Post on 29-Feb-2020
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