Your answer would've been pedantic only if I had not asked that specific question! And, it was certainly not more than I wanted to read. I think you tend toward terseness sometimes more than necessary, John. But I always figure it's 'cause you're busy.

So the explanation I gave for the rarity of earthquake-caused mine failures is consonant with reason #2, though my reference to a "free-surface" was incorrect. Reason #1 would not come into play at the relatively shallow depths of mines.

One additional question, though (I'll Google "free surface correction"!): You state that surface waves' energy "decays with the squre root of distance," and that body waves' energy decays INVERSELY with distance. You may have mis-spoken there, as the decay increases with distance, so that the relationship is direct, not inverse (I'm asking, not lecturing). But then you state that the decay of body waves is more rapid. A variation based on square root should be slower than one that is direct, no? Did you intend to state that surface waves' energy decays with the SQUARE of distance?

Thanks John!

Mike W.
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