Earthquake Hazard

• Earthquake

  • An unexpected and rapid shaking of the earth
  • due to the breakage and shifting of layer underneath the earth and strikes all of a sudden at any time of day or night
• TECTONIC EARTHQUAKE

  
  

  – refers to the movement or shifting of tectonic plates.
• VOLCANIC EARTHQUAKE

  
  

  – it is triggered by volcanic activity near the surface.
• Fault

  
  

  • refers to a fracture, fissure or a zone of weakness where movement or displacement has occurred or may occur again.
• Deformation

  
  

  – when the shape of a rock changes due to stress.
• Kinds of Deformation movement:

  • Upwelling
  • Sinking
• Upwelling

  
  

  – when convection currents point up.
• Sinking

  
  

  – when convection currents go down.
• Stress – is the force applied to a body.
• Compression

  
  

  – squeezing or pushing together (convergent boundaries)
• Tension

  
  

  – forces stretch an object (divergent boundaries)
• Shearing

  
  

  – slicing motion back and forth (transform boundaries)
• FORESHOCKS

  
  

  – are series of light shakings that occur before the main earthquake.
• AFTERSHOCKS

  
  

  – are tremors following the main shocks.
• Ground Shaking

  
  

  – disruptive up-down and sideways movement or motion experienced during an earthquake.
• Ground Rapture

  
  

  – this will be experienced by areas where fault passes through (note not all cracks on the ground that people see after a strong earthquake are faults, some may just be surficial cracks because of

  ground failure)
• Tsunami

  
  

  • sea waves resulting from the disturbance of ocean floor by an earthquake.
  • this is a series of giant sea waves commonly generated by under-the-sea earthquakes and whose heights could be greater than 5 meters.
• Liquefaction – a process that transforms the behavior

  of a body of sediments from that of a solid to that of a

  liquid when subjected to extremely intense shaking.
• Volcano – is a vent or rupture in the earth’s layer over

  which liquefied rocks from under the earth’s exterior

  erupts.
• Volcanic Eruption

  
  

  • a sudden occurrence of a violent discharge of steam and volcanic material.
  • If there is a strong pressure from gases and molten rocks, these gases and molten rocks shoot through the opening of the volcano and will cause explosions and violent reactions
• Volcanic Hazards

  
  

  – are phenomena arising from volcanic activity that pose potential threat to persons or property in a given in a given area within a given period of time.
• LAVA FLOWS

  → flows coming out from a volcano consist of

  molten rocks that oozes from eruption.

  → is ejected during explosive and non-explosive

  lava fountain activities and destroys every

  objects in its paths.
• Major hazards of lava flows:

  ❖ Burying

  ❖ Covering

  ❖ Burning everything in their path

  ❖ Lava flows rarely threaten human life

  because lava usually moves slowly. Most

  characterize this as quiet effusion of lava.
• ASH FALL

  → are showers of airborne fine- to course-

  grained volcanic particles that fallout from

  the plumes of a volcanic eruption

  → ash fall distribution/dispersal is dependent on

  prevailing wind direction
• Ash falls endanger life and property by:

  ❖ Can cause poor or low visibility

  ❖ Burial by ash fall

  ❖ Dangerous for aircrafts

  ❖ Burial by ash fall can collapse roofs of

  buildings, break power and communication

  lines and damage or kill vegetation
• PYROCLASTIC FALLS

  → are turbulent mass of ejected fragmented

  volcanic materials (ash and rocks), mixed

  with hot gases that flow downslope at very

  high speeds.
• Pyroclastic flows can:

  ❖ Destroy anything on its path by direct impact

  ❖ Burn sites with hot rocks debris

  ❖ Burn forests, farmlands, destroy crops and

  buildings
• LAHARS

  → are rapidly flowing thick mixture of volcanic

  sediments and water, usually triggered by

  intense rainfall during typhoons, monsoons

  and thunderstorms.
• Lahars can:

  ❖ Destroy by direct impact (bridges, roads,

  houses)

  ❖ Block tributary stream can bury valleys and

  communities with debris

  ❖ Lead to increased deposition of sediments

  along affected rivers
• VOLCANIC GASES

  → these gases are released into the atmosphere

  from the magma of the volcano during its

  eruptions.
• Sulfur dioxide (SO2) – can lead to acid rain.
• High concentrations of Carbon dioxide

  (CO2)

  • which is colorless and odorless can be lethal

  to people, animals and vegetation.
• Fluorine compounds

  • can deform and kill animals that grazed

  on vegetation covered with volcanic ash
• Hydrogen Sulfide (H2S)

  • is very toxic in high concentrations
• Hydrogen halides (HF, HCL, HBr)

  • are strong, toxic acids.
• Ballistic Projectiles

  → are volcanic materials directly ejected from

  the volcano’s vent with force and trajectory

  → endanger life and property by the force of

  impact of falling fragments, but this occurs

  only close to an eruption vent.
• Tsunami – is a series of giant sea waves commonly

  generated by under-the-sea earthquakes and whose

  heights could be greater than 5 meters.
• A tsunami is commonly generated by

  disturbances associated with earthquake

  occurring below or near the ocean floor.
• Tsunami

  
  

  It occurs when the earthquake is shallow-

  seated and strong enough to displace parts of

  the seabed and disturb the mass of water over

  it.
• In addition, underwater volcanic eruptions

  and landslides can also generate a tsunami.