Matching Items (28)

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The Effect of the IRIS REU Program on Student Retention in Geoscience

Description

For the geoscience community to continue to grow, students need to be attracted to the field. Here we examine the Incorporated Research Institutions for Seismology (IRIS) Research Experience for Undergraduates

For the geoscience community to continue to grow, students need to be attracted to the field. Here we examine the Incorporated Research Institutions for Seismology (IRIS) Research Experience for Undergraduates (REU) program to understand how the participants' experiences' affects their interest in geoscience and educational and career goals. Eleven interns over two years (2013-2014) were interviewed prior to the start of their internship, after their internship, and after presenting their research at the American Geophysical Union annual meeting. This internship program is of particular interest because many of the interns come into the REU with non-geoscience or geophysics backgrounds (e.g., physics, mathematics, chemistry, engineering). Both a priori and emergent codes are used to convert interview transcripts into quantitative data, which is analyzed alongside demographic information to understand how the REU influences their decisions. Increases in self-efficacy and exposure to multiple facets of geoscience research are expressed as primary factors that help shape their future educational and career goals. Other factors such as networking opportunities and connections during the REU also can play a role in their decision. Overall, REU participants who identified as geosciences majors solidified their decisions to pursue a career in geosciences, while participants who identified as non-geosciences majors were inclined to change majors, pursue geosciences in graduate school, or explore other job opportunities in the geosciences.

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Created

Date Created
  • 2016-12

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Using InSAR to Investigate Injection-Induced Deformation and Seismicity in Timpson, Texas

Description

Hydraulic fracturing, or fracking, has become a common practice in United States oil fields for enhancing their productivity. Among the concerns regarding fracking, however, is the possibility that it could

Hydraulic fracturing, or fracking, has become a common practice in United States oil fields for enhancing their productivity. Among the concerns regarding fracking, however, is the possibility that it could trigger shallow earthquakes. The brine that results from fracking is injected into the subsurface for disposal. This brine causes a pore pressure gradient that is commonly believed to trigger failure along critically stressed subsurface faults. In Timpson, a small city in eastern Texas, earthquakes have become much more common since two injection wells were installed in 2007. 16 events of M_W > 2 have been detected since 2008 and are believed to be associated with failure along a subsurface fault. Applying interferometric synthetic aperture radar, we analyzed 3 sets of SAR images from the Advanced Land Observing Satellite (ALOS) from May 2007 to December 2010. Using these data sets, XX interferograms were generated. From these interferograms, it was possible to determine the spatial and temporal evolution of the crustal deformation in the line-of-sight of the satellite. The results show strong evidence of uplift in the region adjacent to the injection wells. While previous studies have established a strong connection between fluid injection and increased seismicity, this is to our knowledge the first observed case of crustal deformation that has been observed as a result of hydraulic fracturing fluid disposal.

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Date Created
  • 2014-05

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The Mineralogy and Chemical Evolution of the Earth’s Deep Mantle

Description

The mineralogy of the deep mantle is one of the key factors for the chemical evolution of the Earth. The constituent minerals of the mantle rock control the physical properties

The mineralogy of the deep mantle is one of the key factors for the chemical evolution of the Earth. The constituent minerals of the mantle rock control the physical properties of the mantle, which have significant impacts on the large-scale processes occurring in the Earth's interior. In my PhD research, I adopted experimental approaches to investigate the mineralogy and the physical properties of the Earth's materials in the deep mantle by using the diamond anvil cells (DACs) combined with in-situ X-ray diffraction techniques.

First, I found that Ca-bearing bridgmanite can be stable in the deeper part of the Earth's lower mantle where temperature is sufficiently high. The dissolution of calcium into bridgmanite can change the physical properties of the mantle, such as compressibility and viscosity. This study suggests a new mineralogical model for the lower mantle, which is composed of the two layers depending on whether calcium dissolves in bridgmanite or forms CaSiO3 perovskite as a separate phase.

Second, I investigated the mineralogy and density of the subducting materials in the Archean at the P-T conditions near 670 km-depth. The experiments suggest that the major phases of Archean volcanic crust is majoritic garnet and ringwoodite in the P-T conditions of the deep transition zone, which become bridgmanite with increasing pressure. The density model showed that Archean volcanic crust would have been denser than the surrounding mantle, promoting sinking into the lower mantle regardless of the style of the transportation in the Archean.

