Themes of the Day:

• Seismic Waves
• Measuring Quakes
• Earthquake Hazards & Mitigation

Seismic Waves

• Measured on a Seismograph - printed record is a seismogram
• Body vs. Surface waves - travel paths, speed
• Body Waves - Slinky demonstration
  • Primary (P-wave) - compressional - particle motion is parallel to propogation direction - like sound waves
  • Secondary (S-wave) - shear - particle motion is transverse (perpendicular) to propogation direction
• Surface Waves
  • Love waves - "L-waves knock the "L" out of you." or "Love waves make the bed rock."
  • Rayleigh waves

Measuring Quakes

• Locating Earthquakes by Triangulation
  • Difference in travel time determines distance to quake
  • Triangulation determines a unique epicenter
• Intensity Scales
  • Modified Mercalli Scale I-XII - local effects
  • Richter Scale - logarithmic, based on maximum amplitude - rapid magnitude determination
  • Moment-Magnitude Scale - most quantitative - best scale for very large quakes
• First Motion Mechanisms - the seismic beach ball

Earthquake Hazards & Mitigation

• Types of Hazards
  • Ground Shaking - e.g., 1964 Good Friday Earthquake, Anchorage, Alaska
    • site effects influenced by geologic materials - e.g., Mexico City, San Francisco
  • Fault Rupture - Displacement - e.g., 1906 San Francisco, California, 1992 M 7.5 Landers, CA fence offset, 1992 M 7.5 Landers, CA fault scarp
  • Landslides - e.g., 2002 Denali Earthquake, Alaska, another view
  • Liquefaction - e.g., 1964 Niigata, Japan
  • Tsunami - mechanism, e.g., 1964 Valdez, Alaska, Pacific Tsunami Travel Times
  • Fire - e.g., 1906 San Francisco, 1995 Kobe, Japan (Figure 5.28)
• Hazard Maps - USA, global
• Mitigation Strategies - zoning, building codes, emergency plans

Some Earthquake-Related Websites Worth Surfing

• USGS Earthquake Hazards Program
• USGS National Earthquake Information Center
• USGS Earthquake Hazards Program - Northern California
• Southern California Earthquake Data Center