Geophysics and Tectonics Seminar - spring-2024
Chasing Darwin’s Shadow: Geophysics and Evolution in the Galapagos
April 3, 2024
noon - 1 p.m.
Geology 1707
Presented By:
- Mark Richards - University of Washington
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In the autumn of 1835, young geologist Charles Darwin spent a month exploring the Galapagos Islands, coming to the realization that these new and ephemeral volcanic habitats had given rise to new species of otherwise familiar creatures, and leading him to conclude that biological evolution was a fact, with natural selection as the primary mechanism. The active Galapagos mantle plume (“hotspot”) and mid-ocean ridge system is a spectacular showplace for plume-ridge interaction, with geophysical and geochemical signatures that elucidate upper mantle dynamics and evolution, and a geological history of continuously emerging and subsiding island habitats that have provided stepping stones for at least 20 million years of evolutionary divergence for mainland-derived species such as iguanas, tortoises, and finches. This talk will discuss how several different lines of geophysical investigations are revealing new secrets about the geological evolution of the Galapagos plume-ridge system, how these discoveries are helping us understand volatile (H2O) fluxes from the deep mantle, and new horizons for how to formally combine increasingly rich genetic constraints on evolutionary biology with the geological history of ancient island habitats to obtain a more integrated understanding of geo-biological evolution in ocean island systems.
How high was sea level in the Holocene?
April 4, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Roger Creel - Woods Hole Oceanographic Institution
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I will present work that aims to constrain sea-level change over the last glacial cycle by merging relative sea-level observations and glacial isostatic adjustment models via Bayesian statistical frameworks. I will first reconstruct Norwegian sea level over the last 16,000 years. I will then infer global mean sea level during the Holocene (11.7 - 0 thousand years ago), which is the last time global temperatures may have exceeded early Industrial (1850 CE) values. I will show that the available evidence is consistent with global mean sea level that exceeded early industrial levels in the mid-Holocene. I will also present the first quantitative estimates of Holocene mountain glacier volume and sea level change due to ocean thermal expansion.
Spatiotemporal Imaging of the Earth’s Near Surface with Fiber-Optic Sensors
April 10, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Yan Yang - Caltech
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Understanding the Earth's subsurface is essential for mitigating natural hazards and ensuring environmental sustainability. Seismological methods, which measure seismic velocity (v) and its relative temporal changes (dv/v), provide a 4D (space-time) view of the subsurface. However, high-resolution imaging and monitoring of the near surface—the top tens of meters subject to rapid spatiotemporal changes—remains challenging. This is primarily due to the prohibitive costs of dense seismic arrays necessary for capturing high-frequency signals that can probe shallow depths. Distributed Acoustic Sensing (DAS) offers an affordable solution by converting telecommunication fiber-optic cables into ultra-dense seismic arrays, enhancing our ability to study environmental phenomena with details as fine as tens of meters. When combined with seismic ambient noise interferometry, DAS enables time-lapse imaging of the near surface. In the talk, I will present an exemplary work in Ridgecrest, California, demonstrating a comprehensive spatiotemporal imaging approach for the near surface. The results provide new insights into high-resolution urban seismic hazard mapping and vadose zone soil moisture monitoring during California's drought periods.
