gmtgravmag3d(1) GMT gmtgravmag3d(1)

## NAME

gmtgravmag3d - Compute the gravity/magnetic effect of a body by the method of Okabe

## SYNOPSIS

gmtgravmag3d-Tpxyz_file[+m]-Tvvert_fileOR-Tr|sraw_file[-Cden-sity] [-D] [-Ethickness] [-Fxy_file] [-Goutputgrid] [-Hf_dec/f_dip/m_int/m_dec/m_dip] [-Lz_observation] [-Sradius] [-Zlevel] [-V[level] ] [-fg]Note:No space is allowed between the option flag and the associated arguments.

## DESCRIPTION

gmtgravmag3dwill compute the gravity or magnetic anomaly of a body described by a set of triangles. The output can either be along a given set of xy locations or on a grid. This method is not particularly fast but allows computing the anomaly of arbitrarily complex shapes.

## REQUIRED ARGUMENTS

-CdensitySets body density in SI. This option is mutually exclusive with-H.-Hf_dec/f_dip/m_int/m_dec/m_dipSets parameters for computing a magnetic anomaly. Usef_dec/f_dipto set the geomagnetic declination/inclination in degrees.m_int/m_dec/m_dipare the body magnetic intensity dec- lination and inclination.-Fxy_fileProvide locations where the anomaly will be computed. Note this option is mutually exclusive with-G.-GoutgridOutput the gravity or magnetic anomaly at nodes of this grid file.-Rxmin/xmax/ymin/ymax[+r][+uunit] (morea|) Specify the region of interest.-Tpxyz_file[+m]-Tvvert_fileORTr|sraw_fileGives names of xyz (-Tpxyz_file[+m]) and vertex (-Tvvert_file) files defining a close surface. The file formats correspond to the output of the triangulate program. The optional+mflag to-Tpinstructs the program that the xyzm file has four columns and that the fourth column contains the magnetization intensity (plus signal), which needs not to be constant. In this case the third argument of the-Hoption is ignored. Arawformat (selected by the-Troption) is a file with N rows (one per tri- angle) and 9 columns corresponding to the x,y,x coordinates of each of the three vertex of each triangle. Alternatively, the-Tsoption indicates that the surface file is in the ASCII STL (Stereo Lithographic) format. These two type of files are used to provide a closed surface.

## OPTIONAL ARGUMENTS

-V[level] (morea|) Select verbosity level [c].-E[thickness] give layer thickness in m [Default = 0 m]. Use this option only when the triangles describe a non-closed surface and you want the anomaly of a constant thickness layer.-L[z_observation] sets level of observation [Default = 0]. That is the height (z) at which anomalies are computed.-Sradiussearch radius in km. Triangle centroids that are further away thanradiusfrom current output point will not be taken into account. Use this option to speed up computation at expenses of a less accurate result.-Z[level] level of reference plane [Default = 0]. Use this option when the triangles describe a non-closed surface and the volume is defined from each triangle and this reference level. An example will be the hater depth to compute a Bouguer anomaly.-fgGeographic grids (dimensions of longitude, latitude) will be converted to meters via aaFlat Earthaapproximation using the current ellipsoid parameters.-^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.

## GRID DISTANCE UNITS

If the grid does not have meter as the horizontal unit, append+uunitto the input file name to convert from the specified unit to meter. If your grid is geographic, convert distances to meters by supplying-fginstead.

## EXAMPLES

Suppose youa| gmt gmtgravmag3d ...

## SEE ALSO

gmt(1),grdgravmag3d(1),talwani2d(1),talwani3d(1)

## REFERENCE

Okabe, M., Analytical expressions for gravity anomalies due to polyhe- dral bodies and translation into magnetic anomalies,Geophysics, 44, (1979), p 730-741.

## COPYRIGHT

2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe 5.4.2 Jun 24, 2017 gmtgravmag3d(1)

gmt5 5.4.2 - Generated Wed Jun 28 16:26:38 CDT 2017