Earthquakes [EARTH SCIENCE]

• An earthquake is the intense shaking of the ground due to the interaction of

  the moving tectonic plates. When tectonic plates build up stress to one another, this might lead to cracks called faults. When one tectonic plate gets stuck along the rough edge of another tectonic plate, as they move apart from one another and overcome the friction and stress, the energy is released and causes shaking of the Earth.

  Since Earth is composed of many pieces of tectonic plates, earthquakes mostly occur along the boundaries where the plates meet.
• Any movement along the fault line might cause energy release in all directions in the form of seismic waves.

  
  

  And the place where there are a lot of plate interactions is the Pacific Ring of Fire.
• There are three types of faults where earthquakes might originate: normal fault, reverse fault, and strike-slip fault.
• A normal fault occurs when the hanging wall block goes down relative to the footwall block because of tensional forces.
• A reverse fault happens when the hanging wall block moves up relative to the footwall block due to compressional forces.
• A strike-slip fault occurs when neither the hanging wall block moves up nor down, but they slide past each other. This is also known as transform plate boundary.
• A hanging wall block is the movable part while the footwall block is the stationary part of the tectonic plate.
• A thrust fault can be either normal or reverse fault, only the dip (angle of faulting) is shallow or less than 45 degrees
• True

  Faults are places of origin of earthquakes.
• False

  Faults may form when two plates move away from one another.
• False

  When two plates converge, a tensional stress is usually felt forming a reverse fault.
• True

  During subduction, compressional stress causes the formation of reverse faults.
• True

  A normal fault can be considered a thrust fault.
• True

  Valleys are formed when there is a normal fault between two footwall blocks.
• True

  Strike-slip faults are found in transform plate boundaries.
• False

  In faults, there are two movable parts.
• True

  A dip refers to the angle of inclination of a fault.
• True

  A normal fault may be formed when two plates exert tensional force toward each other.
• When the seismic waves are released, they originate at a point where the rocks break called the focus. As they propagate like ripples of water in a pond, these waves reach the surface from a point called the epicenter. Seismic waves carry energy that makes any structure sway or even crumble into pieces.
• Seismic waves come in two types: body waves that travel inside the Earth and surface waves that travel on the surface. Body waves are P-waves and S-waves while surface waves are Love waves and Rayleigh waves. The table below summarizes the different types of seismic waves and their characteristics.
• Types of body waves

  • P-waves (primary waves)
  • S-waves (secondary waves)
• Types of surface waves

  • Love waves
  • Rayleigh waves
• P-waves

  • Also known as compression waves
  • Cause the ground to move back and forth parallel to the direction of the waves
  • Fastest body wave
• S-waves

  • Also known as shear waves
  • Move the ground back and forth perpendicular to the direction of the waves
  • Slower than P-waves
• Love waves

  • Has horizontal movement that is perpendicular to the direction of the waves
  • Travels faster than Rayleigh waves
• Rayleigh waves

  • Moves the ground in a circular or rolling motion
  • Slowest surface waves
• Earth builds up and releases energy. When this occurs, we have an earthquake, which is the shaking of the ground when rock below Earth's surface breaks. Energy builds up underground, and once it builds up enough it just can't hold back any longer, and we get the same explosive release of energy as a person might at the end of a long, bad day.
• What exactly causes the rock underground to break? This is the result of stress along plate boundaries on Earth. The plates are dynamic, so they are always moving. Sometimes they move enough that they push into each other or pull apart. Stress is a force that squeezes rock together, stretches or pulls them apart, or pushes them in different directions.
• Types of stress

  • Tensional stress
  • Compressional stress
  • Shear stress
• Tensional stress occurs when rocks are pulled apart. They're being stretched farther than they would be otherwise.
• Compressional stress occurs when rocks are pushed together. They're pressed into one another.
• Shear stress is when rocks slide past each other in opposite directions; it's like rubbing your hands together. They don't push or pull, but there's a lot of friction there.
• When the stress gets to be too much, as all of the events build up on a bad day, the rock breaks, and the ground begins to shake. If the rock splits into separate pieces, we get a fault, which is a break on the Earth’s crust along which significant movement has taken place.
• The point underground where the actual breaking of the rock occurs is called the focus. It might help to remember this by thinking of it as the focal point of the earthquake. The point directly above the focus on the surface of Earth is called the epicenter. This is where the ground shaking is usually the strongest. From this point on the surface, the waves of energy from below ground begin to travel outward, so you can think of this as the central point of shaking above ground. Because the shaking is strongest here, this is also where the most damage usually occurs.
• The energy released during an earthquake is carried by vibrations called seismic waves. As an earthquake occurs, seismic waves move out in all directions of the focus. As the rocks break and move, potential energy is transferred into kinetic energy through seismic waves.
• A seismograph is a machine that records ground movement from earthquakes. The information recorded tells us about the strength and speed of the energy traveling from the breaking point underground.
• Seismographs measure the time of arrival and strength of seismic waves in a record called seismogram. The amplitude of the seismic waves indicates the strength of an earthquake: the higher the wavy lines on the seismogram are, the stronger the earthquake. Using the seismograms from at least 3 geologic stations from different places, the epicenter of an earthquake or its point of origin can be located.
• Magnitude measures the energy released at the source of the earthquake. It is determined from measurements on seismographs.
• Intensity measures the strength of shaking produced by the earthquake at a certain location. Intensity is determined from effects on people, human structures, and the natural environment.
• The magnitude of earthquakes is measured based on the Richter scale. The scale measures the energy of an earthquake on a scale of 1 to 10. Each unit on the Richter scale is 10 times stronger than the preceding number. Any number above 6 indicates a very destructive earthquake.