Fissure and Fault line

Fissure noun - An irregular usually narrow break in a surface created by pressure.

Fault line and fissure are semantically related. In some cases you can replace phrase "Fault line" with "Fissure", this terms are similar.

Fault line noun - (geology) line determined by the intersection of a geological fault and the earth's surface.

Fissure and fault line are semantically related. You can use "Fissure" instead a noun phrase "Fault line".