California has experienced an unusually dry past two decades punctuated by three intense multi-year droughts from 2007-2010, 2012-2015, and 2020-2022. A portion of the water lost during these two decades is due to intense groundwater overdraft of the Central Valley Aquifer. This groundwater overdraft has led to poroelastic compaction of the aquifer system and subsidence of the land surface. Water mass loss also causes elastic deformation of the solid Earth, an opposite and smaller amplitude response than the poroelastic deformation of aquifer systems. These mass changes can disturb the regional stress field, which may influence earthquake activity. Both the elastic and poroelastic deformation responses can be observed using satellite-based geodetic tools including Global Navigation Satellite System (GNSS) station displacements and Interferometric Synthetic Aperture Radar (InSAR). In this dissertation, I model aquifer-system compaction at depth using InSAR-based vertical land motion during the 2007-2010 drought and evaluate hazards related to Earth fissures, tensional cracks that form at the edges of subsidence zones. Next, I forward-calculate the predicted elastic deformation response to groundwater mass loss over the same period and calculate crustal stress change to evaluate what, if any, impact this has on seismicity in California. In addition to modeling deformation caused by water storage change, I also introduce a new method to jointly invert elastic vertical displacements at GNSS stations with water storage anomalies from the Gravity Recovery and Climate Experiment (GRACE) to solve for water storage changes from 2003-2016 over California. Finally, I expand on this joint inversion framework to include poroelastic deformation measured using InSAR over the Central Valley aquifer-system to solve for a change in water storage and groundwater storage over water years 2020-2021, the most recent drought period in California. / Doctor of Philosophy / Changes in the hydrologic system can have wide-reaching societal, geopolitical, economic, ecological, and agricultural impacts. Proper water management, particularly in places that have water scarcity concerns due to overuse, water pollution, or recurrent drought conditions, is essential to ensure this resource is available to future generations. Current projections of climate change scenarios point to more intense and frequent extreme hydroclimate events. With accelerating population growth in many urban centers across the world, measuring water storage changes has never been more important to ensure resiliency of our cities, energy sector, and agricultural systems. Furthermore, water storage changes deform the Earth, which may create or alter geophysical hazards such as subsidence, the development of Earth fissures, and seismicity. Today, a multitude of space-based geodetic tools allow us to monitor changes in the Earth system, including changes in terrestrial water content and associated deformation, with higher spatial and temporal resolution than ever before. These datasets have provided an unprecedented understanding of hydroclimatic hazards and have resolved constraints arising from sparse and infrequent in-situ measurements. Here, I use space-based geodetic tools and geophysical models to measure water storage fluctuations, deformation, and evaluate associated hazards in California, a region that has experienced an unprecedented nearly continuous two-decades long drought. In general, I find that 21st century droughts have caused significant water storage loss, especially groundwater storage loss, in California, which has exacerbated some geophysical hazards including land subsidence and Earth fissure hazards.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/113647 |
| Date | 02 February 2023 |
| Creators | Carlson, Grace Anne |
| Contributors | Geosciences, Shirzaei, Manoochehr, Burbey, Thomas J., Stamps, D. Sarah, Werth, Susanna, Hole, John Andrew |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Coverage | California, United States |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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