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Measuring Earthquakes

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(1) How are earthquakes studied? – or, seismograph, an instrument that measures ground vibrations seismometer – or, seismograph, an instrument that measures ground vibrations – like a telegram, a paper record of the vibrations or seismic waves on a seismometer or seismograph seismogram – like a telegram, a paper record of the vibrations or seismic waves on a seismometer or seismograph

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(2) How big was that ‘quake? Magnitude – a number value for the earthquake’s strength or size of ground motion

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(2) How big was that ‘quake? Magnitude – a number value for the earthquake’s strength or size of ground motion Magnitude is the same no matter where you are, or how strong or weak the shaking was in various locations EXAMPLE- Did the April 4, 2010 earthquake feel different in San Diego, compared to Mexicali?

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(2) How big was that ‘quake? – a number value for the earthquake’s strength or size of ground motion Magnitude – a number value for the earthquake’s strength or size of ground motion Magnitude is the same no matter where you are, or how strong or weak the shaking was in various locations EXAMPLE- Did the April 4, 2010 earthquake feel different in San Diego, compared to Mexicali? Yes! Though it felt different in San Diego, the Mexicali earthquake has been rated at a 7.2 magnitude

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(3) What are 3 kinds of earthquake scales? 1) The - measures the strength of ground motion at the surface 1) The Richter scale- measures the strength of ground motion at the surface

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(3) What are 3 kinds of earthquake scales? 1) The - measures the strength of ground motion at the surface 1) The Richter scale- measures the strength of ground motion at the surface 2) - measures strength based on: 2) Moment magnitude- measures strength based on: the size of the area of the fault that moves, the size of the area of the fault that moves, the distance the fault moved, the distance the fault moved, and the local rigidity of rock and the local rigidity of rock

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(3) What are 3 kinds of earthquake scales? 1) The - measures the strength of ground motion at the surface 1) The Richter scale- measures the strength of ground motion at the surface 2) - measures strength based on: 2) Moment magnitude- measures strength based on: the size of the area of the fault that moves, the size of the area of the fault that moves, the distance the fault moved, the distance the fault moved, and the local rigidity of rock and the local rigidity of rock

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(3) What are 3 kinds of earthquake scales? 1) The - measures the strength of ground motion at the surface 1) The Richter scale- measures the strength of ground motion at the surface 2) - measures strength based on: 2) Moment magnitude- measures strength based on: the size of the area of the fault that moves, the size of the area of the fault that moves, the distance the fault moved, the distance the fault moved, and the local rigidity of rock and the local rigidity of rock 3) The - expresses earthquake intensity or damage, and uses Roman numerals to describe the effects of each intensity level 3) The Mercalli scale- expresses earthquake intensity or damage, and uses Roman numerals to describe the effects of each intensity level

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(4) How does a magnitude 6 compare to a 5 on the Richter? The waves are 10 times greater from a magnitude 6 than those from a magnitude 5 earthquake Richter Magnitude Strength (amplitude) Energy Released 5XY 610X30Y 7100X1000Y

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(4) How does a magnitude 6 compare to a 5 on the Richter? The waves are 10 times greater from a magnitude 6 than those from a magnitude 5 earthquake A magnitude 6 releases about 30 times more energy than a magnitude 5 Richter Magnitude Strength (amplitude) Energy Released 5XY 610X30Y 7100X1000Y

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- measures strength based on: Moment magnitude- measures strength based on: the size of the area of the fault that moves, the size of the area of the fault that moves, the distance the fault moved, the distance the fault moved, and the local rigidity of rock and the local rigidity of rock

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(5) How do the earthquake scales compare? For larger earthquakes, moment magnitude is more accurate than the Richter

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(5) How do the earthquake scales compare? For larger earthquakes, moment magnitude is more accurate than the Richter 9.5 is the highest moment magnitude on record, while the largest Richter earthquakes are about 8.8

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(5) How do the earthquake scales compare? For larger earthquakes, moment magnitude is more accurate than the Richter 9.5 is the highest moment magnitude on record, while the largest Richter earthquakes are about 8.8 The largest ‘quake on the San Andreas in the last 200 years, was in 1906 in San Francisco = 7.9 on the moment magnitude scale, 8.3 on the Richter Loma Prieta was the epicenter of the 1989 earthquake that hit San Francisco = 6.9 on the moment magnitude scale, … 7.0 on the Richter

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(6) With the Mercalli, intensity depends on your location; level I cannot be felt, while level XII is total destruction

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(7) How far away was that earthquake? - graphs the difference in travel time of both the P and S waves S-P interval- graphs the difference in travel time of both the P and S waves

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(7) How far away was that earthquake? - graphs the difference in travel time of both the P and S waves, or, a diagonal line of their average S-P interval- graphs the difference in travel time of both the P and S waves, or, a diagonal line of their average

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Step 1, Subtract the S-wave from the P-wave on a seismogram P-wave ------------ S-wave, subtract S – P = 50 – 0 = 50 seconds (8) Step 1, Subtract the S-wave from the P-wave on a seismogram P-wave ------------ S-wave, subtract S – P = 50 – 0 = 50 seconds

