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dc.contributor.advisorDugan, Brandon
dc.contributor.authorSilver, Maxwell McCartney Wittlake
dc.date.accessioned2023-11-30T22:32:20Z
dc.date.available2023-11-30T22:32:20Z
dc.date.issued2023
dc.identifierSilver_mines_0052E_12662.pdf
dc.identifierT 9590
dc.identifier.urihttps://hdl.handle.net/11124/178599
dc.descriptionIncludes bibliographical references.
dc.description2023 Summer.
dc.description.abstractRemobilization of sea floor sediments (submarine slope failures) presents a hazard to coastlines and coastal communities through its propensity to damage seafloor infrastructure and generate tsunamis. Submarine slope failures and their deposits (mass transport deposits) have been identified on active and passive continental margins, even on slopes < 2°. Despite the global presence and threat of slope failures, understanding of submarine slope failure mechanisms, including factors controlling initiation, evolution, and tsunamigenesis, is limited. Here, I use flume experiments, geotechnical data, and numerical models to investigate the mechanisms of submarine slope failure initiation and behavior. Benchtop flume experiments were conducted to improve understanding of slope response to overpressure using various combinations of quartz sand, cohesive clay (smectite), and non-cohesive quartz powder (clay-sized particles). Numerical models that are commonly used to evaluate natural slope failure (infinite slope factor of safety analyses) were tested against our controlled system. Comparison between experiment results and factor of safety predictions reveals discrepancies between the models and findings, indicating models may over-predict slope stability when over-pressured. Through these experiments, sediment cohesion was shown to dictate slope failure behavior, with brittleness of slope failure directly related to higher cohesion. Sediment permeability controlled the magnitude of overpressure required to induce slope failure when sediments were  25% clay. At higher clay concentrations, permeability did not affect the overpressure required to induce failure. Additionally, when clay contents were ≥ 25%, repeat failure events were observed in experiments and separate, intact sediment blocks were rafted from parent slopes. Additionally, overpressure was found incapable of producing tsunamigenic landslides but could precondition slopes for future tsunamigenic failure. Increased slope failure hazard was identified for clay-rich (≥ 25% wt.) slopes because of the potential for rafted block development and a potential for repeat failures in locations where failures had previously occurred. This work shows additional investigation of models used for hazard assessment of slope failure and tsunamigenesis is needed to assess differences between prediction and reality. This work also shows that local geology (clay content, surface and subsurface deformation) and hydrology (overpressure) need to be considered in hazard assessments to improve the accuracy of slope failure forecasts and preparations. Extending these findings to the natural environment, the geomechanical properties (shear strength, permeability, consolidation state, and overpressure) of submarine slope failure deposits and surrounding background sediments were characterized for a N-S transect of the Japan Trench. Eleven samples from 10 sites were collected by International Ocean Discovery Program Expedition 386: Japan Trench Paleoseismology using giant piston cores. Undrained direct simple shear and constant rate of strain experiments were performed on these samples. Spatial, lithological, and seismic history trends in sediment shear strengths, permeabilities, consolidation states, and overpressures were investigated No trends were found spatially, lithologically, or with seismic history, suggesting that local heterogeneity may be important for failure and seismic strengthening may not be significant. Feedbacks between peak shear strength, overpressure, shear-weakening, and over consolidation were identified indicating once sediment shearing/remobilization begins, continuation of sediment shearing should require progressively less shear strength. To improve regional forecasting and preparation efforts for future tsunami landfall, including identification of areas-at-risk of slope failure in the Japan Trench, a more robust understanding of Japan Trench sediment stability is required. Finally, physical experiments and natural observations were connected to coastal communities through their implications for risk assessments. The importance of local geology and hydrology in assessing failure likelihood and tsunamigenic potential were communicated in language common to the risk assessment community. Specifically, permeability, overpressure, cohesion, and regional seismic history in slopes in relation to coastal community risk assessment, preparations, and response were characterized. Overpressures were identified as capable of lowering slope stability, triggering non-tsunamigenic slope failures, and preconditioning a slope for tsunamigenic failure. Clay concentrations were identified as determining failure behavior, including tsunamigenic potential, and potential for repeated localized failures. Recommendations for modification of current assessment tools, including numerical models, were made that included these parameters. The importance of these parameters and their ramifications on margins not traditionally concerned with tsunamis was reinforced. This work demonstrated the importance of understanding how a slope might be preconditioned for failure and how inclusion of local geology and hydrology is necessary for a more holistic risk assessment of slope failure and tsunamigenesis.  
dc.format.mediumborn digital
dc.format.mediumdoctoral dissertations
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2023 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.subjectfailure
dc.subjectlandslide
dc.subjectseafloor
dc.subjectslope
dc.subjectsubmarine
dc.subjecttsunami
dc.titleSubmarine landslide processes, mechanics, and effects investigated through physical experiments, numerical models, and natural samples
dc.typeText
dc.date.updated2023-11-30T05:06:59Z
dc.contributor.committeememberWood, Lesli J.
dc.contributor.committeememberSingha, Kamini
dc.contributor.committeememberReddy, Elizabeth
dcterms.embargo.expires2024-11-29
thesis.degree.nameDoctor of Philosophy (Ph.D.)
thesis.degree.levelDoctoral
thesis.degree.disciplineGeophysics
thesis.degree.grantorColorado School of Mines
dc.rights.accessEmbargo Expires: 11/29/2024


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