Matching Items (19)

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Dating and Characterizing the Piedmont Fault in the North Virgin Mountains of Arizona

Description

Faults found in the arid to semi-arid Basin and Range Physiographic province of the southwestern US are given broad age definitions in terms of which features appear to be the

Faults found in the arid to semi-arid Basin and Range Physiographic province of the southwestern US are given broad age definitions in terms of which features appear to be the oldest. Particularly in the northwestern corner of Arizona, detailed geomorphic studies on the tectonic history and timing of faulting are not widespread. At the base of the Virgin Mountains in northwestern Arizona is a fault scarp along the Piedmont Fault line. This normal fault crosses a series of alluvial fans that are filled with sediments of ambiguous ages. Previous studies that were done in this region find a broad, Miocene age for the exhumation and uplift of these surfaces, with some indications of Laramide faulting history. However, specific fault characteristics and a time constraint of the tectonic history of the Piedmont Fault scarp has yet to be established. Here, we aim to determine the age, fault-slip rate, seismic history, and potential hazard of the fault scarp near Scenic and Littlefield, Arizona through structure from motion (SfM) modeling, which is a form of photogrammetry using a drone. In addition, we distinguish the climatic and tectonic influences on the geomorphology observed along the scarp through analysis along the fault line. With data collected from a ~500 m section of the fault, we present results from a digital elevation model (DEM) and orthophotos derived through the SfM modelling. Based on field observations and morphologic dating, we determine that the Piedmont Fault experiences an approximately continuous fault-slip and an earthquake recurrence interval in the range of 7,000 years. The approximate age of the scarp is 16.0 ka ± 5 kyr. Therefore, we conclude that the earthquake hazard posed to nearby cities is minimal but not nonexistent. Future work includes further analysis of fault profiles due to uncertainty in the present one and Terrestrial Cosmogenic Nuclide (TCN) dating of samples taken from the tops of boulders in a residual debris flow sitting on faulted and unfaulted alluvia. Determining the ages for these boulder surfaces can hopefully further inform our knowledge of the tectonic activity present in the North Virgin Mountains.

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Date Created
  • 2020-12

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Understanding the Push for Development in Water Stressed Phoenix, Arizona

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Located in the Sunbelt of the Southwestern United States, Phoenix Arizona finds itself in one of the hottest, driest places in the world. Thankfully, Phoenix has the Salt River, Gila

Located in the Sunbelt of the Southwestern United States, Phoenix Arizona finds itself in one of the hottest, driest places in the world. Thankfully, Phoenix has the Salt River, Gila River, Verde River, and a vast aquifer to meet the water demands of the municipal, industrial, and agricultural sectors. However, rampant groundwater pumping and over-allocation of these water supplies based on unprecedented, high flows of the Colorado River have created challenges for water managers to ensure adequate water supply for the future. Combined with the current 17-year drought and the warming and drying projections of climate change, the future of water availability in Phoenix will depend on the strength of water management laws, educating the public, developing a strong sense of community, and using development to manage population and support sustainability. As the prevalence of agriculture declines in and around Phoenix, a substantial amount of water is saved. Instead of storing this saved water, Phoenix is using it to support further development. Despite uncertainty regarding the abundant and continuous availability of Phoenix's water resources, development has hardly slowed and barely shifted directions to support sustainability. Phoenix was made to grow until it legally cannot expand anymore. In order to develop solutions, we must first understand the push for development in water-stressed Phoenix, Arizona.

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Date Created
  • 2017-05

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Evidence for Plio-Pleistocene north-south extension at the southern margin of the Tibetan Plateau, Nyalam region

Description

The southern Tibetan Plateau margin between ~ 83E and 86.5E is defined by an abrupt change from the low-relief Tibetan Plateau to the rugged topography and deep gorges of the

The southern Tibetan Plateau margin between ~ 83E and 86.5E is defined by an abrupt change from the low-relief Tibetan Plateau to the rugged topography and deep gorges of the Himalaya. This physiographic transition lies well to the north of active thrusting, and thus, the mechanism responsible for the distinct topographic break remains the focus of much debate. While numerous studies have utilized thermochronology to examine the exhumation history of the Himalaya, few have done so with respect to variations across the Himalaya-Tibetan Plateau transition. In this work, we examine the nature of the transition where it is accessible and well-defined in the Nyalam valley of south-central Tibet. We employ several new and previously published thermochronologic datasets (with a closure temperature range of ~ 70C–300C) in conjunction with river incision patterns inferred by the longitudinal profile of the Bhote Kosi River. The results reveal a sharp change in cooling rate at ~ 3.5 Ma at a location corresponding to a pronounced river knickpoint representing a sharp increase in river gradient and presumably incision rate (a proxy for rock uplift). Margin retreat models for the physiographic transition are inconsistent with the cooling pattern revealed by low-temperature thermochronologic data. Models invoking passive uplift of the upper crust over a midcrustal ramp and associated duplex to account for the physiographic transition do not explain the observed break in cooling rate there, although they may explain a suggesting in the thermochronologic data of progressively increasing exhumation rates south of the transition. The simplest model consistent with all observations is that passive uplift is augmented by contemporaneous differential uplift across a young (Pliocene-Quaternary) normal fault at the physiographic transition. Drawing on observations elsewhere, we hypothesize that similar structural relationships may be characteristic of the Tibetan Plateau-Himalaya transition from ~83E – 86.5E.

