1 / 19

Earthquakes in our Community

Earthquakes in our Community. Basic Information You Need to Know. An Earthquake is……. A sudden movement or shaking of the earth. Caused by rocks breaking apart. Along a big surface inside the earth.

booth
Download Presentation

Earthquakes in our Community

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Earthquakes in our Community Basic Information You Need to Know

  2. An Earthquake is……. • A sudden movement or shaking of the earth • Caused by rocks breaking apart • Along a big surface inside the earth • This release of energy as the rocks break apart cause big vibrations called seismic waves or earthquake waves

  3. How it works…… • A fault is a surface between two large blocks or regions of rock Fault Line between rocks

  4. How it works…… • Forces in the earth push the fault blocks in different directions Most of these movements are caused by the movement of the Earth’s plates

  5. Earthquakes happen this way….. • When the plates move the blocks of earth, the rocks bend, but they can’t bend forever…. • Just like when you bend a stick, it will break when it is bent too far….. • The amount of force needed to break the rocks is called the shear strength of the rocks

  6. Earthquakes happen this way….. • If the plate forces are larger than the shear strength of the rocks, the rocks break apart • Like the bent stick, the ends snap back.. • This snapping back is called the elastic rebound of the rock.

  7. So why do rocks bend and snap? • The surface between the rocks is rough • Just like 2 pieces of sandpaper pressed together, they get stuck • The friction between the rocks stops them from moving

  8. So why do rocks bend and snap? • And the fault line between the rocks fills up…. • Sand and water and other rock dust get into the fault line • The dust and water act just like cement locking the fault in place

  9. So where do earthquakes happen? • They usually happen below the surface of the earth…. • The place on the fault underground where the rocks break is called the earthquake focus… • The epicenter is the place on the surface of the earth directly above the focus

  10. So where do earthquakes happen? • The movement of the fault can cause a sharp step in the land’s surface This step is called a fault scarp • Movement along the earth can be as much as 10 to 15 meters (30-45 feet)

  11. So where does the shaking come from? • When the rupture happens, waves of energy go out from the focus of the earthquake

  12. What is a wave? • A wave is a disturbance that transmits energy through matter and space No – not that kind of wave…...

  13. Wave direction Wave direction What is a wave? • Waves move either up and down or back and forth and are named by the type of motion • For Longitudinal waves, the ground moves in the same direction as the wave travels • For Transverse waves, the ground moves perpendicular to the motion of the wave • When an earthquake hits, these waves travel through the earth 3 ways and are called by special names…..

  14. What are the 3 kinds of waves? • The first kind of waves are compression or longitudinal waves • These are called primary waves or “P” waves that compress and expand the ground as they travel by • They reach us first and can travel through solids and liquids • And they travel at 5 kilometers per second

  15. What are the 3 kinds of waves? • The second kind is a shear or transverse wave • These are secondary waves or “S” waves and they look like ocean waves but they go through solid rock • They reach us after the “P” waves and can’t go through liquids • And they travel at 3 kilometers per second

  16. What are the 3 kinds of waves? • The last kind of waves to reach us are surface waves • These waves travel along the surface of the earth and are the last to reach us • These are a combination of transverse and longitudinal waves • These are the waves we feel the most when an earthquake hits

  17. What are the 3 kinds of waves? • The last kind of waves to reach us are surface waves • There are 2 kinds of surface waves • The first kind creates an up-and-down rolling motion • The second kind shakes the ground sideways and does the most damage

  18. So, lets review…… • Some combination of up-and-down and side-to-side motion • What kinds of motion would you expect to feel in an earthquake? • Damage or total destruction of buildings, twisting of roads, dropping of bridges, etc. • What effects would earthquake motions have on buildings, roads and houses? • Of the types of waves discussed, which do you think are the most dangerous and why? • Surface waves because P and S waves travel through the earth’s center

  19. Questions?

More Related