Definition - What does Antithetic Fault mean?
Antithetic Fault is a minor crack or a fault whose sense of displacement is completely opposite to its associated major fault. These kinds of faults usually occur in sedimentary rocks and are associated with rotation. They are generally found in areas where the occurrence of normal faulting is high. Antithetic is derived from the Greek word "antithethemi" which simply means set against.
Petropedia explains Antithetic Fault
The formation of antithetic faults seems to be more or less parallel to the major fault. Synthetic and antithetic faults are part of “Growth Faults” which have lot of significance on stratigraphy, E&P industry and structural geology. Antithetic faults help in explaining the lateral thickness variation of sedimentary rock basins near the faults. They also help in the development of updip angle of rocks and downdip angle of rocks over a long period of time. These angular dips are important parameters when determining the presence of hydrocarbons in a reservoir. The updip area on the downthrown block becomes a primary target for E&P activities as it has antithetic and synthetic faults along with rollover anticlines. These faults form the structural traps within the rocks and thus, trap hydrocarbon liquids.