meca

meca(cmd0::String="", arg1=nothing; kwargs...)

meca - Plot focal mechanisms

Description

Reads data values from tables or input arguments and plots focal mechanisms (beachballs). The module reads focal mechanism parameters and plots the corresponding beachballs on a map. Several input format conventions are supported: Aki & Richards, Global CMT, moment tensor, partial focal mechanism, and principal axis.

Focal Mechanism Conventions

Aki & Richards (aki= or Sa)

Columns: lon, lat, depth, strike, dip, rake, magnitude, newlon, newlat, text

Global CMT (CMT= or Sc)

Columns: lon, lat, depth, strike1, dip1, rake1, strike2, dip2, rake2, mantissa, exponent, newlon, newlat, text

Moment Tensor (moment_tensor= or Sm/Sz/Sd)

Columns: lon, lat, depth, mrr, mtt, mff, mrt, mrf, mtf, exponent, newlon, newlat, text

Partial (partial= or Sp)

Columns: lon, lat, depth, strike1, dip1, strike2, fault_type, magnitude, newlon, newlat, text

Principal Axis (principal_axis= or Sx/Sy)

Columns: lon, lat, depth, T_value, T_azim, T_plunge, N_value, N_azim, N_plunge, P_value, P_azim, P_plunge, exponent, newlon, newlat, text

Required Arguments

  • table
    A data table (or matrices/datasets) containing focal mechanism parameters. The format depends on the convention specified.

  • J or proj or projection : – proj=
    Select map projection. More at [proj](../common_opts/opt_J.html)

  • R or region or limits : – limits=(xmin, xmax, ymin, ymax) | limits=(BB=(xmin, xmax, ymin, ymax),) | limits=(LLUR=(xmin, xmax, ymin, ymax),units=“unit”) | …more
    Specify the region of interest. More at [limits](../common_opts/opt_R.html). For perspective view view, optionally add zmin,zmax. This option may be used to indicate the range used for the 3-D axes. You may ask for a larger w/e/s/n region to have more room between the image and the axes.

  • S or convention : Convention-specific options
    Selects the input convention and symbol size. Choose from:

    • aki or Sa : Aki & Richards convention
    • CMT or Sc : Global CMT convention
    • moment_tensor or mt or Sm : Seismic moment tensor (full)
    • dev or Sz : Deviatoric moment tensor (zero trace)
    • dc or Sd : Double couple from moment tensor (zero trace and determinant)
    • partial or Sp : Partial focal mechanism
    • axis or principal_axis or Sx : Principal axis
    • principal or Sy : Best double couple from principal axis

    Append scale to set the symbol size. Use tuple form to add modifiers:

    • aki=(scale=val, ...) or CMT=(scale=val, ...) etc.

    Available modifiers (as named tuple elements):

    • angle : Rotate text angle
    • font : Set text font
    • justify : Text justification
    • radius_moment : Radius will be proportional to the seismic moment
    • same_size : Plot the same size for any magnitude
    • offset : Offset text by dx/dy
    • refmag : Reference magnitude for scaling

Optional Arguments

  • A or offset : – offset=true | offset=(fill=…, offset=.., pen=…, size=…)
    Offsets beachballs to the longitude, latitude specified in the last two columns of the input. A line connects the original and relocated positions. Available modifiers:

    • fill : Symbol fill color
    • offset : Interpret the contents of the two columns as plot offsets instead, or append fixed offset dx[/dy] for all events.
    • pen : Line pen attributes
    • size : Set the size of the symbol. Prepend any of a|c|d|g|h|i|n|p|s|t|x to change the symbol fron the default [c]

  • B or axes or frame
    Set map boundary frame and axes attributes. Default is to draw and annotate left, bottom and vertical axes and just draw left and top axes. More at [frame](../common_opts/opt_B.html)

  • C or color or cmap : – cmap=cpt
    Give a CPT to determine compressive quadrant fill based on depth (3rd column).

  • D or depth_range : – depth_range=(depmin,depmax)
    Plot only events with depths between depmin and depmax.

  • E or extensionfill : – extensionfill=fill
    Selects filling of extensive quadrants [Default is white].

  • F : – Fa=true | Fa=[size[/Psymbol[Tsymbol]]] , Fe|Fg|Fr=fill , Fp|Ft|Fz=pen , Fo=true
    Aliases:

    • Fa or PT_axes : Computes and plots P and T axes with symbols. Optionally specify size and (separate) P and T axis symbols from the following: (c) circle, (d) diamond, (h) hexagon, (i) inverse triangle, (p) point, (s) square, (t) triangle, (x) cross. [Default: 6p/cc]
    • Fe or T_axis_color : Sets the color or fill pattern for the T axis symbol. [Default as set by extensionfill]
    • Fo or psvelo : Old psvelomeca format (no depth in 3rd column)
    • Fg or P_axis_color : Sets the color or fill pattern for the P axis symbol. [Default as set by extensionfill]
    • Fr or label_box : Draw a box behind the label (if any). [Default fill is white]
    • Fp or P_axis_pen : Draws the P axis outline using default pen (see W), or sets pen attributes.
    • Ft or T_axis_pen : Draws the T axis outline using default pen (see W), or sets pen attributes.
    • Fz or zero_trace : Overlay zero trace moment tensor using default pen (see W), or sets pen attributes.

  • G or fill or extensionfill : – fill=color
    Selects filling of compressive quadrants [Default is black].

  • H or scale : – scale=true | scale=scale
    Scale symbol sizes and pen widths on a per-record basis using the scale read from the data file. The symbol size is either provided by convention or via the input size column. Alternatively, append a constant scale that should be used instead of reading a scale column.

