increases by one the magnitude increases by 10
• major earthquakes are 7 and above
• 2011 Tohoku earthquake was 9.0
• largest earthquake recorded at 9.5 in 1960, Chile

Question 3

how is the energy released by an earthquake measured

Answer 3

• the moment magnitude scale is based on the total amount of energy released
• no upper limit
• logarithmic
• more accurate than Richter scale

Question 4

how are the impacts of earthquakes measured

Answer 4

• the Mercalli scale uses observations to measure the impacts of an earthquake
• the scale is between 1 and 12
• 1 is an earthquake detected by instruments
• 12 is an earthquake that causes total destruction

Question 5

how do earthquakes cause tsunamis

Answer 5

• large waves caused by the displacement of water.
• they can be triggered by underwater earthquakes which cause the sea bed to move. this causes wave to radiate from the epicentre
• tsunamis by the coast will be more destructive as they lose energy as they move towards land
• the waves travel quickly in deep water and can hit with little warning causing a high death toll

-travel up to 940km/hr
-25-40km in height
long wavelength,
-10 to 60mins between each wave
2011 Tohoku

Question 6

how do earthquakes cause landslides/avalanches

Answer 6

• shaking if the ground can dislodge rock, soil or snow causing landslides/avalanches
• the loosening of ground material can also make it easier for water to infiltrate
• the extra weight can cause landslides after the shockwaves
• Gorkha 2015

Question 7

how do earthquakes cause soil liquefaction

Answer 7

• when soil is saturated with water the vibrations cause the soil to act like liquid
• this makes soil easier to deform

Question 8

what effects the nature and magnitude of an earthquake

Answer 8

-margin type:
destructive margins: biggest earthquakes occur here as the subduction zone causes pressure to build up.
constructive margins: lower magnitude earthquakes

-depth of focus:
the focus can be close to the earths centre or deep below it.
deeper focuses have higher magnitude but they do less damage as they have to travel further which reduces power.

Question 9

what is the importance of the magnitude and frequency of earthquakes

Answer 9

• lower magnitude earthquakes occur frequently whilst higher magnitude earthquakes occur less frequently
• the number of earthquakes per year varies year to year

Question 10

what is the regularity of earthquakes

Answer 10

-seismic hazards occur randomly

Question 11

predictability of earthquakes

Answer 11

• scientists can monitor tectonic movement to predict areas at risk
• it is currently impossible to predict when an earthquake will occur and what the magnitude will be

Question 12

short term responses to seismic hazards

Answer 12

rescue and evacuation

Question 13

seismic hazards case study
date
plate margin

Answer 13

Japan Tohoku earthquake
March 2011
destructive pacific and Eurasian plate

Question 14

5 social impacts of the Tohoku earthquake

Answer 14

• tsunami killed 15,890 people
• 400,000 buildings destroyed
• 25% of foreigners living in Tokyo left
• people left stranded
• reputation and dignity effected which is important in Japanese culture

Question 15

2 economic impacts of the Tohoku earthquake

Answer 15

• cost japan $199 billion

- livelihoods destroyed and so money isn’t put into the economy

Question 16

3 environmental impacts of the Tohoku

earthquake

Answer 16

• nuclear power plant meltdown
• crops couldn’t be used due to radioactivity
• triggered 40m tsunami

Question 17

4 immediate responses to the Tohoku earthquake

Answer 17

• 452,00 in evacuation facilities
• doctors and nurses flown out from other parts of the country
• military and rescue services cleared roads
• army built temporary shelter

Question 18

4 long term responses to the Tohoku earthquake

Answer 18

• upgraded their tsunami warning systems
• shifting away form nuclear power
• summer festival went ahead
• nuclear plants tested for tectonic movement

Question 19

how vulnerable was Japan to the 2011 Tohoku earthquake

6 reasons

Answer 19

• high ageing population who were unable to evacuate quickly
• residents in Tokyo received warning 1 minute before earthquake hit
• Japanese pride prevented them from accepting emergency
• people flown out didn’t know the area well
• misleading education gave a false sense of security
• had earthquake drills every 1st of September

Question 20

Japan after the earthquake - 2

Answer 20

• 50,000 still in temporary housing in 2017

- 2529 people still missing

Question 21

long term response and risk management: prevention

Answer 21

• seismic hazards cannot be prevented but it can be possible to prevent them posing a risk to people
• liquefication of soils can be prevented through soil stabilization - gravel compounds put in ground
• avalanches can be prevented using controlled explosions

Question 22

long term response and risk management: preparedness

Answer 22

• installing earthquake warning systems
• individuals and businesses can make plans for how to respond - evacuations, plans, training
• tsunami warnings
• community search and rescue
• earthquake prone areas have extensive awareness strategies: Drop, Cover, Hold On

Question 23

long term response and risk management: mitigation

Answer 23

• search and rescue,
• immediate emergency aid
• evacuation
• demolishing older unsafe buildings
• tsunami wave breaks and sea walls

Question 24

long term response and risk management: adaption

Answer 24

• buildings can be designed to withstand earthquakes and tsunamis with escape routes
• move away from areas at risk
• insurance for areas at risk
• change lifestyle: remove valuables from places they can fall