Study of Subsurface Structures Northwest of Ascraeus Mons, Mars, Based on Variational Bayesian Monte Carlo

Tharsis Montes is the largest volcanic province on Mars, and Ascraeus Mons in its northeastern part is the largest volcano of the province. The material composition of the lava flows and lava plains to the northwest of Ascraeus Mons is important for the understanding of the volcanic activity and geological history of Mars. SHARAD (SHAllow RADar), an orbital radar onboard MRO (Mars Reconnaissance Orbiter), can be used to study the electrical properties of subsurface materials and subsurface geological structures. In this paper, Variational Bayesian Monte Carlo (VBMC) is used to calculate the dielectric constant and loss tangent of lava flows and lava plains material to the northwest of Ascraeus Mons, determining the electrical parameters without knowing the depth of the subsurface reflector. The range of dielectric constants and loss tangents of these lava flows and plains is consistent with basaltic lava flows, with dielectric constants of the lava flows in the range of 7.7-14.4, and loss tangent in the range of 0.025-0.037. The differences in the electrical parameters of the lava flows may be caused by spatial and temporal differences in volcanic activities and the different sources of the lava flows. The permittivity of the surface layer of the lava plain ranges from 8.8 to 14.4, and the loss tangent ranges from 0.015 to 0.037. If the lava flows are directly overlying the lava plains, the plains underneath the lava flows would have a larger permittivity, but our calculations of the permittivity of the lava flow and the lava plain are similar, and therefore, the reason for the subsurface reflectors may not be the difference in dielectric constants of the materials in the different geological units, but rather the presence of a thin weathered layer with a low dielectric constant between the two layers of lava material.