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Earthquake WavesChapter 6-2
Focus and epicenter
Actual location of faultUp to 700 km below surface
Focus and epicenter
Surface location directly above the focus
Actual location of faultUp to 700 km below surface
P-waves
Primary waves- Compression waves
- Travel in a horizontal direction
- First to arrive at a distant location
S-waves
• Secondary waves
- vibrate at right angles
to p-wave
- particles move back
and forth but wave
moves forward
- second to arrive at
distant location
Surface Waves
• Surface waves- travel parallel to Earth’s surface- have greatest height- move like an ocean
wave- last to arrive at
distant location
- are responsible for damage
Locating Epicenter• Time lag between P-wave and S-wave indicate
how far the earthquake is from a seismograph station.
Lag Time
Locating Epicenter
• The lag time tells us how far we are from an earthquake but not from which direction
Epicenter can be any where on radius of the circle
Locating Epicenter
• At least ____ seismograph stations are needed to pinpoint the epicenter of an earthquake
Infinite number of possibleepicenters
Locating Epicenter
• At least ____ seismograph stations are needed to pinpoint the epicenter of an earthquake
Possibleepicenter
Possibleepicenter
Two seismograph stations narrow possible epicenters down to two
Locating Epicenter
• At least three seismograph stations are needed to pinpoint the epicenter of an earthquake
Three epicenters narrows possible locations down to one
epicenter
Measuring Earthquakes
• Mercalli Scale- rates earthquake
according to level of
damage at a given
location
- 12 steps to scale
- same earthquake can
have different rating at
different locations
Measuring Earthquakes
• Richter Scale- rates earthquake’s
magnitude based
on size of seismic
waves
- works well with
small, nearby
quakes
- waves are
measured by a
seismograph
Measuring Earthquakes• Moment Magnitude
Scale- estimates the total
energy released by an earthquake
- can rate all earthquakes- scientists look at type
and strength of waves, amount of movement, and strength of rocks that broke