Bridging seismology and oceanography with seafloor fiber-optic sensing
April 11, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Ethan Williams - University of Washington
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Observational geophysics conventionally relies on point sensors, from locating earthquakes and imaging subsurface structure with seismometers to forecasting coastal wave heights and detecting tsunamis with buoys. The emerging field of fiber-optic sensing offers a fundamentally different paradigm: distributed instead of point sensing, leveraging pre-existing telecommunications infrastructure to construct inherently multi-scale images of Earth’s dynamic processes over distances >100 km using a single instrument. In two topical vignettes, I will summarize some of my recent and ongoing research utilizing distributed acoustic sensing (DAS) on seafloor cables at the intersection of seismology and oceanography. (1) Offshore site characterization and ground motion. From quantitative estimation of tsunamigenic landslide hazard to interpretation of the turbidite record as a paleo-seismometer, accurate models of shallow sediment shear-wave velocity structure are required to anticipate the distribution of offshore ground motion in great earthquakes. Yet, because the water column is opaque to shear waves, this structure often remains poorly constrained, especially in the top 100s of meters. Interferometry of ambient seismic Scholte waves recorded with DAS reveals a typical power-law shear wave velocity profile immediately below the seafloor, with Vs30 as low as 150 m/s at locations ranging from the North Sea to the Oregon margin. This value is nearly an order of magnitude lower than used in Cascadia M9 simulations and in previous studies of turbidite triggering, suggesting that offshore site amplification has been systematically underestimated. With physics-based modeling of ambient seismic noise amplitude, I will show site amplification varies by nearly an order of magnitude over sub-kilometer distances and is strongly correlated with topography. Finally, I will summarize an ongoing experiment offshore southern Alaska combining seafloor compliance under ocean surface gravity wave loading with recordings of over 3000 local earthquakes to infer the nonlinear response of shallow sediment to strong ground motion. (2) Long-period DAS: from ocean mixing to seafloor geodesy. Where fiber-optic cables are unburied and exposed at the seafloor, DAS is also sensitive to temperature fluctuations from internal wave and tide dynamics in the bottom boundary layer, a region of enhanced ocean mixing but scarce observations. I will highlight two novel DAS datasets and discuss ongoing work to quantify rates of turbulent kinetic energy dissipation. DAS data recorded on a power cable across the Strait of Gibraltar show temperature transients up to 4 K associated with passing large-amplitude internal waves propagating on the near-surface thermocline. On the slope of Gran Canaria, an island off the coast of west Africa, temperature variability of about 2 K at 1-km depth decreasing to 0.2 K at 2.5-km depth reveals the bore-like propagation of the nonlinear internal tide at locations where the slope is near critical. The latter dataset also includes a long-wavelength signal proportional to the barotropic tidal pressure, including the lunar fortnightly variation, likely due to elastic strain from ocean-tidal loading. The demonstrated sensitivity of order 1 microstrain at 14-day period suggests that contemporary DAS already possesses sufficient long-period stability for (some) seafloor geodetic applications.
New Earth and Planetary Science Discoveries Enabled by the Optical Fiber Sensing Revolution
April 17, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Bradley Lipovsky - University of Washington
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Optical fiber sensors constitute the biggest revolution in geophysical and environmental sensor technology since digitization. Although traditional sensors have been refined through decades of incremental progress, optical fiber sensors provide an entirely new lens with which to study fundamental processes. These sensors are particularly advantageous for systems that require high spatial and temporal resolution (i.e., on the order of 1-10m spatial scale and 100 s to 100 kHz sampling rate). As director of the UW Fiber Lab, Dr. Bradley Paul Lipovsky has deployed these technologies in Antarctica, Greenland, Alaska, New Zealand, and at a dozen sites in Europe and the lower United States. The main focus of this research has been on studying Earth's cryosphere, submarine, urban, and otherwise difficult-to-instrument environments. This talk will focus specifically on use cases where basic knowledge has been gained regarding the calving front of large, ocean-terminating glaciers in Greenland, paleoclimatic history of the Antarctic ice sheet, monitoring of clean energy systems, and earthquake detection and ground motion hazard characterization. The presentation will conclude with a forward looking discussion regarding the rapid pace of development of basic optical physics and engineering, and the prospects for future growth at the intersection of optical fiber sensors and the Earth, Planetary, and Space Sciences
Geophysics of the changing hydro-cryosphere: From California’s aquifers to Greenland’s supraglacial lakes
April 18, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Stacy Larochelle - Columbia University
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Human activity and climate change are rapidly transforming Earth's hydrological and glaciological systems, posing critical challenges for global water security, coastal communities, and ecosystem resilience. In recent years, geophysics has become pivotal in both tracking hydro-cryospheric changes and unveiling the physics behind them. In this talk, I will discuss insight gained from applying a comprehensive geophysical approach to two critical and rapidly evolving systems: The Sacramento Valley aquifer system in California and supraglacial lakes on the Greenland Ice Sheet. Combining GNSS, InSAR, and GRACE/-FO satellite observations with in situ groundwater level measurements and lithologic logs in the Sacramento Valley reveals that the aquifer system has transitioned from a primarily reversible to irreversible deformation regime over the 2021-22 drought, indicating severe permanent compaction and loss of aquifer storage capacity that pose a serious threat to California’s water resources and infrastructure. In Greenland, we harness observations from on-ice GNSS stations, satellite imagery, ice-penetrating radar, seismometers, and water pressure instruments to decipher how meltwater lakes that form at the surface of the ice sheet interact through englacial stress to rapidly funnel surface meltwater to the ice-sheet bed and modulate ice basal sliding. Together, these case studies highlight the importance of multi-technique geophysical surveys in understanding the Earth’s changing hydro-cryosphere and enabling space-based monitoring at the global scale.
