Earthquake

• Earthquake


  A weak to violent shaking of the ground produced by the sudden movement of rock materials below the Earth's surface
• Anatomy of an earthquake

  • Focus
• Types of Earthquakes


  • Volcanic quakes
  • Tectonic quakes
• Volcanic quakes


  EQ produced by movement of magma beneath volcanoes
• Tectonic quakes


  EQ produced by sudden movement along faults and plate boundaries
• Faults


  • Fractures in the Earth's crust along which slippage or displacement has occurred or may occur again
  • Dip slip faults - move along the direction of the dip plane and are described as either normal or reverse (thrust), depending on their motion
  • Strike-slip faults - two blocks slide past one another
• How do earthquakes occur?

  Elastic Rebound Theory - gradual accumulation and release of stress and strain
• Seismometer


  Instrument that records seismic waves
• Seismogram


  Record produced by a seismometer
• Seismology


  Study of behavior of seismic waves
• Magnitude


  Calculated from seismic records and estimates the amount of energy released at the source
• Richter Scale


  Scale used to describe the magnitude of an earthquake
• Intensity


  Degree of ground shaking at a given locale based on the amount of damage
• Modified Mercalli Intensity Scale


  Scale used to describe the intensity of an earthquake
• Philippine Earthquake Intensity Scale (PEIS)


  Scale used to describe the intensity of an earthquake in the Philippines
• Intensity Scale


  • I - Scarcely Perceptible
  • II - Slightly Felt
  • III - Weak
  • IV - Moderately Strong
  • V - Strong
  • VI - Very Strong
  • VII - Destructive
  • VIII - Very Destructive
  • IX - Devastating
  • X - Completely Devastating
• Earthquake hazards


  • Ground rupture - deformation on the ground that marks, the intersection of the fault with the earth's surface
  • Ground shaking - disruptive up, down and sideways vibration of the ground during an earthquake
  • Liquefaction - phenomenon wherein sediments, especially near bodies of water, behave like liquid similar to a quicksand
• Secondary effects of earthquakes

  • Landslide - down slope movement of rocks, solid and other debris commonly triggered by strong shaking
  • Tsunamis - series of waves caused commonly by an earthquake under the sea
• Tsunamigenic earthquake


  Earthquake that generates a tsunami
• Tsunamigenic earthquake events


  • November 9, 1828 - Manila Bay, 6.6 magnitude
  • June 3, 1863 - Manila Bay, 6.5 magnitude
  • August 15, 1918 - Southern Mindanao, 8.0 magnitude
  • November 11, 1921 - Manay, Davao Oriental, 7.5 magnitude
  • April 14, 1924 - Mati, Davao Oriental, 8.3 magnitude
  • August 2, 1968 - Casiguran Bay, 7.3 magnitude
  • April 7, 1970 - Baler, Aurora, 7.0 magnitude
  • October 31, 1975 - Borongan, Eastern Samar, 7.2 magnitude
  • July 16, 1990 - Luzon, 7.8 magnitude
• Not all earthquakes generate tsunamis
• Shallow earthquakes generate the most destructive tsunamis
• Large tsunamis are likely to be generated by earthquakes with magnitude > 7.0
• Structural damage due to earthquake vibrations

  • Wave amplitudes
  • Duration of vibrations
  • Nature of material upon which the structure rests
  • Design of structure
• Locating the epicenter of an earthquake