Integrated multi-scale methods for modeling the deformation field of volcanic sources

The modeling of volcanic deformation sources represents a crucial task for investigating and monitoring the activity of magmatic systems. In this framework, inverse methods are the most used approach to image deforming volcanic bodies by considering the assumptions of the elasticity theory. However, several issues affect the inverse modeling and the interpretation of the ground deformation phenomena, such as the inherent ambiguity, the theoretical ambiguity and the related choice of the forward problem. Despite assuming appropriate a priori information and constraints, we are led to an ambiguous estimate of the physical and geometrical parameters of volcanic bodies and, in turn, to an unreliable analysis of the hazard evaluation and risk assessment. In this scenario, we propose a new approach for the interpretation of the large amount of deformation data retrieved by the SBAS-DInSAR technique in volcanic environments. The proposed approach is based on the assumptions of the homogeneous and harmonic elastic fields, which satisfy the Laplace's equation; specifically, we consider Multiridge, ScalFun and THD methods to provide in a fast way preliminary information on the active volcanic source, even for the analysis of complex cases, such as the depth, the horizontal position, the geometrical configuration and the horizontal extent. In this thesis, firstly we analyse the biharmonic general solution of the elastic problem to state the deformation field surely satisfy the Laplace's equation in the case of hydrostatic pressure condition within a source embedded in a homogeneous elastic half-space. Then, we show the results of different simulations by highlighting how the proposed approach allows overcoming many ambiguities since it provides unique information about the geometrical parameters of the active source. Finally, we show the results of Multiridge, ScalFun and THD methods used for the analysis of the deformation components recorded at Okmok volcano, Uturuncu volcano, Campi Flegrei caldera, Fernandina volcano and Yellowstone caldera. We conclude this thesis by remarking the proposed approach represents a crucial tool for fixing modeling ambiguities and to provide useful information for monitoring purposes and/or for constraining the geometry of the volcanic systems

Doctor of Philosophy

dissertationHere I evaluate the relationship between the seismicity in the Yellowstone region, in particular the properties of the dominant earthquake swarms, and the three-dimensional Vp seismic velocity structure employing local earthquake tomography. The Yellowstone region averages ~1,500-2,000 earthquakes per year and ~40% occur in swarms. Two of the largest Yellowstone swarms have provided an important opportunity to better understand how and why swarms occur in Yellowstone and how they may be related to active volcanic and tectonic processes. The 2008-2009 Yellowstone Lake swarm consisted of ~800 events with magnitudes ranging from -0.5 ≤ MC ≤ 4.1 and was modeled by a migration at up to 1 km per day as an upper-crustal dike-intrusion of magma or magmatically-derived aqueous fluids. The 2010 Madison Plateau swarm exhibited over 2,200 earthquakes with magnitudes ranging from -0.6 ≤ MC ≤ 3.9 and may have occurred on structures at depth related to the nearby Hebgen Lake fault or may have been facilitated by the movement of hydrothermal fluids away from the Yellowstone caldera. Both swarms occurred during a period of caldera deformation reversal from uplift to subsidence and may be indicative of processes involving pressurized fluids escaping the caldera into the surrounding region, allowing the caldera to enter into a time of subsidence. These fluids are derived from the Yellowstone magma reservoir, a large body of crystallizing rhyolite magma that underlies most of the Yellowstone caldera. To better understand the extent and composition of the Yellowstone magmatic system, we have used data from the Yellowstone Seismic Network from 1984-2011 to image the P-wave velocity structure of the Yellowstone crust using local earthquake tomography using the 83-station Yellowstone seismic network. P-wave tomographic images revealed a large, low P-wave anomaly with values up to -7% change from a background normal crustal velocity structure, underlying most of the Yellowstone caldera at depths of 5-16 km, notably ~50% larger than imaged in earlier studies. The low P-wave velocity body extends ~20 km beyond the caldera to the NE at depths of less than 5 km and has aerial dimension of 30 km wide and 90 km long

