Geophysics Seismic Waves: Deep Earth Probes The Navy Reveals The Sea Floor CH 17 & 18 Seismic Waves 26 Dec 2004 Banda Aceh Earthquake WV Geological Survey Morgantown Seismograph Record 2 New Madrid Seismic zone Quakes in Illinois April 2008 5.2 4.6 1
Body Waves P Waves and S waves diagram Body Waves PRIMARY or Push-Pull Wave (Compression) Motion Parallel to Wave Motion Body Waves SECONDARY or Shear Wave Motion Perpendicular to Wave Motion 2
Go to http://www.eas.purdue.edu/~braile /edumod/slinky/slinky.htm Look at figure 13 for P wave Then look at figure 14 for S wave Image from Seismic Waves and the Slinky: A Guide For Teachers (v.2.2, December, 2000) Prof. Lawrence W. Braileã Department of Earth and Atmospheric Sciences Purdue University West Lafayette, IN 47907 braile@purdue.edu Image from Seismic Waves and the Slinky: A Guide For Teachers (v.2.4, December, 2003) Prof. Lawrence W. Braileã Department of Earth and Atmospheric Sciences Purdue University West Lafayette, IN 47907 braile@purdue.edu 3
See Figure 16.5, 10 th edition Surface Waves = Long (L) Waves Includes Tsunamis (700-800 km/h) 4
26 Dec 2004 Sumatra Earthquake killed >290,000 Measuring Earthquakes Seismograph Seismograph Record P Wave Arrival S Wave Arrival 5
Finding the Location of Quakes P-S Interval P-S Interval P-S Interval Tells How Far Away, but in What Direction? Use 3 Different Seismograph Locations, Plot Arcs from Each Station on a Map 6
SEISMIC WAVES: DEEP EARTH PROBES SEISMIC WAVES: DEEP EARTH PROBES Some Waves Reflect Some Waves Refract (Bend) P Wave Paths Through Earth P Wave Refraction Produces Shadow Zone 7
S Wave Paths Through Earth S Waves Absorbed by the Outer Liquid Core Seismic Waves Reveal Earth s Layers Seismic Waves Reveal Earth s Layers 8
Details of Upper Layers Isostacy ~= Buoyancy Mountains Have Roots Isostacy Mountains Have Roots 9
Erosion (Unloading) Causes Uplift; Deposition (Loading) Causes Subsidence Whole Earth Structure Temperatures & Pressures in the Earth 10
Rock Strength with Depth Lithosphere Asthenosphere Earth s Magnetic Field May Stem from Convection in Liquid Outer Core! Inclination: Deviation from Horizontal Declination: Deviation from True N-S Earth s Changing Magnetic Field Variable Strength & Orientation Normal: Magnetic N ~ True N Reversal: Magentic N ~ True S (last one: 788,000 y) Chrons: Paleomagnetic Time Interval 11
How Can We Study Paleomagnetic Fields? Remnant Magnetism Remnant Magnetism Magnetic Anomalies 12
Gravity is NOT Constant High Normal Low Gravity Reveals Underlying Rock Bouger Anomaly North American Gravity Bouger Anomalies 13
Seismic network reports 'jolt' on WV-VA border Tuesday April 14, 2009 by The Associated Press ATHENS, W.Va. (AP) -- The Southeast United States Seismic Network says a small earthquake occurred over the weekend along the West Virginia-Virginia border. The network says the quake had a magnitude of 2.4 and occurred at approximately 11:09 a.m. Saturday. The quake struck about 9 miles northeast of Athens and 10 miles north of Glen Lyn, Va. There were no reports of damage or injuries. Local officials in the area said there were no reports that anyone even felt the quake. Earthquake analyst Don Blakeman with the National Information Center in Colorado says a quake of that magnitude is at most a "jolt'' that won't do any damage. Modified Richter (Total Energy) Magnitude Scale Sumatra 2004 Alfred Wegener s Evidence for Continental Drift 1. Continental Fit 14
Include Continental Shelves for Best Puzzle Fit Continental Drift Bacon, 1620 Continental Drift 15
Alfred Wegener s Evidence for Continental Drift 1. Continental Fit 2. Similar Rocks, Ages Wegener s Evidence: Similar Rocks, Similar Ages Batholith Alfred Wegener s Evidence for Continental Drift 1. Continental Fit 2. Similar Rocks, Ages 3. Similar Fossils 16
Similar Fossils Glossopteris (Common Tree in Coal Seams) Fresh-Water Fish Mammal-Like Reptiles http://toad.asu.edu/rs chmag/gloss.html http://www.dme.qld.gov.au/gsd/fossils/perm.htm 17
Similar Fossils: Different Continents Alfred Wegener s Evidence for Continental Drift 1. Continental Fit 2. Similar Rocks, Ages 3. Similar Fossils 4. Widespread Glaciation Widespread Glaciation Gondwana Glaciation of Antarctica, South America, Africa, Australia and India during Permian 18
Strange Climate Zones Laurasia: North America, Europe, most of Asia Source: http://vishnu. glg.nau.edu/ rcb/jur.jpg Gondwanaland: Antarctica, South America, Africa, Australia and India Laurasia Gondwanaland Source: http://vishnu.glg.nau.edu/rcb/160_1st.jpg 19
Pangaea = Gondwanaland + Laurasia Ice Sheet Source: http://vishnu.glg.nau. edu/rcb/perm.jpg Pangaea = Gondwanaland + Laurasia Source: http://vishnu.glg.nau.edu/rcb/perm.jpg Pangaea = Gondwanaland + Laurasia Source: http://vishnu.glg.nau. edu/rcb/penn.jpg 20
Pangaea = Gondwanaland + Laurasia Source: http://vishnu.glg.nau. edu/rcb/penn.jpg Alfred Wegener s Evidence for Continental Drifts Was NOT Accepted in USA. Problem: No Mechanism for Continents to Plow Through Oceanic Crust Answer lies on the Sea Floor & in Ch. 18 + 19 21