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

hudnut@usgs.gov

(626)583-7232