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Date Created
  • 2013-05-30

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Evidence for Pleistocene Low-Angle Normal Faulting in the Annapurna-Dhaulagiri Region, Nepal

Description

North-south-directed extension on the South Tibetan Fault System (STFS) played an important role in Himalayan tectonics of the Miocene Period, and it is generally assumed that orogen-perpendicular extension ceased in

North-south-directed extension on the South Tibetan Fault System (STFS) played an important role in Himalayan tectonics of the Miocene Period, and it is generally assumed that orogen-perpendicular extension ceased in this orogenic system before the Pliocene. However, previous work in the Annapurna and Dhaulagiri Himalaya of central Nepal revealed evidence for local Pleistocene reactivation of the basal STFS structure in this area (the Annapurna Detachment). New structural mapping and (U-Th)/He apatite and zircon thermochronology in this region further document the significance of Pleistocene N-S extension in this sector of the Himalaya. Patterns of (U-Th)/He accessory-mineral ages are not disrupted across the reactivated segment of the STFS basal detachment, indicating that Pleistocene offset was limited. In contrast, the trace of a N-dipping, low-angle detachment in the hanging wall of the reactivated Annapurna Detachment—formerly linked to the STFS, but here named the Dhaulagiri Detachment—coincides with an abrupt break in the cooling-age pattern in two different drainages ∼20 km apart, juxtaposing Miocene hanging-wall dates against Pleistocene footwall dates. Our observations, combined with previous fission-track data from the region, provide direct evidence for significant N-S extension in the central Himalaya as recently as the Pleistocene.

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Date Created
  • 2015-03-01

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Sustaining Sustainability: Key Environmental Education

Description

The project was designed to increase awareness of sustainability and environmental science in public high school students who would otherwise not be exposed to complex environmental problems. This was done

The project was designed to increase awareness of sustainability and environmental science in public high school students who would otherwise not be exposed to complex environmental problems. This was done by testing the effectiveness of a simple yet comprehensive curriculum that could satisfy and expand the scope of the Arizona Education Science Standard, Essential HS.E1U3.14, while simultaneously being accessible to (and teachable by) any school instructor. Another goal of the project is to stimulate the minds of students who would otherwise not be introduced to the topics of sustainability and environmental science. Utilizing proven visualization and engagement techniques, the curriculum focuses on five key subjects: waste, water, energy, ecosystems, and environmental challenges. Each of these subjects had an educational presentation, interactive activities, question and answer sessions, and bonus activities. To test the overall effectiveness of the curriculum, students were given a pretest to gauge initial comprehension, and then after the five subjects (or modules) were taught, the same test was distributed again to the students. The aforementioned was done with two groups of students. Posttest results support the project effectiveness. The data indicate that the lessons had a positive impact on the test results, with one class averaging 33.6% better on the posttest than the pretest, indicating that the concepts taught did resonate with the students in a measurable way.

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Date Created
  • 2020-05

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Wind-driven modification of small bedforms in Gusev Crater, Mars

Description

ABSTRACT

The Spirit landing site in Gusev Crater has been imaged by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) camera more than thirty times since 2006. The

ABSTRACT

The Spirit landing site in Gusev Crater has been imaged by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) camera more than thirty times since 2006. The breadth of this image set allowed a study of changes to surface features, covering four Mars years.

Small fields of bedforms comprised of dark material, and dark dust devil tracks are among the features revealed in the images. The bedforms are constrained within craters on the plains, and unconstrained in depressions less than 200m wide within the topography of the Columbia Hills, a ~120m-high structure in center of Gusev. Dust devil tracks appear in many images of the bedforms.

Within the Columbia Hills, three bedform fields approximately 180m2 and composed of fine dark basaltic sand were studied, using five HiRISE images taken from 2006 to 2014. Both bedform crests and the dust devil tracks superimposed on them were evaluated for change to azimuth and length, and for correlation between the features. The linear to slightly sinuous transverse crests ranging from less than 1m to 113m in length and two to three meters in wavelength, are primary bedforms. During the study they shifted as much as 33 degrees in azimuth, and individual crests moved on the surface as much as 0.75m. The greatest changes corresponded to a global dust storm in 2007. Average crest movement was documented at the rate of 0.25m per year. Rather than moving progressively, the crests eventually returned to near their original orientation after the storm. The dust devil tracks, reflecting a more complex wind regime, including vortex development during diurnal heating, maintained predominantly NW-SE orientations but also reflected the effects of the storm.

The observed modifications were neither progressive, nor strictly seasonal. The apparent stability of the bedform geometry over four seasons supports the predictions of the Mars Regional Atmospheric Modeling System (MRAMS): low speed (1-7.5 ms-1), daily alternating winds of relatively equal force. Crest profiles were found to be nearly symmetrical, without slipfaces to indicate a preferential wind direction; this finding also is supported by the MRAMS model.

