Grand Challenges for EarthScope in Geodesy

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Grand Challenges for EarthScope in Geodesy

• Jim Davis
• Harvard-Smithsonian Center for Astrophysics

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Bennett et al. 2003
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GPS Horizontal Velocity Errorsseven-year timespan
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white noise error correlated error
120-d boxcar smoothing
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Time-Correlated Site Motions

• Our tectonic framework predicts (generally)
  time-linear site motions
• Exceptions coseismic, postseismic, magmatic
  events
• Nonlinear site motions (even if real) ? geodetic
  error
• Power spectra of nonlinearities are used to
  derive error models ?

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• Deformation interpret-ed as periodic slow
  earthquakes in Cas-cadia subduction zone Miller
  et al., 2002?
• More recently, defor-mation associated with
  tremor activity

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• Deformation associated with deep swarm of M lt 2.2
  earthquakes beneath Lake Tahoe
• GPS measurements at BARGEN site SLID compared to
  cumula-tive moment ?
• From Smith et al., submitted

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• Temporally nonlinear motions of BARGEN sites
  modeled with acceleration terms
• See Davis and Wernicke poster

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Great Salt Lake Loading
Elósegui et al. 2003.
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Grand Geodetic Questions for EarthScope

• Under what conditions, and on what time and space
  resolution and scales, is crustal deformation
  continuous and secular?
• Is the time-linearity default simply a
  convenient approximation for the Earths behavior
  in the era of gt1 mm/yr level (campaign)
  geodesy?
• What can this nonsecular behavior tell us about
  forces in the Earths crust and interior and the
  response of the crust to those forces?

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Challenges for Geodesy

• Quantify (accurately) GPS error and its temporal
  and spatial behavior
• Must be independent (as possible) of assumptions
  concerning Earths behavior
• Will rely heavily on multiple techniques and data
  types
• Must be applicable to EarthScopes spatial and
  temporal scales (inner and outer)
• Develop analysis strategies that allow for
  non-secular behavior

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Conclusions from Early Space Geodetic Work

• Global plate motion is ongoing
• Plate tectonic motion is continuous and linear
• Exceptions are known episodic events
• At right Figure from Larson et al. 1997