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JRGK Earthquakes


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  • 1. EarthquakesEarth Science Unit 12
  • 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. 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. 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. 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. 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. 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. Seismic Waves Use Arrows Amount of Time in Describe Wave to Describe Damage Earthquake Movement Movement CausedP WaveS WaveLoveWaveRayleighWave
  • 9. WhereWhat kinds of plate boundaries usually create earthquakes?
  • 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. 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. 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. 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. Underwater Convergent Boundary Aleutian Islands, Alaska
  • 15. Terrestrial Convergent Boundary
  • 16. Terrestrial Convergent Boundary Andes Mountains, South America
  • 17. The Pacific Ring of FireOne of 3 major earthquake zones in the worldSurrounds the Pacific OceanContains Transform & Convergent boundaries.
  • 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. 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. The Mid-Atlantic Ridge One of 3 major earthquake zones in the world Splits the Atlantic Ocean Mostly underwater
  • 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. The Richter Scale
  • 23. The Richter Scale
  • 24. Mercalli Scale
  • 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. Finding Epicenter & Magnitude  Execute.html
  • 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.