Evidenze della rapida variazione di profondità della Moho, in corrispondenza dell'area di Città di Castello (Appennino Settentrionale), dall'analisi di funzioni ricevitore

In questo studio è stata sfruttata l’opportunità di poter analizzare dati provenienti da una densa rete sismica locale temporanea costituita da 30 stazioni a tre componenti, installata nell’ambito di un progetto del Gruppo Nazionale per la Difesa dei Terremoti (GNDT) nel periodo compreso fra l’Ottobre 2000-Maggio 2001, in un’area che si estende per circa 2800 km2 a circa 43° N in Appennino Settentrionale (Piccinini et al., 2003), al fine di ottenere un dettagliato andamento della topografia della Moho, in una zona così complessa, attraverso un’analisi delle Funzioni Ricevitore (Langston, 1979), definendo la struttura di velocità delle onde di taglio (S) al di sotto di ciascuna delle 28 stazioni sismiche. Sono stati analizzati circa 400 eventi telesismici registrati da 28 stazioni con valori di magnitudo M>5 e distanza epicentrale Δ compresi fra 25°-100°. Per il calcolo delle RFs è stato utilizzato il metodo sviluppato da Di Bona (1998), tale metodo consente di ottenere una stima della varianza, permettendo l’utilizzo di forme d’onda generate da eventi di bassa magnitudo (aventi valori di varianza accettabili), con un conseguente ampliamento del data-set. Modellando ampiezze e tempi di arrivo delle fasi Ps in funzione dell’azimuth di provenienza (BAZ) e della relativa distanza epicentrale (Δ), si possono ricostruire le geometrie delle superfici di discontinuità al di sotto delle stazioni sismiche. La fase di modellazione è stata condotta attraverso l’applicazione dell’algoritmo di inversione “neighbourhood” di Sambridge (1999) mediante un approccio monodimensionale. Questo metodo consente di campionare in maniera estensiva lo spazio dei parametri (profondità delle varie interfacce e valori di velocità negli strati compresi fra le interfacce), concentrando la ricerca in quelle regioni dello spazio multiparametrico dove i modelli di velocità trovati hanno un miglior misfit rispetto al dato (la RF) reale. Tale fase di modellazione ha consentito di ricostruire i modelli di velocità delle onde S (Vs) al di sotto di ciascuna stazione. L’analisi comparata dei modelli di velocità delle onde S (Vs) così ottenuti, per ogni singola stazione, mette in luce la natura fortemente eterogenea della porzione più superficiale della crosta dell’area in studio. Nonostante la complessità delle RFs calcolate che si riflette sulla eterogeneità della porzione più superficiale dei profili di Vs ottenuti, è stata individuata con buona continuità l’andamento di una superficie di discontinuità sismica da noi interpretata come transizione crosta-mantello superiore o Moho

Crustal structure and Moho depth profile crossing the central Apennines (Italy) along the N42 degree parallel.

We present results from a teleseismic receiver-function study of the crustal structure in the central Apennines (Italy). Data from fifteen stations deployed in a linear transect running along the N42 degree parallel were used for the analysis. A total number of 364 receiver functions were analyzed. The crustal structure has been investigated using the neighborhood algorithm inversion scheme proposed by Sambridge [1999a], obtaining crustal thicknesses, bulk crustal VP/VS ratio and velocity-depth models. In each inversion, the degree of constraint of the different parameters has been appraised by the Bayesian inference algorithm by Sambridge [1999b]. The study region is characterized by crustal complexities and intense tectonic activity (recent volcanism, orogenesis, active extensional processes), and these complexities are reflected in the receiver functions. However, the relatively close spacing among the seismometers (about 20 km) helped us in the reconstruction of the crustal structure and Moho geometry along the transect. Crossing the Apennines from west to east, the Moho depth varies by more than 20 km, going from a relatively shallow depth (around 20 km) on the Tyrrhenian side, deepening down to about 45 km depth beneath the external front of the Apenninic orogen, and rising up again to about 30 km depth in correspondence of the Adriatic foreland. Despite the strong variability of the crustal thickness, the average crustal VS values show little variation along the transect, fluctuating around 3 km/s. The average VP values obtained from the VS and VP /VS are generally lower than 6 km/s

Heterogeneities along the 2009 L’Aquila normal fault inferred by the b-value distribution

In this study we map the distribution of the b-value of the Gutenberg-Richter law—as well as complementary seismicity parameters—along the fault responsible for the 2009 MW 6.1 L'Aquila earthquake. We perform the calculations for two independent aftershock sub-catalogs, before and after a stable magnitude of completeness is reached. We find a substantial spatial variability of the b-values, which range from 0.6 to 1.3 over the fault plane. The comparison between the spatial distribution of the b-values and the main-shock slip pattern shows that the largest slip occurs in normal-to-high b-values portion of the fault plane, while low b-value is observed close to the main-shock nucleation. No substantial differences are found in the b-value computed before and after the main-shock struck in the small region of the fault plane populated by foreshocks

Seismic activity in the Pollino region (Basilicata-Calabria border)

