Tectonics related to the North Anatolian Fault in the Sea of Marmara: evidence from seismic reflection data

The North Anatolian Fault crosses the Sea of Marmara from east to west. Tectonic features of the Sea of Marmara were studied using multi-channel deep seismic reflection data. The northern branch of the North Anatolian Fault is active as a right lateral strike-slip fault zone and indicates both negative and positive flower structures. The North Anatolian Fault splays into two faults at the Sea of Marmara as a northern branch and north segment of the southern branch. The northern branch named the Main Marmara Fault extends in a complicated manner from the north of the Kapıdağı Peninsula to westward in the Sea of Marmara. The north segment of southern branch extends between the Gemlik and Bandırma gulfs in the south of the Sea of Marmara. In addition, uplift areas arose by compression and a push-up style in between the Kapıdağı Peninsula and the Main Marmara Fault. The North Anatolian Fault is characterized by a negative flower structure in basins and push-up style in uplift areas in the Sea of Marmara. An uplift area arose between the north segment of the southern branch and the northern branch of the North Anatolian Fault. The north segment of the southern branch of the North Anatolian Fault is a strike-slip fault and displays a pull-apart style in the seismic reflection data.     

Quaternary evolution of the Gulf of İzmit (NW Turkey): a sedimentary basin under control of the North Anatolian Fault Zone

The Quaternary evolution of the Gulf of İzmit, situated on the tectonically active North Anatolian Fault Zone (NAFZ), was investigated using seismic reflection, paleontologic, and sediment textural data. On the basis of seismic stratigraphic and sedimentologic-paleontologic interpretations, four depositional units were distinguished within the Plio-Quaternary sequence of the Gulf of İzmit. According to these data, Plio-Quaternary deposits supplied from the northern terrestrial area started to accumulate during a progradational phase, in a south-facing half-graben. A coarse-grained sedimentary unit prograding into the gulf from the south since 200 ka b.p. indicates a dramatic variation in the evolution of the gulf, with the initiation of a new strike-slip fault of the NAFZ and a corresponding uplift of the Armutlu Peninsula in the south of the gulf. During the evolution of this fault from a wide shear zone consisting of right-stepped strike-slip faults and pull-apart basins to a localized principal fault zone, sediments were deposited under the influence of northerly prograding terrestrial and shallow-marine conditions due to relative sea-level fluctuations in the Marmara Sea. During this period, the Gulf of İzmit was invaded mainly by Mediterranean and partly by Black Sea waters. In the latest glacial period, shallow areas in the gulf became subaerially exposed, whereas the central and western sub-basins of the gulf turned into lakes. The present evolution of the Gulf of İzmit is controlled by the after effects of the new rupture of the NAFZ and the estuarine nature of the gulf environment.     

Determination of the tectonic evolution of the Edremit Gulf based on seismic reflection studies

The Edremit Gulf, which developed during the Neogene-Quaternary, is a seismically active graben in NW Anatolia (Turkey) surrounded by the Sakarya continent. The sedimentary deposits in the gulf overlie the bedrock unconformably and can be separated into two parts as upper and lower deposits based on similarity of their seismic characteristics, and because the contact between them is clear. The lower deposits are characterized in the seismic profiles by the absence of well defined, continuous reflectors and are strongly disturbed by faults. A tectonic map and structural model of the Edremit Gulf was derived from interpreting 21 deep seismic profiles trending NE–SW and NW–SE within the gulf. Two fault systems were distinguished on the basis of this compilation. The NNW–SSE trending parallel faults are low-angle normal faults formed after compression. They controlled and deformed the lower basin deposits. A syncline and anticline with a broad fold-curvature length resulted in folds that developed parallel to basin boundaries in the lower basin deposits. The ENE–WSW trending high-angle faults have controlled and deformed the northern basin of the Edremit Gulf. The folds developed within the northern lower deposits originated from the listric geometry of the faults. These faults are normal faults associated with regional N–S extension in western Anatolia. The Edremit Gulf began to open under the control of low-angle NNW–SSE trending faults that developed after the compression of western Anatolia in an E–W direction in the early Neogene. Subsequently, regional N–S extensional stress and high-angle normal faults cut the previous structures, opened the northern basin, and controlled and deformed the lower basin deposits in the gulf. As a result, the Edremit Gulf has not been controlled by any strike-slip faults or the Northern Anatolian Fault. The basin developed in the two different tectonic regimes of western Anatolia as an Aegean type cross-graben from the Neogene to Holocene.     

