Intermediate‐Depth Earthquakes Controlled by Incoming Plate Hydration Along Bending‐Related Faults

Intermediate‐depth earthquakes (focal depths 70–300 km) are enigmatic with respect to their nucleation and rupture mechanism and the properties controlling their spatial distribution. Several recent studies have shown a link between intermediate‐depth earthquakes and the thermal‐petrological path of subducting slabs in relation to the stability field of hydrous minerals. Here we investigate whether the structural characteristics of incoming plates can be correlated with the intermediate‐depth seismicity rate. We quantify the structural characteristics of 17 incoming plates by estimating the maximum fault throw of bending‐related faults. Maximum fault throw exhibits a statistically significant correlation with the seismicity rate. We suggest that the correlation between fault throw and intermediate‐depth seismicity rate indicates the role of hydration of the incoming plate, with larger faults reflecting increased damage, greater fluid circulation, and thus more extensive slab hydration

A Paleomagnetic Exploration of the Sierra Madre Oriental

Honors (Bachelor's)Earth and Environmental SciencesUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/112089/1/erschott.pd

[Direct descendents of Emmanuel Moers and of Hyman Schottenfels].

Lee B. Schottenfels, 1996Family trees of the Schottenfels and Moers families // 1990sdigitize

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

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

Bathymetric Signatures of Submarine Forearc Deformation: A Case Study in the Nankai Accretionary Prism

Abstract Large earthquakes and tsunamis in subduction zone forearcs occur via slip on the shallow plate boundary and upper plate faults, but the locations, geometries, and slip histories of these faults can be difficult to constrain in regions with minimal subsurface geophysical and stratigraphic data. Here, we test a new approach to quantify the submarine seafloor geomorphic response to forearc deformation in order to identify structures that contribute to active deformation, to interpret their geometry and kinematics, and to evaluate their relative rates, magnitudes, and timing of deformation. We develop a workflow that uses filtered bathymetric digital elevation models, where long wavelength topography has been removed, to isolate the slope, relief, curvature, ridgelines, and trough lines associated with faults, fault‐related folds, and slope failures. We apply these methods to the Kumano region of the Nankai accretionary prism, southeastern Japan, where existing constraints on fault geometry, kinematics, and deformation history allow us to both evaluate the efficacy of our approach and to identify the lateral continuity of deformation processes. Our bathymetric analyses yield a high‐resolution tectono‐geomorphic map of active structures and reveal along strike variations in strain accumulation and out‐of‐sequence deformation. These metrics also demonstrate the importance of a strike‐slip fault system at the seaward edge of the Kumano Basin as a primary structure that accommodates deformation and partitions strain in the Nankai forearc. These results show the utility of using a submarine tectono‐geomorphic approach to evaluate active deformation in forearcs, particularly in regions with limited geophysical and core data