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SNARF Working Group - FINAL REPORT (2004-2006)


Workshops for Establishing a Stable North American Reference Frame (SNARF) to Enable Geophysical and Geodetic Studies with EarthScope: Final Report (2004-2006).

Prepared by SNARF Working Group, UNAVCO Inc., Boulder, CO.

G. Blewitt (Chair), K. Larson (PI), J. Davis (Co-PI), D. Argus, R. Bennett, Y. Bock, E. Calais, M. Craymer (NRCan rep.), T. Dixon, J. Freymueller, T. Herring, D. Johnson, M. Miller, G. Sella, R. Snay (NGS rep.), and M. Tamisiea.

PART 2: PROJECT FINDINGS

OVERVIEW OF FINDINGS

Year 1 was considered to be primarily a time to consider a broad range of pertinent research problems, in preparation for a synthesis of ideas in Year 2, when more conclusive recommendations would be made. In Year 3 (a no-cost extension year), these recommendations were made concrete, and SNARF was officially adopted as the reference frame for geodetic products resulting from operational analysis of EarthScope's Plate Boundary Observatory. The following summarizes, in a nutshell, the findings. More details on the findings are given in the attached references.

(1) Demonstrated geodetic precision and accuracy appears to have reached the level that the development of a reference frame with sub-millimeter self-consistency is not limited by geodetic observations, but rather by our current ability to model the observations in a predictive way.

(2) Nevertheless, there are numerous specific examples of poor quality data (in various respects) that careful quality assessment and the judicious selection of stations representing 'stable North America' have proved to be important for the realization of a frame with mm-level precision, and therefore continuing quality assessment and appropriate station selection is required.

(3) The discussion on Earth models concluded that inconsistencies between various GIA models is currently the most limiting factor toward defining SNARF with sufficient accuracy. It is therefore clear that much research (which we estimate would take many years) will be required to resolve this issue to a satisfactory degree.

(4) Therefore, until an accurate GIA model can be adopted, it was agreed to pursue an innovative interim solution based on stochastic modeling. This approach is based on the observation that various GIA models may agree better in some regions and with favored directionality of surface motions. Using the level of agreement between models together with the GPS observations themselves have enabled the definition of a GIA velocity field that in turn can be used to define a stable plate-fixed frame (SNARF).

(5) The above realization of SNARF has been successfully adopted by the operational analysis centers of the Plate Boundary Observatory. Also, it is now clear that operational analysis of GPS data throughout Stable North America (in Canada and USA) can be performed successfully by the national geodetic agencies, NRCan and NGS, thus leading the way to the future adoption of a legal North American Reference Frame (NAREF) that is based on SNARF concepts and data.

In summary, the SNARF project has successfully met its initial objectives and finds that future improvements are currently limited by the accuracy of GIA models and the quality of existing geodetic stations in stable North America (versus the relatively higher quality of stations in PBO). We therefore recommend that future research efforts be directed to improved GIA models and their impact on reference frame definition, and into improving the quality and density of geodetic infrastructure within stable North America, far from the tectonically active plate boundary.

Details on the research leading to these findings can be found on-line at:

SNARF

REFERENCES: SNARF-Related Research by Members of the SNARF Working Group (2003-2006).

Argus, D.F., Defining rotational and translation velocity, presentation given at the 3rd SNARF Workshop, held in Santa Ana Pueblo, NM, March 2005.

Argus, D.F., M.B. Heflin, G.Peltzer, F.H. Webb, and F. Crampe, Interseismic strain accumulation and anthropogenic motion in metropolitan Los Angeles, J. Geophys. Res. 101, B04401, doi:10.1029/2003JB002934, 2005.

Argus, D.F., Defining translational velocity of Earth's reference frame, presentation given at the 6th SNARF Workshop, held in Ottawa, Canada, November 2006.

Bennett, R.A., Current reference frame treatment and future needs: Regional arrays from the southwestern US perspective, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Bennett, R.A., Shift happens: quantifying the time-dependence of plate boundary deformation using continuous GPS, Pardee Symposium Keynote presentation, GSA Annual meeting, 2005.

