Transcript Grand Challenges for EarthScope in Geodesy

Grand Challenges for
EarthScope in Geodesy
Jim Davis
Harvard-Smithsonian Center for
Astrophysics
VE
RI
TAS
3 mm/yr
GreatBREAK Workshop
Bennett et al. [2003]
GPS Horizontal Velocity Errors
seven-year timespan
0
Velocity Standard Deviation (mm/yr)
10
-1
10
Ion-free
LC Receiver
Noise Only
L1 Receiver
Noise Only
-2
10
-3
10
Assume Linear = True
Random walk
error model
Whole-Error
“Effective”
LCMethod
Phase
Noisefor
time series
(1–3
mm/√yr)
(Accounts
(Ignores
formal
for
multipath
errors;
and
Other model
Looks
at velocity
errors)
fit to model;
Combines model & data errors)
-4
10
-5
10
-6
10
L1 Obs. Noise
LC Obs. Noise
"Effective" LC Noise
GreatBREAK Workshop
Whole-Error
Random Walk
8
Linear
+ white noise error
+ correlated error
6
CEDA North (mm)
4
2
0
-2
-4
-6
-8
1996
120-d boxcar smoothing
1997
1998
1999
2000
Epoch
GreatBREAK Workshop
2001
2002
2003
2004
Time-Correlated Site Motions
• Our tectonic framework
0
10
-1
10
2
Power Spectral Density (mm per cpd)
predicts (generally) timelinear 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 
-2
10
-3
10
seasonal
-4
10
-5
10
0.1
GreatBREAK Workshop
1
10
Frequency (cycles per year)
100
• Deformation interpreted as periodic slow
earthquakes in Cascadia subduction
zone [Miller et al.,
2002]
• More recently, deformation associated
with tremor activity
GreatBREAK Workshop
• Deformation
associated with deep
swarm of M < 2.2
earthquakes beneath
Lake Tahoe
• GPS measurements
at BARGEN site SLID
compared to cumulative moment 
• From Smith et al.,
submitted
GreatBREAK Workshop
• Temporally nonlinear
motions of BARGEN
sites modeled with
acceleration terms
• See Davis and
Wernicke poster
GreatBREAK Workshop
Great Salt Lake Loading
Elósegui et al. [2003].
GreatBREAK Workshop
8
6
CEDA North (mm)
4
2
0
-2
-4
-6
-8
1996
1997
1998
1999
2000
Epoch
GreatBREAK Workshop
2001
2002
2003
2004
8
6
CEDA North (mm)
4
2
0
-2
-4
-6
-8
1996
1997
1998
1999
2000
Epoch
GreatBREAK Workshop
2001
2002
2003
2004
QuickTime™ and a
Video decompressor
are needed to see this picture.
GreatBREAK Workshop
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 Earth’s behavior in the era
of “>1 mm/yr” level (campaign) geodesy?
• What can this nonsecular behavior tell us about
forces in the Earth’s crust and interior and the
response of the crust to those forces?
GreatBREAK Workshop
Challenges for Geodesy
• Quantify (accurately) GPS error and its temporal
•
•
•
•
and spatial behavior
Must be independent (as possible) of
assumptions concerning Earth’s behavior
Will rely heavily on multiple techniques and data
types
Must be applicable to EarthScope’s spatial and
temporal scales (inner and outer)
Develop analysis strategies that allow for nonsecular behavior
GreatBREAK Workshop