There was a period where this happened all the time in Georgetown (D.C.). Something about cables reaching a certain age/stress level and the chemicals in the rubber insulation doing... blow-up-y things.

I imagine we're seeing the same thing here; some set of cables reaches its lifespan, plus load grows as people use more electronics, plus once a cable goes out, the load on neighboring cables increases, etc. etc.

It's incredible just how much more electricity we use than 25 years ago. I didn't realize it till I moved into a once-modern apartment built in the early '80s. There was one phone jack - in the kitchen. Naturally! Who would need a phone in the living room? And there wasn't even an outlet for that phone jack, because who needs to plug in a phone?

Add in computers, cell phones, chargers, home theatres, central A/C, etc. etc. The whole apartment had maybe 100-amp service; other than dedicated appliances, no one room had more than one 20-amp circuit.

but I haven't heard of incidents like this happening so often either -- I've lived in Boston for 11 years. These weird explosions have started recently -- the first time I heard of one was about two years ago, I think.