Download or read book Deformation Along the Subduction Plate Interface Above and Below the Seismogenic Zone written by Caroline Seyler and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Subduction zones host the world’s largest earthquakes, but seismic slip is only one style of deformation along the subduction interface. The deformation processes above and below the seismogenic zone are equally fundamental to understanding how relative motion is accommodated during subduction. The plate interface updip from the seismogenic zone is commonly localized within seafloor sediments overlying the subducting slab. Whether or not an earthquake propagates through those sediments to the surface controls the likelihood tsunami generation, making the mechanical behavior of seafloor sediments essential to our understanding of shallow earthquake rupture. On the downdip portion below, high temperatures allow continuous sliding that progressively loads the seismogenic zone. This thesis investigates the deformation behavior of the updip and downdip subduction interface through experimental, field, and microstructural studies on the active Cascadia subduction system and an exhumed analog, the Leech River Fault.To investigate the likelihood of earthquakes rupturing to the surface, high velocity rotary shear experiments were conducted over a range of normal stresses on three samples of Ocean Drilling Program core retrieved from Cascadia input sediments and a suite of individual clay species to measure their frictional properties and fracture energy. The Cascadia input sediment cores show little variation in fracture energy between samples. Clay species were tested under wet and dry conditions, and difference between extremely low fracture energy wet gouges and moderately low fracture energy dry gouges was more significant than the differences between species. Comparing these results with a global compilation of fracture energy estimates, wet clay-rich gouges have the lowest fracture energy of all lithologies, which may enhance earthquake rupture to the trench. Yet Cascadia sediments have a fracture energy that is nearly an order of magnitude higher than input sediments from other subduction zones, possibly inhibiting shallow earthquake rupture propagation and tsunamigenesis.Field, petrological, microstructural, and geochronological data rewrite the history of the Leech River Fault (LRF) as a subduction interface shear zone. The shear zone is defined by mylonites developed along the contact between the schist and metamorphosed basalt, whose strong, steeply dipping foliation, downdip lineation, and kinematic indicators indicate sinistral-reverse motion. Garnet and amphibole chemical zoning in the schist and metabasalt, respectively, indicate prograde, syn-kinematic growth. Syn-kinematic metamorphic conditions of ~575 °C and ~800 MPa were determined from the schist mylonite, which match the qualitative P-T conditions of amphibolite facies determined from amphibole rim compositions in the metabasalt mylonite. The structural and metamorphic history of the shear zone confirm that it was active as the downdip portion of the subduction interface.The strength of the subduction interface downdip is an important parameter for understanding subduction dynamics that cannot be determined geophysically. Integrating microstructural observations of the mylonites with experimentally derived flow laws, I determined the controls on shear zone rheology and estimated bulk rock strength under in situ conditions. Multiple deformation mechanisms operating in the schist and metabasalt mylonites were required to accommodate deformation, and the available flow laws indicate that the bulk strength of these rocks was significantly reduced by hydrous phases like phyllosilicates and amphibole. These observations suggest that hydration and metamorphic reactions play an essential role in weakening rocks and allowing the plate interface to creep aseismically at low stresses. Together, these new observations place important constraints on the dynamics of deformation above and below the seismogenic zone"--