EARTHQUAKES Shaking Crust B48a

EARTHQUAKES 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

FAULT surface along which rocks move (B7, Figure 19)

FOCUS V. EPICENTER FOCUS - point below the surface where rocks actually break EPICENTER - point on surface directly above the focus (B7, Figure 20)

SEISMIC WAVES Body Waves –primary –secondary –travel through the earth Surface Waves –travel on the earth (B7, Figure 21)

PRIMARY SEISMIC WAVES P wave move out from focus longitudinal wave –particles move parallel to wave direction fastest least destructive (B7, Figure 22)

SECONDARY SEISMIC WAVES 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 WAVES L wave move out from epicenter particles move in ellipses compared to wave direction slowest Most destructive (B7, Figure 24)

LAG 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 GRAPH compares distance from epicenter to lag time (B9, Figure 26)

LOCATING AN EPICENTER triangulation use information from at least three seismic stations Draw 3 circles Intersection = epicenter (B9, Figure 27)

RICHTER 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 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