Earthquake hazards Aims 1. To know how hazards are classified 2. To be able to explain how the hazards occur 3. To be able to rank order hazards
Types of hazard Primary A direct result of the earthquake Secondary A hazard caused by a primary effect Can you name some primary and secondary hazards?
Earthquake hazards Primary Hazards Ground shaking Secondary hazards Landslides/avalanches Soil liquefaction Tsunamis - underwater landslides of tectonic uplift Flooding Rank order hazards from most damaging to least damaging
GROUND SHAKING The ground shakes or vibrates as the seismic waves cause small temporary displacements of the ground. The intensity can be affected by the size of the earthquake, the geology of the ground below and the location of the focus. p waves compressional waves cause the crust to move back and forth. S waves shearing waves cause the ground to move vertically up and down and horizontally Worst impacts is from high intensity and high magnitude earthquakes. Also damaging impacts from high intensity or high magnitude earthquakes.
Landslides
Earthquake Causes waves Waves cause shaking Shaking Shakes material Slope more unstable Landslide Material moves down the slope
Earthquake-triggered landslides More widespread and sudden Rock falls and slides on steep slopes IF WET Earth flows, debris flows and avalanches of rock, earth and debris
Landslides cause slope failure Block mountain roads, happened in Nepal 2015 Block rivers, creating natural dams and causing flooding, happened in Kashmir 2005 Displace water from reservoirs, happened in Italy 1963, drowned 3000 people.
Effects of Landslides... Economic Decline: Damage to property which brings losses to the economy Damage to Infrastructure: such as buildings, roads, pipe lines, bridges Loss of Life: many lives are lost as people try to run away and are not fast enough Changes in the Surface Landscape: dammed rivers or lakes may become shallower as they fill with debris.
Example Iran (1990) An earthquake measuring 7.7 on the Richter scale causes mud slides that bury towns, roads, and take 50,000 lives.
Soil liquefaction Fine grained sands, or alluvium, with a high water content are squeezed. Vibrations cause the soil to turn from a liquid to a solid It causes river banks to collapse, foundations to be damaged and housing to tilt. Kobe EQ led to 200 berths at the Osaka port being destroyed affecting world trade.
Soil liquefaction https://www.youtube.com/watch?v=-eh5fh0yeuq https://www.youtube.com/watch?v=rjcidfj-x9m
Japanese tsunami 2011 https://www.youtube.com/watch?v=noq8fyvrqgs https://www.youtube.com/watch?v=owzdgbnfhqu
Tsunamis Convergent plate margin, sial is dragged downwards by denser sima. Pressure builds Earthquake occurs, causing the sial to flick upwards, displacing water from the ocean trench Tsunami occurs, spreading outwards in all directions from the epicentre.
How EQ trigger tsunami https://www.youtube.com/watch?v=chbbis CczB8
(a) Study Figure 1 which shows changes in sea level following a seismic event in the Pacific Ocean basin. Figure 1 Comment on the changes in seas level shown, and suggest why these changes illustrate the hazards associated with a tsunami. (7 marks)
Long wave length, short wave height. Cross-section of a tsunami Increase in wave height, decrease in wave length, due to friction with the sea bed as it become shallower. Rapid speed in ocean 800km/h to 950km/h Speed decreases as it reaches land 50-80km/h 10m Drawback: water in front of the wave is sucked into to maintain wave height. Tide appears to go out a very long way. Tsunamis are caused by an earthquake. When the sial flicks upwards, as the pressure is released this causes elastic rebound. Sendai 11/3/11 9 on Richter scale Destructive Plate Margin Pacific plate = sima, North American Plate = sial
http://www.bbc.co.uk/news/scienceenvironment-12739417 http://news.bbc.co.uk/1/hi/sci/tech/753397 2.stm http://www.bbc.co.uk/news/world-asiapacific-12731781
Tsunamis Underwater landslides, triggered by earthquakes Displaces water This generates a tsunami wave, which radiates out in all directions. Doesn t have power to cross oceans but can have devastating local effects 1998, 2200 villagers in Papua New Guinea were killed.
landslides Blocked reservoirs Rivers blocked Flooding tsunami Soil liquefaction Tectonic uplift global Underwater landslides local
Produce a detailed case study of the Japanese earthquake and Tsunami.