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Speaker:  Kiki Schulz, Research Fellow, University of Texas at Austin Oden Institute

Host: Patrick Heimbach

Title: Mixing in a changing Arctic Ocean

Abstract: The Arctic Ocean is a distinct and beautiful marine environment, and severely affected by the ongoing climate crisis. A nearly perennial ice cover in most regions of the Arctic has maintained a very specific structure of the underlying ocean, characterized by low nutrient availability and light-limitation, which favored the development of a highly specialized ecosystem featuring many species exclusively found at high latitudes. In response to anthropogenic warming, which is strongly amplified in the Arctic compared to the global average, sea ice cover is further and further retreating in the summer months, and the local ice-free seasons become longer. Without a separating layer of ice in between, energy transfer from the atmosphere to the ocean is facilitated, providing the kinetic energy to transport both heat and nutrients from deep water layers of Atlantic origin to the ocean surface. There, enhanced nutrient availability – in combination with longer open water seasons – can alter the structure of the ecosystem, allowing invasive Atlantic species to out-compete the endemic Arctic species. Despite its importance for the coupled Arctic system, the spatial and temporal distribution of enhanced vertical mixing, and the underlying energy conversion mechanisms, are still not conclusively mapped. This talk will start with a brief outline of the history and current state of oceanographic research in the Arctic Ocean, before summarizing recent advances in the understanding of turbulent mixing and transport in the Siberian Seas.

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Contact edward.clennett@utexas.edu for a link to join the talk.

Speaker: Edward Clennett, PhD Candidate, UTIG

Title: Assessing plate reconstruction models using plate driving forces.

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Speaker: Jonathan Delph, Assistant Professor, Department of Earth, Atmospheric and Planetary Sciences, Purdue University

Host: Shuoshuo Han

Title: Linking heterogeneous expressions of subduction along the Cascadia margin

Abstract: Spatial correlations between lateral heterogeneity in geophysical, seismogenic, and tectonic features is observed along the Cascadia margin. Both the overriding and downgoing plate have been invoked to play the dominant role in controlling along-strike correlations between seismogenic behavior, potential field measurements, morphological/tectonic characteristics, and seismic structure; however, significant feedbacks likely exist between the two. Our recent seismic images suggest that zones of basal accretion of material from the downgoing plate to the overriding plate may link the seismogenic, geological, and morphological expression of subduction in Cascadia. In the northern and southern portions of the forearc, this “subcreted” material is also characterized by thick (~10 km) anomalously low shear-wave velocity zones. The thickness, high internal reflectivity, and low Bouguer gravity signatures likely indicate that this subcreted material is composed of dominantly (meta)sedimentary material that has been emplaced through successive subcretion events over geologic timescales. Furthermore, the anomalously low velocities and spatial correlation with high non-volcanic tremor (NVT) density and short slow slip recurrence intervals indicate that these regions are fluid-rich. While 1st order variations in the fluids that control NVT and slow slip likely result from differences in the permeability of the downgoing slab as inferred from its stress state and the distribution of intraslab seismicity, these subcreted packages likely represent thick, vertically-impermeable regions in the lower crust that further accentuate this correlation. Variability in the amount of subcretion explains patterns of exhumation and uplift along the Cascadia margin and the resulting forearc topography over geologic timescales, and is likely controlled by some combination plate interface geometry/rheology and overriding plate architecture.

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Speaker: Sean Peters, Assistant Professor, Naval Postgraduate School

Host: Duncan Young

Title: TBA

Abstract: TBA

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Speaker: Carson Miller, PhD Candidate, UTIG.

Title: Identifying paleo-barrier island deposits to understand preservation potential. 

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This is a hybrid seminar. Join us in the UTIG Seminar Room for coffee, snacks and Dr. Fichtner’s live streamed talk. Contact costa@ig.utexas.edu for a link to join remotely.

Speaker: Andreas Fichtner,  Professor of Seismology & Wave Physics, Institute of Geophysics, ETH Zurich

Host: Sean Gulick

Title: Fiber-optic seismology in volcanic, glacial and other challenging environments

Abstract: Fiber-optic deformation sensing provides new opportunities for seismic data acquisition with high spatio-temporal resolution. The relative ease of deploying fiber-optic cables, or the possibility to piggyback on existing telecom infrastructure make this technology particularly attractive for environments where large numbers of conventional seismic instruments may be difficult to install. These include active volcanoes, glaciers or densely populated urban centers.

In the first, more observational part of this talk, we will present a series of case studies where Distributed Acoustic Sensing (DAS) greatly improved the location of glacial icequakes, enabled the observation of previously unknown volcanic tremor and resonance phenomena, and increased the number of detected seismic events by two orders of magnitude – all relative to data from existing seismometer networks.

In the second, more theoretical part, we will report on the development of a novel fiber-optic sensing system that is based on the transmission of microwave-modulated laser pulses. While being more than 10 times cheaper than most DAS systems, the microwave system allows for interrogation distances of hundreds or thousands of kilometers. We show theoretically that different segments of the fiber can have different sensitivities for deformation sensing, largely depending on fiber curvature. Data from a large-scale experiment in Athens support this theory, thereby suggesting that tomographic imaging in remote regions and in the oceans should be possible.