EPSS Colloquium - fall-2023
Earthquake Response of Sacramento / San Joaquin Delta Levees
Oct. 3, 2023
3 p.m. - 4 p.m.
, 3853 Slichter Hall
Presented By:
- Scott Brandenberg - UCLA
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The Sacramento / San Joaquin Delta is a 3400 km2 estuary located at the confluence of the Sacramento and San Joaquin rivers in northern California. The Delta is the hub of California's water distribution system, serving over 22 million agricultural and urban users in the San Joaquin Valley and southern California. Delta levees circumscribe "islands" that are commonly 3 to 5 m below sea level due to oxidation and wind erosion of the organic peat soils that are prevalent in the Delta. A major concern is that an earthquake could simultaneously fail multiple levees, drawing saline water from the west into the flooding islands, thereby inundating farmland and wildlife habitat, and halting water delivery. This presentation will discuss the history of the Delta, field and centrifuge model testing of levees resting atop peat soil, fundamentals of peat behavior, performance of non-Delta levees that have been strongly shaken by past earthquakes, and provide an overview of a system reliability procedure suitable for application to spatially distributed infrastructure systems like levees.
Into the Deep: Geobiological Explorations with the Submersible Alvin
Oct. 10, 2023
3 p.m. - 4 p.m.
3853 Slichter Hall
Presented By:
- Tina Treude - EPSS, UCLA
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Deep-sea exploration is a fascinating, yet complex research endeavor. In this seminar I will take the audience on board the WHOI-operated deep-sea submersible Alvin to provide insights into deep-sea exploration. How do you prepare for an Alvin dive? How does it feel working inside a 171 cubic feet titan sphere with two other persons for 6-7 hours at the bottom of the ocean? How do we collect samples and data? This summer, my group participated in two back-to-back expeditions with Alvin to study geomicrobiological processes in the oxygen-deficient Santa Barbara Basin and at methane seeps off the coast of southern California. I will introduce our overarching scientific hypotheses and the methods we applied to test them in the field. Preliminary data will be presented as they become available. Come on board and enjoy! And PB4UGO!
The importance of “stuff getting stuck” in hydro(geo)logy
Oct. 17, 2023
3:30 p.m. - 4:30 p.m.
, 3853 Slichter Hall
Presented By:
- Professor Kamini Singha - Colorado School of Mines
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Most of us are familiar with “local” mathematics, which are calculated at a point, and less familiar with “non-local” math, which suggests longer-range dependencies in time or space. Non-local mathematics are important in a broad range of scientific disciplines; in hydrogeology, they have been used to describe solute transport through preferential flowpaths—including “stuff getting stuck” in the subsurface. Observational challenges and the complexity of hydrogeological systems lead to severe prediction challenges with standard measurement techniques. One prediction challenge is “anomalous” solute-transport behavior, defined by characteristics such as concentration rebound, solute retention, early solute breakthrough, and long breakthrough tailing. These behaviors lead to consequences like poor 1) pump-and-treat efficiency, 2) descriptions of mixing or spreading and 3) prediction of biogeochemical storage, release, and transformation processes. These phenomena have been observed in diverse geologic settings, and are not predicted by classical, local mathematics. Numerous conceptual models have been developed to explain anomalous transport, such as the presence of two distinct populations of connectivity—one where solutes are highly mobile and another where they are not—but verification and inference of controlling parameters in these models in situ remains problematic, and often estimated based on data fitting alone. Here, I explore some experimental methodologies that can be used to determine parameters controlling anomalous solute transport behavior given hydrologic and geophysical measurements and their applications in a variety of hydrologic settings.
The Tipping Point: How Humans and a Warming Climate Drove Pleistocene Mammal Extinctions and Re-shaped California’s Landscapes
Oct. 24, 2023
3:30 p.m. - 4:30 p.m.
, 3853 Slichter Hall
Presented By:
- Emily Lindsey - La Brea Tar Pis Museum
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: At the end of the Pleistocene, most of Earth’s large mammals suddenly disappeared. Scientists have long debated the relative roles that late-Quaternary climate changes and human activities played in driving these extinctions. One key challenge is that the fossil record in most regions is too poorly-constrained to precisely pinpoint the disappearance times of different species and align these with environmental and anthropogenic changes. In this talk, I will describe how a large-scale, interdisciplinary effort brought together several remarkable records from southern California to paint a regional picture of climate change, fire, extinction, and ecosystem state shift, and will discuss the implications of this work for megafaunal extinctions and global change research.
