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.     

Recent structures in the Alboran Ridge and Yusuf fault zones based on swath bathymetry and sub-bottom profiling: evidence of active tectonics

The seafloor of the Alboran Sea in the western Mediterranean is disrupted by deformations resulting from convergence between the African and Eurasian plates. Based on a compilation of existing and new multibeam bathymetry data and high-resolution seismic profiles, our main objective was to characterize the most recent structures in the central sector, which depicts an abrupt morphology and was chosen to investigate how active tectonic processes are shaping the seafloor. The Alboran Ridge is the most prominent feature in the Alboran Sea (>130 km in length), and a key element in the Gibraltar Arc System. Recent uplift and deformation in this ridge have been caused by sub-vertical, strike-slip and reverse faults with associated folding in the most recent sediments, their trend shifting progressively from SW–NE to WNW–ESE towards the Yusuf Lineament. Present-day transtensive deformation induces faulting and subsidence in the Yusuf pull-apart basin. The Alboran Ridge and Yusuf fault zones are connected, and both constitute a wide zone of deformation reaching tens of kilometres in width and showing a complex geometry, including different active fault segments and in-relay folds. These findings demonstrate that Recent deformation is more heterogeneously distributed than commonly considered. A narrow SSW–NNE zone with folding and reverse faulting cuts across the western end of the Alboran Ridge and concentrates most of the upper crustal seismicity in the region. This zone of deformation defines a seismogenic, left-lateral fault zone connected to the south with the Al Hoceima seismic swarm, and representing a potential seismic hazard. Newly detected buried and active submarine slides along the Alboran Ridge and the Yusuf Lineament are clear signs of submarine slope instability in this seismically active region.     

Tectonics of the Mid-Atlantic Ridge, 6–8° South latitude

A regional geophysical traverse of the Mid-Atlantic Ridge in the northern South Atlantic was obtained during CIRCE cruise of the Scripps Institution of Oceanography. During the traverse, four detailed surveys were made of small areas on the crest and east flank. The geomagnetic anomaly profile can be used as a time base for the interpretation of tectonic events of the ridge. The profile also suggests that the rate of sea-floor spreading in this part of the South Atlantic accelerated twice, approximately 40 and 4.5 million years ago, and decelerated at least twice, 38 and 10 million years ago. Accelerations were probably accompanied by uplift and normal faulting of the central part of the ridge, while decelerations produced subsidence with modest contraction, reflected in reverse faulting and folding. The effects of uplift are clearly present in the reflection seismic records, which are, however, not well suited to detect reverse faulting.Spreading without creation of significant relief occurred on the ridge until approximately 5 million years ago. This process produced a low relief with small rifts, strongly reminiscent of the present crestal topography of the East Pacific Rise. A markedly linear secondary relief of 100–200 m, parallel to the ridge axis, developed later by faulting of the flanks. Portions of the crust that were near the crest during periods of uplift are more intensely faulted than those that were remote at all times. The importance of the last uplift of the crest and associated faulting on the flanks is reflected by a decrease in the density of faulting away from the ridge crest.The present crestal zone is very different from the flanks and from the older crests; the relief is nearly ten times greater, transverse disturbances are common, and there is conflicting evidence regarding its age. This striking change in character indicates either a recent change in the spreading process or a recent period of strong deformation which has affected only the crestal zone.Contribution from Scripps Institution of Oceanography, University of California, San Diego.     

