FROM FAULTING ON EARTH TO FAULTING ON OTHER WORLDS: MODELING THE STRESS EVOLUTION OF STRIKE-SLIP FAULTING ON THE SAN ANDREAS FAULT SYSTEM, ON TITAN, AND ON GANYMEDE
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2022
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Strike-slip interaction between rigid lithosphere plates causes many of the world's most dangerous earthquakes since plate displacement can be quite large in a single event. Strike-slip tectonism appears to be also widespread throughout the icy ocean worlds in our Solar System, acting as a driver of surface structural evolution and perhaps as a conduit for the exchange of surface and subsurface materials via shear heating processes. Understanding the stress variations of such fault networks can give us an insight into the geologic evolution of planetary bodies throughout the universe. The first study presented in this work models the stress changes of the San Andreas Fault System, analyzing the magnitude and build-up of Coulomb stress along the segments in the area of the Cajon Pass in southern California. As in the past, similar joint ruptures of these segments might occur in the future, and our work suggests that the junction between the San Andreas and San Jacinto faults at the Cajon Pass plays a larger role in seismic hazard in southern California than previously understood because it could function as an ‘earthquake gate’. This research also demonstrates how we can evaluate paleoseismic data sets and comprehend prehistoric and historic fault activity using physics-based models. The second study presented focuses on modeling the possibility of strike-slip faulting on Titan, an icy moon of Saturn, where limited returned data at present hinders the remote exploration of the surface. Titan has stable liquids both on the surface and in the subsurface, and is consequently a prime candidate for astrobiological exploration. We investigate the potential of strike-slip tectonics governed by Coulomb failure laws and tidal stresses, and undertake a sensitivity analysis of Titan's shear failure inclinations, given optimal failure circumstances that may occur due to pore fluid interactions. Findings of this study indicate that shear failure is possible at shallow fault depths and for ideally orientated faults under diurnal tidal stress conditions due to such pore fluid pressures, especially in the polar areas. Strike-slip faulting is not only plausible, but it may also be an active deformation process on Titan's surface and subsurface based on interpretation of geologic features observed in radar imagery. On Ganymede, an icy moon of Jupiter, strike-slip faulting has been identified through observational data and studied with tidal stress models, suggesting that a higher past eccentricity and/or nonsynchronous rotation must have existed to generate the stresses needed for fault displacement. In the last study presented in this work, we produce a crater count analysis on Ganymede to verify the published relative ages and shear deformation of tectonic units, investigate a period of higher eccentricity using the previously established methods and raise the hypothesis of impacts producing widespread tectonic features. The unique geodynamics of an ice shell may permit an extensive effect from an impact generated seismic event, causing rapid fault slip and spreading features. The analyzed tectonic features in the Nippur/Philus Sulci region appear to be clustered in age, suggesting three eras of distinct activity: One era was ancient, following the high impact rate that produced the heavily cratered dark terrain, the second intermediate era could be correlated with a period of higher orbital eccentricity, causing fault slip and deformation, and some features in the third and youngest era might be associated in time with the most recent basin-forming impact of Gilgamesh. Taken together, these three studies motivate future research and investigations into strike-slip tectonism and impact craters on icy moons and elsewhere, as they can help uncover the tectonic past and form estimates for the future.
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Geophysics, Geology, Coulomb failure, earthquake gate, icy moons, strike-slip faults, tidal stress
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171 pages
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