Browsing by Author "Schutt, Derek, committee member"

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Open Access
Event detection and analysis of a dense three-component near-summit seismic array deployed at Erebus volcano
(Colorado State University. Libraries, 2022) Jaski, Erika, author; Aster, Richard C., advisor; Schutt, Derek, committee member; Cheney, Margaret, committee member
Erebus volcano on Ross Island, Antarctica has maintained an erupting phonolitic lava lake for at least five decades. During active periods, the lava lake hosts large (up to ~10-m diameter) gas slugs rising through the conduit that create impulsive Strombolian eruptions and produce very long period (VLP) signals on broadband seismograms. We combine near-summit broadband observations and reanalyze data from a 100-station three-component short-period (4.5 Hz geophones) network deployed in an approximately 3 by 3 km region around the Main Crater during December 2008. Lava lake eruption template events are identified on broadband seismograms from their characteristic and repeating VLP spectral signature of nonharmonic modes between 0.033 and 0.2 Hz. Multi-channel and multi-station waveform matched filter correlations are performed across the short-period network using template events and correlation values that are three or more standard deviations are extracted into a working Inner Crater event catalogue, yielding 819 event detections over 19 days. While 94% of the signals in this catalogue are unique, 17 "families" of repeating lava lake events can also be identified through similar waveforms determined by Ward clustering on 5 stations, which are further interpreted for trends in location, size, and occurrence. We observe time-varying quasi-Poissonian interevent times and an approximately power-law size-frequency distribution with an excess of small events. Investigating the various event families that transpire in the Inner Crater region contributes to improved characterization and understanding of the seismogenic behavior of the lava lake degassing system and assists in the creation of a workflow that can be applied in volcanic and other circumstances that generate prolific low-level impulsive seismicity.
Open Access
From the Colorado Front Range to global topography: evaluating the roles of tectonics and climate on long term landscape evolution
(Colorado State University. Libraries, 2022) Marder, Eyal, author; Gallen, Sean, advisor; Pazzaglia, Frank, committee member; Wohl, Ellen, committee member; Schutt, Derek, committee member; Kampf, Stephanie, committee member
Landscapes are primarily shaped by the interactions between tectonics and climate, and their interplay and relative roles in landscape evolution over thousands to millions of years have a significant impact on global erosion and nutrient and sediment productions. Thus, understanding and quantifying the impact of tectonics and climate on short- to long-term landscape evolution has large implications on natural global cycles (e.g., climate change, atmospheric and terrestrial carbon circulations), biodiversity and ecological sustainability, hazard management (e.g., earthquakes, landslides), infrastructure planning, and decision making. In the last decades, significant progress has been made in the field of tectonic geomorphology to try and resolve the relative roles of tectonics and climate in landscape evolution. Yet, many questions remained unresolved, for instance: - What drives landscape evolution in post-orogenic settings? - What is the relative role of climate in landscape evolution at the global scale? In my PhD, I address these questions by investigating the impact of tectonics and climate on fluvial topography and geomorphology at different spatiotemporal scales. In my first chapter, I present a local study in the southern Colorado Front Range to explore the relative roles of tectonics and climate on observed landscape unsteadiness that affected the area during the late Cenozoic. In the second chapter, I extend this study and address this question to the scale of the entire Colorado Front Range. In my third chapter, I explore the impact of climate on fluvial topography at the global scale. For all these studies, I integrate field data, digital topographic analysis, geochronology, and modeling to compare new and existing predictions for the roles of tectonics and climate at the local (chapter I), regional (chapter II), and global (chapter III) scales to empirical observations. Results from these studies shed light on some ongoing controversies (e.g., what drives topographic rejuvenation in the Colorado Front Range) and resolve misunderstood concepts (e.g., how climate is recorded in fluvially-dominated landscapes). The first and third chapters in this dissertation were submitted to peer-reviewed journals and are under review, while the second chapter is in its final stage as a third manuscript for a peer-reviewed journal. FIRST CHAPTER: LATE CENOZOIC DEFORMATION IN THE SOUTHERN COLORADO FRONT RANGE REVEALED BY RIVER PROFILE ANALYSIS AND FLUVIAL TERRACES Post-orogenic landscapes are important sources of sediment and nutrients relevant to many natural global cycles and ecological sustainability. Many of these settings exhibit evidence of recent landscape unsteadiness, but their driving mechanisms are poorly understood. The Colorado Front Range (FR), a post-orogenic