Spring 2019

April 5, 2019

Speaker: Nicholas Ouellette, Stanford

Title: Incipient Motion in Erodible Beds Driven by Shear Flows


April 12, 2019

Speaker: Erik Petigura, UCLA

Title: Formation and Erosion of Small Planet Cores and Envelopes

Abstract: One startling result from the Kepler mission was that nearly every Sun-like star has a planet between the size of Earth and Neptune. Given the lack of such planets orbiting the Sun, Kepler has demonstrated that the Solar System is not a typical outcome of planet formation, in at least that one key respect. Therefore, to build a complete understanding of planet formation physics, we must look to extrasolar planets. I will present some new insights into the physics of planet formation, made possible by spectra from the California-Kepler Survey and astrometry from Gaia DR2. This bird's eye view sheds light on where planets form, the speed at which they are assembled, and the deep connection between planets and their host stars.

April 19, 2019

Speaker: Anne Socquet, University Grenoble Alpes

Title: Intriguing observations of the long term preparation of subduction earthquakes

April 26, 2019

Speaker: Kimberly Hill, University of Minnesota

Title: Discrete element modeling of bed surface variability and particle entrainment statistics in alluvial channels

Abstract: As they transport sediment downstream, alluvial channels deposit and erode materials along their beds in such a way that they play important roles in determining evolution of landscapes, longterm stratigraphy, and certain aspects of environmental health. To account for the non-uniformity of the bed material, the conservation of sediment in the alluvial bed is typically expressed in a discrete, or layer-based, formulation with a sharp geometric interface between the topmost part of the alluvial deposit, the active layer, and the rest of the deposit or substrate. However, due to the discrete representation of the deposit, which limits entrainment and deposition to the topmost part of the alluvial bed, active layer-based models are limited in their representation of features important for surface morphology, substrate evolution, and aspects related to ecological health: They cannot account for vertical sediment fluxes associated with bedform migration; they cannot reproduce the infiltration of fine particles in a coarse substrate; they fail to reproduce the fine details of the alluvial stratigraphy, and they cannot capture tracer and contaminant dispersal. Nearly two decades ago, Parker and colleagues (2000) provided a framework for a solution to this “discrete” dilemma in the form of a probabilistic Exner equation. We present a computational model designed to develop a physics-based framework for understanding the interplay between physical parameters of the bed and flow and parameters in the Parker (2000) probabilistic formulation. To do so we use Discrete Element Method simulations to relate local time-varying parameters to long-term macroscopic parameters. In this presentation we consider time varying parameters such as bed heights, velocity variations, and particle entrainment and deposition rates with long-term macroscopic parameters such as average bed shear stress and the standard deviation of bed height variations. While relatively simple, these simulations reproduce long-accepted empirically determined transport behaviors such as the Meyer-Peter and Muller (1948) relationship and provide the capability to build a physically robust framework in an efficient continuum-like framework.

May 3, 2019

Speaker: Walter Mooney, USGS

Title: New Insights into the Seismic Structure of the North American Upper Mantle

Abstract: I present new seismic images of the key structural elements of the upper mantle beneath North America. These images are significantly different from all previous studies. Unlike earlier work, we successfully image the cratonic lithosphere-asthenosphere boundary (LAB), and the 250-km-deep Lehmann discontinuity. We see evidence for plate tectonics in the mid-Proterozoic, and we identify a pronounced, if enigmatic, low velocity layer (LVL) above the mantle transition zone (410-discontinuity). These results have important implications for the evolution of the lithosphere and upper mantle.

May 10, 2019

Speaker: Justin Filiberto, Lunar and Planetary Institute

Title: Volatiles in the Martian Interior


May 17, 2019

Speaker: Ming-Chang Liu, UCLA

Title: Aluminum-26 chronology of dust coagulation and early Solar System evolution

Ming Chang

May 24, 2019

Speaker: Kathryn Materna, UC Berkeley

Title: Fault coupling on plate boundary faults at the Mendocino Triple Junction


May 31, 2019

Speaker: Gary Glatzmaier, UCSC

Title: Attempts to learn about the dynamics of Jupiter's deep interior by comparing computer simulations with what the Juno mission is measuring

June 7, 2019

Speaker: Mike Wong, UC Berkeley

Title: Interpretation of Juno measurements of Jupiter's composition

Abstract: Preliminary Juno Microwave Radiometer measurements have confirmed observational constraints over the past two decades on Jupiter's O/H ratio, finding a modest supersolar enrichment. The Juno O/H ratio is consistent with supersolar enrichments of other volatile species previously measured by the Galileo Probe. Although the O/H ratio is an important cosmochemical constraint on the formation of Jupiter and planets in general, there is some uncertainty in the bulk planetary O/H ratio due to partitioning of heavy elements between the core and the envelope of the planet. An additional cosmochemical ratio, the C/O ratio, largely avoids the issue of core/envelope partitioning. Jupiter's C/O ratio renders it unlikely that the primary vehicle for heavy element enrichment of Jupiter was large planetesimals with water ice clathrate composition. Other processes, such as accretion of amorphous ice, non-water ices, disk photoevaporation, and Bondi-Hoyle accretion are more plausible ways for Jupiter to have formed with the observed C/O, C/H, and O/H ratios. However, the wide range of chemical modification processes at work in the giant planet formation era means that firm conclusions regarding the planet's formation history require much more data. Specifically, the full composition (envelope and core) of all four giant planets must be measured to decode the cosmochemical markers of planet formation.