Late Pleistocene–Holocene evolution of the southern Marmara shelf and sub-basins: middle strand of the North Anatolian fault,southern Marmara Sea,Turkey

Although there are many research studies on the northern and southern branches of the North Anatolian fault, cutting through the deep basins of the Sea of Marmara in the north and creating a series of pull-apart basins on the southern mainland, little data is available about the geometrical and kinematical characteristics of the middle strand of the North Anatolian fault. The first detailed geometry of the middle strand of the North Anatolian fault along the southern Marmara shelf, including the Gemlik and Band?rma Bay, will be given in this study, by a combined interpretation of different seismic data sets. The characteristic features of its segments and their importance on the paleogeographic evolution of the southern shelf sub-basins were defined. The longest one of these faults, the Armutlu-Band?rma segment, is a 75-km long dextral strike-slip fault which connects the W–E trending Gençali segment in the east and NE–SW trending Kap?da?-Edincik segment in the west. In this context, the Gemlik Bay opened as a pull-apart basin under the control of the middle strand whilst a new fault segment developed during the late Pleistocene, cutting through the eastern rim of the bay. In this region, a delta front forming the paleoshoreline of the Gemlik paleolake was cut and shifted approximately 60 ± 5 m by the new segment. The same offset on this fault was also measured on a natural scarp of acoustic basement to the west and integrated with this paleoshoreline forming the slightly descending topset–foreset reflections of the delta front. Therefore the new segment is believed to be active at least for the last 30,000 years. The annual lateral slip rate representing this period of time will be 2 mm, which is quite consistent with modern GPS measurements. Towards the west, the Band?rma Bay is a rectangular transpressional basin whilst the Erdek Bay is a passive basin under the control of NW–SE trending faults. When the water level of the paleo-Marmara lake dropped down to ?90 m, the water levels of the suspended paleolakes of Band?rma and Gemlik on the southern shelf were ?50.3 (?3.3 Global Isostatic Adjustment—GIA) and ?60.5 (?3.3 GIA) m below the present mean sea level, respectively. As of today a similar example can be seen between the Sea of Marmara and the shallow freshwater lakes of Manyas and Uluabat. Similarly, the paleolakes of Gemlik and Bandirma were affected by the water level fluctuations at different time periods, even though both lakes were isolated from the Sea of Marmara during the glacial periods.     

Submarine structures in the Gulf of İzmit,based on multichannel seismic reflection and multibeam bathymetry

Multichannel seismic reflection and multi-beam bathymetry data were used to study the active tectonic and syn-tectonic stratigraphic setting of the Gulf of ?zmit in the Marmara Sea (Turkey). The gulf and its near surroundings are deformed by the northern strand of the dextral North Anatolian Fault. Three connected basins of the gulf, the western (Dar?ca), central (Karamürsel) and eastern (Gölcük) basins are formed by active faults, as observed in the stacked and migrated seismic sections, as well as the bathymetry map. The main branch and its surrounding sedimentary strata are confined by normal faults to the north and south. These normal faults converge at depth towards the main fault, forming a negative flower structure in the gulf. The average maximum sedimentation rate is 0.4 mm/year according to the three most recent seismo-stratigraphic units that are located to the south of the main fault branch within the central basin. A 20° south-dipping major discontinuity along the northern shoreline of the gulf represents the top of Paleozoic basement.     

Interaction between trench retreat and Anatolian escape as recorded by neogene basins in the northern Aegean Sea