setting that maintains high relief, elevated topography, and evidence of ongoing unsteadiness, is a good example of this enigma. Two prevailing hypotheses have been proposed to explain the geologically-recent landscape unsteadiness in the FR: (1) mantle dynamics and active tectonics during the late Cenozoic; (2) enhanced erosional efficiency associated with a Quaternary climate change. Here we evaluate these end-member hypotheses through a case study of tectonic geomorphology of the Upper Arkansas River basin in southern Colorado. We perform river profile analysis on bedrock channels in the eastern Rockies and map and analyze fluvial terraces in the western High Plains. We find that knickpoints in the eastern Rockies record a one- to two-stage increase in base level fall rate downstream of the FR mountain front and an eastward increase in the magnitude of incision. Similarly, terraces in the western High Plains record an eastward increase in the magnitude of incision. Collectively, and supported by flexural and supplemental geomorphic analyses, these results suggest a previously undetected regional-scale, west-directed back tilting signal associated with differential rock uplift. Based on existing geodynamic models, we interpret these deformation patterns and related landscape response as a result of a migrating dynamic topography that swept the southern FR from west to east during the late Cenozoic. SECOND CHAPTER: TECTONIC AND GEODYNAMIC CONTROL ON REJUVENATION IN THE COLORADO ROCKY MOUNTAINS The Colorado Rocky Mountains (CRM) ancient foreland basin, currently known as the High Plains, shows a steeper long-wavelength tilt away from its hinterland relative to other active mountain range foreland basins worldwide. Further, studies showed that the High Plains experienced a transition from a system of net deposition to one characterized by net erosion at ~5 Ma. However, the mechanisms proposed to explain these observations are the center of ongoing debate. Some argue that the tilting and the transition from deposition to erosion were facilitated by tectonically- or geodynamically-driven changes in rock uplift rate, while others argue that these records are simply the result of an increase in erosional efficiency driving river incision and relaxation with some amount of isostatic rebound. One of the main reasons this controversy continues is that empirical studies trying to address this question were conducted mostly in the High Plains, where landscape geomorphic signatures used to distinguish between these two hypotheses are ambiguous. Here, we conduct a geomorphic analysis of the Colorado Rockies, which lies upstream of the High Plains province and is characterized by a harder crystalline basement, where bedrock rivers might still achieve a record of the transient landscape of the CRM and help clarify potential drivers. We combine river profile analysis with a compilation of new and existing basin average erosion rates from cosmogenic 10Be and channel incision rates from luminescence dating on fluvial terraces to differentiate two geomorphic zones in the Colorado Rockies: 1. an upper, relict topography upstream of convex upward knickpoints that is consistent with lower long-term background erosion rates of ~0.03 mm/yr and lower channel steepness of ~80-100 m0.9; 2. a transient landscape downstream of these knickpoints that is consistent with higher channel incision rates of ~0.3 mm/yr and higher channel steepness that increases systematically from ~150 m0.9 in the northern CRM to 300 m0.9 in the southern CRM. These results and their spatial patterns across the CRM are inconsistent with existing predictions from a climate-induced increased erosional efficacy during the last Cenozoic. Rather, they imply a long-wavelength deformation and a sustained tectonic uplift rate associated with active tectonics and geodynamics that impacted the CRM in the last 5 Ma. THIRD CHAPTER: CLIMATE CONTROLS ON FLUVIAL TOPOGRAPHY Conceptual and theoretical models for landscape evolution suggest that fluvial topography is sensitive to climate. However, it has remained challenging to demonstrate a compelling link between fluvial topography and climate state in natural landscapes. One possible reason is that many studies compare erosion rates to climate data, although theoretical studies note that, at steady-state, climate is encoded in topography rather than in erosion rates. Here, we use an existing global compilation of 10Be basin average erosion rates to isolate the climate signal in topography for fluvially-dominated catchments underlain by crystalline bedrock that appear to be in morphological steady state. Our results show that the nonlinearity between erosion rates and the normalized river channel steepness index, which is a proxy for fluvial relief, systematically increases with increasing mean annual precipitation and decreasing aridity. When interpreted in the context of detachment-limited bedrock incision models that account for incision thresholds and stochastic distribution of floods, this systematic pattern can be explained by a decrease in discharge variability in landscapes that are wetter and less arid, assuming incision thresholds are important. Our results imply a climate control on topography at a global scale and highlight new research directions that can improve understanding of climate’s impact on landscape evolution.
