Matching Items (21)
Description
Earth's topographic surface forms an interface across which the geodynamic and geomorphic engines interact. This interaction is best observed along crustal margins where topography is created by active faulting and sculpted by geomorphic processes. Crustal deformation manifests as earthquakes at centennial to millennial timescales. Given that nearly half of Earth's human population lives along active fault zones, a quantitative understanding of the mechanics of earthquakes and faulting is necessary to build accurate earthquake forecasts. My research relies on the quantitative documentation of the geomorphic expression of large earthquakes and the physical processes that control their spatiotemporal distributions. The first part of my research uses high-resolution topographic lidar data to quantitatively document the geomorphic expression of historic and prehistoric large earthquakes. Lidar data allow for enhanced visualization and reconstruction of structures and stratigraphy exposed by paleoseismic trenches. Lidar surveys of fault scarps formed by the 1992 Landers earthquake document the centimeter-scale erosional landforms developed by repeated winter storm-driven erosion. The second part of my research employs a quasi-static numerical earthquake simulator to explore the effects of fault roughness, friction, and structural complexities on earthquake-generated deformation. My experiments show that fault roughness plays a critical role in determining fault-to-fault rupture jumping probabilities. These results corroborate the accepted 3-5 km rupture jumping distance for smooth faults. However, my simulations show that the rupture jumping threshold distance is highly variable for rough faults due to heterogeneous elastic strain energies. Furthermore, fault roughness controls spatiotemporal variations in slip rates such that rough faults exhibit lower slip rates relative to their smooth counterparts. The central implication of these results lies in guiding the interpretation of paleoseismically derived slip rates that are used to form earthquake forecasts. The final part of my research evaluates a set of Earth science-themed lesson plans that I designed for elementary-level learning-disabled students. My findings show that a combination of concept delivery techniques is most effective for learning-disabled students and should incorporate interactive slide presentations, tactile manipulatives, teacher-assisted concept sketches, and student-led teaching to help learning-disabled students grasp Earth science concepts.
ContributorsHaddad, David Elias (Author) / Arrowsmith, Ramon (Thesis advisor) / Reynolds, Stephen (Committee member) / Semken, Steven (Committee member) / Shirzaei, Manoochehr (Committee member) / Whipple, Kelin (Committee member) / Zielke, Olaf (Committee member) / Arizona State University (Publisher)
Created2014
Description
Seismic observations have revealed two large low shear velocity provinces (LLSVPs) in the lowermost mantle beneath Pacific and Africa. One hypothesis for the origin of LLSVPs is that they are caused by accumulation of subducted oceanic crust on the core-mantle boundary (CMB). Here, I perform high resolution geodynamical calculations to test this hypothesis. The result shows that it is difficult for a thin (~ 6 km) subducted oceanic crust to accumulate on the CMB, and the major part of it is viscously stirred into the surrounding mantle. Another hypothesis for the origin of LLSVPs is that they are caused by thermochemical piles of more-primitive material which is remnant of Earth's early differentiation. In such case, a significant part of the subducted oceanic crust would enter the more-primitive reservoir, while other parts are either directly entrained into mantle plumes forming on top of the more-primitive reservoir or stirred into the background mantle. As a result, mantle plumes entrain a variable combination of compositional components including more-primitive material, old oceanic crust which first enters the more-primitive reservoir and is later entrained into mantle plumes with the more-primitive material, young oceanic crust which is directly entrained into mantle plumes without contacting the more-primitive reservoir, and depleted background mantle material. The result reconciles geochemical observation of multiple compositional components and varying ages of oceanic crust in the source of ocean-island basalts. Seismic studies have detected ultra-low velocity zones (ULVZs) in some localized regions on the CMB. Here, I present 3D thermochemical calculations to show that the distribution of ULVZs provides important information about their origin. ULVZs with a distinct composition tend to be located at the edges of LLSVPs, while ULVZs solely caused by partial melting tend to be located inboard from the edges of LLSVPs. This indicates that ULVZs at the edges of LLSVPs are best explained by distinct compositional heterogeneity, while ULVZs located insider of LLSVPs are better explained by partial melting. The results provide additional constraints for the origin of ULVZs.