Bennett, R.A., Geodetic deformation rates in the eastern California shear zone, Penrose Conference Keynote presentation, April 2005.

Bennett, R.A., L. Lavier, M.L. Anderson, J. Matti, R.E. Powell, Holocene deceleration of the San Andreas fault zone in San Bernardino and implications for the eastern California shear zone rate debate, Eos trans. AGU, 86(18), Jt. Assem. Suppl., 2005.

Blewitt, G., Self-consistency in reference frames, geocenter definition, and surface loading of the solid Earth, Journ. Geophys. Res., Vol. 108(B2) 210, doi: 10.1029/2002JB002082, 2003.

Blewitt, G. and P. Clarke, Inversion of Earth's changing shape to weigh sea level in static equilibrium with surface mass redistribution, Journ. Geophys. Res., 108 (B6), 2311, doi:10.1029/2002JB002290, 2003.

Blewitt, G., A reference frame for PBO: What do we have; what do we need? Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract G32B-02 INVITED, 2003.

Blewitt, G., First SNARF workshop: Introduction, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Blewitt, G., Reference frame theory and practice: Implications for SNARF, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Blewitt G., K. Larson K, R. Bennett, E. Calais, M. Craymer, T. Herring, M. Miller, G. Sella, R. Snay, and M. Tamisiea, First report of the Stable North America Reference Frame (SNARF) Working Group, Abstracts of the UNAVCO 2004 Annual Meeting, p. 21, Boulder, Colorado, held Feb 25-27, 2004.

Blewitt G., Loading effects and reference frame definition, Abstracts of the UNAVCO 2004 Annual Meeting, (invited plenary talk) p. 22, Boulder, Colorado, held Feb 25-27, 2004.

Blewitt, G., P. Clarke, D. Lavallée, R. Gross, K. Nurutdinov, and T. van Dam, Relationahips between surface mass, station position, geocenter, & Earth rotation: IGS GNAAC results, IGS Workshop & Symposium Abstracts, p. 38, University of Berne, Switzerland, held March 01-05, 2004.

Blewitt, G., Fundamental ambiguity in the definition of vertical motion, Cahier du Centre Européen de Géodynamique et de Séismologie, Ed. T. van Dam & O. Francis, Vol. 23, p. 1-4, 2004.

Blewitt, G., R. Bennett, E. Calais, T. Herring, K. Larson, M. Miller, G. Sella, R. Snay, and M. Tamisiea, First report of the Stable North America Reference Frame (SNARF) Working Group, Eos Trans. AGU, 85(17), Jt. Assem. Suppl., Abstract G21C-01, 2004.

Blewitt, G., D. Argus, R. Bennett,Y. Bock, E. Calais, M. Craymer, J. Davis, T. Dizon, J. Freymueller, T. Herring, D. Johnson, K. Larson, M. Miller, G. Sella, R. Snay, and M. Tamisiea, Workshops for Establishing a Stable North American Reference Frame (SNARF) to Enable Geophysical and Geodetic Studies with EarthScope:Annual Report 2004-2005, EarthScope National Meeting, New Mexico, 2005.

Blewitt, G., D. Argus, R. Bennett, Y. Bock, E. Calais, M. Craymer, J. Davis, T. Dixon, J. Freymueller, T. Herring, D. Johnson, K. Larson, M. Miller, G. Sella, R. Snay, and M. Tamisiea, A stable North America reference frame (SNARF): First release, abstracts of the 2005 UNAVCO/IRIS Joint Workshop, held in Stevenson, WA, June 2005.

Blewitt, G., P. Clarke, D. Lavallée, and K. Nurutdinov, Application of Clebsch- Gordan Coefficients and isomorphic frame transformations to invert Earth's changing geometrical shape for continental hydrological loading and sea level's passive response, Int. Assoc. Geodesy Symp. Vol. 128, 6 pp., 2005.

