faultline

/F AO1 L T L AY0 N/
noun
  1. 1

    The line formed by the intersection of the plane of a fault with the surface of the Earth

  2. 2

    (by extension) A minor split (in public opinion etc) that may develop into something larger

Source: https://en.wiktionary.org/wiki/fault%20line, https://en.wiktionary.org/wiki/faultline