ContributorsLi, Mingming (Author) / McNamara, Allen K (Thesis advisor) / Garnero, Edward J (Committee member) / Shim, Sang-Heon (Committee member) / Tyburczy, James (Committee member) / Clarke, Amanda (Committee member) / Arizona State University (Publisher)
Created2015
Description
Energy harvesting from ambient is important to configuring Wireless Sensor Networks (WSN) for environmental data collecting. In this work, highly flexible thermoelectric generators (TEGs) have been studied and fabricated to supply power to the wireless sensor notes used for data collecting in hot spring environment. The fabricated flexible TEGs can be easily deployed on the uneven surface of heated rocks at the rim of hot springs. By employing the temperature gradient between the hot rock surface and the air, these TEGs can generate power to extend the battery lifetime of the sensor notes and therefore reduce multiple batteries changes where the environment is usually harsh in hot springs. Also, they show great promise for self-powered wireless sensor notes. Traditional thermoelectric material bismuth telluride (Bi2Te3) and advanced MEMS (Microelectromechanical systems) thin film techniques were used for the fabrication. Test results show that when a flexible TEG array with an area of 3.4cm2 was placed on the hot plate surface of 80°C in the air under room temperature, it had an open circuit voltage output of 17.6mV and a short circuit current output of 0.53mA. The generated power was approximately 7mW/m2.
On the other hand, high pressure, temperatures that can reach boiling, and the pH of different hot springs ranging from <2 to >9 make hot spring ecosystem a unique environment that is difficult to study. WSN allows many scientific studies in harsh environments that are not feasible with traditional instrumentation. However, wireless pH sensing for long time in situ data collection is still challenging for two reasons. First, the existing commercial-off-the-shelf pH meters are frequent calibration dependent; second, biofouling causes significant measurement error and drift. In this work, 2-dimentional graphene pH sensors were studied and calibration free graphene pH sensor prototypes were fabricated. Test result shows the resistance of the fabricated device changes linearly with the pH values (in the range of 3-11) in the surrounding liquid environment. Field tests show graphene layer greatly prevented the microbial fouling. Therefore, graphene pH sensors are promising candidates that can be effectively used for wireless pH sensing in exploration of hot spring ecosystems.
On the other hand, high pressure, temperatures that can reach boiling, and the pH of different hot springs ranging from <2 to >9 make hot spring ecosystem a unique environment that is difficult to study. WSN allows many scientific studies in harsh environments that are not feasible with traditional instrumentation. However, wireless pH sensing for long time in situ data collection is still challenging for two reasons. First, the existing commercial-off-the-shelf pH meters are frequent calibration dependent; second, biofouling causes significant measurement error and drift. In this work, 2-dimentional graphene pH sensors were studied and calibration free graphene pH sensor prototypes were fabricated. Test result shows the resistance of the fabricated device changes linearly with the pH values (in the range of 3-11) in the surrounding liquid environment. Field tests show graphene layer greatly prevented the microbial fouling. Therefore, graphene pH sensors are promising candidates that can be effectively used for wireless pH sensing in exploration of hot spring ecosystems.
ContributorsHan, Ruirui (Author) / Yu, Hongyu (Thesis advisor) / Jiang, Hanqing (Committee member) / Yu, Hongbin (Committee member) / Garnero, Edward (Committee member) / Li, Mingming (Committee member) / Arizona State University (Publisher)
Created2018
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 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.
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.
ContributorsMiller, Megan Marie (Author) / Shirzaei, Manoochehr (Thesis advisor) / Reynolds, Stephen (Committee member) / Tyburczy, James (Committee member) / Semken, Steven (Committee member) / Werth, Susanna (Committee member) / Arizona State University (Publisher)
Created2018
Description
The dynamic Earth involves feedbacks between the solid crust and both natural and anthropogenic fluid flows. Fluid-rock interactions drive many Earth phenomena, including volcanic unrest, seismic activities, and hydrological responses. Mitigating the hazards associated with these activities requires fundamental understanding of the underlying physical processes. Therefore, geophysical monitoring in combination with modeling provides valuable tools, suitable for hazard mitigation and risk management efforts. Magmatic activities and induced seismicity linked to fluid injection are two natural and anthropogenic processes discussed in this dissertation.