The basins of Sundaland (SE Asia): Evolution and boundary conditions

Most of the basins developed in the continental core of SE Asia (Sundaland) evolved since the Late Cretaceous in a manner that may be correlated to the conditions of the subduction in the Sunda Trench. By the end of Mesozoic times Sundaland was an elevated area composed of granite and metamorphic basement on the rims; which suffered collapse and incipient extension, whereas the central part was stable. This promontory was surrounded by a large subduction zone, except in the north and was a free boundary in the Early Cenozoic. Starting from the Palaeogene and following fractures initiated during the India Eurasia collision, rifting began along large faults (mostly N–S and NNW–SSE strike-slip), which crosscut the whole region. The basins remained in a continental fluvio-lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust (Phu Khanh, Natuna, N. Makassar) or even reached the ocean floor spreading stage (Celebes, Flores). Western Sundaland was a combination of basin opening and strike-slip transpressional deformation. The configuration suggests a free boundary particularly to the east (trench pull associated with the Proto-South China Sea subduction; Java–Sulawesi trench subduction rollback). In the Early Miocene, Australian blocks reached the Sunda subduction zone and imposed local shortening in the south and southeast, whereas the western part was free from compression after the Indian continent had moved away to the north. This suggests an important coupling of the Sunda Plate with the Indo-Australian Plate both to SE and NW, possibly further west rollback had ceased in the Java–Sumatra subduction zone, and compressional stress was being transferred northwards across the plate boundary. The internal compression is expressed to the south by shortening which is transmitted as far as the Malay basin. In the Late Miocene, most of the Sunda Plate was under compression, except the tectonically isolated Andaman Sea and the Damar basins. In the Pliocene, collision north of Australia propagated toward the north and west causing subduction reversal and compression in the short-lived Damar Basin. Docking of the Philippine Plate confined the eastern side of Sundaland and created local compression and uplift such as in NW Borneo, Palawan and Taiwan. Transpressional deformation created extensive folding, strike-slip faulting and uplift of the Central Basin and Arakan Yoma in Myanmar. Minor inversion affected many Thailand rift basins. All the other basins record subsidence. The uplift is responsible for gravity tectonics where thick sediments were accumulated (Sarawak, NE Luconia, Bangladesh wedge).     

The formation and tectonic evolution of Philippine Sea Plate and KPR

The Philippine Sea Plate has an extremely special tectonic background. As an oceanic plate, it is almost entirely surrounded by subduction zones with complex internal tectonic features. On the basis of enormous published literature, this paper offers a comprehensive overview of the tectonic and evolution history of the Philippine Basin and the Kyushu-Palau Ridge (KPR) in the Philippine Sea Plate, and discusses the geological features of KPR. Referring to relevant definitions of various "ridges" stipulated in United Nations Convention on the Law of the Sea, so the KPR is believed to be a remnant arc formed during the opening of the Parece Vela and Shikoku Basins in the Philippine Sea Plate. It is a submarine ridge on oceanic plate rather than a submarine elevation. And thus, it is not a natural component of the Japan continental margin.     

Oblique subduction of the Gagua Ridge beneath the Ryukyu accretionary wedge system: Insights from marine observations and sandbox experiments

The Gagua Ridge, carried by the Philippine Sea Plate, is subducting obliquely beneath the southernmost Ryukyu Margin. Bathymetric swath-mapping, performed during the ACT survey (Active Collision in Taiwan), indicates that, due to the high obliquity of plate convergence, slip partitioning occurs within the Ryukyu accretionary wedge. A transcurrent fault, trending N95° E, is observed at the rear of the accretionary wedge. Evidence of right lateral motion along this shear zone, called the Yaeyama Fault, suggests that it accommodates part of the lateral component of the oblique convergence. The subduction of the ridge disturbs this tectonic setting and significantly deforms the Ryukyu Margin. The ridge strongly indents the front of the accretionary wedge and uplifts part of the forearc basin. In the frontal part of the margin, directly in the axis of the ridge, localized transpressive and transtensional structures can be observed superimposed on the uplifted accretionary complex. As shown by sandbox experiments, these N330° E to N30° E trending fractures result from the increasing compressional stress induced by the subduction of the ridge. Analog experiments have also shown that the reentrant associated with oblique ridge subduction exhibits a specific shape that can be correlated with the relative plate motion azimuth.These data, together with the study of the margin deformation, the uplift of the forearc basin and geodetic data, show that the subduction of the Gagua Ridge beneath the accretionary wedge occurs along an azimuth which is about 20° less oblique than the convergence between the PSP and the Ryukyu Arc. Taking into account the opening of the Okinawa backarc basin and partitioning at the rear of the accretionary wedge, convergence between the ridge and the overriding accretionary wedge appears to be close to N345° E and thus, occurs at a rate close to 9 cm yr^–1. As a result, we estimate that a motion of 3.7 cm yr^–1±0.7 cm should be absorbed along the transcurrent fault. Based on these assumptions, the plate tectonic reconstruction reveals that the subducted segment of the Gagua Ridge, associated with the observable margin deformations, could have started subducting less than 1 m.y. ago.     

