Earthquakes

Earthquakes

Terms:

epicenter vs. focus
seismic waves
magnitude
- daily occurance (USGS maps)
- Richter scale (logarithmic increase)
- aftershocks (independent quakes)
where?

Lateral fault systems
- generally - strike-slip faults
- often associated with transform faults
  - San Andreas

Causes:
- Pacific Ring of Fire
  - shift in earth’s crust
  - faults & bedrock type

California’s most infamous natural hazard: earthquakes
- most recent major "quake" - Loma Prieta (1989) measuring 7.1 magnitude
- most devastating - San Francisco’s great earthquake of 1906 - 7.7 mag!
- most powerful ? - historic records show around 7.8; only 150 years old...
- other notable "quakes": Northridge - 6.7 (1994)
- Mendocino - 7.0 (1994)
- San Fernando - 6.6 (1971)
- Hollister - 5.6 (1961)
- Long Beach - 6.3 (1933)
- Lone Pine - 7.6 (1872)
- Tejon - 7.8 upwards (1857)

Hazards associated with earthquakes:
- landfill and alluvial soils (USGS info.)
  - liquefaction
- Major quake to strike S.F. by 2032
- old brick buildings and stucco parapets
- development on existing faults

Preventative maintenance:
- retrofit projects
- buildings on rollers
- appropriate long-term planning

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