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We have applied an attribute-based autopicking algorithm to reflection seismics with the aim of reducing the influence of the user’s subjectivity on the picking results and making the interpretation faster with respect to manual and semiautomated techniques. Our picking procedure uses the cosine of the instantaneous phase to automatically detect and mark as a horizon any recorded event characterized by lateral phase continuity. A patching procedure, which exploits horizon parallelism, can be used to connect consecutive horizons marking the same event but separated by noise-related gaps. The picking process marks all coherent events regardless of their reflection strength; therefore, a large number of independent horizons can be constructed. To facilitate interpretation, horizons marking different phases of the same reflection can be automatically grouped together and specific horizons from each reflection can be selected using different possible methods. In the phase method, the algorithm reconstructs the reflected wavelets by averaging the cosine of the instantaneous phase along each horizon. The resulting wavelets are then locally analyzed and confronted through crosscorrelation, allowing the recognition and selection of specific reflection phases. In case the reflected wavelets cannot be recovered due to shape-altering processing or a low signal-to-noise ratio, the energy method uses the reflection strength to group together subparallel horizons within the same energy package and to select those satisfying either energy or arrival time criteria. These methods can be applied automatically to all the picked horizons or to horizons individually selected by the interpreter for specific analysis. We show examples of application to 2D reflection seismic data sets in complex geologic and stratigraphic conditions, critically reviewing the performance of the whole process.

The analyses of about 800 km of Chirp sub-bottom profilers and 600 km2 of Multibeam data acquired during the 2005 and 2007 surveys of the R/VOGS Explora, and their correlation with one new, and several public, multichannel seismic profiles, allow us to propose a relation between the distribution of gas seepages, fracture systems and deep salt features present in the Central Adriatic Sea. Gas seepage is evident from pockmarks on the seabed and in the shallow sub-bottom, where acoustic chimneys and bright spots have been highlighted and analyzed. The Mid-Adriatic Depression (MAD) is a distinct morphological feature in the Central Adriatic Sea elongated in a NE-SW direction. The area is affected by salt doming of Triassic evaporites which cause the two main alignments of the Mid-Adriatic Ridge as far as the Palagruza High and the Jabuka Ridge. These salt tectonics have existed since, at least, Paleogene times and are still active: they characterize sectors with less resistance to deformation produced by successive regional compressive regimes that have affected the area differently during the different geodynamic phases. Gas- seep features are distributed preferentially above and along the fracture systems produced above and around the salt mounds.

The compactness and continuity of the Apulia carbonate platform, outcropping on the Salento peninsula, contrasts with the structural complexity that developed during the Mesozoic–Miocene in the most southern region, which was later affected by the Neogenic compression of the Calabrian and Hellenic Chains. Although the north-eastern margin of the Apulia carbonate platform has been clearly defined by seismic profiles in the South Adriatic basin, the identification of the southern platform margin and the transition between the Apulia and Pre-Apulia units are more difficult. Our analysis, based on seismic facies interpretation, suggests a complex trend of a reefal margin between the carbonate platform and a newly recognized deep basin, herein called as the South Apulia basin. This margin transversely crosses the Otranto Channel from the Apulian coast, where it outcrops, to the Albanian/Greek coasts, where the platform sinks below the Albanian/Hellenic Chain. The South Apulia basin originated from an extensional phase that was probably active during the Jurassic. Furthermore, this pelagic sequence depicts a trough that was almost partially separating the Apulia from the Pre-Apulia units, these last being widely exposed on the Ionian islands of Greece. The alternation of pelagic and differently evolved carbonate platform domains of the South Adria plate affected the westward migration of the Hellenic Arc quite significantly. The thinner fractured foreland, which is characterized by pelagic sequences, is more suitable for underthrusting the chain, as does the South Apulia basin below the Corfu external front. In contrast, the thicker foreland sectors, which are associated with the carbonate platform, resist flexural subsidence, similar to the Apulia and Pre-Apulia carbonate platform domains. At a certain location, the thick, less-heaving foreland, which is resistant to subsiding, was overcome by compressional stress and thrusted as the Apulia units in the Karaborun peninsula/Sazani isle. In the Paxos island, the carbonate platform has been uplifted by a salt diapir that was triggered by the Hellenic compression. The Cephalonia system cuts the Hellenic Chain with right transpressional tectonics, in response to the different buoyancies of the foreland sectors to the westernmost prolongation of the North Anatolia Fault. While on the northern sector, the front of the chain currently has stopped to the east of the Apulia carbonate platform, on the southern sector, the Ionian oceanic foreland is subducting below the Pre-Apulia units, a previous foreland of the Ionian units. This shifting of the Hellenic front through the Cephalonia system (from the eastern margin of the Apulia carbonate platform to the western margin of the Pre-Apulia zone) has caused an apparent horizontal displacement that is greater than the actual throw of the overriding sequences.