Lastly, I further investigated the mineralogies and densities of the ancient volcanic crusts for the Archean and Proterozoic at the P-T conditions of the lower mantle. The experiments suggest that the mineralogy of the ancient volcanic crusts is composed mostly of bridgmanite, which is systemically denser than the surrounding lower mantle. This implies that the ancient volcanic crusts would have accumulated at the base of the mantle because of their large density and thickness. Therefore, the distinctive chemistry of the ancient volcanic crusts from the surrounding mantle would have given a rise to the chemical heterogeneities in the region for billions of years.

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Created

Date Created
  • 2020

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Modeling the interior of Haumea

Description

The Kuiper Belt Object Haumea is one of the most fascinating objects in the solar system. Spectral reflectance observations reveal a surface of almost pure water ice, yet it

The Kuiper Belt Object Haumea is one of the most fascinating objects in the solar system. Spectral reflectance observations reveal a surface of almost pure water ice, yet it has a mass of 4.006 × 1021 kg, measured from orbits of its moons, along with an inferred mean radius of 715 km, and these imply a mean density of around 2600 kg m−3. Thus the surface ice must be a veneer over a rocky core. This model is supported by observations of Haumea's light curve, which shows large photometric variations over an anomalously rapid 3.9154-hour rotational period. Haumea's surface composition is uniform, therefore the light curve must be due to a varying area presented to the observer, implying that Haumea has an oblong, ellipsoidal shape. If Haumea's rotation axis is normal to our line of sight, and Haumea reflects with a lunar-like scattering function, then its axis ratios are p = b/a = 0.80 (in the equatorial cross section) and q = c/a = 0.52 (in the polar cross section). In this work, I assume that Haumea is in hydrostatic equilibrium, and I model it as a two-phase ellipsoid with an ice mantle and a rocky core. I model the core assuming it has a given density in the range between 2700–3300 kg m−3 with axis ratios that are free to vary. The metric which my code uses calculates the angle between the gravity vector and the surface normal, then averages this over both the outer surface and the core-mantle boundary. When this fit angle is minimized, it allows an interpretation of the size and shape of the core, as well as the thickness of the ice mantle. Results of my calculations show that Haumea's most likely core density is 2700–2800 kg m−3, with ice thicknesses anywhere from 12–32 km over the poles and as thin as 4–18 km over the equator.

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Created

Date Created
  • 2015

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Transitions in eruption style at silicic volcanoes: from stable domes to pyroclastic flows and explosive plumes

Description

Silicic volcanoes produce many styles of activity over a range of timescales. Eruptions vary from slow effusion of viscous lava over many years to violent explosions lasting several hours. Hazards

Silicic volcanoes produce many styles of activity over a range of timescales. Eruptions vary from slow effusion of viscous lava over many years to violent explosions lasting several hours. Hazards from these eruptions can be far-reaching and persistent, and are compounded by the dense populations often surrounding active volcanoes. I apply and develop satellite and ground-based remote sensing techniques to document eruptions at Merapi and Sinabung Volcanoes in Indonesia. I use numerical models of volcanic activity in combination with my observational data to describe the processes driving different eruption styles, including lava dome growth and collapse, lava flow emplacement, and transitions between effusive and explosive activity.

Both effusive and explosive eruptions have occurred recently at Merapi volcano. I use satellite thermal images to identify variations during the 2006 effusive eruption and a numerical model of magma ascent to explain the mechanisms that controlled those variations. I show that a nearby tectonic earthquake may have triggered the peak phase of the eruption by increasing the overpressure and bubble content of the magma and that the frequency of pyroclastic flows is correlated with eruption rate. In 2010, Merapi erupted explosively but also shifted between rapid dome-building and explosive phases. I explain these variations by the heterogeneous addition of CO2 to the melt from bedrock under conditions favorable to transitions between effusive and explosive styles.

At Sinabung, I use photogrammetry and satellite images to describe the emplacement of a viscous lava flow. I calculate the flow volume (0.1 km3) and average effusion rate (4.4 m3 s-1) and identify active regions of collapse and advance. Advance rate was controlled by the effusion rate and the flow’s yield strength. Pyroclastic flow activity was initially correlated to the decreasing flow advance rate, but was later affected by the underlying topography as the flow inflated and collapsed near the vent, leading to renewed pyroclastic flow activity.

