Browsing University of Alaska Southeast by Subject "vertical ground motion"
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Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water SystemSubglacial water ﬂow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5‐ to 10‐Hz seismic tremor that we associate with subglacial water ﬂow, that is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequency‐dependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in melt‐water input. We suggest that conduit formation requires sustained water input and that multiconduit ﬂow paths can be distinguished from single‐conduit ﬂow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely ﬂows through a single‐conduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable conﬁgurations that last 3–7 days, while tremor produced by single‐conduit ﬂow remains more stationary. We also ﬁnd that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2–6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.