EAS & The Global Change Program Presents Dr. Marshall Shepherd, University of Georgia

Dr. J. Marshall Shepherd is a leading international expert in weather and climate and is the Georgia Athletic Association Distinguished Professor of Geography and Atmospheric Sciences at the University of Georgia. 

Dr. Shepherd was the 2013 President of American Meteorological Society (AMS), the nation’s largest and oldest professional/science society in the atmospheric and related sciences. Dr. Shepherd serves as Director of the University of Georgia’s (UGA) Atmospheric Sciences Program and Full Professor in the Department of Geography where he is Associate Department Head. 

Dr. Shepherd is also the host of The Weather Channel’s Award-Winning Sunday talk show Weather Geeks, a pioneering Sunday talk podcast/show and a contributor to Forbes Magazine. Dr. Shepherd is the 2018 recipient of the prestigious AMS Helmut Landsberg Award for pioneering and significant work in urban climate and in 2017, he was honored with the AMS Brooks Award, a high honor within the field of meteorology. 

Ted Turner and his Captain Planet Foundation honored Dr. Shepherd in 2014 with its Protector of the Earth Award. Prior recipients include Erin Brockovich and former EPA Administrator Lisa Jackson. He is also the 2015 Recipient of the Association of American Geographers (AAG) Media Achievement award, the Florida State University Grads Made Good Award and the UGA Franklin College of Arts and Sciences Sandy Beaver Award for Excellence in Teaching. 

In 2015, Dr. Shepherd was invited to moderate the White House Champions for Change event. He is an alumni of the prestigious SEC Academic Leadership Fellows program. Prior to UGA, Dr. Shepherd spent 12 years as a Research Meteorologist at NASA-Goddard Space Flight Center and was Deputy Project Scientist for the Global Precipitation Measurement (GPM) mission, a multi-national space mission that launched in 2014. 

President Bush honored him on May 4th 2004 at the White House with the Presidential Early Career Award for pioneering scientific research in weather and climate science. Dr. Shepherd is a Fellow of the American Meteorological Society. Two national magazines, the AMS, and Florida State University have also recognized Dr. Shepherd for his significant contributions. Dr. Shepherd was the 2016 Spring Undergraduate Commencement speaker at his 3-time Alma Mater, Florida State University. He was also the 2017 Graduate Commencement speaker at the University of Georgia.

Dr. Shepherd is frequently sought as an expert on weather, climate, and remote sensing. He routinely appears on CBS Face The Nation, NOVA, The Today Show, CNN, Fox News, The Weather Channel and several others. His TedX Atlanta Talk on “Slaying Climate Zombies” is one of the most viewed climate lectures on YouTube. 

Dr. Shepherd is also frequently asked to advise key leaders at NASA, the White House, Congress, Department of Defense, and officials from foreign countries. In February 2013, Dr. Shepherd briefed the U.S. Senate on climate change and extreme weather. He has also written several editorials for CNN, Washington Post, Atlanta Journal Constitution, and numerous other outlets and has been featured in Time Magazine, Popular Mechanics, and NPR Science Friday. He has over 90 peer-reviewed scholarly publications. Dr. Shepherd has attracted $3 million dollars in extramural research support from NASA, National Science Foundation, Department of Energy, Defense Threat Reduction Agency, and U.S. Forest Service. 

Dr. Shepherd was also instrumental in leading the effort for UGA to become the 78th member of the University Corporation for Atmospheric Research (UCAR), a significant milestone for UGA and establishing UGA’s Major in Atmospheric Sciences.

Dr. Shepherd currently chairs the NASA Earth Sciences Advisory Committee and was a past member of its Earth Science Subcommittee of the NASA Advisory Council. He was a member of the Board of Trustees for the Nature Conservancy (Georgia Chapter), National Oceanic and Atmospheric Administration (NOAA) Science Advisory Board, Atlanta Mayor Kasim Reed’s Hazard Preparedness Advisory Group United Nations World Meteorological Organization steering committee on aerosols and precipitation, 2007 Inter-governmental Panel on Climate Change (IPCC) AR4 contributing author team, National Academies of Sciences (NAS) Panels on climate and national security, extreme weather attribution, and urban meteorology. 

