Unless water is introduced, whereupon they fail:

"Oil Drilling into a Salt Dome: Catastrophic Failure: Evidence Lake Peigneur 1980 Disaster BP"

https://www.youtube.com/watch?v=OhwjSI3UOIw

This is why fracking is associated with earthquakes. Salt mining has a long and well-documented history of damaging subsurface and consequently surface structure, especially in 19th-century England.

Frackers were "whistling past the graveyard" by denying that fracking caused earthquakes. They've essentially replicated the history of salt mining associations and corporations who destroyed homes and even towns in their rabid search for salt profits:

"Salt: A World History" by Mark Kurlansky

"Northwich sinks!":

http://jsbookreader.blogspot.com/2011/09/northwich-sinks.htm...

"Extraction of Bastard Brine in Northwich":

http://www.cheshirebrine.com/history/extraction-of-bastard-b...

You certainly wouldn't want to frack in the salt dome, but you are conflating entirely separate issues. No one is pumping ultra-high pressure drill fluid into waste repos.