Active thrust tectonics in western Sicily (southern Italy): the 1968 Belice earthquake sequence

The 1968 Belice earthquake sequence, characterized by six main shocks with 5 < M < 5.4, represents the strongest seismic event recorded in western Sicily in historical times. The epicentral area is located in the Belice Valley, a region lacking any topographic lineament likely to result from a fault with significant offsets of any kind. Instrumental data show that hypocentres of the major shocks are distributed along a roughly N-dipping plane extending from about 36 km to 1 km depth. Fault plane solutions show pure thrusting mechanisms on N-dipping, ENE-trending planes, or oblique slip with a right-lateral component of motion along steep WSW-dipping planes, both as a result of approximate N-S shortening. The observed destruction indicates that isoseismal areas are elongated in an ENE direction. Similarly, the epiccntral distribution of events with M ≥ 4 outlines a roughly elliptical ENE-elongated area located 20 km NW of the Sciacca-Rocca Ficuzza thrust front. This ENE-striking structure, representing the regional morphotectonic feature closest to the epicentral area, consists of two main imbricate fan systems. In the southernmost system, Quaternary deposits (tentatively dated as 1.0–0.7 Myr old) are involved in a large ramp anticline uplifting them to a maximum altitude of 346 m. The occurrence of Holocene lacustrine piggy-back basins on the rear of this structure also indicates late Quaternary activity of the underlying thrust. Seismological, structural and morphotectonic observations suggest that multiple ruptures might have occurred during the 1968 sequence on a blind crustal thrust ramp located beneath the epicentral area. Slip propagated southwards along the shallow ramp-flat system characterizing the thin-skinned foreland fold and thrust belt of southwestern Sicily, being dispersed in flexural folding processes and diffuse strain along this path.     

Intracontinental tectonic melange in Southern Apennines

On the axial zone of the Southern Apennines the major tectonic boundary between the inner platform (Western platform unit) and the pelagic (Lagonegro units) domains is represented by a thick level of highly deformed rock‐assemblage. Structural analysis reveals that this tectonic unit represents an intracontinental melange complex characterized by a block‐in‐matrix fabric that contains blocks from both hangingwall platform and footwall basin units. This unit comprises different sets of structures that, caused by shearing processes, developed at depths ranging from about 8–9 km to the surface. These tectonites represent the product of a crustal shear zone developed at the major boundary between platform‐basin domains of Adria during the thick‐skinned tectonic processes controlling the Southern Apennines mountain building.     

Characterisation of dispersed organic matter from lower Palaeozoic metasedimentary rocks by organic petrography, X-ray diffraction and micro-Raman spectroscopy analyses

Dispersed organic matter (DOM) concentrates of C-rich rocks from areas with different metamorphic characteristics were studied by organic petrography, X-ray diffraction (XRD) and micro-Raman spectroscopy analysis. The concentrates contain several types of DOM with different morphologies, reflectance, X-ray diffraction and micro-Raman characteristics.Four different morphological types were identified in the two studied areas. The different types have different distributions and their reflectance is quite variable in the four types, with a dominance of the highest reflectance values in the DOM from the area with the highest metamorphic grade.XRD analyses of samples from the areas reveal the presence of fine graphite together with non-graphitised carbons.The Raman spectral profiles show the usual bands G (1582 cm⁻¹) and D1 (1350 cm⁻¹), on the first-order Raman spectrum, and S1 (2700 cm⁻¹) on the second-order spectrum. Additional weaker bands, D2 (1620 cm⁻¹), and more rarely D3 (1500 cm⁻¹) and S2 (2900 cm⁻¹), are present. These are characteristic for disordered carbons in the different types of DOM and in both studied areas. However, the Raman parameters (D1/G intensity area ratio and the frequency and width of G band) indicate variable degrees of organisation in all DOM types.The existence of different types of DOM with different degrees of ordering in the same lithologies and metamorphic grade seems to be related to different organic precursors, as they are graphitised to different extents under the same metamorphic conditions. However, in the same lithologies and metamorphic grade, the existence of various stages of graphitisation within the same type of DOM can only be explained though the interaction of DOM with the metamorphic fluids present in the rocks. The ordering graphitisation process may be due to the existence of metamorphic fluid circulation events with a variety of compositions.     

