The displacement-length ratio for the central composite graben in Valles Marineris, inferred from topography and likely stratigraphic offsets to be Dmax/L≈4--6¿10-3, is consistent with the scaling relations derived from terrestrial faults and grabens that also demonstrate a systematic variation in displacement with position along the structure. The large, 10-km depth in central Valles Marineris is therefore not unusual, but rather, should be expected for a fault system 2240 km long. In contrast, existing measurements of throw along the numerous shallow radial grabens in Tharsis, while apparently inconsistent with the scaling relations, demonstrate the importance of recognizing mechanical-segment length along linked or echelon graben sets. Faults on other planetary surfaces should scale with their terrestrial counterparts as long as they extend substantially deeper than the gravity-dependent near-surface rock-mass zone (~1 km for Earth, ~2.5 km for Mars).¿ 1997 American Geophysical Union