A 3D Glacial Isostatic Adjustment Model Reconciles Conflicting Geographic Trends in North American Marine Isotope Stage 5a Sea Level Observations
Oct. 31, 2023
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Dr. Jessica JC Creveling - Oregon State University
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Reconstructions of peak global mean sea level (GMSL) during past warm intervals serve to calibrate ice sheet sensitivity to past climate and contextualize future change. One method to estimate GMSL is to fit sea level predictions from numerical glacial isostatic adjustment (GIA) models to compilations of geological and geomorphological relative sea level indicator elevations corrected for tectonics. Glacial isostatic adjustment simulations using earth models that vary viscoelastic structure with depth alone cannot simultaneously fit geographic trends in the elevation of marine isotope stage (MIS) 5a (80 kya) relative sea level indicators across continental North America and the Caribbean and yield conflicting estimates of global mean sea level. We present simulations with a GIA model that incorporates three-dimensional (3-D) variation in North American viscoelastic earth structure constructed by combining high-resolution seismic tomographic imaging with a new method for mapping this imaging into lateral variations in lithospheric thickness and mantle viscosity. We pair this earth model with a global ice history based on updated constraints on ice volume and geometry. The GIA prediction provides the first simultaneous reconciliation of MIS 5a North American and Caribbean RSL high stands and strengthens arguments that MIS 5a peak GMSL reached values close to that of the Last Interglacial. This result highlights the necessity of incorporating realistic 3-D earth structure into GIA predictions with continent-scale RSL data sets. (Thompson et al., Geology, 2023)
Earthquake Gates, Recurrence Intervals and Expected Magnitude Range for Strike-slip Faults
Nov. 7, 2023
3 p.m. - 4 p.m.
3853 Slichter Hall
Presented By:
- Mike Oskin - UC Davis
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Earthquake surface-rupture maps reveal that discontinuities, such as bends and stepovers, are present at all scales. These act as earthquake gates, each with a probability of stopping an earthquake rupture related to its size or angle. From the natural example of the Altyn Tagh fault, I show how along-strike changes in fault slip rate and earthquake recurrence reveal the effectiveness of earthquake gates over multiple earthquake cycles. I generalize this approach to build a probabilistic earthquake recurrence model using passing probabilities for each gate type and the cumulative distribution of gates along mapped surface ruptures. I then compare this model to long earthquake recurrence records (n≥9 events) from the San Andreas, San Jacinto, Alpine, and Altyn Tagh faults. I find that earthquake recurrence is well described by a Weibull distribution, with hazard increasing in proportion to time raised to a power, k. Most paleoseismic sites exhibit k < 1, which I interpret as a result of frequent, smaller, partial-length ruptures interrupting progress to a system-spanning event. The exception is the Alpine fault of New Zealand, with much more regular recurrence and k ~ 2. The longer mean recurrence of the Alpine fault, relative to its slip rate, is consistent with a narrow range of earthquake sizes and a preponderance of large, system-spanning events. Overall, this analysis shows that strike-slip faults should not exhibit characteristic earthquake size or recurrence. Instead, with the possible exception of the Alpine fault, strike-slip faults host a range of event sizes along their length, the majority of which are partial ruptures. This results in an overall higher hazard due to the shorter mean recurrence interval between surface-rupturing events.
Aeolian Unknowns on Earth and Mars
Nov. 14, 2023
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Mackenzie Day - UCLA
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Abstract: Aeolian, or wind-driven, sediment transport changes landscapes via erosion and deposition, forming fields of dunes or carving yardang canyons. Both Earth and Mars host a variety of complex aeolian morphologies and related but distinct unresolved questions. In this talk, we will survey unanswered questions related to aeolian geoscience on Earth and Mars, and explore examples of how one planet can help us understand another. For example, some bedforms that are common on Mars are only rarely observed on Earth. By leveraging our understanding of dune migration on Earth, we can both solve how these unusual martian bedforms develop, and test a hypothesis about aeolian stratal patterns on Earth. Approaches to understanding aeolian transport vary from remote sensing to hands-on experimentation. We will explore how all avenues are pursued at UCLA to tackle open questions in aeolian geology.
“Rivers Flow Not Past, but Through” A Fluvial Perspective on Earth’s Elemental Cycles
Nov. 21, 2023
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Mark Torres - Rice University
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What makes and keeps planets habitable? Taking an Earth-centric view, it is clear that an equitable climate is required, which implicates the carbon and related biogeochemical cycles in regulating habitability. With the ultimate goal of understanding the factors that modulate the carbon cycle, my research group studies the chemistry of modern river systems. The premise behind this work is that rivers integrate over land surface heterogeneity and thus provide a means to relate land surface properties (e.g., climate, rock type, etc.) to the rates of different carbon cycle processes. Our prior work on global river systems revealed an intriguing effect of glacial cover wherein glaciated catchments appear to release carbon dioxide to the atmosphere while non-glaciated catchments consume carbon dioxide. To explore this finding further, we have turned to river systems in Iceland where geologic factors simplify the inverse analysis of river chemistry and climate factors juxtapose catchments with different glacial histories. So far, we have found evidence for an important role of isostatic rebound in modifying carbon fluxes, direct evidence that glaciers enhance weathering over millenial timescales, and more complex water-rock interactions than had previously been assumed.
