slickenside
noun
slick·en·side ˈsli-kən-ˌsīd 
: a smooth often striated surface produced on rock by movement along a fault or a subsidiary fracture —usually used in plural
Example Sentences
Recent Examples on the Web The 150-foot-long and 75-foot-tall surface is one of the largest chert slickensides exposures in California. 
Thomas Graham, SFChronicle.com, 28 June 2018
Thomas Graham, SFChronicle.com, 28 June 2018 Word History
Etymology
English dialect slicken smooth (from slick entry 1) + English side
First Known Use
1822, in the meaning defined above