1. Geodesy & Crustal Deformation
Geology 6690/7690
Geodesy & Crustal Deformation
27 Sep 2017
GPS Reference Frames
• GPS Reference Frame relates Earth-fixed to satellite
motion; reference frame effects are part of position error
• Must somehow account for (secular) plate motions, (secular)
deformation, (approximately secular) glacial isostatic
adjustment, and any/all transients including deformation due
to water/ice mass changes...
Read for Fri 29 Sep: Wahr § (67-75)
© A.R. Lowry 2017

2. Read for Monday, Oct 2:
Herring et al. (2016) Plate Boundary Observatory and related
networks: GPS data analysis methods and geodetic
products, Reviews of Geophysics, 54(4),

3. Left out sites based on <100 km distance from a Bird (2003) plate
Altamimi et al.
JGR 2012
Left out sites based on <100 km distance from a Bird (2003) plate
boundary (red); glacial isostatic adjustment from a model (blue);
large velocity residuals (black, > 3s or 3 mm).

4. GRACE geoid rate (Detlef &
Ivins, J. Geodynamics, 2008)
GPS vertical velocities show
some general correspondence
to the GRACE measurements…
Difficult to see given differences
in projections here, but there is
a sampling issue with GPS.
Sella et al. (GRL, 2004) used
both campaign and continuous
GPS data; get better spatial
sampling than Calais et al….

5. But the effects of glacial isostatic adjustment on
horizontal velocity (especially
that which could be interpreted
as plate motion) is MUCH more
widespread than the vertical
perturbation.
Latychev et al, GRL, 2005

6. Residuals of their plate model (at sites included in the model)…
Mostly sub-mm/yr (but island sites are problematic!)

7. Left side is the difference between the ITRF2008 (GPS)
reference frame and the NNR version of NUVEL-1A (derived
from geological and earthquake data)...
Right side is the difference between the ITRF2008 (GPS)
Altamimi et al. [2012]. The most current International
Terrestrial Reference Frame is ITRF2014 (published Jan
2016). Previous GPS RFs were WGS84, ITRF89, 90, … 94,
96, 97, 2000, 2005, 2008, 2014.

8. Another thing to consider in comparing GPS-derived and other
(geologically-defined) plate models…
Sella et al. (2002)

9. Geological evidence for past changes suggests collisions…
~30 Ma
~15 Ma
Geological evidence for past
changes suggests collisions…
Knesel et al., Nature, 2008

10. For Nazca/SoAm/ Nubia, maybe slab flattening?
Pérez-Gussinyé et al., G3, 2008