A large seismic dataset has allowed us to regionally study the West Mediterranean Sea with particular focus on the West Sardinia and South Balearic continental margins and adjacent oceanic basins. The main seismic and geological evidences are related to the presence of the Messinian Trilogy in the deep basins and lower slopes, and coeval erosional truncation on the intermediate and upper margins. During the deposition of the upper Messinian sequence (UU), a thin salt layer has been highlighted, thanks to the high resolution of recent profiles. This salt layer, precipitated during the initial re-filling of the Mediterranean Sea, has been correlated to an erosional surface on the lower slope inner the UU and interpreted as the effect of a temporary sea level drop. The underlying salt layer (MU) shows halokinetic deformations in the deep basins which started since the Upper Messinian and developed principally during the Pliocene, sometimes until the Present, as testified by sea bottom piercings. The halokinetics has affected by different intensity, on the base of its original thickness, of the sediments and water load, and of the proximity of the lower slopes, where the sliding of salt toward the deep basin determined compressive stress and enhancing diapirism.

We processed and interpreted a newly acquired geophysical dataset (WS10 project) integrated with vintage seismic profiles to study the evolution of the Sardinian passive margin of the Sardo-Provencal basin. The most prominent features of the area of study are a consequence of the Messinian Salinity Crisis (MSC) which produced a thick salt layer in the deep basin. Complex halokinetic tectonics deformed the overlying Messinian Upper Unit (UU) and the Pliocene–Quaternary (PQ) sediments, sometimes also bending the sea bottom. A thinner autochthonous salt in the UU suggests at least one further low stand during the late MSC. The Messinian Erosional Surface (MES) separates the erosional truncation of the pre-Messinian sedimentary sequence from the overlaying Plio-Pleistocene sequence with a clear angular discordance, which almost completely masks possible earlier erosional events. The MES is present across the middle and upper slopes of the Sardinian margin and can be easily recognized down to the lower slope, where it interfingers with the Messinian evaporites which gradually thicken basinward. We propose a correlation between the main erosional surface of the lower slope and the salt layer recognized in the UU as a consequence of a falling stage during the last part of the MSC. The seismic profiles now available along the West Sardinian margin provide novel and crucial information to correlate the Messinian depositional units in the deep basin with those present in the lower continental slope and with the erosional surface of the middle and upper slopes. Our data and interpretation highlight the main units of the Messinian trilogy and further internal sequences that are probable related to cyclic fluctuations during their deposition.

