Earthquakes

• Other names of earthquake:

  • quake
  • tremor
  • temblor
• Types of earthquakes:

  1. Tectonic earthquake
  2. volcanic earthquake
  3. volcanic-tectonic
• Tectonic earthquake

  • produced by sudden movement along faults or plate boundaries
• Volcanic earthquake

  • produced by movement of magma or magmatic fluids or rock fracturing beneath volcanoes
• Volcano-tectonic (VT)

  • associated with failure or breakage of rock material along faults and fractures beneath active volcanoes
• Volcanic-tectonic

  • Normally triggered by excess heat and pressure or adjustment of the crust around a magmatic body
• Elastic rebound theory

  • explains why we have tectonic earthquakes
• Epicenter:

  • the point on the earth’s surface vertically above the hypocenter (or focus)
  • Described by geographic coordinates (latitude and longitude)
• Focus

  • the point within the earth where an earthquake rupture starts
  • Described by geographic location (epicenter) and focal depth/hypocenter
• Describing an earthquake

  1. epicenter
  2. focus
  3. magnitude
  4. intensity
• Magnitude

  • A number that characterizes the relative size of an earthquake (based on energy released)
  • calculated by seismograph
• True of False:

  True - higher magnitude earthquakes occur less frequent than low magnitude ones
• Intensity

  • Strength of an earthquake perceived and felt by people in a certain locality. Intensity is generally higher near the epicenter
• PHIVOLCS Earthquake Intensity Scale

  • intensity scale used in philippines
• Modified Mercalli Earthquake Intensity Scale

  • intensity scale used by other countries
• Types of body waves:

  1. P-wave
  2. s-wave
• Types of surface waves:

  1. love wave
  2. rayleigh wave
• P-waves

  • Primary waves
  • push-pull
  • May be transmitted through gasses, liquids, or solids
• S-waves

  • Secondary waves - shear waves
  • only travels to solids
• Surface waves

  • Travel across the Earth’s surface
  • Propagate more slowly than seismic body waves
• Love wave

  • Horizontal
  • side-to-side motion
• Rayleigh wave

  • Rolling motion
  • Movement similar to water waves
• Secondary Hazards of ground shaking:

  1. Damage and casualties
  2. landslides
  3. liquefaction
  4. tsunami
• Stable soil

  • loosely packed grains of soil are held together by friction
  • pore spaces filled with water
• soil liquefaction

  • Shaking destabilizes the soil by increasing the space between grains. With its structure lost, the soil flows like a liquid
• tsunami

  • Series of big waves that are usually generated by earthquakes under the sea