Occam razor here would be internal fighting about Russia factions. The cost/benefit of getting discovered vs not here are not in favor of any external NATO-ish player since there is already enough cohesion, while getting caught would be catastrophic. Literally little to gain and all to lose. And the temporal difference between the reported seismic events is also against the idea of an external country doing it: you wouldn't wait that long between events since it would massively increase the risk of getting discovered. If you are doing a proper sabotage you'd have events close to each other (30m or so) or very spread (days away)

The US/NATO/Ukraine has 100% control over the media narrative in the West, it would be impossible to "get caught". Anything that comes out that is against the desired narrative is simply waved away as Russian propaganda.