morphology and environment of cold water coral carbonate mounds on the nw european margin cold water coral carbonate mounds owing their presence mainly to the framework building coral lophelia pertusa and the activity of associated organisms are common along the european margin with their spatial distribution allowing them to be divided into a number of mound provinces variation in mound attributes are explored via a series of case studies on mound provinces that have been the most intensely investigated belgica hovland pelagia logachev and norwegian mounds morphological variation between mound provinces is discussed under the premise that mound morphology is an expression of the environmental conditions under which mounds are initiated and grow cold water coral carbonate mounds can be divided into those exhibiting inherited morphologies where mound morphology reflects the morphology of the colonised features and developed morphology where the mounds assume their own gross morphology mainly reflecting dominant hydrodynamic controls finer scale surface morphological features mainly reflecting biological growth forms are also discussed

paleomagnetic study of plio pleistocene sediments in the concentrated deformation zone along the eastern margin of the japan sea abstract paleomagnetic results are presented for a concentrated deformation zone cdz in a convergent plate boundary region along the eastern eurasian margin we sampled late pliocene early pleistocene tuffs and clastic sediments of the sasaoka formation 750 m thick in northeastern honshu japan to test whether the late pliocene quaternary crustal deformation within the cdz along the eastern margin of the japan sea was accompanied by rotation about a vertical axis rock magnetic experiments suggest that the principal magnetic carrier is magnetite in the fine tuffs and magnetic iron sulfide in the fine sandstones pre folding characteristic remanent magnetization was confirmed using a positive bootstrap fold test we obtained 21 acceptable site mean characteristic directions that include our preliminary published results and which cover an interval from ca 2 7 to 1 7 ma on the basis of magnetostratigraphic correlations an updated age depth model is given and this allowed us to make numerical age estimates for key interbedded tuff beds tephras a positive fold test also suggests that the gojome syncline began to develop after 1 7 ma which means the folding began long after the initiation of late pliocene crustal shortening in northeastern honshu after 100 unfolding the overall mean direction d 359 7 i 54 9 95 6 7 is indistinguishable from the geocentric axial dipole field direction indicating that the gojome syncline the most prominent structural element in the study area developed without vertical axis rotation a comparison of our results with plio pleistocene directions reported from other areas reveals no paleomagnetically detectable rotation in or adjacent to the cdz except for local rotation near strike slip faults in central honshu

structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

lithoherms on the florida hatteras slope sections of the florida hatteras slope were investigated during dives of the johnson sea link i submersible and us navy s submarine nr 1 numerous calcareous coral capped lithoherms often exceeding 40 m in elevation were encountered in the subphotic depths below 440 m one huge lithoherm complex was explored that forms a long slope parallel ridge perched on the seaward edge of mid slope terrace this lithoherm belt is 400 m wide more than 4 4 km long and 150 m high on its down slope flank direct observations and side scan imaging indicate that the long axes of individual ridge crest mounds trend perpendicular to the regional current flow away from the ridge individual lithoherms trend more parallel with regional current flow and occur without obvious bedrock control all of these structures have very steeply sloping flanks frequently 30 60 where cemented crusts are exposed by erosion thickets of living ahermatypic coral coat the crest and up stream flanks of these topographic features living deep water coral have modern 14c ages 700 80 year bp and trap older 3250 100 year bp sediment rich in fine grained aragonite elsewhere older deep water coral rubble 20 230 230 year bp traps younger sediment 13 760 140 year bp the trapped sediments contain 50 aragonite fines 62 5 m the friable crusts exposed on these flanks are generally similar in composition to the sediments that accumulate on the crests of these structures they are older 14c ages of 17 770 330 and 32 710 570 year bp and contain less aragonite 20 and more high magnesium calcite apparently lithoherms grow upwards by trapping fine sediments within ahermatypic coral thickets on their crests and upstream flanks cemented crusts may be a consequence of earlier paleoceanographic conditions or a result of gradual and ongoing cementation and diagenesis the large size platform edge position and linear trend of this deep water lithoherm complex are strikingly similar to a shallow marginal reef system

classification of sea floor features associated with methane seeps along the gulf of cadiz continental margin abstract based on recently gathered swath bathymetry high to ultra high resolution seismic and underwater camera data along with dredging and coring samples this paper examines the relationship between sea floor features and the nature of hydrocarbon enriched fluid and gas leaks from degassing of deeply buried sediments along the continental margin of the gulf of cadiz eastern central atlantic a classification into three main groups is proposed on the basis of the morphology and nature of deposits 1 mud volcanoes 2 methane derived authigenic carbonates mdac mounds and 3 crater like pockmarks mud volcanoes are topographically cone shaped sea floor edifices built up from catastrophic mud and fluid degassing intercalated with periods of inactivity so far more than 25 mud volcanoes have been discovered in the gulf of cadiz named in memory of deceased colleagues e g ginsburg and baraza or researchers birth places e g faro cibeles almazan san petersburgh yuma rabat bonjardim coruna gades these structures range from 800 to 2500 m in diameter and tower 150 300 m above the seabed the volcanoes consistently feature a well defined outer ring or circular terrace and an inner dome all mud volcanoes are built up of episodes of mud breccia flows intercalated with deep current deposits with evident indications of gas saturation degassing structures a strong h2s smell and chemosynthetic fauna such as pogonophora sp tube worms and calyptogena sp commonly observed carbonate crusts and slabs overlying some mud volcanoes are thought to have been formed by slow diffuse venting during periods of inactivity or slower rates of fluid venting following the ejection of mud a fermentation process the result of microbial mediated oxidation of hydrocarbon enriched fluids seems to play an important role in the growth of large deep water carbonate mounds and chimneys during periods of low methane seep fluid pressure more than 400 crater like pockmarks a common sea floor feature in the tasyo field have been observed their seabed diameter ranges from 500 to 3000 m with steep slopes ranging from 12 to 35 according to their internal structure pockmarks can be grouped into 1 pockmarks with low central mounds and 2 crater like pockmarks apparently collapse structures lacking central mounds with a flat to slightly undulating sea bottom surrounded by steep slopes up to 25

interseismic stress accumulation at the locked zone of nankai trough seismogenic fault off kii peninsula abstract a primary source of stress variation prior to great subduction zone earthquakes is the tectonic loading due to plate convergence we have calculated the elastic stress around the locked zone accumulated during an interseismic period numerically using a 2d plane strain finite element model in the nankai trough off kii peninsula and examined its dependence on elastic properties and some boundary conditions for the modeling we used the geometry of subducting plate interface determined previously through seismic surveys and the physical properties that were obtained through iodp scientific drilling offshore kii peninsula to construct a physically realistic model a dislocation along the plate interface is calculated from a 5 m displacement imposed on one side of the subducting plate with the locked zone defined at a depth of 10 to 25 km along the plate interface calculated shear stress is maximized at the downdip edge of the locked zone decreases exponentially seaward and is almost zero near the updip edge maximum shear stress is primarily proportional to the young s modulus of the overlying section comparing the maximum shear stress with the average stress drop for subduction earthquakes 3 4 mpa the most appropriate young s modulus and poisson s ratio ranges are 50 70 gpa and 0 3 respectively which are in good agreement with previous estimations from observed vp vs the stress accumulated during one seismic cycle can be reasonably explained by a linear elastic model with an appropriately sized locked region we found that the envelope of simulated horizontal displacement on the surface agrees well with gps velocity data which also supports this inference disturbance near the updip edge is no larger than 0 1 mpa of stress or 0 1 radian of tilt which are difficult to detect with current borehole measurement techniques and likely complex borehole conditions

vent type taxa in a hydrocarbon seep region on the louisiana slope recent discoveries on the northern gulf of mexico continental slope have altered our understanding of biological and chemical processes occurring in the deep ocean a biological community of hydrothermal vent type organisms was recently discovered at the base of the florida escarpment1 where the fauna are apparently nourished by hydrogen sulphide rich hypersaline water seeping out onto the sea floor dense colonies of deep living chemosynthetic benthic organisms were first discovered during investigations of warm water anomalies along the axis of the galapagos rift in the pacific ocean in 19772 4 and this first discovery of clusters of clams tube worms and other filter feeders in the immediate proximity of warm water vents has been followed by the discovery of a number of other hydrothermal vent sites for example guaymas basin east pacific rise at 21 n the dense population assemblages at these sites are apparently restricted to small areas of the ocean floor where hydrogen sulphide rich water is escaping from spreading centres but the florida escarpment discovery indicates that these communities can also exist on passive margins here we report the discovery of dense biological communities associated with regions of oil and gas seepage on the louisiana continental slope these communities of large epi and infaunal organisms are similar to those associated with the vents of the pacific and the hypersaline brine seeps of the florida escarpment carbon isotope analyses suggest that these communities are chemosynthetic and derive their energy from hydrogen sulphide and or hydrocarbons similar communities may be widely distributed on the sea floor in other oil producing regions of the ocean

the fugloy reef at 70 n acoustic signature geologic geomorphologic and oceanographic setting this is the first in depth study of a cluster of cold water coral reefs the fugloy reefs found at 70 n on the norwegian margin combining high resolution seismic reflection data side scan sonar video images and oceanographic measurements reveals the geologic geomorphologic and oceanographic setting in which the reefs occur the reefs consist mainly of the scleractinian ahermatypic lophelia pertusa and exist below the thermocline at water depths between 140 m and 190 m the reefs appear as cone shaped acoustically transparent features on seismic reflection data consistently located in places characterized by the availability of hard substrate high relief and periodical exposure to high tidal currents 30 cm s these currents transport water of the norwegian atlantic current to the reefs from an area with fluid expulsion related pockmarks the spatial relationship between reef pockmark locations and current directions suggests that seepage of biogenic gas might be a catalyst to reef growth with a height of more than 40 m some of the fugloy reefs are among the highest reported from the norwegian margin this indicates highly favourable growth conditions and conservative estimates indicate a net growth rate for the reefs of 5 mm year we expect that cold water reefs will be found further north along the barents sea margin as general awareness on the geophysical signature and appearance of the reefs increases because all known factors involved in reef establishment and growth are within the required intervals also further north