Pillows and hyaloclastites on the island of Ustica (Sicily)

Bulletin of Volcanology -     

Egg production of the copepodAcartia tonsa in Florida Bay during summer. 1. The roles of food environment and diet

The diet and egg production rate ofAcartia tonsa were measured during the thermally stable period between June and October 1995 at four locations in inner and outer Florida Bay. We sought to characterize the role ofA. tonsa in the bay’s pelagic food web, which has been changing since 1987, when the dominant submerged vegetation began shifting from benthic seagrasses to planktonic algae. At Rankin Lake, a shallow basin on the north side of the inner bay, where extensive seagrass mortality and persistent cyanobacteria blooms have occurred, microplankton biomass was relatively high and dominated by heterotrophic protists and dinoflagellates. Nanoplankton at Rankin, Lake, while numerically abundant, usually contributed only a small portion of the biomass. The ingestion rate ofA. tonsa in Florida Bay varied independently of food concentration (i.e., total microplankton biomass), but rates were higher (mean±SD =3.88 ± 0.73 μg C copepod^?1 d^?1) on the north side of the bay than on the south side (0.78 ±0.11 μg C copepod^?1 d^?1). Microzooplankton and dinoflagellates were important dietary constituents, especially in the vicinity of Rankin Lake. Egg production in this region (mean ± SD = 14.2 ± 7.7 eggs female^?1 d^?1) was considerably high than the baywide mean (5.8±0.81 eggs female^?1d^?1), and principal components analysis revealed associations between egg production and both dietary microzooplankton and dinoflagellate biomass. However, although grazing rates were relatively high in the inner bay,A. tonsa removed only 1–6% of the primary production from the water column during the summer and its egg production rates were low relative to typical rates for the species.     

Re-testing the JET-X Flight Module No. 2 at the PANTER facility

The Joint European X-ray Telescope (JET-X) was the core instrument of the Russian Spectrum-X- γ space observatory. It consisted of two identical soft X-ray (0.3–10 keV) telescopes with focusing optical modules having a measured angular resolution of nearly 15 arcsec. Soon after the payload completion, the mission was cancelled and the two optical flight modules (FM) were brought to the Brera Astronomical Observatory where they had been manufactured. After 16 years of storage, we have utilized the JET-X FM2 to test at the PANTER X-ray facility a prototype of a novel X-ray polarimetric telescope, using a Gas Pixel Detector (GPD) with polarimetric capabilities in the focal plane of the FM2. The GPD was developed by a collaboration between INFN-Pisa and INAF-IAPS. In the first phase of the test campaign, we have re-tested the FM2 at PANTER to have an up-to-date characterization in terms of angular resolution and effective area, while in the second part of the test the GPD has been placed in the focal plane of the FM2. In this paper we report the results of the tests of the sole FM2, using an unpolarized X-ray source, comparing the results with the calibration done in 1996.     

A nonlinear programming analysis of unconfined steady-state seepage

A finite element, variable mesh analysis of unconfined steady-state seepage problems is presented based on a nonlinear programming algorithm. It is shown that the minimization of an objective function which merely represents a measure of the total flux leaving or entering the mesh at the free surface nodes (except those that belong also to pervious boundaries) does not permit a unique definition of the free surface geometry. This problem, which is apparently related to the numerical instabilities often met when using variable mesh approaches, can be eliminated by adding to the objective function a term representing a sort of overall ‘regularity’ condition for the shape of the free surface. The modified solution procedure turns out to be stable and able to provide meaningful results for practical problems even when rather coarse meshes are adopted.     

Monitoring Seismo-volcanic and Infrasonic Signals at Volcanoes: Mt. Etna Case Study

Volcanoes generate a broad range of seismo-volcanic and infrasonic signals, whose features and variations are often closely related to volcanic activity. The study of these signals is hence very useful in the monitoring and investigation of volcano dynamics. The analysis of seismo-volcanic and infrasonic signals requires specifically developed techniques due to their unique characteristics, which are generally quite distinct compared with tectonic and volcano-tectonic earthquakes. In this work, we describe analysis methods used to detect and locate seismo-volcanic and infrasonic signals at Mt. Etna. Volcanic tremor sources are located using a method based on spatial seismic amplitude distribution, assuming propagation in a homogeneous medium. The tremor source is found by calculating the goodness of the linear regression fit (R ²) of the log-linearized equation of the seismic amplitude decay with distance. The location method for long-period events is based on the joint computation of semblance and R ² values, and the location method of very long-period events is based on the application of radial semblance. Infrasonic events and tremor are located by semblance–brightness- and semblance-based methods, respectively. The techniques described here can also be applied to other volcanoes and do not require particular network geometries (such as arrays) but rather simple sparse networks. Using the source locations of all the considered signals, we were able to reconstruct the shallow plumbing system (above sea level) during 2011.