CHAPTER 12: EARTHQUAKES

Earthquake

• sudden release of energy from a fault (crack in a body of rock)

• “locked” faults undergo stress…they deform, slip, and then rebound

Elastic rebound

■sudden return

to Earth’s

un-deformed

shape

■ BODY WAVES travel

through Earth

■ Begins at FOCUS

■ Point directly above –

EPICENTER

■ Vibrations – SEISMIC

WAVES

Earthquake Waves (copy this & take your notes around it)

Seismic Waves

Body Waves

P Waves

S Waves

Surface Waves

Love Waves

Rayleigh Waves

Seismic Waves

P waves: compression waves, parallel, Fastest

http://web.ics.purdue.edu/~braile/edumod/wa

ves/Pwave.htm

S waves: shear waves, perpendicular, ONLY IN

SOLIDS, 2nd Fastest

http://web.ics.purdue.edu/~braile/edumod/wa

ves/Swave.htm

• Surface waves: travel along the surface, slowest moving, GREATEST DAMAGE

• Rayleigh Wave http://web.ics.purdue.edu/~braile/edumod/waves/Rwave.htm

• Love Wave http://web.ics.purdue.edu/~braile/edumod/waves/Lwave.htm

*Measuring seismic waves detects Earth’s internal layers

*Earth’s interior can change the size and/or direction of seismic waves

Shadow Zone: The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.

Convergent Oceanic —plates move toward each other and collide. Divergent Oceanic —(mid-ocean ridges)—plates move away from each other. Continental -convergent/divergent/transform

Recording Earthquakes

■ Seismograph –

machine

■ Seismogram –

recording/report

■ The closer S+P

waves are, the closer

to the earthquake

How the waves look on a seismograph

Measuring Earthquakes■ Moment Magnitude (BEST): magnitude scale based on size of

the fault area, how far fault blocks move, and rigidity of the rocks

■ Richter Scale: measures ground motion

■ Modified Mercalli Scale: measures basic EQ intensity (after effects)

*Buildings may sway or collapse, constructed to “sway”

U.S. Earthquake Risk Map