DRRR WEEK 3

• Hazard


  Anything that is a source of danger or interruption
• Types of hazards


  • Safety hazards (can cause physical harm)
  • Moral hazards (financial risks)
• Hazards


  • Potentials for damage to man and his environment that may result from the occurrence of natural events
  • An event per se does not constitute a hazard
  • It is only when a man and his environment are threatened that these events can be considered hazards
  • Without a threat to a population, the eruption of an isolated volcano remains an event but when volcanic activity occurs close to or right at the center of a populated area, a mere event becomes a hazard
• Hazard


  A situation that poses a level of threat to life, health, property, or, the environment
• Potential impacts of hazards

  • People - death, injury, disease, and stress
  • Human activity - economic, educational, etc.
  • Property - property damage, economic loss
  • Environment - loss of fauna and flora, pollution, loss of amenities
• Hazards


  • Involve something that could potentially be harmful to a person's life, health, property, or, environment
  • Involve the presence of stored energy that, when released, can cause damage
• Classification of hazards


  • Natural hazards (arise from purely natural processes)
  • Quasi-natural hazards (arise through the interaction of natural processes and human activities)
  • Technological (or man-made) hazards (arise directly as a result of human activities)
• Modes of a hazard

  • Dormant (potential hazard, but no people, property, or environment is currently affected)
  • Armed (people, property, or the environment are in potential harm's way)
  • Active (a harmful incident involving the hazard has actually occurred)
• Types of hazards and examples

  • Geologic (earthquakes, volcanic eruption, etc.)
  • Hydrologic (floods, tsunami, etc.)
  • Atmospheric (typhoons, thunderstorms, etc.)
  • Biologic (epidemic in humans, plants, animals)
  • Man-made (transport accidents, industrial explosions, etc.)
• Types of hazards and examples (continued)

  • Geologic (rainfall-induced landslide, subsidence, etc.)
  • Atmospheric (hail, blizzards, etc.)
  • Man-made (WMD, computer virus, etc.)
• Types of workplace hazards

  • Chemical hazards
  • Noise hazards
  • Radiation hazards
  • Electrical hazards
  • Lighting hazards
  • Vibration hazards
  • Biological hazards
  • Ergonomic hazards
  • Physical hazards
• Earthquake hazard


  Ground shaking (buildings can be damaged by the shaking itself or by the ground 'beneath them settling to a different level than it was before the earthquake)
• Earthquake hazard


  Ground displacement (ground movement along a fault, which can seriously damage or rip apart structures built across the fault)
• Liquefaction


  The way in which soil liquefies during ground shaking
• Types of ground failure due to liquefaction

  • Flow failures (blocks of overlying material slide down so fast that they reach distances tens of kilometers from the source)
  • Lateral spreads (blocks or the broken pieces of the flat or very gentle ground above a liquefied zone move laterally)
  • Ground oscillation (the ground is unable to spread and instead oscillates)
• Buildings can be damaged by

  • The shaking itself
  • The ground beneath them settling to a different level than it was before the earthquake (subsidence)
• Ground displacement


  Ground movement along a fault
• If a structure is built across a fault, the ground displacement during an earthquake could seriously damage or rip apart that structure
• Flow Failures


  • Considered the most dangerous type of ground failure due to liquefaction
  • Blocks of overlying material slide down so fast (as much as 10 kms/hr) that these reach distances tens of kilometers from the source
• Lateral Spreads


  • Blocks or the broken pieces of the flat or very gentle ground (less than 3 degrees) above a liquefied zone move laterally
• Ground Oscillation


  • Due to the flat or nearly flat slope, the ground is unable to spread and instead oscillates like a wave (back and forth and up and down)
  • Water and wet sand are ejected through the fissures that form conical-shaped mounds of sand at the surface (sand blows)
• Loss of Bearing Strength


  • Loss of strength of sediments resulting in tilting of houses and floating of buoyant structures (e.g., fuel tank) that are anchored on the liquefied zone
• Vertical Settlement


  • Readjustment or settlement within the liquefied zone as a result of dissipation of pore-water pressure or the ejection of materials during the formation of sand boils (fountains of water and sediment coming from the pressurized liquefied zone)
• Tsunamis


  Water waves or seismic sea waves caused by large scale sudden movement of the sea floor, due usually to earthquakes and on rare occasions to landslides, volcanic eruptions, or man-made explosions
• How do earthquakes generate tsunami wave?

  1. Local Tsunami: confined to coasts within a hundred kilometers of the source usually earthquakes and a landslide or a pyroclastic flow, can reach the shoreline within 2 to 5 minutes

  2. Far field or distant tsunamis: can travel from 1 to 24 hours before reaching the coast of the nearby countries, come from the countries bordering Pacific Ocean like Chile (1960, 2010, 2015), Alaska in USA and Japan (2011)
• Effects of Tsunami


  • Loss of lives due to drowning, building collapse, impact of various kinds of debris, and sometimes by electrocution
• Seiches


  Phenomena similar to tsunamis but occur in inland bodies of water, generally in elongated lakes, lower (less than three meters high) than those of tsunamis and are oscillatory in nature
• Damaged residential areas in Malabang, South Cotabato and in Zambaoanga due to the Tsunami triggered by the 1976 Moro Gulf Earthquake
• Tsunami Mitigation Measures


  1. Avoid tsunami run up areas in new development except marine installations and others requiring proximity to water, prohibit setting of high-occupancy and critical structures

  2. Place areas of potential inundation under floodplain zoning, prohibiting all new construction and designating existing occupancies as non-conforming

  3. Where economically feasible, establish constraints to minimize potential inundation or to reduce force of waves

  4. Constructing sea walls along low-lying stretches of coast and breakwaters at the entrances of bays and harbors

  5. Planting belts of trees between the shoreline and the areas require ring protection

  6. Where development exists, establish warning and evacuation systems

  7. Set standards of construction for structures within harbors and known runup areas
• Not only can earthquakes trigger landslides, they can also cause the soil to liquefy in certain areas
• Causes of Landslides


  • Removal of support at the base of a slope
  • Groundwater (pore water) pressure
  • Volcanic eruptions
  • Intense rainfall
  • Snowmelt
  • Human Interventions
• Effects of Earthquake-induced Landslides


  • Loss of lives
  • Damage to properties
• Topples

  • Occur suddenly when a massive part of very steep slopes break loose and rotate forward
• Rock Falls


  • Involve chunks of detached rock that falls freely for some distance or bounce and roll down the steep slope
• Lateral Spreads


  • Are triggered by earthquakes and affect gentle slopes with less than 10 degrees inclination
• Flows


  • Involve downslope motion of fine grained clay, silt, and fine sand made mobile by water saturation, include mudflows and earthflows and are common during rainy season
• Debris Flow


  • A form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water mobilize as a slurry that flows downslope
• Debris Avalanche


  • A variety of very rapid to extremely rapid debris flow
• Earthflow


  • The slope material liquefies and runs out, forming a bowl or depression at the head, has an "hourglass" shape
• Slides


  • Involve large blocks of bedrock that break free and slide down along a plane or curved surface