Introducing the Jackson School’s 2020-21 Doctorates
June 22, 2021
Please join us in welcoming newly minted Ph.D.s!
During the 2020-21 academic year, a number of Jackson School of Geosciences graduate students successfully defended their dissertations. Kudos to James Biemiller, Ken Ikeda, Eric Goldfarb, Dominik Kardell, Kelly Olsen, Junwen Peng, Son Phan, Evan Ramos, Simon Scarpetta, Natasha Sekhon, Lily Serach, Brian Shuck, Logan West, and Wen-Ying Wu. Additional graduated students will be added to this list as they complete their doctorates during this academic year.
Multi-Timescale Mechanics of an Active Low-Angle Normal Fault
The project, defended on November 9, 2020, was supervised by Dr. Luc Lavier and Dr. Laura Wallace with committee members including Drs. Susan Ellis, Demian M Saffer and Omar Ghattas.
Abstract: Detachment faults dipping < 30° commonly accrue 10’s of kms of offset and accommodate a large portion of crustal extension in moderately-to-highly extended regions. Slip on these high-offset low-angle normal faults remains perplexing due to their apparent misorientation relative to Andersonian principal stress directions. Classic fault mechanical theory predicts that normal faults should frictionally lock up and become abandoned at dips < 30°, yet geologic, seismological, and geodetic evidence shows that some low-angle normal faults slip actively. Despite evidence for actively slipping low-angle normal faults, few large earthquakes have been recorded on these structures. The scarcity and low long-term slip rates of active low-angle normal faults make it difficult to determine whether these faults rupture in large earthquakes based solely on seismological or geodetic records. In this dissertation, multi-disciplinary studies of the world’s most rapidly slipping low-angle normal fault are integrated to better understand the structural and tectonic evolution of detachment faults as well as to determine whether these faults slip in large earthquakes or predominantly creep aseismically. Bounding the actively exhuming Dayman-Suckling metamorphic core complex, the Mai’iu fault in Papua New Guinea dips 16-24° at the surface and has been estimated to slip at dip-slip rates of 8.6 ± 1.0 mm/yr to 11.7 ± 3.5 mm/yr. Geodynamic models suggest that weak zones and thermomechanical heterogeneities inherited from a previous subduction phase may have facilitated the formation of this long-lived detachment fault system (Chapter 2). Models of seismic-cycle deformation governed by rate-and-state friction show that the spatial distribution of fault rock frictional stability parameters strongly controls whether low-angle normal faults creep aseismically, slip in periodic large earthquakes, or slip in a mix of episodic creep events and earthquakes (Chapter 3). Surveying and U/Th dating of emerged coral reef platforms along the Goodenough Bay coastline show that tectonic uplift is episodic and imply that this segment of the detachment system slips in infrequent (440 – 1520 year recurrence) large (Mw > 7.0) earthquakes (Chapter 4). Velocities from a newly installed network of densely spaced campaign GPS sites reveal horizontal extension rates of 8.3±1.2 mm/yr (~8-11 mm/yr dip-slip) on the Mai’iu fault (Chapter 5). Laboratory friction experiments on exhumed Mai’iu fault rocks showing depth-dependent transitions in frictional stability help constrain inversions of kinematic models of the GPS velocities indicating that the Mai’iu fault is more strongly locked at ~5-16 km depth and creeping interseismically above 5 km depth. This result suggests that large (Mw > 7.0) earthquakes nucleate downdip of the low-angle portion of the Mai’iu fault and can propagate to the surface along the shallowly-dipping segment and/or more steeply-dipping splay faults in its hanging wall. In contrast to previous studies suggesting that active low-angle normal faults predominantly creep aseismically, this work implies that the active Mai’iu low-angle normal fault slips in infrequent large earthquakes accompanied by some shallow interseismic creep.
Upper Flow Regime Sediment Gravity Flows in Deepwater Environments: Spatio-temporal Bedform and Flow Evolution in Supercritical Fans
The project, defended on November 16, 2020, was supervised by Dr. Cornel Olariu and Dr. Ron Steel with additional committee members Drs. Mauricio Perillo, Brian K Horton, David Mohrig, and Jacob A Covault.
