R. Castaldo

Magma injection beneath the urban area of Naples: a new mechanism for the 2012–2013 volcanic unrest at Campi Flegrei caldera

We found the first evidence, in the last 30 years, of a renewed magmatic activity at Campi Flegrei caldera from January 2012 to June 2013. The ground deformation, observed through satellite interferometry and GPS measurements, have been interpreted as the effect of the intrusion at shallow depth (3090 ± 138 m) of 0.0042 ± 0.0002 km3 of magma within a sill. This interrupts about 28 years of dominant hydrothermal activity and occurs in the context of an unrest phase which began in 2005 and within a more general ground uplift that goes on since 1950. This discovery has implications on the evaluation of the volcanic risk and in the volcanic surveillance of this densely populated area.

Ground deformation and source geometry of the 24 August 2016 Amatrice earthquake (Central Italy) investigated through analytical and numerical modeling of DInSAR measurements and structural-geological data

We investigate the ground deformation and source geometry of the 2016 Amatrice earthquake (Central Italy) by exploiting ALOS2 and Sentinel-1 coseismic differential interferometric synthetic aperture radar (DInSAR) measurements. They reveal two NNW-SSE striking surface deformation lobes, which could be the effect of two distinct faults or the rupture propagation of a single fault. We examine both cases through a single and a double dislocation planar source. Subsequently, we extend our analysis by applying a 3-D finite elements approach jointly exploiting DInSAR measurements and an independent, structurally constrained, 3-D fault model. This model is based on a double fault system including the two northern Gorzano and Redentore-Vettoretto faults (NGF and RVF) which merge into a single WSW dipping fault surface at the hypocentral depth (8 km). The retrieved best fit coseismic surface deformation pattern well supports the exploited structural model. The maximum displacements occur at 5–7 km depth, reaching 90 cm on the RVF footwall and 80 cm on the NGF hanging wall. The von Mises stress field confirms the retrieved seismogenic scenario.

Coseismic Fault Model of Mw 8.3 2015 Illapel Earthquake (Chile) Retrieved from Multi-Orbit Sentinel1-A DInSAR Measurements

On 16 September 2015, a Mw 8.3 interplate thrust earthquake ruptured offshore the Illapel region (Chile). Here, we perform coseismic slip fault modeling based on multi-orbit Sentinel 1-A (S1A) data. To do this, we generate ascending and descending S1A interferograms, whose combination allows us to retrieve the EW and vertical components of deformation. In particular, the EW displacement map highlights a westward displacement of about 210 cm, while the vertical map shows an uplift of about 25 cm along the coast, surrounded by a subsidence of about 20 cm. Following this analysis, we jointly invert the multi-orbit S1A interferograms by using an analytical approach to search for the coseismic fault parameters and related slip values. Most of the slip occurs northwest of the epicenter, with a maximum located in the shallowest 20 km. Finally, we refine our modeling approach by exploiting the Finite Element method, which allows us to take geological and structural complexities into account to simulate the slip along the slab curvature, the von Mises stress distribution, and the principal stress axes orientation. The von Mises stress distribution shows a close similarity to the depth distribution of the aftershock hypocenters. Likewise, the maximum principal stress orientation highlights a compressive regime in correspondence of the deeper portion of the slab and an extensional regime at its shallower segment; these findings are supported by seismological data.

Magma and fluid migration at Yellowstone Caldera in the last three decades inferred from InSAR, leveling, and gravity measurements

We studied the Yellowstone caldera geological unrest between 1977 and 2010 by investigating temporal changes in differential Interferometric Synthetic Aperture Radar (InSAR), precise spirit leveling and gravity measurements. The analysis of the 1992–2010 displacement time series, retrieved by applying the SBAS InSAR technique, allowed the identification of three areas of deformation: (i) the Mallard Lake (ML) and Sour Creek (SC) resurgent domes, (ii) a region close to the Northern Caldera Rim (NCR), and (iii) the eastern Snake River Plain (SRP). While the eastern SRP shows a signal related to tectonic deformation, the other two regions are influenced by the caldera unrest. We removed the tectonic signal from the InSAR displacements, and we modeled the InSAR, leveling, and gravity measurements to retrieve the best fitting source parameters. Our findings confirmed the existence of different distinct sources, beneath the brittle-ductile transition zone, which have been intermittently active during the last three decades. Moreover, we interpreted our results in the light of existing seismic tomography studies. Concerning the SC dome, we highlighted the role of hydrothermal fluids as the driving force behind the 1977–1983 uplift; since 1983–1993 the deformation source transformed into a deeper one with a higher magmatic component. Furthermore, our results support the magmatic nature of the deformation source beneath ML dome for the overall investigated period. Finally, the uplift at NCR is interpreted as magma accumulation, while its subsidence could either be the result of fluids migration outside the caldera or the gravitational adjustment of the source from a spherical to a sill-like geometry.

The Ivancich Active Landslide Process (Assisi, Central Italy) Analysed via Numerical Modeling Jointly Optimized by DInSAR and Inclinometric Data

The analysis of the displacement field due to a landslide process can be performed by means of either forward or inverse numerical models. Concerning the evolution of slow landslides, the Finite Element Method (FEM) represents a powerful tool to assess the relationships existing between the causative factors and the related effects, being the latter generally detected by field monitoring data. In this context, inverse models are useful to deduce the values of physical or mechanical parameters that control the landslide behavior over time. In this paper, we combined the potentiality of the FEM with Monte Carlo optimization procedures, based on a Genetic Algorithm (GA) technique, to back-analyze and interpret the kinematical evolution of very slow active landslides. In particular, we performed a two-dimensional time-dependent FE analysis by using a deviatoric creep model to simulate the evolution of the displacement field of the very slow Ivancich landslide (Assisi, Central Italy); an optimization procedure was performed by considering the Differential SAR Interferometry (DInSAR) data to derive the soil creep rate distribution, according to an inverse analysis approach. In particular the long-term Small BAseline Subset (SBAS) DInSAR analysis covering about 20 years was compared with the slope velocities calculated by the numerical model and the best-fit creep model was identified by considering the minimum Root Mean Square Error between field data and model results. Finally the model results in terms of slope displacements over time have been also compared with the available inclinometric measurements.