A HUMAN BEHAVIORAL ECOLOGICAL ASSESSMENT OF THE YELLOWSTONE LAKE BASIN, YELLOWSTONE NATIONAL PARK, WYOMING

The Yellowstone Lake Basin has been an important region for hunter-gatherers since the close of the Late Pleistocene that has provided an abundance and well diverse suite of subsistence resources ( i.e prey animals and edible plants). Due the diversity found within this ecosystem, the primary objective of this thesis is to demonstrate that through the tenants of human behavioral ecology, it can be argued that the subsistence and settlement strategies of mobile foragers were heavily influenced by the abundance and availability of subsistence resources. This is based on the premise that resource patches comprising of riparian and grassland habitats obtain high productions of subsistence resources which would have encouraged mobile foragers to occupy these areas. Furthermore, these tenants can be applied on a macro-evolutionary scale to demonstrate how shifts in climate over the past 12,000 years affected the subsistence and settlement strategies of hunter-gatherers. Like all ecosystems, the Yellowstone Lake Basin is constantly undergoing ecological transformations in response to disturbances in the climate. Shifts in climate may have had significant impacts on the distribution and compositions of vegetative zones that in turn affected the quality and production of resource patches. It is suspected that when poor patch conditions existed, mobile foragers responded by dispersing to new resource patches that were more productive. Conversely, when patch conditions became favorable, mobile foragers occupied these areas more frequently and over longer periods of time. The final objective of this thesis was to determine if the spatial distribution of prehistoric sites could be associated to paleo-shorelines that reflected past lake levels. This objective was carried out by applying the principle tenants used in the geosciences. Using Nicolaus Steno’s principle of superposition, it will be demonstrated that archaeological sites with intact and undisturbed contexts will only be associated with paleo-shoreline features that were exposed prior to any drops in lake levels. This is based on the geologic principle that younger layers of strata will overlie older deposits, which can be applied here by arguing that older archaeological deposits should be associated with lake levels reflecting similar ages while younger deposits should correspond to lake levels reflecting younger ages

Triggering and modulation of geyser eruptions in Yellowstone National Park by earthquakes, earth tides, and weather

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 119 (2014): 1718–1737, doi:10.1002/2013JB010803.We analyze intervals between eruptions (IBEs) data acquired between 2001 and 2011 at Daisy and Old Faithful geysers in Yellowstone National Park. We focus our statistical analysis on the response of these geysers to stress perturbations from within the solid earth (earthquakes and earth tides) and from weather (air pressure and temperature, precipitation, and wind). We conclude that (1) the IBEs of these geysers are insensitive to periodic stresses induced by solid earth tides and barometric pressure variations; (2) Daisy (pool geyser) IBEs lengthen by evaporation and heat loss in response to large wind storms and cold air; and (3) Old Faithful (cone geyser) IBEs are not modulated by air temperature and pressure variations, wind, and precipitation, suggesting that the subsurface water column is decoupled from the atmosphere. Dynamic stress changes of 0.1−0.2 MPa resulting from the 2002 M-7.9 Denali, Alaska, earthquake surface waves caused a statistically significant shortening of Daisy geyser's IBEs. Stresses induced by other large global earthquakes during the study period were at least an order of magnitude smaller. In contrast, dynamic stresses of >0.5 MPa from three large regional earthquakes in 1959, 1975, and 1983 caused lengthening of Old Faithful's IBEs. We infer that most subannual geyser IBE variability is dominated by internal processes and interaction with other geysers. The results of this study provide quantitative bounds on the sensitivity of hydrothermal systems to external stress perturbations and have implications for studying the triggering and modulation of volcanic eruptions by external forces.K. Luttrell and S. Hurwitz were supported by the USGS Volcano Hazards Program, and Michael Manga was supported by NSF grant EAR1114184.2014-09-0

Triggering and modulation of geyser eruptions in Yellowstone National Park by earthquakes, earth tides, and weather

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 119 (2014): 1718–1737, doi:10.1002/2013JB010803.We analyze intervals between eruptions (IBEs) data acquired between 2001 and 2011 at Daisy and Old Faithful geysers in Yellowstone National Park. We focus our statistical analysis on the response of these geysers to stress perturbations from within the solid earth (earthquakes and earth tides) and from weather (air pressure and temperature, precipitation, and wind). We conclude that (1) the IBEs of these geysers are insensitive to periodic stresses induced by solid earth tides and barometric pressure variations; (2) Daisy (pool geyser) IBEs lengthen by evaporation and heat loss in response to large wind storms and cold air; and (3) Old Faithful (cone geyser) IBEs are not modulated by air temperature and pressure variations, wind, and precipitation, suggesting that the subsurface water column is decoupled from the atmosphere. Dynamic stress changes of 0.1−0.2 MPa resulting from the 2002 M-7.9 Denali, Alaska, earthquake surface waves caused a statistically significant shortening of Daisy geyser's IBEs. Stresses induced by other large global earthquakes during the study period were at least an order of magnitude smaller. In contrast, dynamic stresses of >0.5 MPa from three large regional earthquakes in 1959, 1975, and 1983 caused lengthening of Old Faithful's IBEs. We infer that most subannual geyser IBE variability is dominated by internal processes and interaction with other geysers. The results of this study provide quantitative bounds on the sensitivity of hydrothermal systems to external stress perturbations and have implications for studying the triggering and modulation of volcanic eruptions by external forces.K. Luttrell and S. Hurwitz were supported by the USGS Volcano Hazards Program, and Michael Manga was supported by NSF grant EAR1114184.2014-09-0

