1. VII. Earthquakes A.Introduction B.Source of seismic energy C.Propagation of seismic energy D.Recording earthquakes E.Magnitude scales

2. Building design could not withstand accelerations $Millions of damage Thousands of people killed San Francisco, 1906

3. Geology in the News Two die in 6.5 magnitude Earthquake near San Lois Obispo California Earthquake triggers mudslides http://news.nationalgeographic.com/news/2003 California, 2003 San Andreas Fault

4. Earthquake Bam, Iran A Magnitude 6.5 Earthquake hits a stone- and mud- house city of 100,000 in Iran December 26, 2003 30,000 Dead 30,000 Refugees US sends aid and releases sanctions Relations improved Photos from AP

5. Geological Hazards Related to Earthquakes Landslides Volcanoes MudslidesTsunamis

6. B: Sources of Seismic Energy Elastic Rebound Buildup of elastic energy during elastic strain Sudden release due to slippage along a fault or brittle rupture

7. Anatomy of an Earthquake Fig. 8.35 Focus: Source of energy Epicenter: Location directly above focus at the surface (ground motion is greatest) Fault Trace: Shows intersection of fault and the surface of the land Fault Scarp: Indicates vertical motion of fault

8. Propagation of Seismic Energy Body Waves travel through the earths interior (crust, mantle, core) P wave: Compression and expansion of rock S Wave: Shearing motion of particles Fig. 8.42

9. Propagation of a P-Wave

10. Propagation of Seismic Energy Body Waves travel through the earth’s interior (crust, mantle, core) P wave: Compression and expansion of rock S Wave: Shearing motion of particles Surface Waves

11. Propagation of an S-Wave

12. Propagation of Surface Waves Surface Waves travel along the earth’s surface Love Wave: Lateral movement of the surface Rayleigh Wave: Rolling movement of the surface (similar to an ocean wave)

13. Propagation of a Surface Wave

15. Recording Earth Motion Seismograph: An instrument that measures the horizontal or vertical motion of Earth’s surface Seismograms: The plot of the motion

16. Measuring Velocity of Seismic waves Because the P wave travels faster the the S wave The S-P interval increases with distance Time of Earthquake

17. Reading a Seismogram Ground motion vs. Time Each tick mark is 1 minute P-S Time interval indicates distance to epicenter First P wave Arrival First S wave Arrival First Surface wave P-S Interval See Fig. 8.44

18. Time-Distance Relationships Use P-S interval to determine distance to focus See Fig. 8.45 Distance from focus (Kilometers)

19. Seismic Waves and Velocities P-waves  =  (  + ¾  )   : Bulk modulus  : Mod. of rigidity   : Density S-waves  =  /  Body Waves and Surface Waves

20. Locating the Epicenter Triangulation using 3 seismograph stations Depth can be determined with four or more stations

21. Finding the Depth of Earthquakes Using 4 or more seismograph stations Seismicity of the Pacific Rim 1975-1995 Depth (km) 0 33 70 300 150 500 800 Shallow quakes at mid ocean ridges (<33km) and Oceanic trenches Deep quakes over the subduction zone (>70 km)

22. Earthquakes, Plate Interior New Madrid Fault Zone Faults activated by crustal warping Bowling Green Fault Largest Earthquake on the N. American Continent

23. New Madrid Earthquake, 1811 Modified Mercalli Intensity Scale Subjective observations of Damage and Ground motion Is not a quantitative measure

24. Earthquake Intensity Scales Modified Mercalli Scale Subjective observations of Damage and Ground motion Is not a quantitative measure Richter Scale Indicates Ground Motion Amplitude Logarithmic ( e.g., 6 is ten times stronger than 5 ) Does not directly indicate energy or destruction

25. Earthquakes around the World

26. Assessing Risk “Major Quake Likely to Strike San Francisco Bay Region Between 2003 and 2032” Assessing Risks Avoiding Risks Preventing Damage Predicting Impact Geologic Hazards

27. Seismic Risk Analysis Quake history (statistics) Locations of active faults Competency of surficial materials (soil and rock) Ocean basin source  Tsunamis

28. Solomon Islands Earth Quake and Tsunami 4-1-07

34. Profiling Earth’s Interior Velocities of seismic waves vs depth Fig. 19.19 & 20

35. Imaging Earth’s Interior P and S waves are refracted (bent) within the earth S waves do not travel through fluids Fig. 9.21