Global Geodetic strain rate model
Kreemer, C., E. Klein, Z-K Shen, M. Wang, L. Estey, S. Wier, F. Boler
This is the final report produced in the context of the GEM Strain Rate Project, one of the global components of the GEM Foundation. The project was charged to analyse and synthesize all available geodetic data in order to create a global data set of geodetic velocities that can be used to model plate motions and strain rates in plate boundary zones. To this end, we estimated 6533 velocities from position time-series that we derived from the analysis of RINEX data that was either freely available or made available to us specifically for this project. All but 15 of these velocities were used in the modelling. In a separate analysis, we also reanalysed all RINEX data in China and effectively added 1143 velocities to the data set. Finally, we added 13,318 velocities from 216 studies in the published literature (or from personal communications) to achieve a grand total of 20,979 velocities at 17,491 unique locations used in the modelling. Of all velocities, 16,325 are in plate boundary zones (as defined by us) and the remaining 4654 velocities are for points on, predefined, rigid tectonic plates or blocks. We created a global mesh that has 144,827 deforming cells of 0.2° (latitudinal) by 0.25° (longitudinal) dimension covering the plate boundary zones, with the remaining cells covering 50 rigid plates and blocks. For 36 of these plates, we estimated the rigid-body rotation from our data set, and the rotations of the remaining plates are taken from the literature. The rigid-body rotations are used as boundary conditions in the strain rate calculations. The strain rate field is modelled using the Haines and Holt method, which uses splines to obtain an interpolated velocity gradient tensor field, from which strain rates, vorticity rates, and expected velocities are derived. We also estimated model uncertainties, specific for this 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 second invariant of the model strain rates, and we created an online tool that would allow a user to upload his own velocities and plot them with the velocities in the GEM dataset in 53 different reference frames.