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Spatial Reference Networksin California
Kenneth W. Hudnut
U. S. Geological Survey
Spatial Reference Systems SeminarU. C. Riverside - Oct. 26, 2000
Continuous GPS & strainmeters
• Best tools ever devised for highly accurate, automated, constant monitoring of crustal strain for– long baselines– absolute ref. frame– displacement field– very high precision
• SCIGN & other PBO elements require sub-millimeter velocities on the plate boundary scale in order to answer the scientific questions
Existing Continuously Operating Reference Stations (CORS): 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)
• Contin. Operating Reference Stations (CORS)
• SuomiNet, FSL, INEGI, WCDA, etc.
Faults & Earthquakes
• San Andreas fault zone– North American and Pacific
plate relative motions of 56 mm/yr in a right-lateral sense
• Eastern Californiashear 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?
Plate tectonic motions• As the
Farallon plate subducted, the San Andreas fault was born
• In the past 5 million years, this motion has been steady at about 5 cm/yr (that’s 50 km per million years!) movie by Tanya Atwater, UCSB
regional active faults
Californiarelative plate motions forthe past 20
million years
movie by Tanya Atwater, UCSB
SCEC crustal motion map
Combined EDM,
VLBI, survey-
mode and
continuous GPS
rigorouslyReleased as a
SCEC productSet the bar very
high for the
SCIGN project
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
SCIGN project installation status
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 longevitymovie by John Galetzka, USGS
Hector Mine (Mw7.1)Photo by Paul ‘Kip’ Otis-Diehl,USMC, 29 Palms
Helicopter support by OES and National Guard
Hector Mine eq.: modelled displacement field
InSAR results
ESA data rapidlyavailable from goodrepeat of recent pass
JPL, Scripps andCaltech investigatorsquickly made resultsavailable on WWW
Gilles Peltzer, JPL
Post-seismic deployment
• GPS for precise absolute position changes
• GPS data from
these instruments will also show us afterslip and other post-seismic phenomena
Short-braced rod monuments
• Good bedrock is needed
• Drill to one meter depth
• Epoxy rods in place
• Weld rods together
movie by John Galetzka, USGS
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
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
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
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)
Structure monitoring• Pacoima dam GPS
monitoring since Sept. 1995 with LA County
• GPS data can indicate damage to engineered structures such as overpasses and tall buildings
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
New initiatives
• EarthScope - NSF– Plate Boundary
Observatory
• Proposed USGS budget initiative– 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
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
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
For More Information:
http://pasadena.wr.usgs.gov/scign/
http://www.scign.org/
Ken Hudnut
(626)583-7232