This electronic supplement contains figures showing tangential velocity spectra for four Oklahoma Mw 5 earthquakes. These sixteen figures illustrate source corner frequency estimation from tangential velocity spectra at four stations for four Mw 5 Oklahoma earthquakes. All time histories have leaky-mode surface waves in the P and S waveforms (see, e.g., Fig. 2 in the main article). Surface-wave peaks in spectra are labeled along with the corner frequency peak (fc) and important site resonances/amplifications. The leaky-mode surface waves and site resonances contaminate the source spectral shape and must be identified. These spectral shape alterations may increase the difficulty in estimating corner frequencies using any method. High-pass filtering of recordings can appear in these spectral plots as sharp decreases in spectral amplitude, usually below 0.1 Hz.
13 September 2016 Mw 5.8 Pawnee, Oklahoma, earthquake: Figures S1–S4 show consistency of spectral shape and corner frequency peak at four stations.
6 November 2011 Mw 5.7 Prague, Oklahoma, earthquake: Figures S5 and S6 show consistency of spectral shape and peaks, and Figures S7 and S8 show degrading effects of noise and site response to spectral shape but still a consistent corner frequency with larger uncertainty.
13 February 2016 Mw 5.1 Fairview, Oklahoma, earthquake: Figure S9 shows a fairly clean spectral shape with some site response above 5 Hz. Figures S10–S12 show progressive degradation due to site response and noise. Site response appears in both signal and pre-event noise spectra, making it easier to identify. Corner frequency is consistent for first three records with larger uncertainty.
7 November 2016 Mw 5.0 Cushing, Oklahoma, earthquake: Figures S13–S15 show a consistent spectral shape and some added noise near 3 Hz. Figure S16 is for a station 189 km from the event but still consistent with closer-in stations in Figures S13–S15. This shows that regional attenuation is not distorting the spectral shape significantly when the corner frequency is near 1 Hz (see the Approach section of the main article for details and discussion of this effect). In Figure S16 a site resonance near 3 Hz complicates the interpretation.
Figure S1. Transverse Fourier velocity spectra of the signal (red) and pre-event noise (blue) from OK031 for the Mw 5.8 Pawnee, Oklahoma, earthquake. The leaky-mode surface-wave peak is indicated by the asterisk and label.
Figure S2. Similar plot as Figure S1 at OK914 for the Mw 5.8 Pawnee, Oklahoma, earthquake.
Figure S3. Similar plot as Figure S1 at OK915 for the Mw 5.8 Pawnee, Oklahoma, earthquake.
Figure S4. Similar plot as Figure S1 at OK030 for the Mw 5.8 Pawnee, Oklahoma, earthquake (same plot as Fig. 3 in the main article).
Figure S5. Transverse Fourier velocity spectra of the signal (red) and pre-event noise (blue) from OK010 for the Mw 5.7 Prague, Oklahoma, earthquake. The leaky-mode surface-wave peak is indicated by the asterisk and label.
Figure S6. Similar plot as Figure S5 at W35A for the Mw 5.7 Prague, Oklahoma, earthquake.
Figure S7. Similar plot as Figure S5 at OK009 for the Mw 5.7 Prague, Oklahoma, earthquake. A major high-frequency site response/amplification peak is also labeled.
Figure S8. Similar plot as Figure S5 at OK001 for the Mw 5.7 Prague, Oklahoma, earthquake.
Figure S9. Transverse Fourier velocity spectra of the signal (red) and pre-event noise (blue) from U35A for the Mw 5.1 Fairview, Oklahoma, earthquake. The leaky-mode surface-wave peak is indicated by the asterisk and label.
Figure S10. Similar plot as Figure S9 at OK009 for the Mw 5.1 Fairview, Oklahoma, earthquake. A major high-frequency site response/amplification peak is also labeled.
Figure S11. Similar plot as Figure S10 at OK035 for the Mw 5.1 Fairview, Oklahoma, earthquake.
Figure S12. Similar plot as Figure S10 at OK032 for the Mw 5.1 Fairview, Oklahoma, earthquake.
Figure S13. Transverse Fourier velocity spectra of the signal (red) and pre-event noise (blue) from OK031 for the Mw 5.0 Cushing, Oklahoma, earthquake. The leaky-mode surface-wave peak is indicated by the asterisk and label.
Figure S14. Similar plot as Figure S13 at OK915 for the Mw 5.0 Cushing, Oklahoma, earthquake.
Figure S15. Similar plot as Figure S13 at OK033 for the Mw 5.0 Cushing, Oklahoma, earthquake. A major high-frequency site response/amplification peak is also labeled.
Figure S16. Similar plot as Figure S15 at OK035 for the Mw 5.0 Cushing, Oklahoma, earthquake.
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