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Earthquakes Selected learning objectives: 1. Define an earthquake, as well as its epicenter and focus. 2. Explain the relationship between earthquakes and faults. 3. Explain the occurrence of earthquakes according to elastic rebound theory. 4. Describe where (in a Plate Tectonic sense) different types of earthquakes are generated. 5. Describe the process of locating earthquake epicenters using P and S waves. 6. Explain how earthquakes are used to reveal the deep structure of the earth, particularly the liquid nature of the outer core. Where we are • Today: Earthquakes & the deep earth - Elastic Rebound Theory - Types of seismic waves - Measuring quake location & magnitude • Next: Seismic Hazards • Then: Climate Current Quake Info • Tons of info at: - http://earthquake.usgs.gov Tectonics in action • When plates move, how do they move? • [Show Pangaea animation] How do quakes happen? • Elastic Rebound Theory: How do quakes happen? • Elastic Rebound Theory: - Stress builds up… How do quakes happen? • Elastic Rebound Theory: - Stress builds up… - until it exceeds the friction along a fault surface How do quakes happen? • Elastic Rebound Theory: - Stress builds up… - until it exceeds the friction along a fault surface - (or breaks rock, forming a new fault surface) Show elastic rebound movie Elastic Rebound Theory Winch and Brick Demonstration (version 1.0) Earthquake Waves • Several different kinds generated by every earthquake (e.g. P, S, surface) • Differ in terms of particle motion Show Seismic waves movie Do student waves demo Earthquake Waves • Different wave motion allows us to determine material properties (e.g. the outer core is liquid (no S waves!)) Earthquake Waves • Different wave motion allows us to determine material properties (e.g. the outer core is liquid (no S waves!)) Student wave demo - Earthquake Waves • Different wave motion allows us to determine • material properties (e.g. the outer core is liquid (no S waves!)) Student wave demo What would we expect for the global distribution of P & S waves? - Quick check • In the brick and winch demo, the cranking winch represents: A. The movement of tectonic plates B. The strain released during an earthquake C. The steady build up of stress in the rocks Quick check • In the brick and winch demo, the stretching bungee represents: A. The movement of tectonic plates B. The strain released during an earthquake C. The steady build up of stress in the rocks Measuring Quakes • Different wave speeds allow location by triangulation: Measuring Quakes • Different wave speeds allow location by triangulation: - Which is faster, P or S? Measuring Quakes • Different wave speeds allow location by triangulation: - Which is faster, P or S? • Location Measuring Quakes • Different wave speeds allow location by triangulation: - Which is faster, P or S? • Location - Time lag between P & S wave Measuring Quakes • Different wave speeds allow location by triangulation: - Which is faster, P or S? • Location - Time lag between P & S wave • Magnitude Measuring Quakes • Different wave speeds allow location by triangulation: - Which is faster, P or S? • Location - Time lag between P & S wave • Magnitude - Size of P wave at the given distance CA Quake 4/08 M=5.3 Maple Falls Helena, MT Mammoth Lakes, CA Show Seismograph movie Time since the earthquake 60 P Mammoth, Mammoth Lakes,SCA, USA BHZ 40 MLAC Amplitude microns/sec Mammoth CA 00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00 20 0 -20 -40 -60 P S Time since the earthquake TA.A05A. .BHZ.2 P S 4.00 A05A Amplitude microns/sec Maple Falls WA 00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00 2.00 0.00 -2.00 -4.00 -6.00 P S Time since the earthquake 8.00 East Helena, MT, USA BHZ P S 6.00 E16A Amplitude microns/sec Helena MT 