lesson 4 earthquakes

• the most dangerous part of any tectonic plate is at its edges because this is where it comes in contact with or separates from another plate. Hence, when two plates move, the boundaries of both plates would have the highest risk of disaster.
• ground shaking

  ground rupture

  liquefaction

  earthquake induced subsidence

  tsunami

  earthquake induced landslide


  Potential Earthquake Hazards
• Ground shaking


  The shaking of the ground is caused by the passage of seismic waves, forms of energy that travel through the different layers of Earth caused by vibration or movement.
• Ground rupture


  – This occurs when ground movement happens on a

  fault line and breaks through to the surface. This may happen in an instant during an earthquake.

  • Most of the time, fault rupture follows preexisting faults known as zones of weakness.
• Liquefaction


  This occurs when seismic shaking causes loose materials

  in the soil to mix with groundwater or soil saturated with water.

  • Eventually, the soil behaves like a quicksand that has lost its strength to hold and support objects on top of it.
• Earthquake-induced ground subsidence


  lowering of land due to various causes, one of which is the earthquake on a fault line. The movement of ground during an earthquake could be horizontal,

  vertical, or both.
• The word tsunami is a Japanese word that means harbor wave, coined as such because of the destructive effects experienced by the Japanese living on low-lying coastal communities.
• Tsunami


  The term is now generally used to mean series of waves that are generated by a sudden displacement on the ocean floor caused by large-scale undersea landslide or earthquake, submarine volcanic eruption, or even a large meteor crash at sea.
• Signs of an Impending Tsunami

  Feel the earth shake.

  See the ocean drop.

  Hear an unusual roaring sound.
• Signs of an Impending Tsunami/ earthquake

  animal behaviour

  drawback

  change in atmospheric conditions

  electromagnetic disturbance

  boom sound
• Earthquake-induced landslide


  – Landslides may happen during or after an earthquake

  when a weakened section of land falls off primarily due to gravity. The weak land may be due to its composition of frail rocks or its soft soil foundation
• 1. Death and injury to human beings

  2. Damage to the built and natural environments


  The primary consequence of concern in earthquake is of course human casualties, i.e., deaths and injuries. The physical

  consequence of earthquakes for human beings is generally viewed into two headings:
• These physical effects in turn are considered as to their social and economic consequences:

  1. Number of casualties

  2. Trauma and bereavement

  3. Loss of employment

  4. Loss of employees/skills

  5. Loss of heritage

  6. Material damage cost

  7. Business interruption

  8. Consumption of materials and energy

  9. Macro-economic impacts
• earthquake


  is the perceptible shaking of the surface of the earth, resulting from the sudden release of energy in the Earth’s crust that creates seismic waves
• Tectonic Earthquake

  Plutonic Earthquake

  Volcanic Earthquake


  Classification of Earthquakes
• • caused by abrupt movement of earth along faults.
  • Most of the powerful earthquakes that we experience fall in this category.
  • preceded by foreshocks and followed by aftershocks.
  • most dangerous and powerful kind of earthquake.

  Tectonic Earthquake
• • This classification of earthquake has a deep focus, with

  depth of disturbance around 300 kilometers to 800 km.

  • The depth affects the amount of energy that will be

  released in the surface.

  • Plutonic earthquakes are less destructive than

  shallow ones.

  Plutonic Earthquake
• Caused by the movement of magma deep within

  the earth’s crust.

  Occur almost exclusively at convergent

  boundaries in association with subducted

  oceanic lithosphere.

  Plutonic Earthquake
• • This earthquake happens because of volcanic eruptions.
  • Directly related to volcanic activity
  • Magma movement, gas release, or the collapse of volcanic structures, typically occurring near active volcanoes.


  Volcanic Earthquake
• Animal Behavior


  Some zoologists’ hypothesize that some animal species like

  elephants have the ability to sense subsonic Rayleigh waves

  from an earthquake or a tsunami.
• Drawback


  This is an observable natural sign of an impending tsunami

  that is noteworthy. Serves as brief warning.
• Change in atmospheric condition


  Strange changes in color or glow of sky (white, blue and

  light orange) are said to show that an earthquake is about

  to hit.
• Electromagnetic disturbance


  There are speculations that there is a relationship between magnetic and electrical charges in rock material and earthquakes. Some scientists have hypothesized that these electromagnetic fields change in a certain way just before an earthquake
• Earthquakes are also classified according to its effects in the

  Environment.

  1.Magnitude

  2. Intensity
• Boom Sound


  There are instances that trembling sound occurs

  before and during earthquakes.

  It could be the cause of minor earthquakes but

  are too shallow to be detected by a seismograph.
• Magnitude


  this measures the energy released by an earthquake and is assessed through seismograph. The stronger the shaking, the larger the waves
• Landslides occur due to gravitational force triggered by

  ground shaking.
• 2.5 or less


  Usually not felt, but can be recorded by seismograph
• 2.5 to 5.4


  Often felt, but only causes minor damage
• 5.5 to 6.0


  Slight damage to buildings and other structures
• 6.1 to 6.9


  May cause a lot of damages in very populated areas
• 7.0 to 7.9


  Major earthquake. Serious damage
• 8.0 or grater


  Great earthquake. Can totally destroy communities near the

  epicenter
• seismograph


  is a device for measuring the

  movement of the earth, and consists of a

  ground-motion detection sensor, called

  a seismometer,
• seismometer


  is an instrument

  used to measure movements in Earth's

  surface. It can detect vibrations from

  seismic waves generated by earthquakes

  and volcanic eruptions.
• Seismology


  The study of earthquake and seismic waves

  that move through and around the world.
• seismic waves


  – are vibrations

  generated by a sudden impulse

  in the earth such as earthquakes
• Surface waves

  Body waves


  Types of seismic

  waves
• Surface waves


  These waves only travel through the earth’s crust

  and have lower frequency than a body waves.
• Rayleigh Waves

  Love waves


  2 kinds of Surface waves