Free-oscillation spectrograms

Currently recording the aftermath of :
2017-09-08 04:49:17 UPDATED: (M8.0) OFFSHORE CHIAPAS, MEXICO 15.0 -93.8 (43a6c)
(Source: USGS email service)

           
Remark: The persistent resonance at 2.0 mHz is from the sensor in the gravimeter. The frequency variation along the trace appears to correlate with air pressure:
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