introduction of covariance components in slip inversion of geodetic data following a non uniform spatial distribution and application to slip deficit rate estimation in the nankai trough subduction zone when spatial distribution of observation stations has bias in geodetic slip inversion modeling errors in the inversion scheme may result in significant unnatural short wave components in estimated slip distribution which overfit to data combined use of both land and seafloor geodetic data in slip inversion often leads to such situations to avoid overfitting i proposed a method to incorporate proper covariance components in the data covariance matrix originated by modeling errors in the geodetic slip inversion because linearity of the inversion problem is retained widely known approaches to introduce prior constraints to the inversion which assumes linear inversion are easily applied to the proposed method synthetic tests showed that the introduction of covariance components allowed for the estimation of slip distributions closer to the true one avoiding overfitting to geodetic data in biasedly distributed observation stations compared to a conventional approach that does not introduce covariance components i applied the proposed method to the estimation of the slip deficit rate in the nankai trough subduction zone using geodetic data of displacement rates provided by land gnss stations and seafloor gnss acoustic stations the proposed method estimated a reasonably smooth distribution of slip deficit rate compared to the conventional approach spatial distribution of residuals in the displacement rates suggested that the proposed method successfully avoids overfitting to the block motion at the south of the median tectonic line which the physical model i assumed here cannot describe

strain partitioning in the zone of transition from nankai subduction to izu bonin collision central japan implications for an extensional tear within the subducting slab abstract the izu bonin ridge collision with central japan is a type example of collision of two island arcs in a subduction context based on the analysis of active faults paleomagnetic data and recent seismicity in the northern tip of the izu bonin arc and the adjacent oceanic plate we propose a tectonic schema of the izu collision system and its transition to the nankai subduction to the west the dense gps network deployed in central japan allows us to constrain the kinematics of the different blocks identified this new kinematic model demonstrates the essential role of strain partitioning there as the northward component of the izu bonin arc motion is locked in the collision zone 30 of the convergence between the philippine sea plate and central japan is accommodated within the philippine sea slab along the zenisu east izu deformation system we show that this pattern of deformation is related to an extensional tear of the philippine sea slab propagating southward along the volcanic arc we discuss the implications of this kinematic model on the seismogenic potential of the area and the dynamics of the central japan convergence zone

mud volcanoes at the shelf margin of the east china sea abstract roughly circular sediment mounds varying from tens to hundreds of meters in diameter and from a few meters up to 40 m in height have been mapped for the first time at the shelf edge of the east china sea ecs high resolution seismic profiles together with swath bathymetric and acoustic data indicate that these features are common on the ecs outer shelf and on the upper western slope of the okinawa trough they are associated with unusually large pockmarks up to 40 m in depth and 600 m in diameter on seismic records bright spots phase inversions and other acoustic anomalies indicate that gas and or fluid escape plays an important role in the formation of these mounds they are often associated with normal faults that occur along the western slope of the okinawa trough these faults acting as conduits for migrating fluid based on regional stratigraphic correlation we propose that the source of mud and fluid is deeper older than 235 ka the seepage process is suspected to be very recent and probably still active based on the facts that 1 despite high sedimentation rate the mounds are not buried by recent sediments and 2 last glacial maximum deposits are reworked at the emplacement of the mounds carbonate cemented sediments and deep water reefs possibly associated with fluid seepage could be the origin of local patches of very high backscattering acoustic facies mapped with the swath bathymetric system

collision and fan shaped compressional stress pattern in the izu block at the northern edge of the philippine sea plate the izu block in central japan which is surrounded by the nankai suruga trough and the sagami trough is considered to be colliding with the eurasian eur plate at the northern edge of the philippine sea phs plate the stress state in the izu block is investigated from focal mechanism data mainly obtained by the seismic network of the national research institute for earth science and disaster prevention the predominant focal mechanisms in the central to eastern part of the izu block indicate strike slip faulting with p axes oriented n s to nw se and t axes oriented e w to ne sw whereas focal mechanisms in the western part are strike slip and reverse faulting with p axes oriented n s to ne sw indicating that the compressional axes remain horizontal throughout the region the compressional stress trajectories estimated from the p axes show a fan shaped pattern radiating from the northern edge of the izu block where the collision is considered to be occurring the fan shaped pattern of compressional stress trajectories is interpreted to be the result of the collision of the izu block with eur plate plane stress analysis by the finite element method supports this conclusion the stable distribution of the t axis directions in the central to eastern part is basically interpreted as resulting from the slab pull force by the subducting phs plate along the sagami trough furthermore this model can explain the seismic quiescence in the northern part of the suruga bay region

australian offshore natural hydrocarbon seepage studies a review and re evaluation abstract surprisingly few natural hydrocarbon seeps have been identified in australia s offshore basins despite studies spanning thirty years early studies of natural hydrocarbon seepage around the australian margin were generally based on the geochemical analysis of stranded bitumens water column geochemical sniffer sampling synthetic aperture radar or airborne laser fluorosensor later studies involved the integration of these remote sensing and geochemical techniques with multi channel and shallow seismic a review of these earlier studies indicates that many seepage interpretations need to be re evaluated and that previous data sets when placed in a global context often represent normal background hydrocarbon levels low recent burial and subsidence rates are not favourable for high rates of seepage there are also difficulties in proving seepage on high energy shallow carbonate shelves where seabed features may be rapidly re worked and modern marine signatures are overprinted on authigenic seep carbonates thus the relatively few sites of proven natural hydrocarbon seepage in australia s offshore sedimentary basins can be reconciled relative to their geological occurrences and the dominantly passive margin setting active thermogenic methane seepage on the yampi shelf the only proven documented occurrence in australia is driven by deposition of a thick late tertiary carbonate succession and late miocene tectonic reactivation therefore to increase the success of detecting and correctly interpreting natural hydrocarbon seepage data need to be analysed and integrated within the context of the local geological setting and with an understanding of what is observed globally

simple spring mass model simulation of earthquake cycle along the nankai trough in southwest japan along the nankai trough in southwest japan due to the subduction of the philippine sea plate great earthquakes have occurred repeatedly the rupture zone is divided into five segments historical documents show the characteristic features of the past several earthquake cycles such as almost simultaneous rupture occurrence in segments in spite of different convergence rates the recurrence time of 90 to 150 years the existence of segment pairing in earthquake ruptures and the different coseismic slip behaviors in respective segments

identification and numerical modelling of hydrocarbon leakage in the lower congo basin implications on the genesis of km wide seafloor mounded structures abstract we present a combined approach of interpretation of 2d seismic reflection data and numerical modelling of hydrocarbon generation and migration across the southern slope of the lower congo basin in order to investigate the factors controlling timing and distribution of hydrocarbon leakage in this area we identified three main families of past and present day leakage features 1 mid upper miocene seismic chimneys concentrated basinwards and ending up on buried pockmarks 2 plio pleistocene chimneys rather clustered to the east of the study area and ending up in seafloor pockmarks and 3 fewer scattered chimneys identified within the miocene sequences ending up in shallow enhanced reflectors flat spots stratigraphic and structural elements seem to control the distribution of these features at least two major events of leakage occurred during the middle late miocene and intermittently during the pliocene present external factors as sediment supply are associated to the miocene leakage event whilst internal structural elements probably triggered the pliocene to present day leakage a major seabed morphological feature represented by a margin paralleled belt of more than 1 km wide mounds was identified above growth faults to the east of the study area data constrained 2d hc generation and migration modelling suggests a genetic link between these structures and vertical migration leakage of thermogenic methane sourced from either currently mature oligo miocene source rocks or secondary cracking and further expulsion from over mature upper cretaceous source rocks hence the mounds are likely to represent a lineation of methane derived carbonate build ups despite the natural limitations of a 2d migration model when combined and calibrated with observations from seismic data it can be used as a valid tool to assess petroleum migration routes in sedimentary basins to the best of our knowledge this is the first integrated approach combining both seismic observations and numerical modelling carried out in the angola basin

the geochemistry of metalliferous sediments and waters associated with shallow submarine hydrothermal activity santorini aegean sea abstract detailed investigations on the geochemistry of waters and sediments associated with shallow water submarine hydrothermal activity within santorini caldera has helped to clarify the nature of this hydrothermal system and shown it to have features in common with recently discovered deep water hydrothermal systems at oceanic spreading centres metals discharging from hydrothermal vents are selectively precipitated at increasing distances from the hydrothermal sources leading to a compositional zonation in both sediments and waters fe is markedly enriched in both the waters and sediments of the inner exhalative zone close to the hydrothermal vents but decreases rapidly in the former to values similar to those of normal seawater in the outer exhalative zone 50 100 m from the vents generally mn also decreases in the waters away from the vents as does zn but both less sharply than fe by contrast mn shows an enrichment in sediments at increasing distances from the vents the distribution of the minor elements can be related to both their rate of supply in the hydrothermal fluids and their removal to the sediments by scavenging although other controls on their abundance such as detrital and biogenic supply are of variable importance at increasing distances from the vents

characterisation and correlation of active hydrocarbon seepage using geophysical data sets an example from the tropical carbonate yampi shelf northwest australia abstract for the first time in australia active present day hydrocarbon seepage has been imaged on the tropical carbonate yampi shelf in 50 and 90 m water depth seepage is evidenced by gas plumes in the water column that are associated with seabed features such as clusters of reflective blocks hard grounds pockmark fields and mounds seepage activity and intensity seems to vary with changes in pressure related to macro tidal cycles the seabed features coincide with sub surface features such as areas of seismic signal attenuation under high amplitude reflectors seismic discontinuities and bright spots hydrocarbon migration seepage pathways appear to be controlled by the reactivation of pre existing fractures and dykes within the basement the types of seabed features and their preservation on a tropical carbonate shelf are strongly influenced by the coarse bioclastic nature of sediments and the high energy of macro tidal currents and storm reworking

