grdspotter(1) GMT grdspotter(1)
NAME
grdspotter - Create CVA image from a gravity or topography grid
SYNOPSIS
grdspotter [grdfile] -Erotfile -GCVAgrid
-Iincrement
-Rregion [ -Aagegrid ] [ -DDIgrid ] [ -LIDgrid ] [ -M ] [ -Nup-
per_age ] [ -PPAgrid ] [ -QIDinfo ] [ -S ] [ -Tt|ufixed_val ] [ [
-V[level] ] [ -Wn_try ]] [ -Zz_min[/z_max[/z_inc]] ] [ -r ]
Note: No space is allowed between the option flag and the associated
arguments.
DESCRIPTION
grdspotter reads a grid file with residual bathymetry or gravity and
calculates flowlines from each node that exceeds a minimum value using
the specified rotations file. These flowlines are then convolved with
the volume of the prism represented by each grid node and added up to
give a Cumulative Volcano Amplitude grid (CVA).
REQUIRED ARGUMENTS
grdfile
Data grid to be processed, typically residual bathymetry or
free-air anomalies.
-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 rota-
tion cannot be found.
-G Specify name for output CVA grid file.
-Ixinc[unit][+e|n][/yinc[unit][+e|n]]
x_inc [and optionally y_inc] is the grid spacing. Optionally,
append a suffix modifier. Geographical (degrees) coordinates:
Append m to indicate arc minutes or s to indicate arc seconds.
If one of the units e, f, k, M, n or u is appended instead, the
increment is assumed to be given in meter, foot, km, Mile, nau-
tical mile or US survey foot, respectively, and will be con-
verted to the equivalent degrees longitude at the middle lati-
tude of the region (the conversion depends on PROJ_ELLIPSOID).
If y_inc is given but set to 0 it will be reset equal to x_inc;
otherwise it will be converted to degrees latitude. All coordi-
nates: If +e is appended then the corresponding max x (east) or
y (north) may be slightly adjusted to fit exactly the given
increment [by default the increment may be adjusted slightly to
fit the given domain]. Finally, instead of giving an increment
you may specify the number of nodes desired by appending +n to
the supplied integer argument; the increment is then recalcu-
lated from the number of nodes and the domain. The resulting
increment value depends on whether you have selected a grid-
line-registered or pixel-registered grid; see App-file-formats
for details. Note: if -Rgrdfile is used then the grid spacing
has already been initialized; use -I to override the values.
-Rwest/east/south/north[/zmin/zmax][+r][+uunit]
west, east, south, and north specify the region of interest, and
you may specify them in decimal degrees or in
[A+-]dd:mm[:ss.xxx][W|E|S|N] format Append +r if lower left and
upper right map coordinates are given instead of w/e/s/n. The
two shorthands -Rg and -Rd stand for global domain (0/360 and
-180/+180 in longitude respectively, with -90/+90 in latitude).
Alternatively for grid creation, give Rcodelon/lat/nx/ny, where
code is a 2-character combination of L, C, R (for left, center,
or right) and T, M, B for top, middle, or bottom. e.g., BL for
lower left. This indicates which point on a rectangular region
the lon/lat coordinate refers to, and the grid dimensions nx and
ny with grid spacings via -I is used to create the corresponding
region. Alternatively, specify the name of an existing grid
file and the -R settings (and grid spacing, if applicable) are
copied from the grid. Appending +uunit expects projected (Carte-
sian) coordinates compatible with chosen -J and we inversely
project to determine actual rectangular geographic region. For
perspective view (-p), optionally append /zmin/zmax. In case of
perspective view (-p), a z-range (zmin, zmax) can be appended to
indicate the third dimension. This needs to be done only when
using the -Jz option, not when using only the -p option. In the
latter case a perspective view of the plane is plotted, with no
third dimension.
OPTIONAL ARGUMENTS
-Aagegrid
Supply a crustal age grid that is co-registered with the input
data grid. These ages become the upper ages to use when con-
structing flowlines [Default extend flowlines back to oldest age
found in the rotation file; but see -N].
-DDIgrid
Use flowlines to determine the maximum CVA encountered along
each flowline and create a Data Importance (DI) grid with these
values at the originating nodes.
-LIDgrid
Supply a co-registered grid with seamount chain IDs for each
node. This option requires that you also use -Q.
-M Do not attempt to keep all flowlines in memory when using -D
and/or -P. Should you run out of memory you can use this option
to compute flowlines on-the-fly. It will be slower as we no
longer can reuse the flowlines calculated for the CVA step. Can-
not be used with -W or the multi-slice mode in -Z.
-Nupper_age
Set the upper age to assign to nodes whose crustal age is
unknown (i.e., NaN) [no upper age]. Also see -A.
-PPAgrid
Use flowlines to determine the flowline age at the CVA maximum
for each node and create a Predicted Age (PA) grid with these
values at the originating nodes.
-QIDinfo
Either give (1) a single ID to use or (2) the name of a file
with a list of IDs to use [Default uses all IDs]. Each line
would be TAG ID [w e s n]. The w/e/s/n zoom box is optional; if
specified it means we only trace the flowline if inside this
region [Default uses region set by -R]. Requires -L.
-S Normalize the resulting CVA grid to percentages of the CVA maxi-
mum. This also normalizes the DI grid (if requested).
-Tt|ufixed_val
Selects ways to adjust ages; repeatable. Choose from -Tt to
truncate crustal ages given via the -A option that exceed the
upper age set with -N [no truncation], or -Tufixed_val which
means that after a node passes the test implied by -Z, we use
this fixed_val instead in the calculations. [Default uses indi-
vidual node values].
-V[level] (more a|)
Select verbosity level [c].
-Wn_try
Get n_try bootstrap estimates of the maximum CVA location; the
longitude and latitude results are written to stdout [Default is
no bootstrapping]. Cannot be used with -M.
-Zz_min[/z_max[/z_inc]]
Ignore nodes with z-values lower than z_min [0] and optionally
larger than z_max [Inf]. Give z_min/z_max/z_inc to make separate
CVA grids for each z-slice [Default makes one CVA grid].
Multi-slicing cannot be used with -M.
-r (more a|)
Set pixel node registration [gridline].
-^ or just -
Print a short message about the syntax of the command, then
exits (NOTE: on Windows just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion 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 all options, then exits.
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 coordi-
nates. 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
To create a CVA image from the Pacific topography grid Pac_res_topo.nc,
using the DC85.d Euler poles, and only output a grid for the specified
domain, run
gmt grdspotter Pac_res_topo.nc -EDC85.d -GCVA.nc -R190/220/15/25 -I2m -N145 -Tt -V
This file can then be plotted with grdimage.
NOTES
GMT distributes the EarthByte rotation model Global_Earth-
Byte_230-0Ma_GK07_AREPS.rot. To use an alternate rotation file, create
an environmental parameters named GPLATES_ROTATIONS that points to an
alternate rotation file.
SEE ALSO
gmt(1), grdimage(1), project(1), mapproject(1), backtracker(1),
gmtpmodeler(1), grdpmodeler(1), grdrotater(1), hotspotter(1),
originator(1)
REFERENCES
Wessel, P., 1999, aHotspottinga tools released, EOS Trans. AGU, 80
(29), p. 319.
Wessel, P., 2008, Hotspotting: Principles and properties of a plate
tectonic Hough transform, Geochem. Geophys. Geosyst. 9(Q08004):
doi:10.1029/2008GC002058.
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 grdspotter(1)
gmt5 5.4.2 - Generated Thu Jun 29 08:28:47 CDT 2017