00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00 4.00 2.00 0.00 -2.00 -4.00 -6.00 -8.00 P S Time since the earthquake 60 lag P Mammoth, Mammoth Lakes,SCA, USA BHZ 40 MLAC Amplitude microns/sec Mammoth CA 00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00 20 0 -20 -40 -60 P S Time since the earthquake TA.A05A. .BHZ.2 lag P 4.00 A05A Amplitude microns/sec Maple Falls WA 00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00 S 2.00 0.00 -2.00 -4.00 -6.00 P S Time since the earthquake 8.00 East Helena, MT, USA BHZ P 6.00 E16A Amplitude microns/sec Helena MT 00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00 lag S 4.00 2.00 0.00 -2.00 -4.00 -6.00 -8.00 P S Maple Falls Helena, MT Mammoth Lakes, CA Maple Falls Helena, MT Mammoth Lakes, CA Maple Falls Helena, MT Mammoth Lakes, CA Maple Falls Helena, MT Mammoth Lakes, CA Maple Falls Helena, MT Mammoth Lakes, CA Hawaii Seismograph (Idaho) Hawaii Seismograph (Idaho) Quake occurs (18:44 UTC) Hawaii Seismograph (Idaho) Quake occurs (18:44 UTC) P-wave arrives in Idaho (18:57 UTC) Hawaii Seismograph (Idaho) S-wave arrives (19:08 UTC) Quake occurs (18:44 UTC) P-wave arrives in Idaho (18:57 UTC) Hawaii Seismograph (Idaho) S-wave arrives (19:08 UTC) Quake occurs (18:44 UTC) Surface wave arrives (19:24 UTC) P-wave arrives in Idaho (18:57 UTC) N. CA (4/29/06) M5.3 N. CA (4/29/06) M5.3 Seismic Hazards • How many have been in a decent-sized quake? What kinds of seismic hazards are there? • Quakes (ground shaking) • Liquefaction • Tsunamis • Landslides • Volcanic eruptions? Microsoft Office, Nisqually Quake, 2001 Microsoft Office, Nisqually Quake, 2001 Liquefaction: Kobe, Japan, 1995 Liquefaction: Kobe, Japan, 1995 Liquefaction: Niigata, Japan, 1964 [show liquefaction movie] Shaking: Nimitz Freeway (S.F., CA), 1957 & 1989 Shaking: Nimitz Freeway (S.F., CA), 1957 & 1989 Alaska Way Viaduct, Seattle Possible risk of same thing? Post-2001 Inspection Seismic Hazards • Where on earth are there lots of earthquakes? Seismic Hazards • Where on earth are there lots of earthquakes? • Seismic Risk Where is there high earthquake risk? Risk = Probability x Consequence - MMI VII = “...considerable damage to ordinary buildings, with partial collapse...” Modified Mercalli Map for M6.5 • Seismic Risk Where is there high earthquake risk? Risk = Probability x Consequence New Madrid: Probability > 90% chance of >6.0 by 2040 Consequence: • Building codes in area are not as quakeconscious • - MMI VII = “...considerable damage to ordinary buildings, with partial collapse...” Modified Mercalli Map for M6.5 What controls death/damage? • Nature of buildings What controls death/damage? • Nature of buildings - “Quakes don’t kill people, buildings do!” What controls death/damage? • Nature of buildings - “Quakes don’t kill people, buildings do!” - Worst: brick What controls death/damage? • Nature of buildings - “Quakes don’t kill people, buildings do!” - Worst: brick - Best: ? Tents ? What controls death/damage? • Nature of buildings - “Quakes don’t kill people, buildings do!” - Worst: brick - Best: ? Tents ? • Energy released by quake What controls death/damage? • Nature of buildings - “Quakes don’t kill people, buildings do!” - Worst: brick - Best: ? Tents ? • Energy released by quake • Nature of geology: What controls death/damage? • Nature of buildings - “Quakes don’t kill people, buildings do!” - Worst: brick - Best: ? Tents ? • Energy released by quake • Nature of geology: - Best: Strong bedrock What controls death/damage? • Nature of buildings - “Quakes don’t kill people, buildings do!” - Worst: brick - Best: ? Tents ? • Energy released by quake • Nature of geology: - Best: Strong bedrock - Worst: Fill / loose sediment Variation in shaking / damage Variation in shaking / damage Bellingham Bay, 1998 Bellingham Bay, 1888 Bellingham Bay, 1888 Bellingham Bay, 1880’s