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Plate Tectonics

P-waves, S-waves, and Surface waves

Elastic Rebound and Seismic Gap theory

  • P-waves are a type of seismic wave that can travel through a continuum of gases as sound waves they are the primary wave .
  • S-waves are a type of elastic body wave that moves through the body of an object instead of the surface and are the secondary wave.
  • A surface wave is a mechanical wave that occurs along the interface between different media, usually two liquids with different density
  • The elastic rebound theory isn't necessarily what causes earthquakes but a way in which the energy of one is released.
  • As rocks and other formations on the fault lines are subject to force and shift they begin to deform until their internal strength is exceeded in which they snap back.
  • Seismic gap is a highly active seismic zone that has not experienced seismic activity for an unusual amount of time making it more likely to have an earthquake.

The Epicenter

3 Types of Faults

  • The epicenter of an earthquake occurs directly above the hypocenter or focus.
  • In an earthquake the epicenter is where the most damage occurs and is directly above where the fault ruptured.
  • The epicenter of an earthquake can be found by: measuring the distance between the first P-wave and first S-wave, find the point on the chart that represents the time between the P and S-waves which gives distance of epicenter, measure the amplitude and find it on the chart, then take a ruler and measure from point to point, where the line crosses the middle line is the magnitude. Once you have found the magnitude of the quake you can then find the exact location of the epicenter: find the scale of your map, find the the distance to the epicenter on the map, then use that measurement in a compass and draw a circle around the location of where the seismograph is located, then use 2 more locations and draw circles, where all the circles meet is the exact epicenter.
  • A fault is a planar fracture or discontinuity in a volume of rock.
  • There are 3 types of faults: a Dip-slip fault, a strike-slip fault, and a oblique-slip fault.
  • A dip-slip is a fault where the slip on the fault plane is vertical.
  • A strike-slip is a fault where the slip is horizontal.
  • An oblique-slip fault has non-zero components of both strike and dip-slip.

Mercalli scale, Richter scale, and Moment of magnitude

Faults and Plate boundaries

  • The Mercalli scale is a seismic scale used for measuring the intensity of an earthquake. The Mercalli scale measures the effect of an earthquake and is distinct from the moment magnitude, it doesn't measure the energy of a quake but the damage it causes.
  • Unlike the Mercalli the Richter scale measures the amount of energy that is released in an earthquake. This is known as the magnitude and since soil, infrastructure, and rock forms are not accounted for intensity is not given.
  • The moment of magnitude scale or MMS is another scale used to measure energy, the MMS is better at determining the size of an earthquake
  • Faults are formed when major tension between two plates causes a break in the earth's crust.
  • A plate boundary is simply where two plates meet, plate boundaries also form mountain ranges, trenches, and underwater ridges.

Mapping theEarth's Structure

  • Scientists can map the Earth's interior by monitoring the body waves that penetrate deep into the earth and act as an x-ray.

photo credit Nasa / Goddard Space Flight Center / Reto Stöckli

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