Seminar – UCLA EPSS

Speaker: Kevin Pham

Date: Friday, May 1, 2026

Time: 3:30 PM

Abstract

On May 10, 2024, the Earth’s geospace system and existing models were pushed to their limits by the largest geomagnetic storm in two decades. While the resulting auroras were a global spectacle, the underlying physics revealed a system undergoing a rapid and large-scale structural reconfiguration. This talk explores the science of this extreme event across the whole geospace system, emphasizing how the ionosphere responded to these unique drivers. By examining the magnetospheric and upper atmospheric responses together, the complex coupling and energy exchange between these regions become clearer. These observations demonstrate the necessity of a coupled whole geospace approach to analyze how these systems communicate and what happens when that global conversation turns into a shout.

————————————————————-

Speaker: Omakshi Agiwal

Affiliation: Boston University

Date: Friday, April 24, 2026

Time: 3:30PM

Abstract

Decades of spacecraft and telescope observations of Jupiter’s upper atmosphere reveal that plasma emissions, densities, temperatures and vertical structure do not appear to be controlled by sunlight alone. In this talk, I will present a recently developed unified picture in which neutral winds, acting along Jupiter’s spatially complex magnetic field via field aligned ion–neutral coupling, drive vertical transport that organizes the non auroral ionosphere and creates the steady spatial patterns seen in ~60 years of observations.

This unified view has been informed by 5 complementary studies: a reanalysis of ~6 decades of spacecraft radio occultations (Pioneer, Voyager, Galileo, Juno) which reveal significant variability in plasma vertical structure; over 175,000 spectra from ground-based telescopes (KECK/NIRSPEC), collected across four years, that produce high resolution global maps of ion densities and temperatures; a coordinated 2023 campaign (Juno, JWST, Keck) that delivered simultaneous continuous electron and ion vertical profiles; a new general circulation model of Jupiter’s thermosphere (JTIM) and ionosphere, which produces the first global wind maps consistent with observed temperatures; and a novel Jovian ionosphere model (JAMMIES) which includes an approximation of Jupiter’s magnetic field geometry and can reproduce various observed phenomena through its comprehensive treatment of ionospheric transport at Jupiter.

Finally, I will briefly discuss the outstanding mysteries still persist, concerning how such an ionosphere feeds back on magnetospheric currents, and the unknown drivers that control ionospheric dynamics in regions where neutral wind control is weak.

Speaker: Lan Hu

Affiliation: EPSS, UCLA

Date: Thursday, April 23, 2026

Time: 1:00PM

Abstract

Xenon isotopes trace Earth's deep volatile history, but present-day mantle Xe observations display a paradox: atmospheric-like isotopic ratios require substantial regassing, while the low concentration requires limited regassing. Previous models resolved this by invoking early limited regassing, but this is hard to reconcile with evidence for early plate tectonics, higher Xe concentrations in the ancient atmosphere, and incomplete noble gas removal from subducting slabs. We use a parameterized thermal evolution and material recycling framework to explore time-dependent degassing and regassing histories, including Xe loss through continental crust extraction, mid-ocean ridge and plume melting, and Xe recycle via subduction. We show that strong early Xe loss driven by rapid early continental crust generation reduces the bulk mantle concentration enough to make later regassing effective at reproducing the isotopic ratios. Fissiogenic Xe constraints and the required intense early degassing together favor lower initial mantle uranium concentration, pointing to starting compositions with at least an enstatite-chondrite component rather than purely CI-chondritic material. Analytical solutions with simplified approximation and machine learning analysis confirm that these requirements are linked: low uranium and large early crustal extraction are coupled, and early degassing controls the timescale over which the system transitions to moderate degassing or regassing. Our results show that a major early degassing episode with prolonged moderate regassing can explain both the isotopic ratios and concentrations, offering an alternative to limited regassing scenarios and new constraints on Earth's starting materials and early history.

Speaker: Dr. Danica Adams

Affiliation: Earth, Planetary, and Space Sciences, UCLA

Date: Wednesday, April 29, 2026

Time: 12:00 PM

Abstract

Early atmospheric chemistry and climate play an important part in what worlds have liquid water and how life could emerge, but preserving evidence for this over geologic time often presents a challenge. Compared to Earth, which undergoes continuous erosion by plate tectonics, Mars offers a superb window into its earliest history, preserved right on its surface, and is therefore an excellent case study for planet evolution. What we learn here can extend to other planets in the solar system, the early Earth, Venus, and even outside the solar system at exoplanets.

