I don't know how they picked the 15 events -, but otherwise the study looks fine.

I don't have a subscription to Nature Geoscience yet, but Tom Parsons posted the text on his web page.

It would be a tremendous amount of work to analyze 300 events at the 500+ global seismic stations. Even with just 15 events, it looks like close to 100,000 detections were tabulated.

They seem to see perhaps 10,000 extra events in the 5 hours after the surface waves, which must be highly statistically significant. The increase comes at the time of the Love waves, and bumps up even further with the Rayleigh waves, just what one might expect.

Roger, in the global catalogs, big earthquakes can mask small earthquakes for a while. This is why Pankow high-passed at 5Hz - to highlight little events and avoid the noise of distant big events. It might explain why you see 250 less rather than more.