Boom and Shake detect tiny local EQ

EQ magnitude 2.5 at 4 km depth centred 9.6 km away was detected by both instruments (upper is Boom, lower is RS1D):


This has happened again. This time it was magnitude 3.2, 5 km depth, 11 km away:

Notice that the Shake (upper plots) detected the waves shortly before the Boom and the Boom waves were spread over a wider frequency range.
Using the IASP91 model, the travel times were 2.08 s for P waves and 3.59 s for S waves.
My hypothesis is that the S waves made the building shake and that this is what the Boom is sensing.
This would explain the delay in arrival time and the wider spectral spread, I think.

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