CSC 599: Computational Scientific Discovery

1. Lecture 5b: The Plate Tectonics Paradigm CSC 599: Computational Scientific Discovery

2. Outline Importance Pre-Plate Tectonics Big Picture Ramifications Complications Earthquake Patterns Earthquake Database

3. Importance Plate tectonics gives geologists there first wholestic view of the Earth over time and space . . . • Most earthquakes • Volcanos • Mountains • Continents but it does not explain everything: • Earthquakes in middle of continent? • Early, early Earth? • Maybe ancient Mars, but today's Venus?

4. Pre-Plate Tectonics Theory 1: Earth made by God Evidence: Bible Explains: Mountains formed during flood Theory 2: Earth was hot, cooled off, shrunk Evidence: Further go down in mine hotter it gets Explains: Mountains are shrink ripples Theory 3: Geomorphic Cycles Evidence: Appalachian mountains built out of mountains Those mountains were built out of earlier mountains

5. Geomorphic Cycles • Mountain is lifted • No idea what lifts rock • Erodes into sea • Sand, mud forms plain at sea level • Eroded rock solidifies underground • Sand to sandstone • Mud to shale • Solidified rock lifted • Cycle starts again • What lifts rock? Rebound?

6. Geomorphic Cycles (2)‏ Explains Appalachian Mountians • Taconic Orogeny (550 – 440 MYA)‏ • Explains carbonate (ie. Marine shell) rock in NY, New England • Acadian Orogeny (360 – 320 MYA)‏ • Explains: • Angular unconformities (nonparallel strata)‏ • Igneous intrusions, • Regional metamorphism • Deformation of older rock • Alleghenian Orogeny (299 - 251 MYA)‏ • Also called “Appalachian” • Created “piedmont” from NJ to Alabama

7. Continental Drift (1)‏ “Hey! Africa matches South American” • Abraham Ortelius (1596)‏ • Dutch/Belgian Cartographer & geographer • Francis Bacon (1620)‏ • British Philosopher, Statesman • Benjamin Franklin (1700s)‏ • British/American Publisher, Scientist and Statesman • Antonio Snider-Pellegrini (1858)‏ • French geographer

8. Continental Drift (2)‏ Franklin Coxworthy Roberto Mantovani (1889-1909)‏ Italian Geologist William Henry Pickering (1907)‏ US astronomer Frank Bursley Taylor (1908)‏ Amateur US geologist Alfred Wegener (1912)‏ • German meteorologist • Compared • Coastlines • Rock types • Fossils

9. Continental Drift (3)‏ Fossil Evidence for joined continents • Laurasia (N. supercontinent) broke up before Gondwanaland (S. continent)‏ • Dinosaurs more diverse in N. hemisphere than S. • Coal fields in Europe and N. America line up • Evidence stronger in S. hemisphere than N.

10. Continental Drift (4)‏ Continental Drift's Downfall • Anglo-American geologists dismissed Wegener Fuddy-duddies: “How can rocks move?” Wegener: “Continents move by centrifugal force to equator” Fuddy-duddies: “It takes way more force to plow thru ocean rock” • Wegener died in Greenland in Greenland, 1930s • Doing experiments with balloons & jet stream

11. Plate Tectonics Explains most • Earthquakes • Volcanoes • Magnetism • Fossils among continents • Rock ages among continents • Over WHOLE planet for MUCH of its life! Plate ideas of geology and plate tectonics • Geological time • Rocks flow! • Continents come and go

12. Geological Time Earth way old MYA = Millions of Years Ago Don't know most history • No fossils before Cambrian Explosion • Old rocks cycled

13. Big Picture (2)‏ 2. Rocks flow! • Continents move at a couple of cm/year • Continents float on top of and moved by mantle • Mantle gently churning • Liquid outer core churning • Causes magnetic field

14. Big Picture (3)‏ 3. Life of Plates • Spreading ridges • New (ocean) plate made • Subduction zone • Ocean recycled in mantle • Transform fault • Plates slide past each other • Plates come and go • Continental plates • light, old and float (N. America)‏ • Ocean plates • heavy, new and sink (Juan de Fuca)‏

15. Evidence (beyond Wegener's)‏ Magnetism and spreading ocean ridges Closest to ridge = youngest Farthest from ridge = oldest Symmetric magnetism both sides

16. Ramifications Subduction zones in more detail: • Ocean under continent • Ocean under ocean • Continent under continent

17. Complications 1. Hot spots • Upwelling of mantle rock punch thru continent • Get volcanic mountain • As continent moves above hot spot volcano moves on continent • Get volcanic rock mtn chain eroding away from active volcano • Hot spots may be necessary to keep plates buoyant and moving

18. Complications (2)‏ 2. Plate boundaries not always clear • India and Australia? 3. Plates deform internally China = Australia smashing into Eurasia Chinese rocks are a mess, very few level strata Basin and Range in N. America

19. Problems 1. Earthquakes in middle of continents? New Madrid faulting system • Two estimated mag 8 quakes, 1811 & 1812

20. Problems (2)‏ 2. Early-early Earth? • Pangaea only 500 MY Old • Earth 4500 MY Old • Much more hotter way back when • More initial heat • Several times more radioactive decay • When Iron melted it fell to core • Released 1022 megatons of gravitational energy • What was “crust” like then? • Isolated island arcs?

21. Problem (3)‏ 3. If plate tectonics such a good theory why don't we see it on other Earth-like planets? • Mars • Maybe at one time • Some evidence of ancient ridge-like bands • Mars is smaller --> cooled faster --> no tectonics now • Venus • Magellan spacecraft radar-imaged whole planet • “Know more about surface of Venus than of Earth” • Expected “ocean crust” (spreading ridge, subduct zone)‏ • See “continental crust” (mountains, strike-slip faults)‏ • Explanation: “Venus' surface so hot that is naturally buoyant”

22. Earthquakes

23. Earthquake patterns (1)‏ In space: Along faults Transform faults Subduction zones Wadati-Benioff zone = seismically active portion of fault

24. Earthquake patterns (2)‏ In Time: Measured in months: Fore shocks Main shocks After shocks Measured in centuries (?)‏ “Elastic rebound theory” BIG QUAKE (releases most energy)‏ (many years of many small quakes)‏ BIG QUAKE (releases most energy)‏ (many years of many small quakes)‏ BIG QUAKE (releases most energy)‏ Is it true? Not enough data to say Japanese have longest record of (large) quakes: several centuries

25. Earthquake patterns (3)‏ In magnitude By definition “main shock” bigger than: • fore shocks • after shocks Gutenberg-Richter Relationship • Lower magnitude -> more earthquakes • Log(N(M)) = a-bM M = magnitude N(M) = # quakes of mag M & greater a,b = constants

26. Modeling earthquakes Spring-slider block model • 2 moving plates • matrix of blocks between them w/friction • blocks connected by springs • when one block moves, can trigger others • Reproduces Gutenberg/Richter stats!

27. Earthquake Databases USGS records (http://neic.usgs.gov/neis/epic/)‏ Where: longitude: -180 to 180 degrees latitude: -90 to 90 degrees depth: 0 to 700 (?) km When: time since 1973 How big: Magnitude ML: “Richter Scale” Just a measure of earth-shaking in California MS: Travel along surface Mb: Travel deep MW: Seismic moment = (rock rigidity)(fault area)(slip dist)‏ Has more “rational” relationship w/the energy

28. Problems with db Location • Missing if too small/under sea • Inaccurately placed if too small/under sea Time • Missing if too small/under sea Magnitude • Inconsistent scale • Missing if too small/under sea