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Since August 24, 2016 a destructive seismic sequence has been occurring in Central Italy, between the Amatrice and Norcia towns. The seismic sequence started with the event of Mw 6.0 that was followed one hour later by the Mw 5.4 earthquake and by thousands of aftershocks along the NW-SE fault system extended for about 30 km. On October 26 the Mw=5.9 seismic event struck the area, followed by the strong Mw 6.5 earthquake on the October 30, at a depth of 9 km with epicenter located between the Norcia and Visso towns. The three months of seismicity activated the nearby 60 km long normal fault system of Mt. Vettore - Mt. Porche - Mt. Bove. The area was struck by several moderate to large earthquakes in historical times. In detail, in the Amatrice sector we mention the earthquakes of 1627 (Io=7-8 MCS, Mw 5.3), 1639 (Io=9-10 MCS, Mw=6.2), 1672 (Io=7-8 MCS, Mw=5.3) A.D. The main historical earthquakes of Valnerina, the area closest to the epicentre of the October 30 2016 earthquake, occurred in 1328 (Io=10 MCS, Mw=6.5), 1719 (Io= 8 MCS, Mw=5.6), 1730 (Io =9 MCS, Mw=6) 1859 (Io=8-9 MCS, Mw= 5.7) A.D. It is important also to remember the complex sequence of the 1703 A.D. (January 14, Valnerina, Io=11, Mw= 6.9; February 2, Aquilano, Io 10, Mw= 6.7) that had a considerably devastating impact on the area. Nevertheless, the historical seismicity correlated with the more external fault system of the Umbria-Marche- Abruzzi Apennine ridge is characterized by absence of strong energy seismicity along the Mt. Bove - Mt. Vettore- Vettoretto sector, suggesting that the fault system was “silent” until the 2016 seismic sequence. Our study consists in a multiparametric data analysis in GIS (Geographic Information System) environment which integrates tectonic, seismic and gravimetric datasets with the aim of investigating the neotectonic activity of the area. The gravimetric dataset contains the Multiscale Derivative Analysis (MDA) data of the gravity field, in which each maximum corresponds to a density contrast at some depth or to topographic features.We have minimized the topography effects to make sure that the MDA maxima are related only to faults. We have analyzed the seismogenic structures and investigated the geometry of the main fault planes through a combined analysis of hypocentral sections and the DEXP (Depth from Extreme Points) results on gravity data. In this study, we have validated our method based on literature geological and geophysical data. This will allow us to employ our approach for investigating possible buried/silent active faults for contributing to the knowledge of the Apennine seismic hazard.

We analyzed new magnetic, bathymetric, and seismic data acquired in the offshore sector of Somma-Vesuvius volcano (Italy). We detected a group of high-intensity, short wavelength magnetic anomalies corresponding to partly buried volcanic dome-like structures located by seismic data. The magnetic anomalies are aligned along a NW-SE strike that is the preferential orientation of an eruptive fracture of the pre-19 ka activity of Vesuvius. Three cones emplaced before the Last Glacial Maximum, whereas a fourth one emplaced after 19 ka suggesting a rejuvenation of the eruptive system offshore the volcano in historical times. We also identified a NE-SW elongated magnetic anomaly consistent with a dike-like body associated to an on-land tectonic structure that was active in recent times at Vesuvius. A delta-like area with diffuse low-intensity magnetic anomalies reflects the seaward fronts of lava flows that entered the sea mainly during the Middle Ages.

The aim of this study is to identify and constrain the geometry of the seismogenic structures (active, outcropping and buried fault systems) of the Abruzzo area (central Italy), through an integrated analysis of geo-structural, seismic and gravimetric data. We generated three thematic: “faults”, “earthquakes” and “gravimetric" data: i) The fault dataset consists of data extracted from the available structural and geological maps (ITHACA catalogue; the "Neotectonic Map of Italy" 1:500.000; several geological sheets 1:50.000 from ISPRA CARG project; the Geological Map 1:100.000 Sheet 1), and many geological studies. ii) The earthquakes datasets was created by merging the data from historical and instrumental Catalogues (CPTI04 and CPTI11; ISIDE - INGV). iii) The gravimetric datasets consists in the Multiscale Derivative Analysis (MDA) of the Bouguer anomaly map of the area, whose maxima show the presence of density lineaments. The merge of these datasets in GIS environment, highlighted four possible scenarios of correlation between faults, earthquakes and MDA maxima: 1) the existence of active faults, revealed by a strong correlation between epicentral location of seismic clusters, fault positions and MDA maxima; 2) the existence of buried active faults, highlighted by a good correlation between MDA maxima and epicentral positions, without correspondence with faults known from geological data; 3) the existence of inactive or silent faults, detected by the presence of faults reported in the geological datasets and literature which are associated with MDA maxima, without correlation of earthquakes; 4) the existence of faults not correlated with MDA maxima; this could be due to faults putting in contact two lithologies with a similar density. A comparison between seismic hypocentral locations and the fault geometry retrieved by DEXP analysis on gravity data was performed over some significant active faults of the area, such as the Paganica fault. Our analysis yielded new insights into the fault characteristics (dip direction and angle) and its activity.

