Ancient subsurface structure beneath crater Clavius: constraint by recent high-precision gravity and topography data

Abstract

With the increasing precision of the GRAIL gravity field models and topography from LOLA, it is possible to investigate the substructure beneath crater Clavius. An admittance between gravity and topography data is commonly used to estimate selenophysical parameters, including load ratio, crustal thickness and density, and elastic thickness. Not only a surface load, but also a subsurface load is considered in estimation. The algorithm of particle swarm optimization (PSO) with a swarm size of 400 is employed as well. Results indicate that the observed admittance is best-fitted by the modeled admittance based on a spherical shell model, which was proved to be unsatisfactory in the previous study. The best-fitted load ratio f is around −0.194. Such a small load ratio conforms to the direct proportion between the nearly uncompensated topography and its corresponding negative gravity anomaly. It also indicates that a surface load dominates all the loads. Constrained within 2σSTD, a small crustal thickness (∼30 km) and a crustal density of ∼2587 kgm−3 are found, quite close to the results from previous GRAIL research. Considering the well constrained crustal thickness and density, the best-fitted elastic thickness (∼7 km) is rational. This result is slightly smaller than the previous study (∼12 km). Such difference can be attributed to the difference in crustal density used and the precision of gravity and topography data. Considering that the small difference between the modeled gravity anomaly and observations is quite small, a parameter inversed here could be an indicator of the subsurface structure beneath Clavius.

Estimation of the elastic thickness over ancient Mare Moscoviense

“…To estimate best-fitted parameters, we first evaluate the subsurface topography at the crust-mantle interface to produce a synthetic gravity anomaly (Turcotte et al 1981). The relief can be calculated according to observed surface topography or the possible prefilling depth (McGovern et al 2002;Crosby & McKenzie 2005;Zhong et al 2018Zhong et al , 2019. As the nonlinearity of the thin elastic spherical shell, Zhong et al (2018) introduced an updated version of spherical harmonic thin elastic-shell loading model.…”

“…Given a serial of estimated parameters mentioned above, we can evaluate a corresponding modeled gravity anomaly for the shell, which is described in Appendix A. In light of equations ( 2)-( 5) and equations ( 7)-( 9) in the recent study of Zhong et al (2019), we can get the resulted gravity anomaly and its modeled admittance. By minimizing misfit between the modeled admittance and the observations, we can estimate the aforesaid parameters.…”

“…The elastic thickness is generally investigated through the admittance, which is estimated from topography and gravity data. (Belleguic et al 2005;Grott & Wieczorek 2012;Huang & Wieczorek 2012;Zhong et al 2014Zhong et al , 2018Zhong et al , 2019. This approach supposes that the lithosphere of the Moon behaves elastically as a spherical shell or an elastic plate.…”

“…By minimizing the misfit between the modeled admittance and observations, several parameters designating the properties of the lithosphere can be estimated. These include the crustal thickness (b c ) and density (ρ c ), load ratio (f ) and the effective elastic thickness (T e ) (McGovern et al 2002;Zhong et al 2018Zhong et al , 2019.…”

“…With the improvements in gravity information accuracy from SELENE mission, Huang & Wieczorek (2012) evaluate the possible elastic thickness not only on the nearside but also on the farside of the Moon. Subsequently, a multi-parameter inversion based on Particle Swarm Optimization (PSO) algorithm was introduced by Zhong et al (2014Zhong et al ( , 2019 to increase computational efficiency. These inversions are successful on high-land areas with strong correlation between gravity and topography, but not mare basins or craters.…”