Length and self-similar clustering analyses of Ganymede&#8217;s grooves
Authors: Lucchetti Alice , Rossi Costanza , Mazzarini Francesco , Pajola Maurizio , Pozzobon Riccardo , Massironi Matteo , Cremonese Gabriele 
Published: October 2020

IntroductionGrooves represent the evidence of tectonic activity that deformed Ganymede surface during its geologic evolution and may have played a key role in the possible connection between surface and the subsurface ocean. In this context, the analysis of Ganymede deformed surface could provide hints regarding its interior, as well as its ice shell&#8217;s mechanical behaviour. Indeed, faults distribution and fault populations on icy satellites can reveal insights into the evolution of their surface that cannot be gained with other techniques. In particular, statistical characterization of fault-population attributes, such as length and clustering, are fundamental means to explore deformation rates, stress transmission modes, rheology of the medium, and mechanical layering [1,2,3,4,5]. The fractal analysis has been used in terrestrial planets studies to determine the thickness of the fractured crust [e.g., 6,7,8]. In the same fashion, on icy satellites the exploration of the depth at which fractures penetrate the icy layer could be constrained investigating the main characteristics of fault populations, such as length size-distribution and clustering [9]. In this work, we analyse the grooves&#8217; length and spatial distribution to estimate the potential thickness of the icy crust above the deep ocean required to develop densely populated structures at the surface of Ganymede (i.e. the grooves).Dataset and MethodsOur analysis is based on the regional scale grooves mapping [10] that represents a useful dataset to improve the knowledge of the tectonic evolution of the satellite and to recognize the main characteristics of these features. Thanks to these comprehensive grooves mapping dataset, we were able to select four different type-regions located on the equatorial belt of Ganymede. The choice is based on the high density and homogeneous spatial distribution of the grooves located on those regions, which is necessary for the following analysis. The four datasets are in selected regions located in Uruk Sulcus, Babylon Sulci, Phrygia Sulcus and Mysia Sulci, respectively. We investigate the main characteristics of Ganymede&#8217;s grooves populations on the four different areas analyzing i) the grooves length distribution to describe the propagation and growing evolution of the faults underlying grooves systems. and ii) the grooves self-similar clustering to infer their vertical penetration inside Ganymede icy shell.&#160;Results and DiscussionFrom the length distribution analysis, we found the presence of both an exponential and power-law trends reflecting the possible coexistence of (i) distributed fault systems, with strain regularly partitioned along evenly spaced faults and confined within specific mechanical layers in the crust (exponential fitting curve/curves) and (ii) localized fault systems, with few large faults cutting across the whole crust (power-law fitting curve) [e.g., 2,4]. From the self-similar clustering analysis, we estimated the potential thickness of the icy crust ranging between 105 and 130 km for the datasets considered. This value agrees with independent estimates of the thickness of the icy shell (from 80 to 150 km, [12,13,14]). Hence, our results support the hypothesis of shorter structures vertically confined in different mechanical layers within the icy crust and few very long faults propagating down to the liquid ocean underneath.AcknowledgementsThe activity has been realized under the ASI-INAF contract 2018-25-HH.0.References[1] Benedicto, A et al. (2003), Geophysical Research Letters, 30, 20, 2076.[2] Soliva, R., and Schultz, R.A., (2008), Tectonics, 27, TC2003.[3] Gudmundsson, A., et al. (2010), Journal of Structural Geology, 32, 1643-1655.[4] Schultz, R.A., et al. (2010). In: Planetary Tectonics, Cambridge University Press, 457-510.[5] Gudmundsson, A., et al. (2013), Tectonophysics, 608, 1298-1309.[6] Mazzarini F., D&#8217;Orazio, M. (2003), Journal of Volcanology and Geothermal Research, v. 125, p. 291-305.[7] Mazzarini, F., (2004), Geophysical Research Letters, v. 31.[8] Mazzarini, F., Isola, I. (2010), Geosphere, v. 6, p. 567-582.[9] Lucchetti, A. et al.,. (2017), Icarus, 297, 252-264.[10]Rossi, C. et al., (2020) Journal of Maps.[11] Collins, G.C., et al., 2013. Global geologic map of Ganymede: U.S. Geological Survey Scientific Investigations Map 3237.[12] Schenk, P.M. (2002), Nature, 417-419, 21.[13] Kivelson, M.G. et al., 1996. Nature, 384, 537-541.[14] Saur, J. et al., 2015. JGR Space Physics, 120, 1715-1737.