The evolution of the North Aegean Sea is studied through the development of three deep basins: the North Aegean Trough, the North Skyros Basin and the Ikaria Basin. Bathymetric data, a 2D seismic dataset and the well-investigated stratigraphic records of the onshore deep basins of northern Greece and Western Turkey were used to make structural and seismic stratigraphic interpretations. The study area shows two sharp unconformities that correspond to the Eocene-Oligocene transition and the Miocene-Pliocene shift. These discontinuities were used as marker horizons for a more detailed structural and seismic stratigraphic interpretation resulting in the identification of several seismic units. A general seismic signature chart was established using onshore basin stratigraphy and well data, which was then used to constrain the ages of the different seismic units. The main features observed in the basins are interpreted as: 1) trans-tensional growth patterns in Pliocene and Quaternary sediments that combine NE–SW trending and steeply dipping fault zones that likely correspond to strike-slip corridors and E-W/WNW-ESE trending normal faults, 2) regional erosional truncations of Miocene sediments, likely related to the Messinian Salinity Crisis (MSC), 3) thick delta-turbidite deposits of Neogene age. Only the North Aegean Trough shows evidence of earlier development and polyphase deformation through inversion structures, and additional seismic units. Extension processes in the Aegean region have been driven by the Hellenic slab rollback since the middle Eocene. The widespread development of Neogene basins at the whole Aegean scale attests to a major tectonic change due to an acceleration of the trench retreat in the middle Miocene. The present study shows that the Neogene basins of the North Aegean Sea developed in dextral transtension with the northward migration of the associated NE-SW trending strike-slip faults. At regional scale, this tectonic pattern indicates that the westward escape of Anatolia started to interact with the trench retreat in the middle Miocene, around 10 Myr before the arrival of the North Anatolian Fault in the North Aegean Sea.     

Evidence of NW extension of the North Anatolian Fault Zone in the Marmara Sea: a new interpretation of the Marmara Sea (Izmit) earthquake on 17 August 1999

Active faults aligning in NW–SE direction and forming flower structures of strike-slip faults were observed in shallow seismic data from the shelf offshore of Avcılar in the northern Marmara Sea. By following the parallel drainage pattern and scarps, these faults were traced as NW–SE-directed lineaments in the morphology of the northern onshore sector of the Marmara Sea (eastern Thrace Peninsula). Right-lateral displacements in two watersheds of drainage and on the coast of the Marmara Sea and Black Sea are associated with these lineaments. This right-lateral displacement along the course of these faults suggests a new, active strike-slip fault zone located at the NW extension of the northern boundary fault of the ?ınarcık Basin in the Marmara Sea. This new fault zone is interpreted as the NW extension of the northern branch of the North Anatolian Fault Zone (NAFZ), extending from the ?ınarcık Basin of the Marmara Sea to the Black Sea coast of the Thrace Peninsula, and passing through B üy ük ?ekmece and K ü ? ük ?ekmece lagoons. These data suggest that the rupture of the 17 August 1999 earthquake in the NAFZ may have extended through Avcılar. Indeed, Avcılar and İzmit, both located on the Marmara Sea coast along the rupture route, were strongly struck by the earthquake whereas the settlements between Avcılar and İzmit were much less affected. Therefore, this interpretation can explain the extraordinary damage in Avcılar, based on the newly discovered rupture of the NAFZ in the Marmara Sea. However, this suggestion needs to be confirmed by further seismological studies.     

渤海海域晚更新世—全新世的活动构造

利用在渤海最新获得的约5 000 km的浅层地震资料,发现在渤海海域发育大量晚更新世—全新世断裂和褶皱,进而对其分布、浅层结构、运动学性质和活动性进行了研究,绘制了渤海海域活动断裂分布图。研究结果表明:渤海晚更新世—全新世活动断裂主要走向为北北东向、北西向和近东西向,东西向断裂数量最多;断裂的形成受区域应力场和早期断裂的控制,而褶皱则以背斜居多,通常沿早期断裂带发育;就分布密度而言,辽东湾内断裂密度远小于其他海域,而同一构造单元其边界部位断裂密度大于单元内部;具继承性发展的断裂多具有复杂的破裂结构,破裂带剖面上呈耙形或"Y"字型,晚更新世沉积层变形明显;受断裂错动地层的形成时代表明,多数断裂的最新活动发生在晚更新世中期-晚期,部分断裂在全新世发生过活动;多数断裂具有明显正断拉张作用,而郯庐断裂带和张家口-蓬莱断裂带内次级断裂还可能具走向滑移分量;渤海浅层断裂的活动性与现代地震震中的分布具有较好的相关性,这对于渤海地震危险性评价具有重要意义。     

Investigation on the tectonic significance of Izmir,Uzunada Fault Zones and other tectonic elements in the Gulf of Izmir,western Turkey,using high resolution seismic data