Dr. Shepherd is a past editor for both the Journal of Applied Meteorology and Climatology and Geography Compass, respectively.

Dr. Shepherd received his B.S., M.S. and PhD in physical meteorology from Florida State University. He was the first African American to receive a PhD from the Florida State University Department of Meteorology, one of the nation’s oldest and respected. He is also the 2nd African American to preside over the American Meteorological Society. He is a member of the AMS, American Geophysical Union, Association of American Geographers (AAG), Sigma Xi Research Honorary, Chi Epsilon Pi Meteorology Honorary, and Omicron Delta Kappa National Honorary. He is also a member of the Alpha Phi Alpha Fraternity, Inc. and serves on various National Boards associated with his alma mater. Dr. Shepherd co-authored a children’s book on weather and weather instruments called Dr. Fred’s

Weather Watch. He is also the co-founder of the Alcova Elementary Weather Science Chat series that exposes K-5 students to world-class scientists. Dr. Shepherd is originally from Canton, Georgia. He is married to Ayana Shepherd and has two kids, Anderson and Arissa.

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The School of Earth and Atmoshperic Sciences Presents Dr. Frances Rivera-Hernandez, Dartmouth University

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A School of Earth and Atmospheric Sciences Presents Dr. Eric O. Lindsey, Nanyang Technical University

Portrait of an Earthquake: Geodetic Perspectives on the Physics of Faulting in the Himalaya

Plate-boundary faults are massive, complex structures that display a wide range of seismic and aseismic behavior, and understanding the physics that govern their activity requires a highly multidisciplinary approach. 
 
In this talk, I will use a combination of geodetic, geologic, and numerical results to show how the 3D structure of the Main Himalayan thrust controls its frictional behavior, and offer a new perspective on the interplay between earthquakes and long-term fault evolution.

Following the 2015 Nepal earthquake, I provided the first high-resolution, wide-swath synthetic aperture radar image of the resulting ground deformation to the geophysics community. These data reveal clearly where the fault slipped, and by integrating them with 3D structural models, we show that the earthquake was bounded on all sides by sharp bends or ramps along the fault.

Combining these results with long-term GPS observations of ground motion, I demonstrate how the fault structure controls both the long- and short-term behavior of the megathrust throughout the Himalaya, and in turn, how fault friction interacts to control the fault structure over time.

In the future, developing a better understanding of the interaction between the structure and behavior of faults will require input from a diverse set of geophysical techniques and disciplines. 
 
In addition to mapping ground deformation at high precision with synthetic aperture radar, I will show some promising new ground-based geodetic methods and physics-based numerical tools I have pioneered. Together with seismic and geologic observations, they will enable us to paint a more complete picture of how earthquakes interact with and control the faults they occur on.

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The School of Earth and Atmospheric Sciences Presents Dr. Behrooz Ferdowsi, Princeton University

Granular Physics of Rock Friction at Low Slip Rates

Modeling earthquake fault slip requires reliable constitutive relations describing friction. A commonly accepted empirical framework, known as “Rate- and State-dependent Friction” (RSF), suggests that frictional strength depends on the fault slip rate and (history dependent) ‘state’ variable. 

Although none of the empirical RSF laws proposed thus far, including RSF “Aging” and “Slip” versions, adequately describes the full range of laboratory friction data, the Slip law is clearly superior, and does an excellent job of modeling both velocity steps and slide-holds rock laboratory loading protocols.  Despite this, and unlike the Aging law, there is no clearly-established physical basis for the Slip law.

In this seminar, I will first provide an overview of the RSF laboratory observations and the empirical (standard) RSF modeling framework. I will discuss the shortcomings of the standard model and that at the moment, unfortunately, no physics-based constitutive relation exists for rock friction. 

It is noteworthy that natural fault zones typically contain a localized shear zone, also known as the granular gouge layer, and that laboratory experiments on even initially bare rock surfaces develop a gouge layer through mechanical wear. 

Based on this observation, I have developed a granular physics-based simulation to investigate the origins of RSF in rocks. In my model, I have intentionally left out time-dependent plasticity at the grain contact-scale, that is traditionally thought to be the primary origin of RSF in the standard model. 

