As Paul explained, it's a large cave in North-West Nelson, New Zealand. Now the bottom half of a 1200m deep 2-3 day through trip. As well as good earthquakes (& good caves), NZ also does good nettles - the sort that can kill a man/horse, and makes english nettles look rather prim & pretty. The...

In general, sub-surface shaking is less than on the surface. Think of how much the top of a jelly shakes compared with the inside, away from the free surface. A large EQ in NZ (1940s?) wasn't felt much in a deep mine on the west coast, but those looking up the shaft could see daylight being...