Bock, Y., L. Prawirodirdjo, P. Fang, and P. Jamason, SOPAC's instantaneous global plate motion model: Contributions to a North-American fixed reference frame, Eos. Trans. AGU 85(17) Jt. Assem. Suppl., Abstract G21D-05, 2004.

Bock, Y., Spatial and temporal filtering for high-rate GPS regional networks: Implications for reference frame definition (2004), Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract G21B-02, 2004.

Bock, Y., Various projects related to SNARF objectives, presentation given at the 5th SNARF Workshop, held in Denver, CO, March 2006.

Calais, E., Testing intraplate deformation in the North American plate interior, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Calais, E., Summary report on intraplate deformation, Reports of the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Calais, E., J. Han, and C. DeMets, Testing intraplate deformation in the North American plate interior  from a combined geodetic solution: implication for strain accumulation  on potentially seismogenic faults in the central and eastern U.S., Fall AGU, 2004.

Calais, E., G. Mattioli, C. DeMets, S. Stein, A. Newman, and P. Rydelek, Tectonic strain in the interior of the North American plate? Nature, Vol. 438, doi:10.1038/nature004428, 2005.

Calais, E., Deformation of the North American plate interior from a decade of continuous GPS measurements, J. Geophys. Res., Vol. 111, B06402, doi:10.1029/2005KB-004253, 2006.

Calais, E., J.Y. Han, C. DeMets, and J.M. Nocquet, Deformation analysis in the North American plate's interior, presentation given at the 6th SNARF Workshop, held in Ottawa, Canada, November 2006.

Craymer, M., North American Reference Frame (NAREF) Working Group, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Craymer,M., R. Snay, The NAREF Perspective on a New Plate-Fixed Reference Frame for North America (abstract/poster). AGU/CGU Joint Assembly, Montreal, May 17-21, 2004.

Craymer, M., J. Henton. NAREF Analysis and ITRF2004 Densification. Presented at the 3rd SNARF Workshop, Santa Ana Pueblo, NM, March 28, 2005.

Craymer, M. International Reference Frames: ITRF/IGS, NAREF and SNARF. Presented at the Canadian Geodetic Reference System Committee, Ottawa, April 18-20, 2005.

Craymer, M. Canadian GPS Networks in the Great Lakes Region. Presented at the 78th Meeting of the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data, Ottawa, May 10-11, 2005

Craymer, M., G. Blewitt, D. Argus, R. Bennett, Y. Bock, E. Calais, M. Craymer, J. Davis, T. Dixon, J. Freymueller, T. Herring, D. Johnson, K. Larson, M. Miller, G. Sella, R. Snay, M. Tamisiea. Defining a Plate-Fixed Regional Reference Frame: The SNARF Experience. 2005 IAG Scientific Assembly, Cairns, Australia, August 22-26, 2005.

Craymer, M., NRCan velocity fields and comparison with some NA plate motion estimates, presentation given at the 5th SNARF Workshop, held in Denver, CO, March 2006.

Craymer, M., Reprocessing of continuous and campaign data in Canada, Greenland, and northern US, presentation given at the 5th SNARF Workshop, held in Denver, CO, March 2006.

Craymer, M., J. Henton, and M. Piraszweski, NRCan velocity fields for SNARF, presentation given at the 6th SNARF Workshop, held in Ottawa, Canada, November 2006.

Davis, J., and T. Herring, Thoughts on the GIA issue in SNARF, presentation given at the 2nd SNARF Workshop, held in Montreal, Canada, May 2004.

Davis, J., M. Tamisiea, and T. Herring, Horizontal GIA velocities and reference frame determination, presentation given at the 3rd SNARF Workshop, held in Santa Ana Pueblo, NM, March 2005.

Davis, J., and T. Herring, Stable North American Reference Frame (SNARF) Version 1, presentation and discussion given at the SNARF WG meeting of the Joint UNAVCO/IRIS Workshop, held in Stevenson, WA, June 2005.