Successful forecasting of the timing, style, and intensity of a volcanic eruption is made possible by improved understanding of the volcano life cycle as well as building quantitative models incorporating the processes that govern rock melting, melt ascending, magma storage, eruption initiation, and interaction between magma and surrounding host rocks at different spatial extent and time scale. One key part of such models is the shallow magma chamber, which is generally directly linked to volcano’s eruptive behaviors. However, its actual shape, size, and temporal evolution are often not entirely known. To address this issue, I use space-based geodetic data with high spatiotemporal resolution to measure surface deformation at Kilauea volcano. The obtained maps of InSAR (Interferometric Synthetic Aperture Radar) deformation time series are exploited with two novel modeling schemes to investigate Kilauea’s shallow magmatic system. Both models can explain the same observation, leading to a new compartment model of magma chamber. Such models significantly advance the understanding of the physical processes associated with Kilauea’s summit plumbing system with potential applications for volcanoes around the world.
The unprecedented increase in the number of earthquakes in the Central and Eastern United States since 2008 is attributed to massive deep subsurface injection of saltwater. The elevated chance of moderate-large damaging earthquakes stemming from increased seismicity rate causes broad societal concerns among industry, regulators, and the public. Thus, quantifying the time-dependent seismic hazard associated with the fluid injection is of great importance. To this end, I investigate the large-scale seismic, hydrogeologic, and injection data in northern Texas for period of 2007-2015 and in northern-central Oklahoma for period of 1995-2017. An effective induced earthquake forecasting model is developed, considering a complex relationship between injection operations and consequent seismicity. I find that the timing and magnitude of regional induced earthquakes are fully controlled by the process of fluid diffusion in a poroelastic medium and thus can be successfully forecasted. The obtained time-dependent seismic hazard model is spatiotemporally heterogeneous and decreasing injection rates does not immediately reduce the probability of an earthquake. The presented framework can be used for operational induced earthquake forecasting. Information about the associated fundamental processes, inducing conditions, and probabilistic seismic hazards has broad benefits to the society.
Successful forecasting of the timing, style, and intensity of a volcanic eruption is made possible by improved understanding of the volcano life cycle as well as building quantitative models incorporating the processes that govern rock melting, melt ascending, magma storage, eruption initiation, and interaction between magma and surrounding host rocks at different spatial extent and time scale. One key part of such models is the shallow magma chamber, which is generally directly linked to volcano’s eruptive behaviors. However, its actual shape, size, and temporal evolution are often not entirely known. To address this issue, I use space-based geodetic data with high spatiotemporal resolution to measure surface deformation at Kilauea volcano. The obtained maps of InSAR (Interferometric Synthetic Aperture Radar) deformation time series are exploited with two novel modeling schemes to investigate Kilauea’s shallow magmatic system. Both models can explain the same observation, leading to a new compartment model of magma chamber. Such models significantly advance the understanding of the physical processes associated with Kilauea’s summit plumbing system with potential applications for volcanoes around the world.
The unprecedented increase in the number of earthquakes in the Central and Eastern United States since 2008 is attributed to massive deep subsurface injection of saltwater. The elevated chance of moderate-large damaging earthquakes stemming from increased seismicity rate causes broad societal concerns among industry, regulators, and the public. Thus, quantifying the time-dependent seismic hazard associated with the fluid injection is of great importance. To this end, I investigate the large-scale seismic, hydrogeologic, and injection data in northern Texas for period of 2007-2015 and in northern-central Oklahoma for period of 1995-2017. An effective induced earthquake forecasting model is developed, considering a complex relationship between injection operations and consequent seismicity. I find that the timing and magnitude of regional induced earthquakes are fully controlled by the process of fluid diffusion in a poroelastic medium and thus can be successfully forecasted. The obtained time-dependent seismic hazard model is spatiotemporally heterogeneous and decreasing injection rates does not immediately reduce the probability of an earthquake. The presented framework can be used for operational induced earthquake forecasting. Information about the associated fundamental processes, inducing conditions, and probabilistic seismic hazards has broad benefits to the society.
ContributorsZhai, Guang (Author) / Shirzaei, Manoochehr (Thesis advisor) / Garnero, Edward (Committee member) / Clarke, Amanda (Committee member) / Tyburczy, James (Committee member) / Li, Mingming (Committee member) / Arizona State University (Publisher)
Created2018
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 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.
