Evaluating spatial variations in upper plate deformation at the northeast Japan and Nankai subduction zones using submarine tectonic geomorphology and seismic reflection data

Schottenfels, Emily Rose (2022) Evaluating spatial variations in upper plate deformation at the northeast Japan and Nankai subduction zones using submarine tectonic geomorphology and seismic reflection data. Doctoral thesis, Northern Arizona University.

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Abstract

The outer forearc, frontal prism, and the shallow plate boundary interface (décollement) of subduction zones are deformational domains that accommodate plate boundary strain and have the potential to host shallow, tsunamigenic earthquakes. Asperities on the incoming plate, such as outer-rise normal faults, can modulate décollement mechanics and upper plate deformational processes as they are subducted, which can influence the potential to promote or inhibit shallow plate boundary slip. Therefore, it is important to quantify spatial variations in upper plate deformation that can elucidate décollement heterogeneity, mechanics, and frontal prism evolution. Furthermore, evaluating spatial variations in the magnitudes and rates of upper plate deformation has important implications for strain accommodation, partitioning, and the potential for seismogenic and tsunamigenic hazards.Upper plate deformation and the physical properties of the décollement are typically constrained using subsurface geophysical and geological data, such as direct sampling of sub-seafloor drill cores, borehole geophysical measurements, and seismic surveys. However, even in the most densely instrumented and imaged subduction zones, spatial gaps between seismic data, cored geologic data, and the varied resolution of geophysical imaging can limit our understanding of the lateral continuity of décollement and upper plate deformational processes. High-resolution seafloor digital elevation models (DEMs) are spatially continuous, and therefore provide the opportunity to interpret the bathymetric expression of faulting and deformation in the submarine setting. In this dissertation, I develop bathymetric criteria for mapping the tectono-geomorphic signatures of faulting, folding, and slumping, and methods for evaluating spatial variations in magnitudes and rates of forearc and frontal prism deformation. This dissertation research demonstrates the utility of using bathymetric DEMs and DEM derivatives for determining spatial variations in subduction zone deformation in settings that may have limited or lack subsurface geological and geophysical data. I apply tectono-geomorphic, bathymetric methods to evaluate forearc deformational processes and décollement mechanics at the Nankai and NE Japan subduction zones. In Nankai, high-resolution, tectono-geomorphic mapping shows a possible out-of-sequence thrust fault and an active, margin parallel, strike-slip fault that may partition active plate boundary strain and accommodate active, shallow, seismogenic slip. At the Japan trench, mapping of seismic reflection data shows the importance of incoming plate properties, namely sediment thickness and outer-rise fault throw, for controlling styles of frontal prism deformation, lateral variations in the relative occurrence of sediment accretion, sediment subduction, and frontal tectonic erosion, and shallow décollement heterogeneity. Additionally, tectono-geomorphic analyses at the Japan trench show that the upper plate has direct topographic responses to the subduction of horsts and grabens that are modulated by styles of frontal prism deformation and sediment flux along-strike of the margin. Results from this dissertation research in both margins in Japan demonstrate how bathymetric signatures of the upper plate deformation revealed from tectono-geomorphic methods can elucidate the mechanics and evolution of the décollement at depth.

Item Type:	Thesis (Doctoral)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Japan; Nankai subduction zone; Plate tectonics; Plate deformation; Plate boundary slip; Bathymetric signatures
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	07 Jun 2023 16:08
Last Modified:	07 Jun 2023 16:08
URI:	https://openknowledge.nau.edu/id/eprint/5972

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