First: John, the following is not intended to be picking a fight with you ... Yours was just a convenient foil for a few points I wanted to make. Remember, I grew up in Silly Con Valley, I work in the industry, and I know what the infrastructure & politics look like from the trenches. Or holes in the ground, if you prefer.
"Apparently heavy manhole covers do not provide enough protection for such critical infrastructure."
They never have. I mean, they are only 100 lbs. That ain't heavy. A crowbar & a hacksaw & 3-4 minutes is all a reasonably fit human needs to commit this particular crime.
"And cables were cut in four different locations, which could mean that the network did contain a degree of redundancy."
A large degree of redundancy, at least for the most part. Most of the areas that went down were (by my estimation) semi-rural, with limited or no redundancy. SLV and Santa Cruz, especially.
"While Internet service is mostly used for casual purposes"
Mostly? Probably better than 98.5% ... Our Percentage[tm] (STR)
"telephone and emergency communications need to be better protected"
"and it should be possible to achieve this at relatively modest expense given the lower-bandwidth nature of the links."
Actually, the folks who need it have their own radio systems for emergencies. The problem here was that the public wire going into dispatch was down. In other words, the emergency folks couldn't get calls from the public. That's a difficult, but not impossible, nut to crack.
As a side note, what's the aggregate bandwidth for all the telephone calls happening in Silly Con Valley at this moment? How about just the calls between Santa Clara County & Sacramento? The numbers might surprise you.
"I trust the relevant authorities will treat this as a wake-up call, and act swiftly to ensure it cannot happen again."
I doubt it. It's been discussed on RISKS Digest on many occasions (Metacrawl comp.risks for the archives) ... And I personally have discussed the issue with City, County & State people here in California. Nobody who has any power has any idea of the issues involved. Management is not interested in RealLife[tm] security that will cost a bunch of money to fix, unless it's a lot more photogenic than a bunch of street-level padlocks.
"Because next time, it could really be terrorists."
There aren't any. So-called "terrorists" are weapons of mass distraction. (Queue amfM ...)