EARTHQUAKESEARTHQUAKES• vibrations produced by breaking of
lithosphere (crust and upper mantle)
• elastic limit = amount that rocks can stretch and bend
–When surpassed --> rocks break and move
–seismic waves (vibrations) sent out in all directions
FOCUS V. EPICENTERFOCUS V. EPICENTER• FOCUS - point
below the surface where rocks actually break
• EPICENTER - point on surface directly above the focus
(B7, Figure 20)
SEISMIC WAVESSEISMIC WAVES• Body Waves
–primary–secondary–travel through the earth
• Surface Waves–travel on the earth
(B7, Figure 21)
PRIMARY SEISMIC PRIMARY SEISMIC WAVESWAVES• P wave
• move out from focus
• longitudinal wave
–particles move parallel to wave direction
• fastest
• least destructive
(B7, Figure 22)
SECONDARY SEISMIC SECONDARY SEISMIC WAVESWAVES• S wave
• move out from focus
• transverse wave
–particles move at right angles to wave direction
• slower than P waves
• more destructive than P
(B7, Figure 23)
SURFACE WAVESSURFACE WAVES• L wave
• move out from epicenter
• particles move in ellipses compared to wave direction
• slowest
• Most destructive
(B7, Figure 24)
LAG TIMELAG TIME• LAG TIME = difference between first
S wave and first P wave arrival at a seismic station
• longer lag time = further from epicenter
(B9, Figure 25)
LOCATING AN LOCATING AN EPICENTEREPICENTER
• triangulation
• use information from at least three seismic stations
• Draw 3 circles
• Intersection = epicenter
(B9, Figure 27)
RICHTER SCALERICHTER SCALE• Measures amount
of energy released
• Increase of “1” = 10 times more energy released
• OBJECTIVE SCALE
• Not influenced by other factors
• Used to compare earthquakes