REVIEW OUTLINE:  PLATE TECTONICS & EARTH STRUCTURE

Plate Tectonics: The Unifying Theory

• Continental Drift
• Sea-floor spreading
• Plate subduction
• Transform faulting

Types of Plate Boundaries

• Divergent – Plates moving apart
• Oceanic: Mid-ocean ridge
• Continental: Continental rift
• Convergent – Plates moving toward one another
• Oceanic: subduction zone
• Continental: continent colllision
• Transform – plates moving parallel to boundary
• Oceanic: fracture zones at mid-ocean ridge
• Continental: strike-slip faults

Continental Drift: Early evidence for Plate Tectonics

• Evidence from climate
• Evidence from fossil record
• Evidence from rock types
• Evidence from shape of continents

Sea-floor Spreading:  Creation of new plates

• Shape of sea floor (mid-ocean ridges)
• Active volcanoes at mid-ocean ridge
• Hydrothermal activity at mid-ocean ridge
• Earth’s magnetic field reversals & ‘stripes’ on the sea floor

Plate Subduction: The Cemetery for old plates

• Deep-sea trenches
• Volcanic island arcs
• Intermediate-depth and deep earthquakes
• Great earthquakes (like Indonesia earthquake)

Transform Faulting

• Lateral motion between plates
• Fracture zones offsetting mid-ocean ridges
• Continental strike-slip faults (San Andreas)

Plate Tectonics: The Driving Force

• Convection within Earth’s solid mantle
• Earth as “thermal engine”

Earth Internal Structure

• Crust (solid, elastic)
• Mantle (solid, plastic)
• Core
• Outer core (liquid)
• Inner core (solid)
• Lithosphere = rigid outer shell = crust + uppermost mantle
• Asthenosphere = plastic layer within mantle

Relation of earthquakes to Plate Tectonics:

• Intraplate vs. interplate seismicity
• EQs restricted to narrow seismic belts at plate boundaries
• Most earthquakes < 30 km depth
• Exception: deep earthquakes (to 700 km) at subduction zones
• Wadati-Benioff Zone = inclined seismic zone associated with subducted lithosphere
• Relation between earthquakes and volcanoes
• Plate tectonics as driving force for earthquake cycle