2010/2011 RIASSUNTO Durante i tre anni di Dottorato di Ricerca sono state studiate ed applicate delle specifiche tecniche di analisi del segnale sismico a riflessione mirate alla identificazione di livelli di idrocarburi all’interno di sedimenti marini Plio-Quaternari. Particolare attenzione è stata inoltre dedicata alla correlazione tra questi reservoir di idrocarburi e le strutture geologiche profonde che ne possono aver favorito l’accumulo. Le metodologie utilizzate sono costituite da: 1) metodi diretti, chiamati Direct Hydrocarbon Indicators, che si basano sull’osservazione delle caratteristiche acustiche di un riflettore legato a gas; 2) metodo AVO-Amplitude Variation with Offset, che si basa sull’analisi delle variazioni delle ampiezze di riflessione in funzione dell’offset, fortemente dipendente dalla presenza di idrocarburi; 3) calcolo degli attributi sismici, grazie al quale è possibile estrarre dall'onda sismica informazioni supplementari non direttamente evidenziate nei profili sismici standard osservabili dal dato originale, che contribuiscono a verificare la presenza di gas. E’ questo il caso analizzato nel Canale d’Otranto: lungo il profilo sismico MS-29 si sono riscontrate evidenze di possibili accumuli di idrocarburi all’interno della sequenza Plio-Quaternaria; gli attributi sismici sono stati applicati al bright spot osservato, sia in fase pre-stack che in fase post-stack; il metodo è risultato fondamentale per individuare le caratteristiche di ampiezza, fase e frequenza che caratterizzano un riflettore legato a idrocarburi. L’analisi AVO, ha consentito di rinvigorire l’ipotesi di un livello saturo a gas. Il bright spot osservato è ubicato in corrispondenza del margine della piattaforma carbonatica Apula. Questa avrebbe costituito l’elemento strutturale all'origine della deformazione dei sedimenti in una blanda anticlinale: in essa sarebbero stati intrappolati gli idrocarburi grazie allo sviluppo di fenomeni di compattazione differenziata tra i sedimenti di copertura di bacino e di piattaforma. Anche in Adriatico Centrale l’analisi di un possibile livello a gas lungo il profilo sismico ADRIA-95 ha fatto supporre l’esistenza di orizzonti saturi a gas all’interno della serie sabbiosa-argillosa Plio Quaternaria. In questo caso è stato effettuato l’analisi del bright spot mediante attributi sismici e AVO, i quali hanno confermato l’ipotesi. Oltretutto, sul dato sismico è stato eseguito il re-processing mirato alla definizione delle unità sedimentarie che caratterizzano la sequenza Post-Messiniana dell’area attraversata dal profilo. Sulla base dei risultati ottenuti è stato proposto l’utilizzo degli attributi per il miglior riconoscimento delle geometrie degli strati, da cui si è potuta affinare l’interpretazione dell’assetto geologico. Si è osservato nel dettaglio che l’evidenza di gas risulta collocata in corrispondenza di strati deformati da spinte profonde legate a domi salini triassici. Oltre a questi casi di studio, sono state effettuate delle analisi di possibili livelli saturi in gas riconosciuti lungo profili sismici ubicati nel Bacino Mediterraneo, in particolare nell'offshore della Sardegna Occidentale, nel Canale di Sicilia e nel Bacino Levantino. AVO e attributi sismici sono serviti a validare l’ipotesi di presenza di idrocarburi nei sedimenti Plio-Quaternari, valutando le correlazioni ai diversi contesti geologici in cui si sono impostati. L’effetto delle procedure è stata anche testata al caso specifico dei gas-idrati, con l’obiettivo di definire se un riflettore individuato lungo un profilo sismico della Penisola Antartica, potesse essere un bottom simulating reflector (BSR); questo rappresenta la tipica manifestazione sismica di gas idrato. Le procedure di AVO sono risultate efficaci anche in presenza di idrocarburi che si trovano in specifiche condizioni di temperatura, pressione e composizione. Le medesime procedure di analisi del segnale sismico sono state quindi applicate a dati che furono acquisiti con diverse sorgenti, modalità di registrazione e geometrie di acquisizione, in funzione dei diversi target da raggiungere. Grazie a ciò è stato possibile fare un confronto tra le varie risposte del metodo a questi “parametri" e giudicare le condizioni del dato originale che consentono di ottenere i risultati più soddisfacenti. L'insieme delle analisi effettuate conferma l'utilità di un approccio sempre più avanzato di analisi AVO e di Attributi Istantanei via via più complessi. Suggerisce inoltre l'opportunità di correlare la presenza di idrocarburi agli elementi geologici presenti, riconoscibili attraverso una accurata interpretazione del dato sismico. ABSTRACT During the three years of the PhD course specific techniques of analysis of seismic reflection data have been studied and applied, aimed at identifying the hydrocarbon saturated levels within Plio-Quaternary marine sediments. Particular attention was also devoted to the correlation between these hydrocarbon reservoirs and some deep geological structures that have favored their accumulation. The used techniques consist of: 1) direct methods, called Direct Hydrocarbon Indicators, which are based on observation of the acoustic characteristics of a gas-related reflector; 2) AVO Amplitude Variation with Offset method, which is based on the analysis of amplitude variations as a function of the offset, strongly influenced by the presence of hydrocarbons; 3) estimation of seismic attributes, from which additional information, not directly evidenced in standard seismic data, can be extracted from the reflected wave, thus contributing to verify gas presence. A first case study has been analyzed in the Otranto Channel: evidences of possible hydrocarbon accumulations along the seismic profile MS-29 have been shown within the Plio-Quaternary sequence. Seismic attributes have been applied to the observed bright spots in both pre-stack and post-stack data; the method has resulted essential to identify the characteristics of amplitude, phase and frequency parameters, that usually contribute to define an hydrocarbon related reflector. AVO analysis has allowed to strengthen the hypothesis of a gas filled layer. The studied bright spots is located over the margin of the Apulia Carbonate platform. This would represent the structural feature at the origin of the sediments deformation in a gentle anticline: here, the hydrocarbons would be trapped due to the development of differential compaction phenomena between the sediments covering the basin and the platform. A possible gas saturated level identified along the seismic profile ADRIA-95 in the Central Adriatic suggested the existence of another reservoir within the Plio-Quaternary sediments. In this case study, the analysis of the bright spots has been achieved with application of seismic attributes and AVO, which have confirmed the hypothesis. Furthermore, re-processing of the seismic data was performed, aimed at the definition of the sedimentary units that characterize the post-Messinian sequence of the area. Based on the obtained results, the attributes analysis were also applied to the improvement of definition of the strata geometries: this allowed the refining of the interpretation. It has been observed, in detail, that the evidence of gas is placed in correspondence of deformed layers by pressures derived from deep Triassic salt domes. In addition to these case studies, some other analysis have been performed after the recognition of possible gas saturated horizons along seismic profiles located in the Mediterranean Basin, especially offshore of West Sardinia, Sicily Channel and in the Levantine Basin. AVO and seismic attributes have been used to validate the hypothesis of the presence of hydrocarbons in Pliocene-Quaternary sediments, also considering the correlations to the different geological contexts in which they are set. Finally, the effect of these procedures was also tested for gas-hydrates, with the aim of defining if a reflector observed along a seismic profile of the Antarctic Peninsula, could be a bottom simulating reflector (BSR), that represents the typical seismic manifestation of gas hydrate. The procedures for AVO are found to be effective even in the typical conditions of temperature, pressure and composition related to the BSRs. The same procedures of seismic signal analysis have been applied to data that were acquired with different sources, recording mode and acquisition geometries, depending on the different target to be reached. Thanks to that, the comparison among the different responses of the methods to these "parameters" has been possible, evaluating the conditions of the original data that could produce the most satisfactory results. All the applied methods confirm the utility of a more and more advanced approach for analysis of AVO and instantaneous attributes increasingly complex. It also suggests the opportunity to correlate the presence of hydrocarbons presence with the geological elements, identified through a rigorous seismic data interpretation. XXIV Ciclo 1982

