Merging active and passive data sets in traveltime tomography: The case study of Campi Flegrei caldera (Southern Italy)

We propose a strategy for merging both active and passive data sets in linearized tomographic inversion. We illustrate this in the reconstruction of 3D images of a complex volcanic structure, the Campi Flegrei caldera, located in the vicinity of the city of Naples, southern Italy. The caldera is occasionally the site of significant unrests characterized by large ground uplifts and seismicity. The P and S velocity models of the caldera structure are obtained by a tomographic inversion based on travel times recorded during two distinct experiments. The first data set is composed of 606 earthquakes recorded in 1984 and the second set is composed of recordings for 1528 shots produced during the SERAPIS experiment in 2001. The tomographic inversion is performed using an improved method based on an accurate finite‐difference traveltime computation and a simultaneous inversion of both velocity models and earthquake locations. In order to determine the adequate inversion parameters and relative data weighting factors, we perform massive synthetic simulations allowing one to merge the two types of data optimally. The proper merging provides high resolution velocity models, which allow one to reliably retrieve velocity anomalies over a large part of the tomography area. The obtained images confirm the presence of a high P velocity ring in the southern part of the bay of Pozzuoli and extends its trace inland as compared to previous results. This annular anomaly represents the buried trace of the rim of the Campi Flegrei caldera. Its shape at 1.5 km depth is in good agreement with the location of hydrothermalized lava inferred by gravimetric data modelling. The Vp/Vs model confirms the presence of two characteristic features. At about 1 km depth a very high Vp/Vs anomaly is observed below the town of Pozzuoli and is interpreted as due to the presence of rocks that contain fluids in the liquid phase. A low Vp/Vs body extending at about 3–4 km depth below a large part of the caldera is interpreted as the top of formations that are enriched in gas under supercritical conditions.     

Application of Surface-Wave Methods for Seismic Site Characterization

Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic.     

Freezing of the Venetian Lagoon since the 9th century A.D. in comparision to the climate of western Europe and England

In the first part of this study, typical of historical climatology, the various sources regarding freezing of the Venetian Lagoon since the 9th century A.D., are reported and discussed. The events are related, where possible, to teleconnections. Two synoptic patterns (weather type A: northerly and D: easterly) seem to have played an important role. After having discussed the dynamics of the icing processes, the problem of comparing the data is considered, as over the centuries many works were made on the Lagoon, in order to divert the major tributaries. In fact, the hydrological regime and the physical characteristic of the Lagoon environment were changed, so that the conditions necessary for freezing were no longer the same. The series was compared with the severe winters in westtern Europe and England, in order to reconstruct the past climate of the Mediterranean region and discuss the observed secular changes in the light of the widely accepted ideas of climatic variations. The comparison shows some differences: e.g. at Venice the Medieval Climatic Optimum with the occurrence of severe winters ended earlier and the Little Ice Age was broken by a milder interval.     

Analysis at medium scale of low-resolution DInSAR data in slow-moving landslide-affected areas

Landslide studies over large areas call for multidisciplinary analyses supported by accurate ground displacement measurements. At present, conventional techniques can be valuably complemented by innovative satellite techniques such as Differential SAR Interferometry (DInSAR), furnishing huge amounts of data at competitively affordable costs. This work investigates the remote sensed data potential in landslide studies starting from the awareness of the present constraints of the technique. To this end, with reference to a sample area–within the territory of the National Basin Authority of Liri-Garigliano and Volturno rivers (Central-Southern Italy)–for which detailed base and thematic maps are available, quantitative examples of DInSAR data coverage on both different land-uses and landslide-affected areas are shown. Then, an original tool for “a priori DInSAR landslide visibility zoning” is proposed to address the choice of the most suitable image datasets. Finally, referring to the visible zones, the outcomes of DInSAR data for checking/updating landslide inventory maps at 1:25,000 scale highlight appealing perspectives, also holding the promise of obtaining relevant information in the landslide hazard evaluation.     

Fluid geochemistry of the Mondragone hydrothermal systems (southern Italy): water and gas compositions vs. geostructural setting

International Journal of Earth Sciences - The geochemistry of natural thermal fluids discharging in the Mondragone Plain has been investigated. Thermal spring emergences are located along the...     