Abstract: To be added
The Structural and Thermal Evolution of Upper Oceanic Crust in the Western South Atlantic: Insights from Seismic Velocities and Hydrothermal Models
The project, defended November 16, 2020, was supervised by Dr. Gail Christeson and Dr. Sean Gulick with additional committee members Drs. Robert Reece, Marc A Hesse, Luc L Lavier, and Nicholas W Hayman.
Abstract: The evolution of oceanic crust plays an integral role in global heat flow, geochemical cycles, and in shaping the environmental conditions harboring the crustal biosphere. Because oceanic crust is normally buried beneath several kilometers of water and encompasses a vast area of the Earth’s rigid surface, spatially extensive and coherent geophysical data are difficult to acquire in the oceanic domain. Consequently, our current understanding of the evolution of oceanic crust is based on partially conflicting compilations of data that are acquired at different scales and using different methods. Here I present geophysical constraints from an extensive seismic dataset that continuously covers 0-70 Ma crust in the western South Atlantic. Analysis of regional seismic velocity trends in the upper crust shows a continuous increase in basement velocity to crustal ages of at least 58 Ma. This trend indicates an evolution of upper crustal velocities that lasts significantly longer than measured or predicted by previous studies. The results provide evidence for ongoing hydrothermal circulation in relatively old upper crust, which is consistent with heat flow studies. To further test this concept, I used high-resolution seismic velocity models to estimate detailed porosity and permeability distributions that constrain models of hydrothermal fluid flow at five different crustal ages. The resulting advective and conductive surface heat fluxes are consistent with both predictions of heat flux by lithospheric cooling models and measured conductive heat flux at the seafloor. Additionally, computed hydrothermal volume fluxes largely agree with global estimates for the modeled crustal ages. The models are therefore consistent with a “sealing age” of ~65 Ma, which is also inferred from a compilation of global heat flow measurements at the seafloor. Close to the Rio Grande Rise, an oceanic plateau west of the study area, a fine-scale seismic velocity model reveals multiple large fault zones penetrating at least ~1.5 km into the crust. These faults likely accommodate differential subsidence between thickened, warm oceanic plateau crust and cold oceanic crust. Modeled fluid fluxes are elevated along the interpreted fault zones and across the seafloor. Crust adjacent to oceanic plateaus may exhibit elevated levels of tectonic activity and fluid flow globally. The estimated global volume of fluid entering the ocean in this type of setting amounts to 43 km³, which is ~2% of the hydrothermal flux in the axial region. This potentially has implications for global chemical cycles, the hydration of mature oceanic crust, and the oceanic crustal biosphere.
Heterogeneity Characterization and Genetic Mechanism of Deepwater Fine-grained Sedimentary Rocks During Icehouse Period: A Case Study
The project, defended March 25, 2021, was supervised by Dr. Xavier Janson and Dr. Qilong Fu with additional committee members Drs. William L Fisher, Timothy M Shanahan, Kitty L Milliken, and Ronald J Steel.
Abstract: To be added
Miocene Modernization of the North American Lizard Fauna
The project, defended on April 9, 2021, was supervised by Dr. Chris Bell with additional committee members Drs. Krister Smith, Daniel O Breecker, Timothy B Rowe, David Cannatella, and Travis J Laduc.
Abstract: To be added
Frequency-dependent Elastic Properties of Geomaterials: Laboratory Experiments and Digital Rock Physics
The project, defended on April 12, 2021, was supervised by Dr. Nicola Tisato with additional committee members Drs. Mrinal K Sen, Marc A Hesse, Luc L Lavier, Kyle T Spikes, and Beatriz Quintal.
Abstract: Geoscientists often model the subsurface by studying the propagation of seismic waves. As a seismic wave propagates through a medium, its amplitude and phase change according to the medium physical properties. Geoscientists often simplify the rheology of geomaterials to elastic media where elastic properties are frequency-independent. However, geomaterials possess frequency-dependent properties. Such oversimplification can create inaccurate subsurface models. Therefore, often geomaterials should be modeled as frequency-dependent materials using appropriate attenuation models.