Extensive surface evidence suggests Mars once hosted large volumes of liquid water, implying a warmer climate sustained by a thicker atmosphere than present day. Previous studies propose that CO2-dominated atmospheres enriched with H2 or CH4 could have driven warming, though such gases exhibit short atmospheric lifetimes. This talk will first present a novel explanation for sustaining warm climates up to 40 million years: hydrogen release through crustal hydration. Evidence of atmospheric climate and redox transformations may remain preserved on the surface and in meteorites. To test our hypothesis, we show that deposits measured by Mars Science Laboratory and isotopic fractionation measured in meteorites can both be explained photochemically under specific climates and atmospheric redox states. We also present predictions of isotopic signals under different climate and redox states that Mars Sample Return missions should search for.

Like Mars, Venus may have also experienced large climate changes during its evolution too. Modern Venus is a hot, arid environment, yet the possibility of an early cool, habitable phase remains unresolved. The talk will explore when sulfuric acid hazes in Venus’ history could have sufficiently cooled the planet to allow surface rainfall. This scenario may be testable using NASA’s upcoming Habitable Worlds Observatory (HWO), which will observe exoplanets with Venus-like characteristics.

While HWO’s launch lies years ahead, exciting exoplanet data have already been measured with JWST, Hubble, and Spitzer. When we observe planets also influences their chemistry, and the presentation will explain a new hypothesis for missing methane at warm Neptunes. The talk also highlights ongoing efforts to develop modeling tools to interpret future data, including microphysics and 3D dynamics. These analyses aim to refine atmospheric interpretations and advance our understanding of planetary evolution across diverse environments.

Speaker: Benjamin Tan

Affiliation: EPSS, UCLA

Date: Wednesday, June 3, 2026

Time: 12:00 PM

Abstract

Wildfire fundamentally alters hillslope and channel sediment transport by rapidly mobilizing dry ravel, which accumulates in channels immediately following burning and is subsequently flushed during the first post-fire rainfall. Using repeat high-resolution topographic surveys and channel-scale swath analyses within the Palisades burn scar, we examine how first-flush sediment storage and redistribution relate to channel steepness (k_{sn}) and underlying lithologic gradients. The Palisades wildfire provides a natural laboratory to examine these dynamics, as the study area spans a pronounced east–west lithologic gradient associated with systematically increasing channel steepness. We show that post-wildfire sediment transport and hillslope failure can be partitioned into two coupled but distinct processes: (1) dry ravel production, which occurs exclusively in steep, high-k_{sn} lower-order channels, and (2) precipitation-driven mobilization and redistribution of this material into channel trunks during early storm events. Dry ravel does not accumulate ubiquitously across the drainage network, but is instead restricted to channels that exceed a critical steepness threshold, indicating a strong topographic control on post-fire sediment supply. We further demonstrate that dry ravel accumulation in steeper lower order channels is spatially coincident with active scouring of the underlying channel bed, leading to sediment budgets that exceed existing infrastructural design capacities. Following rainfall, dominant patterns of erosion and deposition are negatively correlated with k_{sn}: deposition dominates in low-k_{sn} reaches, while high-k_{sn} channels experience net erosion and sediment export. Together, these observations suggest that first-flush sediment response following wildfire is governed not only by burn severity and rainfall intensity, but also by broader lithologic and topographic controls that regulate transport efficiency, sediment storage, and channel–hillslope coupling.

Speaker: Yang Ma

Affiliation: EPSS, UCLA

Date: Wednesday, June 3, 2026

Time: 12:00 PM

Abstract

Static, long-term deformation generated by earthquakes provides essential constraints on fault slip, stress redistribution, and crustal rheology. However, measuring earthquake-induced static deformation remains challenging, particularly for moderate earthquakes, due to their small strain amplitudes. Traditional geodetic observations, such as high-frequency Global Navigation Satellite System (GNSS) and tiltmeter measurements, are susceptible to noise and limited in spatial resolution. Fortunately, Distributed Acoustic Sensing (DAS) offers a novel technology by converting pre-existing optical fiber into thousands of dense strain sensors, enabling high-resolution observations over large areas. This approach has been successfully applied to monitor static deformation associated with magma migration in volcanic systems.

Here, using DAS data from the Taiwan Milun Fault Drilling and All-inclusive Sensing (MiDAS) project, we demonstrate that static strain from more than a dozen aftershocks (Ml > 5) following the 2024 Mw 7.4 Hualien earthquake can be clearly recorded. Interestingly, at short spatial scales (~100 m), the strain field exhibits complex patterns, with even alternating extensional and compressional signals. Through numerical simulations, we hypothesize that this phenomenon is linked to anomalies in the medium's Poisson's ratio, which is consistent with the fractured structure of the Milun Fault. Overall, our results highlight DAS as a reliable complement to conventional geodetic observations, offering a useful tool for investigating seismic deformation fields.