Open Access
Investigating the carbonate-shale facies transition and deposition on the Scandinavian Ordovician Shelf – the Arnestad Formation, southern Norway
(Colorado State University. Libraries, 2018) Schuller, Kathryn M., author; Egenhoff, Sven O., advisor; Harazim, Dario, committee member; Schutt, Derek, committee member; von Fischer, Joe, committee member
The Upper Ordovician Arnestad Formation was located on the northwestern edge of Baltica in the region near modern day Oslo, Norway. This formation was found to be 60 m thick and consists of intercalated siliciclastic mudstones and thin, nodular carbonate beds. Six outcrops and 38 thin sections were used to describe the Arnestad Formation in detail and divide the formation into six key facies. Dark grey silicilastic mudstones dominate the succession and contain lenses of fossil fragments. Interbedded nodular carbonates are mud- to wackestones, contain lenses of fossil fragments, and often form continuous beds. All facies show varying amounts of bioturbation from Chondrites, and Phycosiphon-like fecal strings can be found in the siliciclastic mudstone facies. The Arnestad Formation can be divided stratigraphically into a lower portion with siliciclastic mudstones and continuous carbonate beds, a central part dominated by siliciclastic mudstones with local ash and carbonate beds, and an upper portion containing both thick siliciclastic mudstone beds and intercalated stacks of siliciclastic and carbonate mudstones. The Arnestad Formation is interpreted as representing sedimentation on a ramp-like shelf with carbonate facies deposited proximally to siliciclastic mudstone facies, below normal wave base with sediment and bioclasts being transported basinward due to bed load processes. Fair-weather and storm generated deposits are found in all facies, with storms eroding the sediment and producing shell lenses throughout the formation, but increasing in frequency upwards independent of sea-level. In the lower part of the succession, the Arnestad Formation records a relatively low sea-level stand, shifting to an overall high sea-level position during the middle part, and back to another low sea-level position in the upper portion. Ash beds are found almost exclusively in the middle portion and seem to have higher preservation potential during high versus low sea-level positions. There were likely more ash beds deposited than were found that were later biogenitically homogenized, rendering the beds mostly unrecognizable from the surrounding sediment. The frequent intercalation of the siliciclastic mudstones with carbonate beds most likely shows the influence of climate cycles on deposition. Based on dividing the length of deposition (~3.5 my) by the estimated cycle count (215 – 220), these small-scale cycles were found to have periods between 15,900 and 16,300 years and are interpreted as precessional Milankovitch cycles.
Open Access
Paleozoic facies architecture in low-inclined mixed carbonate-siliciclastic sedimentary systems: depositional and tectonic signatures
(Colorado State University. Libraries, 2019) Novak, Aleksandra, author; Egenhoff, Sven, advisor; Stright, Lisa, committee member; Schutt, Derek, committee member; von Fischer, Joe, committee member
To view the abstract, please see the full text of the document.
Open Access
Scale-dependent wear and re-roughening processes in a single fault zone
(Colorado State University. Libraries, 2015) Shervais, Katherine, author; Kirkpatrick, James D., advisor; Nelson, Peter, committee member; Schutt, Derek, committee member
One factor that exerts a major control on earthquake source parameters is the geometry of a fault zone. Observations previously compiled from multiple faults show that fault surface shape evolves with displacement. The specific processes driving fault evolution within a single fault zone and their influence on fault geometry are not well known. Here, we characterize the deformation history and geometry of an extraordinarily well-exposed fault using maps constructed with the Structure from Motion photogrammetric method. The geometry of cross sectional traces of contacts of different relative age was analyzed with power spectral density and variogram calculation. The last slip zone to form in the fault is smoothest of any surface and is distinct from other surfaces, recording significant smoothing on a single structure and localization of strain onto thinner layers. We infer that smoothing occurred abruptly due to localization of slip onto a new slip zone rather than as a result of progressive wear of a fault surface. Continuous wear from processes such as grain plucking and sliced asperities also smoothed surfaces at scales larger than the clast dimension, and also re-roughened surfaces at scales smaller than the clast dimension. Spatially discontinuous wear due to complexities within the fault zone results in periodic fault traces reflecting a characteristic wavelength for the contact. Additionally, periodic variations in fault thickness define the characteristic asperity size and are a signature of wear on the fault surface. Scale dependent smoothing and re-roughening and the interplay between these processes explain the varying geometry of immature and mature faults. The evolution of roughness and asperity size we observe can explain differences in the source characteristics of earthquakes as faults mature.