Tectonic effects of a subducting aseismic ridge: The subduction of the Nazca Ridge at the Peru Trench

A 1987 survey of the offshore Peru forearc using the SeaMARC II seafloor mapping system reveals that subduction of the Nazca Ridge has resulted in uplift of the lowermost forearc by as much as 1500 m. This uplift is seen in the varied depths of two forearc terraces opposite the subducting ridge. Uplift of the forearc has caused fracturing, minor surficial slumping, and increased erosion through small canyons and gullies. Oblique trending linear features on the forearc may be faults with a strike-slip component of motion caused by the oblique subduction of the Nazca Ridge. The trench in the zone of ridge subduction is nearly linear, with no re-entrant in the forearc due to subduction of the Nazca Ridge. Compressional deformation of the forearc due to subduction of the ridge is relatively minor, suggesting that the gently sloping Nazca Ridge is able to slide beneath the forearc without significantly deforming it. The structure of the forearc is similar to that revealed by other SeaMARC II surveys to the north, consisting of: 1) a narrow zone (10 to 15 km across) of accreted material making up the lower forearc; 2) a chaotic middle forearc; 3) outcropping consolidated material and draping sediment on the upper forearc; and 4) the smooth, sedimented forearc shelf.The subducting Nazca plate and the Nazca Ridge are fractured by subduction-induced faults with offsets of up to 500 m. Normal faulting is dominant and begins about 50 km from the trench axis, increasing in frequency and offset toward the trench. These faults are predominantly trench-parallel. Reverse faults become more common in the deepest portion of the trench and often form at slight angles to the trench axis.Intrusive and extrusive volcanic areas on the Nazca plate appear to have formed well after the seafloor was created at the ridge crest. Many of the areas show evidence of current scour and are cut by faulting, however, indicating that they formed before the seafloor entered the zone of subduction-induced faulting.     

台湾增生楔的构造单元划分及其变形特征

台湾增生楔位于欧亚板块、菲律宾海微板块和南海的结合部位,是现代弧陆碰撞研究的理想场所。通过对南海973航次在该区域的多道地震剖面的解释,对该增生楔进行了构造单元的划分,并分析了变形特征。认为台湾增生楔是由3个部分,即弧陆碰撞产生的增生部分、洋内俯冲产生的增生部分和增生楔后端在恒春海脊和北吕宋海槽之间的构造楔组成,研究区的高屏斜坡、恒春海脊和北吕宋海槽西端变形带分别是3个部分的反映。自中中新世以来,南海洋壳开始沿着马尼拉海沟向菲律宾海微板块俯冲,形成增生楔中洋内俯冲增生部分;与此同时菲律宾海微板块开始向NW方向移动,前缘的吕宋岛弧自6．5Ma B．P以来与亚洲陆缘斜向碰撞,形成增生楔中弧陆碰撞增生部分。碰撞首先发生在台湾岛的北部,由于弧陆强烈的挤压作用,增生楔后端部分向北吕宋海槽倒冲楔人,使得上部的北吕宋海槽的沉积发生隆升变形。滨海的各个地貌单元可以和台湾陆上的地貌单元相联系,它们具有相似的地质特征,但是由于陆上部分增生历史久,不仅抬升为陆,而且地层的年代也更老。     

The D'Entrecasteaux Zone (Southwest Pacific). A petrological and geochronological reappraisal

