This is the recording of the ~09:30 UTC Southern Indian Ocean event from Kilima Mbogo, Kenya. The signal has had a highpass filter applied to it at 0.01 Hz, 0.05 Hz, 0.1 Hz & 0.2 Hz respectively. As can be seen the signal is very low frequency
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Narrowing the location down the origin area appears to be in the region of the Comoros/Mayotte. A news article today suggests that the Mayotte swarm which began earlier this year may indeed be magmatic-related. Was this event a submarine volcanic eruption? lejournaldemayotte.yt/seismes-carte-
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Confirmation of location places it near the Comoros. Arrival times from FOMA (Southern Madagascar) & KMBO (Kenya) are almost identical, with FOMA perhaps slightly closer (<1 minute prior arrival time) - sadly I cannot narrow down the arrival time any better for FOMA.
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Closest easily available BRB seismic station is GE SBV in north Madagascar.
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SBV, like the other stations, shows long monochromatic signal with ~17s period (mono-freq Rayleigh waves?). But filtered above 1Hz SBV (lower plot) also shows seismic(?) signals from repeating sources, with some ~50s apart. Maybe some large, shallow, oscillating volcanic source?
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Assuming epicenters just east of Mayotte, high-frequency (lower trace) arrivals at SBV correspond well to P & S from at least 3 sources resembling tectonic earthquakes, & the long period wave train (upper trace) correspond to the set of Rayleigh surface waves from these sources.
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So in other words some event, of uncertain type but perhaps volcanic in nature, caused three quakes in quick succession & generated an ultra-low-frequency signal which was detected around most of the world?
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The low frequency signal seems to be normal Rayleigh surface waves, but their large amplitude relative to the P and S body waves probably indicate a very shallow source.
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Interesting that there's very little of the long-period signal on the east-component. Wonder if this can tell us something about the radiation pattern and/or propagation direction of the "failure". Wonder if there are strong T-phases on hydroacoustic sensors?
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The traces are rotated so that the magenta trace is transverse to the direction from the station to the Mayotte region. This helps identify the long-period signal as Rayleigh waves, with elliptical motion on the vertical (cyan) and longitudinal (yellow) traces.
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Please can you tell me what frequency in Hz these waves were ringing at? I know they were on a 17s repeat, but what was their Ξ½?
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The long wavetrains with about 17s period oscillations would have a frequency of about 0.06Hz
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