This work describes previously poorly understood mechanisms of silicic lava emplacement, including multiple causes of pyroclastic flows, and improves the understanding, monitoring capability, and hazard assessment of silicic volcanic eruptions.

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Created

Date Created
  • 2016

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Remote Sensing and Modeling of Stressed Aquifer Systems and the Associated Hazards

Description

Aquifers host the largest accessible freshwater resource in the world. However, groundwater reserves are declining in many places. Often coincident with drought, high extraction rates and inadequate replenishment result in

Aquifers host the largest accessible freshwater resource in the world. However, groundwater reserves are declining in many places. Often coincident with drought, high extraction rates and inadequate replenishment result in groundwater overdraft and permanent land subsidence. Land subsidence is the cause of aquifer storage capacity reduction, altered topographic gradients which can exacerbate floods, and differential displacement that can lead to earth fissures and infrastructure damage. Improving understanding of the sources and mechanisms driving aquifer deformation is important for resource management planning and hazard mitigation.

Poroelastic theory describes the coupling of differential stress, strain, and pore pressure, which are modulated by material properties. To model these relationships, displacement time series are estimated via satellite interferometry and hydraulic head levels from observation wells provide an in-situ dataset. In combination, the deconstruction and isolation of selected time-frequency components allow for estimating aquifer parameters, including the elastic and inelastic storage coefficients, compaction time constants, and vertical hydraulic conductivity. Together these parameters describe the storage response of an aquifer system to changes in hydraulic head and surface elevation. Understanding aquifer parameters is useful for the ongoing management of groundwater resources.

Case studies in Phoenix and Tucson, Arizona, focus on land subsidence from groundwater withdrawal as well as distinct responses to artificial recharge efforts. In Christchurch, New Zealand, possible changes to aquifer properties due to earthquakes are investigated. In Houston, Texas, flood severity during Hurricane Harvey is linked to subsidence, which modifies base flood elevations and topographic gradients.

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Created

Date Created
  • 2018

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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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Created

Date Created
  • 2018

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Extreme Seismic Anomalies near Earth’s Core Mantle Boundary

Description

The interior of Earth is stratified due to gravity. Therefore, the lateral heterogeneities observed as seismic anomalies by seismologists are extremely interesting: they hold the key to understand the composition,

The interior of Earth is stratified due to gravity. Therefore, the lateral heterogeneities observed as seismic anomalies by seismologists are extremely interesting: they hold the key to understand the composition, thermal status and evolution of the Earth. This work investigates seismic anomalies inside Earth’s lowermost mantle and focuses on patch-like ultra-low velocity zones (ULVZs) found on Earth’s core-mantle boundary (CMB). Firstly, all previous ULVZ studies are compiled and ULVZ locations on the CMB are digitized. The result is a database, which is publicly available online. A key finding is that there is not a simple mapping between the locations of the observed ULVZs and the large low velocities provinces (LLVPs). Instead, ULVZs are more likely to occur near LLVP boundaries. This spatial correlation study supports a compositionally distinct origin for at least some ULVZs. Next, the seismic structure of the basal mantle beneath the Central America is investigated. This region hosts present and past subducted slabs, which could have brought compositionally distinct oceanic basalt all the way down to the CMB. The waveform distortions of a core-reflected seismic phase and a forward modeling method are used to constrain the causes of the CMB structures. In addition to ULVZ structures, isolated patches of thin zones with shear velocity increased by over 10% relative to background mantle are found for the first time. Ultra-high velocity zones (UHVZs) are interspersed with ULVZs and could be caused by subducted mid-ocean ridge basalt (MORB) that undergoes partial melting and melt segregation. Fe-rich partial melt of MORB can form ULVZs, and silica polymorphs (SiO2) and calcium-perovskite (CaPv) rich solid residue can explain the UHVZs. Finally, large-scale heterogeneities in the lowermost mantle are investigated using S waveform broadening observations. Several basal layer models are case-studied via synthetic calculations. S wave arrivals received at a distance larger than 80˚ in a global dataset from large earthquakes between the years 1994 and 2017 are examined and S waveform broadenings are documented. This approach exploits large distance data for the first time, and therefore is complementary to previous studies in terms of sampling locations. One possible explanation of S waveform broadening is velocity discontinuity inside the D″ layer due to the temperature controlled Bm-pPv phase transition.