The D'Entrecasteaux Zone (Southwest Pacific) is an arched submarine horst- and graben structure, which extends from the northern end of the New Caledonia ridge to the western border of the New Hebrides island arc. A review of the bathymetry, seismic-reflection data, paleomagnetism, gravimetry, seismology and DSDP data available for this area is combined with a study of basaltic samples dredged along the horsts of this regional fracture zone. These basalts show strong petrographic and chemical affinities with MORB. Their fissiontrack ages range between 56 Ma (Paleocene-Eocene boundary) and 36 Ma (Eocene-Oligocene boundary). It is suggested that the D'Entrecasteaux Zone represents the northern arcuate extension of the northeast-dipping Eocene subduction/obduction zone, located along the New Caledonia/Loyalty Islands ridge, while its present morphology appeared from post-obduction extensional movements, resulting in a progressive uplift of basaltic ocean floor since Middle Miocene times.     

日本九州俯冲带b值成像及其构造意义 *

日本九州俯冲带是菲律宾海板块与欧亚板块汇聚边界上一个独具特色的区域, 也是研究俯冲带内板块构造作用的理想场所。为了解该俯冲带内的板间应力状态和相互作用, 本研究利用震源深度大于20km的97251个地震事件, 通过b值计算详细刻画了该俯冲板片上表面以及垂直海沟走向的剖面特征。结果发现, b值表现出明显的空间变化, 整体上沿南海海槽和琉球海沟从东北往西南方向逐渐增大, 同时在俯冲的九州-帕劳海脊上存在显著的低值区。从b值与应力的负相关性推断, 进入俯冲带的海脊以及海脊东北侧的四国海盆洋壳与俯冲带上覆板片耦合作用较强; 而在海脊西南侧, 俯冲带内汇聚板片的耦合作用相对较弱。究其原因, 本文认为九州-帕劳海脊两侧俯冲洋壳在形成时代和汇聚速率上的差异起着重要作用。对于九州-帕劳海脊来说, 俯冲带浅部的低b值区主要是由于隆起的海脊增强了与上覆板块的耦合作用。随着俯冲深度的增加和俯冲板片倾角的急剧变陡, 沿海脊可能发生了板片撕裂, 从而释放了海脊与上覆板片间的挤压-剪切应力, 使耦合程度大大减弱。     

Morpho-tectonic evolution of the ?anakkale Basin (NW Anatolia): evidence for a recent tectonic inversion from transpression to transtension

Onshore and offshore seismic and geologic-morphologic evidence from the wider region of the ?anakkale Basin indicates that this area has been widely exposed to transpressional tectonism, which already commenced in the Pliocene. During this transpressional tectonism, the Gelibolu Fault and the Anafartalar Shear Zone on the Gelibolu Peninsula, as well as the Bozcaada-Biga Shear Zone on the Biga Peninsula were activated. As a consequence, the northern part of the Gelibolu Peninsula, and a broad zone between Bozcaada Island and the Karaburun Peninsula were uplifted to form the northern and southern boundaries of the ?anakkale Basin, respectively. This remained a low-elevation intermontane basin between these two highlands. The original morphology of the ?anakkale Basin may have developed as a coastal and shelf section of the large extensional Marmara Sea Basin at the end of the Late Miocene. This tectonic phase was followed in the Pliocene by the transpressional tectonism of the North Anatolian Fault Zone, which destroyed the initial morphology and formed the present V-shaped basin. The activity of the Gelibolu Fault and the Anafartalar Shear Zone along the northern boundary of the ?anakkale Basin ended in the late Pleistocene with the initiation of the northern segment of the North Anatolian Fault Zone. The tectonism along the northern boundary of the ?anakkale Basin thus shifted from a transpressional to a transtensional regime. Seismic data indicate that the Bozcaada-Biga Shear Zone continues to be active to the present day.     