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Date Created
  • 2016

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Constraining Source Models, Underlying Mechanisms, and Hazards Associated with Slow Slip Events: Insight from Space-Borne Geodesy and Seismology

Description

The movement between tectonic plates is accommodated through brittle (elastic) displacement on the plate boundary faults and ductile permanent deformation on the fault borderland. The elastic displacement along the fault

The movement between tectonic plates is accommodated through brittle (elastic) displacement on the plate boundary faults and ductile permanent deformation on the fault borderland. The elastic displacement along the fault can occur in the form of either large seismic events or aseismic slip, known as fault creep. Fault creep mainly occurs at the deep ductile portion of the crust, where the temperature is high. Nonetheless, aseismic creep can also occur on the shallow brittle portion of the fault segments that are characterized by frictionally weak material, elevated pore fluid pressure, or geometrical complexity. Creeping segments are assumed to safely release the accumulated strain(Kodaira et al., 2004; Rice, 1992)(Kodaira et al., 2004; Rice, 1992)(Kodaira et al., 2004; Rice, 1992)(Kodaira et al., 2004; Rice, 1992)(Kodaira et al., 2004; Rice, 1992) on the fault and also impede propagation of the seismic rupture. The rate of aseismic slip on creeping faults, however, might not be steady in time and instead consist of successive periods of acceleration and deceleration, known as slow slip events (SSEs). SSEs, which aseismically release the strain energy over a period of days to months, rather than the seconds to minutes characteristic of a typical earthquake, have been interpreted as earthquake precursors and as possible triggering factor for major earthquakes. Therefore, understanding the partitioning of seismic and aseismic fault slip and evolution of creep is fundamental to constraining the fault earthquake potential and improving operational seismic hazard models. Thanks to advances in tectonic geodesy, it is now possible to detect the fault movement in high spatiotemporal resolution and develop kinematic models of the creep evolution on the fault to determine the budget of seismic and aseismic slip.

In this dissertation, I measure the decades-long time evolution of fault-related crustal deformation along the San Andrea Fault in California and the northeast Japan subduction zone using space-borne geodetic techniques, such as Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR). The surface observation of deformation combined with seismic data set allow constraining the time series of creep distribution on the fault surface at seismogenic depth. The obtained time-dependent kinematic models reveal that creep in both study areas evolves through a series of SSEs, each lasting for several months. Using physics-based models informed by laboratory experiments, I show that the transient elevation of pore fluid pressure is the driving mechanism of SSEs. I further investigate the link between SSEs and evolution of seismicity on neighboring locked segments, which has implications for seismic hazard models and also provides insights into the pattern of microstructure on the fault surface. I conclude that while creeping segments act as seismic rupture barriers, SSEs on these zones might promote seismicity on adjacent seismogenic segments, thus change the short-term earthquake forecast.

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Date Created
  • 2018

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Distribution of windblown sediment in small craters on Mars

Description

Many shallow craters near the Spirit Mars Exploration Rover landing site contain asymmetric deposits of windblown sediments which could indicate the predominant local wind direction at the time of deposition

Many shallow craters near the Spirit Mars Exploration Rover landing site contain asymmetric deposits of windblown sediments which could indicate the predominant local wind direction at the time of deposition or redistribution. Wind tunnel simulations and field studies of terrestrial craters were used to determine trends in deposition as a function of crater morphometry and wind direction. Terrestrial analog field work at the Amboy lava field, Mojave Desert, California, included real-time wind measurements and assessments of active sediment deposition in four small (<100 m) craters. Preliminary results indicate that reverse flow or stagnant wind and deposition on the upwind side of the crater floor occurs in craters with depth-to-diameter (d/D) ratios ≥0.05. Measurements taken within a crater of d/D of ~0.02 do not indicate reverse flow. Therefore, reverse flow is expected to cease within a d/D range of 0.02 to 0.05, resulting in wind movement directly over the crater floor in the downwind direction with no asymmetric sediment deposition. Wind tunnel simulations using six crater models, including a scaled model of a crater from the Amboy lava field, were completed to assess the wind flow in and around craters as a function of crater morphometry (depth, diameter). Reverse flow occurred in craters with d/D ratios ≥0.033, resulting in sediment deposition in the upwind portion of the crater floor. Visual observations of a crater with a d/D of ~0.020 did not indicate reverse flow, similar to the results of field studies; therefore, reverse flow appears to cease within a d/D range of 0.020 to 0.033. Craters with asymmetric aeolian deposits near the Mars Spirit landing site have d/D ratios of 0.034 to 0.076, suggesting that reverse flow occurs in these craters. Thus, the position of windblown sediments in the northwest parts of the crater floors would indicate prevailing winds from the northwest to the southeast, consistent with late afternoon winds as predicted by the Mars Regional Atmospheric Modeling System (MRAMS) circulation model.

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Created

Date Created
  • 2011

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Combining tectonic geomorphology and paleoseismology for understanding of earthquake recurrence

Description

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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Date Created
  • 2016

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

Description

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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Date Created
  • 2016