In recent years, Gravity Gradient Tensor (GGT) has been successfully used in applied and environmental geophysics, also in light of the development of gradiometers. In this paper, we aim at analyzing the inversion, either joint or separate, of different GGT components and of the sole gravity field vertical component. We perform our analysis by inspection of the Picard Plot, a well-known Singular Value Decomposition tool, and employ both synthetic data and gradiometer measurements carried out at the Vredefort structure, South Africa. We show that the main factors controlling the quality of the inversion are algebraic ambiguity and signal-to-noise ratio. Provided that algebraic ambiguity is kept low – by different combinations of GGT components and/or only gravity field data – the choice of components involved in the inversion is non-crucial to the quality of the reconstructions. Nonetheless, the use gradiometers allows a quicker and more effective way, with respect to the sole gravity field, to improve algebraic ambiguity.

Modern technologies in the field of marine geophysical surveys allow us to obtain accurate and detailed information on the characteristics of the seabed and the marine substrate. In this paper we present a new magnetic high-resolution map of the Somma-Vesuvius offshore (Gulf of Naples, Southern Italy) depicting some main volcanological and tectonic structures of the area. The analysis of a new marine magnetic dataset, acquired during the oceanographic survey “SAFE_2014”, highlighted the presence of a group of NNW-SSE trending anomalies. This magnetic alignment suggests a volcano-structural correlation with the major faults in the area. We was also identified a NE-SW trend of magnetic anomalies, which may be associated with a tectonic structures interpreted as a magma preferential path of Somma-Vesuvius. Furthermore morphological irregularities of the seabed, shown by new morpho-bathymetric data, were found in correspondence with some of the main magnetic anomalies of Vesuvius offshore. This confirms the hypothesis of a possible connection between the Vesuvian volcanic structures and the tectonic regime of the Gulf of Naples, which controls this region since the Neogene-Quaternary.

The paper proposes a method to evaluate the potential for electric power production at any site of possible geothermal interest. Accounting for geological data of the reservoirs, the method allows the computation of the available electrical power of the investigated site. Electrical energy production from geothermal sources is realized through different techniques, such as single flash and double flash, dry steam, and binary ORC plants. The technique chosen to be the most productive is determined by analyzing a specific range of geofluid properties, mainly temperature and pressure. Moreover, each plant typology has a global efficiency that may be correlated to geofluid enthalpy by empiric relations available in literature. The proposed evaluation method brings together all these correlations, yielding the power availability from a geosource, once its temperature and pressure are known. The method takes as input the geofluid available flow rate, its pressure, temperature and non-condensable gas content. It defines the best plant option from these parameters, calculates its global efficiency and finally returns the actual available power. For sites of geothermic interest, the results of the application of this new method clearly highlight the most suitable zones for power plants installations.

The Island of Socorro is located 700 km off the western coastline of Mexico on the northern Mathematicians Ridge, an abandoned mid-ocean ridge spreading centre. Together with three other islands and numerous seamounts, the Revillagigedo archipelago represents the product of post-abandonment alkaline magmatism. The last volcanic event in the area of Socorro took place in 1993 AD, when a submarine basaltic eruption occurred off the SW coast. Up to now, due to the remote location of the island, little knowledge has been available concerning the subsurface structure of the volcanic edifice. Thus, a high-resolution airborne survey was conducted by the Geological Survey of Austria in February 2009. The survey included magnetic, electromagnetic and gamma-ray measurements, in order to have an overall view of the main structural/lithological features of the island. The survey covered an area of 200 square kilometres, with E-W flight lines, an average line spacing of 100 m and an average clearance from rough terrain of the island of about 100 m. The aeromagnetic map of Socorro is characterized by a dipolar anomaly of about 2000 nT amplitude whose maximum-minimum orientation is non-aligned with the direction of the local current Earth’s magnetic field (inclination 44° and declination 9°). In order to locate the position of the magnetic sources of the anomalies of the island, we computed pole-reduced data by accounting for the presence of sources with a component of remanent magnetization (inclination 40 and declination 357). The so-obtained pole-reduced map shows a large negative anomaly in the central part of the island. This may be connected to: a high temperature region (above the Curie temperature) in the deeper part of the volcano due to magma ascent, and/or low total remanent magnetization of pyroclastic caldera-filling sediments due to non-aligned sedimentation, and/or the influence of hydrothermal alteration. The computation of the horizontal gradient (hg) of the draped data highlights a rather good match between the maxima of the hg data and the caldera wall, and suggests the possible presence of a nested caldera structure. The analytic signal map shows correlation between its maxima and some of the scoria cones, such as the Lomas Coloradas cones in the SE area of the island. The study of the deeper magnetic structures of the island was performed by analyzing data after upward continuation to 1200 m a.s.l.. The analytic signal (as) map of the upward continued data is characterized by maxima both in the northern and southern sectors of the island, highlighting the presence of two deep and wide sources. A depth analysis of this as data, performed through the use of the "Depth from Extreme Points" (DEXP) method, pointed out the existence of two large sources located at about 5 km depth. This important result requires further investigation to establish its relevance in the evaluation of future hazards.

