Plate Tectonics and Earthquakes • Objectives: • Students will learn key terms associated with • plate tectonic processes. (Part A) • Students will understand the specific plate • motions associated with divergent, • convergent, and transform plate boundaries. • (Part B) • Students will gain a global view of EQ’s • (where EQ’s typically occur). (Part C) • Students will evaluate and apply concepts • from lab parts A, B, and C to answer critical • thinking questions. (Part D)
Continental Drift vs. Plate Tectonics – The Debate Alfred Wegener 1912- observed the possible fit between So. America and Africa. • Hypothesized the continents were • all together forming the supercontinent • Pangaea – 250 million years ago • Supported by the following evidence: • fossil evidence • lithologic evidence • climatic evidence Wegener became the laughing stalk of the science world – WHY? Pangaea
Continental Drift vs. Plate Tectonics – The Debate • Mid-Atlantic Ridge • 1947 – mapping of the ridge • linear mountain range • active EQ and volcanism • area of sea floor spreading • Sea Floor Spreading • Magma rises in between the • ocean floor (ridge). • Magma pushes the ocean • floor – spreading the floor • apart. Can scientists actually see “spreading” of the ocean floor? How do scientists know the floor is actually moving?
Paleomagnetism --- the evidence that the sea floor is active and moving (by the late 1960’s) • Paleomagnetism: paleo (past) magnetism (magnetic) • past magnetism of lava flows are recorded on the sea floor • Iron in magma will point to the current north pole. Evidence shows north pole switches location to the south pole over geologic time (magnetic reversals). South reversal North reversal creating magnetic reversals on both sides of the plate (pattern of stripes) magnetic pattern 13
The Plate Tectonic Model lithosphere Volcanism Patterns Asthenosphere (upper mantle) Earthquake Patterns • The plate tectonic model describes surface features, geologic • environments, and patterns of EQ’s and volcanism. • Ridgid lithospheric plates (continents + ocean floor) ride • along the soft layer (like hot wax) called the asthenosphere • Plates spread apart, collide, and slide past one another. • EQ’s, crustal deformation, and volcanism take place at plate • boundaries.
Plate Boundaries Divergent Boundary – plates move AWAY from each other Convergent Boundary – plates move TOWARD each other Transform Boundary – plates SLIDE past each other
Divergent Boundary: • plate material separating • Earthquake activity Extensional forces create EQ’s ocean plate divergence continental divergence Extension creates faulting
Convergent Boundary: • interaction of two plates moving toward one another • making contact– hence, collision or convergence • collisions produce earthquakes, volcanic activity, and • crustal deformation Ocean-Cont Ocean-Ocean Cont-Cont Subduction zone Subductioin zone Oregon-Washington Coast Himalayan Mountains Aleutian Island (Alaska area)
thinner and more dense plate • subducts • subducted plates melt (160 km) • below the surface, and magma • rises • EQ’s occur along the subduction • zone, and magma plumes rise ocean-continent • Earthquake activity • typically, the older plate will • subduct (more dense) beneath • younger plate material • melting plate material rises, • creating volcanic arc systems • most EQ’s occur within the • subduction zone ocean-ocean • two plates converge with the • same density • same density prevents • subduction • extensive deformation cont-cont
Transform Boundary: • two plates are sliding past one another • lack the spectacular features associated with • divergent/convergent boundaries • marked by linear valleys (slices through the • earth’s crust) • shallow-focused EQ’s occur along the slip area of the • sliding plates SAF
Transform boundaries offsetting • spreading ridges • Typical EQ’s occur along • the transform boundary. Earthquakes • Cross-sectional view of the SAF • and associated LA faults • SAF – transform motion • LA faults- vertical motion SAF-transform fault Los Angeles
What moves or drives the plates? What could Wegener have told the geological society? Only a Model – Think Convection Convection – heat transfer through a liquid or gas that results in circular movement of particles Cooler water sinks Hot water rises
Earth Crust The Earth’s Mantle Can you see the convection? mantle mantle Convection Rise Fall
Earth’s Surface Mantle operates like a “lava lamp,” producing swelling and shrinking of magma plumes. 57
Latitude and Longitude • Where are you on earth? • Latitude/Longitude • a grid system used to locate features on • the earth’s surface • Latitude: • parallel lines that move north • and south • 0o latitude = equator • Longitude: • meridian lines that move east • and west • 0o longitude is through • Greenwich, England 11
Los Angeles, Ca 350 N-lat, 1210 W-long Spokane, Wa 470 N-lat, 1180 W-long 12 New York, NY 420 N-lat, 750 W-long
West East Latitude (+) Longitude (+) Latitude (+) Longitude (-) North Equator South Latitude (-) Longitude (-) Latitude (-) Longitude (+) Latitude ( Prime Meridian
13 52 N-lat, 78 E long B 15 N-lat, -132 W-long A -25 S-lat, 136 E long D E -18 S-lat, -162 W-long -55 S-lat, -15 W-long C
Plate Tectonics Lab: • Part A: Plate tectonic definitions • use lab text • use textbook resources in classroom • Part B: Identification of plate boundaries • use lab text, colored pencils • use textbook resources in classroom • Part C: Plotting EQ location • use provided long/lat handouts • use colored pencils • Part D: Critical thinking questions • use parts A, B, and C and your • synthesizing brain.