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Earthquake Amplitude
Magnitude and Intensity.
• Which of the stations is farthest from the
epicenter?
• Which of the stations is closest?
• How do you know?
Difference between P-wave and S-wave arrival can be
used to locate the location of an earthquake more
effectively
Difference between p- and s-waves can be used to track location
 Collect data from at least 3 seismograms from an
earthquake
 Use the Time-Distance graph to find distance
from epicenter for
each seismogram
 Use each distance to draw a circle of possible
epicenters
 The actual earthquake epicenter is found at the
spot where all 3
intersect
Need a minimum of 3 stations to isolate location (and
the more the better)
• Measuring the size of the earth quake
• 1- Where did the earthquake occur?
• 2- How big was the earthquake?
Modified Mercalli Scale
Mercalli Scale
• Mercalli Scale
a seismic scale used for
measuring the intensity
of an earthquake
• the scale are based on
observed structural
damage
• based on observed
effects
The Richter Scale
• The first widely-used
method
• Based on amplitude of
the largest wave
recorded and the
distance between the
earthquake and the
seismometer
• Two pieces of information used to calculate size of Earthquake on
the Richter Scale:
a) Deflection of seismometer,
b) b) distance from source (based on P & S wave arrivals)
The Richter Scale
• Earliest measure of earthquake
size
• Easy to measure
• Empirical -no direct tie to
physics of faulting
The Richter Scale
• Magnitude – varies by powers of 10
– One point increase in magnitude means that the
amplitude of the seismic wave is 10 times
greater.
– Example - Mag 5  Mag 6
• The seismic wave is 10x bigger)
• Energy released ( 31 X more energy )
• How much bigger is the amplitude of a 8.3
magnitude earthquake compared to 4.3
magnitude earthquake?
• 8.3-4.3 = 4 104 = 10,000 bigger
• And on million times more energy
•https://www.youtube.co
m/watch?v=05kBRmJh3F8
• Richter scale, do not provide accurate
estimates for large magnitude earthquakes
• Measures how much energy is released.
• Today we use Moment magnitude scale,
abbreviated MW
• works over a wider range of earthquake sizes
and is applicable globally
• moment magnitude (MW) scale is based on the
total moment release of the earthquake
• product of the distance a fault moved and the
force required to move it
• about the same as Richter magnitudes
• (MW) can read ‘magnitude 8 and greater
events accurately
• sudden slip of one part
of the Earth's crust,
relative to another,
along a fault surface.
• Thrust fault scarp at El
Asnam, Algeria
• Connecting Earthquakes
and Faults
• Connecting Earthquakes
and Faults
-Interested in the amount
of displacement between
points
• Link between (
magnitude) energy with
the severity of fault
rupture
• The seismic moment
(Mo) analysis of seismic
waves, directly
proportional to the
extent of the actual
fault rupture
• 1999 Chi-Chi
earthquake, Taiwan
• How big is an
earthquake?
• Depends on how big a
patch of the fault
breaks
• 1999 Chi-Chi
earthquake, Taiwan
• magnitude scales are
logarithmic
• The area of the circle is
proportional to the
energy of an event at
moment magnitude +1
versus moment
magnitude +2.
• https://www.youtube.c
om/watch?v=HL3KGK5e
qaw
"drop, cover and hold on"
• a consensus has been
building that "drop,
cover and hold on" is a
more appropriate
method for developed
countries like the U.S.,
where there are the
best constructing codes
triangle of life
• Before: Survival supplies
•
Identify safe zones inside and outside
•
Evacuation plan and plan where to meet
• During: Inside-Seek cover under table, desk,
•
Outside- Face down away from buildings,
trees,
powerlines
• After: Stay out of damaged buildings, be prepared
for aftershocks
• Mass damper- helps compensate for building
movement
• Active tendon system- helps compensate for building
movement
• Base isolators- shock absorbers that stop the passing of
seismic
waves
• Cross braces-counteracts the pull and push stresses
• Flexible pipes- prevent water and gas lines from
rupturing