Winter 2020

Tuesdays at 3:30 PM
Nat Sci Annex 101

January 7, 2020

Speaker: Harriet Lau, UC Berkeley

Title: Tidal Tomography: What an often-neglected phenomenon known as Earth tides can tell us about buoyancy in the deepest part of the mantle


Host: Mathis Hain

January 14, 2020

Speaker: David Dralle, CSU Sacramento

Title: The Salmonid and The Subsurface: The Importance of Rock Type for Understanding and Sustaining Stream Ecosystems

Abstract: How does the structure of the critical zone — especially below shallow soils and into saprolite and weathered rock — control water storage and release to California forests and streams? In this talk, I will address this question with a synthesis of observational and modeling results from three intensively studied California catchments. Findings reveal bottom-up, lithologic controls on weathering profiles, subsurface water storage capacity, and summer baseflow drainage from the critical zone. Results highlight how, in addition to plant physiology and climate, the subsurface is a key regulator of ecosystem productivity, stream temperature, water availability, and forest response to drought.


Host: Margaret Zimmer

January 21, 2020

Speaker: Demian Saffer, Penn State

Title: Recurring and triggered slow slip events near the trench along the Nankai subduction thrust

Abstract: Slow slip events (SSE), non-volcanic tremor, and very low-frequency earthquakes (VLFE) are well documented down-dip of the seismogenic zone of major faults, yet similar observations for the shallowest reaches of subduction megathrusts are rare. We document a family of repeating strain events in the Nankai subduction zone, updip of rupture zone of great (M8) earthquakes, using data from two borehole observatories which penetrate the hanging wall accretionary prism: IODP Site C0002, located 36 km landward of the trench; and Site C0010, located 25 km landward.

After filtering oceanographic noise using a local hydrostatic reference at each site, the pressure records over a 6 year period from 2010-2016 reveal 8 strain transients that are synchronous at the two holes. Of these, 6 arise spontaneously, and occur at ~1 yr intervals with durations of ~7-21 days. All are positive in sign at C0010, with consistent magnitudes of ~0.3-0.9 kPa; at Site C0002 three are negative in sign and two are positive, with magnitudes of ~0.3-0.7 kPa. The remaining 2 events are larger (1.7-2.7 kPa), negative in sign at both sites, and immediately follow: (1) the 2011 M9 Tohoku earthquake; and (2) the 2016 M7 Kumamoto earthquake. In some cases, the pressure transients are accompanied by swarms of low-frequency tremor and VLFE activity that appear to migrate trenchward. We interpret the pressure signals to reflect volumetric strain in response to SSEs. The data are well fit by slip of ~1-4 cm on a patch at the plate interface that extends 20-40 km in the dip direction, and is centered beneath Site C0002 (spontaneous events) or slightly updip (triggered events). A key implication is that the SSE accommodate ~30-50% of plate convergence across the outer ~40 km of the forearc. This coincides with a region of the shallow-most megathrust characterized previously by: (1) elevated pore fluid pressure; (2) transitional frictional behavior that promotes the nucleation of unstable slip at low sliding velocities; and (3) low stress magnitudes as constrained by analysis of wellbore failures. The repeating nature of the events, taken together with apparent triggering by regional earthquakes and the inference of low in situ stress magnitudes, indicates that the outermost reaches of the megathrust are highly sensitive to perturbation and are perched near a state of failure.

Host: Emily Brodsky

January 28, 2020

Speaker: Sonia Tikoo-Schantz, Stanford

Title: Magnetism with an impact: Chicxulub crater


Host: Ian Garrick-Bethell

February 4, 2020

Speaker: Gregor Steinbrügge, UT Austin/Stanford

Title: The structure and dynamics of Europa’s ice shell

Abstract: Jupiter’s moon Europa is a fascinating world and a prime candidate for life within our Solar System. I will focus on the outer ice shell of the satellite where the dissipated tidal energy sustains a subsurface ocean. If the ice shell allows for exchange processes, exogenic material deposited on the surface would be an important factor for habitability. If the exchange of material with the ocean is reciprocal, the shell can also serve as a window to the interior of the moon. I will discuss the recent progress in understanding the structure and dynamics of Europa’s ice shell and give an overview on how NASA’s upcoming Europa Clipper mission can contribute to the exploration of this unique icy satellite by radar sounding.


Host: Slawek Tulaczyk

February 18, 2020

Speaker: Xinting Yu, UCSC

Title: Integrating Materials Science Techniques into the Study of Planetary Hazes

Abstract: Photochemical produced hazes are prevalent in the atmospheres of planetary bodies in the solar system and could also be ubiquitous in exoplanetary atmospheres. Haze has been shown to affect the thermal structure and dynamics of planetary and exoplanetary atmospheres. It could also be a source of the surface material on planetary bodies and thus get involved in various surface processes. However, many physical and chemical processes involving the haze are unknown due to the lack of knowledge of the haze as a material. Because of its chemical complexity, many of the intrinsic properties of the haze are highly material dependent and currently have large uncertainties in models. At UCSC, I am using laboratory facilities across the campus to characterize cohesive and thermal properties of planetary and exoplanetary hazes. With the measured properties of the haze, I am exploring cloud-haze interactions in planetary and exoplanetary atmospheres, aeolian transport in the outer solar system with organics being the main transporting material, and haze evolution in deep planetary and exoplanetary atmospheres.


Host: Xi Zhang

February 25, 2020

Speaker: Gabrielle Wong-Parodi, Stanford

Title: Communication, Preparation, and Response: The Effects of Environmental Threats on Health and Behavior

Abstract: The social and behavioral sciences are critical for informing the development of policies to meet the challenge of global environmental change. Policies for mitigating environmental change or reducing the harm that it causes inevitably make assumptions about the behavior of the people who must execute or respond to those policies. Unless those assumptions are realistic, those policies may fail. Applying the social and behavioral sciences, decision science approaches any problem through three interrelated activities: formal analysis, characterizing the choices a fully informed rational actor would take; descriptive research, examining how people actually behave in those circumstances; interventions, designed to create viable, effective options and help decision makers choose among them. Each activity requires substantive collaboration with technical experts (e.g., climate scientists, geologists, engineers, hydrologists, regulatory analysts) and continuing engagement with decision makers. I apply a decision science approach in a variety of domains related to mitigating global environmental change or adapting to its effects, including preparing for sea level rise, adoption of emerging green transportation technologies, managing freshwater resources, and investment in green infrastructure. This talk will illustrate the approach through an example of my work on adapting to and preparing for episodic environmental threats (hurricanes), followed by ideas for moving forward. When successful, decision science can facilitate creating environmental policies that are behaviorally informed, realistic, and respectful of the people for whom they seek to aid. It can also help uncover critical relationships that affect the dynamics of human-environmental systems, suggesting targets for further collaborative research.


Host: Mathis Hain

March 3, 2020

Speaker: Adi Torfstein, Hebrew U of Jerusalem

Title: Uranium decay series as a quantitative link between climate change, landscape evolution and seawater compositions


Host: Terry Blackburn

March 10, 2020

Speaker: Elisa Mantelli, Princeton

Title: The origin of fast ice flow in continental ice sheets. A tale of fluid flow instabilities


Host: Slawek Tulaczyk