Dario Luzio

The structure of a hydrothermal system from an integrated geochemical, geophysical and geological approach: the Ischia Island case study

The complexity of volcano-hosted hydrothermal systems is such that thorough characterization requires extensive and interdisciplinary work. We use here an integrated multidisciplinary approach, combining geological investigations with hydrogeochemical and soil degassing prospecting, and resistivity surveys, to provide a comprehensive characterization of the shallow structure of the southwestern Ischias hydrothermal system. We show that the investigated area is characterized by a structural setting that, although very complex, can be schematized in three sectors, namely, the extra caldera sector (ECS), caldera floor sector (CFS), and resurgent caldera sector (RCS). This contrasted structural setting governs fluid circulation. Geochemical prospecting shows, in fact, that the caldera floor sector, a structural and topographic low, is the area where CO2-rich (>40 cm3/l) hydrothermally mature (log Mg/Na ratios 150 g m−2 d−1), is clearly captured by electrical resistivity tomography (ERT) and transient electromagnetic (TEM) surveys as a highly conductive (resistivity 10,000 mg/l) and poorly conductive meteoric-derived (TDS < 4,000 mg/l) waters are observed, respectively. We finally integrate our observations to build a general model for fluid circulation in the shallowest (<0.5 km) part of Ischias hydrothermal system.

Local Earthquake Tomography in the Southern Tyrrhenian Region of Italy: Geophysical and Petrological Inferences on the Subducting Lithosphere

We obtained a high-resolution seismic tomography of the Ionian lithosphere subduction using a new approach based on: (a) the Double-Difference technique for inversions and (b) the statistical post-processing of a great number of preliminary models (Weighted Average Model, WAM method); the latter was used to increase reliability and resolution. In the tomographic model, the high-velocity portion of the steeply dipping Ionian slab is well imaged, as is an underlying low-Vp (≈7.0 km/s) aseismic region. We propose that the low-velocity region can be assigned to a partially hydrated (serpentinized) mantle of the subducting Ionian slab, which progressively dehydrates with depth in dense high-pressure phases. In the mantle wedge overlying the slab, large areas, characterized by low-Vp (≤7.0 km/s) and high Vp/Vs (≥1.85), have been imaged beneath the Stromboli and Marsili volcanoes down to a maximum depth of 180 km. We have interpreted these areas as being regions where mantle partial melts form and accumulate and which then feed the present-day Aeolian Archipelago magmatism

Simultaneous seismic wave clustering and registration

In this paper we introduce a simple procedure to identify clusters of multivariate waveforms based on a simultaneous assignation and alignment procedure. This approach is aimed at the identification of clusters of earthquakes, assuming that similarities between seismic events with respect to hypocentral parameters and focal mechanism correspond to similarities between waveforms of events. Therefore we define a distance measure between seismic curves in R^dd>=1, in order to interpret and better understand the main features of the generating seismic process.

A regional‐scale discontinuity in western Sicily revealed by a multidisciplinary approach: A new piece for understanding the geodynamic puzzle of the southern Mediterranean

The results of an integrated stratigraphic, structural, geophysical, and geochemical study reveal the presence of a crustal discontinuity in western Sicily that, at present, runs roughly N-S along a band from San Vito Lo Capo to Sciacca (SVCS). The boundary between the two zones of this discontinuity is nearly orthogonal to the main thrust propagation of the Sicilian thrust-and-fold belt. The different Permian to Tertiary sedimentary evolution recorded by the two zones appears related to this discontinuity, with thick carbonate platforms in the western sector facing deep-water successions in the eastern one. The presence of Upper Triassic reefs, huge megabreccias bodies, and widespread submarine volcanisms along the transition zone suggest the presence of a long lasting weakness zone. This zone has been reactivated episodically as transpressional and/or transtensional faults in relation to the different geodynamic stress acting in central Mediterranean area in different epochs. We speculate that this transition zone has represented a segment of the passive margin of the Ionian Tethys. During the Maghrebian convergence a different style of deformation has affected the two sectors floored by different sedimentary multilayers. The orthogonal-to-oblique differential convergence between the two sectors has resulted in right-lateral transpressional motions, leading to oblique thrusting of deep-water-derived thrusts onto platform-derived thrusts associated with clockwise rotations. The oblique convergence is still ongoing as demonstrated by the seismicity of the area, by the geothermal field with high mantle-derived helium fluxes and by the GPS measurements collected by different authors.

Nonparametric Clustering of Seismic Events

In this paper we propose a clustering technique, based on the maximization of the likelihood function defined from the generalization of a model for seismic activity (ETAS model, (Ogata (1988))), iteratively changing the partitioning of the events. In this context it is useful to apply models requiring the distinction between independent events (i.e. the background seismicity) and strongly correlated ones. This technique develops nonparametric estimation methods of the point process intensity function. To evaluate the goodness of fit of the model, from which the clustering method is implemented, residuals process analysis is used.

