Data for Plate Tectonics

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Data for Plate Tectonics

• Earthquakes
• World wide network for detecting nuclear tests
• Magnetic stripes
• From World War 2 submarine detection
• Bathymetry from above
• Then satellite mapping

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Global map of predicted seafloor depth Smith and
Sandwell, 1997 and elevation fromGTOPO-30.
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Mapping ocean floorkey to understanding Sea
Floor Spreading

• Accomplished by military literally overnight
• By satellite (starting with SEASAT)
• Determination of geoid by satellite observations.
  Because the geoid is the actual equipotential
  surface of the Earth (relative to the reference
  spheroid), it is the same as the sea surface
  elevation.

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Effect of ocean floor on gravity and therefore
ocean surface
Gravitational potential V VG(constant)xM(mass)/R(
distance to mass) (Mass is dominated by whole
earth) (R is dominated by distance to center of
mass of earth) To stay on an equipotential (no
change in V) need to increase R (distance from
mass) to keep V the same.
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Ship tracks of soundings
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History of mapping oceans

• Archive the digital sounding data and assemble
  the data into large databases
• access to the 30-year mapping effort Wessel and
  Watts, 1988 Smith, 1993.
• Radar altimeters aboard the ERS-1 and Geosat
  spacecraft
• have surveyed the marine gravity field over
  nearly all of the world's oceans to a high
  accuracy and moderate spatial resolution.
• In March of 1995, ERS-1 completed its dense
  mapping (8 km track spacing at the equator) of
  sea surface topography between latitudes of
  81.5.
• July of 1995, all of the high-density radar
  altimeter data collected by the Geosat spacecraft
  were declassified.

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Initial results of mapping ocean surface (geoid)
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The CSR98 mean sea surface model determined by
satellite altimeter datacollected from GEOSAT,
ERS-1, ERS-2 and TOPEX/POSEIDON missions
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