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(9) Step 2 Find where the time meets the distance on the diagonal line (the average of S – P) and match it to the distance S-P interval of 50 sec. = 490 km

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(10) On a map, a circle is drawn to show the distance- how far the seismograph is from the epicenter On a map, a circle is drawn to show the distance- how far the seismograph is from the epicenter The epicenter could be anywhere on the edge of that circle The epicenter could be anywhere on the edge of that circle We need 2 more seismographs to find the earthquake We need 2 more seismographs to find the earthquake

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(10) On a map, a circle is drawn to show the distance- how far the seismograph is from the epicenter On a map, a circle is drawn to show the distance- how far the seismograph is from the epicenter The epicenter could be anywhere on the edge of that circle The epicenter could be anywhere on the edge of that circle We need 2 more seismographs to find the earthquake We need 2 more seismographs to find the earthquake

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(11) The radius of each circle represents the distance from the epicenter The radius of each circle represents the distance from the epicenter If only 2 stations are used, we end up with 2 possible epicenters ! If only 2 stations are used, we end up with 2 possible epicenters ! [ Without Station C we wouldn't know for sure] There can be only one epicenter, and to find it, you need 3 seismographs There can be only one epicenter, and to find it, you need 3 seismographs

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http://blogs.agu.org/mountainbeltway/cate gory/japan/ http://blogs.agu.org/mountainbeltway/cate gory/japan/ http://blogs.agu.org/mountainbeltway/cate gory/japan/ http://blogs.agu.org/mountainbeltway/cate gory/japan/ Penn. State Univ. http://eqseis.geosc.psu.edu/~cammon/HT ML/Classes/IntroQuakes/Notes/waves_an d_interior.html Penn. State Univ. http://eqseis.geosc.psu.edu/~cammon/HT ML/Classes/IntroQuakes/Notes/waves_an d_interior.html http://eqseis.geosc.psu.edu/~cammon/HT ML/Classes/IntroQuakes/Notes/waves_an d_interior.html http://eqseis.geosc.psu.edu/~cammon/HT ML/Classes/IntroQuakes/Notes/waves_an d_interior.html http://earthquake.usgs.gov/regional/nca/19 06/18april/magnitude.php http://earthquake.usgs.gov/regional/nca/19 06/18april/magnitude.php

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Step 1, Subtract the S-wave from the P-wave on a seismogram P-wave ------ S-wave, subtract S – P = 40 – 0 = 40 seconds How far away was that earthquake? Step 1, Subtract the S-wave from the P-wave on a seismogram P-wave ------ S-wave, subtract S – P = 40 – 0 = 40 seconds

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Step 1, Subtract the S wave from the P wave S wave 6 P wave 3 Seismograms can be used to find the distance Step 1, Subtract the S wave from the P wave S wave 6 P wave 3 S – P = 6 – 3 = 3

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Step 2 Find where the time meets the distance on the diagonal line (the average of S – P) and match it to the distance S-P interval of 3 min. = 1500 km

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What kind of range? 9.5 is the highest moment magnitude on record, while 2.5 or below is not felt by most people 9.5 is the highest moment magnitude on record, while 2.5 or below is not felt by most people In the Mercalli scale, an intensity level I cannot be felt, while a XII will totally destroy an area In the Mercalli scale, an intensity level I cannot be felt, while a XII will totally destroy an area The 8.9 earthquake in March 2011, 80mi. off of the coast of Sendai, caused a 30ft tsunami that traveled several miles inland The 8.9 earthquake in March 2011, 80mi. off of the coast of Sendai, caused a 30ft tsunami that traveled several miles inland The 6.7 Northridge earthquake in 1994, caused about $20 billion in damage, making it one of the costliest natural disasters in the US The 6.7 Northridge earthquake in 1994, caused about $20 billion in damage, making it one of the costliest natural disasters in the US Loma Prieta was the epicenter of the 1989 earthquake that hit San Francisco = 6.9 on the moment magnitude scale, or 7.0 on the Richter = 63 dead, 3,757 injured, and several thousand made homeless Loma Prieta was the epicenter of the 1989 earthquake that hit San Francisco = 6.9 on the moment magnitude scale, or 7.0 on the Richter = 63 dead, 3,757 injured, and several thousand made homeless The largest ‘quake on the San Andreas in the last 200 years, was in 1906 in San Francisco = 8.25 on the Richter The largest ‘quake on the San Andreas in the last 200 years, was in 1906 in San Francisco = 8.25 on the Richter **The largest ‘quake recorded in the U.S., magnitude 9.2, occurred in Alaska in 1964 **The largest ‘quake recorded in the U.S., magnitude 9.2, occurred in Alaska in 1964 **The world's largest recorded earthquake, magnitude 9.5, occurred in 1960 in Chile **The world's largest recorded earthquake, magnitude 9.5, occurred in 1960 in Chile

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