1. Southern California Integrated GPS Network (SCIGN)
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Southern California Integrated GPS Network (SCIGN)
Kenneth W. Hudnut
U. S. Geological Survey
U.S. – Japan Natural Resources Panel on Earthquake Research
U. S. Geological Survey, Menlo Park - November 14, 2000

2. Continuous GPS
Best tool ever devised for highly accurate, automated, constant monitoring of crustal strain for
long baselines
absolute ref. frame
displacement field
high precision
SCIGN & other PBO elements require sub-millimeter velocities on the plate boundary scale in order to answer the scientific questions

3. Faults & Earthquakes San Andreas fault zone
North American and Pacific plate relative motions of 56 mm/yr in a right-lateral sense
Eastern California shear zone
Accomodation of right-lateral motion inboard of Sierra Nevada block
Estimated rates of some 8-12 mm/yr (geological & space geodetic)
Easier to go through than the Big Bend?

4. SCEC crustal motion map
Combined EDM, VLBI, survey-mode and continuous GPS rigorously
Released as a SCEC product
Set the bar very high for the SCIGN project

5. Plate tectonic motions
For the past 5 million years, this motion has been very steady at about 5 cm/yr
From long-base laser strainmeter and geodolite data, steady rates of motion are seen
Will higher resolution instruments see temporal variation in strain rate?
tectonic reconstruction and movie by Tanya Atwater, UCSB

6. The major objectives of the SCIGN array are:
To provide regional coverage for estimating earthquake potential throughout Southern California
To identify active blind thrust faults and test models of compressional tectonics in the Los Angeles region
To measure local variations in strain rate that might reveal the mechanical properties of earthquake faults
In the event of an earthquake, to measure permanent crustal deformation not detectable by seismographs, as well as the response of major faults to the regional change in strain

7. SCIGN project installation: 250 sites by end of 2000

8. SCIGN station installation
Each of 5 legs is drilled to 10 meters
Lowermost 6 meters is anchored to earth by concrete grout
Uppermost 4 meters is isolated from soil by foam
Stainless for longevity
movie by John Galetzka, USGS

9. Analysis comparisons by King, Hurst, van Domselaar & Langbein
Time series reprocessed by JPL and SIO; similar -
reference frame implementation
processing strategy
Mean differences for each of baselines
Line length proportional differences at <9 ppb

10. Hector Mine (Mw7.1) Photo by Paul ‘Kip’ Otis-Diehl, USMC, 29 Palms
Helicopter support by OES and National Guard

11. Hector Mine eq.: modelled displacement field

12. Post-seismic deployment
GPS for precise absolute position changes
GPS data from these instruments will also show us afterslip and other post-seismic phenomena

13. Short-braced monument
Requires bedrock
Remote installation is feasible
Half as expensive as drilled-braced (but not as stable)
Useful for special post-earthquake network deployments

14. Post-seismic deformation
Stations near the earthquake fault continue to move after the earthquake
Less than 20 mm motion recorded, so we required extremely high precision data
Too much motion to be explained by aftershocks
Requires a deep source in the lower crust
Large scale relaxation phenomenon
May explain fault interaction between large earthquakes

15. Inboard shear strain transfer (preliminary & speculative)
Savage et al. (1993) and Johnson et al. (1994) showed NW-SE pull apart of 8 mm/a in USGS geodolite data prior to 1992 Landers sequence [orange]
We see similar pattern after Hector Mine, farther to northeast [red]

16. GPS & telemetry/networking
Market for GPS boards is driven by Moore’s law (like PC’s) toward faster/better/cheaper, miniaturization, etc.
Spread spectrum radio and satellite telemetry leading to high bandwidth IP field networking (e.g., TDMA)
Allows higher sampling rates and more affordable real-time telemetry

17. SCIGN data acquisition and processing system

18. New methods: high-resolution topographic mapping and digital photography
Laser scanning using an airborne platform requires high sampling-rate GPS data during flight to control aircraft position and attitude
SCIGN stations were operated at 1 and 2 sample per second rates via the radio network

19. Existing GPS Networks in North America
International GPS Service (IGS)
So. Calif. Integrated GPS Network (SCIGN)
Bay Area Regional Deformation (BARD)
Basin and Range GPS Network (BARGEN)
Pacific Northwest GPS Array (PANGA)
Eastern Basin and Range & Yellowstone (EBRY)
Contin. Operating Reference Stations (CORS)
SuomiNet, FSL, INEGI, WCDA, etc.

20. Conclusions
Networks of continuously operating GPS stations in the U. S. and Japan give us a higher resolution method to search for temporal variations in strain with renewed hope of learning about earthquake related processes
Geodesy is now feasible in a network mode, similar to seismology – it is time to incorporate both, side by side, into modern earthquake monitoring networks – extending our reach to truly broad-band observational capabilities so that we can detect and study a wider range of seismic and aseismic phenomena

21. Short-braced rod monuments
Good bedrock is needed
Drill to one meter depth
Epoxy rods in place
Weld rods together
movie by John Galetzka

22. Land Surveying and GIS
New methods such as RTK require higher sampling rate base station data in real-time
This is necessary for all work at accuracies of a few tens of centimeters or better
Approximate georeferencing for GIS applications such as fleet management of inventorying can be met by non-differential GPS (SA is off now) or C/A code differential

23. Assess damage to infrastructure
Were tilts or strains large enough to damage systems? (from regional measurements)
Did damage occur to critical structures or systems? (from site-specific monitoring)

24. Structure monitoring
Pacoima dam GPS monitoring since Sept with LA County
GPS data can indicate damage to engineered structures such as overpasses and tall buildings

25. New initiatives EarthScope - NSF USGS budget initiative
Plate Boundary Observatory
USGS budget initiative
$12M/yr add-on partly in response to a new FEMA report
State of California Governor’s initiative
California Spatial Reference Center
A non-profit organization to support spatial information infrastructure in California
Will seek to sustain the infrastructure built with earthquake research funding

26. The Plate Boundary Observatory
PBO’s GPS sites could provide spatial reference infrastructure throughout the Western U. S. A., as well as in Canada and Mexico

27. The San Andreas fault zone ‘focus array’ of PBO
Geodetic networks for earthquake monitoring can provide the GPS infrastructure network that is also needed for Land Surveying and GIS applications

28. For More Information: http://pasadena.wr.usgs.gov/scign/
Ken Hudnut
(626)

29. InSAR results ESA data rapidly available from good
repeat of recent pass
JPL, Scripps and
Caltech investigators
quickly made results
available on WWW
Gilles Peltzer, JPL

30. regional active faults

31. California relative plate motions for the past 20 million years
Tectonic reconstruction and movie by Tanya Atwater, UCSB