bolting speakers to floor?

If they keep getting moved, yes, I would bolt them to the floor.

Blueswan and Jctubes are correct. Bolting your speakers to the floor may keep them from hitting you in the head during an earthquake but will screw up the sound the other 99.95 of the time. Sistrum platforms will transfer at a high speed, all extranous noise to ground. If properly sized your speakers will remain stable resting upon Sistrum Platforms and will at the same time become more musical.

My friend offers an engineered composite stand solution using (removable) adhesives. This assembly could be either spiked or bolted to the subfloor. If you use this solution you would not have to penetrate your speaker cabinet. An added benefit is that it increases the rigidity of the speaker. Contact me via email if interested.