The Pollino region and the whole Calabria-Lucania border are known for the absence of destructive (M>6) historical earthquakes. This lack of historical seismicity is noticeable in the analysis of Southern Apennines and Calabria earthquake history (Rovida et al., 2011). At the same time, paleoseismological studies found evidence for significant active faulting (Cinti et al., 1997; Michetti et al., 1997) pointing to the Pollino area as a seismic gap. Instrumental seismicity in the region is characterized by the occurrence of seismic sequences, one of the most significant in the last decades is the Mercure seismic sequence, Mw 5.6 in September 1998 (Brozzetti et al., 2008). For this reason, the sequence started in 2010 raised a big concern in the population and local authorities. INGV is following the evolution of the sequence since its beginning, in March 2010, increasing the seismic monitoring and planning several activities and projects. The area was proposed by INGV to DPC (Dipartimento di Protezione Civile nazionale) for inclusion in the projects to be carried out in the present INGV-DPC agreement. This project has just started and will try to provide better constraints to the active tectonics and fault identification of the region. In this paper we describe what INGV is doing to understand better the tectonics of the region using microseismicity, and try to offer some cue to the discussion about the seismogenic faults in the area.Published5-92T. Tettonica attivaN/A or not JCRope

Investigating the Origin of Seismic Swarms

According to the U.S. Geological Survey’s Earthquake Hazards Program, a seismic swarm is “a localized surge of earth- quakes, with no one shock being conspicuously larger than all other shocks of the swarm. They might occur in a variety of geologic environments and are not known to be indicative of any change in the long- term seismic risk of the region in which they occur” (http://vulcan.wr.usgs.gov/Glossary/ Seismicitydescription_earthquakes.html). The definition reveals how little is actually known about seismic swarms. For example, could certain seismic settings be more prone to swarms? Could a fault zone prone to large energetic earthquakes release part of its stress through seismic swarms? Do swarms keep hazards in balance, or could their onset increase hazards? To gain insight into the nature of seismic swarms in nonvolcanic areas and to better understand their influence on seismic hazards, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the German Research Centre for Geoscience (GFZ) began a combined research project within the framework of the Network of European Research Infrastructures for Earthquake Risk Assessment and Mitigation (NERA; see http:// www.nera-eu.org/). The project focused on monitoring swarm activity occurring in the Pollino range in Southern Apennines, Italy.Published361-3721.1. TTC - Monitoraggio sismico del territorio nazionaleN/A or not JCRrestricte

Natural bovine coronavirus infection in a calf persistently infected with bovine viral diarrhea virus: Viral shedding, immunological features and s gene variations

The evolution of a bovine coronavirus (BCoV) natural infection in a calf persistently infected with bovine viral diarrhea virus (BVDV) was described. The infected calf developed intermittent nasal discharge, diarrhea and hyperthermia. The total number of leukocytes/mL and the absolute differential number of neutrophils and lymphocytes resulted within the normal range, but monocytes increased at T28 (time 28 post‐infection). Flow‐cytometry analysis evidenced that the CD8+ subpopulation increased at T7 and between T28 and T35. BCoV shedding in nasal discharges and feces was detected up to three weeks post infection and high antibody titers persisted up to T56. The RNA BCoV load increased until T14, contrary to what was observed in a previous study where the fecal excretion of BCoV was significantly lower in the co‐infected (BCoV/BVDV) calves than in the calves infected with BCoV only. We can suppose that BVDV may have modulated the BCoV infection exacerbating the long viral excretion, as well as favoring the onset of mutations in the genome of BCoV detected in fecal samples at T21. An extensive study was performed to verify if the selective pressure in the S gene could be a natural mode of variation of BCoV, providing data for the identification of new epidemic strains, genotypes or recombinant betacoronaviruses

SEISMIC SWARM vs MAINSHOCK‐AFTERSHOCKS SEQUENCE: REFINED HYPOCENTERS LOCATIONS AT THE APENNINES‐CALABRIAN ARC BOUNDARY (SOUTHERN ITALY)

In the last years the Apennines-Calabrian arc boundary has been affected by intense seismicity concentrated in the Pollino mountain region. The Pollino is located at the northernmost edge of the Calabrian Arc, the last remnant of subduction along the Africa- Eurasian boundary. The area is subject to Northeast- Southwest extension, which results in a complex system of normal faults striking Northwest-Southeast, nearly parallel to the Apenninic mountain range. The Italian Seismic Network between 2010 and 2014 detected more than 5500 earthquakes in the area (Italian Seismological Instrumental and Parametric Data- Base; http:// iside .rm .ingv .it). In 2010 and 2011 the earthquake rate has been variable, with increasing and decreasing phases and maximum magnitudes below M=4. On May 28th 2012, a shallow event with local magnitude of 4.3 struck, about 5 kilometers east of the previous swarm. The seismic activity remained concentrated in the M=4.3 source region until early August. At that time seismicity jumped back westward to the previous area, with several earthquakes of magnitude larger than 3, culminating with a M=5.0 earthquake on 25 October 2012. The seismic rate remained high for some months, but aftershock magnitudes did not exceed magnitude 3.7. The seismic rate then suddenly decreased at the beginning of 2013 and stayed quite low for the rest of the year up to the beginning of 2014. During these years several temporary seismic stations were deployed in the area, improving the detecting threshold of the Italian Seismic Network and giving us the opportunity to refine the location of the earthquakes hypocenters. A combined dataset, including three-component seismic waveforms recorded by both permanent and temporary stations, has been analyzed in order to obtain an appropriate 1-D and 3D velocity model for earthquake location in the study area. Here we describe the main seismological characteristics of this seismic sequence and, relying on refined earthquakes location, we make inferences on the geometry of the fault system responsible for the two strongest shocks. Swarm activity seems to occur on a diffuse crustal volume more than on fault planes. To yield a better understanding of the origin of the ongoing seismic activity in the Pollino area, using thousand of seismograms, we analyze vp and vp/vs models and anisotropic parameters in the crust. The main goal of this study is to increase the understanding of the physical mechanisms behind the seismic swarm and its influence on the seismic hazard of the Apennines- Calabrian arc boundary region.EAEE - ESCPublishedIstanbul - August 24-29 20142T. Tettonica attivaope