I will show results from the granular simulations that reproduce and explain robust features of real rock and gouge friction data. Namely, the granular model captures: (i) the functional form of the transition to new values of the dynamic friction following a change in shearing velocity; (ii) logarithmic-with-time healing of the frictional interface and its dependence on prior shear rate, during the load-point hold. 

These laboratory observations currently have no other first-principles or physics-based explanations. The success of the granular model seems to be arising from the logarithmic-with-time (slow) compaction and slow relaxation dynamics in the model that is a hallmark of granular materials and disordered solids.

I will next discuss how I am working to further unify the search for constitutive relations for friction and deformation of rocks with the recent exciting developments within the broader community of soft condensed matter physicists for a state variable and an Equation of State for granular systems. Such a state variable and equation of state are essential for confidently applying laboratory-derived friction laws to fault slip in the Earth.  

In addition to earthquake fault zones, the RSF behavior is ubiquitously observed in friction of disordered Earth materials and interfaces, including ice-on-rock, sediments on Earth’s surface and damaged rocks in the shallow crust. 

Therefore, the implications and applications of my work are broad. I will discuss some of my near future research plans related to Earth’s near-surface processes, in addition to earthquake source physics.

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The School of Earth and Atmospheric Sciences Presents Dr. Hao Cao, Harvard University

A Magnetic Perspective on the Interiors of Saturn and Mercury

Magnetic fields are windows into planetary interiors. The existence and properties of the planetary magnetic fields reflect the interior structure, dynamics, and evolution of the host planets. Recent observations from the MESSENGER, the Cassini, and the Juno missions have revealed many surprising features in the magnetic fields and interiors of Mercury, Saturn, and Jupiter, respectively. 

In this talk, I will mainly present my analyses and interpretations of the magnetic fields of Saturn and Mercury. For Saturn, the new features of the planet’s magnetic field revealed by the Cassini Grand Finale will be reported, including the small-scale axisymmetric magnetic structures and the new upper limit on the non-axisymmetry of the field. Implications on deep zonal flows (differential rotation) and stable stratification inside Saturn will be discussed. 

For Mercury, with the help of numerical dynamo experiments, I will show that the peculiar north-south asymmetry in Mercury’s magnetic field can be reconciled with the slow rotation of Mercury, extensive iron snow within Mercury’s liquid core, and a relatively small solid inner core. 

In closing, I will highlight the magnetic aspects of the ongoing Juno mission and a few upcoming planetary missions (e.g. Psyche mission to asteroid 16 Psyche, Clipper to Europa, BepiColombo to Mercury, JUICE to Ganymede, and a possible mission to Uranus/Neptune) and how they will help answer questions ranging from the thermal evolution history of asteroid 16 Psyche to the salinity of Europa’s ocean.

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The School of Earth and Atmospheric Sciences Presents Dr. Christopher Milliner, NASA Jet Propulsion Laboratory

Using Novel Geodetic Imaging Techniques to Understand How Faults Release Strain and Track Water Storage Changes Following Extreme Hydrologic Events

Measurements of surface deformation using geodetic imaging techniques can provide observational constraints on the way faults rupture the surface and the amount of terrestrial water mass held in a region. 

Recent advancements in the resolution of optical satellite imagery, increasing density of continuous GPS networks, and near-global coverage of radar interferometry (InSAR), now offer a diverse toolset with which to study fault zone deformation and transient hydrologic processes. Here, I will first show how the use of pixel tracking applied to satellite images taken before and after two large-magnitude earthquakes can provide spatially complete measurements of the strain distribution across the fault damage zone. 

I will explore how these observations can deepen our understanding of faulting kinematics and mechanics such as, how the magnitude and width of inelastic strain may differ between fault systems, to variations of slip along ruptures and with depth.

Second, I will show how networks of continuous GPS stations can be used to track transient changes in terrestrial water storage following extreme precipitation events, such as large hurricanes. 

The mass loading effect of water on Earth’s elastic crust causes millimeter subsidence and uplift as water accumulates and dissipates, respectively, which can be measured using precise GPS elevation positioning. Using GPS measurements of elevation changes following Hurricane Harvey I will show we can infer a region’s hydrologic properties, from the amount of water a drainage area can hold, to how fast an area can dissipate water and by what means. 