Active faults at a range in scales are observed in different directions (E-W, N-S and NE-SW) in the extensional tectonic regime of the Aegean region, western Turkey. However, mechanisms and types of faults in the Gulf of Izmir have not been investigated properly. Tectonic setting in the gulf together with the origin and characteristics of faults were studied in this study by integrating interpretation from various very high resolution acoustic data (multibeam bathymetry and CHIRP very high resolution seismic) acquired in the Gulf of Izmir.The Gulf of Izmir has thick, unconsolidated, stratified sediment cover. The water depth increases from the inner part (SE) to the outer part (NW) of the gulf with complex sea floor morphology. However, northeastern part of the coastal region is very shallow because of the sedimentary influx transported by the Gediz River. The western margin and the southern part of the gulf were formed under the influence of Uzunada (Uzun Island) and Izmir Faults, respectively. In the southern offshore, there is only one, E-W directional normal fault dipping through the north and corresponding to the offshore segment of the Izmir Fault Zone to the west. The acoustic data enable identification of the Uzunada Fault Zone extending as a simple lineament from near Guzelbahce in the south but bifurcating toward the NE of the Cicek Archipelago and terminating with left-lateral slip in the E-NE of the Hekim Island. After the sinistral strike-slip, the fault re-extends in the NW direction untill the mid of Uzunada as a single fault segment. Then, the fault is observed as a bunch of many active fault segments (like horse-tail splays) to the east of Uzunada with N-NW elongation through the outer gulf. These segments were chronologically succeeded from the east to the west. This progradational pattern is attributed to westward extension of the Gulf of Izmir with anti-clockwise rotational escape of the Anatolian Plate. In addition, progradation of faults was controlled by the NE-SW directional tear faults which may have played a key role in the shoreline extension and general pattern of the outer gulf islands. A very young graben in the central part of the gulf, also dislocated by the tear faults was observed parallel to the Uzunada Fault Zone as another indicator of ongoing fan-shaped opening of the gulf. These tectonic elements are consistent with earlier interpretation of GPS-based observations indicating a four-wheel gear system of rigid-body rotations. Additionally, a new fault extending from the far offshore of Foca to Suzbeyli village to the south was identified in this study. Its NW-SE extension is angular to the previous tectonic elements. All these elements apparently project at least 10 km farther northward, in the offshore Foca where the earthquake epicenters cluster.     

Neogene history of Bone Gulf,Sulawesi, Indonesia

Bone Gulf is one of the inter-arm basins of the unusual K-shaped island of Sulawesi. Its age, character and origin are disputed. This study is based on recently acquired 2D seismic lines, seabed multibeam mapping and limited well data, and is linked to stratigraphy on land. The gulf is probably underlain by pre-Neogene volcanogenic, sedimentary, metamorphic and ultramafic rocks, and includes crust of Australian origin. We favour basin initiation in the Miocene rather than Eocene, by extension associated with strike-slip deformation. The main basin trends N–S and is divided into several sub-basins and highs. The highs segment the gulf and their WNW–ESE orientations reflect pre-Neogene basement structures. They are interpreted as strike-slip fault zones active at different times in the Neogene. A southern high was active relatively early, whereas further north there is evidence of young displacements during the Late Neogene. These are visible on the seabed above a high linked to the Kolaka Fault on land. Early basin-bounding faults are oriented NNW–SSE and record extension and strike-slip movements, like the sub-parallel Walanae Fault of South Sulawesi which can be traced offshore into extensional faults bounding the young and narrow Selayar Trough. Sediment in the basins came mainly from the north with contributions from both west and east. Carbonate deposits formed at the margins while deeper marine sediments were deposited in the axial parts of the gulf. An Early Pliocene unconformity can be mapped across the study area marking major uplift of Sulawesi and subsidence of Bone Gulf. This regional event caused major influx of clastic sediments from the north, development of a southward-flowing canyon system, and back-stepping and drowning of carbonates at the basin margins. Hydrocarbons are indicated by seeps, and Bone Gulf has potential sources, reservoirs and seals, but the complex faulting history is a risk.     

南昆嵩地区断裂?构造演化特征及其控制因素

南昆嵩地区是万安盆地西部负向构造单元,其中部N–S向断裂贯穿南北,独特的构造特征使其成为研究万安盆地西部构造演化与区域断裂走滑活动的窗口。将研究区沉积地层划分为3套构造层,通过回剥法绘制南昆嵩地区构造–沉积充填剖面,并计算南昆嵩地区构造沉降量以及构造沉降速率,论述南昆嵩地区构造演化史与沉降过程以及控制因素。研究结果表明:下部构造层和中部构造层中断裂组合样式主要为卷心型断层、“Y”型断层、阶梯状断层和高角度花状构造等,断裂延伸方向大致可分为:N–S向、W–E向和NE–SW向3种;上部构造层断裂不发育,为稳定沉积;在区域走滑断裂以及南海扩张运动的控制下,南昆嵩地区始新世以来构造演化经历4个阶段:初始裂谷期、伸展断拗期、走滑改造期和热沉降期,新生代地层构造性质也表现为以伸展与走滑作用为主–走滑断裂控制–热沉降的三段式转变。     