crustal block kinematics and seismic potential of the northernmost philippine sea plate and izu microplate central japan inferred from gps and leveling data 1 we clarify the contemporary deformation observed by gps and leveling for the greater tokyo kanto eastern tokai and the izu islands region where the izu ogasawara bonin arc is subducting and colliding with the central part of the japan arc from these data we develop a kinematic model of fault sources with variable components of seismic and aseismic slip under the assumption that the contemporary deformation during 1995 2000 is representative of the long term interseismic strain field the geodetic data are inverted to estimate the rotation poles of the crustal blocks the degree of elastic strain accumulation on faults and the volumetric inflation sources beneath volcanoes the present crustal movements are explained by four crustal blocks the izu microplate the central japan block the pacific plate and the philippine sea plate along the suruga and sagami margins of the philippine sea plate lie strongly coupled faults which include sites of the 1854 m 8 4 tokai 1923 m 7 9 kanto and 1703 m 8 2 genroku kanto earthquakes in contrast the philippine sea plate boundary immediately north of the izu peninsula site of m 7 5 collisional earthquakes is only weakly coupled the boundary between the izu microplate and the philippine sea plate experiences left lateral motion with the rate of 30 mm yr most of this boundary is locked and thus has a large potential of future earthquakes the izu microplate is found to rotate rapidly clockwise at 10 myr with a rotation pole relative to the central japan block located just north of its northern boundary the pole and angular velocity of the izu microplate depends however on the assumed location of the boundary with the exception of the site of the 1938 m 7 earthquake swarm which we infer has the current potential to produce a m 8 1 earthquake the pacific megathrust has a very low seismic potential although the geodetic data have little resolving power for much of the pacific plate interface east of tokyo

geofem kinematic earthquake cycle simulation in southwest japan we construct a viscoelastic fem model with 3 d configuration of the subducting philippine sea plate in southwest japan to simulate recent 300 year kinematic earthquake cycles along the nankai suruga sagami trough based on the kinematic earthquake cycle model this 300 year simulation contains a series of three great interplate earthquakes the inclusion of viscoelasticity produces characteristic velocity field during earthquake cycles regardless of the assumed constant plate coupling throughout the interseismic period just after the occurrence of interplate earthquakes the viscoelastic relaxation creates the seaward motion in the inland region in the middle period the seaward motion gradually decreases and the resultant velocity field is similar to the elastic one later just before the next interplate earthquake displacements due to the interplate coupling in the viscoelastic material are distributed more broadly in the forearc region than in the purely elastic one since the viscoelastic relaxation due to the previous earthquake mostly disappears the effects of such interplate earthquake cycles on five major inland faults in southwest japan where large intraplate earthquakes occurred during this period are quantitatively evaluated using the coulomb failure function cff the calculated change in cff successfully predicts the occurrence of the 1995 kobe earthquake m 7 the occurrence of other inland earthquakes however cannot be explained by the calculated changes in cff and especially the 1891 nobi earthquake m 8 the largest inland earthquake in japan which occurred at the time close to the local minimum of cff this implies that further improvements are necessary for our fem modeling such as the modeling of steady east west compressive force and stress interactions between the inland faults

sediment dynamics of a sandy contourite the sedimentary context of the darwin cold water coral mounds northern rockall trough grainsize mineralogy and current meter data from the northern rockall trough are presented in order to characterise the sandy contourite that forms the sedimentary environment of the darwin cold water coral mounds and to investigate the impact of this environment on the mound build up large clusters of small cold water coral mounds 75 m across and 5 m high have been found southwest of the wyville thomson ridge at 900 1 100 m water depth their present day sedimentary environment consists of a subtly sorted sandy contourite elongated ne sw roughly parallel to the contours critical erosional and depositional current speeds were calculated and trends in both the quartz feldspar and foraminifera fractions of the sands show a bi directional fining from bedload erosion dominated sands in the ne to suspension deposition dominated sediments in the sw and towards the s downslope this is caused by a gradual reduction in governing current speed linked to a reduction in slope gradient and by the increasing distance from the current core in the downslope direction no specific characteristics were found distinguishing the mound sediments from the surrounding sands they fit in the overall spatial pattern some mound cores show hints of a fining upward trend overall the mound build up process is interpreted as a result of sediment baffling

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

mineralogy and geochemistry of alteration induced by hydrocarbon seepage in an evaporite formation a case study from the zagros fold belt sw iran abstract leaking hydrocarbon and associated fluids produce a reduced environment which initiates diagenetic reactions in the rocks and soils overlying hydrocarbon reservoirs this article introduces mineralogical and geochemical alterations induced by hydrocarbon seepages in the gachsaran evaporite formation masjed soleiman zagros folded belt sw iran using various geochemical methods x ray diffraction xrd analysis revealed two dominant groups of mineralogical changes in the anomalous zone including 1 spotty occurrences of jarosite natroalunite and sulfur 2 simultaneous decrease of sulfate and increase of carbonate the 13c values of carbonate phases vary between 8 9 and 32 3 which support a partial contribution of hydrocarbon in these phases ph measurements of rock samples indicated that hydrocarbon seepage causes decrease of ph though not very significantly however ph in areas that show ongoing sour hydrocarbon seepage among rarely pure gypsum beds decrease to 0 09 which produces acid sulfate soil trace element concentrations indicated that cr co ni v cd u cu and zn increase in various patterns around the hydrocarbon seepages excepting the areas with very low ph

oligocene to holocene hydrocarbon migration and salt dome carbonates northern gulf of mexico abstract the geochemistry and geology of damon mound salt dome in brazoria county texas provides an insight to the timing of hydrocarbon migration and carbonate caprock development in the houston salt dome province reservoir rocks flanking the salt dome received a charge of crude oil from deeply buried eocene source rocks during early oligocene early miocene time the light 13c of the carbonate caprock at damon mound 24 8 to 31 7 pdb is consistent with an origin from bacterial oxidation of crude oil with similar 13c 27 1 to 28 8 pdb a minimum weight estimate of carbonate caprock at damon mound is 32 7 106 metric tons suggesting bacterial oxidation of about 34 2 106 barrels of crude oil to form the carbonate late oligocene early miocene erosional exposure of the carbonate caprock provided a hard substratum to initiate the development of a coral reef in an otherwise unfavourable mud dominated environment although the bulk of the reef carbonate displays normal marine 13c some late carbonate cements show light 13c values 22 1 to 29 6 from bacterial hydrocarbon oxidation buried carbonate caprocks and coral reef facies serve as carbonate reservoir rocks over gulf of mexico salt domes lending support to the hypothesis that intense hydrocarbon oxidation can in itself give rise to some carbonate reservoir rocks ongoing hydrocarbon migration from deeply buried cretaceous source rocks and the development of embryonic carbonate caprocks over shallow salt domes on the present gulf of mexico continental slope offer analogies and contrasts to the processes that gave rise to carbonates at damon mound in the geological past

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

fault related biogenic mounds in the ceduna sub basin australia implications for hydrocarbon migration abstract the early cenozoic in the bight basin represents a transitional period from the slow to fast oceanic crust spreading of the southern ocean between australia and antarctica this period is characterised by widespread igneous activity and the occurrence of biogenic mound complexes in the proximal part of the ceduna sub basin these mound complexes thrive on local topographic highs exploiting the shut down in siliciclastic sediment supply during the eocene new interpretation of 2d and 3d seismic data from the central ceduna sub basin shows additional undrilled paleocene eocene biogenic mound complexes they display rugose morphology progradational and aggradational internal organisation and high impedance contrast with the surrounding sediments these mounds typically show a clear relationship with underlying reactivated fault segments these faults intersect potential oil mature cretaceous source rock intervals and therefore one plausible mechanism for the development of fault related mound complexes in the central ceduna sub basin relies on natural hydrocarbon seeps along faults supplying nutrients for a benthic chemosynthetic organisms and localised biogenic mound growth the presence of a sub bottom profile anomaly overlaid by a vertical water column acoustic contact in close vicinity of a mound complex support this model the occurrence of seep related biogenic mounds would validate the presence of mature source rock s and hydrocarbon charge in the central ceduna sub basin if confirmed the biogenic mounds would imply fluid migration occurrence until at least the eocene

hypocenters in the nankai trough determined by using data from both ocean bottom and land seismic networks and a 3d velocity structure model implications for seismotectonic activity abstract we investigated the hypocenter distribution along the nankai trough off the kii peninsula japan by using data from both ocean bottom and land based seismic networks because seismic velocity structures differ greatly below land and ocean we used a 3d velocity model based on a structural model of the philippine sea plate phs which provides much more accurate estimations of source locations than 1d velocity models derived from either onshore or ocean bottom seismic data alone especially for sources between the coast and the trough axis we identified intensive seismic activity below the axis of the nankai trough which we interpreted to be aftershocks of the 2004 off the kii peninsula earthquakes m jma 7 1 7 4 and 6 5 but found much less seismic activity along the subducting phs the earthquake sources below the trough axis lie on dipping planes within the phs from which we inferred that a fracture zone is developing within the phs our estimated focal mechanisms for these earthquakes showed that their p axes were oriented north south to northeast southwest similar to those of the 2004 events which were rotated clockwise by 45 90 from the northwest southeast direction of convergence between the phs and the eurasian plates we consider that the fracture zone represents a boundary between the phs and the izu microplate which are converging in a north south direction and that the 2004 earthquakes and subsequent seismic activity were caused by the collision of these plates

short term slow slip and correlated tremor episodes in the tokai region central japan 1 we observe the related phenomenon of short term slow slip event sse and low frequency nonvolcanic tremor on the deeper extension of the 1944 tonankai and the anticipated tokai earthquake rupture areas central japan japan nation wide seismometer and tiltmeter array nied hi net has recorded these correlated episodes of sse and tremor known as episodic tremor and slip ets in 2004 and 2005 the events are located on two areas in the tokai region one is near the shima peninsula and the other is around the aichi area both episodes have a typical duration of 2 3 days and released seismic moment corresponding to mw 6 0 moreover these episodes repeatedly occur with a recurrence interval of about six months in both areas this evidence suggests that the coincidence between the sse and the tremor is a characteristic behavior in the whole tremor belt like zone in the nankai trough subduction zone

