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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If the body-waves are observable does that mean a magnitude could be estimated? Given that the Rayleigh waves are incredibly high amplitude I suppose the surface-wave magnitude will grossly overestimate the true magnitude.
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Good questions! A simple body wave M may underestimate and simple surface wave M may overestimate, but a waveform-based moment-tensor inversion type M for the surface waves may confirm shallow depth and produce a usefully accurate M...
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Hi Guys, loving this work. Am sure you have seen this, but in case it was missed, there is a active on Mayotte. Must have been real close.
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Actually, maybe not as close. Looks like arrival may be slightly later, by ~1min, than the station on Madagascar?
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No, I think the arrivals on the are earlier and correspond well to the P1 and P2 events on the SBV seismogram in Madagascar! And there are more events on the . So the source is likely much closer to Mayotte.
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Some more evidence here. I remember seeing a talk at EGU a few years ago by Goran Ekstrom (who now partly runs the Global CMT project) and he showed their automatic surface detections show additional events from landslides, glacier calving etc not detected by NEIC etc
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So I wondered if GCMT has detected this event since it has lots of energy at long periods.
And what do you know, here it is! It's given a magnitude of 5.0, which presumably is Mw or Ms. ldeo.columbia.edu/~ekstrom/Resea
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and here are those seismic surface waves rolling across Canada, ~13,000 - 16,000 km distant!
Wooooaaahhhhhh! That's absolutely amazing. Surely the equivalent magnitude is greater than 5.0.
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When I first saw how widely observed the event was I was trying to get my head around what type of event (which was at the time I believed was non-seismic) must have been >M5.5 - I did find it at Hawaii too, which is an close to antipodal as you can get (17,700km or 158 degrees)
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