[downut]

My wife and I spelunked quite a lot in the East, especially north GA and TN. I thought the cramped muddy passages were a lot of fun, ditto climbing up waterfalls. Prusiking straight up a 100', NBD. We're from FL and GA. Nice stable ground.

And then we lived through a dozen or so Bay Area earthquakes, including '89. I was able to get a ballpark estimate of the speed of the waves by counting the seconds it took them to move through the grasslands on the Bay side of NASA Ames (I was jogging, ground fell away from my feet). Measured the distance, and the result (I forget now), was within 20%.

Gotta different perspective now about how stable rocks are.