Matching Items (7)

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Detrital-Zircon and Paleontological Constraints on Correlations of Pennsylvanian-Permian Rocks Near Sedona, Arizona

Description

This research focuses on a geologic controversy regarding the stratigraphic position of the Hermit Formation outside of the Grand Canyon, specifically in Sedona, Arizona. The goal of this research is

This research focuses on a geologic controversy regarding the stratigraphic position of the Hermit Formation outside of the Grand Canyon, specifically in Sedona, Arizona. The goal of this research is to provide additional constraints on this dispute by pinpointing the transition to the Hermit Formation in Sedona, if possible. To accomplish this, we use field observations and detrital zircon dating techniques to compare data we collected in Sedona with data previously published for the Grand Canyon. Fossil evidence in Sedona and near Payson, Arizona is also used to aid correlation. Starting from the Grand Canyon, the Hermit Formation pinches out to the southeast and, hypothetically obstructed by the Sedona Arch, does not reach Sedona. Detrital zircon data show similar age distributions between the Grand Canyon and Sedona rock units, but the results are not strong enough to confidently correlate units between these two localities. The data collected for this study suggest that if the Hermit Formation is present in Sedona, it is limited to higher up in the section as opposed to occupying the middle portion of the section as is currently interpreted. To determine with greater accuracy whether the Hermit Formation does exist higher in the section of Sedona, more detrital zircons should be collected and analyzed from the part of the section that yielded a relative increase in young zircons aged 200-600 Ma.

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  • 2017-05

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Combining tectonic geomorphology and paleoseismology for understanding of earthquake recurrence

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There is a need to understand spatio-temporal variation of slip in active fault zones, both for the advancement of physics-based earthquake simulation and for improved probabilistic seismic hazard assessments. One

There is a need to understand spatio-temporal variation of slip in active fault zones, both for the advancement of physics-based earthquake simulation and for improved probabilistic seismic hazard assessments. One challenge in the study of seismic hazards is producing a viable earthquake rupture forecast—a model that specifies the expected frequency and magnitude of events for a fault system. Time-independent earthquake forecasts can produce a mismatch among observed earthquake recurrence intervals, slip-per-event estimates, and implied slip rates. In this thesis, I developed an approach to refine several key geologic inputs to rupture forecasts by focusing on the San Andreas Fault in the Carrizo Plain, California. I use topographic forms, sub-surface excavations, and high-precision geochronology to understand the generation and preservation of slip markers at several spatial and temporal scales—from offset in a single earthquake to offset accumulated over thousands of years. This work results in a comparison of slip rate estimates in the Carrizo Plain for the last ~15 kyr that reduces ambiguity and enriches rupture forecast parameters. I analyzed a catalog of slip measurements and surveyed earth scientists with varying amounts of experience to validate high-resolution topography as a supplement to field-based active fault studies. The investigation revealed that (for both field and remote studies) epistemic uncertainties associated with measuring offset landforms can present greater limitations than the aleatoric limitations of the measurement process itself. I pursued the age and origin of small-scale fault-offset fluvial features at Van Matre Ranch, where topographic depressions were previously interpreted as single-event tectonic offsets. I provide new estimates of slip in the most recent earthquake, refine the centennial-scale fault slip rate, and formulate a new understanding of the formation of small-scale fault-offset fluvial channels from small catchments (<7,000 m2). At Phelan Creeks, I confirm the constancy of strain release for the ~15,000 years in the Carrizo Plain by reconstructing a multistage offset landform evolutionary history. I update and explicate a simplified model to interpret the geomorphic response of stream channels to strike-slip faulting. Lastly, I re-excavate and re-interpret paleoseismic catalogs along an intra-continental strike-slip fault (Altyn Tagh, China) to assess consistency of earthquake recurrence.

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Created

Date Created
  • 2016

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The roles of erosion rate and rock strength in the evolution of canyons along the Colorado River

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For this dissertation, three separate papers explore the study areas of the western Grand Canyon, the Grand Staircase (as related to Grand Canyon) and Desolation Canyon on the Green River

For this dissertation, three separate papers explore the study areas of the western Grand Canyon, the Grand Staircase (as related to Grand Canyon) and Desolation Canyon on the Green River in Utah.

In western Grand Canyon, I use comparative geomorphology between the Grand Canyon and the Grand Wash Cliffs (GWC). We propose the onset of erosion of the GWC is caused by slip on the Grand Wash Fault that formed between 18 and 12 million years ago. Hillslope angle and channel steepness are higher in Grand Canyon than along the Grand Wash Cliffs despite similar rock types, climate and base level fall magnitude. These experimental controls allow inference that the Grand Canyon is younger and eroding at a faster rate than the Grand Wash Cliffs.

