The late stage of retreating subduction in the Alpine-Mediterranean region: constraints from travel time seismic tomography

Seismological modelling of the upper mantle of the Africa-Eurasia collision region has given images of its structure which can be used to supplement surface (geologic) information in the attempt to understand past and active tectonic processes. A foremost feature of the region is given by the sinuous Alpine-Mediterranean thrust belt, under which subducted lithosphere is imaged by seismic tomography as seismically fast material (colder than ambient rock). Several arcuate structures are present, combining an external thrust front with an internal extensional basin, originated by slab rollback: the Hellenic arc with the Aegean basin, the Calabrian arc with the Tyrrhenian Sea, the Betic-Rif with the Alboran Sea, and the Carpathians with the Pannonian basin. These systems are at different stages of their life, and all but the Hellenic-Aegean appear close to their terminal phase. Shape and extent of subducted slabs provide constraints on their evolution. Tomographic results, in all but the Hellenic-Aegean system, show a general lack of overall continuity of the subducted bodies, and in many cases support the idea that other processes, such as slab detachment or mantle delamination, contributed to shape the present day tectonics. Although tomographic results have steadily improved image resolution with time, differences between studies may lead to different interpretations. Better understanding of processes active at the late phases of subduction needs a close interplay between tomography, geology, and mantle dynamics calculations

High-resolution imaging of basin-bounding normal faults in the Southern Apennines seismic belt (Italy) by traveltime and frequency-domain full-waveform tomography

We apply a two-step seismic imaging flow by combined first-arrival traveltime and frequency-domain waveform tomographies to dense wide aperture data collected in the Val d’Agri basin (southern Italy). A large wavelength Vp model determined by first-arrival traveltime tomography is used as a starting model for waveform tomography. The multiscale waveform tomography consisting of successive inversion of increasing frequencies allows to progressively reconstruct the short wavelengths of the velocity model, providing valuable information on the Quaternary basin and on range-bounding normal-faulting systems

IL BLOG INGVTERREMOTI: UN NUOVO STRUMENTO DI COMUNICAZIONE PER MIGLIORARE L’INFORMAZIONE SUI TERREMOTI DURANTE LA SEQUENZA SISMICA NELLA PIANURA PADANA

