It's a fault that's not always present - otherwise known as an 'intermittent fault' for example, a TV screen may work fine when first switched on, but as it 'warms up', it goes blank - indicating a 'dry-joint'
There are 3 main types of faults 1. Normal2. Strike slip3. Reverse(Thrust)In a normal fault the foot wall stays in place while the hanging wall moves DOWNWARDSIn a strike slip the tectonic plate(s)...