Date of Degree
MS (Master of Science)
Barnhart, William D.
First Committee Member
Gilotti, Jane A.
Second Committee Member
Finzel, Emily S.
Temporally and spatially clustered earthquake sequences along plate boundary zones indicate that patterns of seismicity may be influenced by earthquake-induced stress changes. Many studies invoke Coulomb stress change (CSC) as one possible geo-mechanical mechanism to explain stress interactions between earthquakes, their aftershocks, or large subsequent earthquakes; however, few address the statistical robustness of CSC triggering beyond spatial correlations. To address this, I evaluate the accuracy of CSC predictions in subduction zones where Earth’s largest earthquakes occur and generate voluminous and diverse aftershock sequences. A series of synthetic tests are implemented to investigate the accuracy of inferred stress changes predicted by slip distributions inverted from suites of geodetic observations (InSAR, GPS, seafloor geodetic observations) that are increasingly available for subduction zone earthquakes. Through these tests, I determine that inferred stress changes are accurately predicted at distances greater than a critical distance from modeled slip that is most dependent on earthquake magnitude and the proximity of observations to the earthquake itself. This methodology is then applied to the 2010 Mw 8.8 Maule, Chile earthquake sequence to identify aftershocks that may be used to perform statistically robust tests of CSC triggering; however, only 13 aftershocks from a population of 475 events occurred where confidence in CSC predictions is deemed to be high. The inferred CSC for these events exhibit large uncertainties owing to nodal plane uncertainties assigned to the aftershock mechanisms. Additionally, tests of multiple published slip distributions result in inconsistent stress change predictions resolved for the 13 candidate aftershocks. While these results suggest that CSC imparted by subduction megathrust earthquakes largely cannot be resolved with slip distributions inverted from terrestrial geodetic observations alone, the synthetic tests suggest that dramatic improvements can be made through the inclusion of near-source geodetic observations from seafloor geodetic networks. Furthermore, CSC uncertainties will likely improve with detailed earthquake moment tensor catalogs generated from dense regional seismic networks.
Earth’s largest magnitude earthquakes occur in subduction zones, where tectonic plates converge and one plate slides beneath the other. In these settings, earthquakes commonly trigger tsunamis, extensive aftershock sequences, and in some cases, subsequent large earthquakes. Therefore, it is important to understand the physical mechanisms that allow earthquakes to interact (how one earthquake potentially triggers another) to properly assess and mitigate the associated hazards, as well as to constrain the state of stress in the Earth’s crust. The goal of this project is to test if static stress changes can lead to earthquake triggering by using aftershocks of the 2010 Mw8.8 Maule, Chile earthquake as a statistically robust proxy for larger triggered earthquakes. Stress change triggering stipulates that an earthquake changes the stress state on nearby faults and brings them either closer to or further from failure. To test this, it is crucial to first assess the limitations of resolving earthquake source properties in subduction zones using the tools that are commonly available to geodesists (GPS and satellite radar observations). Using synthetic tests to simulate subduction zone earthquake scenarios, it is determined that earthquake magnitude and proximity of observations to the earthquake dominate the accuracy of the inferred stress changes. These tests are applied to the Maule earthquake sequence and only 13 aftershocks are identified for confident predictions of stress changes. Due to the small sample size of aftershocks and large stress change uncertainties the stress change triggering hypothesis cannot be adequately tested without improved coverage of geodetic observations, which can be made possible with the addition of seafloor instrumentation in global subduction zones.
Coulomb stress change, earthquake triggering, geodesy, subduction zone
vii, 56 pages
Includes bibliographical references (pages 25-30).
Copyright © 2017 Bryan James Stressler
Stressler, Bryan James. "Characterization of stress changes in subduction zones from space- and ground-based geodetic observations." MS (Master of Science) thesis, University of Iowa, 2017.