Using deep seismic reflection data from the Italian lithospheric exploration project CROP in the Central Mediterranean region, a 400-km-long section, composed of three different profiles crossing the Northern Tyrrhenian Sea (CROP M-12A profile), the Northern Apennines (CROP-03) and the Adriatic Sea (CROP M-16) is reconstructed and discussed. New data allow us to outline a seismically consistent tectono-stratigraphic setting for the crust and upper mantle of the Northern Apennines thrust–belt system and its Adriatic foreland. Time–space analysis of the deformation of the investigated chain and identification of existing macrostratigraphic crustal intervals and tectonic units allow a reasonably controlled interpretation of the geodynamic evolution and of the main orogenic stages. Careful seismic reprocessing and application of advanced techniques to key zones of the explored area (such as the Tuscan Archipelago) were determinants in obtaining fundamental information for understanding of the complex lithospheric structures and their evolution. Profile interpretation supports that the Northern Apennine chain is dominated by a compressive thrust system. Crustal extension, assumed by some authors as the dominating tectonic process for the whole Tuscan Apennine area, represents a subordinate geodynamic event of the last stage (Tyrrhenian). In the Early Cretaceous–Late Jurassic, the paleogeographic framework consisted of the Europe and Adria plates separated by the Alpine Tethys Ocean. During the Late Cretaceous–Early Eocene, Adria–Europe convergence (eo-Alpine stage) and subduction beneath the Adria plate closed the Alpine Tethys Sea, with the Tethyan slab being clearly seismically imaged. The first Apenninic geodynamic stage occurred in the Late Oligocene–Early Miocene with the opening of the Balearic Basin, which generated a first “lithospheric root” of the Apenninic chain in the Tuscan Archipelago area. This root is represented by Adria-verging thrust faults that progressively flatten eastward. Upper parts of the west-verging eo-Alpine thrust blocks were truncated by the east-verging thrust faults of the Balearic stage. A deeper seismic reflector, attributed to the top of the asthenosphere, forms a mantle high below the Elba Island. From the Late Miocene to Present, the Corsica basin and western hinterland area were affected by extensional tectonics related to the Tyrrhenian opening, whereas compressional tectonics continued in the eastern hinterland and mostly on the eastward migrating foreland, with development of a second “lithospheric root” constituted by high-angle thrust faults. These faults give rise to a huge basement culmination below the main Apennines watershed. Impressive E-directed gravity-sliding of sedimentary blocks over their sloping basement occur, generating the Umbria–Marche shallow seismicity. Crustal shortening of the Apennines system amounts to 170 km, 14 km of which are due to the eo-Alpine stage, 71 km to the Balearic and 85 km to the Tyrrhenian one. In the frame of Africa–Europe convergence, the Tyrrhenian–Apennines tectonodynamics were mainly conditioned by the Mesozoic paleogeography.

