Oblique faulting slip vector

The figures above show a type of faulting known as thrust faulting, in which the overlying block moves upward and over the underlying block. Considered in 3 dimensions, however, the fault blocks could also move in-and-out of the page (screen) as shown by this perspective figure. 

Oblique faulting such as this can occur in a subduction zone when the downgoing plate is moving at an oblique angle (θ) relative to the overriding plate. The obliquity of the slip vector (D) in the fault plane of dip (δ) is measured by the angle (λ) that the slip vector makes with a horizontal line in the fault plane.