The aim of the study is to identify and better constrain the geometry of the seismogenic structures (active, outcropping and buried fault systems) in the Abruzzo area (central Italy), through an integrated analysis of geo-structural, seismic and gravimetric data. The studied area is one of the most active zones from a geodynamic point of view of the Italian Apennines, characterized by the occurrence of intense and widely spread seismic activity. The integrated analysis of structural, seismic and gravimetric data (Gaudiosi et al., 2012) of the areas was carried out through the use of Geographic Information System (GIS). More specifically, the analysis consisted of the following main steps: (a) collection and acquisition of aerial photos, numeric cartography, Digital Terrain Model (DTM) data, geological and geophysical data; (b) generation of the vector cartographic database and alpha-numerical data; c) image processing and features classification; d) cartographic restitution and multi-layers representation. Three thematic data sets have been generated: “faults”, “earthquakes” and “gravimetric” data. The fault dataset was built by merging all Plio- Quaternary structural data extracted from the available structural and geological maps, and many geological studies (Boncio et al., 2004; Galadini et al., 2000, 2003; Falcucci et al., 2011; Moro et al., 2013). The earthquake data set consists of seismic data collected in the available historical and instrumental Catalogues (Gruppo di lavoro CPTI, 2004); CPTI11, Rovida et al., 2011; ISIDE, INGV database). Seismic data have been standardized in the same format and merged in a single data set. As regards the gravimetric data set, we performed a Multiscale Derivative Analysis (MDA) of the gravity field, based on the good resolution properties of the Enhanced Horizontal Derivative (EHD) signal (Fedi et al., 2005). The main results of our integrated analysis show a good correlation among faults, epicentral location of earthquakes and MDA lineaments from gravity data. Furthermore, 2D seismic hypocentral locations were correlated with the information yielded by the application of the DEXP method to gravity data (Fedi and Pilkington, 2012), to estimate strike, dip direction and dip angle of some faults of the areas.

We present the results of a geophysical study at the site of Pian della Tirena, near the town of Nocera Terinese (Calabria, Italy). Geophysical imaging is a recent technique providing a reliable mapping of the three-dimensional magnetization distribution below the ground and, thus, effectively estimating the depth of buried structures. The site studied gained archaeological interest following the hypothesis of the presence of two adjacent, but distinct, settlements. The first one of Hellenic/Hellenistic age (the Temesa of Brettian age), the second (called Tempsa) of Roman age. Even though the site was recently excavated, extensive investigation was not possible due to the broadness of the area and the scarceness of traces at the surface, making it difficult to plan a targeted survey. Two detailed geophysical (magnetic and electromagnetic) surveys were performed in 2006 and 2013 to provide the archaeologists with precise information about the type and position of the buried structures, and increase the efficiency of the investigation. The survey aimed to: (i) confirm and outline the existence of a true urban settlement instead of isolated dwellings; (ii) locate centres of manufacturing activities (local pottery and metal handicrafts); (iii) verify the existence of a boundary wall or road around the settlement. Our three-dimensional analysis and interpretation detected several anomaly trends, most of which show a rather regular shape and orientation. This allowed us to infer the possible existence of a well-developed urban network. The final results provided an archaeological interpretation, building upon the urban network and different use-zones within the town.