Landslide analysis through the multi-sensor SBAS-DInSAR approach: The case study of Assisi, Central Italy

We exploit advanced Differential SAR Interferometry (DInSAR) techniques for enhanced analyses of slope instability phenomena. In particular, we focus on the Ivancich urban area, in the worldwide known historic town of Assisi, Central Italy, affected by a deep-seated, slow moving active landslide for which geological and geotechnical data are also available. Furthermore over the landslide site, large datasets of SAR acquisitions collected in the last two decades by the C-band ERS-1/2 and ENVISAT SAR sensors, and by the X-band radars of the COSMO-SkyMed constellation are available. In our study, we applied the advanced DInSAR technique referred to as Small BAseline Subset (SBAS), benefiting from its ability to generate deformation time series at full spatial resolution from multi-sensor SAR data, that allowed us to characterize the temporal and spatial pattern of ground deformations induced by the landslide. Furthermore, we experimented an innovative approach for landslide modeling, based on the integration of DInSAR measurements with conventional geological and geotechnical data used in landslide studies.

Multiridge Method for Studying Ground-Deformation Sources: Application to Volcanic Environments

Volcanic phenomena are currently monitored by the detection of physical and chemical observations. Generally, the ground deformation field is the most relevant shallow expression of the geometric and physical parameters variations in the magmatic reservoir. In this study, we propose a novel method for the direct estimation of the geometric parameters of sources responsible for volcanic ground deformation detected via the DInSAR technique. Starting with the biharmonic properties of the deformation field, we define an approach based on the Multiridge and ScalFun methods to achieve relevant information about both the positions and shapes of active sources, such as the Mogi source. Our methodology is definitely different from the methods currently used for modeling ground-deformation sources, mainly based on forward or inverse techniques. In fact, (i) it does not require any assumptions about the source type, and (ii) it is not influenced by the distribution of medium elastic parameters or (iii) the presence of high-frequency noise in the dataset. For synthetic cases, we accurately estimate the depth to the source within a 3% error. Finally, we study the real case of the Okmok volcano ground-deformation field and achieve results compatible with those in previous works.

The Use of Massive Deformation Datasets for the Analysis of Spatial and Temporal Evolution of Mauna Loa Volcano (Hawai’i)

In this work, we exploited large DInSAR and GPS datasets to create a 4D image of the magma transfer processes at Mauna Loa Volcano (Island of Hawai’i) from 2005 to 2015. The datasets consist of 23 continuous GPS time series and 307 SAR images acquired from ascending and descending orbits by ENVISAT (ENV) and COSMO-SkyMed (CSK) satellites. Our results highlight how the joint use of SAR data acquired from different orbits (thus with different look angles and wavelengths), together with deformation data from GPS networks and geological information can significantly improve the constraints on the geometry and location of the sources responsible for the observed deformation. The analysis of these datasets has been performed by using an innovative method that allows building a complex source configuration. The results suggest that the deformation pattern observed from 2005 to 2015 has been controlled by three deformation sources: the ascent of magma along a conduit, the opening of a dike and the slip along the basal decollement. This confirms that the intrusion of the magma within a tabular system (rift dikes) may trigger the sliding of the SE portion of the volcanic edifice along the basal decollement. This case study confirms that it is now possible to exploit large geodetic datasets to improve our knowledge of volcano dynamics. The same approach could also be easily applied in other geodynamical contexts such as geothermal reservoirs and regions with complex tectonics.

Integration of SBAS-DInSAR and in-situ observations for 3D numerical optimization modelling: The case study of Ivancich landslide (Assisi, Italy)

In this work we propose a numerical optimization procedure constrained by field and SBAS-DInSAR measurements, as an alternative to standard forward Finite Elements (FE) models, to deeply analyze slope instabilities. The performed optimization procedure is based on the minimization of the difference between SBAS-DInSAR data and the results of the FE model, in terms of the displacement rate. As case study to evaluate the performances of the proposed procedure, we select the Ivancich landslide, located in the eastern part of the Assisi municipality (central Italy), and affected by an active slow-moving landslide since its first urbanization process. In this case, we focused on the Newtonian approach by considering a creeping flow approximation, suitable to simulate the kinematic trend of the investigated site. In addition, a set of 39 SAR images, acquired by COSMO-SkyMed constellation between 2009 and 2012, was exploited to generate deformation time series.

Ground deformation associated with the 2012 Emilia (Northern Italy) seismic crisis retrieved through spaceborne SAR interferometry

In this work we present a detailed analysis of the co-seismic deformation signals associated with the 2012 Emilia (Northern Italy) seismic crises through spaceborne Differential Synthetic Aperture Radar (SAR) Interferometry. In particular, we provide a general picture of the ground deformation fields relevant to the Ml 5.9 and Ml 5.8 main shocks, by generating four co-seismic displacement maps from X-band COSMO-SkyMed and C-band RADARSAT-1/2 SAR data, collected by descending orbits over the investigated area. Subsequently, we perform an analytical modelling of the seismic events by exploiting the RADARSAT-2 displacement map through a finite dislocation fault, in order to get more information about the earthquake source locations and their geometries.