JRGK Earthquakes


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JRGK Earthquakes

  1. 1. EarthquakesEarth Science Unit 12
  2. 2. Why & How So…why do earthquakes happen? Tectonic plates are always moving The boundary between 2 tectonic plates is called a fault Faults are areas where earthquakes happen…how?
  3. 3. Why & HowThe rocks on each side of the fault are moving slowly.As they move, sometimes they get stuck. If they stay stuck for a while, a lot of pressure builds up.When the rocks finally get un-stuck they break (fracture) and move again, and the rocks “rebound” past the place where they were stuck and keep moving slowly past each other.This is the Elastic Rebound Theory
  4. 4. Mechanics of an Earthquake Where the plates actually get stuck is where the earthquake begins…called the focus. The point on Earth’s surface directly above the focus is the epicenter. Which plate boundary would have deeper focus earthquakes?
  5. 5. Seismic GapsSometimes the plates get stuck for a long timeWhy could this be bad?We identify these places because they haven’t released any seismic waves in a long time.This is a “gap” in the record of seismic activity
  6. 6. What makes an EarthquakeDangerous?So, plates get stuck and then move quickly…what does this really do?This creates vibrations (waves) that travel through the ground.What does a wave look like?
  7. 7. Seismic WavesThere are 4 types of seismic waves released in an earthquake.The first two move deep within the Earth, and are called Body WavesThe second two move through the surface of the Earth and are called Surface Waves
  8. 8. Seismic Waves Use Arrows Amount of Time in Describe Wave to Describe Damage Earthquake Movement Movement CausedP WaveS WaveLoveWaveRayleighWave
  9. 9. WhereWhat kinds of plate boundaries usually create earthquakes?
  10. 10. Quick Quiz #1The place underground where an earthquake actually begins.The seismic wave that arrives first in an earthquakeLove and Rayleigh waves are the two types of ____________ waves.Why is a seismic gap dangerous?
  11. 11. WhereWhat kinds of plate boundaries can create earthquakes?ANY kind of plate boundary!Boundaries are places where tectonic plates rub against each other.How are their earthquakes different?
  12. 12. Transform Boundary EarthquakesForm where the plates move past one anotherUsually begin near the surface…why?Create lots of vibrations near the surface, which cause a lot of damageLargest in the world is along the coast of California
  13. 13. Convergent Boundary EarthquakesWhere one plate subducts beneath another plateUsually begin deep underground…why?Their vibrations are felt over a large areaIf they are totally underwater, they form:  Underwater volcanoes, which can make island arcs  Tsunamis  Example: Aleutian IslandsIf they are on land, they form:  Terrestrial volcanoes  Example: West coast of South America
  14. 14. Underwater Convergent Boundary Aleutian Islands, Alaska
  15. 15. Terrestrial Convergent Boundary
  16. 16. Terrestrial Convergent Boundary Andes Mountains, South America
  17. 17. The Pacific Ring of FireOne of 3 major earthquake zones in the worldSurrounds the Pacific OceanContains Transform & Convergent boundaries.
  18. 18. The Eurasian-MelanesianMountain Belt One of the 3 major earthquake zones in the world Mountains that extend from Europe into Asia Contains mostly Convergent Boundaries
  19. 19. Divergent BoundaryEarthquakes Form where the plates spread apart Usually begin near the surface Usually too small to be felt by people Most found on the Ocean Floor
  20. 20. The Mid-Atlantic Ridge One of 3 major earthquake zones in the world Splits the Atlantic Ocean Mostly underwater
  21. 21. Magnitudes of Earthquakes The Richter Scale: Measures Energy Released Measures from 1-12, with 1 being the smallest and 12 being the highest. Major Earthquake: over 7 Moderate Earthquake: 6-7 Minor Earthquake: 2.5-6 Microquake: less than 2.5 (cannot be felt by people) The Mercalli Scale Measures in Roman numerals from 1-12 (I – XII)
  22. 22. The Richter Scale
  23. 23. The Richter Scale
  24. 24. Mercalli Scale
  25. 25. Magnitudes of EarthquakesThe largest earthquake ever recorded was estimated at 9.6 on the Richter scale, and caused massive damage. It is the only earthquake ever recorded over 9.Most major earthquakes are between 7 and 8, and most scientists believe only 1 or 2 earthquakes over 8 will happen in 100 years.Most scientists do not believe that an earthquake larger than 10 on the Richter Scale could ever happen.On the Richter Scale, the highest number (12) is described as “total destruction of the Earth, where the Earth would be split in two.
  26. 26. Finding Epicenter & Magnitude  http://www.sciencecourseware.org/virtualearthquake/VQuake Execute.html
  27. 27. Quick Quiz #2The deepest earthquakes are found at ________________ boundaries.The west coast of North America is part of an earthquake zone known as the ___________________.To find the epicenter of an earthquake, you need to know the arrival time of the ______ wave from 3 recording stations.A ________________ earthquake has a Richter magnitude between 6 & 7.