A careful management of the data errors in potential field inversion is crucial for obtaining reliable information about the source distribution with respect to depth. The Depth Resolution Plot introduced by Fedi, Hansen and Paoletti provides a convenient tool for this analysis: it allows a computational/visual analysis of how much the depth resolution in a potential-field inversion problem is influenced by the way the problem is discretized and regularized. Here we present a variant of the Depth Resolution Plot, called Approx Depth Resolution Plot, which is better suited for large-scale problems, and we employ it to study the retrievable depth resolution in the inversion of the gravity field of the Neapolitan Volcanic Area.

We demonstrate the effectiveness of the potential-field multiscale approach when used as a tool for analyzing and characterizing geological features such as magnetized complex basements. This approach allows estimations of the source structural index and depth by methods analyzing a 3D dataset obtained by upward continuation of the original data. These data can be analysed by: 1) a geometrical approach (Multiridge Geometric Method, Fedi et al., 2009), looking for the intersection, in the source domain, of the field ridges (i.e.: lines defined by the position of the extreme points of the field at different scales); 2) the numerical analysis of the values of the field along ridges through the scaling function method (Fedi and Florio, 2006, Fedi, 2007; Florio et al., 2009) or the Euler method (Florio and Fedi, 2014); the DEXP transformation of the field (Fedi, 2007). The mentioned methods enjoy a good stability and resolution due to the inherent properties of a smoothing-enhancing filter which is applied to the original data to obtain the 3D dataset. It was shown that, when properly tuned, this filter (including upward continuation and vertical differentiation) can effectively act as a band-pass filter, controlling the noise amplification as well as the interference. Our approach may be employed to effectively analyze different datasets of magnetized basements. As an example, for the Bishop complex basement model (Williams et al., 2005) the analysis of the field ridges of different nth-order derivatives lead to structural index estimates in agreement with the basement structure morphology and allowed a good reconstruction of the complex basement relief.

In potential-field inversion problems, it can be difficult to obtain reliable information about the source distribution with respect to depth. Moreover, spatial resolution of the solution decreases with depth, and in fact the more ill-posed the problem – and the more noisy the data – the less reliable the depth information. Based on early work in depth resolution, defined in terms of the singular value decomposition, we introduce a tool APPROXDRP which uses an approximation of the singular vectors obtained by the iterative Lanczos bidiagonalization algorithm, making it well suited for large-scale problems. This tool allows a computational/visual analysis of how much the depth resolution in a computational potential-field inversion problem can be obtained from the given data.We show that when used in combination with a plot of the approximate SVD quantities, APPROXDRP may successfully show the limitations of depth resolution resulting from noise in the data. This allows a reliable analysis of the retrievable depth information and effectively guides the user in choosing the optimal number of iterations, for a given problem.

The Island of Socorro (Fig. 1) is located 700 km off the western coastline of Mexico at the northern Mathematicians Ridge, an abandoned mid‐ocean ridge spreading centre. Together with several other islands (e.g., San Benedicto and Clarion) and numerous seamounts, the so called Revillagigedo archipelago represents post‐abandonment alkaline magmatism (e.g., Taran et al., 2002 and references therein). The last volcanic event in the area of Socorro took place in 1993 (e.g., Siebe et al., 1995), when a submarine basaltic eruption threatened the small settlement on the island. Until today, due to the remote location of the island, little knowledge is available concerning the subsurface structure of the volcanic edifice. In support of plans of the Mexican government to enlarge the settlement on the island, a combined geophysical survey was conducted in February 2009 to open up new resources for local groundwater supply. Investigations were focused on determining the resistivity structure of the shallow subsurface of the volcanic edifice, as this parameter is directly related to the water content of subsurface structures. However other parameters such as clay content, fluid conductivity and temperature control the subsurface resistivity and these parameters normally show significant variations in volcanic areas. Thus, we conducted other investigations/analyses over the island, such as airborne magnetic, electromagnetic and gamma-ray measurements in order to have an overall view of the main structural/lithological features of the island. The aim of this work is to retrieve information about the surface and subsurface geology of the island based on the analysis and interpretation of magnetic and gamma-ray airborne data, integrated with available geo-volcanological information.

In this paper we demonstrate the efficiency of a new approach to upward continue potential field data, the Volume Upward Continuation (VUC), coupled with traditional horizontal derivative techniques. By using VUC it is immediate showing that upward continuation of the signal to higher altitudes yield information about progressively deeper sectors of the discontinuity. In particular, looking at the position of the maxima of the horizontal derivative of the continued field, we can observe that they will be laterally shifted toward the dipping direction of the discontinuity, in a way proportional to the continuation height. We applied VUC followed by horizontal derivative to a gravity profile extracted from a gravity survey on the Venelin-Aksakov fault in Bulgaria, in order to get further information on the dipping direction of this structure.

