Alternative Division of Earth:  based on how Earth rocks behave mechanically
     lithosphere ("rocky sphere"), includes crusts plus some upper mantle
          lithosphere: outer layer, coldest and therefore strongest rocks, rigid layer
          lithosphere is strong but brittle, breaks dramatically (earthquakes...)
     asthenosphere ("weak sphere"), rest of mantle below lithosphere
          asthenosphere:  inner layer, hottest and weakest rocks, solid but gooey
          asthenosphere is weak and gooey solid, flows like cold honey but as a solid

Plate Tectonics: movement of plates on the surface of the Earth
     plates: pieces of lithosphere (outermost cold rigid layer of Earth)
         each plate moving at own speed (1-15 cm/year) in own direction: absolute motion
          plate movement driven by solid state convection of Earth's mantle
              motion of plate reflects motion of mantle + complications
         present day motion of plates determined by Global Positioning Satellite (GPS)
         past motion of plates determined by hot spot tracks (e.g. Hawaiian Islands)
         past motion also determined partly by ancient magnetic field of Earth
              ancient magnetic field trapped in old rocks, tells original latitude

Plate Tectonics Rules (tektos:  to move around)
     (1) lithosphere divided into pieces called plates: rigid slabs of lithosphere
     (2) plates are moving around on surface of Earth!!  moving a few inches per year
     (3) asthenosphere is heated from below, light asthenosphere rises as solid to surface
     (4) as asthenosphere cools and sinks, plates dragged around on surface of Earth
     (5) plates grind past, bump into and pull way from each other, creating geology!

North American Plate:  WA is currently at western/leading edge of NAM
     in PNW, NAM currently moving towards southwest about 5 cm/year
     overall, NAM currently rotating CCW about an axis somewhere off Florida
          (our data base changing fast with direct measurements by GPS)
     NAM has been moving uniformly for at least the last 20 Ma
     leading edge of NAM is taking some abuse, deforming internally, not rigid
          Olympics/Willapa Hills/Coast Range being pushed to NE and rotating
          see this from PANGA study (Pacific Northwest Geodetic Array)

Juan de Fuca, Gorda and Explorer Plates:  all made of oceanic crust + mantle
     very small plates today.  motions poorly known (no islands, no GPS)
         JDF was enormous in past, called the Farallon plate
      probably moving 5 cm/year towards NE (Cobb seamount chain)
     Gorda Plate may have been/is being ripped off of JDF plate
          Gorda Plate deforming internally with many quakes on many faults
           therefore not obeying 1st law of plates (must be rigid internally)

Pacific Plate:  nearby to south and north of PNW; PAC is biggest plate today
     moving 10-15 cm/year towards WNW, pretty uniform for a big plate
     big change in plate motion about 35 Ma ago, PAC was going N, then turned

Two Plates Interact:  diverge, converge and slide past each other sideways
     motion of one plate relative/compared to another is relative motion

NAM-JDF Relative Motion:  two plates converging about 10 cm/year NE-SW
     plate boundary called Cascadia subduction zone: JDF subducting under NAM
              recycling of JDF oceanic crust into mantle beneath NAM
      creates East-dipping plane of earthquakes getting deeper to east
           shallow/low angle subduction because JDF crust is still quite warm
           1999 Satsop 5.5 quake most recent big one along subduction zone
      creates arc of explosive, Andean-type volcanoes (St. Helens, Rainier...)
      scrapes off sediment from JDF plate and piles it up along plate margin
     JDF sliding NE under North-South edge of NAM = oblique convergence
          convergence NOT at right angles to N-S plate boundary
          oblique convergence here produces Northward drag on NAM by JDF

NAM-PAC Relative Motion: sideways/transform about 10-15 cm/year
     along San Andreas transform and Queen Charlotte transform
     eventually (5-10 Ma from now) have transform in Puget Sound......

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