Centers of tectonic activity in the eastern hemisphere of Mars

We compiled a paleotectonic map for the eastern hemisphere of Mars to determine if extensional tectonic features (graben) are radial or compressional tectonic features (wrinkle ridges) are concentric to centers of tectonic activity defined by axisymmetric stress fields. Using a vector analysis technique all latitude and longitude points (1° bins) are tested to see if they lie on great circle extensions of extensional structures (the plane defined by the maximum and intermediate principal stresses) or great circle perpendiculars to compressional structures (the plane defined by the maximum and minimum compressional stresses). Centers of tectonic activity are defined as 5° areas whose concentrations of great circle extensions of tectonic features are statistically significant (e.g., 3σ or 7.4σ for large populations) and therefore are not the result of random noise. Our paleotectonic investigation has identified four statistically significant centers of tectonic activity within the eastern hemisphere: Elysium, Hadriaca/Tyrrhena-Hellas, Isidis-Syrtis, and Arabia Terra. Two of these centers (Hadriaca/Tyrrhena and Isidis-Syrtis) meet the 7.4σ statistical criteria and thus represent primary centers of tectonic activity with axisymmetric stress fields. The remaining two meet the 3σ statistical criteria and thus are defined as secondary centers of tectonic activity. Because the structures that define the centers extend over 80° of the planet the defined centers of tectonic activity are regional in character and related to modified impact basins or volcanic centers (all are more limited in extent than the Tharsis stress system that extends over the entire western hemisphere). The observation that statistically significant centers of tectonic activity are quantifiably and statistically identified argues that the crust and lithosphere of the eastern hemisphere at a regional scale is not dominated by regional inhomogeneities and anisotropies.