Durante una sequenza sismica è estremamente importante che la popolazione colpita dai terremoti abbia un’informazione tempestiva e continua sull’attività sismica in corso. Si genera un grande bisogno di informazione e di conoscenza da parte dei cittadini sulle caratteristiche del fenomeno fisico, sulle sue cause e i suoi effetti, sui risultati degli studi preliminari, su quanto si può fare per evitare situazioni di rischio, sulle iniziative messe in campo per gestire e superare l’emergenza. Questo bisogno è particolarmente rilevante in occasione di sequenze sismiche di lunga durata e che hanno un certo livello di complessità. Anche in occasione della sequenza simica attivatasi con il terremoto del 20 maggio 2012 (ore 02:03 UTC, ML 5.9) nella Pianura Padana, l’esigenza di avere informazioni si è resa evidente. Ne è testimonianza l’enorme numero di visitatori e contatti ricevuti all’Home Page dell’INGV (http://www.ingv.it) con circa 610.000 visitatori il 20 maggio e circa 930.000 il 29 maggio, ma anche le centinaia di telefonate ed e-mail arrivati all’Istituto. Altra testimonianza la mole di tweet (interazione degli utenti con il canale INGVterremoti su Twitter) relativi al terremoto che circolavano già dagli istanti successivi alla scossa del 20 maggio e successivamente per tutta la sequenza. Anche durante la sequenza del 2009 a L’Aquila si era verificata una situazione simile. Infatti, nei giorni successivi all’evento del 6 aprile 2009, grazie anche alla presenza del Centro Operativo Emergenza Sismica a L’Aquila (Moretti et al., 2011), abbiamo capito che la richiesta, da parte delle autorità pubbliche e locali e dei cittadini, di informazioni complete e autorevoli, era più elevata di quanto si pensasse. In particolare, nelle situazioni di emergenza del 2009 e ancor più del 2012, oltre alle informazioni classiche sui siti web, molte persone hanno cercato informazioni e aggiornamenti sui siti dei social media grazie anche alla diffusione di nuovi dispositivi tecnologici quali cellulari, smartphone, tablet e notebook ultra-portatili. Per rispondere a tale esigenza, pochi giorni dopo i primi eventi di maggio 2012 in Emilia Romagna (20 maggio 2012 ore 02:03 UTC, ML 5.9, 29 maggio 2012 ore 07:00, ML 5.8; ore 10:55 ML 5.3; 11:00 ML 5.2) si è deciso di realizzare e aprire un nuovo canale informativo chiamato INGVterremoti, un blog, (http://ingvterremoti.wordpress.com), attraverso il quale sono stati pubblicati tantissimi aggiornamenti e approfondimenti scientifici sulla sequenza sismica in corso, contemporaneamente alle informazioni fornite in tempo quasi reale attraverso i siti web istituzionali dell’INGV. Scopo principale del blog è stato quello di raccogliere in unico ambiente web tutta l’informazione prodotta dai vari canali e siti web dell’INGV, sia orientati al pubblico che agli addetti ai lavori. Il blog ha quindi aggregato il più possibile i vari aggiornamenti dai siti istituzionali come l’Home Page INGV (www.ingv.it), la pagina del Centro Nazionale Terremoti (http://cnt.rm.ingv.it) e il database Iside (http://iside.rm.ingv.it) che forniscono informazioni sui terremoti recenti e notizie più specifiche e dettagliate sui terremoti storici (http://cpti11.mi.ingv.it) e sulla pericolosità sismica (http://zonesismiche.mi.ingv.it). Inoltre il blog ha affiancato ai siti tradizionali anche l’informazione proveniente dai canali sviluppati sul WEB 2.0 che negli ultimi due anni sono stati realizzati dall’INGV con la denominazione comune di INGVterremoti. Tra il 2009 e il 2011, l’INGV infatti ha iniziato a testare diversi social media, come YouTube, Twitter, Facebook e sviluppato un’applicazione per iPhone, per rilasciare informazioni sui terremoti in tempo quasi reale ed inserendo approfondimenti sulla pericolosità sismica e in generale sui terremoti. I social media hanno dimostrato di essere molto importanti per le informazioni in caso di crisi (Bruns et al, 2012; Earle et al., 2011), infatti per tutti questi nuovi canali di comunicazione, abbiamo osservato aumenti significativi del numero di visualizzazioni e di download in corrispondenza di eventi sismici risentiti dalla popolazione (Amato et al., 2012; Nostro et al., 2012). Sia i siti che i canali raggiungono centinaia di migliaia o milioni di contatti nel caso di forti terremoti: le persone possono trovare molte notizie specifiche sui singoli terremoti, sulla storia sismica, ma durante questa emergenza è apparso evidente come non fosse ancora disponibile un canale di informazione dove la gente potesse trovare aggiornamenti in tempi rapidi e spiegazioni sulle attività in corso, con un linguaggio semplice ed efficace. Fornire notizie tempestive è particolarmente importante nel caso di sequenze sismiche che durano diverse settimane e sono caratterizzati da diverse scosse con magnitudo maggiore di 5.0, come nel caso dei terremoti della Pianura Padana. Contemporaneamente alla gestione dell’emergenza, abbiamo lavorato per fornire un’informazione scientificamente valida, costantemente aggiornata relativa a tutta l’area interessata dalla sequenza, anche al fine di contrastare la cattiva informazione e combattere le voci, le dicerie, i rumors

The INGVterremoti blog: a new communication tool to improve earthquake information during the Po Plain seismic sequence

