1. Geodesy & Crustal Deformation
Geology 6690/7690
Geodesy & Crustal Deformation
30 Aug 2017
Geodesy is the measurement and representation of the
shape of the Earth and its gravity field
Motivation: Most active processes that are of interest to
Earth scientists change the shape of the planetary
surface and change the gravity field.
Applications of geodesy include legal & construction
industry (“surveying”), navigation & many other… Research
applications include studies of tectonics & the earthquake
cycle, hazard analyses/modeling (landslide & mass wasting,
volcano studies & monitoring), climate studies (sea level,
water & ice mass), and water monitoring
Read for Fri 1 Sep: Wahr §1 (1-3); §
© A.R. Lowry 2017

2. Geodesy is the study of the shape of
the Earth’s surface, and its gravitational
field…

3. Example: The Geoid
Satellite altimeter measurements of sea surface height used to
estimate the geoid have greatly aided study of seafloor tectonics

4. Example: Gravity Studies
“Mascons” (mass concentrations) within annular rings have
long been recognized as evidence of impact structures in
planetary science… Recognition of a signal consistent with a
mascon near Chicxulub (Yucatan) MX prompted a closer look…

5. Example: Landslide Monitoring
Velocities of
“permanent
scatterers”
in the Arno
basin,
Tuscany,
from
multiple
Interfero-
metric
Synthetic
Aperture
Radar
(InSAR)
images.

6. Example: Surface Hydrology
River height changes can be
difficult to measure accurately
using surface gauges because
“dynamic” water heights on
different channels and different
parts of channels can vary by
> 1 m in height…
Amazon heights are found to
change by about 10 meters
peak-to-peak annually
using satellite Synthetic
Aperture Radar altimetry.
Can use similar altimetry for
rivers, lakes and oceans

7. Example: Sea Level Change
Climatological models of sea level rise used in 2007 IPCC
reports predicted a likely rise of 30 cm from 1990 to 2100, with
envelope from 10 to 90 cm.
Laser altimetry from TOPEX and Jason satellite measurements
show rise of 3.4 mm/yr from 1993 to 2016, or ~ around 8 cm
from … Near the upper 2 envelope for that
period from IPCC models.

8. Example: Sea Level Change
Regional rates of altimetric height change show evidence of
both dynamical effects (ENSO) and geoid change.

9. Measurements of sea level
change show a sharp drop
in global levels starting
~mid 2011, coincident with
a switch from El Nino to
La Nina ocean current
conditions…
Time-variable gravity
measurements
showed the water
temporarily moved to
land-surface via
precipitation!

10. Example: Groundwater Hydrology
Gravity And Climate Experiment (GRACE) measurements of
surface mass change in the Amazon basin indicate ~100%
greater amplitude and a phase delay in annual storage of
water mass relative to hydrological models based on surface
measurements of precipitation and river outflow

11. Example: Cryosphere (Greenland)
Barletta et al., Cryosphere,
2013 (via polarportal.dk)
GRACE shows ~200 km3/yr
decrease in ice mass from
2002 to 2017, mostly from
coastal areas
0.6 mm/yr of sea level
change

12. Example: Cryosphere (Antarctica) GRACE measurements of
mass change in Antarctica
indicate –165±71 km3/year
2002 to 2010 (from W Ant)