Through the integration of advanced radar and seismic interferometry analysis techniques, the portions of the internal structure of the Phlegraean supervolcano, currently most active in terms of stress concentration, soil dynamics and surface fumarole emissions, have been mapped. This was revealed by a study conducted by Cnr, Ingv and Federico II University of Naples, published in Remote Sensing of Environment
The most active internal regions of the Campi Flegrei have been identified by integrating geophysical investigations, seismicity and ground deformations of the remotely sensed area. The most active parts of the Phlegrean supervolcano, located to the west of the Neapolitan urban area, are highlighted by a study conducted by the Institute for electromagnetic sensing of the environment of the National Research Council (Cnr-Irea), by the Vesuvius Observatory of the 'National Institute of Geophysics and Volcanology (Ingv-Ov) and the Department of Environmental Earth Sciences and Resources of the University of Naples Federico II, in collaboration with INVOLCAN (Instituto Volcanológico de Canarias, Tenerife, Spain) and Institute for Geosciences JGU (Johannes Gutenberg-Universität Mainz). The research, 'Volcanic structures investigation through SAR and seismic interferometric methods', was published in Remote Sensing of Environment.
“The integration of innovative satellite and seismic data analysis techniques”, explains the scientific coordinator Pietro Tizzani, Cnr-Irea researcher, “has made it possible to map the portions of the internal structure of the Phlegrean supervolcano that are currently more active both in terms of efforts, than of soil dynamics”. In particular, the results are obtained from the X-band satellite radar data of the Cosmo-SkyMed constellation of the Italian Space Agency (ASI), processed at the Cnr-Irea laboratories in Naples together with the seismic data acquired by the permanent monitoring network of the Ingv-Ov.
Furthermore, explains Francesca Bianco, director of Ingv-Ov, the integrated analyzes highlighted "how the area east of the solfatara, near the fumarolic region of Pisciarelli, represents the portion of the caldera characterized by the highest relative rates of ground deformation, between 2011 and 2014, which would correspond, at a depth between 0.8 and 1.2 km, to a region characterized by the maximum concentration of seismicity recorded: a trend that continues even after 2014”.
The results of the seismic interferometry technique used in the analysis, known as Ambient Noise Tomography (ANT), then highlighted in this area a portion of the crust in which there is a significant change in the propagation speed of the seismic waves, which would testify to the presence of geological bodies with different mechanical characteristics compared to the region east of Pisciarelli. Variations probably linked to intense hydrothermal phenomena extending between the topographic surface and about 1.5 km of depth, which would structurally constitute the interconnection system of the deep magmatic source with the surface. This interpretation is also supported by the intense fumarolic activity recorded between the solfatara and Pisciarelli in the period 2011-2014.
"The development of new potential field analysis techniques in the context of remote sensing ground deformation data", underlines Maurizio Fedi, full professor of applied geophysics at the University of Frederick II and co-author of the research, "is a valuable added value for the characterization- identification of subvolcanic structures and in the study of the surface dynamics of volcanoes. The analysis of the structural features obtained from these data, integrated with those already deduced from the gravimetric and magnetometric data, is very significant for low-velocity structures at a depth of about 1 km”.
These analysis methodologies open up new and significant paths in the study of multi-platform geodetic signals.
"The research", concludes Riccardo Lanari, director of Cnr-Irea, "represents an example of how the multidisciplinary collaboration and integration of the professionals present in the Neapolitan scientific context of the earth sciences, have led to a significant advance in the knowledge of nature and of the behavior of the Phlegrean volcano and of the technological development of volcanic monitoring systems, fundamental both for the study of their internal structure and for the recognition of the most dynamically active regions with relative risk management".
Rome, October 21 2019
Figure 1: SAR interferometry analysis for the period 2011-2014. (a, b) Map of Vertical and EW displacements, respectively, measured during phase 1, between February 2011 - May 2012, (c, d) phase 2, between May 2012 - April 2013 and (e, f) the transition 3, between April 2013 and January 2014. At the bottom left, the time series of vertical and east-west displacement are reported. The time period analyzed is divided into three phases (grey regions) characterized by periods of homogeneous linear deformation. On the right are the results of the THD analysis (horizontal total derivatives) of the vertical strain component related to step 2 (May 2012 - April 2013). The green crosses identify the maximum of the THD. The magenta circles represent the position of the site of Pozzuoli (PZ), of the city of Naples (NA) Monte Nuovo (NU), of the port of Pozzuoli (HR), of the Astroni crater (AS), of the Solfatara crater (SO), of the Pisciarelli (PI) fumarole spring, of Monte Gauro (GA) and San Vito (SA). The green box indicates the analysis period.
Figure 2: Model of the ANT group speeds. Maps of the speed of group of surface waves (Rayleigh) relating to the period 1,2s the analysis carried out relates to the period 2011-2013. The shaded polygon shows an area of low or no resolution.
Figure 3: Seismicity 2005-2016 and SAR vs Seismic Interferometry. (a) Epicentral distribution of the relevant local seismicity for the three time phases reported in Figure 1. (b) Comparison of the THD maxima (green crosses) and the seismic velocity profile map of the period 1.2 s (~ 1 km) with the 2005-2011 (blue circles), 2012-2013 (red circles), 2014-2016 (yellow circles) selected earthquake distributions between 800m and 1200m depth.
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