geol101 2009lect20 seismicwaves platetectonicsipages.geo.wvu.edu/~kite/geol101_2009lect20... ·...
TRANSCRIPT
1
Geophysics
Seismic Waves: Deep Earth ProbesThe Navy Reveals The Sea Floor
CH 17 & 18
26 Dec 2004 Banda Aceh Earthquake
Seismic Waves
WV Geological Survey Morgantown Seismograph Record 2 New Madrid Seismic zone Quakes in Illinois April 2008
5.2
4.6
2
P Waves and S waves diagram
Body Waves
Body WavesPRIMARY or Push-Pull Wave
(Compression) Motion Parallel to Wave Motion
Body Waves
SECONDARY or Shear WaveMotion Perpendicular to Wave Motion
3
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. BraileãDepartment of Earth and Atmospheric Sciences
Purdue UniversityWest Lafayette, IN 47907
Image from
Seismic Waves and the Slinky: A Guide For Teachers
(v.2.4, December, 2003)
Prof. Lawrence W. BraileãDepartment of Earth and Atmospheric Sciences
Purdue UniversityWest Lafayette, IN 47907
4
See Figure 16.5, 10th edition
Includes Tsunamis (700-800
km/h)
Surface Waves = Long (L) Waves
5
26 Dec 2004 Sumatra Earthquake killed >290,000
Measuring EarthquakesSeismograph
Seismograph Record
P WaveP WaveArrivalArrival
S WaveS WaveArrivalArrival
6
Finding the Location of QuakesP-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
7
SEISMIC WAVES:DEEP EARTH PROBES
SEISMIC WAVES:DEEP EARTH PROBES
Some Waves Reflect Some Waves Refract(Bend)
P Wave Paths
Through Earth
P Wave P Wave Refraction Refraction Produces Produces
Shadow ZoneShadow Zone
8
S Wave S Wave Paths Paths
Through Through EarthEarth
S Waves S Waves Absorbed by Absorbed by
the Outer the Outer Liquid CoreLiquid Core
Seismic Waves Reveal Earth’s Layers
Seismic Waves Reveal Earth’s Layers
9
Details of Upper Layers
Isostacy~=
Buoyancy
Mountains Have Roots
Mountains Have Roots
Isostacy
10
Erosion (Unloading) Causes Uplift; Deposition (Loading) Causes Subsidence
Whole Earth
Structure
Temperatures & Pressures in the Earth
11
Rock Strength with Depth
LithosphereAsthenosphere
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 & OrientationNormal: Magnetic N ~ True NReversal: Magentic N ~ True S (last one: 788,000 y)Chrons: Paleomagnetic Time Interval
12
How Can We Study PaleomagneticFields? Remnant Magnetism
Remnant Magnetism
Magnetic Anomalies
13
Gravity is NOT Constant
High Low“Normal”
Gravity Reveals Underlying Rock
Bouger Anomaly
North American Gravity
Bouger Anomalies
14
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 ScaleModified Richter (Total Energy) Magnitude Scale
Sumatra 2004
Alfred Wegener’s Evidence for Continental Drift
1. Continental “Fit”
15
Include Continental Shelves for Best “Puzzle” Fit
Continental Drift
• Bacon, 1620
Continental Drift
16
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
17
Similar Fossils
Glossopteris (Common Tree in Coal Seams)Fresh-Water Fish
Mammal-Like Reptiles
http://toad.asu.edu/rschmag/gloss.html
http://www.dme.qld.gov.au/gsd/fossils/perm.htm
18
Similar Fossils: Different Continents
Alfred Wegener’s Evidence for Continental Drift
1. Continental “Fit”2. Similar Rocks, Ages
3. Similar Fossils4. Widespread Glaciation
Widespread GlaciationGondwana Glaciation of Antarctica,
South America, Africa, Australia and India during Permian
19
Strange Climate Zones
Gondwanaland: Antarctica, South America, Africa,
Australia and India
Laurasia: North America, Europe,
most of Asia
Source:http://vishnu.glg.nau.edu/rcb/Jur.jpg
Laurasia
Gondwanaland
Source: http://vishnu.glg.nau.edu/rcb/160_1st.jpg
20
Source:http://vishnu.glg.nau.
edu/rcb/Perm.jpg
Pangaea = Gondwanaland
+ Laurasia
Ice Sheet
Pangaea = Gondwanaland
+ Laurasia
Source:http://vishnu.glg.nau.edu/rcb/Perm.jpg
Source:http://vishnu.glg.nau.
edu/rcb/Penn.jpg
Pangaea = Gondwanaland +
Laurasia
21
Source:http://vishnu.glg.nau.
edu/rcb/Penn.jpg
Pangaea = Gondwanaland +
Laurasia
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