Issue 1643 - Implements Attenuation frequency dependence output curve.

[lsawade]

Description

This adds an executable code path

specfem Qplots 80 0.003 0.06

To output attenuation curves for the a given Q value. It uses internal routines so that the user may visually inspect what the code does to a given constant Q.

The outputs can be used to reproduce Savage et al. 2010, Figure 3, and (somewhat) Dahlen & Tromp 1998, Figure 6.8. For D&T figure we would need a lot of standard linear solids which does not make from a computational standpoint and will not accuracy to most applications.

specfem Qplots --help for options and default values.

This also fixes an error in the tau_epsilon computation to match the computation in fortran specfem3d

Issue Number

Closes #1643

Checklist

Please make sure to check developer documentation on specfem docs.

• I ran the code through pre-commit to check style
• THE DOCUMENTATION BUILDS WITHOUT WARNINGS/ERRORS
• I have added labels to the PR (see right hand side of the PR page)
• My code passes all the integration tests
• I have added sufficient unittests to test my changes
• I have added/updated documentation for the changes I am proposing
• I have updated CMakeLists to ensure my code builds
• My code builds across all platforms

[lsawade]

Can plot this: