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A Reference Frame for PBO: What do we Have; What do we Need? Geoff Blewitt Nevada Bureau of Mines & Geology, and Seismological Laboratory, University of Nevada, Reno, USA Stable North America Reference Frame Working Group

A Reference Frame for PBO: What do we Have; What do we Need?

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A Reference Frame for PBO: What do we Have; What do we Need?. Geoff Blewitt Nevada Bureau of Mines & Geology, and Seismological Laboratory, University of Nevada, Reno, USA Stable North America Reference Frame Working Group. Plate Boundary Observatory. PBO - PowerPoint PPT Presentation

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Page 1: A Reference Frame for PBO:  What do we Have; What do we Need?

A Reference Frame for PBO: What do we Have; What do we Need?

Geoff Blewitt Nevada Bureau of Mines & Geology,and Seismological Laboratory,University of Nevada, Reno, USA

Stable North America Reference FrameWorking Group

Page 2: A Reference Frame for PBO:  What do we Have; What do we Need?

Plate Boundary Observatory

PBO Image the ongoing

tectonic deformation of North America

Physics of earthquakes, magmatic processes, plate boundary dynamics and evolution

~1000 Permanent GPS: 800-900 clustered sites,

5-50 km spacing 100 “backbone” sites,

~200 km spacing

Page 3: A Reference Frame for PBO:  What do we Have; What do we Need?

PBO Backbone

Alaska + western U.S. ~20 existing GPS stations + 100 new

Eastern U.S. ~20 GPS at IRIS/USGS Global Seismographic Network sites

Page 4: A Reference Frame for PBO:  What do we Have; What do we Need?

Where are we Now?

WUSC GPS velocity map[Bennett, Davis, Wernicke, Normandeau, 2002]

GPS strain rate magnitude[Blewitt, Coolbaugh, Sawatzky,Holt, Davis, Bennett, 2003]

Page 5: A Reference Frame for PBO:  What do we Have; What do we Need?

PBO Needs

What are PBO reference frame needs? How can we meet those needs?

Page 6: A Reference Frame for PBO:  What do we Have; What do we Need?

PBO stated requirements: PBO needs

“…that plate boundary deformation be adequately characterized over the maximum ranges of spatial and temporal scales common to active continental tectonic processes.”

[ES Facility Proposal] How broad is the plate boundary? Is there a “stable plate interior”?

to within potential GPS accuracy ~ 0.1 mm/yr would require accurate modeling of non-tectonic

deformation If so, where is this stable plate interior?

PBO will address these questions by Network design including broad GPS spatial coverage

across North America Research

Page 7: A Reference Frame for PBO:  What do we Have; What do we Need?

How Broad is the Plate Boundary?

PBO “mini-proposal”[Holt, Blewitt, Bennett, 2000]

Questions: Is the Colorado Plateau

rotating? 8-13° in Mesozoic

Is accommodated by Rio Grande Rift?

Ignorance may lead to biases elsewhere

Page 8: A Reference Frame for PBO:  What do we Have; What do we Need?

“Geology Plate Tectonics” Residual velocity between:

Strain rates inferred from Quaternary slip vectors integrated from Colorado Plateau to Pacific

[Shen-Tu 1999], [also Humphreys & Weldon 1994]

NUVEL-1A [DeMets et al. 1994] If real, possible mechanisms:

50% can be accounted by errorsin NUVEL-1A [Larson et al. 1997; DeMets and Dixon 1999;Kreemer et al., 2000]

Offshore faults? [Shen-Tu, 1999] Colorado Plateau?

[Holt, Blewitt, Bennett, 2000] Clockwise rotation ~0.1°/Myr 1-3 mm/yr across Rio Grande Rift Consistent with Cenozoic rates Consistent with VLBI [Ma and Ryan,1998]

Page 9: A Reference Frame for PBO:  What do we Have; What do we Need?

Current Frame Stability?

The International GPS Service Network

Page 10: A Reference Frame for PBO:  What do we Have; What do we Need?

Current Frame Stability Accuracy of ITRF2000

Approaching 1 mm/yr at best performing sites [Altamimi et al., 2001] Evidence that current GPS accuracy < 0.5 mm/yr

Comparison of IGS Analysis Center solutions Smoothness of velocity field [“total error”, Davis et al, 2003]. 0.14 mm/yr RMS, GIPSY-GAMIT, BARGEN [Hill et al., 2002]

BUT! Plate rotations are sensitive to stability of Euler’s Fixed Point at frame origin

“Chasles Effect” [Blewitt and Davies, 1995] Biased prediction of plate boundary strain from plate rotations [Lavallée, 1999]

North America – Pacific Plate motion is sensitive to station selection Direction of relative motion changes few degrees

with/without Fairbanks, Alaska [Kreemer et al., 2000] North America may have internal deformation

1-2 mm/yr in “stable North America” [Dixon et al.] Non-tectonic motions can be significant

~1 mm horizontal motion by hydrological loading Few mm horizontal secular motion due to PGR Seismo-isostatic strain at recently activated faults?

Page 11: A Reference Frame for PBO:  What do we Have; What do we Need?

Practical Needs: Consistency

GPS site velocities in North America Are almost universally published in a reference

frame referred to by the authors as “stable North America”

Reference frame varies between groups By definition and by realization procedure Specific procedure to realize the frame is often not

prescribed in sufficient detail Systematic velocity differences exist

1-2 mm/yr (smooth) between group

Page 12: A Reference Frame for PBO:  What do we Have; What do we Need?

Stable North AmericaReference Frame (SNARF)

Working group Appointed by UNAVCO Board, June 2003 And as part of IAG Working Group “NAREF”

Charge: Produce a standard reference frame and specify

standard procedures to realize such a frame to meet the highest precision needs of the scientific community Design frame (concepts, models, …) Realize a specific frame (select sites, geodetic solution) Specify procedures to attach to such a frame

Page 13: A Reference Frame for PBO:  What do we Have; What do we Need?

Conclusions

PBO is developing a reference frame That accounts for non-tectonic deformations

Loading, PGR, … Stable to < 1 mm/yr

Identification of “stable plate interior” Site selection

Frame that is specific & easily implemented For scientific and precision survey applications

Toward a new “North American Datum” (NAD)

Page 14: A Reference Frame for PBO:  What do we Have; What do we Need?

SNARF Working Group Members

Don Argus Frame origin, tectonics, site selection

Rick Bennett Testing and application to BARGEN

Geoff Blewitt Coordinate specs and recommendations

Eric Calais Intraplate deformation

Mike Cramer Testing and application to NAREF

Jim Davis Coordinate specs and recommendations

Tim Dixon Plate stability, site selection

Tom Herring Global GPS, ITRF, site selection

Kristine Larson P.I. (NSF proposal), ITRF, site selection

David Lavallée Global GPS, GPSVEL, seasonal loading

Meghan Miller Testing and application to PANGA

Jerry Mitrovica PGR models, site selection

Frank Webb Testing and application to SCIGN

Richard Snay National geodetic survey applications