With massive amounts of rock rubbing against other massive amounts of rock, it does seem reasonable that massive amounts of static electricity could be generated. And animals may sense changes in the electrical field around them and get nervous.

A test would be to see which ways dogs align themselves when they poop just prior to an earthquake. If it changes from normal, it may sense a change in the electrical fields.

http://www.nbcnews.com/science/do-dogs-possess-poop-compass-other-weird-science-questions-2D11849668

"One of the dogs participating in a study of the canine "inner compass" does its business in Mülheim an der Ruhr (City on the River) in Germany. Researchers found that dogs seem to prefer to align themselves with magnetic field lines when they defecate."