Earthquakes

Question 1

What are Earthquakes

Answer 1

• a sudden release of tension within the earth’s lithosphere caused by plate movement resulting in a violent shaking of the earths crust

Question 2

Classification of Earthquakes

Answer 2

Ricta scale
. measure magnitude or strength of the earthquake
. The scale illustrated from 0-10 or 12 but there is no limit to scale ( limitless)
. logarithmic- means that each value of the magnitude would be 10x greater than the previous magnitude
. The scale is a quantitative scale
. Focus:
- shallow: 0-70 km
- intermediate: 70-300 km
- deep: 300+ km

Mercalli scale
. Describes the impact of the earthquake ( can be very subjects and can depend on the earthquake type and human development )
. The extreme shaking is mostly near the focus because earthquakes weaken when it is far way form the focus
. Qualitative data

Seismometer
. Detects vibration caused my an earthquake

Question 3

Main types of Seismic waves

Answer 3

P waves ( body waves)
. Primary pressure waves
. Fastest waves
. Longitudinal waves
. Travel through liquid and solids
. Compress through crust, mantle ( semi molten) and core ( liquid)
. P wave shadow zone- due to wave refraction (105- 140) they change direction

S waves ( body waves ) radiate from the focus
. Transverse waves
. Compress through the crust and mantle ( solids )
. Travel through solids

Love waves (surface waves ) radiate from the epicentre
. Slow but cause most damage

Rayleigh waves ( surface waves) radiate from the epicentre
. ( move in a rolling motion- faster than love waves but slower than s waves )

Question 4

Managing the earthquake hazard (5)

Answer 4

. Laser reflector- lasers can be used to detect small amounts of movement along a fault
. Unusual animal behaviour can be observed
. Radon gas counter- the amount of radon gas dissolved in groundwater has been shown to increase before some earthquakes ( can be found when ig rapid Roche break )
. Changed in height of the water table have been recorded before an earthquake
. Creep meter to monitor seismic movement along the faults

Question 5

Primary hazard:Ground shaking

Answer 5

. Caused my seismic waves traveling through the crust

Building collapse:
. Primary effect:
- immediate deaths
- destruction of homes
. Secondary effect:
- injustices may result in long term disability and reduce life expectancy
- trapped bodies begin to rot, encouraging vermin causing diseases such as cholera
- grief causes long lasting psychological trauma

CS: Kobe earthquake, January 1995
. Collapse of the earthquake resistant Hanshin Express way. Damage to Kobes port facilities which impacted the global economy
. Anything that happened to Japan would have affected the Global Economy

Question 6

Secondary hazards: soil liquefaction

Answer 6

. Jelly like state of unconsolidated sediments from intense ground shaking- increased pore water pressure reduces shear strength of soil so it fails more easily

Primary effects:
. Building subsidence
- people get trapped in buildings
- building collapse

Secondary effects:
- repairs are difficult and expensive
- weakens building which then collapse during after shocks

CS: Mexico City earthquake, September 1985
. Liquefaction due to city built upon dried out lake sediments

Question 7

Secondary hazards: mass movements events ( landslides)

Answer 7

. Slope failure as a result of ground shaking, particularly in areas of steep relief

Primary effect:
. Blocked rivers
- flooding creating quake lakes

Secondary effects:
. Loss of farmland and food production
. Permanent distribution to natural drainage patterns

CS: Nepal earthquake 2015
. Earthquake triggers thousands of landslides some of which h blocked rivers forming quake lakes

Question 8

Secondary hazards : seiche/ Tsunami

Answer 8

Seiche- a standing wave within confined body of water e.g lake

Tsunami- waves generated by disturbance on the sea floor triggered by earthquakes or submarine landslides

Primary effects:
. Flooding
- deaths by drowning
- vegetation crops and topsoil removed
- contamination of water supplies and soil by salt water

Secondary effects:
- loss of coastal infrastructure takes years to rebuild e.g ports and fishing

CS: seiche- Lisbon earthquake, Portugal, 1755
. Caused seiches in Scotland, Loch Lomond and Loch Ness

CS: Tsunami- Boxing Day Tsunami, Indian Ocean, 2004
. Killed over 230,000 people

Question 9

Secondary hazards: Fire

Answer 9

. Caused by broken gas mains and down powerlines

Destruction of building:
. Primary effects:
- destroys homes and businesses
- Deaths caused by burning and smoke inhalation

Secondary effects:
- Fire and smoke damage is expensive to repair

CS: San Francesco earthquake, April 1906
. 80% of the city was destroyed with 90% of the damage caused by fires