Earthquakes Hazards and Risk Reduction Methods

• Earthquake features:

  • Origin of seismic waves
  • Primary waves
  • Secondary and surface waves (Rayleigh Wave or Love Wave)
• Earthquake hazards:

  • Ground shaking results from the vibrations of the ground during earthquakes
  • Ground rupture is deformation on the ground that marks the intersection with the earth's surface
  • Liquefaction
  • Tsunami
• Effects of an earthquake:

  • Primary effects are permanent features an earthquake can bring out, such as fault scarps, surface ruptures, and offsets of natural or human-constructed objects
  • Secondary effects happen when ground movement results in other types of destruction, like landslides, tsunami, liquefaction, and fire
• Precautionary and safety measures:

  What to do before an earthquake:

  • Have a fire extinguisher, first aid kit, battery-powered radio, flashlight, and extra batteries at home
  • Learn first aid
  • Learn how to turn off gas, water, and electricity
  • Make a plan of where to meet your family after an earthquake
  • Avoid leaving heavy objects on shelves
  • Anchor heavy furniture, cupboards, and appliances to walls or floor
  • Learn the earthquake plan at your school or workplace
• What to do during an earthquake:

  • Stay calm
  • If indoors, stand against a wall near the center of the building, stand in a doorway, or crawl under heavy furniture
  • If outdoors, stay in the open away from power lines or anything that might fall
  • Don't use matches, candles, or any flame
  • If in a car, stop the car and stay inside until the earthquake stops
  • Avoid using elevators
• What to do after an earthquake:

  • Check yourself and others for injuries and provide first aid
  • Check water, gas, and electric lines for damage and shut off valves if damaged
  • Turn on the radio and avoid using the phone unless it's an emergency
  • Stay out of damaged buildings
  • Be careful around broken glass and debris
  • Stay away from beaches and damaged areas
  • Follow the emergency plan or instructions of the person in charge if at school or work
• Primary waves (P-waves) cause particles in rocks to move back and forth in the same direction that the wave is travelling.
• Secondary waves or Shear waves (S-waves) travels slower than P-waves; It travels only through solids and move material side to side perpendicular to the direction of the wave travel.
• Surface waves

  • These waves travel along the Earth's surface and include:
  • Love Waves:
  • Named after A. E. H. Love.
  • Side-to-side horizontal motion.
  • Only travels through solids.
  • Rayleigh Waves:
  • Named after Lord Rayleigh.
  • Rolling motion.
  • Travels along the Earth's surface.
• Fault Scarp:

  • A fault scarp is a steep slope or cliff that is formed by the movement of the Earth's crust along a fault line. It represents the surface expression of a fault, where one side of the fault has moved vertically relative to the other. Fault scarps are often visible in areas that have experienced recent tectonic activity and earthquakes.
• Fault:

  • A fault is a fracture or zone of fractures in the Earth's crust where rocks on either side have moved relative to each other. Faults are the result of tectonic forces that cause the Earth's lithospheric plates to interact. The movement along faults can be vertical, horizontal, or a combination of both. Faults are fundamental to the understanding of plate tectonics and earthquake activity.
• Epicenter:

  • The epicenter is the point on the Earth's surface directly above the earthquake's point of origin (focus or hypocenter). It is the location where the seismic waves, generated by the release of energy during an earthquake, first reach the Earth's surface. The epicenter is typically used to locate and describe the earthquake's location for mapping and reporting purposes.
• Focus (Hypocenter):

  • The focus (or hypocenter) is the actual point within the Earth where an earthquake originates. It is the point where the seismic energy is released, leading to the generation of seismic waves. The focus is usually located at some depth below the Earth's surface, and the point directly above it on the surface is referred to as the epicenter.
• Secondary waves, also known as S-waves, are one of the two main types of seismic waves generated by earthquakes and other seismic events. S-waves are classified as body waves because they travel through the interior of the Earth.
• This motion is in contrast to P-waves, which cause particles to move parallel to the direction of wave propagation
• The presence or absence of S-waves in seismic data helps distinguish between solid and liquid regions in the Earth's interior
• Crust: The Earth's outermost layer is called the crust. It is relatively thin and is divided into two types: the continental crust, which forms the continents, and the oceanic crust, which underlies the ocean basins. The crust is solid and rigid and is made up of various types of rocks.
• Mantle: Beneath the crust lies the mantle, which extends to a depth of about 2,900 kilometers (1,800 miles). The mantle is composed of solid rock that can flow over long periods of time. It's divided into the upper mantle and the lower mantle.
• Outer Core: Below the mantle is the outer core, which is composed of liquid iron and nickel. The movement of molten iron and nickel in the outer core generates Earth's magnetic field through a process called the geodynamo.
• Inner Core: The innermost layer is the inner core, which is solid and composed mainly of iron and nickel. The intense pressure at this depth keeps the iron and nickel in a solid state despite high temperatures.
• The Earth's lithosphere, which includes the crust and part of the upper mantle, is divided into tectonic plates.
• Divergent Boundaries: Plates move away from each other, leading to the creation of new crust. This occurs at mid-ocean ridges.

  Convergent Boundaries: Plates move toward each other, resulting in the subduction of one plate beneath the other. This can lead to the formation of deep ocean trenches, volcanic arcs, and mountain ranges.

  Transform Boundaries: Plates slide past each other horizontally, causing earthquakes along faults. The San Andreas Fault in California is an example of a transform boundary.