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Global Geodetic strain rate model

Report

ThisisthefinalreportproducedinthecontextoftheGEMStrainRateProject,oneoftheglobalcomponents of the GEM Foundation. The project was charged to analyse and synthesize all available geodetic data in order tocreateaglobaldatasetofgeodeticvelocities thatcanbeused tomodelplatemotionsandstrain ratesinplateboundaryzones.To thisend,weestimated6533velocities fromposition time-series thatwe derived fromtheanalysisofRINEXdatathatwaseither freelyavailableormadeavailabletousspecifically forthisproject.Allbut 15ofthesevelocitieswereusedinthemodelling.Inaseparateanalysis,wealsoreanalysed all RINEX data in China and effectively added 1143 velocities to the data set. Finally, we added 13,318velocitiesfrom216studiesinthepublishedliterature(orfrompersonalcommunications)toachievea grandtotalof20,979velocitiesat17,491uniquelocationsusedinthemodelling.Ofallvelocities, 16,325are inplateboundaryzones(asdefinedbyus)andtheremaining4654velocitiesareforpointson,predefined, rigidtectonicplatesorblocks.Wecreatedaglobalmeshthathas144,827deformingcellsof0.2°(latitudinal) by 0.25° (longitudinal) dimension covering the plate boundary zones,with the remaining cells covering 50 rigidplatesandblocks.For36oftheseplates,weestimatedtherigid-bodyrotation fromourdataset,and the rotations of the remaining plates are taken from the literature. The rigid-body rotations are used as boundaryconditionsinthestrainratecalculations.ThestrainratefieldismodelledusingtheHainesandHolt method,whichusessplinestoobtainaninterpolatedvelocitygradienttensorfield,fromwhichstrainrates, vorticityrates,andexpectedvelocitiesarederived.Wealsoestimatedmodeluncertainties,specificforthis high-resolution mesh, which indicates that there still are many areas with large strain rate uncertainties where the data spacing is often much larger than the cell dimensions. Nevertheless, the model and data input are a tremendous improvement to the previous global strain rate model from 2004. All results are transferred to GEM and are also archived and displayed by a dedicated server hosted by UNAVCO (gsrm2.unavco.org), one of the project's partners. In addition, we created a kmz-layer of contour's of the secondinvariantofthemodelstrainrates,andwecreatedanonlinetoolthatwouldallowausertoupload hisownvelocitiesandplotthemwiththevelocitiesintheGEMdatasetin53differentreferenceframes.
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