A set of seismic reflection lines had been interpreted on the Southem Tyrrhenian Margin in order to reconstruct the last evolution joined to the young phase of the Maghrebian-Calabrian Belt and the Tyrrhenian opening. Before that a reprocessing of two particularly significant CROP lines was applied, paying special attention to the deep seated reflectors.

BOLLETTINO SOCIETA' GEOLOGICA ITALIANA

The Apennine-Maghrebides foreland offers very different geological settings favouring gas accumulation within permeable horizons, depending by lithology and tectonic structures. In this paper we analyze the different relationships that may exist between the deep structures and the presence of gas in the Plio- Quaternary sediments. Processing techniques (AVO and complex attributes analysis) and geological interpretation of some deep crustal seismic profiles in the Italian offshore, let us to make a qualitative study of gas presences finding their correlations with deep structures.

The observation of a seismic profile in the offshore of South East Italy outlined the presence of a clear reflector, about 10 km long with prominent negative amplitude and gentle anticlinalic shape: probably it represents a bright spot, connected with the presence of a gas level in the Plio-Quaternary sequence. Below this series the Eastern Apulia carbonate platform margin was interpreted; it represents an important feature for the migration and the accumulation of fluids in the covering sediments. There are not boreholes reaching the bright spot, so we decided to re-process the seismic profile in order to better classify the real origin of this reflector. The AVO technique was used for pore fluids identification and the results were integrated with other seismic attributes analysis, such as instantaneous seismic attributes, and with spectral decomposition analysis. The results confirm the possibility that the considered bright spot may represent a gas saturated level, so we followed this horizon along the public seismic lines of the surrounding region. The mapping of the reflector evidenced the presence of a wide possible gas-reservoir developing toward the inner sector of the Apulia platform, so it could be taken into account for a dedicated survey.

The Kvarner area is located in the Northern Adriatic Sea, between the south-east Istrian Swell, the Rijeka coast and the Croatian sea boundary. It includes several islands, representing the outcropping parts of anticlines produced by the compressional/transpressional deformation of the External Dinaric Chain. An extensive 2D seismic dataset, acquired for hydrocarbon exploration and calibrated by wells, allowed us to reconstruct the time structural maps in Kvarner and unravel its regional fault pattern. The Dinaric compressional phase affected the area in the Late Cretaceous, with both thin- and thick-skinned tectonics related to Adriatic Carbonate Platform (AdCP) succession rigidity. Structural highs facing the Kvarner offshore from the Istrian inland continue through the Kvarner and Rijeka bays and outcrop in the islands. These anticlines, originating from the pre-Messinian Dinaric thrust system, were reactivated by the post-Messinian transpression, as testified by flower structures. Several sharp valleys represent two main low structural lineaments, developed between the anticlines and partially incised during the Messinian. They were observed throughout the entire studied area, specifically in the western part of the bays, where the lineament continues through the valleys and penetrates the SW-Istria land. Data show that the Messinian erosional effect and sedimentation patterns were influenced and driven by the morphology of older structures produced by the Dinaric compressional phase.