grdpmodeler

grdpmodeler - Evaluate a plate model on a geographic grid

Synopsis

grdpmodeler agegrdfile -Erot_file -Goutgrdfile -Sa|d|r|w|x|y|X|Y [ -Fpolygonfile ] [ -Tage ] [ -V[level] ] [ -b[i|o][ncol][type][w][+L|+B] ] [ -h[i|o][n][+c][+d][+rremark][+rtitle] ] [ -icols[l][sscale][ooffset][,...] ] [ -:[i|o] ]

Note: No space is allowed between the option flag and the associated arguments.

Description

grdpmodeler reads a geographical age grid and a plate motion model and evaluates one of several model predictions. Optionally, the user may supply a clipping polygon in multiple-segment format; then, only the part of the grid inside the polygon is used to determine the model prediction; the remainder of the grid is set to NaN.

Required Arguments

ingrdfile
Name of a grid file in geographical (lon, lat) coordinates with ages in Myr.
-Erotfile

Give file with rotation parameters. This file must contain one record for each rotation; each record must be of the following format:

lon lat tstart [tstop] angle [ khat a b c d e f g df ]

where tstart and tstop are in Myr and lon lat angle are in degrees. tstart and tstop are the ages of the old and young ends of a stage. If tstop is not present in the record then a total reconstruction rotation is expected and tstop is implicitly set to 0 and should not be specified for any of the records in the file. If a covariance matrix C for the rotation is available it must be specified in a format using the nine optional terms listed in brackets. Here, C = (g/khat)*[ a b d; b c e; d e f ] which shows C made up of three row vectors. If the degrees of freedom (df) in fitting the rotation is 0 or not given it is set to 10000. Blank lines and records whose first column contains # will be ignored. You may prepend a leading + to the filename to indicate you wish to invert the rotations. Alternatively, give the filename composed of two plate IDs separated by a hyphen (e.g., PAC-MBL) and we will instead extract that rotation from the GPlates rotation database. We return an error if the rotation cannot be found.

-Goutgrdfile
Name of output grid. This is the grid with the model predictions given the specified rotations.
-Sa|d|r|w|x|y|X|Y
Type of model prediction. Choose from a for plate motion azimuth, d for distance between current locations and their origin at the ridge (in km), r for plate motion rate (in mm/yr), w for plate rotation rate (degree/Myr), x change in longitude relative to location of crust formation, y change in latitude relative to location of crust formation, X longitude of crust formation, and Y latitude of crust formation.

Optional Arguments

-Fpolygonfile
Specify a multisegment closed polygon file that describes the inside area of the grid where the model should be evaluated; the outside will be set to NaN [Default evaluates model on the entire grid].
-Tage
Use a fixed age for model evaluation (i.e., override the ages in the age grid). This lets you evaluate the model at a snapshot in time.
-V[level] (more ...)
Select verbosity level [c].
-bi[ncols][type] (more ...)
Select binary input. [Default is 2 input columns].
-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
Skip or produce header record(s).
-icols[l][sscale][ooffset][,...] (more ...)
Select input columns (0 is first column).
-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
-+ or just +
Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exits.
-? or no arguments
Print a complete usage (help) message, including the explanation of options, then exits.
--version
Print GMT version and exit.
--show-datadir
Print full path to GMT share directory and exit.

Geodetic versus Geocentric Coordiinates

All spherical rotations are applied to geocentric coordinates. This means that incoming data points and grids are considered to represent geodetic coordinates and must first be converted to geocentric coordinates. Rotations are then applied, and the final reconstructed points are converted back to geodetic coordinates. This default behavior can be bypassed if the ellipsoid setting PROJ_ELLIPSOID is changed to Sphere.

Examples

We will use a grid with Pacific crust ages (pac_age.nc), a plate motion model (Pac_APM.d), and a polygon that contains the outline of the present Pacific plate (pac_clip_path.d). To evaluate the plate motion azimuths at the present time for the Pacific, try

gmt grdpmodeler pac_age.nc -EPac_APM.d -V -Fpac_clip_path.d \
                -Gpac_dir_0.nc -Sa -T0

To determine the changes in latitude since crust formation for the entire Pacific, try

gmt grdpmodeler pac_age.nc -EPac_APM.d -V -Fpac_clip_path.d \
                -Gpac_dlat.nc -Sy

To determine the plate motion rates in effect when the Pacific crust was formed, try

gmt grdpmodeler pac_age.nc -EPac_APM.d -V -Fpac_clip_path.d \
                -Gpac_vel.nc -Sr

To determine how far the crust has moved since formation, try

gmt grdpmodeler pac_age.nc -EPac_APM.d -V -Fpac_clip_path.d \
                -Gpac_dist.nc -Sd