The INGV sites that deliver information in quasi-realtime are well known. People often connect to the INGV home page (www.ingv.it), to the Centro Nazionale Terremoti (National Earthquake Centre) page (http://cnt.rm.ingv.it) and to the Italian Seismic Instrumental and Parametric (ISIDe) database (http://iside.rm.ingv.it) to obtain information about recent earthquakes. Moreover, people look for more specific and detailed information on the historical earthquake catalog (http://cpti11.mi.ingv.it), the seismic hazard web pages (http://zonesismiche.mi.ingv.it), the INGVterremoti YouTube channel (http://youtube.com/ ingvterremoti), the web-based macroseismic survey (http:// www.haisentitoilterremoto.it/) and others. For all of these sites, some of which are reached by hundreds of thousands, or even millions people in cases of strong earthquakes, people can find a lot of specific information on individual earthquakes, on the seismic history, and so on. However, a place where people could find updates and explanations on the ongoing activity was not available. When the Po Plain seismic sequence started on May 20, 2012, through the enormous number of hits on the website of the INGV, to the many phone calls, emails and tweets, we soon realized that the request for information was huge. There were 0.61 and 0.93 million visits and 12 million and 26 million accesses on May 20 and 29, 2012, respectively. This was not a surprise, of course, because also during the L'Aquila 2009 sequence there was a similar situation. Indeed, in the months after the April 6, 2009, event, also through the installation of the Centro Operativo Emergenza Sismica (Seismic Emergency Operational Centre) in L'Aquila [Moretti et al. 2011], we understood that the request from the public and local authorities for complete and authoritative information was higher than had been previously thought. In particular, in the 2009 emergency, and even more so in the 2012 emergency, as well as classical information on web sites, many people looked for information and updates on social network sites. For this reason, between 2009 and 2011, the INGV started to test different social media, such as YouTube, Twitter, Facebook, and developed an application for the iPhone, to release earthquake information. Social media have proven to be very important for information sharing during crises [Earle et al. 2011, Bruns et al. 2012]. For all of these media, we observed relevant increases in the number of views and downloads corresponding to the important seismic events, when the attention was high [Amato et al. 2012, Nostro et al. 2012]. For this reason, in the days after the May 20, 2012, mainshock, we decided to open a new blog to provide quick updates and in-depth scientific information, such as articles on the ongoing seismic activity. Providing timely information is particularly important when seismic sequences last for several weeks and are characterized by several M >5 events, as was the case of the Po Plain earthquakes. At the same time, we worked to provide fast, but scientifically sound, information, which was constantly updated and distributed throughout the territory, also to counter the bad information, and to fight rumors

Slab disruption, mantle circulation, and the opening of the Tyrrhenian basins

Plate tectonic history, geological, geochemical (element and isotope ratios), and seismological (P-wave tomography and SKS splitting) data are combined with laboratory modeling to present a three-dimensional reconstruction of the subduction history of the central Mediterranean subduction. We fi nd that the dynamic evolution of the Calabrian slab is characterized by a strong episodicity revealed also by the discrete opening of the Tyrrhenian Sea. The Calabrian slab has been progressively disrupted by means of mechanical and thermal erosion leading to the formation of large windows, both in the southern Tyrrhenian Sea and in the southern Apennines. Windows at lateral slab edges have caused a dramatic reorganization of mantle convection, permitting infl ow of subslab mantle material and causing a complicated pattern of magmatism in the Tyrrhenian region, with coexisting K- and Na-alkaline igneous rocks. Rapid, intermittent avalanches of large amounts of lithospheric material at slab edges progressively reduced the lateral length of the Calabrian slab to a narrow (200 km) slab plunging down into the mantle and enhancing the end of the subduction process

Recent tectonic reorganization of the Nubia-Eurasia convergent 2 boundary heading for the closure of the western Mediterranean

