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Chapter 7 Lesson 2 Earthquakes. What is an Earthquake? A sudden trembling of the ground caused by movement happening in the crust.

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Presentation on theme: "Chapter 7 Lesson 2 Earthquakes. What is an Earthquake? A sudden trembling of the ground caused by movement happening in the crust."— Presentation transcript:

1 Chapter 7 Lesson 2 Earthquakes

2 What is an Earthquake? A sudden trembling of the ground caused by movement happening in the crust

3 Where Do Earthquakes Happen? Most earthquakes happen at the edges of plates, where plates meet About 80 percent of all earthquakes happen along the edge of the Pacific Plate Along the edges, plates can collide, they may pull apart, or they may slide past each other These motions can cause the rocks to bend and stretch until they break As a result, faults form at or below the surface of the crust

4 Tectonic Plates

5 Earthquake Locations

6 What is a Fault? Fault- huge cracks in the Earth’s crust

7 Three Kinds of Faults 1. Normal Fault – Produced at divergent boundaries – Rocks above the fault surface move down —http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Nor mal+Fault&flash_file=normalfault&flash_width=220&flash_height=320http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Nor mal+Fault&flash_file=normalfault&flash_width=220&flash_height=320

8 Three Kinds of Faults 2. Reverse Fault – Produced at convergent boundaries – Rocks above the fault move upward – le=Thrust+Fault+and+Reverse+Fault&flash_file=thrustfault&flash_widt h=220&flash_height=320 le=Thrust+Fault+and+Reverse+Fault&flash_file=thrustfault&flash_widt h=220&flash_height=320

9 Three Kinds of Faults 3. Strike Slip Fault – Produced at transform boundaries – Rocks slide past each other in different directions – trike-Slip+Fault&flash_file=strikeslip&flash_width=240&flash_height=310 trike-Slip+Fault&flash_file=strikeslip&flash_width=240&flash_height=310

10 How Earthquakes Start Earthquakes start the moment rocks begin to scrape past each other along a fault.

11 How Earthquakes Start Focus – The point where the earthquake starts, where rocks begin to slide past each other – It is usually below the surface – The sudden movement causes vibrations to spread out from the focus – These vibrations travel through the crust in the form of waves

12 How Earthquakes Start Seismic Waves – A vibration that spreads out away from a focus when an earthquake starts – They soon reach the Earth’s surface at a point directly above the focus

13 How Earthquakes Start Epicenter – The point on the Earth’s surface directly above the focus of an earthquake – People can first feel the ground shaking at the epicenter

14 How Earthquakes Start Epicenter – This shaking is what causes most earthquake damage – Damage is usually greatest at the epicenter because it is so close to the focus – As waves travel away from the focus they get weaker

15 Aftershocks After the first shaking, it may be quiet, and then there are aftershocks This is the shaking of the Earth’s crust after the initial shaking of an earthquake

16 Earthquake Waves There are different kinds of seismic waves which travel differently and at different speeds.

17 Earthquake Waves Primary Waves, or P Waves – Accordion-like motion shaking – Rock material squeezes together and spreads apart repeatedly – This motion produces seismic waves that move in the same direction that the rock is shaking – They are the fastest seismic wave- the first to reach any faraway location – player_embedded player_embedded

18 Earthquake Waves Secondary Waves, or S waves – Shaking like a ruler held off the edge of a desk and “twanged” – This motion in rocks creates seismic waves that move in a perpendicular direction from the vibration – These waves travel slower than primary waves – They are second to arrive at any given faraway location. – 4&feature=player_embedded 4&feature=player_embedded

19 Earthquake Waves Surface Waves – This shaking causes Earths surface to heave up and down like an ocean wave, or sway from side to side – Tears apart structures built on the surface

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21 Earthquake Waves Seismographs – Scientists study and identify waves using a seismograph – A sensitive device that detects the shaking of the Earth’s crust during an earthquake – embedded&v=DX5VXGmdnAg embedded&v=DX5VXGmdnAg

22 Seismograph

23 Seismogram

24 Tsunamis If the focus of the earthquake is beneath the sea floor, the seismic waves can travel through the ocean, producing huge ocean waves called tsunamis Hb8 Hb8

25 See Mrs. Balducci’s Website…. …..For more information on earthquakes such as earthquake current events and earthquake simulations. Look under Chapter 7 Restless Earth LINKS


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