EARTHQUAKESEARTHQUAKESShaking Crust

B48a

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

FAULTFAULT• surface along which rocks move

(B7, Figure 19)

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)

TIME-TRAVEL GRAPHTIME-TRAVEL GRAPH

• compares distance from epicenter to lag time

(B9, Figure 26)

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

MERCALLI SCALEMERCALLI SCALE• Measures

amount of damage done to man-made structures

• SUBJECTIVE SCALE

• Influenced by many factors (height of buildings, age, how built, etc.)

• Used to determine amount of $ for aid