Fault-population statistics at the Valles Marineris Extensional Province, Mars: implications for segment linkage, crustal strains, and its geodynamical development

Abstract

The length distribution of normal faults and grabens in the Valles Marineris region of Mars reveals the importance of fault linkage on fault-length data sets. Fault-length data for the normal-fault segments produce a continuously curving distribution on a cumulative-length vs. frequency plot, assuming that the faults all slip independently, with an approximate slope of −2 for lengths 30< L<200 km. When the Martian fault lengths are modified to account for their interaction and linkage, a more shallowly sloping (approximately −1) distribution is produced for fault lengths 30< L<300 km, reflecting the greater importance of large linked faults in accommodating the regional strains. Incremental-frequency and R-plots of fault lengths demonstrate variations in fault density with linkage and the importance of considering grabens as single structures. Unlike some terrestrial earthquake data, the Martian fault population does not reveal persuasive evidence for a small-to-large fault transition associated with lithospheric thickness or rheology, or with long-term strain. However, the decoupling of maximum fault displacement and length over the full range of the data is consistent with the dependence of displacement-size scaling on fault segment aspect ratio, rather than on the total fault length. The important inverse dependence of population power-law exponent and natural inhomogeneous fault strain, obtained previously from terrestrial fault sets and fault-growth simulations, is supported by using this Martian fault array.