This material addresses an error source in the code of the MATLAB based shear wave splitting software package SplitLab (Wüstefeld et al., 2008). The error causes a wrong temporal alignment of the single traces (Z, N, E components) of one earthquake relative to each other. The resulting wrong horizontal particle motion and wrong waveforms in the ray (LQT) coordinate system lead to a wrong shear wave splitting measurement.
Here we provide a test with seismological data for your personal SplitLab version and a suggested correction
of the SplitLab function getFileAndEQseconds.m for the publicly available SplitLab versions.
This modified SplitLab function is also introduced by StackSplit (Grund, 2017) version 3.0 during the installation process.
If you make use of this material, please cite the relating publication in which this issue is described in detail:
Fröhlich, Y., Grund, M. & Ritter, J. R. R. (2022). On the effects of wrongly aligned seismogram components for shear wave splitting analysis. Annals of Geophysics, volume 65. https://doi.org/10.4401/ag-8781.
Furthermore you can cite the Zenodo DOI given above.
-
Folder
00_SAC_files- Subfolders corresponding to some of the filename formats supported by SplitLab
- Vertical (Z), North (N), East (E) components as SAC-files
- Sampling interval: 0.05 s
-
Folder
01_your_results- Until now empty
- Output folder for your own shear wave splitting measurement results
-
Folder
02_SL_diagnosticplots- SplitLab diagnostic plots for comparison (PDF and PNG format)
- Without (
*_wrong) and with (*_correct) consideration of the milliseconds (msecs)
-
Folder
03_SL_getFileAndEQseconds- Modified SplitLab function
getFileAndEQseconds.m - Publicly available SplitLab versions (
*_SLxyz)
- Modified SplitLab function
0) Choose one of the three provided examples (see subsection "Details on earthquakes and traces")
- Stuttgart (STU), 2001/06/29 (2001.180) 18:35 (UTC)
- Stuttgart (STU), 2009/11/14 (2009.318) 19:44 (UTC)
- Échery (ECH), 2018/08/28 (2018.240) 22:35 (UTC)
1) Set up SplitLab project
Click for single steps
- General
- Seismic data directory
- Go to folder
00_SAC_files - Select subfolder with preferred filename format
- Go to folder
- Output directory
- Select folder
01_your_results
- Select folder
- Seismic data directory
- Station
- Stuttgart
- Station code: STU
- Network code: GE
- Latitude in deg North: 48.771
- Longitude in deg East: 9.194
- Échery
- Station code: ECH
- Network code: G
- Latitude in deg North: 48.216
- Longitude in deg East: 7.159
- Stuttgart
- Event window
- Moment magnitude: 6.00 to 9.75
- Epicentral distance in deg: 90 to 140
- Hypocentral depth in km: 0 to 1000
- Start and end date: corresponding to the date of the chosen example / earthquake
- Phases
- Earth model: IASP91
- Phases: (at least) SKS, SKKS, PKS
- Find files
- File search string: corresponding to the chosen filename format
- Offset: 0 s
- Tolerance: 420 s
2) Perform shear wave splitting measurement
- Bandpass filter: 0.020 Hz (lower corner), 0.20 Hz or 0.15 Hz (upper corner)
- Coordinate system: LQT
- Phase: SKS
3) Compare your result / SplitLab diagnostic plot with the provided diagnostic plots
- Folder
02_SL_diagnosticplots: diagnostic plots for wrong and correct relative temporal alignment - Shape of the E-N particle motion: elliptic or linear?
- SKS phase-related signal on the transverse (T) component: yes or no?