Investigation of Fethiye-Marmaris Bay (SW Anatolia): seismic and morphologic evidences from the missing link between the Pliny Trench and the Fethiye-Burdur Fault Zone

New (2009) multi-beam bathymetric and previously published seismic reflection data from the NE-SW-oriented Fethiye Bay and the neighboring N-S-oriented Marmaris Bay off SW Anatolia were evaluated in order to interpret the seafloor morphology in terms of the currently still active regional tectonic setting. This area lies between the Pliny Trench, which constitutes the eastern sector of the subduction zone between the African and Eurasian plates in the Eastern Mediterranean, and the Fethiye-Burdur Fault Zone of the Anatolian Plate. The bathymetric data document the very narrow shelf of the Anatolian coast, a submarine plain between the island of Rhodes and Marmaris Bay, and a large canyon connecting the abyssal floor of the Rhodes Basin with Fethiye Bay. The latter are here referred to as the Marmaris Plain and Fethiye Canyon, respectively. Several active and inactive faults have been identified. Inactive faults (faults f1) delineate a buried basin beneath the Marmaris Plain, here referred to as the Marmaris Basin. Other faults that affect all stratigraphic units are interpreted as being active. Of these, the NE-SW-oriented Marmaris Fault Zone located on the Marmaris Plain is interpreted as a transtensional fault zone in the seismic and bathymetric data. The transtensional character of this fault zone and associated normal faults (faults f3) on the Marmaris Plain correlates well with the Fethiye-Burdur Fault Zone on land. Another important fault zone (f4) occurs along the Fethiye Canyon, forming the northeastern extension of the Pliny Trench. The transpressional character of faults f4 inferred from the seismic data is well correlated with the compressional structures along the Pliny Trench in the Rhodes Basin and its vicinity. These observations suggest that the Marmaris Fault Zone and faults f3 have evolved independently of faults f4. The evidence for this missing link between the Pliny Trench and the Fethiye-Burdur Fault Zone implies possible kinematic problems in this tectonic zone that deserve further detailed studies. Notably, several active channels and submarine landslides interpreted as having been triggered by ongoing faulting attest to substantial present-day sediment transport from the coast into the Rhodes Basin.     

Cenozoic structural deformation and dynamic processes of the Bohai Bay basin province,China

Cenozoic structures in the Bohai Bay basin province can be subdivided into eleven extensional systems and three strike-slip systems. The extensional systems consist of normal faults and transfer faults. The normal faults predominantly trend NNE and NE, and their attitudes vary in different tectonic settings. Paleogene rifting sub-basins were developed in the hanging walls of the normal faults that were most likely growth faults. Neogene–Quaternary sequences were deposited in both the rifting sub-basins and horsts to form a unified basin province. The extensional systems were overprinted by three NNE-trending, right-lateral strike-slip systems (fault zones). Although the principal displacement zones (PDZ) of the strike-slip fault zones are developed only in the basement and lower basin sequences in some cross sections, the structural deformation characteristics of the upper basin sequences also indicate that they are basement-involved, right-lateral strike-slip fault zones. According to the relationships between faults and sedimentary sequences, the extensional systems were mainly developed from the middle Paleocene to the late Oligocene, whereas the strike-slip systems were mainly developed from the Oligocene to the Miocene. Strike-slip deformation was intensified as extensional deformation was weakened. Extensional deformation was derived from horizontal tension induced by upwelling of hot mantle material, whereas strike-slip deformation was probably related to a regional stress field induced by plate movement.     

