How strong are the strongest Ioquakes? Jupiter's moon Io is the most geologically active celestial body in our system. It has the strongest volcanoes and quakes. Of course in practice these quakes wouldn't be as dangerous as on Earth for someone on the surface due to Io's low surface gravity (0.183 g). Let's ignore that however, do we know some of the strongest Ioquakes, what would be their magnitude on the Richter scale?
I did not find any Richter-scale numbers for Io, probably since there are no direct measurements yet, or how atmosphericprisonescape puts it:

Nobody put a seismometer on Io yet, so we don't know. The only other bodies except for Earth, where seismometers have been placed so far are the Moon and Mars.

But I found some interesting comparison at on NASA's SpacePlace: High Tideo on Io!

On planet Jupiter's moon Io (&quot;EYE-oh&quot;), the ground itself moves up and down like an elevator taking people to the top and bottom of a 30-story building!

This would mean amplitudes for the tidal waves (and therefore also for regular Io-quakes) of ${\rm 60 \dots 90 m}$! I am not sure though where that number comes from, but it compares with ${\rm 0.2m}$ tidal waves of the Earth's solid crust which is not really measurable on Earth, except with interferometers like e.g. GEO600.
References

Wikipedia on Tital Heating of Io
Are planet-destroying quakes possible or observable?