How to detect the extent of gravity crustal sources on terrestrial planets

Boundary analysis methods have been widely used in applied geophysics to properly delimit the edges of sources of potential field anomalies. Here, we revise some of the conventional edge-detection techniques in planetary application and adapt the Total Horizontal Derivative (THD) method to spherical harmonic gravity field models. After comparing the different methods on dataset generated from synthetic sources, we find that THD is more effective and simpler for defining the structural features of sources. We also show how to improve the signal-to-noise ratio and dampen the Gibbs effect, which is even more evident when computing the gradients of the gravity field. We first present and discuss global THD maps of Mercury, Moon, Mars and Venus, which contain information on the location of the main crustal sources and structures. Then, a specific boundary analysis performed in the Victoria quadrangle of Mercury reveals that the major tectonic structures bordering the high-Mg region identified on the surface cut the entire crust, down to the crust-mantle interface. Such analysis also confirms that the Victoria-Endeavour-Antoniadi fault array is instead characterized by shallow-dipping structures. This work shows that the THD is particularly effective for identifying buried impact basins, delimiting the extent of magmatic intrusions, and detecting shallow or deep tectonic structures on terrestrial planets.