Earthquake Hazards

• The Philippines experiences earthquakes on a daily basis due to our location as part of the Pacific Ring of Fire. Most of them are small earthquakes.

  However, our country has also experienced higher magnitude earthquakes in the past century, like the 1990 Great Luzon Earthquake, and has seen the devastation that it can bring.
• Earthquake strengths are usually measured in terms of magnitude and intensity.
• Intensity: depends mainly on the visible effect of an earthquake on the surface.

  • The same earthquake event may have several intensities based on location of the observer.
  • The Philippines uses the Philippine Earthquake Intensity Scale (PEIS) in measuring and reporting earthquake intensities. PEIS is based on the Modified Mercalli Scale.
• PEIS:

  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 Ruptures: Due to the movement of the ground, earthquakes can produce visible fractures on the ground called ground ruptures. These visible changes in ground elevation usually occur along faults.
  • Ground Shaking: Seismic waves, particularly surface waves, can bring about violent low-frequency or high-frequency ground shaking. This can make buildings and structures with weak frameworks wobble and topple during an earthquake.
• Earthquake Hazards:

  • Liquefaction: Sediments near the Earth’s surface become saturated with water and behave like a liquid or quicksand. This happens as seismic waves force some sediments to settle, leaving the areas near the surface to become soupy and less consolidated.
  • Landslides: Earthquakes can also trigger landslides in areas with unstable and steep slopes. Unconsolidated rocks and other debris can flow down the slope and can potentially bury nearby areas and communities.
• Earthquake Hazards:

  • Tsunami: large waves created by movement of faults underneath large bodies of water. The movement of the ground below seas, large lakes, and oceans during earthquake events causes the displacement of large amounts of water, which powers these massive waves.
• Since earthquakes cannot be predicted with accuracy, knowledge of the various hazards it brings and managing risks associated with them is the key in protecting lives and properties.