Open Access
Sedimentary character and processes in mudstone inter-lobe deposits of the Skull Creek Formation, Fort Collins, Colorado
(Colorado State University. Libraries, 2025) Abukhtwa, Ahmed, author; Gallen, Sean, advisor; Schutt, Derek, committee member; Egenhoff, Sven, committee member; Aoki, Eric, committee member
Lobe-fringe deposits and interlobe strata are rarely described in sedimentary systems and often neglected in descriptions of delta successions, which mostly focus on delta top, delta front, and prodelta sediments. This may partly be the case because these deposits consist mostly of mudstones, which are generally neglected in all sedimentary systems except for black shales. Here, we describe nine siliciclastic facies of predominantly mudstones from the Cretaceous Skull Creek Formation of northern Colorado, USA. These nine facies are arranged in a 4.5 m thick predominantly fine-grained unit within the overall 25 m thick Skull Creek Formation. The nine facies are very fine to fine-grained dark massive mudstone lamina (F1), very fine-grained massive mudstone (F2), massive fine- to coarse-grained mudstone (F3), massive mudstone with fecal strings (F4), normally graded coarse to medium-grained mudstone (F5), medium- to coarse- grained lenticular siltstone (F6), siltstone lamina (F7), and massive calcitic coarse silt- to coarse-grained sandstone (F8A and F8B). From all these facies, massive fine- to coarse-grained mudstone (F3), normally graded coarse to medium-grained mudstone (F5) and siltstone lamina (F7) are the most common and comprise about 80-90 vol% of the succession. The succussion consists of 16 coarsening- and fining-upward cycles, with the majority being coarsening- upwards (11), and only (5) fining-upwards. Stratigraphically, these cycles are between 5.5 and 120 mm thick, and are here subdivided into nine distinct stratigraphic zones. These zones alternate between five fine-grained and four silt-rich zones. Each zone consists of a minimum of a portion of a cycle, and/or one or more coarsening- and fining-upwards units. These facies were deposited in three depositional environments: lobe-fringe area, medial inter-lobe area, and distal inter-lobe area. The presence of both high-energy indicators, such as clay clasts, sharp erosional bases, scours, and fragmented fishbones, as well as the occurrence of sediments reflecting suspension deposition, indicates that the lobe-fringe environment was undergoing successive shifts from high to low energy conditions. Moving farther away from the lobe, sediments show overall moderate energy conditions reflected in normal grading and some erosional contact; nevertheless, moderate and low-energy conditions alternated. Furthest away from the lobe are the distal inter-lobe sediments that show tranquil sediment deposition with only minor moderate energy deposition reflected in sharp facies contacts, and some siltstone grains in facies 3. The presence of only one type of fecal string, in these sediments, and the little bioturbated nature of inter-lobe strata suggests that the environment had been likely dysoxic and stressed but was not entirely anoxic. This study indicates that the Skull Creek Formation is primarily dominated by bed-load deposition, although the presence of suspension deposition—recorded only at times—in various facies suggests that quieter conditions occurred across all depositional areas. Even the interlobe deposits are significantly influenced by bed-load transport. Furthermore, the boundaries between the three depositional areas—lobe-fringe, medial inter-lobe, and distal inter-lobe areas—are not clearly defined and are regarded as transitional rather than firm. While unique facies mark each zone, the presence of overlapping facies across these zones makes it challenging to distinguish them clearly.
