PNW_animation_README.txt
  DS-633

  The animation of the hand-generated, 3D model of the 
  Cascadia subduction system (version 1.0) provides fly-
  through views from a variety of perspectives.  The 3D 
  model includes earthquake hypocenters, the Juan de Fuca 
  slab surface, and shaded relief bathymetry and 
  topography.  Plate boundaries, active arc volcanoes, and 
  major cities are also depicted.  See the Location Map for 
  place names.

  Earthquakes below the Juan de Fuca slab surface are 
  denoted by orange dots; earthquakes above the slab 
  surface are denoted by white dots.  The Juan de Fuca slab 
  surface is depicted as a transparent green surface; depth 
  contours (at 10-km intervals) on the slab surface are 
  denoted by gray lines.  Spreading ridge plate boundaries 
  are denoted by red lines; transform fault plate 
  boundaries are denoted by green lines; the Cascadia 
  trench axis (trace of the subduction plate boundary) is 
  denoted by a light yellow line.  Cascade arc volcanoes 
  with seismic activity are denoted by red cones; major 
  cities are denoted by yellow cubes.  The coastline and 
  the statelines are denoted by light yellow lines.  
  Vertical exaggeration of the bathymetry and the 
  topography is 3X; vertical exaggeration of the slab 
  surface and the hypocenters is 2500X.

  Seismicity is the primary constraint determining the 
  location of the slab surface.  While viewing the 
  animation, note how the model divides earthquakes above 
  and below the surface.  Note as well, that a few 
  earthquakes occur just above the surface in some areas.  
  We interpret these earthquakes as occurring within the 
  subducting plate, albeit with depth estimates that are 
  slightly too shallow.  Nonetheless, these earthquakes are 
  included in the files of hypocenters occurring below the 
  slab surface.  The animation begins with a top or map 
  view of the Cascadia subduction system.  The observer 
  perspective then rotates to a side view of the subduction 
  system from the southern end looking northward.  Note how 
  the slab surface cuts through the dense cluster of 
  seismicity at the southern end.  Note as well, that 
  seismicity associated with arc volcanoes forms narrow 
  vertical clusters of white dots.  The observer 
  perspective then rotates clockwise to a view beneath the 
  slab surface.  Note a second, less dense cluster of 
  seismicity near the northern end of the subduction 
  system.  The perspective continues to rotate clockwise, 
  moving into a close-up view that looks upward along a 
  major arch in the slab surface.  The animation finishes 
  by returning to the initial top view.

  Acknowledgments.  We thank Max Gardner for construction 
  of this animation.