What Are Earthquakes 5.1

1. What Are Earthquakes 5.1 Vocabulary to Know: • Seismology • Seismologist • Fault • Plastic Deformation • Elastic Deformation • Elastic Rebound • Transform • Strike-slip fault • Convergent • Reverse fault • Divergent • Normal Fault • Earthquake Zones • Seismic Waves • Body Waves • Surface Waves • P Waves • S Waves

2. Earthquakes

3. Review • Lithosphere – outermost layer of earth • Made up of two parts • Crust and Upper Mantle • Lithosphere is also divided into pieces…. • Tectonic Plates

4. Review • These pieces or tectonic plates move on top of the asthenosphere. • Tectonic plates are the pieces of Earth’s jigsaw puzzle • Boundaries are where • the pieces touch… • Convergent, Divergent, and Transform

5. Study of Earthquakes • Seismology – the studying of earthquakes • Seismologists – scientists who study earthquakes • Most earthquakes take place near the edges of tectonic plates

6. Where do earthquakes happen? • Ring of Fire- belt around the Pacific plate • 80% of all earthquakes occur here

7. Faults • Tectonic plate movement can cause Faults • Fault – break in Earth’s crust • Blocks of the crust slide relative to one another • Earthquakes occur along faults because of the sliding San Andreas Fault

8. What Causes Earthquakes • Stress • This happens when plates either pull, push, or slip past each other • Deformation – change in rock due to stress • Two ways… Plastic deformation (molded clay) or Elastic Deformation (stretching rubber band) • Elastic only leads to earthquakes

9. Elastic Rebound • Sudden return of elastic deformed rock • Like a rubber band that snaps and returns to its unstretched shape. • Happens when their is too much stress for rock to withstand • Energy is released • Energy can travel as seismic waves • These waves cause earthquakes

10. Real Picture of Before/After

11. Faults at Tectonic Plate Boundaries Plate Motion Transform Convergent Divergent Major Fault Type Strike-slip fault Reverse fault Normal fault

12. Normal Fault • Occur at divergent boundaries • Divergent boundary- • Plates drifting apart • Normal fault- • Block slides down relative to the surface • Vertical

13. Reverse Fault • Occur at convergent boundaries • Convergent boundary- • Plates coming together • Reverse fault- • Block slides up relative to the surface • Vertical

14. Strike-Slip Fault • Occur at transform boundaries • Transform boundary- • Plates slide past one another in different directions • Strike-slip fault- • Blocks slide in opposite directions • Horizontal

15. Earthquake Zones • Earthquakes can happen near Earth’s surface or far below it • Most happen at Earthquake zones near tectonic plate boundaries • Earthquake zones have large number of faults • Example…California (San Andreas Fault)

16. Earthquake Waves • Seismic - Waves that travel through Earth • Body waves – travel through earth’s interior • Two Types – P waves & S waves • Waves travel through Earth in different ways and speeds. Depends on material

17. P Waves • Pressure Waves or Primary Waves • Travel through solids, liquids, and gases • First to be detected

18. S Waves • Shear waves or Secondary waves • Second fastest • They shear rock from side to side (stretch it sideways) • Cannot travel through liquid

19. Surface Waves • Move along Earth’s surface…duh right? • Only produce motion in upper portion of crust • Move slow but are more destructive • Two types: • Produce motion up, down, and around • Produce back and forth motion

20. Earthquake Waves

21. Measuring Earthquakes 5.2 and 5.3 • Vocabulary to Know: • Seismographs • Seismogram • Epicenter • Focus • S-P Time Method • Richter Magnitude Scale • Magnitude • Modified Mercalli Intensity Scale • Intensity • Retrofitting

22. Locating Earthquakes • Seismographs – earthquake sensing instruments • At or near Earth’s surface • Seismograph create seismograms • Seismogram – tracing of earthquake motion

23. Time and Location of Earthquakes • Compare seismograms noting differences in arrival times of P and S waves • Seismograms are used to find epicenter of Earthquake • Epicenter – point on Earth’s surface directly above Earthquakes starting point • Focus – inside Earth where Earthquake begins

24. S-P Time Method • Used to find epicenter • Have to collect several seismograms of same earthquake from different locations • Placed on time distance graph • Done in Lab….

25. The S-P time method… • How it’s used: • Collect several seismograms from different seismographs (at different locations) • Plot seismographs on a distance-time graph • Draw circles around the locations based on the distance-time graph • At the point where 3 lines intersect is the earthquake epicenter

26. How do we find the Epicenter of an Earthquake?

27. Richter Magnitude Scale • Richter Magnitude Scale (Richter Scale) – measures strength of Earthquakes • Measures groundmotion recorded by seismograms at seismograph stations

28. Measuring Strength and Intensity • Magnitude - measure of Earthquakes strength • Each time magnitude increases it increases by one unit (10 times larger) • Example 5.0 earthquake ground motion is 10x larger than 4.0, but a 6.0 earthquake will produce 100x more ground motion than a 4.0.

29. Modified Mercalli Intensity Scale • Measures Intensity – degree of which an earthquake is felt by people and the amount of damage it causes • Intensity values change due to location relative of epicenter.

30. Earthquakes and Buildings • Retrofitting – process of making older structures more resistant to earthquakes • Earthquake resistance Technology -