Disasters

Intrinsic to being a DM is the self-knowledge that we're making stuff up intentionally to mess with the players.  For example, the decision to implement a flood, or catch the party in the open with a blizzard.  It seems difficult to justify the random occurrence of an earthquake, without a pre-created table that allows the DM to say, "See, I rolled it!"

However, we don't hesitate to make something intrinsic to the world that's harmless.  No one says, "How dare that DM arbitrarily place a house here, by the side of the road?  The bastard!"  We expect houses.  They happen every day, unlike scenery-wrecking earthquakes.  And yet arguably, we have much evidence to show that earthquakes are inevitable.  In many parts of the world, a mild earthquake does occur with such frequency that a small one is treated blithely.

It isn't the earthquake itself that produces that sense of unfair use of godlike malevolence, is it?  If the setting takes place where earthquakes can happen (or floods, or forest fires, or whatever disruption you like), then we must assume the event depends on the DM's word, eventually.  Nyet?  The real contention is not with existence, but with timing.  This earthquake seems to have occurred awfully conveniently.  Wasn't it thoughtful of the DM to impose this flood just at the time we have to get across this particular river to reach this particular castle.  Hm ...

Even if we do build a table, to get around this timing issue by perhaps rolling on the table everyday (in game), the chance of something occurring is still arbitrary, isn't it?  And just how small should that chance be?  What is the chance of a 7.5 earthquake in downtown Los Angeles, as opposed to Memphis?  [yes, Memphis]  Is it the same?  What is the chance of a spring flood on the Mississippi, in a time before there were levees?  What about Holland?  No doubt, very high.  But how high?  Are you able to judge?  And what if you say there's a 2 in 3 chance ... is that fair to your players, just because you made the determination ahead of time?  That is still arbitrary.

We can go crazy trying to make sure that floods, earthquakes, volcanic eruptions, plagues, famines and other catastrophic events only occur when they're not a part of the narrative; but in game, when would that be?  Never, I should think.  Which I'm guessing is close to what you've decided, particularly if you've ever tried implementing any of these moments.  A second, or a third big event like this is going to seem, well, a bit coincidental, don't you think?

Personally, if it suits the campaign, I say fuck it.  Have an earthquake.  Wreck the city.  Drown a countryside.  You could start every session by selecting two twenty sided dice, like a big ritual, rolling them both in front of the players and saying, "If they both come up 1s, some pretty bad shit is going to come down."

That's fair, isn't it?