DeFord Lecture: Astrid Holzheid

UTIG Seminar Series: Caroline Beghein, UCLA

Speaker: Caroline Beghein, Associate Professor, Dept. of Earth, Planetary, and Space Sciences, University of California Los Angeles

Host: Thorsten Becker

Title: Physical Constraints on the Oceanic Plate From Seismic Tomography and Thermodynamics

Abstract: The nature of the interface between the lithosphere and underlying asthenosphere in oceanic settings is still the subject of debate. In particular, questions remain regarding whether it is a temperature-dependent rheological transition, as expected in a thermal convection system, or it is additionally affected by the presence of melts and/or fluids. In this talk, I will present tomographic models of upper mantle seismic wave velocities and anisotropy under the Pacific plate and discuss their interpretation in terms of temperature, melt, and water content.
Our models resulted from the inversion of fundamental ande surface waves using both regularized inverse techniques and a Monte Carlo approach to quantify uncertainties. We found that both shear-wave velocity anomalies and azimuthal anisotropy patterns vary with seafloor crustal age. The thickness of the plate determined from isotropic velocities increases with crustal age, as expected for a thermal control, though uncertainties can be substantial. Similarly, the depth at which the azimuthal anisotropy is well aligned with the plate motion direction increases with age and tends to display a half-space cooling age dependence. In addition, we found that the depth of the Gutenberg discontinuity, which has been mapped in other studies with body wave data and is often associated with the lithosphere-asthenosphere boundary (LAB) and the presence of melts, coincides with high-vertical gradients in azimuthal anisotropy and is located within the age-thickening seismic lithosphere. We hypothesize that the Gutenberg discontinuity results from dehydration of the mantle underlying the mid-ocean ridge, resulting in a chemically depleted, viscous layer that translates away from the spreading center and becomes overprinted by lower temperatures as the plate cools down.
On the contrary, while radial anisotropy models obtained from inversions of Love and Rayleigh wave dispersion do not display any obvious age dependence, we found that they are generally less robust and reliable than azimuthal anisotropy and isotropic velocity models. They tend to differ in pattern depending on which surface wave dataset is employed and their uncertainties are sufficiently large that they cannot be used to constrain the LAB depth reliably.
To better constrain the physical nature of the LAB, we tested our isotropic shear wave velocity models against synthetic models calculated based on thermodynamic considerations for half-space and plate models. We tested the hypothesis that asthenospheric low seismic velocities may have a solid state origin and can be explained purely by thermal effects, including those on seismic attenuation, without any requirement for an additional effect of melt. Our results suggest that, while any direct signature of sub-ridge melt would be too small-scale to be resolved by our data, no significant fractions of melt are needed to explain the shear wave velocities. We note, however, that tomography uncertainties are large and some amount of melt could thus be present but not resolved. In addition, our tomography results are best explained by synthetic models that include a decrease in attenuation due to dehydration by melting at the ridge than by dry models or plate models. This is generally consistent with our azimuthal anisotropy model interpretation, but additional studies to refine the resolution of the anisotropy models are needed.

DeFord Lecture: Liviu Matenco

UTIG Seminar Series: Chris Glein, Southwest Research Institute

Speaker: Chris Glein, Southwest Research Institute San Antonio

Host: Duncan Young

Title: Enceladus: Pathfinder of alien oceans

Abstract: The past decade brought a remarkable transformation in humanity’s understanding of oceans. We used to really know only one ocean – the one that our species has grown up with on Earth. Now, we are starting to learn about other oceans that exist beyond Earth. This talk will focus on Saturn’s moon Enceladus, which is commonly called an “ocean world”. I will present a historical perspective of our exploration of Enceladus, primarily by NASA’s Cassini mission. I will also describe how we came to learn that Enceladus hosts a deep ocean under its icy exterior, and what the ocean is like mainly in terms of its geochemistry and potential habitability. Lastly, I will discuss ongoing efforts to use our experience at Enceladus to guide future exploration of Enceladus and other ocean worlds of great astrobiological interest, such as Jupiter’s moon Europa.

De Ford Lecture Series: Chris Bell

UTIG Seminar Series: Bob Kopp, Rutgers University

PLEASE NOTE: THIS WILL BE A REMOTE PRESENTATION

THE PRESENTATION WILL BE SCREENED LIVE AT ROC 1.900

Speaker: Bob Kopp, Rutgers University

Host: Pedro DiNezio

Title: Coasts in times of sea-level rise

Abstract: Around the world, sea levels are rising in response to warming oceans, melting glaciers, and shrinking ice sheets – and even faster rise is projected in the coming century. In this talk, I will explore the different physical processes driving sea-level rise, the geological record of past sea-level changes, methods for assessing the probability of different levels of future changes, and the implications for future coastal flood risks.

Hot Science - Cool Talk: Sustainability of Outer Space

Is it really true that there are over 20,000 junked satellites in outer space? What is their fate? Dr. Moriba Jah examines what we can do to make space safe, secure and sustainable in the long term.

Save the Date - Annual Tailgate Party

DeFord Lecture: Sharon Mosher

DeFord Lecture: Melissa Sims

UTIG Seminar Series: Kelly Hereid, Chubb Corp.

Speaker: Kelly Hereid, Chubb Corp.

Host: Pedro DiNezio

Title: Woolly problems in catastrophe modeling

Abstract: Insurance companies rely on catastrophe models, which simulate thousands of years of natural disasters, to quantify their exposure to extreme events. However, many of these extremes are highly susceptible to impacts from climate change. Here I highlight key emerging research areas in the science of catastrophe modeling that may be influenced by climate change, and how catastrophe modeling can be used to quantify economic impacts on the built environment. The effect of sea level rise on hurricane storm surge, expanding boundaries of hurricane impacts, compound disasters that incorporate extreme rainfall events, and high-resolution hazards with a complex relationship to climate change are all opportunities for climate research to inform risk management practices in the public and private sectors.

De Ford Lecture Series: Zoltan Sylvester