Spatio-Temporal Analyses of Cenozoic Normal Faulting, Graben Basin Sedimentation, and Volcanism around the Snake River Plain, SE Idaho and SW Montana

This dissertation analyzes the spatial distribution and kinematics of the Late Cenozoic Basin and Range (BR) and cross normal fault (CF) systems and their related graben basins around the Snake River Plain (SRP), and investigates the spatio-temporal patterns of lavas that were erupted by the migrating Yellowstone hotspot along the SRP, applying a diverse set of GIS-based spatial statistical techniques. The spatial distribution patterns of the normal fault systems, revealed by the Ripley\u27s K-function, display clustered patterns that correlate with a high linear density, maximum azimuthal variation, and high box-counting fractal dimensions of the fault traces. The extension direction for normal faulting is determined along the major axis of the fractal dimension anisotropy ellipse measured by the modified Cantor dust method and the minor axis of the autocorrelation anisotropy ellipse measured by Ordinary Kriging, and across the linear directional mean (LDM) of the fault traces. Trajectories of the LDMs for the cross faults around each caldera define asymmetric sub-parabolic patterns similar to the reported parabolic distribution of the epicenters, and indicate sub-elliptical extension about each caldera that may mark the shape of hotspot’s thermal doming that formed each generation of cross faults. The decrease in the spatial density of the CFs as a function of distance from the axis of the track of the hotspot (SRP) also suggests the role of the hotspot for the formation of the cross faults. The parallelism of the trend of the exposures of the graben filling Sixmile Creek Formation with the LDM of their bounding cross faults indicates that the grabens were filled during or after the CF event. The global and local Moran’s I analyses of Neogene lava in each caldera along the SRP reveal a higher spatial autocorrelation and clustering of rhyolitic lava than the coeval basaltic lava in the same caldera. The alignment of the major axis of the standard deviational ellipses of lavas with the trend of the eastern SRP, and the successive spatial overlap of older lavas by progressively younger mafic lava, indicate the migration of the centers of eruption as the hotspot moved to the northeast

Spatio-Temporal Analyses of Cenozoic Normal Faulting, Graben Basin Sedimentation, and Volcanism around the Snake River Plain, SE Idaho and SW Montana

This dissertation analyzes the spatial distribution and kinematics of the Late Cenozoic Basin and Range (BR) and cross normal fault (CF) systems and their related graben basins around the Snake River Plain (SRP), and investigates the spatio-temporal patterns of lavas that were erupted by the migrating Yellowstone hotspot along the SRP, applying a diverse set of GIS-based spatial statistical techniques. The spatial distribution patterns of the normal fault systems, revealed by the Ripley\u27s K-function, display clustered patterns that correlate with a high linear density, maximum azimuthal variation, and high box-counting fractal dimensions of the fault traces. The extension direction for normal faulting is determined along the major axis of the fractal dimension anisotropy ellipse measured by the modified Cantor dust method and the minor axis of the autocorrelation anisotropy ellipse measured by Ordinary Kriging, and across the linear directional mean (LDM) of the fault traces. Trajectories of the LDMs for the cross faults around each caldera define asymmetric sub-parabolic patterns similar to the reported parabolic distribution of the epicenters, and indicate sub-elliptical extension about each caldera that may mark the shape of hotspot’s thermal doming that formed each generation of cross faults. The decrease in the spatial density of the CFs as a function of distance from the axis of the track of the hotspot (SRP) also suggests the role of the hotspot for the formation of the cross faults. The parallelism of the trend of the exposures of the graben filling Sixmile Creek Formation with the LDM of their bounding cross faults indicates that the grabens were filled during or after the CF event. The global and local Moran’s I analyses of Neogene lava in each caldera along the SRP reveal a higher spatial autocorrelation and clustering of rhyolitic lava than the coeval basaltic lava in the same caldera. The alignment of the major axis of the standard deviational ellipses of lavas with the trend of the eastern SRP, and the successive spatial overlap of older lavas by progressively younger mafic lava, indicate the migration of the centers of eruption as the hotspot moved to the northeast