Davis, J.L., B.L. Wernicke, S. Bisnath, N.A. Neimi, and P. Elosegui, Subcontinental-scale crustal velocity changes along the Pacific-North America tranform plate boundary from BARGEN GPS data, Nature, Vol. 441, 1131, doi:10.1038.nature0478112/2006, 2006.

Dixon, T.H., F. Amelung, A. Ferretti, F. Novali, F. Rocca, R. Dokka, G. Sella, S.W. Kim, S. Wdowinski, and D. Whitman, New Orleans subsidence and relation to flooding after Hurricane Katrina as measured by space geodesy, Nature, Vol. 441, pp. 587-588, 2006.

Dokka, R.K., G.F. Sella, and T.H. Dixon, Tectonic control of subsidence and southward displacement of southeast Louisiana with respect to stable North America, Geophys. Res. Lett., Vol. 33, L23308, doi:10.1029/2006GL027250, 2006.

Dong, D., L. Prawirodirdjo, S. Kedar, P. Fang, B. Newport, P. Jamason, F. Webb, Y, Bock (2004), Improved GPS time series in Southern California through the combination of SOPAC and JPL solutions, Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract G21A-0128.Gonzalez-Garcia, J., R.A. Bennett, K. Hudnut, C. Walls, USMX and YESX: Continuation of United State¹s PBO into Mexico¹s mainland, EarthScope National Meeting, 2005.

Freymueller, J.T., and C. Larsen, Where is the NW corner of stable North America? presentation given at the 2nd SNARF Workshop, held in Montreal, Canada, May 2004.

Freymueller, J.T., Motion of Bering Plate? presentation given at the 6th SNARF Workshop, held in Ottawa, Canada, November 2006.

Freymueller, J.T., Seasonal position variations and regional reference frame realization, presentation given at the 6th SNARF Workshop, held in Ottawa, Canada, November 2006.

Henton, J.A., J.O. Liard, M.R. Craymer, C. Gagnon, E. Lapelle. Absolute Gravity and Global Positioning System Measurements of Uplift in Quebec and Eastern Ontario, Canada. Presented at the AGU Fall meeting, San Francisco, December, 2003.

Henton, J.A., J.O. Liard, M.R. Craymer, T. James, C.G. Gagnon, E. Lapelle, Absolute Gravity and Global Positioning System Measurements of Glacial Isostatic Adjustment in Eastern Canada (abstract/poster),. AGU/CGU Joint Assembly, Montreal, May 17-21, 2004.

Henton, J.A., M.R. Craymer, M. Piraszewski, E. Lapelle. Crustal Deformation Velocities from Episodic Regional Measurements at Canadian Base Network Sites (abstract/poster). AGU 2004 Fall Meeting, San Francisco, December 13-17, 2004.

Hernandez, D, W. Holt, R.A. Bennett, A.J. Haines, L. Dimitrova, Estimation of a Time-Dependent Strain Rate Field in Southern California using Continuous GPS Stations in the SCIGN Network, EarthScope National meeting, 2005.

Hernandez, D, W. Holt, R.A. Bennett, C. Li, A.J. Haines, L. Dimitrova, Estimation of a Time-Dependent Strain Rate Field in Southern California using Continuous GPS Stations in the SCIGN Network, UNAVCO/IRIS meeting, 2005.

Herring, T.A., SNARF: Theory and practice, and implications, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Herring, T.A., SNARF: Theory and practice, and implications, Reports of the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Herring, T.A., SNARF: Theory and practice, and implications, Reports of the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Herring, T.A., Realization of a stable North America reference frame, Eos. Trans. AGU 85(17) Jt. Assem. Suppl., Abstract G21D-04, 2004.

Herring, T.A., and J. Davis, SNARF Presentation, presentation given at the 2nd SNARF Workshop, held in Montreal, Canada, May 2004.

Herring, T.A., SNARF realization for PBO processing, presentation given at the 5th SNARF Workshop, held in Denver, CO, March 2006.

Herring, T.A., PBO Frame definition using SNARF 1.0, presentation given at the 6th SNARF Workshop, held in Ottawa, Canada, November 2006.