dynamic rupture scenarios of anticipated nankai tonankai earthquakes southwest japan 1 we investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the nankai tonankai subduction zone southwest japan to improve the scenario reliability the model parameters should be constrained by available data or derived from their analysis we employed the three dimensional plate interface geometry and the slip deficit rate on the interface accumulated slip deficit was used to obtain the stress drop distribution of anticipated earthquakes the estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes fault friction constitutive parameters however had to be assumed from indirect observations because they cannot be constrained directly by the data based on various geophysical observations we defined three regions where larger fracture energy is required these are the eastern edge of the tonankai area the western edge of the nankai area and the region between the tonankai and nankai areas beneath the kii peninsula such lateral heterogeneity promoted the segmented rupture along the nankai trough with predefined stress drop and constitutive parameters various rupture scenarios for tonankai and nankai asperities were obtained for different initiation locations in some cases a single segment is ruptured while in other cases all the segments are broken due to dynamic linkage at the segment boundary causing a giant earthquake the initiation location is a critical parameter that controls the rupture propagation across the segment boundary these scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest japan

interseismic seafloor crustal deformation immediately above the source region of anticipated megathrust earthquake along the nankai trough japan 1 we monitored seafloor crustal deformation using the gps acoustic seafloor geodetic observation technique at three sites on the kumano basin off southwestern japan which is located immediately above the source region of the anticipated tonankai megathrust earthquake we directly measured landward crustal movements of 40 mm y in the n80 w direction with respect to the amurian plate on the seafloor the directions were found to be the same as those measured at the on land gps stations the magnitudes of the velocity vectors indicated significant crustal shortenings of approximately 10 20 mm y between the kumano basin and the southeastern coast of the kii peninsula of the japanese islands the present observational results show strong and direct evidence for interplate locking during the interseismic period coupling ratios were roughly estimated at 0 6 0 8 on the plate interface up to at least 10 km in depth

holocene methane derived dolomite cemented sandstone pillars from the kattegat denmark abstract dolomite cemented sandstone pillars up to 4 m high and 1 m in diameter are recorded from 10 12 m of water in the kattegat denmark the framework of the sandstone pillars is similar to that of the adjacent sediments i e medium grained well sorted quartz sand the carbonate cement consists of equicrystalline ca rich dolomite mg47 ca53 co3 10 30 m in diameter exhibiting a sucrosic texture the sr content is relatively constant at approximately 1000 ppm whereas the fe and mn contents are highly variable with mean values of 1870 and 320 ppm respectively the carbon isotopic signature of the dolomite cement displays negative 13c values in the range of 44 to 40 the oxygen isotope composition shows 18o values in the range of 3 7 to 3 9 and is enriched in 18o by approximately 3 in comparison with co existing high mg calcite the negative 13c values suggest that the dolomite has derived its carbon via methane oxidation the genetic connection between dolomite cement formation and methane oxidation is visually supported by gas seeps from the seabed and vents in the sandstone pillars themselves it is believed that the methane originates from shallow gas in late quaternary marine deposits which led to a discharge of methane in the diagenetic zones of the topmost sedimentary column the dolomite precipitation most probably took place as a result of anaerobic methane oxidation subsequently the lithified sandstone pillars were exposed on the seafloor by large scale submarine erosion

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

integration of transient strain events with models of plate coupling and areas of great earthquakes in southwest japan we model the crustal deformation caused by two long term subduction slip transients in southwest japan which we refer to as the 2000 2004 tokai and the 2002 2004 bungo channel slow slip events sses we use re analysed geonet position time series and a kalman filter based network inversion method to image the spatiotemporal slip variation of the two events on the plate interface during the period of 1998 2004 67 and 2000 2005 both events are found to have complex slip histories with multiple subevents in addition to a newly identified slip subevent in 2002 2003 we find that the major event in the bungo channel sse initiated in early 2003 beneath the northeastern corner of the region and expanded southwestward in contrast to the slip characteristics suggested by other studies the re analysed gps data in the tokai region shows a renewed slip activity for the tokai sse in early 2003 2004 at a similar location as in the period of 2001 2002 the equivalent m w for both the tokai and bungo channel sses are about 7 0 our results show that the tokai sse appears to start before the miyaki kozu seismovolcanic event integrating plate coupling and sses shows that the transient slip zones are located in a region between the locked zones and the epicentres of the low frequency earthquakes lfes at least part of the interseismic slip deficit is released by episodic sses beneath the bungo channel region we find excellent temporal correspondence between transient slip and adjacent lfes for both sse suggesting that they are closely related and possibly reflect that long term slow slip may modulate the occurrence of lfes

seepage in vietnam onshore and offshore examples abstract hydrocarbon seepages in vietnam are generally linked to migration from tertiary source rocks and seeps are present both onshore and offshore residual oil can be observed at outcrop in breached traps within tertiary sections and in exhumed buried hill traps in pre tertiary rocks in the onshore hanoi basin there is active oil seepage on the western margin of the offshore phu khanh basin through fractured granites that outcrop at the basin margin there are examples of onshore gas seepages in southern vietnam these are predominantly non hydrocarbon mantle derived gases sometimes mixed with biogenic methane and are seeping via hot springs from fractured mezosoic igneous rocks in active fault zones offshore in the nam con son basin sonar seismic data and sea bed cores show a variety of seepage features including shallow gas anomalies mounds and pockmarks on the sea bed and gas effects in the water column sometimes visible on sonar records however sea bed seepage features are not particularly common and have a low preservation potential in the area due to powerful sea bed currents aircraft surveys of the sea surface have revealed several oil slicks that could be related to active oil seepages in the nam con son basin seepage appears to be occurring in vietnam at two fundamentally different rates background seepages flow at low rates typically tens to thousands of cubic feet per day of gas and up to tens of barrels per day of oil these seeps flow episodically for extended periods of months or years and leading to the formation of sea bed mounds higher flow rate eruptive seepages may have formed some of the pockmarks and have a far shorter duration probably only a few hours or days with flow rates of millions of cubic feet per day of gas and any associated liquids

organized patches of bioherm growth where the strait of dardanelles enters the marmara sea turkey abstract high resolution multibeam mosaics show that the seafloor across the southwestern marmara sea is host to remarkably organized near circular bioherm mounds which commonly are arranged into large tightly packed clusters grab samples and gravity cores reveal that the bioherms are predominantly composed of very fine grained calcareous silty mud with abundant bioclasts including centimetre scale masses of coralline red algae and intact disarticulated mollusc shells mainly the genera modiolus and mytilus geometric analysis of multibeam images reveals that the average bioherm is 15 6 m in diameter occupies 190 m2 of seabed stands 113 cm above the adjacent seafloor and its crest is 20 6 m from the crests of neighbouring bioherms in regions of tightly packed bioherm clusters referred to as bioherm colonies the inter mound depressions are on average 4 4 m wide and 33 cm deep although each bioherm mound is nearly circular the surrounding inter mound channels form a more rectilinear mesh of linked pentagonal and hexagonal polygons suggesting densest possible spatial packing of the mounds near neighbour statistics of r 2 11 2 14 indicate an essentially uniform spacing between the bioherms which is the expected result for close packing on a plane and full utilization of the available space the bioherms occur at depths between 30 m and 60 m they are absent above and below these depths in this part of the southwestern marmara sea at the eastern exit of the strait of dardanelles water depth controls important water mass properties such as salinity nutrient supply and availability of light other inferred critical controls are the availability of a suitable hard substrate where holocene muds are thin or absent and nutrient supply potentially including a component from escaping methane rich pore fluids evidence here and elsewhere in the marmara sea provisionally dates the onset of bioherm growth and development to the latest pleistocene earliest holocene after global sealevel rose to the breach depth of the strait of dardanelles at 13 8 cal ka

role of deep sourced fluids on the initiation and growth of isolated carbonate build ups abstract the relative role of the various mechanisms responsible for the formation of isolated carbonate build ups occurring on the seafloor along continental margins is still uncertain the interpretation of an extensive seismic dataset in the central vulcan sub basin nw australia allowed to evaluate the possible role of migration and seepage of deep sourced fluids during the initial growth of isolated carbonate build ups the neogene tectonic activity along the margin generated extensional fault systems that commonly displaced the seafloor thus apparently creating a substratum to the initiation of various carbonate build ups during the pleistocene the seismic data show reflections with enhanced amplitude respect to background values which are associated with both isolated carbonate build ups and normal faults the seismic character of these reflections supports the presence of fluids that migrated within the sedimentary pile throughout the investigated area the interpreted occurrence of methane derived authigenic carbonates mdac on the seismic surface upon which the carbonate build ups lay suggests that seepage of hydrocarbons likely occurred at the time of their initial formation the fluid migration appears focused in the areas above extensional faults which breached the seals of the mesozoic reservoirs combined tectonic activity and seepage are suggested to support the initial growth of the carbonate build ups various smaller buried carbonate build ups developed contemporaneously to those on the present day seafloor in sites that lack evidence of past hydrocarbon seepage their shorter life compared to those on the present day seafloor suggests their inability to keep up with the frequent relative sea level variations during the quaternary and the importance of deep sourced fluids for the carbonate build ups growth in the central vulcan sub basin the initiation of the numerous carbonate build ups documented along continental margins worldwide must be explained considering the complex and dynamic interplay of all factors potentially involved such as geological and oceanographic settings and an active petroleum system in particular the migration and seepage of deep sourced fluid can have an important role in controlling the genesis and growth of isolated carbonate build ups

fault associated seabed mounds carbonate knolls off western ireland and north west australia abstract groups of seabed mounds suspected to be modern carbonate knolls or bioherms have been located on reflection seismic data in the porcupine basin off western ireland and in the vulcan sub basin off north west australia the size of these mounds is impressive often being over 1 km across and over 100 m high in the porcupine basin they occur in water depths of 650 1000 m whereas in the vulcan sub basin they occur in water depths of 200 350 m shallow seabed coring in the porcupine basin has provided data on the age lithological composition and hydrocarbon concentrations in the upper 3 m layer of sediment both on and off the mounds in both basins the mounds occur close to faults which may provide conduits for upward migrating hydrocarbons the seepage of hydrocarbons is suspected to have caused local eutrophication or fertilization by providing nutrients to bacteria which in turn are part of the food chain for higher organisms the dominant organism in the porcupine basin examples appears to be the deep water coral lophelia sp whereas in the vulcan sub basin the mounds appear to be halimeda dominated