Active tectonic morphology and submarine deformation of the northern Gulf of Eilat/Aqaba from analyses of multibeam data

A high-resolution marine geophysical study was conducted during October-November 2006 in the northern Gulf of Aqaba/Eilat, providing the first multibeam imaging of the seafloor across the entire gulf head spanning both Israeli and Jordanian territorial waters. Analyses of the seafloor morphology show that the gulf head can be subdivided into the Eilat and Aqaba subbasins separated by the north-south-trending Ayla high. The Aqaba submarine basin appears starved of sediment supply, apparently causing erosion and a landward retreat of the shelf edge. Along the eastern border of this subbasin, the shelf is largely absent and its margin is influenced by the Aqaba Fault zone that forms a steep slope partially covered by sedimentary fan deltas from the adjacent ephemeral drainages. The Eilat subbasin, west of the Ayla high, receives a large amount of sediment derived from the extensive drainage basins of the Arava Valley (Wadi ’Arabah) and Yutim River to the north–northeast. These sediments and those entering from canyons on the south-western border of this subbasin are transported to the deep basin by turbidity currents and gravity slides, forming the Arava submarine fan. Large detached blocks and collapsed walls of submarine canyons and the western gulf margin indicate that mass wasting may be triggered by seismic activity. Seafloor lineaments defined by slope gradient analyses suggest that the Eilat Canyon and the boundaries of the Ayla high align along north- to northwest-striking fault systems—the Evrona Fault zone to the west and the Ayla Fault zone to the east. The shelf–slope break that lies along the 100 m isobath in the Eilat subbasin, and shallower (70–80 m isobaths) in the Aqaba subbasin, is offset by approx. 150 m along the eastern edge of the Ayla high. This offset might be the result of horizontal and vertical movements along what we call the Ayla Fault on the east side of the structure. Remnants of two marine terraces at 100 m and approx. 150 m water depths line the southwest margin of the gulf. These terraces are truncated by faulting along their northern end. Fossil coral reefs, which have a similar morphological appearance to the present-day, basin margin reefs, crop out along these deeper submarine terraces and along the shelf–slope break. One fossil reef is exposed on the shelf across the Ayla high at about 60–63 m water depth but is either covered or eroded in the adjacent subbasins. The offshore extension of the Evrona Fault offsets a fossil reef along the shelf and extends south of the canyon to linear fractures on the deep basin floor.     

红河断裂带的新生代变形机制及莺歌海盆地的实验证据

红河断裂带是印藏碰撞过程中，印支地块被顺时针旋转挤出的走滑变形带。莺歌海盆地发育于红河断裂带海上延伸带上。根据莺歌海盆地和相邻的NE向琼东南盆地在晚中新世前(5．5Ma B．P．)独立的构造发育和差异的沉降特点，认为红河断裂不可能穿越莺琼盆地界限向北东延伸，而越东断裂和中建南断裂很可能是红河断裂的延续。莺歌海盆地成盆机制的物理模拟结合红河断裂带陆上的变形特征、年代学证据与青藏高原隆升过程的研究，参考莺歌海盆地模拟过程中不同应力场下沉降中心的长轴方向，我们推断红河断裂带新生代的演化大致分4个阶段：(1)50-38Ma B．P．期间的缓慢平移运动；(2)38—25MaB．P．期间的快速左行走滑运动；(3)25—5Ma B．P．期间的左行走滑逐渐停止阶段；(4)5Ma B．P．后的右行走滑阶段。     

The antipodes fracture zone,a major structure of the south‐west pacific

The steep Antipodes Scarp, along the eastern boundary of the Campbell Plateau south‐east of New Zealand, is attributed to dextral tear‐faulting within a NE‐SW belt, the Antipodes Fracture Zone, which also truncates the eastern end of the Chatham Rise. A complementary zone of sinistral movement, the Waipounamu Fracture, separates the Campbell Plateau and Chatham Rise from mainland New Zealand.