A careful management of the ambiguities and errors in potential field inversion is crucial for obtaining reliable information about the source distribution with respect to depth. In this paper we introduce a tool, the ApproxDRP, which is based on an approximation of the singular vectors obtained by the iterative Lanczos bidiagonalization algorithm. This tool allows a computational/visual analysis of how much the depth resolution in a potential-field inversion problem is influenced by the way the problem is discretized and regularized. Since the ApproxDRP is based on an iterative method, it is suitable for large-scale problems. We show that when used in combination with a plot of the approximate SVD quantities, the ApproxDRP may successfully show the limitations of depth resolution resulting from noise in the data. This allows a reliable analysis of the retrievable depth information and effectively guides the user in choosing the optimal number of iterations, for a given problem.

Shear wave velocities have a fundamental role in connection with the mitigation of seismic hazards, as their low values are the main causes of site amplification phenomena and can significantly influence the susceptibility of a territory to seismic-induced landslides. The shear wave velocity and modulus of each lithological unit are influenced by factors such as the degree of fracturing and faulting, the porosity, the clay amount and the precipitation, with the latter two influencing the unit's water content. In this paper we discuss about how those factors can affect the Vs values and report the results of different analyses which quantify the reduction in the rocks' Vs and shear modulus values connected to the presence of clay and water. We also show that significant results in assessing seismic-induced slope failure susceptibility for land planning targets could be achieved through a careful evaluation, based only on literature studies, of the geo-lithological and geo-seismic features of the study area.

La prospezione geoelettrica classica di tipo SEV si basa sul presupposto che il sottosuolo sia caratterizzato da una stratificazione piano-parallela, con strati lateralmente omogenei ed isotropi. Considerare strutture del sottosuolo solo piano-parallele costituisce però un vincolo alquanto limitativo: è infatti evidente che le strutture presenti nel sottosuolo sono spesso più complesse e ne consegue un’ambiguità di risposta. L’ambiguità in tal caso si riferisce al rilevamento di dati il cui diagramma di resistività simula curve riferibili a situazioni del sottosuolo a struttura piano-parallela in presenza di strutture più complesse; in altre parole, i valori di resistività apparente che si registrano in alcuni casi di strutture con variazioni laterali di resistività, faranno assumere alla curva risultante un aspetto non distinguibile da quello che si otterrebbe per una stratificazione regolare piano-parallela. L’entità degli errori commessi nell’interpretazione dati sarà dipendente dal grado di scostamento della reale struttura del sottosuolo dalla condizione di piano-parallelismo. In conclusione, il SEV, pur conservando una discreta validità di informazione anche in presenza di strutture complesse, consegue la massima efficacia solo in situazioni di stratigrafia piano-parallela. Tuttavia, anche per effetto di equivalenza e/o di soppressione, non é la tecnica più idonea ad evidenziare i dettagli del sottosuolo; ne metterà in risalto soltanto gli strati più importanti per spessore e/o per contrasto di resistività, inglobando gli altri in un’unica formazione. In ogni caso indagini basate su uno o pochi SEV, sono prive di significato. L’indagine va correttamente programmata secondo quanto suggerito in § 1.4.1, avendo cura di rilevare i dati in modo corretto e senza trascurarne l’obiettivo e, specialmente, tutte le possibili informazioni di carattere tecnico che possono reperirsi, effettuando, ove possibile, sondaggi di taratura in corrispondenza di perforazioni di stratigrafia certa. Da quanto detto, e da numerosi esempi noti in letteratura (vedi anche § 1.5.10, ed e.g., Mundry, 1984), appare evidente l’importanza di interpretare i dati relativi a situazioni reali in termini bidimensionali. Durante gli ultimi trent’anni sono messe a punto diverse tecniche di acquisizione bidimensionale dei dati di resistività apparente (§ 3.4.2) e sviluppati metodi di modellazione 2D del sottosuolo (§ 3.4.3). Attraverso tali metodi è possibile analizzare la risposta elettrica teorica di tipiche strutture non piano-parallele, quali faglie, strutture inclinate, corpi anomali e irregolarità topografiche (§ 3.4.4). L’interpretazione dei dati può essere in tal caso effettuata sia attraverso metodi diretti di tipo trial and error, nei quali il modello del sottosuolo viene dedotto dal confronto tra la pseudosezione ottenuta sperimentalmente e quella relativa a modelli sintetici, sia attraverso metodi di inversione bidimensionali (§ 3.4.5).