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CIG-LLNL Computational Seismology Workshop

SPECFEM3D_GLOBE Tutorial

Part IV: Adjoint Simulations (Bonus)

In this final part of the tutorial, we will look at how to run adjoint simulations. SPECFEM3D_GLOBE supports two types of adjoint simulations: for source inversions and for finite-frequency kernels. In this tutorial, we will focus on the application to finite-frequency kernels, but the steps required are similar for both applications. The steps we need to take are the following:

Run Forward Simulation and Save State Variables
Prepare the Adjoint Source(s)
Run Kernel Simulation

Prepare the Adjoint Source(s)

After running the forward simulation and saving the state variables in the first step, we now need to select the stations for which we want to compute the time-reversed adjoint sources, and prepare them for use in the kernel simulation.

Choose the stations you want to use from the DATA/STATIONS file and copy them into the DATA/STATIONS_ADJOINT file, which uses the same format as the former file.

For example, in the DATA/STATIONS file we have the following list of available stations:

  AAE        IU        9.0292     38.7656    2442.0     0.0
  AAK        II       42.6390     74.4940    1645.0    30.0
  ABKT       II       37.9304     58.1189     678.0     7.0
  ABPO       II      -19.0180     47.2290    1528.0     5.3
  ADK        IU       51.8823   -176.6842     130.0     0.0
  ...
  XMAS       IU        2.0448   -157.4457      19.0     1.0
  XPF        II       33.6092   -116.4533    1280.0   100.0
  XPFO       II       33.6107   -116.4555    1280.0     0.0
  YAK        IU       62.0310    129.6805     110.0    14.0
  YSS        IU       46.9587    142.7604     148.0     2.0

Say we want to use the IU.ANMO, II.PFO, and IU.TUC stations as adjoint sources in the kernel simulation. Then, we copy these lines from the DATA/STATIONS file and paste them into the DATA/STATIONS_ADJOINT file:

  ANMO       IU       34.9459   -106.4572    1750.0   100.0
  PFO        II       33.6092   -116.4553    1280.0     0.0
  TUC        IU       32.3098   -110.7847     909.0     1.0

Then we need to generate these two adjoint sources by running the gen_adj_source.py script from the root folder. The usage for this script is as follows

      python3 gen_adj_source.py [station_file_names]

In order to generate the IU.ANMO, II.PFO, and IU.TUC sources, we need to provide the path to the associated output seismograms

      python3 gen_adj_source.py ./OUTPUT_FILES/IU.ANMO.BX*.ascii ./OUTPUT_FILES/II.PFO.BX*.ascii ./OUTPUT_FILES/IU.TUC.BX*.ascii

NOTE: The asterix * in the above command is used to include all the components associated with the station of interest. It is necessary to include all the component files for the kernel simulation to work.

This script then copies the relevant seismograms, renames them, and stores them in the SEM/ folder. To check that the adjoint sources were successfully generated, inspect this folder to check that there are three component files associated with each adjoint source. In the example case with the IU.ANMO, II.PFO, and IU.TUC sources, we expect to see the following files in the SEM/ folder:

  IU.ANMO.BXE.adj
  IU.ANMO.BXN.adj
  IU.ANMO.BXZ.adj
  II.PFO.BXE.adj
  II.PFO.BXN.adj
  II.PFO.BXZ.adj
  IU.TUC.BXE.adj
  IU.TUC.BXN.adj
  IU.TUC.BXZ.adj

In this section, we have looked at how to prepare the adjoint sources that will be used in the kernel simulation to back-propagate the wavefiled.

In the next section we will complete the final step and run the kernel simulation.

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Table of Contents

Part IV: Adjoint Simulations (Bonus)

Prepare the Adjoint Source(s)