1/23/12 - Bellringer
► How
might you measure an earthquake?
19.3 – Measuring and
Locating Earthquakes
Magnitude
► Magnitude
= a measure of energy produced
by earthquake
► Amplitude = Height of wave
► Richter Scale = numerical rating system
used to measure the magnitude of an
earthquake
Richter Scale
► Numbers
are determined by amplitude of
largest seismic wave
► Each successive number represent an
increase in amplitude of a factor of 10
► Example:
Magnitude-8 is 10x larger than
magnitude-7
 Energy difference is even greater, = 32x
Richter scale
http://www.maelor-humanities.org.uk/GCSEhum/Resources/PP-photos/pp-KeyIss3/Richter.scale.jpg
Moment Magnitude Scale
► Rating
scale that measures the energy
released by an earthquake taking into
account the size of the fault rupture, the
amount of movement, and the rock’s
stillness
► Comparison with Richter:




New Madrid, MO 1812 - Richter scale 8.7 -- MMS 8.1
San Francisco, CA 1906 - Richter scale 8.3 -- MMS 7.7
Prince William, AK 1964 - Richter scale 8.4 -- MMS 9.2
Northridge, CA 1994 - Richter scale 6.4 -- MMS 6.7
Mercalli Scale
► Measures
intensity of earthquake using
Roman Numerals
 Worse damage = higher numeral
► Intensity
= amount of damage caused by
earthquake
http://www.state.il.us/IEMA/images/Mercalli.jpg
Intensity
► Depends
on amplitude of surface waves
► Surface
waves decrease in size with
increase distance from focus
 Intensity decreases as well
Depth of Focus
► Shallow,
Intermediate, Deep
► Shallow = catastrophic with high intensity
 Produce greater maximum intensity than deep
focus
► Deep
= smaller vibrations
Locating Earthquakes
► Seismogram
and Travel-time Curve allow
scientists to determine distance to epicenter
► Seismogram records time elapsed between
arrival of waves
► Distance is determined by measuring
separation of waves on seismogram and
identifying the same separation on TravelTime curve
Locating Earthquakes Cont.
► Multiple
seismograms are needed because
one just determines certain distance in any
direction
 Circle is drawn around station with radius equal
to distance
► Adding
data from other stations narrows
area of focus
 2 circles overlap @ 2 points
 3 circles overlap @ 1 point = EPICENTER
Epicenter
http://wps.prenhall.com/wps/media/objects/3030/3102952/epicenter_tasa_shad.jpg
Seismic Belts
► Majority
of Earthquakes occur along seismic
belts that separate large regions of little or
no seismic activity
► Most
correspond closely with plate
boundaries
► 80% along Circum-Pacific Belt
 Subduction zone
http://upload.wikimedia.org/wikipedia/commons/thumb/0/09/Pacific_Ring_of_Fire.png/800px-Pacific_Ring_of_Fire.png
In-Class Assignment
► Get
► Mini
out a new sheet of paper!
Lab pg. 541
► Ignore
#1
► Turn in Traced Map with labeled intensities,
contour lines, and analysis question answers
at the end of class