Paleogeographic Boundary Conditions and the Long-term Evolution of Earth’s Climate Stat
Nov. 28, 2023
3:30 p.m. - 4:30 p.m.
Slitchter 3853
Presented By:
- Nicholas Swanson-Hysell - UC Berkeley
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Earth's climate has transitioned between intervals of non-glacial climate with no significant land ice on Earth, glacial climates like today with polar ice caps, and snowball Earth climates when ice extends to all latitudes. Subsequent to global glaciation in the Neoproterozoic Era, there have been three major non-glacial to glacial transitions over the past 500 million years. The most recent transition resulted in Earth being in its current glacial climate regime with ice caps in both hemispheres. While we understand long-term climate change to be controlled by sources of CO2 from the solid Earth and CO2 sinks through the weathering of silicate rocks and organic carbon burial, reconstructing how changes in these sources and sinks have resulted in climatic shifts is a major challenge of Earth science. I will present our work developing and evaluating the hypothesis that the process of arc-continent collision is a major lever for cooling Earth's climate on long timescales when it occurs near the equator. Such orogenesis leads to mountains of rocks with high carbon sequestration potential in the warm-wet tropics. In particular, I will focus on new Neoproterozoic paleogeographic constraints we are developing in order to evaluate hypotheses for the onset of Cryogenian Snowball Earth.
Why the Central Andes are Bigger Than the Himalaya
Dec. 5, 2023
3:30 p.m. - 4:30 p.m.
Slitchter 3853
Presented By:
- Pete Decelles - University of Arizona
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The Central Andean and Himalayan orogenic belts provide an ideal natural experiment to test the potential role of climate in controlling orogeny. Approximately equal in age and along-strike length, both orogenic wedges are forming in plate-marginal convergent tectonic settings: The Andes in a retroarc setting and the Himalaya in a collisional setting against the Tibetan backstop. The Central Andes orogenic wedge is volumetrically and aerially nearly twice as large as the Himalayan orogenic wedge, despite the Himalaya having accommodated two to three times more tectonic shortening. The Himalaya exports at least four times more sediment owing to much greater erosion rates as signified by widespread Cenozoic metamorphic rocks and very young (<10 Ma) low-temperature thermochronologic ages. The Central Andes are thermochronologically old (mostly >20 Ma), have no exposures of Cenozoic metamorphic rocks, and are mantled by volcanic and sedimentary rocks, attesting to shallow, slow erosion. The most likely culprit for this situation is the greater intensity of the Indian Monsoon relative to the South American Monsoon since Oligocene time. When viewed as an orogenic wedge that has developed largely after formation of the Tibetan orogenic collage, the Himalaya is neither the largest nor hottest among Earth's orogens.
Why the Central Andes Are Bigger Than the Himalaya?
Dec. 5, 2023
3 p.m. - 4 p.m.
3853 Slichter Hall
Presented By:
- Peter Decelles - U Arizona
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The Central Andean and Himalayan orogenic belts provide an ideal natural experiment to test the potential role of climate in controlling orogeny. Approximately equal in age and along-strike length, both orogenic wedges are forming in plate-marginal convergent tectonic settings: The Andes in a retroarc setting and the Himalaya in a collisional setting against the Tibetan backstop. The Central Andes orogenic wedge is volumetrically and aerially nearly twice as large as the Himalayan orogenic wedge, despite the Himalaya having accommodated two to three times more tectonic shortening. The Himalaya exports at least four times more sediment owing to much greater erosion rates as signified by widespread Cenozoic metamorphic rocks and very young (<10 Ma) low-temperature thermochronologic ages. The Central Andes are thermochronologically old (mostly >20 Ma), have no exposures of Cenozoic metamorphic rocks, and are mantled by volcanic and sedimentary rocks, attesting to shallow, slow erosion. The most likely culprit for this situation is the greater intensity of the Indian Monsoon relative to the South American Monsoon since Oligocene time. When viewed as an orogenic wedge that has developed largely after formation of the Tibetan orogenic collage, the Himalaya is neither the largest nor hottest among Earth's orogens.