In this dissertation, I explore the elastic properties of rocks at low-frequencies (~0.1–100 Hz) and ultrasonic frequencies (105-106 Hz). I use laboratory measurements to estimate elastic properties of rocks. These measurements are then compared to Digital Rock Physics (DRP) results, where the same laboratory measurements are numerically simulated on Computed-Tomographic (CT) images.
The first part of this dissertation explores elastic properties of a quartz-rich sandstone at ultrasonic frequencies. I demonstrate that the laboratory-measured elastic properties could be efficiently predicted using a new DRP based technique called Segmentation-Less withOut Targets (SLOT). The SLOT method uses the local variation of X-ray attenuation in CT-images to map the density distribution of the corresponding material. Numerical simulations of wave propagations are used to estimate the elastic properties of the sample, and show a small mismatch to the laboratory measurements.
The second part of the dissertation focuses on estimating low-frequency elastic properties using the SLOT technique, which has been extended to accommodate the characteristics of a polymineralic carbonate. The modified-SLOT combines segmentation-based DRP with segmentation-less DRP to create elastic property distribution maps. The DRP predictions agree with the laboratory measurements.
The last part of the dissertation shows the development of a new apparatus to measure low-frequency attenuation: the Low-Frequency Module (LFM). The mechanical and electronic design of the LFM is carefully chosen to accommodate a decametric sample that can be tested at reservoir pressure-temperature conditions. The design and the limitation of the apparatus are discussed.
The newly developed DRP techniques and the state-of-the-art apparatus will help geoscientists exploring the elastic properties of rocks at different bandwidths. Improved estimations of elastic properties will help to better capture subsurface features.
Machine Learning Algorithm for Solving Some Seismic Inversion Challenges
The project, defended on April 16, 2021, was supervised by Dr. Mrinal K Sen with additional committee members Drs. Charles S Jackson, Douglas J Foster, Kyle T Spikes, and Sergey B Fomel.
Abstract: To be added
Predictive Digital Rock Physics
The project, defended on April 22, 2021, was supervised by Dr. Nicola Tisato with committee members including Drs. Gary Mavko, Richard A Ketcham, Sean S Gulick, Kyle T Spikes, and Masa Prodanovic.
Abstract: Geophysical surveys are the most effective way to model the surface and subsurface. Recorded signals can only be converted to properties of interest, such as rock type or saturating fluid, if we understand the relationship between rocks and their physical properties. Digital rock physics (DRP) consists of creating digital models of rocks in order to numerically model their properties.
Computed Tomography (CT) scans are a common starting place for DRP models. Each model consists of voxels (3D pixels), with values in units of CT number, which are an approximation of X-ray attenuation in that location. The conventional method of converting CT-numbers into rock properties is known as segmentation. Users assign physical properties to each voxel based off the visually identified material that the voxel represents. Segmentation introduces arbitrariness causing certain rock properties to be drastically incorrect. Measuring some sample properties in the laboratory for calibration is a common mitigation.
Here, we introduce a new segmentation-less DRP method and present case studies suggesting that we can considerably improve the prediction of rock physical properties and match physical laboratory results. Chapter one demonstrates that by scanning objects of known density alongside the rock sample, we can calibrate the rock model. We refer to the method as “predictive”, as sample laboratory measurements are not required. We explain the steps to create density, porosity, and wave velocity models, and derive a method to estimate uncertainty. In chapter two, we acquired CT scans with varying conditions to test the sensitivity of the method. We provide advice and reasoning on how to set up an effective scan. In chapter three, we estimate rock properties from millimetric sized sandstone fragments too small to test with conventional equipment. We also estimate properties for meteorite samples too rare to invasively test. This shows the method is more than academic, and can meaningfully contribute to scientific debate and industry decisions.
We have shown that CT, a relatively new technology not widely adopted for this purpose, can be used to accurately solve rock physics problems when we combine knowledge from material science. This more accurate methodology could make this powerful technology more mainstream for rock physicists.