do carbonate reefs form due to fluid seepage buried carbonate reefs are favoured hydrocarbon prospecting targets mainly due to their high porosity and potential for containing large quantities of petroleum the question of the true relationship between reef structure and the internally trapped fluids hydrocarbons is here raised as one of cause and effect in other words which came first the hydrocarbons or the carbonate reef itself modern bioherms and seabed carbonate reefs in amongst other locations the north sea and the gulf of mexico are shown to form in close association with active hydrocarbon seepages mainly based on results from ecological studies at deep ocean vent communities a new model for carbonate reef formation is promoted that such reefs form at locations containing high concentrations of bacteria and other microorganisms suspended in the water column as a result of seeping fluids solutions and gases that provide some of the energy basis and carbon source for ecosystems independently of photosynthesis therefore on burial and effective sealing capping these carbonate reefs become hydrocarbon reservoirs trapping and accumulating the very minerals on which they in the first place were dependent

carbonate mounds in a mud volcano province off north west morocco key to processes and controls abstract this paper presents a new cluster of carbonate mounds discovered in 2002 in the gulf of cadiz off morocco r v belgica 2002 in water depths of 500 to 600 m amidst a field of giant mud volcanoes multibeam bathymetry side scan sonar imagery and 2d seismics are analyzed to present four mound provinces 1 the pen duick mound province on the pen duick escarpment 2 the renard mound province on the renard ridge 3 the vernadsky mound province on the vernadsky ridge and the al idrisi mound province on the gas blanked sediments above the buried al idrisi ridge video imagery and surface samples are described to ground truth the different mound areas the paradox is that nearly no live corals are presently being observed at the surface of the mounds while the mound cores display throughout a high number of reef forming cold water coral fragments scleractinians in association with numerous associated fauna formerly inhabiting the econiches provided by the coral framework environmental and oceanographic conditions during the recent past glacials stadials were probably more favourable for cold water coral growth pore water analyses in on mound cores at the south eastern edge of pen duick escarpment give evidence of focused higher methane fluxes and sulphate reduction rates on mounds than in the surrounding sediments cores from several mounds display horizons of strong corrosion and dissolution of the coral fragments a three phase model for carbonate mound evolution in these settings is proposed 1 in a first stage external controls positive oceanographic and environmental conditions the presence of an active planktonic food chain based on a high primary production and a suitable substrate are responsible for the initiation of cold water coral growth 2 once the cold water corals established an initial framework sedimentation becomes an important factor controlling mound growth the cold water corals baffle the sediments 3 throughout mound growth the mound may episodically be affected by diagenetic processes responsible for aragonite dissolution and probably carbonate precipitation

large deep water coral banks in the porcupine basin southwest of ireland the porcupine basin southwest of ireland was one of the earliest sites from where the deep water corals lophelia sp and madrepora sp were recovered these deep water corals have since been found all along the atlantic margins of europe in water depths ranging from 50 to more than 2000 m recent geophysical studies have demonstrated the mound building potential of deep water corals available data indicate that three major provinces of coral bank occurrences can be identified in the porcupine basin 1 high relief surface mounds which have a dimension of 1 by 5 km and a height up to 200 m hovland mounds flanked to the north by 2 a swarm of buried mounds somewhat smaller up to 90 m and with more irregular shapes than those recognised in area 1 magellan mounds and 3 outcropping or buried conical mounds single or in elongated clusters up to 150 m high occurring on the southeastern slope of the basin belgica mounds as far as can be inferred from shallow cores the surface lithology predominantly consists of an upper layer rich in foraminiferal sand and terrigenous silty clay with intercalations of biogenic rubble the banks host a remarkable number of colonies of living and dead lophelia pertusa and madrepora oculata the living and dead assemblages are underlain by a significant layer of coral debris in a muddy matrix deep water coral debris together with a living association of the same species covers the surface of the belgica and hovland mounds which may suggest that these corals have played a significant role in the development of the mound structures the capacity for mound formation by scleractinian corals in the aphotic zone has been known for some time examples are found at different locations along the shelves and the continental margins of the north atlantic the role of the corals in these deep water build ups is still a point of debate though the genesis and initial control of mound settings in this basin might be related to hydrocarbon seeps it appears that the major development of the porcupine coral banks in recent geological times has most likely been controlled by oceanic circulation and dynamics in water masses and nutrient supply

kilauea slow slip events identification source inversions and relation to seismicity 1 several slow slip events beneath the south flank ofkilauea volcano hawaii have been inferred from transient displacements in daily gps positions to search for smaller events that may be close to the noise level in the gps time series we compare displacement fields on kilauea s south flank with displacement patterns in previously identified slow slip events matching displacement patterns are found for several new candidate events although displacements are much smaller than previously identified events one of the candidates 29 may 2000 is coincident with a microearthquake swarm as are all of the previously identified slow slip events the microearthquakes follow the onset of slow slip implying that they are triggered by stress changes during slip the new slow slip event brings the total number of events on kilauea between 1997 and 2007 to eight the smallest having m w 5 3 and the largest having m w 6 0 while the recurrence time between the four largest events is 2 11 0 01 years the repeat time for all eight events is 0 9 0 6 years we invert for the fault geometry and distribution of slip during the slow slip events the optimal source depths of 5 km assuming uniform slip dislocations in an elastic half space are considerably shallower than the accompanying swarm earthquakes 6 5 8 5 km which would place the earthquakes in a zone of decreased coulomb stress inversions including the effects of topography and layered elastic structure in the forward models favor depths comparable to microearthquake depths such that the earthquakes are located in a region of increased coulomb stress we also invert for time dependent fault slip directly from the 30 s gps phase observations constraining the source to the optimal uniform slip geometry on the basis of these inversions the larger events last between 1 5 2 2 days the data are unable to resolve migration of slip along the fault the temporal pattern of accompanying microearthquakes is consistent with the fault slip history assuming a seismicity rate theory based on rate and state friction making the swarm earthquakes coshocks and aftershocks of the slow slip events

observation of coseismic seafloor crustal deformation due to m7 class offshore earthquakes 1 we have developed an observation system for seafloor crustal deformation measurement combining the two following techniques the precise acoustic ranging and kinematic gps global positioning system positioning on july 14 2003 we installed the units for this observation system at the seafloor of the kumano basin japan 33 58 n 136 60 e we performed repeated observation six times on 1 july 15 16 and 21 2004 2 november 9 10 2004 3 may 18 and 20 2005 4 july 19 20 2005 5 august 18 19 2005 and 6 august 29 30 2005 the present observation system can stably determine the seafloor position with an rms repeatability of 3 cm in both horizontal components two m7 class offshore intraplate earthquakes occurred only 60 km from the kumano basin site on september 5 2004 we observed the coseismic horizontal displacement of 18 cm at the kumano basin site using the presently developed seafloor observation system our observation system can provide seafloor crustal deformation associated with crustal activities in offshore areas

chronology and processes of fluvial terrace formation in northeastern kinki district southwest japan based on cryptotephra analysis abstract kinki district is a tectonically active area in southwest japan this area is located far from active volcanoes and eolian deposits covering fluvial terrace deposits are not as thick as those in kanto district thus terrace chronology and processes of terrace formation previously were poorly established in kinki district cryptotephra analysis identified invisible tephra horizons in eolian deposits covering fluvial terrace deposits in takashima sekigahara and inabe regions including the kikai akahoya tephra k ah 7 3 ka aira tn tephra at 26 29 ka and kikai tozurahara tephra k tz 95 ka horizons taisanjino 1 terrace in takashima and md1 terrace in inabe were formed during marine isotope stage mis 5e and nakano terrace in takashima l2 terrace in sekigahara and l2 terrace in inabe were formed during mis 2 based on their ages and geomorphic features aggradational terraces formed during mis 2 exhibit similar geomorphic features among the three regions although these regions have different base levels of erosion and active fault movements this means that the terrace formation during mis 2 was mainly affected by climate changes not by base level changes and active fault movements the main factor of terrace formation during glacial periods was the decrease in precipitation and water discharge due to climate changes because the study area was not affected by glacial and periglacial processes during mis 2 this indicates that aggradational terraces formed during glacial periods not only in glacial and periglacial areas but also in non glacial and non periglacial areas from processes of terrace formation during mis 5e the tectonic base level descent was important for terrace formation during interglacial periods because terraces were formed during mis 5e by active fault movements in the takashima region despite small lake level changes uplift rates of the kamidera and kuwana faults were 1 08 mm y and 0 5 mm y respectively based on the height of terrace surfaces formed during mis 5e

geophysical evidence for structurally controlled authigenic carbonate cementation in the laminaria high bonaparte basin northwest shelf of australia abstract 3d seismic reflection data are used to investigate the processes which have led to the development of amplitude anomalies on reflectors in the faulted cenozoic overburden on the laminaria high northwest shelf of australia amplitude and root mean square rms attributes are mapped on two reflectors seabed and horizon h9 that were deposited synchronous with fault activity and are located adjacent to predominantly ene wsw striking fault traces on the seabed the main anomaly is located on the up dip side of the fault trace and is elongated parallel to the local time structure contours these observations are consistent with the anomalies having developed in response to structurally controlled fluid seepage along and up dip migration away from the fault trace the other amplitude anomalies associated with the h9 reflector are also located adjacent to fault traces but are discordant to the local time structure contours the latter observation is inconsistent with the migration of buoyant fluid at the present day instead it suggests that the anomalies may be due to cemented hardgrounds that formed due to seepage when the faults intersected the palaeo seafloor but were subsequently buried and deformed during ongoing sedimentation and fault growth linkage prominent anomalies mapped on reflectors within the pre faulting succession h10 are located adjacent to and are elongated along sub seismic scale nw se striking faults or as in the case of a deeper horizon h13 show no clear relationship with the faults we conclude that there is no relationship between the occurrence of anomalies and the magnitude of throw or the duration of activity along the cenozoic faults the results suggest that whilst fluid seepage and cementation were structurally controlled these processes were also influenced by permeability variations that cannot be resolved by seismic interpretation methods

