Investigating Elastic Deformation Induced by Surface Loads on Planetary Bodies

Author

Ashlesha Khatiwada, University of MontanaFollow
Hilary Martens, The University Of MontanaFollow
Donald F. Argus, NASA, Jet Propulsion Laboratory

Year of Award

2023

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Department or School/College

Geosciences

Committee Chair

Dr. Hilary R. Martens

Commitee Members

Dr. Donald F. Argus, Dr. Payton Gardner, Dr. Kelsey Jencso

Keywords

Surface Deformation, Half-space, Gravitating Spherical Earth Model, surface loading, Geophysics, Geodesy

Publisher

University of Montana

Subject Categories

Geology | Geophysics and Seismology

Abstract

Planetary bodies, including the Earth, deform when there is a redistribution of surface load. In this thesis, I conduct three independent projects related to surface loading, two of which investigate methods related to the modeling of surface loading and one which seeks to catalog the displacement responses of other planetary bodies to a surface load.

The first project aims to compare four methods for modeling the elastic loading response of the Earth: a homogeneous, non-gravitating, half-space method; a homogeneous, gravitating, spherical method; a homogeneous, non-gravitating spherical method; and a radially stratified gravitating spherical method. Many studies have focused on computing vertical displacement due to uniform pressure applied over a region using a homogeneous linearly elastic half-space model. Although homogeneous, half-space models are simple and fast to implement, the model is less authentic than the more realistic gravitating, spherical models compared to Earth. As remote sensing data (e.g., Global Navigation Satellite System) improves in quality, we require more realistic models to interpret observations of Earth's deformation response to surface loading. We quantify the empirical differences between half-space and spherical models at various load scales. We also consider the empirical analysis of the homogeneous half-space model by examining the ratio at both the center and the periphery of the disk load, comparing various implementations of the half-space problem, and contrast with the gravitating, spherical formulation, examining to what extent self-gravity affects the load solution.

In the second project we build upon the surface loading theme by comparing load solutions obtained through finite element modeling (FEM). Utilizing PyLith, an open-source numerical modeling software, we calculate load solutions for rectangular areas subjected to water loads, contrasting these outcomes with those derived from gravitating spherical models using LoadDef; software that can be used to model elastic deformation resulting from surface loads on a spherical symmetrical body. By investigating the discrepancies and similarities between the two approaches, we aim to investigate how the vertical displacement calculated by PyLith and LoadDef differ and gain insight into the advantages and disadvantages of each modeling method.

The third project will venture beyond Earth to explore the deformation of other planetary bodies within our solar system. Like Earth, these celestial objects experience surface load redistribution and gravity-driven deformations. To quantify the deformation of these planetary bodies using a layered, gravitating, spherical model, we need to compute their load Love numbers (LLN) and load Green's function (LGFs). While Earth's LGFs have been well-studied, other planetary bodies, such as Venus, Mars, Ganymede, Europa, and Titan, still need to be explored in this aspect. Through an extensive literature review, we gather interior structure data for these celestial bodies and calculate their LGFs. With this knowledge, we can create models to simulate vertical displacement caused by variations in surface mass distribution, enriching our understanding of planetary deformations beyond Earth.

Recommended Citation

Khatiwada, Ashlesha; Martens, Hilary; and Argus, Donald F., "Investigating Elastic Deformation Induced by Surface Loads on Planetary Bodies" (2023). Graduate Student Theses, Dissertations, & Professional Papers. 12195.
https://scholarworks.umt.edu/etd/12195