  • I or intens or intensity : – intens=val | intens=:a
    Use the supplied intens value (nominally in the ±1 range) to modulate the compressional fill color by simulating illumination [none]. If no intensity is provided we will instead read intens from an extra data column after the required input columns determined by convention.

  • L or pen_outline : – pen_outline=pen
    Draws the “beach ball” outline using specified pen attributes.

  • M or same_size or samesize : – same_size=true
    Use the same size for all beachballs. Size is set from the magnitude columns, but the same size is used regardless of magnitude.

  • N or no_clip or noclip : – no_clip=true
    Do NOT skip symbols that fall outside the map border [Default clips symbols].

  • T or nodal : – nodal=plane | nodal=(plane=val, pen=…)
    Plot nodal planes and circumference only. Specify which plane(s) to draw:

    • 0 : Both planes
    • 1 : Only first nodal plane
    • 2 : Only second nodal plane

    Use tuple form to set pen: nodal=(plane=0, pen=pen_spec)

    For double couple mechanisms, the nodal option renders the beach ball transparent by drawing only the nodal planes and the circumference. For non-double couple mechanisms, nodal=0 option overlays best double couple transparently.

  • U or time_stamp : – time_stamp=true | time_stamp=(just=“code”, pos=(dx,dy), label=“label”, com=true)
    Draw GMT time stamp logo on plot. More at [timestamp](../common_opts/opt_U.html)

  • V or verbose : – verbose=true | verbose=level
    Select verbosity level. More at [verbose](../common_opts/opt_V.html)

  • W or pen : – pen=pen
    Set pen attributes for features [Default pen is 0.25p,black,solid]. This setting applies to A, L, T, Fp, Ft, and Fz, unless overruled by options to those arguments. See also [Pen attributes]

  • X or xshift or x_offset : xshift=true | xshift=x-shift | xshift=(shift=x-shift, mov=“a|c|f|r”)
    Shift plot origin. More at [xshift](../common_opts/opt_X.html)

  • Y or yshift or y_offset : yshift=true | yshift=y-shift | yshift=(shift=y-shift, mov=“a|c|f|r”)
    Shift plot origin. More at [yshift](../common_opts/opt_Y.html)

  • di or nodata_in : – nodata_in=??
    Substitute specific values with NaN. More at

  • e or pattern : – pattern=??
    Only accept ASCII data records that contain the specified pattern. More at

  • h or header : – header=??
    Specify that input and/or output file(s) have n header records. More at

  • i or incol or incols : – incol=col_num | incol=“opts”
    Select input columns and transformations (0 is first column, t is trailing text, append word to read one word only). More at incol

  • p or view or perspective : – view=(azim, elev)
    Default is viewpoint from an azimuth of 200 and elevation of 30 degrees.
    Specify the viewpoint in terms of azimuth and elevation. The azimuth is the horizontal rotation about the z-axis as measured in degrees from the positive y-axis. That is, from North. This option is not yet fully expanded. Current alternatives are:

    • view=??
      A full GMT compact string with the full set of options.
    • view=(azim,elev)
      A two elements tuple with azimuth and elevation
    • view=true
      To propagate the viewpoint used in a previous module (makes sense only in bar3!) More at [perspective](../common_opts/opt_p.html)

  • q or inrows : – inrows=??
    Select specific data rows to be read and/or written. More at

  • t or transparency or alpha: – alpha=50
    Set PDF transparency level for an overlay, in (0-100] percent range. [Default is 0, i.e., opaque]. Works only for the PDF and PNG formats.

  • yx : – yx=true
    Swap 1st and 2nd column on input and/or output. More at

Examples

[focal_mechanisms]

Plot focal mechanisms using Aki-Richards convention:

using GMT

# Create focal mechanism data  
D = mat2ds([0.0 5.0 0.0 0 90 0 5 0 0], ["Right Strike Slip"])

# Plot with fixed size beachballs
meca(D, region=(-1,4,1,6), proj=:Mercator, aki=2.5, fill=:black, show=true)

Plot using Global CMT convention with depth-based coloring:

# Background map
grdimage("@earth_relief", region=[-74,-59,5,15], proj=:guess, figsize=10, shade=true)
coast!(shorelines=true, borders=((type=1, pen=0.8),(type=2, pen=0.1)))

# Focal mechanisms with offsets
meca!("focal_data.txt", CMT=(scale=0.4, font=6), offset=true, fill=:black, show=true)

Plot multiple mechanisms with varying types:

using GMT

# Right lateral strike slip
D1 = mat2ds([0.0 5.0 0.0 0 90 0 5 0 0], ["Right Strike Slip"])
meca(D1, region=(-1,4,1,6), proj=:Mercator, aki=2.5, fill=:black)

# Thrust fault
D2 = mat2ds([0.0 3.5 0.0 0 45 90 5 0 0], ["Thrust"])
meca!(D2, aki=2.5, fill=:black)

# Normal fault
D3 = mat2ds([0.0 2.0 0.0 0 45 -90 5 0 0], ["Normal"])  
meca!(D3, aki=2.5, fill=:black, show=true)

References

Aki, K., & Richards, P. G. (1980). Quantitative seismology: theory and methods. San Francisco: W. H. Freeman.

Dahlen, F. A., & Tromp, J. (1998). Theoretical global seismology. Princeton, N.J: Princeton University Press.

Frohlich, C. (1996). Cliff’s Nodes Concerning Plotting Nodal Lines for P, SH and SV. Seismological Research Letters, 67(1), 16–24, https://doi.org/10.1785/gssrl.67.1.16.

Lay, T., & Wallace, T. C. (1995). Modern global seismology. San Diego: Academic Press.

See Also

coupe, [polar], velo