cold water corals are they hydrocarbon seep related numerous cold water ahermatypic coral reefs so called lophelia reefs up to 30m high 150m wide and 400m long occur at waterdepths from 100 to 350 m off mid norway after the discovery of relatively high interstitial methane concentrations 204 ppb in sediments collected at the base of one of these reef structures a causative link between the presence of the reefs and local micro seepage through seabed of light hydrocarbons is here suggested shallow seismic records gathered across this and other reef colonies off mid norway also indicate the existence of gas charged sediments below the reefs

correlating seismicity parameters and subsidence in the tokai region central japan 1 we demonstrate that transients in subsidence rate in the tokai area of central japan correlate with changes in the rate and size distribution of earthquakes three largely independent seismic catalogs cover this region national research institute for earth science and disaster prevention nied japanese meteorological agency jma and japan university network catalog junec comparing seismicity patterns between these three data sets offers a unique opportunity to verify seismicity anomalies based on independent sources a study of data quality magnitude reporting consistency and consistency across the three data sources reveals that the nied data for the period 1981 2002 are best suited for seismicity analysis we spatially and temporally map seismicity rates finding that a significant decrease in the earthquake rate of m 2 0 events coincides with an accelerated subsidence period however this anomaly disappears when including smaller magnitudes in the analysis this relative quiescence of larger events can readily be explained when interpreting the transient in seismicity in the framework of a change in the earthquake size distribution or b value the background b value of about 0 8 increased in the period 1987 5 1989 5 to a value of b 1 2 a highly significant change that can be confirmed in all three data sets the correlation between subsidence and b value change is significant stress tensor inversions of focal mechanism data for the anomalous period show an increase in thrusting type earthquakes while a unique interpretation of the relationship between subsidence and b value is not possible we propose that an increase in the locking stress a slow stick event is consistent with all observations

depositional environments and oil potential of jurassic cretaceous source rocks within the seychelles microcontinent abstract the seychelles microcontinent became isolated between the somali mascarene and arabian basins of the indian ocean as a result of the mesozoic fragmentation of gondwana major rifting events occurred during the triassic middle jurassic and late cretaceous cenomanian santonian and maastrichtian during which shaly source rock facies accumulated in principally marginal marine deltaic environments between these times post rift passive margin deposition de wit et al 1988 hin restricted to open marine environments produced shaly source rocks during late middle jurassic early cretaceous campanian maastrichtian and paleocene times recent geochemical analysis of cuttings from the seagull shoals l well has identified an oil prone liptinitic type ii coaly shale de wit et al 1988 hin early middle jurassic abandoned deltaic deposits this coaly source rock is regionally developed having also been identified in the majunga and morondava basins of madagascar oil prone type ii organic matter has also been identified in the owen bank a 1 well de wit et al 1988 hin restricted marine shales of late middle jurassic age these shales are part of a thick post rift source rock sequence that extends into the early cretaeous and is in part correlative de wit et al 1988 h the proven late jurassic uarandab shale of somalia analysis of campanian marine shales from reith bank 1 well identified significant dilution of total organic carbon content in composite compared to picked well cuttings samples this finding supports a published inference that these post rift shales have source rock potential the very limited drilling of the various jurassic cretaceous source rock sequences in seychelles only three penetrations all de wit et al 1988 hin a 13 km radius indicates that they span the entire maturity window and that some have generated hydrocarbons however the petroleum system associated de wit et al 1988 h the triassic early cretaceous rift drift sequence has been tested only by three invalid wells at the western extremity of the seychelles plateau whilst that associated de wit et al 1988 h the late cretaceous rift drift sequence remains untested 1998 elsevier science ltd all rights reserved

methane and minor oil macro seep systems their complexity and environmental significance abstract the two main observations characterising marine and lacustrine methane macro seeps are ebullition through holes in the sea or lake bed and hydroacoustic flares in the water column this paper reviews multi year multi scale and multi discipline results from three seep locations in the north sea and combines the knowledge with recent seafloor and water column results from seeps in the santa barbara basin california a seep off west africa seeps in the gulf of mexico and in lake baikal russia we have identified a total of 12 characteristics of methane and minor oil macro seeps that are not only geological in nature but also biological and geochemical these are shown to impact the marine environment in different ways not least in benefactory manners as primary producers mainly bacteria and archaea tend to bloom during seepage therefore the seepage is inferred to have a fertilizing effect on both the seafloor and the water column which may be of broad ecological and biological significance the study concludes with a holistic conceptual seep model which is expected to be of interest to a broad range of researchers in the fields of oceanography and limnology

numerical simulation of afterslips and slow slip events that occurred in the same area in hyuga nada of southwest japan summary we propose a model of numerical simulation for the coexistence of afterslip for m7 earthquake and slow slip events in the hyuga nada region of japan that incorporates 3 d geometry of the philippine sea plate coseismic slip events recurrence of slow slip events and afterslip are qualitatively reproduced using the composite law which is a type of rate and state dependent friction law with higher cut off velocity in addition characteristic slip distances in the area are larger than those in other seismic source areas in our simulation afterslip which occurred at the velocity weakening regime triggered an aseismic transient event after the termination of this event spontaneous slow slip events repeatedly occurred in the same area after a similar event sequence was repeated another afterslip occurrence triggered a larger coseismic slip in a wide area including that of the slow slip events following this coseismic slip the aseismic slip area was locked until the next afterslip propagation which triggered an aseismic transient event these results suggest that detailed observation of spatial and temporal distribution within the area of aseismic slip may indicate the potential of recurring slow slip events and future large earthquakes

lateral variation of the cutoff depth of shallow earthquakes beneath the japan islands and its implications for seismogenesis abstract we estimated the spatial distribution of the cut off depth of shallow seismicity beneath the japan islands based on data from a recently constructed nationwide dense seismic network in order to avoid the effect of heterogeneous seismic velocity structure we determined the 3d seismic velocity structure for the whole of japan which was then used to relocate the hypocenters the cut off depth was determined by calculating d90 the depth above which 90 of the earthquakes occur a spatial distribution of estimated d90 values shows a considerable lateral variation ranging from about 5 km to about 40 km the d90 s are deep along the pacific coast of eastern japan locally shallow d90 s extend along belt like stretches of volcanic areas heat flow is low along the pacific coast in eastern japan and high in the volcanic areas this indicates that the lateral variation of d90 s is formed mainly by lateral geotherm variation cooling by the subducting old very cold pacific plate may cause the deep d90 s along the pacific coast in eastern japan heating by magma supplied from the mantle wedge below is considered to be the main cause of the shallow d90 s in the volcanic areas magma and or aqueous fluids derived from solidified magma contribute not only to locally shallow d90 s but also to the weakening of ambient rocks in the lower crust resulting in stress concentrations in the upper crust just above them large shallow inland earthquakes tend to occur in such areas suggesting that a model of shallow earthquake generation applied to tohoku can be used in other areas in japan as well

estimation of interplate coupling in the nankai trough japan using gps data from 1996 to 2006 we used three component surface velocities in southwest japan to estimate plate coupling on the subducting plate interface at the nankai trough we analyzed continuous gps data from the japanese geonet network from 1996 to 2006 using a consistent analysis strategy that generates bias fixed solutions for the entire network we applied systematic time series analysis methods to estimate common mode error which improved position solutions for the entire network to allow for differences in regional deformation sources we modelled the plate coupling on the plate interface beneath shikoku island to kii peninsula and the tokai suruga trough separately the results show strong coupling at a depth of 10 30 km off shikoku and kii peninsula the spatial variation in plate coupling coincides well with the coseismic rupture zones of the past large earthquakes maximum slip deficit rates of 2 3 cm yr 1 at the depth of 5 25 km are found beneath the tokai area consistent with results from other studies the downdip limits of the highly coupled areas and transition zones beneath shikoku and the kii peninsula correspond approximately to estimates of the 450 c isotherms good correlation is observed between the lateral variations of the slip deficit distribution low frequency earthquakes and coseismic slip this correlation suggests that temperature and possibly fluid variations contribute to such correlation in space the interplate slip deficit derived from the gps velocities over the 10 yr of observations is generally compatible with the results over shorter time spans suggesting that plate coupling in sw japan does not change significantly over the period of these gps measurements

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

critical depth for the survival of coral islands effects on the hawaiian archipelago coral islands drown when sea level rise exceeds the maximum potential of coral reefs to grow upward about 10 millimeters per year during the holocene transgression 18 000 years ago to present sea levels rose at rates of up to 10 to 20 millimeters per year and most coral island reefs situated deeper than a critical depth of30 to 40 meters below present day sea level drowned coral islands that did not drown during the holocene transgression apparently all developed on antecedent foundations shallower than critical depth during low stands in sea level during the pleistocene these islands were elevated and subject to subaerial erosion today in the hawaiian archipelago the depth of drowned banks is inversely related to summit area smaller banks are progressively deeper evidently because of erosional truncation during low sea level stands bank summit area may therefore be an important factor determining the failure or success of coral islands

search for signs of ancient life on mars expectations from hydromagnesite microbialites salda lake turkey the 9white rock9 constituting a portion of what may be a lacustrine sedimentary sequence near the margin of a crater c 90 km across in sabaea terra mars measures 18 15 km 180 540 m high it is re interpreted as a lens of magnesium carbonate precipitated where ground waters seeped into an ancient evaporating crater lake were life to have emerged on mars as seems feasible then the 9white rock9 might be expected to comprise a complex of stromatolitic mounds salda golu lake in turkey is taken as an analogue this enclosed lake is nearly surrounded and underlain by partially serpentinized harzburgite hydromagnesite stromatolites microbialites up to 7 m high coalesce to form a group of small islands 200 m across the microbialites are seen to be growing near the mouth of the usually dry salda river in the southwestern sector smaller developments of hydromagnesite encircle the lake and image processing of satellite data reveals a second extensive zone beneath the lake surface over a delta in the southeast individual columns a few centimetres high constitute bulbous mounds which are about 2 m in diameter these columns terminate in domes a centimetre or so across the domes are often annulated and are covered with a green biofilm a few millimetres thick comprised of cyanobactrial filaments the columns consist of alternating fine and coarse hydromagnesite layers differentiated on a millimetric scale the coarser layers near the surface still contain traces of the biofilm fossil microbialites were also discovered in the friable hydromagnesite cliffs shoreward of the main developments though the structures of the individual microbes have not survived instead the vestiges of microbialites are easily recognized and delineated by their coarse grain size and high porosity annular structures on their upper surfaces can be seen in places the intervening and overlying material also comprised of hydromagnesite is a semi lithified mud bulbous megascopic structures separated by finer grained magnesium carbonate mudstone within strata in the 9white rock9 would be strong evidence of a photosynthetic microbial genesis another deposit of white rock on the western margin of juventae chasma could have a similar origin

interplate coupling in the tokai district central japan deduced from continuous gps data i invert gps displacement rates in the tokai district to investigate strain accumulation associated with the anticipated tokai earthquake i apply a representation of interseismic strain accumulation at subduction zones by savage 1983 and estimate a distribution of virtual normal fault slip back slip on the plate boundary surface estimated back slip takes its maximum value of 30 40mm year under the sea of enshu this value is nearly equal to the relative plate motion there implying almost complete coupling back slip is smaller under suruga bay and its direction is different from the relative motion between the eurasian and the philippine sea plates localized deformation at the northern tip of the philippine sea plate may be responsible for this discrepancy partitioning tectonic strain due to the plate convergence into faults on both sides of the izu peninsula and also distributed strain inside the peninsula

