Great (Mw >8.5) earthquakes occur over long temporal intervals that extend beyond current historical (written and oral) records along most subduction zone coastlines often leading to the underestimation of magnitude, recurrence, and spatial extent of these events. Paleoseismic studies target low energy depositional environments that record primary and secondary evidence of earthquake occurrence within the coastal stratigraphy over much longer temporal scale, thus improving our understanding of the behavior of subduction zone earthquakes. Diatoms preserved within coastal stratigraphic records are sensitive to earthquake-induced environmental change and are useful bioindicators in paloesiesmology studies. The two studies in this dissertation employ diatoms to create novel approaches to investigate behavior and recurrence of earthquakes along two subductions zones: Alaska-Aleutian subduction zone and the Cascadia subduction zone. In these chapters we use diatoms to explore 1) the potential for combined slip along the Patton Bay splay fault system and the eastern Alaska-Aleutian subduction zone within Prince William Sound, Alaska, and 2) lacustrine turbidite source mechanisms in Ozette Lake, Washington to potentially improve the spatial and temporal earthquake record for the northern Cascadia subduction zone. This work has implications for improving our earthquake chronologies along subduction zone coastlines and making important contributions to coastal hazards assessments. / Doctor of Philosophy / Subduction zones are capable of producing great (>Mw 8.5) earthquakes with accompanying tsunamis that can impact nearby coastlines with devastating force. Great earthquakes occur over long timescales (thousands of years) and are often not captured in short historical records, leaving questions about the recurrence, behavior, and range of potential future earthquakes along these boundaries. Paleoseismology, the study of earthquake history, employs methods that use the earthquake-induced environmental changes along subduction zone coastlines to provide long-term records of earthquake occurrence. Diatoms, a type of siliceous microalgae entrained in coastal sediments, react to changes in pH, salinity, water depth, and sediment type, and are important indicators of environmental change that can be used to expand our understanding of earthquake behavior. This dissertation uses diatoms in two projects that explore the earthquake history along the Alaska-Aleutian subduction zone and the Cascadia subduction zone. First, we determine that secondary faults, called splay faults, in Prince William Sound are likely triggered only by slip along the Alaska-Aleutian subduction zone, suggesting that combined slip has occurred during four of the eight total megathrust earthquakes in the last ~4,200 years. Second, we investigate the sediment origins of the youngest six deposits (turbidites) in Ozette Lake, linking them to diatoms located on the subaqueous delta and shallow lake surfaces, leading us to infer the source is likely earthquake-induced slope failure. Both projects help to expand our understanding of subduction zone earthquake behavior, and will help inform future hazards assessments for coastal communities.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/117740 |
| Date | 30 January 2024 |
| Creators | DePaolis, Jessica |
| Contributors | Geosciences, Dura, Tina, Spotila, James A., Witter, Rob, Romans, Brian W. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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