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Online Seminars & Events

Week of October 19, 2020
MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY
GPS Division Seminar
12:00 pm to 1:00 pm
DIX Planetary Science Seminar
4:00 pm to 5:00 pm
Environmental Science and Engineering Seminar
4:00 pm to 5:00 pm
Geoclub Seminar Series
4:00 pm to 5:00 pm
Seismo Lab Seminar
4:00 pm

Division Seminar

Mondays from 12:00pm to 1:00pm
For more information, please contact: Leticia Calderon

" Submarine volcanic eruptions "

Michael Manga, UC Berkeley

I will summarize some open questions about underwater volcanic eruptions and what we have learned from a couple that occurred in the past decade. I will address the following questions: how are submarine eruptions different from those on land? What is the fate of erupted material?

Research Interests

Michael Manga studies the geological processes that shape Earth's surface. This includes understanding the reasons why planets have volcanoes, why those volcanoes erupt in so many different ways, and how those volcanic eruptions affect climate and other Earth systems. He studies how geological processes affect and are affected by groundwater, including the formation of geysers, the effects of earthquakes on fluid flow in Earth's crust, and the origin of springs and mud volcanoes. He also studies similar processes on other planets, including the eruption of water on icy satellites in the outer solar system, and deciphering the coupled history of water and volcanism on Mars.

" Linking microbes and climate: Redox-informed metabolic biogeography and a unified theory for organic matter accumulation "

Emily Zakem, University of Southern California

Abstract: Microbial activity mediates the global cycling of carbon, oxygen, nitrogen, and other elements, which includes the fluxes of radiatively active atmospheric gases. I aim to understand the activity and biogeochemical impact of microorganisms from underlying chemical and physical constraints. For example, the key redox chemistry underlying a metabolism can be used to constrain parameterizations of diverse microbial metabolisms in global biogeochemical models. With this approach, the presence or absence of each metabolism emerges dynamically from ecological interactions, potentially expanding model applicability to diverse and unobserved environments. However, the cycling of organic matter involves additional complexity. Seemingly competing hypotheses have been proposed to explain organic matter accumulation. Using a mechanistic model, I have developed a new theoretical framework that explains how organic matter predictably accumulates due to biochemical, ecological, and environmental factors, which subsumes the previous hypotheses. The framework derives from the ecological dynamics of microorganisms, the dominant consumers of organic matter.

"Repeating earthquakes and deviations from scale invariance of earthquake rupture"

German Prieto, National University of Colombia

Abstract:

Many features in nature seem to be scale invariant - fault size or fault roughness, ocean bathymetry and earthquake rupture – and are often described using a power-law (or scaling law). The scaling of earthquake source parameters has been (and still is) a controversial aspect in earthquake seismology. One such scaling laws suggests that as earthquakes become larger, so does the rupture duration (cubed power) or rupture area (3/2 power). But, do large earthquakes radiate seismic waves more efficiently than their smaller counterparts (e.g., per unit area)? Questions like this have important implications on the dynamics of earthquake rupture.

We study repeating intermediate-depth earthquakes with significantly different magnitudes, thus deviating from scale invariance. We test various rupture models (and corresponding seismic waveforms) along a circular rupture patch, varying its area, rupture velocity and slip to determine what combinations of source parameters can explain the observations. Our results suggest that the rupture area (and rupture duration) is constant regardless of earthquake magnitude and thus earthquake slip significantly increases for larger events. Our model explains the differences in scaling of intermediate-depth earthquakes with respect to shallow events. A major implication is that it is possible to predict the eventual magnitude of these earthquakes within the first few tenths of a second. Caveat: That is assuming you know the earthquake belongs to a particular repeating family.

Brief Bio:
I am Associate Professor at the Departmaento de Geociencias, Universidad Nacional de Colombia in Bogotá. Prior to that appointment, I was a faculty member at MIT, at Universidad de los Andes, a Postdoctoral scholar at Stanford University and did my PhD at Scripps (UC San Diego).

My research focuses on understanding the diversity of earthquakes and the associated ground motions expected on the surface of the Earth. My main interest is to use seismic records to understand the earthquake source, the interior of the Earth and how both affect the ground motions that we feel on the Earth's surface. Seismological observations are affected by the internal structure of the Earth, for example amplification of seismic waves in sedimentary basins. The nature of the earthquake source has also a significant impact on ground motions, and I am interested in a better understanding of earthquake ruptures, i.e., are large earthquakes different from the more common small ones?