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

holocene geohazard events on the southern izu peninsula central japan abstract faunal compositions and 14c ages of emerged sessile assemblages at four sites in the southern part of izu peninsula central japan indicate that co seismic uplift occurred at 1256 950 bc ad 1000 1270 ad 1430 1660 and ad 1506 1815 the data suggest that the stress field in the southern part of izu peninsula changed to its current north south compression at ca 3100 bp and that the recurrence intervals for uplift inducing earthquakes have become shorter during the last 1000 years the main faults responsible for this seismicity appear to be located offshore from the south part of izu peninsula this study also examined a 1 cm thick scoria layer deposited between 6940 and 6810 cal bp in the south part of izu peninsula the layer which had not been previously examined petrographically consists of scoria grains derived from izu oshima volcano located 40 km east of the study area rather than from volcanoes located on izu peninsula itself

pinnacle features at the base of isolated carbonate buildups marking point sources of fluid offshore northwest australia we investigated pinnacle features at the base of late oligocene miocene isolated carbonate buildups using three dimensional seismic and borehole data from the browse basin northwest australia brightened seismic reflections dim spots and other evidence of fluid accumulation occur below most pinnacle features an important observation is that all pinnacles generated topography on successive late oligocene miocene paleoseafloors therefore forming preferential zones for the settlement of reef building organisms by raising the paleo seafloor into the photic zone their height ranges from 31 m to 174 m for a volume varying from 33 km3 to 11 105 km3 most of the pinnacles however are less than 2000 km3 in volume and present heights of 61 80 m as a result of this work pinnacles are explained as the first patch reefs formed in association with mud volcanoes or methanogenic carbonates and they are considered as precluding the growth of the larger isolated carbonate buildups we postulate that pinnacle features above fluidflow conduits demonstrate a valid seep reef relationship and we propose them to be refined diagnostic features for understanding fluid flow through geological time

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

possible slip history scenarios for the hyuga nada region and bungo channel and their relationship with nankai earthquakes in southwest japan based on numerical simulations the nankai earthquakes are great interplate earthquakes with recurrence intervals of 100 200 years occurring along the nankai trough southwestern japan new geological evidences suggest that the rupture area of the 1707 earthquake one of the largest extended farther westward than previously thought and similar magnitude events may have recurrence intervals of several hundred years west of the nankai earthquake segments in the bungo channel region slow slip events sses have occurred with recurrence intervals of several years since 1980 farther westward no m 7 5 interplate earthquakes have occurred except for one in 1968 in the northern hyuga nada region near the bungo channel we numerically simulated the generation cycles of nankai earthquakes hyuga nada earthquakes and bungo channel sses to obtain possible slip histories in these regions particularly during 1707 1980 we showed that the nankai and hyuga nada earthquakes occur mostly independently with average recurrence intervals of 151 and 117 years respectively an sse patch slipped coseismically during both the nankai and hyuga nada earthquakes the rupture of the nankai earthquakes extended to the hyuga nada region every 500 600 years and was followed by quiescence of sses for more than 200 years subsequently sses occurred repeatedly every 8 years current observational findings are generally consistent with the characteristics obtained from our scenarios except regarding the recurrence intervals of hyuga nada earthquakes for which few observations are available further evidence of the slip history in these regions will be required to use information from such simulations to forecast future earthquakes

the origin of deep water coral topped mounds in the northern rockall trough northeast atlantic mounds associated with the cold water coral lophelia pertusa are widespread in the north atlantic although the factors controlling their distribution are not well understood here we examine a group of small coral topped mounds the darwin mounds which occur at 1000 m water depth in the northern rockall trough northwest of the uk individual mounds are up to 75 m in diameter and 5 m high although some mound like targets seen on sidescan sonar have little or even negative relief some mounds are associated with tail like features imaged as elongate patches of moderate backscatter up to 500 m long elongated parallel to prevailing bottom currents high resolution sidescan images and seabed photographs show hundreds of coral colonies each a metre or so across on each individual mound many other organisms mainly suspension feeders occur in association with the coral piston cores from the mounds contain predominantly quartz sand with only scattered coral fragments showing that bioclastic material is not a major contributor to mound building a field of seabed pockmarks occurs immediately south of the darwin mounds on sidescan sonar data pockmarks are low relief circular depressions typically around 50 m in diameter the seafloor around the pockmarks consists of uniform heavily burrowed muddy sediments and no specific biological communities nor any sedimentological or photographic evidence for active seepage were observed the distribution of mounds and pockmarks suggests a gradual transition from mounds in the north to pockmarks in the south this combined with the lack of bioclastic material in the mound sediments suggests that both mounds and pockmarks are created by fluid escape from below the seafloor mounds occur where fluids carry subsurface sand to the surface where it forms mounds because bottom currents are not strong enough to disperse it pockmarks form where muddy material is eroded by fluid escape but dispersed by bottom currents despite the origin of mounds through fluid escape we suggest that it is the elevated mound topography rather than any fluid escape that is advantageous to the corals this is supported 1 by the wide variety of suspension feeding organisms that occur on the mounds since all of these are unlikely to have a specialised seepage related lifestyle and 2 because corals and their associated community do not occur around pockmarks where seepage has also occurred but elevated topography is absent

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

earthquake doublet in an active shear zone southwest japan constraints from geophysical and geochemical findings abstract in 1997 the kagoshima earthquake doublet consisting of two closely associated mw 6 strike slip events five km and 48 days apart has occurred in southwest japan the location is where an e w trending discontinuity along 32 n latitude on southern kyushu island is clearly defined in gps velocities indicating the presence of a highly active left lateral shear zone however there have not been any obvious indications of active faulting at the surface prior to the earthquake doublet which could be associated with this shear zone three dimensional inversion of magnetotelluric sounding data obtained in the source region of the earthquake doublet reveals a near vertical conductive zone with a width of 20 km extending down to the base of the crust and perhaps into the upper mantle toward the okinawa trough the prominent conductor corresponds to the western part of the active shear zone elevated 3 he 4 he ratios in groundwaters sampled from hot spring and drinking water wells suggest the emission of mantle derived helium from the seismic source region the geophysical and geochemical observations are significant indications that the invasion of mantle fluids into the crust driven by upwelling asthenosphere from the okinawa trough triggers the notable left lateral shearing in the zone in the present day subduction system in addition the existence of aqueous fluids in and below the seismogenic layer could change the strength of the zones and alter the local stress regime resulting in the occurrence of the 1997 earthquake doublet

the 1923 kanto earthquake reevaluated using a newly augmented geodetic data set 1 this study revisits the mechanism of the 1923 ms 7 9 kanto earthquake in japan we derive a new source model and use it to assess quantitative and qualitative aspects of the accommodation of plate motion in the kanto region we use a new geodetic data set that consists of displacements from leveling and angle changes from triangulation measurements obtained in surveys between 1883 and 1927 two unique aspects of our analysis are the inclusion of a large number of second order triangulation measurements and the application of a correction to remove interseismic deformation the geometry of the fault planes is adopted from a recent seismic reflection study of the kanto region we evaluate the minimum complexity necessary in the model to fit the data optimally our final uniform slip elastic dislocation model consists of two adjacent 20 dipping low angle planes accommodating reverse dextral slip of 6 0 m on the larger eastern plane and 9 5 m on the smaller western plane with azimuths of 163 and 121 respectively the earthquake was located in the sagami trough where the philippine sea plate subducts under honshu compared to the highly oblique angle of plate convergence the coseismic slip on the large fault plane has a more orthogonal orientation to the strike of the plate boundary suggesting that slip partitioning plays a role in accommodation of plate motion what other structure is involved in the partitioning is unclear uplift records of marine coastal terraces in sagami bay document 7500 years of earthquake activity and predict average recurrence intervals of 400 years for events with vertical displacement profiles similar to those of the 1923 earthquake this means that the average slip deficit per recurrence interval is 50 of the relative plate convergence these findings of plate motion partitioning and slip deficit lead us to suggest that instead of a simple recurrence model with characteristic earthquakes additional mechanisms are necessary to describe the accommodation of deformation in the kanto region so far obvious candidates for these alternative mechanisms have not been discovered

devonian rugose coral amplexus and its relation to submarine fluid seepage the rugose coral amplexus occurs frequently in the sedimentary cover of the devonian submarine volcanic intrusion in the eastern anti atlas southern morocco this study elucidates the palaeoecology of amplexus which forms very rich and mostly monospecific spot assemblages within the lower and middle devonian carbonates geological and isotopic evidences show that these associations developed at hydrothermal vents and at a cold seep site the assemblages are always spatially associated with micritic carbonate bodies occurring within bedded hemipelagic deposits the amplexus corals preferred locations in the close proximity of submarine hydrothermal fluid seepage but they generally avoided places with the most elevated temperatures the corals colonised also a hydrocarbon seep probably only in its terminal phase of development when the fluid flow was still at least periodically active this was only possible as a result of the corals following a calice in calice growth developed due to the environmental toxicity which facilitated selective survival of larvae that settled in the shelter of empty calices the amplexus corals appear to have constituted ecological opportunists thriving in the nutrient rich venting and seepage affected areas that were hostile for other benthic organisms it can be suspected that the unusual extremely simplified morphology of amplexus made it particularly well adapted to living in environments typified by harsh and unstable conditions

