For an entire year preceding the Tonga "eruption", only 1 quake was recorded on that mountain, a 4.7 on 12/18/21.

As for aftershocks, there have been 2-

-A 1.0 only 12 minutes after the "eruption"

-Another 1.0 about a day and a half later.

I'm sure the seismologists have a theory on how you get this type of volcanic activity without the usual associated fore/after tremors.