The Grand Staircase is the headwaters of some of the streams that flow into Grand Canyon. A space-for-time substitution of erosion rates, supported by landscape simulations, implies that the Grand Canyon is the result of an increase in base level fall rate, with the older, slower base level fall rate preserved in the Grand Staircase. Our data and analyses also support a younger, ~6-million-year estimate of the age of Grand Canyon that is likely related to the integration of the Colorado River from the Colorado Plateau to the Basin and Range. Complicated cliff-band erosion and its effect on cosmogenic erosion rates are also explored, guiding interpretation of isotopic data in landscapes with stratigraphic variation in quartz and rock strength.

Several hypotheses for the erosion of Desolation Canyon are tested and refuted, leaving one plausible conclusion. I infer that the Uinta Basin north of Desolation Canyon is eroding slowly and that its form represents a slow, stable base level fall rate. Downstream of Desolation Canyon, the Colorado River is inferred to have established itself in the exhumed region of Canyonlands and to have incised to near modern depths prior to the integration of the Green River and the production of relief in Desolation Canyon. Analysis of incision and erosion rates in the region suggests integration is relatively recent.

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Created

Date Created
  • 2016

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Post-tectonic landscape evolution of sedimentary basins in southeastern Arizona and northern Chile

Description

Sedimentary basins are defined by extensional tectonics. Rugged mountain ranges stand in stark relief adjacent to muted structural basins filled with sediment. In simplest terms, this topography is the result

Sedimentary basins are defined by extensional tectonics. Rugged mountain ranges stand in stark relief adjacent to muted structural basins filled with sediment. In simplest terms, this topography is the result of ranges uplifted along normal faults, and this uplift drives erosion within upland drainages, shedding sediment into subsiding basins. In southeastern Arizona's Basin and Range province extensional tectonics waned at approximately 3-5 Myr, and the region's structural basins began transitioning from internal to external drainage, forming the modern Gila River fluvial network. In the Atacama Desert of northern Chile, some basins of the Central Depression remain internally drained while others have integrated to the Pacific Ocean. In northern Chile, rates of landscape evolution are some of the slowest on Earth due to the region's hyperarid climate. While the magnitude of upland erosion driven by extensional tectonics is largely recorded in the stratigraphy of the structural basins, the landscape's response to post-tectonic forcings is unknown.

I employ the full suite of modern geomorphic tools provided by terrestrial cosmogenic nuclides - surface exposure dating, conventional burial dating, isochron burial dating, quantifying millennial-scale upland erosion rates using detrital TCN, quantifying paleo-erosion rates using multiple TCN such as Ne-21/Be-10 and Al-26l/Be-10, and assessing sediment recycling and complex exposure using multiple TCN - to quantify the rates of landscape evolution in southeastern Arizona and northern Chile during the Late Cenozoic. In Arizona, I also use modern remnants of the pre-incision landscape and digital terrain analyses to reconstruct the landscape, allowing the quantification of incision and erosion rates that supplement detrital TCN-derived erosion rates. A new chronology for key basin high stand remnants (Frye Mesa) and a flight of Gila River terraces in Safford basin provides a record of incision rates from the Pliocene through the Quaternary, and I assess how significantly regional incision is driving erosion rates. Paired nuclide analyses in the Atacama Desert of northern Chile reveal complex exposure histories resulting from several rounds of transport and burial by fluvial systems. These results support a growing understanding that geomorphic processes in the Atacama Desert are more active than previously thought despite the region's hyperarid climate.

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Created

Date Created
  • 2014

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Characterization of landslide geometry and movement near Black Canyon City, Arizona

Description

I investigate the Black Canyon City landslide (BCC landslide), a prominent deep-seated landslide located northeast of Black Canyon City, Arizona. Although the landslide does not appear to pose a significant