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Created

Date Created
  • 2020

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ExoPlex: a new Python library for detailed modeling of rocky exoplanet internal structure and mineralogy

Description

The pace of exoplanet discoveries has rapidly accelerated in the past few decades and the number of planets with measured mass and radius is expected to pick up in the

The pace of exoplanet discoveries has rapidly accelerated in the past few decades and the number of planets with measured mass and radius is expected to pick up in the coming years. Many more planets with a size similar to earth are expected to be found. Currently, software for characterizing rocky planet interiors is lacking. There is no doubt that a planet’s interior plays a key role in determining surface conditions including atmosphere composition and land area. Comparing data with diagrams of mass vs. radius for terrestrial planets provides only a first-order estimate of the internal structure and composition of planets [e.g. Seager et al 2007]. This thesis will present a new Python library, ExoPlex, which has routines to create a forward model of rocky exoplanets between 0.1 and 5 Earth masses. The ExoPlex code offers users the ability to model planets of arbitrary composition of Fe-Si-Mg-Al-Ca-O in addition to a water layer. This is achieved by modeling rocky planets after the earth and other known terrestrial planets. The three distinct layers which make up the Earth's internal structure are: core, mantle, and water. Terrestrial planet cores will be dominated by iron however, like earth, there may be some quantity of light element inclusion which can serve to enhance expected core volumes. In ExoPlex, these light element inclusions are S-Si-O and are included as iron-alloys. Mantles will have a more diverse mineralogy than planet cores. Unlike most other rocky planet models, ExoPlex remains unbiased in its treatment of the mantle in terms of composition. Si-Mg-Al-Ca oxide components are combined by predicting the mantle mineralogy using a Gibbs free energy minimization software package called Perple\_X [Connolly 2009]. By allowing an arbitrary composition, ExoPlex can uniquely model planets using their host star’s composition as an indicator of planet composition. This is a proven technique [Dorn et al 2015] which has not yet been widely utilized, possibly due to the lack of availability of easy to use software. I present a model sensitivity analysis to indicate the most important parameters to constrain in future observing missions. ExoPlex is currently available on PyPI so it may be installed using pip or conda on Mac OS or Linux based operating systems. It requires a specific scripting environment which is explained in the documentation currently stored on the ExoPlex GitHub page.

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Created

Date Created
  • 2018

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Meteorites on Mars as planetary research tools with special considerations for Martian weathering processes

Description

The occurrence of exogenic, meteoritic materials on the surface of any world presents opportunities to explore a variety of significant problems in the planetary sciences. In the case of Mars,

The occurrence of exogenic, meteoritic materials on the surface of any world presents opportunities to explore a variety of significant problems in the planetary sciences. In the case of Mars, meteorites found on its surface may help to 1) constrain atmospheric conditions during their time of arrival; 2) provide insights into possible variabilities in meteoroid type sampling between Mars and Earth space environments; 3) aid in our understanding of soil, dust, and sedimentary rock chemistry; 4) assist with the calibration of crater-age dating techniques; and 5) provide witness samples for chemical and mechanical weathering processes. The presence of reduced metallic iron in approximately 88 percent of meteorite falls renders the majority of meteorites particularly sensitive to oxidation by H2O interaction. This makes them excellent markers for H2O occurrence. Several large meteorites have been discovered at Gusev Crater and Meridiani Planum by the Mars Exploration Rovers (MERs). Significant morphologic characteristics interpretable as weathering features in the Meridiani suite of iron meteorites include a 1) large pit lined with delicate iron protrusions suggestive of inclusion removal by corrosive interaction; 2) differentially eroded kamacite and taenite lamellae on three of the meteorites, providing relative timing through cross-cutting relationships with deposition of 3) an iron oxide-rich dark coating; and 4) regmaglypted surfaces testifying to regions of minimal surface modification; with other regions in the same meteorites exhibiting 5) large-scale, cavernous weathering. Iron meteorites found by Mini-TES at both Meridiani Planum and Gusev Crater have prompted laboratory experiments designed to explore elements of reflectivity, dust cover, and potential oxide coatings on their surfaces in the thermal infrared using analog samples. Results show that dust thickness on an iron substrate need be only one tenth as great as that on a silicate rock to obscure its infrared signal. In addition, a database of thermal emission spectra for 46 meteorites was prepared to aid in the on-going detection and interpretation of these valuable rocks on Mars using Mini-TES instruments on both MER spacecraft. Applications to the asteroidal sciences are also relevant and intended for this database.

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Agent

Created

Date Created
  • 2011