Investigation of Tidal-Seismic Resonance Using 3-D Boundary Element Method
MetadataShow full item record
In this dissertation, I theorize and propose a new astronomical phenomenon, called tidal-seismic resonance for a solid planet-moon system. To fully study the resonance, I develop an open-source modeling code, AstroSeis, to model seismic waves in a planet excited by the tidal force of the orbiting moon. Tidal seismic resonance happens when a tidal force frequency of an orbiting moon matches a free-oscillation frequency of the planet. Here I show that when the moon is close to the planet, the tidal-seismic resonance can cause large-amplitude seismic waves, which can change the shape of the planet and in turn, exert a negative torque on the moon causing it to fall rapidly toward the planet. I present this main finding in the last chapter, Chapter 6. However, I present the necessary preliminaries to understand this major conclusion and development of the modeling tool in the preceding chapters. After introductory materials in Chapter 1, I give a detailed analysis of tidal forces for a co-rotating planet-moon system in Chapter 2. In Chapter 3, I present the basics and preliminaries of the normal modes and free-oscillation frequencies of a solid planet. I present my newly developed seismic modeling tool, AstroSeis, in Chapter 4. This tool is a 3D seismic wavefield modeling code using the boundary element method. It can handle arbitrary surface topography of a planet or an asteroid and allow for a liquid core. Because AstroSeis is formulated in the frequency domain, it is particularly suited to model seismic wavefield caused by long-term forcing such as periodical tidal forces. I also show AstroSeis could be used to study interior and surface processes of planets and asteroids. In Chapter 5, I use the seismic displacement computed by AstroSeis to numerically calculate the traditional tidal torque. The tidal torque is important because it causes the orbital decay of the orbiting moon. The tidal-seismic resonance could also be an important mechanism in other settings such as in the planetary accretion process. On the other hand, AstroSeis can be used to study a wide range of planetary phenomena in particular planetary/asteroid surface processes due to seismic shaking.