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 Frame Working Group. Plate Boundary Observatory. PBO - PowerPoint PPT Presentation
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, USAStable North America Reference Frame Working GroupPlate Boundary ObservatoryPBOImage the ongoing tectonic deformation of North AmericaPhysics of earthquakes, magmatic processes, plate boundary dynamics and evolution~1000 Permanent GPS:800-900 clustered sites, 5-50 km spacing100 backbone sites, ~200 km spacingPBO BackboneAlaska + western U.S.~20 existing GPS stations + 100 newEastern U.S.~20 GPS at IRIS/USGS Global Seismographic Network sitesWhere are we Now?WUSC GPS velocity map [Bennett, Davis, Wernicke, Normandeau, 2002]GPS strain rate magnitude [Blewitt, Coolbaugh, Sawatzky, Holt, Davis, Bennett, 2003]PBO NeedsWhat are PBO reference frame needs?How can we meet those needs?PBO stated requirements:PBO needsthat 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/yrwould require accurate modeling of non-tectonic deformationIf so, where is this stable plate interior?PBO will address these questions byNetwork design including broad GPS spatial coverage across North AmericaResearchHow 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 elsewhereGeology - Plate TectonicsResidual 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 errors in 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/Myr1-3 mm/yr across Rio Grande RiftConsistent with Cenozoic ratesConsistent with VLBI [Ma and Ryan,1998]Current Frame Stability?The International GPS Service NetworkCurrent Frame StabilityAccuracy of ITRF2000Approaching 1 mm/yr at best performing sites [Altamimi et al., 2001]Evidence that current GPS accuracy < 0.5 mm/yrComparison of IGS Analysis Center solutionsSmoothness 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 Eulers Fixed Point at frame originChasles Effect [Blewitt and Davies, 1995]Biased prediction of plate boundary strain from plate rotations [Lavalle, 1999]North America Pacific Plate motion is sensitive to station selectionDirection of relative motion changes few degrees with/without Fairbanks, Alaska [Kreemer et al., 2000]North America may have internal deformation1-2 mm/yr in stable North America [Dixon et al.]Non-tectonic motions can be significant~1 mm horizontal motion by hydrological loadingFew mm horizontal secular motion due to PGRSeismo-isostatic strain at recently activated faults?Practical Needs: ConsistencyGPS site velocities in North AmericaAre almost universally published in a reference frame referred to by the authors as stable North AmericaReference frame varies between groupsBy definition and by realization procedureSpecific procedure to realize the frame is often not prescribed in sufficient detailSystematic velocity differences exist1-2 mm/yr (smooth) between groupStable North AmericaReference Frame (SNARF)Working groupAppointed by UNAVCO Board, June 2003And as part of IAG Working Group NAREFCharge:Produce a standard reference frame and specify standard procedures to realize such a frame to meet the highest precision needs of the scientific communityDesign frame (concepts, models, )Realize a specific frame (select sites, geodetic solution)Specify procedures to attach to such a frameConclusionsPBO is developing a reference frameThat accounts for non-tectonic deformationsLoading, PGR, Stable to < 1 mm/yrIdentification of stable plate interiorSite selectionFrame that is specific & easily implementedFor scientific and precision survey applications Toward a new North American Datum (NAD)SNARF Working Group MembersDon ArgusFrame origin, tectonics, site selectionRick BennettTesting and application to BARGENGeoff BlewittCoordinate specs and recommendationsEric CalaisIntraplate deformationMike CramerTesting and application to NAREFJim DavisCoordinate specs and recommendationsTim DixonPlate stability, site selectionTom HerringGlobal GPS, ITRF, site selectionKristine LarsonP.I. (NSF proposal), ITRF, site selectionDavid LavalleGlobal GPS, GPSVEL, seasonal loadingMeghan MillerTesting and application to PANGAJerry MitrovicaPGR models, site selectionFrank WebbTesting and application to SCIGNRichard SnayNational geodetic survey applications