: In the western Mediterranean area, after a long period (late Paleogene-Neogene) of Nubian northward subduction beneath Eurasia, subduction is almost ceased as well as convergence accommodation in the subduction zone. With the progression of Nubia-Eurasia convergence, a tectonic reorganization is therefore necessary to accommodate future contraction. Previously-published tectonic, seismological, geodetic, tomographic, and seismic reflection data (integrated by some new GPS velocity data) are reviewed to understand the reorganization of the convergent boundary in the western Mediterranean. Between northern Morocco, to the west, and northern Sicily, to the east, contractional deformation has shifted from the former subduction zone to the margins of the two backarc oceanic basins (Algerian-Liguro-Provençal and Tyrrhenian basins) and it is now active in the south-Tyrrhenian (northern Sicily), northern Liguro-Provençal, Algerian, and Alboran (partly) margins. Compression and basin inversion has propagated in a scissor-like manner from the Alboran (c. 8 Ma) to the Tyrrhenian (younger than c. 2 Ma) basins following a similar propagation of the subduction cessation and slab breakoff, i.e., older to the west and younger to the east. It follows that basin inversion is rather advanced in the Algerian margin, where a new southward subduction seems to be in its very infant stage, while it has still to properly start in the Tyrrhenian margin, where contraction has resumed at the rear of the fold-thrust belt and may soon invert the Marsili oceanic basin. GPS-derived strain rates higher in the Tyrrhenian margin than in the Algerian boundary suggest that this latter manner of contraction accommodation (contraction resumption at the rear of the orogenic wedge) is more efficient than subduction inception and basin inversion along newly-generated reverse faults (Algeria), but the differential strain rates may also be explained with the heterogeneous distribution of GPS stations. Part of the contractional deformation may have shifted toward the north in the Liguro-Provençal basin possibly because of its weak rheological properties compared with the area between Tunisia and Sardinia, where no oceanic crust occurs and seismic deformation is absent or limited compared with the adjacent strands of the Nubia-Eurasia boundary. The tectonic reorganization of the Nubia-Eurasia boundary in the study area is still strongly controlled by the inherited tectonic fabric and rheological attributes, which are both discontinuous and non-cylindrical along the boundary. These features prevent, at present, the development of long and continuous thrust faults. In an extreme and approximate synthesis, the evolution of the western Mediterranean is inferred as being similar to a Wilson Cycle in the following main steps: (1) northward Nubian subduction with Mediterranean backarc extension (since ~35 Ma); (2) progressive cessation, from west to east, of Nubian main subduction (since ~15 Ma); (3) progressive compression, from west to east, in the former backarc domain and consequent basin inversion (since ~8-10 Ma); (4) possible future subduction of former backarc basins

Structural control on the Tohoku earthquake rupture process investigated by 3D FEM, tsunami and geodetic data

The 2011 Tohoku earthquake (Mw = 9.1) highlighted previously unobserved features for megathrust events, such as the large slip in a relatively limited area and the shallow rupture propagation. We use a Finite Element Model (FEM), taking into account the 3D geometrical and structural complexities up to the trench zone, and perform a joint inversion of tsunami and geodetic data to retrieve the earthquake slip distribution. We obtain a close spatial correlation between the main deep slip patch and the local seismic velocity anomalies, and large shallow slip extending also to the North coherently with a seismically observed low-frequency radiation. These observations suggest that the friction controlled the rupture, initially confining the deeper rupture and then driving its propagation up to the trench, where it spreads laterally. These findings are relevant to earthquake and tsunami hazard assessment because they may help to detect regions likely prone to rupture along the megathrust, and to constrain the probability of high slip near the trench. Our estimate of ~40 m slip value around the JFAST (Japan Trench Fast Drilling Project) drilling zone contributes to constrain the dynamic shear stress and friction coefficient of the fault obtained by temperature measurements to ~0.68 MPa and ~0.10, respectively

