Focus - where it originates (below surface)

Epicenter - location on the surface
(above the focus)

Where do they occur?

Faults

elastic rebound

stick-slip motion - San Andreas (strike-slip fault) - this produces the "BIG ONES"!

3m/50yr before 1906 quake

fault creep - slow and gradual, little seismic activity

Earthquake Waves

seismology uses seismographs which produce seismograms

Surface waves - outer layer of the Earth

Body waves - Earth’s interior (fig. 6.10, p. 163, & 6.24, p.176)
 

Primary (P) waves

compressional (longitudinal)
travel through solid, liquid and gases

Secondary (S) waves

Transverse
travel through solid only

Plotting Earthquake Epicenters
 

Earthquake Intensity and Magnitude
 

Intensity - measure of local effects - Mercalli intensity scale
(Table 6.1, p. 165)

• strength
• distance from epicenter
• nature of the surface

liquefaction - unconsolidated building materials                          (17302)
tsunami - seismic sea wave

Magnitude - strength is total energy (E) released - Richter scale (Table 6.2, p. 166)

• amplitude of largest wave
• 5 vs 6 - 10x larger wave is 30x more E, so
• it releases (30x30) 900x more E

The Earth’s Interior (Fig. 6.23, 6.24 &6.25)
 

Crust -                 ~50 km
Mantle -          ~2900 km
Outer core -    ~2300 km
Inner core -    ~1200 km
                         ~6500 km radius

Mohorovicic discontinuity (Moho) - found that velocity of seismic wave changes at ~50km

asthenosphere

• located in upper mantle
• starts 100 to 350 km and may extend to 700 km
• hot, weak rock that is easily deformed an may be up to 10% molten


lithosphere

• from the top of the asthenosphere to the surface
• behaves like a rigid solid