Eruptions at Lone Star Geyser, Yellowstone National Park, USA: 1. Energetics and eruption dynamics

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 118 (2013): 4048–4062, doi:10.1002/jgrb.50251.Geysers provide a natural laboratory to study multiphase eruptive processes. We present results from a 4 day experiment at Lone Star Geyser in Yellowstone National Park, USA. We simultaneously measured water discharge, acoustic emissions, infrared intensity, and visible and infrared video to quantify the energetics and dynamics of eruptions, occurring approximately every 3 h. We define four phases in the eruption cycle (1) a 28±3 min phase with liquid and steam fountaining, with maximum jet velocities of 16–28 m s−1, steam mass fraction of less than ∼0.01. Intermittently choked flow and flow oscillations with periods increasing from 20 to 40 s are coincident with a decrease in jet velocity and an increase of steam fraction; (2) a 26±8 min posteruption relaxation phase with no discharge from the vent, infrared (IR), and acoustic power oscillations gliding between 30 and 40 s; (3) a 59±13 min recharge period during which the geyser is quiescent and progressively refills, and (4) a 69±14 min preplay period characterized by a series of 5–10 min long pulses of steam, small volumes of liquid water discharge, and 50–70 s flow oscillations. The erupted waters ascend from a 160–170°C reservoir, and the volume discharged during the entire eruptive cycle is 20.8±4.1 m3. Assuming isentropic expansion, we calculate a heat output from the geyser of 1.4–1.5 MW, which is <0.1% of the total heat output from Yellowstone Caldera.Support comes from NSF (L. Karlstrom, M. Manga), the USGS Volcano Hazards program (S. Hurwitz, F. Murphy, M.J.S. Johnston, and R.B. McCleskey), and WHOI (R. Sohn).2014-02-1

The global aftershock zone

The aftershock zone of each large (M ≥ 7) earthquake extends throughout the shallows of planet Earth. Most aftershocks cluster near the mainshock rupture, but earthquakes send out shivers in the form of seismic waves, and these temporary distortions are large enough to trigger other earthquakes at global range. The aftershocks that happen at great distance from their mainshock are often superposed onto already seismically active regions, making them difficult to detect and understand. From a hazard perspective we are concerned that this dynamic process might encourage other high magnitude earthquakes, and wonder if a global alarm state is warranted after every large mainshock. From an earthquake process perspective we are curious about the physics of earthquake triggering across the magnitude spectrum. In this review we build upon past studies that examined the combined global response to mainshocks. Such compilations demonstrate significant rate increases during, and immediately after (~45 min) M N 7.0 mainshocks in all tectonic settings and ranges. However, it is difficult to find strong evidence for M N 5 rate increases during the passage of surface waves in combined global catalogs. On the other hand, recently published studies of individual large mainshocks associate M N 5 triggering at global range that is delayed by hours to days after surface wave arrivals. The longer the delay between mainshock and global aftershock, the more difficult it is to establish causation. To address these questions, we review the response to 260 M ≥ 7.0 shallow (Z ≤ 50 km) mainshocks in 21 global regions with local seismograph networks. In this way we can examine the detailed temporal and spatial response, or lack thereof, during passing seismic waves, and over the 24 h period after their passing. We see an array of responses that can involve immediate and widespread seismicity outbreaks, delayed and localized earthquake clusters, to no response at all. About 50% of the catalogs that we studied showed possible (localized delayed) remote triggering, and ~20% showed probable (instantaneous broadly distributed) remote triggering. However, in any given region, at most only about 2–3% of global mainshocks caused significant local earthquake rate increases. These rate increases are mostly composed of small magnitude events, and we do not find significant evidence of dynamically triggered M N 5 earthquakes. If we assume that the few observed M N 5 events are triggered, we find that they are not directly associated with surface wave passage, with first incidences being 9–10 h later. We note that mainshock magnitude, relative proximity, amplitude spectra, peak ground motion, and mainshock focal mechanisms are not reliable determining factors as to whether a mainshock will cause remote triggering. By elimination, azimuth, and polarization of surface waves with respect to receiver faults may be more important factors