Tectonics through GPS
05. 09. - 12. 09. 2007
Exercise 1
Bevor starting with the course, please copy the file ~plattner/.tcshrc to your
homedirectory and source it by:
source .tcshrc
Throughout the course you will need to work using tcsh. Switch from bash to tcsh.
Just type into the command line: tcsh
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1.
Look for the webpage of Scripps Orbit and Permanent Array Center (SOPAC).
This webpage contains an archive of all continuous GPS data.
1.1. For the sites FAIR and CHAT look up and list in a table the full station name, in
which country and on which tectonic plate the GPS station is located, the coordinates
and horizontal velocities, plus their uncertainty (Use the site.log file provided at the
SOPAC webpage for some of this information).
1.2. For stations FAIR and TMGO look at the unfiltered and both, the detrended
and NOT-detrended time-series. Describe the trends and noises you see, and try to
give an explanation them, using information about the location of the site. For offsets
within the time-series give the date and try to clarify whether it results from an
Antenna change (see site.log file) or an earthquake (see http://neic.usgs.gov/neis/epic/
search for earthquakes using the circular search, define a radius of ~1000 km around
the site FAIR and set the minimum Magnitude to 5, the maximum Magnitude 10).
For earthquakes list the location and magnitude.
1.3. Evaluate the accuracy of the following 6 GPS time-series (look at the NOTdetrended time-series). Rank them from 1-6 with 1 beeing the best and 6 being the
worst, give each grade only once. Explain in one sentence why the time-series is good
or bad.
CHAT
CASP
BAMO
CNMR
BREW
CPXX
2.
Copy the directory ~plattner/GPS-course/Exercise1 to your home. You will
find various subdirectories with a 4-letter-coded GPS-station, containing GPS data
(*.GD). In these directories you can run the program ../fitline/bin/fitline.out to
calculate the velocities in north, east and upward direction, choosing different modes:
l1 - linear least squares regression
a1 - accounts also for the annual trend
sa - accounts also for semiannual trend
For Time-series that additionally have a file *.GD.break, the program will
automatically solve for the offset at the given date. It may be necessary for some timeseries to allow for different slopes, before and after the offset. This can be chosen by
setting the following options:
l2 – linear least squarea regression solving for two slopes
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Tectonics through GPS
05. 09. - 12. 09. 2007
a2 – accounts also for annual signal, and solves for two slopes
Running the program will create 3 subdirectories:
Data stores the numeric files
GMT contains a plotting routine, execute the file referring to your model. This will
create 4 figures which are stored in the subdirectory plot.
2.1. Calculate the velocities for ANTO using different models. Evaluate the fit of
your model to the GPS data indicated by the reduced Chi² and the WRMS. Sum your
results in a table and discuss the differences you obtain, or not obtain.
Station
ANTO
Models to calculate:
L1
A1
SA
AREQ (Arequipa, Peru) has recorded deformation from an earthquake; an offset is
evident in the time-series. Prepare a break file (AREQ.GD.break) similar to
FAIR.GD.break with the date of the 2001 earthquake.
AREQ
L1
A1
L2
A2
2.2.
Imagine USNA would not be a continuous GPS site, but episodic, and the
time-series would be consisting of data from:
a) 3 randomly choosen time-intervals of GPS campaigns within 6 years, each with 3
consecutive days of observation. Repeat the same for only 2 years of timespan.
b) 6 randomly choosen time-intervals of GPS campaigns within 6 years, each with 3
consecutive days of observation. Repeat the same for only 2 years of timespan.
c) 6 time-intervals of GPS campaigns within 6 years, extracting always data at the
same dates within a year.
d) For the time-series of 2.2c) taking for every GPS campaign only 1 day of
observation.
Prepare such time-series extracting data from USNA.GD. Calculate the velocities for
all of them, using the linear least squares regression model.
3. Literature
For more information read:
T. H. Dixon, 1991. An Introduction to the Global Positioning System and Some
Geological Applications. Reviews of Geophysics, 19, 2, p. 249-276.
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