EARTHQUAKE HAZARDS and its EFFECTS

• Earthquake


  A natural phenomenon wherein the surface of the Earth moves or vibrates due to a sudden release of energy that is caused by the movements of the plates
• Focus


  The spot where an earthquake began
• Epicenter


  The point on the Earth's surface located directly above the focus
• Earthquake hazards

  • Ground shaking
  • Ground or surface rupture
  • Liquefaction
  • Earthquake-induced landslides
• Ground shaking


  • Vibration of the ground where an earthquake occurs, usually recorded in terms of intensity
  • Can be a hazard or trigger for other hazards such as landslides or tsunamis
  • Factors affecting intensity: magnitude of earthquake, distance from epicenter, local geological conditions
• Ground or surface rupture


  • Happens on areas where the fault zone moves
  • Structures built across the fault are at risk of being torn apart as the two sides of the fault slip past each other
  • Surface rupture is not a single line with a fixed width but zones with variable width where fractures have developed
• Earthquake-induced landslides


  • Strong earthquake and ground shaking greatly increase the possibility of landslides in areas susceptible to ground failure
  • If the ground is saturated with water, the shaking will result in more landslides
  • Gravity acting on a steep slope is the primary reason for all landslides, other contributing factors: over steepened slopes, saturated rock and soil slopes, excess weight from rain/snow, weak slopes from human-made structures
• Liquefaction


  • Occurs when sand or soil and groundwater mix during an earthquake with a magnitude of 4.5 and higher, making the ground very soft and exhibiting properties similar to quicksand
  • Areas with groundwater close to the surface and sandy soil are more prone to liquefaction
• Secondary earthquake hazards

  • Tsunamis
  • Seiche
  • Flooding
  • Fire
• Tsunamis


  • Huge waves caused by an earthquake that originate beneath the ocean and can cause great destruction when they reach the land
  • The height of tsunamis can be tens of feet high when they hit the shore and can do massive damage to the coastline
• Seiche


  • Standing waves created in a closed or partially-closed body of water such as lakes, reservoirs, swimming pools and bays due to strong wind or earthquake
  • Has a to-and-fro motion produced by a forcing motion on an enclosed body of water
• Flooding


  • Can occur when a tsunami hits the land or when an earthquake breaks a dam, causing the water to flow out and flood low-lying areas
• Fire


  • Can break out after an earthquake due to tipped over candles/lanterns, gas leaks, or sparks from broken electric and utility wires
• A magnitude-4.0 earthquake is strong enough to trigger rock fall