Speaker: Yifan Sun

Affiliation: EPSS, UCLA

Date: Wednesday, June 3, 2026

Time: 12:00 PM

Abstract

Quantifying spatiotemporal dynamics of landslides, including occurrence, reactivation, and timing, is critical for understanding hazard risk in steep mountains. However, in regions like the Eastern Himalayas, mapping these spatiotemporal patterns is heavily restricted by persistent cloud cover, land-cover variability, and a scarcity of historical ground-truth inventories. To overcome these data and observational limitations, we utilized a novel unsupervised machine learning framework—the Stable Diffusion Change Detector (SDCD)—to extract continuous surface disturbance records directly from time-series optical satellite imagery. By bypassing the limitations of traditional manual labeling, this approach allows us to generate high-resolution landslide inventories in a data-scarce, cloud-prone region. Applying this method, we identify ~300 surface disturbance events, including landslides in hillslopes and channel-adjacent regions, over 1300 km2 and 10 years. We investigate temporal triggering of these events by analyzing daily precipitation and spatial patterns by comparing environmental conditions, including precipitation, long-term erosion rates, and topographic slope. Our time-series analyses indicate that abundant landslides in frontal basins are directly related to the magnitude of daily precipitation events, and the spatial density of overall landslides is highly consistent with independently measured long-term erosion rates. These results highlight the importance of high-resolution landslide datasets, both spatially and temporally, for understanding the complex controls on landscape change over time.

Speaker: Mengfei Qi

Affiliation: EPSS, UCLA

Date: Wednesday, May 27, 2026

Time: 12:00 PM

Abstract

The Pacific Ocean covers a large portion of the Earth’s surface. However, seismic constraints on its crust and upper mantle structure remain limited due to sparse station coverage. Ambient noise tomography provides an effective approach to improving spatial coverage by extracting empirical Green’s functions (EGFs) between station pairs, while also offering enhanced vertical constraints on crustal structure. In this study, I use continuous seismic data from both land-based stations and ocean-bottom seismometers (OBS) to measure Rayleigh wave group and phase velocity dispersion across the Pacific region, targeting the period 1990–2025. Preliminary results based on the 2005–2006 datasets demonstrate that reliable dispersion curves can be obtained for station pairs at appropriate interstation distances over a period range of 5–50 s. Ongoing work focuses on incorporating additional years of data and improving signal quality, particularly for OBS records, to enhance path coverage and support future tomographic imaging of oceanic structure.

Speaker: Saeed Mohanna

Affiliation: EPSS, UCLA

Date: Wednesday, May 27, 2026

Time: 12:00 PM

Abstract

The Mendocino Triple Junction is in a tectonically complex region where a multitude of physical mechanisms contribute to crustal deformation. To discern these physical drivers, our group (1) enhanced the Northern California Seismic Network (NCSN) earthquake catalog spanning the 2022 Ferndale and 2024 Offshore Cape Mendocino sequences using machine learning and template matching approaches, (2) extended a repeating earthquake catalog to study the contribution of aseismic slip to both earthquake sequences (3) analyzed changes in groundwater levels during the both sequences. In this talk, I will present our enhanced catalogs, which reveal ~5-10 times more events than the NCSN catalog, with a clear concentration of seismicity at the edges of the 2024 sequence’s coseismic slip patch. Additionally, I will highlight our study's evidence for accelerating afterslip in the weeks following the 2024 sequence, and an elastic strain mechanism to explain the observed groundwater level changes.

Speaker: Aaron Werlen

Affiliation: EPSS, UCLA

Date: Wednesday, May 20, 2026

Time: 12:00 PM

Abstract

Atmospheric compositions of sub-Neptunes and super-Earths are often interpreted as tracers of formation history and volatile delivery. However, many of these planets likely experience long-lived magma-ocean phases during which their atmospheres can chemically equilibrate with a molten silicate interior. In this talk, I will show how magma-ocean–atmosphere interactions reshape atmospheric compositions and alter observable signatures. Using a global chemical equilibrium framework, I demonstrate that key abundance ratios such as C/O and H2O are not simply inherited from disk accretion, but can be substantially modified by interior processing. This has important implications for the interpretation of apparently water-rich worlds, which may in fact be significantly drier than predicted by previous models. I will also present new extensions of the model including sulfur and nitrogen chemistry, which provide additional diagnostics of volatile redistribution between atmosphere and interior and further strengthen the connection between interior evolution, atmospheric composition, and spectroscopic observations.