"TBD"

Martha Gilmore, Wesleyan University

"TBD"

Boswell Wing, University of Colorado

"TBD"

Sonia Tikoo, Stanford University

"TBD"

Dylan Jones, University of Toronto

DIX Planetary Science Seminar

Tuesdays at 4:00 pm
For more information, please contact Aida Behmard

" The effects of planetary-scale volcanism on Io's interior structure and evolution "

Dan Spencer, Postgraduate, Department of Earth Sciences, Oxford University

Abstract: Global volcanism has dominated the evolution of many worlds from the early Earth at the time when life emerged, to potentially habitable ocean worlds like Enceladus. By affecting large proportions of planetary interiors, far below the surface expressions that we observe, planetary volcanism leads to thermal, structural, and chemical evolution, and in the case of the Earth, has facilitated life. Io is an extreme ‘end-member' that allows us to study planetary volcanism in relative isolation from other processes. A complete picture of planetary volcanism requires an investigation of volcanic systems in the crust together with magmatic processes in the underlying mantle that fuel them. This is a significant challenge because crustal volcanic systems evolve on much shorter timescales than planetary mantles, which has led previous works to focus on each domain separately. I develop a new parametrisation for the rapid, complex processes of volcanic systems that allow them to be investigated alongside much slower mantle processes. With this approach I propose: a) the formation of magmatic intrusions is a fundamental part of Io's crustal heat balance, and controls the crustal thickness; b) magmatism and volcanism leads to a stratification in Io's mantle, predicting the formation of ultra-high-temperature lava at depth; c) Io's long-wavelength topography and crustal thickness variations can be used to infer the underlying tidal heating distribution.

" TBD "

F. Nimmo, UCSC

Environmental Science and Engineering Seminar

Wednesdays from 4:00pm to 5:00pm
For more information, please contact: Bronagh Glaser

"Seismotectonic and climatic controls on the geologic carbon cycle"

Gen Li, Caltech

Abstract:

Plate tectonics and climate are two major drivers of the global carbon cycle over geological timescales. In this talk, I will present two studies examining how large earthquakes and a changing climate impact the carbon cycle, with a focus on particulate organic carbon (OC) – an important, yet less-well-understood component in the carbon cycle. The first study will illustrate how the 2008 Mw7.9 great Sichuan earthquake changed the carbon cycle in the eastern Tibetan mountains. Combining river system sampling and geochemical measurement, I found that the earthquake-triggered landslides accelerated OC erosion and burial, leading to an 8x increase in the capacity of the mountain range to draw down atmospheric CO2. The second study will focus on a tributary floodplain of the Yukon River, central Alaska, where the warming climate has largely altered the carbon cycle. In those Arctic floodplains, OC is eroded from permafrost soils and transported by rivers to the ocean for long-term storage. Previous studies suggest that the OC cycling processes are accelerated by warming-induced bank erosion. I will show that significant loss of OC occurred during transfer from soils to rivers, using measurements of sediment and OC samples collected from the studied floodplain. Overall, these two studies provide modern perspectives on how carbon cycle systems respond to changes in tectonics and climate, emphasizing the importance of landforms and geomorphic processes in regulating the OC cycle.

"Is Global Warming Inhibiting an Incipient Ice Age?"

George Philander, Princeton University

Abstract: The present is a precarious moment in Earth's history. Records of the dramatic amplification of climate fluctuations over the past 3 Myr indicate that an Ice Age is imminent, except that the recent man-induced rise in atmospheric CO2 levels is inducing global warming. What will happen over the next several decades? Answers from a reductionist approach using models based on the laws that govern climate variability have significant uncertainties. There is "deep dissatisfaction with the ability of our models to inform society about the pace of warming, how this warming plays out regionally, and what it implies for the likelihood of surprises" (Palmer and Stevens, 2019, PNAS). An empirical or holistic approach based on records of past climates is also inadequate because "… we still lack a unified mechanistic understanding that links changes in Earth's orbit to the Ice Ages" (Hodell, 2016, Science). That criticism of the hypothesis that polar glaciers wax and wane in response to local Milankovitch forcing stems from questionable assumptions: that the ocean obligingly provides fresh water for glaciers, and that the atmosphere passively transports that water from low to high latitudes. This draws attention to the global structure of Milankovitch forcing. The two main components of this driver of the atmosphere and ocean, precession and obliquity, pose the following questions.

  1. How does precession, which merely redistributes sunlight over the course of a year without changing the annual average, induce a 20 Kyr recurrent signal whose cold phase in tropical Pacific sea surface temperature is at a peak when perihelion coincides with the southern, not northern summer solstice? Why is the ITCZ north of the equator?
  2. How do 40 Kyr obliquity oscillations, which merely redistribute sunlight spatially without changing the global average, induce 40 Kyr oscillations in globally averaged temperature? Why is the phase of that signal such that tropical SST is at a minimum when sunlight is intense in low latitudes?
  3. Could the alternating warming and cooling trends of the saw-tooth signal of the past 0.8 Kyr, and the preceding cooling trend from 3 to 1 Myr, be a natural (as opposed to forced) climate mode with feedbacks sustaining the trends and thresholds reversing them? If so then the saw-tooth would be present in the absence of Milankovitch forcing which serves as pacemaker for the thresholds, lending regularity to an otherwise irregular signal.