Open Access
Sedimentology and diagenesis of the lower Lodgepole Formation, Williston Basin, North Dakota
(Colorado State University. Libraries, 2013) Mackie, James, author; Egenhoff, Sven, advisor; Schutt, Derek, committee member; Rocca, Monique, committee member
The Scallion and overlying False Bakken intervals represent the lowermost portion of the Mississippian Lodgepole Formation, a predominantly carbonate unit located in the Williston Basin of North Dakota (ND) and Montana (MT) in the US, and Saskatchewan and Manitoba in southern Canada. Macroscopic and microscopic observations allow a subdivision of these mostly fine-grained sediments into five carbonate and two siliciclastic facies. These facies form distinct stratigraphic units that can be traced through western ND and easternmost MT with nodular skeletal wackestones and packstones of the Scallion interval at the base showing a distinct coarsening-upward trend, overlain by between one and three black siliciclastic mudstones with interbedded carbonate mudstones of the False Bakken unit. This lowermost part of the Lodgepole Formation represents mid-ramp to basinal settings of a low-inclination carbonate platform system within the half-enclosed intracratonic Williston Basin. The observed stacking patterns reflect relative sea-level changes that influenced facies distribution within the basin throughout its evolution: the coarsening-upward observed within the Scallion interval shows a general shoaling of the setting during progradation, representing a lowstand systems tract. The False Bakken interval consisting of up to three shale beds with intercalated carbonate mudstones shows a significant fining within the lower Lodgepole Formation depositional system and is interpreted as representing the transgressive systems tract. The subdivision into a maximum of three mudstone units reflects three backstepping parasequences during relative sea-level rise. The subsequent renewed onset of fine-grained carbonate deposition on top of the False Bakken interval reflects deposition during highstand conditions. During burial, the Lodgepole Formation experienced a complex series of diagenetic events with nodule formation, dolomitization, and pressure dissolution being the most prominent. The results of these processes are irregularly distributed both stratigraphically and geographically and play a significant role in reservoir quality of the formation.
Open Access
Spectral gamma ray characterization of the Elko Formation, Nevada - a case study for a small lacustrine basin
(Colorado State University. Libraries, 2015) McGowan, Erin M., author; Egenhoff, Sven O., advisor; Schutt, Derek, committee member; Cavdar, Gamze, committee member; Amerman, Robert, committee member
Handheld gamma ray spectrometry is a cost-effective and time-efficient means of furthering understanding of lake facies and small-scale lake systems. Spectral and total gamma ray data were recorded every foot vertically through a succession in situ at four outcrops along a NNW-to-SSE transect representing the lower to middle Eocene Elko Formation in northeast Nevada, USA. The lacustrine Elko Formation consists of, from oldest to youngest, four major units: 1) a basal conglomerate, 2) an overlying carbonate, 3) a fine-grained organic-rich mudstone with intercalated carbonate mudstones, and 4) volcaniclastics. These units comprise fourteen sedimentological facies identifiable in outcrop. In this study, these fourteen facies have been reduced to eight that are discernable by spectral gamma ray (SGR) signals. Each recorded interval in the Elko Formation succession was assigned to one of these eight facies. These eight facies comprise five siliciclastic (plant-bearing mudstone, clay-dominated mudstone, microbial-mat-bearing mudstone, ash-bearing mudstone, and conglomerate) facies, two carbonate (calcareous mudstone and fossiliferous mudstone-wackestone) facies, and one volcanic tuff facies. In conjunction with SGR, outcrop observation, X-ray diffraction (XRD), thin section observation, and total organic carbon (TOC) analyses allowed a thorough understanding of facies composition and its SGR signal. The primary controls of SGR components [potassium (K), uranium (U), and thorium (Th)] reflect K-bearing volcanic minerals (feldspars and micas), U-enriched organic material, and clay abundance (illite and montmorillonite; potentially derived from volcanic ash), respectively. High radioactivity, with signals above 120 American Petroleum Institute (API) units, was demonstrated for five facies (plant-bearing mudstone, clay-dominated mudstone, microbial-mat-bearing mudstone, ash-bearing mudstone, and volcanic tuff) in contrast to the remaining three facies (calcareous mudstone, fossiliferous mudstone-packstone, and conglomerate) exhibiting low radioactivity of less than or equal to 120 API. Distribution of radioactive minerals across the outcrops was largely found to be not only a function of general lithologic composition, but also the paleogeographic locations of the outcrops within the lake basin, due to the differing contributions of organic debris and volcanic constituents. This distribution of radioactive minerals