Geodetic Imaging of 3D Earthquake Cycle Crustal Deformation: San Andreas, CA and Kīlauea, HI

Abstract

Over the last decade there has been a wealth of geodetic data collected globally, that when successfully integrated, make it possible to geophysically image entire fault systems with unprecedented spatial coverage and resolution. Resulting surface velocity and deformation time series products provide critical boundary conditions needed for improving our understanding of how faults and other deformation sources, such as rift zones, are loaded across a broad range of temporal and spatial scales. Moreover, our understanding of how earthquake cycle deformation is influenced by fault zone strength and crust/mantle rheology is still developing. The objective for this PhD dissertation in the Earth and Planetary Sciences, is to study the earthquake cycle deformation of the San Andreas Fault System in southern California, as well as the décollement on the south flank of Kīlauea Volcano on the Big Island of Hawai’i. Both of these regions are experiencing active deformation and rupture events which have and will continue to pose significant seismic hazards to surrounding populations. This research aims to advance next-generation seismic hazard estimates for complex fault systems and explores key questions about earthquake cycle deformation, including: (1) How well can we image and model both horizontal and vertical motions of an earthquake cycle using high-precision geodetic observations? (2) To what extent do variations in crustal composition affect earthquake cycle deformation? (3) How can we utilize our findings to better understand geodetic observations of past and future events? To better characterize the seismic hazards of these regions, several modeling approaches are considered, such as analytical and numerical techniques. These models are used to explore key rheology characteristics, like elastic plate thickness and viscosity of the lower crust and upper mantle, that ultimately control the accumulation of stress and/or strain throughout time. Specific parameters (i.e., strike, dip, and depth) of deformation sources, including faults, rift zones, and magmatic chambers, are also explored. Additionally, these models are constrained using a wide range of geodetic observations (i.e., Global Navigation Satellite System (GNSS), Interferometric Synthetic Aperture Radar (InSAR), triangulation, leveling data, and electronic distance measurements (EDM)). The importance of rheology is specifically considered in Chapters 2 and 3 by exploring heterogeneous elastic plate models for the San Andreas Fault System. Elastic plate heterogeneity is shown to better resolve surface displacement observations (GNSS and InSAR) and ultimately influences seismic hazards levels, where a more compliant or weaker region of the lithosphere experiences increased deformation rates over time. Chapter 4 inspects vertical earthquake cycle deformation of the San Andreas Fault System, using the dense GNSS array time-series to explore postseismic deformation of the 2019 Ridgecrest earthquake sequence. Moreover, the vertical component of deformation is found to be important in differentiating viscoelastic postseismic deformation from non-viscoelastic source contributions and further resolves transient viscosity behavior necessary to match GNSS observations. Chapter 5 considers the broad scale motions of the southeast portion of the Big Island of Hawai’i, encompassing both Mauna Loa and Kīlauea volcanoes, by uniquely collating over 100 years of geodetic observations (triangulation, leveling, EDM, GNSS, and pressure sensor data) and modeling their displacements throughout time. Overall, deformation magnitude and patterns within the Kīlauea region are found to change surrounding the 1975 M_w7.7 Kalapana earthquake. This earthquake occurred along the décollement underlying Kīlauea volcano and the region appears to have stabilized after the 1975 rupture.