+publisher:"Colorado State University" +contributor:("Aster, Richard C.")

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Colorado State University

1. Cole, Hank M. Tidally induced seismicity at the grounded margins of the Ross Ice Shelf, Antarctica.

Degree: MS(M.S.), Geosciences, 2020, Colorado State University

URL: http://hdl.handle.net/10217/212036

► Repeating swarms of local icequakes were recorded by broadband seismograpghs deployed near the grounding line of the Ross Ice Shelf, Antarctica from late 2014 to… (more)

▼ Repeating swarms of local icequakes were recorded by broadband seismograpghs deployed near the grounding line of the Ross Ice Shelf, Antarctica from late 2014 to early 2017. Swarms commonly persist for over six hours and contain thousands of events. Most swarms are induced or enhanced by tidal forcing. The number of events and event amplitudes in a swarm is most correlated with the modeled tide range. Some swarms only occur during cold periods of the austral winter. Icequakes are cataloged using a cross-correlation detector after building a template library from clustered STA/LTA picks and epicenters are estimated for high quality events. Events can be classified into four broad categories. The first event type is the most common (>95% of events) and occurs in diurnal swarms at all times of year. This type of event is interpreted to be sourced by propagation of near surface crevasses due to enhanced tensile stress from downward flexure of the ice shelf during falling tide. The second type of event has similar waveforms but occurs at the crest of large spring tides and appears to have an englacial or basal source. The third type of event is likely sourced from within the firn, possibly related to densification. It is also observed at stations in the ice shelf interior, but appears enhanced by tides at stations near the grounding line. The fourth type of event is only observed at a station on the Steershead Ice Rise. These are sweeping harmonic tremors lasting up to 8 s that start at low frequency and then tail upwards into an impulse like signal. This work characterizes these icequake types and their correlation to tidal and environmental forcing. It also details a single station event location scheme that is to used to further interpret events by finding their back azimuth with a polarization analysis and estimate their source-receiver distance with two methods. These observations provide insight into the deformation and brittle fracture at the grounded margins of the Ross Ice Shelf. Advisors/Committee Members: Aster, Richard C. (advisor), McGrath, Daniel (committee member), Cheney, Margaret (committee member), Benz, Harley (committee member).

Subjects/Keywords: grounding line; icequakes; tides; ice shelf; seismology; Antarctica

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APA (6^th Edition):

Cole, H. M. (2020). Tidally induced seismicity at the grounded margins of the Ross Ice Shelf, Antarctica. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/212036

Chicago Manual of Style (16^th Edition):

Cole, Hank M. “Tidally induced seismicity at the grounded margins of the Ross Ice Shelf, Antarctica.” 2020. Masters Thesis, Colorado State University. Accessed April 12, 2021. http://hdl.handle.net/10217/212036.

MLA Handbook (7^th Edition):

Cole, Hank M. “Tidally induced seismicity at the grounded margins of the Ross Ice Shelf, Antarctica.” 2020. Web. 12 Apr 2021.

Vancouver:

Cole HM. Tidally induced seismicity at the grounded margins of the Ross Ice Shelf, Antarctica. [Internet] [Masters thesis]. Colorado State University; 2020. [cited 2021 Apr 12]. Available from: http://hdl.handle.net/10217/212036.

Council of Science Editors:

Cole HM. Tidally induced seismicity at the grounded margins of the Ross Ice Shelf, Antarctica. [Masters Thesis]. Colorado State University; 2020. Available from: http://hdl.handle.net/10217/212036

2. McMahon, Nicole D. Automated event detectors utilized for continental intraplate earthquakes: applications to tectonic, induced, and magmatic sequences.

