Several groups do this kind of work from various approaches. Some break rocks, some grind already planed rocks, some work with other materials.

Prior to a through-going break, there are acoustic emissions (see work of Lockner et al., for example). AE are just small earthquakes. Other work has seen various deformation, heat, and EM signals as the rock is about to break.

However, the region acting up before the main rupture, which is known as the nucleation zone, could be similar in size to the eventual rupture, or more likely it is the size of the smallest possible rupture, perhaps just meters across. If nucleation zones are small, it may well be that many are popping off every hour, and there is no way to know from observing nucleation whether an M1 or an M8 is coming.

Have to run to dinner, sorry about a fragmentary answer.