The origin of these fracture zones is linked with that of the parallel Alpine Fault of South Island, and is related to a phase of NE‐SW crustal compression that dominated the New Zealand region during the Mesozoic era. It is suggested that this compression resulted from the north‐eastward “drift” of the Australian craton and the simultaneous elevation of the Darwin Rise in the central Pacific.     

The Vema Transverse Ridge (Central Atlantic)

Transverse ridges are elongate reliefs running parallel and adjacent to transform/fracture zones offsetting mid-ocean ridges. A major transverse ridge runs adjacent to the Vema transform (Central Atlantic), that offsets the Mid-Atlantic Ridge by 320 km. Multibeam morphobathymetric coverage of the entire Vema Transverse ridge shows it is an elongated (300 km), narrow (<30 km at the base) relief that constitutes a topographic anomaly rising up to 4 km above the predicted thermal contraction level. Morphology and lithology suggest that the Vema Transverse ridge is an uplifted sliver of oceanic lithosphere. Topographic and lithological asymmetry indicate that the transverse ridge was formed by flexure of a lithospheric sliver, uncoupled on its northern side by the transform fault. The transverse ridge can be subdivided in segments bound by topographic discontinuities that are probably fault-controlled, suggesting some differential uplift and/or tilting of the different segments. Two of the segments are capped by shallow water carbonate platforms, that formed about 3–4 m.y. ago, at which time the crust of the transverse ridge was close to sea level. Sampling by submersible and dredging indicates that a relatively undisturbed section of oceanic lithosphere is exposed on the northern slope of the transverse ridge. Preliminary studies of mantle-derived ultramafic rocks from this section suggest temporal variations in mantle composition. An inactive fracture zone scarp (Lema fracture zone) was mapped south of the Vema Transverse ridge. Based on morphology, a fossil RTI was identified about 80 km west of the presently active RTI, suggesting that a ridge jump might have occurred about 2.2 m.a. Most probable causes for the formation of the Vema Transverse ridge are vertical motions of lithospheric slivers due to small changes in the direction of spreading of the plates bordering the Vema Fracture Zone.     

Relationships between magmatism and tectonics in a continental rift: The Pantelleria Island region (Sicily Channel, Italy)

Field geological data of the Pantelleria Island, a large Late Quaternary volcano located in the Sicily Channel rift zone, integrated with offshore geophysical information, are used to derive the structural setting of the Island and the surrounding region, and to analyse the relationships between tectonics and magmatism. Field work shows that the principal faults exposed on the Island fall into two systems trending NNE–SSW and NW–SE. Mapped faults from offshore multichannel seismic profiles show similar trends, and some of them represent the offshore extension of the Pantelleria Island structures. The NW–SE faults bound the Pantelleria Graben, one of the three main depressions formed since the Late Miocene–Early Pliocene within the African continental platform, which compose the Sicily Channel rift zone. A 3-D Moho depth geometry, derived from inversion of Bouguer gravity data, shows a significant uplift of the discontinuity up to 16–17 km beneath the westernmost part of the Pantelleria Graben and beneath the Pantelleria Island; it lows rapidly to 24–25 km away from the graben north-eastward and south-westward. The Moho uplift could explain the presence of a shallow magma chamber in the southern part of the Island, where processes of magmatic differentiation are documented. Geological and geophysical data suggest that the northwestern part of the Sicily Channel is presently dominated by a roughly E–W directed extensional regime. Crustal cracking feeding the Quaternary volcanism could be also related to this extensional field that would be further responsible for the development of the N–S trending volcanic belt that extends in the Sicily Channel from Lampedusa Island to the Graham Bank. This mode of deformation is confirmed also by geodetic data. This implies that in the northwestern part of the Sicily Channel, the E–W extension replaced the NE–SW crustal stretching that originated the NW-trending tectonic depressions constituting the rift zone.     