This seminar proposes that the available observational and theoretical studies of past and present climates provide tentative answers to these questions – "a unified mechanistic understanding" of Ice Ages – and identify a strategy for improving climate models by means of a marriage of holistic and reductionist approaches. One tentative conclusion: rising CO2 levels are interfering with the oceanic heat budget and, over the course of several decades could restore the warm conditions of the "permanent" El Niño of 3 Myr ago.

"Thermodynamic and Dynamic Mechanisms for Hydrological Cycle Intensification over the Full Probability Distribution of Precipitation Events"

Gang Chen, UCLA

Abstract:

Projected changes to precipitation in a warming climate vary considerably from region to region and between precipitation intensities. While it is well recognized that increases in atmospheric water vapor content in a warmer climate will lead to hydrological cycle intensification, changes in atmospheric circulation play an important role in shaping the spatial distribution of precipitation intensity and frequency. In this talk, I will present a moisture budget perspective of regional precipitation responses to climate warming for the full probability distribution of precipitation in a large ensemble of climate simulations. This approach attributes changes in precipitation to different moisture budget processes from region to region and percentile by percentile. It is shown that the thermodynamic effect, due to increased atmospheric moisture, is relatively uniform spatially and across the probability distribution of precipitation events. In contrast, the dynamical effect, due to changes in intensity and location of weather systems, varies spatially and between intensities. In particular, the upward motion associated with heaviest precipitation events (e.g., a 10-year event) in the subtropics will increase more than the ascent for less intense events, indicating a dynamical amplification of subtropical precipitation that would bring more challenges to water resource managements in a drying subtropical climate.

Geoclub Seminar Series

Thursdays from 4:00pm to 5:00pm
For more information, please contact: Sarah Zeichner

"New Constraints on the Ocean Iron Cycle from Thorium Isotopes"

Frank Pavia, Caltech

Abstract:

Iron is a bio-limiting micronutrient over large swaths of the global ocean, affecting both primary productivity and specific biogeochemical processes like N2-fixation. Global models of oceanic iron distributions have iron inputs, outputs, and residence times that vary across orders of magnitude. Data on iron fluxes are necessary to constrain these models, and improve their ability to simulate biogeochemical feedbacks between changing iron dynamics and marine phytoplankton activity.

I will present new estimates of iron inputs to the modern ocean derived using measurements of dissolved thorium isotopes in seawater. Two case studies will be discussed: First, I will use new estimates of atmospheric iron deposition to derive upper limits on N2-fixation in the South Pacific Gyre; Second, I will show that models underestimate atmospheric iron fluxes to the Southern Ocean by up to two orders of magnitude, and argue that dust constitutes the primary iron source to Southern Ocean phytoplankton. I will conclude by discussing the preliminary progress in extrapolating our findings to the global scale, and the implications for model simulations of the oceanic iron cycle.

" The Many Hats of a Yellowstone Geologist: An Experiential Account of Working with the Yellowstone Volcano Observatory "

Behnaz Hosseini, USGS

" William Smith and The Map that Changed the World "

Simon Winchester et al.

Virtually joining us will be Simon Winchester, a renowned author, who wrote a book all about the W.S. Map, 'The Map That Changed The World', along with Caltech history professor Nicolas Wey-Gomez who has studied humans search for understanding through maps.

Unlike normal Geoclub it will be more of a Geo-Book-Club, with no formal presentation but an open floor for any questions/discussion about the William Smith Map, the history of geology, or any questions for Simon Winchester about his process of writing the book etc.

" Paleomagnetic evidence for partial differentiation of planetesimals and long-lived dynamo activity "

Clara Maurel, MIT

Seismo Lab Seminar

Fridays from 4:00 pm to 5:00 pm
For more information, please contact Seismo Seminar Committee.

" Dynamics of the abrupt change in Pacific Plate motion around 50 Ma "

Jiashun Hu (SUSTech)

ABSTRACT:

Global plate circuits, paleomagnetic data and geodynamic models suggest that the Eocene 47 Ma Hawaiian-Emperor Seamount Bend (HEB) is caused by an abrupt Pacific Plate motion change, a change in mantle plume dynamics or a combination of both. We build high–resolution global dynamic models and find that Izanagi Plate subduction, followed by demise of the Izanagi–Pacific ridge and Izu–Bonin–Mariana subduction initiation alone, is incapable of causing a sudden change in plate motion. Instead, Paleocene slab pull from Kronotsky intraoceanic subduction in the north-west Pacific exerts a north-ward pull on the Pacific Plate, while its Eocene demise leads to a sudden 30–35◦change in plate motion, accounting for about half of the HEB, while the remainder is related to a change in mantle convection.

"TBD"

Alberto Roman, JPL

"TBD"

Sylvain Barbot, USC

Thesis Defense Seminars

For more information, please contact Julie Lee; jlee@gps.caltech.edu