I investigate the Black Canyon City landslide (BCC landslide), a prominent deep-seated landslide located northeast of Black Canyon City, Arizona. Although the landslide does not appear to pose a significant hazard to structures, its prominent features and high topographic relief make it an excellent site to study the geologic setting under which such features develop. This study has the potential to contribute toward understanding the landscape evolution in similar geologic and topographic settings, and for characterizing the underlying structural processes of this deep-seated feature. We use field and remotely-based surface geology and geomorphological mapping to characterize the landslide geometry and its surface displacement. We use the Structure from Motion (SfM) method to generate a 0.2 m resolution digital elevation model and rectified ortho-photo imagery from unmanned aerial vehicle (UAV) - and balloon-based images and used them as the base map for our mapping. The ~0.6 km2 landslide is easily identified through remotely-sensed imagery and in the field because of the prominent east-west trending fractures defining its upper extensional portion. The landslide displaces a series of Early and Middle Miocene volcanic and sedimentary rocks. The main head scarp is ~600 m long and oriented E-W with some NW-SE oriented minor scarps. Numerous fractures varying from millimeters to meters in opening were identified throughout the landslide body (mostly with longitudinal orientation). The occurrence of a distinctive layer of dark reddish basalt presents a key displaced marker to estimate the long-term deformation of the slide mass. Using this marker, the total vertical displacement is estimated to be ~70 m, with maximum movement of ~95 m to the SE. This study indicates that the landslide motion is translational with a slight rotational character. We estimate the rate of the slide motion by resurvey of monuments on and off the slide, and examination of disturbed vegetation located along the fractures. The analysis indicates a slow integrated average landslide velocity of 10-60 mm/yr. The slide motion is probably driven during annual wet periods when increased saturation of the slide mass weakens the basal slip surface and the overall mass of the slide is increased. Results from our study suggest that the slide is stable and does not pose significant hazard for the surrounding area given no extreme changes in the environmental condition. Although the landslide is categorized as very slow (according to Cruden and Varnes, 1996), monitoring the landslide is still necessary.

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Created

Date Created
  • 2016

Rock Traits from Machine Learning: Application to Rocky Fault Scarps

Description

Rock traits (grain size, shape, orientation) are fundamental indicators of geologic processes including geomorphology and active tectonics. Fault zone evolution, fault slip rates, and earthquake timing are informed by examinations

Rock traits (grain size, shape, orientation) are fundamental indicators of geologic processes including geomorphology and active tectonics. Fault zone evolution, fault slip rates, and earthquake timing are informed by examinations of discontinuities in the displacements of the Earth surface at fault scarps. Fault scarps indicate the structure of fault zones fans, relay ramps, and double faults, as well as the surface process response to the deformation and can thus indicate the activity of the fault zone and its potential hazard. “Rocky” fault scarps are unusual because they share characteristics of bedrock and alluvial fault scarps. The Volcanic Tablelands in Bishop, CA offer a natural laboratory with an array of rocky fault scarps. Machine learning mask-Region Convolutional Neural Network segments an orthophoto to identify individual particles along a specific rocky fault scarp. The resulting rock traits for thousands of particles along the scarp are used to develop conceptual models for rocky scarp geomorphology and evolution. In addition to rocky scarp classification, these tools may be useful in many sedimentary and volcanological applications for particle mapping and characterization.

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Date Created
  • 2020

Geologic and Structural Characterization of Shallow Seismic Properties Along The San Jacinto Fault at Sage Brush Flat, Southern California

Description

The study of fault zones is a critical component to understanding earthquake mechanics and seismic hazard evaluations. Models or simulations of potential earthquakes, based on fault zone properties, are a

The study of fault zones is a critical component to understanding earthquake mechanics and seismic hazard evaluations. Models or simulations of potential earthquakes, based on fault zone properties, are a first step in mitigating the hazard. Theoretical models of earthquake ruptures along a bi-material interface result in asymmetrical damage and preferred rupture propagation direction. Results include greater damage intensity within stiffer material and preferred slip in the direction of the more compliant side of the fault. Data from a dense seismic array along the Clark strand of the SJFZ at Sage Brush Flat (SGB) near Anza, CA, allows for analysis and characterization of shallow (<1km depth) seismic structure and fault zone properties. Results indicate potential asymmetric rock damage at SGB, similar to findings elsewhere along the SJFZ suggesting an NW preferred rupture propagation.

In this study, analysis of high resolution topography suggests asymmetric morphology of the SGB basin slopes are partially attributed to structural growth and fault zone damage. Spatial distributions of rock damage, from site mapping and fault perpendicular transects within SGB and Alkali Wash, are seemingly asymmetric with pulverization dominantly between fault strands or in the NE fault block. Remapping of the SJFZ through Alkali Wash indicates the fault is not isolated to a single strand along the main geologic boundary as previously mapped. Displacement measurements within SGB are analogous to those from the most recent large earthquake on the Clark fault. Geologic models from both a 3D shear wave velocity model (a product from the dense seismic array analysis) and lithologic and structural mapping from this study indicate surface observations and shallow seismic data compare well. A synthetic three-dimensional fault zone model illustrates the complexity of the structure at SGB for comparison with dense array seismic wave products. Results of this study generally agree with findings from seismic wave interpretations suggesting damage asymmetry is controlled by a NW preferred rupture propagation.

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Agent

Created

Date Created
  • 2018