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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