Johnson, D.J., Test of a center of lateral figure (CL) reference frame for a global GPS network, rEos. Trans. AGU 85(17) Jt. Assem. Suppl., Abstract G21C-03, 2004.

Johnson, D. J., The vertical component in raw GPS observations, in Proceedings of the workshop: The state of GPS Vertical Positioning Precision: Separation of Earth Processes by Space Geodesy, April 2-4, 2003, Luxemburg, edited by T. van Dam and O. Francis. v. 23, p. 155-160, 2004.

Johnson, D.J., Seasonal variations in GPS site positions in a center of lateral figure (CL) reference frame, European Geosciences Union General Assembly, April 24-29, 2005, Vienna Austria (poster), 2005.

Kreemer, C., Using SNARF: Lessons Learned, presentation given at the 6th SNARF Workshop, held in Ottawa, Canada, November 2006.

Larson, K., Reference frame theory and practice, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Larson, K., Station selection criteria, Reports of the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Latychev, K., J. X. Mitrovica, M. E. Tamisiea, J. Tromp, and R. Moucha, Influence of lithospheric thickness variations on 3-D crustal velocities due to glacial isostatic adjustment, GRL, 32, doi:10.1029/2004GL021454, 2005.

Lavier, L., R.A. Bennett, M.L. Anderson, J. Matti, Constraints on lithospheric rheology from fault displacement rate histories and numerical experiments, Eos Trans. AGU, 86(18), Jt. Assem., Suppl. 2005. Li, C., R.A. Bennett, Hernandez, D., W. Holt, Analysis of time dependent velocity in southern California, using Continuous GPS stations in the SCIGN network, UNAVCO/IRIS meeting, 2005.

Miller, M.M., Applications to regional networks: PANGA, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Miller, M.M., Plan for producing and testing SNARF, Reports of the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Miller, M.M., V.M. Santillan, and D. J. Johnson, Application of a North America reference frame to regional GPS arrays in the deforming plate boundary region: Example from the Pacific Northwest Geodetic Array (PANGA). Eos, Transactions, American Geophysical Union 85(17), Joint Assembly Supp., Abstract G21D-06, 2004.

Mazzotti, S., J. Henton, J. Adams. Crustal Strain Rates and Seismic Hazard from Seismicity and GPS Measurements Along the St. Lawrence Valley, Quebec (abstract/oral). AGU/CGU Joint Assembly, Montreal, May 17-21, 2004.

Menges, C.M., Pavlis, T.L., McMackin, M.R. Serpa, L., Bennett, R.A., Geomorphic and structural evidence for significant noetectonic contractional strain within southern Death Valley and bordering areas, eastern California, GSA Annual meeting, October 2005.

Mitrovica, J. X., K. Latychev, M. E. Tamisiea, J. Tromp, and G. A. Milne (2004), GIA-Induced 3-D Crustal Velocities Predicted Using a New Generation of Viscoelastic Earth Models, Eos Trans. AGU, 85(17), Jt. Assem. Suppl, Abstract G51A-08, 2004.

Plag, H.-P., Special Bureau of Loading status report: Towards a standard model for present-day signals due to postglacial rebound, presentation given at the 5th SNARF Workshop, held in Denver, CO, March 2006.

Prawirodirdjo, L., Y. Ben-Zion, and Y. Bock, Observation and Modeling of Thermoelastic Strain in SCIGN Daily Position Time Series, Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract G53A-109, 2004.

Prawirodirdjo, L. and Y. Bock, Instantaneous Global Plate Motion Model from 12 Years of Continuous GPS Observations, J. Geophys. Res., 109, doi: 10.1029/2003JB002944, 2004.

Sella, G.F., S. Stein, S. Wdowinski, T.H. Dixon, M. Craymer. Glacial Isostatic Adjustment in North America Observed by Continuous and Episodic GPS. Presented at the AGU Fall meeting, San Francisco, December, 2003.

