1. Earthquakes

2. Earthquakes Earthquakes are vibrations of the ground (violent shaking motions) created by the sudden release of energy accumulating in deformed rocks.

3.  Plastic deformation: does NOT cause EQ, changes in rock shape remain  Elastic deformation: shape changes past the breaking point, energy released during break.  Elastic rebound: sudden return of elastically deformed rock to its original (undeformed) shape. Deformation

4. Earthquakes  Stress: The force applied to an object.  Strain: Deformation resulting from stress. Too much stress can cause permanent strain (rupture) = Earthquakes!

6. Earthquakes Focus (hypocenter): The point of the origin of an earthquake. It is below the earth’s surface where rocks begin to rupture or move in an earthquake. Epicenter: The point on the earth’s surface directly above the focus.

8. Seismic Waves  Body Waves P-Waves P-Waves S-Waves S-Waves  Surface Waves L-Waves L-Waves

9. Body Waves: P-Waves Primary Waves  Compressional Waves: waves expand (dilate) and contract  Travel ~6 - 7 km/sec (~4 mi/sec)  Similar to the motion of sound waves  Travel through solid and liquid

11. Body Waves: S-Waves Secondary Waves  Shearing Waves (vertical or horizontal) waves move up/down  Travel ~3.5 km/sec (~2 mi/sec)  Do not move through liquid

14. Surface Waves: L-Waves  Occur close to the surface  Travel ~2.5 km/sec (1.5 mi/sec)  Side to side motion  Up and down motion

16. Fig 19.05

21. Measuring Earthquakes  Seismograph - Device that records seismic wave motion.  Seismogram – paper record of shaking

22. Seismograph Animation Animation

23. Figure 6.14b

24. P travels faster, S slower, Surface wave slowest Seismogram

25.  P-waves (compression) can pass through liquids & solids.  S-waves (shear) cannot pass through liquids.

26. Measurement Scales Mercalli scale  Qualitative  Based on relative destruction  I (least damage) to XII (most damage) Richter scale  Quantitative  Based on amplitude on seismogram  Scale of 1-10

27. Mercalli Scale: Qualitative

28. Mercalli Scale  Qualitative scale  Based on ground observations, not instrument measurement  Depends on earthquake’s  Magnitude  Duration  Distance from the epicenter  Geological conditions  Condition of infrastructure

29. Richter Scale: Quantitative

30. Richter Scale  Quantitative Scale  Based on the amplitude of ground motion  Logarithmic  Increasing one order in magnitude, a tenfold increase in amplitude, and about a 32-times increase in energy

31. What determines strength?  Depth of fault  Total amount of slip (movement) on fault  Strength of rock type