Cautious neotectonic hypotheses for assessing the seismic hazard in northeastern Italy

A simplified tectonic scheme for hazard purposes was recently adopted for northeastern Italy, introducing large generalized seismogenic areas containing systems of complex geometry faults. This scheme considers only major faults with documented seismic activity. In the present analysis, a different tectonic scheme, with linear elements as seismogenic sources, is presented. The assessment of the regional seismic hazard is done with the fault rupture model, its most important advantage being the recognition that the length of fault rupture during an earthquake is an important consideration in probabilistic calculations of seismic hazard. Moreover, some structures with no associated seismicity but with notable neotectonic activity are considered, and their contribution to the results investigated. Important uncertainties such as those in the maximum possible magnitude of future earthquakes, in the location of the fault, in the focal depth, and in the attenuation law are accounted for in the calculations and their influence studied. The results identify a seismic belt running from Lake Garda to Friuli and along the Yugoslav coast and are very similar to those already known for Friuli, with the largest values corresponding to the zone around Gemona. Some slight differences in the shape of the areas of equal acceleration are probably due to the delineation of the seismic sources of the proposed model. For a cautious elaboration, some neotectonic lines without present seismicity were added into the fault model. Their contribution is negligible in the areas of highest acceleration, but increases remarkably in the areas where acceleration is not expected to exceed the medium values.     

The Role of Data Processing and Uncertainty Management in Seismic Hazard Evaluations: Insights from Estimates in the Garfagnana–Lunigiana Area (Northern Italy)

Significantly different estimates of seismic hazard may result for the same site as aneffect of different methodological choices underlying the adopted procedures. In orderto explore this aspect, two approaches devoted to probabilistic seismic hazard assessment are considered for the evaluation of hazard in a seismic area in Northern Italy. In particular, results of a standard procedure are compared with those obtained by an innovative approach. Fundamental features of this last methodology are the extensive use of intensity data relative to seismic effects observed at the site of interest during past earthquakes and the basic role attributed to the parameterisation of uncertainty which affects the considered pieces ofinformation. The analysis indicates that the new approach supplies results significantlydifferent from those obtained from standard methodology and that these differences strongly depend on strategies adopted for data processing and for the management of uncertainties which affect input parameters.     

Aquifer vulnerability and potential risk assessment: application to an intensely cultivated and densely populated area in Southern Italy

The use of indices, describing aquifer vulnerability and the risk of groundwater pollution, is a basic tool for the implementation of a sound water management plan, especially in densely populated and intensely cultivated areas. In this study, the groundwater contamination risk of the Caserta Plain (Southern Italy) was assessed through the integration of hazards defined on the basis of the different land uses, of the intrinsic vulnerability calculated by applying the SINTACS model and of the groundwater value evaluated by considering water wells density. In order to evaluate the evolution of the risk of groundwater pollution, the proposed methods were applied in the study area for both 2001 and 2009. The resulting specific vulnerability (SINTACS-L) and the risk (GRA) maps, created in a GIS environment, were validated by the comparison with the nitrate concentration distribution. The application of the proposed approach to the study area highlighted the strengths and weaknesses of each method and, at the same time, showed that their combination can provide an overall view of the threats posed to groundwater resources by the human activities affecting the territory. Considering both the benefits and the issues of the proposed approach, overall, the groundwater risk map is thought to be a robust tool to support water managers in defining future plans for water resources exploitation and land use.     

Two-mica and tourmaline leucogranites from the Everest–Makalu region (Nepal–Tibet). Himalayan leucogranite genesis by isobaric heating?

In the Higher Himalaya of the region from Cho Oyu to the Arun valley northeast of Makalu, the Miocene leucogranites are not hosted only in the upper High Himalayan Crystallines (HHC); a network of dykes also cuts the lower HHC and the Lesser Himalayan Crystallines (LHC).

The plutons and dykes are mainly composed of two-mica (muscovite+biotite±tourmaline±cordierite±andalusite±sillimanite) leucogranite, with tourmaline≤2.6% and biotite>1.5% modal, and tourmaline (muscovite+tourmaline±biotite±sillimanite ±garnet±kyanite±andalusite±spinel±corundum) leucogranite, with tourmaline>2.2% and biotite<1.5% modal.

Both leucogranite types were produced by partial melting in the andalusite–sillimanite facies series, under LP/HT conditions constrained by the occurrence of peritectic andalusite and cordierite. The geochemical features of the leucogranites suggest that tourmaline leucogranite was produced by muscovite dehydration melting in muscovite-rich metapelites at P350 MPa and T≥640°C, whereas two-mica leucogranite was produced by biotite dehydration melting in biotite-rich metapelites at P300 MPa and T≥660–710 °C.

Melting in fertile muscovite-rich metapelites of the top of both the HHC and LHC produced magmas which were emplaced at the same structural level in which they had been generated. Melting in the biotite-rich gneiss of both the HHC and LHC produced hotter magmas which were transported upwards by dyking and eventually coalesced in the plutons of the upper HHC. A similar process also produced a network of two-mica granite at the top of the LHC in the Ama Drime–Nyönno Ri Range northeast of Makalu.

The prograde character of leucogranite melt-producing reactions in the Everest–Makalu area suggests that, here, the generation of Miocene leucogranites took place in a regime of nearly isobaric heating following nearly adiabatic decompression.