La rete sismica AlpArray e il contributo dell'INGV

Il progetto AlpArray (PI E. Kissling, Seismology and Geodynamics ETH) è un’iniziativa europea di collaborazione interdisciplinare sismologica e geodinamica, il cui obiettivo principale è quello di migliorare la comprensione della struttura profonda e della geodinamica delle Alpi (la catena montuosa più studiata al mondo) tramite l’acquisizione, l’analisi e l’interpretazione di dati sismologici di alta qualità. Per ottenere delle immagini di estremo dettaglio della crosta e del mantello, AlpArray propone la realizzazione di una rete sismica a maglia il più possibile omogenea (massima distanza inter- stazione 52 km, backbone network), tramite la condivisione dei dati delle reti permanenti esistenti e l’installazione, da parte di ciascun paese partecipante, di numerose stazioni sismiche temporanee a larga banda (BB). Il progetto prevede l'installazione di circa 250 stazioni sismiche in tutta Europa, in particolare in Italia, Francia, Svizzera, Germania, Austria, Croazia, Repubblica Ceca, Bosnia, Ungheria, Slovenia e Polonia. I dati confluiranno all’interno dell’archivio europeo denominato European Integrated Data Archive (EIDA). Considerata l’estensione geografica dell’area, i partecipanti combineranno le infrastrutture esistenti per l’acquisizione dei dati, il loro trattamento, l’applicazione delle tecniche più avanzate di imaging e l’interpretazione e modellazione dei risultati, in uno sforzo transnazionale ad una scala mai realizzata prima in Europa. Si tratta quindi di un’occasione fondamentale per lo scambio di competenze tecniche e scientifiche all’avanguardia. L’INGV, oltre a condividere i dati delle proprie stazioni permanenti nell’area di interesse, si occupa della installazione e della manutenzione sul territorio italiano di 20 nuove stazioni-BB temporanee i cui dati verranno trasmessi in tempo reale (partecipando così alla realizzazione del backbone) e coadiuva l’ETH nella ricerca dei siti italiani per altrettante stazioni svizzere e nella loro manutenzione ordinaria. L’acquisizione di una mole notevole di nuovi dati permetterà di raffinare le conoscenze sulla struttura e la composizione della litosfera e del mantello al di sotto dell’area alpina: Queste conoscenze sono anche utili ai fini della modellazione geodinamica. Il potenziamento del monitoraggio sismico aiuterà ad individuare e studiare in maggior dettaglio le aree sismogenetiche della regione alpina

AlpArray-Italy: Site description and noise characterization

Within the framework of the European joint research initiative AlpArray (http://www.alparray.ethz.ch/), we de- ployed overall 20 seismic broad-band stations in Northern Italy and on two islands in the Tyrrhenian Sea (Capraia and Montecristo) during Fall-Winter 2015. All the stations, connected in real-time, were installed at sites selected according to the AlpArray Seismic Network plan: 16 temporary stations running for two to three years and 4 new permanent stations in sites already occupied by accelerometers of the INGV national network. Most temporary stations are equipped with REF TEK 130S digitizers and Nanometrics Trillium Compact 120s sensors (a couple have Nanometrics Trillium 120P and one Streckeisen STS2). For each site we describe the settings and discuss the noise levels, the site effects and the preliminary sensitivity analysis.PublishedVienna, Austria1T. Geodinamica e interno della Terraope

The Slab Puzzle of the Alpine‐Mediterranean Region: Insights from a new, High‐Resolution, Shear‐Wave Velocity Model of the Upper Mantle

Mediterranean tectonics since the Lower Cretaceous has been characterized by a multi‐phase subduction and collision history with temporally and spatially‐variable, small‐scale plate configurations. A new shear‐wave velocity model of the Mediterranean upper mantle (MeRE2020), constrained by a very large set of over 200,000 broadband (8‐350 s), inter‐station, Rayleigh‐wave, phase‐velocity curves, illuminates the complex structure and fragmentation of the subducting slabs. Phase‐velocity maps computed using these measurements were inverted for depth‐dependent, shear‐wave velocities using a stochastic particle‐swarm‐optimization algorithm (PSO). The resulting three‐dimensional (3‐D) model makes possible an inventory of slab segments across the Mediterranean. Fourteen slab segments of 200‐800 km length along‐strike are identified. We distinguish three categories of subducted slabs: attached slabs reaching down to the bottom of the model; shallow slabs of shorter length in down‐dip direction, terminating shallower than 300 km depth; and detached slab segments. The location of slab segments are consistent with and validated by the intermediate‐depth seismicity, where it is present. The new high‐resolution tomography demonstrates the intricate relationships between slab fragmentation and the evolution of the relatively small and highly curved subduction zones and collisional orogens characteristic of the Mediterranean realm