莱州湾地区郯庐断裂带的构造特征及其新生代演化

郯庐断裂带中段分东西两支从莱州湾进入渤海,在莱州湾地区的构造特征与演化历史一直鲜为人知。通过对横穿研究区的两条地震测线的解释和分析,揭示了该区郯庐断裂带中段在研究区的构造差异,研究表明郯庐断裂带东西两支在该研究区表现出不同的断裂性质,西支断裂表现为正断层,东支断裂表现为走滑断层。郯庐断裂是本研究区的主控断裂,通过对本地区地层形态及其组合、断层的剖面形态和空间展布规律的深入研究,揭示了郯庐断裂带在莱州湾地区新生代以来的构造演化历史:古新世—始新世的伸展阶段、渐新世—中新世早期的挤压和右行走滑阶段、中新世中晚期至今的稳定发展阶段,这几个不同时期的演化阶段主要受太平洋板块运动的方向和速度变化的控制。     

Geological evolution of the Gulf of Saros,NE Aegean Sea

 The Gulf of Saros is an Upper Miocene transtensional basin in NW Anatolia, formed by the interaction between the North Anatolian Fault and the N-S extensional tectonic régime of the Aegean. The present configuration of the basin evolved mainly during the Plio-Quaternary under the increased activity of the North Anatolian Fault. During the late Miocene-late Quaternary, no sedimentation took place on the shelves. After this long hiatus, an important change in tectonic style about 0.2 Ma BP allowed sedimentation to resume in the gulf. Received: 14 February 1997 / Revision received: 12 November 1997     

Seismic structure and tectonics of the Shackleton Fracture Zone (Drake Passage,Scotia Sea)

The structural framework of the southern part of the Shackleton Fracture Zone has been investigated through the analysis of a 130-km-long multichannel seismic reflection profile acquired orthogonally to the fracture zone near 60° S. The Shackleton Fracture Zone is a 800-km-long, mostly rectilinear and pronounced bathymetric lineation joining the westernmost South Scotia Ridge to southern South America south of Cape Horn, separating the western Scotia Sea plate from the Antarctic plate. Conventional processing applied to the seismic data outlines the main structures of the Shackleton Fracture Zone, but only the use of enhanced techniques, such as accurate velocity analyses and pre-stack depth migration, provides a good definition of the acoustic basement and the architecture of the sedimentary sequences. In particular, a strong and mostly continuous reflector found at about 8.0 s two-way traveltime is very clear across the entire section and is interpreted as the Moho discontinuity. Data show a complex system of troughs developed along the eastern flank of the crustal ridge, containing tilted and rotated blocks, and the presence of a prominent listric normal fault developed within the oceanic crust. Positive flower structures developed within the oceanic basement indicate strike-slip tectonism and partial reactivation of pre-existing faults. Present-day tectonic activity is found mostly in correspondence to the relief, whereas fault-induced deformation is negligible across the entire trough system. This indicates that the E–W-directed stress regime present in the Drake Passage region is mainly dissipated along a narrow zone within the Shackleton Ridge axis. A reappraisal of all available magnetic anomaly identifications in the western Scotia Sea and in the former Phoenix plate, in conjunction with new magnetic profiles acquired to the east of the Shackleton Fracture Zone off the Tierra del Fuego continental margin, has allowed us to propose a simple reconstruction of Shackleton Fracture Zone development in the general context of the Drake Passage opening.     

Character of active faulting in the North Aegean Sea

A re-evaluation of the reprocessed seismic reflection data was made for the investigation of the presumed western continuation of the North Anatolian Fault (NAF) in the Aegean and mapping geometries of active faults in the Aegean Sea. Seismic data collected and processed by various national and international companies were selected from the data archives and they were reprocessed after stacking to bring them to the same processing and signal-to-noise ratio standards. The total length of the selected lines is 8000 km. We investigated the character of active faulting in the North Aegean Sea using seismic reflection data. Moreover, the relations of active faults with earthquakes were examined using earthquake fault plane solutions (FPS). We show that the active faults are dominantly normal in character in the NNE Aegean where FPS for earthquakes with M>5 indicate strike-slip movements along these faults. We propose a simple mechanism that potentially explains this inconsistency. Active normal faults are oriented in a NE–SW direction in alignment with the SW escape motion of the Anatolian block in this region and this orientation facilitates instantaneously strike-slip movements along these otherwise normal faults.     