The 2012 Emilia seismic sequence (Northern Italy): Imaging the thrust fault system by accurate aftershock location

Starting from late May 2012, the Emilia region (Northern Italy) was severely shaken by an intense seismic sequence, originated from a ML 5.9 earthquake on May 20th, at a hypocentral depth of 6.3 km, with thrusttype focal mechanism. In the following days, the seismic rate remained high, counting 50 ML ≥ 2.0 earthquakes a day, on average. Seismicity spreads along a 30 km east–west elongated area, in the Po river alluvial plain, in the nearby of the cities Ferrara and Modena. Nine days after the first shock, another destructive thrust-type earthquake (ML 5.8) hit the area to the west, causing further damage and fatalities. Aftershocks following this second destructive event extended along the same east-westerly trend for further 20 km to the west, thus illuminating an area of about 50 km in length, on thewhole. After the first shock struck, on May 20th, a dense network of temporary seismic stations, in addition to the permanent ones, was deployed in the meizoseismal area, leading to a sensible improvement of the earthquake monitoring capability there. A combined dataset, including threecomponent seismic waveforms recorded by both permanent and temporary stations, has been analyzed in order to obtain an appropriate 1-D velocity model for earthquake location in the study area. Here we describe the main seismological characteristics of this seismic sequence and, relying on refined earthquakes location, we make inferences on the geometry of the thrust system responsible for the two strongest shocks

The 2012 Emilia seismic sequence (Northern Italy): Imaging the thrust fault system by accurate aftershock location

Starting from late May 2012, the Emilia region (Northern Italy) was severely shaken by an intense seismic sequence, originated from a ML 5.9 earthquake on May 20th, at a hypocentral depth of 6.3 km, with thrusttype focal mechanism. In the following days, the seismic rate remained high, counting 50 ML ≥ 2.0 earthquakes a day, on average. Seismicity spreads along a 30 km east–west elongated area, in the Po river alluvial plain, in the nearby of the cities Ferrara and Modena. Nine days after the first shock, another destructive thrust-type earthquake (ML 5.8) hit the area to the west, causing further damage and fatalities. Aftershocks following this second destructive event extended along the same east-westerly trend for further 20 km to the west, thus illuminating an area of about 50 km in length, on thewhole. After the first shock struck, on May 20th, a dense network of temporary seismic stations, in addition to the permanent ones, was deployed in the meizoseismal area, leading to a sensible improvement of the earthquake monitoring capability there. A combined dataset, including threecomponent seismic waveforms recorded by both permanent and temporary stations, has been analyzed in order to obtain an appropriate 1-D velocity model for earthquake location in the study area. Here we describe the main seismological characteristics of this seismic sequence and, relying on refined earthquakes location, we make inferences on the geometry of the thrust system responsible for the two strongest shocks.Published44-552T. Tettonica attivaJCR Journalope

The subduction structure of the Northern Apennines: results from the RETREAT seismic deployment

The project Retreating-trench, extension, and accretion tectonics, RETREAT, is a multidisciplinary study of the Northern Apennines (earth.geology.yale.edu/RETREAT/), funded by the United States National Science Foundation (NSF) in collaboration with the Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Grant Agency of the Czech Academy of Sciences (GAAV). The main goal of RETREAT is to develop a self-consistent dynamic model of syn-convergent extension, using the Northern Apennines as a natural laboratory. In the context of this project a passive seismological experiment was deployed in the fall of 2003 for a period of three years. RETREAT seismologists aim to develop a comprehensive understanding of the deep structure beneath the Northern Apennines, with particular attention on inferring likely patterns of mantle flow. Specific objectives of the project are the crustal and lithospheric thicknesses, the location and geometry of the Adriatic slab, and the distribution of seismic anisotropy laterally and vertically in the lithosphere and asthenosphere. The project is collecting teleseismic and regional earthquake data for 3 years. This contribution describes the RETREAT seismic deployment and reports on key results from the first year of the deployment. We confirm some prior findings regarding the seismic structure of Central Italy, but our observations also highlight the complexity of the Northern Apennines subduction system