To determine the fault slip most accurately you could use which of the following?

• A. the offset noted in a cross section drawn in the fault plane
• B. the age of fault rocks
• C. the current displacement at the surface
• D. the seismic moment estimate

Answer: (A)

Measuring how far markers that cut across the fault have been displaced along the fault plane gives the true fault-parallel slip. When you draw a cross-section in the plane of the fault, you can see the actual offset of those markers, which directly reflects how much movement occurred along the fault. This is more accurate because it uses physical displacement along the fault itself, not just surface impressions or later changes.

Relying on the age of fault rocks only tells you when faulting happened, not how much movement occurred. Current displacement at the surface can underrepresent total slip because slip may be distributed along the fault and later processes can erase or modify surface features. Seismic moment estimates the energy released during earthquakes and depends on assumed fault area and rock properties; it provides a slip value only for a given seismic event and may not capture the full, cumulative slip along the fault.