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paudetseis edited this page Sep 5, 2019 · 1 revision

How to setup the model file

In the Jupiter notebooks you will find a folder named models where a few examples are provided. The header of the file model_Audet2016.txt looks like:

################################################
# 
#   Model file to use with `telewavesim` for 
#   modeling teleseismic body wave propagation 
#   through stratified media.
#
#   Lines starting with '#' are ignored. Each 
#   line corresponds to a unique layer. The 
#   bottom layer is assumed to be a half-space
#   (Thickness is irrelevant).
#
#   Format:
#       Column  Contents
#          0    Thickness (km)
#          1    Density (kg/m^3)
#          2    Layer P-wave velocity (km/s)
#          3    Layer S-wave velocity (km/s)
#          4    Layer flag 
#                   iso: isotropic
#                   tri: transverse isotropy
#                   [other]: other minerals or rocks
#          5    % Transverse anisotropy (if Layer is set to 'tri')
#                   0: isotropic
#                   +: fast symmetry axis
#                   -: slow symmetry axis
#          6    Trend of symmetry axis (degrees)
#          7    Plunge of symmetry axis (degrees)
#
################################################

The header is not required and can be deleted when you become familiar with the various definitions. Note that the code requires 8 entries per layer, regardless of whether or not the variable is required (it will simply be ignored if it's not).

Let us break down each line, depending on how you set Layer flag:

Layer flag set to iso

This flag obviously represents an isotropic layer.

Set column 0 (Thickness), column 1 (Density), column 2 (P-wave velocity), column 3 (S-wave velocity) and column 4 (as iso)

Set columns 5 to 7 to 0. or any other numerical value - they will be ignored by the software.

Layer flag set to tri

This flag represents a transversely isotropic layer. We adhere with the definition in Porter et al. (2011), whereby the parameter eta varies with anisotropy for a 2-psi model and is not fixed.

Set all columns to the required numerical value (and column 4 to tri)

Layer flag set to another type of material

This flag should be set to the specific single-crystal or rock abbreviation, for which the elastic properties have been determined in the lab. Currently available options are:

mins = ['atg', 'bt', 'cpx', 'dol', 'ep', 'grt', 'gln', 'hbl', 'jade', \
        'lws', 'lz', 'ms', 'ol', 'opx', 'plag', 'qtz', 'zo']

rocks = ['BS_f', 'BS_m', 'EC_f', 'EC_m', 'HB', 'LHZ', 'SP_37', 'SP_80']

The module Telewavesim.elast contains the definition of the stiffness matrices for these minerals and rocks. Check out the module or the documentation for more details.

In this case the software requires entries in column 0 (Thickness), column 4 (an abbreviation among the above options), and optionally columns 6 and 7 if you wish to rotate the corresponding tensor about two axes (trend and plunge of the equivalent of the symmetry axis in transverse isotropy). Columns 1 to 3 can be set to any numerical value and will be ignored by the software.

Enjoy!

References

  1. Porter, R., Zandt, G., & McQuarrie, N. (2011). Pervasive lower-crustal seismic anisotropy in Southern California: Evidence for underplated schists and active tectonics. Lithosphere, 3(3), 201-220. https://doi.org/10.1130/L126.1
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