Themes of the Day:

• Earthquake Basics
• Earthquake Effects
• Seismic Waves
• Measuring Quakes
• Earthquake Hazards & Mitigation
• Remote Sensing of Earth's Interior

Fault & Earthquake Terminology

• Focus (or hypocenter) - point of initial breakage - seismic body waves emanate from the focus
• Epicenter - point at surface directly above epicenter - seismic surface waves emanate from the epicenter
• Fault Scarp - surface breakage on a fault zone

Earthquake Causes

• Earthquakes occur when rocks under stress undergo brittle failure and slide past each other along a fault plane
• Elastic Rebound Theory
• Foreshocks & Aftershocks
• Fault Types and Plate Boundaries
  • Normal Faults - Divergent Plate Boundaries
  • Reverse Faults - Convergent Plate Boundaries
  • Strike-slip Faults - Transform Plate Boundaries
• 90% of earthquakes occur at or near plate boundaries

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 explained

Earthquake Hazards & Mitigation

• Types of Hazards
  • Ground Shaking - e.g., 1964 Good Friday Earthquake, Anchorage, Alaska
  • Fault Rupture - Displacement - e.g., 1906 San Francisco, California
  • Landslides - e.g., 2002 Denali Earthquake, Alaska
  • Liquefaction - e.g., 1964 Niigata, Japan
  • Tsunami - mechanism, e.g., 1964 Valdez, Alaska
  • Fire - e.g., 1906 San Francisco
• 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

Remote Sensing of Earth's Interior

• Reflection and Refraction of Seismic Waves
• Seismic Wave paths in the Earth
• Seismic wave speed as a function of density in the Earth
• Seismic discontinuities
  • The Moho - crust/mantle boundary - difference in thickness between continental and oceanic crust
  • transitions within the upper mantle
  • Shadow Zones - P-wave and S-wave shadow zones - Evidence of a Liquid Outer Core
• Seismic Tomography - CAT scan of the Earth