across each outcrop supports a recent depositional model of north-to-south diachronous deposition of the Elko Formation (Horner, 2015). The microbial-mat-bearing mudstone facies was a traceable, deep-lake sediment throughout the basin by which outcrops could be assigned to more proximal or more distal positions within the paleo-lake by applying Th/U ratios. The proximal outcrop data show a low Th/U ratio (below 2.5), as opposed to the distal outcrop data that have a high Th/U ratio (2.5–4). These data confirm that most likely Th/U ratios reflect the increase in the amount of clay with distance from the proximal outcrops. Thin section microscopy and scanning electron microscope (SEM) analyses allowed for recognition of eight diagenetic cements reflecting a strongly varying diagenetic history in the Elko Formation sedimentary rocks. One calcite, four stages of dolomite, two types of silica, and one zeolite cement were identified. The calcite, dolomite, and silica cements were typically formed sequentially as listed above, whereas the zeolites formed independently. Intraparticle, interparticle, matrix, shelter, and fracture porosity types are also present, each forming post-deposition, except for interparticle and matrix porosity within volcaniclastics. Calcite, dolomite,and silica cements were found succeeding shelter and fracture porosity, whereas the timing of zeolite cement in matrix porosity was unclear. Overall, cement phases and porosity were found to be minimal, and therefore, probably had only a minor influence on the overall gamma ray signal of the Elko Formation sedimentary rocks. SGR characterization of each of the eight facies across a proximal-to-distal transect of the Elko continental-lacustrine sedimentary basin reflects the strong influence that climate and tectonics have on depositional changes in a small-scale lake. Applying gamma ray techniques to the small-scale lake system of the Elko Formation was found to be a useful tool and provides a framework to apply to lacustrine studies as a predictive tool in future exploration.
Open Access
Studies of oceanic, atmospheric, cryospheric, and fluvial processes through spectral analysis of seismic noise
(Colorado State University. Libraries, 2016) Anthony, Robert Ernest, author; Aster, Richard, advisor; Schutt, Derek, committee member; Thompson, David, committee member; Reusch, David, committee member
During the past decade, there has been rapidly growing interest in using the naturally occurring seismic noise field to study oceanic, atmospheric, and surface processes. As many seismic noise sources, are non-impulsive and vary over a broad range of time scales (e.g., minutes to decades), they are commonly analyzed using spectral analysis or other hybrid time-frequency domain methods. The PQLX community data analysis program, and the recently released Noise Tool Kit that I co-developed with Incorporated Research Institutions for Seismology’s Data Management Center are used here to characterize seismic noise for a variety of environmental targets across a broad range of frequencies. The first two chapters of the dissertation place a strong emphasis on analysis of environmental microseism signals, which occur between 1-25 s period and are dominated by seismic surface waves excited by multiple ocean-solid Earth energy transfer processes. I move away from microseisms in Chapter 3 to investigate the generally higher frequency seismic signals (> 0.33 Hz) generated by fluvial systems. In Chapter 1, I analyze recently collected, broadband data from temporary and permanent Antarctic stations to quantitatively assess background seismic noise levels across the continent between 2007-2012, including substantial previously unsampled sections of the Antarctic continental interior. I characterize three-component noise levels between 0.15-150 s using moving window probability density function-derived metrics and analyze seismic noise levels in multiple frequency bands to examine different noise sources. These metrics reveal and quantify patterns of significant seasonal and geographic noise variations across the continent, including the strong effects of seasonal sea ice variation on the microseism, at a new level of resolution. Thorough analysis of the seismic noise environment and its relation to instrumentation and siting techniques in the Polar Regions facilitates new science opportunities and the optimization of deployment strategies for future seismological research in the Polar Regions, and in mountain glacier systems. Chapter 2 details the analysis of 23 years of microseism observations on the Antarctic Peninsula to investigate wave-sea ice interactions and assess the influence of the Southern Annular Mode (SAM) on storm activity and wave state in the Drake Passage. The lack of landmasses, climatological low pressure, and strong circumpolar westerly winds between latitudes of 50°S to 65°S produce exceptional Southern Ocean storm-driven wave conditions. This combination makes the Antarctic Peninsula one of Earth's most notable regions of high amplitude wave activity and one of the planet’s strongest sources of ocean-swell driven microseism noise in both the