Pietro Tizzani

Uplift and magma intrusion at Long Valley caldera from InSAR and gravity measurements

The Long Valley caldera (California) formed ~760,000 yr ago following the massive eruption of the Bishop Tuff. Postcaldera volcanism in the Long Valley volcanic field includes lava domes as young as 650 yr. The recent geological unrest is characterized by uplift of the resurgent dome in the central section of the caldera (75 cm in the past 33 yr) and earthquake activity followed by periods of relative quiescence. Since the spring of 1998, the caldera has been in a state of low activity. The cause of unrest is still debated, and hypotheses range from hybrid sources (e.g., magma with a high percentage of volatiles) to hydrothermal fluid intrusion. Here, we present observations of surface deformation in the Long Valley region based on differential synthetic aperture radar interferometry (InSAR), leveling, global positioning system (GPS), two-color electronic distance meter (EDM), and microgravity data. Thanks to the joint application of InSAR and microgravity data, we are able to unambiguously determine that magma is the cause of unrest.

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.

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.

Aseismic transient during the 2010-2014 seismic swarm: evidence for longer recurrence of M ≥ 6.5 earthquakes in the Pollino gap (Southern Italy)?

In actively deforming regions, crustal deformation is accommodated by earthquakes and through a variety of transient aseismic phenomena. Here, we study the 2010–2014 Pollino (Southern Italy) swarm sequence (main shock MW 5.1) located within the Pollino seismic gap, by analysing the surface deformation derived from Global Positioning System and Synthetic Aperture Radar data. Inversions of geodetic time series show that a transient slip, with the same mechanism of the main shock, started about 3–4 months before the main shock and lasted almost one year, evolving through time with acceleration phases that correlate with the rate of seismicity. The moment released by the transient slip is equivalent to MW 5.5, significantly larger than the seismic moment release revealing therefore that a significant fraction of the overall deformation is released aseismically. Our findings suggest that crustal deformation in the Pollino gap is accommodated by infrequent “large” earthquakes (MW ≥ 6.5) and by aseismic episodes releasing a significant fraction of the accrued strain. Lower strain rates, relative to the adjacent Southern Apennines, and a mixed seismic/aseismic strain release are in favour of a longer recurrence for large magnitude earthquakes in the Pollino gap.

SBAS-DInSAR time series in the last eighteen years at Mt. Etna volcano (Italy)

We investigate the deformation of Mt. Etna volcano (Italy) by exploiting the advanced Differential Synthetic Aperture Radar Interferometry (DInSAR) technique referred to as the Small BAseline Subset (SBAS) algorithm. In particular, we take advantage of the multi-sensor data processing capability of the SBAS algorithm which allows us to generate Mt. Etna mean deformation velocity maps and the corresponding time series in the last eighteen years. To achieve this task we exploit different set of SAR data collected by the European (ERS-1/2, ENVISAT) satellites in the 1992–2010 time interval, and by the Italian COSMO-SkyMed constellation during 2009–2010 period. We also benefit from the availability of ERS-ENVISAT multi-orbit (ascending and descending) data in order to discriminate the vertical and East-West components of the volcano edifice displacements and generate the relevant time series. Finally, we evidence how the higher spatial resolution and denser temporal sampling of the COSMO-SkyMed data, with respect to the European satellites, permit to follow with more details the complex deformative pattern which has characterized the volcano in the last two years.

A quantitative assessment of DInSAR Time series accuracy in volcanic areas: From the first to second generation SAR sensors

We perform a quantitative assessment of the accuracy of Differential SAR Interferometry (DInSAR) time series in volcanic areas, retrieved through “first” and “second generation” SAR data. In particular, we analyze the impact that the wavelengths and looking geometries may have in the DInSAR measurement retrieval depending on the radar system. To this aim, we focus on the DInSAR algorithm referred to as Small BAseline Subset (SBAS) to generate mean deformation velocity maps and corresponding time series starting from sequences of SAR images. Moreover, we consider collections of SAR data acquired by the ERS-1/2 and ENVISAT (C-band), and COSMO-SkyMed (Xband) sensors over the volcanic area of the Campi Flegrei caldera, Southern Italy. We invert these SAR data sequences through the SBAS-DInSAR technique, thus obtaining C- and X- band deformation time series that we compare to continuous GPS measurements, the latter assumed as reference. The achieved results provide, in addition to a clear picture of the surface deformation phenomena already occurred and occurring in the selected case study, relevant indications for the analysis of the SBAS-DInSAR time series accuracies in volcanic areas passing from the first to second generation SAR sensors.

Current Topics on Deformation Monitoring and Modelling, Geodynamics and Natural Hazards: Introduction

1. Natural and anthropogenic geohazards in Greater London observed from geological and ERS-1/2 and ENVISAT Persistent Scatterers ground motion data: results from the EC FP7-SPACE PanGeo project.- 2. Geohazards monitoring in Roma from InSAR and in situ data: outcomes of the PanGeo Project.- 3. New results on ground deformation in the Upper Silesian Coal Basin (southern Poland) obtained during realization of the DORIS Project (EU - FP 7).- 4. Multi-temporal evaluation of landslide movements and impacts on buildings in San Fratello (Italy) by means of C- and X-band PSI data.- 5. Landslide kinematical analysis through inverse numerical modelling and differential SAR interferometry.- 6. A user-oriented methodology for DInSAR time series analysis and interpretation: landslides and subsidence case studies.- 7. Structure of Alluvial Valleys from 3-D Gravity Inversion: The Low Andarax Valley (Almeria, Spain) Test Case.- 8. Characterization of underground cavities by LIDAR, GPR and GNSS. Application to the Duero Basin, Spain.- 9. Estimation of seismic and aseismic deformation in Mexicali Valley, Baja California, Mexico, in the 2006-2009 period, using precise leveling, DInSAR, geotechnical instruments data, and modeling.- 10. Source parameters of earthquakes recorded near the Itoiz dam (Northern Spain).- 11. Identification of T-waves in the Alboran Sea.-12. An Overview of Geodetic Volcano Research in the Canary Islands.- 13. Shallow hydrothermal pressurization prior to 2010 Mount Sinabung volcano, Indonesia eruption observed with ALOS satellite radar interferometry.- 14. Retrieving the stress field within the Campi Flegrei caldera (Southern Italy) through an integrated geodetical and seismological approach.

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.

A full exploitation of the enhanced SBAS-DInSAR approach in volcanic and seismogenic areas

We present an enhanced version of the SBAS-DInSAR processing chain, which complements the conventional SBAS codes with a simple noise-filtering procedure that allows us to mitigate noise artifacts affecting the sequence of multi-look (multi-temporal) small baseline interferograms used within the SBAS inversion. We demonstrate that the use of such a noise-filtering algorithm permits to significantly improve the quality of the mean deformation velocity maps and displacement time-series retrieved via the SBAS-DInSAR processing chain, thus promoting more detailed analyses of the detected deformation phenomena. The overall effectiveness of the enhanced SBAS-DInSAR approach is confirmed by the experimental results achieved by applying the proposed method to two sets of SAR data collected by the ERS-1/2 and ENVISAT sensors over the Mt. Etna volcano (Southern Italy) and Yellowstone caldera (Wyoming, U.S.).