Why do some rock layers around salt domes form circular depressions?

The circular depressions often observed around salt domes are known as rim synclines. These features form as a direct consequence of the salt's movement during the development of the salt dome.1

As thick salt deposits become gravitationally unstable beneath denser sedimentary strata, the salt begins to flow from the surrounding areas toward a central point to form a salt pillow or dome. As the salt migrates away from the surrounding region to feed the growing central mass, the area from which the salt originated subsides, creating a circular depression or trough known as a rim syncline. This process is part of the broader evolution of diapiric structures, where the upward movement of plastic material like halite causes the overlying rock layers to dome, fracture, and subside in the surrounding zones.1