Degree: PhD, Geosciences, 2018, Colorado State University

URL: http://hdl.handle.net/10217/193146

► Event detection is a crucial part of the data-driven science of seismology. With decades of continuous seismic data recorded across thousands of networks and tens… (more)

▼ Event detection is a crucial part of the data-driven science of seismology. With decades of continuous seismic data recorded across thousands of networks and tens of thousands of stations, and an ever-accelerating rate of data acquisition, automated methods of event detection, as opposed to manual/visual inspection, allow scientists to rapidly sift through enormous data sets extracting event information from background noise for further analysis. Automation naturally increases the numbers of detected events and lowers the minimum magnitude of detectable events. Increasing numbers and decreasing magnitudes of detected events, particularly with respect to earthquakes, enables the construction of more complete event catalogs and more detailed analysis of spatiotemporal trends in earthquake sequences. These more complete catalogs allow for enhanced knowledge of Earth structure, earthquake processes, and have potential for informing hazard mitigation. This study utilizes automated event detection techniques, namely matched filter and subspace detection, and applies them to three different types of continental intraplate earthquake sequences: a tectonic aftershock sequences in Montana, an induced aftershock sequence in Oklahoma, and a magmatic swarm sequence in Antarctica. In Montana, the combination of matched filtering and multiple-event relocation techniques provided a more complete picture of the spatiotemporal evolution of the aftershock sequence of the large intraplate earthquake that occurred near Lincoln, Montana in 2017. The study reveals movement along an unmapped fault that is antithetical to the main fault system trend in the region and demonstrates the hazards associated with a highly faulted and seismically active region encompassing complex and hidden structures. In Oklahoma, subspace detection methodology is used in combination with multiple-event relocation techniques to reveal movement along three different faults associated with the 2011 Prague, Oklahoma induced earthquake sequence. The study identifies earthquakes located in both the sedimentary zone of wastewater injection as well as the underlying crystalline basement indicating that faults traverse the unconformity. Injecting fluid into the overlying sediment can easily penetrate to the basement where larger earthquakes nucleate. In Antarctica, subspace detection is again used in a very remote intraplate region with sparse station coverage to detail the sustained and ongoing magmatic deep, long-period earthquake swarm occurring beneath the West Antarctic Ice Sheet and Executive Committee Range in Marie Byrd Land, Antarctica. These earthquakes indicate the present-day location of magmatic activity, which appears appear to have increased in intensity over the last few years. This dissertation contributes to the growing bodies of literature around three distinctly interesting types of seismicity that are not associated to the first order with plate tectonic boundaries. Large tectonic intraplate earthquakes are relatively uncommon. Induced seismicity has… Advisors/Committee Members: Aster, Richard C. (advisor), Schutt, Derek L. (committee member), Cheney, Margaret (committee member), Benz, Harley M. (committee member).

Subjects/Keywords: earthquakes; intraplate earthquakes; volcanic seismicity; induced seismicity; earthquake detection; seismology

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APA (6^th Edition):

McMahon, N. D. (2018). Automated event detectors utilized for continental intraplate earthquakes: applications to tectonic, induced, and magmatic sequences. (Doctoral Dissertation). Colorado State University. Retrieved from http://hdl.handle.net/10217/193146

Chicago Manual of Style (16^th Edition):

McMahon, Nicole D. “Automated event detectors utilized for continental intraplate earthquakes: applications to tectonic, induced, and magmatic sequences.” 2018. Doctoral Dissertation, Colorado State University. Accessed April 12, 2021. http://hdl.handle.net/10217/193146.

MLA Handbook (7^th Edition):

McMahon, Nicole D. “Automated event detectors utilized for continental intraplate earthquakes: applications to tectonic, induced, and magmatic sequences.” 2018. Web. 12 Apr 2021.

Vancouver:

McMahon ND. Automated event detectors utilized for continental intraplate earthquakes: applications to tectonic, induced, and magmatic sequences. [Internet] [Doctoral dissertation]. Colorado State University; 2018. [cited 2021 Apr 12]. Available from: http://hdl.handle.net/10217/193146.

