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Geology Club Seminar

Thursday, November 1, 2018
4:00pm to 5:00pm
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Arms 151 (Buwalda Room)
Distributed deformation within an accretionary wedge as a possible slow earthquake mechanism
William Schmidt, USC,

Slow earthquake phenomena are commonly observed at the down dip limit of the seismogenic zone in subduction zones and are primarily interpreted as occurring due to motion on a discrete fault interface, but their location in a temperature and pressure regime under which rocks begin to behave in a ductile manner and in which off fault deformation becomes more important has led some workers to interpret them as being caused by alternative mechanisms. This study focuses on a transect of the South Fork Mountain Schist (SFMS), a body of sediments and ocean floor which was subducted and then accreted to the overriding plate in the early Cretaceous . The SFMS was deformed under the conditions which produce slow earthquakes as demonstrated by its mineral assemblage and by laser Raman analysis of carbonaceous material, which establish depths of ~30km and peak metamorphic temperatures of ~350°C respectively. Microfolds show dissolution on their limbs and quartz precipitation in dilational openings in their hinges. Stacks of microfolds combine to form larger folds, suggesting that bursts of dilational microcracking may be able to produce moment release at a variety of scales as well as a seismic signal which matches that observed for slow earthquakes today.