hazards associated with earthquakes

Question 1

Ground shaking and displacement

Answer 1

• Vertical and horizontal movement of ground
• Severity depends on: earthquake magnitude, distance from the epicentre and local geology
• Close to epicentre of high magnitude quake, surface layers are unconsolidated, high-water content = extreme shaking
• Buildings can withstand vertical movements than horizontal – swaying of structures is danger to stability
• Ground movements = displacement of rocks along fault lines = can rip apart pipelines and sewers, rigid structures (railways, roads) = buildings collapse
• Displacement of the surface disrupts natural drainage, diverting streams and rivers = affects movement of groundwater in aquifers
  Implicates public water supplies and irrigation for agriculture

Question 2

Liquefaction

Answer 2

• Earthquake effects areas with surface material = fine-grained sands, alluvium, and landfill with high water content -> vibrations = material to behave like liquid
• Material lose strength; slopes collapse (riverbanks) and structures tilt and sink as their foundations give way

Question 3

Landslides and Avalanches

Answer 3

• Ground shaking and liquefaction = slope failure
• Vulnerability increased by deforestation and heavy monsoon rains = small tremors = landslides
• Landslides block transport routes in mountainous regions increasing difficult accessibility
• Movements of soil and rock on slopes can also block rivers
• Natural dams create temporary lakes – threaten areas downstream with catastrophic floods if dams fail
• Upland valleys = favoured sites for reservoirs
• Earthquake cause landslide on slopes above reservoir = displacement of water weakens and overtop dam

Question 4

Tsunamis

Answer 4

• Underwater earthquakes can cause the seabed to rise vertically displacing water above = powerful wave (spreads via high velocity from the epicentre)
• Low height (<1m) and long wavelength (up to 200km) = pass underneath ship at sea unnoticed
• Wave height increases as approaches shore and enters shallow water
• Before wave breaks, water in front of wave is pulled back out to sea -> drawnout
• Tsunami rushes in as a wall of water, can exceed 25m height – height affected by shape of the sea bed and the coastline, depends on relief of coastal zone
• Can spread inland to variable distances

Question 5

Underwater landslides = tsunami waves

Answer 5

• large volume of rock shaken and slides downslope = water dragged behind it from all sides and collides in centre
• Affects: no enough power to cross ocean BUT local effects devastating because if short warning times