There are a large number of tectonic shortening structures distributed across the planet Mercury, which are interpreted as the product of lithospheric deformation mainly attribute to secular cooling of the planetary interior. As the largest single volcanic deposit on Mercury, the northern smooth plains (NSP) is dominated by thrust fault-related landforms, showing particularity in their geomorphic features and requires an assumed weak layer at a shallow depth to account for the thin-rooted deformation in the lithosphere. However, there is a lack of proper mechanical model to account for such layer in the lithosphere beneath the NSP. In this work, we propose a new mechanical model allowing for a mechanically discontinuous lithosphere by introducing the semi-brittle deformation style, with detailed model configurations. Our work simulates a compressive dynamic process to mimic the formation for thrust fault-related landforms in the NSP of 3.8 billion years ago through 2-D numerical simulations. This simulation lasts for 70 million years, resulting in a concentrated and high strain rate region (i.e., weak layer) at shallow depth in the crust and geomorphically consistent surface topography with commonly observed thrust fault-related landforms. Geomorphically steady surface relief suggests that these shortening landforms were formed in a short period of time on geological time scales, and have maintained their basic geomorphic features to present day. The potential influence of the topography at the crust-mantle boundary on the surface relief is also recognized. Additional set of numerical simulations emphasizes that a larger topography facilitates the formation for higher surface relief.

The Free Core Nutation (FCN) is a rotational mode related to non-alignment of the rotation axis of the core and of the mantle. There is a big gap between the observed FCN period (about 430 Sidereal days) and the theoretically calculated period (ranging from 450 Sd to 470 Sd). We propose a spectral element method to compute the period of FCN and obtain a good result, which is $437$ Sd. {\bf Keywords: } FCN, Spectral Element Method

The purposes of this work are (1) clarifying the specific latitude range in which the currently physical model of the equatorial trapped Magnetic-Archimedes-Coriolis (namely eMAC) waves propagating atop the Earth’s core can own the enough accuracy to describe the hydromagnetic waves; (2) presenting the systematically analytical expressions to represent the physical properties (e.g., the equatorial confinement and latitudinal distribution, damping rate α, eigen-period T) of the eMAC waves. Here, the new results indicate that: 1) the eMAC wave model can own the high accuracy (i.e., the relative errors are less than 5%) to describe the core waves in the regions with latitude below 25 degrees ; 2) the equatorial confinement and latitudinal distribution law is essentially governed by a specific solution form with the typical Hermite polynomial term of degree n; 3) the damping rate can be estimated by α ≈-π^2/(μσH^2) (μ being the vacuum permeability, σ being the core electrical conductivity; H being the stratified layer thickness of the core), showing that the magnetic diffusivity η (=1/(μσ))can cause the ohmic dissipation of the waves; besides, the H value is predicted to be larger than 20km, when T matches the observed 8.5yr period. This work also presents the analytical models for the perturbed magnetic fields due to the eMAC waves, presenting that the azimuthal perturbed magnetic field bφ(with degree n=1) is mainly confined to the equatorial regions with latitude below ~15 degrees, the profile of which coincides with the observed core surface azimuthal flows.