Fault slip

The relative displacement across a fault surface. Its vector and the fault normal determine an ideal double-couple seismic moment; a finite rupture can have spatially and temporally variable slip.

The observed separation of an originally correlated marker across a fault. Its value depends on marker geometry and measurement direction; apparent map separation is not automatically the full fault slip vector. Matching channel reaches, beds or dated surfaces supplies candidate piercing constraints.

Displacement across a fault per unit time, with the component and averaging interval specified. A long-term geological average and a short-term geodetic rate need not coincide.

A marker that starts with zero offset and accumulates displacement at a constant fault slip rate $v$ has age $t=d/v$. More generally $d={\int }_0^{t}v(s)ds$. The inferred age belongs to the establishment, abandonment or last resetting of that particular marker. A channel incised into an alluvial fan can be younger than the sediment it cuts. Uncertain channel correlation, erosion, distributed slip and time-variable rates require corresponding age uncertainty; a numerical ratio alone does not date a fan’s deposition.

The horizontal dip-direction component of displacement across a fault. The displayed expression assumes pure dip slip, with magnitude $D$ and fault dip $\delta$.

The vertical component of displacement between correlated markers across a fault. For pure dip slip of magnitude $D$ at fault dip $\delta$, the displayed formula applies. Erosion and ground slope can make surface fault scarp height different from throw.