Click for more information
Stuttgart (STU), 2001/06/29 (2001.180)
- Earthquake
- Date: 2001/06/29 (2001.180)
- Time: 18:35:51 (UTC)
- Moment magnitude: 6.1
- Source region: Southern Bolivia
- Hypocentral depth: 274 km
- Backazimuth: 246.5 deg
- Epicentral distance: 95.29 deg
- Traces
- msecs of start times: North = 0027, East = 0927, Vertical = 0627
- Relative msec difference: |E-N| = |900|, i.e., |18| samples
Stuttgart (STU), 2009/11/14 (2009.318)
- Earthquake
- Date: 2009/11/14 (2009.318)
- Time: 19:44:29 (UTC)
- Moment magnitude: 6.2
- Source region: Jujuy province, Argentina
- Hypocentral depth: 220 km
- Backazimuth: 244.5 deg
- Epicentral distance: 98.15 deg
- Traces
- msecs of start times: North = 0145, East = 0895, Vertical = 0945
- Relative msec difference: |E-N| = |750|, i.e., |15| samples
Échery (ECH), 2018/08/28 (2018.240)
- Earthquake
- Date: 2018/08/28 (2018.240)
- Time: 22:35:13 (UTC)
- Moment magnitude: 6.5
- Source region: Mariana Islands
- Hypocentral depth: 60 km
- Backazimuth: 40.1 deg
- Epicentral depth: 106.00 deg
- Traces
- msecs of start times: North = 0950, East = 0000, Vertical = 0950
- Relative msec difference: |E-N| = |950|, i.e., |19| samples
- Folder
03_SL_getFileAndEQseconds- SplitLab 1.0.5 (
*_SL105) (Wüstefeld et al., 2008) - SplitLab 1.2.1 (
*_SL121) (Porritt, 2014) - SplitLab 1.3.0 (
*_SL130) (Creasy, 2020) (based on SplitLab 1.2.1) - SplitLab 1.9.0 (
*_SL190)
- SplitLab 1.0.5 (
- The filename part
xyzorx.y.zindicates the SplitLab version - Go to the folder
~/SplitLabx.y.z/Tools/on your computer - Rename the existing function
getFileAndEQseconds.m, e.g.,getFileAndEQseconds_original.min this folder - Copy and past the modified function
getFileAndEQseconds_SLxyz.minto this folder - Remove the end of the filename
_SLxyz - Assign earthquake catalogue and seismological data in your SplitLab project
| release | Zenodo DOI |
|---|---|
| dev | reflects main branch |
| v1.0 |  |
For details on the single releases see the changelog.
For bug reports, suggestions, or recommendations feel free to open an issue or submit a pull request directly here on GitHub.
Bowman, J. R. & Ando, M. (1987). Shear-wave splitting in the upper-mantle wedge above the Tonga subduction zone. Geophysical Journal International, volume 88, issue 1, pages 25-41. https://doi.org/10.1111/j.1365-246X.1987.tb01367.x.
Creasy, N. M. (2020). SplitLab version 1.3.0. available at https://github.com/nmcreasy/SplitLab1.3.0.
GEOFON Data Centre (1993). GEOFON (GeoForschungsNetz). Deutsches GeoForschungsZentrum (GFZ), Seismic Network. https://doi.org/10.14470/TR560404.
GEOSCOPE (1982). French Global Network of broad band seismic stations. Institut de physique du globe de Paris (IPGP) & Ecole et Observatoire des Sciences de la Terre de Strasbourg (EOST). https://doi.org/10.18715/GEOSCOPE.G.
Grund, M. (2017). StackSplit - a plugin for multi-event shear wave splitting analyses in SplitLab. Computers & Geosciences, volume 105, pages 43-50. https://doi.org/10.1016/j.cageo.2017.04.015. versions 1.0, 2.0, and 3.0 available at https://github.com/michaelgrund/stacksplit.
Porritt, R. W. (2014). SplitLab version 1.2.1. available at https://robporritt.wordpress.com/software/.
Silver, P. G. & Chan, W. W. (1991). Shear wave splitting and subcontinental mantle deformation. Journal of Geophysical Research, volume 96, issue B10, pages 16429-16454. https://doi.org/10.1029/91JB00899.
Walsh, E., Arnold, R. & Savage, M. K. (2013). Silver and Chan revisited. Journal of Geophysical Research: Solid Earth, volume 118, issue 10, pages 5500-5515. https://doi.org/10.1002/jgrb.50386.
Wüstefeld, A., Bokelmann, G., Zaroli, C. & Barruol, G. (2008). SplitLab: A shear-wave splitting environment in Matlab. Computers & Geosciences, volume 34, issue 5, pages 515-528. https://doi.org/10.1016/j.cageo.2007.08.002. version 1.0.5 available at http://splitting.gm.univ-montp2.fr/ and version 1.9.0 available at https://github.com/IPGP/splitlab.