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.
ContributorsKhoshmanesh, Mostafa (Author) / Shirzaei, Manoochehr (Thesis advisor) / Arrowsmith, Ramon (Committee member) / Garnero, Edward (Committee member) / Tyburczy, James (Committee member) / Whipple, Kelin (Committee member) / Arizona State University (Publisher)
Created2018
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 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.
ContributorsLorenzo, Alejandro M., Jr (Author) / Desch, Steven (Thesis advisor) / Shim, Dan S.-H. (Committee member) / Line, Michael (Committee member) / Li, Mingming (Committee member) / Arizona State University (Publisher)
Created2018
Description
Understanding the structural evolution of planetary surfaces provides key insights to their physical properties and processes. On the Moon, large-scale tectonism was thought to have ended over a billion years ago. However, new Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) high resolution images show the Moon’s surface in unprecedented detail and show many previously unidentified tectonic landforms, forcing a re-assessment of our views of lunar tectonism. I mapped lobate scarps, wrinkle ridges, and graben across Mare Frigoris – selected as a type area due to its excellent imaging conditions, abundance of tectonic landforms, and range of inferred structural controls. The distribution, morphology, and crosscutting relationships of these newly identified populations of tectonic landforms imply a more complex and longer-lasting history of deformation that continues to today. I also performed additional numerical modeling of lobate scarp structures that indicates the upper kilometer of the lunar surface has experienced 3.5-18.6 MPa of differential stress in the recent past, likely due to global compression from radial thermal contraction.
Central pit craters on Mars are another instance of intriguing structures that probe subsurface physical properties. These kilometer-scale pits are nested in the centers of many impact craters on Mars as well as on icy satellites. They are inferred to form in the presence of a water-ice rich substrate; however, the process(es) responsible for their formation is still debated. Previous models invoke origins by either explosive excavation of potentially water-bearing crustal material, or by subsurface drainage of meltwater and/or collapse. I assessed radial trends in grain size around central pits using thermal inertias calculated from Thermal Emission Imaging System (THEMIS) thermal infrared images. Average grain size decreases with radial distance from pit rims – consistent with pit-derived ejecta but not expected for collapse models. I present a melt-contact model that might enable a delayed explosion, in which a central uplift brings ice-bearing substrate into contact with impact melt to generate steam explosions and excavate central pits during the impact modification stage.
Central pit craters on Mars are another instance of intriguing structures that probe subsurface physical properties. These kilometer-scale pits are nested in the centers of many impact craters on Mars as well as on icy satellites. They are inferred to form in the presence of a water-ice rich substrate; however, the process(es) responsible for their formation is still debated. Previous models invoke origins by either explosive excavation of potentially water-bearing crustal material, or by subsurface drainage of meltwater and/or collapse. I assessed radial trends in grain size around central pits using thermal inertias calculated from Thermal Emission Imaging System (THEMIS) thermal infrared images. Average grain size decreases with radial distance from pit rims – consistent with pit-derived ejecta but not expected for collapse models. I present a melt-contact model that might enable a delayed explosion, in which a central uplift brings ice-bearing substrate into contact with impact melt to generate steam explosions and excavate central pits during the impact modification stage.
ContributorsWilliams, Nathan Robert (Author) / Bell, James (Thesis advisor) / Robinson, Mark (Committee member) / Christenen, Philip (Committee member) / Farmer, Jack (Committee member) / Shirzaei, Manoochehr (Committee member) / Arizona State University (Publisher)
Created2016
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 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.
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.
ContributorsCarr, Brett B (Author) / Clarke, Amanda B (Thesis advisor) / Arrowsmith, Ramon (Committee member) / Mcnamara, Allen (Committee member) / Shirzaei, Manoochehr (Committee member) / Williams, Stanley (Committee member) / Arizona State University (Publisher)
Created2016
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 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.
ContributorsSalisbury, J. Barrett (Author) / Arrowsmith, Ramon (Thesis advisor) / Shirzaei, Manoochehr (Committee member) / DeVecchio, Duane (Committee member) / Whipple, Kelin (Committee member) / Heimsath, Arjun (Committee member) / Arizona State University (Publisher)
Created2016