Council of Science Editors:

McMahon ND. Automated event detectors utilized for continental intraplate earthquakes: applications to tectonic, induced, and magmatic sequences. [Doctoral Dissertation]. Colorado State University; 2018. Available from: http://hdl.handle.net/10217/193146

Colorado State University

3. Baker, Michael G. Ambient and teleseismic elastic wavefields of the Ross Ice Shelf, Antarctica, and their application to crustal scale seismic imaging.

Degree: PhD, Geosciences, 2020, Colorado State University

URL: http://hdl.handle.net/10217/208575

► Laterally extensive floating tabular ice, such as the Ross Ice Shelf in Antarctica, is mechanically equivalent to a floating elastic plate and thus supports a… (more)

▼ Laterally extensive floating tabular ice, such as the Ross Ice Shelf in Antarctica, is mechanically equivalent to a floating elastic plate and thus supports a variety of vibrational modes, including short-period (< 20 s) elastic waves, intermediate-to-long period (20–100 s) buoyancy-coupled elastic plate waves, and ultra long period (>100 s) gravity waves. Vibrational energy may be excited by near-field sources such as intra-shelf crevassing or the impingement of ocean gravity waves at the shelf ice front, and also by far-field sources such as teleseismic earthquake waves incident at the sub-shelf seafloor and the shelf grounded margins. Broadband seismometers deployed on an ice shelf readily observe these signals and facilitate large scale studies of ice shelf properties (via, e.g., travel-time tomography or velocity dispersion analysis) and near-field environment processes (via remote signal detection and analysis). Using two years of continuous data from a 34-station broadband seismic array deployed to the Ross Ice Shelf, Antarctica, I analyzed spatial and temporal variations in the short-to-intermediate period (0.4–25 s) ambient and teleseismic vibrational wavefields. I show that the ambient, ocean-wave-coupled wavefields are strongly modulated by sea ice concentrations in the adjacent Ross Sea, and identify three separate source processes operating in distinct period bands. Next, I show that body wave and surface wave arrivals from teleseismic earthquakes (>3000 km distant) are observed on the vertical components of ice shelf-sited seismometers with signal-to-noise ratios generally sufficient for crustal and mantle scale tomographic studies. I also show that teleseismic S-waves incident at the grounded margins routinely generate symmetric mode Lamb waves which propagate a minimum of 250 km into the ice shelf interior; this phenomenon occurs throughout the year, with broad azimuthal distribution, and may be exploited for travel-time tomography of the ice shelf. Finally, I present an algorithm for processing vertical channel autocorrelations of teleseismic P-wave coda, as recorded by floating-ice-sited seismometers, to illuminate crustal-scale features such as the Mohorovičić discontinuity. I present Markov Chain Monte Carlo inversions of these autocorrelations which yield crustal thickness estimates that are compatible with previous studies of crustal thicknesses for the Ross Sea Embayment and West Antarctica. Advisors/Committee Members: Aster, Richard C. (advisor), Schutt, Derek L. (committee member), Krueger, David A. (committee member), Dueker, Ken G. (committee member).

Subjects/Keywords: environmental seismology; seismology; ice shelves; cyroseismology

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APA (6^th Edition):

Baker, M. G. (2020). Ambient and teleseismic elastic wavefields of the Ross Ice Shelf, Antarctica, and their application to crustal scale seismic imaging. (Doctoral Dissertation). Colorado State University. Retrieved from http://hdl.handle.net/10217/208575

Chicago Manual of Style (16^th Edition):

Baker, Michael G. “Ambient and teleseismic elastic wavefields of the Ross Ice Shelf, Antarctica, and their application to crustal scale seismic imaging.” 2020. Doctoral Dissertation, Colorado State University. Accessed April 12, 2021. http://hdl.handle.net/10217/208575.