The use of emerging geodetic techniques, with higher rate and more precise positioning, now allows new approaches to characterize the seismic hazard faults pose to the built environment, how faults accumulate and release strain, and improved monitoring of a region’s water security and preparation for future extreme precipitation events.

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The School of Earth and Atmospheric Sciences Presents Dr. Matthew Siegler, NASA Jet Propulsion Laboratory

 Dr. Matthew Siegler will provide an overview of ongoing and future geothermal heat flow projects on the Moon and Mars. We will look at the recently landed InSight mission, new analysis of Apollo heat flow data, Orbital microwave-wavelength measurements, and a dawning era of or subsurface planetary exploration and planetary geophysics.

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The School of Earth and Atmospheric Sciences Presents Dr. Elvira Mulyukova, Yale University

Grain Scale Physics of Plate Boundaries: Tectonic Processes from Geological to Human Time Scales

 The motion of tectonic plates along our planet’s surface shapes the relationship between the solid Earth and its surrounding elements, including the atmosphere, ocean, and life. 

Examples include the chemical reactions between minerals and water at seafloor spreading centers, as well as volcanic degassing at subduction zones, both of which link plate tectonics to the global volatile cycles. Furthermore, volcanism and seismicity along plate boundaries have a clear impact on human life. 

However, Earth is enigmatic in that it is the only known terrestrial body that has plate tectonics. Understanding how plates and plate boundaries form and evolve is fundamental to our understanding of the Earth system as a whole. 

In order for a new tectonic plate to form, the cold and stiff oceanic lithosphere must be weakened sufficiently to deform at tectonic rates. The weakening mechanisms involve the microscale physics of mineral grains and their control on the strength of the lithosphere. 

In this talk, I will present the microphysics of lithospheric weakening by mineral grain size reduction, known as grain damage, and its application to tectonic scale processes, such as subduction initiation. 

I will also present the newly developed theory of grain mechanics, which couples evolution of grain size and intragranular defects. The new model predicts oscillations in grain size, and possibly material strength, on a time scale that is relevant to earthquake cycles and postseismic recovery, thus connecting plate boundary formation processes to the human time scale.

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The School of Earth and Atmospheric Sciences Presents Dr. Laura Stevens, Columbia University

Mass loss from the Greenland Ice Sheet contributes a quarter of today’s global sea level rise. Roughly half of this Greenland Ice Sheet mass loss is derived from accelerated flow of the ice sheet due in part to the ability of surface meltwater to access, lubricate, and enhance sliding along the ice-bed interface. 

Determining the processes that govern the ice sheet’s dynamic flow response to increased surface meltwater production is critical for understanding how ice sheets work and predicting how ice sheets will behave in our warming climate. 

This talk will examine the influence of meltwater on two regimes of Greenland Ice Sheet flow: (1) rapid supraglacial lake drainages in the slowly-flowing inland margin, and (2) diurnal meltwater influences on fast-flowing marine-terminating outlet glaciers. 

A combination of Global Positioning System (GPS) observations of ice-sheet surface displacement, inverse methods, and time series analysis will be used to investigate these processes.

In the slow-flowing regime, rapid supraglacial lake drainages provide an ideal natural experiment that enables us to probe the upper limits of meltwater’s influence on ice-flow acceleration. These lake drainages are spectacular events, where hydro-fractures—water-driven crevasses—drain ~3-km diameter lakes from the surface to the bed of the ice sheet in a matter of hours at rates equivalent to the discharge across Niagara Falls. 

This half of the talk will investigate what triggers rapid lake drainage using a Network Inversion Filter (NIF) to invert a dense, local network of GPS observations during three lake drainage events.

In the fast-flowing regime, marine-terminating outlet glaciers are the gatekeepers of the inland ice sheet’s access to the sea. The dynamics of these glaciers are governed by complex interactions between the atmosphere, ocean, and ice-sheet bed. 

This half of the talk will investigate how atmospheric and oceanic forcing influence short-term (hourly) variations in horizontal flow of Helheim Glacier, East Greenland as observed by an array of GPS receivers. Improved mechanistic understanding of how tidal and atmospheric forcing drive marine outlet glacier flow is critical for determining how rapidly ice will be discharged into the ocean as these regions warm.

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