Carpenter, Philip J.
M.S. (Master of Science)
Department of Earth, Atmosphere and Environment
Little is known of the structure and seismic nature of planetary bodies that have an outer shell of ice instead of a rocky crust. These bodies are called icy satellites and one such body, Saturn’s moon Titan, is unique because of its thick atmosphere, methane cycle, and assumed salty subsurface ocean. NASA’s Dragonfly mission, set to launch in 2026, will use a robotic rotorcraft to transport various instruments, including a seismometer, to the Shangri-La dune field on Titan. Until then, Titan’s seismic regime can be estimated by simulating wave propagation through assumed subsurface layers using source models. Ridge belts with low slope angles suggest fold-and-thrust belts, possibly caused by fluid overpressure in Titan’s icy shell. These have been observed in synthetic aperture radar images from the Cassini spacecraft and may be a likely site for titanquakes. Synthetic seismograms were calculated for titanquakes by using Instaseis, a Python-based software sourced by Green’s function databases computed by the axisymmetric spectral element method. High-amplitude body wave arrivals are likely waves bottoming in the high-pressure ice layer beneath the ocean. Back-azimuth angles were calculated for different source-receiver configurations. Hypocentral locations were determined using back-azimuth and the S-P interval to a precision within the scale of regional features on Titan, even when the first arrival was a PP-wave at larger epicentral distances. Thus, seismically active regions may be determined by body wave analysis. Faults in these regions may facilitate surface-subsurface methane exchange to sustain prebiotic chemistry. Seismic refraction is not a viable method to determine the thickness of the outer ice shell. However, critically-refracted waves could be used to estimate a velocity for a high-pressure ice layer underlying the ocean. A Mw 5.8 titanquake should be detectable above estimated environmental and mechanical noise levels. However, S-waves arrivals are unclear and may have been poorly constrained by travel times. Body waves may thus be used to constrain quake locations but not layer thicknesses on Titan.
Owens, John William, "Body Wave Analysis For Low-Angle Thrust Quakes on Titan: Implications For Dragonfly" (2020). Graduate Research Theses & Dissertations. 7517.
Northern Illinois University
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