Several Kilometers of Global Contraction on Mercury: A Sample-Size Independent Assessment of Fault Strain

Mercury underwent global contraction due to the sustained cooling of the planet. Positive-relief landforms, found widespread across Mercury, are thought to be the surface expressions of thrust faults accommodating the contraction. Disagreement exists in the literature on the amount of contraction, with estimates of radius change ranging from ∼1 to 7 km. These differences solely arise from the method used to estimate the fault population strain, which relies on the number of structures. Here, we adapt a previous framework by which the continuum approximation to shortening strains can be determined from fault length and displacement statistics for an incompletely sampled fault population. We apply this method to three data sets that sample different numbers of faults. Our results show that even for conservative fault parameters, 2 to 3.5 km of radial contraction are returned, irrespective of the data set used, and thus resolve the debate on the amount of global contraction on Mercury.