Transcript Document
Earthquake Amplitude Magnitude and Intensity
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• 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
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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 10 4 = 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 M
W
works over a wider range of earthquake sizes and is applicable globally
• • • • moment magnitude (M
W)
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 (M
W)
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.
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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 (M o) 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, trees, Outside- Face down away from buildings, 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