New seismo-stratigraphic and marine magnetic data of the Gulf of Pozzuoli (Naples Bay, Tyrrhenian Sea, Italy): inferences for the tectonic and magmatic events of the Phlegrean Fields volcanic complex (Campania)

A detailed reconstruction of the stratigraphic and tectonic setting of the Gulf of Pozzuoli (Naples Bay) is provided on the basis of newly acquired single channel seismic profiles coupled with already recorded marine magnetics gathering the volcanic nature of some seismic units. Inferences for the tectonic and magmatic setting of the Phlegrean Fields volcanic complex, a volcanic district surrounding the western part of the Gulf of Naples, where volcanism has been active since at least 50 ka, are also discussed. The Gulf of Pozzuoli represents the submerged border of the Phlegrean caldera, resulting from the volcano-tectonic collapse induced from the pyroclastic flow deposits of the Campanian Ignimbrite (35 ka). Several morpho-depositional units have been identified, i.e., the inner continental shelf, the central basin, the submerged volcanic banks and the outer continental shelf. The stratigraphic relationships between the Quaternary volcanic units related to the offshore caldera border and the overlying deposits of the Late Quaternary depositional sequence in the Gulf of Pozzuoli have been highlighted. Fourteen main seismic units, both volcanic and sedimentary, tectonically controlled due to contemporaneous folding and normal faulting have been revealed by geological interpretation. Volcanic dykes, characterized by acoustically transparent sub-vertical bodies, locally bounded by normal faults, testify to the magma uprising in correspondence with extensional structures. A large field of tuff cones interlayered with marine deposits off the island of Nisida, on the western rim of the gulf, is related to the emplacement of the Neapolitan Yellow Tuff deposits. A thick volcanic unit, exposed over a large area off the Capo Miseno volcanic edifice is connected with the Bacoli-Isola Pennata-Capo Miseno yellow tuffs, cropping out in the northern Phlegrean Fields.     

琼东南盆地陆架区晚中新世以来断层活动性研究

对琼东南盆地陆架区晚中新世以来的断层活动性进行研究, 有助于理解南海西北部晚中新世以来的构造演化, 也对该区钻井平台的安全性评估、海洋工程勘查以及区域稳定性评价等有重要意义。研究区断层走向主要为NWW向, 多数断层在晚中新世时期停止活动。通过对断层几何形态的统计分析以及使用高分辨率断层落差图法(T-Z图示法)对断层活动性进行量化分析, 结果显示: 断层活动性在晚中新世末期(5.5Ma)发生转变; 研究区南部的断层落差值大于北部; 南部断层停止活动的时间较北部断层稍晚。这些研究成果表明, 晚中新世末期研究区断层受构造应力变化的影响, 在生长发育过程中断层活动性质发生了改变, 由逆断层转为正断层。红河断裂带对琼东南盆地的构造演化起着重要的控制作用, 文章推测研究区断层活动性变化是由红河断裂带的构造反转所导致, 因为红河断裂带在5.5Ma时发生了走滑运动的反转, 与研究区的断层活动性变化在时间和性质上相耦合。     

Faulting, mass-wasting and deposition in an active dextral shear zone, the Gulf of Saros and the NE Aegean Sea, NW Turkey

Structural, mass-wasting and sedimentation processes along an active dextral shear zone beneath the Gulf of Saros and the NE Aegean Sea were investigated on the basis of new high-resolution swath bathymetric data and multi-channel seismics. A long history of dextral shearing operating since the Pliocene culminated in the formation of a NE-SW-trending, ca. 800-m-deep basin (the so-called inner basin) in this region, which is bordered by a broad shelf along its northern and eastern sides and a narrow shelf at the southern side. The western extension of the North Anatolian Fault Zone (the Ganos Fault) cuts the eastern shelf along a narrow deformation zone, and ends sharply at the toe of the slope, where the strain is taken up by two NE-SW-oriented fault zones. These two fault zones cut the basin floor along its central axis and generate a new, Riedel-type pull-apart basin (the so-called inner depression). According to the bathymetric and seismic data, these basin boundary fault zones are very recent features. The northern boundary of the inner depression is a through-going fault comprising several NE-SW- and E-W-oriented, overlapping fault segments. The southern boundary fault zone, on the other hand, consists of spectacular en-echelon fault systems aligned in NE–SW and WNW–ESE directions. These en-echelon faults accommodate both dextral and vertical motions, thereby generating block rotations along their horizontal axis. As the basin margins retreat, the basin widens continuously by mass-wasting of the slopes of the inner basin. The mass-wasting, triggered by active tectonics, occurs by intense landsliding and channel erosion. The eroded material is transported into the deep basin, where it is deposited in a series of deep-sea fans and slumps. The high sedimentation rate is reflected in an over 1,500-m-thick basin fill which has accumulated in Pliocene–Quaternary times.