MLA Handbook (7^th Edition):

Baker, Michael G. “Ambient and teleseismic elastic wavefields of the Ross Ice Shelf, Antarctica, and their application to crustal scale seismic imaging.” 2020. Web. 12 Apr 2021.

Vancouver:

Baker MG. Ambient and teleseismic elastic wavefields of the Ross Ice Shelf, Antarctica, and their application to crustal scale seismic imaging. [Internet] [Doctoral dissertation]. Colorado State University; 2020. [cited 2021 Apr 12]. Available from: http://hdl.handle.net/10217/208575.

Council of Science Editors:

Baker MG. Ambient and teleseismic elastic wavefields of the Ross Ice Shelf, Antarctica, and their application to crustal scale seismic imaging. [Doctoral Dissertation]. Colorado State University; 2020. Available from: http://hdl.handle.net/10217/208575

Colorado State University

4. Heath, David C. Detection and relocation of earthquakes in the sparsely instrumented Mackenzie Mountains region, Yukon and Northwest Territories, Canada.

Degree: MS(M.S.), Geosciences, 2020, Colorado State University

URL: http://hdl.handle.net/10217/208440

► The Mackenzie Mountains are an actively uplifting and seismogenic arcuate thrust belt lying within the Northwest Territories and Yukon, Canada. Seismic activity in the region… (more)

▼ The Mackenzie Mountains are an actively uplifting and seismogenic arcuate thrust belt lying within the Northwest Territories and Yukon, Canada. Seismic activity in the region is poorly constrained due to a historically sparse seismograph distribution. In this study, new data are analyzed from the 40-station, ~875 km-long Mackenzie Mountains temporary network (Baker et al., 2020) crossing the Cordillera-Craton region adjacent to and within the Mackenzie Mountains, in conjunction with Transportable Array and other sparsely distributed arrays in the region. Data from approximately August 2016 – August 2018 are processed and compared to the sparse-network earthquake catalog records maintained by the USGS and Natural Resources Canada. Using algorithms developed by Kushnir et al. (1990), Rawles and Thurber (2015), and Roecker et al. (2006), signals are identified and subsequently associated across the network to note potential events, estimate phase onsets, and resolve hypocenter locations. This study improves the regional earthquake catalog by detecting smaller-magnitude earthquakes and lowering the regional magnitude of completeness from Mc = 2.5 to 1.9. Within the Mackenzie Mountains and immediately surrounding areas we find 524 new events and additionally recommend an updated location for 185 previously cataloged events. Our b-value computation for the updated catalog (0.916 ± 0.08) likely indicates a relatively high level of regional differential stress. We identify the spatial distribution of earthquakes in the Mackenzie Mountains as diffuse, and offer far-field stress transfer as a mechanism for producing widespread reverse faulting observed in the region. Further, we associate regional seismicity with tectonic activity in the context of known faults and orogenic provinces such as the Richardson Mountains. Advisors/Committee Members: Schutt, Derek L. (advisor), Aster, Richard C. (committee member), Wald, David J. (committee member), Cheney, Margaret (committee member).

Subjects/Keywords: earthquake; catalog; seismology

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APA (6^th Edition):

Heath, D. C. (2020). Detection and relocation of earthquakes in the sparsely instrumented Mackenzie Mountains region, Yukon and Northwest Territories, Canada. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/208440

Chicago Manual of Style (16^th Edition):

Heath, David C. “Detection and relocation of earthquakes in the sparsely instrumented Mackenzie Mountains region, Yukon and Northwest Territories, Canada.” 2020. Masters Thesis, Colorado State University. Accessed April 12, 2021. http://hdl.handle.net/10217/208440.

MLA Handbook (7^th Edition):

Heath, David C. “Detection and relocation of earthquakes in the sparsely instrumented Mackenzie Mountains region, Yukon and Northwest Territories, Canada.” 2020. Web. 12 Apr 2021.