Closing Gaps in Polar Geophysics: How Combining Models and Observations Rewrites the Story of Mass Loss Across Antarctica
April 24, 2024
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Eliza Dawson - Stanford University
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Sea-level rise estimates rely on accurate model projections of ice sheet mass loss. However, ice sheet models lack sufficient observational constraints in critical parts of the ice sheet, including the difficult-to-observe ice-bed and ice-ocean interfaces. An important, but poorly constrained field is the temperature of ice sheets. The temperature at the ice sheet base affects the onset of sliding and ice thermo-frictional feedback mechanisms. In this presentation, I will explore fundamental processes related to the thermal state that are capable of driving mass loss in Antarctica but have been largely overlooked. I will show how joint ice sheet model and radar sounding data analysis is able to identify regions that could be vulnerable to basal thawing. This work redefines our understanding of Antarctica, opening the possibility that the East Antarctic Ice Sheet will become a new locus of mass loss.
Origins, evolution, & response to our rapidly changing world
April 25, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Austin Chadwick - Columbia University
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River systems form the arteries of Earth’s water and rock cycles, and directly sustain more than half the global population with food, water, and energy. As a geophysicist, I tackle fundamental questions about the origins and evolution of river systems on Earth and other planets, as well as practical concerns about environmental hazards and sustainability. In this talk, I highlight my research to date on three topics: river deltas, channel patterns, and the connection between rivers and the shallow subsurface. (1) First, I concentrate on river deltas. Using field data, morphodynamic modeling, and laboratory experiments, I quantify the natural river-diversion processes that give deltas their fundamental size and shape. By coupling this river-diversion model with next-century projections for sea-level rise, I show that mitigating flood hazards will require more sediment resources than previously thought. (2) Second, I investigate the origin of fundamental river channel patterns (e.g., meandering, braided). I present a state-of-the-art remote-sensing tool for quantifying riverbank migration—the first of its kind that is equally applicable to all river patterns—and apply it to 36 years of global Landsat imagery. My results demonstrate that river patterns originate from channel width (in)stability. Where riverbank erosion and accretion are in balance, rivers maintain stable meandering patterns. In contrast, where erosion outpaces accretion, rivers repeatedly widen and split to form braided patterns. (3) Third, I present ongoing work on how rivers interact with Earth’s shallow subsurface. Using a suite of geophysical methods (e.g., GPS/GNSS, rod-surface-elevation tables, sediment cores), I am characterizing how rivers build, deform, and at times contaminate subsurface aquifers in lowland Bangladesh. Preliminary results highlight saltwater-contamination risks in coastal farmlands, where man-made embankments disrupt natural connectivity between rivers and the subsurface. In partnership with the leading Bangladesh-based nonprofit organization (BRAC), this ongoing work supports the development of climate-change-adaptation plans to secure drinking water and sustainable agriculture for the 35+ million people living in lowland Bangladesh.
Improving Environmental Security in the Era of Climate Change
May 2, 2024
noon - 1 p.m.
Slichter Hall 3853
Presented By:
- Leonard Ohenhen - National Security Institute Department of Geosciences Virginia Tech
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Climate change is intensifying environmental hazards globally and imposing widespread consequences on human communities and ecosystems. During this century, climate change will cause an increase in the frequency and intensity of heat waves, hurricanes, and wildfires, and severely impact the world's freshwater resources through frequent droughts, alterations in precipitation and evapotranspiration patterns, and sea-level rise (SLR). Among these impacts, SLR is poised to have one of the most profound socioeconomic impacts due to the dense populations, critical infrastructure, and ecosystems situated along coastlines. Global mean sea level has risen by about 17 cm over the past 100 years, however, SLR on local and regional scales are the most relevant for coastal communities. Regional and local SLR are not uniform in space and time and are dependent on vertical land motion (VLM) - the raising or lowering of land. In most coastal communities the risks posed by rising sea levels are recognized, what is often underappreciated is the role of land subsidence (or lowering of land) to exacerbate these hazards. Without incorporating land subsidence into coastal vulnerability assessment, coastal communities may underestimate the environmental threat of rising sea levels, leading to policies that fall short of the required response. This presentation focuses on the use of sophisticated radar satellite data to create high-resolution maps of VLM at mm-level accuracy for the coasts of the United States mainland. I will discuss the impacts of land subsidence as a recognized and an emerging environmental security threat. I will present result of combining land subsidence data with climate change SLR projections to predict areas, people, and properties that will be affected by future flooding hazards in several U.S. coastal cities. The understanding of multi-hazard faced by communities is important to forge a path toward a sustainable future, where communities are shielded from the most severe consequences of environmental hazards in the era of climate change.