rudist coral frameworks associated with submarine volcanism in the maastrichtian of the pachino area sicily maastrichtian strata from the pachino area se sicily provide a model of association between rudist coral frameworks and submarine volcanic activity two successive carbonate units are distinguished a coral rudist bioherms and biostromes developed in a high energy environment b hippuritid build ups and banks overlain by rudist coral clusters which grew under harsher ecological conditions in a weaker current regime at the top of the maastrichtian sequence the growth of rudist coral frameworks ceased as ecological conditions shifted toward restricted environments the inferred succession reflects a gradual decrease in current strengths and water depths related to the maastrichtian regressive phase the frameworks display consistent evolutionary sequences reflecting progressive changes in their biota structure size and shape occurrences of rudist coral frameworks are clearly linked with submarine volcanoes which provided opportunities for their development they sometimes grew in the vicinity of active vent centres a feature reported for the first time in the upper cretaceous

spatial variations in 3he 4he ratios along a high strain rate zone central japan abstract a linear zone with high strain rates along the japan sea coast the niigata kobe tectonic zone nktz is considered to be associated with rheological heterogeneities in the lower crust and or upper mantle helium isotope variations along the nktz reveal a close association with the geophysical evidence for rheological heterogeneities in the crust and mantle in the southern nktz the 3 he 4 he ratios lower than 3 4 ra ra denotes the atmospheric 3 he 4 he ratio of 1 4 10 6 could be interpreted as a two component mixture of helium stored in aqueous fluids driven off the subducting oceanic crust and radiogenic crustal helium higher 3 he 4 he ratios are observed in the central nktz where quaternary volcanoes and high temperature hot springs are concentrated suggesting that the 3 he emanation manifest in the central nktz results from the effective transfer of mantle helium by intrusion and degassing of mantle derived magma in the crust in the northern nktz where two large inland earthquakes occurred recently there appears to be many samples with 3 he 4 he ratios significantly higher than those observed in the fore arc side of northeast japan a plausible source of mantle helium could be attributed to upward mobilization of aqueous fluids generated by dehydration of the subducting pacific plate slab

the precipitation of aragonite from shallow water hydrothermal fluids in a coral reef tutum bay ambitle island papua new guinea the fringing reef in tutum bay on the west side of ambitle island papua new guinea is the only presently known coral reef exposed to the extensive discharge of a hot mineralized hydrothermal fluid there aragonite and ferrihydrite a hydrous ferric oxide are the prominent hydrothermal precipitates aragonite forms two distinct crystal habits a euhedral pseudohexagonal crystals up to 2 cm long and b micro crystals similar in appearance to feather dendrite aragonite encrusts dead coral fragments volcaniclastic boulders and pebbles and fills secondary fracture and remaining primary intergranular porosity within volcaniclastic arenite the hydrothermal aragonite has a distinctively different isotopic composition when compared to normal shallow water marine inorganic and organic carbonate that precipitated from seawater this difference arises from precipitation at high temperature from a mixture of seawater and hydrothermal fluid that has lower 87 sr 86 sr and d 18 o values than seawater based on a 87 sr 86 sr mixing model aragonite precipitated from a hydrothermal fluid seawater mixture of approximately 9 1 precipitation from the hydrothermal solution is mainly caused by co2 degassing but mixing between hydrothermal fluid and seawater may have enhanced precipitation due to an increase in ph the d 13 c of tutum bay hydrothermal aragonite ranges from 1 9xto 2 2x vpdb this range of values is in good agreement with experimental data j phys chem 72 1968 800 geochim cosmochim acta 61 1997 3461 indicating that c 13 equilibirum has been reached during its formation values for d 18 o range from 14 2xto 14 7xand calculated isotopic equilibrium temperatures are approximately 20 jc lower than directly measured vent fluids and those temperatures obtained from fluid inclusion experiments and the 87 sr 86 sr mixing model this indicates that either oxygen isotope equilibrium was not attained or that the calcite water fractionation factor for oxygen isotopes is not applicable for the precipitation of tutum bay hydrothermal aragonite trace element concentrations except for the rees y and sr are low the ree patterns of aragonite are similar to those of tutum bay vent water indicating the hydrothermal origin of the aragonite rare earth element concentrations are higher in the coarse than in the fine grained aragonite which might be caused by a change in precipitation rate and seawater mixing d 2004 elsevier b v all rights reserved

long term changes in the coulomb failure function on inland active faults in southwest japan due to east west compression and interplate earthquakes inland earthquake activity in and around the kinki region southwest japan increases in the period from several decades before to about a decade after the occurrence of great interplate earthquakes along the nankai trough to quantitatively investigate this relationship we calculated long term changes in the coulomb failure function cff on inland active faults in this region with viscoelastic slip response functions as sources for the change in cff we investigated east west compression within the niigata kobe tectonic zone nktz historical interplate earthquakes and interseismic locking along the nankai trough subduction zone and historical inland earthquakes in this region among these sources the nktz east west compression is the primary cause of the long term changes in cff the changes in cff due to interplate earthquakes are mostly negative on reverse faults and positive on strike slip faults this result suggests that the inland reverse faulting activity mostly increases before interplate earthquakes and decreases after the earthquakes whereas strike slip activity is mostly suppressed before interplate earthquakes and increases thereafter this suggestion is supported by spatiotemporal pattern of historical inland earthquakes if focal mechanisms of historical earthquakes correspond to fault geometries in the region the calculated changes in cff are usually consistent with the occurrence of historical inland earthquakes if we use the change in shear stress instead of the change in cff this consistency is enhanced which suggests low apparent coefficients of friction in this region

do norwegian deep water coral reefs rely on seeping fluids hundreds of large coral reefs up to 45 m high exist a on the continental shelf and b on morainic threshold ridges in fjords of northern mid and southwest norway they occur in water depths between 400 and 40 m and contain a large variety of megafauna the most common frame building coral is lophelia pertusa l the oldest reef found to date is 8600 calendar years old determined by radiocarbon dating of buried lophelia skeleton even though many of these reefs have been known to science for over 200 years there is as yet no viable and unifying hypothesis to explain their existence in deep cool waters other than perhaps the hydraulic theory presented by the author in 1990 it states that primary producers mainly bacteria are locally formed and concentrated at reef locations due to seepage of light hydrocarbons mainly methane on the continental shelf and nutrient rich groundwater in the fjords the hydraulic theory is supported by the following topographic reflection seismic and geochemical indicators for the continental shelf reefs a seaward dipping sedimentary permeable strata enhanced acoustic seismic reflectors adjacent pockmark craters locally elevated light hydrocarbon sediment content locally elevated seawater methane content for the fjord reefs b threshold morainic substratum rather than adjacent hardrock substratum sub surface dipping sedimentary layers h2s smell of near surface sediment samples these indicators or reef associated observations have been documented by german british and norwegian researchers over the last 10 15 years however all the listed indicators do not necessarily occur at each of the respective shelf and fjord reef locations simultaneously

dolomitization of atolls by sea water convection flow test of a hypothesis at niue south pacific the core of the former atoll on niue island south pacific is extensively dolomitized a detailed stable isotope study reveals that the dolomites are uniformly enriched in 18o and 13c 18o 2 8 0 5 13c 2 0 0 3 relative to their carbonate precursor the sr isotope ratios are equally constant with depth yielding 87sr 86sr values between 0 70912 and 0 70916 the observed isotopic compositions point to sea water as the dominant dolomitizing fluid the sr age of the dolomites is younger than the biostratigraphic age mid to late miocene placing the dolomitization event at plio pleistocene time a model of sea water convection is proposed for atoll dolomitization on the basis of a thermal gradient between the atoll and the ambient ocean water sea water is drawn through the atoll margin and transferred upward by convective flow delivering mg to the sites of dolomite precipitation transported with the sea water are volcano derived metals fe cu zn mn as evidenced by the chemical gradient in

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

detection and mapping of cold water coral mounds and living lophelia reefs in the galicia bank atlantic nw iberia margin abstract we report for first time the occurrence of cold water coral mounds and large number of living lophelia reefs along the galicia bank atlantic nw iberian margin detection and mapping of living coral reefs and mounds have been carried out by means of multibeam bathymetry backscatter images ultra high resolution and high resolution multichannel seismic reflection data and sampling in addition profiling ctds have been made to characterise environmental conditions as temperature salinity and dissolved oxygen contents of the coral sites based on these dataset two main provinces of cold water coral mounds and reefs have been identified in the galicia bank at water depths between 620 and 1125 m the breogham mound province along the western flank of the galicia bank shows a sequence of well developed mounds composed of 1 stepped semi buried elongated mounds the tallest mounds with heights up 70 m and widths of 450 m lined up in along slope trending ridges and intercalated with upslope migrating sediment drifts at water depths from 1125 to 826 m 2 single and composite seabed mounds show heights of 10 12 m and average widths of 100 m at 825 and 780 m water depths and 3 lophelia reefs forming mini mounds 2 4 m high and 80 100 m width growing on a flat erosional surface at the summit of the bank at 780 750 m water depths otherwise the castelao mound province at the eastern flank of the bank is mainly constituted by cluster of mini mounds hosting living lophelia pertusa and madrepora oculata reefs these living reefs are detected based on ultra high resolutions parametric echosounders as mini mounds with an acoustically transparent interior otherwise semi buried and exposed mounds are mapped with a combination of multibeam and backscatter images identified by their high strength values and seabed expression we conclude that the initiation growth and distribution of cold water coral mounds on the galicia bank have been controlled by the following environmental forcing factors i water masses with a potential density resulted of the turbulent boundary between the mediterranean outflow and the intermediate atlantic water masses which allowed the transport of coral larvae along the ne atlantic margins ii the formation of a hard substrate possibly related to subsurface fluid flow necessary for the initial settle of coral larvae and iii the turbulences created by the mediterranean flow impinging the topography of the bank creating suitable currents that favour intrusion of the nutrient afflux from the atlantic mass waters to deep waters allowing to coral colonies to growth