Vancouver:

Heath DC. Detection and relocation of earthquakes in the sparsely instrumented Mackenzie Mountains region, Yukon and Northwest Territories, Canada. [Internet] [Masters thesis]. Colorado State University; 2020. [cited 2021 Apr 12]. Available from: http://hdl.handle.net/10217/208440.

Council of Science Editors:

Heath DC. Detection and relocation of earthquakes in the sparsely instrumented Mackenzie Mountains region, Yukon and Northwest Territories, Canada. [Masters Thesis]. Colorado State University; 2020. Available from: http://hdl.handle.net/10217/208440

5. Crow, Brian. On quasi-periodic Baroclinic variability in the extratropical circulation.

Degree: MS(M.S.), Atmospheric Science, 2016, Colorado State University

URL: http://hdl.handle.net/10217/178865

► A number of recent studies have demonstrated that large-scale extratropical wave activity is characterized by quasi-periodic behavior on timescales of 20-30 days, particularly in the… (more)

▼ A number of recent studies have demonstrated that large-scale extratropical wave activity is characterized by quasi-periodic behavior on timescales of 20-30 days, particularly in the Southern Hemisphere. This phenomenon has been termed the Baroclinic Annular Mode (BAM), and is responsible for the modulation of eddy heat fluxes, eddy kinetic energy, and precipitation on large scales. However, the extent to which this periodic modulation is discernable or significant on smaller spatial scales had not yet been established. Using data from the ECMWF Interim Reanalysis for the period 1979-2014, this study extensively examines the spatial structure of the BAM. Spectral analyses reveal the spatial limitations of the periodic behavior, while lag-correlation analyses reveal the patterns of propagation and development of anomalies that give rise to the observed periodicity. Periodic behavior is more robust in the Southern Hemisphere than in the Northern Hemisphere, but filtering out low wavenumbers from NH data helps clarify the BAM signal. Additionally, it is demonstrated that the BAM appears very differently in two relatively similar global climate models, suggesting further study is needed to determine how modern GCMs capture the BAM. Supplementing our analyses of observed and modeled data is a simple two-way linear feedback model, which is utilized to demonstrate the principal mechanism underlying periodic behavior in the BAM. The model makes it apparent that the BAM can be modeled as a simple linear feedback between baroclinicity and eddy heat fluxes. The periodicity seen on larger scales is a product of differential advection rates affecting the development of spatially overlapping, out-of-phase anomalies. The large-scale nature of the periodic behavior, however, makes it difficult to draw conclusions about the potential utility of the BAM for weather analysts and forecasters, and the limitations of this study limit our ability to describe its role in the climate system. It is hoped that the research presented here will pave the way to future studies which may more thoroughly answer such questions. Advisors/Committee Members: Thompson, David W. J. (advisor), Barnes, Elizabeth A. (committee member), Aster, Richard C. (committee member).

Subjects/Keywords: extratropical circulation; atmospheric dynamics; weather and climate variability

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APA (6^th Edition):

Crow, B. (2016). On quasi-periodic Baroclinic variability in the extratropical circulation. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/178865

Chicago Manual of Style (16^th Edition):

Crow, Brian. “On quasi-periodic Baroclinic variability in the extratropical circulation.” 2016. Masters Thesis, Colorado State University. Accessed April 12, 2021. http://hdl.handle.net/10217/178865.

MLA Handbook (7^th Edition):

Crow, Brian. “On quasi-periodic Baroclinic variability in the extratropical circulation.” 2016. Web. 12 Apr 2021.

Vancouver:

Crow B. On quasi-periodic Baroclinic variability in the extratropical circulation. [Internet] [Masters thesis]. Colorado State University; 2016. [cited 2021 Apr 12]. Available from: http://hdl.handle.net/10217/178865.

Council of Science Editors:

Crow B. On quasi-periodic Baroclinic variability in the extratropical circulation. [Masters Thesis]. Colorado State University; 2016. Available from: http://hdl.handle.net/10217/178865

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