Centroid-based Cluster Analysis of HVSR Data for Seismic Microzonation

atasets acquired for studies of seismic microzoning in various urban centers of Sicilian towns, have been used to test clustering analysis through a non-hierarchical centroid-based algorithm. In this context clustering techniques may be useful to identify areas with similar seismic behaviour through HVSR data. Centroid-based algorithms generally require the number of clusters, k, and the initial centroid coordinates to be specified in advance. This aspect is considered to be one of the biggest drawbacks of these algorithms. The proposed algorithm doesn’t limit the number of k clusters and choose the initial centroids automatically from the data set. Azimuthal variation of the H/V peaks was also taken into account. Finally different partitions obtained using the centroid-based algorithm were superimposed on the geological map of the analyzed sites to identify possible correlations with geology and topography. The obtained results underline how the most appropriate clustering algorithm for a particular site often needs to be chosen experimentally. In fact in many cases the choice of the partition is strongly linked to the choice of parametric distance and to geological knowledge, while in other cases, the results showed similar results regardless of a priori choices.

An Algorithm for Earthquakes Clustering Based on Maximum Likelihood

In this paper we propose a clustering technique set up to separate and find out the two main components of seismicity: the background seismicity and the triggered one. We suppose that a seismic catalogue is the realization of a non homogeneous space–time Poisson clustered process, with a different parametrization for the intensity function of the Poisson-type component and of the clustered (triggered) component. The method here proposed assigns each earthquake to the cluster of earthquakes, or to the set of independent events, according to the increment to the likelihood function, computed using the conditional intensity function estimated by maximum likelihood methods and iteratively changing the assignment of the events; after a change of partition, MLE of parameters are estimated again and the process is iterated until there is no more improvement in the likelihood.

GPS Monitoring of the Scopello (Sicily, Italy) DGSD Phenomenon: Relationships Between Surficial and Deep-Seated Morphodynamics

The Scopello area, which is located along the north-western Tyrrhenian coastal sector of the Sicilian chain (Italy), is widely affected by Deep-seated Gravitational Slope Deformation (DGSD) phenomena, which are mainly the result of a geomorphologic setting marked by the outcropping of an overthrust plan, limiting a brittle fractured carbonate slab, laid onto a ductile marly-clayey substratum. Due to the very advanced stage of the deformation phenomena, a coupled morphodynamic style has established between shallow landslides and DGSD phenomena, affecting the exhumed ductile substratum and the overlaying rigid dismantled slab, respectively. A GPS network was realized for monitoring the Scopello landslide, consisting of 27 vertexes, which were directly cemented either onto rock or debris blocks or concrete structures rooted on the marly–clayey substratum. The geometry of the network and the geodetic technique adopted for the GPS signal acquisition allow the survey for a sub-centimetric precision in the positioning of the vertexes. On February 2005 earth-flows and block/slab-slides movements affected the head sector of the landslide area. The displacements field, which was derived by comparing the results of a pre- (2004) and a post-event (2005) GPS surveys, is here analyzed and discussed. On the basis of the observed displacement, the connection between surficial and deeper ground deformations is confirmed.

Time-frequency filtering for seismic waves clustering

This paper introduces a new technique for clustering seismic events based on processing, in time-frequency domain, the waveforms recorded by seismographs. The detection of clusters of waveforms is performed by a k-means like algorithm which analyzes, at each iteration, the time-frequency content of the signals in order to optimally remove the non discriminant components which should compromise the grouping of waveforms. This step is followed by the allocation and by the computation of the cluster centroids on the basis of the filtered signals. The effectiveness of the method is shown on a real dataset of seismic waveforms.

Seismic Characterization by Inversion of HVSR Data to Improve Geological Modelling

An application of HVSR inversion is presented in order to verify the effectiveness of this technique for purposes of geological reconstruction of the subsoil finalized to studies of seismic microzonation of heavily urbanized areas, where few stratigraphic and geophysical constraints are available and most of the information are derived from the geological maps. In such cases the uncertainty of the results is is enhanced by doubts on the nature of the H/V peaks, not always caused by stratigraphic discontinuities, and to the subjective choices done especially in the step of signal preprocessing. The investigated area (Altavilla Milicia, Sicily) includes the town center and the adjacent coastal plain, characterized mainly by outcrops of marine terraces and continental Pleistocene deposits that do not indicate directly the oldest geological formations, which, however, outcrop in the surrounding areas. However in order to constrain the inversion of the HVSR curves we uses only the detailed knowledge of the geological formations outcropping in the surrounding area and of the tectonic history, together with the typical seismic velocity of the formation outcropping in the area. In spite of this two geological sections have been constructed, showing the main pattern of geological formations and tectonic structures.