1 / 35

VII. Earthquakes

VII. Earthquakes. Introduction Source of seismic energy Propagation of seismic energy Recording earthquakes Magnitude scales. San Francisco, 1906. Building design could not withstand accelerations $Millions of damage Thousands of people killed.

badu
Download Presentation

VII. Earthquakes

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. VII. Earthquakes Introduction Source of seismic energy Propagation of seismic energy Recording earthquakes Magnitude scales

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

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

  4. Photos from AP EarthquakeBam, 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

  5. Geological Hazards Related to Earthquakes Volcanoes Landslides Tsunamis Mudslides

  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

  14. 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 Time of Earthquake

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

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

  19. P-waves a = (k + ¾m)r k: Bulk modulus m: Mod. of rigidity r: Density S-waves b = m/r Body Waves and Surface Waves Seismic Waves and Velocities

  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 0 33 70 150 • Shallow quakes at mid ocean ridges (<33km) and • Oceanic trenches • Deep quakes over the subduction zone (>70 km) 300 500 800 Depth (km)

  22. Earthquakes, Plate Interior • New MadridFault 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 • RichterScale • 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” Geologic Hazards • Assessing Risks • Avoiding Risks • Preventing Damage • Predicting Impact

  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

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

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

More Related