Transcript Measuring Earthquakes

Warm Up
What stress is acting on a strike slip fault?
**If needed…Turn in your test corrections stapled
to your original test in the homework box.
Attention Astronomy Geeks!! Check out Jupiter
and Venus tonight shining bright next to the
moon! (They’ll look like bright stars.)
Measuring Earthquakes
Where is the center of an
earthquake?
• Focus: Point where rocks break
UNDERGROUND
• Epicenter: Center of earthquake ABOVE
GROUND
Surface Wave
S-Wave
P-Wave
The S-P Method (Locating an
epicenter)
• Distance to the epicenter is measured on a timedistance graph.
• It takes THREE seismograph stations to locate
an epicenter. A circle is drawn around each
location. The epicenter is where the 3 circles
overlap.
Earthquake Scales
•
There are two
different scales
used to measure
earthquakes:
1. The Richter
Magnitude Scale
2. The Modified
Mercalli Intensity
Scale
The Richter Scale
• Measures the amount of ground motion.
• Ranks from 1-10
• Each 1 point jump increases the ground motion
10 times!!
• Measured using a seismograph
Magnitude
Estimated effects
2.0
can be detected only by
seismograph
3.0
4.0
can be felt at epicenter
can be felt by most people in the
area
causes damage at epicenter
can cause widespread damage
can cause great, widespread damage
5.0
6.0
7.0
How does a seismograph work?
• Seismograph: records ground movements
of earthquakes
• The pendulum sits still while the ground
moves.
Seismograph
Animation:
http://www.wwnor
ton.com/college/g
eo/egeo/flash/8_
3.swf
The Mercalli Scale
• Ranks from 1-12
• Measures the
intensity and
DAMAGE
• One Earthquake
can have more
than one intensity
level
What are the worst earthquakes
ever recorded?