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Speaker: Charles Babendreier, Graduate Research Assistant, University of Texas Institute for Geophysics

Host: Shuoshuo Han

Title: Massive submarine landslides imaged offshore southern Oregon

Abstract: Submarine landslides are gravity-driven, mass transports that occur beneath the sea surface along the slopes of underwater geologic features (e.g., continental slopes, submarine canyons). In some cases, submarine landslides can destroy valuable ocean bottom infrastructure and/or generate tsunamis, posing risk to nearby coastal communities. At the Cascadia Subduction Zone off the west coast of the U.S. and Canada, the oceanic Juan de Fuca Plate slides beneath the continental North American Plate. Previous bathymetric and seismic imaging have shown that submarine landslides are ubiquitous along the Cascadia margin. In 2021, new multi-channel seismic data were acquired onboard the R/V M. G. Langseth using a 12 km hydrophone streamer and a 6600 in3 airgun source through the CAscadia Seismic Imaging Experiment 2021 (CASIE21). Using this dataset, we have an unprecedented opportunity to map the buried deposits of submarine landslides and characterize their structure along this margin. We identified 10 massive submarine landslide deposits offshore southern Oregon (latitudes 42°-44° N). Landslide deposits of this scale are not observed elsewhere along this margin. Two of the older deposits, both near 44° N, have the largest spatial extent. They are imaged over 55 km seaward of the deformation front and cover an estimated area of 17000 km2 and 7430 km2, respectively. The mean estimated surface area of the other eight events is 470 km2. Six of the ten observed slides exhibit compressive thrust features contained mostly within the seaward portion of the deposit. These are interpreted to be zones of impact-induced deformation from the slide material. Six of the ten deposits also contain at least one distinct region of high-amplitude, semi-coherent reflections, which we interpret to indicate detached slide blocks. Our observations from the seismic images suggest that most of these slides failed and displaced as cohesive bodies with high seafloor impact-velocities. Given the size and style of deformation of these deposits, some of these events could have generated great tsunamis. We will conduct stratigraphic analysis and integrate existing ocean drilling data to determine the age of these landslide events and investigate their impact on wedge evolution and tsunami hazards in this region.

Speaker: Eric Hiatt, Graduate Research Assistant, University of Texas Institute for Geophysics

Title: Limited Recharge on Early Martian Aquifers: Numeric & Analytic Recharge Rate Estimates As Constrained By Geomorphic and Geochemical Observations

Abstract: The surface of Mars shows past evidence for liquid water at its surface, however the time water remained and its volume remain open questions. In this work, we derive an idealized mathematical solution for an equation often used to study groundwater flow on Mars. We use this solution to analyze and validate a computer model based solution in a configuration that reflects the geometry associated with a planet scale problem. We use publicly available elevation data to populate our model as well as Martian shoreline elevations proposed in previous works. This allows us to investigate possible combinations of shorelines and recharge rates that produce model outputs that resemble observations made on Mars. Large volumes of work have been produced to characterize the deposition and erosional history of landforms on Mars. There is general consensus that specific Martian terrains show evidence that make groundwater upwelling more likely. The same is true regarding groundwater sapping. We use these studies to eliminate model combinations that either produce upwelling or sapping in areas without evidence for these processes. In doing so, we find that recharge rates published in the literature are ten to one hundred times higher than our model predictions.