Colloquium Schedule

Innocent Ezenwa, Carnegie Earth and Planets Laboratory

Electrical Resistivity, Thermal Conductivity and Melting of Fe Alloys at Planetary Core Conditions

February 3, 2023 at 3:00 pm (PLS 1140)

The global magnetic field of the terrestrial planets is generated by the action of the dynamo, with motions thought to be due to convection. For the Earth, compositional convection from the release of light alloying elements at the inner core boundary has been known to be the leading driver of the present-day geodynamo. The onset of the nucleation of the inner core has been estimated to be about 1.5 billion years ago whereas the magnetic field has been in existence for over 4.5 billion years, evidenced in paleomagnetic rock record. The early dynamo has been assumed to be powered thermally before the birth of the inner core. However, literature data from the past decade have raised skepticism in the generation and sustainability of a thermally driven early geodynamo. To closely access this phenomenon, the understanding of the transport properties of Fe and its alloys at core conditions are needed. In this talk, I will present the electrical resistivity, thermal conductivity and the melting processes of Fe and its alloys with light elements (e.g., Si, C, S etc.) at extreme pressure and temperature conditions.

Melissa Sims, Johns Hopkins University

Compression in Multiple Regimes: Studies of Plagioclase, Cu, and MgO 

February 10, 2023 at 3:00 pm (PLS 1140)

Geoscience problems, from meteorite impacts to exoplanet interiors, require study of timescales that span orders of magnitude.  However, the shock and static experiments required to examine these processes occur over limited timescales, strain-rates, and temperatures compared to natural systems. The effects of kinetics and strain-rate are relatively unconstrained. It is therefore important to understand their effects during the experiments used to determine phase diagrams and equation of state models.  In meteoritic systems, understanding kinetic and strain-rate effects is vital due to the millisecond timescales of impact processes. For exoplanetary systems and the deep Earth, temperature, kinetics and strain-rate studies are important because rheological properties, such as viscosity, are dependent on phase identities and deformation mechanisms. In this presentation, I will discuss high pressure deformation and phase relations in plagioclase, copper, and MgO across compression regimes. In plagioclase, I examine the effects of compression-rate and kinetics on deformation, transition mechanisms, and subsequent phase formation using laser heated membrane driven compression. In copper, we compare computational work to laser shock experiments and examine textural changes across the fcc to bcc phase transition. In MgO, we examine the effect of temperature on the B1-B2 transition. We compare our ramp experiments to shock data collected along the Hugoniot and find differences in texture. These studies allow us to more accurately examine geological events with timescales from microseconds to billions of years. 

Click here if you would like to meet with the speaker.

Sean Peters, Middlebury College

February 17, 2023 at 3:00 pm (PLS 1140)

Lucien Nana-Yobo, Texas A&M University

March 10, 2023 at 3:00 pm (PLS 1140)

Rasheed Ajala, Columbia University

Multiscale Earth models: Wavefield verification and space exploration

March 31, 2023 at 3:00 pm (PLS 1140)

Accurate Earth models are fundamental to the study of the composition, structure, and evolution of our planet. Over four decades have passed since the introduction of seismic waveform inversion, yet regional- and global-scale Earth models rarely exceed 0.2 Hz in frequency content. A primary impedance to progress is the computational demand for optimization on a large spatial domain. Urban seismology offers a paradigm shift through advancements in field instrumentation using dense local seismograph arrays and telecommunication cables to provide wavefield records with unprecedented detail. Artificial intelligence also shows promise in accelerating wavefield simulations. One tractable strategy then uses these datasets to develop high-frequency models, possibly exceeding 1 Hz in perceived regions of interest, and incorporate them into longer-wavelength reference Earth models. To illustrate some elements of these research ideas and implementation challenges, we employ a case study in southern California, where earthquake hazard assessment is paramount to the seismological community. Local Earth models with a better characterization of sedimentary basins and fault zones are assimilated into the most popular regional models of the area to enhance them. We further investigate the accuracy of the multiscale models by measuring the errors in their wavefield predictions using complete three-component broadband seismograms. Some of the improvements in the reference models indicate that the approach represents a suitable path forward pending the next technological leap in computing.

Rodney Tollerson II, Caltech

April 7, 2023 at 3:00 pm (PLS 1140)

Lindy Elkins-Tanton, School Of Earth and Space Exploration, ASU

April 21, 2023 at 3:00 pm (PLS 1140)

The coordinator for the Colloquium Series is Dr. Megan Newcombe. You can contact her at newcombe [at] umd [dot] edu.

If you would like to suggest a speaker for a future seminar, click here.