Geological comparative studies of Japan Arc System and Kyushu-Palau Arc

Based on the published data of structure geology,geochronology,petrology and isotope geochemistry,the authors of this paper have conducted studies on the tectonic evolution history of Japan arc system and Kyushu-Palau ridge(KPR) . The studies show that the initial Japan arc system was resulted from the subduction of ancient Pacific plate beneath Eurasian Plate in Permian. It was part of an Andean-type continental volcanic arc which occurred in the offshore in the east of Asian during late Mesozoic era. The formation of tertiary back-arc basin(Japan Sea) resulted in the fundamental tectonic framework of the present arc system. Since Quaternary the system has been lying at E-W compression tectonic setting due to the eastward subduction of Amur Plate. It is expected that Japan arc system will be juxtaposed with Asian continent,which is similar to the present Taiwan arc system. The origin of Philippine Sea Plate(PSP) is still in debate. Some studies argued that it is a trapped oceanic crust segment,while the others insisted that it is a back-arc basin accompanied with ancient IBM arc. However,it is all agreed that the tectonic evolution of PSP started since 50 Ma,i.e.,PSP has drifted from the site around equator at 50 Ma to the present site,and the subduction of PSP along Nankai trough-Ryukyu Trench beneath the Japan arc system during 6-2 Ma led to the formation of the present Ryukyu arc system. Of the PSP,the KPR has been found with the oldest rocks formed at 38 Ma. Combining with its geochemical characteristics of oceanic arc tholeiite,it is suggested that KPR is an intraoceanic volcanic arc,more specifically,a relic arc(i.e.,rear arc of the ancient IBM) after rifting of ancient IBM. In addition,Amami-Daito province is of arc tectonic affinity,but has been affected by mantle plume. Therefore,based on their respective tectonic evolution history and geochemical characteristics of rock samples,it is inferred that there is no genetic relationship between Japan arc system and KPR. It is noted that rocks reflecting continental crust basement feature have been collected on the northern tip of KPR,which may be related to the process of KPR accreting on Japan arc,but the arc-continent accretion process are still at initial stage of modern continental crust accretion model. However,due to the scarcity of data of the northern tip of KPR,crustal structure of this location and its adjacent Nankai trough need to be further constrained by geophysical studies in the future.     

Mud volcanoes and gas vents in the Okhotsk Sea area

Gas emissions from mud volcanoes on Sakhalin Island and water-column gas flares arising from cold seeps in the Okhotsk Sea appear to be related. They are likely activated by tectonic movements along the transform plate boundary separating the Okhotsk Sea Plate from the Eurasian and Amur plates. Gas vents (flares) and methane anomalies occur in the waters offshore Sakhalin Island, along with NE-SW-trending mounds and fluid escape structures on the seafloor. The intersection of the NE-striking transverse faults on land with the Central Sakhalin and Hokkaido-Sakhalin shear zones apparently determines the sites of mud volcanoes, a pattern that continues offshore where the intersection with the East Sakhalin and West Derugin shear zones determines the sites of the submarine gas vents.     

Multidisciplinary geophysical measurements on the ocean floor usingdecommissioned submarine cables: VENUS project

To perform geophysical and multidisciplinary real-time measurements on the ocean floor, it has been attempted to reuse decommissioned submarine cables. The VENUS project reuses the TPC-2, which is one of these systems and runs across the entire Philippine Sea Plate between Guam Island and Okinawa Island. The VENUS system comprises an ocean floor observatory, a submarine cable, and a land system. The major components of the ocean floor observatory are geophysical instruments and a telemetry system. There are seven scientific instrument units including broadband seismometers and a hydrophone array. Digital telemetry using the old analog telephone cable obtains high data accuracy and real-time accessibility to data from a laboratory on land. The bottom-telemetry system and a part of sensor units were installed at a depth of 2157 m on the landward slope of the Ryukyu (Nansei-Syoto) Trench on August 29, 1999. The data from the hydrophone array and tsunami gauge have been correctly transmitted to the data center. The rest of the scientific instruments will be deployed by deep-tow equipment and a remotely operated vehicle. Using a decommissioned submarine cable will greatly reduce construction costs compared to using a new cable system     

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.