Investigating Trench Sediment Consolidation and Upper Plate Structures and their Links to Seismic Behavior Using Active-Source 2D Seismic Data in South-Central Chile and Hikurangi
The project, defended on April 23, 2021, was supervised by Dr. Nathan Bangs with committee members including Drs. Brian K Horton, Luc L Lavier, Harm J Van Avendonk, Jaime D Barnes, and Shuoshuo Han.
Abstract: To be added
Elucidating Biotic and Abiotic Controls Over Soil Carbon Stabilization Using Isotope Geochemistry
The project, defended on June 29, 2021, was supervised by Dr. Dan Breecker with committee members including Drs. Timothy M Shanahan, Philip C Bennett, Charles S Jackson, and Timothy Beach.
Abstract: To be added
Mechanisms of Lithospheric Failure During Late Continental Rifting and Early Subduction
The project, defended on July 1, 2021, was supervised by Dr. Harm van Avendonk and Dr. Sean Gulick with committee members including Drs. Donna Shillington, Nathan L Bangs, Thorsten Becker, and Luc L Lavier.
Abstract: To be added
Toward a Mechanistic Understanding of Silicate Weathering and Li Transfer Across Landscapes, Past and Present
The project, defended on July 1, 2021, was supervised by Dr. Jaime Barnes and Dr. Dan Breecker with committee members including Drs. Brady Foreman, Joel P Johnson, and Daniella M Rempe.
Abstract: To be added
Advancing the Application of Remote Sensing to Improve Land Surface Modeling
The project, defended on July 21, 2021, was supervised by Dr. Zong-Liang Yang with committee members including Drs. Bridget R Scanlon, Bayani Cardenas, and Daniella M Rempe.
Abstract: Over the recent two decades, space agencies have put enormous effort into remote sensing for understanding the global water and energy cycles. Our understanding of global hydrology has advanced in this golden age of satellite hydrology. This dissertation explores the global to continental- scale applications of multiple satellite missions for Earth system models to understand land-surface processes.
Data assimilation is a novel approach to integrated satellite observations and models to provide continuous and more realistic estimates. In Chapter 2, I investigate impacts of land data assimilation (DA) on runoff and streamflow. Multiple experiments with the assimilation of different combinations of remote-sensing datasets are conducted using the Community Land Model version 4 (CLM4), constrained by assimilating observations from the Moderate Resolution Imaging Spectroradiometer (MODIS), Gravity Recovery and Climate Experiment (GRACE), and Advanced Microwave Scanning Radiometer for EOS (AMSR-E). Results show GRACE-DA dominants runoff, and snow-DA-induced runoff are pronounced in high and mid-latitude. GRACE-DA improves the spatial pattern of streamflow during summer and autumn. This study shows how data assimilation help improve streamflow estimation.
Satellite observations are used as benchmarks for diagnosing model performances in Chapter 3. Results show a systematic cold bias over drylands in the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) simulation, associated with overestimated evapotranspiration cooling. The aridity-dependent biases in skin temperatures show modeled deficiencies in land-atmosphere interactions. Results suggest a higher priority to develop and improve related processes to eliminate temperature biases in state-of-art climate models in dry conditions.
Predicting droughts is a great challenge of climate models. In Chapter 4, we investigate the physical process that controls water availability during drought to understand the mechanisms causing the disparities. Results suggest that using different physical parameterizations, such as considering vegetation response, affect water availability but also skin temperature through the modulation of evapotranspiration.
The studies presented in this dissertation demonstrate the applications of satellite information in the field of large-scale climate modeling as data assimilation, benchmarking, and data inputs. Emerging challenges are shown and shed some light on the future research direction of global hydrology.
A monitoring and 20th stalagmite study from a shallow cave in New Mexico elucidating climate controls on geochemical variability with insight into stalagmite suitability for paleoclimate reconstructions
The project, defended on July 23, 2021, was supervised by Dr. Jay Banner and Dr. Dan Breecker with committee members including Drs. Bryan Black, Yuko M Okumura, and Timothy M Shanhan.
Abstract: To be added