Hi Don,
I would imagine that there is a whole range of accelerations associated with
earth movements from slow slides to avalanches and rock slides to fault plane
rupture.
Incidentally, it is hard to follow your discussion because you refer to accelerations
(which are usually given in g- units), but your units are in miles/second - a velocity
measurement. Acceleration has units of miles/sec/sec and is quite different
from velocity, being the first time derivative of velocity.
Rock bursts are a possibility in the Colorado earthquakes. The area is littered
with mines. A colleague of mine who grew up in the area says, however that
the specific location of these events is just a pile of sagebrush.
When I go hiking in the mountains of Colorado, however, it is necessary to
be careful where you step - there could be a hidden mineshaft anywhere.