The basic concept of plate tectonics is that, to a first approximation, the Earth surface is divided into several rigid plates that move with respect to one another but do not deform internally. The motion of each plate can be described by its Eulerian pole (coordinates and angular velocity).
In order to better visualize the internal deformation of a single plate and to visualize the relative movements between plates, we propose a tool to select a reference plate, whose motion can be subtracted (using the option Relative to one plate).
In the ITRF 2008 reference frame
The horizontal velocities displayed on the map are those of the ULR5 solution (Santamaria-Gomez et al., 2012), which is aligned on the ITRF 2008 reference frame. (See information on the ULR5 solution).
For each site, the arrow is colored according to the tectonic plate, based on its geographical coordinates. We use the MORVEL model (DeMets et al., 2010), which comprises 25 plates. Note that the 25 plates are drawn on the figure, but only 19 plates are labeled in the figure caption; the 6 remaining plates (Cocos, Juan de Fuca, Macquarie, Sur, Sandwich and Rivera) do not have GNSS stations processed in ULR5 on them.
Relative to a given (user selected) plate
This tool is proposed to highlight the relative motion of a site or a plate with respect to a specific plate considered as fixed. It allows to better see the deformation within a particular plate or to look at the relative motion between plates.
The movement of each plate at the Earth surface can be described as a rotation, defined by its Eulerian pole. Eulerian poles have been computed by least-squares minimization, using horizontal velocities from the ULR5 GPS solution, for 10 plates (table below) to describe their movement in the ITRF 2008 reference frame.
|Number of stations used for determination||Latitude (°)||Longitude (°)||Angular velocity (deg/My)||RMS in mm/yr (1mm/yr = 0.01 deg/My)|
To select a reference plate, the user must click on the plate. The colored star and dots indicate respectively, for the selected plate, the eulerian pole location and the stations used in its computation.
By selecting a plate, the user can remove the rotation of the specified plate, which is then considered as fixed in the representation. The arrows represent the residual motion after rotation.
Softwares used for Eulerian pole determination and rotation computations were kindly provided by J. M. Nocquet.
Santamaria-Gomez, A., M. Gravelle, X. Collilieux, M. Guichard, B. Martin Miguez, P. Tiphaneau, G. Wöppelmann (2012), Mitigating the effects of vertical land motion in tide gauge records using a state-of-the-art GPS velocity field, Global and Planet. Change, vol. 98-99, pp 6-17.
DeMets, C., R. G. Gordon, D. F. Argus (2010), Geologically current plate motions, Geophys. J. Int., vol. 181 (1), pp. 1-80.