primary (direct wave-coastal region interactions) and secondary (direct ocean floor forcing due to interacting wave trains) period bands. Microseism observations are examined from 1993-2015 from long running seismographs located at Palmer Station (PMSA), on the west coast of the Antarctic Peninsula, and from the sub-Antarctic East Falkland Island (EFI). These records provide a spatially integrative measure of Southern Ocean amplitudes and of the degree of coupling between ocean waves and the solid earth with and without the presence of sea ice (which can reduce wave coupling with the continental shelf). A spatiotemporal correlation-based approach illuminates how the distribution of sea ice influences seasonal primary and secondary microseism power. I characterize primary and secondary microseism power due to variations in sea ice, and find that primary microseism energy is both more sensitive to sea ice and more capable of propagating across ocean basins than secondary microseism energy. During positive phases of the SAM, sea ice is reduced in the Bellingshausen Sea and overall storm activity in the Drake Passage increases, resulting in strongly increased microseism power levels. The field of fluvial seismology has emerged during the past decade, with seismic recordings near fluvial systems showing potential for a continuous, inexpensive, and non-invasive method of measuring flow and, in some cases, bed-load transport, in streams and rivers. In Chapter 3, I extend this research to the South Fork of the Cache la Poudre River in Northern Colorado where I deployed a small seismoaccoustic array while simultaneous measurements of discharge, suspended sediment concentrations, and precipitation were obtained. By placing seismometers within unprecedented proximity to the channel (~ 1 m, and during some time periods submerged), I found a broad range of frequencies excited by discharge, including novel, low-frequency (< 1 Hz) signals. After calibrating horizontal seismic power with flow rates over the course of a rainstorm event for individual sensors, I show that horizontal seismogram power in the 0.33-2 Hz band can be used to accurately invert for fluvial discharge with simple regressions, once a site is properly calibrated to a traditional hydrograph. These signals likely arise from local sensor tilt as the seismometer is directly forced by channel flow and show promise for augmenting seismic monitoring of fluvial systems by introducing a technique to estimate discharge rates from outside the channel with easily deployed noninvasive instrumentation.
Open Access
Using RMS amplitudes from forward seismic-reflectivity modeling of channelized deep-water slope deposits to inform stratigraphic interpretation and sub-seismic scale architecture, Tres Pasos Formation, Magallanes Basin, Patagonia, Chile
(Colorado State University. Libraries, 2018) Nielson, Adam, author; Stright, Lisa, advisor; Schutt, Derek, committee member; Sale, Thomas, committee member
Deep-water slope channels outcropping in the Tres Pasos Formation of the Magallanes Basin in southern Chile are used as the foundation of a forward seismic-reflectivity modeling study to better inform stratigraphic interpretation. The multi-scale architecture of deep-water slope channels is often difficult to interpret from low resolution seismic-reflectivity surveys. Valuable insight can be gained from forward seismic-reflectivity modeling using multiple-scales of architecture as building blocks (i.e., channel elements stacking into channel complexes) to provide insight into subsurface interpretation. Forward seismic-reflectivity models of channel elements with sub-meter scale heterogeneity are interrogated for RMS amplitude and apparent thickness as a function of true stratigraphic thickness and net sand thickness. Relationships between interpreted variables from the forward models (RMS amplitude and apparent thickness) compared to measured variable from the input models (true stratigraphic thickness and net sand thickness) provide recognition criteria for interpreting building blocks in subsurface seismic-reflectivity data. This study shows that decreasing RMS amplitude for constant apparent thickness is primarily controlled by vertically juxtaposed facies between multiple stacked channel elements. Furthermore, laterally stepping and vertically aggrading channel elements increase confidence in stratigraphic interpretation whereas laterally migrating channel elements are harder to delineate. An increase in frequency tends to improve interpretation of net sand thickness for multiple channel elements informing interpretation of lateral facies changes. Results from this study also show that RMS amplitudes and apparent thickness show patterns to help differentiate channel element stacking configurations and can be tied back to the known model variables, true stratigraphic thickness and net sand thickness. However, interpretation of exploration scale data, specifically RMS amplitude and apparent thickness interpretations is complicated by interfering reflections at increased frequency, complicating the recognition of multiple channel elements within a channel complex set.