foible suggests a weak point that is slight and often amusing, manifesting itself in eccentricity rather than in wrongdoing: the foibles of an artist.
A fault plane is the plane that represents the fracture surface of a fault.
By definition, the hanging wall occurs above the fault plane and the footwall occurs below the fault.
Because of friction and the rigidity of rocks, they cannot glide or flow past each other easily, and occasionally all movement stops.
Since faults do not usually consist of a single, clean fracture, geologists use the term fault zone when referring to the zone of complex deformation associated with the fault plane.
The two sides of a non-vertical fault are known as the hanging wall and footwall.
To date a radioactive rock, geologists first measure the “sand grains” in the top glass bowl (the parent radioisotope, such as uranium-238 or potassium-40).