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

Coseismic deformation observed with radar interferometry: Great earthquakes and atmospheric noise

Spatially dense maps of coseismic deformation derived from Interferometric Synthetic Aperture Radar (InSAR) datasets result in valuable constraints on earthquake processes. The recent increase in the quantity of observations of coseismic deformation facilitates the examination of signals in many tectonic environments associated with earthquakes of varying magnitude. Efforts to place robust constraints on the evolution of the crustal stress field following great earthquakes often rely on knowledge of the earthquake location, the fault geometry, and the distribution of slip along the fault plane. Well-characterized uncertainties and biases strengthen the quality of inferred earthquake source parameters, particularly when the associated ground displacement signals are near the detection limit. Well-preserved geomorphic records of earthquakes offer additional insight into the mechanical behavior of the shallow crust and the kinematics of plate boundary systems. Together, geodetic and geologic observations of crustal deformation offer insight into the processes that drive seismic cycle deformation over a range of timescales. In this thesis, I examine several challenges associated with the inversion of earthquake source parameters from SAR data. Variations in atmospheric humidity, temperature, and pressure at the timing of SAR acquisitions result in spatially correlated phase delays that are challenging to distinguish from signals of real ground deformation. I characterize the impact of atmospheric noise on inferred earthquake source parameters following elevation-dependent atmospheric corrections. I analyze the spatial and temporal variations in the statistics of atmospheric noise from both reanalysis weather models and InSAR data itself. Using statistics that reflect the spatial heterogeneity of atmospheric characteristics, I examine parameter errors for several synthetic cases of fault slip on a basin-bounding normal fault. I show a decrease in uncertainty in fault geometry and kinematics following the application of atmospheric corrections to an event spanned by real InSAR data, the 1992 M5.6 Little Skull Mountain, Nevada, earthquake. Finally, I discuss how the derived workflow could be applied to other tectonic problems, such as solving for interseismic strain accumulation rates in a subduction zone environment. I also study the evolution of the crustal stress field in the South American plate following two recent great earthquakes along the Nazca- South America subduction zone. I show that the 2010 Mw 8.8 Maule, Chile, earthquake very likely triggered several moderate magnitude earthquakes in the Andean volcanic arc and backarc. This suggests that great earthquakes modulate the crustal stress field outside of the immediate aftershock zone and that far-field faults may pose a heightened hazard following large subduction earthquakes. The 2014 Mw 8.1 Pisagua, Chile, earthquake reopened ancient surface cracks that have been preserved in the hyperarid forearc setting of northern Chile for thousands of earthquake cycles. The orientation of cracks reopened in this event reflects the static and likely dynamic stresses generated by the recent earthquake. Coseismic cracks serve as a reliable marker of permanent earthquake deformation and plate boundary behavior persistent over the million-year timescale. This work on great earthquakes suggests that InSAR observations can play a crucial role in furthering our understanding of the crustal mechanics that drive seismic cycle processes in subduction zones

Modelización de las deformaciones asociadas a procesos intrusivos en áreas volcánicas y su aplicación a la isla de El Hierro (Islas Canarias)

La actividad volcánica ocurrida entre los años 2011 y 2014 en El Hierro (Islas Canarias) se caracterizó por la ocurrencia de una erupción submarina y el emplazamiento de múltiples intrusiones magmáticas en profundidad. A mediados de julio de 2011 se detectó un intenso enjambre sísmico bajo el centro de la isla que se propagó lateralmente ~15 km de norte a sur hasta culminar, tres meses después, en una erupción submarina a menos de 2 km de su costa sur. La erupción duró 4 meses y produjo grandes burbujas de gas, globos de lava y extensas áreas de cenizas y lapilli en la superficie del mar, así como un cono volcánico en el fondo marino llamado Tagoro. El final de la actividad eruptiva no marcó el final de la actividad volcánica en El Hierro. Entre los cuatro meses y los dos años posteriores se detectaron seis episodios intrusivos bajo la isla. Estos episodios duraron entre 3 y 20 días y produjeron importantes deformaciones del terreno e intensos enjambres sísmicos, lo que confirmó el transporte y acumulación de magma en profundidad. Sin embargo, ninguna de las intrusiones post-eruptivas culminó en una nueva erupción. El objetivo de esta tesis es estudiar desde el punto de vista geodésico la evolución espacial y temporal de los seis episodios intrusivos post-eruptivos ocurridos en El Hierro utilizando, para ello, observaciones del Sistema Global de Navegación por Satélite (GNSS) y de Interferometría Radar de Apertura Sintética (InSAR). Se han utilizado los datos de diez estaciones GNSS de registro continuo y 44 imágenes Radar de Apertura Sintética, captadas por el satélite canadiense RADARSAT-2 y la constelación de satélites italianos COSMO-SkyMed, para cuantificar y caracterizar las deformaciones sufridas por el terreno de la isla durante cada episodio intrusivo. La inversión de los datos geodésicos, empleando para ello un enfoque bayesiano y utilizando modelos analíticos de fuentes de deformación, ha permitido estimar las principales características de las intrusiones responsables de tales deformaciones, como su ubicación, geometría, incremento de volumen o caudales de magma intruido en profundidad, así como su evolución en el tiempo y el espacio..

Multiscale Analysis of DInSAR Measurements for Multi-Source Investigation at Uturuncu Volcano (Bolivia)

Uturuncu volcano (southwestern Bolivia) is localized within one of the largest updoming volcanic zones, the Altiplano Puna Volcanic Complex (APVC). In several geodetic studies the observed uplift phenomenon is analyzed and modeled by considering a deep source, related to the Altiplano Puna Magma Body (APMB). In this framework, we perform a multiscale analysis on the 2003–2010 ENVISAT satellite data to investigate the existence of a multi-source scenario for this region. The proposed analysis is based on Cross-correlation and Multiridge method, pointing out the spatial and temporal multiscale properties of the deformation field. In particular, we analyze the vertical component of ground deformation during two time interval: within the 2005–2008 time interval an inflating source at 18.7 km depth beneath the central zone of the APVC is retrieved; this result is in good agreement with those proposed by several authors for the APMB. Between August 2006 and February 2007, we identify a further inflating source at 4.5 km depth, beneath Uturuncu volcano; the existence of this latter, located just below the 2009–2010 seismic swarm, is supported by petrological, geochemical, and geophysical evidence, indicating as a possible interpretative scenario the action of shallow, temporarily trapped fluids