Faulting and fault scaling on the median valley floor of the trans-Atlantic geotraverse (TAG) segment, ∼26°N on the Mid-Atlantic Ridge

A quantitative assessment of faulting on the median valley floor of a slow spreading ridge is accomplished through the analysis of high-resolution DSL-120 sidescan sonar and coregistered bathymetric data from the TAG segment near 26 degrees N on the Mid-Atlantic Ridge. At this location, faulting is exposed within a 3-5 km wide ridge-parallel zone lying asymmetrically on the eastern half of the median valley floor. Mapped faults have a normal sense of displacement, are < 2 km in length, and accommodate similar to 1.5% brittle extension. Evidence of fault linkage within the fault population includes kinked and bent fault traces in map view, the development of overlapping fault segments or relay ramps, and the presence of multiple local maxima in the displacement-distance profiles of some faults. Faults have a slight tendency to dip to the east, off outward relative to the valley axis, and exhibit little symmetry of fault dip about the axis of the faulted zone or any other ridge-parallel line. Faults exhibit a roughly linear relationship between maximum fault throw and fault length, with a mean ratio of 0.030 for the population. Regression of length-frequency data indicates a power-law distribution, with an exponent of 1.64-1.96, demonstrating that fractal populations can exist in the mid-ocean ridge environment. The fractal nature of this length-frequency distribution and the ratio of maximum fault throw to fault length differ significantly from those described previously for populations of larger abyssal hill faults in the fast spreading environment, where the distribution is exponential and the throw-to-length ratio is similar to 5 times lower. These results suggest that the scaling of fault populations in the midocean ridge setting may vary as a function of spreading rate and/or fault size.