Sella, G.F., Geologically useful reference frame for North America, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Sella, G.F. Definition of stable North America as discussed at the first SNARF meeting, Reports of the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Sella, G.F., S. Stein, S. Wdowinski, and T. Dixon, The hunting of the SNARF, Eos. Trans. AGU 85(17) Jt. Assem. Suppl., Abstract G21D-02, 2004.

Sella, G.F., S. Stein, S. Wdowinski, T.H. Dixon, M. Craymer, T. James. Direct Constraints on GIA Motion in North America Using GPS (abstract/oral). AGU/CGU Joint Assembly, Montreal, May 17-21, 2004.

Sella, G.F., Site monumentation information, presentation given at the 5th SNARF Workshop, held in Denver, CO, March 2006.

Sella, G.F., S. Stein, T.H. Dixon, M. Craymer, T.S. James, S. Mazzotti, and R.K. Dokka, Observation of glacial isostatic adjustment in "stable" North America with GPS, Geophys. Res. Lett., Vol. 34, L02306, doi:10.1029/2006GL027081, 2007.

Smith, K.D., D. von Seggern, G. Blewitt, L. Preston, J.G. Anderson, B.P. Wernicke, J.L. Davis, Evidence for deep magma injection beneath Lake Tahoe, Nevada-California, Science, doi:10.1126/science.1101304, 2004.

SNARF Working Group, Stable North America Reference Frame: Version 1.0, Splinter Group Meeting Presentation at the Joint UNAVCO/IRIS Workshop, Stevenson, WA, June 2005.

Snay, R., Evolving from NAD 83 to SNARF, Reports of the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Snay R., and M. Craymer, Evolving from NAD 83, Eos. Trans. AGU, 85(17), Joint Assembly Suppl., Abstract G21D-01, 2004.

Snay, R., M. Cline, W. Dillinger, and T. Soler. Relating tide gauge records of sea level change to local vertical motions, (abstract), EarthScope 2005 National Meeting, Santa Ana Pueblo, NM, 2005.

Snay R., NGS reanalysis of all CORS data in the context of IGS reanalysis, presentation given at the 5th SNARF Workshop, held in Denver, CO, March 2006.

Soler T., and R. Snay, Transforming positions and velocities between the International Terrestrial Reference Frame of 2000 and North American Datum of 1983, Journal of Surveying Engineering, doi: 10.1061/(ASCE)0733-9453(2004) 130:2(49), 2004.

Tamisiea, M.E., Glacial isostatic adjustment contributions to intraplate motions in North America, presentation given at the 1st SNARF Workshop, held in Boulder, CO, January 2004.

Tamisiea, M. E., J. X. Mitrovica, and J. L. Davis. The Plausible Range of GIA Contributions to 3-D Motions at GPS Sites in the SNARF Network, Eos Trans. AGU, 85(17), Jt. Assem. Suppl, Abstract G21D-03, 2004.

Tamisiea, M.E., Effect of Earth model variations on forward GIA predictions, presentation given at the 3rd SNARF Workshop, held in Santa Ana Pueblo, NM, March 2005.

Tamisiea, M.E., Update on GIA models, presentation given at the 5th SNARF Workshop, held in Denver, CO, March 2006.

Tamisiea, M.E. and J. Davis, Assessing the GIA contribution to SNARF, presentation given at the 6th SNARF Workshop, held in Ottawa, Canada, November 2006.

Williams, S. D. P., Y. Bock, P. Fang, P. Jamason, R. M. Nikolaidis, L. Prawirodirdjo, M. Miller, and D. J. Johnson, Error Analysis of Continuous GPS Position Time Series, J. Geophys. Res., 109, B03412, doi: 10.1029/2003JB0022741, 2004.

Webb, F., Y. Bock, R. Chang, D. Dong, P. Fang, J. Genrich, P. Jamason, S. Kedar, N. King, D. Malveaux, B. Newport, S. Owen, L. Prawirodirdjo, M. Scharber, and K. Stark, GPS Data Products for the Earth Sciences, Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract SF53A-0736, 2004.

 

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